Chapter 18, Problem 18.70P

Interpretation Introduction

Interpretation:

The detailed mechanism for the given reaction of benzaldehyde with a catalytic amount of $\text{KCN}$ is to be drawn.

Concept introduction:

The benzoin condensation involves the addition of two aromatic aldehydes and produces acyloin. The reaction is catalyzed by cyanide ion which acts as a nucleophile. In the first step, the cyanide ion undergoes nucleophilic addition with aromatic aldehyde and forms a cyanohydrine. The cyanohydrin, in presence of base like hydroxide ion, forms a resonance stabilized carbanion, which further adds to the second aromatic aldehyde and forms an intermediate by proton transfer. The intermediate formed then undergoes elimination of cyanide to produce a corresponding acyloin product ($\text{α-}$ hydroxy ketone).