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

In this work, the mechanism of the activation of peroxides by quinones has been investigated through quantum chemical calculations. Hydrogen peroxide (H2O2), peroxomono-sulfate (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 (O-1(2)) 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)-O-center dot). The activation of PMS by TCBQ was similar to that by p-BQ with the kinetical feasibility of O-1(2) 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)-O-center dot) and O-1(2).

Automated summary

The mechanism of the activation of peroxides by quinones has been investigated through quantum chemical calculations. Different quinone compounds activate peroxides in different ways.