CAJ | 학술논문

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， lnk(C-O)=11.19524-2.37134×1000/T； lnk(C-S)=11.68184-3.28612×1000/T； lnk(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。
운용밀도범함(DFT)이론，연구료농약갑알린분자재감성조건하，수해미관반응궤리화속솔상수。재 B3LYP/6-31+G(d,p)수평상분별우화료수용액상반응도경상각반응태적궤하결구，용제화모형채용련속겁화련속모형(CPCM)。병용빈솔분석방법화내품반응좌표(IRC)계산，분별학인료과도태적결구화반응도경。계산결과표명，반응결속보취위제일보경양근리자진공반응물，대3개불동리거기단(갑양기 TS2、갑류기 TS1화안기 TS5)활화자유능분별위15.64 kcal/mol、17.19 kcal/mol 화25.80 kcal/mol。채용경 Wigner 교정적 Eyring 과도태이론，계산료(100~1200) K 온도범위내적각통도반응속솔방정분별위， lnk(C-O)=11.19524-2.37134×1000/T； lnk(C-S)=11.68184-3.28612×1000/T； lnk(C-N)=12.03234-7.73338×1000/T，3개방정적상관계수분별위 R=-0.99809；-0.99891；-0.99981。계산결과현시갑알린재감성조건하불은정，능수해，병수선해리적시갑양기화갑류기，반응구유교대적자발반응추세，안기재감성조건하불역리거。연구결과위해석유궤린살충제재불동조건하적수해반응궤제제공이론의거。
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.