A DFT and catalytic studies of recyclable chitosan based heterogeneous Cu(II) catalyst for the oxidation of tetralin

Abstract

The oxidation of hydrocarbons is an essential transformation for converting petroleum-based raw material into useful chemicals like diols, epoxides, alcohols, and carbonyl compounds. In this context, a chitosan (Cs) based heterogeneous catalyst, {Cu(II)[Cs-L1-L2]Cl2} was developed by the coordination of two different Schiff base ligands, L1 [Cs-HACP] and L2 [ANI-HACP] with the chitosan and followed by complexation with CuCl2·2H2O The prepared catalyst {Cu(II)[Cs-L1-L2]Cl2} was characterized by different techniques such as Scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDX), Brunauer-Emmett-Teller (BET) surface area, Powder X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Ultraviolet visible near-infrared (UV–VIS-NIR), X-Ray photoelectron spectroscopy (XPS) and Density Functional Theory (DFT) studies. DFT studies suggest that {Cu(II)[Cs-L1-L2]Cl2} have octahedral geometry and +2 oxidation state of Copper is identified on the basis of XPS analysis. The Catalytic behavior of newly prepared heterogeneous catalyst {Cu(II)[Cs-L1-L2]Cl2} was studied for the tetralin oxidation using 70 % tert-butyl hydroperoxide [70 % TBHP]. Tetralin on oxidation gave 1-tetralol, 1-tetralone and some other products. A maximum conversion of 82.11 % tetralin with 10.42 % selectivity of 1-tetralol (T-lol) and 74.89 % selectivity of 1-tetralone (T-lone) was obtained after 5 h of reaction at 80 °C. The heterogeneous catalyst, {Cu(II)[Cs-L1-L2]Cl2}was easy to separate and recyclable. The catalyst was recycled seven times.