Revisiting the BHT Oxidation Mechanism in Acetonitrile through an Experimental and Theoretical Approach

Abstract

Electrochemical oxidation of butylated hydroxytoluene (BHT) was revisited in acetonitrile (ACN) using cyclic voltammetry, numerical simulations, and density functional theory (DFT) calculations. BHT exhibited a single irreversible anodic peak at ~1 V vs. Ag/AgNO₃, corresponding to its oxidation to a cationic radical (BHT.+), which subsequently undergoes a deprotonation and second electron transfer to form BHT+. DFT calculations defined the possible oxidation pathways evaluated through experiments and simulations. In ACN, a two-electron ECEC mechanism dominates, where the second electron transfer occurs at a lower standard potential than the first, resulting in a single anodic peak. In contrast, previous studies in aqueous media have shown two distinct voltammetric peaks, due to the first electron transfer being at a lower standard potential than the second redox reaction. Addition of potassium t-butoxide shifted the BHT/BHT- equilibrium toward the formation of BHT-, resulting in an additional redox process at negative potentials; this redox reaction was predicted from DFT calculations. Numerical simulations of the current response aligned with experimental data revealed faster electron transfer kinetics in ACN compared to water. The dimeric oxidation products were elucidated by NMR experiments. These results provide detailed insights into BHT oxidation mechanisms, emphasizing solvent effects and the formation of reactive intermediates.