The vapor-phase condensation of acetone was studied over TiO2-doped with 1 wt% of alkaline metals (Li, Na, K and Cs). The reaction was catalyzed by basic sites and the main products were mesityl oxide (MO), isomesityl oxide (ISMO) and mesitylene (M); other compounds as isophorone (IP) and phorone (P) were also obtained. The basic properties of the samples were determined by chemisorption of carbon dioxide. It was found that the number of the basic sites of the TiO2-doped catalysts increased in the following order: Li/TiO2 > Na/TiO2 similar to K/ TiO2 > Cs/TiO2; in contrast, the trend of the basic strength and total activity was Cs/TiO2 > K/TiO2 similar to Na/TiO2 Li/TiO2. On the other hand, the selectivity patterns showed that the higher formation of MO was obtained with the catalyst which showed the lowest basic force (Li/TiO2)A direct correlation between the activity and the alkaline metal atomic radius was found, while the inverse dependence for the selectivity to mesityl oxide was observed. (c) 2005 Elsevier B.V. All rights reserved.