【摘要】 运用密度泛函(DFT)理论,研究了农药甲胺磷分子在碱性条件下,水解微观反应机理和速率常数。在B3LYP/6-31+G(d,p)水平上分别优化了水溶液相反应途径上各反应态的几何结构,溶剂化模型采用连续极化连续模型(CPCM)。并用频率分析方法和内禀反应坐标(IRC)计算,分别确认了过渡态的结构和反应途径。计算结果表明,反应决速步骤为第一步氢氧根离子进攻反应物,对3个不同离去基团(甲氧基TS2、甲硫基TS1和氨基TS5)活化自由能分别为15.64 kcal/mol、17.19 kcal/mol和25.80 kcal/mol。采用经Wigner校正的Eyring过渡态理论,计算了(100～1200)K温度范围内的各通道反应速率方程分别为,InK(C-O)=11.19524-2.37134×1000/T;Ink(C-S)=11.68184-3.28612×1000/T;Ink(C-N)=12.03234-7.73338×1000/T,3个方程的相关系数分别为R=-0.99809;-0.99891;-0.99981。计算结果显示甲胺磷在碱性条件下不稳定,能水解,并首先解离的是甲氧基和甲硫基,反应具有较大的自发反应趋势,氨基在碱性条件下不易离去。研究结果为解析有机磷杀虫剂在不同条件下的水解反应机制提供理论依据。更多还原

【Abstract】 The microcosmic reaction mechanism of methamidophos hydrolysis in alkaline solution was studied by Density Functional Theory（DFT）.The geometries of the reactants,transition states and products were optimized by using B3LYP method with 6-31 +G（d,p） basis set and CPCM solvation model.Then vibration analysis and intrinsic reaction coordinate（IRC） method were employed to confirm the structure of transition state and search the reaction path.Three probable reaction channels were found with P-O,P-S and P-N bond cleavage in the second step and the activation free energy of rate-determining is（15.64,17.19,25.80） kcal·mol^-1 respectively in the first step,and de-OCH₃ or de-SCH₃ are more easily leaving groups in the molecular than de-NH₂.The thermodynamic and kinetic characters and three rate constant equations are calculated from 100 K to 1200 K by applying of the Eyring transition state theory（TST） with Wigner correction at 101.325 kPa. The rate equation are lnk（C-O）=11.19524-2.37134×1000/T,lnk（C-S）=11.68184-3.28624×1000/T and lnk（C-N）=12.03234-7.73338×1000/T with relationship coeffience R=-0.99809,-0.99891 and -0.99981 respectively.The results show that methamidophos is unstable and can be hydrolysed in alkaline for de-OCH₃ and de-SCH₃,with difficulty for de-NH₂ and the reaction has a higher spontaneity capability.These results are helpful to the further study on reaction mechanism of organophosphate pesticides in different condition.更多还原