9701 · 33.2
Esters
Esters are formed when a carboxylic acid and an alcohol react, losing a water molecule. This reaction can be reversed (hydrolysis), either partially with acid or completely with alkali to form a salt.
Need to know
What you need to know
- **Reactants:** Carboxylic acid and an alcohol.
- **Conditions:** Heat under reflux with a concentrated H₂SO₄ catalyst.
- **Reaction Type:** Reversible condensation reaction.
- **Catalyst Role:** H₂SO₄ acts as a catalyst and a dehydrating agent, shifting the equilibrium to favour the products.
Explanation
Making and Breaking Esters
- The ester functional group, –COO–, is formed by reacting a carboxylic acid (–COOH) with an alcohol (–OH) under reflux with a concentrated H₂SO₄ catalyst.
- Hydrolysis is the reverse reaction. Acid hydrolysis is a reversible equilibrium, whereas alkaline hydrolysis (saponification) is irreversible, forming a carboxylate salt and an alcohol.
- Esters are named with the alkyl group from the alcohol first, followed by the carboxylate part from the acid ending in '-oate'. For example, ethanol + ethanoic acid → ethyl ethanoate, which smells like nail polish remover.
- Polyesters, like Terylene, are condensation polymers formed from monomers with two functional groups: a dicarboxylic acid and a diol. This links to polymerisation chemistry.