The First Pyrazolium-Based Ionic Liquid Containing Phosphotungstic Acid Immobilized on CuFe2O4@SiO2: A Recyclable Organic-Inorganic Nanohybrid Catalyst for the Synthesis of Polyhydroquinolines

Abstract

A new magnetically separable organic-inorganic nanohybrid catalyst denoted as CuFe2O4@SiO2@C3-Pyrazole-C4SO3-H2PW was successfully prepared by grafting of a functionalized ionic liquid containing a pyrazolium cation with a phosphotungstic counter-anion H2PW12O40¯ (H2PW) on silica-coated copper ferrite magnetic nanoparticles (CuFe2O4@SiO2). The prepared catalyst was fully characterized using scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray analysis, inductively coupled plasma optical emission spectrometry, Fourier transform infrared spectroscopy, and vibrating sample magnetometry. The catalytic activity of CuFe2O4@SiO2@C3-Pyrazole-C4SO3-H2PW as a novel heterogeneous catalyst was probed in the synthesis of polyhydroquinolines by one-pot condensation of dimedone, an aromatic aldehyde, ammonium acetate, and ethyl acetoacetate. The results demonstrated a significant catalytic performance of the catalyst for this transformation under solvent-free conditions, giving high yields of the products over short reaction time. Also, the magnetic nanocatalyst could be easily recovered from the reaction mixture and reused many times with no significant loss of its catalytic activity.

Keywords

• ccufe2o4@sio2@c3-pyrazole-c4so3-h2pw
• ionic liquid
• magnetic nanoparticles
• polyhydroquinolines