Kinetics of N-oxyl Radicals' Decay

N-oxyl radicals of various structures were generated by oxidation of corresponding N-hydroxy compounds with iodobenzene diacetate, [bis(trifluoroacetoxy)]iodobenzene, and ammonium cerium(IV) nitrate in acetonitrile. The decay rate of N-oxyl radicals follows first-order kinetics and depends on the structure of N-oxyl radicals, reaction conditions, and the nature of the solvent and oxidant. The values of the self-decay constants change within 1.4 × 10^-4 s^-1 for the 3,4,5,6-tetraphenylphthalimide-N-oxyl radical to 1.4 × 10^-2 s^-1 for the 1-benzotriazole-N-oxyl radical. It was shown that the rate constants of the phthalimide-N-oxyl radicals' self-decay with different electron-withdrawing or -donor substituents in the benzene ring are higher than that of the unsubstituted phthalimide-N-oxyl radical in most cases. The solvent effect on the process of phthalimide-N-oxyl radical self-decomposition was investigated. The dependence of the rate constants on the Gutmann donor numbers was shown.