Water-tolerant solid acid catalysis of Cs2.5H0.5PW12O40 for hydrolysis of esters in the presence of excess water

Hydrolysis reactions of esters, ethyl acetate, cyclohexyl acetate, 2-methylphenyl acetate, and 2-nitrophenyl acetate in the presence of a large excess of water were investigated by using various solid acids. Inorganic solid acids such as an acidic cesium salt of 12-tungstophosphoric acid Cs2.5H0.5PW12O40, H-ZSM-5, SO42-/ZrO2, and Nb2O5, and polymer resins, Amberlyst-15, Amberlite-200C, and Nafion-H catalyzed the reactions, whereas H-Y, H-mordenite, SiO2-Al2O3, and gamma-Al2O3 were inactive. Among inorganic solid acids, Cs2.5H0.5PW12O40 was most active for all reactions in the unit of the activity per catalyst weight. CS2.5H0.5PW12O40 was comparable to Nafion-H in the catalytic activity per unit acid amount of catalysts, and much more active than H-ZSM-5, SO4-2/ZrO2, and Amberlyst-15. The activities of liquid acid catalysts, such as H2SO4, H3PW12O40, and p-toluenesulfonic acid, per unit acid amount were less than that of Cs2.5H0.5PW12O40, although the relative activities per catalyst weight of the liquid acids were higher than that of CS2.5H0.5PW12O40. The activity of Cs2.5H0.5PW12O40 relative to the other catalysts became higher for hydrolysis of bulky esters like 2-methylphenyl acetate and 2-nitrophenyl acetate for which H-ZSM-5 was inactive, demonstrating that CS2.5H0.5PW12O40 is a widely applicable water-tolerant solid acid. When Cs2.5H0.5PW12O40 was separated from the reactant solution and reused for the hydrolysis of ethyl acetate repeatedly, the reaction rate of the 5th run was more than 90% that of the 1st run, whereas the rate on SO4-2/ZrO2 decreased by repeating once to become less than half that of the 1st run. (C) 1997 Elsevier Science B.V.