Carbonyl reduction
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.
- Reagents
- NaBH4; aqueous work-up
- Conditions
- Suitable alcohol solvent; protonation after hydride addition
- Reaction class
- Carbonyl reduction
- Equation
- C6H5CHO + 2[H] -> C6H5CH2OH
Overview
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.
Transformation
- Equation
- C6H5CHO + 2[H] -> C6H5CH2OH
- Reagents
- NaBH4; aqueous work-up
- Environment
- Suitable alcohol solvent; protonation after hydride addition
- Reaction class
- Carbonyl reduction
- Mechanism
- nucleophilic hydride addition
- Evidence level
- source-backed molecular example
Scope and limitations
- Scope
- An aromatic aldehyde follows the aldehyde-to-primary-alcohol pattern.
- Limitations
- The benzene ring remains; no aromatic-ring hydrogenation is implied.
Related reactions
- 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.
- Aldehyde oxidation: Benzaldehyde → Benzoic acid
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.
References
- Organic Chemistry: Nucleophilic Addition of Hydride and Grignard ReagentsJohn McMurry · OpenStax Organic Chemistry · 2023
Supports hydride addition to aldehydes and ketones followed by protonation to form alcohols; used as the mechanism-pattern source for the aldehyde-to-primary-alcohol template.