Benzoin condensation is a classic example of a nucleophilic addition reaction, specifically between two molecules of an aromatic aldehyde such as benzaldehyde.
This reaction is facilitated by catalysts like the cyanide ion (CN⁻) or a N-heterocyclic carbene (NHC), leading to the formation of benzoin, an α-hydroxyketone.
The mechanism unfolds through several steps:
1.Formation of the Cyanohydrin:
Initiated by the cyanide ion attacking the carbonyl carbon of a benzaldehyde molecule, this step results in the formation of a cyanohydrin intermediate.
2.Generation of the Nucleophile:
The cyanohydrin sheds a cyanide ion to produce an anionic α-carbon species, or carbanion, ready to act as a nucleophile.
3.Nucleophilic Attack:
This carbanion then attacks the carbonyl carbon of another benzaldehyde molecule, establishing a new carbon-carbon bond.
4.Proton Transfer:
The final step involves the newly formed intermediate abstracting a proton from a source like the solvent or another benzaldehyde molecule, culminating in the creation of the benzoin product.