Abstract
A continuous-flow photo-bromination reaction on benzyl and phenyl groups was conducted using N-bromosuccinimide as the bromine source inside a preparatory-scale glass plate reactor. This flow reactor system was capable of independently controlling light intensity, wavelength, and reaction temperature, hence exerting an exceptional level of control over the reaction. A short optimisation study for the synthesis of 2-bromomethyl-4-trifluoromethoxyphenylboronic acid pinacol ester resulted in best conditions of 20°C and 10 min residence time using an LED (light-emitting diode) array at 405 nm and acetonitrile as the solvent. The present study evaluates the potential for this easy-to-handle bromination system to be scaled up for chemical manufacture inside a continuous-flow glass plate reactor. The combination with an in-line continuous flow liquid–liquid extraction and separation system, using a membrane separator, demonstrates the potential for continuous flow reaction with purification in an integrated multi-stage operation with minimal manual handling in between.
Highlights
The scale-up of photochemical processes for industry is an underdeveloped field that offers promising opportunities to perform chemical reactions in a green and efficient manner
Batch processes have been utilised for photochemistry using mercury or xenon lamps, which are very inefficient, consume high amounts of energy, and can cause undesired side reactions occurring from broad-wavelength irradiation
We have demonstrated a simple continuous-flow photo-bromination inside a highly efficient preparatory-scale glass plate reactor
Summary
The scale-up of photochemical processes for industry is an underdeveloped field that offers promising opportunities to perform chemical reactions in a green and efficient manner. Batch processes have been utilised for photochemistry using mercury or xenon lamps, which are very inefficient, consume high amounts of energy, and can cause undesired side reactions occurring from broad-wavelength irradiation. Aryl bromides have a very broad and widespread use in the synthesis of fine chemicals. They have applications as intermediates in cross-couplings[3] and halogen displacement reactions.[4] In addition, they are used in the synthesis of antibacterial, antifungal, and antiviral agents.[5]
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