Friedel-crafts acylation of furan using chromium-exchanged dodecatungstophosphoric acid: effect of support, mechanism and kinetic modelling

The Friedel-Crafts acylation of furan to produce 2-acyl furan by using acetic anhydride is industrially important but it uses highly polluting liquid acids as catalysts. In this study, supported but modified heteropoly acids were used as heterogeneous catalysts in a solventless green process. Metal exchanged dodecatungstophosphoric acid (DTP) was loaded on three different supports, and its effect on acylation was evaluated. 20% w/w Chromium substituted DTP was supported on K-10 clay, SiO2, and ZrO2 using the incipient wetness impregnation method. Cr-0.66-DK10 (dodecatungstophosphoric acid on K10) catalyst was found to have excellent activity for Friedel-Crafts acylation of furan. Under optimized condition, the catalyst to furan ratio was 9.6% which is significantly less as per prior art and it gave 88% conversion with 100% selectivity. The characterization of the synthesized catalyst was done using sophisticated techniques, namely, XRD, FT-IR, SEM, TEM, XPS, NH3-TPD, TGA, ICP/OES, and BET. The Eley-Rideal mechanism was used to fit the kinetic data. The apparent activation energy was 18.03 kcal/mol. The catalyst was robust and reusable. The reaction is green and clean because no chlorinated chemicals, reagents, solvent, and polluting catalysts were used.