An acidity scale of 1,3-dialkylimidazolium salts in dimethyl sulfoxide solution
An acidity scale of 1,3-dialkylimidazolium salts in dimethyl sulfoxide solution
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DOI：
10.1021/jo070973i
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发表时间：
2007-09-28
影响因子：
3.6
通讯作者：
Cheng, Jin-Pei
中科院分区：
文献类型：
--
作者：
Chu, Yuan;Deng, Hui;Cheng, Jin-Pei
[图表]通过重叠指示剂法系统地测量了16个1，3-二烷基咪唑类离子液体（IL）分子（1-16）在二甲基亚砜（DMSO）溶液中在25 ℃下的平衡酸度。观察到IL 12的pK（a）值范围为23.4至IL 6的19.7（表1和2），主要与阳离子部分的结构变化有关。1，3，4，5-四甲基咪唑双（三氟甲磺酰基）酰亚胺（12）的pK（a）与NMR滴定法测定的pK（a）吻合得很好，且pK值与文献报道的数据吻合得很好，这为本工作的酸度测量提供了依据。讨论了咪唑环上的取代基效应和反离子对离子液体酸性的影响。
[GRAPHICS]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 pK(a) 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 pK(a) 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.