Phenylglyoxal

Phenylglyoxal is the chemical compound with the formula C6H5C(O)C(O)Hundefined. It contains both an aldehyde and a ketone functional groups. It is yellow liquid when anhydrous but readily forms a colorless crystalline hydrate. It has been used as a reagent to modify the amino acid arginine.

Properties
This aldehyde has interesting behavior that illustrate some properties of aldehydes. The yellow liquid solidifes with time, apparently due to oligomerization. Upon heating, this polymer "cracks" to give back the yellow liquid. Dissolution of phenylglyoxal in water gives crystals of the hydrate, C6H5C(O)CH(OH)2. Again by distillation, the anhydrous material is regenerated.

Preparation
It can be prepared from methyl benzoate by reaction with KCH2S(O)CH3 to give PhC(O)CH(SCH3)(OH), which is oxidized with copper(II) acetate. Alternatively, it can also be prepared by oxidation of acetophenone with selenium dioxide.