Synthesis of quaternary metal oxides immobilized on APTMS-coated magnetite: an efficient and reusable nanocatalyst for Knoevenagel condensation under green conditions

Abstract

A simple, green, and highly efficient procedure has been developed for Knoevenagel condensation of malononitrile and aromatic aldehydes to the corresponding benzylidenemalononitriles in the presence of Fe3O4@APTMS@Zr–Sb–Ni–Zn nanoparticles (NPs) as a durable nanocatalyst. The heterogeneous nanocomposite was prepared by immobilization of Zr–Sb–Ni–Zn mixed metal oxides on APTMS-coated magnetite. The synthesized catalyst was characterized using Fourier-transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD), vibration sample magnetometer (VSM), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller analysis (BET). In this approach, the condensation of malononitrile and aromatic aldehydes were done in water under reflux conditions to give the corresponding products within 3–60 min in 89%–95% yields. The magnetically recoverable catalyst was recycled and reused about four times without remarkable loss of activity. This method offers various benefits such as mild and eco-friendly reaction conditions, short reaction times, high purity of products, excellent efficiency, use of water as green solvent, and reusability and recoverability of the nanostructure catalyst.