[Bmim]Br-AlCl3催化苯与1-十二烯烃烷基化反应机理的研究

利用同位素取代法考察了[Bmim]Br-AlCl3催化苯与1-十二烯烃烷基化反应机理. 首先进行了[Bmim]Br-AlCl3催化氘代苯与1-十二烯烃的反应, 通过GC-MS及NMR分析产物十二烷基苯同分异构体的结构, 验证了氘原子与产物侧链1-位碳相连的结论. 示踪氘原子推导了烷基化反应机理, 结果表明: [Bmim]Br-AlCl3催化苯与长链烯烃的烷基化反应是由[Al2Cl6Br]－发生平衡移动, 生成Lewis酸AlCl3引发的; AlCl3吸电子作用使1-十二烯烃的π电子向1-碳转移, 在烯烃的2-碳上形成正电荷中心, 碳正离子与苯发生亲电反应生成不稳定的σ络合物, 与σ络合物环上的σ-C相连的D＋转移到负电的侧链1-C上形成C—D键, AlCl3离去, 生成产物2-十二烷基苯. Lewis酸催化机理为离子液体催化苯与长链烯烃的反应中, 2-十二烷基苯选择性高于H质子催化产物提供了理论依据.

Alkylation Mechanism of Benzene with 1-Dodecene in [Bmim]Br-AlCl3

Alkylation mechanism of benzene with 1-dodecene in [Bmim]Br-AlCl_3 was investigated. Alkylation of C_6D_6 with 1-dodecene using [Bmim]Br-ALCl_3 as a catalyst was firstly carried out. Molecular structures of products, dodecylbenzene isomers, were analyzed by GC-MS and NMR, and the deuterated atom in the dodecylbenzenes was verified to be connected with 1-carbon of the side chain. Alkylation mechanism was deduced by tracing the deuterated atom. Results demonstrated that alkylation was induced by AlCl_3, which was generated by the dissociation of [Al_2Cl_6Br]~-. The role of AlCl_3 in attracting electrons pushs π electrons to 1-carbon of 1-dodecene, and the positive center is formed at 2-carbon. The carbonium ion reacts with benzene to form a σ complex, which is instable and D~+ connected to the σ carbon of ring is transferred into electronegative 1-C of the side chain to form a C-D bond, accordingly AlCl_3 leaves. 2-Dodecylbenzene is formed. The Lewis acid mechanism provides the evidences for the higher selectivity of 2-dodecylbenzene using ionic liquid as catalyst than that using H~+ as catalyst.