Dithionic acid
Appearance
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Names | |
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IUPAC name
dithionic acid[1]
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Other names
hypodisulfuric acid
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CompTox Dashboard (EPA)
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Properties | |
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).
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Dithionic acid, H2S2O6, is the inorganic compound with the formula H2S2O6. It is the doubly protonated derivative of dithionate, a well-characterized dianion. Dithionic acid is mainly observed and characterized as an aqueous solution.[3]
Synthesis
[edit]Dithionates can be made by oxidizing a sulfite (from the +4 to the +5 oxidation state), but on a larger scale they are made by oxidizing a cooled aqueous solution of sulfur dioxide with 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:
- 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
[edit]- Sodium dithionite
- Hypophosphoric acid, the phosphorus equivalent.
References
[edit]- ^ International Union of Pure and Applied Chemistry (2005). Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSC–IUPAC. ISBN 0-85404-438-8. p. 130. Electronic version.
- ^ Perrin, D. D., ed. (1982) [1969]. Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution. IUPAC Chemical Data (2nd ed.). Oxford: Pergamon (published 1984). Entry 63. ISBN 0-08-029214-3. LCCN 82-16524.
- ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8. pp. 715-716