Esters

Full Notes

Esterification Reactions

Esters can be formed in esterification reactions. You need to know the following reactions.

Carboxylic Acids and Alcohols

Carboxylic acids react with alcohols to form an ester and water:

This is a reversible reaction, often requiring heating under reflux.
Requires an acid catalyst (typically concentrated H₂SO₄).

For Example Ethanoic Acid + Ethanol

CH₃COOH + CH₃CH₂OH ⇌ CH₃COOCH₂CH₃ + H₂O

Acid Anhydrides and Alcohols

Acid anhydrides react with alcohols to form esters and carboxylic acids:

This reaction is usually more reactive and not reversible, giving higher yields.

For Example Ethanoic Anhydride + Ethanol

(CH₃CO)₂O + CH₃CH₂OH → CH₃COOCH₂CH₃ + CH₃COOH

Products: Ethyl ethanoate + ethanoic acid

Hydrolysis of Esters

Esters can be broken apart in hydrolysis reactions. The products obtained depend on the conditions used.

Acid Hydrolysis

Reagent: Dilute H₂SO₄ or HCl
Reaction (Reversible): Ester + Water ⇌ Carboxylic Acid + Alcohol

Example Acid Hydrolysis of Ethyl Ethanoate

CH₃COOCH₂CH₃ + H₂O ⇌ CH₃COOH + CH₃CH₂OH

Alkaline Hydrolysis

Reagent: NaOH
Reaction (Irreversible): Ester + NaOH → Carboxylate Salt + Alcohol

Example Alkaline Hydrolysis of Ethyl Ethanoate

CH₃COOCH₂CH₃ + NaOH → CH₃COO⁻Na⁺ + CH₃CH₂OH

Summary

• Esters can be formed by reacting carboxylic acids with alcohols (reversible) or acid anhydrides with alcohols (irreversible, higher yield).
• Esterification requires heating under reflux with an acid catalyst.
• Esters can be hydrolysed under acidic conditions to give carboxylic acids and alcohols.
• Alkaline hydrolysis gives a carboxylate salt and alcohol and is irreversible.