Anchored sulfonic acid on silica-layered NiFe2O4: A magnetically reusable nanocatalyst for Hantzsch synthesis of 1,4-dihydropyridines

Abstract

In this study, the immobilization of sulfonic acid on silica-layered nickel ferrite, NiFe2O4@SiO2@SO3H, was investigated. The sulfonated Ni-nanocatalyst was then characterized using FT-IR, SEM, EDX, XRD and VSM analyses. Catalytic activity of the Ni-nanocomposite was also studied towards Hantzsch synthesis of 1,4-dihydropyridines via one-pot condensation reaction of 1,3-diketones (ethyl acetoacetate or 4-hydroxycoumarin), aromatic aldehydes and aqueous ammonia in H2O (70 °C) as a green solvent. All reactions were carried out within 10–100 min to afford the products in high to excellent yields. The green aspect of this synthetic protocol was more studied by examining the reusability of NiFe2O4@SiO2@SO3H MNPs for seven consecutive cycles without the significant loss of catalytic activity. The current method represents remarkable advantages in terms of mild reaction conditions, using H2O as an environmental-friendly solvent, stability and easy separation of the magnetic nanocatalyst, high yield of products, wide tolerance of starting materials and the perfect reusability of the applied Ni-nanocatalyst.