Sodium metabisulfite or sodium pyrosulfite (IUPAC spelling; Br. E. sodium metabisulphite or sodium pyrosulphite) is an inorganic compound of chemical formula Na2S2O5. The substance is sometimes referred to as disodium metabisulfite. It is used as a disinfectant, antioxidant, and preservative agent.\
The anion metabisulfite is a hybrid of dithionite (S2O42âˆ’) and dithionate (S2O62âˆ’). The anion consists of an SO2 group linked to an SO3group, with the negative charge more localized on the SO3 end. The Sâ€“S bond length is 2.22 Ã…, and the "thionate" and "thionite" Sâ€“O distances are 1.46 and 1.50 Ã… respectively.