A green and efficient method for the synthesis of pyrroles using a deep eutectic solvent ([CholineCl][ZnCl2]3) under solvent-free sonication

Abstract

An efficient deep eutectic solvent-based synthesis of pyrroles under ultrasound irradiation has been developed to provide a significant improvement of the yield up to 99% in a short reaction time. The synthesis of pyrroles is highly atom-economical, producing water as the sole byproduct. In addition, [CholineCl][ZnCl₂]₃ is easily synthesized from commercially available choline chloride and zinc chloride via a cost-effective and environmentally benign pathway. The obtained [CholineCl][ZnCl₂]₃ has been characterized by FT-IR, ¹H-NMR, ¹³C-NMR, HRMS (ESI), Raman, and TGA. Five new pyrroles are synthesized by the current method. Moreover, [CholineCl][ZnCl₂]₃ could be reused up to four times without significant loss of catalytic activity.