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.

Graphical Abstract

Keywords:

• Ionic liquid
• heterocycles
• one-pot synthesis
• multi-component reaction
• waste prevention

Acknowledgments

The authors are grateful to staff members in the Nanotechnology & Catalysis Research Center, the University of Malaya and Sari Agricultural Sciences and Natural Resources University for partial support of this work.

Disclosure statement

There are no conflicts of interest to declare.

Additional information

Funding

This work was supported by a Research Grant [NANOCAT RU001-2019] for Scientific Research from the University of Malaya, Malaysia.