Synthesis, characterization and catalytic activity of copper (II) complexes containing schiff base ligand in the reduction of 4-nitrophenol

Abstract

This thesis describes the preparation of a series of Schiff base ligands, N’-salicylidene-2-aminophenol [L1], N’-salicylidene-2-aminothiazole [L2], and N,N’-bis(salicylidene)-o-phenylenediamine [L3] and their corresponding copper(II) complexes; N’-salicylidene-2-aminophenol copper(II) acetate [C1], N’-salicylidene-2-aminothiazole copper(II) acetate [C2] and N,N’-bis(salicylidene)-o-phenylenediamine copper(II) acetate [C3]. The synthesized ligands and their copper(II) complexes were characterized using fourier transform infrared (FTIR), nuclear magnetic resonance (NMR) and ultraviolet-visible (UV-Vis) spectroscopy. The catalytic activities of the synthesized copper(II) complexes were evaluated in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of sodium borohydride which acts as reducing agent. The progress of reaction was monitored using UV-vis spectroscopy and the percentage conversion was determined from the spectroscopy data. The results showed that N,N’-bis(salicylidene)-o-phenylenediamine copper(II) acetate [C3] has the highest catalytic activities with 97.5% conversion, followed by N’-salicylidene-2-aminothiazole copper(II) acetate[C2] complex with 95.2% conversion, then N’-salicylidene-2-aminothiazole copper(II) acetate [C1] complex with 90.8% conversion in the order C3>C2>C1. The rate of reaction for the reductions of 4-NP catalyst by copper(II) complexes shows that C3 complex is faster than C2 and C1 complex. The optimization of the catalyst amount shows that 1.0 mg of the catalyst dose was the most optimized amount with the highest conversion of 94.6% than other dose of 0.5 mg (92.4%) and 1.5 mg (91.4%). Recyclability and reproducibility tests of copper(II) complexes confirmed that all the three complexes were active, efficient and possess excellent reproducibility with consistent catalytic performances and could be re-used again without major decrease in the catalytic activities.