Study On Hydrolysis And Photolysis Of Thiamethoxam And Its Effect On Respiration Of Soil

Thiamethoxam belongs to a new class of insecticides known as neonictinoids. It owns higher biological activity, more safety and wider spectrum in applying against insect and has the brighter future in market. In this dissertation, hydrolysis and photolysis of thiamethoxam and the effects of thiamethoxam on respiration of soil were studied thoroughly. The results obtained from the experiments are helpful in forecasting thiamethoxam's environmental behaviors, guiding farmer to apply the pesticide correctly and reducing the pollutions from applying the pesticide.Firstly, in this dissertation, brief introductions on the relative concepts, basic theories background knowledge and advanced study in the field of environmental behavior of pesticide is provided.Secondly, the hydrolysis of thiamethoxam was studied. In this chapter,experiments were conducted to investigate the hydrolysis of thiamethoxam.The results show that alkaline can catalyze the hydrolysis of thiamethoxam and the hydrolysis fit the first-order kinetics. The hydrolytic rate of thiamethoxam was increased with the values of pH and temperatures. By extracting and analyzing the hydrolysis product with GC-MS, it was foundthat 3-(2-chloro-thiazolyl-5-ylmethyl)-5-methyl-4 -oxo- oxadiazine is the primary hydrolysis product, base on which the hydrolysis mechanism was proposed. Cu²⁺and Fe(OH)₃ could catalyze the hydrolysis of thiamethoxam and HA could baffle the hydrolysis of thiamethoxam. The hydrolytic mechanism and the catalytic mechanism of Cu²⁺ were suggested as followed: (1)Cu2+ is coordinated with the atom of N of the group of C=N, and leads towithdrawing electron density away from the carbon atom and generating amore reactive electrophile. So the bond of C-N is more easily brokenwhen it was attacked by OH^-. (2) Cu²⁺ can induce the deprotonation of coordinated water molecules, thereby generating metal hydroxo species, which is the stronger nucleophile than OH^-. The potential catalysis mechanism ofFe(OH)₃ were suggested as followed: (1) Fe(OH)₃ is coordinated with theatom of N of the group of C=N, and leads to withdrawing electron densit...