吡唑衍生物与碘甲烷反应的密度泛函理论研究

Density Functional Theory Study on the Reactions of Pyrazole Derivatives with CH_(3)I

采用密度泛函方法对3-甲硫基-4氰-基-5-氨基吡唑与碘甲烷反应的机理进行了研究.提出了两种可能的反应途径:反应途径Ⅰ为反应物先脱去吡唑上的质子,生成阴离子中间物,然后碘甲烷分别进攻中间物吡唑环上的2个氮原子,生成两种异构产物;反应途径Ⅱ为反应物通过分子间氢转移存在两种异构体,碘甲烷直接进攻每个异构反应物吡唑上的氮原子,形成中间物,然后脱去碘化氢,生成产物.计算结果表明,途径Ⅱ应为主要反应途径.还找出了两种异构产物间甲基迁移反应的过渡态,得出该反应的活化能为278.5 kJ/mol,在常温下甲基迁移反应不容易进行.

Density functional（B3LYP） calculations, using the 6-31 G^＊ and LANL2DZdp ECP Polarization basis sets, were employed to study the reaction pathway involving 3-methylthio-4-cyano-pyrazole and iodomethane. According to the structure of pyrazole derivatives, two possible reaction pathways were examined. Pathway Ⅰ proceeded associated with the dehydrogenation of the reactants and the attack of CH3I on both nitrogen atoms of pyrazole. Pathway Ⅱ was as follows ： first, due to the hydrogen transfer of the reactants, two isomers are formed; then CH3I attacks on nitrogen atom of the isomers to form intermediates; finally the intermediates dehydroiodinate to form two products. The results from the calculation suggest that pathway Ⅱ is the dominant reaction channel.