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

Abstract

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 .

Peroxydisulfate-Driven Reductive Dechlorination as Affected by Soil Constituents: Free Radical Formation and Conversion

“…Alternately, SO 4 •– / • OH radicals were previously reported to convert oxygen moieties present in humic constituents into SQ •– species, which are capable of degrading antibiotics and phenolic compounds, with mild second-order reaction rate constants in the range of 10 4 to 10 6 M –1 s –1 . , Interestingly, reminiscent of the above EPR outcomes (Figure c), a huge upsurge in the signal intensity for the TEMP– 1 O 2 adduct was recorded with HA dosages ranging from 20 to 500 mg (Figure b). Recent studies have found that persulfate could induce the nucleophilic attack on the carbonyl carbons of quinones to release 1 O 2 . − We therefore speculate that quinone moieties may be involved in the formation of 1 O 2 .…”

Enhanced Peroxymonosulfate Activation by a Benzoquinone-Functionalized Carbon Nanotube Filter for Micropollutant Degradation

“…This indicated that the loading of AQPDA on the CNT generated ROS through a sequence of reactions involving the breakdown of essential intermediates, displacement, and nucleophilic addition to PMS, thereby greatly increasing SMX degradation. Similar phenomena were previously described. ,, …”

Reactive Oxygen Species and Chromophoric Dissolved Organic Matter Drive the Aquatic Photochemical Pathways and Photoproducts of 6PPD-quinone under Simulated High-Latitude Conditions

“…While 1 O 2 production was confirmed in this system with FFA ([ 1 O 2 ] ss = 2 pM) and may have contributed to the degradation of 6PPDQ, it is apparent that there is a second unknown reaction contributing to 6PPDQ attenuation in these microcosms. Previous work has reported that semiquinones, produced by the one-electron reduction of quinones, may catalyze metal-independent reduction of hydrogen peroxide to generate a hydroxyl radical. − While this work focuses on photochemical pathways, future work should investigate the potential interplay between 6PPDQ redox properties and environmental photoproduction of hydrogen peroxide . To further test the hypothesis that the production of 1 O 2 in sunlit waters by dissolved organic matter may contribute to its degradation in the environment, we conducted additional experiments employing either furfuryl alcohol (FFA, 5 mM) or sodium azide (NaN 3 , 1 mM) as a 1 O 2 scavenger in SRFA microcosms.…”