Multiple reversible electrochemical reduction of aromatic hydrocarbons in liquid alkylamines

Abstract

The thermodynamic reduction potentials of many aromatic hydrocarbons have been known since the work of Hoytink. Their values obtained either by polarographic or by voltammetric techniques have been reported several times in the literature. Recently, the further reduction of these species to their respective dianions or higher charged states has attracted increasing interest. The reason is that their electronic and spectroscopic behavior offers new insights into the unconventional properties of charged /pi/-systems. Moreover, highly charged aromatics are interesting model compounds for the study of thermodynamics of charge storage. Although chemical reduction of such systems is now easily achieved by the reaction with alkali metals, e.g., in dry THF/sup 3/, electrochemical reduction experiments leading to stable higher redox states still demand skill and a sophisticated technique. Therefore, up to now, relatively few reduction potentials for the formation of aromatic diions have been given in the literature. Many are the result of irreversible processes due to protonation reactions induced by impurities in the solvent or by reactivity of the supporting electrolyte. In these cases the desired thermodynamic information cannot be derived from the measured data. Therefore, the authors will report here on an easily accessible technique of measuring thermodynamic redox potentials ofmore » dianions and even higher charged anions of aromatic hydrocarbons using methylamine (MA) and dimethylamine (DMA) as solvents.« less