CBSE Class 12-science Answered

Dear Student

The reaction in which aldehydes that do not have a hydrogen attached to the carbon adjacent to the carbonyl group, upon encountering strong alkali, readily form an alcohol and an acid salt. The reaction involves the base-induced disproportionation of an aldehyde lacking a hydrogen atom in the alpha position.

The characteristic features of Cannizzoaro reaction are:

1) It is a disproportionate reaction.

2) It involves a reaction with aldehydes which have no alpha hydrogen atoms.

3) The products are an alcohol and a carboixylic acid.

Mechanism ofcannizaro reaction :   

step 1: Nucleophillic attack

The Nucleophile attacks the carbonyl carbon which is electron deficient due to the presence of the electron withdrawing O group.

Step 2: Deprotonation and formation of Dianion

The proton is abstracted by the nucleophile and the di anion formation takes place simultaneously, resulting in a reactive intermediate.

Step 3: Hydride ion transfer

Hydride ion is transfered from one molecule to another mnolecule and neutralisation of charge results in the formation of a carboxylate ion and a alkoxide ion.

Step 4: Formation of the salt and the alcohol

Due to the formation of the sodium salt of carboxylate ion and methanol, the reactive intermediate in this reaction is very important. It does not have a stable existence but is quickly transformed into the sodium salt which is ionic in nature.

We hope that clarifies your query.

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