Zeolite catalysts of various structures and type and concentration of acid sites were investigated in a liquid phase acylation of toluene with derivatives of isobutyric acid. The highest conversions of isobutyryl chloride or isobutyric anhydride were obtained over three-dimensional large-pore zeolite Beta and zeolite Y possessing medium concentration of acid sites. In general, the conversion of acylating agents increases with increasing pore size diameter and dimensionality of the channel system. Large-pore zeolites with three-dimensional channel system enable easier desorption and transport of bulky isopropyltolyl ketone. The activity of the zeolites used can be also controlled by tailoring their hydrophobic/hydrophilic properties. The higher initial rate of toluene acylation with isobutyric anhydride compared to isobutyryl chloride was found. However, only one possible acylating group of isobutyric anhydride is used for acylation reaction. (C) 2004 Elsevier B.V. All rights reserved.