Oxovanadium(IV) unsymmetrical salophen complex supported on modified silica-coated CoFe2O4 nanoparticles: A magnetically recoverable nanocatalyst for efficient and selective oxidation of sulfides and thiols

Abstract

In this study, an oxovanadium(IV) unsymmetrical salophen complex, VO(salophen-OH) where salophen-OH = 4-[(E)-{(2-[(E)-2-hydroxybenzylidene)amino]phenyl}imino)methyl]benzene-1,3-diol, was synthesized and immobilized on the surface of chloro-functionalized silica-coated CoFe2O4 (CoFe2O4@SiO2@CPTMS) magnetic nanoparticles. FT-IR and EDX spectra, TEM and SEM images, XRD pattern, TGA, ICP, and VSM measurements were applied to characterize the resulting CoFe2O4@SiO2@CPTMS@VO(salophen-OH) nanoparticles. The developed CoFe2O4@SiO2@CPTMS@VO(salophen-OH) magnetic nanoparticle was used as a remarkably efficient nanocatalyst, which facilitates the chemo-selective oxidation of sulfides to sulfoxides using 30 % H2O2 and also enables the oxidative coupling of thiols to disulfides using urea/H2O2 (UHP) in ethanol at room temperature. This catalytic system presented disulfides and sulfoxides as optimal products that showed good to excellent yields, and there was no over-oxidation of disulfides and sulfoxides to undesirable by-products. An external magnet can be used to recover this nanocatalyst magnetically, and it can be recycled up to five times in both oxidation reactions without losing its catalytic action. Moreover, the recycled catalyst shows no major differences in its XRD pattern and FT-IR spectrum compared to the fresh catalyst.