Zinin reaction or Zinin reduction was discovered by a Russian organic chemist Nikolay Zinin (Russian: Николай Николаевич Зинин) (25 August 1812, Shusha – 18 February 1880, Saint Petersburg). This reaction involves conversion of nitro aromatic compounds like nitrobenzene to amines by reduction with sodium sulfides. The reaction exhibits excellent selectivity for the nitro group and is useful in cases where other easily reduced functional groups (e.g., aryl halides and C=C bonds) are present in the molecule. Moreover, dinitrobenzenes can often be reduced selectively to the nitroaniline.
Reaction mechanism
Many details of the reaction mechanism are obscure, but it is known that 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 shown that disulfide (which is likely to be generated in situ) is a more active reducing agent and may be involved. The reaction is believed to proceed through oxygen transfer to sulfur to give ArNO, followed by further reduction to ArNHOH and, finally, to ArNH2.