Theoretical Research On The Reaction Mechanism Of TCDD/TCDF And H₂O₂

Persistent organic pollutants?POPs?have posed a serious threat to human health and ecological environment and have been attracted extensive attentions increasingly.However,it is difficult to degrade for POPs due to their special structures.Thus,it is necessary to look for species to react with POPs so as to change their geometries and properties for the studies on the transformation and degradation of POPs.A large number of studies have shown that the halogenated quinones can react with the organic hydroperoxides via the nucleophilic attack modes to form an unstable intermediate containing the O-O bond.After then,the intermediate decomposes via the homolytical cleavage of the O-O bond,resulting in the formation of radicals,such as hydroxyl radical,organic alkoxyl radicals,and quinone ketoxy radicals.Due to the fact that the formed extremely reactive radicals may cause potential damage to organisms,so the above reaction can be used to elucidate the toxicity mechanism of halogenated quinones.Inspired by the above reaction between the halogenated quinones and organic hydroperoxides as well as many similarities in geometry and property between dioxins and halogenated quinones,in this study,the feasibility and reaction process to produce the radicals for the reactions of the2,3,7,8-tetrachlorodibenzo-p-dioxin?TCDD?and 2,3,7,8-tetrachlorodibenzofuran?TCDF?with H₂O₂ and its anion have been systematically investigated theoretically employing the B3LYP/6-311++G?d,p?level of theory in combination with the atoms in molecules?AIM?theory.The main research contents include the following two parts:In the first part,the processes to produce the OH radical for the reaction of the TCDD with H₂O₂ have been systematically investigated with the assistance of different numbers of water molecules.It was shown that,an initial intermediate can be formed between TCDD and H₂O₂.After then,the nucleophilic attack of TCDD by H₂O₂ takes place to form an intermediate containing the O-O bond,which is the rate-determining step and the explicit water molecules play an important catalytic role in this process.Finally,the O-O bond of this intermediate cleavages homolytically to produce two radicals.Moreover,considering the nature of HO₂^–as a good nucleophile,we have also examined the reaction of TCDD with HO₂^–.As a result,it was found that this reaction is easier to occur relative to that of the reaction involving the neutral H₂O₂.In addition,the reactions between F-and Br-substituted TCDD and H₂O₂ as well as the reaction between TCDD and CH₃-substituted H₂O₂ have also been investigated to further confirm the reactivity of the organic hydroperoxides with TCDD-like pollutants.In the second part,to further enrich the understanding of the reactivity of the TCDF dioxin with organic hydroperoxides,the reaction of the TCDF with H₂O₂ has been systematically investigated in the presence of the different numbers of water molecules.It was shown that an initial complex can be formed firstly between TCDF and H₂O₂.After then,the nucleophilic attack of TCDF by H₂O₂ takes place to form an intermediate containing the O-O bond,which is the rate-determining step and the explicit water molecules play an important catalytic role in this process.Finally,the O-O bond of this intermediate cleavages homolytically to produce two radicals.Moreover,given the nature of HO₂^–as a good nucleophile,we have also examined the reaction of TCDF with HO₂^–.As a result,it was found that the reaction can occur easily.In addition,the reactions between F-and Br-substituted TCDF and H₂O₂ as well as the reaction between TCDF and CH₃-substituted H₂O₂ have also been investigated to further confirm the reactivity of the organic hydroperoxides with TCDF-like pollutants.