Electrochemical Behavior of Organic Compounds at the ( SN ) x Paste Electrode

Abstract

The electrochemical characteristics of several types of organic compounds have been investigated at the paste electrode in acetonitrile/TEAP solution. The current density for reduction of benzoquinone in the presence of protons, formed either by hydroquinone oxidation or by addition of to benzoquinone, was found to be considerably less than that for this process at platinum or vitreous carbon. A similar effect was observed for proton reduction at paste, indicating, as for single‐crystal electrodes, a high hydrogen overpotential for the electrode surface. Comparative experiments investigating the redox behavior of the benzoquinone/hydroquinone system in aqueous media at paste indicate that slow protonation kinetics are involved in the voltammetric behavior observed for this system. Electrochemical oxidation of representative aromatic amines and hydrocarbons (including phenothiazine, N,N‐dimethyl‐o‐phenylenediamine, N,N‐dimethylaniline, 2,3‐diphenylindole, 2,3‐benzanthracene, and perylene) involved behavior similar to that observed at platinum, showing that the oxidized species produced, both stable and unstable, undergo no specific interaction with the electrode surface. Oxidation of pyrrole occurs at the anodic background limit of paste, producing a black film on the electrode surface which has voltammetric properties similar to those of polypyrrole films formed at other electrodes. Although the heterocyclic compounds pyridine, quinoline, and acridine are not themselves oxidizable in the paste potential range, addition of these compounds caused the appearance of an oxidation process at a potential approximately 100 mV negative of the anodic background oxidation. The dependence of the current observed for the process upon heterocycle concentration indicates that the process corresponds to a shift of the oxidation caused by a nucleophilic interaction of the heterocycles with the as it undergoes oxidation. Further negative shifts in the potential for oxidation were observed in the presence of several alkylpyridines having greater nucleophilicities than that of pyridine itself. Addition of the less nucleophilic compound thiazole did not produce this effect. These results indicate that the oxidation of itself leads to the formation of rather reactive products, while the surface behaves essentially as a noninteracting, metallic electrode in the potential region between +0.95 and −0.40V vs. SCE, over which is electrochemically stable in acetonitrile.