Supercritical CO2 has been found to be a very convenient reaction medium for the Friedel-Crafts hydroxyalkylation of anisole with paraformaldehyde. The high diffusion coefficients of molecules in the supercritical state are a crucial factor contributing to the catalytic activity when the reaction is carried out with microporous zeolites. Thus, the activity of mordenite for the hydroxyalkylation in supercritical CO2 at 60 degreesC is about threefold higher than that observed for the same zeolite in toluene at 110 degreesC. (C) 2003 Elsevier Inc. All rights reserved.