标题：New Insight into the Formation Mechanism of Imidazolium-Based Ionic Liquids from N-Alkyl Imidazoles and Halogenated Hydrocarbons: A Polar Microenvironment Induced and Autopromoted Process
作者：Mu, Xueli; Jiang, Nan; Liu, Chengbu; Zhang, Dongju
作者机构：[Mu, Xueli; Liu, Chengbu; Zhang, Dongju] Shandong Univ, Sch Chem & Chem Engn, Inst Theoret Chem, Jinan 250100, Peoples R China.; [Jiang, Nan] Donggu 更多
通讯作者地址：[Liu, CB; Zhang, DJ]Shandong Univ, Sch Chem & Chem Engn, Inst Theoret Chem, Jinan 250100, Peoples R China.
来源：JOURNAL OF PHYSICAL CHEMISTRY A
摘要：To illustrate the formation mechanism of imidazolium-based ionic liquids (ILs) from N-alkyl imidazoles and halogenated hydrocarbons, density functional theory calculations have been carried out on a representative system, the reaction of N-methyl imidazole with chloroethane to form 1-ethyl-3-methyl imidazolium chloride ([Emim]Cl) IL. The reaction is shown to proceed via an S(N)2. transition state with a free energy barrier of 34.4 kcal/mol in the gas phase and 27.6 kcal/mol in toluene solvent. The reaction can be remarkably promoted by the presence of ionic products and water molecules. The calculated barriers in toluene are 22.0, 21.7, and 19:9 kcal/mol in the presence of 1-3 ionic pairs of [Emim] Cl and 23.5, 21.3, and 19:4 kcal/mol in the presence of 1-3 water molecules, respectively. These ionic pairs and water molecules do not participate directly in the reaction but provide a polar environment that favors stabilizing the transition state with large charge separation. Hence, we propose that the synthesis of imidazolium-based ILs from N-alkyl imidazoles and halogenated hydrocarbons is an autopromoted process and a polar microenvironment induced reaction, and the existence of water-molecules (a highly polar solvent) in the reaction may be mainly responsible for the initiation of reaction.