Study On Synthesis Of Carbonates By The Immobilized Ionic Liquids

Ionic liquids are liquid salts at room temperature which are composed by anions and cations, and they have important meaning and application for the green chemical engineering. The ionic liquids have excellent catalytic activity to the cycloaddition of carbon dioxide and epoxides, and the CO₂ are founded that which can dissolved in ionic liquids largely by the decades of research. So, the ionic liquids have been the aroused general interest by the scientists. But there are also many deficiencies on the ionic liquids. For example, the high price, the high usage, uneasily separated and purified and so on. So it is a great interest by the scientists on that the ionic liquids are immobilized to the inorganic porous materials or polymer materials to been the heterogeneous catalyst by the adsorption method or bonding method.In this paper, three types of ionic liquids with imidazole cation immobilized to the Inorganic silica were synthesized by the author ([mim]Cl, [mim]BF4, [mim]PF6), and the molecular structures were confirmed by FT-IR, EA and CNMR, etc. For optimizing the reaction condition, the influence of several factors on reaction was studied, and we concluded that when the Immobilized ionic liquids were used as catalyst only, the conversion of the Propylene oxide(PO) is only 67.74%.But when the promoter AlCl₃ were added to the action, the conversion is greatly improved. So the final satisfied reaction condition was obtained in 4 hours at 120℃, 3MPa of carbon dioxide with 2.0g propylene oxide, 0.03g AlCl₃ and 0.3g catalyst [mim]Cl. In this condition, the conversion and selection of propylene oxide and propylene carbonate were 99.74% and over 99.3%. What is more, this catalytic system can be recycled and reused for four runs without any significant loss of catalytic activity. In this paper, the author also makes the traditional cycloaddition reaction and transesterification into one-pot synthesis of dimethyl carbonate. For optimizing the reaction condition, the influence of several factors on reaction was studied, and the satisfied reaction condition was obtained in 6h hours at 120℃, 4MPa of carbon dioxide with 25mmol propylene oxide, 200mmol methanol, 0.25g sodium methoxide and 0.75g catalyst [mim]BF₄. In this condition, the conversion of propylene oxide is 85.14% and the selection and yield of dimethyl carbonate are 45.99% and over 39.16%. What is more, this catalytic system can be recycled and reused for four runs without any significant loss of catalytic activity. So the one-pot synthesis of dimethyl carbonate has important meaning and application for been in-depth studied and exploited.