Study On Catalytic Performance Of Task-specific Ionic Liquids In Esterification Reaction

Used as a new kind of environment-friendly solvents and acid catalysts, ionic liquids can be functioned to achieve special properties according to the given reactions. In this paper, we had investigated the relationship between structure and catalytic activity of ionic liquid catalysts using prepared seventeen of task-specific ionic liquids (TSILs) and heteropolyanion-based ionic liquids that bear an alkane sulfonic acid group such as imidazolium, pyridinium and acyclic trialkanylammonium as catalysts, and benzyl octanoate and dioctyl succinate and trioctyl citrate as model reaction, respectively, in conventional heating and microwave heating way. The catalysts with the best activity was employed to study the effect of acid alcohol ratio, amount of the catalyst, temperature, reaction time and microwave power on yield of esterification reaction. The results showed that acidity, solubility and stability of TSILs were effected by both anion and cation.For the synthesis of benzyl octanoate from benzil alcohol and octanoic acid in conventional heating way, the conversion of octanoic acid reached 95.3% by using [PSPy]HSO4 as catalyst under conditions of n octanoic acid: n benzil alcohol=1:1.5,20 mol% of octanoic acid for TSILs,120℃and 2.5 h. In addition, the catalyst could be reused ten times without considerable loss of activity and still had a conversion of 94.2%. While in microwave heating way, the conversion of octanoic acid reached 94.9%, under a microwave power of 375 W and 15 min. It indicated that the catalyst exhibited excellent stability and high catalytic activity in both heating ways.For the synthesis of dioctyl succinate used succinic acid and octanol as reactants and these TSILs as catalyst, the results showed that the conversion of succinic acid reached 93.49% by using [PSPy]HSO4 as catalyst under conditions of n succinic acid:n octanol=1:4,3 wt% of succinic acid for TSILs,150℃and 3 h in conventional heating heating. The catalyst could be reused three times without considerable loss of activity and still had a conversion of 93.79%. In microwave heating way, the conversion of succinic acid reached 95.47% in 15 min and a microwave power of 400 W. The catalyst could be reused six times and still had a conversion of 93.58%.The synthesis of trioctyl citrate was also investigated, the results showed that heteropolyanion-based ionic liquids was a reaction-induced self-separation catalyst. In conventional heating way, the conversion of citric acid reached 93.9% by using [MIMPS]3PWi204o as catalyst under conditions of n citric acid:n octanol=1:5.5,8wt% of citric acid for the catalyst,130℃and 3 h. In the microwave heating way, the conversion reached 93.48% by using 6 wt% of citric acid for [MIMPS]3PW12O40 in 20 min and 400 W. The catalyst was reused eight times and still had a conversion more than 90%. It indicated that the catalyst had excellent stability and catalytic activity.