Question

The method by which aniline cannot be prepared is

• A. Nitration of benzene followed by reduction with Sn and con. HCl
• B. Degradation of benzamide with bromine in alkaline solution
• C. Reduction of nitrobenzene with H₂ /Pd is ethanol
• D. Potassium salt of pthalimide treated with chlorobenzene followed by the hydrolysis with aqueous NaOH solution

Answer 1

The Correct Option is D

To solve this problem, we need to determine which method cannot be used to prepare aniline (C₆H₅NH₂).

1. Analyzing Each Method:
Let's evaluate each option based on known organic reactions:

• Option (A) "Nitration of benzene followed by reduction with Sn and conc. HCl": This is a classic method for preparing aniline. In this method, benzene is first nitrated to form nitrobenzene (C₆H₅NO₂). The nitro group is then reduced to an amino group (-NH₂) using tin (Sn) and concentrated hydrochloric acid (HCl), resulting in aniline (C₆H₅NH₂). This is a valid method for preparing aniline.
• Option (B) "Degradation of benzamide with bromine in alkaline solution": This reaction is known as Hofmann degradation. In this reaction, benzamide (C₆H₅CONH₂) is treated with bromine in an alkaline solution, which leads to the removal of the carbonyl group and the formation of aniline (C₆H₅NH₂). This is also a valid method for preparing aniline.
• Option (C) "Reduction of nitrobenzene with H₂/Pd is ethanol": The reduction of nitrobenzene (C₆H₅NO₂) to aniline (C₆H₅NH₂) using hydrogen (H₂) and palladium (Pd) catalyst in ethanol is a valid and common method for preparing aniline. This reaction effectively reduces the nitro group to an amine group.
• Option (D) "Potassium salt of phthalimide treated with chlorobenzene followed by hydrolysis with aqueous NaOH solution": This is a method known as the Gabriel synthesis, where the potassium salt of phthalimide is treated with an alkyl halide (like chlorobenzene) to form a phthalimide derivative, which upon hydrolysis with aqueous NaOH yields an amine. However, this method does not lead to aniline (C₆H₅NH₂) directly; instead, it forms a primary amine in the case of alkylation of phthalimide, not specifically aniline. This method does not directly form aniline and thus is not suitable for its preparation.

Final Answer:
The method by which aniline cannot be prepared is (D) "Potassium salt of phthalimide treated with chlorobenzene followed by hydrolysis with aqueous NaOH solution."

Answer 2

Aniline can be synthesized by several methods, but option (D) is not a valid method. The reaction involving the potassium salt of phthalimide and chlorobenzene followed by hydrolysis with aqueous NaOH does not lead to the formation of aniline. This method is used to form phthalic acid or derivatives, not aniline. The other methods (A), (B), and (C) all produce aniline under the given reaction conditions.

The correct answer is (D) : Potassium salt of pthalimide treated with chlorobenzene followed by the hydrolysis with aqueous NaOH solution.