Silica Sulfuric Acid as an Efficient Solid Acid Catalyst for Friedel-Crafts Acylation Using Anhydrides

Friedel Crafts acylation reaction has been studied exten sively and affords aromatic ketones.1 The traditional method used acid chlorides or acid anhydrides as acylating agents and a stoichiometric or an excess amount of reaction promoter such as AICI3, BF3, TiCU, FeCh, ZnCb> SnCU or various Bronsted acids.These halogenated catalysts impo sed several drawbacks including corrosion, environmental problems due to strongly acidic wa아e streams and necessity of more than stoichiometric amounts of cataly아s.In addition, the acylating agents used in most of the traditional processes are the expensive and polluting acyl halides that require special cares in handling and working up.Therefore, the development of new methods using solid acid cataly아s with the use of inexpensive and available non-polluting carboxylic acids and anhydrides as beneficial candidates is desirable.Recently, considerable efforts have been made to use solid acid cataly아s in Friedel-Crafts acylation reaction, since these heterogeneous cataly아s can be easily separated from the reaction mixture.They are generally producing no problematic side products.Various classes of compounds which have been used as solid acid catalysts include zeolites,2'4 clays/6 heteropoly acids and their salts，응 Nafion-H?sulfate-doped metal oxides10 and silica sulfuric acid.11-bIn continuing of our intere아 in Friedel-Crafts acylation reaction,16 we now report the acylation reaction in the presence of silica sulfuric acid (SSA) under solvent free conditions (Scheme 1).Anisole and acetic anhydride were chosen as model compounds and their reaction in different solvents and solvent-free condition at 80 °C was treated using 25 mol% of silica sulfuric acid.The corresponding ketone was obtained in excellent yield (97%) after 20 min in solvent-less condition as shown in Table 1.The effect of cataly아 amount was tested and the results OCH3 OCH3