Mesoxalic acid

Mesoxalic acid, also called oxomalonic acid or ketomalonic acid, is a natural organic compound found in beet molasses. It can be obtained synthetically by hydrolysis of alloxan with baryta water, by warming caffuric acid with lead acetate solution, or from glycerin diacetate and concentrated nitric acid in the cold. It crystallizes in deliquescent prisms and melts with partial decomposition at 119–120 °C. It behaves as a ketonic acid, being reduced in aqueous solution by sodium amalgam to tartronic acid, and also combining with phenylhydrazine and hydroxylamine. It reduces ammoniacal silver solutions. When heated with urea to 100 °C, it forms allantoin. By continued boiling of its aqueous solution it is decomposed into carbon dioxide and glyoxylic acid.

Mesoxalic acid readily absorbs and reacts with water to form the monohydrate known as dihydroxymalonic acid or mesoxalic acid hydrate which is a white solid that melts at 113-121 °C. Dihydroxymalonic acid is unusual in containing a stable geminal hydroxy groups.