Phenylglyoxylic acid is the organic compound with the formula C<sub>6</sub>H<sub>5</sub>C(O)CO<sub>2</sub>H. The conjugate base, known as benzoylformate, is the substrate of benzoylformate decarboxylase, a thiamine diphosphate-dependent enzyme:
It is a colourless solid with a melting point of 64âÂÂ66 ðC and is moderately acidic (pK<sub>a</sub> = 2.15).
Phenylglyoxylic acid can be synthesized by oxidation of mandelic acid with potassium permanganate. An alternative synthesis involves hydrolysis of benzoyl cyanide.