The correct answer is Option (4) → Potassium phthalimide
The synthesis is a classic method for preparing pure primary amines while avoiding the formation of secondary or tertiary amines.2
- Role of Phthalimide: The reaction begins with phthalimide, which is treated with ethanolic potassium hydroxide ($KOH$) to form potassium phthalimide.
- Nitrogen Attachment: The nitrogen atom in the phthalimide ring acts as a nucleophile. It attacks an alkyl halide ($R-X$) via an $S_N2$ mechanism to form $N$-alkylphthalimide.
- Liberation of the Amine: Finally, the $N$-alkylphthalimide is hydrolyzed (often using hydrazine or an aqueous base) to release the primary aliphatic amine, where the nitrogen atom originates directly from the phthalimide starting material.
Analysis of Other Options
- Sodium azide: Used in the Schmidt reaction or Curtius rearrangement to form amines, but not in the Gabriel synthesis.
- Sodium nitrile: Not a standard reagent for amine synthesis in this context; nitrites ($R-ONO$) are different from amines ($R-NH_2$).
- Potassium cyanide: Used to add a carbon atom and a nitrogen atom (forming a nitrile), which can then be reduced to an amine, but it is not the reagent for the Gabriel synthesis.
Correct Option: Potassium phthalimide |
