Carboxylic acids, esters and
triglycerides
L.O:
Explain the water solubility of carboxylic acids
Describe the reactions of carboxylic acids with
metals, carbonates and bases
Describe the esterification of carboxylic acids
with alcohols in the presence of an acid catalyst,
and also of acid anhydrides with alcohols
Describe the hydrolysis of esters
Describe a triglyceride as a triester of glycerol
and fatty acids.
Homework: carbonyl tests exam questions
CARBOXYLIC ACIDS
O
O H
-COOH or –CO2H
NAMING CARBOXYLIC ACIDS
Select the longest chain of C atoms containing
the COOH group;
•
• Remove the e and add oic acid after the basic
name
• Side chain positions are based on the C in
COOH being 1.
Name this carboxylic acids:
O
H C
OH
H O
H C C
OH
H
HCOOH
CH3COOH
H H H O
H C C C C
OH
H H H
CH3CH3CH2COOH
H H Br O
H C C C C
OH
H H H
CH3CH2CHBrCOOH
Methanoic acid
Ethanoic acid
Butanoic acid
2-Bromobutanoic acid
CH3
H
H O
H C C C C
OH
H H H
CH3CH(CH3)CH2COOH
3-methylbutanoic acid
In pairs discuss the solubility of acids.
Clues: like dissolves in like, think about
intermolecular forces between solvent and
solute.
O
R C
O
R C
O H
+
O
Carboxylate ion
Carboxylic acids are weak acids. The
equilibrium is well over to the left.
H+
In pairs: deduce the products of the reaction of
carboxylic acids with:
a) NaOH
b) Carbonates
c) Na
CH3COOH(aq) + NaHCO3(aq)
CH3COOH(aq) + NaOH(aq)
2 CH3COOH(aq) + Na2CO3(aq)
CH3COONa (aq) + H2O (l) + CO2(g)
CH3COONa(aq) + H2O
2 CH3COONa(aq) + H2O(l) + CO2(g)
Esters
• Made through the esterification reaction from
a carboxylic acid and an alcohol
Write out your own esterification reaction
between methanol and methanoic acid
using structural formula
Now draw out the reaction between:
1.
Ethanol and ethanoic acid
2.
Propanoic acid and hexan-3-ol
3.
3,3-dichloro-2-methylhexanoic acid and
butan-1-ol
4.
Extension work: Name them
Naming esters
Draw these esters and name the alcohols
and the carboxylic acids that made them:
The smell of oranges is from the ester:
1. Octyl ethanoate
Banana is made from:
2. Pentyl ethanoate
Name these esters
1. Found in banana,
pineapple,
strawberry
2. Found in apple
3. Found in butter
and cream
4.
Making esters with acid anhydrides
Hydrolysis of esters
O
R C
O C2H5
O
H+ catalyst
+
H2O
+
R C
O H
When an acid catalyst is used an
equilibrium mixture of reactants and
products is obtained
CH2H5OH
Base hydrolysis
O
R C
O C2H5
O
+
+
R C
H2O
CH2H5OH
O H
NaOH
O
R C
O
+
Na
+
+
H2O
The salt of an acid is produced. This
removes the acid from the reaction mixture
so an equilibrium is not established. The
reaction goes to completion .
Uses of esters
Uses of esters
• Oil of wintergreen contains the ester methyl
salicylate which is used to help relieve pains in
mucles
• Benzyl ethanoate is used to flavour foods to
taste like apples and pears
Fats and oils
Fats and oils
• Essential to maintain health
• Solid fats = melting point above room temp,
e.g. butter
• Liquid oils = m.p below room temp, e.g. olive
oil
Esters of long-chain carboxylic acids.
Name these two fatty acids
• What does “saturated” and “unsaturated”
mean?
Quick questions
1.
2.
3.
4.
Draw a molecule of glycerol
What is the systematic name for glycerol?
How does glycerol combine with fatty acids?
What is the name for the bond?
Abbreviating fatty acids