Anodic Reactions of Simple Phenolic Compounds

Abstract

A study of the anodic reactions of phenols was made using the techniques of voltammetry, coulometry, and controlled potential electrolysis. It was shown that two entirely different anodic reactions are possible with phenolic compounds. The first is an electrophilic attack on the aromatic nucleus of the nonionized phenol with the irreversible removal of two electrons to give a mesomeric phenoxonium ion. As an example of this process an electrolysis of 2,6‐di‐tert‐butyl‐p‐cresol in acetonitrile at a platinum anode resulted in the addition of methanol to form 2,6‐di‐tert‐butyl‐4‐methyl‐4‐methoxy‐cyclo‐hexadienone in 65% yield. The second possible electrode reaction is the reversible removal of one electron from the phenoxide anion to give a phenoxy free radical. This process was illustrated by the electrolysis of the vanillinate anion in acetonitrile at a platinum anode to give dehydrodivanillin in 65% yield. It was found that half‐wave potentials for both electrode reactions could be correlated by Hammett‐type equations. Brief voltammetric experiments in 50% aqueous isopropanol on a carbon electrode indicated that both reactions could also occur in this system, depending on the pH and on the of the phenol being investigated.