Write a note on the ‘reduction of nitro benzene under different conditions.

Explanation

(i) Strongly Acidic Medium : When reduced with tin and hydrochloric acid, aromatic nitro compounds are converted to aryl amines.
`{:(C_6H_5NO_2+6[H]underset(Fe"/"con.HCl)overset(Sn"/"con.HCl)(to)C_6H_5NH_2+2H_2O),(" Aniline "):}`
(ii) Neutral Medium : When reduced with a neurtal, reducing agents like zinc dust and aqueous ammonium chloride, aromatic nitro compounds form aryl hydroxylamines.
`{:(C_6H_5NO_2+4[H]overset(Zn"/"NH_4Cl)(to)C_6H_5NHOH+H_2O),(" Phenyl hydroxylamine "):}`
(iii) Alkaline Medium : In alkaline medium, Nitro benzene on reduction forms the intermediate products nitrosobenzene `(C_6H_5NO)` and phenyl hydroxylamine `(C_6H_5NHOH)`. These undergo bimolecular condensation reactinon. According to the appropriate reducing agent in alkaline medium different products are obtained.

(iv) Catalytic Reduction : Lithium Aluminium hydride is a powerful hydride ion donor. So it reduces nitro benzene to Aniline. This reduction can also be carried out by `H_2"/"Ni`.
`C_6H_5NO_2overset(LiAlH_4)(to)C_6H_5NH_2[" Aniline "]`
`C_6H_5NO_2underset(" Catalytic hydrogenation ")overset(H_2"/"Ni)(to)C_6H_5NH_2`
(v) Electrolytic Reduction : When nitro benzene is reduced electrolytically in presence of concentrated sulphuric acid, phenyl hydroxylamine is first produced which rearranges to give p-amino phenol.