Kinetic studies on free radical reactions : I. Reaction of DPPH with free radicals formed by the photolysis of azo-bis-isobutyronitrile

Abstract

The formation of free radicals produced by the photo-dissociation of azo-bis-isobutyronitrile (AIBN) in a benzene solution was investigated by the ultra-violet spectrophotometric and ESR methods using DPPH as radical scavenger. From the change of the ultra-violet and ESR spectra of DPPH in the course of irradiation, it was found that the influence of dissolved oxygen on the free radical reaction of AIBN is significant. The peroxy free radicals formed by the reaction of free radicals with dissolved oxygen react with DPPH. The intermediate found by ESR is rather stable and consists of two kinds of free radicals. The results obtained by the ESR method show that both free radicals contain an unpaired electron mainly localized on N^14 nucleus. From the view-point of kinetics, the reaction mechanism of DPPH with the free radicals formed in the course of irradiation of AIBN is discussed both in the presence and absence of dissolved oxygen.