L11 - Production of Esters

objectives

• investigate the production, in a school laboratory, of simple esters

Structure

Structure Substitute an organic group for the H in carboxylic acids

Nomenclature first part from alcohol, second part from acid

e.g. methyl ethanoate CH₃COOCH₃

Preparation From carboxylic acids

Reactivity Unreactive compared with acids and acyl chlorides

Isomerism Esters are structural isomers of carboxylic acids

Structural Isomerism - Functional Group

Preparation

Reagent(s) alcohol + carboxylic acid

Conditions reflux with a strong acid catalyst (e.g. conc. H₂SO₄ )

Equation e.g. CH₃CH₂OH(l) + CH₃COOH(l) CH₃COOC₂H₅(l) + H₂O(l)

ethanol ethanoic acid ethyl ethanoate

Notes Conc. H₂SO₄ is a dehydrating agent - it removes water

causing the equilibrium to move to the right and thus

increases the yield of the ester

For more details see under ‘Reactions of carboxylic acids’

HYDROLYSIS OF ESTERS

Hydrolysis is the opposite of esterification

ESTER + WATER CARBOXYLIC ACID + ALCOHOL

The products of hydrolysis depend on the conditions used...

acidic CH₃COOCH₃ + H₂O CH₃COOH + CH₃OH

alkaline CH₃COOCH₃ + NaOH ——> CH₃COO¯ Na⁺ + CH₃OH

If the hydrolysis takes place under alkaline conditions,

the organic product is a water soluble ionic salt

The carboxylic acid can be made by treating the salt with HCl

CH₃COO¯ Na⁺ + HCl ——> CH₃COOH + NaCl

Uses of Esters

Despite being fairly chemically unreactive, esters are useful as ...

• flavourings apple 2-methylbutanoate

pear 3-methylbutylethanoate

banana 1-methylbutylethanoate

pineapple butylbutanoate

rum 2-methylpropylpropanoate

• solvents nail varnish remover - ethyl ethanoate

• plasticisers

Method of Production

You may then need to use Fractional Distillation to separate the mixture formed.