Production of dimethyl carbonate via alkylene carbonate transesterification catalyzed by basic salts

Dimethyl carbonate (DMC) is actually recognized as an environmentally benign chemical because of its negligible ecotoxicity and low bioaccumulation and persistence. The diffusion of DMC as safe chemical necessarily implies a clean and safe route for its production, such as the base-catalyzed transesterification reaction with methanol of alkylene carbonates. Until now few bases were reported to be effective as heterogeneous catalysts under mild conditions (low temperature and atmospheric pressure). Therefore inorganic salts, namely, Na 3PO 4 and Na 2CO 3, were selected because of their basic properties and their negligible ecotoxicity. Using Na 3PO 4 as catalyst, the equilibrium yield for the reaction ethylene carbonate → DMC is reached in about 1 h at atmospheric pressure and at a temperature above 50 °C, while in the case of the propylene carbonate → DMC reaction, the equilibrium yield is difficult to reach, because the kinetics of this reaction are 5 times slower than those of the EC → DMC reaction. Both reactions can be well represented with first-order kinetics and present a similar activation energy, suggesting a diffusional rate-determining step. The quite different frequency factors suggest that the PC → DMC reaction is slow because of steric factors. © 2006 American Chemical Society.