ESTERS
What is an ester?
• Responsible for tastes and odours.
• Contain the ester linkage
O
C
R
R'
O
• Made from an alcohol and a carboxylic acid.
• Compare the properties of esters with carboxylic
acids
NAMING
•
Use the “yl” form of the alcohol proceeded with
the “oate” form of the carboxylic acid.
i.e. “alkyl oate”
•
Compare the name of the ester to that of the alcohol and
acid from which it was synthesize. What is the pattern?
Examples:
a) ethyl butanoate ==> CH3CH2COOCH2CH3
b) 3-methylbutyl ethanoate ==>
CH3COOCH2CH2CH(CH3)CH3
Reactions of Esters
1. Preparation

H
S
O
/
2
4
c
a
r
b
o
x
y
l
i
c
a
c
i
d
+
a
l
c
o
h
o
l
HO
H
HO H
O
H
O
CH+
HCC
2

H
S
O
/
2
4
H
C
HCC + H
O
H
O
H
H
e
t
h
a
n
o
i
c
a
c
i
d
(
a
c
e
t
i
c
a
c
i
d
)
2.
e
s
t
e
r+
w
a
t
e
r
H
H
m
e
t
h
y
l
e
t
h
a
n
o
a
t
e
(
m
e
t
h
y
l
a
c
e
t
a
t
e
)
m
e
t
h
a
n
o
l
Hydrolysis (reverse of 1)
e
s
t
e
r+
e
x
c
e
s
s
w
a
t
e
r
H
S
O
/
2
4
a
l
c
o
h
o
l+
c
a
r
b
o
x
y
l
i
c
a
c
i
d
H
OH
O
H
H
H
S
O
/

2
4
H
C
H+ C
H
O
H+
O
C
C
C
H
C
H
2
H
O H
O
H
H
H
m
e
t
h
y
l
e
t
h
a
n
o
a
t
e
(
m
e
t
h
y
l
a
c
e
t
a
t
e
)
m
e
t
h
a
n
o
l
e
t
h
a
n
o
i
c
a
c
i
d
(
a
c
e
t
i
c
a
c
i
d
)
•
For the above reactions, if there is an excess of
the alcohol and carboxylic acid, reaction 1 is
favoured and if there is an excess of water,
reaction 2 will be favoured.
3. Irreversible Hydrolysis
Basic Solution
ester + water
H
H O
H C CO C H
H
H
methylethanoate
(methylacetate)
•
+ H2O
NaOH
alcohol + carboxylate ion
O H
H
C C H
H C H +
-O
H
O H
Na+
methanol
sodium ethanoate
(sodium acetate)
Since these conditions produce a stable carboxylate
ion, the reaction is not reversible
Waxes
• Waxes are mixtures of esters having carbon chains
in the range of 16 to 34 carbons on each side of
the ester linkage.
Example
O
C
H3C(H2C)7
(CH2)29CH3
O
Beeswax
•
Since the hydrocarbon chains are so long, waxes
are very water repellant.
•
Biological Importance: fruit, leaves, insects
Fats and Oils
• Fats and oils are triesters of glycerol that contain
at least one fatty acid.
• Fatty acids are carboxylic acids that contain 14-18
carbon and having varying degrees of unsaturation
OH OH OH
H C
C
C H
H
H
H
glycerol
1,2,3-propanetriol
O
CH3(CH2)15 C OH
stearic acid
glycerol + 1 fatty acid  monoglyceride + water
glycerol + 2 fatty acids  diglyceride + water
glycerol + 3 fatty acids  triglyceride + water
Fats in Plants
• The hydrocarbon chains are unsaturated with 1,2,
or 3 C=C bonds.
• The double bonds reduce the intermolecular forces
by causing “kinks” in the chain resulting in lower
melting and boiling points.
• For this reason the fats are generally liquid (oils)
• Since the double bonds provide a site for
reactions, the break down of unsaturated fats is
more effective (i.e. less cholesterol).
• The double bonds are easily oxidized meaning
edible oils will go rancid (i.e. spoil) and oil based
paints/varnish will crosslink to produce tough
films.
Fats in Animals
• The hydrocarbon chains are fully saturated.
• The chains are fairly straight allowing for close
packing and greater intermolecular forces.
• Due to the lack of unsaturation, they are not
broken down easily by the body and can cause the
build up of cholesterol.
• Solids at room temperature.
Salicylates
• Contain salicylic acid.
• Most common is acetyl salicyclic acid “ASA”
(AKA aspirin) which is used for pain relief and as
an antiseptic.
HO
O
HO
O
HO
O
OH
O
salicylic acid
acetyl salicylic acid
ASA
Saponification

Fats and oils are esters of long chain acids,
which can be heated with a strong base
(NaOH) to produce acid salts which we
call soap. This process is called
saponification.