Effects of alkyl chain length and solvents on thermodynamic dissociation constants of the ionic liquids with one carboxyl group in the alkyl chain of imidazolium cations.
Effects of alkyl chain length and solvents on thermodynamic dissociation constants of the ionic liquids with one carboxyl group in the alkyl chain of imidazolium cations.
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DOI：
10.1021/jp501731j
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发表时间：
2014-04
期刊：
影响因子：
--
通讯作者：
Yuehua Chen;Huiyong Wang;Jianji Wang
中科院分区：
文献类型：
--
作者：
Yuehua Chen;Huiyong Wang;Jianji Wang
酸性离子液体的热力学离解常数对于其催化和分离应用具有重要意义。本文合成了一系列烷基链上带有一个羧酸取代基的溴化咪唑（[{（CH 2）nCOOH}mim]Br，n = 1，3，5，7），并测定了它们在水溶液和有机水溶液中的离解常数（pKa）。在298.2K下，用电位滴定法测定了二甲基亚砜的含量。根据扩展的Debye-Hückel方程计算了离子液体在这些溶剂中的标准热力学解离常数（pKa（T））。结果表明，随着介质离子强度的增加和有机溶剂在水中的加入，pKa值增加。随着离子液体阳离子烷基链长的增加，离子液体的pKa（T）值也随之增加。此外，溶剂性质对pKa（T）值的影响是从溶剂化的离解组分和它们的吉布斯自由能从水转移到有机水溶液解释。
Thermodynamic dissociation constants of the Brønsted acidic ionic liquids (ILs) are important for their catalytic and separation applications. In this work, a series of imidazolium bromides with one carboxylic acid substitute group in their alkyl chain ([{(CH2)nCOOH}mim]Br, n = 1,3,5,7) have been synthesized, and their dissociation constants (pKa) at different ionic strengths have been determined in aqueous and aqueous organic solvents at 0.1 mole fraction (x) of ethanol, glycol, iso-propanol, and dimethyl sulfoxide by potentiometric titrations at 298.2 K. The standard thermodynamic dissociation constants (pKa(T)) of the ILs in these solvents were calculated from the extended Debye-Hückel equation. It was found that the pKa values increased with the increase of ionic strength of the media and of the addition of organic solvent in water. The pKa(T) values also increased with the increase of the alkyl chain length of cations of the ILs. In addition, the effect of solvent nature on pKa(T) values is interpreted from solvation of the dissociation components and their Gibbs energy of transfer from water to aqueous organic solutions.