Question

The source of nitrogen in Gabriel synthesis of amines is:

• A. sodium azide
• B. potassium phthalimide
• C. sodium cyanide
• D. potassium nitrate

Answer 1

The correct option is B potassium phthalimide

In the Gabriel synthesis of primary amines, N-potassium phthalimide is used as a source of the nitrogen atom.
MECHANISM
Step 1: When potassium hydroxide is introduced to the phthalimide, an acid-base reaction occur. The hydroxide ion deprotonates the imide. The resulting proton is more acidic than any simple amine, generating a strong nucleophile – the potassium phthalimide​ ion.

Step 2:
The nucleophilic potassium imide ion attacks the electrophilic carbon of the alkyl halide. The nitrogen atom subsequently replaces the halogen (Fluorine, Chlorine, Bromine or Iodine) in the alkyl halide and bonds with the carbon itself. This results in the formation of an N-Alkyl Phthalimide.
Step 3:
The product N-Alkyl phthalimide is hydrolysed with aq. $NaOH$ to form primary amine, i.e. Alkylamine.