Interfacial Catalysis within Pickering Emulsion Droplets for Selective Imine Synthesis

Abstract

The oxidative coupling of benzylamine driven by reactive oxygen species (ROS) is an efficient route to imines; however, the targeted generation of superoxide anion radicals (•O2−), which are crucial for controlling the coupling process, remains a significant challenge. In this study, we developed an amphiphilic manganese dioxide (MnO2) nanocatalyst capable of preferentially adsorbing at liquid−liquid biphasic interfaces, enabling the stabilization of a water-in-oil Pickering emulsion system. The unique interface of the Pickering emulsion droplets not only provides a vast interfacial area for the reaction but also facilitates the enrichment of tert-butyl hydroperoxide (TBHP) at the interface. Meanwhile, the abundant Mn3+ species generated by nitrogen doping in MnO2 promote the heterolytic cleavage of TBHP to generate favorable •O2−. As a result, the Pickering emulsion system achieves a benzylamine conversion >99.0% and an imine selectivity >99.0%, significantly outperforming the single oil phase, aqueous phase, and conventional biphasic system, thus demonstrating exceptional catalytic performance. These findings demonstrate that Pickering emulsion engineering can overcome mass-transfer limitations and precisely regulate selectivity in imine synthesis, offering a sustainable and highly efficient strategy for the catalytic oxidative coupling of amines.