Highly accessible catalytic sites on recyclable organosilane-functionalized magnetic nanoparticles: An alternative to functionalized porous silica catalysts

Abstract

Diaminosilane-functionalized cobalt spinel ferrite (CoFe 2O 4) magnetic nanoparticles are synthesized and used as efficient heterogeneous base catalysts for the Knoevenagel condensation of aromatic and heteroaromatic aldehydes with malononitrile. The magnetic nanoparticle catalyst is characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), and nitrogen physisorption measurements. Quantitative conversion of the reactants is achieved under mild conditions. Recovery of the catalyst is easily achieved by magnetic decantation. The supported catalyst is reused five times without significant degradation in catalytic activity. No contribution from homogeneous catalysis due to active amine species leaching into reaction solution is detected. The performance of the magnetic base catalyst in the Knoevenagel reaction is directly compared with diamine-functionalized SBA-15 and MCM-48. Reaction rates over the non-porous, magnetic nanoparticle catalyst are comparable to the large pore mesoporous silica materials and faster than the small pore MCM-48 material with ∼22 Å diameter pores. A significant effect of the acidity of the magnetic nanoparticle support on catalyst activity in the Knoevenagel condensation is also observed.