Those carbonyl compound which donot  contain α-H  react in the presence of conc. base gives alcohol ( reduced product) and acidic  salt (oxidized Product).

• It is base induced disproportionation reaction
• Here oxidized product is acid and and reduced product is alcohol
• Here reducing agent show hydride transfer.

Reaction of cannizzaro:

Cannizzaro Reaction Mechanism:

Step(01) formation of dianion:

In this  reaction , we use typical base OH which react on less hindered product because our preference is to make acid of that salt which has no steric hindrance . Thus OH attack on formic acid and give dianion.

Step(02) hydride shift:

Here hydride of dianion shifted towards benzaldehyde.

Step(03) Deprotonation of water:

In this step  the ions are protonated with water and give respected product.

Types of Cannizzaro Reaction:

1. Simple cannizzaro reaction
2. Cross Cannizzarro Reaction

Simple Cannizzaro Reaction:

When two same carbonyl compound having no α-H react with each other and give only one product . This type of reaction is called simple cannizarro reaction.

Cannizzaro reaction of benzaldehyde:

Cannizzaro reaction of formaldehyde:

Cross Cannizzaro Reaction:

Those reaction in which two different carbonyl compound having no α-H are present react with each other give four different products which as follows;

Cross cannizzaro reaction is also called as intramolecular (with in molecule) reaction.

Example No.01:

Example No.02:

Application of Cannizzaro Reaction:

1. Synthesis of Spiro Compound
2. Reaction of 2-methyl propanal with formaldehyde

Synthesis of Spiro Compound:

When acetaldehyde and formaldehyde react with each other in the presence of base (OH)-HBr to give bromo compound , which on reduction with zinc/dust give spiro compounds.

Reaction:

Mechanism:

Reaction of 2-methyl propanal with formaldehyde:

Reaction:

Mechanism:

Step(01):

Step(02):

Step(03):