Sodium Hydrosulfite, Sodium Dithionite
Sodium hydrosulfite (sodium dithionite, Na2S2O4) is an inexpensive and safe reducing agent, which for example enables the reduction of aromatic nitro and diazonium compounds to anilines.
The hydrogenation of α,β-epoxy ketones can be mediated by a catalytic amount of BNA+Br- using Na2S2O4 as primary reducing agent to form the corresponding β-hydroxy ketones in high yield. A radical mechanism has been proposed.
H.-J. Xu, Y.-C. Liu, Y. Fu, Y.-D. Wu, Org. Lett., 2006, 8, 3449-3451.
The of silica-coated magnetic nanoparticles allowed the construction of magnetically recoverable organic hydride compounds. Magnetic nanoparticle-supported BNAH (1-benzyl-1,4-dihydronicotinamide) showed efficient activity in the catalytic reduction of α,β-epoxy ketones. After reaction, the catalyst can be separated by simple magnetic separation and can be reused.
H.-J. Xu, X. Wan, Y.-Y. Shen, S. Xu, Y.-S. Feng, Org. Lett., 2012, 14, 1210-1213.
A highly efficient and versatile method for the synthesis of a series of 2-substituted N-H, N-alkyl, and N-aryl benzimidazoles containing a wide range of functional groups was achieved in one step via the Na2S2O4 reduction of o-nitroanilines in the presence of aldehydes. D. Yang, D. Fokas, J. Li, L. Yu, C. M. Baldino, Synthesis, 2005, 47-56.
In a simple one-pot procedure for the preparation of 2-(het)arylquinazolin-4(3H)-ones from readily available 2-nitrobenzamides and aryl aldehydes, sodium dithionite is used as the reducing agent for the nitro group. Sodium dithionite also decomposes in aqueous N,N-dimethylformamide under air to form sulfur dioxide, which is the oxidant in the final oxidation step that leads to the desired heterocyclic compounds.
A. H. Romero, J. Salazar, S. E. López, Synthesis, 2013, 45, 2043-2050.
Various azobenzenes have been reduced to the corresponding hydrazines by using an aqueous solution of sodium dithionite. The yield is generally excellent, but two compounds, viz. 4,4-dimethoxyazobenzene and 2,2,4,4,6,6-hexamethylazobenzene, gave no hydrazine at all.
L. K. Sydnes, S. Elmi, P. Heggen, B. Holmelid, D. Malthe-Sřrensen, Synlett, 2007, 1695-1696.