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 (H 2 O 2 ), peroxomonosulfate (PMS), peracetic acid (PAA), and CH 3 OOH 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 HO 2 - , CH 3 OO - , 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 HO 2 - and CH 3 OO - to p -BQ. Comparatively, singlet oxygen ( 1 O 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, HO 2 - 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 1 O 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) and 1 O 2 .