Phenylglyoxal
Phenylglyoxal is the organic compound with the formula C6H5CCH. It contains both an aldehyde and a ketone functional group. 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. It has also been used to attach chemical payload to the amino acid citrulline and to peptides/proteins.
Properties
Like some other aldehydes, phenylglyoxal polymerizes upon standing, as indicated by solidification of the liquid. Upon heating, this polymer "cracks" to give back the yellow aldehyde. Dissolution of phenylglyoxal in water gives crystals of the hydrate:Upon heating, the hydrate loses water and regenerates the anhydrous liquid.
Preparation
Phenylglyoxal was first prepared by thermal decomposition of the sulfite derivative of the oxime:It may also be prepared from methyl benzoate by a reaction with potassium dimsyl to give an intermediate β-ketosulfoxide, which undergoes a Pummerer-type rearrangement, followed by oxidation by with copper(II) acetate. Alternatively, it can also be prepared by oxidation of acetophenone with selenium dioxide.