In situ monitoring of photocatalyzed isomerization reactions on a microchip flow reactor by IR-MALDI ion mobility spectr
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RESEARCH PAPER
In situ monitoring of photocatalyzed isomerization reactions on a microchip flow reactor by IR-MALDI ion mobility spectrometry Chris Prüfert 1 & Raphael David Urban 2 & Tillmann Georg Fischer 3 & José Villatoro 1 & Daniel Riebe 1 & Toralf Beitz 1 & Detlev Belder 2 & Kirsten Zeitler 3 & Hans-Gerd Löhmannsröben 1 Received: 18 June 2020 / Revised: 17 August 2020 / Accepted: 27 August 2020 # The Author(s) 2020
Abstract The visible-light photocatalytic E/Z isomerization of olefins can be mediated by a wide spectrum of triplet sensitizers (photocatalysts). However, the search for the most efficient photocatalysts through screenings in photo batch reactors is material and time consuming. Capillary and microchip flow reactors can accelerate this screening process. Combined with a fast analytical technique for isomer differentiation, these reactors can enable high-throughput analyses. Ion mobility (IM) spectrometry is a costeffective technique that allows simple isomer separation and detection on the millisecond timescale. This work introduces a hyphenation method consisting of a microchip reactor and an infrared matrix-assisted laser desorption ionization (IR-MALDI) ion mobility spectrometer that has the potential for high-throughput analysis. The photocatalyzed E/Z isomerization of ethyl3-(pyridine-3-yl)but-2-enoate (E-1) as a model substrate was chosen to demonstrate the capability of this device. Classic organic triplet sensitizers as well as Ru-, Ir-, and Cu-based complexes were tested as catalysts. The ionization efficiency of the Z-isomer is much higher at atmospheric pressure which is due to a higher proton affinity. In order to suppress proton transfer reactions by limiting the number of collisions, an IM spectrometer working at reduced pressure (max. 100 mbar) was employed. This design reduced charge transfer reactions and allowed the quantitative determination of the reaction yield in real time. Among 14 catalysts tested, four catalysts could be determined as efficient sensitizers for the E/Z isomerization of ethyl cinnamate derivative E-1. Conversion rates of up to 80% were achieved in irradiation time sequences of 10 up to 180 s. With respect to current studies found in the literature, this reduces the acquisition times from several hours to only a few minutes per scan. Keywords Microchip . Reaction monitoring . IR-MALDI . Ion mobility spectrometry . Photochemistry . Photocatalysis . Olefin isomerization
Introduction Chris Prüfert, Raphael David Urban and Tillmann Georg Fischer contributed equally to this work. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00216-020-02923-y) contains supplementary material, which is available to authorized users. * Chris Prüfert [email protected] * Hans-Gerd Löhmannsröben [email protected] 1
University of Potsdam, Physical Chemistry, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany
2
Institute of Analytical Chemistry, Leipzig University, Linnéstraße 3, 04103 Leipzig, Germany
3
Institute of O
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