One pot cascade conversion of furfural to alkyl levulinate over Lu(OTf)3 without external H2

Abstract

Biochemicals and biofuel derived from biomass conversion have received much attention over past decades. Alkyl levulinates are considered as promising building block chemicals and green fuel additive. This work presents a facile and efficient catalytic strategy for one pot cascade conversion of furfural to alkyl levulinates over rare earth metal trifluoromethanesulfonates (RE(OTf)3) in alcohol without external H2. Experimental results demonstrate that RE(OTf)3 binds to the alcohol ((OTf)3-RE-O(H)R), possessing both Brønsted acid and Lewis acid, plays a key role for this cascade process. Meanwhile, the selectivity of alkyl levulinate is closely related to charge density of selected metal ion and the reduction potential of the selected alcohol. Among various tests, Lu(OTf)3, possessing the greatest charge density, exhibits the best catalytic activity in the lowest reduction potential of 2-propanol. 100% furfural conversion and 52.8% ispropanyl levulinate yield can be achieved at 190°C within 45 min. This catalyst can be recycled five times by direct vacuum distillation and regenerated by oxidative elimination of formed humins. Besides, a plausible reaction mechanism is also proposed.