Solvent-Free Aerobic Oxidation of Ethylbenzene Promoted by NHPI/Co(II) Catalytic System: The Key Role of Ionic Liquids

The synergistic action between imidazolium based ionic liquid (IL) [bmim][OcOSO(3)] and Co(II)/N-hydroxyphthalimide (NHPI) systems in the catalytic aerobic oxidation of ethylbenzene under solvent-free conditions have been here demonstrated by reaching a 35 % conversion with 83 % of selectivity in acetophenone at 80 degrees C. This highly performing catalytic system have been selected after screening several different IL and Co(II) salt combinations, and making sure that the complete solubilization of the polar NHPI in the lipophilic medium, without thus requiring any chemical modification of the organic catalyst, could be attained. This solubilizing effect can be ascribed to a direct interaction between [bmim][OcOSO(3)] IL and NHPI as revealed by a detailed NMR investigation which also allowed to exclude the formation of higher IL aggregates in the form of micelles or vesicles.