Chemistry 1B – CHEM1102
O
O
O
OH
OH
O
Cl
!
"# $
%
#&
%
'(
%
$
$ %
$
O
NaOH
OH
Octanoic acid
O
O Na
sodium octanoate - a soap
Structure
– Carboxylic acid derivatives all have an acyl group, attached to a
heteroatom (O, N, halogen)
– Four classes to consider here:
R
O
O
O
O
O
C
C
C
C
C
Cl
R
R
R
acid anhydride
acid chloride
)(
O
%
* +
O
R'
R
R'
amide
ester
$$ ,
%
%
N
$
R"
All carboxylic acid derivatives can be hydrolysed to the parent acid and
another product with water
acid chloride
O
C
R
Cl
acid anhydride
O
O
C
R
C
O
R
ester
O
C
R
amide
O
R'
O
C
R
N
R"
R'
+ H2O
+ H2O
O
R
O
C
OH
acid
+
H
+ H2O
Cl
hydrochloric acid
R
H
O
C
OH
acid
+ O
O
+ H2O
C
acid
R
R
H
O
C
OH
acid
+
O
R'
alcohol
R
C
OH
acid
+
H
R"
N
R'
amine
Rate of hydrolysis depends on reactivity of derivative
Acid chlorides and anhydrides hydrolyse in water at pH 7
Esters require H+ or OH- catalyst and heat to hydrolyse
Amides require conc H+ or OH- and prolonged heating
acid chloride
O
R
C
Cl
most
reactive
acid anhydride
O
O
R
C
O
C
R
ester
O
R
C
increasing reactivity
amide
O
O
R'
R
C
N
R"
R'
least
reactive
Mechanism: Nucleophilic acyl substitution
δ
O
δ C
R
Cl
δ
acid chloride
(electrophile)
+
δ
H
δ
O
step 1
H
δ
nucleophilic
addition
water
(nucleophile)
R
C
C
O
Cl
step 3
H +
carboxylic acid
H
Cl
hydrochloric acid
elimination
R
step 1: nucleophilic
addition to electrophilic
carbon of acid chloride
... gives a tetrahedral
intermediate
step 2: acid base
reaction (deprotonation
of the tetrahedral
intermediate)
O
O
H
step 2
acid-base
reaction
O
R
H
O
C
H
O
Cl
+ H
step 3: collapse of the
tetrahedral intermediate
to regenerate the C=O
π-bond with elimination
of chloride anion as
leaving group
!
-
%
%
O
"
O
NH2
H3O+
OH
heat
+ NH4+
NaOH(aq)
NaOH(aq)
heat
O
O
+NH3
A more reactive carboxylic acid derivative can be converted into
a less reactive one
Involves substituting heteroatom part attached to acyl group
Reaction mechanism is nucleophilic acyl substitution
Mechanism is essentially the same for all conversions
acid chloride
O
R
C
Cl
most
reactive
acid anhydride
O
O
R
C
O
C
R
ester
O
R
C
increasing reactivity
amide
O
O
R'
R
C
N
R"
R'
least
reactive
O
R
C
H
+
Cl
acid chloride
O
O
R'
R
alcohol
+
C
H
R
C
H
O
ester
R'
+
N
+
N
+
H
Cl
+
H
Cl
O
R"
R
N
R"
amide
=
O
R"
amine
C
R
C
N
R"
+
H
+
alcohol
OR'
R'
=
+
H
Cl
+
H
Cl
R'
amine
R'
+
+
R'
Cl
acid chloride
O
O
R'
ester
=
O
R
C
amide
"
Cl
#
O
MeOH
O
O
O
O
EtOH
O
O
O
O
O
NaOH
OH
O
$
O
O
NaOH
O
O
O
O
ONa
O
OH
OH
2
-
O
3 14
%
-
OH
OH
O
-
OH
&'.
$
O
O
/
-
"
/
$
$
O
O
OH 0
0
&&'
1$
% &
'
Small carboxylic acids have an unpleasant, sour smell. In
contrast esters tend to have sweet smells.
Ester
Formula
Flavour/fragrance
Methyl butyrate
CH3CH2CH2COOCH3
Apple
Ethyl butyrate
CH3CH2CH2COOCH2CH3
Pineapple
Propyl acetate
CH3COOCH2CH2CH3
Pear
Pentyl acetate
CH3COOCH2CH2CH2CH2CH3
Banana
Pentyl butyrate
CH3(CH2)2COOCH2(CH2)3CH3
Apricot
Octyl acetate
CH3COOCH2(CH2)6CH3
Orange
Methyl benzoate
C6H5COOCH3
Ripe kiwi
Ethyl formate
HCOOCH2CH3
Rum
Methyl salicylate
HOC6H4COOCH3
Wintergreen
Benzyl acetate
CH3COOCH2C6H5
jasmine
(
Fats are esters of long chain fatty acids and glycerol
Glycerol has three alcohol groups
forms a triester
Fats are also called triglycerides
Base hydrolysis of fats is used in the manufacture of soap (e.g.
sodium stearate)
H2C
OH
HOOC (CH2)16CH3
O
HC
OH
HOOC (CH2)16CH3
O
H2C
OH
HOOC (CH2)16CH3
O
glycerol
O
O
O
3 x stearic acid
saturated fat
( (
) More attraction between molecules
higher melting point
) *Attraction * = intermolecular forces
depend on functional groups present and geometry
Name
No Cs
Lauric
Structure
Mp (°C)
12
CH3(CH2)10COOH
44
Myristic
14
CH3(CH2)12COOH
58
Palmitic
16
CH3(CH2)14COOH
63
Stearic
18
CH3(CH2)16COOH
70
Arachidic
20
CH3(CH2)18COOH
75
Palmitoleic
16
(Z)-CH3(CH2)5CH=CH(CH2)7COOH
32
Oleic
18
(Z)-CH3(CH2)7CH=CH(CH2)7COOH
16
Ricinoleic
18
(Z)-CH3(CH2)5CH(OH)CH2CH=CH(CH2)7COOH
5
Linoleic
18
(Z,Z)-CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
-5
Arachidonic
20
(all Z)-CH3(CH2)4(CH=CHCH2)4(CH2)2COOH
-50
+(
Saturated fats (&
unsaturated fats with
an E double bond)
pack well and tend to
be solids at room
temperature
Unsaturated fats with
a Z double bond pack
together poorly and
tend to be liquid at
room temperature
(
Natural lipids contain a mixture of fatty acids
Source
Saturated fatty acids (%)
Unsaturated fatty acids
C12
C14
C16
C18
C18
C18
Lard
-
1
25
15
50
6
Butter
2
10
25
10
25
5
Human fat
1
3
25
8
46
10
Whale fat
-
8
12
3
35
10
50
18
8
2
6
1
Corn
-
1
10
4
35
45
Olive
-
1
5
5
80
7
Peanut
-
-
7
5
60
20
Linseed
-
-
5
3
20
20
Animal fat
Vegetable oil
Coconut
(
O
H+
O
O
SOCl2
O
OH
Cl
OH
H3O+
NaOH
heat
heat
O
N
H
MeNH2
O
O
8
3
0
0
1 1
16
%
%
%
9
5 6" $
$
%
%
$
%
% 16
$ $
%%
71
1
5