Dihydroxydisulfane

Dihydroxydisulfane or hypodithionous acid is a reduced sulfur oxyacid with sulfur in a formal oxidation state of +1, but the valence of sulfur is 2. The structural formula is HO\sS\sS\sOH, with all atoms arranged in a chain. It is an isomer of thiosulfurous acid but is lower in energy. Other isomers include HOS(=O)SH, HOS(=S)OH, and HS(=O)2SH. Disulfur monoxide, S2O, can be considered as the anhydride. Unlike many of these other reduced sulfur acids, dihydroxydisulfane can be formed in a pure state by reacting hydrogen sulfide with sulfur dioxide at −70 °C in dichlorodifluoromethane.


 * H2S + SO2 → H2S2O2

Dihyroxydisulfane may exist in an equilibrium with thiosulfurous acid.

Organic derivatives such as dimethoxydisulfane, diaceto disulfide, and bis(trifluoroaceto) disulfide also exist.

The conjugate bases are called disulfanediolate and hypodithionite.

Properties
Calculations predict that the S−S bond length is 2.013 Å, O−S bond length is 1.645 Å, H−O bond length is 0.943 Å.

Related compounds
Related compounds include the isoelectronic substances hydrogen tetroxide HOOOOH, hydroxotrisulfane HOSSSH, HSOSSH, and tetrasulfane HSSSSH.