Studies of the Anodic Oxidation of 1,4-Diazabicyclo[2.2.2]octane. Reactions of the Radical Cation

Abstract

The title compound (1) was studied at platinum and gold electrodes in acetonitrile. A reversible oxidation peak occurs at +0.30 V vs the standard potential for ferrocenium ion/ferrocene. This process is followed by a second irreversible anodic peak that is due to the oxidation of the initially formed radical cation to the dication. The principal ultimate product of the first oxidation, the conjugate acid of 1, is also oxidized over the range of potentials corresponding to the second anodic peak. The rate of disappearance of the radical cation of 1 has been determined by cyclic voltammetry. The results are best interpreted in terms of parallel pseudo-first-order decay (k₁ = 0.6 s^-1) and second-order reactions. The first of these second-order reactions is either proton transfer from the radical cation to neutral 1 or hydrogen atom abstraction by the radical cation from neutral 1, reactions that give the same products (k₂ = 100 M^-1 s^-1) and are kinetically indistinguishable. The other second-order reaction is the hydrogen-atom-transfer disproportionation of the radical cation giving the conjugate acid of 1 and the immonium ion (k₃ = 100 M^-1 s^-1). Both second-order processes must be included to account for the results. The present results are thought to be the first experimental evidence for the occurrence of hydrogen-atom-transfer disproportionation of amine radical cations.