Sulfur oxoacids are chemical compounds that contain sulfur, oxygen, and hydrogen. The best known and most important industrially used is sulfuric acid. Sulfur has several 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:
| Acid | Formula | Formal oxidation number | Structure | Related anions | Notes | |
|---|---|---|---|---|---|---|
| Sulfuric acid | H2SO4 | +6 | Sulfate, and hydrogen sulfate commonly known as bisulfate, | Best known and industrially significant. | ||
| Polysulfuric acids including disulfuric acid (pyrosulfuric acid) | H2SO4·nSO3 | +6 | Disulfate (commonly known as pyrosulfate), and trisulfate, | Pure disulfuric acid melts at 36 °C. Present in fuming sulfuric acid, oleum. Examples known for n = 1 and n = 2. | ||
| Peroxymonosulfuric acid | H2SO5 | +6 | Peroxomonosulfate, | "Caro's acid", a solid melting at 45 °C | ||
| Peroxydisulfuric acid | H2S2O8 | +6 | Peroxydisulfate, | "Marshall's acid", a solid melting at 65 °C. | ||
| Dithionic acid | H2S2O6 | +5 | Dithionate, | Not isolated in pure form, only concentrated solutions have been prepared | ||
| Thiosulfuric acid | H2S2O3 | 0 (for the terminal sulfur), +4 (for the central atom) | Thiosulfate, Hydrogenthiosulfate (ammonium salt prepared in anhydrous methanol at −80 °C[1]) | Aqueous solutions decompose. | ||
| Disulfurous acid or pyrosulfurous acid | H2S2O5 | +5 (of the sulfur atom bonded to 3 oxygen atoms), +3 (of other sulfur atom) | Disulfite commonly known as metabisulfite, | Not known. | ||
| Sulfurous acid | H2SO3 | +4 | Bisulfite, and sulfite, | Not known. | ||
| Dithionous acid | H2S2O4 | +3 | Dithionite, | Not known. | ||
| Sulfoxylic acid | H2SO2 | +2 | Sulfoxylate, | Free acid not known | ||
| Polythionic acid | H2SxO6 | 0 (for the bridging S atoms), +5 (for the terminal central S atoms) | Polythionates, . 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. | ||
| Thiosulfurous acid | H2S2O2 | −1 (for the exterior sulfur atom), +3 (for the central atom) | Thiosulfites | Not known | ||
| Dihydroxydisulfane | H2S2O2 | +1 | Acid known |