Sodium metabisulfite

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. 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. Sodium metabisulfite can be prepared by evaporating a solution of sodium bisulfite saturated with sulfur dioxide: which yields a residue of colorless solid Na2S2O5. The anion metabisulfite is a hybrid of dithionite (S2O42−) and dithionate (S2O62−). The anion consists of an SO2 group linked to an SO3 group, with the negative charge more localized on the SO3 end. The S–S bond length is 2.22 Å, and the 'thionate' and 'thionite' S–O distances are 1.46 and 1.50 Å respectively. It is used as a preservative and antioxidant in food and is also known as E223. It can be used to preserve color of some fruits, such as bananas. It may cause allergic reactions in those who are sensitive to sulfites, including respiratory reactions in asthmatics, anaphylaxis, and other allergic reactions in sensitive individuals. Sodium metabisulfite and potassium metabisulfite are the primary ingredients in Campden tablets, used for wine and beer making. The acceptable daily intake is up to 0.7 milligrams per kilogram of body weight. Sodium metabisulfite oxidizes in the liver to harmless sulfate which is excreted in the urine.