Kinetic study by use of electron spin resonance of the autoxidation of NN-dibenzylhydroxylamine

Abstract

The autoxidation of NN-dibenzylhydroxylamine (DBH) in aqueous alcoholic alkali has been studied kinetically by e.s.r. measurement of the free dibenzylnitroxide radical (PhCH₂)₂N–O·(I) which is formed during the reaction. The rates of formation of the end-products, N-benzylisobenzaldoxime, PhCH:[graphic omitted](CH₂Ph)–Ō(II) and titratable peroxides, have also been estimated. When this autoxidation occurs in the absence of catalysts the initial rate of formation of radical (I) seems to depend on the formation of the double anion of DBH, but it can be copper catalysed and then appears to involve only the mono-anion.

The maximum concentration of radicals (I) is attained in ca. 1 min. from admixture; both for the catalysed and uncatalysed reactions its value is approximately proportional to [DBH]^½. Thus, it is considered that radical destruction occurs by a bimolecular (radical)+(radical) interaction which is faster than the rate of radical formation, the latter being of the first order with respect to [DBH].

However, the rate dependence in oxygen concentration and also the product analyses both indicate that reactions involving (I) and free oxygen which give short-lived peroxy-radicals are also involved in the autoxidation.