Question

Given below are two statements, one is labelled as Assertion $\left(A\right)$ and other is labelled as Reason $\left(R\right)$.

Assertion $\left(A\right)$: Gabriel phthalimide synthesis cannot be used to prepare aromatic primary amines.
Reason $\left(R\right)$ : Aryl halides do not undergo nucleophilic substitution reaction.

In the light of the above statements, choose the correct answer from the options given below :

• A. Both $\left(A\right)$ and $\left(R\right)$ are true but $\left(R\right)$ is not the correct explanation of $\left(A\right)$
• B. $\left(A\right)$ is false but $\left(R\right)$ is true
• C. $\left(A\right)$ is true but $\left(R\right)$ is false
• D. Both $\left(A\right)$ and $\left(R\right)$ are true and $\left(R\right)$ is correct explanation of $\left(A\right)$

Answer 1

The correct option is D Both $\left(A\right)$ and $\left(R\right)$ are true and $\left(R\right)$ is correct explanation of $\left(A\right)$

Gabriel phthalimide synthesis cannot be used to prepare aromatic primary amines because aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide.

Hence, option (b) is correct.

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.