Sodium metabisulfite
Sodium metabisulfite or sodium pyrosulfite (IUPAC spelling; Br. E. sodium metabisulphite or sodium pyrosulphite) is an inorganic compound of chemical formula NaSO. The substance is sometimes referred to as disodium metabisulfite. It is used as a disinfectant, antioxidant, and preservative agent. Preparation. Sodium disulfite can be prepared by treating a solution of sodium hydroxide with sulfur dioxide. When conducted in warm water, NaSO initially precipitates as a yellow solid. With more SO, the solid dissolves to give the disulfite, which crystallises upon cooling. which yields a residue of colourless solid NaSO. Chemical structure. The anion metabisulfite consists of  an SO group linked to an SO group, with the negative charge more localised on the SO 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. Reactivity. Upon dissolution in water, bisulfite is generated: Uses. Sodium and potassium metabisulfite have many major and niche uses. It is widely used for preserving food and beverages.