Hydrogen atom abstraction mechanism for organic compound oxidation by acetylperoxyl radical in Co(II)/peracetic acid...

Peracetic acid (PAA) has been widely used as an alternative disinfectant in wastewater treatment, and PAA-based advanced oxidation processes (AOPs) have drawn increasing attention recently. Among the generated reactive species after PAA activation, acetylperoxyl radical (CH₃CO₃•) plays an important role in organic compounds degradation. However, little is known about the reaction mechanism on CH₃CO₃• attack due to the challenging of experimental analysis. In this study, a homogeneous PAA activation system was built up using Co(II) as an activator at neutral pH to generate CH₃CO₃• for phenol degradation. More importantly, reaction mechanism on CH₃CO₃•-driven oxidation of phenol is elucidated at the molecular level. CH₃CO₃• with lower electrophilicity index but much larger Waals molecular volume holds different phenol oxidation route compared with the conventional •OH. Direct evidences on CH₃CO₃• formation and attack mechanism are provided through integrated experimental and theoretical results, indicating that hydrogen atom abstraction (HAA) is the most favorable route in the initial step of CH₃CO₃•-driven phenol oxidation. HAA reaction step is found to produce phenoxy radicals with a low energy barrier of 4.78 kcal mol^-1 and free energy change of -12.21 kcal mol^-1. The generated phenoxy radicals will undergo further dimerization to form 4-phenoxyphenol and corresponding hydroxylated products, or react with CH₃CO₃• to generate catechol and hydroquinone. These results significantly promote the understanding of CH₃CO₃•-driven organic pollutant degradation and are useful for further development of PAA-based AOPs in environmental applications.