Thiosulfuric acid

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Thiosulfuric acid[1]
Structural formula
Ball-and-stick model
IUPAC name
sulfurothioic O-acid[3]
Systematic IUPAC name
Other names
thiosulfuric acid
sulfurothioic O,O-acid[2]
3D model (JSmol)
Molar mass 114.14 g/mol
Melting point decomposes below 0 °C
Acidity (pKa) 0.6, 1.74
Conjugate base Thiosulfate
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

Thiosulfuric acid is a sulfur oxoacid. The acid cannot be made by acidifying aqueous thiosulfate salt solutions as the acid readily decomposes in water. The decomposition products can include sulfur, sulfur dioxide, hydrogen sulfide, polysulfanes, sulfuric acid and polythionates, depending on the exact reaction conditions.[5] Anhydrous methods of producing the acid were developed by Carol Schmidt:[5][6]

H2S + SO3 → H2S2O3·n Et2O (in diethyl ether at −78 °C)
Na2S2O3 + 2 HCl → 2 NaCl + H2S2O3·2Et2O (in diethyl ether at −78 °C)
HSO3Cl + H2S → HCl + H2S2O3 (low temperature)

The anhydrous acid also decomposes below −5 °C:[5]

H2S2O3 → H2S + SO3

The S-acid isomer is believed to be more stable than the O-acid isomer based on Hartree–Fock/ab initio calculations with a 6-311 G** basis set and MP2 to MP4 refinements.[7] There is another isomeric form, a white crystalline adduct of hydrogen sulfide and sulfur trioxide, H2S·SO3, which can also be prepared at low temperature.[5]


  1. ^ a b Macintyre, Jane Elizabeth titys, ed. (1992), Dictionary of Inorganic Compounds, Chapman & Hall, p. 3362, ISBN 0-412-30120-2
  2. ^ ACD Chemsketch Name Free
  3. ^ a b International Union of Pure and Applied Chemistry (2005). Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSCIUPAC. ISBN 0-85404-438-8. p. 139. Electronic version.
  4. ^ Page, F. M. (1953), "The dissociation constants of thiosulphuric acid", J. Chem. Soc.: 1719–24, doi:10.1039/JR9530001719
  5. ^ a b c d Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 846–48. ISBN 978-0-08-022057-4..
  6. ^ Schmidt, Max (1957), "Über Säuren des Schwefels. I. Zur Kenntnis der wasserfreien Thioschwefelsäure", Z. Anorg. Allg. Chem., 289: 141–57, doi:10.1002/zaac.19572890113
  7. ^ Miaskiewicz, Karol; Steudel, Ralf (1992), "The Structures of Thiosulfuric Acid H2S2O3 and Its Monoanion HS2O3", Angew. Chem. Int. Ed. Engl., 31 (1): 58–59, doi:10.1002/anie.199200581