Mechanism of Slug Flow Enhancing Photon Transport and Its Application to Photobromination in Microreactors

To address the issue of severe photon attenuation in the oxime ether photobromination, slug flow was introduced to enhance photon transport in microreactors. Using the photochemical transformation of o-nitrobenzaldehyde as a benchmark reaction, response surface analysis was employed to systematically investigate the effects of various factors, including concentration, aqueous phase-to-organic phase flow rate ratio, and light intensity, on the reaction performance. The photon loss in the slug flow photomicroreactor was obtained through experimental measurements. The enhancement of photon transport by slug flow was attributed to the effects of internal circulation, refraction, and liquid film effects. Finally, the slug flow was applied to enhance the oxime ether photobromination, achieving an 84.6% yield of brominated oxime ether as a key intermediate of trifloxystrobin within 4 min. The slug flow could also suppress the formation of the z-type isomer of the main product and improve the reaction selectivity significantly. The space-time yield was 37 times higher than in the batch reactor and 3.5 times higher than in the single-phase flow microreactor. The slug flow strategy effectively reduced the E-factor from 30.99 to 23.22, indicating its applicability for green chemical transformations, holding crucial guiding significance for the industrial-scale production of trifloxystrobin.