Electrochemical oxidation of 2,6-di-tert-butyl-4-isopropylphenol

Abstract

The anodic oxidation of 2,6-di-tert-butyl-4-isopropylphenol, Ia, as well as the 4-ethyl (Ib) and 4-methyl (Ic) derivatives, has been studied in acetonitrile using carbon electrodes. Depending upon solution conditions and electrode potential, products derived from intermediate phenoxy radicals or phenoxonium ions are found. Oxidation of the phenoxides, IIa–c, leads to phenoxy radicals. Disproportionation of phenoxy radicals to form quinone methides is important for all three phenols, and in the case of IIa the quinone methide so formed, 2,6-di-tert-butyl-4-isopropylidene-2,5-cyclohexadienone, is susceptible to tautomerization followed by oxidation to a bis-quinone methide. The phenoxy radicals formed by oxidation of IIb are known to take part in a reversible dimerization to form a para-quinol ether and this reaction affects the cyclic voltammetry in a particularly interesting manner. Oxidation of Ia (or oxidation of its phenoxy radical) gives principally 2,6-di-tert-butyl-4-hydroxy-4-isopropyl-2,5-cyclohexadienone, a product formally derived from a phenoxonium ion intermediate. 2,6-Di-tert-butyl-4(2-hydroxy-2-propyl)phenol can also be formed on oxidation of Ia. The electrochemical behavior of these phenols is discussed in relation to chemical and electrochemical data of other phenols.