Choose the correct statement/statements for Cannizaro reaction.

A. Takes place in aldehydes and ketones having absence of a-hydrogen

B. Takes place in aldehydes having absence of a- hydrogen

C. It is a disproportionation reaction

D. Get a mixture of carboxylic acid salt and ethers

Choose the correct answer from the options given below:

B, C only

The correct answer is option 3. B, C only.

The correct statements for the Cannizzaro reaction are:

B. Takes place in aldehydes having absence of α-hydrogen.
C. It is a disproportionation reaction.

The Cannizzaro reaction occurs in aldehydes lacking α-hydrogen atoms, where one molecule of the aldehyde is oxidized to the corresponding carboxylic acid, while another molecule is reduced to the corresponding alcohol. This process is a disproportionation reaction because one molecule is simultaneously oxidized and reduced.

Let us look at Cannizzaro reaction in detail:

1. Reaction Conditions:
The Cannizzaro reaction typically occurs under basic conditions, often in the presence of a strong base like sodium hydroxide (\(NaOH\)).
   - It involves aldehydes that lack an α-hydrogen atom. In other words, the aldehyde group (―CHO) must not be adjacent to a hydrogen atom attached to a carbon atom (α-carbon) for the reaction to proceed.

2. Mechanism:

The Cannizzaro reaction is a redox process, specifically a disproportionation reaction, wherein one molecule is oxidized while another molecule of the same compound is simultaneously reduced.

In the presence of a strong base, the aldehyde undergoes nucleophilic attack by hydroxide ions (\(OH^-\)).

The reaction proceeds via a nucleophilic addition-elimination mechanism. The hydroxide ion attacks the electrophilic carbon atom of the aldehyde, forming a carboxylate anion and an alkoxide ion.

The alkoxide ion acts as a reducing agent, abstracting a hydrogen atom from another molecule of the aldehyde to form an alkoxide-alcohol and regenerate the hydroxide ion.

The carboxylate anion is further protonated by the hydroxide ion to yield the corresponding carboxylic acid.

3. Overall Reaction:

The Cannizzaro reaction involves the simultaneous oxidation of one molecule of the aldehyde to form the corresponding carboxylic acid and the reduction of another molecule to yield the corresponding alcohol.

The general equation for the Cannizzaro reaction is:

\[ 2 \text{RCHO} + \text{OH}^- \rightarrow \text{RCOOH} + \text{RCH}_2\text{OH} \]

(Where R represents an alkyl group.)

4. Products:

The products of the Cannizzaro reaction are one molecule of the corresponding carboxylic acid and one molecule of the corresponding alcohol.

Since no other functional group is present in the reactant molecule, the reaction yields a mixture of the carboxylic acid and alcohol.

5. Applications:

The Cannizzaro reaction is important in organic synthesis, especially for the preparation of carboxylic acids from aldehydes that do not have α-hydrogens.

It is also utilized in the industrial synthesis of certain organic compounds.

In summary, the Cannizzaro reaction is a disproportionation reaction that occurs in aldehydes lacking α-hydrogen atoms under basic conditions, yielding a carboxylic acid and an alcohol as products.