Study Of Esterification Reaction Catalyzed By Ionic Liquid Microemulsion System

Esterification is one of the most common reactions in organic chemistry. Oleic acid eaters are widely used in fine chemistry. The traditional catalysts used in esterification are sulfuric acid, superacid and heteropoly acid, but they have several drawbacks such as side reactions, low reaction activity, deep color products, and difficulties of separation. Ionic liquids(ILs) can overcome the shortcomings of traditional catalysts. However, the ILs, which have better catalytic performance, are the pyrrole type ILs with sulfonic acid group. This kind of ILs is complex to synthesis. Microemulsion can provide a very large interfacial area. But esterification in traditional microemulsion needs more than 24 h to reach equilibrium.Ionic liquid microemulsions(ILMs) have more advantages owing to the unique features of the ILs and microemulsion. Cyclohexane or toluene were used as organic phase. Triton X-100 and [Hmim]HSO4 or [Omim]HSO4 were used as surfactants. [Bmim]BF4 or [Bmim]NTf2 were used as ionic liquid phase. A series of ILMs, which revealed relatively high temperature-independence, were prepared and characterized by pseudo ternary phase diagrams. The used ILs are simple to synthesis and convenient to purification.A series of ILMs as reaction media and catalysts were prepared and their catalysis performance in the reaction were studied. Results showed that [Bmim]BF4/TX-100+[Hmim]HSO4/cyclohexane system revealed a much higher catalytic activity than other ILM systems. The results of orthogonal experiment showed the primary and secondary factors in the esterification of oleic acid and lauryl alcohol: catalyst dosage > molar ratio of reactants > temperature > reaction time. The maximum yield of lauryl oleate reaches 91.17% and its selectivity reaches 98.55% under optimum reaction conditions. The reaction was carried out with 8 wt.% catalyst, molar ratio of oleic acid to lauryl alcohol was 0.2 at 100 ℃ for 6 h. The effect of fatty alcohols with different alkyl chain on the reaction was studied, and the results proved that the fatty alcohols with a long alkyl chain demanded relatively longer reaction time. The effect of the presence of ILMs in the esterification was studied. The probable mechanism for the esterification was deduced according to experiments. [Hmim]HSO4 could be used as a surfactant-type Br?nsted-acid catalyst. [Bmim]BF4/TX-100+[Hmim]HSO4/cyclohexane system provided a high interfacial area of contact to promote the reaction rate. Polar acid heads of [Hmim]HSO4 would congregate because of the formation of ILMs, leading to a relatively high acidity in the interfacial area, and an effective catalytic machinery for esterification. The [Bmim]BF4 microdomain in ILM system entrapped the generated water by hydrogen bonding, which accelerated the formation of ester and promoted the equilibrium process in favor of the products. Esterification occurred in the interface should follow the mechanism of the esterification with proton acid catalyst.