Polythionic acid

Polythionic acid is an oxoacid which has a straight chain of sulfur atoms and has the chemical formula H₂S_nO₆ (n > 2). Trithionic acid (H₂S₃O₆), tetrathionic acid (H₂S₄O₆) are simple examples. The compounds of n < 80 are expected to exist, and those of n < 20 have already been synthesized. Dithionic acid (H₂S₂O₆) does not belong to the polythionic acids due to strongly different properties.

All polythionates anion contains chains of sulfur atoms attached to the terminal SO₃H-groups. Names of polithionic acids are determined by the number of atoms in the chain of sulfur atoms:

Numerous acids and salts of this group have a venerable history, and chemistry systems, where they exist, dates back to the studies John Dalton devoted to the behavior of H
2S in aqueous solutions of SO
2 (1808). This solution now has the name of Heinrich Wilhelm Ferdinand Wackenroder, who conducted a systematic study (1846). Over the next 60–80 years, numerous studies have shown the presence of ions, in particular tetrathionate and pentathionate anion (S₄O₆²⁻ and S₅O₆²⁻, respectively).

In the last few decades in the work of Schmidt and other scientists in Germany, a new idea formed: as H
2S can react with SO
3 or HSO
3Cl, forming thiosulfuric acid H
2S
2O
3, as the analogous reaction with H
2S
2 forms disulfonmonosulfonic acid H
2S
2SO
3H; similarly polysulfanes H₂S_n (n = 2-6) give HS_nSO₃H. Reactions from both ends of the polysulfane chain lead to the formation of polysulfondisulfonic acid HO₃SS_nSO₃H.

...
Wikipedia