Sodium Hydrosulfite (Na₂S₂O₄) 7775-14-6

Sodium Hydrosulfite, also known as sodium dithionite or sodium sulfoxylate, is a white to grayish-white crystalline powder with the formula Na₂S₂O₄ and a molecular weight of 174.11 g/mol. It is a powerful reducing agent that is highly soluble in water and widely used as a bleaching agent in textiles and paper, and as an oxygen scavenger in water treatment.

Sodium Hydrosulfite is primarily used as a reductive bleaching agent in textile vat dyeing for cotton and linen, for mechanical pulp bleaching and paper deinking, as an oxygen scavenger in boiler water treatment and industrial process water, as a reducing agent in organic synthesis, and as a stripping agent for correcting dyeing errors in textile manufacturing.

In textile dyeing, Sodium Hydrosulfite is used as a reducing agent in vat dyeing and indigo dyeing processes. It reduces insoluble vat dyes into their water-soluble leuco form, allowing them to penetrate cotton and linen fibers. After the reduced dye is absorbed by the fabric, air oxidation converts it back to its insoluble form, fixing the color permanently within the fiber.

Sodium Hydrosulfite must be stored in a cool, dry, well-ventilated area in tightly sealed containers away from moisture, heat, and direct sunlight. The product is oxygen-sensitive and decomposes when exposed to air or moisture, releasing sulfur dioxide. Keep away from oxidizers, acids, and water. Under proper storage conditions in sealed containers, shelf life is typically 6-12 months.

Sodium Hydrosulfite decomposes in the environment into sodium bisulfite, sodium sulfite, and ultimately sodium sulfate — all of which are common, relatively benign minerals. Its decomposition products have low toxicity to aquatic life. However, during use, proper ventilation is required as decomposition can release sulfur dioxide gas. In wastewater treatment, the decomposition products are readily biodegradable and do not bioaccumulate.