react with  or , forming thiosulfuric acid , as the analogous reaction with  forms disulfonomonosulfonic acid ; similarly polysulfanes HS (n = 2–6) give HSSOH. Reactions from both ends of the polysulfane chain lead to the formation of polysulfonodisulfonic acid HOSSSOH.
Many methods exist for the synthesis of these acids, but the mechanism is unclear because of the large number of simultaneously occurring and competing reactions such as redox, chain transfer, and disproportionation. Typical examples are:
* Interaction between hydrogen sulfide and sulfur dioxide in highly dilute aqueous solution. This yields a complex mixture of various oxyacids of sulfur of different structures, called Wackenroder solution. At temperatures above 20 °C solutes slowly decomposes with separation unit sulfur, sulfur dioxide, and sulfuric acid.
::HS + HSO → HSO + HO
::HSO + 2 HSO → HSO + 2 HO
::HSO + HSO → HSO + HSO
* Reactions of sulfur halides with  or , for example :
:: SCl + 2  → [OSSSO ] + 2 HCl
:: SCl + 2  → [OSSSO] + 2 HCl
:: SCl + 2  → [OSSSO] + 2 HCl
Anhydrous polythionic acids can be formed in diethyl ether solution by the following three general ways:
: HSSOH + SO → HSO (n = 1, 2 ... 8)
: HS + 2 SO → HSO (n = 1, 2 ... 8)
: 2 HSSOH + I → HSO + 2 HI (n = 1, 2 ... 6)
Polythionic acids with a small number of sulfur atoms in the chain (n = 3, 4, 5, 6) are the most stable. Polythionic acids are stable only in aqueous solutions, and are rapidly destroyed at higher concentrations with the release of sulfur, sulfur dioxide and - sometimes - sulfuric acid. Acid salts of polythionic acids do not exist. Polythionate ions are significantly more stable than the corresponding acids.
Under the action of oxidants (potassium permanganate, potassium dichromate) polythionic acids and their salts are oxidized to sulfate, and the interaction with strong reducing agents (amalgam of sodium) converts them into sulfites and dithionites.