Preparation and characterization of a novel Wells–Dawson heteropolyacid-based magnetic inorganic–organic nanohybrid catalyst H6P2W18O62/pyridino-Fe3O4 for the efficient synthesis of 1-amidoalkyl-2-naphthols under solvent-free conditions

Abstract

A novel magnetic inorganic–organic nanohybrid material H₆P₂W₁₈O₆₂/pyridino-Fe₃O₄ (HPA/TPI-Fe₃O₄) was fabricated and performed as an efficient, eco-friendly, and highly recyclable catalyst for the solvent-free, one-pot, and multi-component synthesis of various substituted 1-amidoalkyl-2-naphthols from the reaction of β-naphthol, an aldehyde, and benzamide with good to excellent yields (47–94%) and in a short span of time (25–60 min). The nanohybrid catalyst was prepared by the chemical anchoring of Wells–Dawson heteropolyacid H₆P₂W₁₈O₆₂ onto the surface of modified Fe₃O₄ nanoparticles with N-[3-(triethoxysilyl)propyl]isonicotinamide (TPI) linker. The magnetically recoverable catalyst was easily recycled at least eight times without any loss of catalytic activity. XRD, TEM, UV-vis, and FTIR confirmed that the heteropolyacid H₆P₂W₁₈O₆₂ is well dispersed on the surface of the solid support and its structure is retained after immobilization on the pyridine modified Fe₃O₄ nanoparticles. This protocol is developed as a safe and convenient alternate method for the synthesis of 1-amidoalkyl-2-naphthols utilizing an eco-friendly, and a highly reusable catalyst.