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

The Friedel-Crafts alkylation reaction is frequently used for C-C coupling, particularly in the pharmaceutical and fine chemical industries. The commo n Friedel-Crafts catalysts, namely sulfuric acid, hydrofluoric acid, or alu minium trichloride, pose considerable environmental problems. Particularly AlCl3, which generally has to be used in stoichiometric rather than catalyt ic quantities, leads to large volumes of waste. A more environmentally bene ficial process has therefore to be developed. AlCl3 or ZnCl2 immobilised on clay or silica have been described as convenient heterogeneous catalysts f or Friedel-Crafts alkylation. We show that AlCl3 immobilised on mesoporous silica gel constitutes a good catalyst for the propylation of 1,3-difluorob enzene. The reaction can be particularly well controlled if it is conducted in a continuous packed bed reactor. (C) 2001 Elsevier Science B.V. All rig hts reserved.