Heteropoly acid cesium salt/cetyltrimethylammonium bromide a catalytic heterogeneous system which highly controls regioselective bromination of aromatic compounds with bromine

Regioselective and high-yielding bromination of aromatic compounds especially phenols is an important protocol from different point of views. In this article, we have reported regioselective mono-bromination of phenol, its derivatives and some aromatic compounds with bromine in the presence of a heterogeneous catalytic system which is composed of CS2.5H0.5PW12O40/cetyltrimethylammonium bromide (CTAB) in high yields. For reactions performed on 1 mmol scale of phenol, the optimum PhOH/Br-2/CS2.5H0.5PW/CTAB molar ratio was found to be 1:1.1:0.05:0.025. Phenols with electron-releasing groups were rapidly and selectively mono-brominated at their para positions in good to excellent yields. 2-Chlorophenol and 2,6-dichlorophenol were also mono-brominated at para positions in high yields. In the presence of this catalytic system, bromination of polycyclic aromatic compounds proceeded efficiently and furnished mono-brominated products by the control of bromine concentration. (C) 2002 Elsevier Science B.V. All rights reserved.