Heteropolytungstostannate as a homo- and heterogeneous catalyst for Knoevenagel condensations, selective oxidation of sulfides and oxidative amination of aldehydes

Abstract

Heteropolytungstostannate K₁₁H[P₂W₁₈O₆₈(HOSn^IVOH)₃]·20H₂O (1) is used as a homo- and heterogeneous catalyst for Knoevenagel condensations. New Fe₃O₄@SiO₂@CH₂(CH₂)₂NH₃⁺[P₂W₁₈O₆₈(HOSn^IVOH)₃]¹¹⁻ nanocatalyst was fabricated through electrostatic grafting of (1) on amine-modified silica-coated magnetic nanoparticles. The new magnetically recoverable nanocatalyst was characterized using infrared spectroscopy (IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffractometry (XRD), energy-dispersive X-ray analysis (EDX) and alternating gradient force magnetometry (AGFM). The results indicate that the particles are mostly spherical in shape and have an average size of approximately <30 nm. The catalytic activity of the catalyst was investigated in the selective oxidation of sulfides to sulfoxides and oxidative amination of aldehydes in an aqueous medium. The catalyst was reused at least five times without significant decrease in catalytic activities, and the structure of the catalyst remained unchanged after recycling.