Theoretical Studies On The Aminolysis Of Methomyl And Hydrolysis Of Chlordimeform Mechanism

The widespread application of pesticides in agricultural has caused some environmental damage.They are continuously accumulated in crops,vegetables and water which also poses a potential threat to human health.Hydrolysis and aminolysis are important degradation pathways for pesticides in the environment.Therefore,it is very important to study the hydrolysis and aminolysis behavior of pesticides in the environment.However,as far as we know,there are few studies on the aminolysis mechanism of methomyl and the hydrolysis mechanism of acetamiprid and the mechanism has remained unclear.Therefore,we will systematically investiage the ammonolysis and hydrolysis mechanisms for the two insecticides.In this thesis,we divide the dissertation into five parts:The first part is the introduction which will introduce the background and development of our research problems and then state the main contents.Next,the theoretical methods and theoretical tools used in this thesis are introduced.Methomyl is a common type of carbamate insecticide.It has the advantages of strong efficacy,low residue,and safety to crops.Therefore,it is widely used in agricultural production.However,it was found that a large amount of methomyl was accumulated in crops,vegetables and water,which would endanger human health.Therefore,the investigation of its degradation mechanism can help guide the rational use of the pesticide.As the aminolysis process belongs to alkaline hydrolysis.We chose ammonia as the research object not only because ammonia is alkaline,but also because the aminolysis reaction of carbamate has a crucial role in the process of organic synthesis and biosynthesis.The aminolysis mechanisms of methomyl are systematically investigated through the M06-2X/6-311++G?d,p?and MP2/6-311+G?d,p?methods.The uncatalyzed,base-catalyzed and water-catalyzed aminolysis processes are also taken into consideration together with the concerted,B_AC2 and E1cB pathways.The solvent effects are discussed in detail by using the conductor-like polarized continuum model?CPCM model?with the M06-2X/6-311++G?d,p?method.The results provide the convincing evidence that the three alternative pathways possess similar energy barriers for the uncatalyzed aminolysis.It can be concluded that the base-catalyzed and water-catalyzed aminolysis processes are more favorable compared with the uncatalyzed reaction.Concerning the base-catalyzed process,the E1cB pathway is preferable to other channels.However,the water-catalyzed aminolysis is dominated by the B_AC2 mechanism.In a word,the aminolysis reactions in solution could readily occur and the solvent effects do not remarkably alter the mechanism.Chlordimeform,a kind of insecticides known as an organicnitrogen insecticide in agriculture,has been widely used to control the insects which are resistant to organochlorine,organophosphorus,and carbamate insecticides.It has been found that chlordimeform is carcinogenic on mice,and poisoning has also occurred in agricultural fields.It has now been classified as a highly toxic pesticide species.From the early experimental work,it was known that the hydrolysis process of chlordimeform belongs to alkaline hydrolysis,but it has not been studied in detail for its hydrolysis mechanism and transition state structure.In this thesis the hydrolysis mechanism of chlordimeform in acid,basic and neutral conditions are investigated at B3LYP and M06-2X levels together with the 6-311++G?d,p?basis set.In addition,the hydrolysis of the three conditions are taken into account including two different reaction pathways.In the gas phase,the geometric structures of the reaction complex?RC?,transition state?TST?,intermediate?INT?and product complex?PC?are optimized in each pathway and frequency analysis is also performed.The solvent effect of water is obtained by fully reoptimized the geometric structures of each stable point in the gas phase at the M06-2X/6-311++G?d,p?level combined with the conductor polarization continuous medium model?CPCM?.The results show that both in gas phase and in aqueous solution the most favorable hydrolysis of chlordimeform is Path A under alkaline condition.The last part is the conclusion and the outlook,including the research results and future research direction.The results can also provide very useful information for future research on this type of reaction.