Magnetically-separable quasi-homogeneous catalyst: Brush-type ionic liquid polymer coated magnetic polymer microspheres for tandem reactions to produce 4H-pyrans/biodiesel

Abstract

Employing magnetic polystyrene microspheres as the core and brush-type alkaline imidazolium ionic liquid polymers as the covalent bonds, a robust magnetically-separable quasi-homogeneous magnetic brush-type ionic liquid polymers ([Im][OH]/MP-B) was synthesized. Due to the features of brush-type ionic liquid polymer (BILPs), [Im][OH]/MP-B demonstrated high catalytic activity. With a broad variety of substrates, [Im][OH]/MP-B was applied in Knoevenagel-Michael tandem reactions for the synthesis of 4 H-pyrans (achieving 99.99% conversion and 93.6% yield) and transesterification tandem reactions for sustainable biodiesel production (achieving 99.9% conversion and 95.2% yield). Furthermore, the catalytic performance of [Im][OH]/MP-B was superior to that of [Im][OH]/MP-CL and [Im][OH]/MP-L and comparable with that of homogeneous catalysts. The reasonable and feasible reaction mechanism of magnetic ionic liquid polymers catalyzing tandem reactions was explored in-depth based on the catalytic performance and kinetics, which clearly demonstrated the catalytic activity and stability of [Im][OH]/MP-B. Notably, [Im][OH]/MP-B was effortlessly recovered by magnetic separation and reutilized numerous times with no evident change in catalytic performance, composition, or microstructure, indicating promising possibilities for ecologically friendly procedures. This work provides a potential strategy for the synthesis of magnetic BILPs for tandem reactions, which could serve as a platform for ecologically friendly and sustainable chemistry.