Highly selective bromination of toluene in a bromine-oxirane-zeolite system

The liquid-phase bromination of toluene in a zeolite-bromine-oxirane system has been studied. This system increases selectivity toward the para-bromotoluene isomer due to two factors: first, the oxirane deactivates the sites located on the external surface of the zeolite and, second, a bromine-oxirane complex is formed that is less active and bulkier than is bromine. Using this method, 98% pure para-bromotoluene can be obtained. The catalyst system is deactivated rapidly, presumably due to epoxide polymerization.