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Esr spin trapping study of the radicals produced in nitrogen oxide olefin reactions a mechanism for the production of the apparently long lived radicals in gas phase cigarette smoke

, : Esr spin trapping study of the radicals produced in nitrogen oxide olefin reactions a mechanism for the production of the apparently long lived radicals in gas phase cigarette smoke. Journal of the American Chemical Society 106(18): 5073-5087

Gas-phase cigarette smoke contains high concentrations of both oxygen- and carbon-centered free radicals. These radicals were detected using several variations of the ESR spin-trapping technique, including the use of spin traps in the solid state, to show that the radicals are trapped directly from the gas phase. These gas-phase radicals can still be trapped from gas-phase smoke that is more than 5 min old, a result that is clearly inconsistent with the highly reactive nature of oxygen- and carbon-centered radicals. To rationalize this apparent paradox, it is hypothesized that free radicals are continuously produced and destroyed in cigarette smoke and exist in a steady state. One mechanism by which radicals can be formed involves the slow oxidation of the relatively unreactive nitric oxide (which acts as a radical reservoir) to the much more reactive nitrogen dioxide. Nitrogen dioxide can then react with a number of the species that are present in smoke to produce the radicals detected. As a model, the reactions of NO/air mixtures with unsaturated hydrocarbons were studied. Isoprene is one of the most abundant species in smoke and is known to be very reactive toward NO2; therefore, the nature of the radicals that can be spin trapped from gaseous mixtures of NO, isoprene and air were studied. The NO/air/isoprene model system gives essentially the same types of radicals (oxygen and carbon centered) as does cigarette smoke. The gas-phase reaction of NO2 with several small olefins and 1,3-butadiene were also studied and evidence was found for peroxyl radical intermediates. In solution, NO2 reacts with isoprene much faster than it does with the spin-trap phenyl-tert-butylnitrone (PBN). NO2 oxidizes PBN to benzoyl tert-butyl nitroxide, and a mechanism is proposed for this reaction.


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