Green and Efficient Synthesis of Fluorescent Bis(pyrazolyl)methanes in Choline Chloride/Urea Deep Eutectic Solvent

Abstract

A series of pyrazole-based heteroaromatic compounds were synthesized by the reaction of 3-methyl-5-pyrazolone and aromatic aldehydes in Choline chloride/urea DES as a green solvent. This simple and green procedure has advantages such as easy operation, short reaction times, efficient yields, low cost and minimum use of hazardous solvents and catalysts. The structure of compounds was determined by IR, 1H and 13C NMR spectra, and the crystal structure of 4a was confirmed using X-ray crystallographic analysis. The optical properties of Pyrazole derivatives 4a-g have also been studied with UV/vis and fluorescence spectroscopy. All of these pyrazole-containing heteroaromatic compounds displayed maximum emission peak from 340 to 360 nm.