Sodium dithionite is a strong reducing agent, used in textile dyeing and reductive bleaching. It is also used to remove yellow discoloration of cellulose based products in the pulp and paper industry, to reduce iron stains on cultural artifacts, to control iron flash on white fabrics in bleaching environments, and as an oxygen scavenger in boilers.
The boiling point of sodium dithionite is -420 C. It is a colorless, odorless, tasteless solid that is highly soluble in water. It is readily decomposed in methanol. It can be oxidized to sodium metabisulfite (NaMBS) by a ferric oxy-hydroxide, which donates one of its sulfur atoms to the Na dithionite.
In aqueous solutions, it reacts with aldehydes and ketones to reduce them to a-hydroxy-sulfates at room temperature or to alcohols above 85 degC. In the presence of nitrites, it reduces them to nitrosamines.
Human health: Sodium dithionite may irritate the respiratory tract and induce bronchospasm in some humans. It is converted to sulfite and hydrogen sulfite in the lower gastrointestinal tract. Consequently, it can be harmful to infants and children.
LD50: For oral toxicity, the acute LD50 of sodium dithionite in rats was about 2500 mg/kg bw. At doses near or exceeding the LD50, atony, gastro-intestinal irritation and diarrhea were observed. Gross pathology showed hyperemic congestion, cardiac dilatation and gastrointestinal irritation in animals administered doses of 2500 mg/kg bw or more.
Toxicity: Conclusion: Sodium dithionite is not known to be a carcinogen. However, it is a known mutagen. In some animal species, it can mutate erythrocytes to form Heinz bodies, a substance that is toxic in humans. In the absence of a tumor, this can cause hemolysis and liver damage.