Electrochemical reactivity of bulky-phenols with superoxide anion radical

Abstract

The 2,6-di-tert-butyl-4-methylphenol (1), and its analogues 2,6-di-tert-butylphenol (2), 2,4,6,-tri-tert-butylphenol (3), 2-tert-butylphenol (4), and 4-tert-butylphenol (5), were evaluated with respect to their reactivities with superoxide anion radical (O2-), using a variety of electrochemical methods including cyclic voltammetry and square wave voltammetry. The current intensity associated with anodic peak of O2- oxidation into O2 (−1.16 ± 0.02 V) was used to measure effectiveness of compounds 1–5. All phenolic compounds reduced the anodic current intensity associated with O2- oxidation into O2. Compounds 2 and 4 produced reversible oxidation/reduction peaks associated with the corresponding quinones. The C10% and C60% values, related to the reduction of anodic O2-/O2 current to 10% or 60% of its original value, were in 2.2–3.2 and 0.8–1.3 mM range, respectively. Compound 4 exhibited the lowest C10% and C60% values and was the most effective radical quencher. Data indicate that compounds belonging to the same class exhibited different radical activity (extent of reactivity with O2-), and that electrochemical methods are extremely useful in analyzing reactivity patterns in antioxidants of similar structures.