Question

Gabriel's phthalimide synthesis can be used to prepare

• A. ethanamine
• B. N-methylmethanamine
• C. benzeneamine
• D. N,N-dimethylmethanamine
• E. p-toluidine

Hint:

Think of Gabriel's synthesis as the "Primary Aliphatic Only" tool. If the amine name has "N-something" in it (indicating $2^\circ$ or $3^\circ$) or involves a benzene ring attached directly to N, it's the wrong answer!

Answer 1

The Correct Option is A

Concept: Gabriel's phthalimide synthesis is a versatile method for the preparation of pure primary aliphatic amines.
• Process: Phthalimide reacts with ethanolic KOH to form potassium phthalimide, which then reacts with an alkyl halide (RX) followed by alkaline hydrolysis to yield a primary amine.
• Limitations: This reaction is nucleophilic substitution ($S_N2$). Aryl halides do not undergo nucleophilic substitution with potassium phthalimide easily; hence, aromatic primary amines (like aniline or p-toluidine) cannot be prepared this way.
• Substitutions: It specifically produces $1^\circ$ (primary) amines. Secondary ($2^\circ$) and tertiary ($3^\circ$) amines cannot be prepared by this method.

Step 1: Evaluate the amine types in the options.
• (A) Ethanamine: Primary aliphatic amine ($CH_3CH_2NH_2$). (Suitable)
• (B) N-methylmethanamine: Secondary amine ($(CH_3)_2NH$). (Unsuitable)
• (C) Benzeneamine: Primary aromatic amine ($C_6H_5NH_2$). (Unsuitable due to aryl halide limitation)
• (D) N,N-dimethylmethanamine: Tertiary amine ($(CH_3)_3N$). (Unsuitable)
• (E) p-toluidine: Primary aromatic amine. (Unsuitable due to aryl halide limitation)

Step 2: Conclusion. Since Gabriel's synthesis is exclusively for primary aliphatic amines, only ethanamine can be prepared using this method.