Water-tolerant solid acid catalysis of Cs 2.5H 0.5PW 12O 40 for hydrolysis of esters in the presence of excess water

Abstract

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 Cs 2.5H 0.5PW 12O 40, H-ZSM-5, SO 4 2−/ZrO 2, and Nb 2O 5, and polymer resins, Amberlyst-15, Amberlite-200C, and Nafion-H catalyzed the reactions, whereas H-Y, H-mordenite, SiO 2—Al 2O 3, and γ-Al 2O 3 were inactive. Among inorganic solid acids, Cs 2.5H 0.5PW 12O 40 was most active for all reactions in the unit of the activity per catalyst weight. Cs 2.5H 0.5PW 12O 40 was comparable to Nafion-H in the catalytic activity per unit acid amount of catalysts, and much more active than H-ZSM-5, SO 4 2−/ZrO 2, and Amberlyst-15. The activities of liquid acid catalysts, such as H 2SO 4, H 3PW 12O 40, and p-toluenesulfonic acid, per unit acid amount were less than that of Cs 2.5H 0.5PW 12O 40, although the relative activities per catalyst weight of the liquid acids were higher than that of Cs 2.5H 0.5PW 12O 40. The activity of Cs 2.5H 0.5PW 12O 40 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 Cs 2.5H 0.5PW 12O 40 is a widely applicable water-tolerant solid acid. When Cs 2.5H 0.5PW 12O 40 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 SO 4 2−/ZrO 2 decreased by repeating once to become less than half that of the 1st run.