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

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 Bronsted 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 similar to 8.4 kcal/mol, and CF2CICOOH with a proper Bronsted 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 similar to 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 CF2CICOOH and Sc(OTf)(3) as catalysts for possible extensions of the reaction. (C) 2016 Elsevier B.V. All rights reserved.