Multikilogram per Hour Continuous Photochemical Benzylic Brominations Applying a Smart Dimensioning Scale-up Strategy

Although continuous flow technology can facilitate the scale-up of photochemical processes it is not yet routinely implemented on production scale in the fine chemical industries. This can be attributed to additional challenges compared to thermal processes, mostly in the homogeneous irradiation of the flow reactor. Here, we detail the process of bringing a previously developed photochemical benzylic bromination, utilizing in situ bromine generation, from lab to pilot scale. The process setup is discussed in detail, alongside a comprehensive risk assessment and discussion of problems encountered in the investigation of key reaction parameters. Ultimately, an assay yield of 88% was obtained in 22 s irradiated residence time, resulting in a productivity of 4.1 kg h(-1) (space-time yield = 82 kg L-1 h(-1)) representing a 14-fold scale-up versus the lab-scale process.