In situ acidic carbon dioxide/water system for selective oxybromination of electron-rich aromatics catalyzed by copper bromide

Carbon dioxide, being one of the major greenhouse gases responsible for global warming, its atmospheric level grows ever faster since the beginning of industrial era. Great efforts have been devoted to developing versatile technologies/processes to adjust and manipulate the rapid growth of CO2 emission. Besides CO2 capture and storage/sequestration (CCS) to control its emission, chemical utilization of the captured CO2 (CCU) emerges to be a rational technique for economical benefits as well as environmental concerns. As for the aim of CO2 utilization, an environmentally benign CO2/water reversible acidic system was developed for the copper (II)-catalyzed selective oxybromination of electron-rich aromatics without the need of any conventional acid additive and organic solvent. Notably, up to 95% yields of the bromination products were attained with good regio-selectivity when cupric bromide was used as the catalyst and lithium bromide as a cheap and easy handling bromine source under supercritical CO2. The catalytic system worked well for electron-rich aromatics including ethers, sulfides and mesitylene. Carbonic acid in situ formed from CO2 and water is supposed to act as the proton donator in the Brønsted acid-promoted reaction. Notably, CO2 in this study serves as a reaction medium and a promoter in conjunction with water and also provides safe environment for aerobic reactions. Given with excellent reaction efficiency as well as no need of neutralization disposal, this process thus represents an environmentally friendly approach for aerobic bromination of aromatics with essential reduction of CO2 emission as well as an economically beneficial way for application of captured CO2.

Figure optionsDownload high-quality image (139 K)Download as PowerPoint slideHighlights
► Carbonic acid offers simple neutralization and does not require any waste disposal with essential reduction of CO2 emission.
► Copper bromide-catalyzed oxybromination performs well under in situ acidic CO2/H2O.
► High yield and regio-selectivity are attractive.
► CO2 serves as a reaction medium and a promoter in conjunction with water and also provides safe environment for aerobic reactions.