CHAPTER 5

Homogeneous and Heterogeneous Catalytic Oxidation of Substituted

Benzyl alcohol, Hydrocarbons, 1,10-Phenanthroline and

substituted alkynes

Chapter 5

163 

CHAPTER 5

HOMOGENEOUS AND HETEROGENEOUS CATALYTIC OXIDATION OF

SUBSTITUTED BENZYL ALCOHOL, HYDROCARBON, 1,10-

PHENTHROLINE AND SUBSTITUTED ALKYNES

5.1. Introduction

This chapter deals with the use of the schiff base copper (II) complexes as

catalysts for various oxidation reactions. Catalytic activity of copper (II) complexes of

the schiff bases is divided into four sections. Section 5.3 deals with studies on the

oxidation of p-chlorobenzyl alcohol. Section 5.4 presents the studies on the oxidation

of hydrocarbons, section 5.5 deals with the study of oxidation of 1,10-phenanthroline

and section 5.6 deals with the oxidation of substituted alkynes.

Catalytic oxidation of alcohols to carbonyl compounds is a major reaction in

organic transformation, for both fundamental research and industrial manufacturing

[1]. Conventionally, stoichiometric oxidants (e.g., chromate, permanganate,

ruthenium(VIII) oxide and chromium(VI) reagents) have been used for oxidation of

alcohols that produce environmentally undesirable heavy toxic wastes [2]. Selective

catalytic oxidation of alcohols by inexpensive reagents such as oxygen, hydrogen

peroxide or tert-butyl hydroperoxide is relatively useful way of generating products

like aldehydes, ketones and acids [3]. Similarly, the oxidation of primary and

secondary alcohols to carbonyl compounds is a simple and useful transformation in

organic chemistry [4]. The oxidation of benzyl alcohol to benzaldehyde is an

important organic transformation, since benzaldehyde has applications in the perfume,

pharmaceutical, dyestuff, and agrochemical industries [5]. Many transition metal

complexes are used as homogeneous and heterogeneous catalyst for the oxidations of

different alkenes, alkanes, alcohols, thioethers, etc. [6,7]. Some of the copper (II)

complexes of schiff base with NNO donor sites have been found to catalyze the

benzyl alcohol oxidation [8]. Section 5.3 reports the oxidation of p-chlorobenzyl

alcohol using copper (II) schiff base complexes of L1 series, heterogeneously.

Multinuclear copper (II) complexes and monomeric compounds, show

excellent catalytic activity towards oxidation of toluene, alkenes, benzene, catechol

Chapter 5

164 

etc.[9-11].Substituted aromatic hydrocarbons and their oxidation productsare

industrially and commercially important[12]. Velusamy et al [13] reports the

oxidation of alkylbenzenes into the corresponding ketones using H2O2. The controlled

oxidation of toluene using copper complexes leads to benzyl alcohol, benzaldehyde

and benzoic acid which are very important for industrial purpose [14]. Copper schiff

base complexes have been used for oxidation of hydrocarbons and result in the

formation of carbonyl compounds [15,16]. Roy et al [17] reported the oxidation of

cyclohexane and toluene using tetranuclear copper (II) complexes resulting in the

formation of corresponding alcohol and aldehyde. Biswas et al [18] found the schiff

base with N2O2 donor atom as an efficient catalyst for the oxidation of aromatic

hydrocarbons to the corresponding aldehyde and alcohol. In section 5.4 we report the

catalytic oxidation of toluene, ethylbenzene and 2-methylnaphthalene using copper

(II) complexes of L2 schiff base series under mild condition, Homogeneously.

1,10-Phenanthroline 5,6-dione (Phen-dione) and its derivatives play important

role as building blocks for the synthesis of metallo-dendrimers and supramolecular

assemblies [19]. Phen-dione possesses two types of basic centers, nitrogen and an

oxygen atom, both in the sp2-hybridized state [20]. Due to this Bi-functionality, it is

used as quinone equivalent ligand with metals in a low oxidation state and bipyridine

equivalent ligand in reactions with Lewis acids resulting in the formation of

complexes of higher nuclearity [21]. Due to its varied ligating ability it is able to

generate complexes with transition metal ions including Zn, Cd and Hg, inner

transition as well as group 4 and 5 metals in high and low oxidation state [22,23]. This

ligand is of biological interest owing to its redox activity [24] and ability to covalently

bind proteins and interact with DNA [25]. Phen-dione was found to be cytotoxic

against human kidney and hepatocellular adenocarcinomas and has an estimated IC50

value lower than that of cisplatin [26,27]. Oxidation of 1,10-Phenanthroline has been

reported earlier with variety of oxidizing agents. Fedprova et al [28] oxidized 1,10-

Phenanthroline by H2O2 and obtained 2,2-bipyridyl 3,3’-dicarboxaldehyde, while 2,2-

bipyridyl 3,3’-dicarboxylic acid was obtained by Wimmer et al [29] using alkaline

permanganate. Panari et al [30] obtained the 2,2-bipyridyl 3,3’-dicarboxaldehyde as

the major oxidation product from 1,10-Phenanthroline oxidation using alkaline

permanganate. The formation of Phen 5,6-dione is reported by oxidation of 1,10-

Chapter 5

165 

Phenanthroline using KMnO4 [31], K2MnO4, oleum and conc. nitric acid [31].

Calderazzo et al [32] obtained the Phen 5,6-dione by using a oxidizing mixture of

HNO3/H2SO4/KBr modifying the procedure adopted by Yamada et al [33] and

obtained the product with relatively high yield. In section 5.5 we report the aerobic

oxidation of 1,10-phenanthroline in the presence of copper (II) complexes of L3

schiff base series to form the phen-dione.

The oxidation of olefins in the presence of catalytic amounts of transition

metal complexes has led to a large number of reports [34]. Allylic oxidation,

epoxidation, and the formation of ketone and aldehyde have wide applications in

organic synthesis [35]. Ren et al [36] reported the Wacker type oxidation of alkenes

and alkynes catalyzed by PdBr2 and CuBr2resulting in the formation of diketones

using molecular oxygen [37]. Alvarez et al [38] reports the copper-catalyzed

oxidation of alkenes and alkynes using TBHP as the oxidant with the formation of

ester. Gao et al [39] reports the formation of 1,2-diketones as major oxidation

products using Pd/Cu as catalyst. Dicarbonyl derivatives are very useful building

blocks in the construction of a variety of organic intermediates, especially in the

synthesis of biologically active heterocyclic compounds [40]. Although these copper-

catalyzed oxidation of terminal alkynes are highly efficient, the difficulty in

separating the catalyst from the reaction mixture and the impossibility of reusing it in

subsequent reactions are disadvantages of homogeneous catalysis. In addition,

homogeneous catalysis might result in unacceptable copper contamination of the

desired isolated product. In comparison the heterogeneous catalysts can be easily

separated from the reaction mixture by a simple filtration and reused in successive

reactions, provided that the active sites have not become deactivated. Heterogeneous

catalysis also helps to minimize waste derived from reaction work-up, so contributing

to the development of green chemical processes. In section 5.6 we report the

oxidation of 1-phenylpropyne and 1-phenyl pentyne using copper (II) complexes of

L4 Schiff base series, heterogeneously.

5.2. Physical measurements

All the reagents and solvents were purchased from commercial sources. 4-

Chloro benzyl alcohol, Toluene, ethyl benzene, 2-methyl naphthalene, 1,10-

Chapter 5

166 

phenthroline, 1-Phenyl Propyne, 1-Phenyl Pentyne tert-butyl hydroperoxide (TBHP)

and hydrogen peroxide (H2O2)were purchased from Sigma Aldrich. HPLC grade

solvents were used for spectral work. 1H (400 MHz) NMR spectra were recorded on a

JEOL ECX-400P NMR spectrometer using tetramethylsilane (TMS) as an internal

reference. Electronic spectra were obtained on a Shimadzu UV-Vis-1601

Spectrometer at University of Delhi, Delhi, India. The SEM micrographs were

recorded on an Environmental Scanning Electron Microscope model FEI Quanta

200F with gold coating in SMITA research lab IIT Delhi, India. GC-MS spectra were

recorded on a Shimadzu GCMS-QP2010 plus gas chromatograph mass spectrometer

with AOC-20i auto injector and TD-20 thermal desorption system at AIRF, JNU

Delhi, India. The powder X-ray diffraction patterns were recorded using High

resolution D8 Discover Bruker diffractometer, equipped with point detector

(scintillation counter), employing monochromatized Cu Kα1 radiation with a scan rate

of 1.0 second/step and step size 0.02° at 298 K over the range of 2θ = 5º–35°.

Solution state EPR spectra were recorded on an X-Band JEOL JES–FA200 ESR

Spectrometer with a variable temperature liquid Nitrogen cryostat at 120 K at IIT-

Bombay, Mumbai, India.

Results and discussions

5.3. Catalytic oxidation of p-chlorobenzyl alcoholusing copper (II) complexes (1),

(2), (3) and (4), heterogeneously

Heterogeneous catalysts are widely used in industry, can be easily separated

from the reaction mixture, and are often reused. Thus the use of heterogeneous

catalyst has attracted a lot of interest [41]. Catalysis has been found to be dependent

on the crystal face [42], as well as on the shape of the catalyst [43, 44]. Several

studies of catalysis processes have been reported with distinct shapes, truncated

octahedral [45], tetrahedral, cubic or spherical compounds [46]. However, there are

few studies that report the changes in size distribution after recycling along with

catalytic activity [47].It has been earlier reported that both size and shape changes

occur during the catalysis process [48]. In this section we report the morphology

dependent catalytic activity of mononuclear and binuclear copper (II) complexes of

Chapter 5

167 

schiff baseL1, changes are observed by SEM and PXRD study. EPR and UV-visible

spectroscopy are used for identification of any intermediate species.

Copper (II) complexes [Cu(L1)Cl].MeOH(1), [Cu(L1)Br].MeOH

(2),[Cu(L1)(NO3)]2(3)and [Cu(L1)NCS] (4) were used heterogeneously for the

oxidation of p-chlorobenzylalcohol to its respective aldehyde, using tert-butyl-

hydroperoxide as an alternate source of oxygen in CH2Cl2. In a typical reaction,

catalyst (0.011 mmol), benzyl alcohol (0.11 mmol), and oxidant (0.056 mmol, 70%)

[1:10:5] were mixed in 15 mL dichloromethane and warmed at 35–40 °C for 3 h

(Scheme 1). The progress of reaction was monitored by TLC (5% ethyl acetate in

petroleum ether). The formation of DNP derivative confirms the formation of p-

chlorobenzaldehyde which was the product in all the cases. The reaction mixture was

centrifuged and the isolated copper (II) catalyst was washed. The clear filtrate of the

reaction mixture was checked for any dissolution of the catalyst during reaction, no

band in the visible range of 500-900 nm was observed ruling out the possibility of any

dissolution of the copper (II) catalyst. The clear filtrate was subjected to GC-MS

analysis and the formation of p-chlorobenzaldehyde was confirmed. The isolated

catalyst was reused for the oxidation of p-chlorobenzyl alcohol keeping the ratio of

catalyst: substrate: oxidant fixed as 1: 10: 5 in each cycle. A decrease in the yield of

benzaldehyde was observed for repeat cycles, as analyzed through GC-MS using

naphthalene as an internal standard. All the complexes [(1) to (4)] were reused three

times and their percentage conversions for the each cycle are summarized in Table 1.

Catalyst

C

O HOH

Cl

TBHP

Cl

[Cu(L1)X],

 

Scheme 5.1. Oxidation of p-chloro Benzyl Alcohol 

Kinetic study

To study the kinetics of the oxidation of p-chlorobenzyl alcohol, the reaction

was monitored spectrophotometrically by measuring the increase in the characteristic

p-chlorobez

(1), (2), (3)

Figure 5.1.Benzaldehyd(2):(C) 1st ru

zaldehyde a

) and(4)were

.Time depende for everyun (D) 3rd run

absorption b

e used as ca

ndent uv-viy 10 min timn

168

band at 256

atalyst and t

sible absorbme interval. C

A

C

8 

6 nm as a fu

tert butylhy

bance spectComplex (1)

unction of ti

ydroperoxid

tra for the ):(A) 1strun

C

ime[49].Com

e as an alter

formation (B) 3rd run,C

Chapter 5

mplexes

rnate

of p-Cl-Complex

B

D

Figure Benzald(4):(C) 1 source

substrat

mixture

develop

concent

5.2.Time ddehyde for ev1st run (D) 3r

of oxygen.

te: oxidant)

e and diluted

pment of n

tration of pr

dependent uvery 10 min rd run

. The react

). After eve

d to 2 ml. T

new band a

roduct form

uv-visible abtime interva

ion was se

ery 10 minu

This solution

at 256 nm

med was cal

A

C

169 

bsorbance spal. Complex

etup in the

utes, 0.04 m

n was taken

was record

lculated usin

A

pectra for x (3):(A) 1st

proportion

ml was tak

n in a sealed

ded (Figure

ng the extin

the formatiorun (B) 3rd r

of 1: 10:

ken out of t

d quartz cuv

e 5.1, 5.2

nction coeff

Chapter 5

on of p-Clrun Complex

5 (catalyst

the reaction

vette and the

(A-D). The

fficient of p-

B

D

5

-x

t:

n

e

e

-

chlorobenz

plot of conc

Figure 5.3.Pcomplex (2) Table 1. T

general the

drops upon

complexes

percentage

comparison

A

C

aldehyde (ε

centration o

Plots of Con): 1st& 3rd us

he dimeric

e data sugge

n each reuse

(1, 2 &4)

change in

n to the chan

A

C

ε = 15920 M

of aldehyde

nc. vs time fse(C) compl

complex (

est that eac

e. This drop

when com

the rate of

nge in the r

170

M-1cm-1)[50]

formed vs

for the complex(3): 1st , 2

(3) has the

ch catalyst

p in rate of

mpared to th

f reaction u

rate of react

0 

]. The avera

time {Fig.

plexes. (A)nd& 3rduse(D

highest rat

is reusable,

reaction is

he dimeric

upon reuse

tion upon re

D

B

age rate wa

5.3(A-D)}

complex(1):D) complex (4

e of reactio

, however t

substantial

complex (

is only 7%

euse for mon

C

s obtained f

and is give

: 1st , 2nd&3r

4): 1st , 2nd&

on in the se

the rate of

for the mo

(3). The m

% for the d

nomeric com

Chapter 5

from the

en in

 

 

rd use(B) & 3rd use

eries. In

reaction

nomeric

maximum

dimer in

mplexes

Chapter 5

171 

(1), (2) and (4) are 12%, 30% and 27% respectively. This may explain the higher rate

of reaction and yields obtained for the dimeric complex.

Table 5.1. Rate of oxidation reaction of p-chlorobenzyl alcohol and its % conversion to the aldehyde of complexes (1) to (4).

Catalyst Reusability Rate of reaction*10-6 *Yield (%)

[Cu(L1)Cl] (1)

1st use 15.2 68

2nd use 14.6 -----

3rd use 12.1 52

[Cu(L1)Br] (2)

1st use 14.6 65

2nd use ----- -----

3rd use 10.5 50

[Cu(L1)NO3]2(3)

1st use 18.0 84

2nd use 17.3 74

3rd use 16.8 66

[Cu(L)NCS] (4)

1st use 12.6 74

2nd use 11.9 ------

3rd use 9.03 48

*Based on GC-MS with naphthalene as Internal Standard

Scanning electron microscopy

In order to observe the impact of surface morphology on catalysis during

recycling, the catalyst was recovered after the oxidation reaction was complete. A

gold coated sample of the recovered catalyst was prepared for SEM measurement.

The SEM micrograph shows that the mononuclear complexes (1) & (2) before use as

catalyst have a cuboid (rectangular box) like morphology whose average length lies

between 75-140 μm for complex (1) and 90-170μm for complex (2) (Figure 5.4A,

5.5A) [51]. Its subsequent reuse in the catalytic oxidation of p-chlorobenzyl alcohol

causes changes and the morphology changes to more or less flat 2-dimensinal boxes

(wafer type) with length varying from 25-40 μm for complex (1) and 10-30 μm for

complex (2) (Figure 5.4B, 5.5 B). Magnified image of complex (1) before and after

use are shown in Figure 5.4 C, D.

Figure 5.4.Complex (Bafter use

Figure 5.5.Complex (B

The

[52] and co

A

C

A

. Variation B) After 3rd u

.Variation inB) After 3rd us

e mononucl

ontains peta

in the Moruse in catalys

n the Morpse in catalysi

ear comple

als. The mic

172

rphology of sis.(C) Magn

phology of cis.

ex (4) is fou

cro-petals ar

2 

f complex (nified image

complex (2)

und to poss

re flat and t

(1) during cbefore use (

) during ca

sess a flowe

the length o

C

catalysis. (A(D) Magnifie

atalysis. (A)

er like mor

of each peta

Chapter 5

A)Unused ed image

Unused

rphology

al ranges

B

D

B

from 1.

upto 0.8

formati

Figure 5(B) Afte

Figure Complex

hexagon

μm (Fig

dimensi

C

A

A

3 to 1.01 μm

86 μm, whi

on (Fig. 5.6

5.6.Variationer 3rd use in c

5.7. Variatix (B) After 1

The pheno

nal rod type

g. 5.7A). A

ion 1.5–1.6

A

m (Fig. 5.6

ile some pe

6B), this cou

n in the Morpcatalysis.

ion in the M1st use (C) Af

oxo bridged

e morpholo

After 1st us

μm (Fig. 5

A). After 3

etals are fou

uld have led

phology of c

Morphology fter 2nd use (D

d dimeric c

ogy and the

se, some o

.7B). After

173 

rd use the p

und to conjo

d to the inac

omplex (4) d

of complexD) After 3rd

copper(II) c

width of th

f the rods

2nd and 3r

etals shows

oin together

ctivation of

during cataly

x (3) Duringuse in cataly

complex (3

he rod lies i

are found

rd use they a

s a shortenin

r, giving ris

the catalyst

ysis. (A) Unu

g catalysis. ysis.

3) is found

in the range

to degrade

are in the ra

Chapter 5

ng in length

se to cluster

t.

used complex

(A) Unused

d to have a

e of 5.6–9.9

e to rods of

ange of 1.2–

B

D

B

5

h

r

x

d

a

9

f

–

Chapter 5

174 

0.9 μm (Fig. 5.7C and D). Minimal morphology changes take place when the

complex is reacted with only tert-butyl-hydroperoxide in the absence of substrate

under similar experimental conditions.

From SEM studies it is observed that morphology changes are taking place

upon reuse of the catalyst and this change may have a bearing on the loss in catalytic

efficiency to carry out the oxidation reaction. The morphology changes for the

monomeric complexes are more drastic in comparison to the dimeric counterpart.

Powder X-Ray Diffraction

It is interesting to compare the Powder XRD pattern of all the complexes and

the changes which occur after successive use of the catalyst for the oxidation of p-

chlorobenzyl alcohol to p-chlorobenzaldehyde. The monomeric copper (II)

complex(1) show that the parent complex has sharp intense peaks at 2θ (hkl) 7.6(001),

8.8(010), 11.5(100), 12.7(110), 14.3(101) 17.8(002), 21.8(020) and 26.8(202). After

reuse there is significant loss in intensity at peaks7.6, 8.8, 11.5, 12.7, 21.8 and 26.8for

the complex (1) and two new peaks are also formed after reuse at 9.7 and 24.7 (Fig.

5.8 A,B,). The PXRD of complex (2) show that the parent complex has sharp intense

peaks at 2θ (hkl) 7.5(001), 8.7(010), 11.3(100), 12.7(110), 14.0(101) 17.6(002),

21.6(020) and 26.6(202). After reuse there is significant change in intensity at peaks

7.5, 8.8, 11.3, 17.6 and26.6 for the complex (2) (Fig. 5.9 A, B,). The above results

indicate that changes occur in the unit cell of the copper catalysts upon reaction; some

planes diminish in intensity and could be responsible for the inactivation of the

catalyst. This is also reflected in their SEM measurements where a change in parent

cuboid like morphology to wafer type morphology is indicated.

The monomeric copper (II) thiocyante bound complex (4) shows sharp peak at

2θ 10.1(011), 11.3(021), 16.2, 24.4, 25.8(080), 29.2 and 30.6. After reuse of the

catalyst the peak at 10.1, 11.3 and 25.8 are destroyed while the peaks at 16.2, 24.4,

29.2 and 30.6 remain intact with small change in intensity of other peaks. This

suggests that the diffraction planes associated with at 10.1, 11.3 and 25.8 could be

involved in the promotion of catalysis, while the other planes remain inert to catalytic

activity (Fig. 5.10 A,B,C). SEM studies have shown that surface morphology changes

occur and agglomeration take place upon reuse.

F

F

Figure 5.8. P

Figure 5.9.PX

XRD pattern

XRD pattern

n of complex

n of complex

175 

x (1):(A) Unu

x (2):(A) Unu

used comple

used complex

x (B) After 3

x (B) After 3

Chapter 5

 

3rd use

 

3rd use

5

Figure 5.10use (C) Repr

Figure 5.112nd use

.PXRD patteresent After

. PXRD patt

ern of compl3rd use

tern of compl

176

lex (4): (A) U

lex (3): (A) U

6 

Unsed comp

Unused com

lex (B) After

mplex (B) Aft

C

r 1st use (B)

ter 1st use (C

Chapter 5

After 2nd

 

) After

The Dim

in the p

10.3, 11

5.11 B)

suggest

and 002

with 2θ

the PXR

(4) com

upon re

the cata

EPR St

electron

Figure nitrogen

meric coppe

parent form

1.1 and 13.

). These cha

ted that the

2) could be

θ, 7.8(100) i

RD of com

mpounds; wh

euse. Thus o

alytic activit

tudies

To further

n paramagn

5.12.X-Bandn temperature

er (II) comp

(Fig. 5.11 A

0 diminish

anges rema

diffraction

involved in

is seemingly

mplex (3) are

hile there ar

one may con

ty of the com

r investigat

netic resona

d EPR specte for Unused

plex (3) sho

A). After th

to about 10

ain nearly c

n planes ass

n the promo

y inert to ca

e minimal i

re substanti

nclude that

mplexes as

te the chan

ance (EPR)

trum of [Cud complex an

177 

ws sharp pe

he 1st use th

0–11% with

constant in t

sociated wit

otion of cat

atalytic activ

in comparis

al changes

the surface

oxidizing c

nges occur

spectroscop

u(L1)Cl] (1)nd after 3rduse

eaks at 2θ, 7

he relative in

h respect to

the next cy

th peaks at

talysis, whi

vity. Never

son to the m

in the morp

morpholog

catalysts.  

rring during

py was use

)complex in e in catalysis

7.8, 10.3, 11

ntensity of

o unused co

ycle (Fig. 5.

2θ 10.3 an

ile the plane

the less the

monomeric

phology of c

gy plays a m

g the cata

ed for mon

DMF soluts

Chapter 5

1.1 and 13.0

peaks at 2θ

mplex (Fig

.11 C). It is

nd 11.1(011

e associated

e changes in

(1), (2) and

complex (3)

major role in

alytic cycle

nomeric 

  

ion at liquid

5

0

θ,

g.

s

1

d

n

d

)

n

e,

d

Figure 5.13nitrogen tem

Figure 5.14

nitrogen tem

3.X-Band EPmperature for

.X-Band EPR

mperature for

PR spectrumr Unused com

R spectrum o

r unused com

178

m of [Cu(L1)mplex and aft

of [Cu(L1)N

mplex and aft

8 

)Br] (2) comfter 3rd use in

NCS] (4) com

ter 3rd use cat

mplex in DMn catalysis

mplex in DMF

talysis.

C

MF solution

F solution at

Chapter 5

 

at liquid

t liquid

complex

peaks

tempera

diminis

signal i

Cu(II) t

taking p

 

Figure 5shows: p

xes. X-ban

with g||=2

ature in M

sh with chan

ntensity du

to Cu(I) dur

part during t

5.15. Variatiparent compl

d EPR spe

.24-2.35, a

eOH. With

nges in g|| a

uring catalyt

ring catalys

the catalytic

on in the d-dlex, 2: After

ctra of the

and g┴=2.0

h the reuse

and g┴ as s

tic cycle co

sis, thus an i

c cycle.

d band intens2nd use, 3: A

179 

complexes

03-2.07, (A

e of the ca

shown in Fi

uld be ratio

intermediat

sity for monoAfter 3rd use i

s (1), (2) an

A||=146-170

atalyst the p

ig.5.12 to 5

onalized in

te copper (I)

omeric coppein catalysis.

nd (4) give

0) at liqui

peaks in E

5.14. The d

terms of co

) species is

er(II) comple

Chapter 5

e four sharp

id nitrogen

EPR spectra

drop in EPR

onversion of

likely to be

exes. Unused

5

p

n

a

R

f

e

d

d-d band c

The

solution of

5.15). It is

intensity in

intensity by

third use. T

during cata

X-Ray Pho

X-ray phot

this fast te

Earlier it h

species [55

increase w

Figure 5.16catalysis

changes

e d-d band

f the used co

also interes

n visible r

y 22% for c

The loss in

alytic cycle a

otoelectron

toelectron s

chnique is

has been us

5]. It has be

ith higher o

.XPS spectra

spectral c

omplex (1),

sting to note

region. The

omplex (1),

d-d band in

and has bee

Spectrosco

spectroscopy

well suited

sed for the

en shown e

oxidation s

a of complex

180

changes we

, (2)and (4)

e that after r

emonomeric

, 32% for co

ntensity is

en observed

opy Study

y shows pr

d for the as

e analysis o

earlier that t

tate. In Cu

x [Cu(L1)NC

0 

ere measure

and measu

repeat cycle

c complexe

omplex (2)

indication o

d earlier also

rimary ioniz

ssignment o

of Cu(I), C

the binding

u(I), metal →

CS] (4)for un

(eV

ed by mak

uring their v

es there is d

es shows

and 28% fo

of the form

o [53].  

zation proc

of mixed ox

Cu(II) and m

energies of

→ Ligand

nused compl

After

V)

C

king a 3.8

visible spec

drop in the d

drop in d-

or complex

mation of co

cess in abou

xidation sta

mixed Cu(I

f the core e

back bondi

ex and after

use

Chapter 5

mmolar

tra (Fig.

d-d band

-d band

(4) after

opper (I)

ut 10-7s,

ate [54].

I)/Cu(II)

electrons

ing may

3rduse in

Chapter 5

181 

cause a shift of electron density from filled d-orbitals of copper to empty antibonding

π-orbital of the ligand causing a lowering of binding energy. The [Cu(L1)NCS]

complex shows two main peak at 935 eV and 955 eV with a satellite peak at 945 eV.

These peak positions have been reported to be associated with copper in +2 oxidation

state [56] (Fig. 5.16). The XPS of the reused complex shows the presence of a new

shoulder, observed at 933 eV (Fig. 5.16 inset) along with peak at 935eV and 953eV

with a satellite peak at 942 [57]. The appearance of a prominent shoulder at 933eV

has been reported to be due to copper in +1 oxidation state [57b]. This shows that the

reused complex has some proportion of copper (I) besides copper (II). This is an

added support for EPR and uv-visible data which indicates the formation of copper (I)

species from copper(II) during catalysis. Thus it is found that the all the Cu(II)

complexes carry out a selective oxidation of p-chloro benzyl alcohol to the

corresponding aldehyde, and the catalysis is dependent on the morphological changes

taking place during recycling, with copper (I) species being generated during

catalysis.

5.4. Catalytic oxidation of Aromatic Hydrocarbons using copper(II) complexes

(5), (6), (7) and (8)

Copper (II) complexes [Cu(L2)Cl](5), [Cu(L2)Br] (6), [Cu(L2)(NO3)]2(7)and

[Cu(L2)NCS] (8) were used homogeneously for the oxidation of toluene,

ethylbenzene and 2-methylnaphthalene using hydrogen peroxide as an alternate

source of oxygen in acetonitrile (Scheme 5.2). In a typical reaction, the complex

(0.0124 mmol) was mixed with hydrogen peroxide (0.124 mmol) in 10 ml, to this was

added 40 μl of HNO3 followed by the addition of substrate (0.124 mmol). The final

ratio of catalyst, substrate and oxidant was 1: 10: 10 for a 10 ml solution. It has been

evident from previous studies that the presence of nitric acid has a positive role in

such catalytic reactions [58-60]. Nitric acid has been used, mainly, for two reasons:

(a) protonates the ligand bound to the copper (II) there by increasing the oxidative

property of the catalyst; (b) in the presence of nitric acid, decomposition of peroxide

is slow increasing the stability of peroxo intermediate [61].

Chapter 5

182 

The reaction mixture was stirred for 8-10 h at 40°C temperature. The progress of

reaction was monitored by TLC (10% ethyl acetate in pet. ether). The formation of

DNP derivative confirms the formation of carbonyl product. The product was

extracted from the reaction mixture using diethyl ether and the sample from the

organic phase was analyzed by GC-MS using naphthalene as an internal standard

(Table 5.2). Blank experiments for the oxidation of toluene, ethylbenzene and 2-

methylnaphthalene were carried out without any catalyst keeping other experimental

conditions unaltered; these did not produce any significant amount of oxidized

samples.

Table 5.2. Rate of oxidation Reaction and % conversion of different hydrocarbon with retention time

Complex Substrate Products

Rx. Time % Conversion

Cu(L2)Cl (5)

Toluene

Ph-CHO

16.5 68%

Ethyl Benzene

Ph-CO-CH3 Ph-CH(OH)-CH3 Ph-CHO

7.0 8.7 16.4

60% 11% 15%

2-Methyl Naphthalene

Phthalic acid 15.2 57%

Cu(L2)Br (6)

Toluene Ph-CHO 16.5 64%

Ethyl Benzene

Ph-CO-CH3 Ph-CH(OH)-CH3 Ph-CHO

7.0 8.7 16.4

54% 9% 12%

2-Methyl Naphthalene

Phthalic acid 15.2 47%

Cu(L2)NO3 (7)

Toluene Ph-CHO

6.7

78%

Ethyl Benzene

Ph-CO-CH3 Ph-CH(OH)-CH3 Ph-CHO

7.0 8.7 16.4

65% 11% 17%

2-Methyl Naphthalene

Phthalic acid 15.2 60%

Cu(L2)SCN (8)

Toluene Ph-CHO

16.5

57%

Ethyl Benzene

Ph-CO-CH3 Ph-CH(OH)-CH3 Ph-CHO

7.0 8.7 16.4

51% 7% 11%

2-Methyl Naphthalene

Phthalic acid 15.2 46%

Chapter 5

183 

H2O2

Catalyst

C

O

X CH

OH

XC

O

OHX

Where X= H, CH3

Scheme 5.2. Reaction for the oxidation of Hydrocarbon

All the complexes of L2 catalyze the oxidation of toluene, ethylbenzene and 2-

methylnaphthalene under mild condition. There could be a role of E1/2for the

respective copper (II) complex in this oxidation reaction studied as above. It is found

that [Cu(L2)NO3] has the most anodic E1/2 and also show the largest yields of

oxidized products. It is likely that copper complexes having anodic E1/2 may catalyze

H2O2 to a greater extent. This is followed by [Cu(L2)Cl], [Cu(L2)Br] and

[Cu(L2)NCS] which have relatively cathodic E1/2.

5.5. Aerobic Oxidation of 1,10-Phenthroline using copper(II) complexes (9), (10),

(11) and (12)

Four Copper(II) complexes [Cu(L3)Cl] (9), [Cu(L3)Br] (10),

[Cu(L3)(NO3)](11)and [Cu(L3)NCS] (12) were used homogeneously for the aerobic

oxidation of 1,10-phenanthroline in methanol (Scheme 5.3). The reaction between

1,10-Phenantholine and dioxygen in presence of catalytic amount of complex as

catalyst was studied using UV-Visible spectroscopy. For this a known amount of

complex (0.0030mmol) saturated with O2 in 2 ml is mixed with 1,10-phenantholine

solution (0.030mmol) in 1 ml and the mixture is scanned spectrophotometrically. The

final concentrations of complex and phenanthroline are 1 mM and 10 mM for 3 ml

solution. A new band starts to increase in intensity at λmax= 480 nm with the passage

of time {Fig. 5.17, 5.18(A-D)}, confirming the formation of 1,10-phenanthroline 5,6-

dione [62]. This band increases in intensity with time over a period of 100 min of

serial scanning, after which it becomes nearly constant.

Chapter 5

184 

N N

O2

Catalyst

N N

O O

Scheme 5.3. Oxidation of 1,10-phenanthroline using molecular oxygen

For kinetic studies, the amount of 1,10-phenanthroline (0.056, 0.039, 0.028,

0.016, 0.0056 mmol) was varied while keeping the amount of catalyst fixed (0.0056

mmol) in 3 ml. The ratio of complex: substrate was: 1:10, 1:7, 1:5, 1:3 and 1:1. The

plot of absorbance vs time for ratio 1:10, 1:7, 1:5, 1:3 and 1:1 (Catalyst: substrate) are

given in Fig. 5.19(A-D). The average rates of reaction were obtained from the slope

of the best fit line using the plots shown in Fig. 5.19(A-D). The optimum rate of

reaction is found when the ratio between catalyst to substrate is 1:10. The oxidation

by the Cu(II) catalyst appears to be quite selective. The product was quantified by

forming its 2,4-DNP derivative. The final product was isolated by preparative thin

layer chromatography (10% ethyl acetate in pet. Ether) and confirmed by 1H-NMR.

NMR spectra of the phen-dione shows two peaks at 8.4 ppm and 9.0 ppm each

corresponds to two proton assign a and c, while the a peak observed at 7.7 ppm

correspond to two proton assign b is shown in Figure 5.20 [31(a), 62]. The yield of

the phen-dione was determined by weighing the isolated products. Yield 25%.

Monitoring the d-d band of the complex (11) during the catalytic cycle

The [Cu(L3)NO3] complex shows a d-d band at 640 nm. During the oxidation

reaction it is found that this band drops in intensity and starts to shift its position,

finally after 100 min of the reaction, it changes into a shoulder at ~ 600 nm (Fig.5.21).

The drop in intensity of the d-d band is understood in terms of conversion of Cu(II) to

Cu(I) as the catalysis proceeds. In this case the drop in band intensity is not very

large, possibly due to rapid conversion of Cu(I) back to Cu(II) under a solution

saturated with molecular oxygen.

Figure and (10)serial sc

5.17.Time d) Curve 1: Tanning, show

dependent UVTwo min. of wing the gen

V-Visible spmixing, Cur

neration of a n

185 

 

pectra of therve 2: After 5new band at

e reaction m50 mins, Cu480nm.     

mixture of Courve 3: After

Chapter 5

 

omplexes (9)100 mins o

5

) f

Figure 5.18and (12) Curserial scanni

 

.Time depenrve 1: Two ming, showing

ndent UV-Vimin. of mixing the generati

186

sible spectrang, Curve 2: ion of a new

6 

a of the reactiAfter 50 minband at 480

ion mixture ons, Curve 3: nm.

C

of ComplexeAfter 100 m

Chapter 5

es (11) mins of

Figure complex

5.19.Plots oxes. (A) com

of absorbancmplex (9), (B)

ce vs time ) Complex (1

A

C

187 

for the diff10), (C) Com

ferent sets omplex (11) an

of reaction nd (D) compl

Chapter 5

for the fourlex (12)

B

D

5

r

Figure 5.21catalysis in

1. Changes n MeOH

Figure 5.20

in the d-d b

188

0. 1H-NMR s

band of the

8 

spectra of phe

complex [C

en-dione

Cu(L3)NO3]

C

] (11) during

Chapter 5

g

Study o

To furth

spectros

peaks w

(Fig. 5.

without

observe

as the o

only a b

intensity

catalysi

Figure MeOH scatalysis

of EPR of t

her investig

scopy was u

with g||=2.2

22 A).The

t saturating

ed in EPR p

oxidation pr

broad weak

y during ca

is.

5.22.X-Bandsolution at lis.

the complex

gate this ca

used. X-ban

3, and g┴=2

substrate w

the solutio

parameters:

roceeds, the

k peak is ob

atalytic cycl

d EPR spectiquid nitroge

x during ca

atalytic syst

nd EPR spe

2.05, (A||=1

was then ad

on with mo

g||=2.25, g┴

e signal inte

bserved, as s

le confirms

trum of [Cuen temperatu

189 

atalytic cyc

tem, electro

ectra of the

180) at liqu

dded in the

olecular oxy

┴=2.05 (A||=

ensity drops

shown in fi

that Cu(II)

u(L3)NO3](1ure showing

cle

on paramag

unused com

uid nitrogen

ratio of 1:1

ygen. Initia

=174) (Fig.

s (Fig. 5.22

ig.5.22 D. T

) is being re

11) complex drop in EPR

gnetic reson

mplex gives

temperatur

10 (catalyst

ally minor c

5.22 B). Af

2 C), and af

The drop in

educed to C

and substraR signal inte

Chapter 5

nance (EPR)

s four sharp

re in MeOH

: substrate)

changes are

fter 40 mins

fter 75 mins

EPR signa

Cu(I) during

ate (1:10). inensity during

5

)

p

H

,

e

s

s

al

g

n g

Role of Mo

The

Cu(NO3)2 s

(Fig.5.23 A

shifted to 6

phenanthol

1: 10, the v

vanishes (F

oxidative c

oxygen wa

480 nm (Fi

Figure 5.23phenanthroli

while the b

suggests th

olecular ox

e oxidation

salt (0.0033

A). As the

646 nm (Fig

ine (0.033 m

visible band

Fig. 5.23 C)

catalysis und

s passed in

g. 5.23 F) a

.UV-visible ine under aer

band 678 n

at there is a

ygen

reaction wa

3 mmol) in

schiff base

g.5.23 B), f

mmol) was

d shifted to

). Upon rep

der nitrogen

the reaction

and continue

spectra of Inrobic conditi

nm in C dro

a loss of inte

190

as also carr

n 3 ml MeO

e ligand (0

forming the

added in so

o 678 nm an

peat scannin

n atmosphe

n mixture, i

ed to increa

n-situ generation (F-Q)

ops in inten

ermediate C

0 

ried out by

OH gives a

.0033 mmo

e schiff base

olid form. T

nd the shou

ng for 1 hr t

ere (Fig. 5.2

it was found

ases in inten

ted complex

nsity and s

C upon oxid

an in-situ g

a absorbanc

ol) was add

e complex,

The ratio wa

ulder forme

this solution

23(D-E)). A

d that a new

nsity with tim

(A-E) and o

hifts back

dative cataly

C

generated c

ce band at

ded to it, th

subsequent

as [Cu: L: p

ed at ~500 n

n did not sh

After 1hr m

w band gene

me (Fig. 5.2

oxidation of 1

to ~ 642 n

ysis (Fig.5.2

Chapter 5

complex.

792 nm

he band

tly 1,10-

phen]; 1:

nm at B

how any

molecular

erated at

23 Q),

1,10-

nm. This

23 F-Q).

Figure complexcomplex

Figure 5

5.25. (a) Rax as a catalyx (6) (iii) Stri

5.24.Formati

ates for the dyst under: (i)ictly anaerob

ion of Phen-d

different set) Molecular bic condition

191 

dione under

ts of oxidatioO2(1-5) (ii)

n (7)

strict anaerob

on reaction Molecular O

bic condition

using [Cu(LO2 with in-si

Chapter 5

n

L3)NO3] (11)itu generated

5

) d

Figure 5.26absence of s

This

oxidation o

of reaction

complex in

In o

out under s

was first re

remove the

the same r

septum sea

nitrogen fl

spectrophot

condition i

using the e

condition is

6.Formation oschiff base

s confirms

of 1,10-phen

for the in-

n the presenc

order to furt

strict anaero

emoved by

e dissolved

ratio [1:10]

aled two ne

ushed sept

tometrically

s shown in

extinction c

s found to b

of Cu-Phena

s that the

nanthroline

-situ genera

ce of oxyge

ther determi

obic condit

a freeze–th

oxygen. Su

in this deo

eck flask. T

tum sealed

y. A plot o

Fig. 5.24.

coefficient o

be 6.4 times

192

anthroline co

in situ ge

but only in

ated comple

en.

ine the role

ion. Any ox

haw cycle.

ubsequently

oxygenated

This mixtur

UV-quartz

of phen-dio

The concen

of 18.2 mo

s lower (rat

2 

omplex at 73

enerated co

n presence o

ex is 3.6 tim

e of O2, the

xygen prese

This was r

the catalys

MeOH un

re was then

z cell and

one formed

ntration of

l-1 L cm-1.T

te = 1.34*1

32 nm in the

omplex als

of molecula

mes lower

oxidation r

ent in solve

repeated at

st and subst

nder nitroge

n immediate

the reactio

versus tim

phen-dione

The averag

0-4 molmin

C

visible regio

so shows c

ar oxygen. T

than that o

eaction was

ent (HPLC-

least 2–3 t

trate were m

en atmosph

ely syringed

on was mo

me under an

e was calcu

e rate in an−1) when co

Chapter 5

on in the

catalytic

The rate

of parent

s carried

-MeOH)

times to

mixed in

ere in a

d into a

onitored

naerobic

lated by

naerobic

ompared

Chapter 5

193 

to the original rate in presence of oxygen. This suggests that the absence of oxygen

retards the reaction but does not inhibit it completely. The comparative rates for

various sets using [Cu(L3)NO3] (11) complex are given in Fig. 5.25.

In summary, The copper (II) complexes show homogeneous catalysis for the selective

oxidation of 1,10-phenanthroline using molecular oxygen. The rate of reaction shows

that the catalyst is 6.4 times highly efficient under aerobic condition. In-situ generated

catalyst is also capable of oxidizing 1,10-phenenthroline under aerobic condition,

however the rate is 3.6 times lower than the original catalyst.

A blank experiment was also carried out, 1,10-phenanthroline was mixed up with

Cu(NO3)2 salt under molecular O2, No oxidation occurs upon repeat scanning. The

band around 732 nm corresponds to the Cu-phenanthroline complex (Fig.5.26).

5.6. Catalytic oxidation of substituted Alkynes using copper (II) complexes (13),

(14), (15) and (16), under Acidic, Basic and Neutral condition, Heterogeneously

Copper (II) complexes [Cu(L4)Cl] (13), [Cu(L4)Br] (14),[Cu(L4)(NO3)] (15)

and [Cu(L4)NCS] (16) were used heterogeneously for the oxidation of alkynes like 1-

Phenyl propyne and 1-phenyl pentyne under variable condition like changes in pH,

Oxidant and in presence of a surfactant. In a typical reaction, catalyst (0.0218 mmol),

substrate (0.1092 mmol) and Oxidant (0.1092 mmol, 70%) in ratio of [1:5:5] were

mixed in 15 mL acetonitrile and stirred at 35-40oC for 10 hrs. The progress of the

reaction was monitored by TLC and formation of DNP derivative confirms the

formation of carbonyl compound. The reaction mixture was centrifuged after a 10 hr

reaction to isolate the copper (II) catalyst. The clear filtrate of the reaction mixture

was checked for any dissolution of the catalyst during reaction, no band in the visible

range of 500-900 nm was observed ruling out the possibility of any dissolution of the

copper (II) catalyst. The clear filtrate was subjected to GC-MS analysis. The

complexes were used for the oxidation of 1-phenyl-propyne, 1-phenyl-pentyne and

their percentage conversions were analyzed through GC-MS using naphthalene as an

internal standard (Table 5.3). In other reactions the pH of the solution was maintained

at ~4.0 by using a sodium acetate + acetic acid buffer, while pH ~9.0 was maintained

by adding 0.6 ml of 10 mM sodium acetate to the reaction solution.

Scanning e

A S

SEM micro

found to po

lies in the r

Figure 5.27(C): [Cu(L4)

In o

catalyst [C

sample wa

participatio

observed in

the comple

under simil

A

C

electron mi

SEM study w

ograph sho

ossess a rod

ranges of 5-

7.Morphology)Cl] (11), (D

order to obs

u(L4)NO3](

as prepared

on in the o

n Figure (5.2

x [Cu(L4)N

lar experime

icroscopy

was underta

ws that the

d type morp

16 μm (Fig

y of the comD): [Cu(L4)N

erve the im

(15) and [C

d for SEM

oxidation o

28 B,C, 5.2

NO3](15) is

ental condit

194

aken for ea

e all the m

phology. Th

.5.27).

mplexes of L4NCS] (12)

mpact of surf

Cu(L4)NCS

M measurem

of alkynes

29 B). Minim

reacted onl

tions. When

4 

ach copper (

mononuclear

he rods are

4. (A): [Cu(

face morph

S] (16) was

ment. The

show chan

mal morpho

y with oxid

n the comple

(II) complex

r complexes

flat and the

(L4)Cl] (9),

ology on ca

recovered

catalyst (1

nges in the

ology chang

dant in the a

ex [Cu(L4)N

C

x of L4 ser

s of this se

e length of

(B):[Cu(L4)

atalytic activ

and a gold

15) and (1

eir morpho

ges take plac

absence of s

NO3] (15) i

Chapter 5

ries. The

eries are

the rods

Br] (10),

vity, the

d coated

6) after

ology as

ce when

substrate

s used

B

D

Figure 5Pure Co

at pH~9

the com

catalyti

some cl

catalyti

Figure 5Pure Co

A

A

5.28. Variatimplex (B) A

9.0, all the r

mplex is use

c activity i

luster forma

c cycle as s

5.29. Variatimplex (B) A

ion in the MAfter Reaction

rods collaps

ed with sur

is greatly d

ation taking

hown in Fig

on in the MoAfter Reaction

Morphology on with substr

se and clust

rfactant the

diminished.

g palce afte

g.5.29 B.

orphology ofn with substr

B

195 

of the Cu(L4rate (C) Chan

ter formatio

rods rema

The larger

r using the

f the [Cu(L4)rate

4)NO3 complnges at pH 9

on take plac

ain intact du

r rods break

catalyst [C

)NCS] comp

lex during C9.0

ce (Fig. 5.28

uring cataly

ks into sma

Cu(L4)NCS]

plex during C

Chapter 5

Catalysis: (A)

8 C). When

ysis, but the

aller rod or

] (16) in the

Catalysis: (A)

C

B

5

)

n

e

r

e

)

Powder XR

The comple

during use

The copper

18.3, 22.4,

loss in inten

with small

during recy

peaks could

inert to cata

Figure 5.30After 2nd us

The

10.1, 16.4,

loss in inte

intensity. T

RD Study

exes(15) an

of the cataly

r (II) nitrate

26.1, 27.1

nsity at pea

change in i

ycle [63]. T

d be involv

alytic activi

0 PXRD Pase

e copper (II

19.8, 25.0

ensity at p

This indicat

nd (16)show

yst for the o

e bound com

, 29.6 and

aks 11.1, 22

intensity. Th

This sugges

ved in the pr

ity (Fig. 5.3

attern of com

I) thiocyana

, 26.7 and

eaks 7.9, 1

tes a some

196

w the change

oxidation of

mplex (15)

33.5. After

.4, 26.1 and

his indicate

sts that the

romotion of

0 A,B,C).

mplex (15) (

ate bound co

38.6. After

10.1 and 25

distortion

6 

es in the pow

f 1-phenylp

shows shar

r reuse of th

d 33.5 while

es a conside

diffraction

f catalysis,

(A) Unused

omplex (16

r reuse of th

5.0 while t

in the catal

wder XRD

ropyne.

rp peak at 2

he catalyst

e the other p

erable distor

n planes ass

while the o

d complex (B

6) shows sh

he catalyst

the peak at

lyst during

C

study, whic

2θ 11.1, 12

there is sig

peaks rema

rtion in the

sociated wi

other planes

B) After 1st

harp peak at

there is sig

t 19.8 incre

recycle [6

Chapter 5

ch occur

.2, 16.6,

gnificant

ain intact

catalyst

ith these

s remain

t use (C)

t 2θ 7.9,

gnificant

eases in

3]. This

suggest

involve

activity

Figure 5

Table 5L4(13) t

Table 5

Comple

Cu(L)C

Propyne

Cu(L)B

Propyne

ts that the di

ed in the pro

y [55] (Fig. 5

5.31. PXRD

5.3 : The peto (16)

.3a: Percenta

ex Subst

Cl (13)

e

Br (14)

e

iffraction pl

omotion of c

5.31 A,B).

Pattern of co

ercentage con

age conversion

trate

1-Phenyl

1-Phenyl

lanes assoc

catalysis, w

omplex (16)

nversion of

n of products u

Products

Ph-CO-C

Ph-C=C-

Ph-COOH

Ph-CO-C

Ph-C=C-

Ph-COOH

197 

iated with p

while the oth

(A) Unused

the alkynes

using complex

s

CO-CH3

-CHO

H

CO-CH3

-CHO

H

peaks that sh

her planes r

complex (B

products us

x (13) and (14

Conv

1

1

1

1

2

1

hows chang

emain inert

) After 1st us

ing copper c

4) at pH 7.0 w

%

version C

9%

7%

3%

1%

23%

3%

Chapter 5

ges could be

t to catalytic

se

complexes o

with TBHP

Total

Conversion

49%

47%

5

e

c

f

n

Chapter 5

198 

Table 5.3b: Percentage conversion of products using complex (15) and (16) at pH 7.0 with TBHP

Cu(L)NO3(15)

1-Phenyl

Propyne

Ph-CO-CO-CH3 23%

60% Ph-C=C-CHO 20%

Ph-COOH 17%

1-Phenyl

Pentyne

Ph-CO-CH2-CH2-COOH 11%

38% Ph-C=C-C-CO-CH3 17%

Ph=COOH 10%

Cu(L)SCN(16)

1-Phenyl

Propyne

Ph-CO-CO-CH3 13%

33% Ph-C=C-CHO 10%

Ph-COOH 10%

1-Phenyl

Pentyne

Ph-CO-CH2-CH2-COOH 7%

24% Ph-C=C-C-CO-CH3 11%

Ph=COOH 6%

Table 5.3c: Percentage conversion of products using complex (15)at pH 9.0 with TBHP

Complex Substrate At pH 9.0 %Conversion Total

Conversion

Cu(L4)NO3

1-Phenyl Propyne

Ph-CO-CO-CH3 25%

81% Ph-C=C-CHO 42%

Ph-COOH 14%

Table 5.3d: Percentage conversion of products using complex (15)at pH 4.0 with TBHP

Complex Substrate At pH 4.0 %Conversion Total

Conversion

Cu(L4)NO3

1-Phenyl

Propyne

Ph-CO-CO-

CH3

47%

69%

Ph-C=C-CHO 17%

Ph-COOH 5%

Chapter 5

199 

Table 5.3e: Percentage conversion of products using complex (15)at pH 9.0 with H2O2

Complex Substrate With H2O2 %Conversion Total

Conversion

Cu(L4)NO3

1-Phenyl

Propyne

Ph-CO-CO-CH3 6%

18% Ph-C=C-CHO 8%

Ph-COOH 4%

Table 5.3f: Percentage conversion of products using complex (15)at pH 9.0 with TBHP in presence of surfactant

Complex Substrate At pH 9.0 %Conversion Total

Conversion

Cu(L)NO3

1-Phenyl

Propyne

Ph-CO-CO-

CH3

14%

22%

Ph-C=C-CHO 5%

Ph-COOH 3%

Effect of pH, Oxidant and Surfactant on the oxidation of Alkynes

All the complexes show efficient heterogeneous catalysis for the oxidation of

1-phenylpropyne and 1-phenyl pentyne. In case of 1-phenyl propyne the products are

the diketone, aldehyde and acid. For all the catalyst, the conversion to the diketones is

highest followed by the aldehyde and acid. No specific selectivity could be observed

for the four catalyst employed. The overall conversion (60%) to the three products is

highest for the complex [Cu(L4)NO3] in this series. With 1-phenyl pentyne the overall

conversion are found to be lower, 38% and 33% for the two catalyst employed.

However in this case no diketone are generated rather a mono ketone with the triple

bond intact is found to be the major product (Table 5.3).

When the oxidation reaction of 1-phenylpropyne is carried out at pH 9.0 by adding to

the reaction mixture sodium acetate (0.6 ml, 10 mM.). The yield of the aldehyde is

found to be much higher than the diketone and the total yield is enhanced to 81%;

while the same reaction at pH~4.0 results in a higher yields for the diketone. The data

Chapter 5

200 

reveals that the catalyst [Cu(L4)NO3] is relatively more selective for the aldehyde

(42%) in basic medium, while it has greater selectively for the diketone (47%) in

acidic medium (Table 5.3 c,d).

Utilization of another oxidant like H2O2 at pH~9.0 results in much poorer yields. Thus

the oxidizing reaction is catalyzed to a greater extent by the copper (II) complexes in

the presence of tert butyl hydroperoxide rather than H2O2. Addition of a a surfactant

CTAB (Cetyl trimethyl ammonium bromide) causes inactivation of the catalyst even

in the presence of tert butyl hydroperoxide (Table 5.3).

Upon comparing the morphology changes of [Cu(L4)NO3] after the oxidizing reaction

is complete, it is found that the initial rod like morphology changes to cluster type for

reaction at pH ~7.0 an pH ~9.0. Figure 5.28, yet the percentage yield is much higher

for reaction at pH~ 9.0 rather than pH~ 7.0. This suggests that the morphology is not

found to have any profound effect on the oxidation of phenyl alkynes.

Chapter 5

201 

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