Which of the following compounds can be prepared in good yield by Gabriel phthalimide synthesis?

Solution

Chemistry ma’am · 3 steps

Gabriel gives only primary amines from S_N2-friendly halides, so look for RCH₂NH₂.

1. How Gabriel works. Phthalimide with KOH gives potassium phthalimide. Its N⁻ attacks an alkyl halide by S_N2, and hydrolysis (or hydrazine) then releases R-NH₂.

   C₆H₄(CO)₂N⁻K⁺ + R-X → C₆H₄(CO)₂N-R →(hydrolysis) R-NH₂

2. Two conditions. Only one R group attaches to nitrogen, so the product is always a primary amine. The halide must undergo S_N2, so aryl halides do not work.

   Option	Compound	Needed halide	Gabriel works?
   (a)	Aniline, C₆H₅NH₂	C₆H₅Cl, aryl halide	No, there is no S_N2 on an aryl carbon
   (b)	Benzylamine, C₆H₅CH₂NH₂	C₆H₅CH₂Cl, benzyl halide	Yes, fast S_N2 gives a primary amine
   (c)	C₆H₅CH₂CONH₂	not an amine at all	No, it is an amide
   (d)	CH₃CH₂NHCH₃	would need two R groups on N	No, it is a secondary amine

3. So. Benzylamine comes from benzyl chloride in good yield, so the answer is (b).

The idea to keep. Gabriel synthesis means primary amines from halides that undergo S_N2. Aryl amines, secondary or tertiary amines, and amides are all out.

Answer from the NTA final answer key. Solution by PrepWiser.