Novel aryl-imidazolium ionic liquids with dual Brønsted/Lewis acidity as both solvents and catalysts for Friedel-Crafts alkylation

Abstract

Unique tunable aryl-imidazolium magnetic ionic liquids with dual functions as a solvent-catalyst and dual Brønsted-Lewis acidity (B-L MILs) are applied for Friedel-Crafts alkylation without additional solvents. The catalytic properties of these B-L MILs in the Friedel-Crafts alkylation of p-xylene with benzyl chloride are investigated. The various reaction parameters, including the catalyst dosage, reaction time, reaction temperature, molar ratio of reactants, and reusability, are discussed. The results show that the B-L MIL 5c has more excellent product selectivity (> 99%) and reactant conversion (> 99%) under the following optimum conditions (reaction temperature = 80 °C, reaction time = 0.5 h, molar ratio of p-xylene to benzyl chloride = 6:1, and catalyst 5c dosage = 1.0 mole %) than traditional catalysts reported in the previous literature. Specifically, due to the mesomeric effect between the FeCl4 anion and hydrogen atom at cationic moiety, the catalyst B-L MILs with the molar fraction of FeCl3 equal to 0.5 can be easily recovered and provide satisfactory catalytic activity after being re-used six times.