Characterization of the hydroxyl radical in some photochemical reactions

Quantitative estimation of OH by measuring its reaction with benzene in the presence of oxygen to give phenol and hydroxymucondialdehyde (HMD) shows that in the photolysis of hydrogen peroxide at 2970 to 3650 A OH radicals account for all the primary decomposition. In the photolytic reduction of Fe/sup 3 +/ in water, the average quantum yield of OH for 2970 to 4358 A is approximately 0.02, of the same order of magnitude as the earlier estimate of the Fe/sup 2 +/ yield for 2537 A. The oxidation of benzene to phenol by Cu/sup 2 +/, in contrast, yields no HMD, and must be by oxygen uptake not involving an OH intermediate. Inner filter corrections are deduced for the accumulation of product interfering with light absorption.