Sulfur oxoacid

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:

• tetrahedral sulfur when coordinated to oxygen
• terminal and bridging oxygen atoms
• terminal peroxo groups
• terminal S=S
• chains of (−S−)_n

Acid	Formula	Formal oxidation number	Structure	Related anions	Notes
Sulfuric acid	H2SO4	+6		Sulfate, SO2− 4 and hydrogen sulfate commonly known as bisulfate, HSO− 4	Best known and industrially significant.
Polysulfuric acids including disulfuric acid (pyrosulfuric acid)	H2SO4·nSO3	+6		Disulfate (commonly known as pyrosulfate), S 2O2− 7 and trisulfate, S 3O2− 10	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, OOSO2− 3	"Caro's acid", a solid melting at 45 °C
Peroxydisulfuric acid	H2S2O8	+6		Peroxydisulfate, O 3SOOSO2− 3	"Marshall's acid", a solid melting at 65 °C.
Dithionic acid	H2S2O6	+5		Dithionate, O 3SSO2− 3	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, S 2O2− 3 Hydrogenthiosulfate HS 2O− 3 (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, S 2O2− 5	Not known.
Sulfurous acid	H2SO3	+4		Bisulfite, HSO− 3 and sulfite, SO2− 3	Not known.
Dithionous acid	H2S2O4	+3		Dithionite, O 2SSO2− 2	Not known.
Sulfoxylic acid	H2SO2	+2		Sulfoxylate, SO2− 2	Free acid not known
Polythionic acid	H2SxO6	0 (for the bridging S atoms), +5 (for the terminal central S atoms)		Polythionates, O 3S(S x−2)SO2− 3. 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

See also

• Chlorosulfuric acid
• Fluorosulfuric acid
• Nitrosylsulfuric acid
• Peroxydisulfuric acid
• Sulfinic acids
• Sulfonic acids