Synthesis Of Ionic Liquids And Application In The Esterfication/transesterfication

Ionic liquids are new types of environment-friendly materials and can be used as catalysts as well as biological response of the green non-aqueous media. At present, ionic liquids have been successfully applied to many different areas, such as organic synthesis, biocatalysis reaction, separation process, electrochemistry etc. In addition, ionic liquids can resolve the increasingly serious environmental problems, improve product quality and reduce the cost of production. Therefore, it is significance to degisn the new ionic liquids with special function that can satisfy the various demands and enrich the fundamental theory about the ionic liquids.In this work, we designed and synthesized five acidic ionic liquids including two no reported composite ionic liquids, sulfuric acid-1,3-di-n-pentylimidazolium tetrafluoroborate (H₂SO₄-[D(n-C₅)Im][BF₄]) and phosphoric acid-1,3-di-n-pentylimidazolium tetrafluoroborate (H₃PO₄-[D(n-C₅)Im][BF₄]), and three new 1,3-dipentylimidazolium hexafluorophosphate ionic liquids'isomers, 1,3-di-n-pentylimidazolium hexafluorophosphate ([D(n-C₅)Im][PF₆]), 1,3-di-isopentylimidazolium hexafluorophosphate([D(i-C₅)Im][PF₆]) and 1,3-di(2-methylbutyl)imidazolium hexafluorophosphate ([D(2-mb)Im][PF₆]). We taken no solvent and temperature programmed to improve traditional two-step synthesis method which improved product purity, and we obtained that the speed of intermediate product 1,3-dialkyl imidazolium bromide ([RIm][Br]) generated was the control response. After we characterized the products by using infrared spectroscopy and NMR, we researched the physical and chemical properties, including polarity, viscosity, water content, melting point and density, and displayed ionic liquids'configuration is an important factor that affected their properties.Five acidic ionic liquids were investigated to synthesize palm acide polyol esters, the results indicated triethylammonium sulfate ([Et₃NH][HSO₄]) offered best catalytic activity. Based on temperature-controlled characteristics of [Et₃NH][HSO₄], we designed a novel method for preparation of palm acide polyol esters, in which the reaction under relatively high temperature combined with the separation under relatively low temperature. By studying on the effect of various factors on the conversion rate, we obtained optimal conditions to produce palm acide pentaerythritol esters, these include a 6:1 of palm acide/pentaerythritol, 5% of the ionic liquid, 210℃of the reaction temperature and 3.5h of reaction time.Under corresponding optimal conditions, three palm acide polyol esters, which included palm acide pentaerythritol ester, palm acide trimethylolpropane ester, and palm acide dihydroxymethylneopentane ester were synthesized, their conversions were 94.63 %, 94.47%, and 96.97%, respectively。After the reaction completed, [Et₃NH][HSO₄] would precipitate and separate from the system with decreasing the temperature. The ionic liquid obtained can be used to subsequent new synthesis of palm acide polyol ester. Although the conversion slightly reduced after the ionic liquid was reused for two times, it catalytic activity can reach to original level by adding suit acid. The physicochemical properties of three palm acide polyol esters were investigated in detail, the results exhibited these are of excellent fluid and low temperature characteristics, their viscosity index and pour point were in the range of 184³88 and -38℃^-23℃, these data indicate palm acide polyol esters can be used as base oil of biodegradable lubricant. Comparing with classical strong acid catalysts, the reaction system using ionic liquid [Et₃NH][HSO₄] as catalyst offers many advantages of colour of the product, recovery, and reuse of the catalyst.In order to research the reaction mechanism of palm acide polyol esters, the kinetics of three palm acide polyol esters were researched and we found that the structure of polyol had a major impact on activation energy. The activation energy increased by the branched-chain alcohols increased, the reaction rate was acceleration with the increasing temperature, because the more branched chain, the more hydroxy, the reaction was more difficulity, the higher the reaction temperature was required.The synthesis of octyl acetate catalyzed by Canadida Rugosa Lipase was selected as the modern reaction to investigate effect of different medium on the lipase performance. It was found activity and reactivity of the lipase in these ionic liquids studied are obviously higher than that in organic solvent hexane, especially to [D(2-mb)Im][PF₆]. Based on the temperature-controlled characteristics of [D(2-mb)Im][PF₆], a novel synthesis scheme was developed for synthesis of octyl acetate catalyzed by lipase, in which the reaction and the separation of the product from the system were carried out under a relatively high and low temperature, respectively. By investigating the influence of various factors on the conversion of 1-octanol, the optimal conditions for synthesis of octyl acetate was obtained, which are reaction temperature of 35℃, amounts of the lipase of 20mg, the ionic liquid of 1.0g, reaction time of 8h and water content of 1%. Under the optimal conditions, the conversion of 1-octanol was up to 99.3%. And the stability of the lipase in the [D(2-mb)Im][PF₆] medium was as same as 8.3-fold that in hexane. Also, the ionic liquid can be reused for five times without obvious reduction of catalytic properties. Moreover, circular dichroism and autofluorescence spectrum were also applied to research on molecular structure change of the lipase in different solvent. The results exhibited the lipase in the ionic liquid is of excellent secondary structure stability and slightly big exposure level of amino-acid residue in the lipase.