Theoretical Study on the Conversion Mechanism of Biobased 2,5-Dimethylfuran and Acrylic Acid into Aromatics Catalyzed by Brønsted Acid Ionic Liquids

The use of 2,5-dimethylfuran (DMF) and acrylic acid (AA) as the reactants to produce aromatics catalyzed by Brønsted acid ionic liquids (ILs) has been achieved successfully under mild conditions. The whole conversion process including Diels–Alder (D–A) cycloaddition, ring-opening/decarboxylation, and dehydration was investigated by density functional theory (DFT) calculations which were also verified by experiments. Two pathways for the activation of DMF were proposed: unprotonated oxygen of the DMF (UPOD) and direct protonated oxygen of the DMF (POD). In the UPOD pathways, two routes (endo and exo), in which the overall rate was limited by the ring-opening step, produce p-xylene or 2,5-dimethylbenzoic acid (DMBA), respectively, whereas in POD pathways, the limiting step of DMBA production was attributed to the D–A cycloaddition. The role of Brønsted acid ILs was mainly reflected in the proton transferability. The present study provides basic aids to understand the mechanism of converting furanics and AA into aromatics catalyzed by Brønsted acid ILs.