Dithionous acid

Dithionous acid

Names
IUPAC name Dithionous acid
Other names Hydrosulfurous acid; Hyposulfurous acid
Identifiers
CAS Number	15959-26-9 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:29253 Y
ChemSpider	22898 Y
PubChem CID	24490
CompTox Dashboard (EPA)	DTXSID70274771
InChI 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
SMILES O=S(O)S(=O)O
Properties
Chemical formula	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

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.

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.