Photolytic determination of SO4- rate constants

Based on a photolytic system p-nitrosodimethylaniline (RNO)S2O82−H2O, a method for the determination of SO4- rate constants is described. SO4- radicals produced from S2O82− in u.v. photolysis bleach the RNO chromophoric group, as determined by the change of its absorption at 440 nm. By introducing another scavenger into the system, a competition for SO4- radicals ensues. In certain cases (methanol, ethanol, benzene, etc.) simple competition kinetics are obeyed from which relative rate constants can be deduced. The results presented in this paper show that SO4- radicals react generally slower than OH radicals.