Question

Assertion (A) : Aromatic primary amines can easily be prepared by Gabriel phthalimide synthesis. Reason (R) : Gabriel phthalimide synthesis is used to prepare only aliphatic primary amines.

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

Gabriel phthalimide synthesis is an excellent method for preparing pure aliphatic primary amines but is generally not applicable to aryl halides.

Answer 1

The Correct Option is D

Concept: Gabriel phthalimide synthesis is a highly useful method for preparing primary amines. However, it is mainly applicable to alkyl halides and not aryl halides. The reaction proceeds through nucleophilic substitution.

Step 1: Principle of Gabriel synthesis. Potassium phthalimide reacts with alkyl halides: \[ R-X \] to produce N-alkyl phthalimide, which upon hydrolysis yields a primary amine. \[ RNH_2 \]

Step 2: Applicability to aromatic halides. Aryl halides such as chlorobenzene generally do not undergo nucleophilic substitution easily because:

• Carbon-halogen bond possesses partial double bond character.

• The aromatic ring stabilizes the bond.

• Backside attack is difficult.
Therefore aromatic primary amines cannot be prepared conveniently by Gabriel synthesis. Hence the Assertion is false.

Step 3: Analyze the Reason. Gabriel phthalimide synthesis is primarily employed for preparing aliphatic primary amines. It is not suitable for preparing aromatic primary amines. Therefore the Reason is true.

Step 4: Final conclusion. Assertion is false whereas Reason is true. \[ \boxed{\text{Option (D)}} \]