Imidazolium-containing diselenides for catalytic oxidations with hydrogen peroxide and sodium bromide in aqueous solutions

The design and synthesis of imidazolium-containing diselenides 4a-c is described. The introduction of the N-methylimidazolium group gives freely soluble compounds in water, unlike the majority of common organic diselenides. Catalytic amounts of 4a-c effectively promote bromination of organic substrates using a safe and inexpensive NaBr/H2O2 system in water. Kinetics experiments revealed that the bromination of 4-pentenoic acid has a first-order dependence with respect to both NaBr and H2O2 concentrations The rate of reaction was also sensitive to the pH of the solution. Preparative reactions showed that, compared to 4a, diphenyl diselenide 5 was a poor catalyst and the ionic liquid 1-benzyl-3-methylimidazolium bromide 6 showed no catalytic activity with H2O2 indicating synergy from the combined functionality.