Alkaline Ionic Liquids Immobilized on Protective Copolymers Coated Magnetic Nanoparticles: An Efficient and Magnetically Recyclable Catalyst for Knoevenagel Condensation

A novel three-layered catalyst was successfully synthesized by the copolymerization of divinylbenzene and vinyl benzyl chloride in the presence of 3-mercaptopropyltrimethoxysilane-functionalized magnetic nanoparticles (MNPs) followed by quaternization reaction with N-propyl imidazole and alkaline ion exchange, aiming at improving the recyclability of MNPs supported catalysts. The results obtained by FTIR, TG/DTA, SEM, TEM, DLS, and VSM showed that the prepared catalyst consisted of a catalytic layer, protective layer, and magnetic core. The investigation of catalytic performance indicated that the catalyst displayed a remarkable activity for Knoevenagel condensation due to the large amount of OH ^- ions loading on the surface and a lower activation energy than that of NaOH, but it was sensitive to the polarity of solvent. Furthermore, the existence of a protective layer incorporated between the MNPs and the catalytic layer provided a good way to avoid the corrosion of magnetic nanoparticles, and the catalyst exhibited good stability in alkaline medium. The catalyst could be recycled by an external magnet at least six times without significant change.