Continuous Flow Photocatalytic Hydrogen‐Transfer Reduction of Benzaldehydes in a Helical Packed‐Bed Reactor

ABSTRACT

Heterogeneous photocatalysis has emerged as a promising environmentally benign alternative to thermal catalytic processes; however, the realization of continuous photocatalytic production remains a significant challenge due to mass‐transfer limitations and nonuniform light irradiation. Herein, we report the continuous photocatalytic Meerwein–Ponndorf–Verley (MPV)‐like hydrogen‐transfer reduction of benzaldehyde derivatives to the corresponding benzyl alcohols using a fixed‐bed helical photocatalytic flow reactor consisting of a perfluoroethylene propylene copolymer (FEP) tube, titanium(IV) oxide (TiO ₂ )‐coated zircon beads (ZB), and a 10 W black light. Systematic optimization of TiO ₂ loading, aldehyde concentration, flow rate, and reactor configuration enabled continuous and highly chemoselective production of benzyl alcohol derivatives under ambient conditions without the use of hydrogen gas (H ₂ ). The helical flow configuration effectively suppressed concentration gradients within the catalytic phase and ensured stable irradiation from a black light, resulting in improved catalytic performance. The reactor system tolerated benzaldehyde derivatives bearing readily reducible functional groups while maintaining high chemoselectivity toward alcohol formation. Furthermore, numbering‐up of the reactor led to a proportional increase in benzyl alcohol productivity without loss of efficiency, demonstrating the scalability of the process. These findings highlight the potential of helical fixed‐bed photocatalytic flow reactors for continuous and scalable implementation of synthetically important MPV‐type reductions.