SELECTIVE BROMINATION OF HALOBENZENES USING ZEOLITE CATALYSTS

The substitution of halobenzenes by bromine at 25 °C is catalyzed by Y-type zeolites, partially exchanged with di- and trivalent cations. Catalyst activity and para/ortho ratio depend upon the type of cation, the extent of cation exchange, the activation temperature, the solvent, and the amount of catalyst used. In all cases the para/ortho ratio was substantially higher than with conventional procedures. Catalyst deactivation by hydrogen bromide, liberated during the reaction, was suppressed by adding sodium hydrogen carbonate and zeolite KA. The highest para/ortho ratios were obtained in a solvent-free procedure. The acidic Brønsted sites of the zeolite are considered to be the catalytically active sites. © 1979.