The acylation with acetic anhydride of six aromatic substrates with different features (degree of activation of the aromatic ring towards electrophilic substitution, number of rings, i.e., 1 or 2) was carried out in a batch reactor at 373 K over a H-BEA zeolite (Si/Al = 15) with nitrobenzene as a solvent. The acetylation rate was found to be very dependent on the degree of ring activation, with diffusion limitations playing only a limited role. The decrease of the rate with reaction time, which was very pronounced with poorly activated and deactivated substrates, is mainly due to the inhibiting effect of acetic acid and of the products of acetic anhydride condensation. (c) 2004 Elsevier Inc. All rights reserved.