Thiosulfuric acid

Thiosulfuric acid^[1]
Names
	IUPAC name Sulfurothioic S-acid
	Systematic IUPAC name Dihydroxidooxidosulfidosulfur
	Other names Thiosulfuric acid; Sulfurothioic O,O-acid
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 OS(=O)(=O)S;
Properties
Chemical formula	H2S2O3
Molar mass	114.13 g·mol−1
Melting point	decomposes below 0 °C
Solubility in water	decomposes
Acidity (pKa)	pKa1 = 0.6; pKa2 = 1.74;
Conjugate base	Thiosulfate
Related compounds
Other cations	Lithium thiosulfate; Sodium thiosulfate; Potassium thiosulfate; Ammonium thiosulfate;
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

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.^[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 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

^ ^a ^b Macintyre, Jane Elizabeth, ed. (1992), Dictionary of Inorganic Compounds, Chapman & Hall, p. 3362, ISBN 0-412-30120-2
^ ACD Chemsketch Name Free
^ ^a ^b 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.
^ ^a ^b 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.
^ Page, F. M. (1953), "The dissociation constants of thiosulphuric acid", J. Chem. Soc.: 1719–24, doi:10.1039/JR9530001719
^ ^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..
^ 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
^ ^a ^b Miaskiewicz, Karol; Steudel, Ralf (1992), "The Structures of Thiosulfuric Acid H
₂S
₂O
₃ and Its Monoanion HS
₂O⁻
₃", Angew. Chem. Int. Ed. Engl., 31 (1): 58–59, doi:10.1002/anie.199200581

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

[2] ACD Chemsketch Name Free

[redbookrefname-3] 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.

[P82db-4] 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.

[5] Page, F. M. (1953), "The dissociation constants of thiosulphuric acid", J. Chem. Soc.: 1719–24, doi:10.1039/JR9530001719

[G&E-6] Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 846–48. 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

[Steudel-8] Miaskiewicz, Karol; Steudel, Ralf (1992), "The Structures of Thiosulfuric Acid H
₂S
₂O
₃ and Its Monoanion HS
₂O⁻
₃", Angew. Chem. Int. Ed. Engl., 31 (1): 58–59, doi:10.1002/anie.199200581

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