Study On The Reactions Of Knoevenagel And Biginelli In Pyrazolium-based Ionic Liquids

Pyrazolium-based ionic liquids?ILs?have been shown to be very promising substances for use in electrochemistry field because of their most significant advantages including their high thermal stability,negligible vapour pressure.In contrast to imidazolium-based ILs's application for a number of organic reactions,there are less detailed research reports about the utilization of pyrazolium-based ILs in organic reactions so far.Thus,design and synthesis of pyrazolium-based ILs for organic chemical applications both in academia and industry is an indispensable area.In this paper,the application of pyrazolium-based ionic liquids in Knoevenagel and Biginelli reactions is studied.The main contents are as follows:A series of pyrazolium-based ILs are synthesized.In the first step,1,3,5-trimethyl-1H-pyrazole is synthesized by Knorr reaction of methyl hydrazine and acetylacetone.2-butyl-1,3,5-trimethyl-1H-pyrazol-2-ium bromide is obtained by the direct n-butylation of N2 in 1,3,5-trimethyl-1H-pyrazole.After replacement of anions,2-butyl-1,3,5-trimethyl-1H-pyrazol-2-ium hexaflurophosphate,2-butyl-1,3,5-trimethyl-1H-pyrazol-2-ium hydrogen sulfate are synthesized.Structures of pyrazolium-based ILs are characterized by NMR and IR spectrography.The 2-butyl-1,3,5-trimethyl-1H-pyrazol-2-ium bromide as the reaction medium for Knoevenagel condensation reactions.The results showed that the IL accelerates the reactions with improved reaction efficiency,a shortened reaction time,suitability and high recyclability.The application of 2-butyl-1,3,5-trimethyl-1H-pyrazol-2-ium hydrogen sulfate in Biginelli reaction showed that[BTMPz][HSO₄]is an excellent reaction medium and a catalyst with improved reaction efficiency,shortened reaction time,catalytic suitability and high recyclability.