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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The acenaphthene oxidation with molecular oxygen in the presence of Nhydroxyphthalimide (NHPI) has been investigated. It is shown that the main oxidation product is acenaphthene hydroperoxide. The phthalimide-N-oxyl (PINO) radical has been generated in situ from its hydroxyimide parent, NHPI, by oxidation with iodobenzenediacetate. The rate constant of H-abstraction (k H ) from acenaphthene by PINO has been determined spectroscopically in acetonitrile. The kinetic isotope effect and the activation parameters have also been measured. On the basis of the results of our studies and available published literature data, a plausible mechanism for the oxidation process of acenaphthene with dioxygen catalyzed by NHPI was discussed. C 2013 Wiley Periodicals, Inc. Int J Chem Kinet 45: [515][516][517][518][519][520][521][522][523][524] 2013 Polycyclic aromatic hydrocarbons with secondary C-H bonds, for example, acenaphthenes (AcNph) are oxidized by using dioxygen to their corresponding oxygenated derivatives, naphthalic acid and naphthalic anhydride, which are used as intermediates for the synthesis of the important raw materials (such as esters, amides, and imides) for the manufacture of dyes, pharmaceuticals, pesticides, plastics, fibers, curing agents, plasticizers, pigments, fluorescent whiteners, and many other items [9]. Polynuclear hydrocarbons were oxidized during catalysis of NHPI [10], [11], but no literature report has been published on the efficient oxidation of acenaphthene except [10], where authors used the NHPI/anthraquinone system. In this paper, we have reported the kinetic study of the acenaphthene oxidation by molecular oxygen in the presence of NHPI, to better understand the mechanism of the NHPI-catalyzed aerobic oxidation of alkylbenzenes. We have described