(g) Esters
4.38C Functional group of esters (Page 297)
• Esters have the functional group
4.39C ethyl ethanoate (Page 298)
• Heating a mixture of ethanoic acid and ethanol with a few drops of concentrated sulfuric
acid produces a liquid called ethyl ethanoate.
• Starting materials: ethanol and ethanoic acid
• Catalyst: Concentrated sulfuric acid
• Conditions: Heat
• The concentrated sulfuric acid isn’t written into the equation because it is a catalyst, and
it isn’t consumed in the reaction.
• This reaction is called esterification.
• It can also be described as a condensation reaction because water is made when two
molecules are joined together.
4.40C Structural and displayed formulae of ethyl ethanoate (Pages 298 – 299)
• Structural formula: - CH3COOCH2CH3
• Displayed formula: -
1
4.41C Writing the structural and displayed formulae of an ester, given the name or formula of
the alcohol and carboxylic acid from which it is formed and vice versa (Pages 298 – 299)
1) Drawing esters: -
• To work out the structure of the ester formed when an alcohol and a carboxylic acid
react together, start by drawing the alcohol and carboxylic acid so that their OH groups
are next to each other.
• H2O is removed and whatever left is joined together.
• Question: -
Draw the esters that could be formed when the following alcohol and carboxylic acids
react together.
1) methanol and methanoic acid
SKZN_R3SKZNGTUGZK
methyl methanoate
2) methanol and ethanoic acid
SKZN_R3KZNGTUGZK
methyl ethanoate
3) methanol and propanoic acid
methyl propanoate
SKZN_R3VXUVGTUGZK
2
4) methanol and butanoic acid
SKZN_R3H[ZGTUGZK
methyl butanoate
5) ethanol and methanoic acid
KZN_R3SKZNGTUGZK
ethyl methanoate
6) ethanol and ethanoic acid
KZN_R3KZNGTUGZK
ethyl ethanoate
7) ethanol and propanoic acid
ethyl propanoate
KZN_R3VXUVGTUGZK
3
8) ethanol and butanoic acid
ethyl butanoate
9) propan-1-ol and methanoic acid
propyl methanoate
10) propan-1-ol and ethanoic acid
propyl ethanoate
11) propan-1-ol and propanoic acid
propyl propanoate
4
12) propan-1-ol and butanoic acid
propyl butanoate
13) butan-1-ol and methanoic acid
butyl methanoate
14) butan-1-ol and ethanoic acid
butyl ethanoate
15) butan-1-ol and propanoic acid
butyl propanoate
5
16) butan-1-ol and butanoic acid
butyl butanoate
2) Naming esters: -
• 1st part of the name comes from alcohol.
• -anol is removed from the name of alcohol and is replaced with -yl.
• Example: -
propan-1-ol → propyl
• 2nd part of the name comes from carboxylic acid.
• -oic acid is removed from the name of carboxylic acid and is replaced with -oate.
• Example: -
ethanoic acid → ethanoate
4.42C Uses of esters (Page 299)
• Esters are volatile liquids (they turn to vapour easily) with distinctive smells.
• Chemists create artificial flavourings and perfumes using mixtures of esters and other
organic compounds.
4.43C Practical: prepare a sample of an ester such as ethyl ethanoate (Page 300)
• Prepare a sample of an ester such as ethyl ethanoate: -
1) Put 1 cm3 of ethanoic acid and 1 cm3 of ethanol into a boiling tube.
2) Mix well and carefully add a few drops of concentrated sulfuric acid.
3) Place the boiling tube in a beaker of hot water at about 80 °C for 5 minutes.
4) Allow the contents of the tube to cool.
5) When cool, pour the mixture into a beaker half-full of 0.5 mol/dm3 sodium carbonate
solution.
6) Smell the product by gently wafting the odour towards the nose with the hand.
6
https://www.youtube.com/watch?v=V6HVI7F6C8Q
• Questions: -
1) What is the purpose of the concentrated sulphuric acid?
To act as a catalyst for the reaction
2) Why does adding the final reaction mixture to sodium carbonate solution help to smell
the ester better?
Sodium carbonate solution removes the acid present in the mixture and allows the
formed ester to float on top of the water. So, it will be easy to smell the ester.
3) Grapes contain esters. The formula of an ester is shown.
Deduce the name of the carboxylic acid and the alcohol that can react together to make
this ester.
carboxylic acid propanoic acid
alcohol butan-1-ol
Chapter questions (Page 301)
1 a i CH3COOCH2CH3
ii CH3CH2CH2COOCH2CH2CH2CH3
7
bi
ii
c i methyl propanoate
ii ethyl methanoate
2 a CH3COOCH2CH3, CH3COOCH2CH2CH3, CH3CH2COOCH2CH3, CH3CH2COOCH2CH2CH3
c Esters can be detected by smelling the product: gently waft the odour towards nose.
d Used as food flavourings
Used as perfumes
3 a methanol - CH3OH
propanoic acid - CH3CH2COOH
b propan-1-ol - CH3CH2CH2OH
methanoic acid – HCOOH
c butan-1-ol - CH3CH2CH2CH2OH
ethanoic acid - CH3COOH
4a
b ethanoic acid
c By heating with potassium dichromate(VI) in dilute sulfuric acid.
d CH3COOH (l) + CH3CH2OH (l) ⇌ CH3COOCH2CH3 (l) + H2O (l)
e Heat at about 80 °C with a few drops of concentrated sulfuric acid as a catalyst.
8
5 Test 1: Take out 3 cm3 of each of the three samples and put them into three separate
test-tubes. Add a few pieces of Mg or a spatula tip worth of Na2CO3 solid into each of the
test-tubes. The one that bubbles contains ethanoic acid.
Test 2: To the remaining two samples, take out another 3 cm3 of each and put them into two
separate boiling tubes. Add a few drops of potassium dichromate(VI) in dilute sulfuric acid.
Heat the boiling tubes in a warm water bath. The one that changes colour from orange to
green contains ethanol. The one without the colour change is ethyl ethanoate.
