Solid acid catalysts for the efficient synthesis of 2-(2,4-difluorophenyl) propane Original Research Article

The Friedel–Crafts alkylation reaction is frequently used for C–C coupling, particularly in the pharmaceutical and fine chemical industries. The common Friedel–Crafts catalysts, namely sulfuric acid, hydrofluoric acid, or aluminium trichloride, pose considerable environmental problems. Particularly AlCl3, which generally has to be used in stoichiometric rather than catalytic quantities, leads to large volumes of waste. A more environmentally beneficial process has therefore to be developed. AlCl3 or ZnCl2 immobilised on clay or silica have been described as convenient heterogeneous catalysts for Friedel–Crafts alkylation. We show that AlCl3 immobilised on mesoporous silica gel constitutes a good catalyst for the propylation of 1,3-difluorobenzene. The reaction can be particularly well controlled if it is conducted in a continuous packed bed reactor.