Photoreaction of Valerophenone in Aqueous Solution

Abstract

Kinetics and products of the photoreaction of the phenyl ketone valerophenone were investigated as a function of temperature, pH, and wavelength in aqueous solution. Under these conditions (<10-4 M), the photoreactions are pseudo-first-order with respect to valerophenone concentration. Type II quantum yields for photoreaction were close to unity throughout the 290−330 nm spectral region and in the temperature range from 10 to 40 °C. The quantum yields for the photoproducts were 0.65 ± 0.04 for cleavage to acetophenone and propene and an overall yield of 0.32 ± 0.03 for cyclization to two cyclobutanols at 20 °C. A small amount of 1-phenylcyclopentanol (∼2% yield) also was formed. These photoreactions were quenchable by additions of the triplet quenchers sorbic alcohol or sorbic acid, and Stern−Volmer plots were linear up to at least 80% quenching of the photoreactions. On the basis of quenching studies with steady-state irradiations, the triplet lifetime of valerophenone at 20 °C was estimated to be 52 ns,...