Investigation On Atmospheric Oxidation Mechanisms Of Chlorpyrifos-methyl,Trifluralin,Galaxolide And Cypermethrin

Production and use of pesticides bring convenience to human-beings but also potential danger. Many studies have detected pesticide residues in gas, water, and soil. Self-purification ability of nature cannot fully digest these pesticides which pose potential threat on human health and the natural environment. Therefore understanding the chemical behaviors of pesticides in the environment is necessary to study how to eliminate them. Besides pesticides, some emerging contaminants also have gained general concern around the world. These new emerging contaminants’ usage amount is large and they lack legal supervision. And they can cause potential threats on humans and other organisms. Sp ecific chemical behaviors of contaminants obtained by theoretical calculation method may set as relevant supplemental reference criteria for experimental research.In this article we selected chlorpyrifos-methyl, trifluralin (pesticides) and galaxolide, cypermethrin (emerging contaminants) as the research object. High oxidants (OH radical and O3 molecule) were chosen as initiator. All the molecules involved in the degradation mechanisms of the four pollutants were carried out using density functional theory method at MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G (d,p) level. Thermodynamics and kinetics data of the reactions in gas phase were also calculated.1. Mechanism for OH-initiated atmospheric oxidation investigation on chlorpyrifos-methylThe reaction processes of OH radical with chlorpyrifos-methyl have been studied using a high precision quantum chemistry method. The reactions mainly fall into three categories:OH addition to the P atom, OH addition to the pyridyl ring and H abstraction. The reactions of primary activated intermediates were also studied in the presence of O2/NO. Theoretical results show that the reaction of OH addition to P atom is the main reaction path. The dominant products for OH-initiated atmospheric oxidation of chlorpyrifos-methyl are O,O-diethyl phosphorothioate, C5HNCl3O radical, chlorpyrifos oxon, and SOOH.2. Mechanism for OH-initiated atmospheric oxidation investigation on trifluralinTrifluralin is a selective pre-sowing or pre-emergence herbicide and can be detected in the environment frequently because of its high vapor pressure (1.5×10-2 Pa). The degradation mechanism for OH-initiated atmospheric oxidation reactions with trifluralin has been investigated. The detailed mechanisms of primary reactions and main secondary reactions are given in this article as well. As shown in the results, the final products were 4-trifluoromethyl-2,6-dinitrotoluene, N(C3H7)2 radical, ethyl radcal and dinitrobenzene derivatives. By means of canonical variational transition state theory with small curvature tunneling correction, the kinetic properties of primary reactions were estimated. At 298 K and 1 atm, the overall rate constant of trifluralin intiated with OH is 2.36×10-11 cm3 molecule s-1, and its atmospheric lifetime is 12.52 h.3. Mechanism for OH-initiated atmospheric oxidation investigation on galaxolideThe oxidation reactions of OH radical with galaxolide have been studied in this article, and double hydroxyl compounds, alcohol ether compounds are dominant degradation products. In addition, rate constants of individual primary reactions and overall reactions were calculated by employing Polyrate 9.7 program at a temperature range of 180-370 K. The calculated atmospheric lifetime of 16.69 h is in favor of a possible phenomenon of medium range atmospheric transport for galaxolide.4. Atmospheric ozonolysis study mechanism of cypermethrinGeometrical optimizations of reactants, products, intermediates and transition states were operated at the basis set of 6-31+G(d,p). More accurate single-point energy calculations were performed at the 6-311+G(3df,2p) level. Potential barriers and reaction enthalpies are also shown in this text. Reaction pathways contain addition process to ordinary C=C bond and double bond of the benzene ring. As the results shown, O3 molecule tends to attack the former. The main reaction products are phosgene, peroxy radicals and aldehyde compounds.