Friedel-Crafts-type reaction of p-xylene with gamma-butyrolactone or vinylacetic acid over H4SiW12O40 supported on SiO2 have been investigated with different loadings of H4SiW12O40. The catalytic performance of H4SiW12O40/SiO2 have been compared with those of typical solid acid catalysts such as zeolites, ion-exchanged resins, and binary oxides. H4SiW12O40 supported on SiO2 was superior in activity and selectivity to 5,8-dimethyl-alpha-tetralone compared to other catalysts for the reaction between p-xylene and gamma-butyrolactone. SiO2-supported H4SiW12O40 also was efficient for the formation of 3,4,7-tetramethyl-alpha-indanone from p-xylene and vinylacetic acid. The formation of 5,8-dimethyl-a-tetralone is extremely sensitive to the load of H4SiW12O40 on SiO2, reaching a maximum at approximately 30 wt%, due to the change in the acid amount of the outermost surface as determined by benzonitrile-temperature programmed desorption. By analogy with reaction between 1,3,5-trimethylbenzene and gamma-butyrolactone, the reaction pathway involves initial alkylation of p-xylene with gamma-butyrolactone, followed by intramolecular acylation to 5,8-dimethyl-alpha-tetralone, which was supported by quantum calculations of gamma-butyrolactone and protonated gamma-butyrolactone. (c) 2006 Elsevier B.V. All rights reserved.