Synthesis and performance of piperidinium-based ionic liquids as catalyst for alkylation of p-xylene with 1-hexadecene

Piperidinium-based ionic liquids (ILs) were synthesized under mild conditions by coordinating N -alkyl- N -methylpiperidinium bromide ([Pip 1,x ]Br) with anhydrous AlCl 3 . The weak basicity of N -methylpiperidine had little impact on downstream problems from proton impurities and catalyst poisoning. The results of Fourier transform infrared (FT-IR), electrospray ionization mass spectrometry (ESI-MS), and nuclear magnetic resonance ( 27 Al NMR) confirmed that the active components in [Pip 1,x ]Br-2AlCl 3 ( χ = 0.67) were [Al 3 Cl 9 Br] − and [Al 2 Cl 6 Br] − . Besides, the reaction performance of [Pip 1,8 ]Br-2AlCl 3 under different conditions was carried out by single-factor experiment and further confirmed by orthogonal experimental method. Among these reaction conditions, the optimal combination was the reaction temperature of 40°C, ILs/O molar ratio of 0.2:1, px/O molar ratio of 12:1, and the reaction time of 30 min. Furthermore, [Pip 1,8 ]Br-2AlCl 3 had excellent stability and can be recycled 14 times. It was the high-efficiency catalytic activity and prominent recyclability that made continuous industrial production possible.