To face the challenge of industrial sustainability, new production technologies must be developed, in particular via process intensification. Part of a more general concept of “green engineering”, process intensification groups together a set of tools and methods enabling to implement Green Chemistry principles. Fine Chemical and Pharmaceutical industries are naturally concerned by this challenge.
Organic photochemistry has the potential to emerge as a key synthesis pathway and technology for sustainable chemistry. Selective transformations with high chemical and quantum yields are achieved, and in many case without chemical activation. The ability to address molecular complexity and diversity with a “flick of a switch” makes photochemistry indispensable for the synthesis of biologically active compounds in medicine or agriculture, but in many other fields (e.g. material science). Among the large portfolio of photochemical transformations, sensitized photo-oxygenations involving singlet oxygen in its first excited state are particularly attractive (e.g oxygenation of terpenes such as alpha-pinene, citronellol, or furfural, synthesis of the antimalarial drug artemisinin). Paradoxically, they have not found widespread implementations in the chemical industry. Such reluctance is mainly due to currently available technology, which requires (i) outdated batch reactors (often operating in a circulating loop and with large dilution, requiring intensive cooling), equipped with energy-demanding mercury lamps having a limited lifetime, (ii) soluble sensitizer and often non eco-friendly solvents.
Continuous microstructured technologies are a key part of process intensification strategy. Their advantages for preparative photochemistry have been recently highlighted at lab-scale, and flow photochemical industrial studies are still rare. Combining continuous microstructured technologies and LEDs light sources clearly emerges as a promising alternative for industrial implementation of photochemistry under greener, safer and atom- and energy-efficient conditions.