Friedel-Crafts acylation and related reactions catalyzed by heteropoly acids

Abstract

The Friedel-Crafts acylation of anisole (AN) with acetic anhydride (AA) and the Fries rearrangement of phenyl acetate in the liquid phase catalyzed by bulk and silica-supported heteropoly acids (HPA), mainly H 3 PW 12 O 40 (PW), have been studied. In anisole acylation, PW exhibits very high activity, yielding up to 98% para and 2-4% ortho isomer of methoxyacetophenone (MOAP) at 90-110°C and an AN/AA molar ratio of 10-20. The reaction appears to be heterogeneously catalyzed; no contribution of homogeneous catalysis by HPA was observed. PW is almost 100 times more active than the zeolite H-Beta, which is in agreement with the higher acid strength of HPA. The PW catalyst is reusable, although gradual decline of activity was observed due to the coking of the catalyst. The acylation is inhibited by the product because of adsorption of MOAP on the catalyst surface. In contrast to anisole, the acylation of toluene with HPA is far less efficient than that with H-Beta. Evidence is provided that the activity of HPA in toluene acylation is inhibited by preferential adsorption of acetic anhydride on the catalyst. It is demonstrated that PW is a very efficient and reusable catalyst for the Fries rearrangement of phenyl acetate in homogeneous or heterogeneous liquid-phase systems at 100-150°C.