Thiosulfuric acid

Thiosulfuric acid
Names


IUPAC name sulfurothioic O-acid
Systematic IUPAC name dihydroxidooxidosulfidosulfur
Other names thiosulfuric acid sulfurothioic O,O-acid
Identifiers
CAS Number	13686-28-7^N
3D model (JSmol)	Interactive image
ChEBI	CHEBI:29279^Y
ChemSpider	22886^Y
PubChem CID	24478
InChI InChI=1S/H2O3S2/c1-5(2,3)4/h(H2,1,2,3,4)^Y Key: DHCDFWKWKRSZHF-UHFFFAOYSA-N^Y InChI=1/H2O3S2/c1-5(2,3)4/h(H2,1,2,3,4)
SMILES O=S(=S)(O)O
Properties
Chemical formula	H₂S₂O₃
Molar mass	114.14 g/mol
Melting point	decomposes below 0 °C
Solubility in water	decomposes
Acidity (pK_a)	0.6, 1.74
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N (what is ^YN ?)
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. Anhydrous methods of producing the acid were developed by Carol Schmidt:

The anhydrous acid also decomposes below -5 °C:

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. 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.

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