{{chembox | Watchedfields = changed | verifiedrevid = 443847685 | Name = Glyoxylic acid | ImageFile_Ref = | ImageFile = Glyoxylic acid.png | ImageSize = 150px | ImageAlt = Skeletal formula of glyoxylic acid | ImageFile1 = Glyoxylic acid 3D spacefill.png | ImageSize1 = 160px | ImageAlt1 = Space-filling model of glyoxylic acid | PIN = Oxoacetic acid | SystematicName = Oxoethanoic acid | OtherNames = Glyoxylic acid2-Oxoacetic acidFormylformic acid |Section1= |Section2={{Chembox Properties | C=2 | H=2 | O=3 | MeltingPtC = 80 | MeltingPt_ref = <ref name=Merck>Merck Index, 11th Edition, 4394</ref> | BoilingPtC = 111 | Density = 1.384 g/mL | pKa = 3.18, 3.32 }} |Section4= }} Glyoxylic acid or oxoacetic acid is an organic compound. Together with acetic acid, glycolic acid, and oxalic acid, glyoxylic acid is one of the C2 carboxylic acids. It is a colourless solid that occurs naturally and is useful industrially. Structure and nomenclature Although the structure of glyoxylic acid is described as having an aldehyde functional group, the aldehyde is only a minor component of the form most prevalent in some situations. Instead, it often exists as a hydrate or a cyclic dimer. For example, in the presence of water, the carbonyl rapidly converts to a geminal diol (described as the "monohydrate"). The equilibrium constant (K) is 300 for the formation of dihydroxyacetic acid at room temperature: In solution, the monohydrate exists in equilibrium with a hemiacylal dimer form: In isolation, the aldehyde structure has as a major conformer a cyclic hydrogen-bonded structure with the aldehyde carbonyl in close proximity to the carboxyl hydrogen: The Henry's law constant of glyoxylic acid is KH = 1.09 × 104 × exp[(40.0 × 103/R) × (1/T − 1/298)]. Preparations The conjugate base of glyoxylic acid is known as glyoxylate and is the form that the compound exists in solution at neutral pH. Glyoxylate is the byproduct of the amidation process in biosynthesis of several amidated peptides. For the historical record, glyoxylic acid was prepared from oxalic acid electrosynthetically: in organic synthesis, lead dioxide cathodes were applied for preparing glyoxylic acid from oxalic acid in a sulfuric acid electrolyte. Hot nitric acid can oxidize glyoxal to glyoxylic; however this reaction is highly exothermic and prone to thermal runaway. In addition, oxalic acid is the main side product. Also, ozonolysis of maleic acid is effective. Biological role Glyoxylate is an intermediate of the glyoxylate cycle, which enables