Lipophilic N-hydroxyphthalimide Catalysts for the Aerobic Oxidation of Cumene: Towards Solvent-Free Conditions ... and Back

A new class of lipophilic N-hydroxyphthalimides catalysts designed for the aerobic oxidation of cumene in solvent-free conditions were synthesized and tested. The specific strategy proposed for the introduction of lipophilic tails on the NHPI moiety leads to lipophilic catalysts which, while completely preserving the activity of the precursor, allow to conduct the catalytic oxidation in neat cumene for the very first time. The corresponding cumyl hydroperoxide is obtained in good yields (28-52%) and high selectivity (95-97%), under mild conditions. Importantly, the presence of a polar solvent is no longer required to guarantee the complete solubilization of the catalyst. On the other hand, the oxidation conducted in neat cumene unearths the unexpected necessity of using small amounts of acetonitrile in order to fully promote the hydrogen atom transfer process and prevent the catalyst from detrimental hydrogen bond (HB) driven aggregation.