杀螟丹中间体与异构体互变异构理论研究

Theoretical Study on the Tautomerization of Cartap Intermediate and Its Isomer

研究了合成杀虫剂杀螟丹的关键中间体2-N,N-二甲胺基-1,3-二硫氰基丙烷(有效体)及其异构体1-N,N-二甲胺基-2,3-二硫氰基丙烷(无效体)互变异构反应中溶剂和温度的影响.采用密度泛函理论B3LYP/6-31G(d)方法研究了其在气相中的反应机理,确定了相应的过渡态和反应活化能.量子化学计算结果表明,反应首先通过分子内亲核取代环化生成吖丙啶盐活性中间体,硫氰基进攻N-三元环中间体过程中发生了分子内重排转位,转化为异构体.采用极化连续(Polarizable continuum model,PCM)模型研究了反应体系在甲苯、氯仿、丙酮、乙醇、甲醇、乙腈和DMSO溶液中的溶剂效应.结果表明,该重排反应溶剂化效应非常明显,极性溶剂有利于过渡态的稳定,降低反应活化能,提高反应速率.理论研究结果与实验观察结果相符,很好地解释了有关实验现象.

The byproduct 1-（dimethylamino）-2,3-dithiocyanatopropane （2） can be recycled and partly converted into its isomer 2-（dimethylamino）-1,3-dithiocyanatopropane（ 1 ）, the key intermediate of Cartap, and finally achieved dynamic equilibrium, which can be used to increase the yield. Effects of temperature, catalyst and solvent on the tautomerization of compound 1 and its isomer 2 were investigated. The rearrangement mechanism was studied by density functional theory（DFF） method at B3LYP/6-31G（d） level. The calculation results indicated that the ring closure leading to aziridinium ion and further ring opening by thiocyanate at less substituted aziridine carbon atom via an SN 2 mechanism. The solvent effect （toluene, chloroform, acetone, methanol, ethanol, acetonitrile and DMSO ） on tautomerization was also taken into account via polarizable continuum model（PCM）. Ionization of a neutral substrate results in charge separation, and solvent polarity has a greater effect at the transition state than that for the reactants. Polar solvents lower the energy of the transition more than the solvents of lower polarity. The results show that the solvent effect plays an important role which was supported by experiment data.