One pot acetalization of ketones with methanol over rare earth metal exchanged NaFAU-Y zeolites

Aromatic ketones (acetophenone and benzophenone) as well as the cyclic ketone (cyclohexanone) can be converted to their corresponding dimethyl acetal in near quantitative yields at ambient or refluxing temperatures by reacting with methanol. Large pore zeolites H-Y, Na-Y, different rare earth exchanged Na-Y zeolites, mesoporous K-10 montmorillonite clay, and silica have been used as catalysts. Molecular sizes of the ketones are critical in deciding the acetalization ability over any catalysts. Zeolites undergo fast deactivation as evidenced by reaction time Studies. These catalysts are poisoned by water (especially at low temperatures used in the present study) and the reaction will stop as soon as sufficient water is produced in the reaction to fully poison the catalyst. The activity of ketones follows the order: cyclohexanone > acetophenone > benzophenone, which is the reverse order of molecular size. The electron withdrawing property of phenyl groups is also important in decreasing the reactivity of acetophenone and benzophenone. The optimum number of acidic sites as well as dehydrating ability of K-10 montmorillonite clay and various rare earth exchanged Na-Y zeolites seem to work well in shifting the equilibrium to the product side. The method provides an efficient, simple and eco-friendly protocol for synthesizing dimethyl acetals.