Polythionic acid
Polythionic acid is an
Nomenclature
All polythionates anion contains chains of sulfur atoms attached to the terminal SO3H-groups. Names of polythionic acids are determined by the number of atoms in the chain of sulfur atoms:
- H
2S
2O
6 – dithionic acid - H
2S
3O
6 – trithionic acid - H
2S
4O
6 –tetrathionic acid] - H
2S
5O
6 – pentathionic acid, etc.
History
Numerous acids and salts of this group have a venerable history, and chemistry systems, where they exist, dates back to the studies
4O2−
6 and S
5O2−
6, respectively).
Preparation and properties
H
2S react with SO
3 or HSO
3Cl, forming thiosulfuric acid H
2S
2O
3, as the analogous reaction with H
2S
2 forms disulfonomonosulfonic acid HS
2SO
3H; similarly polysulfanes H2Sn (n = 2–6) give HSnSO3H. Reactions from both ends of the polysulfane chain lead to the formation of polysulfonodisulfonic acid HO3SSnSO3H.
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
- 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.[1]
- H2S + H2SO3 → H2S2O2 + H2O
- H2S2O2 + 2 H2SO3 → H2S4O6 + 2 H2O
- H2S4O6 + H2SO3 → H2S3O6 + H2S2O3
- Reactions of sulfur halides with HSO−
3 or HS
2O−
3, for example :
- SCl2 + 2 HSO−
3 → [O3SSSO 3]2− + 2 HCl - S2Cl2 + 2 HSO−
3 → [O3SS2SO3]2− + 2 HCl - SCl2 + 2 HS
2O−
3 → [O3SS3SO3]2− + 2 HCl
- SCl2 + 2 HSO−
Anhydrous polythionic acids can be formed in diethyl ether solution by the following three general ways:
- HSnSO3H + SO3 → H2Sn+2O6 (n = 1, 2 ... 8)
- H2Sn + 2 SO3 → H2Sn+2O6 (n = 1, 2 ... 8)
- 2 HSnSO3H + I2 → H2S2n+2O6 + 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 (
Occurrence
Polythionic acids are rarely encountered, but polythionates are common and important.
Polythionic acids have been identified in crater lakes.[2] The phenomenon may be useful to predict volcanic activity.
References
- ISBN 9788173817274.
- S2CID 19856265.