Phenylglyoxylic acid is the organic compound with the formula C6H5C(O)CO2H. The conjugate base, known as benzoylformate 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.
Phenylglyoxylic acid can be synthesized by oxidation of mandelic acid with potassium permanganate. An alternative synthesis involves hydrolysis of benzoyl cyanide.

Appearance and properties: light yellow solid

Density: 1.38

Boiling point: 84 °C0.1 mm Hg

Melting point: 62-65 °C(lit.)

Flash point: 147-151°C/12mm

Refractive index: 1.568

Stability: Stable at room temperature in closed containers under normal storage and handling conditions.

Storage conditions: Keep container closed when not in use. Store in a tightly closed container. Store in a cool, dry,  well-ventilated area away from incompatible substances.

Production method

It is obtained by hydrolysis of benzoyl cyanide with concentrated hydrochloric acid.

Use

Organic synthesis.