A rapid and scalable method for visible light induced bromination of uracil derivatives in falling film looping photoreactor

A looping falling film reactor protocol was applied for the visible light induced green synthesis of 5-bromouracil derivatives using N-bromosuccinimide (NBS). Readily available cool white LEDs of emission spectrum 400 nm to 700 nm were used. A minimum of 2.2 equivalent NBS was required to reach the maximum yield. Nonhazardous solvent acetonitrile was found to be most effective compared to other solvents. This methodology has also shown excellent tolerance with various 6-substituted and N-substituted uracil. We successfully synthesized sixteen novel 5-bromouracil and pyrimidine derivatives and characterized them using various spectroscopic methods such as 1H-NMR, 13C-NMR, HRMS, and SC-XRD. Finally, the reaction between 6-chloro-3-methyluracil and NBS was used in three different reactor modules of looping falling film reactor to show the successive scalability of the process with comparable photonic characteristics and reaction conditions. We achieved milligram to multigram scale reaction with almost equal efficiency and maximum productivity up to 1.2 kg/day.