Center for Intelligent Chemical Instrumentation, †Department of Chemistry and Biochemistry, ‡Edison Biotechnology Institute, Ohio University , Athens, Ohio 45701, United States.
Anal Chem. 2014 Apr 15;86(8):4024-32. doi: 10.1021/ac500527q. Epub 2014 Apr 4.
Green chemistry minimizes chemical process hazards in many ways, including eliminating traditional solvents or using alternative recyclable solvents such as ionic liquids. This concept is now adopted in this study for monitoring solvent-free reactions and analysis of ionic liquids, solids, and catalysts by mass spectrometry (MS), without using any solvent. In our approach, probe electrospray ionization (PESI), an ambient ionization method, was employed for this purpose. Neat viscous room-temperature ionic liquids (RTILs) in trace amounts (e.g., 25 nL) could be directly analyzed without sample carryover effect, thereby enabling high-throughput analysis. With the probe being heated, it can also ionize ionic solid compounds such as organometallic complexes as well as a variety of neat neutral solid chemicals (e.g., amines). More importantly, moisture-sensitive samples (e.g., [bmim][AlCl4]) can be successfully ionized. Furthermore, detection of organometallic catalysts (including air-sensitive [Rh-MeDuPHOS][OTf]) in ionic liquids, a traditionally challenging task due to strong ion suppression effect from ionic liquids, can be enabled using PESI. In addition, PESI can be an ideal approach for monitoring solvent-free reactions. Using PESI-MS, we successfully examined the alkylation of amines by alcohols, the conversion of pyrylium into pyridinium, and the condensation of aldehydes with indoles as well as air- and moisture-sensitive reactions such as the oxidation of ferrocene and the condensation of pyrazoles with borohydride. Interestingly, besides the expected reaction products, the reaction intermediates such as the monopyrazolylborate ion were also observed, providing insightful information for reaction mechanisms. We believe that the presented solvent-free PESI-MS method would impact the green chemistry field.
绿色化学通过多种方式最大限度地减少化学过程危害，包括消除传统溶剂或使用替代可回收溶剂，如离子液体。本研究采用这一概念，通过质谱（MS）对无溶剂反应和离子液体、固体和催化剂进行监测和分析，而无需使用任何溶剂。在我们的方法中，采用探针电喷雾电离（PESI）这种大气离子化方法。痕量（例如 25 nL）的粘性室温离子液体（RTIL）无需样品残留效应即可直接进行分析，从而实现高通量分析。由于探针被加热，它还可以使有机金属配合物等离子固体化合物以及各种中性固体化学物质（例如胺）电离。更重要的是，能够成功地对水分敏感的样品（例如[bmim][AlCl4]）进行离子化。此外，由于离子液体的强烈离子抑制作用，传统上难以在离子液体中检测到的有机金属催化剂（包括对空气敏感的[Rh-MeDuPHOS][OTf]）也可以使用 PESI 进行检测。此外，PESI 可以成为监测无溶剂反应的理想方法。我们使用 PESI-MS 成功地考察了醇对胺的烷基化反应、吡喃鎓向吡啶鎓的转化反应以及醛与吲哚的缩合反应，以及空气和水分敏感的反应，如二茂铁的氧化反应和吡唑与硼氢化钠的缩合反应。有趣的是，除了预期的反应产物外，还观察到了反应中间体，如单吡唑硼酸离子，为反应机制提供了有价值的信息。我们相信，所提出的无溶剂 PESI-MS 方法将对绿色化学领域产生影响。
