Microphotochemistry - a new resources efficient synthesis tool approach

Abstract

Microphotochemistry, i.e. photochemistry in microstructured reactors, is a novel research area of the 21st century. It combines established techniques in organic photochemistry and continuous flow microsystem engineering with advances in light technology. This research work aimed to develop a novel resource- and energy-efficient approach in synthetic chemistry and to demonstrate that microflow-photochemistry can serve as a compact, rapid and resource efficient R&D tool. A series of homogeneous and heterogeneous photoreactions have been studied in microreactors to evaluate the potential of microphotochemistry. A range of acetonesensitized photodecarboxylation reactions involving phthalimides was investigated in commercially available microreactor dwell device and a number of isopropanol additions to furanones were studied in newly designed within the project LED-driven microchip. All results were compared to analogous experiments in conventional Rayonet reactor. In all cases examined, the reactions performed in the chosen microreactors gave higher conversions or yields. This finding was explained by the generated data of light penetration, irradiated surface-to-volume ratio, energy efficiency and space-time yield. The numbers achieved for continuous flow systems were notably higher compared to the conventional setup. This finding nicely proved superiority of microphotochemistry concept. Another commercially available device falling film microreactor was successfully adapted for the photooxygenation of -terpinene and new safer methodology have been developed for the synthesis of potentially explosive endoperoxide ascaridole. Major disadvantages of commercially available microreactors are, however, the fixed length of the reaction channel and the single-channel design. Although numbering-up can be achieved using an array of microreactors, which required significant costs investment. Flexible PTFE capillaries represent a cost-efficient alternative. Thus a simple continuous microflow dual-capillary reactor and its optimised version multimicrocapillary tower were developed. The tower design enables parallel operation of 10 experiments and it was successfully tested for reaction optimization, library synthesis and scale-up. The multi-capillary design may be easily transferred to other microflow applications such as parallel testing of biologically active compounds, process modeling, in situ analysis and combinatorial chemistry. Consequently, micro-photochemistry may serve as a compact, rapid and resource efficient R&D tool and opens new approaches for synthetic chemistry