Regioselective bromination of aromatic compounds with Br2/SO2Cl2 over microporous catalysts

A new selective brominating system Br2/SO2Cl2/zeolite, has been discovered. Partially cation-exchanged Ca2+-Y zeolite efficiently catalyzes the selective para-bromination of neat chlorobenzene (CB) by Br2/SO2Cl2 affording a CB conversion of ∼89% and a para-selectivity of ∼97%. During the bromination reaction, SO2Cl2 oxidizes HBr, prevents its accumulation within the zeolite pores and yields a more active brominating species. The Ca2+-Y catalyst was found to be stable under the bromination conditions, and can easily be regenerated by calcination. The Br2/SO2Cl2/Ca2+-Y brominating system could be applicable to other activated aromatic compounds such as o-xylene, toluene and fluorobenzene.