Greener and facile synthesis of 4,4′-(arylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)s through a conventional heating procedure

Abstract

A new catalytic application of tetraethylammonium L-prolinate for the facile and cleaner synthesis of 4,4′-(arylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)s is developed. This amino acid-based ionic liquid could be recycled up to five runs, and a negligible reduction of catalytic activity was detected within the experimental error. A variety of substituted 4,4′-(arylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)s were obtained in good to high yields under eco-friendly conditions. Tetraethylammonium L-prolinate is easy to prepare, as well as it shows moderate thermal stability and good solubility in water. This work revealed that this amino acid-based ionic liquid, containing L-prolinate anion, can catalyze the tandem Knoevenagel-Michael condensation reaction due to hydrogen bond donor and Lewis base moieties. The current methodology has other advantages, including (a) wide substrate-scope, (b) relatively short reaction times, (c) the use of a nontoxic, biocompatible, biodegradable and metal-free ionic liquid, and (d) simple workup procedure.