Orthocarbonic acid

Orthocarbonic acid or methanetetrol is the name given to a hypothetical 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 CO₄⁴⁻ (orthocarbonate), and is therefore considered an oxoacid of carbon.

Orthocarbonic acid is highly unstable, decomposing spontaneously into carbonic acid monohydrate:

Orthocarbonic acid is one of the group of carboxylic ortho acids that have the general structure of RC(OH)₃.The term ortho acid is also used to refer to the most hydroxylated acid in a set of oxoacids.

Orthocarbonate anions

By loss of one through 4 protons, orthocarbonic acid could yield four anions: H₃CO₄⁻, H₂CO₄²⁻, HCO₄³⁻, and CO₄⁴⁻.

As of 2002, salts of these anions had yet to be observed. However, theoretical studies suggest that Na₄CO₄ might be stable.

Orthocarbonate esters