N-Hydroxyphthalimide Anchored on Diamond Nanoparticles as a Selective Heterogeneous Metal-free Oxidation Catalyst of Benzylic Hydrocarbons and Cyclic Alkenes by Molecular O2

Abstract

[EN] N-hydroxyphthalimide (NHPI) derived from trimellitic anhydride has been covalently anchored (4wt%) through ester bonds to the surface of commercial diamond nanoparticles previously functionalized by chemical and thermal treatments (DH). IR spectroscopy of the NHPI/DH solid shows the presence of a characteristic peak at 1735cm(-1) attributable to the ester bond, while solid-state MAS (CNMR)-C-13 spectroscopy shows two broad bands corresponding to carbon atoms of carbonyl groups (167ppm) and aromatic carbons (127ppm). NHPI/DH promotes autoxidation of isobutylbenzene involving superoxide (O-2(.-)) and hydroperoxide (HOO) radicals; NHPI/DH can be reused at least three times and reach a minimum turnover number as high as 20600, which is probably due to the inertness of the diamond surface, allowing free diffusion of reactive oxygen species. Analogous materials in which NHPI was anchored on activated carbon and multiwall carbon nanotubes were inefficient as autoxidation catalysts. NHPI/DH is able to promote also selective aerobic oxidation of other benzylic hydrocarbons and cycloalkenes.