Sulfur oxoacids

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 and bridging peroxo groups
• terminal S=S
• chains of (–S–)_n

Acid	Formula	Sulfur oxidation state	Structure	Related anions	Notes
Sulfuric acid	H2SO4	VI		Sulfate, SO42− and hydrogen sulfate commonly known as bisulfate	Best known and industrially significant
Disulfuric acid or pyrosulfuric acid	H2S2O7	VI		Disulfate commonly known as pyrosulfate, S2O72−	Pure form melts at 36 °C. Present in fuming sulfuric acid, oleum
Peroxymonosulfuric acid	H2SO5	VI	peroxymonosulfuric	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	dithionic	Dithionate, O3SSO32−	Not obtained pure, only concentrated solutions
Thiosulfuric acid	H2S2O3	IV		Thiosulfate, S2O32− Hydrogenthiosulfate HS2O3− (ammonium salt prepared in anhydrous methanol at −80 °C)	Aqueous solutions decompose.
Disulfurous acid	H2S2O5	IV		Disulfite commonly known as metabisulfite, S2O52−	Not known
Sulfurous acid	H2SO3	IV	sulfurous	Bisulfite, HSO3− and sulfite, SO32−	Not known
Dithionous acid	H2S2O4	III		Dithionite, O2SSO22−	Not known.
Polythionic acid	H2SxO6			Polythionate, O3S(Sx−2)SO32−. Example tetrathionate.	Examples known with x = 3, 4, 5, 6, 7, 8, 10, 12, 14.