Theoretical Investigation of the Action Mechanisms of N,N-Di-Alkylated Diarylamine Antioxidants.

In this work, a density functional theory-based method was used to study the antioxidant properties and some reaction mechanism involved in the free radical-scavenging reactions of eight N,N-dialkylaminated diarylamines. The analyzed properties are the bond dissociation enthalpies of NH bond, electron transfer enthalpies, ionization potentials, proton affinities and proton dissociation enthalpies. The reaction mechanisms are hydrogen atom transfer, single electron transfer–proton transfer and sequential proton loss electron transfer. Computations were performed in two different solvents: water, and chlorobenzene. The aim of the work was to establish the effect of the progressive addition of nitrogen atoms into the diarylamines aryl rings on the thermodynamic parameters above mentioned, to individuate the preferred action mechanism of these compounds and the influence of media of different polarities. Results we have obtained indicate that the hydrogen atom transfer or more precisely the proton-coupled electron transfer from antioxidant to a particular free radical that was chosen as target, is the most probable action mechanism, that structural change made including nitrogen atoms into aryl rings does not give benefits nor from thermodynamic neither from kinetic point of view and that polarity of solvent has no significant influence.