Zinin reaction

Zinin reaction or Zinin reduction involves reduction of nitro aromatic compounds to the amines using sodium sulfide. It is used to convert nitrobenzenes to anilines. The reaction selectively reduces nitro groups in the presence of other easily reduced functional groups (e.g., aryl halides and C=C bonds) are present in the molecule.

Reaction mechanism and example
The reaction requires water. Thiosulfate is one product. A possible stoichiometry for the reaction is:
 * 4 ArNO2  +   6 S2-   +  7 H2O  → 4  ArNH2   +   3 S2O32- +  6 OH-

Mechanistic studies have implicated a role for disulfide that is generated in situ. Nitrosobenzenes (ArNO) and phenylhydroxylamine (ArNHOH) are probable intermediates.

Dinitrobenzenes can often be reduced selectively to the nitroaniline.

History
The reaction was discovered by a Russian organic chemist Nikolay Zinin (Russian: Николай Николаевич Зинин) (25 August 1812, Shusha – 18 February 1880, Saint Petersburg).