The sulfur oxoacids are chemical compounds that contain sulfur, oxygen and hydrogen. The best known and most important industrially is sulfuric acid. Sulfur has a number of oxoacids; however, some of these are known only from their salts (these are shown in italics in the table below). The acids that have been characterised contain a variety of structural features, for example:
- tetrahedral sulfur when coordinated to oxygen
- terminal and bridging oxygen atoms
- terminal peroxo groups
- terminal S=S
- chains of (-S-)n
| Acid | Formula | Oxidation state(s) | Structure | Related anions | Notes |
| Sulfuric acid | H2SO4 | VI | Sulfate, SO42− and hydrogen sulfate commonly known as bisulfate, HSO4− | Best known and industrially significant. | |
| Polysulfuric acids including disulfuric acid or pyrosulfuric acid | H2SO4.nSO3 | VI | Disulfate (commonly known as pyrosulfate), S2O72− and trisulfate, S3O102− | Pure disulfuric acid melts at 36 °C.
Present in fuming sulfuric acid, oleum. Examples known for n=1,2. |
|
| Peroxymonosulfuric acid | H2SO5 | VI | Peroxymonosulfate, OOSO32− | "Caro's acid", a solid melting at 45 °C | |
| Peroxydisulfuric acid | H2S2O8 | VI | Peroxydisulfate, O3SOOSO32− | A solid melting at 65 °C. | |
| Dithionic acid | H2S2O6 | V | Dithionate, O3SSO32− | Not isolated in pure form, only concentrated solutions have been prepared | |
| Thiosulfuric acid | H2S2O3 | 0 (for the terminal S atom), IV (for the central S atom) | Thiosulfate, S2O32− Hydrogenthiosulfate HS2O3− (ammonium salt prepared in anhydrous methanol at −80 °C) |
Aqueous solutions decompose. | |
| Disulfurous acid or pyrosulfurous acid | H2S2O5 | IV | Disulfite commonly known as metabisulfite, S2O52− | Not known. | |
| Sulfurous acid | H2SO3 | IV | Bisulfite, HSO3− and sulfite, SO32− | Not known. | |
| Dithionous acid | H2S2O4 | III | Dithionite, O2SSO22− | Not known. | |
| Polythionic acids | H2SxO6 | 0 (for the bridging S atoms), V (for the terminal central S atoms) | Polythionates, O3S(Sx-2)SO32−. Example trithionate, tetrathionate, pentathionate, hexathionate, heptathionate, octathionate, nonathionate, decathionate, undecathionate, dodecathionate, tridecathionate and tetradecathionate. | Examples known with x= 3, 4, 5, 6, 7, 8, 10, 12, 14. |