Esters

  • Formed through a reaction, known as “esterification”, between alcohols and carboxylic acids

  • They are often sweet smelling compounds (strong, pleasant). These smells may occur naturally (e.g. fruit flavours/scents) or can be synthetic (e.g. polyesters, terylene).

  • Esters can be used for food flavouring and perfumes

  • Their functional group is -COO, located in the middle of the chain

    two examples of esters

    Smell of esters

Ester

Smell/flavour

ethyl 2-methylbutanoate

apple

3-methylbutyl ethanoate

pear

1-methylbutyl ethanoate

banana

butyl butanoate

pineapple

octyl ethanoate

orange

methylpropyl methanoate

raspberry

pentyl butanoate

strawberry

Naming an ester: alcohol name + carboxylic acid name

E.g. methanoic acid + propanol → propyl methanoate

The alcohol side will be attached to an O by a single bond, whereas the acid side will be attached to an O by a double bond.

a diagram showing the formation of an ester

Making esters

Generally, when we make esters, we use a concentrated sulphuric acid (H2SO4) catalyst. s

Carboxylic acid + alcohol → ester + water

ethanoic acid + ethanol → ethyl ethanoate + water

CH3COOH + C2H5OH → CH3COOC2H5 + H2O

the circled atoms come off and form the water molecule, the parts left over join to form an ester

It is a condensation reaction as a small molecule of water is eliminated