1. In the presence of concentrated aqueous or alcoholic alkali, aldehydes which do not have α – hydrogen atom undergo self oxidation and reduction to give a mixture of alcohol and a salt of carboxylic acid. This reaction is called Cannizaro reaction.
2. Benzaldehyde on treatment with concentrated NaOH (50%) gives benzyl alcohol and sodium benzoate.
Mechanism
Cannizaro reaction involves three steps.
3. Step 1:
Attack of OH- on the carbonyl carbons.
4. Step 2:
Hydride ion transfer
5. Step 3:
Acid – base reaction