物理化学学报 >> 2006, Vol. 22 >> Issue (02): 230-233.doi: 10.3866/PKU.WHXB20060220

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多羧基咪唑离子液体的酸性表征

耿卫国; 李雪辉; 王乐夫; 段红丽; 潘微平   

  1. 华南理工大学化工与能源学院, 广东省绿色化学产品技术重点实验室, 广州 510640
  • 收稿日期:2005-07-28 修回日期:2005-09-08 发布日期:2006-01-22
  • 通讯作者: 李雪辉 E-mail:cexhli@scut.edu.cn

Acidic Characterization of Polycarboxyl Imidazolium Ionic Liquids

GENG Wei-guo; LI Xue-hui; WANG Le-fu; DUAN Hong-li; PAN Wei-ping   

  1. The Guangdong Provincial Laboratory of Green Chemical Technology, School of Chemical and Energy Engineering, South China University of Technology, Guangzhou 510640, P. R. China
  • Received:2005-07-28 Revised:2005-09-08 Published:2006-01-22
  • Contact: LI Xueh-Hui E-mail:cexhli@scut.edu.cn

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摘要： 通过电位滴定法测得多羧基咪唑离子液体的离解常数pKa值(25 ℃)在1.43～1.92范围内, 说明多羧基咪唑离子液体酸性接近乙二酸, 比丁二酸以及乙酸强. 由于多羧基咪唑离子液体结构中咪唑环具有较强的吸电子诱导效应, 使多羧基咪唑离子液体具有中等强度的酸性. 三羧基咪唑离子液体酸性比含相同阴离子的二羧基咪唑离子液体酸性强. 阳离子相同、阴离子不同的多羧基咪唑离子液体酸性强弱顺序为: HSO4－ ＞ NO3－ ＞ PF6－ ＞ H2PO4－＞ Cl－、Br－ ＞ CF3CO2－ ＞ BF4－ ＞ CF3SO3－. 同时, 吡啶红外光谱探针法研究表明, 多羧基咪唑离子液体具有Brønsted酸性.

关键词: 离子液体, 多羧基, 酸性表征

Abstract: The acid-dissociation constant pKa of different polycarboxyl imidazolium ionic liquids (ILs) has been determined by potentiometric titration method at 25 ℃, and the values are in the range of 1.43 to 1.92, which are close to that of oxalic acid, but much smaller than those of succinic acid and acetic acid. The stronger acidity of polycarboxyl imidazolium ILs results from the strong electron withdrawing effect of positively charged imidazolium ring. It is also demonstrated that the acidity of the ILs is enhanced as the number of carboxylic groups appended to cations increases from two to three. The acidity of the ILs also depends on properties of the anions, and decreases in the order HSO4－ ＞ NO3－ ＞ PF6－ ＞ H2PO4－＞ Cl－、Br－ ＞ CF3CO2－ ＞ BF4－ ＞ CF3SO3－. The Brønsted acidity of the polycarboxyl imidazolium ILs has also been studied by IR technique using pyridine as the spectroscopic probe.

Key words: Ionic liquid, Polycarboxylic group, Acidic characterization