Pyridinium trifluoroacetate ionic liquids as proficient catalysts for synthesis of 3,5,5‐trimethyl‐2‐pyrazoline

Abstract

In this work, pyridinium trifluoroacetate ionic liquids, as a protonic acid catalyst, were used to catalyze intramolecular cyclization of ketazine to synthesize 2‐pyrazoline. The investigation encompassed the impact of temperature, solvent, dosage of ionic liquid catalyst, and the structure‐activity relationship in the cyclization reaction of 2‐propyl ketazine. The optimal catalytic performance was achieved at 100 °C with 8 mol % of 3,5‐dimethylpyridinium trifluoroacetate in a solvent‐free environment. Moreover, thermodynamic and kinetic data were determined through density functional theory calculations and calorimetric experiments. These protonic acid ionic liquids address the issue of excessive traditional protonic acid dosage in the intramolecular cyclization of ketazine, while also presenting a viable pathway for the catalytic synthesis of 2‐pyrazolines.