Dithionous acid

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Dithionous acid
Dithionous acid.svg
IUPAC name
Dithionous acid
Other names
Hydrosulfurous acid; Hyposulfurous acid
3D model (JSmol)
Molar mass 130.144 g/mol
Acidity (pKa) 0.35, 2.45 [1]
Conjugate base Dithionite
Related compounds
Related compounds
Oxalic acid
Sodium dithionite
Potassium dithionite
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Dithionous acid is a sulfur oxoacid with the chemical formula H2S2O4. It is unstable in pure form,[2] but its salts, known as dithionites, are stable.

It was initially assumed that the C2 symmetric structure HOS(=O)-S(=O)OH is the most stable among molecules with the formula H
using ab initio calculations.[3] The reason for this is the existence of intermolecular hydrogen bonds. It is now known that dithionous acid spontaneously decomposes to SO2 and S(OH)2.

Sodium dithionite is a white powder used as a reductant and a bleaching agent. It is also used to reduce the nitro group to an amino group in organic reactions.

See also[edit]


  1. ^ Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 16: The group 16 elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 520. ISBN 978-0-13-175553-6. 
  2. ^ Drozdova, Yana; Steudel, Ralf; Hertwig, Roland H.; Koch, Wolfram; Steiger, Thomas (1998). "Structures and Energies of Various Isomers of Dithionous Acid, H2S2O4, and of Its Anion HS2O4- 1". The Journal of Physical Chemistry A. 102 (6): 990. doi:10.1021/jp972658d. 
  3. ^ Drozdova, Y.; Steudel, R.; Hertwig, R. H.; Koch, W.; Steiger, T. J. Phys. Chem. A 1998, 102, 990-996. DOI: 10.1021/jp972658d