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 radicalsʼ 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.

Nitroxyl radicals are widely used in chemistry, materials sciences, and biology. Imide-N-oxyl radicals are subclass of unique nitroxyl radicals that proved to be useful catalysts and mediators of selective oxidation and CH-functionalization. An efficient metal-free method was developed for the generation of imide-N-oxyl radicals from N-hydroxyimides at room temperature by the reaction with (diacetoxyiodo)benzene. The method allows for the production of high concentrations of free radicals and provides high resolution of their EPR spectra exhibiting the superhyperfine structure from benzene ring protons distant from the radical center. An analysis of the spectra shows that, regardless of the electronic effects of the substituents in the benzene ring, the superhyperfine coupling constant of an unpaired electron with the distant protons at positions 4 and 5 of the aromatic system is substantially greater than that with the protons at positions 3 and 6 that are closer to the N-oxyl radical center. This is indicative of an unusual character of the spin density distribution of the unpaired electron in substituted phthalimide-N-oxyl radicals. Understanding of the nature of the electron density distribution in imide-N-oxyl radicals may be useful for the development of commercial mediators of oxidation based on N-hydroxyimides.

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A series of substituted N-hydroxyphthalimides (NHPI) with electronwithdrawing groups (4-C(O)OH, C=O) and an electron-donating group (4-C(CH 3 ) 3 ) were investigated as catalysts for cumene oxidation. The initial reaction rates, measured by the oxygen uptake, conversion of substrate and yield of oxidation products are discussed. The catalytic activity of oxidation rate enhancement of NHPI derivatives in acetonitrile follows the order 4-tert-BuNHPI [ NHPI [ 4-carb-NHPI [ NDHPI [ NAPI. NMPT, trityl-NPI and NHPLI are inactive.