Theoretical investigation into activation of hydroperoxides by excited quinones under ultraviolet irradiation

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In this work, quantum chemical calculations have been applied to explore the reaction of hydroperoxides (hydrogen peroxide, CH3OOH, peroxomonosulfate and peracetic acid) with the first triplet states of quinones (p-benzoquinone, tetrachloro-p-benzoquinone and 2-methoxy-p-benzoquinone) (3Q*), which were excited from the ground states of quinones by the UV irradiation. With the much larger forward energy barriers than the reverse ones, the attack of the ionized hydroperoxides on the CO and CH(Cl) bonds of 3Q* was kinetically unfeasible, which was independent of the substitutes in the structures. Surprisingly, based on the bond lengths, the charge distributions and the molecular orbitals, the single electron transfer from the ionized hydroperoxides to 3Q* was tentatively determined for the activation of ionized hydroperoxides by 3Q*, with the formation of peroxy radicals and semiquinone radicals. The peroxy radicals may be able to transform to other highly oxidative radicals (e.g., sulfate radical). Moreover, not only the electron-withdrawing groups but also the electron-donating ones in the structures might not inhibit the single electron transfer from the ionized hydroperoxides to 3Q*. With quinones as the photosensitizers, the UV irradiation enriched the types of highly reactive species during the activation of hydroperoxides, which may make the combination of quinones and hydroperoxides suitable for the degradation of different pollutants. These theoretical findings may help to verify the influence of UV irradiation on the activation of hydroperoxides by quinones for the decontamination and promote the understanding of the reaction of chromophoric dissolved organic matter with hydroperoxides in natural waters.