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Accelerated gas-liquid visible light photoredox catalysis with continuous-flow photochemical microreactors


In this protocol, we describe the construction and use of an operationally simple photochemical microreactor for gas-liquid photoredox catalysis using visible light. The general procedure includes details on how to set up the microreactor appropriately with inlets for gaseous reagents and organic starting materials, and it includes examples of how to use it to achieve continuous-flow preparation of disulfides or trifluoromethylated heterocycles and thiols. The reported photomicroreactors are modular, inexpensive and can be prepared rapidly from commercially available parts within 1 h even by nonspecialists. Interestingly, typical reaction times of gas-liquid visible light photocatalytic reactions performed in microflow are lower (in the minute range) than comparable reactions performed as a batch process (in the hour range). This can be attributed to the improved irradiation efficiency of the reaction mixture and the enhanced gas-liquid mass transfer in the segmented gas-liquid flow regime.

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Figure 1
Figure 2: Overview of the compounds prepared with the photomicroreactor setup.
Figure 3
Figure 4: An overview of the different microfluidic parts to construct the photomicroreactor.
Figure 5: Regulation of gas flow rates with a MFC or a needle valve.
Figure 6: Construction of the capillary photomicroreactor.
Figure 7: Drilled holes in the larger-diameter syringe used to fixate the photomicroreactor and to fit the exit of the microreactor.
Figure 8: Overview of the different constructional parts to establish a leak-free microfluidic fitting.
Figure 9: Construction and assembly of the cross micromixer.
Figure 10: Example of a reactor exit and reaction mixture collection.
Figure 11: Example of the preparation of a reaction solution.

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Y.S. thanks the European Union for a Marie Curie Intra-European Fellowship (no. 622415). T.N. acknowledges financial support from the Dutch Science Foundation (NWO) for a VENI grant (no. 12464) and from the European Union for a Marie Curie Career Integration Grant (Flach). Funding by the Advanced European Research Council (grant no. 267443 for V.H.) is kindly acknowledged. T.N. thanks all M.Sc. and B.Sc. students who have worked on this topic in the past years for their efforts.

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Authors and Affiliations



N.J.W.S. and Y.S. carried out the experiments and designed the protocol. N.J.W.S. and T.N. developed the visible light photocatalytic transformations. Y.S., V.H. and T.N. developed the final photomicroreactor design. T.N. designed and supervised the project. All authors contributed in the writing of the manuscript.

Corresponding author

Correspondence to Timothy Noël.

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Competing interests

The authors declare no competing financial interests.

Integrated supplementary information

Supplementary Figure 1 Overview of the microfluidic setup.

(1) Trifluoroiodomethane gas bottle; (2) Pressure regulator; (3) Mass Flow Controller (MFC); (4) Syringe pump I containing Reagents and catalyst; (5) Syringe pump II containing Quenching and/or dilution; (6) Cross micromixer section: mixing of the gaseous and liquid streams; (7) Photomicroreactor assembly; (8) Tee micromixer section: dilution or quenching of the reaction mixture; (9) Collection vial.

Supplementary Figure 2 Emission spectrum for the 3.12 W white LED stripe.

The emission of the used light sources was recorded using an integrating sphere equipped with a Labsphere LPS 100-0260 light detector array.

Supplementary Figure 3 Emission spectrum for the 3.12 W blue LED stripe.

The emission of the used light sources was recorded using an integrating sphere equipped with a Labsphere LPS 100-0260 light detector array.

Supplementary information

Supplementary Text and Figures

Supplementary Figures 1–3 (PDF 381 kb)

Supplementary Data

This ZIP file contains a copy of all spectra of the different compounds synthesized in this manuscript. (ZIP 2504 kb)

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Straathof, N., Su, Y., Hessel, V. et al. Accelerated gas-liquid visible light photoredox catalysis with continuous-flow photochemical microreactors. Nat Protoc 11, 10–21 (2016).

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