吗啡啉功能化酸性离子液体的合成、表征及其催化酯化性能

制备和表征了三种新型质子酸离子液体: 吗啡啉硫酸氢盐(Hnhm]HSO4)、4-甲基吗啡啉硫酸氢盐 (Hnmm]HSO4)和SO3H-功能化的4-(3-磺丙基)吗啡啉硫酸氢盐(C3SO3Hnhm]HSO4). 以氯乙酸(CAA)和乙醇合成氯乙酸乙酯的酯化反应考察了它们的酸性和催化活性, 并与1-(3-磺酸基)丙基-3-甲基咪唑硫酸氢盐、1-(3-磺丙基)吡啶硫酸氢盐、1-(3-磺丙基)-2-吡咯烷酮硫酸氢盐等三种具有不同氮杂环的SO3H-功能化酸性离子液体以及浓硫酸相对照. 结果表明, 上述SO3H-功能化离子液体对酯化反应的催化性能比非SO3H-功能化的Hnhm]HSO4和Hnmm]HSO4都高, 等同甚至优于浓硫酸. 当反应条件为: n(EtOH)∶n(CAA)∶n(C3SO3Hnhm]HSO4)＝1.3∶1∶0.2, 反应温度80 ℃, 反应时间3 h, 酯收率可达93.4%. 而且离子液体经真空干燥重复使用9次, 催化活性仍无明显下降. 以C3SO3Hnhm]HSO4催化乙酸和不同醇的酯化反应获得较高的酯收率和选择性, 离子液体跟酯产物均能自动分相. 还考察了SO3H-功能化酸性离子液体对奥氏体316不锈钢的腐蚀性. 尽管SO3H-功能化离子液体与硫酸的酸性相近, 但对钢试样的腐蚀率不到硫酸的1/3.

Functionalized Acidic Ionic Liquid with Morpholinium Cation: Synthesis, Characterization and Catalysis Performance in Esterification

Three new protic ionic liquids based on morpholinium including morpholinium hydrogen sulfate (Hnhm]HSO4), 4-methylmorpholinium hydrogen sulfate (Hnmm]HSO4) and 4-(3-sulfopropyl)mor-pholinium hydrogen sulfate (C3SO3Hnhm]HSO4) were synthesized and characterized. Their acidities and catalytic activities for the esterification of chloroacetic acid (CAA) with ethanol were examined and com-pared with other three SO3H-functionalized ionic liquids with various N-heterocycles, 1-(3-sulfopropyl) pyridinium hydrogen sulfate (C3SO3Hpy]HSO4), 1-methyl-3-(3-sulfopropyl)imidazolium hydrogen sulfate (C3SO3Hmim]HSO4) and 1-(3-sulfopropyl)-2-pyrrolidonium hydrogen sulfate (C3SO3Hnhp]HSO4). The catalytic performance of SO3H-functionalized ionic liquids could be much better than that of non-SO3H- functionalized Hnhm]HSO4 and Hnmm]HSO4, as good as or even better than that of sulfuric acid as catalyst. Under the optimized conditions of n(EtOH)∶n(CAA)∶n(C3SO3Hnhm]HSO4)＝1.3∶1∶0.2, 80 ℃, and 3 h, the yield of ethyl chloroacetate reached 93.4%. C3SO3Hnhm]HSO4 was reused at least 9 times without significant decrease in activity after drying under vacuum. The esterifications of acetic acid with various alcohols in C3SO3Hnhm]HSO4 have also been investigated. Good yields and selectivities were ob-tained, and all the produced esters could be easily recovered due to their immiscibility with the ionic liquid. In addition, Austenitic stainless steel 316 was used for conducting the corrosion test under the above esteri-ficaion condition. Although the acidities of SO3H-functionalized ionic liquids were close to that of sulfuric acid, the corrosion rates of the steel plates immersed in the systems with these ionic liquids were less than one third of that with sulfuric acid.