微液滴中N,N-二甲基苯胺类化合物的氧化行为研究

Study on the Oxidation Behavior of N,N-Dimethylaniline Compounds in Microdroplets

小尺寸、高电场的微液滴具有独特的化学性质,可以加速化学反应或实现液相中一些无法进行的反应。本文基于微液滴的化学特点,搭建了微液滴喷雾质谱平台,研究N,N-二甲基苯胺(DMA)类化合物的氧化行为和裂解反应。利用微液滴在空气-水界面自发产生的超高电场,使DMA类化合物发生氧化反应,形成了丰富的、其他手段难以获得的高活性自由基阳离子(DMA^(+·)),发现在整个微液滴反应中,DMA^(+·)占据主导地位,引导其他氧化反应进行。另外,通过改变DMA反应条件,探究实验条件和取代基模式对产生DMA^(+·)丰度和稳定性的影响,结果表明,对位有供电子基团有利于自由基阳离子的稳定。此外,DMA^(+·)解离后主要丢失氢自由基以及进一步发生甲基迁移反应丢失HC≡N,当DMA的对位连有供电子基团时,会促进该迁移反应的发生。该研究有助于加深对水微滴化学促进氧化反应特性的理解,有望将制备的高活性自由基阳离子等活性物种应用于化工或制药等领域。

Microdroplets have many unique features such as small size and high electric field,therefore they can be accelerated to initiate chemical reactions and even promote some reactions that cannot be carried out in liquid phase.N,N-Dimethylaniline(DMA)is commonly used in medicine as a raw material for the synthesis of pharmaceutical intermediates.At present,the study involving in the detection of DMA is mainly focused on quantitative detection,and there is few reports on oxidation reaction and gas phase dissociation reaction of DMA.In this paper,the oxidation behavior and dissociation reaction of DMA and related compounds were studied by microdroplet spray mass spectrometry and tandem mass spectrometry.It was found that the ultra-high electric field spontaneously generated by microdroplets at the air-water interface can enable the oxidation reaction of DMA and related compounds to form abundant radical cation DMA^(+·).By changing the reaction distance,carrier gas pressure,injection velocity,sample concentration and substituent groups,the influence of experimental conditions and substituent modes on the generation of DMA^(+·)was explored.The result showed that the presence of electron donor groups is benefit for the stability of radical cations.After the dissociation of DMA^(+·),the main product ions were generated by elimination of hydrogen radical and a successive elimination of HC≡N via methyl migration reaction.In addition,when the electron-donating CH 3 group was connected with DMA,the intensity of related radical cation increased obviously,indicating that the electron-donating groups promoted the migration reaction.In conclusion,the stable transient intermediate DMA^(+·)that is difficult to prepare by other means,was obtained by microdroplet reaction in this study.This method is helpful to deepen the understanding of the chemical promoted oxidation reaction characteristics of water droplets and enriches the rearrangement reaction types of aniline compounds in gas phase dissociation.It is expected that the prepared active species such as high reactivity radical cations will be applied to chemical industry or pharmaceutical fields in the future.