Poly Ethylene Glycol Based Dicationic Acidic Ionic Liquid [PEG-DAIL][Cl] Used as Cost Effective and Recyclable Catalyst for Biginelli Reactions

Background: Poly ethylene glycol based dicationic acidic ionic liquid catalysts [PEG-DAIL, Cl] have been prepared by mono chloroacetic acid and used as a cost effective alternative to [PEG1000DAIL, HSO3], a sultone based catalyst. Biginelli reaction is found in a large family of biologically active molecules exhibiting a wide range of important pharmacological properties. Synthesis of 3,4-dihydropyrimidin-2(1H)-ones has been already reported using wide variety of acid catalysts. Method: Three materials were prepared using different molecular weights of PEG. These catalysts are termed as (i) [PEG600-DAIL, Cl] (ii) [PEG1500-DAIL][Cl] and (iii) [PEG4000-DAIL, Cl]. The synthesized material [PEG-DAIL, Cl] were characterized by FT-IR, 1H-NMR, 13C-NMR, ESI-MS, DSC and TGA techniques. The products were further confirmed by the GC-MS and NMR techniques. Results: Synthesized material is acidic in nature, which is proved by pH studies. These materials have good thermal stability and wide range of solubility in different solvents. These catalysts explored for test reaction as Biginelli reaction for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones as a acid catalyst under mild reaction conditions. Conclusion: The present method provides yet another series of catalysts for the Biginelli reaction. On comparison of initial rate mmol.min-1 and acidity of the catalyst for the said reaction, [PEG1500-DAIL][Cl] shows better results as compared to other two. The catalyst system was found that reusable up to five cycles without much loss in activity. Separation and reuse of this catalyst is simple and economical.