Thiosulfuric acid

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Thiosulfuric acid [1]
Structural formula H2S2O3Steudel.svg
Structural formula
Ball-and-stick model Thiosulfuric-acid-3D-balls-B.png
Ball-and-stick model
Names
IUPAC name
Sulfurothioic S-acid [2]
Systematic IUPAC name
Dihydroxidooxidosulfidosulfur [2]
Other names
Thiosulfuric acid
Sulfurothioic O,O-acid [3]
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
PubChem CID
UNII
  • InChI=1S/H2O3S2/c1-5(2,3)4/h(H2,1,2,3,4) Yes check.svgY
    Key: DHCDFWKWKRSZHF-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/H2O3S2/c1-5(2,3)4/h(H2,1,2,3,4)
  • OS(=O)(=O)S
Properties [1] [4]
H2S2O3
Molar mass 114.13 g·mol−1
Melting point decomposes below 0 °C
decomposes
Acidity (pKa)
  • pKa1 = 0.6 [5]
  • pKa2 = 1.74 [5]
Conjugate base Thiosulfate
Related compounds
Other cations
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.

Contents

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. [6] Anhydrous methods of producing the acid were developed by Max Schmidt: [6] [7]

H2S + SO3 → H2S2O3
Na2S2O3 + 2 HCl → 2 NaCl + H2S2O3
HSO3Cl + H2S → HCl + H2S2O3

The anhydrous acid also decomposes above −5 °C: [6]

H2S2O3 → H2S + SO3

Structure

The structure of the conjugate base of thiosulfuric acid. HS2O3anion.svg
The structure of the conjugate base of thiosulfuric acid.

The isomer (O=)2S(−OH)(−SH) is more stable than the isomer (O=)(S=)S(−OH)2 as established by Hartree–Fock/ab initio calculations with a 6-311 G** basis set and MP2 to MP4 refinements. [8] [ clarification needed ] 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. [6]

References

  1. 1 2 Macintyre, Jane Elizabeth, ed. (1992), Dictionary of Inorganic Compounds, Chapman & Hall, p. 3362, ISBN   0-412-30120-2
  2. 1 2 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. 139. Electronic version.
  3. ↑ ACD Chemsketch Name Free
  4. ↑ Page, F. M. (1953), "The dissociation constants of thiosulphuric acid", J. Chem. Soc.: 1719–24, doi:10.1039/JR9530001719
  5. 1 2 Perrin, D. D., ed. (1982) [1969]. Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution. IUPAC Chemical Data (2nd ed.). Oxford: Pergamon (published 1984). Entry 239. ISBN   0-08-029214-3. LCCN   82-16524.
  6. 1 2 3 4 Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 846–848. ISBN   978-0-08-022057-4..
  7. ↑ 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
  8. 1 2 Miaskiewicz, Karol; Steudel, Ralf (1992), "The Structures of Thiosulfuric Acid H
    2    S
    2    O
    3     and Its Monoanion HS
    2    O−
    3    ", Angew. Chem. Int. Ed. Engl., 31 (1): 58–59, doi:10.1002/anie.199200581
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