Sulfoxylic acid

Sulfoxylic acid (H2SO2) (also known as hyposulfurous acid or sulfur dihydroxide) is an unstable oxoacid of sulfur in an intermediate oxidation state between hydrogen sulfide and dithionous acid. It consists of two hydroxy groups attached to a sulfur atom. Sulfoxylic acid contains sulfur in an oxidation state of +2. Sulfur monoxide (SO) can be considered as a theoretical anhydride for sulfoxylic acid, but it is not actually known to react with water.

Sulfoxylic acid
Names
Other names
hyposulfurous acid
sulfur dihydroxide
dihydroxidosulfur sulfanediol
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
1452
  • InChI=1S/H2O2S/c1-3-2/h1-2H
    Key: HRKQOINLCJTGBK-UHFFFAOYSA-N
  • OSO
Properties
S(OH)2
Molar mass 66.07 g·mol−1
Conjugate base Bisulfoxylate (chemical formula SO2H−)
Related compounds
Related isoelectronic
 trioxidane
trisulfane
Related compounds
 hydroxysulfonyl radical HOSO2
sulfinic acid
sulfenic acid HSOH
dihydroxydisulfane HOSSOH
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

The complementary base is the sulfoxylate anion SO2−
2 which is much more stable. In between these states is the HSO−
2 ion, also somewhat stable.

Sulfoxylate ions can be made by decomposing thiourea dioxide in an alkaline solution. To do this, thiourea dioxide first forms an amidine-sulfinic acid tautomer, H2NC(=NH)SO2H, which then breaks apart. Sulfoxylate reacts with formaldehyde to yield a hydroxymethanesulfinate called rongalite:

HSO−
2 + H2CO → HOCH
2SO−
2,

which is an important chemical for dyeing.

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