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Nitrobenzene is treated with Sn / HCl to give a compound (X) which on treatment with NaNO2 and HCl at 278 K gives compound (Y). When the compound (Y) is treated with Cu / HBr , compound 'Z' is obtained. The compound 'Z' is

  • A.Benzene
  • B.Benzene diazonium bromide
  • C.Phenol
  • D.Bromobenzene
  • E.Chlorobenzene

Answer: D

Compound Z is Bromobenzene.

The sequence is three standard steps:

  1. Sn and HCl reduce nitrobenzene to aniline: X is C6H5NH2.
  2. NaNO2 and HCl at 273-278 K diazotise aniline: Y is benzenediazonium chloride, C6H5N2+Cl-.
  3. Copper powder with HBr replaces the diazonium group by bromine with loss of nitrogen (the Gattermann reaction): Z is C6H5Br.

Benzene diazonium bromide is not formed; the diazonium salt is the intermediate Y, and it is decomposed in the last step. Phenol would come from warming Y with water, benzene from reduction with H3PO2, and chlorobenzene from Cu/HCl rather than Cu/HBr.

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