The Effective Catalysts For Synthesis Of Styrene Carbonate Directly From Styrene And CO₂

Carbon dioxide is one of the most abundant wastes produced by human activities and industrial emission. In order to prevent risky reinforcement of the greenhouse effect, the accumulation of CO2 in the atmosphere should be controlled by removing it from industrial effluents. On the other hand, CO2 is recognized as a safe and cheap C1 building block. Under these circumstances, the conversion of carbon dioxide to industrially useful compounds has recently attracted much attention in view of the so-called"sustainable society"and"green chemistry"concepts. Up to date, one of the most effective methodologies is the synthesis of five-membered cyclic carbonate via the coupling of CO2 with epoxides and, in this process, one carbon atom and two oxygen atoms can be incorporated without forming any byproducts with high atom efficiency. Moreover, cyclic carbonates have found extensive use as excellent aprotic polar solvents, precursors for polycarbonates and other polymeric materials, electrolytic element of lithium secondary batteries and chemical ingredients for pharmaceutical/fine chemicals like dialkyl carbonates, glycols, carbomates, pyrimidines, purines, etc.After Inoue et al first reported the cyclic carbonate could be prepared by cycloaddition of CO2 to epoxides in 1969, numerous catalysts such as alkali metal halides, organic bases, metal oxides, zeolites, smectites, and metal complexes have been investigated. However, activity, stability, and recovery of the catalysts still remain to be improved. Besides the direct coupling of CO2 with epoxides to cyclic carbonate, alternative synthetic route from CO2 is oxidative carboxylation of olefin, which couples two sequential reactions of epoxidation of olefin and CO2 cycloaddition to epoxides formed. Synthesis of cyclic carbonate from olefin and CO2 gives a simple route that avoids the preliminary synthesis and isolation of epoxides. Furthermore, easily available and low-priced chemicals of olefins may be used to produce valuable chemicals as compared with epoxides as substrates. This direct synthesis route for cyclic carbonate from olefin is not only energy saving but also simple and economical. Despite the usefulness of this reaction, little efforts have been given to it so far, in contrast to extensive study on the coupling reaction of CO2 and epoxides.Herein, we synthesized highly effective Co-MCM-41 catalyst which was very active for the epoxidation of styrene, and then supported gold catalyst was coupled withBu4NBr which catalyzed CO2 cycloaddition reaction. It was shown the two components, Co-MCM-41and Bu4NBr efficiently catalyzed the direct oxidative carboxylation of styrene to styrene carbonate. The influence of factors such as catalyst pretreatments, Co loadings, kinds of oxidants and CO2 pressure are investigated in detail. An improved styrene carbonate yield (46%) was obtained under mild reaction conditions of 80 oC, 7 h, and 4 MPa CO2 pressure. To overcome the complexity of catalyst system, a heterogeneous catalyst Au supported basic resin D201 was synthesized, denoted as Au/ D201. Styrene carbonate was obtained at 50.6% by"one-pot two-steps"route. The catalyst is simple and easily recyclable, which is important for the industrial application.