Single Electron Reduction Behavior Of O-tetrachlorophenylhydrazine And Its Relationship With HTheoretical Study On The Reaction Of 2 O 2 And N-methylphenyl Hydroxamic Acid

As the main metabolic products of the persistent organic pollutant pentachlorophenol?PCP?,halogenated quinones are a kind of toxic and harmful species with strong hepatotoxicity,nephrotoxicity,and carcinogenicity.It was found that halogenated quinones can react with hydrogen peroxide to form an unstable intermediate containing O-O bond through nucleophilic attack.After then,the hydroxyl radical and alkoxyl radicals can be produced via the homolytical decomposition of the O-O bond,which can be used to explain the potential carcinogenicity of polyhalogenated quinones.In addition,halogenated quinones can also react with benzohydroxamic acid to produce the corresponding intermediate through nucleophilic.Subsequently,this intermediate decomposes homolytically to produce radicals.To obtain the detailed reaction mechanism for the formations of free radicals in the reactions of halogenated quinones with hydrogen peroxide and benzohydroxamic acid,in this study,the one-electron reduction behavior of tetrachloro-o-benzoquinone?o-TCBQ?and the reaction mechanism of o-TCBQ with hydrogen peroxide?H₂O₂?and N-methyl benzohydroxamic acid?N-MeBHA?have been systematically investigated employing density functional theory?DFT?method in combination with the atoms in molecules?AIM?and ab initio molecular dynamics.The main conclusions have been summarized as follows:Firstly,the one-electron reduction behavior of o-TCBQ has been systematically investigated at the B3LYP/6-311++G** level of theory in combination with the ab initio molecular dynamics.It was shown that microhydration and bulk salvation have a little effect on the geometry of o-TCBQ.However,it has been significantly influenced upon capturing an electron,which can be reflected from the large the deformation energy of anionic form compared with the neutral state.Moreover,the C_2v symmetry of neutral and anionic o-TCBQ in the gas phase has been changed to be C₂ symmetry in solution.All the electron affinity and vertical detachment energies are positive in the gas phase and in solution,increasing with the increasing of the dielectric constant of the bulk solvent.Therefore,explicit water molecules and bulk solvents can efficiently enhance the electron accepting ability of the o-TCBQ,reflecting the intrinsic nature of o-TCBQ as a good electron acceptor in different media.Secondly,the reaction mechanism of o-TCBQ with H₂O₂ has been systematically investigated at the B3LYP/6-311++G** level of theory.It was found that an initial intermediate was formed firstly as the first step of the title reaction.After that,the nucleophilic attack of H₂O₂ to o-TCBQ occurs to produce an unstable intermediate containing O-O bond.Subsequently,the unstable intermediate decomposes homolytically via the cleavage of the O-O bond,resulting in the formation of the OH radical.Note that explicit water molecules play an important positive role in the nucleophilic attack process of H₂O₂ to o-TCBQ.The nucleophilic attack process is the rate-determing step in the whole reaction.Especially,as an alternative reaction approach,it was found,for the first time,that the formed unstable intermediate containing O-O bond mentioned above can be produced directly via the nucleophilic attack of the anionic form of H₂O₂ to o-TCBQ in the absence of explicit water molecules.In addition,the selected substitution effects on the title reaction have also been studied.Finally,the reaction mechanism between o-TCBQ and N-MeBHA has been systematically explored.Firstly,it was found that the nucleophilic attack of neutral N-MeBHA to o-TCBQ in the absence and presence of explicit water molecules is difficult to occur.However,the anionic N-MeBHA can react with o-TCBQ.Namely,the nucleophilic attack of anionic N-MeBHA to o-TCBQ to form an unstable intermediate containing N-O bond followed by its homolytical decomposition to produce the O-centered quinine enoxy radical and N-centered radical.Finally,the produced radicals react with each other to produce the products containing C-N bond.In addition,the reaction between tetrachloro-p-benzoquinone?p-TCBQ?and N-MeBHA has also been studied for comparison.