Abstract

Applications of Flow Photochemistry Towards Industrial Scale Processing

Oliver Kappe, Professor, Karl Franzens University of Graz

In recent years the popularization of synthetic photochemistry has brought with it a plethora of new methodologies, significantly enriching the chemist’s synthetic toolbox. Alongside classical UV-mediated photochemical methodologies, modern visible light methods (including photoredox transformations) are now being routinely included in synthetic routes at a small scale. These often offer unique disconnections, unachievable by alternative means, therefore, an efficient scale up strategy must be capable of including such transformations. As these molecules progress through stages of development, the process chemistry and manufacturing communities must be prepared, in terms of both equipment and expertise. Despite the inherent scalability implied by continuous flow processing, numerous obstacles are still present, including: reactor fouling, particularly when using UV irradiation; long reaction times, leading to low productivity; control of light flux over prolonged periods; and many more. With some extent of fundamental understanding around the reaction’s kinetic regime and irradiation requirements, the most suitable reactor and conditions can be chosen or developed. Accordingly, these obstacles can be overcome, or at least minimized, towards a robust and productive process. Herein, we present our experiences in developing a range of modern and classical photochemical transformations in continuous flow, in collaboration with industrial partners. These case studies will include: direct excitation and sensitized transformations, LED and arc lamp irradiation, tubing and plate-based reactors. The practical considerations, hurdles and solutions will be discussed, whilst maintaining a focus on application to processing on larger scales.