Bimolecular OH rate constants of organic compounds in solution. 1. Measurements in water using hydrogen peroxide as...

A method of measuring relative kOH rate constants in water is described. OH radicals are created by photolysis of H2O2, using a Hg high-pressure lamp. Test and reference substances are irradiated for several hours in dilute, aqueous solutions containing 0.1 to 1.0% H2O2. The relative rate constants are determined from the decay of test and reference substances as a function of time, as measured by chemical analysis. Using the known kOH of reference substances, absolute kOH data for test substances are obtained. The following rate constants at 298 K have been measured (liter mol-1 sec-1): kOH (isopropanol) = 2.7 x 10(9) (relative to kOH (methanol) = 8.46 x 10(9]; kOH (toluene) = 6.0 x 10(9); and kOH (p-xylene) = 4.5 x 10(9) (relative to kOH (benzene) = 7.8 x 10(9]. The stationary OH concentrations are on the order of 5 x 10(-14) mol/liter. The kinetics of H2O2 photolysis is discussed, including the estimation of OOH/O2- concentrations during irradiation.