Esters

C.I. 13.5

What are they?How are they made?

Formed when an alcohol reacts with a carboxylic acid.

Very slow reaction, unless! an acid catalyst used (usually sulphuric acid)

A condensation reactionThe condensation reaction between

the hydroxyl group and the carboxylic acid known as esterification.

Reverse reaction = ester hydrolysis

NamingNamed after alcohol & carboxylic acid

from which they are derived.

Names of esters end in –oate.

CH3C

CH2 O

O

CH3

ethyl ethanoate

this part from the acid and is named after it

this part comes from the alcohol & is named after it

let’s name some

esters!

Structural formulaeAlthough the previous structural formula are the clearest way of showing esters, they can draw out in a shortened form.

ethyl ethanoate

CH3CCH2 O

O

CH3

Either…Or…

CH3C CH2O

O

CH3

In this version the acid part has been

written first

Identify the group attached to the C=O – this is from the acid

The group attached to the –O- is from the alcohol.

Wait! What’s that smell?

• Esters have strong, sweet smells.• Their bouquet is often floral or fruity.• This means they are used in food flavourings &

perfumes.• Also, very good at dissolving organic

compounds so often used as solvents.

ester fragrance

ethyl methanoate raspberries

3-methylbutyl ethanoate pears

ethyl 2-methylbutanoate apples

phenylmethyl ethanoate jasmine

Ester hydrolysis

Breakdown of an ester by water.Process sped up by catalysisCan use an acid to catalyse (H2SO4)

This is why it is a condensation reaction because water is produced!

R

R’C

H2O

+

O H

H O

OR’C

R O

O

+⇋

Definition of a condensation reaction = two molecules reacting to form a larger molecule with the elimination of a small molecule such as water

CH3

CH

CH2 O

O

CH3

CH2C

CH3 O

O

CH

CH3 O

O

ethyl methanoate

methyl propanoate

methyl methanoate

R

R’C

H2O

+

O H

H O

OR’C

R O

O

+⇌

FORWARD REACTION = condensation reaction, the esterification of an alcohol using acid catalyst under reflux.

REVERSE REACTION = ester hydrolysis, same catalyst works for both forward & reverse reactions.