Radical reactions in the coordination field of transition metals. VII—H‐transfer between phenolic and aryl‐aminic H‐donors and their radicals

Abstract

AbstractAn ESR method for studying the mechanism of H‐transfer reactions between H‐donors of different reactivity (A1H, A2H…) and their free radicals (A1; A2.…) in non‐polar solvents at ambient temperature is presented. The new technique is based on a pulsed initiation of various secondary phenoxy or nitroxy radicals in binary mixtures of hindered phenols, unhindered phenols, partially hindered thiobisphenols and diphenylamine, employing a high concentration of free RO2. and coordinated (CoIII)RO2. tert‐butyl peroxy radicals generated in the redox‐reaction of Co(acac)2 with tert‐butyl hydroperoxide. The consecutive H‐transfer reactions proceed to equilibrium until the most stable radicals are formed. In this way criteria are obtained for ranking the compared free and coordinated phenoxy radicals according to their relative stabilities. The secondarily generated phenoxy radicals from unhindered phenols after coordination to CoIII are stabilized and cannot take part in further H‐transfer reactions.