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1
Carboxylic Acids
Chapter 20 2
• Adapted from:
Organic Chemistry, 6th Edition;
Chapter 20, Carboxylic Acids
L. G. Wade, Jr.
2
Chapter 20 3
carboxyl group
• (-C=O) + (-OH) on the same carbon.
• -COOH.
• Aliphatic acids: R-COOH.
• Aromatic acids: Ar-COOH.
• Fatty acids: long-chain aliphatic acids.
=>
Chapter 20 4
Common Names
• Many aliphatic acids have historical names.
• Positions of substituents on the chain are
labeled with Greek letters.
=>
3
Chapter 20 5
IUPAC Names• Remove -e from alkane (or alkene)
name, add -oic acid.
• The carbon of the carboxyl group is #1.
CH3CH2CHC
Cl
OH
O
2-chlorobutanoic acid
PhC
H
C
H
COOH
trans-3-phenyl-2-propenoic acid
(cinnamic acid)
=>
Chapter 20 6
order of precedence in the nomenclature
http://www.chemgapedia.de/vsengine/vlu/vsc/en/ch/12/oc/vlu_organik/c_acid/nomenklatur_und_strukt_carbons.vl
u/Page/vsc/en/ch/12/oc/c_acid/nomenklatur/nomenklatur.vscml.html
4
Chapter 20 7
Naming Cyclic Acids
• Cycloalkanes bonded to -COOH are named
as cycloalkanecarboxylic acids.
• Aromatic acids are named as benzoic acids.COOH
CH(CH3)2
2-isopropylcyclopentanecarboxylic acid
COOH
OH
o-hydroxybenzoic acid
(salicylic acid)=>
Chapter 20 8
5
Chapter 20 9
219 ºC31.0 ºCdecanoic acidgoats (L. caper)capric acidCH3(CH
2)
8CO
2H
253 ºC12.0 ºCnonanoic acidpelargonium (an herb)pelargonic acidCH3(CH
2)
7CO
2H
239 ºC16.3 ºCoctanoic acidgoats (L. caper)caprylic acidCH3(CH
2)
6CO
2H
223 ºC-7.5 ºCheptanoic acidvines (Gk. oenanthe)enanthic acidCH3(CH
2)
5CO
2H
205 ºC-4.0 ºChexanoic acidgoats (L. caper)caproic acidCH3(CH
2)
4CO
2H
186 ºC-34.5 ºCpentanoic acidvalerian rootvaleric acidCH3(CH
2)
3CO
2H
164 ºC-5.5 ºCbutanoic acidbutter (L. butyrum)butyric acidCH3(CH
2)
2CO
2H
141 ºC-20.8 ºCpropanoic acidmilk (Gk. protus
prion)propionic acidCH
3CH
2CO
2H
118 ºC16.6 ºCethanoic acidvinegar (L. acetum)acetic acidCH3CO
2H
101 ºC8.4 ºCmethanoic acidants (L. formica)formic acidHCO2H
Boiling PointMelting PointIUPAC NameSourceCommon NameFormula
Nomenclature
Chapter 20 10
Dicarboxylic Acids
• Aliphatic diacids are usually called by
their common names (to be memorized).
• For IUPAC name, number the chain from the end closest to a substituent.
• Two carboxyl groups on a benzene ring
indicate a phthalic acid.
HOOCCH2CHCH2CH2COOH
Br
3-bromohexanedioic acid
β-bromoadipic acid
COOH
COOH
1,3-benzenedicarboxylic acid
m-phthalic acid =>
6
Chapter 20 11
Dicarboxylic acids
Oxalic acid (ethanedioic acid)
Malonic acid
(propanedioic acid)
Succinic acid
(butanedioic acid)
found in distillate of succinite
Glutaric acid
(pentanedioic acid)
Adipic acid
(hexanedioic acid)
Chapter 20 12
Dicarboxylic acids
Maleic acid
(cis-2-butenedioic acid)Fumaric acid
(trans-2-butenedioic acid)
isolated from the plant Fumaria officinaliswhich was burnt in the past to drive away evil
spirits
Maleic acid is relatively less stable than fumaric acid.
Upon exposure to light, maleic acid is converted into fumaric acid
7
Chapter 20 13
Saturated fatty acids
76 ºCarachidic acidCH3(CH
2)
18CO
2H
69 ºCstearic acidCH3(CH
2)
16CO
2H
63 ºCpalmitic acidCH3(CH
2)
14CO
2H
55 ºCmyristic acidCH3(CH
2)
12CO
2H
45 ºClauric acidCH3(CH
2)
10CO
2H
Melting PointCommon NameFormula
Chapter 20 14
-49 ºCarachidonic acidCH3(CH2)4(CH=CHCH2)4(CH2)2CO2H
-11 ºClinolenic acidCH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7CO2H
-5 ºClinoleic acidCH3(CH2)4CH=CHCH2CH=CH(CH2)7CO2H
13 ºColeic acidCH3(CH2)7CH=CH(CH2)7CO2H
0 ºCpalmitoleic acidCH3(CH2)5CH=CH(CH2)7CO2H
Melting PointCommon NameFormula
Unsaturated fatty acids
8
Chapter 20 15
Chapter 20 16
Structure of Carboxyl
=>
9
Chapter 20 17
Boiling PointsHigher boiling points than similar alcohols,
due to dimer formation.
Acetic acid, b.p. 118°C =>
Chapter 20 18
Melting Points• Aliphatic acids with more than 8
carbons are solids at room temperature.
• Double bonds (especially cis) lower the melting point. Note these 18-C acids:
�Stearic acid (saturated): 72°C
�Oleic acid (one cis double bond): 16°C
�Linoleic acid (two cis double bonds): -5°C=>
10
Chapter 20 19
Solubility
• Water solubility decreases with the length
of the carbon chain.
• Up to 4 carbons, acid is miscible in water.
• More soluble in alcohol.
• Also soluble in relatively nonpolar
solvents like chloroform because it
dissolves as a dimer.
=>
Chapter 20 20
11
Chapter 20 21
Acidity
=>
Chapter 20 22
Delocalized molecular orbitals
=>
12
Chapter 20 23
Substituent Effects on Acidity
=>
Chapter 20 24
Salts of Carboxylic Acids
• Sodium hydroxide removes a proton to
form the salt.
• Adding a strong acid, like HCl, regenerates the carboxylic acid.
CH3 C
O
OHNaOH
CH3 C
O
O
_Na
+
HCl
=>
13
Chapter 20 25
Naming Acid Salts
• Name the cation.
• Then name the anion by replacing the
-ic acid with -ate.
CH3CH2CHCH2COO- K
+
Cl
potassium 3-chloropentanoate
potassium β-chlorovalerate=>
Chapter 20 26
Properties of Acid Salts
• Usually solids with no odor.
• Carboxylate salts of Na+, K+, Li+, and
NH4+ are soluble in water.
• Soap is the soluble sodium salt of a
long chain fatty acid.
• Salts can be formed by the reaction of
an acid with NaHCO3, releasing CO2.
=>
14
Chapter 20 27
Purifying an Acid
=>
Chapter 20 28
Some Important Acids
• Acetic acid: food, solvent, catalyst, and
reagent.
• Fatty acids: fats and oils.
• Benzoic acid: in drugs, preservatives.
• Adipic: nylon 66.
• Phthalic acid: polyesters.=>
15
Chapter 20 29
IR Spectroscopy
=>
Chapter 20 30
NMR Spectroscopy
=>
16
Chapter 20 31
UV Spectroscopy
• Saturated carboxylic acids absorb very
weakly around 200-215 nm.
• If C=C is conjugated with C=O, molar absorptivity = 10,000 at 200 nm.
• An additional conjugated double bond
increases the absorption wavelength to
250 nm.
=>
Chapter 20 32
Mass Spectrometry
=>
17
Chapter 20 33
Synthesis Review
• Oxidation of primary alcohols and aldehydes with chromic acid.
• Cleavage of an alkene with hot KMnO4
produces a carboxylic acid if there is a hydrogen on the double-bonded carbon.
• Cleavage of an alkyne with ozone or hot permanganate.
• Alkyl benzene oxidized to benzoic acid by hot KMnO4 or hot chromic acid.
=>
Chapter 20 34
18
Chapter 20 35
Chapter 20 36
Organometallic reagents
=>
19
Chapter 20 37
Hydrolysis of Nitriles
Basic or acidic hydrolysis of a nitrile
produces a carboxylic acid.
BrNaCN
CNH
+
H2O
COOH
=>
Chapter 20 38
Arndt-Eistert Synthesis
20
Chapter 20 39
Arndt-Eistert mechanism
Chapter 20 40
β-Homoamino Acids
Synthesis of Fmoc-β-Homoamino Acids by Ultrasound-
Promoted Wolff RearrangementA. Müller, C. Vogt, N. Sewald, Synlett, 2006, 837-841
21
Chapter 20 41
Reactions of Carboxylic Acids
• Salt Formation
• Substitution of the Hydrogen in COOH
• Substitution of the OH
• Reduction
• Oxidation
Chapter 20 42
RCO2δ(-) Agδ(+) + H2OAgOH+RCO2H
RCO2(–) (CH3)3NH(+)(CH3)3N:+RCO2H
RCO2(–)
Na(+) + CO2 + H2ONaHCO3+RCO2H
R > C6 amphiphilicmonolayers
micelles,
22
Chapter 20 43
Acid Derivatives
• The group bonded to the acyl carbon
determines the class of compound:
�-OH, carboxylic acid
�-Cl, acid chloride
�-OR’, ester
�-NH2, amide
• These interconvert via nucleophilic acyl
substitution. =>
Chapter 20 44
from -COOH to -COOR
23
Chapter 20 45
from -COOH to -COOR
Chapter 20 46
24
Chapter 20 47
From -COOHto –COOR, COX, CON
Chapter 20 48
25
Chapter 20 49
Chapter 20 50
26
Chapter 20 51
Chapter 20 52
27
Chapter 20 53
Chapter 20 54
Fischer Esterification
• Acid + alcohol yields ester + water.
• Acid catalyzed for weak nucleophile.
• All steps are reversible.
• Reaction reaches equilibrium.
COOH
+ CH3CH2OHH
+ COCH2CH3
O
+ HOH
=>
28
Chapter 20 55
Diazomethane
• CH2N2 reacts with carboxylic acids to
produce methyl esters quantitatively.
• Very toxic, explosive. Dissolve in ether.
C
O
OH +C
O
OCH3 +CH2N2 N2
=>
Chapter 20 56
Mechanism for Diazomethane
=>
29
Chapter 20 57
Amides from Acids
• Amine (base) removes a proton from
the carboxylic acid to form a salt.
• Heating the salt above 100°C drives off steam and forms the amide.
C
O
OH +C
O
O-
+NH3CH3
+
CH3NH2
heat
C
O
NHCH3
H2O
=>
Chapter 20 58
Reduction to 1° Alcohols
• Use strong reducing agent, LiAlH4.
• Borane, BH3 in THF, reduces carboxylic
acid to alcohol, but does not reduce ketone.
=>
30
Chapter 20 59
Reduction to Aldehyde
• Difficult to stop reduction at aldehyde.
• Use a more reactive form of the acid (an
acid chloride) and a weaker reducing agent, lithium aluminum tri(t-butoxy)hydride.
CCl
O
C
O
HLiAl[OC(CH3)3]3H
=>
Chapter 20 60
Alkylation to Form Ketones
React 2 equivalents of an organolithium
reagent with a carboxylic acid.
COOH 1)
2)
CH3CH2 Li2
H2O
C
O
CH2CH3
=>
31
Chapter 20 61
Oxidation (decarboxylation )
Chapter 20 62
Oxidation
32
Chapter 20 63
Acid Chlorides
• An activated form of the carboxylic acid.
• Chloride is a good leaving group, so
undergoes acyl substitution easily.
• To synthesize acid chlorides use thionyl
chloride or oxalyl chloride with the acid.
C
O
OHC
O
C
O
Cl Cl+
C
O
Cl
+ + +HCl CO CO2
=>
Chapter 20 64
Esters from Acid Chlorides
• Acid chlorides react with alcohols to
give esters in good yield.
• Mechanism is nucleophilic addition of the alcohol to the carbonyl as chloride
ion leaves, then deprotonation.
CCl
O
+ CH3OH
COCH3
O
+ HCl=>
33
Chapter 20 65
Amides from Acid Chlorides
• Acid chlorides react with ammonia and
amines to give amides.
• A base (NaOH or pyridine) is added to remove HCl by-product.
CCl
O
+ CH3NH2
CNHCH3
O
NaOHNaCl H2O+ +
=>
Chapter 20 66
• http://www.cem.msu.edu/~reusch/Virtua
lText/intro1.htm
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