sodium dithionite melting point is the temperature at which solid sodium dithionite (Na2S2O4) spontaneously decomposes in air or water to form sodium sulfite and sulfur dioxide. This decomposition is exothermic and generates dense poisonous vapors of sulfur dioxide. It can occur in closed vessels or open containers and is highly flammable and explosive in contact with certain metals. It is also susceptible to chemical reactions involving humidity. It must be stored under conditions that prevent moisture from affecting its stability.
Typical sodium dithionite solutions have a low alkalinity, between pH8 and 13, which stabilizes the dithionite crystals and protects them from decomposition at low temperature. Sodium dithionite is used for many applications in the textile industry such as dyeing, bleaching mechanical paper pulp (cotton, wool and kaolin clay), and iron removal in paper making. It is also used in conservation for the removal of iron stains on cultural artifacts, and as an oxygen scavenger in paper manufacturing. Other uses include food processing, water treatment, gas purification, cleaning and stripping, polymers, and photography.
The strong reducing activity of sodium dithionite allows it to reduce some aldehydes, forming a-hydroxy-sulfinates, at room temperature, or to reduce ketones to the corresponding alcohols above 85 degC. Sodium dithionite also has the ability to reduce substituted N-alkylpyridinium salts, especially those with electron-withdrawing groups in the 3- and 3,5- positions, to afford the corresponding 1,4-dihydropyridines