title: Theoretical study on the atmospheric transformation mechanism of pirimiphos-methyl initiated by O3.
abstract: Pirimiphos-methyl (PMM) is a widely used organophosphorus pesticide that can be released into the atmosphere in gas and condensed phases. It possesses a PS bond and an N,N-dialkyl group adjacent to pyrimidine, which are common functional groups for pesticides. Currently, the reaction mechanisms of O3 with these functional groups are poorly understood. In this study, the mechanisms and possible degradation products for O3-initiated atmospheric oxidation of PMM were investigated using the Density Functional Theory (DFT) method. The results show that H abstraction from the alpha carbon of the N,N-diethyl group and its subsequent reactions (hydroxylation, N-dealkylation, and carbonylation reactions), as well as the transformation of the PS bond to the PO oxone form, are the most favorable reaction pathways for PMM and O3. The Gibbs free energy (ΔG) indicates that the subsequent reactions tend to take place more spontaneously once the initial reaction occurs. In addition, theoretical calculations indicate that water can serve as an effective catalyst in the N-dealkylation reaction process. Water-assisted reactions lead to the activation energy decreasing by 20.2 kcal mol(-1) compared with direct reactions, and thus may represent a dominant reaction pathway for the N-dealkylation process in the atmosphere. These theoretical results provide new insights into O3-initiated degradation of PMM and its analogues.
authors.affiliation: Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. Electronic address: boyang@rcees.ac.cn.
authors.forename: Bo
authors.initials: B
authors.lastname: Yang
authors.affiliation: Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Youfeng
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Jinian
authors.initials: J
authors.lastname: Shu
authors.affiliation: Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Zhang
authors.affiliation: Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Wanqi
authors.initials: W
authors.lastname: Sun
authors.affiliation: Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Nana
authors.initials: N
authors.lastname: Li
authors.affiliation: Beijing City Environmental Protection Bureau of Xicheng District, Beijing 100032, China.
authors.forename: Yani
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D000388:Air / Q000032:analysis*; D000393:Air Pollutants / Q000737:chemistry*; D006900:Hydroxylation; D007700:Kinetics; D008956:Models, Chemical; D009946:Organothiophosphorus Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010126:Ozone / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D000393:Air Pollutants; D009946:Organothiophosphorus Compounds; D014867:Water; C014153:pirimiphos methyl; D010126:Ozone
keywords: Atmospheric transformation; DFT; O(3); Pesticides; Pirimiphos-methyl; Reaction mechanism