The catalytic behavior of water-insoluble cesium or rubidium tungstosilicates was studied in phenol tetrahydropyranylation and depyranylation reactions. The salts were synthesized and characterized using Fourier transform infrared spectroscopy, BET surface area measurements, thermogravimetric and differential thermal analysis and acidity evaluation by potentiometric titration with n-butylamine. Solids with high specific surface area, high thermal stability, and undegraded Keggin structure of the anion were obtained. The cesium salts showed a higher acidity than the rubidium salts. Both reactions were carried out at room temperature, using toluene in the tetrahydropyranylation and methanol in the depyranylation as solvents. It was observed that there is an influence of the acid strength of the different catalysts on the yields obtained in both reactions, although the textural properties of the salts must also be taken into account. The cesium salts were more active than rubidium salts, the latter being only active in the depyranylation reaction. (c) 2005 Elsevier B.V. All rights reserved.