Introduction and characterization of a novel Cu(<sc>ii</sc>)-based quaternary deep eutectic solvent and its application in the efficient synthesis of triazoles and tetrazoles under mild conditions as an inexpensive, reusable, benign, and dual solvent/catalyst medium

Deep eutectic solvents consist of hydrogen bond donor and acceptor components. They are a new type of ionic liquids, and they have attracted the attention of many chemists in recent years. In this work, a quaternary deep eutectic solvent (QDES) was prepared using choline chloride, glycerol, l-arginine, and copper acetate. Its physicochemical properties were determined by Fourier transform infrared spectroscopy (FT-IR), thermal analysis (TGA), differential scanning calorimetry (DSC), hydrogen potential (pH), cyclic voltammetry (CV), viscosity, density, refractive index, ionic conductivity and spectrophotometer ultraviolet-visible (UV-Vis). Further, as a novel benign solvent/catalyst for the synthesis of 1,4-disubstituted-1,2,3-triazole, 4-substituted-1H-1,2,3-triazole, and 5-substituted-1H-tetrazole derivatives were used in a click reaction strategy. The special features of this method include mild conditions, a non-toxic environment, short reaction time, easy operation, biodegradability, deep eutectic solvent/catalyst recovery, access to cheaper raw materials, and environmental compatibility.