Bromination in microemulsion

Bromination of four different aromatic compounds, two phenols and two anisoles, was performed in a cationic surfactant-based microemulsion using the surfactant counterion, i.e., bromide, as reagent. The bromide ion was oxidized to elemental bromine by dilute nitric acid, which in turn reacts with the aromatic compounds. The results have been compared with two-phase procedures using either an in situ-prepared or a pre-prepared complex between bromine and a quaternary ammonium salt as oxidizing reagent and also with conventional bromination using elemental bromine. We report an easier, safer and more selective para-bromination when the reaction was performed in the microemulsion.