Mechanical Insights into Activation of Peroxides by Quinones: Formation of Oxygen-Centered Radicals or Singlet Oxygen

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Abstract

In this work, the mechanism of the activation of peroxides by quinones has been investigated through quantum chemical calculations. Hydrogen peroxide (H₂O₂), peroxomonosulfate (PMS), peracetic acid (PAA), and CH₃OOH were chosen as the model peroxides and p-benzoquinone (p-BQ) and tetrachloro-1,4-benzoquinone (TCBQ) as the model quinones. The nucleophilic attack of peroxides can occur on the carbonyl and olefinic carbons of quinones. For p-BQ, the nucleophilic attack of HO₂-, CH₃OO-, PMS, and PAA might prefer to occur on the carbonyl carbons, which have more positive atomic charges. Then, further transformation could not be induced from the addition of HO₂- and CH₃OO- to p-BQ. Comparatively, singlet oxygen (1O₂) could be generated in the cases of PMS and PAA. For TCBQ, the chlorine atoms cause the olefinic carbons to carry more positive atomic charges, and then, HO₂- preferred to add to the olefinic carbons, which might induce the formation of the hydroxyl radical (•OH). The activation of PMS by TCBQ was similar to that by p-BQ, with the kinetical feasibility of 1O₂ formation. These findings may provide some theoretical insights into the reaction of peroxides with quinones, especially into the interconnection between the substitutes and the formation of oxygen-centered radicals (e.g., •OH) and 1O₂.

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