Benzoin Condensation
Benzoin Condensation is a coupling (or addition) reaction between two aromatic aldehydes in the presence of aq. ethanolic NaCN to form α-hydroxyketones (Benzoin). This reaction involves self condensation of aromatic aldehyde in the presence of CN− ion as catalyst.
Benzoin condensation can also be occurs in a mixture of two different aldehydes, or even with an aldehyde and a ketone. The more reactive aldehyde act as a nucleophile in such mixed benzoin condensations. Likewise, if a mixture of an aldehyde and a ketone is taken, the aldehyde will acts as a nucleophile.
Cyanide anion reacts with aldehyde in nucleophilic addition reaction and rearrange to carboanion which then adds to the second carbonyl group in the second nucleophilic addition and produce benzoin by the following process-
Benzoin condensation can also be occurs in a mixture of two different aldehydes, or even with an aldehyde and a ketone. The more reactive aldehyde act as a nucleophile in such mixed benzoin condensations. Likewise, if a mixture of an aldehyde and a ketone is taken, the aldehyde will acts as a nucleophile.
Mechanism of Benzoin Condensation
Benzoin condensation reaction mechanism was proposed by A. J. Lapworth in 1903.Cyanide anion reacts with aldehyde in nucleophilic addition reaction and rearrange to carboanion which then adds to the second carbonyl group in the second nucleophilic addition and produce benzoin by the following process-