A Continuous Electrochemical Bromine Generator for Telescoped Photochemistry, Oxidation, and Rearrangement Processes

Abstract

Despite its synthetic versatility, bromine is commonly avoided as a stoichiometric reagent in scaled synthesis due to safety concerns regarding its handling and the quenching of reaction mixtures. Generating bromine in situ from simple and readily available precursors therefore offers clear advantages. This study demonstrates the electrochemical generation and use of bromine exploiting a small footprint continuous flow reactor technology. Electrolysis of an acidic aqueous solution of sodium bromide is coupled with inline membrane extraction as well as inline UV-vis analysis allowing monitoring the generation and consumption of bromine under steady state conditions. This continuous bromine generator is then coupled with three downstream transformations, namely photochemical brominations, aldehyde oxidations and Hofmann rearrangements, demonstrating the versatility and robustness of this approach across a small collection of industrially relevant processes. Moreover, we demonstrate the recirculation of the remaining bromide solution which offers additional advantages in terms of sustainability and overall process efficiency. The exploitation of electrochemical in situ bromine generation, inline separation and monitoring, as well as reaction telescoping clearly shows the advantages of this holistic approach and is expected to facilitate future exploitation of this concept in academic and industrial settings alike.