Gabriel phthalimide synthesis method is used for the preparation of:

Primary Amine

The correct answer is Option (2) → Primary Amine

Core Concept:

Gabriel phthalimide synthesis is a method used specifically for preparing primary amines from alkyl halides. In this reaction, phthalimide first reacts with a strong base (like KOH) to form potassium phthalimide, which then undergoes nucleophilic substitution with an alkyl halide to form N-alkyl phthalimide. On hydrolysis (acidic or basic), this compound releases the primary amine. Since the nitrogen atom is initially bonded within the phthalimide ring, it can attach to only one alkyl group during the substitution step, preventing further alkylation and ensuring formation of only primary amines.

Option 1: Secondary Amine

Incorrect because the nitrogen atom in phthalimide can form only one bond with an alkyl group during the reaction. After hydrolysis, the product contains only one alkyl group attached to nitrogen, so a secondary amine is not formed.

Option 2: Primary Amine

Correct because Gabriel synthesis is specifically designed to produce primary amines. The structure of phthalimide restricts nitrogen from undergoing multiple alkylation steps, and upon hydrolysis, the reaction yields an amine having only one alkyl group attached to nitrogen.

Option 3: Tertiary Amine

Incorrect because tertiary amines require three alkyl groups attached to nitrogen, but Gabriel synthesis prevents multiple substitutions on nitrogen, making such formation impossible.

Option 4: Quaternary Amine

Incorrect because quaternary ammonium salts require four substituents on nitrogen, which cannot be achieved in this synthesis due to the structural limitation of the phthalimide intermediate.