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 sulfuric 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 disulfuric Disulfate (commonly known as pyrosulfate), S
2
O2−
7
and trisulfate, S
3
O2−
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 peroxymonosulfuric Peroxomonosulfate, OOSO2−
3
"Caro's acid", a solid melting at 45 °C
Peroxydisulfuric acid H2S2O8 +6 peroxydisulfuric Peroxydisulfate, O
3
SOOSO2−
3
"Marshall's acid", a solid melting at 65 °C.
Dithionic acid H2S2O6 +5 dithionic Dithionate, O
3
SSO2−
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) thiosulfuric Thiosulfate, S
2
O2−
3

Hydrogenthiosulfate HS
2
O
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) disulfurous Disulfite commonly known as metabisulfite, S
2
O2−
5
Not known.
Sulfurous acid H2SO3 +4 sulfurous Bisulfite, HSO
3
and sulfite, SO2−
3
Not known.
Dithionous acid H2S2O4 +3 dithionous Dithionite, O
2
SSO2−
2
Not known.
Sulfoxylic acid H2SO2 +2 sulfoxylic Sulfoxylate, SO2−
2
Free acid not known
Polythionic acid H2SxO6 0 (for the bridging S atoms), +5 (for the terminal central S atoms) polythionic Polythionates, O
3
S(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 hypodithionous Acid known

See also

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References

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  1. ^ Raman spectroscopic discovery of the hydrogenthiosulphate anion, HSSO
    3
    , in solid NH4HS2O3
    Steudel Rr.; Prenzel A Zeitschrift für Naturforschung 1989,44, 12, 1499-1502
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