Acid-Catalyzed Hydrolysis of Esters
Acid-Catalyzed Hydrolysis of Esters: An ester reacts with water under acidic conditions to form a carboxylic acid and an alcohol.
What happens
An ester reacts with water under acidic conditions to form a carboxylic acid and an alcohol. It is reversible and it is the reverse of Fischer esterification: more alcohol or removing water favors the ester, more water favors hydrolysis. The acid catalyst is regenerated. This is a nucleophilic acyl substitution and the carbonyl carbon is retained.
Reaction summary
Ester + water (H₃O⁺, heat) ⇌ carboxylic acid + alcohol (COOR → COOH)
Reagents and conditions
- Starting material: Ethyl acetate (ester)
- Reagents: H₃O⁺; H₂O
- Conditions: Heat (Δ); The acid acts as a catalyst
- Products: Acetic acid (carboxylic acid); Ethanol (alcohol)
Mechanism
- Protonate the Carbonyl: The ester carbonyl oxygen gets H⁺. This makes the carbonyl carbon more electrophilic and easier to attack.
- Water Attacks: H₂O attacks the carbonyl carbon, the C=O opens, and a tetrahedral intermediate forms.
- Proton Transfers: Protons move between the oxygen atoms. This converts the original –OR′ into a better leaving group: R′OH.
- Alcohol Leaves: The intermediate collapses, the C=O reforms and R′OH leaves.
- Deprotonation: A proton is removed. The final product is R–COOH and the acid catalyst is regenerated.
Memory trick
Hydrolysis = water breaks the ester. OR OUT → OH IN. Fischer esterification builds the ester; acidic hydrolysis breaks the ester.