Orthocarbonic acid

Orthocarbonic acid
Names
	Preferred IUPAC name Methanetetrol
	Systematic IUPAC name Orthocarbonic acid
	Other names Carbon tetrahydroxide;
Identifiers
CAS Number	463-84-3 ;
3D model (JSmol)	Interactive image;
ChemSpider	7826887 ;
PubChem CID	9547954;
CompTox Dashboard (EPA)	DTXSID40429519 ;
	InChI InChI=1S/CH4O4/c2-1(3,4)5/h2-5H Key: RXCVUXLCNLVYIA-UHFFFAOYSA-N ;
	SMILES OC(O)(O)O;
Properties
Chemical formula	C(OH)4
Molar mass	80.039 g·mol−1
Related compounds
Other cations	Orthosilicic acid; Orthogermanic acid; Tin(IV) hydroxide; Lead(IV) hydroxide; Titanic acid; Zirconium(IV) hydroxide; Beryllic acid; Boric acid; Aluminic acid; Gallium(III) hydroxide; Indium(III) hydroxide; Thallium(III) hydroxide; Zinc hydroxide; Orthonitrate; Phosphorous acid; Telluric acid;
Related compounds	Tetramethoxymethane; Tetraethoxymethane; Tetrapropoxymethane; Tetraphenyl orthocarbonate; Orthoformic acid;
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Orthocarbonic acid (also known as methanetetrol) is a chemical compound with the chemical formula H₄CO₄ or C(OH)₄. Its molecular structure consists of a single carbon atom bonded to four hydroxyl groups. It would be therefore a fourfold alcohol. In theory, it could lose four protons to give the hypothetical oxocarbon anion orthocarbonate CO4−4, and is therefore considered an oxoacid of carbon.

Orthocarbonic acid is highly unstable and long held to be a hypothetical chemical compound. Calculations show that it decomposes into carbonic acid and water:

H₄CO₄ → H₂CO₃ + H₂O

However, orthocarbonic acid was first synthesized in 2025 from the electron-irradiation of a frozen mixture of water and carbon dioxide and identified by mass spectrometry.

Researchers predict that orthocarbonic acid is stable at high pressure; thus, it may form in the interior of the ice giant planets Uranus and Neptune, where water and methane are common.