cannizzaro Reaction

What is Cannizzaro Reaction?

The Cannizzaro reaction, named after its discoverer Stanislao Cannizzaro.

In this reaction, two molecules of an aldehyde are reacted with strong base to produce a primary alcohol and a carboxylic acid using a hydroxide base.

•  It is a redox reaction means in this reaction; the aldehyde undergoes both the oxidation and reduction. The oxidation product is a salt of a carboxylic acid and the reduction product is an alcohol.

• Only aldehydes that do not have alpha hydrogen show Cannizzaro reaction.(Alpha hydrogen is the hydrogen atom attached to C next to aldehyde functional group i.e. with  (C* - CHO) like formaldehyde HCHO, acetaldehyde CH₃CHO etc).

Mechanism:

 The reaction begins with hydroxide attack on the carbonyl carbon followed by deprotonation to give a dianion.

This unstable intermediate releases a hydride anion which attacks another molecule of aldehyde. In this process the dianion converts to a carboxylate anion and the aldehyde to an alkoxide.

The alkoxide is more basic than water so it picks up a proton from water to gives alcohol as final product.

On the other hand, the carboxylate which is less basic than water, cannot pick a proton from water. Thus, after acid work up it converts into carboxylic acid.