Friedel-Crafts acylation of toluene catalyzed by solid superacids

Benzoylation of toluene (141mmol) with 2mmol of benzoic anhydride or benzoyl chloride was carried out in liquid phase over 0.5 g of solid superacids of sulfated and supported metal oxides at 100 degrees C for 3 h. Yields of o-, m-, and p-methylbenzophenones in the distribution of 20-30% o-, 2-4% m-, and 70-80% p-isomers were 92, 48, 28, 27, 26, and 0% for the sulfated oxides of SO4/ZrO2, SO4/SnO2, SO4/TiO2, SO4/Al2O3, SO4/HfO2, and SO4/Fe2O3 With benzoic anhydride as the acylating reagent. The supported oxides of WO3/ZrO2, WO3/TiO2, WO3/SnO2, and MoO3/ZrO2 gave yields of 55, 26, 16, and 15%, respectively; WO3/Fe2O3 and B2O3/ZrO2 gave no yields. As a whole, yields by the reactions with benzoyl chloride were lower than those with the anhydride. When benzoyl chloride was the acylating agent, the reactions over SO4/Fe2O3 and WO3/Fe2O3 were homogeneously catalyzed by FeCl3 produced during the reaction, though other reactions were heterogeneously catalytic. The activity of SO4/ZrO2 was largely promoted by the addition of Pt and Ru (2 wt.%). Silica-aluminas, zeolites, and mordenites were almost inactive under the conditions. It was shown from the acid strength and the catalytic activity for disproportionation of toluene that inactivity of the aluminosilicates for the acylation is based on their catalytic action by Bronsted acid sites. A rough relationship was obtained between the highest acid strength of the present catalysts and the acylated yields. The present catalysts were also satisfactorily effective for the acetylation of toluene with acetic anhydride and acetyl chloride. (C) 2000 Elsevier Science B.V. All rights reserved.