Phenylglyoxalic acid is the organic compound with the formula C6H5C(O)CO2H. The conjugate base, known as benzoyl formate is the substrate of benzoylformate decarboxylase, a thiamine diphosphate-dependent enzyme:
- benzoylformate + H+ benzaldehyde + CO2
It is a colourless solid, m.p. 64–66 °C.
Phenylglyoxalic acid can be synthetized by oxidation of mandelic acid with potassium permanganate. An alternative synthesis involves hydrolysis of benzoyl cyanide.