Question

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

• A. Hydrocyanic acid
• B. A Grignard reagent
• C. Hydrazine in the presence of a feebly acidic solution
• D. None of these

Answer 1

The correct option is C

Hydrazine in the presence of a feebly acidic solution

Explanation for correct option:

(C) Hydrazine in the presence of a feebly acidic solution

Carbonyl compound and reagent interaction

• The nucleophilic nitrogen atom attacks the electrophilic carbon atom of the carbonyl group when a carbonyl compound is allowed to react with hydrazine in a weakly acidic media.
• The end result is an imine, which is generated when the water molecule is lost in the presence of a weak acidic media.
• The hydroxyl group is assisted in leaving this area by a weak acidic media.

$\mathbf{\alpha }\mathbf{-}$hydroxy amines

• Because they are unstable, -hydroxy amines invariably transform into imines when they lose water molecules.
• Being a weak base, sodium hydrogen sulfite only interacts with substances that are extremely acidic.

Explanation for incorrect options:

(A) Hydrocyanic acid

• Cyanide ion functions as the nucleophile in Hydrocyanic acid, or $\mathrm{HCN}$.
• It has the ability to attack the carbonyl group and produce cyanohydrins. Since the cyanohydrins are stable enough, they don't lose any water molecules. As a result, it is not the right response.
• Hence, hydrocyanic acid is not the reagent that involves in the reaction of carbonyl compounds.

(B) A Grignard reagent

• The carbonyl group of the carbon can be attacked by a Grignard reagent via a nucleophile, but no water molecules are lost in the process.
• As a result, it is not the right response.
• Hence, as a reagent, Grignard is not involved in the reaction of carbonyl compounds.

Therefore, the correct option is C i.e Hydrazine in the presence of a feebly acidic solution.