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Biological Chemistry
FIRST YEAR ORGANIC CHEMISTRY
Lecture Eight
Carboxylic acids +
Esters
Convenor : Dr. Fawaz Aldabbagh
Carboxylic Acids
O
C
pKa = 4 - 5 ,
O
water = 16
C
O H
+
H2O
O
+
H3O
We can distinguish a water-insoluble carboxylic acid and phenol from
an alcohol
O
C
O
O H
Benzoic acid
+
H2O
NaOH
C
O
Na
Sodium Benzoate
Carboxylic Acids
Highly Polar
Low molecular weight acids show Appreciable Solubility in Water
High Bpt – Extensive H-bonds to themselves and water
NAMES
O
O
H
CH3
OH
Methanoic acid
O
OH
CH3CH2
Ethanoic acid
OH
Propanoic acid
O
O
HO
Red ants
rhubarb
O
HO
O
( )n
C
C
OH
OH
O
Br
4-Bromo-2-ethylpentanoic acid
Ethanedioic acid (oxalic acid)
OH
n = 1 = malonic acid
n = 2 = succinic acid
n = 3 = glutaric acid
HO2C
CO2H
Terephthalic acid
CO2H
CO2H
Phthalic acid
Esterification
O
O
+ CH3CH2
OH
CH3
Acetic acid
(ethanoic acid)
OH
CH3
Ethyl acetate
HCl or H2SO4
H+(catalyst)
O
O
+
OH
Ph
O CH2 CH3
H3C OH
Benzoic acid
Ph
H+(catalyst)
O
Ethyl propanoate
Methyl benzoate
O
O
O
O CH3
O
O
Methyl formate
vinyl acetate
H
Alcohol part appears first in the name
Mechanism
Equilibrium reaction
-Reversible with acid
And water
H+
O
H
H O H
O
Ph
Ph
OH
Ph
OH
C O CH3
O H
O
H3C
H
Ester molecules cannot H-bond to each
other, because they do not have an –OH
O
Consequently, B.pt is much lower than
that of alcohols and acids of
- H3O
Ph
OCH 3
comparable mass
H-bonding to water is possible
-low mw esters are soluble in water
Solubility rapidly decreases with carbon
H O
chain length.
H
O
H O
H
R
O
R
H O
Ph
C O CH3
O H
H
Esters are also largely responsible for the flavour and smell of
fruits and flowers
Salicyclic acid is the active ingredient of aspirin.
- It has analgesic, antipyretic and anti-inflammatory properties
Buffered aspirin contains bases.
O
O
OH
+ HO
O H
O
H+ , Heat
CH3
OH
- H2O
O
Aspirin
Salicylic acid
CH3
O
O
O
H+ , Heat
O H
O H
Salicylic acid
+
H3C O H
O CH3
- H2O
OH
Oil of Wintergreen
Esters are hydrolysed in acid and base
catalysed reactions
Ester Saponification
O
R
O
- is the base-catalysed hydrolysis of an ester
O
NaOH
R'
+
H2O
O
R
O Na
carboxylate salt
O
NaOH
Ph
OCH 3
H2O
methyl benzoate
R' OH
alcohol
Ph
+ H3C OH
methanol
O Na
sodium benzoate
Mechanism
O
O
'
R
O
OH
R
R
O
OR'
R
OH
+ R'O
O H
O
O
R
O H
+ R'
OR'
R
O
Na
OH
HO




O
HO
R CH CH2 CH2 CH2 C
OH
OH
O
H
H
C CH2OH
+
H2O, H


O
H
O
O

O
H
Vitamin C
Lactone

cyclic ester
Only 5 and 6 membered lactones are stable
Write a mechanism for the acid and base hydrolysis of a lactone
Redox Reactions
Addition of Oxygen or Removal of Hydrogen is OXIDATION
Removal of Oxygen or Addition of Hydrogen is REDUCTION
CH4
+O
CH3OH
- 2H
H
C O
H
R
Reduction
R
Oxidation
Reduction
Ketones
C O
- 2H
HO
H
H
Primary Alcohols
H
R C O
C O
R
H
H
R C O
C O
H
Aldehydes
+O
Oxidation
H
R
Secondary Alcohols
O
C
O
Examples of Reduction Reactions
CH3 O
H3C
CH3 O
H2 , Pd-C
H
H
H3C
3-Methylbutanal
O
H
3-Methylbutanol
H
O
H
H
H2 , Pt
Cyclohexanone
Cyclohexanol
Examples of Oxidation Reactions
OH
H
Overoxidation
K2Cr2O7, H2SO4, H2O O
OH
O