Dithionic acid

Dithionic acid
Ball-and-stick model of dithionic acid
Names
IUPAC name
dithionic acid[1]
Other names
hypodisulfuric acid
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
UNII
  • InChI=1S/H2O6S2/c1-7(2,3)8(4,5)6/h(H,1,2,3)(H,4,5,6) checkY
    Key: RMGVZKRVHHSUIM-UHFFFAOYSA-N checkY
  • InChI=1/H2O6S2/c1-7(2,3)8(4,5)6/h(H,1,2,3)(H,4,5,6)
    Key: RMGVZKRVHHSUIM-UHFFFAOYAM
  • O=S(=O)(O)S(=O)(=O)O
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

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

References

  1. ^ 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.
  2. ^ 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.
  3. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8. pp. 715-716