Disulfite

Disulfite is the common name for metabisulfite, the salt of the metabisulfite anion S2O5^2-. The most widely used examples are sodium metabisulfite (Na2S2O5) and potassium metabisulfite (K2S2O5). In aqueous solution the metabisulfite anion equilibrates with sulfite and bisulfite species and can release sulfur dioxide (SO2) upon acidification.

Metabisulfites are typically produced by reacting sodium sulfite (Na2SO3) with sulfur dioxide (SO2): Na2SO3 + SO2 → Na2S2O5. In the solid state they appear as white to pale gray crystalline powders and decompose upon heating to release SO2. Structurally, the anion is described as two sulfite units linked by an S–S bond (S2O5^2-).

Uses: In food and beverage processing, metabisulfites serve as antioxidants and preservatives, restricting browning and microbial growth. They are commonly added to wine, dried fruits, fruit juices and some canned products. They also function as reducing agents in various industrial processes and as bleaching agents in pulp and paper and textile applications.

Safety: Sulfites can cause hypersensitivity in some individuals, including asthma and other reactions. Labeling is required in many jurisdictions when used as food additives. They should be handled with care, and exposure to concentrated solutions avoided.