Ionic liquid immobilized on Fe3O4 nanoparticles: a magnetically recyclable heterogeneous catalyst for one-pot three-component synthesis of 1,8-dioxodecahydroacridines

A magnetically recoverable nanocatalyst based on 1-methylimidazolium hydrogen sulfate ionic liquid has been synthesized by reaction of 1-methylimidazole with 3-(trimethoxysilyl)propyl chloride group, leading to formation of 1-methyl-3-(triethoxysilyl)propyl imidazolium chloride ([pmim]Cl). The ionic liquid was anchored onto silica-coated magnetic Fe3O4 particles, and Cl- anion exchange by treatment with H2SO4 afforded the corresponding immobilized ionic liquid MNP-[pmim]HSO4. The synthesized catalyst was characterized by various techniques such as Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), (differential) thermogravimetry (TG/DTG), CHN analysis, and vibrating-sample magnetometry (VSM), revealing the superparamagnetic nature of the particles. From electron microscopy (SEM and TEM) studies it can be inferred that the particles were mostly spherical in shape with average size of 20 nm. The loading amount of ionic liquid supported on the magnetic particles was indicated to be 0.98 mmol/g by the results of elemental and thermogravimetric analyses (CHN and TG). The catalytic activity of the supported ionic liquid was examined in synthesis of 1,8-dioxodecahydroacridines by condensation reaction of cyclic diketones with aromatic aldehydes and ammonium acetate or primary amines under solvent-free conditions. The catalyst could be easily recovered by applying an external magnetic field and reused for at least nine runs without deterioration in catalytic activity.