Polythionic acid

Polythionic acid is an oxoacid which has a straight chain of sulfur atoms and has the chemical formula Sn(SO3H)2 (n > 2). Trithionic acid (H2S3O6), tetrathionic acid (H2S4O6) are simple examples. They are the conjugate acids of polythionates. 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. Polythionic acid is an oxoacid which has a straight chain of sulfur atoms and has the chemical formula Sn(SO3H)2 (n > 2). Trithionic acid (H2S3O6), tetrathionic acid (H2S4O6) are simple examples. They are the conjugate acids of polythionates. 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 hydrogen sulfide in aqueous solutions of sulfur dioxide (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 (S4O2−6 and S5O2−6, respectively). In the last few decades in the work of Schmidt and other scientists in Germany, a new idea formed: as H2S can react with SO3 or HSO3Cl, forming thiosulfuric acid H2S2O3, as the analogous reaction with H2S2 forms disulfonomonosulfonic acid HS2SO3H; similarly polysulfanes H2Sn (n = 2–6) give HSnSO3H. Reactions from both ends of the polysulfane chain lead to the formation of polysulfonodisulfonic acid HO3SSnSO3H. There are many known methods for the synthesis of these acids, but the reaction mechanism is unclear because of the large number of simultaneously occurring and competing reactions such as redox, chain transfer, and disproportionation. Typical examples are: Anhydrous polythionic acids can be formed in diethyl ether solution by the following three general ways: 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. Polythionic acids are often found in crater lakes. There are various kinds of ions containing sulfur atoms derived by hydrogen sulfide and they make the strongly acidic conditions. It is observed that polythionates in crater lakes are drastically decreased before an eruption occurs. The phenomenon may be useful to predict volcanic activity.