IMOTHY NOËL¹*, XIAO WANG², VOLKER HESSEL1
*Corresponding author
1. Eindhoven University of Technology, Department of Chemical Engineering and Chemistry, Micro Flow Chemistry and Process TechnologyDen Dolech 2 (STW 1.48), 5600 MB Eindhoven, The Netherlands
2. Harvard Medical School and Brigham & Women’s Hospital, Harvard NeuroDiscovery Center, Laboratory for Drug Discovery in Neurodegeneration65 Landsdowne Street, Cambridge, Massachusetts, 02139, United States

Abstract

Owing to the generally mild reaction conditions, photoredox catalysis has become very popular in recent years and has affected a renewed interest in the use of solar energy to establish chemical transformations. In the last decade, continuous microflow reactors have received an increasing amount of attention to facilitate photochemical reactions. In such reactors, improved irradiation of the reaction medium and the ability to immobilize the photocatalyst have impacted the photoredox catalyzed process significantly and have allowed to reduce both the catalyst amount and the reaction times. Hereby, we highlight recent efforts in the application of continuous microflow reactors in photoredox catalysis. The use of transition metal catalyzed photoredox processes as well as metal free photoredox processes in continuous microflow are discussed and compared with their batch counterparts.

INTRODUCTION

In the past few years, photoredox catalysis has become a flourishing field in the research of synthetic methodologies (1-3). Unlike conventional photochemical processes which often need UV light and additional requirements of reaction vessel and safety protocol, some photoredox catalysts are able to absorb visible light and transform it to electric potential energy, to complete chemical reactions via the single electron transfer (SET) pathway. Owing to the mild reaction conditions and the visible light as an infinite and green energy source, in many circumstances, this type of reactions has become the ideal way to realize difficult transformations in terms of both yield and selectivity.
Microreactor technology has enabled synthetic chemists and process engineers to perform reactions with a high degree of control over reaction/residence time, heat and mass transfer and other process parameters, which results in an enhanced reproducibility (4, 5). In addition, due to the small dimensions, this technology provides reduced safety hazards and high surface-to-volume ratios. The latter is particularly advantageous for photochemical synthese ...