Sodium bisulfite (sodium hydrogen sulfite, NaHSO3) is a mild reducing agent, that for example can be used for the decomposition of oxidizing agents during work-up, including halogens and highly oxidized transition metals.
A synthesis of N-arylsulfonamides from readily available nitroarenes and sodium arylsulfinates was realized in the presence of FeCl2 as catalyst and NaHSO3 as reductant under mild conditions. A broad range of functional groups were tolerated. Mechanistic studies indicated that the N-S bond might be generated through direct coupling of nitroarene with sodium arylsulfinate prior to the reduction.
W. Zhang, J. Xie, B. Rao, M. Luo, J. Org. Chem., 2015, 80, 3504-3511.