Question

Which of the following is a disproportionation reaction: Clemmensen, Wolff–Kishner, or Cannizzaro?

• A. Clemmensen reaction
• B. Wolff–Kishner reaction
• C. Cannizzaro reaction
• D. None of these

Hint:

Cannizzaro reaction occurs in aldehydes lacking \(\alpha\)-hydrogen and results in one molecule being oxidized to a carboxylate and another reduced to an alcohol.

Answer 1

The Correct Option is C

Concept: A disproportionation reaction is a type of redox reaction in which the same substance undergoes both oxidation and reduction simultaneously, forming two different products.
Step 1: {Understand the Cannizzaro reaction.} The Cannizzaro reaction occurs when aldehydes without \(\alpha\)-hydrogen react with a strong base such as \(NaOH\) or \(KOH\). In this reaction:

• One molecule of aldehyde is oxidized to a carboxylate ion.
• Another molecule of aldehyde is reduced to an alcohol.

Step 2: {Example of Cannizzaro reaction.} For example, benzaldehyde undergoes Cannizzaro reaction: \[ 2C_6H_5CHO + NaOH \rightarrow C_6H_5CH_2OH + C_6H_5COONa \] Here:

• \(C_6H_5CHO\) is reduced to \(C_6H_5CH_2OH\)
• \(C_6H_5CHO\) is oxidized to \(C_6H_5COONa\)

Thus, the same compound undergoes both oxidation and reduction.
Step 3: {Analyze the other reactions.}

• Clemmensen reaction: Reduction of carbonyl compounds using \(Zn(Hg)/HCl\).
• Wolff–Kishner reaction: Reduction of carbonyl compounds using hydrazine and strong base.

Both are reduction reactions, not disproportionation. Therefore, the correct answer is the Cannizzaro reaction.