Disulfuric acid

Disulfuric acid
IUPAC name

Disulfuric acid [1]
Other names

Pyrosulfuric acid
Identifiers
CAS number 7783-05-3 Y
PubChem 62682
ChemSpider 56433 Y
EC number 231-976-8
MeSH Pyrosulfuric+acid
ChEBI CHEBI:29211 Y
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Properties
Molecular formula H2O7S2
Molar mass 178.14 g mol−1
Exact mass 177.924193798 g mol-1
Melting point

36 °C, 309 K, 97 °F
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Disulfuric acid is an oxoacid of sulfur. It is a major constituent of fuming sulfuric acid, oleum, and this is how most chemists encounter it. It is also a minor constituent of liquid anhydrous sulfuric acid due to the equilibria:

H2SO4 ⇌ H2O + SO3
SO3 + H2SO4 ⇌ H2S2O7

The acid is prepared by reacting excess SO3 with sulfuric acid:

H2SO4 + SO3 → H2S2O7

Disulfuric acid can be seen as the sulfuric acid analogue of an acid anhydride. The mutual electron-withdrawing effects of each sulfuric acid unit on its neighbour causes a marked increase in acidity. Disulfuric acid is strong enough to protonate "normal" sulfuric acid in the (anhydrous) sulfuric acid solvent system. There are salts of disulfuric acid, commonly called pyrosulfates, e.g. potassium pyrosulfate.

There are other related acids with the general formula H2O.(SO3)x though none are isolable.

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.

Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419.