Porous organic polymer as an efficient organocatalyst for the synthesis of biofuel ethyl levulinate

Levulinic acid (LA), a lignocellulosic biomass-derived compound has been recognized as one of the versatile building blocks for the synthesis of commodity chemicals having biofuel properties together with potential as precursor for the synthesis of several value-added pharmaceuticals and polymers. Herein, we report the synthesis of catalytically active functionalized porous organic polymer and its utilization as heterogeneous organocatalyst for the synthesis of EL from LA in very high yield. Here, sulfonic acid functionalized porous organic polymer SBZ@POP have been prepared via simple Friedel-Crafts alkylation of benzene with dimethoxymethane followed by sulfonation of the aromatic rings. The structure and properties of the material was examined through PXRD, N2 sorption, HR TEM, 13C CP-MAS NMR, NH3-TPD, TG-DTA and FTIR analysis. Our characterization data suggested nanoscale porosity with high surface acidity in SBZ@POP. The effects of reaction time, catalyst loading, molar ratio of levulinic acid to ethanol and reaction temperature were studied thoroughly to optimize the catalytic activity of SBZ@POP. Under optimized reaction conditions EL yield of 88 % has been achieved with 1:15 molar ratio of LA to ethanol under refluxing conditions in 10 h. This porous organic polymer based organocatalyst displayed good recyclability for consecutive five reaction cycles suggesting the sustainable application potential of this acidic organocatalyst.