Acid hydrolysis
Water attacks the acid-activated acetyl carbonyl. Acyl-oxygen cleavage and proton transfer restore the phenolic OH of salicylic acid, while the removed acetyl group becomes ethanoic acid.
- Reagents
- Water; aqueous acid catalyst
- Conditions
- Warm in aqueous acid
- Reaction class
- Acid hydrolysis
- Equation
- C9H8O4 + H2O <=> C7H6O3 + CH3COOH
Overview
Water attacks the acid-activated acetyl carbonyl. Acyl-oxygen cleavage and proton transfer restore the phenolic OH of salicylic acid, while the removed acetyl group becomes ethanoic acid.
Transformation
- Equation
- C9H8O4 + H2O <=> C7H6O3 + CH3COOH
- Reactants
- Aspirin + Water
- Products
- Salicylic acid + Ethanoic acid
- Reagents
- Water; aqueous acid catalyst
- Environment
- Warm in aqueous acid
- Reaction class
- Acid hydrolysis
- Mechanism
- acid-catalysed ester hydrolysis
- Evidence level
- source-backed molecular example
Scope and limitations
- Scope
- Cleavage of the acetyl ester; the aromatic carboxyl group remains.
- Limitations
- Rate and mechanism depend on pH. The displayed acid-hydrolysis branch differs from alkaline hydrolysis, which gives salts before acidification.
Related reactions
- O acetylation: Salicylic acid → Aspirin
The phenolic oxygen of salicylic acid receives an acetyl group from ethanoic anhydride. Acyl substitution forms an ester while retaining the separate carboxyl group; proton transfer gives ethanoic acid as the co-product.
- Alkaline hydrolysis and acidification: Methyl salicylate → Salicylic acid
Hydroxide adds at the ester carbonyl and displaces the methoxy fragment, which becomes methanol. Alkaline conditions leave the salicylate groups deprotonated; subsequent acidification restores the neutral acid and phenolic OH.
References
- Aspirin Hydrolysis: Chemistry 382/378, Experiment 10John P. Walters · St. Olaf College, Department of Chemistry · 2001
Pages 1 and 7 describe aspirin hydrolysis and pH-dependent pathways; checked 2026-09-16.