MSTFA及其含氟衍生物的特征质谱重排反应

发布时间：2018-05-28 06:30

本文选题：N-甲基-N-(三甲基硅烷)三氟乙酰胺(MSTFA) + 气相色谱-质谱法(GC/MS)　；参考：《质谱学报》2017年06期

【摘要】：N-甲基-N-(三甲基硅烷)三氟乙酰胺(MSTFA)是一种重要的衍生化试剂,其质谱峰的归属对于深入研究其反应机理具有深刻意义。本工作对含氟和不含氟的两类衍生化产物和含氟芳香酚化合物的质谱裂解进行研究,结果表明,通过MSTFA衍生化后的含氟化合物生成了具有显著特征的m/z 77碎片离子,在谱图上多为基峰或接近基峰。而不含氟化合物的衍生化产物未能生成该特征离子,经高分辨质谱分析确认该离子组成为C2H6FSi+,是骨架重排反应产物,表明了骨架重排在m/z77产生过程的重要作用。推断该特征离子的生成途径为单分子内的亲核反应(SN1):首先中性分子被电离得到分子离子,游离基中心定域在杂原子O(N)上,游离基中心诱导分子离子通过α裂解脱去甲基自由基形成π键,提供了稳定的电荷中心;电荷中心诱导迫使π键上的一对电子进行迁移,正电荷同时转移到硅原子上,形成了能够促进下一步反应进行的活化中心;最大电负性的氟原子携带组成C—F键的一对电子亲核进攻硅正离子,生成新的F—Si键,同时迫使O(N)—Si键的一对电子发生转移造成O(N)—Si键的裂解;通过分子内的亲核消除反应脱去中性分子,从而得到特征离子m/z77。
[Abstract]:N-methyl-N-trifluoroacetamide (MSTFAA) is an important derivatization reagent. The assignment of its mass spectrum peak is of great significance for the further study of the reaction mechanism of N- methyl-N-trifluoroacetamide. In this work, the mass spectrometry cleavage of fluorine-containing and non-fluorinated derivatives and fluorinated aromatic phenols was studied. The results showed that the fluorinated compounds derived by MSTFA generated m / z 77 fragment ions with remarkable characteristics. Most of them are base peaks or close to base peaks. However, the derivative product without fluorine could not produce the characteristic ion, which was confirmed as C2H6FSi by high resolution mass spectrometry, which indicated that the skeleton rearrangement played an important role in the production of m/z77. It is inferred that the formation pathway of the characteristic ions is the nucleophilic reaction in monolayers: first, the neutral molecules are ionized to get molecular ions, and the free radical centers are located on the heteroatom ONs. The free radical center induces molecular ions to form 蟺 bond through 伪 -cleavage to remove methyl radical, which provides a stable charge center, and charge center induces a pair of electrons on 蟺 bond to migrate, and the positive charge is transferred to silicon atom at the same time. The largest electronegativity fluorine atoms carry a pair of electrons that form the C-F bond to attack the silicon positive ion to form a new F-Si bond. At the same time, a pair of electron transfer in the O(N)-Si bond was forced to cause the cleavage of the O(N)-Si bond, and the neutral molecule was removed by the intramolecular nucleophilic elimination reaction, and the characteristic ion m / z _ (77) was obtained.
【作者单位】：西安瑞联新材料股份有限公司;
【分类号】：O621.25

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