[bmim]Cl/FeCl_3离子液体催化苯与乙烯烷基化的反应机理

Mechanism of Alkylation of Benzene with Ethylene Catalyzed by [bmim]Cl/FeCl_3 Ionic Liquid

利用FT IR和1HNMR对KOH无水乙醇溶液滴定前后的氯化 1 正丁基 3 甲基咪唑 ([bmim]Cl)无水乙醇溶液进行分析发现 ,[bmim]Cl咪唑环上的 2 H具有显著的质子酸性 ,滴定后的NMR谱中化学位移为 9 5处的 2 H信号完全消失 ,且在滴定过程中有KCl生成 .通过 [bmim]Cl/FeCl3 离子液体的1HNMR分析发现 ,咪唑环上的氢质子尤其是 2 H的化学位移与FeCl3 含量密切相关 ,随着FeCl3 与 [bmim]Cl摩尔比的增大 ,2 H的化学位移向低场移动 ,说明其去屏蔽作用增强 ,2 H更容易脱离 .将合成的 [bmim]Cl/FeCl3 离子液体脱水 ,并采用同位素置换的方法研究了离子液体催化全氘代苯与乙烯的烷基化反应机理 .结果表明 ,脱水后的离子液体仍然可以催化烷基化反应 .通过对反应后液体产物的GC MS分析 ,提出了离子液体催化的苯与乙烯烷基化反应的正碳离子机理 .反应前后离子液体的1HNMR分析表明 ,反应后离子液体中咪唑环上的 2 H的信号强度较反应前降低了 2 3% ,说明引发反应所需要的H+ 一部分是由咪唑环上的 2 H提供的 .

The acidic properties of the 2-position H of 1-n-butyl-3-methylimidazolium chloride ([bmim]Cl) were measured by titration, FT-IR, and 1H NMR analysis. The 2-H signal at a chemical shift of 9.5 disappeared completely and KCl was produced after titration with KOH solution, implying the significant Brnsted acidic property of the 2-H. When FeCl 3 was added into [bmim]Cl to form an ionic liquid, the chemical shift of 2-H shifted downfield, which indicated that 2-H was deshielded by FeCl 3 and was easy to disengage from imidazole. The alkylation of deuterated benzene with ethylene catalyzed by the dehydrated [bmim]Cl/FeCl 3 ionic liquid was investigated by GC-MS and 1H NMR. The intensity of NMR signal of 2-H was reduced by 23% after reaction. This suggested that the H+ for initiating the reaction was supplied partly by the 2-H of imidazole. On the basis of these results, a typical carbocation mechanism for the alkylation of benzene with ethylene catalyzed by the [bmim]Cl/FeCl 3 ionic liquid was proposed.