The Photochemical Generation of Hydroxyl Radicals in the UV−vis/Ferrioxalate/H₂O₂ System

A reaction mechanism has been validated for the photochemical generation of hydroxyl radicals by ultraviolet or visible irradiation of oxalato iron(III) complexes (ferrioxalate) in the presence of hydrogen peroxide and 2-propanol as a model substrate. A kinetic simulation program incorporating the set of reactions was written to predict the behavior of this photochemical system. The program calculates the quantum yield of oxidation of 2-propanol used as a hydroxyl radical scavenger. The scavenger's oxidation product, 2-propanone, was analyzed by gas chromatog raphy after controlled exposure of the solution to a calibrated light source. The theoretical quantum yields of 2-propanol oxidation, Φ RH, agreed reasonably well with experimentally determined Φ RH values under a variety of initial reaction conditions. The value of Φ RH, which under appropriate conditions is directly proportional to the quantum yield for the generation of hydroxyl radicals, Φ OH, was considerably greater than unity in most cases (often Φ RH = 3.0−4.0), indicative of a chain mechanism involving iron cycling between the II and III oxidation states.