Chemistry:Thiosulfurous acid

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Thiosulfurous acid
Structure of thiosulfurous acid
Thiosulfurous acid Ball and Stick.png
Thiosulfurous acid Space Fill.png
IUPAC names
sulfurothious S-acid[1]
sulfurothious O,S-acid[2]
Systematic IUPAC name
Other names
sulfurothionous acid
3D model (JSmol)
Molar mass 98.14668
Conjugate base Thiosulfite
Related compounds
Related compounds
thiosulfuric acid
thiosulfinic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references
Tracking categories (test):

Thiosulfurous acid (HS−S(=O)−OH) is a hypothetical compound with the formula S2(OH)2. Attempted synthesis leads to polymers.[3] It is a low oxidation state (+1) sulfur acid.[4] It is the equivalent acid for disulfur monoxide. Salts derived from thiosulfurous acid, which are also unknown, are named "thiosulfites" or "sulfurothioites". The ion is S=SO2−2.

Other possible isomers are dihydroxydisulfane or hypodithionous acid HOSSOH, a linear chain, and thiothionyl hydroxide (S=S(OH)2) a tautomer where the hydrogen has moved from a sulfur to an oxygen.[5] HOSSOH can have two different rotamers with symmetry C1 and C2. The isomer with one hydrogen on sulfur and one on oxygen is the most stable according to calculations.[6]


It apparently decomposes to polysulfane oxide or polythionic acids in water, which is termed Wakenroder's liquid.[5]

In alkaline conditions thiosulfurous acid rapidly deteriorates forming a mixture of sulfide, sulfur, sulfite, and thiosulfate. In acidic conditions it will form hydrogen sulfide and sulfur dioxide as well. Some of these react to form pentathionate and other polythionates. Thiosulfurous acid reacts with sulfurous acid to give tetrathionate, and with thiosulfuric acid to make hexathionate.[7]


Four isomers are possible for R2S2O2, at least restricting sulfur to di- and tetravalency: (RO)2S=S, ROSSOR, RS(O)2SR, and RS(O)SOR. For the first two, the R groups are equivalent, and in the latter two they are nonequivalent. A simple example is diethylthiosulfite, (EtO)2S=S. It is also known as diethylthionosulfite. It is a stereochemically rigid on the NMR timescale to about 140 °C, somewhat similar to diethylsulfoxide. Many derivatives have been prepared from glycols. From meso-hydrobenzoin (PhCH(OH)−CH(OH)Ph), one obtains two isomers; a third isomer results from d,l-PhCH(OH)−CH(OH)Ph.[8][9]

The reaction with simple alkoxide sources with disulfur dichloride gives the unbranched ROSSOR. They are immiscible in water, but dissolve in benzene or carbon tetrachloride.[7] These species are less rigid than the thiosulfite esters.


  1. 1.0 1.1 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.
  2. ACD Chemsketch Name Free
  3. Schmidt, Heinar; Ralf Steudel; Detlev Suelzle; Helmut Schwarz (1992). "Sulfur compounds. 148. Generation and characterization of dihydroxy disulfide, HOSSOH: the chainlike isomer of thiosulfurous acid". Inorganic Chemistry 31 (6): 941–944. doi:10.1021/ic00032a004. ISSN 0020-1669. 
  4. +1 is the average oxidation state of the two structurally different sulfur atoms. The exterior atom has an oxidation number of −1 while the central sulfur atom has the oxidation state of +3.
  5. 5.0 5.1 Wiberg, Egon; Wiberg, Nils (2001). Inorganic Chemistry. Academic Press. p. 552. ISBN 9780123526519. Retrieved 3 November 2013. 
  6. Miaskiewicz, Karol; Ralf Steudel (1991). "Sulphur compounds. Part 140. Structures and relative stabilities of seven isomeric forms of H2S2O2". Journal of the Chemical Society, Dalton Transactions (9): 2395. doi:10.1039/DT9910002395. ISSN 0300-9246. 
  7. 7.0 7.1 Nair, C. G. Ramachandran; A. R. Vasudeva Murthy (19 June 1961). "Hydrolytic Reactions of Esters and Amides of Thiosulfurous Acid". Proceedings of the Indian Academy of Sciences (Bangalore) 56 (3): 130–140. doi:10.1007/BF03045863. 
  8. Eli Zysman-Colman David N. Harpp "Dialkoxy Disulfides And Their Branch-bonded Thionosulfite Isomers" J. Sulfur Chemistry 2004, vol. 25, pp. 155–182. doi:10.1080/1741599342000202176
  9. Zysman-Colman, Eli; Charles B. Abrams; David N. Harpp (2003). "Synthesis of New Cyclic Thionosulfites". The Journal of Organic Chemistry 68 (18): 7059–7062. doi:10.1021/jo0346306. ISSN 0022-3263. PMID 12946149.