Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig, Linnéstraße 2, 04103 Leipzig, Germany.
J Phys Chem A. 2021 Apr 15;125(14):2801-2815. doi: 10.1021/acs.jpca.0c11371. Epub 2021 Mar 26.
Ephemeral intermediates often hold the key to a more detailed understanding of chemical reaction pathways. Online methods to unambiguously identify the structure of such molecular entities, in particular in the presence of multiple isomers, are scarce. This paper presents a methodology that allows real-time monitoring of isomeric solution-phase reaction intermediates of continuous-flow reactions by coupling a microfluidic chip-reactor to a cryogenic ion trap triple mass spectrometer. The technique combines the excellent reaction control associated with microfluidic chips with the unique specificity and sensitivity of infrared photodissociation (IRPD) spectroscopy, which allows for an unambiguous structural assignment of gaseous ions based on their IR fingerprint. It represents a valuable extension to the instrumentation for online-analysis of reactive intermediates and proves particularly valuable whenever the sensitivity of NMR is not sufficient. After a brief description of the experimental approach, illustrative examples are provided to highlight the application of the chip-IRPD setup for mechanistic studies, particularly for stereoselective processes. The article concludes with an outlook on future challenges and perspectives.
瞬态中间体常常是更深入了解化学反应途径的关键。然而，目前在线方法在明确识别此类分子实体的结构方面（特别是在存在多种异构体的情况下）还很缺乏。本文提出了一种方法，通过将微流控芯片反应器与低温离子阱三重四极杆质谱仪相耦合，实现了连续流反应中处于溶液相的瞬态中间体异构体的实时监测。该技术结合了微流控芯片所具有的优异反应控制能力与红外光解离（IRPD）光谱的独特特异性和灵敏度，可根据其红外指纹对气态离子进行明确的结构分配。这是对反应中间体在线分析仪器的一个有价值的扩展，尤其是在 NMR 的灵敏度不足时，该方法特别有用。在简要描述实验方法后，本文提供了一些示例来说明芯片-IRPD 装置在机理研究中的应用，特别是在立体选择性过程中。最后，本文展望了未来的挑战和前景。
