Diels-Alder and dehydration reactions of furan derivatives with ethylene catalyzed by liquid Brønsted acids and Lewis acids

• Diels-Alder/dehydration reactions of furan derivatives with ethylene catalyzed by liquid Brønsted and Lewis acids.
• Quasi-homogeneous reaction formed with optimized catalysts and solvents.
• Optimal acidity of haloacetic acids and metal triflates for p-xylene production established.
• Rare-earth metal triflates are better catalysts than haloacetic acids for the reaction.

The tandem Diels-Alder and dehydration reactions of furan derivatives with ethylene represent a promising approach for the production of renewable aromatics. Herein, a series of haloacetic acids and rare-earth metal triflates are employed as liquid Brønsted and Lewis acid catalysts, respectively, in the Diels-Alder and dehydration reactions of 2,5-dimethylfuran with ethylene to get an insight of this type of acid-catalyzed reaction. With the carefully selected catalysts and solvent, a quasi-homogeneous reaction system can be formed, where accurate kinetic studies could be performed. Haloacetic acids exhibit considerable activity in the Diels-Alder and dehydration reactions with a similar apparent activity energy value of ∼8.4 kcal/mol, and CF2ClCOOH with a proper Brønsted acidity is optimized for the reaction. Rare-earth metal triflates also exhibit considerable activity in the Diels-Alder and dehydration reactions with a similar apparent activity energy value of ∼13.0 kcal/mol, and Sc(OTf)3 with the highest Lewis acidity is optimized. On the basis of kinetic analysis results, the impacts of acidity on the performance of catalysts are discussed in detail and the reaction network is proposed. Besides, the substrate scope of furan derivatives for the Diels-Alder and dehydration reactions with ethylene is investigated using CF2ClCOOH and Sc(OTf)3 as catalysts for possible extensions of the reaction.

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