Theoretical Studies On The Hydrolysis Mechanism Of Acetamiprid

Acetamiprid, a new kind of insecticides known as chloro-neonicotinoids, has been widely used to control sucking-type insects in agriculture for its unique action mechanisms and relatively low environment toxicity. Due to frequent and extensive usage, AAP accumulated in the crops, vegetables and water will cause potential risk to human health. Despite the widespread use of acetamiprid, there is little degradation mechanism of acetamiprid up to now. It is reported that acetamiprid can be dissolved in most organic solvents, such as acetone, methanol, ethanol, acetonitrile, and its solubility in water is even greater(4.25 g/L). In addition, the hydrolysis process is a primary degradation way of acetamiprid in environment. Therefore, it is necessary to investigate its hydrolysis mechanism. However, to our best knowledge, the detailed hydrolysis mechanism for acetamiprid has remained unclear, and no theoretical work on it has been reported. In our present work, more attention focus on the theoretical studies on the hydrolysis process of acetamiprid.The pH is one of the most important influencing factors. In chapter 3, the hydrolysis mechanisms of acetamiprid in acid, basic and neutral conditions were investigated at the B3 LYP and MP2 levels of theory using the 6-311+G(d,p) basis set. In the gas phase, the geometric structures for the reactant complexes, transition states, intermediates and product complexes in the reactions were fully optimized and frequency analysis was also performed. Furthermore, to simulate the title reaction in aqueous solution, the fully reoptimized calculation was performed to test the solvent effect of water by means of the conductor-like polarized continuum model(CPCM). The results of calculation show that in the gas and in aqueous solution, the hydrolysis reaction of acetamiprid undergoes more easily in the basic condition, however, the hydrolysis process proved to be slow in acidic and neutral solvents. So, we inferred that the hydrolysis process of acetamiprid, belongs to alkaline hydrolysis, which is essentially consistent with the experimental result. The most favorable pathway in the gas phase is the proton transfer toward the N atom in the single bond of AAP in the hydrolysis with OH-. The energy barrier height of 26.77 kcal/mol(111.90 kJ/mol) is in excellent agreement with the available experimental value(106.3 kJ/mol), inferring from the Arrhenius equation k=A·exp(-EA/RT). Our calculations clarify a detailed hydrolysis mechanism of AAP. The theoretical calculation can not only give support to the experimental results, but also can provide the prediction for the experiments, providing new details for the corresponding hydrolysis intermediate and transition state structures which cannot be detected on the experiment, thereby improve the efficiency of experiments. Meanwhile, this investigation may provide very useful information for studying this type of reaction.