Question

Assertion (A): Aromatic primary amines cannot be prepared by Gabriel Phthalimide synthesis. 
Reason (R): Aryl halides do not undergo nucleophilic substitution reaction with the anion formed by phthalimide.

• A. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

The Gabriel synthesis is a way of synthesizing primary amines from alkyl halides, but does not work effectively with aryl halides due to their poor reactivity in nucleophilic substitution reactions.

Answer 1

The Correct Option is B

To address the problem, we must assess the validity of Assertion (A) and Reason (R) concerning the synthesis of aromatic primary amines via the Gabriel Phthalimide method and their causal relationship.

1. Analysis of Assertion (A):
Assertion (A) posits that aromatic primary amines cannot be synthesized using the Gabriel Phthalimide method. This method is designed for the preparation of primary aliphatic amines. It involves reacting potassium phthalimide with an alkyl halide to form an N-alkyl phthalimide intermediate, which is subsequently hydrolyzed to yield a primary aliphatic amine. For aromatic primary amines, such as aniline (C\(_6\)H\(_5\)NH\(_2\)), the required starting material would be an aryl halide (e.g., C\(_6\)H\(_5\)X). However, aryl halides are generally unreactive towards nucleophilic substitution reactions (e.g., SN2) under standard conditions due to the inherent stability of the aromatic ring and the poor leaving group character. Consequently, the Gabriel Phthalimide synthesis is not applicable to the preparation of aromatic primary amines, validating the assertion.

2. Analysis of Reason (R):
Reason (R) states that aryl halides do not undergo nucleophilic substitution reactions with the phthalimide anion. In the Gabriel Phthalimide synthesis, the phthalimide anion acts as a nucleophile and reacts with an alkyl halide via an SN2 mechanism. In contrast, the carbon-halogen bond in aryl halides is strengthened by resonance with the aromatic ring, rendering them resistant to nucleophilic attack via SN2 mechanisms. Furthermore, SN1 mechanisms are disfavored due to the instability of aryl carbocations. Aryl halides typically react only under stringent conditions (e.g., high temperatures or specific catalysts) or through alternative pathways like benzyne formation with strong bases, which are not employed in typical Gabriel synthesis protocols. Therefore, the reason is accurate, as aryl halides do not readily participate in the required nucleophilic substitution with the phthalimide anion.

3. Evaluation of the Relationship:
The reason provided correctly explains the assertion. The inability to synthesize aromatic primary amines using the Gabriel Phthalimide method (A) is a direct consequence of the unresponsiveness of aryl halides to nucleophilic substitution by the phthalimide anion (R). The enhanced stability of the aryl halide bond prevents the formation of the N-aryl phthalimide intermediate, a crucial step for the synthesis. Thus, R serves as a valid explanation for A.

4. Conclusion:
- Assertion (A) is true; aromatic primary amines cannot be prepared via Gabriel Phthalimide synthesis.
- Reason (R) is true; aryl halides do not undergo nucleophilic substitution with the phthalimide anion.
- Reason (R) accurately explains Assertion (A), as the failure of aryl halides to react accounts for the limitation stated in the assertion.

Final Answer:
Assertion (A) is true, Reason (R) is true, and R is the correct explanation for A.