Cellulose sulfuric acid as a bio-supported and efficient solid acid catalyst for synthesis of pyrazoles in aqueous medium

Abstract

A convenient and practical method was described for the regioselective synthesis of pyrazoles from hydrazines/hydrazides and 1,3-dicarbonyl compounds via the Knorr synthesis in water with cellulose sulfuric acid (CSA) as a biopolymer-based solid acid catalyst. Various hydrazines and hydrazides were reacted with 1,3 diketones and the desired pyrazoles were obtained in high yields. The reaction of less reactive hydrazines with 1,3-dicarbonyl compounds stopped at the corresponding hydrazone derivatives. Hydrazides were employed with β-ketoester, and imine adducts were the only isolated product. Simple isolation of products, mild reaction conditions, reusability of solid acid catalysts and short reaction times are advantages of this green procedure.