Alkylation of benzene with 1-dodecene in ionic liquids [Rmim]+Al2Cl6X− (R = butyl, octyl and dodecyl; X = chlorine, bromine and iodine)

Alkylation of benzene with 1-dodecene had been investigated in 1-alkyl-3-methylimidazolium halide-aluminum chloride ionic liquids comprising various alkyl groups (butyl-, octyl- and dodecyl-) and various halogens (chlorine, bromine and iodine) on the cations and anions, respectively. Among all these ionic liquids, [bmim]+Al2Cl6Br− exhibited the best catalytic performance, which was ascribed to the proper strength of its Lewis acidity and its molecular polarizability demonstrated by FT-IR. The effects of varying anion molar compositions, ionic liquid dosage, reaction temperature, molar ratio of benzene to 1-dodecene and reactant moisture were explored using [bmim]+Al2Cl6Br− as the catalyst; the results were systematically explained by the mechanism of the carbenium ions. The optimum conversion of 1-dodecene 91.8% with the selectivity to 2-dodecylbenzene 38.0% was obtained when the molar ratio of the ionic liquid [bmim]+Al2Cl6Br− to 1-dodecene was as low as 0.005 under the mild reaction condition. The reuse of the ionic liquid was examined. The main cause of the deactivation was the loss of the highly Lewis acidic species Al2Cl6Br−.