Chu Yuan, Deng Hui, Cheng Jin-Pei
Department of Chemistry, State Key Laboratory of Elemento-organic Chemistry, Nankai University, Tianjin 300071, China.
J Org Chem. 2007 Sep 28;72(20):7790-3. doi: 10.1021/jo070973i. Epub 2007 Aug 29.
Equilibrium acidities of 16 1,3-dialkylimidazolium-type ionic liquid (IL) molecules (1-16) were systematically measured by the overlapping indicator method at 25 degrees C in dimethyl sulfoxide (DMSO) solution. The pKa values were observed to range from 23.4 for IL 12 to 19.7 for IL 6 (Tables 1 and 2), responding mainly to structural variations on the cation moiety. Excellent agreement between the spectrophotometrically determined pKa and that derived from NMR titration for 1,3,4,5-tetramethylimidazolium bis(trifluoromethanesulfonyl)imide (12) and the close match of the obtained pK values with the reported data in literature provide credence to the acidity measurements of the present work. The substituent effects at the imidazolium ring and the effects of counterions on the acidities of ionic liquids are discussed.
在25摄氏度下，于二甲基亚砜（DMSO）溶液中，采用重叠指示剂法系统地测定了16种1,3 - 二烷基咪唑型离子液体（IL）分子（1 - 16）的平衡酸度。观察到pKa值范围从IL 12的23.4到IL 6的19.7（表1和表2），这主要取决于阳离子部分的结构变化。对于1,3,4,5 - 四甲基咪唑双（三氟甲磺酰）亚胺（12），分光光度法测定的pKa与NMR滴定法得到的pKa之间具有极好的一致性，并且所获得的pK值与文献报道的数据紧密匹配，这为当前工作的酸度测量提供了可信度。讨论了咪唑环上的取代基效应以及抗衡离子对离子液体酸度的影响。
