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 solve the problem, we need to evaluate the Assertion (A) and Reason (R) regarding the preparation of aromatic primary amines using Gabriel Phthalimide synthesis and determine their validity and relationship.

1. Analyzing the Assertion (A):
Assertion (A) states that aromatic primary amines cannot be prepared by Gabriel Phthalimide synthesis. The Gabriel Phthalimide synthesis is a method to prepare primary aliphatic amines. It involves the reaction of potassium phthalimide with an alkyl halide to form N-alkyl phthalimide, which is then hydrolyzed to yield a primary aliphatic amine. For aromatic primary amines (e.g., aniline, C\(_6\)H\(_5\)NH\(_2\)), the starting material would be an aryl halide (e.g., C\(_6\)H\(_5\)X). However, aryl halides typically do not undergo nucleophilic substitution reactions (like SN2) required for this synthesis under standard conditions, due to the stability of the aromatic ring and poor leaving group displacement. Thus, Gabriel Phthalimide synthesis is not suitable for preparing aromatic primary amines, making the assertion true.

2. Analyzing the Reason (R):
Reason (R) states that aryl halides do not undergo nucleophilic substitution reaction with the anion formed by phthalimide. In Gabriel Phthalimide synthesis, the phthalimide anion (a nucleophile) reacts with an alkyl halide via an SN2 mechanism to displace the halide. Aryl halides, however, have a carbon-halogen bond strengthened by resonance with the aromatic ring, making them resistant to nucleophilic attack in SN2 reactions. Additionally, SN1 mechanisms are unfavorable for aryl halides due to the instability of aryl carbocations. Only under harsh conditions (e.g., high temperature or specific catalysts) or via alternative mechanisms (e.g., benzyne formation with strong bases) do aryl halides react, but these are not applicable in standard Gabriel synthesis conditions. Thus, the reason is true, as aryl halides do not readily undergo the required nucleophilic substitution with the phthalimide anion.

3. Evaluating the Relationship:
The reason explains why the assertion is true. The inability of aromatic primary amines to be prepared via Gabriel Phthalimide synthesis (A) is directly due to the fact that aryl halides do not undergo nucleophilic substitution with the phthalimide anion (R). The stability of the aryl halide bond prevents the formation of the N-aryl phthalimide intermediate, a necessary step in the synthesis. Therefore, R is a correct explanation for A.

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

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