The reactivity of antioxidants with peroxy and alkoxy radicals in the presence of transition metals. II. Radical processes in multicomponent antioxidant systems

Abstract

In nonpolar solvents the mechanism of bimolecular substitution reactions between t-butyl-peroxy and t-butoxy radicals with different phenols and diarylamines was quantitatively studied by means of electron paramagnetic resonance (EPR) spectroscopy in the temperature range of +70 to −140°C. The selective reactivity, in the ligand field, of cobalt complex-bonded radicals [Co] BuO2, [Co] BuO., and the free continuously generated noncomplex-bonded BuO2 and BuO radicals to antioxidants are compared. The antioxidant ArH forms with cobalt (II)-acetylacetonate a complex [Co(acac)2]2 [Arh]n = 1-4 and prevents the subsequent reactions of the primarily generated RO. radicals with the transition metal (RO. + Co(II) RO′ + Co(III)) and with the excess of hydroperoxides (RO. + ROOH ROH + RO2). The concentration and the ratio of RO. and RO.2 radicals in a chain oxidation process in the presence of phenyl β- or α-napthylamine (Ar1HNAr2) can be determined from the different EPR spectra of fixed [Co] [Ar1 NAr2]. and free stable nitroxy (Ar1HNAr2) radicals.