Journal of Molecular Catalysis A: Chemical 195 (2003) 289–294 Heteropoly acid cesium salt/cetyltrimethylammonium bromide a catalytic heterogeneous system which highly controls regioselective bromination of aromatic compounds with bromine Habib Firouzabadi ∗ , Nasser Iranpoor 1 , Kamal Amani Department of Chemistry, Shiraz University, Shiraz 71454, Iran Received 7 August 2002; accepted 21 October 2002 Abstract Regioselective and high-yielding bromination of aromatic compounds especially phenols is an important protocol from dif- ferent point of views. In this article, we have reported regioselective mono-bromination of phenol, its derivatives and some aro- matic compounds with bromine in the presence of a heterogeneous catalytic system which is composed of Cs 2.5 H 0.5 PW 12 O 40 / cetyltrimethylammonium bromide (CTAB) in high yields. For reactions performed on 1mmol scale of phenol, the opti- mum PhOH/Br 2 /Cs 2.5 H 0.5 PW/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. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Phenol; Bromination; Heteropoly acid cesium salt; Cetyltrimethylammonium bromide; Heterogeneous catalysis 1. Introduction Bromoarenes are widely used intermediates of commercial importance [1,2] and methods reported in the literature for the electrophilic bromination of aromatic compounds include: (i) solid brominating agents such as PyHBr 3 [3], DBUHBr 3 [4], Me 4 NBr 3 [5], PhMe 3 NBr 3 [6]; (ii) Br 2 -Lewis acids [7], Br 2 - zeolite [8–10], Br 2 -silica or clay supported ZnBr 2 [11] Br 2 -supported resin [12]; (iii) oxidative nuclear bromination using metal-oxo catalysts [13–17]; (iv) ∗ Corresponding author. Tel.: +98-711-2284822; fax: +98-711-2280926. E-mail address: firouzabadi@chem.susc.ac.ir (H. Firouzabadi). 1 Co-corresponding author. N-bromosuccinimide, NBS in solid state reactions [18], NBS-HZMS-5 zeolite [19], NBS-Amberlyst [20], NBS-HCl [21], NBS-SiO 2 [22], and NBS-HBF 4 · Et 2 O [23]. Heteropoly acids and their acidic salts having the Keggin structure are known to be excellent acid cata- lysts [24–26]. Tungstophosphoric acid (H 3 PW 12 O 40 ) that belongs to Keggin type heteropoly acids has low surface area (ca. 5 m 2 g -1 ), whereas its cesium salt has much higher surface area (ca. 150 m 2 g -1 ) [27,28]. This high surface area makes it a more active cata- lyst than the parent acid and also other known solid acid catalysts such as zeolites [27,28]. Heteropoly acid cesium salt has been used for decomposition of cyclohexyl acetate into cyclohexene and acetic acid [29], alkylation and acylation of aromatics [30–32], 1381-1169/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S1381-1169(02)00589-7