Chemistry:Thiosulfuric acid

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Thiosulfuric acid[1]
Structural formula
IUPAC name
sulfurothioc 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
Related compounds
Other cations
Lithium thiosulfate
Sodium thiosulfate
Potassium 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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Thiosulfuric acid is the inorganic compound with the formula H2S2O3. It has attracted academic interest as a simple, easily accessed compound that is labile. It has few practical uses.

Preparation and degradation

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 reaction conditions.[5] Anhydrous methods of producing the acid were developed by Max Schmidt:[5][6]

H2S + SO3H2S2O3·n
Na2S2O3 + 2 HCl → 2 NaCl + H2S2O3
HSO3Cl + H2S → HCl + H2S2O3

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

H2S2O3H2S + SO3


The structure of the conjugate base of thiosulfuric acid.[7]

The isomer (HS)(HO)SO2 is more stable than the isomer (HO)2SO(S) as established by Hartree–Fock/ab initio calculations with a 6-311 G** basis set and MP2 to MP4 refinements.[7] The theoretically predicted structure conforms with the double bond rule.

An isomer of thiosulfuric acid is the adduct of hydrogen sulfide and sulfur trioxide, H2S·SO3, which can also be prepared at low temperature. It is a white crystalline solid.[5]


  1. 1.0 1.1 Macintyre, Jane Elizabeth, ed. (1992), Dictionary of Inorganic Compounds, Chapman & Hall, p. 3362, ISBN 0-412-30120-2 
  2. ACD Chemsketch Name Free
  3. 3.0 3.1 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. 5.0 5.1 5.2 5.3 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 (1–4): 141–57, doi:10.1002/zaac.19572890113 
  7. 7.0 7.1 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