Question

Reaction of carbonyl compound with one of the following reagents involves nucleophilic addition followed by elimination of water. The reagent is :

• A. hydrocyanic acid
• B. sodium hydrogen sulphite
• C. a Grignard reagent
• D. hydrazine in presence of feebly acidic solution

Answer 1

The Correct Option is D

The question involves the reaction of a carbonyl compound with various reagents, where we are to identify which reagent involves nucleophilic addition followed by the elimination of water.

1. To tackle this question, let's first understand the mechanism of reaction with each reagent:
2. Hydrocyanic acid (HCN):
   • HCN reacts with carbonyl compounds via simple nucleophilic addition to form cyanohydrins.
   • No water elimination occurs in this reaction.
3. Grignard reagent:
   • Grignard reagents attack the carbonyl carbon, resulting in an addition reaction.
   • The molecule undergoes nucleophilic addition but not elimination of water.
4. Sodium hydrogen sulphite:
   • Sodium hydrogen sulphite forms an addition product known as the bisulfite addition compound with carbonyls.
   • Again, there's no elimination of water involved.
5. Hydrazine in presence of feebly acidic solution:
   • This is known as the Wolff-Kishner reduction or could form a hydrazone.
   • The carbonyl compound first forms a hydrazone by nucleophilic addition of hydrazine and subsequently loses water. This satisfies both the nucleophilic addition and elimination of water steps.
6. The correct answer therefore involves the formation of a hydrazone from a carbonyl compound and hydrazine, where nucleophilic addition is followed by water elimination.

Conclusion: The correct answer is hydrazine in the presence of a feebly acidic solution, as it meets the criteria of nucleophilic addition followed by water elimination.