Thiosulfuric acid

Thiosulfuric acid[1]
Names
	IUPAC name sulfurothioic O-acid[2]
	Systematic IUPAC name dihydroxidooxidosulfidosulfur[2]
	Other names thiosulfuric acid; sulfurothioic O,O-acid[3]
Identifiers
CAS Number	13686-28-7 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:29279 ;
ChemSpider	22886 ;
PubChem CID	24478;
UNII	7K79Y2EKKP ;
CompTox Dashboard (EPA)	DTXSID00159981 ;
	InChI InChI=1S/H2O3S2/c1-5(2,3)4/h(H2,1,2,3,4) Key: DHCDFWKWKRSZHF-UHFFFAOYSA-N ; InChI=1/H2O3S2/c1-5(2,3)4/h(H2,1,2,3,4);
	SMILES O=S(=S)(O)O;
Properties[1][4]
Chemical formula	H2S2O3
Molar mass	114.14 g/mol
Melting point	decomposes below 0 °C
Solubility in water	decomposes
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]

References

Macintyre, Jane Elizabeth titys, ed. (1992), Dictionary of Inorganic Compounds, Chapman & Hall, p. 3362, ISBN 0-412-30120-2
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.
ACD Chemsketch Name Free
Page, F. M. (1953), "The dissociation constants of thiosulphuric acid", J. Chem. Soc.: 1719–24, doi:10.1039/JR9530001719
Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 846–48. ISBN 978-0-08-022057-4..
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
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

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[DIC-1] Macintyre, Jane Elizabeth titys, ed. (1992), Dictionary of Inorganic Compounds, Chapman & Hall, p. 3362, ISBN 0-412-30120-2

[redbookrefname-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

[G&E-5] 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