# Dithionic acid

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Dithionic acid Names IUPAC name dithionic acid[1] Other names hypodisulfuric acid Identifiers CAS Number 14970-71-9 N 3D model (JSmol) Interactive image ChEBI CHEBI:29208 Y ChemSpider 25128 Y PubChem CID 26985 UNII 9MP5KH5623 Y CompTox Dashboard (EPA) DTXSID50164368 InChI InChI=1S/H2O6S2/c1-7(2,3)8(4,5)6/h(H,1,2,3)(H,4,5,6) Y Key: RMGVZKRVHHSUIM-UHFFFAOYSA-N Y InChI=1/H2O6S2/c1-7(2,3)8(4,5)6/h(H,1,2,3)(H,4,5,6) Key: RMGVZKRVHHSUIM-UHFFFAOYAM SMILES O=S(=O)(O)S(=O)(=O)O Properties Chemical formula H2S2O6 Molar mass 162.14 g mol−1 Acidity (pKa) −3.4 (estimated)[2] Conjugate base Dithionate Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Chemical compound

**Dithionic acid**, H2S2O6, is the [inorganic compound](/source/Inorganic_compound) with the formula H2S2O6. It is the doubly protonated derivative of [dithionate](/source/Dithionate), a well-characterized dianion. Dithionic acid is mainly observed and characterized as an aqueous [solution](/source/Solution_(chemistry)).[3]

## Synthesis

Dithionates can be made by [oxidizing](/source/Redox) a [sulfite](/source/Sulfite) (from the +4 to the +5 [oxidation state](/source/Oxidation_state)), but on a larger scale they are made by oxidizing a cooled aqueous solution of [sulfur dioxide](/source/Sulfur_dioxide) with [manganese dioxide](/source/Manganese_dioxide):

- 2 MnO2 + 3 SO2 → MnS2O6 + MnSO4

The manganese dithionate solution formed can then be converted to dithionate salts of other metals by [metathesis reactions](/source/Salt_metathesis_reaction):

- Ba2+ (aq) + MnS2O6 (aq) + MnSO4 (aq) → BaSO4 (s)↓ + BaS2O6 · 2 H2O (aq)

Concentrated solutions of dithionic acid can subsequently be obtained treating a barium dithionate solution with sulfuric acid:

- BaS2O6 (aq) + H2SO4 (aq) → H2S2O6 (aq) + BaSO4 (s)↓

## See also

- [Sodium dithionate](/source/Sodium_dithionate)

- [Hypophosphoric acid](/source/Hypophosphoric_acid), the phosphorus equivalent.

## References

1. **[^](#cite_ref-1)** [International Union of Pure and Applied Chemistry](/source/International_Union_of_Pure_and_Applied_Chemistry) (2005). *[Nomenclature of Inorganic Chemistry](/source/Nomenclature_of_Inorganic_Chemistry)* (IUPAC Recommendations 2005). Cambridge (UK): [RSC](/source/Royal_Society_of_Chemistry)–[IUPAC](/source/International_Union_of_Pure_and_Applied_Chemistry). [ISBN](/source/ISBN_(identifier)) [0-85404-438-8](https://en.wikipedia.org/wiki/Special:BookSources/0-85404-438-8). p. 130. [Electronic version.](https://old.iupac.org/publications/books/rbook/Red_Book_2005.pdf)

1. **[^](#cite_ref-P82db_2-0)** Perrin, D. D., ed. (1982) [1969]. *Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution*. [IUPAC](/source/IUPAC) Chemical Data (2nd ed.). Oxford: Pergamon (published 1984). Entry 63. [ISBN](/source/ISBN_(identifier)) [0-08-029214-3](https://en.wikipedia.org/wiki/Special:BookSources/0-08-029214-3). [LCCN](/source/LCCN_(identifier)) [82-16524](https://lccn.loc.gov/82-16524).

1. **[^](#cite_ref-G&E_3-0)** [Greenwood, Norman N.](/source/Norman_Greenwood); Earnshaw, Alan (1997). *Chemistry of the Elements* (2nd ed.). Butterworth-Heinemann. [doi](/source/Doi_(identifier)):[10.1016/C2009-0-30414-6](https://doi.org/10.1016%2FC2009-0-30414-6). [ISBN](/source/ISBN_(identifier)) [978-0-08-037941-8](https://en.wikipedia.org/wiki/Special:BookSources/978-0-08-037941-8). pp. 715-716

v t e Hydrogen compounds H3AsO3 H3AsO4 HArF HAt HSO3F H[BF4] HBr HBrO HBrO2 HBrO3 HBrO4 HCl HClO HClO2 HClO3 HClO4 HCN HCNO H2CrO4/H2Cr2O7 H2CO3 H2CS3 HF HFO HI HIO HIO2 HIO3 HIO4 HMnO4 H2MnO4 H2MoO4 HNC NaHCO3 HNCO HNO HNO2 HNO3 H2N2O2 HNO5S H3NSO3 H2O H2O2 H2O3 H2O4 H2O5 H3PO2 H3PO3 H3PO4 H4P2O7 H5P3O10 H[AuCl4] H2[PtCl6] H2OsCl6 H2S H2S2 H2Se H2SeO3 H2SeO4 H4SiO4 H2[SiF6] H2[ZrF6] HSCN HNCS H2SO3 H2SO4 H2SO5 H2S2O3 H3O H2S2O6 H2S2O7 H2S2O8 CF3SO3H H2Te H2TeO3 H6TeO6 H4TiO4 CHCl3O3S H2Po H[Co(CO)4]

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