Selective aerobic oxidation of toluene to benzaldehyde catalyzed by covalently anchored N-hydroxyphthalimide and cobaltous ions

Selective oxidation of toluene to benzaldehyde via dioxygen is of great significance industrially but suffers from a severely low selectivity due to a much higher reactivity of the desired product than the reactant. A combination of homogeneous N-hydroxyphthalimide (NHPI) and cobaltous ions was found active and selective for the transformation from toluene to benzaldehyde in the presence of hexafloropropan-2-ol. In this work, homogeneous NHPI was covalently anchored onto the surface of commercial mesoporous SiO 2 to facilitate the separation and recovery of the catalyst, aiming at a possible industrial application. The grafting bonds were well confirmed by FT-IR, TGA and XP spectra, and the density of > N OH groups anchored was up to 0.6 mmol/g in the immobilized NHPI catalysts. The resulting catalysts exhibited an excellent activity for selective oxidation of toluene to benzaldehyde, and there was no appreciable loss in catalytic activity observed after repeated evaluations, suggesting a promising prospect for its further investigation and possible application.