Question

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

• A. $N-$Methylbenzylamine
• B. $2-$Phenylethylamine
• C. Isobutyl amine
• D. Aniline

Answer 1

Answer: (B), (C)

Isobutyl amine

Gabriel phthalimide synthesis
Gabriel phthalimide synthesis is used for the preparation of primary amines. Phthalimide on treatment with ethanolic potassium hydroxide forms potassium salt of phthalimide, which on heating with alkyl halide followed by alkaline hydrolysis produces the corresponding primary amine. Aromatic primary amines cannot be prepared by this method because aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide.

Steps involved in Gabriel phthalimide synthesis
The mechanism for the preparation of primary amine using Gabriel phthalimide synthesis is shown below:



Analysing the options
Option $\left(A\right)$


Isobutyl amine is a primary amine. Hence, isobutyl amine can be prepared by Gabriel phthalimide synthesis.

Option $\left(B\right)$


$2-$Phenylethylamine is a primary amine.
Hence, $2-$Phenylethylamine can be prepared by Gabriel phthalimide synthesis.

Option $\left(C\right)$


Since $N-$methylbenzylamine is a secondary amine, it can not be prepared by Gabriel phthalimide synthesis.

Option $\left(D\right)$


Since aniline is an aromatic primary amine, it can not be prepared by Gabriel synthesis.

So, options $\left(A\right)$ and $\left(B\right)$ are the correct answers.