Catalytic Oxidation of Benzyl Alcohol using Nanosized Ni/Cu Schiff-Base Complexes and their Metal Oxides Nanoparticles

Three novel nanosized Cu and Ni Schiff-base complexes (ahpvCu, ahpnbCu, and ahpvNi) incorporating imine ligands derived from the condensation of 2-amino-3-hydroxypyridine with either 3-methoxysalicylaldehyde or 4-nitrobenzaldehyde were synthesized by a sonochemical approach. The structure of the ligands and their complexes was confirmed by IR, NMR spectroscopy, electronic spectra, elemental analysis, TGA, molar conductivity, and magnetic moment analyses. The results revealed the formation of 1:1 (metal:ligand) complexes for ahpvCu and ahpvNi and 1:2 for ahpnbCu. Based on the magnetic moment and spectral data, an octahedral geometry is proposed for ahpnbCu and ahpvNi, while ahpvCu presents a tetrahedral structure. Metal oxide (MO = CuO and NiO) nanoparticles were prepared by calcination of the respective nanosized complexes at 500 °C, as confirmed by powder X-ray diffraction and transmittance electron microscopy. The catalytic activity of the as-prepared Schiff-base complexes and MOs in the oxidation of benzyl alcohol (BzOH) was investigated. The oxidation of BzOH to benzaldehyde (BzH) catalyzed by the ahpvCu complex and CuO nanoparticles in aqueous H₂O₂/DMSO solution at 70 °^ͦC for 2 h yielded 94% and 98% BzH, respectively, with 100% selectivity. Overall, the MO nanoparticles present a slightly higher catalytic activity than their parent complexes.