S2O42

S2O4^2−, commonly written S2O4^2− or S2O42−, is the dithionite anion, a sulfur-oxygen polyatomic ion with two sulfur atoms linked by a single bond and four oxygens. In this ion, the two sulfur atoms have an average oxidation state of +3. Dithionite occurs mainly in its salt forms, such as sodium dithionite (Na2S2O4) and potassium dithionite (K2S2O4), which are widely used in industry.

Structure and properties

The dithionite anion consists of two sulfur centers bonded together, each associated with two oxide groups. It is best described as a strong reducing agent that is stable in strongly basic solutions but decomposes under acidic conditions. In aqueous solution, dithionite is typically encountered as various solvated forms and equilibria with bisulfite and sulfite species, depending on pH.

Preparation and occurrence

Industrial dithionite salts are prepared by reducing sulfite species under alkaline conditions, often employing sulfur dioxide and base to promote formation of S2O4^2−. The salts are soluble in water and are used directly as reducing agents in various processes.

Reactions and applications

Dithionite is a potent reducing agent that can reduce metal ions and organic substrates. It is used in textile and paper bleaching, as well as in certain mineral processing and organic synthesis applications. In acidic media, dithionite decomposes, releasing sulfur-containing gases such as sulfur dioxide, which underscores the need for careful handling and storage.

Safety and handling

Dithionite salts are reactive and can cause irritation or allergic response upon contact. They should be stored in sealed containers away from oxidizers and acids, and solutions should be prepared and used under appropriate ventilation.