Dithionic acid

Dithionic acid
IUPAC name dithionic acid [1]
Other names hypodisulfuric acid
Identifiers
CAS number	14970-71-9
PubChem	26985
ChemSpider	25128 Y
ChEBI	CHEBI:29208 Y
Jmol-3D images	Image 1
SMILES O=S(=O)(O)S(=O)(=O)O
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
Properties
Molecular formula	H2S2O6
Molar mass	162.14 g mol−1
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Dithionic acid, H₂S₂O₆, is a chemical compound known only in solution^[2].

Salts

Main article: Dithionate

Dithionic acid is dibasic and salts called dithionates are known. No acid salts have been discovered. All dithionates are readily soluble in water^[2]. They are mild oxidizing and mild reducing agents. The structure of dithionate ion is like ethane, but two SO₃ groups adopt an almost eclipsed conformation. The S—S length is 2.15 Å; S—O bonds are rather short with bond length of 1.43 Å.

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 MnO₂:

2MnO₂ + 3SO₂ → 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)↓ + BaS₂O₆·2H₂O(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)↓

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. ^ ^{a b} Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419.  pp. 715-716

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