Abstract
The abatement of aromatic pollutants in water requires their oxidation to nontoxic products by resource-intensive reactions with hydroxyl radicals (•OH). We elucidate the mechanisms of •OH-induced aromatic ring degradation by combining kinetic measurements, electron paramagnetic resonance spectroscopy, density functional theorycalculations, and kinetic modelling. We demonstrate that benzyl alcohol, a model aromatic compound, is oxidized by •OH radicals, generated by ultrasonic irradiation in an O2-rich environment, into aromatic compounds (benzaldehyde and phenol derivatives) and C1-C2 oxygenates (formic acid, glyoxal, and oxalic acid). Through pathways akin to atmospheric chemistry, these •OH radicals de-aromatize and fragment benzyl alcohol, producing 5-hydroxy-4-oxo-pentenal and other dicarbonyl products. Unique to the aqueous phase, however, superoxide (•O2-) forms by •OOH deprotonation, which is generated by ultrasound (alongside •OH) and as a byproduct of •OH-benzyl alcohol reactions. •O2-acts as a nucleophile, oxidizing 5-hydroxy-4-oxo-pentenal into oxalic acid and C1 oxygenates via aldehyde and ketone intermediates. This process regenerates •O2-and does not consume •OH, thereby further degrading ring fragmentation productswhile preserving•OH to activate the refractory aromatic ring of benzyl alcohol. These nucleophilic•O2-reactions can therefore reduce the energy and number of chemical initiators needed to degrade aromatic compounds, thus advancing •OH-based oxidation processes in water treatment.
Published Version
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