The Influence of Preparation Methods on the Catalytic Performance of Imidazole Based Acidic Poly(Ionic Liquids)for Prins Reaction
The preparation of immobilized acidic ionic liquids through radical polymerization was investigated,focusing on the effects of polymerization solvent,polymerization sequence,and solvent used during the acidification of poly(ionic liquids)(PILs)on the structure of imidazolium-based acidic poly(ionic liquids)(APILs)and their catalytic performance in the Prins reaction of aromatic alkenes with paraformaldehyde.Various physicochemical characterization techniques were employed to reveal the structure-activity relationships.The results indicate that PILs synthesized with ethanol as the solvent and through the direct polymerization of crosslinkers with vinyl imidazolium salts exhibit higher thermal stability and S content,likely due to solvation effects and differences in the charges of the polymerization monomers.The acid catalyst obtained by acidifying PILs with dichloromethane(DCM)shows the highest acidity(5.69 mmol·g-1),enabling efficient catalysis of the reaction between styrene and paraformaldehyde to produce 4-phenyl-1,3-dioxane.Under mild reaction conditions,the styrene conversion reaches 100%,with a target product selectivity of 98%.Moreover,the catalyst demonstrates good reusability,maintaining its activity after six cycles with no significant decline.Additionally,this catalyst exhibits broad substrate applicability,showing excellent performance in the Prins condensation reactions of various substituted aromatic alkenes.
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