A Mg-doped manganese-based layered double oxide catalyst realizes the highly selective oxidation of toluene derivatives to aldehydes

Abstract

The efficient and selective oxidation of toluene derivatives to produce the corresponding aldehydes over a heterogeneous catalyst remains a challenge in industrial production. In this study, an effective catalytic system based on a Mg-doped Mn-based layered double oxide (MnMgAl-LDO) catalyst and NHPI (N-hydroxyphthalimide) has been developed. This system enables the liquid-phase oxidation of toluene and its derivatives into aromatic aldehydes, with hexafluoroisopropanol (HFIP) serving as the solvent. The incorporation of Mg increases the amount of oxygen vacancies and the surface basicity of the catalyst, thereby enhancing the reaction efficiency and aldehyde selectivity. In the model reaction over MgMnAl-LDO, the conversion of toluene reached 77%, with an 86% selectivity of benzaldehyde under the selected conditions. A possible reaction pathway for the selective oxidation of toluene to benzaldehyde was proposed based on the obtained results and a series of control experiments, and the active intermediates PINO (phthalimide-N-oxyl) were generated from NHPI simultaneously through the HAT (hydrogen atom transfer) and PCET (proton-coupled electron transfer) processes in the present reaction system. This catalytic system also exhibits good substrate applicability, as well as excellent stability and reusability, providing an efficient strategy for the green synthesis of aromatic aldehydes.