kinetics

KINETICS OF OXIDATION OF SOME REDUCING SUGARS BY

POTASSIUM PERMANGANATE IN ACIDIC MEDIUM BY

VISIBLE SPECTROPHOTOMETRY

___________________________________________________________

By

RAHEELA NAZ M.Sc.

DEPARTMENT OF CHEMISTRY

JINNAH UNIVERSITY FOR WOMEN

KARACHI-74600

PAKISTAN

2008

KINETICS OF OXIDATION OF SOME REDUCING SUGARS BY

POTASSIUM PERMANGANATE IN ACIDIC MEDIUM BY

VISIBLE SPECTROPHOTOMETRY

A THESIS

SUBMITTED FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

OF THE JINNAH UNIVERSITY FOR WOMEN

KARACHI

By

RAHEELA NAZ M.Sc.

DEPARTMENT OF CHEMISTRY

JINNAH UNIVERSITY FOR WOMEN

KARACHI-74600. PAKISTAN

2008

DDEEDDIICCAATTIIOONN

I DEDICATE MY EFFORTS IN THE LOVE OF MY DEAR PARENTS

MR. MANZOOR HUSSAIN AND MRS. REHANA SHAHNAZ,

ESPECIALLY HUSBAND MR. SYED MUDASSIR HASAN AND MY

SWEET DAUGHTER SYEDA HANI

WHO HAVE LISTENED AND SHARED MY FEELINGS,

GIVEN COMFORTS, STRENGTH AND HAVE

REALLY CARED FOR ME

ALL THE TIME.

sTable of Content

i

TTaabbllee ooff CCoonntteennttss

Table of Contents................................................................................................ i

Acknowledgements….......................................................................................vi

Abstract…...........................................................................................................vii

Chapter 1 INTRODUCTION……………………………………………… 1

1.1 SUGARS........................................................................................................... 1

1.2 EQUILIBRIA AND MUTAROTATION OF SUGARS...................................2

1.3 OXIDATION PRODUCTS OF SUGARS……………………………………4

1.4 REDUCING AND NON-REDUCING SUGARS…………………………….6

1.5 OXIDATION WITH SOME IMPORTANT OXIDIZING AGENTS………...7

1.5.1 Bromine water: the synthesis of aldonic acids………………………7

1.5.2 Nitric acid oxidation: Aldaric Acids………………………………...7

1.5.3 Periodate oxidations: oxidative cleavage of polyhydroxy

compounds…………………………………………………………..8

1.5.4 Other Sugar Oxidation Products…………………………………….9

Chapter 2 LITERATURE SURVEY …...…………………………….…10

2.1 OXIDATION OF REDUCING SUGAR BY HALOGENS .………..………10

2.1.1 Bromine as an oxidant …………………………………………….11

2.1.2 Use of Iodine for oxidation of Sugars…………………………..….11

2.2 OXIDATION THROUGH HALO COMPOUNDS………………………....12

2.2.1 Hypobromous Acid………………………………………………...12

2.2.2 Oxidation with Potassium bromate……………………………...…12

2.2.3 Oxidation by Periodic acid………………………………………....13

2.2.4 Periodate………………………………………………………...…14

2.2.5 Electron transfer reaction involving Perchlorate as an oxidant……17

2.2.6 Hypochlorite……………………………………………………….17

2.2.7 Chloroamine-T……………………………………………………..17

2.3 N-HALO COMPOUNDS……………………………………………………18

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2.4 OXIDATION THROUGH TRANSITION METALS……………………….21

2.4.1 Manganese (Mn)…………………………………………………...21

2.4.2 Cerium (Ce)………………………………………………………..22

2.4.3 Vanadium (V)……………………………………………………...23

2.4.4 Chromium (Cr)……………………………………………………..24

2.4.5 Osmium (Os)……………………………………………………….26

2.4.6 Copper (Cu)………………………………………………………..26

2.5 TRANSITION METALS AS CATALYST IN OXIDATION

REACTIONS……………..………………………………………………….26

2.5.1 Bismuth (Bi)……………………………………………………….26

2.5.2 Rhodium (Rh)……………………………………………………...27

2.5.3 Ruthenium (Ru)…………………………………………………....27

2.5.4 Platinum (Pt)……………………………………………………….28

2.5.5 Palladium (Pd)……………………………………………………..28

2.5.6 Mercury (Hg)…………………………………………………..…..28

2.6 AIR OXIDATION…………………………………………………………...29

2.7 HYDROGEN PEROXIDE (H2O2)……………………………………….….30

2.8 OXIDATION INVOLVING TRANSITION METAL COMPLEXES AS

OXIDANTS……..………………………………………………………...…30

2.9 INORGANIC OXIDANTS…………………………………………………..31

2.10 OTHER OXIDATION REACTIONS……………………………………...32

2.11 REACTIVE FORMS OF SUGARS IN ALKALINE MEDIUM…………..37

2.12 PERMANGANATE AS AN OXIDIZING AGENT……………………….38

2.13 AIMS AND OBJECTIVE OF CURRENT RESEARCH…………………..43

Chapter 3 EXPERIMENTAL ASPECTS…...….………………………45

3.1 LABORATORY PREPARATION………………………………………..…45

3.1.1 Glass Wares………………………………………………………..45

3.1.2 Thermostatic Bath………………………………………………….45

3.1.3 Stop Watch…………………………………………………………46

3.1.4 Digital Balance……………………………………………………..46

3.1.5 Spectrophotometer…………………………………………………46

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3.1.6 Mass Spectrometer…………………………………………………46

3.1.7 NMR Spectrometers………………………………………………..46

3.1.8 TLC………………………………………………………………...46

3.1.9 Chemicals…………………………………………………………..47

3.2 PREPARATION OF STOCK SOLUTIONS……………………………..…47

3.2.1 Stock Solution of KMnO4…….……………………………………47

3.2.2 Stock Solution of Galactose….…………………………………….47

3.2.3 Stock Solution of Fructose…………………………………………48

3.2.4 Stock Solution of Maltose………………………………………....48

3.2.5 Stock Solution of Lactose……………………………………….…48

3.2.6 Stock Solution of Potassium Nitrate……………………………….48

3.2.7 Sulphuric Acid…………………………………………………..…48

3.3 KINETIC EXPERIMENTS……………………………………………….…48

3.3.1 Effect of Substrate Concentration on “kobs”..………………………49

3.3.2 Effect of Oxidant Concentration on “kobs”...………………….……49

3.3.3 Effect of [H+] Concentration on “kobs”..…….…………………..…49

3.3.4 Effect of Salt on “kobs” …………………..…………………...……49

3.3.5 Effect of Temperature on “kobs” ………..……………………….…49

3.4 DATA ANALYSIS………………………………………………………..…50

3.5 STOICHIOMETRY AND PRODUCTANALYSIS ……………………...…50

3.6 ANALYSIS OF REACTION MIXTURE..…………………………………51

3.7 PREPARATION OF REACTION MIXTURES………………………….…52

3.7.1 For Galactose………………………………………………………52

3.7.2 For Fructose………………………………………………………..52

3.7.3 For Maltose……………………………………………………...…53

3.7.4 For Lactose…………………………………………………………53

3.8 ANALYSIS OF OXIDATION PRODUCTS……………………………..…54

Chapter 4 RESULTS……………………………………………………..…55

4.1 EFFECT OF CONCENTRATION OF KMnO4 ON THE RATE OF

OXIDATION OF SUGARS WITH KMnO4……………………..………....56

4.2 EFFECT OF CONCENTRATION OF SUGARS ON THE RATE OF

OXIDATION OF SUGARS WITH KMnO4…………………….……….…65

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4.3 EFFECT OF CONCENTRATION OF H2SO4 ON THE RATE OF

OXIDATION OF SUGAR WITH KMnO4……………………………….…74

4.4 EFFECT OF IONIC STRENGTH ON RATE OF OXIDATION OF

SUGARS WITH KMnO4…......………………………………………...……83

4.5 EFFECT OF TEMPERATURE ON RATE OF OXIDATION OF

SUGARS WITH KMnO4………..………………………………………...…92

Chapter 5 DISCUSSION………...…………………..…………………….101

5.1 INFLUENCE OF VARIATION OF CONCENTRATION OF KMnO4

ON THE OXIDATION OF REDUCING SUGARS…………….…………102

5.2 INFLUENCE OF VARIAITION OF CONCENTRATION OF SUGARS

ON THE OXIDATION BY KMnO4……………………………………….115

5.3 INFLUENCE OF VARIATION OF CONCENTRATION OF H+ IONS

ON THE OXIDATION OF SUGARS BY KMnO4………………………..128

5.4 NFLUENCE OF THE IONIC STRENGTH ON THE OXIDATION OF

SUGARS BY KMnO4……………………..……………………………….141

5.5 EFFECT OF TEMPERATURE ON RATE OF OXIDATION OF

SUGARS BY KMnO4...................................................................................151

5.6 REACTIVE SPECIES OF MnO4-……………………………………….…156

5.7 REACTIVE SPECIES OF Hg (II) CHLORIDE IN ACIDIC MEDIUM......156

5.8 SPECTRAL EVIDENCE FOR THE FORMATION OF COMPLEXES

DURING COURSE OF REACTION………….…………………………..157

5.9 REACTIONS FOR OXIDATION OF SUGARS INTO ALDONIC

ACIDS……………………………………………………………………...162

5.9.1 Reaction Pathway of the Oxidation of Galactose and Fructose….162

5.9.2 Mechanism of Catalytic Oxidation of Maltose and Lactose……...163

5.10 REACTIONS FOR OXIDATION OF SUGARS INTO OTHER

ACID……………………………………………………………….……...166

5.10.1 Reaction Pathway for Oxidation of Galactose and Fructose……168

5.10.2 Mechanism for Oxidation of Maltose and Lactose……………...170

5.11 CHARACTERIZATION OF ACID OF D-GALACTOSE……………….173

5.12 CHARACTERIZATION OF ACID OF D-FRUCTOSE…………………176

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5.13 CHARACTERIZATION OF ACID OF D-MALTOSE…..………………179

5.14 CHARACTERIZATION OF ACID OF D-LACTOSE………………...…183

5.15 PROPOSED MECHANISM OF KINETICS OF OXIDATION

AGAINST KMnO4……………………………………………………….187

5.16 COMPARATIVE STUDIES……………………………………………...190

5.17 CONCLUSIONS………………………………………………………….193

5.18 FUTURE PERSPECTIVES……………………………………………….195

5.19 RESEARCH IMPORTANCE, APPLICATION AND USE……………...196

Chapter 6 REFERENCES……………………………………...…………198

PUBLISHED PAPER

Acknowledgements

vi

AACCKKNNOOWWLLEEDDGGEEMMEENNTTSS

I am very much grateful to Allah who bestowed upon me the blessing of

accomplishing this work.

I am thankful to my respected supervisor Dr. Rafia Azmat, Department of Chemistry,

Jinnah University for Women, Karachi, who has provided me the research facilities of

lab. I am grateful for her help, cooperation, suggestions and kind guidance throughout

my work.

I am also thankful to Prof. Dr. Fahim Uddin (Former Chairman), Deparment of

Chemistry and Former Dean Faculty of Science for his kind suggestions regarding

thesis.

I am grateful to my respected Vice Chancellor Prof. Dr. Riaz Ahmed Hashmi for

providing me research facilities.

I am thankful to Chairperson of Chemistry Department, Colleagues and “Dean”

Faculty of Science for their cooperation.

My special thanks to Mr. Imran Malik, Dr. Qaiser Fatimi, “H.E.J. Research Institute

of Chemistry, University of Karachi”, and Mr. Khalid Ahmed of University of

Karachi, who were always ready to helped me whenever I needed.

I am thankful to Ms. Zubaida, Ms. Bina and Mr. Shan for their help in providing me

reagents and support at the time of experimental work.

I am also grateful to my brothers Mr. Zahid Hussain and Mr. Syed Hamid Hasan, my

husband Mr. Syed Mudassir Hasan who helped me at the time of compiling thesis.

RAHEELA NAZ M. Sc.

Abstract

vii

AABBSSTTRRAACCTT Sugars containing either aldehyde (aldose), ketone (ketose ) or hemiacetal groups can

be oxidized and are classified as reducing sugars. As oxidation of carbohydrates is

widely studied under the field of organic chemistry, the present research has been

conducted to study the oxidation of reducing sugars (galactose, fructose, maltose and

lactose) with potassium permanganate as an oxidizing agent in sulphuric acid

medium. The rate of oxidation of sugars was monitored by recording the change in

optical density of MnO4- ion at λmax 545nm. The reactions exhibit first order with

respect to [H+], [Sugar] & [MnO4-]. Plots of kobs vs [substrate] were found to be

linear for the oxidation of galactose, fructose, maltose and lactose. A plot of

log[sugar] vs logk gave straight line with slope of the order of unity (0.81, 0.84, 0.48

and 1.20 in galactose, fructose, maltose and lactose respectively). The oxidation

showed that configuration of sugars has some bearing on rate of oxidation. At lower

concentration of oxidants, the linear dependence of reaction rate tends towards new

order at their higher concentration. Poor dependence on ionic strength suggests the

presence of molecular species in the rate determining step.

The rate of reaction was affected at elevated temperature where thermodynamic

activation parameters like activation energy (Ea), enthalpy change of activation

(∆H#), free energy change of activation (∆G#) and entropy change of activation (∆S#)

were determined by Arrhenius and Erying equations. The negative value of entropy of

activation suggests the existence of highly solvated transition intermediate state and

the value of energy of activation suggests the slow kinetics. Hg catalyst was used to

increase the rate of reaction in case of maltose and lactose where reactions proceed

very slowly with respect to time as compared to other sugars used.

[Hg(H2O)6]+2 + MnO4-+ H3O+ O Mn O

OH

O

Hg(H2O)5

+2

+ 2 H2O

Abstract

viii

The positive value for the free energy of activation indicated high electrostatic

interaction between solute and solvent which was supported by the negative value of

∆S# indicating the solvated intermediate state. By considering the first order kinetics

with respect to sugars concentration a mechanism consistent with above findings has

been proposed in the relevant section of this thesis.

TLC and conventional (spot test) methods were used for the verification of oxidation

products of sugars. The main products were formic acid and arabinonic acids which

were detected in the oxidation of all sugars (Galactose, Fructose, Maltose and

Lactose). The other respective acids of each sugar were identified as galacturonic,

fructuronic, malturic and lacturic acid by Fab mass, 1H-NMR and 13C-NMR

spectroscopy.

−− ++⎯→⎯+

+

3610546126 22 MnOHCOOHOHCMnOOHC H

Galactose / Fructose Arabinonic acid Formic acid

−− ++⎯⎯⎯ →⎯++

++

36105/

24112212 42242

MnOHCOOHOHCOHMnOOHC HgH

Maltose / Lactose Arabinonic acid Formic acid

−− ++⎯→⎯++

32710646126 22 MnOOHOHCMnOOHC H

Galactose / Fructose galacturonic / fructuronic acid

−− ++⎯⎯⎯ →⎯+

++

32131812/

4112212 42242

MnOOHOHCMnOOHC HgH

Maltose / Lactose malturic/ lacturic acid

The reactions pathways leading to the formation of above acids have been proposed by

presenting four schemes in relevant section.

Abstract

ix

CHAPTER # 1

IINNTTRROODDUUCCTTIIOONN

Introduction 1Chapter

1

1. INTRODUCTION

1.1 SUGARS Sugars are a class of organic compounds containing several hydroxyl functional

groups and a carbonyl group (aldehyde or ketone) with the capability of forming

an intramolecular hemiacetal or hemiketal.1 The nomenclature suffix "ose" is used

to denote a sugar. The common usage of the word "sugar" signifies table sugar,

which is a disaccharide (sucrose) containing one monosaccharide each of D-

glucose and D-fructose. The monosaccharides also known as simple sugars

possess the general formula CnH2nOn. The name carbohydrate originates falsely

from "carbon hydrate" [C(H2O)]n in which one water molecule was said to be

bound to carbon.1 Despite this initial structural description, the name

carbohydrate has been adapted in literature.

The monosaccharides are classified according to the number of carbon

atoms they contain: triose (n = 3), tetrose (n = 4), pentose (n = 5), hexose (n = 6),

heptose (n = 7) etc.2 The simple basic building block is glyceraldehyde possessing

only one asymmetric centre and therefore two enantiomers. Another type of

classification of sugar compounds is by the nature of the carbonyl groups in their

free, open chain form. A sugar containing an aldehyde is denoted by "aldose" and

one containing a ketone is denoted by "ketose".

Based on the fundamental works of van't Hoff and Fischer, an aldopentose has

eight isomers and an aldohexose has sixteen isomers i.e. eight sets of

enantiomeric pairs.3,4 Two diastereomers, which differ at only one inverted

asymmetric centre, are called epimers.


2

The epimeric relations starting from all–equatorial D-glucose and all axial D-idose

are outlined as follows:

Fig:1.1 Epimeric relations of α- and β-D-glucopyranose and α- and

β-D-idopyranose.

It is evident that there are a large number of sugars exhibiting increasing

structural complexity. The structural complexity increases further when

consideration is given to combinations of monosaccharides leading to

disaccharides, oligosaccharides and polysaccharides.2,5

The most abundant monosaccharide is (+)-D-glucose, also commonly known as

grape sugar, followed by (+)-D-mannose and (+)-D-galactose.1 The least available

monosaccharides are L-altrose, L- and D-idose as well as L- and D-gulose, all of

which are hexoses.

1.2 EQUILIBRIA AND MUTAROTATION OF SUGARS

α-/β-D-Glucopyranose is very stable as a solid. However, isomerization occurs

rapidly in aqueous solution through mutarotation as shown in the following

scheme.2,6 In aqueous solution seven equilibria exist within the D-glucose

system.1 All products of these equilibria are isomers of D-glucose with the

exception of 7, which is a hydrated form. The transformations pathways to all

products occur via the open chain form of D-glucose.


3

The most predominant form is α-D-glucopyranose (1) followed by β-D-

glucopyranose (2). The two five membered ring forms are the α-D-

glucopyranoses 3 with α configuration and 4 with β respectively. The least stable

seven membered forms 5, 6 play only a very minor role in the equilibria network.

The hydrated specie 7 is acyclic similar to D-glucose.

Fig: 1.2 Equilibria of glucose in aqueous solution.

)1( )2(

)3(

)4(

)5( )6(

)7(


4

1.3 OXIDATION PRODUCTS OF SUGARS Aldopyranonses and -furanoses possess three different alcohol functionalities: a

primary alcohol, three secondary alcohol groups and one hemiacetal

hydroxylgroup. These hydroxyl functionalities are identified in figure 1.3 with α-

D-glucopyranose as an example.

Figure 1.3 Different hydroxyl groups of α-D-glucopyranose.

Each of these OH groups can be oxidized to corresponding sugar derivatives as

shown in Figure 1.4. Aldonic acids can be generated by the oxidation at the C1

terminus. These are generally found in lactone form. Three possible keto-sugars

can be generated by oxidation of any of the secondary alcohol function. By

oxidation of the primary alcohol an aldehydo-sugar is formed.


5

Fig:1.4 First oxidation products of glucopyranose.

An aldonic acid is any of a family of sugar acids obtained by oxidation of the

aldehyde functional group of an aldoses to form a carboxylic acid functional

group. Thus, their general chemical formula is HOOC-(CHOH)n-CH2OH.

Oxidation of the terminal hydroxyl group instead of the terminal aldehyde yields

a uronic acid, while oxidation of both terminal ends yields an aldaric acid.

Aldonic acids are typically prepared by oxidation of the sugar with bromine. They

are generally found in their lactone form, with the ring structure essentially the

same as in the original sugar's cyclic hemiacetal form, which is the form the sugar

is usually found in. However, unlike hemiacetals, lactones do not have a chiral

anomeric carbon, and they cannot form glycosidic linkages.

Aldonic acids are found in many biological systems, and are the products of the

oxidation of aldoses by Benedict's or Fehling's reagents. Their lactones are key

intermediates in the Kiliani-Fischer synthesis of sugars.


6

1.4 REDUCING AND NON-REDUCING SUGARS Sugars may be classified as reducing or non reducing based on their reactivity

with Tollen’s, Benedict’s or Fehling’s reagent. If a sugar is oxidized by these

reagents it is called reducing, since the oxidant (Ag+ or Cu+2) is reduced in the

reaction CHO

(CHOH)n

CH2OH

Cu+2 + Cu2O + Oxidation Products

All carbohydrates that contain a hemiacetal group give positive tests (Fig 1.5). In

aqueous solution these hemiacetals exist in equilibrium with relatively small

concentrations of non cyclic aldehydes or α-hydroxy ketones that undergo the

oxidation.

C

O

R/

OHC

C

Fig 1.5 Hemiacetal (R' = H or =CH2OH) Reducing sugar

Carbohydrates that contain only acetal groups do not give positive tests with

Benedict’s Tollen’s solution, and they are called non reducing sugars (Fig 1.6).

Acetals do not exist in equilibrium with aldehydes or α-hydroxy ketones in the

basic aqueous media of the test reagents.

C O

C

R/

O

C

R

Fig 1.6 Acetal (R = Alkyl group or another sugar, R' = H or = CH2OH)

Non-reducing sugar


7

1.5 OXIDATION WITH SOME IMPORTANT OXIDIZING

AGENTS

1.5.1 Bromine Water: The Synthesis of Aldonic Acids The free sugar acids can be obtained by oxidation with aqueous bromine solutions

or electrochemically from their corresponding free monosaccharides.7,8,9 Bromine

water is a general reagent that selectively oxidizes the —CHO group to a —CO2H

group.

CHO

(CHOH)n

COOH

(CHOH)n

CH2OHH2O

Br2

(CH2OH)

Another access to aldonic acids is possible through the Kiliani method, in which

the aldose sugar is reacted with cyanide and the resulting epimeric cyanohydrins

are then hydrolyzed to the homologous aldonic acids.10,11 In this case the carbon

chain is of course lengthened by one atom, i.e. a hexose would yield a heptonic

acid.

CHO

R

HCN CN

ROH

H3O+ COOH

ROH

1.5.2 Nitric Acid Oxidation: Aldaric Acids Dilute nitric acid, a stronger oxidizing agent than bromine water, oxidizes both

the —CHO group and the terminal —CH2OH group of an aldose to —CO2H

groups. These dicarboxylic acids are known as aldaric acids.

CHO

(CHOH)n

CH2OH

HNO3

COOH

(CHOH)n

COOH


8

1.5.3 Periodate Oxidations: Oxidative Cleavage of Polyhydroxy Compounds Compounds that have hydroxyl groups on adjacent atoms undergo oxidative

cleavage when they are treated with aqueous periodic acid (HIO4). The reaction

breaks carbon-carbon bonds and produces carbonyl compounds (aldehydes,

ketones or acids). The stoichiometry of the reaction is

C OH

C OH

+ HIO4 2 C O + HIO3 + H2O

Periodate oxidations are thought to take place through a cyclic intermediate:

C OH

C OH

+ IO4-

C O + IO3--H2O

C O

In these periodate oxidation that for every C—C bond broken, a C—O bond is

formed at each carbon.


9

1.5.4 Other Sugar Oxidation Products

The oxidation of sugar compounds has been widely studied as there is a general

interest to produce value-added chemical building blocks from feedstock other

than petroleum based sources such as cellulose and starch.12-16 e.g. the

modification of cellulose is being studied as part of material science to create new

compounds with improved physical properties such as high water absorption.

CHAPTER # 2

LLIITTEERRAATTUURREE SSUURRVVEEYY

Literature Survey2 Chapter

10

2. LITERATURE SURVEY The study of carbohydrates is one of the most exciting fields of organic chemistry.

Vast literature is available on the kinetics of oxidation of carbohydrates by

various organic and inorganic oxidants.

2.1 OXIDATION OF REDUCING SUGAR BY HALOGENS The oxidation of aldoses by chlorine, bromine and iodine has been reported in

alkaline media.17-19 Patel and co-workers20 worked on oxidation of starch and its

derivatives with chlorine and sodium hypochlorite. The oxidation rate of starch

with NaOCl in buffered systems was highest at pH 7. The OH groups of starch

take an active part in the oxidation rate which decreased when C-2 and C-3 OH

groups were blocked. Zienius and purves21 studied the oxidation of D-

Galacturonic acid with some delignifying and bleaching agents. It was observed

that D-galacturonic acid was oxidized with decreasing ease, and in the

approximate order shown, by excess of the following agents; Sodium chlorite near

pH 2.8 and 75o; sodium hypochlorite at pH 10-11 and 25o; chlorine dioxide, pH

1.3 of 5 at 75o; chlorine 0o and pH 5 (slight); and hydrogen peroxide at pH 10 –

11 and 25o (negligible). Some uronic acid was always recovered uncharged, even

from conditions that would have oxidized glucose quantitatively to gluconic acid.

The only other products were mucic acid, together with DL-tartaric acid and

tartronic acid presumably derived there from. Chlorine dioxide, however, never

produced tartronic acid. Methyl-α-D-galacturonic side methyl ester yielded some

galacturonic acid when exposed to alkaline hypochlorite or peroxide, and this

cleavage of the glycosidic group was tentatively attributed to the oxidants rather

than to the alkalinity of the systems, Anhydrous bromine degraded the silver salt

of Methyl-α-D-galacturonoside in poor yield to a syrup which was probably

L-arabotrihydroxyglutartic dialdehyde.


11

2.1.1 Bromine as an Oxidant The aldonic acids as primary products of oxidation of aldoses by bromine have

been extensively studied by Isbell and co-workers.22-25 It was suggested that

differences in the rates of oxidation of the α and ß anomers are largely determined

by differences in the free energy required by the reactants for passing from the

ground state to the complex in the transition state. The relative rates of oxidation

are in accordance with the hypothesis that each of the aldoses in the ground state

has the conformation predicted by Reeves, and in the plane formed by the ring

oxygen atom, C-1, C-2 and C-5. Presumably, this conformation is stabilized by

resonance involving the oxygen atom of the ring. For aldoses having high stability

in one chair conformation, the rates of oxidation of the anomers differ widely; in

each instance, the anomer in which the C-l hydroxyl group is axial is oxidized

more slowly than the anomer in which this group is equatorial.

2.1.2 Use of Iodine for Oxidation of Sugars

Prasad et al 26 gave the kinetics of oxidation of arabinose and xylose by iodine

in alkaline solution. The order of reaction with respect to iodide ion is unity.

Nizami et al27 studied that kinetics of the oxidation of maltose and lactose by

alkaline iodine solution. The reactions of different concentrations of sugars and

iodine at different pH and temperature were studied. The findings revealed that

iodine followed zero kinetics and the different sugars concentrations followed

first order kinetics. The rate of oxidation of sugars in iodine was independent of

different iodine concentrations. Iodine reacted with sodium hydroxide and then

was converted to triiodide (I3-), Hypoiodate (OI-) and hypoiodous acid (HOI). The

most effective oxidizing agent was HOI.


12

The rate of oxidation reaction was followed first order kinetics with respect to

disaccharide concentration. The rate of reaction was affected by change in pH.

The maximum rates of oxidation of maltose and lactose occurred at pH 11.0. Salt

electrolyte did not affect the reactions. The activation energy for maltose was

60.29 KJ/mol. Singh et al28 investigated the kinetics of oxidation of mellibiose

and cellobiose by alkaline aqueous iodine at different pH. The results indicated

that the active oxidizing species is hypoiodous acid. A first order dependence in

hypoiodous acid, melibiose and cellobiose has been observed.

2.2 OXIDATION THROUGH HALO COMPOUNDS

2.2.1 Hypobromous Acid Yang et al29 studied that the kinetics of the oxidation of glucose with

hypobromous acid in a nearly neutral medium by using spectrometry technique.

The reaction was of first order with respect to glucose and to hypobromous acid

and had a negligible salt effect.

2.2.2 Oxidation with Potassium Bromate

Potassium Bromate has been widely used in the oxidation of various compounds. 30-38 Kalyan et al39 described the kinetics of oxidation of some aldoses and amino

sugars by potassium bromate in hydrochloric acid medium. The reactions appear

to proceed through the intermediate formation of bromate esters followed by the

decomposition of the esters to give products. Hydrogen ion accelerates the rate of

each reaction.


13

Shukla and Bajpai40 studied the kinetics of oxidation of D-(+)-glucose by

potassium bromate in acidic medium. The order with respect to KBrO3 was

determined by Vant Hoff's differential method where as in case of D-(+)-glucose

and H+ it was determined by Vant Hoff's differential method. The reaction is of

first order with respect to substrate and oxidant. A combination of sulphuric acid

and potassium bromate in the presence of SiO2 were used as an effective

oxidizing agent for the oxidation of alchohols to their corresponding aldehyde or

ketone derivatives in dichloromethane, acetonitrile or toluene with good yields.41

Ru (III) catalyzed oxidation of maltose by bromate in acidic as well as alkaline

medium was also studied by Srivastava and co-workers.42,43 They observed first

order kinetics in the lower KBrO3 concentration which become zero order at

higher concentration. The order of reaction with respect to Ru(III) is one.

Srivastava and co-workers44 also studied the Ru(III) catalyzed oxidation of xylose

by an acidified solution KBrO3 in presence of mercuric acetate as a scavenger for

Br- ion. First order kinetics in the lower KBrO3 concentration range tended to zero

order at higher concentration. The order of reaction with respect to substrate is

zero but the order with respect to Ru(III) is one.

2.2.3 Oxidation by Periodic Acid Xiong et al45 showed the oxidation of cellulose with periodic acid by using the

additives under heterogeneous method. The results showed the degree of

oxidation was 100%, when the reaction temperature was increased about 30-40º

and the reaction was shortened to 4 hours.


14

2.2.4 Periodate Reports regarding the use of periodate in the uncatalyzed oxidized oxidation of

carbohydrates and polymeric substrate and Ru(III) and ruthenate ion catalyzed

oxidation of reducing sugars in alkaline medium are also available. 46-48 Singh

et al48 studied the kinetics and mechanism of oxidation of D-glucose and D-

fructose by alkaline solution of potassium iodate in the presence of Ru (III) as

homogenous catalyst. Their results show that the order with respect to [Ru (III)] is

unity and the order wit respect to [reducing sugar] is zero in the oxidation of both

glucose and fructose. Variation in [Cl-] and ionic strength used of the medium

does not affect the oxidation rate.

Varma and Kulkarni49 gave the detailed studies on the sodium metaperiodate

oxidation of cellulose to yield 2,3-dialdehyde cellulose. It has been carried out to

ascertain the effects of concentration of periodate relative to cellulose,

temperature of reaction, pH of the medium. Microcrystal, cellulose had slightly

higher reactivity than cellulose because of its greater purity and lower molecular

weight, which gave rise to more reactive end groups.

Tripathi and Upadhyay50 investigated the kinetics of oxidation of some reducing

sugars viz. glucose, galactose, fructose, maltose and lactose by Os (VIII) in

presence of sodium metaperiodate in alkaline medium. The reactions are zero

order in periodate. The order of reaction in substrate and OH- decreases from

unity to zero at higher [substrate] and [OH-] respectively. Rate of oxidation is

proportional to [Os (VIII)]. Os (VIII) serves as an effective oxidant which oxidizes

reducing sugars and itself reduces to Os (VI). Role of IO4- is to regenerate Os (VIII)

from Os (VI). An evidence for the complex formation between Os (VIII) and

reducing sugar has also been obtained.


15

Singh et al51 gave a general mechanism for Ru (III) catalyzed oxidation of

L(+)arabinose (Ara) and D(+)galactose (Gal) with periodate in aqueous alkaline

medium. The most reactive species of the catalyst was found to be

[RuCl3 (OH)2 H2O]2-. The reactions exhibit pseudo-first order kinetics with

respect to Ru (III) and are first order with respect to lower [IO4-] and [OH-] but

tend towards zeroth order to both higher [IO4 -] and [OH-]. The reactions are zero

order with respect to each aldose. Positive effect of Cl- on the rate of reaction is

also evident in the oxidation of both reducing sugars. The kinetics of oxidation of

maltose by periodate in alkaline medium have also been investigated.52 The

reaction rate is zero order dependent in [IO-4] while the order with respect to

[maltose] and [OH-] is unity.

Oxidation of some reducing sugars by sodium metaperiodate in alkaline medium

was also studied in presence of Ru (III) as a catalyst.53 The kinetic results may be

represented by the following rate law:

[ ] [ ] [ ] [ ] [ ][ ] [ ] [ ]−−

−−−

++=−

40

44

IOSubstratekOHkk

CatalystIOSubstrateOHkdtIOd

IIII

Shenai and Wagh54 reported that the rates of oxidation by sodium periodate of

cellulose and cellulose dyed with reactive dyes at 32oC was markedly increased

by the addition of alkali metal chlorides or sulfates. The extent of oxidative

degradation of cellulose was assessed in terms of oxygen consumption during

oxidation. Srivastava and Singh55 investigated the kinetics of Rh (III) catalyzed

oxidation of sucrose by sodium periodate in acidic medium in the temperature

range 30-50oC. The reaction is carried out in the presence of mercuric acetate as a

scavenger for bromide ion. The rate shows first order kinetics with respect to the

oxidant i.e, sodium periodate and Rh (III) for sucrose.


16

Negligible effect of mercuric acetate and ionic strength of the medium was

observed and the reaction showed no effect of [Cl-] and [H+] on the reaction rate

for sucrose. Srivastava et al56 also studied the kinetics of oxidation of dextrose

and maltose under same conditions. The rate shows first order kinetics with

respect to the oxidant, sodium periodate and Ru (III) for the dextrose and maltose.

Singh et al57 worked on the Ir (III) catalysis of the iodate oxidation of xylose and

maltose in aqueous alkaline medium. The reactions show first order kinetics with

respect to lower [IO-3 ] and [OH-] and show zero order kinetics at their higher

concentrations. Unity order at low concentration of maltose becomes zero order at

its higher concentration whereas zero order kinetics with respect to [xylose] was

observed throughout its variation. The reaction rate is found to be directly

proportional to [Ir (III)].

It is reported that KIO3 has also been used as an oxidant in the oxidation of

acetophenones, 58 ferrocyanide, 59 thiocynate 60 and 1.3-dihydroxybenzene 61 in

acidic medium. In each case IO3- has been regarded as the reactive species of

KIO3 in acidic medium. Kinetic studies for Os (VIII)-59 and Ru (III) catalyzed 59, 62

oxidation of organic compounds by an acidic solution of iodate are also reported.

In these cases either HIO3 or IO3- has also been concluded to be the reactive

species of KIO3 in acidic medium. A few reports are available where NaIO4 has

been as an oxidant in Ru (III) and ruthenate ion-catalyzed oxidation of reducing

sugars in alkaline medium. On the basis of equivalence and kinetic studies for

both the redox processes, IO4- is reported to be finally converted into IO3

-, which

very well supports the existence of IO3- in alkaline medium. In view of the

reported kinetic data and spectral evidence, it can very easily be concluded that

the species IO3- is the reactive species of KIO3 in oxidation of xylose and maltose

in alkaline medium.


17

2.2.5 Electron Transfer Reactions Involving Perchlorate as an

Oxidant Fadnis and Arzare63 determined the kinetics of electron transfer reactions of aquo-

thallium (III) perchlorate with aldo-pentoses (D-xylose, D-arabinose and D-ribose)

under the pseudo-first order conditions. The fractional order with respect to aldo-

pentoses concentrations suggests Michaelis-Menten type of kinetics. The rate

decreases with acid concentration, and is strongly inhibited by the complex

chloride, acetate ions and acetic acid. A free radical mechanism involving aldo-

pentoses derived free radical has been proposed for these reactions.

2.2.6 Hypochlorite Singh64 discussed the rate of uncatalyzed, Mn (II)-catalyzed, and Co (II)-catalyzed

hypochlorite oxidation of cellulose:

[ ] [ ]21

−=− OClHOClkdtdc

The reaction proceeds by a free-radical mechanism. The maximum rate occurred

of cellulose is

[ ][ ]−=− OClHOClkdtdc /

The maximum rate occurs at pH 7.5.

2.2.7 Chloroamine-T Kambo and Upadhay65 studied the kinetics of the Ru (III) catalyzed oxidation of

reducing sugars, viz, arabinose, xylose, galactose, glucose, fructose, lactose and

maltose by chloramines-T in alkaline medium. The reactions exhibit a first order

rate dependence with respect to: [substrate], [chloramine-T] and [OH-]. The rate is

proportional to {k'+k" [Ru (III)]}, where k' and k" are rate constants for

uncatalyzed and catalyzed way respectively.


18

Kambo and Upadhay66 also investigated the kinetics of Pt (IV) catalyzed

chloroamine-T oxidation of glucose, galactose and fructose in alkaline medium.

The reactions are first order in oxidant, while the order reaction in substrate and

OH- decreases from unity at higher [substrate] and [OH-] respectively.

2.3 N-HALO COMPOUNDS The catalyzed and uncatalyzed oxidation sugars have been studied in detail by

using N-halo compounds.67-75 Rangappa et al76 proposed the kinetics and

mechanism of oxidation of three methyl pentoses, namely D-fructose, L-fructose

and L-rhamnose with sodium-N-chloro benzene sulfonamide in alkaline medium

at 313K. Benzene sulfonamide and chloride ion, the reduced product of oxidant

has no effect on the reaction rate. Kanchugarakoppal et al77 studied the kinetics

and mechanism of oxidation of D-glucose, D-mannose, D-fructose, D-arabinose

and D-ribose with N chloro-p-toluene-sulfonamide in alkaline medium. The rate

of reaction was influenced by change in ionic strength of the medium and the

dielectric effect was found to be negative.

N-Bromo-arylsulfonamides of different oxidizing strengths are used for studying

the kinetics of oxidation of D-fructose and D-glactose in aqueous alkaline

medium.78 The results are analysed and compared with those from the

sodium salts of N-bromo-benzenesulfonamide and N-bromo-4-methyl-

benzenesulfonamide. The reactions show zero order kinetics in [oxidant],

fractional order in [Fructose/Glucose] and nearly first order in [OH-].

Gowada et al79 also employed nine sodium salts of mono and di-substituted N-

Chloroarylsulfonamides as an oxidant for studying the kinetics of oxidation of

D-fructose and D-glucose in aqueous alkaline medium. The reactions show first

order kinetics each in [oxidant], [Fructose/Glucose] and [OH-]. The rates slightly

increase with increase in ionic strength of the medium.


19

Rahmani et al80 studied the kinetics of Ir (III)-catalyzed and Hg (II)-co-catalyzed

oxidation of D-glucose (Glu) and D-fructose (Fru) by N-bromoacetamide (NBA)

in acidic medium. The reactions follow identical kinetics, being zero order in each

sugar concentration. The experimental results show a first-order dependence on

NBA and Ir (III) at low concentrations, but tending towards zeroth order at higher

concentrations. A negative effect of variation of [H+], [Cl-] and [NBsA] was

observed whereas the ionic strength (I) of the medium has no influence on

oxidation rate. The important feature of the reaction is that it follows a second-

order dependence on mercury (II) ion concentration at low concentrations, but it

tends towards first order at higher concentrations. The corresponding acids were

identified as the main oxidation products of the reaction.

Kumar et al81 gave the kinetics of oxidation of reducing sugars D-galactose and

D-ribose by N-bromoacetamide (NBA) in the presence of Ru (III) chloride as a

homogenous catalyst and in perchloric acid medium, using mercuric acetate as a

scavenger for Br- ions, as well as a co-catalyst.

Singh et al82, 83 studied the kinetics of Pd (II) catalyzed and Hg (II) co-catalyzed

oxidation of D-glucose D-fructose, D-mannose and D-maltose by N-

bromoacetamide (NBA) in the presence of perchloric acid using mercury (II)

acetate as a scavenger for Br- ions. The results showed first-order kinetics with

respect to NBA at low concentrations, tending to zero order at high

concentrations. First order kinetics with respect to Pd (II) and inverse fractional

order in Cl- ions throughout their variation have also been noted. The observed

direct proportionality between the first order rate constant (k1) and the reducing

sugar concentration shows departure from the straight line only at very higher

concentration of sugar. Addition of acetaminde (NBA) decreases the first order

rate constant while the oxidation rate is not influenced by the change in the ionic

strength (µ) of the medium.


20

Variation of [Hg(OAc)2] shows a positive effect on the rate of reaction. The

observed negative effect in H+ at lower concentrations tends to an insignificant

effect at its higher concentrations.

Kinetic studies have also been made for the oxidation of reducing sugars by acidic

solution of N-bromosuccinimide (NBS) in presence of Ir (III) as the homogenous

catalyst.84 Moreover, the role of Pd (Il) chloride as a catalyst in NBS oxidation of

arabinose, xylose and galactose by N-bromosuccinimde (NBS) in acidic medium

using Hg (OAc)2 as a scavenger for the Br- ion has also been reported.85 The

reaction data showed the first order kinetics in each pentose and hexoses at low

concentration tend to zero order at high concentration. First order kinetics with

respect to NBS and Pd (II) and inverse fractional order, i.e, decreasing effect of

[H+] and [Cl-], were observed, whereas ionic strength Hg (OAc)2 and succinimde

did not influence the oxidation rate. Various activation parameters have been

calculated and recorded. The corresponding acids, arabinonic, xylonic and

galactonic were identified as the main oxidation products of the reactions.

Several researchers worked upon oxidation kinetics involving N-

bromosucccinimide (NBS) and esters86, alcohols 87 and 88, ketones 89-91, polyhydric

alcohols 92 and glycol 93 as oxidizing agents. It is also known that NBS oxidation

of organic compound is complicated by parallel bromine oxidation. However,

bromine oxidation is obviated by using Hg (II).86 The repeating sequences of

elastin, glycyl–glycyl–alanyl–proline (GGAP) glycyl–glycyl–isoleucyl–proline

(GGIP) and more hydrophobic glycyl–glycyl–phenylalanyl–proline (GGPP), were

synthesized by classical solution phase methods and characterized.94 The kinetics

of oxidation of tetrapeptides (TPs) and their constituent amino acids (AAs) by N-

bromosuccinimide (NBS) was studied in the presence of perchlorate ions in acidic

medium at 28 °C. The reaction was followed spectrophotometrically at

λmax 240 nm.


21

The reactions follow identical kinetics, being first order each in [NBS], [AA] and

[TP]. No effect on the rate of [H+], reduction product [succinimide] and ionic

strength was observed. Effects of dielectric constant of the medium and the added

anions such as chloride and perchlorate were studied. Activation parameters have

been computed. The oxidation products of the reaction were isolated and

characterized. An apparent correlation was noted between the rate of oxidation

and the hydrophobicity of AAs and TPs.

2.4 OXIDATION THROUGH TRANSITION METALS

2.4.1 Manganese (Mn) Khan and Kumar95 describe the oxidative degradation of gum Arabic by colloidal

manganese dioxide (MnO2). Monitoring the disappearance of the MnO2

spectrophotometrically at 375 nm was used to follow the kinetics. The oxidation

obeyed fractional-order kinetics with respect to the [gum Arabic]. Effects of

various experimental parameters such as the initial colloidal [MnO2], [HClO4],

temperature, and complexing agents (P2O74-, F-, and Mn2+) for the oxidation of

gum arabic were studied. The reaction was acid catalyzed. Addition of P2O74-, F-,

and Mn2+ ions enhances the rate of oxidation significantly. Gum arabic adsorbs on

to the surface of the colloidal MnO2 through the equatorial – OH groups of the

rhamnose moiety, and the complex breaks down into products. The reducing

nature of gum arabic is found be due to the presence of –OH group in the

skeleton.

Gupta and Begum96 studied the kinetics of oxidation of some aldoses, amino

sugars and methylated sugars by tris- (pyridine-2-carboxylato) manganese (III)

spectrophotometrically in sodium picolinate-picolinic acid buffer medium.


22

Sricar et al97 determined the glucose, fructose, xylose, arabinose, and sucrose

titrimetrically using Mn (III) sulfate as an oxidant. On reaction in the dark, glucose

consumes 5, fructose 7, xylose and arabinose 6 each, and sucrose after hydrolysis

12 equivalent of Mn (III)/mol, respectively.

2.4.2 Cerium (Ce) Pottenger and Johnson98 examined that Ce (IV) oxidations of model compounds

for the hydroxylic functional groups of cellulose in 1.0 mol dm-3 perchloric acid.

Glucose, the model selected for the reducing end group was oxidized 360 times

faster than Schardinger β-dextrin, the model for anhydro-D-glucose repeating

units. In the presence of a fourfold excess of glucose, stoichiometry indicated

specific conversion to arabinose; the competitive oxidation of arabinose produced

is insignificant. Kinetic studies showed that chelate complexes were involved in

the oxidations of glucose, methyl β-D-glucopyranoside, 1, 5-anhydro-D-glucitol

and Schardinger-dextrin.

Agarwal99 studied the kinetics of oxidation of mannitol by Ce (IV) in sulphuric

acid medium. The spectral analysis of hydrazone derivative of the product

indicates the product to be an aldehyde. The substrate forms an intermediate

complex with the oxidant as observed both kinetically and

spectrophotometrically. Ce (SO4)2 has been considered to be the reactive species.

The rate of bromide catalyzed oxidation of fructose by Ce (IV) has been measured

by Sah100 in aqueous sulphuric acid medium at constant ionic strength. The

reaction is first order dependent each in fructose and Ce (IV). The rate of reaction

decreases on increasing the concentration of hydrogen ion. The bromide ion

shows positive catalytic effect on the reaction rate.

Sharma and Sah101 discussed the kinetics of bromide catalyzed oxidation of

dextrose by Ce (IV) in aqueous sulphuric acid medium which showed first order

dependence each in dextrose and Ce (IV). The reaction rate decreases on

increasing the concentration of hydrogen ion. The bromide ion shows positive


23

catalytic effect on the reaction rate. The kinetics and mechanism of cerium (IV)

oxidation of hexitols i.e. D-sorbitol and D-mannitol in aqueous sulfuric acid

media have been studied in the presence and absence of surfactants.102 The over

all process shows first order dependence on [Ce (IV)]T and [S]T and is acid

catalyzed and inhibited by [HSO4-]. Singh et al103 examined the Ce (IV) oxidation

of dextrose and sorbose in aqueous sulphuric acid medium. This reaction shows

first order kinetics with respect to both Ce (IV) as well as the substrate. The

reaction rate decreases on increasing the concentration of hydrogen ion. The

variation of sulphate ions shows retarding effect on the reaction rate.

Din et al104 observed the effect of surfactant micelles on the kinetics of oxidation

of D-fructose by cerium (IV) in sulphuric acid medium. Kinetics of the oxidation

of D-fructose by cerium (IV) has been investigated both in the absence and

presence of surfactants (cetyltrimethylammonium bromide, CTAB, and sodium

dodecyl sulphate, SDS) in sulphuric acid medium. The reaction exhibits first

order kinetics each in [Ce (IV)] and [D-Fructose] and inverse first order in

[H2SO4]. The Arrhenius equation is found to be valid for the reaction between 30-

50oC. While SDS has no effect, CTAB increases the reaction rate with the same

kinetic behavior in its presence. The catalytic role of CTAB micelles is discussed

in terms of the pseudo phase model proposed by Menger and Portony. The

association constant Ks that equals to 286 mol-1 dm3 is found for the association of

Ce (IV) with the positive head group of CTAB miscelles.

2.4.3 Vanadium (V) Khan et al105 proposed the oxidative degradation of D-fructose by V (V) in the

presence of H2SO4 as an induction period followed by auto acceleration. The

kinetics and mechanism of the induction period has been studied at constant ionic

strength. The reaction was followed spectrophotometrically by measuring the

change in absorbance at 350nm. V (V) is only reduced to V (IV).


24

The reaction is first and fractional order in [V (V)] and [D-fructose], respectively;

but dependence on [H+] is complex. At constant [H2SO4] sodium hydrogensulfate

accelerates the reaction. The effect of added sodium sulfate on the H2SO4 and

HSO4– catalyzed reaction is also reported. Reaction products are also examined

and it is concluded that oxidation of D-fructose by V (V) involves consecutive

one-electron abstraction process. Rizvi and Singh106 reported the reaction of some

monosaccharides with ammonium metavanadate in sulphuric acid. It has been

followed potentiometrically and kinetically. The results are consistent with the

mechanisms proposed by Water and Soffyn. Bhattnagar and Fadnis107 discussed

the rate of oxidation of D-ribose with quinquevalent vanadium. The reaction

involving C-C bond fission and via free radical has been proposed.

The kinetics of oxidation of lactose by vanadium (V) in sulfuric acid perchloric

acid and hydrochloric acid media was studied.108 The reaction was of first order

with respect to oxidant and substrate. The reaction was catalyzed by acids but the

dependence on acidity is complex. Kumar and co-workers109 studied the kinetics

of oxidation of D-maltose by quinquevalent vanadium in aqueous sulphuric acid.

The order of reaction with respect to the oxidant and substrate has been found to

be one.

2.4.4 Chromium (Cr) Sala et al110 studied the oxidation of D-lactose, D-maltose, D-melibiose and

D -cellobiose by Cr (VI) yield the corresponding aldobionic acid and Cr (III) as the

final products, when an excess of reducing disaccharides over Cr (VI) is used. The

rate law for the Cr (VI) oxidation reaction is expressed by

( )[ ] [ ] ( )[ ]VICrdedisaccharikdt

VICrdH=−

where the second order rate constant kH depends on [H+]. The relative reactivity

of the disaccharides with Cr (VI) is expressed as Mel.> Lac.> Cel.> Mal.


25

At 33ºC in acidic medium, intermediate Cr (V) forms and reacts with the substrate

faster than Cr (VI). The EPR spectra show that five- and six- coordinate oxo-Cr (V)

intermediates are formed, with the disaccharide acting as a bidentate ligand. Five-

coordinate oxo-Cr(V) species are present at any [H+], where as six- coordinate

ones are observed only at pH<2 where they rapidly decompose to the redox

products.

Sala et al111 also discussed the kinetics of oxidation of L-rhamnose and D-

mannose by Cr (VI) in perchloric acid leading to L-1,4-rhamnonelactone and D-

1,4-mannonelactone. Relative values of kinetic constants are interpreted in terms

of primary hydroxyl group participation in the chromic ester formed in the first

reaction step. The free radicals formed during the reaction react with Cr (VI) to

yield Cr (V). Sharma and Rai112 showed the oxidation of D-galactose, D-xylose

and D-arabinose by chromium peroxydichromate in very dilute sulphuric acid.

The reaction is of first order each in substrate, oxidant and sulphuric acid. HCrO4-

appears to be the predominant oxidant.

The kinetics of the reduction of Cr (VI) to Cr (III) by D-fructose in HClO4 was

studied by Garcia et al.113 The redox reaction involves the formation of

intermediate Cr (V) and Cr (V) species. Cr (IV) reacts with fructose much faster

than Cr (V) and Cr (VI) do. The kinetics and mechanism of Cr (VI) oxidation of

fructose in the presence and absence of 2,2-bipyridyl (bipy) and 1,10-

phenanthroline (phen) in aqueous media have been studied.114 The monomeric

species of Cr (VI) has been found to be kinetically alkaline in the absence of bipy

and phen whereas in the heteroaroms.


26

2.4.5 Osmium (Os) Singh et al115 proposed the general mechanism for oxidizing reducing sugars

(pentoses, hexoses and disaccharides) by OsO4 in alkaline medium. The reactions

exhibit pseudounimolecular kinetics with respect to OsO4, are first order with

respect to lower [sugar] and [OH-], but tend towards zero order with respect to

both higher [sugar] and [OH-].

2.4.6 Copper (Cu) Singh116 reported the oxidation of maltose and lactose by Cu (II) in the presence of

ammonium hydroxide. The reactions are zero order in Cu (II) and first order in

substrate and hydroxide ion concentration. It was suggested that the rate

determining step involves the reaction between hydroxyl ion and reducing sugar,

leading to an intermediate active product which is rapidly oxidized by Cu (II)

complex through an electron transfer process. Cu (II) oxidation of D-xylose, L-

arabinose, D-glucose, D-fructose, D-mannose, D-galactose, L-sorbose, lactose,

maltose, cellobiose and melibiose in alkaline medium was studied by Singh and

co-workers.117 The reaction showed a first order dependence with reducing sugar

and alkalis concentration and the oxidation process was independent of

Cu (II) concentration for all the reducing sugars.

2.5 TRANSITION METALS AS CATALYST IN OXIDATION

REACTIONS

2.5.1 Bismuth (Bi)

Karshi and Witonska118 determined the effect of Bi on the catalytic properties

used for oxidation with oxygen of glucose to gluconic acid in liquid phase at

1 atm pressure, 333K temperature and pH 9. Addition of Bi resulted in an

increased activity and selectivity of the Pd/SiO2 catalyst.


27

Wenkin et al119 showed that Bi is a well-established promoter of noble metal

based catalysts for the selective liquid phase oxidation of alcohols, aldehydes and

carbohydrates with molecular oxygen. Experiments were carried out to improve

the understanding of the promoting role of bismuth in bimetallic Pd-Bi catalysts

used for the selective oxidation of glucose to gluconate. These catalysts undergo

substantial bismuth bleaching under the reaction conditions. The bleaching

process and the promoting effect itself are discussed in line with formation of

Bi-glucose and the Bi-gluconate complexes present in solution but also as

adsorbed species at the catalyst surface.

2.5.2 Rhodium (Rh) The use of Rh (III) chloride as catalyst has been reported by several workers. 120, 21

Srivastava and Singh55 investigated the kinetics of Rh (III) catalyzed oxidation of

sucrose by sodium periodate in acidic medium in the temperature range 30-50oC.

The reaction is carried out in the presence of mercuric acetate as a scavenger for

bromide ion. The rate shows first order kinetics with respect to the oxidant i.e,

sodium periodate and Rh (III) for sucrose.

2.5.3 Ruthenium (Ru) Ru (III) catalyzed oxidation of maltose by bromate in acidic as well as in alkaline

medium was also studied by Srivastava and co-workers.42,43 Singh et al48 studied

the kinetics and mechanism of oxidation of D-glucose and D-fructose by alkaline

solution of potassium iodate in the presence of Ru (III) as homogenous catalyst. Kinetic studies for Os (VIII)59 and Ru (III) catalyzed 59, 62 oxidation of organic

compounds by an acidic solution of iodate are also reported. Kumar et al81 gave

the kinetics of oxidation of reducing sugars D-galactose and D-ribose by N-

bromoacetamide (NBA) in the presence of Ru (III) chloride as a homogenous

catalyst and in perchloric acid medium, using mercuric acetate as a scavenger for

Br- ions, as well as a co-catalyst.


28

2.5.4 Platinum (Pt) Basson et al122 showed that the glucose and the gluconate aqueous solutions were

oxidized with air (atmospheric pressure, 333K, pH 7) on active charcoal-

supported, platinum catalysts. The activity of unpromoted Pt/C catalysts for

glucose oxidation was comparable with that of Pd-Bi/C catalysts and there was no

deactivation. The oxidation of gluconate on very well dispersed Pt catalysts

prepared by cationic exchange or anionic adsorption leads to higher glucarate

selectivities. Van Dam et al123 showed that the factors affecting the activity of the

Pt catalyzed oxidation of glucose 1-phosphate I glucuronic acid 1-phosphate II. A

partial loss of starting material occurs through side reactions starting with the

oxidation of secondary hydroxyl groups, followed by C-C bond cleavage.

2.5.5 Palladium (Pd) Basson et al124 investigated the influence of the size of Pd particle and of their

location supports on the activity of glucose oxidation. Abbadi et al125 showed the

effect of pH on the palladium catalyzed oxidation of glucose to gluconic acid. The

oxidation reactions were performed in the pH range 2 to 9 in a batch reactor using

Pd/C or Pd black as the catalysts. It is concluded that gluconic acid in its free

form reversibly inhibits the oxidation process in acidic media.

2.5.6 Mercury (Hg) Mercury has been widely used as a catalyst or a co-catalyst by many researchers

for the oxidation of sugars. Rahmani et al80 studied the kinetics of Ir (III)-catalyzed

and Hg (II)-co-catalyzed oxidation of D-glucose (Glu) and D-fructose (Fru) by N-

bromoacetamide (NBA) in acidic medium. Kumar et al81 gave the kinetics of

oxidation of reducing sugars D-galactose and D-ribose by N-bromoacetamide

(NBA) in the presence of Ru (III) chloride as a homogenous catalyst and in

perchloric acid medium, using mercuric acetate as a scavenger for Br- ions, as

well as a co-catalyst.


29

Singh et al82-83 studied the kinetics of Pd (II) catalyzed and Hg (II) co-catalyzed

oxidation of D-glucose D-fructose, D-mannose and D-maltose by N-

bromoacetamide (NBA) in the presence of perchloric acid using mercury (II)

acetate as a scavenger for Br- ions.

2.6 AIR OXIDATION Heinen et al126 discussed the oxidation of D-fructose with molecular oxygen on

Pt/C catalysts. Two major products are formed: 2-keto-D-gluconic acid

D-threohexo-2, 5-diulose. Deactivation of the catalyst was observed, caused both

by over-oxidation of the active surface and inhibition of the reaction by 2-keto

gluconic acid. Bao et al127 discussed the air oxidation of glucose catalyzed by free

and immobilized glucose oxidase. It was carried out in the gluconate buffer

solution prepared to develop an efficient production of calcium gluconate crystals.

The optimal pH, temperature and gluconate concentration as well as the kinetic

parameters in the Michaelis-Menten rate expression were determined for the free

enzyme reaction in an airtight batch reactor. The fine manganese dioxide particles

were entrapped together with glucose oxidase within the calcium alginate gel

beads to decompose hydrogen peroxide produce in the oxidation. Shalaby et al128

discussed the chromatographic method for the separation, identification and

estimation of the products formed when saccharides are oxidized in alkaline

solution with oxygen. The technique was then used to quantitate the acids

produced when glucose is subjected to such an oxidation.

Gleason and Barker129 studied the oxidation of pentoses ( D-xylose, D-ribose and

L-arabinose and D-lyxose) with oxygen in alkaline solution. The reaction of

pentoses with oxygen in dilute aqueous sodium hydroxide at 25.00 + 0.05o has

been studied by determining the initial rate of oxygen uptake and the rate of

disappearance of reducing sugar. Pentoses reactivity decreased through the series:

D-ribose, D-lyxose, D-xylose and L-arabinose.


30

2.7 HYDROGEN PEROXIDE (H2O2) Nogues et al130 studied the structure changes, i.e. crystallinity, induced in

cellulose fibers by oxidation during mercerization, laundering, etc. using FTIR

Spectroscopy and measurements of total crystallinity index and lateral order

index. The treatment with H2O2 of ramie and flax fibers resulted in an increase in

the ratio of crystallinity in cellulose due to oxidative hydrolysis. At high H2O2

concentration, partial transformation of cellulose 1 to cellulose 2 occurred.

Velarde et al131 determined the oxidation of D-glucose with hydrogen peroxide as

an oxidant over several titanium-containing zeolites and Titania as catalysts. The

oxidation of D-glucose occurred mainly to gluconic acid, glucuronic acid, tartaric

acid, glycolic acid and glyceric acid.

2.8 OXIDATION INVOLVING TRANSITION METAL

COMPLEXES AS OXIDANTS Bajpai et al132 observed an inhibited effect of PdCl2 on the rate of oxidation of

sugars by alkaline hexacyanoferrate (III). The order of reactions in

hexacyanoferrate (III) and OH- is zero and unity respectively, while that in sugars

decreases from unity at higher sugar concentration. The kinetic data and

spectrophotometric evidence support the formation of {Pdll – (sugar)} and

{Pdll – (sugar)2} complexes and their resistance to react with Fe(CN)63-.

Hexacyanoferate (III) was also used by Srivastava and co-workers133 for the

oxidation of some disaccharides in alkaline medium. The order of reaction is zero

with respect to ferricyanide and first with respect to reducing sugar.

Krishna and Rao134 investigated the kinetics of oxidation of D-glucose,

D-galactose, D-fructose, D-ribose, D-arabinose, D-xylose and 2-deoxy-D-glucose

by diperiodatoargentate (III) (DPA) in an alkaline medium. The order of the

reaction with respect to [DPA] is unity while the order with respect to [sugar]

is < 1 over the concentration range studied. The rate increases with an increase in

[OH-] and there is a marginal decrease in rate with an increase in [IO4-]. No


31

significant dependence on ionic strength was found, but the rate increases with a

decreasing dielectric constant. Formic acid and the corresponding aldonic acids

were detected as the products of oxidation. Srivastava et al135 worked on

oxidation of D-maltose by aquasulfate cerium (IV) complex. The rate determining

step is the formation of free radicals from the hydrolyzed substrate molecule.

Gupta et al136 investigated the kinetics and mechanism of oxidation of lactose and

maltose by tetraaminecopper (II) in ammonical and buffered medium. The rate of

the reaction is dependent of [Cu(II)] and directly proportional to [dissacharide]

and square root of [NH3]. On addition of NH4Cl the reaction rate decreases due to

common ion effect.

2.9 INORGANIC OXIDANTS Inorganic oxidants such as Cu (II), ammonical Ag (I) and Nesseler’s reagent have

been used in the uncatalyzed oxidation of sugars in aqueous alkaline medium.137-

139 Nessler's reagent was used to oxidize maltose and cellobiose. The reaction rate

is completely independent of initial [Hg(II)] and is first order with respect to

reducing [Sugar]. The reaction rate followed first order kinetics at low [OH-] and

retarded with increasing iodide ion concentration.

Modi and Ghosh140 gave the kinetic studies of oxidation of fructose by

ammonical silver nitrate. The rate of reaction is of first order with respect to silver

nitrate but has a tendency to increase at a lower temperature or decreasing

ammonia concentration. The mechanism of the oxidation of fructose by

ammonical silver nitrate is suggested through the enolic transformation of the

carbonyl group. The determination of the number of equivalents of silver

consumed per mole of monosaccharide shows that the molecule undergoes a

fission reaction to yield glycolic and oxalic acid as oxidized products. Cerchiaro

et al141 described an interesting Isatin-Schiff base copper (II) complex,

[Cu(isapn)](ClO4)2 where (isapn)=N,Nt –[bis-(3,3t-indolin-2-one)]-1,3-diamine-

propane, was prepared and characterized by different techniques, both in the solid

state and in solution, and its reactivity toward carbohydrate oxidation was


32

verified. This compound was shown to catalyze the oxidation of hexoses (glucose,

fructose and galactose), in alkaline media, via reactive oxygen species, which

were detected by using specified enzymes, and by E.P.R. spin trapping. The

reaction was monitored at (25.0 ± 0.1) ºC by the consumption of oxygen, and

showed first-order dependence on catalyst, followed by a saturation effect. First-

order kinetics with respect to [OH-] concentration was also observed, indicating

that enolization of the substrate as well as the metal-catalyzed enediol oxidation

are the rate-determining steps.

Abualreish142 worked on the mechanism of oxidation of arabinose, fructose and

lactose by peroxydisulphate. The reactions are first order in peroxydisulphate and

of fractional order in substrate concentrations. Tomar and Kumar143 studied the

oxidation of D-fructose by tetraethyl ammonium chlorochromate

[(C2H5)4NCrO3Cl] in aqueous acetic acid. The reaction has been found to be first

order with respect to each of the oxidant and substrate under pseudo first order

conditions. The reaction follows a first order dependence on H+ ion concentration

while variation of ionic strength has no effect on the reaction rate. The kinetics

and mechanism of oxidation of D-ribose, D-glucose and D-fructose by

dichloroisocynauric acid (DCICA) in aqueous acetic acid-pechloric acid mixtures

catalyzed by Ru (III) have been investigated.144 The oxidation has the following

kinetic order: first order in oxidant and Ru (III) and zero order in substrate and H+.

2.10 OTHER OXIDATION REACTIONS Tronchet and Bourgeoes145 discussed the treatment of the 1,2,5,6-di-O-

isopropylidene-α-D-ribo- and xylo-hexofuranos-3-uloses with cyanomethylene

triphenylphosphorane led in each case, and in almost quantitative yields, to a pair

of geometrical isomers of C-cyanomethylenic sugars having respectively the ribo

and the xylo configurations. Permanganate oxidation of these branched-chain

unsaturated sugars yielded the corresponding gemhydroxyformyl compounds

bearing the formyl group on the more hindered face of the molecule. The formyl


33

group of these sugars is easily reduced to a hydroxymethyl group. Tildom et al146

observed the rates of [6-14C]-glucose oxidation by reconstituted systems of

cytosol and mitochondria or cytosol and synaptosomes were essentially the same

as the rate of oxidation of [3-14C]-3-hyroxybutyrate. However, the rate of [U-14C]-

glutamine oxidation by mitochondria was 2.5 times that by synaptosomes. The

addition of glutamine (5 mM) caused a reduction in the rates of oxidation of [6-14C]-glucose of 20% and 40% by mitochondria and synaptosomes respectively.

Singh et al147 discussed the kinetic study of oxidation of D-glucose, D-fructose,

D-mannose and D-galactose by quinolinium chlorochromate C9H7NH [CrO3Cl] in

the presence of perchloric acid in aqueous acetic acid medium. The reaction

exhibits first order dependence in oxidant and substrate both under pseudo-first

order conditions. The reaction is catalyzed by acid and a medium of low dielectric

constant favors the oxidation process. Lu et al148 gave the synthesis of sorbitol

and gluconic acid by electro-reduction and electro-oxidation of glucose. The

optimum conditions of sorbitol synthesis and gluconic synthesis include Cc.d.0.18

A.cm-2,temperature of reaction: 30º, initial concentration of glucose: 0.11 mol L-1,

concentration of supporting electrolyte: 0.15 mol L-1 and c.d.0.18 A.cm-2,

temperature of reaction: 50º, initial concentration of glucose: 0.04 mol L-1,

concentration of supporting electrolyte: 0.2 mol L-1 respectively. Under these

conditions the current efficiency was 86.84% and 76.50% respectively.

King et al149 studied that cellulose web was fabricated by electrospinning process

under high voltage. Also, oxidized cellulose web was made by oxidation process,

which involved the reaction of cellulose web with a mixture of nitrogen dioxide

and perfluorocarbon. It was developed to prevent the adhesion of human body.

Biella et al150 described the selective oxidation of D-glucose to D-gluconic acid. It

was performed at both controlled (7-9.5) and free pH values in an aqueous

solution in the presence of gold on carbon catalyst using dioxygen. No

isomerisation of glucose to fructose was observed during the reaction, and total


34

selectivity to D-gluconate was obtained. Ibert et al151 gave the side products

formed in the TEMPO-mediated oxidation of glucose to glucaric acid. Next to

gluaric acid, gluconic acid, the intermediate in the oxidation and the degrading

products, oxalic acid, tartonic acid, meso-(erytharic) and DL-threaric (tartaric)

acid were detected. The DL-tartaric acid to be non-racemic mixtures of L-and D-

tartaric acid, with inverse D/L ratios depending on the oxidation of the D- of L-

glucose.

Lundt et al152 showed the references on the chemoenzymic oxidation, reduction

and deoxygenation reactions at the anomeric carbon of unprotected and protected

carbohydrates and glycosides in preparation of lactose and alditols. Reactions on

metal catalysts using oxygen and hydrogen peroxides, as well as microbial

oxidation of carbohydrates, are emphasized. Wang et al153 reported that the starch

adhesive was prepared from cassava starch by mixing it with water, oxidizing

with KMnO4 in the presence of moderator. The effects of added concentration of

oxidizing agent and oxidation time on the quality of the adhesive were studied.

Cassiano and Almeida154 proposed the anodic oxidation of 0.80 mol L-1glucose (I)

in the presence of fructose, from HCl hydrolysis of sucrose (II) in the presence of

0.050 mol L-1 bromide as catalyst and 0.80 mol L-1 as supporting electrolyte.

Preliminary electrolytic studies with I allowed the best working conditions with II

hydrolyzates to be established. The sodium gluconate solution obtained was

precipitated with a stoichiometric concentration of CaCl2 in order to obtain Ca

gluconate.

Pao et al155 discussed a method of analysis where the sample was treated with

oxidase to produce H2O2, and H2O2 reacts with a color reagent in the presence of

peroxidase and is detected through Raman spectroscopy. Delobeau and Moine156

showed that the lactose solutions are hydrolyzed, the resulting glucose-galactose

mixture is oxidized to give mixtures of D-arabinose and D-xylose, and this

mixture is hydrogenated to give D-arabitol.


35

Agarwal and Tiwari157 gave the kinetics of oxidation of D-mannose with

pyridinium chlorochromate, C5H5NHCrO3Cl, in aqueous perchloric acid medium.

The ionic strength of the medium was maintained constant by adding sodium

perchlorate solution. The oxidation process exhibits unit dependence in each of

the reactants, namely D-mannose and pyridinium chlorochromate. The reaction is

acid catalyzed. A 3:2 stoichiometry is observed in the oxidation and the reaction

did not induce polymerization of acrylonitrile. Miljkovic et al158 determined the

oxidation of D-glucose (I) with 36 % H2O2 in presence of CaCO3 and I2 in

1:5:3:0:1 ratio gave 18.8 % Ca D-gluconate (II) after 4 hours at 60º. Oxidation of

(I) with I2 in H2O containing CaCO3 in 1:1:2 ratios at 90º for 3 hours gave 59.5%

II. D-fructose was inert to these conditions, and did not affect I oxidation to II.

Blazicek and Langr159 discussed that the oxidation of cotton cellulose with N2O4

gave monocarboxycellulose with less ordered structure than that of the initial

material.

Glattfeld and Hanke160 used hydrogen peroxide and air to oxidize maltose in

alkaline solution. They explained the formation of oxidation products by

assuming that the free glucose unit of maltose is first enolized and the enols, after

breaking, either become oxidized at once or undergo certain rearrangements with

subsequent oxidation.

Ross and McCarl161 observed the rates of uptake and oxidation of glucose, lactate,

pyruvate, and palmitate were measured for "mixed" cultures of rat heart cells that

exhibit a myocyte-to-fibroblast ratio similar to that observed in vivo. Glucose

uptake and conversion to lactate were also measured using enriched cultures of

myocytes and fibroblasts. The metabolism of mixed cultures, which contain 70-

80% myocytes, closely resembles that of enriched myocyte cultures. The energy

production and substrate oxidation rates of cultured neonatal heart cells, adult

myocytes, and perfused hearts are compared. It appears that the energy

requirements of cultured heart cells are much lower than that of whole tissue.


36

Kuptsan et al162 showed that CoSO4-catalyzed oxidative degradation of cellulose

in alkaline medium is a free radical process. The presence of catalyst increases the

rate and extent of the degradation.

Giffhorn et al163 and Freimund et al164-165 reported that the enzyme 2-glucose-

oxidase catalyzed the oxidation of sugar substrates to 2-oxo-sugars as illustrated

in Fig.2.1. The enzyme had been harvested from fungi. The proposed actual

oxidant used by the enzyme was oxygen from the air generating hydrogen

peroxidase by-product. The generated hydrogen peroxide was disproportionated

to water and oxygen by a peroxidase in order to avoid undesired side reactions of

hydrogen peroxide with the sugar products and enzyme present in the reaction

solution.

α-D-glucopyranose 2-oxo-α- D-glucopyranose

Fig: 2.1 Synthesis of 2-oxo-α- D-glucopyranose from α- D-glucopyranose with an enzymatic process.


37

2.11 REACTIVE FORMS OF SUGARS IN ALKALINE

MEDIUM It is reported that in the presence of alkali reducing sugars undergo a tautomeric

change resulting in the formation of an enediol anion and enediol.166

C O

C OH

H

R

+ OH-

C O-H

C OH

R

+ H2OH

CH

C OH

O-

R

+ H2O

CH

C OH

OH

R

+ H2O

enediol anion

enediol anion (1,2-endiol)

C OH

H

C

R

O + OH-

C OHH

C

R

O- + H2O

C OHH

C

R

O- + H2O

CH

C OH

OH

R

+ OH-

(1,2-endiol)enediol anion

The formation of the enediol anion and the enediol in the presence of alkali is also

supported by the work of Isbell and co-workers. 167


38

2.12 PERMANGANATE AS AN OXIDIZING AGENT

Rao et al168 discussed the kinetics of oxidation of some monosaccharide viz., D-

ribose, D-xylose, D-arabinose, D-glucose, D-fructose, D-galactose, 2-

deoxyglucose, and α-methyl glucopyranoside by MnO4- in aqueous alkaline

medium. The rate of oxidation has been found to be first-order both with respect

to [oxidant] and [sugar]. The rate is independent of [OH-] under experimental

conditions of [OH-] > 0.5 M where the oxidant is stable. The effect of ionic

strength is negligible on the rate. A mechanism involving the formation of a 5-

membered cyclic intermediate complex between MnO4- and 1,2enediol form of

the sugar is proposed.

Ahmed et al169 observed the kinetics of oxidation of chitosan as polysaccharide by

permanganate in aqueous perchlorate media at a constant ionic strength. The

reaction was found to have second-order overall kinetics and to be first-order in

the concentration of both reactants, the results obtained show that the reaction is

acid catalysed. It has been discovered that potassium permanganate is an effective

heterogeneous oxidant, even without resorting to the use of a solid support, if

acetonitrile is employed as the solvent.170 Primary benzylic and secondary

alcohols are converted to the corresponding aldehydes and ketones, alkyl arenes

are oxidized to the corresponding α-ketones in good yields using this procedure,

and both alkyl and aryl sulfides are smoothly converted to the corresponding

sulfones, also in excellent yields. When methylene chloride is used as the solvent,

instead of acetonitile, the yields of aldehydes, ketones, α-ketones, and sulfones are

reduced. However, the oxidation of thiols to disulfides proceeds satisfactorily

when methylene chloride is the solvent.


39

Huang et al171 studied the oxidation of chlorinated ethenes by potassium

permanganate. It has been observed that several materials can be used as KMnO4

carriers for scrubbing ethylene; rice hull ash, lahar (volcanic ejecta) ash and

coconut coir dust have been evaluated. The ethylene scrubbing efficiency and

stability of rice hull ash, lahar ash and coconut coir dust were studied. The

oxidation of C2H4 by KMnO4 was found to be approximately first order for the

three carriers. Based on the calculated values of the reaction rate coefficients, the

most efficient KMnO4 carrier for KMnO4 oxidation was rice hull ash per gram of

scrubber followed by lahar ash and then coconut coir dust. Calculated values of

the intrinsic rate coefficient indicate that, at the same KMnO4 loading, lahar ash

scrubs ethylene more efficiently, followed by rice hull ash and then coconut coir

dust. However, in practical terms, the most efficient scrubber is that based on rice

hull ash. This material was also found to be the most stable among three carriers

based on the color intensity (chromacity) of the reflected light from the scrubber.

The kinetics of the oxidation of mandelic acid (MA) by permanganate in aqueous

alkaline medium at a constant ionic strength of 1.0 mol dm-3 was studied by

Panari et al172 spectrophotometrically. The reaction shows first-order kinetics in

[permanganate ion] and fractional order dependences in [MA] and [alkali].

Addition of products, manganate and aldehyde has no significant effect on the

reaction rate. An increase in ionic strength and a decrease in dielectric constant of

the medium increase the rate. The oxidation process in alkaline medium under the

conditions employed in the present investigation proceeds first by formation of an

alkali permanganate complex, which combines with mandelic acid to form

another complex. The latter decomposes slowly followed by a fast reaction

between the free radical of mandelic acid and another molecule of permanganate

to give products. The reaction was studied at different temperatures and activation

parameters were computed with respect to the slow step of the proposed

mechanism.


40

Desai et al172 studied the kinetics of oxidation of (R)-(+)-pantothenic acid (PA) by

permanganate in aqueous alkaline medium at constant ionic strength

0.20 mol dm−3 spectrophotometrically. The reaction showed first-order kinetics in

(MnO4−) and an apparent less than unit order dependence each in (pantothenic

acid) and (alkali). Initial addition of products had no significant effect on the rate

of the reaction. An increase in ionic strength and decrease in dielectric constant of

the medium increases the rate. The results suggest that first the alkali reacts with

pantothenic acid to form its anionic species with deprotonation catalysis which

reacts with one molecule of oxidant species i.e., permanganate species to form the

free radical of pantothenic acid in a slow step.

The oxidation of As (III) with potassium permanganate was studied under

conditions including pH, initial As (III) concentration and dosage of Mn (VII). 174

The results have shown that potassium permanganate was an effective agent for

oxidation of As (III) in a wide pH range. The pH value of tested water was not a

significant factor affecting the oxidation of As (III) by Mn (VII). Although

theoretical redox analysis suggests that Mn (IV) should have better performance in

oxidation of As (III)within lower pH ranges, the experimental results show that the

oxidation efficiencies of As (III) under basic and acidic conditions were similar,

which may be due to the adsorption of As (III) on the Mn (OH)2 and MnO2

resulting from the oxidation of As (III).

Kolb175 studied the permanganate oxidation of cyclohexane, cyclohexene, and

cyclohexanol. Alkaline potassium permanganate is treated with cyclohexane,

cyclohexene, and cyclohexanol. The cyclohexene reacts more rapidly than

cyclohexanol. Cyclohexane does not react. The secondary alcohol cyclohexanol is

oxidized by permanganate to give the ketone cyclohexanone. The alkene

cyclohexene reacts to give cis-1, 2-cyclohenanediol. The permanganate ion is

reduced to the green manganate ion.


41

Selective oxidation of alkylarenes in dry media with potassium permanganate is

reported on Montmorillonite K10.176 The solvent-free oxidation of alkylarenes

with KMnO4 supported on Montmorillonite K10 is reported. The beneficial

effects of microwave and ultrasound irradiation on the reactions are described.

OKMnO4/K10 O

O

/MW/>>>

Berka and Zavesky177 used potassium permanganate as oxidizing agent to

determine organic substances. The questions of performance of blank

determinations of organic substances, when excess potassium permanganate is

used in weekly acid solutions, were studied.


42

Igov et al178 studied the catalytic effect of traces of Al (III) ion on

oxidation of 4-hydroxycoumarin by potassium permanganate. Oxidation of

4-hydroxycoumarin by potassium permanganate in acid media of acetate buffer is

catalyzed by Al (III) ions, which is the proposed new homogeno-catalytic method

for determination of Al (III)in solutions. Under the optimum conditions, Al(III) has

been determined at 525 min solutions containing analyte at 50-1000 ng/ml with

probable relative error of 15.6 – 5 % and detection limit of 20 ng/ml).

Appropriate kinetic questions for both catalytic and noncatalytic processes have

been derived and the mechanism of catalytic effect of Al(III) investigated.

Interferences studies show that most of the common cations and anions do not

interfere.

Latona179 studied the kinetics of oxidation of sugar in alkaline potassium

permanganate and chromic acid media. The reactions were monitored under

pseudo-first order condition. The effects of ionic strength, pH, sugar

concentration and temperature were kinetically investigated.

Kinetics of oxidation of fructose, sucrose and maltose by potassium permanganate

in NaHCO3/NaOH buffer and of fructose and sucrose by hexachloro-iridate (IV) in

acidic buffer have been measured spectrophotometrically under pseudo-first

order condition.180 The rate of oxidation of sugars follow the order

maltose>fructose>sucrose, and increase with pH in both acidic and alkaline

media.


43

2.13 AIMS AND OBJECTIVES OF CURRENT RESEARCH

The study of carbohydrates is one of the most exciting fields of Organic/

Biochemistry. Vast literature is available on the kinetics of oxidation of

carbohydrates by various organic and inorganic oxidants. The oxidations of

aldoses by, chlorine, bromine and iodine have been reported in alkaline media.17-

19 The catalyzed and uncatalyzed oxidation of sugars have been reported in

detail by using N-halocompounds.67-75 N-Bromoacetamide181-183 ,N-

Bromosuccinamide184-186 and Potassium bromate30-38 ,Sodium Periodate187-190

have been earlier used in oxidation of various compounds. In organic oxidants

such as Cu(II), ammonical Ag(I) and Nessler’s reagent have been used in the

uncatalyzed oxidation of sugars in aqueous alkaline medium.137-139 The

uncatalyzed oxidation of oxalic acid, benzaldehydes and Ru(III)-catalyzed

oxidation of α-hydroxy acids by iodate in acidic medium have been reported.191-

193 The mechanism for the oxidation of some aldoses by Cr(VI), V(V), Ce(II), Ir(IV),

Au(III) and periodic acid have been investigated in acidic media.194

In the light of the biological importance of reducing sugars and also in a view of

the fact that the KMnO4 based reactions have been found relatively rare

application in the oxidation of sugars leads to corresponding acids through further

oxidation of aldehyde formed by alcohols especially for the oxidation of hydroxyl

group of substrates and a few investigations have been reported on the kinetics

of oxidation of reducing sugars with potassium permanganate in acidic medium to

drawn a mechanism of oxidation by using advanced techniques.

This research covers the following aspects:

i. To study the kinetics of reducing sugars by potassium permanganate

spectrophotometrically.

ii. Determination of rate of reaction by the change in optical density of

KMnO4 in acidic medium.


44

iii. To study the reaction kinetics in acidic medium at different parameters

like concentration of sugar, oxidant, pH and temperature.

iv. Determination of order of reaction with respect to concentration of sugar,

oxidant and pH of the medium.

v. Evaluation of thermodynamics activation parameters (Ea, ∆H #, ∆G #, ∆S# )

were determined by using Arrhenius & Erying equations.

vi. Establishment of reaction mechanism of oxidation of sugars.

vii. Isolation of the product formed by establishing equilibrium in

heterogeneous solvent system. TLC was checked and product subjected to

–ve & +ve Fab mass spectrophotometery, 13C-NMR, 1H-NMR and

establishment of the reaction mechanism and stoichiometric equations.

CHAPTER # 3

EEXXPPEERRIIMMEENNTTAALL AASSPPEECCTTSS

Experimental Aspects3Chapter

45

3. EXPERIMENTAL ASPECTS The oxidations of sugars have been investigated by various researchers by using

various oxidizing agents.17-60 Several workers used classical methods to study

reaction kinetics. A scant attention has been paid to spectrophotometric method.

Therefore the spectrophotometric method has been adapted to study the reaction

kinetics of oxidation of sugars with potassium permanganate in acidic medium.

The experiment was planned for 2-3 hrs laboratory sessions. This includes time

for:

1) Laboratory preparation

2) Preparation of solutions

3) Kinetic Experiments

4) Data Analysis

Effect of different experimental parameters such as concentration of oxidant,

reductant, hydrogen ion, ionic strength and temperature was studied.

3.1 LABORATORY PREPARATION

3.1.1 Glass Wares

All the volumetric apparatus used were of Pyrex. All the glass wares used were

washed with detergent solution and tap water, washing with double distilled and

deionized water and ultimate drying in an oven (W.T.C binder, 7200, Tuttlinger /

Germany Type E 28 No. 89248) at temperature 150 ºC for 2 hrs. before starting

reaction kinetics.

3.1.2 Thermostatic Bath Thermostatic bath model # FJPS0 (Made in England) was used throughout the

experiment which maintained a constant temperature within + 0.1 ºC.


46

3.1.3 Stop Watch AVICON AVTN Stopwatch having a least count + 0.1 was used for the

determination of time elapsed.

3.1.4 Digital Balance For weighing purpose the digital balance model # Mettler College 150 was used

having least count + 0.0001.

3.1.5 Spectrophotometer

The present kinetic study was followed by the change in optical density of KMnO4

as a function of time. In all the reactions the optical density or change in optical

density was in visible region and for monitoring change in optical density a digital

spectrophotometer S 104 D (Cambridge UK) No. 1229 was used.

A spectrum of potassium permanganate was recorded on Schimadzu

spectrophotometer to obtain wavelength maximum of KMnO4. All other spectra

were also recorded on the same instrument.

3.1.6 Mass Spectrometer The electron impact (EI) mass spectra were recorded on Finnigem Mat – 112

Spectrometer coupled with PDP 11\34 Computer System.

3.1.7 NMR Spectrometers The 1H – NMR were recorded at 300 and 400 MHz on Bruker AM – 300 and AM – 400 Spectrometers with aspects. 300 date system.

3.1.8 TLC

The TLC was performed on DC. Micro cards SiF 5 × 10 cm (Silica gel with

fluorescent indicator 254 nm and for reversible TLC was performed on

RP18F252 S.


47

3.1.9 CHEMICALS

(i) Sugars

Sugars i.e. Galactose, Fructose, Lactose, and Maltose were of A R grades and

were used without further purification.

(ii) Potassium Permanganate

Potassium Permanganate used in present investigation was of Fluka

(Switzerland).

(iii) Salt Potassium nitrate (KNO3) of E. Merck was used throughout the experiment to

investigate the salt effect.

(iv) Sulphuric Acid

H2SO4 used to provide H+ ions in the reaction mixture was of E. Merck.

(v) Water

Double distilled and deionized water was used throughout the experimental work.

3.2 PREPARATION OF STOCK SOLUTIONS

3.2.1 Stock Solution of KMnO4 A 0.01 M stock solution of KMnO4 was prepared by dissolving 0.157g/100ml of

KMnO4 in water.

3.2.2 Stock Solution of Galactose A 0.1 M stock solution of galactose (C6H12O6) was prepared by dissolving known

weight of galactose in 100 ml of water.

3.2.3 Stock solution of fructose A 0.1 M stock solution of fructose (C6H12O6) was prepared by dissolving known

weight of fructose in 100 ml of water.


48

3.2.4 Stock Solution of Maltose A 0.1 M stock solution of maltose (C12H22O11) was prepared by dissolving known

weight of maltose in 100 ml of water.

3.2.5 Stock Solution of Lactose A 0.1 M stock solution of lactose (C12H22O11) was prepared by dissolving known

weight of maltose in 100 ml of water.

3.2.6 Stock Solution of Potassium Nitrate A 1 M stock solution of potassium nitrate (KNO3) was prepared by dissolving

known weight of KNO3 in 100 ml of water.

3.2.7 Sulphuric Acid

A 1 M stock solution of sulphuric acid (H2SO4) was prepared by diluting known

volume of concentrated H2SO4 (18 M) in 100ml of water.

3.3 KINETIC EXPERIMENTS

Initially, the spectrum of KMnO4 solution was scanned to determine the

wavelength of maximum absorption. All stock solutions of various sets of

experiments were immersed in water bath for at least 10-15 minutes before directly

drawn in the cuvet placed in the cell holder of spectrophotometer.

The change in optical density of KMnO4 was recorded after 60 s at λmax 545 nm.

The requisite ionic strength of the medium was maintained by adding appropriate

volumes of 0.3M KNO3 solution. The reaction was initiated by adding sugar

solution. At least five kinetic runs were performed for each individual experiment

designed for every parameter studied.


49

3.3.1 Effect of Substrate Concentration on “kobs” Dilutions of the required concentrations were made from the various stock solutions

of substrates. The change in optical density was monitored by keeping oxidant, [H+]

and salt concentration constant at a wavelength of 545 nm at a temperature of 32ºC

+ 1ºC. The influences of various parameters were studied on reaction kinetics of

oxidation of sugars by KMnO4 in acidic medium.

3.3.2 Effect of Oxidant Concentration on “kobs” Dilutions of the required concentrations were made from the stock solution of

KMnO4. The change in optical density was monitored by keeping substrate, [H+]

and salt concentration constant at a wavelength of 545 nm at a temperature of 32ºC

+ 1ºC.

3.3.3 Effect of [H+] Concentration on “kobs” For finding out the dependence of k on [H+], appropriate dilutions of H2SO4 stock

solution were prepared. The change in optical density was monitored at a

wavelength of 545 nm by keeping oxidant, substrate and salt concentration constant

at a temperature of 32ºC + 1ºC.

3.3.4 Effect of Salt on “kobs” To investigate the dependence of k on salt, different dilutions of KNO3 were

prepared from the KNO3 stock solution. The change in optical density was recorded

by keeping the [H+], oxidant and substrate concentration constant at a λmax 545 nm

at a temperature of 32ºC + 1ºC.

3.3.5 Effect of Temperature on “kobs” To study the effect of different temperatures viz 30ºC, 35ºC, 40ºC, 45ºC and 50ºC

fresh dilutions were made for each kinetic run. Arrhenius and Erying equations

were used to calculate the thermodynamic activation parameters like Ea, ∆H#, ∆S#

and ∆G#.


50

3.4 DATA ANALYSIS Beer Lambert law was used to analyze the experimental data. According to the

Beer-Lambert law, the absorbance (A) of a dilute solution is proportional to its

concentration, c and path length, l:

A = εcl

where ε is molar absorptivity. Change in optical density of MnO4- was used as

reaction monitoring tool at different optimum conditions. Rates of reaction were

determined from plots of optical density vs time (t) where as a plot of

ln Ao -A∞/ At -A∞ was used to determine pseudo-first-order rate constant (k).

ln Ao -A∞/ At -A∞ = kt

where Ao , At , and A∞ represents optical density at beginning, at time t and at

infinity respectively.

3.5 STOICHIOMETRY AND PRODUCT ANALYSIS Varying [MnO4

-]: [sugar] ratios were equilibrated at room temperature for 72 h

with condition [MnO4-] >> [sugar].Estimation of residual [MnO4

-] in different sets

showed that 1mol of sugar consumed 2 (for galactose and fructose) and 4 (for

maltose and lactose) mol of MnO4-. Accordingly, the following stoichiometric

equations could be formulated:

−− ++⎯→⎯+

+



−− ++⎯⎯⎯ →⎯++

++

36105/

24112212 42242




51

−− ++⎯→⎯+

+


Galactose / Fructose galacturonic acid/ fructuronic acid

−− ++⎯⎯⎯ →⎯+

++

32131812/

4112212 42242

MnOOHOHCMnOOHC HgH

Maltose / Lactose malturic acid/ lacturic acid

The main products of the oxidation formic acid and arabinonic acids were detected 17 by TLC and by conventional (spot test) methods18, 19. Surprisingly, the products

formed from all sugars (Galactose, Fructose, Maltose and Lactose) were same. The

other oxidation products i.e galacturonic acid, fructuronic acid, malturic acid and

lacturic acid were identified by Fab mass, 1H-NMR and 13C-NMR spectroscopy.

3.6 ANALYSIS OF REACTION MIXTURE

Analysis of reaction mixture was carried out by taking 0.2g of KMnO4, 1g of

reducing sugars viz. galactose, fructose, maltose and lactose which were mixed in

50 ml of deionised water and 50ml of hexane. The mixture was allowed to stand to

complete the reaction for 2hrs then 5ml of conc. H2SO4 was added. The complete

decolorization took place within 30 minutes. After 5 days solution was shacked and

two layers were separated by using separating funnel. Then hexane was evaporated

by rotary evaporator. Crystals obtained were dissolved in methanol. TLC was taken

which did not show any promising spot.

Therefore the polarity of solvent was increased as follows:

20ml H2O + 80ml CH3OH, 40ml H2O + 60ml CH3OH, 60ml H2O + 40ml CH3OH,

80ml H2O+20ml CH3OH. Then B.A.W was taken and TLC was checked but no

promising spot appeared but only streaking was present on the plate. Analysis of

reaction mixture was then performed with Chloroform instead of hexane, again

only streaking was observed on the TLC plate.

The mole method was used for the preparation of reaction mixtures for the

oxidation of sugars.


52

3.7 PREPARATION OF REACTION MIXTURES 3.7.1 For Galactose Molecular wt. of Galactose = 180 g Molecular wt. of KMnO4 = 163 g

1 mole of Galactose = 180 g of Galactose.

Mole = Mass Mol.wt. Mole = 1 180 Mole = 5.55 x 10-3 mole of Galactose used for oxidation. 1 mole of Galactose = 2 moles of KMnO4

5.55 x 10-3 mole of Galactose = 2 × 5.55 x 10-3 mole of KMnO4

5.55 x 10-3 mole of Galactose = 1.11 x 10-2 mole of KMnO4 Mass = mole × mol.wt. = 1.11 x 10-2 × 163 g Mass = 1.8093 g of KMnO4 used to oxidize 1 g of Galactose.

3.7.2 For Fructose Molecular wt. of fructose = 180 g Molecular wt. of KMnO4 = 163 g

1 mole of fructose = 180 g of fructose

Mole = Mass Mol.wt. Mole = 1 180 Mole = 5.55 x 10-3 mole of fructose used for oxidation. 1 mole of fructose = 2 moles of KMnO4

5.55 x 10-3 mole of fructose = 2 × 5.55 x 10-3 mole of KMnO4

5.55 x 10-3 mole of fructose = 1.11 x 10-2 mole of KMnO4


53

Mass = mole × mol.wt. = 1.11 x 10-2 × 163 g Mass = 1.8093 g of KMnO4 used to oxidize 1 g of fructose.

3.7.3 For Maltose 1 mole of maltose = 342 g of maltose.

Mole = Mass Mol.wt. Mole = 1 342 Mole = 2.9x 10-3 mole of maltose used for oxidation. 1 mole of Maltose = 4 moles of KMnO4

2.9x 10-3mole of Maltose = 2 × 2.9x 10-3 mole of KMnO4

2.9x 10-3 mole of Maltose = 1.16 x 10-2 mole of KMnO4 Mass = mole × mol.wt. = 1.16 x10-2 × 163 gm Mass = 1.89 g of KMnO4 used to oxidize 1 g of Maltose.

3.7.4 For Lactose 1 mole of lactose = 342 g lactose

Mole = Mass Mol.wt. Mole = 1 342 Mole = 2.9x 10-3 mole of lactose used for oxidation. 1 mole of lactose = 4 moles of KMnO4

2.9x 10-3mole of lactose = 2 × 2.9x 10-3 mole of KMnO4

2.9x 10-3 mole of lactose = 1.16 x 10-2 mole of KMnO4


54

Mass = mole × mol.wt. = 1.16 x10-2 × 163 gm Mass = 1.89 g of KMnO4 used to oxidize 1 g of lactose.

3.8 ANALYSIS OF OXIDATION PRODUCTS In reagent bottle 1g galactose with 1.8093 g of KMnO4, 1 g fructose with 1.8093 g

KMnO4, 1 g maltose with 1.89 g KMnO4 and 1 g lactose with 1.89 g KMnO4 were

mixed in 20 ml deionized water. 0.5ml conc. H2SO4 was also added in each

solution. The bottles were covered with stop cork and kept overnight. The water

was evaporated under reduced pressure to set product in bottom. The obtained

product in each case dissolved in DMSO and checked on reversible TLC plate in

the solvent (1:1 water and MeOH). It was observed that product is uv.active. Ceric

sulphate was sprayed to check the compound which gave brown spot. Therefore it

was confirmed that compound belongs to –COOH group. Finally the isolated

product was submitted for Fab, mass and other spectroscopic techniques.

CHAPTER # 4

RREESSUULLTTSS

Results4Chapter

55

4. RESULTS The present research has been conducted by monitoring change in absorbance of

MnO4- with respect to time. The absorption spectrum of MnO4

- was recorded in

aqueous solution (Fig 4.1) to obtain maximum wavelength of absorption. The

spectrum shows two maxima at 525nm and 545nm respectively. Magnesedioxide

(MnO2), a reduction product of MnO4- also absorbs at 525nm therefore, 545nm

was considered as λmax.

Fig 4.1 Absorption spectrum of KMnO4

Results4Chapter

56

4.1 EFFECT OF CONCENTRATION OF KMnO4 ON THE

RATE OF OXIDATION OF SUGARS WITH KMnO4

The oxidation of sugar with potassium permanganate in acidic medium has been

investigated spectrophotometrically. In order to evaluate the effect of

concentration of KMnO4 on rate of oxidation, the reaction was studied at various

initial concentrations of KMnO4 ranging from 1-5x10-3 mol dm-3. The

concentration of sugars was maintained constant at 2x10-3 mol dm-3 galactose,

4x10-2 mol dm-3 fructose, 4x10-2 mol dm-3 maltose, 3x10-2 mol dm-3 lactose while

KNO3 concentration at 0.3 mol dm-3. The temperature was kept constant at 305 K.

The reaction was followed by change in optical density of KMnO4 in reaction

mixture at λmax 545 nm. The values of optical density were plotted against time to

evaluate rate of reaction. It clearly indicates the rate increases as the concentration

increases.

The values of rate constants were obtained from the slope plot of ln Ao-A∞/At- A∞

vs time (Figs 4.2 to 4.9). These values are tabulated in Tables 4.1 to 4.4 showing

first order kinetics with respect to KMnO4.

Results4Chapter

57

Table: 4.1 Effect of Concentration of KMnO4 on the Rate of Oxidation of Galactose with KMnO4

[Galactose] = 2×10-2 mol dm-3 [H2SO4 ] = 1×10-1 mol dm-3

[KNO3 ] = 0.3 mol dm-3 T = 305 K.

λmax = 545 nm

[KMnO4] x 103

(mol dm-3)

υ x 103

(mol dm-3 s-1)

k x 103

(s-1)

1.0

2.6 ± 0.53

3.2 ± 1.23

2.0

5.3 ± 0.53

8.7 ± 1.23

3.0

3.5 ± 0.53

9.1 ± 1.23

4.0

5.2 ± 0.53

9.3 ± 1.23

5.0

4.9 ± 0.53

10.0 ± 1.23

Confidence Interval (95%) 1.48 3.42

Results4Chapter

58

Fig 4.2 : Plots of O.D vs time for concentrations (1-5)x10-3 mol dm-3 of KMnO4

Fig 4.3 : Plots of ln Ao-A∞/At-A∞ vs time for concentrations

(1-5)x10-3 mol dm-3 of KMnO4

00.20.40.60.8

11.21.41.61.8

2

0 100 200 300 400

time (s)

O.D

1×10-3 mol dm-3

2×10-3 mol dm-3

3×10-3 mol dm-3

4×10-3 mol dm-3

5×10-3 mol dm-3

0.00

0.50

1.00

1.50

2.00

2.50

0 50 100 150 200

time (s)

ln [(

Ao-

A∞)/

(At-A

∞)]

1×10-3 mol dm-3

2×10-3 mol dm-3

3×10-3 mol dm-3

4×10-3 mol dm-3

5×10-3 mol dm-3

Results4Chapter

59

Table: 4.2 Effect of Concentration of KMnO4 on the Rate of Oxidation of Fructose with KMnO4

[Fructose] = 4×10-2 mol dm-3 [H2SO4 ] = 1×10-1 mol dm-3

[ KNO3 ] = 0.3 mol dm-3 T = 305 K.

λmax = 545 nm

[KMnO4] x 103

(mol dm-3)

υ x 103

(mol dm-3 s-1)

k x 103

(s-1)

1.0

4.7 ± 1.1

4.5 ± 2.8

2.0

3.7 ± 1.1

7.5 ± 2.8

3.0

8.5 ± 1.1

11.9 ± 2.8

4.0

9.5 ± 1.1

15.4 ± 2.8

5.0

6.8 ± 1.1

20.3 ± 2.8


Results4Chapter

60

Fig 4.4 : Plots of O.D vs time for concentrations (1-5)x10-3 mol dm-3 of KMnO4

Fig 4.5 : Plots of ln Ao-A∞/At-A∞ vs time for concentrations (1-5)x10-3 mol dm-3 of KMnO4

0

1

2

3

4

5

6

0 50 100 150 200 250 300 350time(s)

1×10-3 mol dm-3

2×10-3 mol dm-3

3×10-3 mol dm-3

4×10-3 mol dm-3

5×10-3 mol dm-3

0 0.5

11.5 2

2.5 3

0 100 200 300 400time (s)

O.D

1×10-3 mol dm-3

2×10-3 mol dm-3

3×10-3 mol dm-3

4×10-3 mol dm-3

5×10-3 mol dm-3

ln [(

Ao-

A∞)/(

At-A

∞)]

Results4Chapter

61

Table: 4.3 Effect of Concentration of KMnO4 on the Rate of Oxidation of Maltose with KMnO4.

[Maltose] = 4×10-2 mol dm-3 [ H2SO4 ] = 1×10-1 mol dm-3

[KNO3 ] = 0.3 mol dm-3 T = 305 K

λmax = 545 nm

[KMnO4] x 103

(mol dm-3)

υ x 103

(mol dm-3 s-1)

k x 103

(s-1)

1.0

0.7 ± 0.38

1.5 ± 0.78

2.0

2.2 ± 0.38

5.9 ± 0.78

3.0

2.6 ± 0.38

5.4 ± 0.78

4.0

2.8 ± 0.38

4.4 ± 0.78

5.0

2.7 ± 0.38

5.3 ± 0.78


Results4Chapter

62

Fig 4.6: Plots of O.D vs time for concentrations (1-5)x10-3 mol dm-3 of KMnO4

Fig 4.7: Plots of ln Ao-A∞/At-A∞ vs time for concentrations


00.20.40.60.8

11.21.41.61.8

0 200 400 600

time (s)

1×10-3 mol dm-3

2×10-3 mol dm-3

3×10-3 mol dm-3

4×10-3 mol dm-3

5×10-3 mol dm-3

0.00

0.50

1.00

1.50

2.00

2.50

0 200 400 600 800

time (s)

ln [(

Ao-

A∞)/(

At-A

∞)]

1×10-3 mol dm-3

2×10-3 mol dm-3

3×10-3 mol dm-3

4×10-3 mol dm-3

5×10-3 mol dm-3

O.D

Results4Chapter

63

Table: 4.4 Effect of Concentration of KMnO4 on Rate of Oxidation of Lactose with KMnO4

[Lactose] = 3×10-2 mol dm-3 [KMnO4 ] = 1×10-3 mol dm-3

[KNO3] = 0.3 mol dm-3 T = 305 K.

λmax = 545 nm

[KMnO4] x 103

(mol dm-3)

υ x 103

(mol dm-3 s-1)

k x 103

(s-1)

1.0

0.3 ± 1.27

1.4 ± 1.54

2.0

0.3 ± 1.27

1.6 ± 1.54

3.0

0.4 ± 1.27

2.8 ± 1.54

4.0

5.5 ± 1.27

7.2 ± 1.54

5.0

5.6 ± 1.27

8.9 ± 1.54


Results4Chapter

64

Fig 4.8: Plots of O.D vs time for concentrations (1-5)x10-3 mol dm-3 of KMnO4



0

0.5

1

1.5

2

0 200 400

Time (s)

1×10-3 mol dm-3

2×10-3 mol dm-3

3×10-3 mol dm-3

4×10-3 mol dm-3

5×10-3 mol dm-3

O.D

0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

4.000

4.500

0 2 4 6 8

time (s)

ln [(

Ao-A

∞)/(

At-A

∞)]

1×10-3 mol dm-3

2×10-3 mol dm-3

3×10-3 mol dm-3

4×10-3 mol dm-3

5×10-3 mol dm-3

Results4Chapter

65

4.2 EFFECT OF CONCENTRATION OF SUGARS ON THE RATE OF OXIDATION OF SUGARS WITH KMnO4

The oxidation of sugars by potassium permanganate in acidic medium has been

studied spectrophotometrically at various initial concentrations of sugars keeping

potassium permanganate, sulphuric acid, salt concentration and temperature

constant. The Effect of concentration of sugars was investigated at different

concentrations ranging from 1-5x10-2 mol dm-3. The concentration of KMnO4,

H2SO4 and KNO3 was maintained at 1x10-3 mol dm-3, 1x10-1 mol dm-3 and 0.3

mol dm-3 respectively. The temperature was kept constant at 305 K. The reaction

was followed by change in optical density of KMnO4 in reaction mixture at λmax

545 nm,. The absorbance was obtained after each 60sec.

Plots of optical density vs time were obtained from which rate of reaction was

calculated (Tables 4.5 to 4.8 and Figs 4.10, 4.12, 4.14 and 4.16). It is obvious

from the table that rate of reaction increase as the concentration of sugar

increases. It means that rate of reaction depend upon the sugar concentration.

Plots of ln Ao-A∞/At- A∞ Vs time were also obtained. (Figs 4.11, 4.13, 4.15 and

4.17) to evaluate the values of rate constant. The plots gave straight line whose

slopes provided the values of rate constant, tabulated in Tables 4.5 to 4.8. The

values indicate that it is first order reaction with respect to sugar.

Results4Chapter

66

Table: 4.5 Effect of Concentration of Galactose on the Rate of Oxidation of Galactose with KMnO4.

[KMnO4 ] = 1×10-3 mol dm-3 [H2SO4 ] = 1×10-1 mol dm-3

[KNO3 ] = 0.3 mol dm-3 T = 305 K.

λmax = 545 nm

[Galactose] x 102

(mol dm-3)

υ x 103

(mol dm-3 s-1)

k x 103

(s-1)

1.0

3.9 ± 0.79

4.3 ± 2.23

2.0

3.3 ± 0.79

8.8 ± 2.23

3.0

5.3 ± 0.79

10 ± 2.23

4.0

3.6 ± 0.79

12 ± 2.23

5.0

3.6 ± 0.79

18 ± 2.23


Results4Chapter

67

Fig 4.10 : Plots of O.D vs time for concentrations (1-5)x10-2 mol dm-3 of Galactose

Fig 4.11 : Plots of ln Ao-A∞/At-A∞ vs time for concentrations (1-5)x10-2 mol dm-3 of Galactose

00.20.40.60.8

11.21.4

0 100 200 300 400time (s)

1×10-2 mol dm-3

2×10-2 mol dm-3

3×10-2 mol dm-3

4×10-2 mol dm-3

5×10-2 mol dm-3

O

.D

0

1

2

3

4

5

6

0 100 200 300 400time (S)

1×10-2 mol dm-3

2×10-2 mol dm-

3×10-2 mol dm-3

4×10-2 mol dm-3

5×10-2 mol dm-3

ln [(

Ao-

A∞

)/(A

t-A∞

)]

Results4Chapter

68

Table: 4.6 Effect of Concentration of Fructose on the Rate of Oxidation of Fructose with KMnO4.

[KMnO4] = 1×10-3 mol dm-3 [H2SO4] = 1×10-1 mol dm-3

[KNO3 ] = 0.3 mol dm-3 T = 305 K.

λmax = 545 nm

[Fructose] x 102 (mol dm-3)

υ x 103

(mol dm-3 s-1)

k x 103

(s-1)

1.0

1.6 ± 0.97

2.3 ± 1.12

2.0

3.0 ± 0.97

3.4 ± 1.12

3.0

5.6 ± 0.97

5.9 ± 1.12

4.0

6.3 ± 0.97

7.2 ± 1.12

5.0

6.5 ± 0.97

8.3 ± 1.12


Results4Chapter

69

Fig 4.12 : Plots of O.D vs time for concentrations (1-5)x10-2 mol dm-3 of Fructose


(1-5)x10-2 mol dm-3 of Fructose

0

0.5

1

1.5

2

0 200 400

time (s)

1×10-2 mol dm-3

2×10-2 mol dm-3

3×10-2 mol dm-3

4×10-2 mol dm-3

5×10-2 mol dm-3

O.D

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

0 100 200 300 400time (s)

ln [(

Ao-

A∞

)/(A

t-A∞

)]

1×10-2 mol dm-3

2×10-2 mol dm-3

3×10-2 mol dm-3

4×10-2 mol dm-3

5×10-2 mol dm-3

Results4Chapter

70

Table: 4.7 Effect of Concentration of Maltose on the Rate of Oxidation of Maltose with KMnO4.

[KMnO4 ] = 1×10-3 mol dm-3 [H2SO4] = 1×10-1 mol dm-3

[KNO3 ] = 0.3 mol dm-3 T = 305 K.

λmax = 545 nm

[Maltose] x 102 (mol dm-3)

υ x 103

(mol dm-3 s-1)

k x 103

(s-1)

1.0

0.3 ± 0.21

1.2 ± 0.28

2.0

1.6 ± 0.21

1.3 ± 0.28

3.0

0.9 ± 0.21

1.4 ± 0.28

4.0

1.3 ± 0.21

2.4 ± 0.28

5.0

1.1 ± 0.21

2.5 ± 0.28


Results4Chapter

71

Fig 4.14: Plots of O.D vs time for concentrations

(1-5)x10-2 mol dm-3 of Maltose


(1-5)x10-2 mol dm-3 of Maltose

0

0.5

1

1.5

2

0 200 400 600

time (s)

O.D

1×10-2 mol dm-3

2×10-2 mol dm-3

3×10-2 mol dm-3

4×10-2 mol dm-3

5×10-2 mol dm-3

0.00

0.50

1.00

1.50

2.00

2.50

0 200 400 600 800time (s)

ln [(

Ao-

A∞

)/(A

t-A∞

)]

1×10-2 mol dm-3

2×10-2 mol dm-3

3×10-2 mol dm-3

4×10-2 mol dm-3

5×10-2 mol dm-3

Results4Chapter

72

Table: 4.8 Effect of Concentration of Lactose on the Rate of Oxidation of Lactose with KMnO4.

[Lactose] = 3×10-2 mol dm-3 [H2SO4] = 1×10-1 mol dm-3

[KNO3] = 0.3 mol dm-3 T = 305 K.

λmax = 545 nm

[Lactose] x 102

(mol dm-3)

υ x 103

(mol dm-3 s-1)

k x 103

(s-1)

1.0

2.0 ± 0.58

1.4 ± 1.54

2.0

2.0 ± 0.58

1.6 ± 1.54

3.0

3.0 ± 0.58

2.8 ± 1.54

4.0

4.0 ± 0.58

7.2 ± 1.54

5.0

5.0 ± 0.58

8.9 ± 1.54


Results4Chapter

73


(1-5)x10-2 mol dm-3 of Lactose


(1-5)x10-2 mol dm-3 of Lactose

0

0.05

0.1

0.15

0.2

0 200 400

time (s)

O.D

1×10-2 mol dm-3

2×10-2 mol dm-3

3×10-2 mol dm-3

4×10-2 mol dm-3

5×10-2 mol dm-3

0.000

0.200

0.400

0.600

0.800

1.000

1.200

1.400

1.600

1.800

2.000

0 100 200 300 400

time (s)

ln [(

Ao-

A∞)/(

At-A

∞)]

1×10-2 mol dm-3

2×10-2 mol dm-3

3×10-2 mol dm-3

4×10-2 mol dm-3

5×10-2 mol dm-3

Results4Chapter

74

4.3 EFFECT OF CONCENTRATION OF H2SO4 ON THE RATE OF OXIDATION OF SUGAR WITH KMnO4

The influence of hydrogen ion concentration has been studied by changing

sulphuric acid concentration (1-5)x10-1 mol dm-3 at constant sugars, 2x10-2 mol

dm-3 galactose, 4x10-2 mol dm-3 fructose, 4x10-2 mol dm-3 maltose, 3x10-2 mol

dm-3 lactose, KMnO4 concentration 1x10-3 mol dm-3, KNO3 concentration

0.3 mol dm-3 and temperature 305 K. The reaction was followed by change in

optical density of KMnO4 in reaction mixture at λmax 545 nm. The absorbance was

obtained after each 60 seconds.

The absorbance values are plotted against time to obtain rate of reaction which

clearly indicates that rate increases as the concentration of acid increases as

shown in the Figs 4.18, 4.20, 4.22 and 4.24.

Plots of ln Ao-A∞/At- A∞ Vs time were also obtained as straight lines (Figs 4.19,

4.21, 4.23 and 4.25) which indicates that it is first order reaction with respect to

sulphuric acid. The values of rate constant obtained from the slope of above plots

are tabulated in (Tables 4.9 to 4.12). These values are also in a good agreement

with first order kinetics.

Results4Chapter

75

Table: 4.9 Effect of Concentration of H2SO4 on the Rate of Oxidation of Galactose with KMnO4

[Galactose] = 2×10-2 mol dm-3 [KMnO4 ] = 1×10-3 mol dm-3

[KNO3] = 0.3 mol dm-3 T = 305 K.

λmax = 545 nm

[H2SO4 ] x 101

(mol dm-3)

υ x 103

(mol dm-3 s-1)

k x 102

(s-1)

1.0

3.0 ± 0.94

1.40 ± 0.06

2.0

6.7 ± 0.94

1.47 ± 0.06

3.0

6.9 ± 0.94

1.26 ± 0.06

4.0

8.8 ± 0.94

1.65 ± 0.06

5.0

5.8 ± 0.94

1.56 ± 0.06


Results4Chapter

76

Fig 4.18: Plots of O.D vs time for concentrations (1-5)x10-1 mol dm-3 of H2SO4

Fig 4.19: Plots of ln Ao-A∞/At-A∞ vs time for concentrations (1-5)x10-1 mol dm-3 of H2SO4

0

0.5

1

1.5

2

0 100 200 300

time (s)

O.D

1×10-1 mol dm-3

2×10-1 mol dm-3

3×10-1 mol dm-3

4×10-1 mol dm-3

5×10-1 mol dm-3

0.000

0.500

1.000

1.500

2.000

2.500

3.000

0 200 400 600 800

time (s)

ln [(

A-A

)/ (A

-A)]

1×10-1 mol dm-3

2×10-1 mol dm-3

3×10-1 mol dm-3

4×10-1 mol dm-3

5×10-1 mol dm-3

Results4Chapter

77

Table: 4.10 Effect of Concentration of H2SO4 on the Rate of Oxidation of Fructose with KMnO4

[Galactose] = 2×10-2 mol dm-3 [ KMnO4 ] = 1×10-3 mol dm-3

[H2SO4] = 1×10-1 mol dm-3 T = 305 K.

λmax = 545 nm

[H2SO4 ] x 101

(mol dm-3)

υ x 103

(mol dm-3 s-1)

k x 102

(s-1)

1.0

6.2 ± 0.22

1.73 ± 0.19

2.0

6.8 ± 0.22

1.73 ± 0.19

3.0

5.8 ± 0.22

2.43 ± 0.19

4.0

5.8 ± 0.22

2.43 ± 0.19

5.0

6.8 ± 0.22

2.70 ± 0.19


Results4Chapter

78


(1-5)x10-1 mol dm-3 of H2SO4


00.20.40.60.8

11.21.4

0 200 400

time (s)

O.D

1×10-1 mol dm-3

2×10-1 mol dm-3

3×10-1 mol dm-3

4×10-1 mol dm-3

5×10-1 mol dm-3

0

1

2

3

4

5

0 50 100 150 200 250 300 350time (s)

1×10-1 mol dm-3

2×10-1 mol dm-3

3×10-1 mol dm-3

4×10-1 mol dm-3

5×10-1 mol dm-3

ln [(

Ao-

A∞

)/(A

t-A∞

)]

Results4Chapter

79

Table: 4.11 Effect of Concentration of H2SO4 on the Rate of Oxidation of Maltose with KMnO4

[Maltose] = 4×10-2 mol dm-3 [KMnO4 ] = 1×10-3 mol dm-3

[KNO3] = 0.3 mol dm-3 T = 305 K.

λmax = 545 nm

[H2SO4 ] x 101

(mol dm-3)

υ x 103

(mol dm-3 s-1)

k x 102

(s-1)

1.0

4.4 ± 0.83

5.9 ± 1.53

2.0

1.5 ± 0.83

2.8 ± 1.53

3.0

4.8 ± 0.83

8.6 ± 1.53

4.0

4.3 ± 0.83

9.4 ± 1.53

5.0

0.8 ± 0.83

1.6 ± 1.53


Results4Chapter

80


(1-5)x10-1 mol dm-3 of H2SO4


(1-5)x10-1 mol dm-3 of H2SO4

0

0.5

1

1.5

2

0 200 400

time (s)

1×10-1 mol dm-3

2×10-1 mol dm-3

3×10-1 mol dm-3

4×10-1 mol dm-3

5×10-1 mol dm-3

O.D

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0 100 200 300 400Time (s)

ln [(

Ao-

A∞

)/(A

t-A∞

)]

1×10-1 mol dm-3

2×10-1 mol dm-3

3×10-1 mol dm-3

4×10-1 mol dm-3

5×10-1 mol dm-3

Results4Chapter

81

Table: 4.12 Effect of Concentration of H2SO4 on the Rate of Oxidation of Lactose with KMnO4

[Lactose] = 3×10-2 mol dm-3 [KMnO4] = 1 × 10-3 mol dm-3

[KNO3] = 0.3 mol dm-3 T = 302 K.

λmax = 545 nm

[H2SO4 ] x 101

(mol dm-3)

υ x 103

(mol dm-3 s-1)

k x 102

(s-1)

1.0

5.0 ± 0.58

1.4 ± 0.20

2.0

6.0 ± 0.58

2.1 ± 0.20

3.0

7.0 ± 0.58

2.2 ± 0.20

4.0

8.0 ± 0.58

2.5 ± 0.20

5.0

8.0 ± 0.58

2.5 ± 0.20


Results4Chapter

82

Fig 4.24: Plots of O.D vs time for concentrations (1-5)x10-1 mol dm-3 of H2SO4


0

0.10.2

0.30.4

0.50.6

0 200 400 600time (s)

O.D

1×10-1 mol dm-3

2×10-1 mol dm-3

3×10-1 mol dm-3

4×10-1 mol dm-3

5×10-1 mol dm-3

0

0.5

1

1.5

2

2.5

3

0 5 10 15time (s)

1×10-1 mol dm-3

2×10-1 mol dm-3

3×10-1 mol dm-3

4×10-1 mol dm-3

5×10-1 mol dm-3

ln [(

Ao-

A∞

)/(A

t-A∞

)]

Results4Chapter

83

4.4 EFFECT OF IONIC STRENGTH ON RATE OF OXIDATION OF SUGARS WITH KMnO4 The effect of ionic strength on the rate of oxidation of galactose by KMnO4 in

acidic medium has been investigated by varying KNO3 concentration (0.3 mol

dm-3, 0.5 mol dm-3, 0.7 mol dm-3, 0.9 mol dm-3, 1.1 mol dm-3) by keeping sugar

and KMnO4 concentration and temperature constant at 2×10-2 mol dm-3 galactose,

4×10-2 mol dm-3 fructose, 4×10-2 mol dm-3 maltose and 3×10-2 mol dm-3 lactose,

1×10-3 mol dm-3 and 305 K respectively. The reaction was followed by change

in optical density of KMnO4 in the reaction mixture at λ max 545 nm. The

absorbance was obtained after each 60 sec. It was observed that KMnO4 was

decolorized after a certain time. Results are tabulated in Tables 4.13 to 4.16.

Plots of ln Ao-A∞/At- A∞ Vs time were also obtained as straight lines (Figs 4.26 to

4.29).The values of rate constant were calculated from the slope of these plots

which indicated no salt effect on the reaction.

Results4Chapter

84

Table: 4.13 Effect of Ionic Strength on Rate of Oxidation of Galactose

[Galactose] = 2×10-2 mol dm-3 [KMnO4] =1×10-3 mol dm-3

[H2SO4] = 1 x 10-1 mol dm-3 T = 305 K.

λmax = 545 nm

[KNO3]

(mol dm-3)

k x 103 (s-1)

0.3

9.5 ± 0.06

0.5

9.3 ± 0.06

0.7

9.6 ± 0.06

0.9

9.3 ± 0.06

1.1

9.5 ± 0.06

Confidence Interval (95%) 0.16

Results4Chapter

85


(0.3- 1.1 mol dm-3) of KNO3

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 100 200 300

time (s)

ln [(

Ao-

A∞)/(

At-A

∞)]

0.3 mol dm-3

0.5 mol dm-3

0.7 mol dm-3

0.9 mol dm-3

1.1 mol dm-3

Results4Chapter

86

Table: 4.14 Effect on Ionic Strength on Rate of Oxidation of Fructose:

[Fructose] = 4×10-2 mol dm-3 [KMnO4] = 1×10-3 mol dm-3

[H2SO4 ] = 1×10-1 mol dm-3 T = 305 K

λ max = 545 nm

[KNO3] (mol dm-3)

k x 103 (s-1)

0.3

7.4 ± 0.08

0.5

7.7 ± 0.08

0.7

7.2 ± 0.08

0.9

7.6 ± 0.08

1.1

7.5 ± 0.08


Results4Chapter

87


(0.3- 1.1 mol dm-3) of KNO3

0

1

2

3

4

0 50 100 150 200 250 300 350time (S)

0.3 mol dm-3

0.5 mol dm-3

0.7 mol dm-3

0.9 mol dm-3

1.1 mol dm-3

ln [(

Ao-A

∞)/(

At-A

∞)]

Results4Chapter

88

Table: 4.15 Effect of Ionic Strength on Rate of Oxidation of Maltose

[Maltose] = 4×10-2 mol dm-3 [KMnO4] = 1×10-3 mol dm-3

[H2SO4] = 1×10-1 mol dm-3 T = 305 K

λmax = 545 nm

[KNO3]

(mol dm-3)

k x 103 (s-1)

0.3

6.3 ± 0.04

0.5

6.5 ± 0.04

0.7

6.4 ± 0.04

0.9

6.5 ± 0.04

1.1

6.3 ± 0.04


Results4Chapter

89


(0.3- 1.1 mol dm-3) of KNO3

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 100 200 300 400

time (s)

ln [(

Ao-A

∞)/(

At-A

∞)]

0.3 mol dm-3

0.5 mol dm-3

0.7 mol dm-3

0.9 mol dm-3

1.1 mol dm-3

Results4Chapter

90

Table: 4.16 Effect of Ionic Strength on Rate of Oxidation of Lactose

[Lactose ] = 3×10-2 mol dm-3 [KMnO4] = 1×10-3 mol dm-3

[H2SO4 ] = 1×10-1 mol dm-3 T = 305 K

λmax = 545 nm

[KNO3]

(mol dm-3)

k x 103 (s-1)

0.3

3.5 ± 0.06

0.5

3.7 ± 0.06

0.7

3.7 ± 0.06

0.9

3.9 ± 0.06

1.1

3.7 ± 0.06


Results4Chapter

91

Fig 4.29: Plots of ln Ao-A∞/At-A∞ vs time for concentrations (0.3- 1.1 mol dm-3) of KNO3

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0 200 400 600 800

time (s)

ln [(

Ao-

A∞)/

(At-A

∞)]

0.3 mol dm-3

0.5 mol dm-3

0.7 mol dm-3

0.9 mol dm-3

1.1 mol dm-3

Results4Chapter

92

4.5 EFFECT OF TEMPERATURE ON RATE OF OXIDATION OF SUGARS WITH KMnO4 Dependence of k rate constant for oxidation of sugars by KMnO4 on temperature

has been studied at constant substrate, oxidant and acid concentration 2×10-2 mol

dm -3 galactose, 4×10-2 mol dm -3 fructose, 4×10-2 mol dm -3 maltose, 3×10-2 mol

dm -3 lactose, 1×10-3 mol dm -3 KMnO4 and 1×10-1 mol dm -3 H2SO4 respectively.

The rate data was collected at different temperatures (30-50oC) by using KNO3 to

vary ionic strength. The values of rate constants at different temperature was

obtained by plotting ln Ao-A∞/At-A∞ vs time. Values are tabulated in Tables

4.17 to 4.20. It was observed that rate constant increases with increasing

temperature.

The reaction has also been studied by varying initial concentrations of KNO3 at

different temperatures. As ionic strength has no effect on rate constant, it remains

unchanged at one temperature.

Plots between log k Vs 1/T were obtained with negative slopes to calculate the

values of activation energy (Ea). The corresponding plots are shown in Figs 4.30

to 4.33.

Results4Chapter

93

Table: 4.17 Effect of Temperature on Rate of Oxidation of Galactose with KMnO4

[Galactose] = 2×10-2 mol dm-3 [KMnO4] =1×10-3 mol dm-3

[H2SO4] = 1×10-1 mol dm-3 λmax = 545 nm

RATE CONSTANT x 103

√µ

(mol dm-3)0.5

TEMPERATURE ºC

30 35 40 45 50

0.775 9.0 ±0.06

11.2 ±0.09

15.0 ±0.06

23.1 ±0.07

24.3 ±0.16

0.894 9.2 ±0.06

10.9 ±0.09

14.9 ±0.06

22.9 ±0.07

24.9 ±0.16

1.000 8.9 ±0.06

10.8 ±0.09

15.2 ±0.06

23.2 ±0.07

24.8 ±0.16

1.095 9.0 ±0.06

11.0 ±0.09

15.0 ±0.06

22.8 ±0.07

24.6 ±0.16

1.183 8.8 ±0.06

11.3 ±0.09

14.8 ±0.06

23.0 ±0.07

24.0 ±0.16

Confidence Interval (95%) 0.18 0.25 0.18

0.19 0.45

Results4Chapter

94

Fig: 4.30 A plot of lnk vs 1/T of Galactose against KMnO4 at √µ 0.775 (mol dm-3)0.5

-6-5-4-3-2-103.05 3.1 3.15 3.2 3.25 3.3 3.35

lnk

1/Tx103(K-1)

Results4Chapter

95

Table: 4.18 Effect of Temperature on Rate of Oxidation of Fructose with KMnO4

[Fructose] = 4×10-2 mol dm-3 [KMnO4] = 1×10-3

mol dm-3

[H2SO4] = 1×10-1 mol dm-3

λmax = 545 nm

RATE CONSTANT x 103

√µ

(mol dm-3)0.5

TEMPERATURE ºC

30 35 40 45 50

0.775 4.4 ±0.07

5.8 ±0.09

7.6 ±0.05

11.3 ±0.07

14.7 ±0.07

0.894 4.1 ±0.07

5.5 ±0.09

7.4 ±0.05

11.0 ±0.07

14.6 ±0.07

1.000 4.0 ±0.07

5.3 ±0.09

7.5 ±0.05

11.4 ±0.07

14.8 ±0.07

1.095 4.3 ±0.07

5.4 ±0.09

7.3 ±0.05

11.3 ±0.07

14.5 ±0.07

1.183 4.3 ±0.07

5.3 ±0.09

7.4 ±0.05

11.1 ±0.07

14.9 ±0.07

Confidence Interval (95%) 0.20 0.25 0.14 0.20 0.19

Results4Chapter

96

Fig: 4.31 A plot of lnk vs 1/T of Fructose against KMnO4 at √µ 0.775 (mol dm-3)0.5

-6-5-4-3-2-103.05 3.1 3.15 3.2 3.25 3.3 3.35

lnk

1/Tx103(K-1)

Results4Chapter

97

Table: 4.19 Effect of Temperature on Rate of Oxidation of Maltose with KMnO4

[Maltose] = 4×10-2 mol dm-3 [KMnO4 ] =1×10-3 mol dm-3

[H2SO4] = 1×10-1 mol dm-3 λmax = 545 nm

RATE CONSTANT x 103

√µ

(mol dm-3)0.5

TEMPERATURE ºC

30 35 40 45 50

0.775 6.3 ±0.10

6.9 ±0.05

7.7 ±0.10

8.8 ±0.06

12.3 ±0.12

0.894 6.0 ±0.10

7.0 ±0.05

7.5 ±0.10

8.5 ±0.06

12.1 ±0.12

1.000 6.2 ±0.10

7.1 ±0.05

7.9 ±0.10

8.7 ±0.06

11.6 ±0.12

1.095 5.8 ±0.10

6.9 ±0.05

7.4 ±0.10

8.5 ±0.06

11.7 ±0.12

1.183 6.4 ±0.10

7.2 ±0.05

7.3 ±0.10

8.8 ±0.06

12.0 ±0.12


Results4Chapter

98

Fig: 4.32 A plot of lnk vs 1/T of Maltose against KMnO4

at √µ 0.775 (mol dm-3)0.5

-5.2-5

-4.8-4.6-4.4-4.2

3.05 3.1 3.15 3.2 3.25 3.3 3.35

lnk

1/Tx103(K-1)

Results4Chapter

99

Table: 4.20 Effect of Temperature on Rate of Oxidation of Lactose with KMnO4

[Lactose] = 3×10-2 mol dm-3 [KMnO4] =1×10-3 mol dm-3

[H2SO4 ] = 1×10-1 mol dm-3 λmax = 545 nm

RATE CONSTANT x 103

√µ

(mol dm-3)0.5

TEMPERATURE ºC

30 35 40 45 50

0.775 3.6 ±0.11

4.1 ±0.06

6.0 ±0.21

9.6 ±0.29

11.6 ±0.12

0.894 3.6 ±0.11

4.3 ±0.06

5.8 ±0.21

9.1 ±0.29

11.1 ±0.12

1.0 3.1 ±0.11

4.2 ±0.06

6.0 ±0.21

9.9 ±0.29

11.7 ±0.12

1.095 3.3 ±0.11

4.3 ±0.06

6.8 ±0.21

8.2 ±0.29

11.5 ±0.12

1.183 3.1 ±0.11

4.5 ±0.06

6.8 ±0.21

9.6 ±0.29

11.8 ±0.12


Results4Chapter

100

-8

-6

-4

-2

03.05 3.1 3.15 3.2 3.25 3.3 3.35

1/Tx103(K-1)

lnk

Fig: 4.33 A plot of lnk vs 1/T of Lactose against KMnO4 at √µ 0.775(mol dm-3)0.5

CHAPTER # 5

DDIISSCCUUSSSSIIOONN

Chapter 5 Discussion

101

5. DISCUSSION Carbohydrates are a major source of energy for living organisms and the

understanding of the mechanisms of oxidation of sugars is therefore of immense

importance. The kinetics of oxidation of sugars by a variety of oxidants has been

reported 17-50 in both acidic and alkaline media. Several different mechanisms

showing the importance of enediols, cyclic forms of sugars, etc have been

proposed and there do not seem to appear any common features even in a single

medium. Studies involving the oxidation of sugars by metal ions or their

complexes in alkaline medium are limited.198, 199. The present study involves the

kinetics of D-galactose, D-fructose, D-maltose and D-lactose by KMnO4 in acidic

medium at constant ionic strength maintained by KNO3. The reaction was

followed by change in optical density of KMnO4 in reaction mixture at λmax

545nm. The rate constants were calculated from the slope of the plot of ln Ao-A∞ /

Ao-A∞ Vs time. The rate data was obtained in the form of pseudo-first order rate

constant (kobs) under varying kinetics conditions.

Considering MnO4-, reducing sugars, H+ ions as the main reactants, the general

form of rate equation for the reaction can be written as

[ ] [ ] [ ]γβα +−= HSugarMnOkrate 4

or

[ ] [ ] [ ] [ ]γβα +−−

=− HSugarMnOk

dtMnOd

44 — (1)

For the determination of the experimental rate law, first of all a series of

experiments with varying initial concentrations of MnO4- were performed at

constant concentration of all other reactants and at constant temperature 308 K. In

the light of Ostwald's isolation method the concentration of reducing sugars and

H+ ions were fixed in large excess with respect to MnO4- throughout its variation.


102

Since the concentration of those in excess will not change very much during the

course of reaction and Hg (II) being a catalyst is reproduced in the reaction, the

rate law (Eq-1) under this condition becomes

[ ]α−= 4MnOkrate obs

Where kobs the apparent rate constant

[ ] [ ]γβ += HSugarkobs

5.1 INFLUENCE OF VARIATION OF CONCENTRATION

OF KMnO4 ON THE OXIDATION OF REDUCING

SUGARS

The oxidation of fructose, galactose, maltose and lactose with KMnO4 has been

studied at various initial concentrations (1-5x10-3 mol dm-3) of oxidant keeping

the substrates as well as sulphuric acid and temperature constant at 308 K

respectively. Ionic strength was maintained constant by using KNO3 of 0.3M.

Kinetic results obtained with the variation of MnO-4 with aforesaid sugars are

presented in Tables 4.1 to 4.4. The plots of kobs Vs [MnO4-] were obtained (Figs

5.1, 5.4, 5.7 and 5.10). It is clear from figures that in oxidation of all sugars, there

is direct proportionality between the rate and [MnO4-] throughout its variation.

This shows that the order of reaction with respect to [MnO4-] is unity.

The plot of log [MnO-4] Vs log kobs was also linear as shown in Figs 5.3, 5.6, 5.9

and 5.12 with slopes equal to 0.68 with galactose 0.94 with fructose 0.67 with

maltose and 1.2 with lactose. These values are nearly equal to unity suggesting

first order dependence with respect to KMnO4. The oxidation of reducing sugars

showed that configuration of disaccharides and monosaccharide is bearing some

effect on rate of reaction.


103

TABLE: 5.1 Influence of Variation of Concentration of KMnO4

on the Oxidation of Galactose

[Galactose] = 2 x 10-2 mol dm-3 [H2SO4] = 1 x 10-1 mol dm-3

[KNO3] = 0.3 mol dm-3 T = 305 K

[MnO4-] x 103

(mol dm-3) 1/[MnO4

-]x10-2

(mol-1dm3) log

[MnO4-]

k x 103

(s-1) 1/k x10-2

(s) log k

1 10.00 -3.00 3.00 1.42 -2.50

2 5.00 -2.69 8.70 1.14 -2.06

3 3.33 -2.52 9.10 1.09 -2.00

4 2.50 -2.39 9.30 1.07 -2.03

5 2.00 -2.30 1.00 1.00 -2.00


104

Fig: 5.1 A plot of k Vs [MnO4

-] for the oxidation of Galactose

Fig: 5.2 A plot of 1/k Vs 1/ [MnO4

-] for the oxidation of Galactose

00.0020.0040.0060.008

0.010.012

0 0.002 0.004 0.006

[MnO 4-]mol dm-3

k (s

-1)

0

50

100

150

200

0 200 400 600 800 1000 1200

1/[MnO 4-]mol -1dm3

1/k

(s)


105

Fig: 5.3 A plot of log k Vs log [MnO4-] for the oxidation of Galactose

-3-2.5

-2-1.5

-1-0.5

0-3.2-3-2.8-2.6-2.4-2.2

log[MnO4-]

logk


106


on the Oxidation of Fructose

[Fructose] = 4 x 10-2 mol dm-3 [H2SO4] = 1 x 10-1 mol dm-3

[KNO3] = 0.3 mol dm-3 T = 305 K

[MnO4-] x 103

(mol dm-3) 1/[MnO4

-]x10-2 (mol-1dm3)

log [MnO4

-]k x 103

(s-1) 1/k x10-2

(s) log k

1 10.00 -3.00 4.50 1.58 -2.35

2 5.00 -2.69 7.50 1.33 -2.12

3 3.33 -2.52 11.90 0.84 -1.92

4 2.50 -2.39 15.40 0.64 -1.81

5 2.00 -2.30 20.30 0.49 -1.69


107


-] for the oxidation of Fructose



0

0.005

0.01

0.015

0.02

0.025

0 0.001 0.002 0.003 0.004 0.005 0.006

[MnO 4-] mol dm-3

k (s

-1)

0

50

100

150

200

250

0 200 400 600 800 1000 1200

1/[MnO 4-] mol -1dm3

1/k

(s)


108

Fig: 5.6 A plot of log k Vs log [MnO4


-2.5

-2

-1.5

-1

-0.5

0-3.2-3-2.8-2.6-2.4-2.2

logk

log[MnO4-]


109


on the Oxidation of Maltose

[Maltose] = 4 x 10-2 mol dm-3 [H2SO4] = 1 x 10-1 mol dm-3

[KNO3] = 0.3 mol dm-3 T = 305 K

[MnO4-] x 103

(mol dm-3) 1/[MnO4

-]x10-2

(mol-1dm3) log

[MnO4-]

k x 103 (s-1)

1/k x10-2 (s) log k

1 10.00 -3.00 1.50 6.66 -2.82

2 5.00 -2.69 5.90 1.69 -2.23

3 3.33 -2.52 5.40 1.85 -2.27

4 2.50 -2.39 4.40 2.27 -2.36

5 2.00 -2.30 5.30 1.88 -2.28


110


-] for the oxidation of Maltose



0

0.002

0.004

0.006

0.008

0 0.001 0.002 0.003 0.004 0.005 0.006

[MnO 4-] mol dm-3

k (s

-1)

0100200300400500600700

0 200 400 600 800 1000 1200

1/[MnO 4-] mol -1dm3

1/k

(s)


111



-3-2.5

-2-1.5

-1-0.5

0-3.2-3-2.8-2.6-2.4-2.2

logk

log[MnO4-]


112


on the Oxidation of Lactose

[Lactose] = 3 x 10-2 mol dm-3 [H2SO4] = 1 x 10-1 mol dm-3

[KNO3] = 0.3 mol dm-3 T = 305 K

[MnO4-] x 103

(mol dm-3) 1/[MnO4

-]x10-2 (mol-1dm3)

log [MnO4

-]k x 103

(s-1) 1/k x10-2

(s) log k

1 10.00 -3.00 1.40 7.14 -2.85

2 5.00 -2.69 1.60 6.25 -2.79

3 3.33 -2.52 2.80 3.57 -2.55

4 2.50 -2.39 7.20 1.38 -2.14

5 2.00 -2.30 8.90 1.12 -2.05


113


-] for the oxidation of Lactose



0

0.002

0.004

0.006

0.008

0.01

0 0.001 0.002 0.003 0.004 0.005 0.006

[MnO 4-] mol dm-3

k (s

-1)

0

200

400

600

800

1000

0 200 400 600 800 1000 1200

1/[MnO 4-] mol dm-3

1/k

(s)


114



-3.5-3

-2.5-2

-1.5-1

-0.50

-3.2-3-2.8-2.6-2.4-2.2

log[MnO4-]

logk


115

5.2 INFLUENCE OF VARIAITION OF CONCENTRATION

OF SUGARS ON THE OXIDATION BY KMnO4

After establishing the first order kinetics with respect to [MnO-4] nearly ten-fold

variations in the concentration of sugars were made under pseudo-first order

conditions.

The effect of changing sugars (maltose, lactose, galactose and fructose)

concentration has been investigated at constant oxidant (1x10-3 mol dm-3) and acid

concentration (1x10-1 mol dm-3) at 308 K. The values of rate constants are

summarized in Tables 4.5 to 4.8. It is obvious from the Tables that an increase in

sugar concentration enhances the rate of oxidation. The values of rate constants

for the oxidation of sugars are in the order fructose>galactose>maltose>lactose.

This indicates faster kinetics with monosaccharide as compared with

disaccharides which may be attributed with structural difference of studied sugars

or may be related with the hydrolysis of disaccharides. Maltose and lactose

exhibited slower rates of oxidation which were enhanced by the addition of

catalyst mercuric chloride. Figs 5.13, 5.16, 5.19 and 5.22 represent the plots of

kobs against [sugar] concentration. A straight line is obtained passing through

origin which confirms that the order of reaction with respect to sugar is also unity.

The second order rate constant (k1) evaluated by the slope of the plot between kobs

and [sugar] has been found to be 3.45 x 10-1 in case of galactose, 1.76 x 10-1 of

fructose, 5.4 x 10-2 of maltose and 1.56 x 10-1 of lactose and comparable with the

work reported earlier. 121. The plots of 1/k vs 1 / [sugars] were found to be linear

(Figs 5.14, 5.17, 5.20 and 5.23) showing first order kinetics with respect to

sugars. These indicate a direct influence of concentration of substrate over the rate

constant.

A plot of logk vs log [sugar] gives a straight line with a slope near unity (0.81,

0.84, 0.48 and 1.20 in galactose, fructose, maltose and lactose respectively) which

confirms first order dependence of the reaction on sugars.


116

TABLE: 5.5 Influence of Variation of Concentration of Galactose

on the Oxidation by KMnO4

[KMnO4] = 1 x 10-3 mol dm-3 [H2SO4] = 1 x 10-1 mol dm-3

[KNO3] = 0.3 mol dm-3 T = 305 K

[Galactose] x 102 (mol dm-3)

1/[Galactose]x10-2

(mol-1dm3) log

[Galactose] k x 103

(s-1) 1/kx10-2

(s) log k

1 10.00 -2.00 4.30 2.32 -2.37

2 5.00 -1.69 8.80 1.13 -2.05

3 3.33 -1.52 10.00 1.00 -2.00

4 2.50 -1.39 12.00 0.83 -1.92

5 2.00 -1.30 18.00 0.55 -1.74


117

Fig: 5.13 A plot of k Vs [Galactose] for the oxidation by KMnO4

Fig: 5.14 A plot of 1/k Vs 1/ [Galactose] for the oxidation by KMnO4

0

0.005

0.01

0.015

0.02

0 0.02 0.04 0.06

[Galactose] mol dm-3

k (s

-1)

050

100150200250300

0 20 40 60 80 100 120

1/[Galactose]mol -1 dm3

1/k

(s)


118

Fig: 5.15 A plot of log k Vs log [Galactose] for the oxidation by KMnO4

-2.5

-2

-1.5

-1

-0.5

0-2.5-2-1.5-1-0.50

log [Galactose]

logk


119

TABLE: 5.6 Influence of Variation of Concentration of Fructose on the Oxidation by KMnO4


[KNO3] = 0.3 mol dm-3 T = 305 K

[Fructose] x 102 (mol dm-3)

1/[Fructose] x10-2 (mol-1dm3)

log [Fructose]

k x 103 (s-1)

1/kx10-2 (s) log k

1 1.00 -2.00 2.30 4.34 -2.64

2 0.50 -1.69 3.40 2.94 -2.47

3 0.33 -1.52 5.90 1.69 -2.23

4 0.25 -1.39 7.20 1.38 -2.14

5 0.20 -1.30 8.30 1.20 -2.08


120

Fig: 5.16 A plot of k Vs [Fructose] for the oxidation by KMnO4

Fig: 5.17 A plot of 1/ k Vs 1/ [Fructose] for the oxidation by KMnO4

0

0.002

0.004

0.006

0.008

0.01

0 0.01 0.02 0.03 0.04 0.05 0.06

[Fructose] mol dm -3

k (s

-1)

0100200300400500600

0 20 40 60 80 100 120

1/[Fructose] mol-1

dm3

1/k

(s)


121

Fig: 5.18 A plot of log k Vs log [Fructose] for the oxidation by KMnO4

-3-2.5

-2-1.5

-1-0.5

0-2.5-2-1.5-1-0.50

log [Fructose]

log

k


122

TABEL: 5.7 Influence of Variation of Concentration of Maltose



[KNO3] = 0.3 mol dm-3 T = 305 K

[Maltose] x 102

(mol dm-3) 1/[Maltose]x10-2

(mol-1dm3) log

[Maltose]k x 103

(s-1) 1/k x10-2

(s) log k

1 1.00 -2.00 1.20 8.33 -2.92

2 0.50 -1.69 1.30 7.69 -2.89

3 0.33 -1.52 1.40 7.14 -2.85

4 0.25 -1.39 2.40 4.16 -2.62

5 0.20 -1.30 2.50 4.00 -2.60


123

Fig: 5.19 A plot of k Vs [Maltose] for the oxidation by KMnO4

Fig: 5.20 A plot of 1/k Vs 1/ [Maltose] for the oxidation by KMnO4

00.0005

0.0010.0015

0.0020.0025

0.003

0 0.01 0.02 0.03 0.04 0.05 0.06

[Maltose] mol dm-3

k (s

-1)

0200400600800

10001200

0 20 40 60 80 100 120

1/[Maltose] mol-1

dm3

1/k

(s)


124

Fig: 5.21 A plot of log k Vs log [Maltose] for the oxidation by KMnO4

-3

-2.9

-2.8

-2.7

-2.6

-2.5-2.5-2-1.5-1-0.50

log [Maltose]

log

k


125

TABLE: 5.8 Influence Of Variation of Concentration of Lactose



[KNO3] = 0.3 mol dm-3 T = 305 K

[Lactose] x 102

(mol dm-3) 1/[Lactose]x10-2

(mol-1dm3) log

[Lactose] k x 103

(s-1) 1/k x10-2

(s) log k

1 1.00 -2.00 1.40 7.14 -2.85

2 0.50 -1.69 1.60 6.25 -2.79

3 0.33 -1.52 2.80 3.57 -2.55

4 0.25 -1.39 7.20 1.38 -2.14

5 0.20 -1.30 8.90 1.12 -2.05


126

Fig: 5.22 A plot of k Vs [Lactose] for the oxidation by KMnO4

Fig: 5.23 A plot of 1/k Vs 1/ [Lactose] for the oxidation by KMnO4

0

0.002

0.004

0.006

0.008

0.01

0 0.01 0.02 0.03 0.04 0.05 0.06

[Lactose] mol dm -3

k (s

-1)

0

200

400

600

800

1000

0 20 40 60 80 100 120

1/[Lactose] mol-1 dm3

1/k

(s)


127

Fig: 5.24 A plot of log k Vs log [Lactose] for the oxidation by KMnO4

-3.5-3

-2.5-2

-1.5-1

-0.50

-2.5-2-1.5-1-0.50log [Lactose]

log

k


128

5.3 INFLUENCE OF VARIATION OF CONCENTRATION

OF H+ IONS ON THE OXIDATION OF SUGARS BY

KMnO4

The oxidation of sugars by various oxidizing agents in acidic medium was studied

earlier 39, 103, 85, 55. The reactions have been investigated at different [H+]

concentration varied by hydrochloric acid 39 or dilute sulphuric acid 112. Both

reactions exhibited a uniform increase in Pseudo-first order rate constant with

increasing concentration of an acid. The slopes of plot of logk vs log [Acid] were

equal to the unity showing first order dependence in acid. The present study

involves the oxidation of galactose, fructose, maltose and lactose by KMnO4 in

dilute sulphuric acid medium.

The reactions have been studied at different hydrogen ion concentrations varied

by the addition of sulphuric acid but at constant ionic strength i.e. 0.3 moldm-3,

oxidant and substrate concentrations. It was observed that the reactions were

accelerated by an increase in acidity of the medium (Tables 4.9 to 4.12). This can

be shown by the plots of 1/k vs 1/ [H+] (Figs 5.26, 5.29, 5.32 and 5.35) .The plots

of kobs against [H+] for all the substrates are linear with positive intercept on y-

axis (Figs 5.25, 5.28, 5.31 and 5.34) indicating that the redox reactions have acid-

dependent as well as acid-independent paths.200

The values of “n” were determined from the slope of the plot of log kobs vs log

[H+] at constant temperature. The values of n were found to be 0.06 for galactose,

0.57 for fructose, -0.24 for maltose and 0.36 for lactose. The values for the

galactose and maltose may be explained on basis of their configuration which

plays a significant role in oxidation of sugars. The corresponding plots are shown

in Figs 5.27, 5.30, 5.33 and 5.36.


129

TABLE: 5.9 Influence Of Variation of Concentration of H+ Ions

on the Oxidation of Galactose by KMnO4

[KMnO4] = 1 x 10-3 mol dm-3 [Galactose] = 2 x 10-2 mol dm-3

[KNO3] = 0.3 mol dm-3 T = 305 K

[H2SO4] x 101 (moldm-3)

1/[H2SO4] (mol-1dm3)

log [H2SO4]

k x 103 (s-1)

1/k (s) log k

1 10.00 -1.00 14.00 71.43 -1.85

2 5.00 -0.69 14.70 68.03 -1.83

3 3.33 -0.52 12.60 79.36 -1.89

4 2.50 -0.39 16.50 60.60 -1.78

5 2.00 -0.30 15.60 64.10 -1.81


130

Fig: 5.25 A plot of k Vs [H2SO4] for the oxidation of Galactose

by KMnO4

Fig: 5.26 A plot of 1/k Vs 1/ [H2SO4] for the oxidation of Galactose by KMnO4

0

0.005

0.01

0.015

0.02

0 0.2 0.4 0.6

[H2SO 4]mol dm-3

k (s

-1)

0

20

40

60

80

100

0 2 4 6 8 10 12

1/[H2SO4]mol-1dm3

1/k

(s)


131

Fig: 5.27 A plot of log k Vs log [H2SO4] for the oxidation of Galactose

by KMnO4

-1.9-1.88-1.86-1.84-1.82

-1.8-1.78-1.76

-1.2-1-0.8-0.6-0.4-0.20

logk

log [H2SO4]


132

TABLE: 5.10 Influence of Variation of Concentration of H+ ions

on the Oxidation of Fructose by KMnO4

[KMnO4] = 1 x 10-3 mol dm-3 [Fructose] = 4 x 10-2 mol dm-3

[KNO3] = 0.3 mol dm-3 T = 305 K

[H2SO4] x 101 (mol dm-3)


log [H2SO4]

k x 103 (s-1)

1/k (s) log k

1 10.00 -1.00 17.30 57.80 -1.76

2 5.00 -0.69 17.30 57.80 -1.76

3 3.33 -0.52 24.30 41.15 -1.61

4 2.50 -0.39 24.30 41.15 -1.16

5 2.00 -0.30 27.00 37.03 -1.57


133

Fig: 5.28 A plot of k Vs [H2SO4] for the oxidation of Fructose

by KMnO4

Fig: 5.29 A plot of 1/k Vs 1/ [H2SO4] for the oxidation of Fructose

by KMnO4

00.005

0.010.015

0.020.025

0.03

0 0.1 0.2 0.3 0.4 0.5 0.6

[H2SO 4]mol dm-3

k (s

-1)

010203040506070

0 2 4 6 8 10 12

1/[H2SO 4]mol -1dm3

1/k

(s)


134

Fig: 5.30 A plot of log k Vs log [H2SO4] for the oxidation of Fructose

by KMnO4

-2

-1.5

-1

-0.5

0-1.2-1-0.8-0.6-0.4-0.20

log [H2SO4]

log

k


135

TABLE: 5.11 Influence of Variation of Concentration of H+ Ions

on the Oxidation of Maltose by KMnO4

[KMnO4] = 1 x 10-3 mol dm-3 [Maltose] = 4 x 10-2 mol dm-3

[KNO3] = 0.3 mol dm-3 T = 305 K

[H2SO4] x 101 (mol dm-3)


log [H2SO4]

k x 103 (s-1)

1/k x 10-2 (s) log k

1 10.00 -1.00 5.90 1.69 -4.07

2 5.00 -0.69 2.80 3.57 -4.40

3 3.33 -0.52 8.60 1.16 -3.91

4 2.50 -0.39 9.40 1.06 -3.87

5 2.00 -0.30 1.60 6.25 -4.64


136

Fig: 5.31 A plot of k Vs [H2SO4] for the oxidation of Maltose

by KMnO4

Fig: 5.32 A plot of 1/ k Vs 1/ [H2SO4] for the oxidation of Maltose

by KMnO4

0

0.002

0.004

0.006

0.008

0.01

0 0.1 0.2 0.3 0.4 0.5 0.6

[H2SO 4]mol dm-3

k (s

-1)

0100200300400500600700

0 2 4 6 8 10 12

1/[H2SO 4]mol -1dm3

1/k

(s)


137

-4.8

-4.6

-4.4

-4.2

-4

-3.8-1.2-1-0.8-0.6-0.4-0.20

log [H2SO4]

log

k

Fig: 5.33 A plot of log k Vs log [H2SO4] for the oxidation of Maltose

by KMnO4


138

TABLE: 5.12 Influence of Variation of Concentration of H+ Ions

on the Oxidation of Lactose by KMnO4

[KMnO4] = 1 x 10-3 mol dm-3 [Lactose] = 3 x 10-2 mol dm-3

[KNO3] = 0.3 mol dm-3 T = 305 K

[H2SO4] x 101 (mol dm-3)


log [H2SO4]

k x 103 (s-1)

1/kx10-2 (s) log k

1 10.00 -1.00 1.40 7.14 -2.85

2 5.00 -0.69 2.10 4.76 -2.67

3 3.33 -0.52 2.20 4.54 -2.65

4 2.50 -0.39 2.50 4.00 -2.60

5 2.00 -0.30 2.50 4.00 -2.60


139

Fig: 5.34 A plot of k Vs [H2SO4] for the oxidation of Lactose

by KMnO4

Fig: 5.35 A plot of 1/k Vs 1/ [H2SO4] for the oxidation of Lactose

by KMnO4

00.0005

0.0010.0015

0.0020.0025

0.003

0 0.1 0.2 0.3 0.4 0.5 0.6

[H2SO 4]mol dm-3

k (s

-1)

0

200

400

600

800

0 2 4 6 8 10 12

1/[H2SO 4]mol -1dm3

1/k

(s)


140

-2.9-2.85-2.8

-2.75-2.7

-2.65-2.6

-2.55-1.2-1-0.8-0.6-0.4-0.2

log [H2SO4]

log

k

Fig: 5.36 A plot of log k Vs log [H2SO4] for the oxidation of Lactose

by KMnO4


141

5.4 INFLUENCE OF THE IONIC STRENGTH ON THE

OXIDATION OF SUGARS BY KMnO4

In aqueous solutions, ionic strength plays an important role in theories of reaction

rates. It can be studied by varying the concentration of an inert electrolyte. The

Bronsted equation (5.1) predicts the influence of ionic concentration and charges on

the reaction rate in dilute solutions.

≠= iBAkk γγγ /0 (5.1)

where k0 is the limiting value of the rate constant as ionic strength tends to zero and

γA. γB and γi# are the activity coefficients for A, B, and activated complex,

respectively. The Debye-Hückel limiting (eq 5.2) presents the relationship between

the ionic strength (µ) and the activity coefficients (γ) of the reacting ions in the

solutions.

5.02log µγ ii zA= (5.2)

where z is the ionic charge and A is a constant that depends on the dielectric

constant and temperature of the solution. By substituting eq 5.2 in eq 5.1 a

relationship between the rate constant and ionic strength (µ) is derived. For the

reactions in dilute aqueous solutions, the equation may be given as

5.00 02.1loglog µBAzzkk += (5.3)

Therefore, a plot of log k versus µ0.5 should be linear, with the slope and intercept

equal to 1.02 zAzB and log k0, respectively. The slope represents the product of

charges, on the species involved in the rate-limiting step. If the rate-limiting step is

between the species of like charges, a positive slope is expected. When the reaction

is between opposite charges, it results in a negative slope.201


142

In present study effect of ionic strength was studied by varying the concentration of

KNO3 while other parameters were kept constant. It was observed that change in

ionic strength of the medium does not alter the rate constant. (Tables 4.13 to 4.16).

The absence of salt effect indicates that the reaction does not take place between

ionic substances. Hence, at least one of the reactants must be non-ionic. These

findings were confirmed by the plot of logk vs √µ (Figs 5.36 to 5.39).

The values of slopes in case of galactose, fructose, maltose and lactose were found

to be zero. Therefore, it was concluded that the rate determining step must involve

at least one neutral molecule as mentioned earlier. 26, 28


143

Table: 5.13 Effect of Ionic Strength on the Oxidation of Galactose by KMnO4

[Galactose] = 2x10-2 mol dm-3 [KMnO4] = 1x10-3 mol dm-3

[H2SO4] = 1x10-1 mol dm-3 T = 305 K

√µ

(mol dm-3)0.5

logk

0.775 -2.02

0.894 -2.03

1.000 -2.00

1.095 -2.03

1.183 -2.02


144

Fig: 5.36 A plot of √µ vs logk for the oxidation of Galactose

by KMnO4

-2.032-2.03

-2.028-2.026-2.024-2.022

-2.02-2.018-2.016

0 0.5 1 1.5

logk

√µ (mol dm-3) 0.5


145

Table: 5.14 Effect of Ionic Strength on the Oxidation of Fructose

by KMnO4

[Fructose] = 4x10-2 mol dm-3 [KMnO4] = 1x10-3 mol dm-3

[H2SO4] = 1x10-1 mol dm-3 T = 305 K

√µ

(mol dm-3) 0.5

logk

0.775 -2.13

0.894 -2.11

1.000 -2.14

1.095 -2.11

1.183 -2.12


146

Fig: 5.37 A plot of √µ vs logk for the oxidation of Fructose

by KMnO4

-2.145

-2.14

-2.135

-2.13

-2.125

-2.12

-2.115

-2.11

-2.1050 0.5 1 1.5

logk

√µ (mol dm-3) 0.5


147

Table: 5.15 Effect of Ionic Strength on the Oxidation of Maltose

by KMnO4

[Maltose] = 4x10-2 moldm-3 [KMnO4] = 1x10-3 moldm-3

[H2SO4] = 1x10-1 moldm-3 T = 305 K

√µ (mol dm-3) 0.5

logk

0.775 -2.20

0.894 -2.18

1.000 -2.19

1.095 -2.18

1.183 -2.20


148

Fig: 5.38 A plot of √µ vs logk for the oxidation of Maltose by KMnO4

-2.205

-2.2

-2.195

-2.19

-2.1850 0.5 1 1.5

logk

√µ (mol dm-3) 0.5


149

Table: 5.16 Effect of Ionic Strength on the Oxidation of Lactose

by KMnO4

[Lactose] = 4x10-2 mol dm-3 [KMnO4] = 1x10-3 mol dm-3

[H2SO4] = 1x10-1 mol dm-3 T = 305 K

√µ (mol dm-3) 0.5

logk

0.775 -2.45

0.894 -2.43

1.000 -2.43

1.095 -2.41

1.183 -2.43


150

Fig: 5.39 A plot of √µ vs logk of for the oxidation of Lactose

by KMnO4

-2.46-2.45-2.44

-2.43-2.42-2.41

-2.40 0.5 1 1.5

logk

√µ (mol dm-3) 0.5


151

5.5 EFFECT OF TEMPERATURE ON RATE OF OXIDATION OF SUGARS BY KMnO4

Effect of temperature on rate of oxidation of sugars by KMnO4 was studied at five

different temperatures i.e. 30, 35, 40, 45 and 50 oC. The reactions were found to

be affected by the increase in temperature. The results are tabulated in Table 4.17

to 4.20. The activation parameters were determined. Arrhenius equation was used

to evaluate the energy of activation (Ea).

RTEa

eAk−

=

Or

RT

EAk a

303.2loglog −=

The slope of the plot of log k vs 1/T gave the value of Ea (Figs. 4.30 to 4.33). Other

thermodynamic parameters such as change in enthalpy of activation (∆H#) and

entropy of activation (∆S#) were calculated by using theory of absolute reaction

rate.

RTS

RTH

eeh

kTk∆∆−

=

Dividing by T and taking ln we get,

.1lnln##

RS

TRH

hk

Tk ∆

+∆−

+=

TR

HRS

hk

Tk 1.lnln

## ∆−

∆+=

ln k/ T was plotted against 1/T (Fig 5.40 to 5.43) to obtain ∆H# from slope and ∆S#

from the intercept. Free energy of activation (∆G#) was determined by using the

following relation.

### STHG ∆−∆=∆


152

These thermodynamic values are tabulated in Table 5.17. The values of activation

energy for the reactions of galactose, Fructose, Maltose and lactose were found to

be 43.5, 50, 25.4 and 50.2 KJ mol-1 respectively. The low values of Ea indicate

that at least one of the reacting substances of rate determining reaction may be a

neutral molecule. The value of Ea for maltose is 25.4 KJ mol-1 is due to the

addition of mercuric chloride as a catalyst which reduced Ea.

The values of enthalpy change of activation (∆H#) and entropy change of

activation (∆S#) for galactose, fructose, maltose and lactose were calculated as

40.9, 47.6, 23, 47.9 KJmol-1 and -149.8, -133.8, -212, -134 JK-1mol-1. The high

negative value of entropy of activation indicates highly solvated state of transition

complex that showed a great degree of freedom of molecules in the transition

state as compared to that in the reactive specie as supported by the earlier work53.

The values of free energy change of activation (∆G#) were found to be 86.6, 88.4,

87.6 and 89.0 KJ mol-1 in the oxidation of galactose, fructose, maltose and lactose

respectively. These high values of free energy of activation suggest that transition

state is highly solvated as mentioned earlier 26, 85.


153

Table 5.17 Values of Activation Parameters

[Galactose] = 2x10-2 mol dm-3 [Fructose] = 4x10-2 mol dm-3

[Maltose] = 4x10-2 mol dm-3 [Lactose] = 3x10-2 mol dm-3

[KMnO4] = 1x10-3 mol dm-3 [H2SO4] = 1x10-1 mol dm-3

[KNO3] = 0.3 mol dm-3 T = 305 K

Sugars Ea

KJmol-1

∆H#

KJmol-1

∆S#

JK-1mol-1

∆G#

KJmol-1

Galactose 43.5 40.9 -149.8 86.6

Fructose 50.0 47.6 -133.8 88.4

Maltose 25.4 23.0 -212.0 87.6

Lactose 50.2 47.9 -134.6 89.0


154

-10.6

-10.4

-10.2

-10

-9.8

-9.6

-9.43.05 3.1 3.15 3.2 3.25 3.3 3.35

1/Tx103(K-1)

lnk/

T

Fig: 5.40 plot of lnk/T vs 1/T of Galactose against KMnO4

at √µ 0.775 (mol dm-3)0.5

-11.4-11.2

-11-10.8-10.6-10.4-10.2

-10-9.8

3.05 3.1 3.15 3.2 3.25 3.3 3.351/Tx103(K-1)

lnk/

T

Fig: 5.41 plot of lnk/T vs 1/T of Fructose against KMnO4

at √µ 0.775 (mol dm-3)0.5


155

-11-10.8-10.6-10.4-10.2

-103.05 3.1 3.15 3.2 3.25 3.3 3.35

1/Tx103(K-1)

lnk/

T

Fig: 5.42 plot of lnk/T vs 1/T of Maltose against KMnO4

at √µ 0.775 (mol dm-3)0.5

-12

-11.5

-11

-10.5

-103.05 3.1 3.15 3.2 3.25 3.3 3.35

1/Tx103(K-1)

lnk/

T

Fig: 5.43 plot of lnk/T vs 1/T of Lactose against KMnO4

at √µ 0.775 (mol dm-3)0.5


156

5.6 REACTIVE SPECIES OF MnO4-

On the basis of stoichiometric studies it can be easily concluded that MnO-4 is the

active reactive oxidizing specie in acidic medium which forms permanganic acid

when combine with H+ ion. This permanganic acid is highly oxidative unstable

inorganic acid which with catalyst or lonely oxidizes the sugar via the formation

of unstable intermediate complex which leads to the formation of aldehyde

hydrate. This aldehyde hydrate frequently reacts with MnO-3 species and

converted into respective carboxylic acid

H+ + MnO4- HMnO4

5.7 REACTIVE SPECIES OF Hg (II) CHLORIDE IN ACIDIC

MEDIUM Aqueous HgCl2 solution was subjected to spectrophotometric studies which

suggest rate constant and equilibrium constant K for the reversible reaction.

HgCl2 +6H2O [Hg(H2O)6]+2 + 2Cl-

k1

k-1

The above equation is comparable with the work reported earlier 84 and 71 where

kinetic studies have been made for the oxidation of reducing sugars by acidic

solution of N-bromosuccinimide and NBA in presence of Ir (III) as a homogeneous

catalyst. In this case existence of following equilibrium was suggested.

[Ir Cl6]3- + H2O [IrCl5(H2O)]-2 + Cl-

In catalyzed oxidation of maltose and lactose in acidic medium, since the solution

of catalyst is prepared in water therefore it is reasonable to assume that the reactive

specie of catalyst is [Hg(H2O)6]+2 .


157

5.8 SPECTRAL EVIDENCE FOR THE FORMATION OF

COMPLEXES DURING COURSE OF REACTION In the kinetic studies of reducing sugars, it has been observed that metal ions such

as Ru (III)22 & Pd(II)67 form complexes with the reducing sugars in acidic

medium. It is also reported 67,68 that the complex thus formed have tendencies to

react with the reacting species of NBA & also with Hg(II), whose function in the

reaction was as a Br- ion scavenger and as co-catalyst. In the oxidation of maltose

& lactose with permanganate ion in acidic medium, order with respect to sugars

concentration was first throughout its 10-fold variation. This shows that OH group

of sugar involves in the oxidation before the rate determining step although it will

combine with the most reactive complex to form the reaction products along with

the regeneration of Hg catalyst.

In order to probe the possible formation of complex MnO4- and [Hg(H2O)6]+2

spectra for the solution of MnO4-, H+ and for the solution of MnO4

- , H+ and

[Hg(H2O)6]+2 have been collected (Fig.5.44 and 5.45). From the spectra, it is clear

that the addition of [Hg(H2O)6]+2 solution there is an increase of absorbance from

1.79 to 2.00 (λmax 545 nm). This increase in absorbance can be considered as an

indication of increased formation of the complex between reactive species of

[Hg(H2O)6]+2 in acidic medium according to the following equilibrium:

[Hg(H2O)6]+2 + MnO4-+ H3O+ O Mn O

OH

O

Hg(H2O)5

+2

+ 2 H2O

When maltose and lactose solutions were added to the solutions of MnO4- , H+ and

[Hg(H2O)6]+2 a decrease in absorbance from 2.00 to 1.631 & 1.99 (λmax 545 nm)

for maltose & lactose was noted (Fig.5.48 and5.49 ).


158

This shows that the complex formed subsequently combines with maltose to give

a highly solvated activated complex of the type

according to the following equilibrium

RC

H O

H

H

+ O Mn O Hg(H2O)5

OH

O

+2 H

RC

H

H

O+ Mn

O

O

O Hg(H2O)5

O

H

+2

Conclusions for the formation of complexes in the reactions of galactose and

fructose have been drawn on the basis of the spectra collected for MnO4- , H+

solutions and MnO4- , H+ with galactose and fructose solutions. From the observed

spectra it is apparent that absorbance was decreased as the solutions of galactose

and maltose were added.(Fig.5.46 and 5.47).This decrease in absorbance with

MnO4- can be considered as an indication of increased formation of the complex

between reacting species of MnO4- and sugar in acidic medium.

H

RC

H

H

O+ Mn

O

O

O-

O

H

CH O

H

H

R

+ MnO4- + H3O+ + H2O

H

RC

H

H

O+ Mn

O

O

O Hg(H 2O) 5

O

H

+2


159

Fig: 5.44 Absorption Spectra of MnO4- and H+ solutions.

Fig: 5.45 Absorption Spectra of MnO4-, H+ and

[Hg(H2O)6]+2 solutions.


160

Fig: 5.46 Absorption Spectra of MnO4- , H+ and

galactose solutions.

Fig: 5.47 Absorption Spectra of MnO4- , H+ and

fructose solutions.


161

Fig: 5.48 Absorption Spectra of MnO4-, H+,[Hg(H2O)6]+2

and maltose solutions.

Fig: 5.49 Absorption Spectra of MnO4- , H+,[Hg(H2O)6]+2

and lactose solutions.


162

5.9 REACTIONS FOR OXIDATION OF SUGARS INTO

ALDONIC ACIDS

−− ++⎯→⎯++



−− ++⎯⎯⎯ →⎯++

++

36105/

24112212 42242



5.9.1 Reaction Pathway for the Oxidation of Galactose and

Fructose

MnO4- + H3

+O HMnO4+ H2Ok1

k2

C6H12O6 + HMnO4 + H2O R C C O

HH

OOH

Mn OO

O

+ H3Ok3

slow

Where R = C4H9O5


163

R C C O

HH

OOH

Mn OO

O

+ H R C H

O

+ H C OH

O

+ HMnO3fast

R C H

O

MnO4-/ H3O

R C

OH

H

O

MnO

O

O

R C

OH

H

O

MnO

O

O

fastR C

O

OH + HMnO3

Scheme 5.1 Formation of Formic and Arabinonic Acid as a result of

Oxidation of Galactose and Fructose


164

5.9.2 Reaction Pathway for Catalytic Oxidation of Maltose and

Lactose

MnO4- + H3

+O HMnO4+ H2Ok1

k2

[Hg(H2O)6]+2 + HMnO4 O Mn O

OH

O

Hg(H2O)5

+2

+ H2Ofast

O Mn O

OH

O

Hg(H2O)5

+2

+ C6H12O6 + H2O k3

slowR C C O

HH

OOH

Mn OO

O+ H3O

Hg(H2O)5

+

R C C O

HH

OOH

Mn OO

O

+ H3O R C H

O

+ H C OH

O

+ HMnO3fast

Hg(H2O)5 + Hg(H2O)6+2


165

R C H

O

MnO4-/ H3O

R C

OH

H

O

MnO

O

O

Hg(H2O)+2

R C

OH

H

O

MnO

O

O

fastR C

O

OH + HMnO3

Scheme 5.2 Formation of Formic and Arabinonic Acid as a result of

Oxidation of Maltose and Lactose


166

5.10 REACTIONS FOR OXIDATION OF SUGARS INTO

OTHER CARBOXYLIC ACID

−− ++⎯→⎯++


Galactose / Fructose galacturonic acid/ fructuronic acid

−− ++⎯⎯⎯ →⎯+

++

32131812/

4112212 4242

MnOOHOHCMnOOHC HgH

Maltose / Lactose malturic acid/ lacturic acid

These reactions can be shown as follows:

O

OH

HO

OH

OH

OH

O

OOH

HO

OH

OH

HOH2C

MnO4/ H3O

Galactose Galacturonic acid

OHO

O

OH

OH

OH

OH

O

OHOH

OH

OH

OH

MnO4/ H3O

Fructose Fructuronic acid


167

O

O

O

HO

OH

OH

OHOH

OHOH

O

O

OH

O

OH

OH

OH

OH

OH

OHOH

OH

MnO4/H3O

Hg+2

Maltose Malturic Acid

O

O

O

OH

OH

OH

OHOH

OHOH

O

OHO

O

O

OH

OH

OH

OHOH

OHOH

OH

O

MnO4/H3O

Hg+2

Lactose Lacturic Acid


168

5.10.1 Reaction Pathway for Oxidation of Galactose and Fructose

in absence of Catalyst

RC

H

H

O

H

Mn

O

OO

OH O H

H

Mn

O

OO

O O

H

H

RC

H

HH O H

H

OHH

Mn

O

OO

O ORC

H

H

H H

Mn

O

OO

ORC

H

H

OH H

Fast K

Fast

(A) (B)

(C) (D)

Sugar

Permanganate ionSolvated activated complex

Intermediate transition complexManganate ester

Fast


169

C

H

R

O

OH H

+Mn

O

O

O

C

H

R

O

O

H

H C

H

R

O

O

H

H

MnO4- ,H+

C

R

H

OH

O Mn

O

O

O

OHH

R C

O

OH + Mn

O

O

Solvated aldehyde

k1

k2

Aldehyde hydrate

(E)

k3

slowCarboxylic acid

O

_

where R = C5H9O5

Scheme 5.3 Formation of Galacturonic and Fructuronic Acid as a result of

Oxidation of Galactose and Fructose


170

5.10.2 Reaction Pathway for Oxidation of Maltose and Lactose in

presence of Catalyst

RC

H

H

O

H

Mn

O

OO

O

H O H

H

Mn

O

OO

O O

H

H

RC

H

HH O H

H

OHH

Mn

O

OO

O ORC

H

H

H H

Mn

O

OO

ORC

H

H

OH H

Fast

Fast

(A) (B)

(C)(D)

Sugar

Permanganate ionSolvated activated complex

Intermediate transition complex

Manganate ester

Fast

+ + Hg(H2O)6+2

Hg(H2O)5

+3

Hg(H2O)5

+2

_Hg(H2O)6+2


171

C

H

R

O

OH H

+Mn

O

O

O

C

H

R

O

O

H

H C

H

R

O

O

H

H

MnO4- ,H+

C

R

H

OH

O Mn

O

O

O

OHH

R C

O

OH + Mn

O

O

Solvated aldehyde

k1

k2

Aldehyde hydrate

(E)

k3

slowCarboxylic acid

O

_

where R = C11H17O11

Scheme 5.4 Formation of Malturic and Lacturic Acid as a result of Oxidation

of Maltose and Lactose


172

Reaction Pathway which showed the catalytic oxidation of maltose and lactose

into respective carboxylic acid by potassium permanganate in acidic medium is

interesting because it involves the change in oxidation state of permanganate, an

inorganic compound and between the organic compounds. Permanganate ion,

active reactive species (A) in acidic medium is highly oxidative and reacts with

the alcoholic group of sugars rapidly.

Reaction is initiated when alcohol donates an electron pair to the manganese atom

as one of the oxygen extracts a proton. At this stage Hg (II) accepts electron pair

from oxygen forming a highly unstable solvated activated intermediate (B). The

equilibrium is established into two possible activated intermediates (B) and (C)

which later on converted into Manganate ester (D) through (C). A manganate

ester is formed when a water molecule departs as a leaving group. In this step

Hg (II) catalyst is recovered by donating electron pair to oxygen as a result double

bond formed in between manganese and oxygen. Manganese atom then departs

from the ester (D) with a pair of electron that formerly belonged to the alcoholic

group.

The alcoholic group is there by oxidized and reduction of manganese takes place

with the formation of solvated aldehyde or aldehyde hydrate. This aldehyde

hydrate reacts with MnO4- in presence of H+ ion and slowly converts into

respective carboxylic acid. This is the rate determining step which is represented

by k3.


173

5.11 CHARACTERIZATION OF ACID FORMED THROUGH

THE OXIDATION OF D-GALACTOSE

The acid formed as a result of oxidation of D-Galactose 202,203 was identified by

Fab(+) mass spectrometry, the M+1 peak was at 195.

Table: 5.18 13C-NMR Chemical Shifts (δ) values

O

OH

OH

OH

OH

OH

O

9 9 .1 7

7 1 .8 77 2 .0 1

7 3 .1 9

7 7 .8 6

1 7 0 .3 1

Fig: 5.50 Galacturonic Acid


174

The 13C-NMR chemical shift value of anomeric carbon is 99.17 while that of

carboxylic carbon of acid of galactose is found to be 170.31 ppm.

Carbons δ

(ppm)

C 99.17

C 71.87

C 72.01

C 73.19

C 77.86

C 170.31


175

Table: 5.19 1H-NMR Chemical Shifts (δ) values of acid of

D-Galactose

O

OH

OH

OH

OH

OH

O

H

H

H

H

H

6.09

6.09

6.09

6.09

6.09

2.81

3.35

3.35

4.32

3.92

Node δ

(ppm)

OH 6.09

OH 6.09

OH 6.09

OH 6.09

H 2.81

H 3.35

H 3.35

H 4.32

H 3.92

The 1H-NMR chemical shift value of anomeric hydrogen of acid of galactose is

found to be 2.81ppm.


176

5.12 CHARACTERIZATION OF ACID FORMED THROUGH

THE OXIDATION OF D-FRUCTOSE

The acid formed as a result of oxidation of D-Fructose 204 was identified by Fab

(+) mass spectrometry; the M+1 peak was at 195.

Table: 5.20 13C-NMR Chemical Shifts (δ) values of acid of D-

Fructose

OH

OHO

OH

OH

O

OH 102

166

78.0872.38

71.90

100.78

Fig: 5.51 Fructuronic acid


177

The 13C-NMR chemical shift value of anomeric carbon is 100.78 while that of

carboxylic carbon of acid of fructose is found to be 166.00 ppm.

Carbon δ

(ppm)

C 100.78

C 71.90

C 72.38

C 78.08

C 102

C 166.00


178

Table: 5.21 1H-NMR Chemical Shifts (δ) values

OH

OHO

OH

OH

O

OH

H

H

H

H

H5.17

5.17

5.17

5.17

5.17

4.38

4.14

4.20

3.49

3.54

Node δ

(ppm)

OH 5.17

OH 5.17

OH 5.17

OH 5.17

H 3.49

H 3.54

H 4.02

H 4.14

H 4.38

The 1H-NMR chemical shift value of anomeric hydrogens of acid of fructose is

found to be 3.49 and 3.54 ppm.


179

5.13 CHARACTERIZATION OF ACID FORMED AS A

RESULT OF OXIDATION OF D-MALTOSE

The acid formed as a result of oxidation of D-Maltose was identified by Fab(+)

mass spectrometry, the M+1 peak was at 371.


O

O

O

OH

OH

OH

OH

OH

OH

OH

OH

O

O

102.3

75.3873.99

72.64

78.9279.32

76.70

170.01

98.47

77.26

79.52

172.97

Fig: 5.52 Malturic acid


180

Carbon δ

(ppm)

C 102.30

C 75.38

C 73.99

C 72.64

C 78.92

C 79.32

C 79.52

C 98.47

C 77.26

C 76.70

C 170.01

C 172.97

The 13C-NMR chemical shift values of anomeric carbons are 102.30 and

98.47ppm while that of carboxylic carbons of acid of maltose are found to be

170.01 and 172.97 ppm.


181

Table: 5.23 1H-NMR Chemical Shifts (δ) values

O

O

O

OH

OH

OH

OH

OH

OH

OH

OH

O

O

H

H

H

H

4.99

3.5

4.48

H

H

H

H

H

H

6.50

6.50

6.50

6.50

6.50

6.50

6.50

6.50

4.44

4.72

4.00

4.30

4.34

3.50

4.17


182

Node δ

(ppm)

OH 6.50

OH 6.50

OH 6.50

OH 6.50

OH 6.50

OH 6.50

OH 6.50

OH 6.50

H 4.72

H 4.00

H 4.30

H 4.34

H 3.50

H 4.99

H 3.50

H 4.48

H 4.44

H 4.17

The 1H-NMR chemical shift values of anomeric hydrogens of acid of maltose are



183

5.14 CHARACTERIZATION OF ACID FORMED AS A

RESULT OF OXIDATION OF D-LACTOSE

The acid of D-Lactose was identified by Fab (+) mass spectrometry, the M+1

peak was at 371.


O

O

O

OH

OH

OH

OH

OH

OH

OH

O

O

102.3

75.3873.99

72.64

78.9279.32

76.70

170.01

98.47

77.26

79.52

172.97

OH

Fig: 5.53 Lacturic acid


184

Carbon δ

(ppm)

C 102.30

C 75.38

C 73.99

C 72.64

C 78.92

C 79.32

C 79.52

C 98.47

C 77.26

C 76.70

C 170.01

C 172.97

The 13C-NMR chemical shift values of anomeric carbons are 102.30 and

98.47ppm while that of carboxylic carbons of acid of lactose are found to be

170.01 and 172.97 ppm.


185

Table: 5.25 1H-NMR Chemical Shifts (δ) values of

acid of D-Lactose

O

O

O

OH

OH

OH

OH

OH

OH

OH

OH

O

O

H

H

H

H

4.99

3.5

4.48

H

H

H

H

H

H

6.50

6.50

6.50

6.50

6.50

6.50

6.50

6.50

4.44

4.72

4.00

4.30

4.34

3.50

4.17


186

Node δ

(ppm)

OH 6.50

OH 6.50

OH 6.50

OH 6.50

OH 6.50

OH 6.50

OH 6.50

OH 6.50

H 4.72

H 4.00

H 4.30

H 4.34

H 3.50

H 4.99

H 3.50

H 4.48

H 4.44

H 4.17

The 1H-NMR chemical shift values of anomeric hydrogens of acid of lactose are



187

5.15 PROPOSED MECHANISM OF KINETICS OF

OXIDATION AGAINST KMnO4

Thus based on above experimental facts the proposed reaction mechanism

involves the formation [O] by the action of H2SO4 on KMnO4.

2KMnO4 + 3H2SO4 K2SO4 + 2MnSO4 + 8[O] + 3H2O

RCHO +[O] RCOOH The permanganate ion reacts with galactose to form complex [C6H11O6---MnO4

-]

.This complex finally gives the aldonic acid in presence of nucleophile.

The probable rate law might be proposed.

[ ] [ ][ ]−−

=−

44 MnORCHOk

dtMnOd

Where RCHO represents the concentration of galactose or maltose and MnO4 - is

of Oxidant.

The following mechanism is proposed to explain the path of oxidation of sugars :

[ ] [ ]oductComplex k Pr3⎯→⎯

slow

RCHO + MnO4 + H [ RCHO----MnO4 ] Complex

k1

k2


188

where k1 and k2 represent the rate constant in the forward and reverse direction

and k3 is the rate constant of the formation of product. Rate of formation of

complex will be given as:

[ ] [ ][ ] [ ] [ ]ComplexkkMnORCHOkdt

Complexd3241 −−= − (1)

At steady state,

[ ] 0=dt

Complexd (2)

From equation no.(1) and (2) concentration of complex comes out to be:

[ ] [ ][ ]32

41

kkMnORCHOkComplex

+=

−

(3)

At steady state rate of disappearance of MnO4

- may be:

[ ] [ ]ComplexkdtMnOd

34 =

− −

(4)

[ ] [ ][ ]( )32

4314

kkMnORCHOkk

dtMnOd

+=

− −−

(5)

Now the total [MnO4

-] may be considered as:

[ ] [ ] [ ]ComplexMnOMnO T += −−44 (6)

Now put the value of Complex:

[ ] [ ] [ ][ ]( )32

4344 kk

MnORCHOkMnOMnO T ++=

−−− (7)


189

from equation (7) the value of [MnO4-] comes out :

[ ] ( )[ ]( ) [ ]RCHOkkk

MnOkkMnO T

132

4324 ++

+=

−− (8)

The final rate law from 5 to 8 :

[ ] { }[ ][ ][ ]( ) [ ]{ }[ ]32132

432314

kkRCHOkkkMnOkkRCHOkk

dtMnOd T

+++

+=

− −−

(9)

[ ][ ][ ] [ ]RCHOkkk

MnORCHOkk

131

431

++=

−

(10)

In present experimental conditions, [ ]RCHOkkk 132 >+ Hence above equation reduces to,

[ ] [ ][ ] [ ][ ]TT MnORCHOkkk

MnORCHOkkdtMnOd −

−−

=+

=−

432

4314 (11)

where,

32

31

kkkkk+

=

The above equation indicates first order kinetics with respect to sugar and

permanganate ion concentration.


190

5.16 COMPARATIVE STUDIES The results of the present study of the oxidation of galactose, fructose, maltose

and lactose by potassium permanganate in acidic medium were compared with the

results supported for the oxidation of some aldoses by chromium

peroxydichromate in very dilute sulphuric acid 112 and the reactivities of some

aldoses and aldoseamines towards potassium bromate in hydrochloric acid

medium. 39

When the present study in respect of the role of MnO4- was compared, it is found

that the MnO4- is the reactive species of potassium permanganate in acidic as well

as in alkaline medium, as far as the kinetic order with respect to MnO4- is

concerned, it is first order throughout the variation of [MnO4-].

When the present study has been made for the effect of [sugar] on the rate of

oxidant, it is found that the reactions are first order with respect to all the sugars.

The reported 39, 103 first order kinetics in [sugar] seems to be similar with the

present study. The reducing sugar molecules participate in the reactions as such in

present study as well as in the previous work. The effect of H+ ion concentration

have the same effect as in the oxidation of some aldoses by peroxydichromate in

dilute sulphuric acid 112 and reactivities of some aldoses and aldoseamines

towards potassium bromate in hydrochloric acid medium. 39

The reported results in these studies are quite similar i.e. these reactions exhibited

a uniform increase in pseudo_first order rate constant with increasing

concentration of an acid. The reported influence of H+ ion concentration also

seems to be similar with present study i.e. the reaction was accelerated by an

increase in the acidic of the medium kobs vs [H2SO4] plot shows a linear

relationship with positive intercept on the Y-axis.


191

Table: 5.26 Comparison of Rate Constants with reported Data

a N-Bromoacetamide b Diperiodatoargentate (III)

Oxidant

[Oxidant] (mol dm-3)

Sugar [Sugar] (mol dm-3)

k (s-1) Reference

NBAa 8 x 10-4

Mannose

Maltose

2 x 10-2 4 x 10-2 2 x 10-2 4 x 10-2

2.0 x 10-5 3.2 x 10-5 1.6 x 10-5 3.1 x 10-5

83

Potassium

Iodate

1 x 10-3 Xylose Maltose

2 x 10-2

2 x 10-2 6.0 x 10-4 2.0 x 10-4 57

DPAb 9 x 10-5 Glucose

Galactose Fructose

1 x 10-4 1 x 10-4 1 x 10-4

3.6 x 10-4 2.5 x 10-4 8.1 x 10-4

134

Potassium Bromate 1 x 10-2

Glucose Mannose Galactose

Xylose

1 x 10-1 1 x 10-1 1 x 10-1 1 x 10-1

6.0 x 10-4 7.2 x 10-4 8.4 x 10-4

9.4 x 10-4

39

Potassium Permanganate 1 x 10-3

Galactose Fructose Maltose Lactose

2 x 10-2 4 x 10-2 4 x 10-2 3 x 10-2

8.8 x 10-3 7.2 x 10-3 2.4 x 10-3 2.8 x 10-3

Present Study


192

Table: 5.27 Comparison of Activation Parameters

Sugar

Ea

(KJmol-1)

∆H# (KJmol-1)

∆S# (JK-1mol-1)

∆G# (KJmol-1) Reference

Sucrose 63.7

72.4

-8.84

75.1 55

Glucose Mannose Galactose

Xylose

-

40.0 37.0 35.0 32.0

-170 -178 -185 -194

- 39

Arabinose

Xylose

45.4 42.3

43.3 40.8

-83.6 -85.4

68.12 66.32 53

Glucose Galactose Fructose

- 67.6 48.1 63.5

-66.7 -140.0 -75.3

- 134

Mannose Maltose

76.2 82.8

73.6 80.1

8.4 29.0

70.9 71.1

83

Galactose Fructose Maltose Lactose

43.5 50.0 25.4 50.2

40.9 47.6 23.0 47.9

-149.8 -133.8 -212.0 -134.6

86.6 88.4 87.6 89.0

Present Study


193

5.17 CONCLUSIONS

The following conclusions were drawn from the observed kinetic data and from

the spectral information collected for the oxidation of galactose, fructose, maltose

and lactose by potassium permanganate in acidic medium while Hg was used in

the oxidation of maltose and lactose.

1. MnO4- and [Hg (H2O)6]+2 have been assumed as the reactive species of

potassium permanganate and Hg(II) in acidic medium.

2. The complex,

R C C O

HH

OOH

Mn OO

Oand the complex,

R C C O

HH

OOH

Mn OO

O

Hg(H2O)5

+

has been proposed as the most unstable activated

complex in the oxidation of galactose, fructose and maltose, lactose respectively.

3. The formation of highly solvated activated complex (scheme 1, 2, 3 & 4) is

supported by observed negative value of entropy of activation.

4. First order kinetics has been observed with respect to oxidant and sugar.


194

5. Linear dependence of rate is observed when acidity of medium increased.

6. The rate of oxidation of galactose, fructose, maltose and lactose is unaffected

by the change in ionic strength of the medium.

7. Formic acid and arabinonic acid are identified as main oxidation products along

with the other acids such as galacturonic, fructuronic, malturic and lacturic acid.


195

5.18 FUTURE PERSPECTIVES Oxidation of carbohydrates including reducing and non reducing sugars with

different inorganic and organic oxidizing agents have been studied very widely. A

lot of literature has been reported on the oxidation of aldoses and ketoses,

oligosaccharides and polysaccharides. This project of oxidation of carbohydrates

(monosaccharides and disaccharides) can be extended in many ways like:

• Oxidation of reducing and non reducing sugars with KMnO4 can be

studied by recording the time of decoloration of KMnO4 visually.

• Pb and Cd can be used as a catalyst in presence of KMnO4.

• A comparative study can be carried out to study the oxidation of pentose

with hexoses, dextroses and other group of carbohydrates.

• KMnO4 with base should be tested to oxidize the sugar into respective

acid.

• Effect of pH with temperature can be studied in oxidation of sugars with

KMnO4.

• KMnO4 with different buffer in alkaline and acidic medium should be

checked for the oxidation of carbohydrates.

• Compound may be analyzed by using Gas Chromatography, HPLC, Mass

Spectrum, negative and positive fab.

• New organic and inorganic oxidants should be searched with different

catalyst using alkaline and acidic medium to extend the oxidation of

carbohydrates.

• New mechanism should be developed to establish the reaction kinetics of

oxidation of sugars.


196

5.19 RESEARCH IMPORTANCE, APPLICATION

AND USE Carbohydrates are the structural backbone of the DNA, RNA and nucleic acids

and play major role in nutrition. The biochemical importance of the carbohydrates

lies in the fact that they form the direct link between the radiant energy emitted by

the sun and the demand of living tissues, plant and animal, for supplies of energy

required for the purpose of metabolism. They are further important due to their

wide occurrence and multihydroxy functionality that allows coordination and

chelation to many metal ions. Besides acting simply as effective chelators, 205 in

many cases they are also reducing agents. 17-50 .

Potassium permanganate (KMnO4) is used primarily to control taste and odors,

remove colour, control biological growth in treatment plants and remove iron and

manganese, where as secondary role of it, may be useful in controlling the

formation of THMS and DBPS. 206

Potassium permanganate is highly reactive under conditions found in the water

industry. It will oxidize a wide variety of inorganic and organic substances.

Potassium permanganate (Mn+7) is reduced to (MnO2) (Mn+4).206 Under acidic

conditions the following reaction has been established:

OHMnOeHMnO 22344 +→++ −+−

OHMneHMnO 22 4584 +→++ +−+−

Current research based on the oxidative property of KMnO4 with organic reducing

sugars in acidic medium where HMnO4 specie was reported as an oxidizing agent.


197

The importance of this investigation lies in the fact that there is no pertinent work

related with the oxidation of sugars in acidic medium has been reported in which

the compound formed during oxidation is isolated and subjected to advanced

techniques in elucidation of mechanism and structure of compound formed.

All the steps involve in the kinetics measurement including the value of Ea, ∆H#,

∆G# & ∆S# were used to establish the complex formed between permanganate ion

and sugar lead to the formation of acid derivative. This project will be helpful in

understanding the mechanism of oxidation of sugars with KMnO4 as an oxidizing

agent for the research scholars and other students of learning process.

CHAPTER # 6

RREEFFEERREENNCCEESS

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