Disulfurous acid

Disulfurous acid, metabisulfurous acid or pyrosulfurous acid is an oxoacid of sulfur with the formula H₂S₂O₅. Its structure is HO−S(=O)₂−S(=O)−OH. The salts of disulfurous acid are called disulfites or metabisulfites. Disulfurous acid is, like sulfurous acid (H₂SO₃), a phantom acid, which does not exist in the free state.^[2] In contrast to disulfate (S₂O2−7), disulfite has two directly connected sulfur atoms. The oxidation state of the sulfur atom bonded to three oxygen atoms is +5 and its valence is 6, while that of the other sulfur is +3 and 4 respectively.

Disulfurous acid ¹H NMR spectrum.

Disulfurous acid

Names
IUPAC name disulfurous acid[1]
Other names pyrosulfurous acid
Identifiers
CAS Number	33669-61-3 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:29252 Y
ChemSpider	26062 Y
PubChem CID	28020
CompTox Dashboard (EPA)	DTXSID40274768
InChI InChI=1S/H2O5S2/c1-6(2)7(3,4)5/h(H,1,2)(H,3,4,5) Y Key: WBZKQQHYRPRKNJ-UHFFFAOYSA-N Y InChI=1S/H2O5S2/c1-6(2)7(3,4)5/h(H,1,2)(H,3,4,5)
SMILES O=S(=O)(O)S(=O)O
Properties
Chemical formula	H2S2O5
Molar mass	146.13 g·mol−1
Conjugate base	Disulfite
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