Dawson Heteropoly Salts Catalyzed Synthesis Of Propylene Carbonate And Ethylene Carbonate

Catalysis by polyoxometalate clusters is a field of increasing importance. Polyoxometalate clusters have several advantages as catalysts which make them economically and environmntally attractive, and provide a good basis for the molecular design of mixed oxide catalysts. The relationship among the following information can be established on the molecular basis: catalysis performance; chemical and physical properties; molecular and bulk composit ion and structure; and method of synthesis of catalysts. The transformation of CO2 into cyclic carbonates by the coupling raction with epoxides has attached much attention in view of the "environmental benign", "atom economy" and "green catalysis" concepts. One of the most well-known successful example is the cycloaddition between epoxides and CO2 to afford the propylene carbonate(PC), ethylene carbonate (EC) which are widely used as raw materials. Under mild reaction conditions,cycloaddition reaction of carbon dioxide to propylene oxide or ethylene oxide without any additional organic solvents has been investigated. Here tetra-n-butylammonium salts of Dawson-type polyoxotungstate complexes, namely transition-metal -monosubstituted α2-[(n-C4H9)4N](11-n)P2W17O61(Mn+·Br) (abbreviated as α2-P2W17M·Br),with M = Co(II), Mn(III), and Cu(II), and saturated [(n-C4H9)4N]6P2W18O62 (abbreviated as P2W18) complex were used as catalysts. Meanwhile, P2W17Co?Br/(n-C4H9)4NBr, and P2W17Co?Br /(n-C4H9)4NBr/PEG (MW 400) are the catalytic system which are studied for synthesis of PC and EC. A plausible cocatalysis mechanism was proposed.