Aldehydes with no $\alpha$-hydrogen when treated with concentrated alkali or other strong bases undergo self oxidation and reduction to produce an alcohol and the salt of a carboxylic acid. The disproportionation reaction is known as a Cannizzaro's reaction.
Thus, aromatic aldehydes, formaldehydes, trialkyl acetaldehyde, heterocyclic aldehydes undergo Cannizaro reaction.
MechanismBack to Top
The mechanism of cannizzaro reaction is shown below.
At the present time various oxidizing and reducing agents can be used to carry out such conversion, so that today the Cannizzaro reaction has limited synthetic utility. The Cannizzaro reaction should be kept in mind as a source of potential side products when aldehydes are treated under basic conditions.
ApplicationsBack to Top
- o-Methoxybenzyl alcohol is prepared in 79% yield by the cannizzaro reaction of o-methoxy benzyl alcohol is exclusively obtained by crossed cannizzaro reaction of o-methoxy benzaldehyde with formaldehyde.
- Benzyl alcohol is obtained by the crossed Cannizzaro reaction of benzaldehyde and formaldehyde.
- The Internal cannizzaro reaction of o-formyl benzaldehyde gives o-carboxylbenzyl alcohol.