PHOTOCHEMICAL-REACTIONS OF ALKYL PHENYLGLYOXYLATES

Three new photoproducts, ethyl O-benzoyl mandelate (5a), ethyl O-acety lmandelate (6a), and biphenyl triketone (7a) are isolated and identifi ed in the reactions of ethyl phenylglyoxylate (la) in benzene. Quantum yields and initial rate constants of product formation are shown to b e concentration dependent. For the formation of carbonyl product 3 at lower starting material concentrations (<0.01 M), quantum yields great er than 1 are observed. Variations in the quantum yields as a function of reaction time are due to the accumulation of alpha-hydroxyphenyl k etene (D). The relative reactivities of triplet excited states of phen ylglyoxylates 1 and phenyl ketones are compared. A mechanism involving both intramolecular gamma-H abstraction and intermolecular H abstract ion, which leads to radical chain reaction, is proposed. Rate constant s for intramolecular gamma-H abstraction (k(N)) and intermolecular H a bstraction (k(I)) of methyl phenylglyoxylate (Id) are measured.