Sodium Hydrosulfite
Sodium Sulfhydrate, Sodium dithionite or sodium hypodisulfite
- CAS
- 16721-80-5
- EC
- 240-778-0
- Sectors
- Textiles, Leather & Paper, Water & Wastewater Treatment
Sodium Hydrosulfite (CAS 16721-80-5), also known as sodium dithionite, is a white crystalline powder that acts as a powerful reducing agent, serving textile dyeing for reducing vat dyes like indigo, paper bleaching for pulp whitening, and water treatment for deoxygenation. It has a density of 2.38 g/cm³, decomposes above 90°C, and emits a faint sulfurous odor. Highly soluble in water (up to 182 g/L at 20°C) but insoluble in alcohols; unstable in air, oxidizing to sodium bisulfate. Acts as a powerful reducing agent, produced from zinc and SO2 or formate reduction.
Typical Properties
| Molecular formula | HNaS |
|---|---|
| Molecular weight | 56.06 g/mol |
| Appearance | white crystals or powder with a very unpleasant smell |
| Form | Solid |
| Color | Off-white |
| Melting point | 350 °C |
| Density | 1.79 g/cm³ |
| Water solubility | 620 g/L (20 °C) |
| Flash point | 90°C |
| GHS signal word | Danger · Flammable, Corrosive, Acute toxicity, Irritant / harmful, Health hazard, Environmental hazard |
| Grades available | Technical Grade |
Typical literature values for identification; lot-specific results are stated on the certificate of analysis (COA) and the safety data sheet (SDS) that accompany every delivery.
Sodium Hydrosulfite
Applications
Key in textile dyeing for reducing vat dyes like indigo; in paper bleaching for pulp whitening; water treatment for deoxygenation; organic synthesis, photography, and as a quencher in biochemistry.
Safety & Risks
Spontaneously combustible in moist air; reacts with water or acids to release toxic SO2. Irritates skin, eyes, and respiratory system. Store dry and cool; UN1384, Hazard Class 4.2; use PPE.
Packaging
In 50kg iron or fiber drums with PE liners to exclude moisture. Handle carefully to prevent ignition from friction.