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

Graphical Pyridinium trifluoroacetate-based ILs effectively catalyzed the cyclization of 2-propyl ketazine to pyrazolines, achieving conversion and selectivity rates of 98 % and 99 %, respectively. Thermodynamic data were obtained through DFT calculations and calorimeter tests, providing valuable insights for the practical application of ketazine intramolecular cyclization to synthesize pyrazolines. 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.