Electron Spin Resonance Studies of the Addition of Nitrogen Dioxide to Alkenes

Abstract

The addition of solutions of nitrogen dioxide to alkenes has been studied under various reaction conditions. Solutions of low concentration of nitrogen dioxide react with alkyl-substituted alkenes to produce dialkyl nitroxides, and react with a, β-unsaturated carbonyl compounds to produce iminoxy radicals. Most of these reaction mixtures when kept unexposed to air, and light over a period of time showed the decay of nitroxides, and iminoxy radicals, and the formation of acyl nitroxide radicals. Other reaction conditions, for example upon exposure to oxygen, or raising reaction temperature to 100° are found to accelerate the rates of both the formation of acyl nitroxide radicals, and the disappearance of nitroxides, and iminoxy radicals. The reactions of solutions of high concentration of nitrogen dioxide with alkenes are found to produce mixtures of nitroxides, or iminoxy radicals, together with acyl nitroxide radicals. The reactions of alkenes with nitric oxide in the presence of a trace of nitrogen dioxide provide the information that vic-nitronitrites may have major role in continuing the reactions of addition of nitrogen dioxide to alkenes to produce acyl nitroxide radicals, and other reaction products. The effect of substituents of alkenes in deciding the radical products, and the reaction mechanisms are discussed. Finally, the existence of β-nitroalkyl radicals which are initial radicals formed from addition of nitrogen dioxide to alkenes is confirmed by employing nitrosobenzene as spin trap.