20819-55-0Relevant articles and documents
Critical phenomena in ethylbenzene oxidation in acetic acid solution at high cobalt(II) concentrations
Gavrichkov,Zakharov
, p. 1878 - 1882 (2005)
Critical phenomena in ethylbenzene oxidation in an acetic acid solution at high cobalt(III) concentrations (from 0.01 to 0.2 mol L-1) were studied at 60-90 °C by the gasometric (O2 absorption), spectrophotometric (CoIII accumulation), and chemiluminescence (relative concentration of radical RO2?) methods. These phenomena are as follows: (1) increase in the oxidation rate above the theoretical limiting rate of radical autooxidation (k3 2[RH]2/2k6); (2) achievement of a maximum and a sharp decrease in the oxidation rate and concentration of radical RO 2? with the further increase in the CoII concentration (existence of critical concentrations). The oxidation rate increases due to the reaction RO2? + CoII + H+ → → ROOH + CoIII, while the inhibition effect is caused by the decay of RO2? radical involving two cobalt(II) atoms: RO2? + 2 Co II → R'CO + CoIII + CoII (k(70 °C) ≈ 300 L2mol-2s-1). The detailed scheme (through the formation of the complex RO2?Co II) describing the conjugation of these reactions was proposed.
EPR investigation of persistent radicals produced from the photolysis of dibenzyl ketones adsorbed on ZSM-5 zeolites
Turro, Nicholas J.,Lei, Xue-Gong,Jockusch, Steffen,Li, Wei,Liu, Zhiqiang,Abrams, Lloyd,Ottaviani, M. Francesca
, p. 2606 - 2618 (2007/10/03)
Photolysis of ketones (1, 1-oMe, 2, 2-oMe, 3, and 4) adsorbed on ZSM-5 zeolites produces persistent carbon-centered radicals that can be readily observed by conventional steady-state EPR spectroscopy. The radicals are persistent for time periods of seconds to many hours depending on the supramolecular structure of the initial radical@zeolite complex and the diffusion and reaction dynamics of radicals produced by photolysis. The structures of the persistent radicals responsible for the observed EPR spectra are determined by a combination of alternate methods of generation of the same radical, by deuterium substitution, and by spectral simulation. A clear requirement for persistence is that the radicals produced by photolysis must either separate and diffuse from the external to the internal surface or be generated within the internal surface and separate and diffuse apart. The persistence of radicals located on the internal surface is the result of inhibition of radical-radical reactions. Radicals that are produced on the external surface and whose molecular structure prevents diffusion into the internal surface are transient because radical-radical reactions occur rapidly on the external surface. The reactions of the persistent radicals with oxygen and nitric oxide were directly studied in situ by EPR analysis. In the case of reaction with oxygen, persistent peroxy radicals are formed in high yield. The addition of nitric oxide scavenges persistent radicals and leads initially to a diamagnetic nitroso compound, which is transformed into a persistent nitroxide radical by further photolysis. The influence of variation of radical structure on transience/persistence is discussed and correlated with supramolecular structure and reactivity of the radicals and their parent ketones.
