Esters
Esters
- An ester has the –COO– group.
- It often smells sweet or fruity.
- It is made from an alcohol and a carboxylic acid, and can be split back apart.
Practice
Esters are often recognised by their:
Many esters have pleasant, fruity smells.
Making esters
- An ester forms by condensation of an alcohol and a carboxylic acid (conc. $\text{H}_2\text{SO}_4$ catalyst). A water molecule is lost, and the reaction is reversible:
$$\text{CH}_3\text{COOH} + \text{C}_2\text{H}_5\text{OH} \rightleftharpoons \text{CH}_3\text{COOC}_2\text{H}_5 + \text{H}_2\text{O}$$
Practice
An ester is made by reacting:
Esterification is a reversible condensation of an alcohol and a carboxylic acid, releasing water.
Hydrolysis of esters
The conditions change the products:
- dilute acid, heat (reversible) → the carboxylic acid + the alcohol.
- dilute alkali, heat (not reversible) → the carboxylate salt + the alcohol.
Practice
Hydrolysing an ester with dilute acid gives:
Acid hydrolysis is the reverse of esterification, giving back the carboxylic acid and alcohol.
Practice
Hydrolysing an ester with dilute alkali gives:
Alkali hydrolysis gives the salt of the carboxylic acid (plus the alcohol) and is not reversible.
You've got it
Key idea
- an ester = –COO– group, often sweet-smelling
- made by condensation of alcohol + carboxylic acid (conc. H₂SO₄, water lost, reversible)
- acid hydrolysis (reversible) → acid + alcohol; alkali hydrolysis (not reversible) → carboxylate salt + alcohol