Hydrogenoxalate

Hydrogenoxalate, also known as bioxalate or the hydrogen oxalate ion, is an anion with the chemical formula HC2O4-. It is formed when oxalic acid (H2C2O4) loses one of its acidic protons. Oxalic acid is a dicarboxylic acid, meaning it has two carboxyl groups, each capable of donating a proton. In aqueous solution, oxalic acid exists in equilibrium with its conjugate bases, the hydrogenoxalate ion and the oxalate ion (C2O4^2-). The dissociation of oxalic acid into hydrogenoxalate is the first step: H2C2O4 <=> H+ + HC2O4-. The hydrogenoxalate ion can then further dissociate to form the oxalate ion and another proton: HC2O4- <=> H+ + C2O4^2-. The relative amounts of these species in solution depend on the pH.

Hydrogenoxalate is an amphoteric species, meaning it can act as both an acid and a base. As an acid, it can donate a proton to form the oxalate ion. As a base, it can accept a proton to reform oxalic acid. This property contributes to the buffering capacity of solutions containing oxalic acid and its salts. Hydrogenoxalate is found in various chemical compounds, often as a salt with a metal cation. For example, potassium hydrogenoxalate (KH(C2O4)) is a common laboratory reagent. The presence of hydrogenoxalate can be significant in biological systems due to oxalic acid's role in metabolism and its presence in certain foods. It can also be relevant in industrial processes involving oxalic acid.