Sodium hydrosulphite is the sodium salt of dithionous acid and is also called as sodium dithionite. Sodium Hydrosulphite was discovered at the beginning of the 20th century and was first applied for textile printing. Due to structural changes in the textile industry, the importance of Sodium hydrosulphite for the application of the bleaching of wood pulp in the paper industry, increased continuously.

General properties of Sodium Hydrosulphite

  • Sodium hydrosulphite is a white monoclinic crystalline powder with a weak sulphurous odour.
  • Sodium hydrosulphite is a stable compound under all ambient dry conditions and is slowly oxidized by air. Thus solution of sodium dithionite cannot be stored for a long period of time.
  • Sodium hydrosulphite can acts as a reductive bleaching agent and mainly used in the textile and paper industries.
  • It will decompose in hot water and in acid solutions.
  • Sodium hydrosulphite can act as a sulfonating agent and in a variety of chemical reactions.
  • Sodium hydrosulphite does not undergo biodegradation, bioaccumulation & photo degradation.
  • Sodium hydrosulphite is soluble in water and slightly soluble in ethanol.
  • Sodium hydrosulphite can be used as a reducing agent in aqueous solutions.
  • Aqueous solution of sodium hydrosulphite is acidic and the reactivity rate is higher under strong activity.
  • Sodium hydrosulphite can also acts as a cation source in the chemical reaction.


Production of Sodium Hydrosulphite

Sodium hydrosulphite is obtained from the reaction mixture of Sodium bisulphite with zinc catalyst as a Zinc hydroxide as one of its by-product.
2 NaHSO3 + Zn -> Na2S2O4 + Zn(OH)2

  • Paper Industry
  • In paper and pulp industry, sodium hydrosulphite is used as an additive and reducing agent. It is used in the paper industry for bleaching, brightening and decolorization of recycled fiber.

  • Photography Industry
  • Sodium hydrosulphite is used in the photography industry as a developing agent. It has unique features to reduce film speed and quickly fogs the image in the photographic industry.

  • Textile Industry
  • In the textile industry, sodium hydrosulphite acts as a dyeing agent. It is used in the dyeing process as water-insoluble dye and it can be reduced into a water-soluble alkali metal salt.

  • Chemical Industries
  • Sodium hydrosulphite is used in chemical industries for various purposes such as water treatment, gas purification, cleaning and stripping. It can also be used in the chemical processes as a sulfonating agent for the preparation of various chemicals

  • Geoscience
  • Sodium hydrosulphite is used in chemical enhanced oil recovery to stabilize polyacrylamide polymers.It is also used in environmental applications in order to reduce pollutants such as Chromium.

  • Other applications
  • Sodium hydrosulphite is used in the leather, food and polymer industry to reduce the low toxicity of the compound.It is used in physiology experiments for lowering the reduction potential and is used in soil chemistry experiments for the determination of iron in soil chemicatry experiments. In electrochemical industries it is used as an oxidizing agent.It can even be used as a chelating agent.

Product Identification

  CAS   Number   7775-14-6
  PubChem   24489
  EC Number   231-890-0
  RTECS  Number   JP2100000
  Molecular   Formula   Na2S2O4
  Systematic   Name   Disodium dithionite
  SMILES   [Na+].[Na+].[O-]S(=O)S([O-])=O
  HS CODE   2831.10
  SYNONYMS Sodium dithionite, Disodium dithionate, Disodium dithionite,   Dithionous acid, disodium salt, Sodium hypodisulfite,
Sodium hyposulfite, Reductone, Sodium sulfoxylate, Vatrolite   and V-Brite B

Physical & Chemical Properties

  Physical State and   Appearances   Solid (Solid Powder)
  Odor   Faint Sulfurous (slight)
  Molecular Mass/Weight   174.107 g/mol (anhydrous)
  210.146 g/mol (dihydrate)
  Density   2.38 g/cm3 (anhydrous)
  1.58 g/cm3 (dihydrate)
  Melting Point   52 °C, 325 K, 126 °F
  Boiling Point   Decomposes
  FLASH Point   1000 °C
  Solubility   Soluble in cold water, Slightly Soluble in Alcohol
  Solubility in water   18.2 g / 100 ml (anhydrous, 20 °C)
  21.9 g /100 ml (Dihydrate, 20 °C)
  pH   Acidic in Solution
  NFPA 704   Reactivity – 1, Health – 2, Flammability – 3
  Stability   Stable under ordinary condition (Decomposes in hot   water and acid)

Sales Specification

  Appearance   White to grey crystalline powder, light-lemon colored flakes
  Na2S2O4   85% OR 88% OR 90% min
  Insoluble in Water   0.1% max
  Na2S2O3   1.2% max
  Na2S2O5   5-7%
  NaHSO3   0.5% max
  Na2CO3   0.6-2%
  HCOONa   0.5% max
  Zn   0.0001% max
  Pb   0.0001% max
  Fe   0.005% max