Aldehyde oxidation
Water reversibly adds to the aldehyde to form a hydrate, which can then be oxidised. The aldehyde carbon becomes the acid carbonyl carbon; acid work-up converts the initially formed benzoate into benzoic acid.
- Reagents
- KMnO4 / OH-; then acid work-up
- Conditions
- Oxidise in aqueous base, then acidify
- Reaction class
- Aldehyde oxidation
- Equation
- C6H5CHO + [O] -> C6H5COOH
Overview
Water reversibly adds to the aldehyde to form a hydrate, which can then be oxidised. The aldehyde carbon becomes the acid carbonyl carbon; acid work-up converts the initially formed benzoate into benzoic acid.
Transformation
- Equation
- C6H5CHO + [O] -> C6H5COOH
- Reagents
- KMnO4 / OH-; then acid work-up
- Environment
- Oxidise in aqueous base, then acidify
- Reaction class
- Aldehyde oxidation
- Mechanism
- aldehyde oxidation
- Evidence level
- source-backed molecular example
Scope and limitations
- Scope
- The aldehyde carbon becomes the carboxyl carbon.
- Limitations
- Benzoate forms before acid work-up in this mild aldehyde oxidation.
Related reactions
- Side chain oxidation: Toluene → Benzoic acid
Toluene gives benzoic acid through side-chain oxidation.
- Complete oxidation: Benzyl alcohol → Benzoic acid
Oxidation first changes the benzylic CH2OH group into an aldehyde and then into carboxylate under the alkaline conditions. Acid work-up gives benzoic acid; the ring is retained while the side-chain carbon becomes more oxidised.
- Carbonyl reduction: Benzaldehyde → Benzyl alcohol
Hydride attacks the aldehyde carbon and the C=O pi electrons move to oxygen. Protonation of the alkoxide gives benzyl alcohol; neither a new carbon-carbon bond nor reduction of the aromatic ring is involved.
- Acyl chloride preparation: Benzoic acid → Benzoyl chloride
Reaction with phosphorus(V) chloride replaces the carboxyl OH group with chlorine, retaining the acyl carbon and aromatic ring. The new acyl chloride is more susceptible to nucleophilic substitution, while POCl3 and HCl account for the remaining atoms.
- Esterification: Benzoic acid → Ethyl benzoate
Acid activation allows ethanol to add to benzoic acid; proton transfers and water loss produce ethyl benzoate. The aromatic ring stays intact throughout the acyl substitution.
References
- Organic Chemistry: Oxidation of Aldehydes and KetonesJohn McMurry · OpenStax Organic Chemistry · 2023
Supports functional-group chemistry used to curate the linked examples. Checked 2026-09-16; named examples are applications of textbook scope, without claimed experimental yields.