3-甲基环状乙撑磷酸二酯醇解的反应途径的理论研究

Theoretical Study on Reaction Pathways for Methanolysis of 3-Methyl Cyclic Ethylene Phosphate

采用密度泛函理论和MP2方法研究了3-甲基环状乙撑磷酸二酯(MEP)与甲醇的反应途径:(I)CH3O-+MEP;(II)CH3OH+MEP;(III)CH3O-+HMEP(MEP的质子化形式);(IV)CH3OH+HMEP.在B3LYP/6-31++G(d,p)水平上优化了四条反应途径的反应物、中间体、过渡态及产物的几何构型,并在同水平上进行了自然电荷分析,然后在MP2/6-311++G(3df,2p)水平上计算了各驻点的单点能.采用极化连续介质模型(PCM)研究了各途径在苯、甲醇和水溶液中的溶剂化效应.计算结果表明,溶剂效应使途径(I)的自由能垒降低,而使途径(II)和(IV)的决速步骤的自由能垒升高.在气相和苯溶剂中途径(IV)是反应的优势途径,在甲醇和水溶剂中途径(I)则成为最优.研究结果进一步表明实验条件下途径(II)与(IV)对总醇解反应的贡献相当.

The density functional theory and MP2 method were employed to study the reaction pathways of methanolysis of 3-methyl cyclic ethylene phosphate （MEP）： （I） CH3O^-＋MEP; （II） CH3OH＋MEP; （Ⅲ） CH3O^-＋HMEP （protonated form of MEP）; （IV） CH3OH＋HMEE The geometries for the reactants, intermediates, transition states and products were optimized at B3LYP/6-31＋ ＋G（d,p） level, and the natural charge was analyzed at the same level. The single point energy of each stationary point was calculated at MP2/6-311 ＋ ＋ G（3df,2p） level. The effect of various solvents such as benzene, methanol and water on the reaction pathways was assessed by the polarizable continuum model. The calculated results show that the solvent effects reduce the free energy barrier for pathway I, while increase the free energy barriers for rate-controlling step of pathways II and IV. Pathway IV is the most favorable one in the gas phase and benzene, while pathway I becomes the most favorable one in both methanol and water. Our calculated results also indicate that the pathways II and IV contribute to the total reaction equally under the experimental condition.