Highly efficient and recyclable phosphoric acid functionalized zirconia encapsulated-Fe3O4 nanoparticles: clean synthesis of 1,4-dihydropyridine and 1-amidoalkyl-2-naphthol derivatives

A novel type of magnetically recoverable acid nanocatalyst was synthesized by means of grafting phosphoric acid groups on the surface of core-shell zirconia-coated magnetite nanoparticle (nano-Fe3O4@ZrO2). The active nano-Fe3O4@ ZrO2 supported phosphoric acid (n-Fe3O4@ZrO2-H3PO4) catalyst was studied in detail by the aid of various analyses, e.g. pH measurement, Fourier transform infrared spectroscopy, thermogravimetric analysis, energy-dispersive X-ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction and vibrating sample magnetometry. Additionally, the reactivity, reusability, and stability of the new catalyst were probed in the multicomponent one-pot reactions for the synthesis of dihydropyridines as well as 1-amidoalkyl-2-naphthols. The significant merits of the catalyst were related to its facile recyclability using an external magnetic field, reusability for at least five reaction cycles, excellent activity, high stability, mild reaction conditions and high isolated yields of the products.