Synthesis of [P4-VP]-Fe3O4 supported Brønsted acid ionic liquid and its application as a highly efficient heterogeneous and reusable nanocatalyst in the Biginelli reaction under solvent-free conditions

Abstract

In this paper, for the first time, [P4-VP]-Fe3O4 MNP [cross-linked poly (4-vinylpyridine) supported Fe3O4 nanoparticle] supported Bronsted acid ionic liquid was easily prepared, as a highly efficient heterogeneous nanocatalyst, by using a simple and convenient method. First [P4-VP]-Fe3O4 MNPs was prepared by functionalization of [P4-VP] 2% DVB [Poly (4-vinylpyridine) cross-linked with 2% divinyl benzene] with magnetic nanoparticles using 3-chloropropyltrimethoxysilane as a linker. Subsequently, the HSO4− anion was incorporated into the polymer via a well-known ion exchange reaction to form acidic ionic liquid. Energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR) clearly approved that the cationic polymer was successfully loaded with Bronsted acid. The catalyst structure and its magnetic properties were investigated by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) analysis. Thereafter, it was applied as a highly efficient Bronsted acid nanocatalyst for the synthesis of 3,4-dihydropirimidinones by Biginelli reaction. Biginelli products were prepared by the one-pot three-component reaction of urea, ethyl acetoacetate and aldehydes under solvent-free conditions. The formation of Biginelli products were confirmed by FT-IR, proton and carbon-13 nuclear magnetic resonance spectroscopy and melting points. Our procedure benefits from advantages including: short reaction time, high selectivity and purity, reusability and easy magnetically separation of the catalyst, clean and fast workup.