Synthesis, characterization and first application of keggin-type heteropoly acids supported on silica coated NiFe2O4 as novel magnetically catalysts for the synthesis of tetrahydropyridines

Abstract

In this study, two heteroploly acids with Keggin structures (phosphotungestic acid (PWA) and phosphomolybdic acid (PMA)) have been supported on silica coated nickel ferrite nanoparticles (NiFe₂O₄@SiO₂). The synthesized catalysts were characterized by several methods (FT-IR, SEM, TEM, VSM, XRD, BET and ICP-AES), and the catalytic activities of these new and magnetic catalysts in synthesis of tetrahydropyridine derivatives have been investigated. These new catalysts showed that they can carry out reactions at room temperature in a short time and under solvent-free conditions. Moreover, the obtained results indicated that PWA supported NiFe₂O₄@SiO₂ is a stronger acid than PMA to run these reactions. More importantly, the catalysts were easily isolated from the reaction mixture by a magnetic bar and reused at least five times without significant degradation in their activities.