Brønsted acidic Heteropolyanion-Based ionic Liquid:A highly efficient Reaction-induced Self-separation catalyst for Baeyer-Villiger reaction

Abstract

A novel Brønsted acidic heteropolyanion-based ionic liquid (IL) ([MIMPS]3PW12O40) was synthesized and employed to catalyze the Baeyer-Villiger (BV) reaction to produce ε-Caprolactone (ε-CL). Noteblely, the prepared IL catalyst exhibited higher catalytic activity compared to solid acid catalysts duo to its behavior of reaction-induced self-separation. It meaned that the IL catalyst could switch from solid to liquid, then back to solid state during the reaction, which broke the limit of the constant heterogeneous state of the catalyst in the reaction system. The characterization results of FT-IR, 1H NMR, XRD, and XPS indicated that the phosphotungstic anion (PW12O403-) was successfully modified by the organic precursor MIMPS. And TG-DTA and Py-IR results illustrated that the catalyst possessed good thermal stability and Brønsted acidity. Furthermore, the activity evaluation experiment of the catalyst confirmed that the introduced SO3H group of the cation part and the active component tungsten of the anion part were the key to the activity of the IL catalyst. More importantly, the synergistic effect between SO3H group and the active component tungstencatalyst leading to a superior catalytic performance such as cyclohexanone conversion attained 93.51 % and the yield and selectivity of ε-CL that were up to 93.26 % and 99.73 % under the optimum conditions. Finally, the kinetic process of the BV reaction was appropriately described by the second-order reversible reaction kinetics model and the calculated results were also in good agreement with the experimental datas.