The electro-oxidation of polycyclic aromatic hydrocarbons in acetonitrile studied by cyclic voltammetry

Abstract

The electro-oxidation of 9,10-diphenylanthracene results in a relatively stable radical-cation with a rate of charge-transfer of the order 1 cm sec − at a platinum electrode in acetonitrile. 1,2-Benzanthracene exhibits behaviour approaching that of diphenylanthracene at high rates of voltage change (500 V sec −. At lower sweep-rates, irreversible chemical reactions intervene leading to further oxidation, the standard potentials of subsequent steps being close to that for the first charge-transfer. Anthracene, pyrene, phenanthrene and triphenylene exhibit similar limiting behaviour of anodic currents and peak potentials at high scan-rates, which is identified with the formation of radical cations: the cations of these hydrocarbons have a life-time of a few milliseconds. The common supposition that the primary electrode process involves the formation of the dipositive ion is thus incorrect. Moreover, conventional polarographic oxidation potentials of the unsubstituted compounds are controlled by chemical reaction. The reversible oxidation potentials for the charge-transfer step have been evaluated from the data at high rates of voltage sweep.