Difference between revisions of "Dithionic acid"

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[[Image:Dithionic-acid-3D-balls.png|thumb|right|150px|[[Ball-and-stick model]] of the dithionic acid molecule]]
 
[[Image:Dithionic-acid-3D-balls.png|thumb|right|150px|[[Ball-and-stick model]] of the dithionic acid molecule]]
  
'''Dithionic acid''', H<sub>2</sub>S<sub>2</sub>O<sub>6</sub>, is a chemical compound known only in [[solution]]<ref name=G&E>{{Greenwood&Earnshaw}} pp. 715-716</ref>.
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'''Dithionic acid''', H<sub>2</sub>S<sub>2</sub>O<sub>6</sub>, is a chemical compound known only in [[solution]]<ref name="G&E">{{Greenwood&Earnshaw2nd|pages=715–16}}.</ref>.
  
 
== Salts ==
 
== Salts ==
 
{{main|dithionate}}
 
{{main|dithionate}}
Dithionic acid is dibasic and [[Salt (chemistry)|salts]] called [[dithionate]]s are known. No [[acid salt]]s have been discovered. All dithionates are readily soluble in [[water]]<ref name=G&E />. They are mild oxidizing and mild reducing agents. The structure of dithionate ion is like [[ethane]], but two SO<sub>3</sub> 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.
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Dithionic acid is dibasic and [[Salt (chemistry)|salts]] called [[dithionate]]s are known. No [[acid salt]]s have been discovered. All dithionates are readily soluble in [[water]]<ref name="G&E"/>. They are mild oxidizing and mild reducing agents. The structure of dithionate ion is like [[ethane]], but two SO<sub>3</sub> groups adopt an almost eclipsed conformation. The S–S length is 215&nbsp;pm; S–O bonds are rather short with bond length of 143&nbsp;pm.
  
 
== Synthesis ==
 
== Synthesis ==

Revision as of 13:03, 20 August 2009

Structural formula of the dithionic acid molecule
Ball-and-stick model of the dithionic acid molecule

Dithionic acid, H2S2O6, is a chemical compound known only in solution[1].

Salts

Dithionic acid is dibasic and salts called dithionates are known. No acid salts have been discovered. All dithionates are readily soluble in water[1]. 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 215 pm; S–O bonds are rather short with bond length of 143 pm.

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. 1.0 1.1 Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements, 2nd ed.; Butterworth-Heinemann: Oxford, 1997; pp 715–16. ISBN 0-7506-3365-4.
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