Sulfur oxoacid

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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 sulfuric 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 disulfuric 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 peroxymonosulfuric Peroxymonosulfate, OOSO32− "Caro's acid", a solid melting at 45 °C
Peroxydisulfuric acid H2S2O8 VI peroxydisulfuric Peroxydisulfate, O3SOOSO32− "Marshall's acid", a solid melting at 65 °C.
Dithionic acid H2S2O6 V dithionic Dithionate, O3SSO32− Not isolated in pure form, only concentrated solutions have been prepared
Thiosulfuric acid H2S2O3 -II (for the terminal sulfur) , VI (for the central atom) thiosulfuric Thiosulfate, S2O32−
Hydrogenthiosulfate HS2O3 (ammonium salt prepared in anhydrous methanol at −80 °C[1])
Aqueous solutions decompose.
Disulfurous acid or pyrosulfurous acid H2S2O5 V (of the sulfur atom bonded to 3 oxygen atoms), III (of other sulfur atom) disulfurous Disulfite commonly known as metabisulfite, S2O52− Not known.
Sulfurous acid H2SO3 IV sulfurous Bisulfite, HSO3 and sulfite, SO32− Not known.
Dithionous acid H2S2O4 III dithionous Dithionite, O2SSO22− Not known.
Sulfoxylic acid H2SO2 II sulfoxylic Sulfoxylate, SO22− Free acid not known
Polythionic acid H2SxO6 0 (for the bridging S atoms), V (for the terminal central S atoms) polythionic 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.
Thiosulfurous acid H2S2O2 -I (for the exterior sulfur atom ) , III (for the central atom) Thioschweflige Säure.svg Thiosulfites Not known
Dihydroxydisulfane H2S2O2 I hypodithionous Acid known

See also[edit]


  1. ^ Raman spectroscopic discovery of the hydrogenthiosulphate anion, HSSO3, in solid NH4HS2O3 Steudel Rr.; Prenzel A Zeitschrift für Naturforschung 1989,44, 12, 1499-1502

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