Thiosulfurous acid is a hypothetical chemical compound with the formula HS−S(=O)−OH or HO−S(=S)−OH. Attempted synthesis leads to polymers. It is a low oxidation state (+1) sulfur acid.+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. 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 constitutional 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. The isomer with one hydrogen on sulfur and one on oxygen is the most stable according to calculations. For HOSSOH, two different rotamers are possible, one with symmetry C1 and the other C2.
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.
Reactions It apparently decomposes to polysulfane oxide or polythionic acids in water, which is termed Wakenroder's liquid.
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 There are four possible R2S2O2 isomers (restricting sulfur to di- and tetravalence): (RO)2S=S A simple example is diethylthiosulfite, (EtO)2S=S, also known as diethylthionosulfite. It is stereochemically rigid on the NMR timescale to about 140 °C, somewhat similar to diethylsulfoxide.
Many cyclic derivatives have been prepared from glycols. meso-Hydrobenzoin (PhCH(OH)−CH(OH)Ph) gives two stereoisomers; a third isomer results from d,l-PhCH(OH)−CH(OH)Ph.Eli Zysman-Colman David N. Harpp "Dialkoxy Disulfides And Their Branch-bonded Thionosulfite Isomers" J. Sulfur Chemistry 2004, vol. 25, pp. 155–182. ROSSOR Simple alkoxides react with disulfur dichloride to give the unbranched ROSSOR. They are immiscible in water, but dissolve in benzene or carbon tetrachloride. These species are less rigid than thiosulfite-type esters. RS(O)2SR These compounds are the thiosulfonates. RS(O)SOR Disulfoxides are unstable, rearranging to the thiosulfonate.
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