摘要/Abstract

甲基迁移反应在合成化学和生命科学领域具有重要意义.迄今为止，所报道的甲基迁移反应大多数发生在不同种类分子之间.因此，寻找新型甲基迁移反应具有一定的研究价值.本研究以环境中常见的杀虫剂倍硫磷为研究对象，采用电喷雾质谱技术为分析工具对反应体系进行高灵敏分析，探究在CF₃COOH及纳米二氧化钛（TiO₂）条件下，倍硫磷分子中发生甲基迁移反应的可能性.结果表明，在CF₃COOH和TiO₂共同作用下，倍硫磷分子中的甲基可以从同一分子的氧原子上迁移到不饱和硫原子上，发生分子内1，3-甲基迁移反应，形成异构体硫甲基化产物；同时，异构体产物中的甲基还可以从硫原子上再继续迁移到另一分子倍硫磷的不饱和硫原子上，发生分子间甲基迁移反应.同时结合密度泛函理论计算对倍硫磷分子内和分子间甲基迁移反应的过程进行动态模拟，并对其迁移机理进行解释.本研究发现了倍硫磷能发生分子内和分子间甲基迁移反应，提供了一种研究甲基迁移反应的质谱方法，为倍硫磷的降解研究提供了新思路.
关键词: 倍硫磷, 分子内甲基迁移, 分子间甲基迁移, 电喷雾质谱, 三氟乙酸, 纳米二氧化钛
Methyl transfer reactions are of great significance in the field of synthetic chemistry and life sciences. So far, most of the reported methyl migration reactions have occurred between different types of molecules. Therefore, it is of certain value to search for new methyl transfer reactions. In this study, fenthion, a most common insecticide in the environment, was selected as the studied object, and electrospray ionization mass spectrometry (ESI-MS) was used as the analytical tool to conduct highly sensitive analysis of the reaction system, so as to explore the possibility of methyl transfer reaction in fenthion molecules under the condition of trifluoroacetic acid and nanometer titanium dioxide. Other than m/z 279 (protonated fenthion), some new product ions (m/z 293 and m/z 265) could be observed in the fingerprint MS of fenthion reaction solution. Tandem MS experiments showed that the intensity of product ion m/z 231 (elimination of CH₃SH) in the dissociation of m/z 279 from fenthion reaction solution were different from that from protonated fenthion standard. This indicated that the methyl in the fenthion could transfer from oxygen atom to unsaturated sulfur atom via 1,3-methyl transfer, forming isomer a2, which led to the high intensity of product ion m/z 231 in the dissociation of m/z 279 from fenthion reaction solution. Under the assistance of acid, the methyl cation continued to transfer from sulfur atom in a2 to the unsaturated sulfur atom in another fenthion molecule, forming a3 (m/z 293) and a4 via intermolecular methyl transfer reaction, which was verified by tandem MS experiments of ions at m/z 293 and m/z 265. In addition, density functional theory (DFT) calculations were carried out to confirm the mechanism of intramolecular and intermolecular methyl transfer reactions of fenthion. In order to observe the phenomenon of methyl transfer more intuitively, the effects of different acids, metal oxides, reaction time and reaction temperature on the signal intensities of ions at m/z 265 and m/z 293 of intermolecular methyl transfer reactions of fenthion were investigated. It could be concluded that under the conditions of trifluoroacetic acid and nanometer titanium dioxide, and 60℃ ultrasound reaction for 6 h, the proportion of intermolecular methyl transfer reactions of fenthion was the highest. In this study, intramolecular and intermolecular methyl transfer reactions were both discovered and investigated in fenthion, which can not only provide a method to study methyl transfer reactions, but also propose a new idea for the study of degradation of fenthion.
Key words: fenthion, intramolecular methyl transfer, intermolecular methyl transfer, electrospray ionization mass spectrometry, trifluoroacetic acid, nanometer titanium dioxide


PDF全文下载地址:

点我下载PDF