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Which of the following amines can be prepared by the Hofmann bromamide reaction but NOT by the Gabriel phthalimide reaction, and also gives a positive isocyanide (carbylamine) test?

1. (A) CH3NH2
2. (B) Me-NH-Me
3. (C) Me3N
4. (D) Ph-NH2

Correct answer: (D) Ph-NH2

Solution

Hofmann bromamide reaction works for both aliphatic and aromatic amides, giving primary amines (RNH2 from RCONH2). Gabriel phthalimide synthesis requires an alkyl halide (SN2 on N of phthalimide); aryl halides (PhBr) are unreactive under these conditions, so aniline (Ph-NH2) cannot be made by Gabriel. CH3NH2 can be made by both Gabriel and Hofmann. Secondary and tertiary amines (Me2NH, Me3N) do not give a positive isocyanide test. Aniline (Ph-NH2) is a primary amine, gives positive isocyanide test, can be made by Hofmann but NOT Gabriel.

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