An Atmospheric Pressure Chemical Ionization Mass Spectrometry (APCI-MS) approach for in-situ monitoring of reactions in ionic liquid media

Imidazolium-based ionic liquids (Im-ILs) have gained attention in modern chemistry owing to their unique physicochemical properties, such as low volatility, non-flammability, and air/ water stability. Their exceptional tunability as solvents and catalysts makes them valuable tools in promoting a variety of reactions, particularly within sustainable and green synthesis, where they are increasingly replacing traditional volatile organic solvents (VOCs). [1] Despite these advantages, their inherently ionic composition poses challenges when applying electrospray ionization mass spectrometry to monitor reaction progress in such media. Specifically, the strong ionic signals from the IL's cations, anions, and their aggregates in the gas phase can overshadow or suppress the signals of neutral organic compounds, preventing the detection of reaction reactants, products, and intermediates. [2] In this study, we have introduced a mass spectrometric method based on atmospheric pressure chemical ionization (APCI-MS) designed ad-hoc to overcome this obstacle and reduce the background interference from ILs. We also explored the potential of this technique for the in-situ quantification of the reaction products by constructing calibration curves for three different model systems, namely the Knoevenagel condensation, benzoin addition, and oxidative esterification. When applied in the real reaction environment, a good correlation between the yields determined by APCI-MS and those obtained from NMR analysis was achieved. Accordingly, this approach can prevent quenching the reactions when they are still in progress and optimise the reaction time before extracting the products. References 1. Z. Lei, B. Chen, Y.-M. Koo, D. R. MacFarlane; Chemical Reviews, 117 (2017), pp 6633-6635. 2. L. L. Khemchyan, E. A. Khokhlova, M. M. Seitkalieva, V. P. Ananikov; ChemistryOpen, 2 (2013), pp 208-214.