Sodium dithionite is an alkali metal salt. It has a colorless, crystalline solid form, and a pronounced sulfur dioxide-like odor. Because it is readily soluble in water, it is used as a reducing agent in aqueous solutions.
It is also used in chemical enhanced oil recovery. It is an important reducing agent in dyeing, and is often used in vat dyeing. In dyeing, it reduces aqueous dyes to water-soluble alkali metal salts. This improves the color fastness and overall appearance of the final product.
As a reducing agent, sodium dithionite lowers the redox potential of the solution. In addition, it is flammable and can ignite when it comes in contact with moist air or combustible materials.
It has been used as a sulfonating agent, chelating agent, and a gas purifier. Other uses include bleaching paper pulp, cotton, and wool. Sodium thiosulfonate is also widely used in the food industry.
It is usually produced from sodium formate or sulfur dioxide. Commercially available forms include a 150-gram-per-liter solution, powder, and crystals. These must be stored in an airtight container and in a dry, cool environment. They may be explosive when heated, and they should be handled according to local fire regulations.
When heated, some dithionite crystals will break apart and decompose in an explosive fashion. Dithionite is an air-sensitive substance and can ignite on contact with moist air or combustible material. The product is classified as self-igniting hazardous goods by the United Nations.