Question

Given below are two statements, one is labelled as Assertion (A) and other is labelled as Reason (R).
Assertion (A) : Gabriel phthalimide synthesis cannot be used to prepare aromatic primary amines.
Reason (R) : 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 (A) and (R) are true and (R) is correct explanation of (A).
• B. Both (A) and (R) are true but (R) is not the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Gabriel Phthalimide Synthesis = \(1^\circ\) Aliphatic Amines only. Nucleophilic Aromatic Substitution (\(S_NAr\)) requires very strong electron-withdrawing groups (like \(-NO_2\)) at ortho/para positions, which are not present in simple aryl halides used for amine synthesis.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Gabriel phthalimide synthesis is a method used to prepare primary aliphatic amines. It involves the nucleophilic attack of the phthalimide anion on an alkyl halide via an \(S_N2\) mechanism.
Step 3: Detailed Explanation:
- Assertion (A): To prepare an aromatic primary amine like aniline, one would need to react potassium phthalimide with an aryl halide (like chlorobenzene). However, Gabriel phthalimide synthesis fails for this because aniline cannot be produced this way. The assertion is True.
- Reason (R): Aryl halides are extremely unreactive towards nucleophilic substitution (\(S_N2\)) because the \(C-X\) bond has partial double bond character due to resonance, the carbon is \(sp^2\) hybridized (more electronegative), and there is electronic repulsion from the \(\pi\)-cloud. Thus, the phthalimide anion cannot displace the halide from the benzene ring. The reason is True.
- Conclusion: Since the failure to prepare aromatic amines is directly due to the inability of aryl halides to undergo the required nucleophilic substitution step, (R) is the correct explanation for (A).
Step 4: Final Answer:
Both (A) and (R) are true, and (R) explains why Gabriel synthesis is restricted to aliphatic amines.