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From which of the following does Nitrobenzene give N-phenylhydroxylamine?
A) Sn/HCl
B) H2/PdC
C) Zn/NaOH
D) Zn/NH4Cl

Answer
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Hint:As we know that aromatic nitro compounds undergo reduction under different conditions to provide a variety of products. Their reduction can be carried out in four mediums which are acidic, basic, neutral and electrolytic and phenylhydroxylamine is obtained in a neutral medium only.

Complete answer
As we know that aromatic nitro compounds react with different reducing agents to provide a variety of products under various conditions of solutions. In the given question nitrobenzene is giving N-phenylhydroxylamine so we should have an amine, hydroxyl and phenyl groups in our product.

In acidic medium, when Sn/HCl is present as a reagent and we know that it is a strong reducing agent, so it will reduce the nitro group in nitrobenzene into aniline and release two molecules of water as well, thus it is not a correct answer.

Next we have H2/PdC as a reagent and it is also a strong reducing agent acting as a catalyst so it will also reduce the nitro group to amine and results in aniline formation.

Then comes the reagent Zn/NaOH which in alkaline medium is again a reducing agent and it will not be able to provide the hydroxyl group to the product rather under different conditions it will form different products. Like when Zn dust and aqueous NaOH is present as a reagent the product formed will be Hydrazobenzene. When Zn/NaOH is present along with CH3OH it will form Azobenzene as a product.

Lastly the reagent is Zn/NH4Cl which in neutral medium that means Zn dust and aqueousNH4Cl are present in solution, so they will reduces the nitrobenzene and results in the formation of N-phenyl hydroxylamine.

Therefore the correct answer is option (D).

Note:Most of the aromatic nitro compounds are yellow crystalline solids whereas the nitrobenzene is a liquid with a characteristic odour of bitter almonds. Zinc dust and aqueous ammonium chloride in solution acts as a mild reducing agent thereby reducing the nitro group to amine.