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Review
. 2024 May 7;29(10):2166.
doi: 10.3390/molecules29102166.

Heterogeneous Organocatalysts for Light-Driven Reactions in Continuous Flow

Graziano Di Carmine  1 , Carmine D'Agostino  2   3 , Olga Bortolini  1 , Lorenzo Poletti  4 , Carmela De Risi  4 , Daniele Ragno  4 , Alessandro Massi  4
Affiliations
Review

Heterogeneous Organocatalysts for Light-Driven Reactions in Continuous Flow

Graziano Di Carmine et al. Molecules. .

Abstract

Within the realm of organic synthesis, photocatalysis has blossomed since the beginning of the last decade. A plethora of classical reactivities, such as selective oxidation of alcohol and amines, redox radical formation of reactive species in situ, and indirect activation of an organic substrate for cycloaddition by EnT, have been revised in a milder and more sustainable fashion via photocatalysis. However, even though the spark of creativity leads scientists to explore new reactions and reactivities, the urgency of replacing the toxic and critical metals that are involved as catalysts has encouraged chemists to find alternatives in the branch of science called organocatalysis. Unfortunately, replacing metal catalysts with organic analogues can be too expensive sometimes; however, this drawback can be solved by the reutilization of the catalyst if it is heterogeneous. The aim of this review is to present the recent works in the field of heterogeneous photocatalysis, applied to organic synthesis, enabled by continuous flow. In detail, among the heterogeneous catalysts, g-CN, polymeric photoactive materials, and supported molecular catalysts have been discussed within their specific sections, rather than focusing on the types of reactions.

Keywords: flow chemistry; green chemistry; heterogeneous catalysis; photocatalysis; synthetic methodologies.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
An example of catalysis classification in terms of the catalyst type or catalysis mode: (A) organocatalysis and (B) photocatalysis. * means excited state.
Figure 2
Figure 2
Simplified mechanisms, which involve molecular photocatalysts and semiconductors. * means excited state.
Figure 3
Figure 3
The image shows some advantages of continuous flow reactions compared to batch ones.
Figure 4
Figure 4
Mechanism of redox transformations mediated by generic semiconductors.
Figure 5
Figure 5
Mechanism of injection of the sensitizer into the semiconductor. * means excited state.
Figure 6
Figure 6
Attenuation of light with distance.
Figure 7
Figure 7
Triazine units and heptazine units are the building blocks composing the layers that, by stacking, make all the forms of g-CN.
Figure 8
Figure 8
(a) Diffuse reflectance spectra of MCN and HMCN-2. (b) Band structure of MCN and HMCN-2. (c) XRD spectra of MCN and HMCN-2. (a–c) reprinted with permission from ref. [62]. Copyright 2021 Elsevier.
Figure 9
Figure 9
Oxidative coupling of benzyl alcohol with methanol promoted by HMCN-2 and light in continuous flow conditions.
Figure 10
Figure 10
O1s XPS spectra of PES (a), PES-CN (b), and PES-CN (treated) (c). (a–c) reprinted with permission from ref. [63]. Copyright 2022 Elsevier.
Figure 11
Figure 11
Set-up for the oxidation of anisyl alcohol into p-anisaldehyde, mediated by g-CN coated PES.
Figure 12
Figure 12
Oxidation of benzyl alcohol and scope extension involving a small range of benzyl alcohol derivates in continuous flow.
Figure 13
Figure 13
SEM image for g-CN (a) and 1.0 Ci-CN (b). In figure (b), the presence of a nanotubular structure is clear in square and cycle. (a,b) reprinted with permission from ref. [66]. Copyright 2023 American Chemical Society.
Figure 14
Figure 14
One-pot protocol mediated by 1.0 Ci-CN in continuous flow, in gram scale. * means excited state.
Figure 15
Figure 15
Continuous flow set-ups: (A) quasi-homogeneous decarboxylative 1,6-conjugate addition to p-QMs vs. (B) heterogeneous reductive coupling of p-QMs. (C) Proposed mechanisms.
Figure 15
Figure 15
Continuous flow set-ups: (A) quasi-homogeneous decarboxylative 1,6-conjugate addition to p-QMs vs. (B) heterogeneous reductive coupling of p-QMs. (C) Proposed mechanisms.
Scheme 1
Scheme 1
Trifluoromethylation in continuous flow, mediated by mpg-CN.
Figure 16
Figure 16
Continuous flow set-up for decarboxylative alkylation of BOC-protected proline.
Figure 17
Figure 17
Schematic representation of the photoreactor set-up, with reaction parameters for the dichloromethylation of I-chalcone.
Figure 18
Figure 18
C-H azolation of arenes in continuous flow, with packed-bed reactor, promoted by mpg-CN.
Figure 19
Figure 19
C–N coupling in an automated high-speed circulation flow, promoted by mpg-CN and NiCl2.glyme.
Figure 20
Figure 20
PET-RAFT polymerization in continuous flow, promoted by light and hPorBDP.
Figure 21
Figure 21
Schematic representation of MA-2IBDP-based microchip photoreactor.
Figure 22
Figure 22
Bromination of 1,3,5-trimethoxybenzene promoted by 1-PDI, supported on both PFA tubes and glass.
Figure 23
Figure 23
Schematic representation of set-up employed in the oxidation of DHN in continuous flow by TMPyP@SiO2.
Figure 24
Figure 24
Birch reduction of phenyl naphthalene by PXX-PDMS in continuous flow.
Figure 25
Figure 25
Schematic set-up of coupling between benzenediazonium salts and furan, promoted by MR-EY, in continuous flow.
Figure 26
Figure 26
Light-harvesting system AMCA−BY40−PhB cotton fiber.
See this image and copyright information in PMC

References

    1. de Marco B.A., Rechelo B.S., Tótoli E.G., Kogawa A.C., Salgado H.R.N. Evolution of Green Chemistry and Its Multidimensional Impacts: A Review. Saudi Pharm. J. 2019;27:1–8. doi: 10.1016/j.jsps.2018.07.011. - DOI - PMC - PubMed
    1. DeVierno Kreuder A., House-Knight T., Whitford J., Ponnusamy E., Miller P., Jesse N., Rodenborn R., Sayag S., Gebel M., Aped I., et al. A Method for Assessing Greener Alternatives between Chemical Products Following the 12 Principles of Green Chemistry. ACS Sustain. Chem. Eng. 2017;5:2927–2935. doi: 10.1021/acssuschemeng.6b02399. - DOI
    1. Di Carmine G., Abbott A.P., D’Agostino C. Deep Eutectic Solvents: Alternative Reaction Media for Organic Oxidation Reactions. React. Chem. Eng. 2021;6:582–598. doi: 10.1039/D0RE00458H. - DOI
    1. Clarke C.J., Tu W.-C., Levers O., Bröhl A., Hallett J.P. Green and Sustainable Solvents in Chemical Processes. Chem. Rev. 2018;118:747–800. doi: 10.1021/acs.chemrev.7b00571. - DOI - PubMed
    1. Davidson M.G., Elgie S., Parsons S., Young T.J. Production of HMF, FDCA and Their Derived Products: A Review of Life Cycle Assessment (LCA) and Techno-Economic Analysis (TEA) Studies. Green Chem. 2021;23:3154–3171. doi: 10.1039/D1GC00721A. - DOI