烷基咪唑型卤盐类离子液体的合成机理研究

用密度泛函理论考察了甲基咪唑和一系列的卤代烷烃(氯乙烷,氯丁烷,溴乙烷,溴丁烷)反应合成咪唑类离子液体的反应机理. 在B3LYP/6-31++G**//B3LYP/6-31G*基组水平上找到了两条反应路径：路径A(反应物→TS1→P1)和路径B(反应物→TS2→P2). 在路径A中, 卤素离子和咪唑环C2上的氢质子形成氢键；在路径B中, 卤素离子和咪唑环C5上的氢质子形成氢键. 计算发现, 氢键的形成在反应中起到了非常重要的作用, 特别是咪唑环C2上的氢质子在和卤素离子成氢键后形成了一个五员环结构的过渡态, 该过渡态能量较低. 经过渡态TS1的反应途径其活化能要低于经过渡态TS2的反应途径, 反应路径A为主要的反应通道. 计算结果表明, 经过渡态TS1的反应途径是一放热过程, 这和实验观察现象一致.

Reaction Mechanism Study for the Synthesis of Alkylimidazolium-based Halide Ionic Liquids

The reaction mechanisms of 1-methylimidazole with a number of alkyl halides including ethyl chloride,butyl chloride, ethyl bromide and butyl bromide were determined using density-functional theory(DFT). At the B3LYP/6-31++G* *//B3LYP/6-31G* basis sets, two mechanisms were found: path A (reactants→TS1→P1) and path B (reactants→TS2→P2). For path A, the halide ions form hydrogen bonds with the C2-H; for path B, the halide ions form hydrogen bonds with the C5-H. Hydrogen bonds play a fundamental role in the synthesis of the alkylimidazolium-based ionic liquids, especially the hydrogen on the C2 affects the reaction significantly. The activation energies of reactions passing through TS1 are lower than that passing through TS2, which indicate that reactions passing through TS1 are favored by reaction dynamics. In agreement with experimental findings, the calculations showed that the reactions through TS1 are exothermic processes.