Synthesis of various 2-benzylbenzoxazole derivatives catalyzed by deep eutectic solvent-supported onto magnetic nanoparticles

Abstract

Magnetic nanoparticle supported deep eutectic solvents have been synthesized by preparing and grafting [Urea]4[ZnCl2] deep eutectic solvent onto the surface of silica-coated Fe3O4 magnetic nanoparticles using 3‐ chloropropyltrimethoxysilane as a linker. DES@MNP was fully characterized using scanning and transmission electron microscopies, Fourier transforms infrared, energy-dispersive X-ray spectroscopies, vibrating sample magnetometer X-ray diffraction, and thermogravimetric analysis. In this study, we have developed the synthesis of 2-benzylbenzoxazole via condensation reaction of 2-nitrophenols and acetophenones using a magnetic nanoparticle supported [Urea]4[ZnCl2] deep eutectic solvent as a novel, green and efficient catalyst. In the presence of 1,4-diazabicyclo[2.2.2]-octane, elemental sulfur acted as an excellent reductant in promoting oxidative rearranging coupling in this reaction. The reaction has been conducted via the stirring method and the reaction conditions were surveyed (16 h, 130 °C, acetophenone, 2-nitrophenol, DABCO and sulfur molar ratio of 2:1:1:3, 10 mol% DES@MNP catalyst). Six 2-benzylbenzoxazole derivatives have been synthesized via this method with good yield (86-91%). The structure of the pure product has been confirmed through FT-IR, 1H NMR, 13C NMR, and GC-MS methods. More importantly, DES@MNP has been separated from the reaction mixture by a magnet and reused over five consecutive runs without significant loss of catalytic activity.