Dihydroxymethylidene

Dihydroxymethylidene or carbonous acid is a chemical compound with formula C(OH)₂. It is an unstable tautomer of formic acid. There is no evidence that this compound exists in solution, but the molecule has been detected in the gas phase.^[1] Many related carbenes are known, although they are often transient.^[2]

Dihydroxymethylidene

Structural formula of dihydroxymethylidene
Ball and stick model of dihydroxymethylidene Ball and stick model of dihydroxymethylidene   Carbon, C   Hydrogen, H   Oxygen, O
Names
IUPAC name Carbon(II) hydroxide Carbon dihydroxide Carbonous hydroxide
Preferred IUPAC name Dihydroxymethylidene
Other names Carbonic(II) acid Carbonous acid Dihydroxycarbene Dihydroxymethylene Dihydroxycarbon(2•)
Identifiers
CAS Number	71946-83-3 Y
3D model (JSmol)	Interactive image
ChemSpider	11646598 Y
MeSH	Dihydroxycarbene
PubChem CID	191992
CompTox Dashboard (EPA)	DTXSID70222232
InChI InChI=1S/CH2O2/c2-1-3/h2-3H Y Key: VZOMUUKAVRPMBY-UHFFFAOYSA-N Y
SMILES O[C]O
Properties
Chemical formula	C(OH)2
Molar mass	46.025 g·mol−1
Related compounds
Related compounds	Tin(II) hydroxide Lead(II) hydroxide Formic acid Orthocarbonic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Production and properties

Dihydroxymethylidene is produced in the gas phase by high vacuum flash vacuum pyrolysis of oxalic acid:

H₂C₂O₄ → C(OH)₂ + CO₂

The species is a bent molecule with an O−C−O angle of 105.6° for the C_2v all-trans rotamer. Although stable at 10 K, at higher temperatures it isomerizes to formic acid.

The double ionized ion, CO2−2, is known as the carbonite ion.