Thiosulfurous acid explained

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

Structures

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. 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.[3]

Dithiosulfurous acid

The sulfur analog of thiosulfuric acid, in which two sulfur atoms branch off of the central sulfur atom of a linear dihydrogen trisulfide structure (tetrathiosulfuric acid, or) has also been computationally studied.[4]

Reactions

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.

Esters

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.[6] [7]

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.[8] These species are less rigid than the thiosulfite esters.

Notes and References

  1. 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. 0020-1669. 10.1021/ic00032a004.
  2. +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.
  3. 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. 0300-9246. 10.1039/DT9910002395.
  4. Hypervalency in sulfur? Ab initio and DFT studies of the structures of thiosulfate and related sulfur oxyanions . Nishimoto . Akiko . Zhang . Daisy Y. . Sulfur Letters . 5/6 . 2003 . 26 . 171–180 . 10.1080/02786110310001622767 . 95470892 .
  5. Book: Wiberg. Egon. Wiberg. Nils. Inorganic Chemistry. 3 November 2013. 2001. Academic Press. 9780123526519. 552.
  6. Eli Zysman-Colman David N. Harpp "Dialkoxy Disulfides And Their Branch-bonded Thionosulfite Isomers" J. Sulfur Chemistry 2004, vol. 25, pp. 155–182.
  7. Zysman-Colman. Eli. Charles B. Abrams . David N. Harpp . 2003. Synthesis of New Cyclic Thionosulfites. The Journal of Organic Chemistry. 68. 18. 7059–7062. 0022-3263. 10.1021/jo0346306. 12946149.
  8. 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. 10.1007/BF03045863. 35057986.