Highly Efficient Glycerol Acetalization over Supported Heteropoly Acid Catalysts

The acetalization of glycerol with acetone to yield solketal was catalyzed by Cs2.5H0.5PW12O40 (Cs2.5) supported on mesoporous silica under mild conditions. It gave a high glycerol conversion and selectivity to the targeted product even at room temperature (23 degrees C). We studied the use of both bulk and supported Cs2.5 as catalysts in another highly efficient glycerol acetalization reaction with paraformaldehyde, which gave much higher activity than with formaldehyde solution. For the reaction with acetone, the supported Cs2.5 showed a higher activity than the bulk material because of the high surface area of the mesoporous support. Interestingly, the supported Cs2.5 gave a lower conversion than the bulk for the reaction with paraformaldehyde. This is probably because of the high viscosity of the reaction system with the solid reagent paraformaldehyde. Overall, there is a complex relationship between catalyst, reaction conditions, which include the molar ratio of reactants and temperature, reaction mechanism and thermodynamics that affects the achieved activity and byproduct formation. A discussion about these interactions is included for each reaction.