Abstract

Photochemical Transformations Accelerated in Continuous-flow Microreactors

Timothy Noël, Professor, University of Amsterdam

Notwithstanding the apparent advantages of light energy, implementation of this energy source in organic synthetic methodologies and in the large scale production of fine chemicals has been largely neglected. Two main reasons have restrained substantial progress in photochemistry. The first reason concerns the photophysical aspects of organic molecules. Due to the absence of efficient chromophores in its core structure, most organic compounds are unable to efficiently absorb light energy to induce photochemical transformations. The second reason involves the limited scale-up potential of photochemistry. Large scale applications are hampered by the limited penetration depth of light irradiation due to absorption (Bouguer-Lambert-Beer law). Photoredox catalysis is emerging as a new and powerful tool in synthetic organic chemistry to facilitate such photochemical reactions by means of visible light.[1] Notable examples involve the use of ruthenium(II)polypyridine complexes which upon irradiation produce a photoexcited state. This photoexcited state gives rise to a single electron transfer process (SET) with organic substrates which can undergo subsequently a synthetic transformation. Whereas a myriad of different reactions have recently succumbed to this mode of catalysis, it is important to note that several challenges still remain with respect to high catalyst loadings, extended reaction times, scalability, quantum yield and generality of the catalyst system.