Which of the following amines can be prepared by Gabriel synthesis?

(A) Isobutyl amine

(B) 2-Phenyl ethylamine

(C) N-Methyl benzyl amine

(D) Aniline

Choose the correct answer from the options given below:

(A), (B) only

The correct answer is option 1. (A), (B) only.

Gabriel synthesis, also known as Gabriel phthalimide synthesis, is a method used for preparing primary amines. Here is a step-by-step outline of the process:

Formation of N-alkylphthalimide: 

Phthalimide (\( C_6H_4(CO)_2NH \)) is first reacted with an alkyl halide (such as an alkyl bromide) in the presence of a base (e.g., potassium hydroxide) to form N-alkylphthalimide. The general reaction is:

Hydrolysis of N-alkylphthalimide:

The N-alkylphthalimide intermediate is then hydrolyzed with a strong base (e.g., sodium hydroxide) or an acid to yield the primary amine and phthalic acid. The hydrolysis reaction is:

Analysis of Each Option

(A) Isobutyl Amine:

Phthalimide is reacted with isobutyl bromide (\( \text{(CH}_3\text{)_2CH-CH}_2\text{Br} \)) to form N-isobutylphthalimide. N-isobutylphthalimide is then hydrolyzed to yield isobutyl amine. Isobutyl amine can indeed be synthesized using Gabriel synthesis.

(B) 2-Phenyl Ethylamine:

Phthalimide is reacted with 2-phenyl ethyl bromide (\( \text{C}_6\text{H}_5-\text{CH}_2\text{CH}_2\text{Br} \)) to form N-(2-phenyl ethyl)phthalimide. N-(2-phenyl ethyl)phthalimide is hydrolyzed to yield 2-phenyl ethylamine. 2-Phenyl ethylamine can be synthesized using Gabriel synthesis.

(C) N-Methyl Benzyl Amine:

N-Methyl benzyl amine has a methyl group on the nitrogen atom, which makes it a secondary amine. The Gabriel synthesis is specifically designed to yield primary amines without additional substituents on the nitrogen atom. Secondary or tertiary amines cannot be synthesized by this method. N-Methyl benzyl amine cannot be prepared using Gabriel synthesis.

(D) Aniline:

Aniline cannot be prepared using Gabriel phthalimide synthesis. The Gabriel phthalimide synthesis is primarily used to prepare primary amines from alkyl halides.  Aniline, which is an aromatic amine, cannot be synthesized directly using this method because the Gabriel synthesis is not suitable for aromatic substrates. Instead, aniline is typically synthesized by reducing nitrobenzene or through other methods suited for aromatic compounds.

Summary

Gabriel Synthesis can prepare primary amines like isobutyl amine and 2-phenyl ethylamine by first forming N-alkylphthalimide intermediates and then hydrolyzing them. N-Methyl benzyl amine is a secondary amine and cannot be synthesized by Gabriel synthesis.

Thus, the correct answer is: (1) (A), (B) only.