Mechanism And Kinetic Study On Oxidative Degradation Of Acetofenate And Triallate In Atmosphere

Organic pesticides have played a very important role in controlling species in industry, agriculture, and public health. They will have different negative impacts on the biology and human health by the migration, transformation into the atmosphere, soil and water environment. As an analogue of DDT, acetofenate (AF) is the only commercial organochlorine pesticide in China. Although the extensive application of AF has contributed to human life, there are varieties of drawbacks. Previous studies have proved that AF may cause reproductive toxicity, neurodevelopmental toxicity, and adverse immune system effects on subjects exposed to AF. Triallate (TDTD) is an indispensable herbicide which contributes to the world’s production of barley. TDTD mainly used in the controlling of wild oats in field crop. It has high volatile, which always works well with other material. However, there still has a small amount of ingredient of TDTD come into the atmosphere environment inevitably. The degree of TDTD accumulation effect on the body of animals is medium. In addition, there is a moderate irritation to the skin, has low toxicity effect on human.In this paper, quantum chemistry method was applied to reveal the degradation mechanisms of AF and TDTD, and establish the feasible of reaction pathways. The mechanism of HOX, NO3, O3, and Cl initiated oxidation reactions of AF and TDTD were investigated with density functional theory. All work calculated at the MPWB1K/6-31+G(d,p) level, and thermodynamic parameters are also included. Based on quantum chemistry information, the rate constants are calculated using the transition state theory method. The study leads to some meaningful conclusions:1. Mechanism of AF with OH、HO2、O3、NO3、ClFor each of the OH, NO3, and Cl, both addition and hydrogen abstraction were investigated, for each of the HO2 radicals and O3, addition reactions were investigated. The 03-adducts can undergo unimolecular decomposition, leading to C-C/C-O bond cleavage. For cis-addition HO2, NO3, and Cl added to C4 are the most favorable reaction pathways, while they added C1 are the most favorable reaction pathways among the trans-addition. Those adducts can be further degraded in the atmosphere with.O2/NO/HbO, and generated small molecule compounds like ketene and aldehyde.At 298.15 K, the total rate constants of AF with OH, HO2, NO3, O3, and Cl, are 4.04×10-13,7.02×10-33,6.93×10-20,1.45×10-25, and 5.07×10-12 cm3 molecule-1s-1, respectively. The rate branching ratio of OH initiated reactions are dominant. The HO2, NO3, O3 and Cl initiated reactions make little contribution to the reaction rate of AF from 200 to 400K compared with the OH initiated reactions. The τ for all OH, HO2, NO3,O3, and Cl initiated oxidation reactions is 2.14 days.2. Mechanism of TDTD with OH、HO2、O3、NO3、ClThe reactions of TDTD with OH、NO3 and Cl have two patterns, addition and H atom abstraction. During those reactions, the branching ratios of addition reactions are positively correlation with temperature, while the branching ratios of abstraction reactions are negative correlation with temperature. TDTD can only react with HO2 radical by addition reaction. All the five oxidation can easily react with TDTD. As for OH, NO3, and Cl, the radicals added to C1 are the most favorable reaction pathways, whilst they abstract the H atom of isopropyl are the most easily reaction pathways. Those adducts from TDTD with HO2 can further generate ether or ketone by leaving OH away. The 03-adducts can undergo unimolecular decomposition, leading to C1-C2/O-O bond cleavage. Adducts from TDTD with OH, NO3, and Cl can be further degraded in atmosphere of.O2/NO, and could generate phosgene directly or indirectly.At 298.15 K, the total rate constants of TDTD with OH, HO2, NO3, O3, and Cl, are 9.94×10-14,2.33×10-19,2.54×10-16,9.96×10-18, and 9.86×10-10 cm3 molecule-1s-1, respectively. From 200 to 400K, the O3 initiated reactions make most contribution to the degradation of TDTD, followed by OH and Cl. The τ for all OH, HO2, NO3, O3, and Cl initiated oxidation reactions is 1.55 days.