Sodium dithionite (also known as sodium hydrosulfite) is a white crystalline powder with a weak sulfurous odor. Although it is stable in dry air, it decomposes in hot water and in acid solutions.

Sodium dithionite is produced industrially by reduction of sulfur dioxide. ... NaBH4 + 8 NaOH + 8 SO2 → 4 Na2S2O4 + NaBO2 + 6 H2O. Each equivalent of H− reduces two equivalents of sulfur dioxide. Formate has also been used as the reductant.

Dithionite was produced for the first time in 1906 by BASF in Germany in powder form. Initially, the product was obtained by the zinc dust process. Zinc is first converted into zinc dithionite in an aqueous solution with sulfur dioxide and then by sodium hydroxide to sodium dithionite and zinc oxide

SODIUM DITHIONITE PURIFIED