Chemical Fixation Of Carbon Dioxide To Cyclic Carbonate In The Presence Of Dialkylimidazolium Trifluoroacetate And Zinc Salt

Carbon dioxide is the main gas causing the greenhouse effect. Actually carbon dioxideis an important carbon-source and can be used as C1building block to synthesis usefulorganic compounds. Ionic liquids, because of their low vapor pressure, thermal stability,nonflammability, and ability to act as catalysts, have been frequently used as “green”reaction media in clean organic synthetic processes as substitutes for conventional toxic andvolatile solvents. Therefore, chemical fixation of carbon dioxide in the ionic liquids canreduce the emissions of carbon dioxide and the usage of conventional toxic and volatilesolvents, which are beneficial to the environment.In the present work,[BMIm][CF₃COO] with Zn（CF₃COO）₂were used to catalyze thereation of propylene oxide and carbon dioxide to form propylene carbonate. The effects ofvarious reaction conditions on the yeilds of propylene carbonate were investigated. Thepropylene carbonate was obtained in95%yeild at temperature of80℃under3.0Mpa ofcarbon dioxide pressure （25℃） after6h of reaction in the presence of [BMIm][CF₃COO]/Zn （CF₃COO）₂（molar ratio2:1,[BMIm][CF₃COO]2%）. Coupling reactions of carbondioxide and mono-substituted terminal epoxides to form cyclic carbonates were achieved inexcellent yeilds under the optimized reaction conditions.A variety of imidazolium trifluoroacetate bearing different alkyl chain length weresythesized and tested for the reaction of propylene oxide and carbon dioxide to formpropylene carbonate. The ionic liquids of bulker alkyl chain length have higher catalyticactivity. When the alkyl chain length was longer than C4, further increase in the length ofthe alkyl chain did not show significant improvement in propylene carbonate yeild. In orderto investigate the mechanism of the reation in our catalytic system, IR and NMR were usedto study the interactions between ionic liquids and zinc salts. Different metallic salts with[BMIm][CF₃COO] were tested for the reaction of carbon dioxide and propylene oxide to form propylene carbonate. Among the various metallic salts used, Zn （Ⅱ） showed thehighest activity. Imidazolium salt ionic liquids bearing different anions were also tested forthis reation. The catalytic activity of the ionic liquid was in the order [CF₃COO]-，[CH₃COO]^->[NO₃]>[OTs]^-, which is consistent with the nucleophilicity of the anion. Atlast, coupling reactions of CO2and mono-substituted terminal epoxides to form cycliccarbonates were achieved in good yeilds under mild conditions using ZnBr2/[BMIm][CF₃COO] as the catalyst and this catalyst could be used six times almost withoutlosing its catalytic activity.