Dithionous acid

Dithionous acid is a sulfur oxoacid with the chemical formula H2S2O4. It is unstable in pure form, but its salts, known as dithionites, are stable.

Dithionous acid
Names
IUPAC name
Dithionous acid
Other names
Hydrosulfurous acid; Hyposulfurous acid
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
  • InChI=1S/H2O4S2/c1-5(2)6(3)4/h(H,1,2)(H,3,4) Y
    Key: GRWZHXKQBITJKP-UHFFFAOYSA-N Y
  • InChI=1/H2O4S2/c1-5(2)6(3)4/h(H,1,2)(H,3,4)
    Key: GRWZHXKQBITJKP-UHFFFAOYAX
  • O=S(O)S(=O)O
Properties
H2S2O4
Molar mass 130.144 g/mol
Acidity (pKa) 0.35, 2.45
Conjugate base Dithionite
Related compounds
Related compounds
 Oxalic acid
Sodium dithionite
Potassium dithionite
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y verify (what is YN ?)
Infobox references

It was initially assumed that the C2 symmetric structure HOS(=O)-S(=O)OH is the most stable among molecules with the formula H
2S
2O
4 using ab initio calculations. The reason for this is the existence of intermolecular hydrogen bonds. It is now known that dithionous acid spontaneously decomposes to SO2 and S(OH)2.

Sodium dithionite is a white powder used as a reductant and a bleaching agent. It is also used to reduce the nitro group to an amino group in organic reactions.

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