It readily loses two protons to yield the divalent anion C3O2−5, called mesoxalate, oxomalonate, or ketomalonate.

Mesoxalic acid can be obtained synthetically by hydrolysis of alloxan with baryta water,[2] by warming caffuric acid[3] with lead acetate solution,[2] or from glyceryl diacetate and concentrated nitric acid in ice-cold water.

The product can be obtained also by oxidation of tartronic acid[4] or glycerol.

[5] Since they are carried out in water, these procedures generally give the dihydroxy derivative.

It is also prepared by the oxidation of glycerol with the help of bismuth(III) nitrate.