Dithionite

Dithionite refers to the dianion S2O4^2-, most commonly encountered in its salt forms such as sodium dithionite (Na2S2O4) and potassium dithionite (K2S2O4). It is a strong reducing agent used in a variety of industrial and laboratory applications. In aqueous solution, dithionite tends to oxidize over time, and its primary oxidation product is dithionate (S2O6^2-). Under acidic conditions, it can release sulfur dioxide, reflecting its tendency to decompose when exposed to protons.

Properties and behavior: Dithionite salts are typically white to somewhat off-white powders that dissolve in water to give highly reducing solutions. The species are stable when stored dry and in the absence of air and strong oxidizers, but solutions are best prepared fresh or stored under inert conditions. The redox chemistry is pH-dependent, with alkaline media generally favoring stability of the dithionite form, while exposure to air and heat accelerates oxidation to dithionate or other oxidized sulfur oxyanions.

Applications: Sodium and potassium dithionite are widely used as reducing agents in the pulp and paper industry for bleaching and brightening wood pulp, in textile processing for dye reduction and decolorization, and in certain chemical syntheses and wastewater treatments. They can reduce metal ions and organic chromophores, enabling selective cleaning, bleaching, or decolorization depending on the process.

Safety and handling: Dithionite compounds are strong reducing agents and can react vigorously with oxidizers or acids, sometimes releasing sulfur dioxide. They can irritate skin and eyes and should be handled with appropriate protective equipment. Solutions should be prepared and stored away from acids and oxidizing agents, and containers should be kept closed and protected from prolonged exposure to air.