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.

Application

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.