物理化学学报 >> 2020, Vol. 36 >> Issue (11): 2004014.doi: 10.3866/PKU.WHXB202004014

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1-烷基-3-甲基咪唑氯化物焓变的热重分析

刘璐, 徐玉萍, 陈霞, 洪梅, 佟静()   

  • 收稿日期:2020-04-04 录用日期:2020-04-24 发布日期:2020-04-28
  • 通讯作者: 佟静 E-mail:tongjinglnu@sina.com
  • 基金资助:
    国家自然科学基金(21773100)

Thermogravimetric Analysis of Enthalpy Variation of 1-Alkyl-3-methylimidazole Chloride

Lu Liu, Yuping Xu, Xia Chen, Mei Hong, Jing Tong()   

  • Received:2020-04-04 Accepted:2020-04-24 Published:2020-04-28
  • Contact: Jing Tong E-mail:tongjinglnu@sina.com
  • Supported by:
    the National Natural Science Foundation of China(21773100)

摘要:

通过核磁共振(NMR)氢谱和碳谱表征1-烷基-3-甲基咪唑氯化物离子液体(1-乙基-3-甲基咪唑氯化物,1-丁基-3-甲基咪唑氯化物和1-己基-3-甲基咪唑氯化物)的结构,并借助热重仪器研究该类离子液体的蒸发特性。热重实验包括动态热重实验和恒温热重实验。前者的目的是确定实验样品的初始分解温度和恒温热重实验的温度范围。后者是在实验温度范围内记录实验样品的质量随时间的变化。借助Langmuir方程和Clausius-Clapeyron方程对数据进行拟合,从而获得该类离子液体在平均温度下的蒸发焓。查阅文献得到关于物质密度和表面张力的实验数据。借助本课题组之前提出的新模型,估算了1-辛基-3-甲基咪唑氯化物的蒸发焓,并将其与文献值进行比较。结果表明,估算值与文献值在同一数量级。与前期工作中的羧酸和氨基酸咪唑类离子液体的蒸发焓比较,发现阳离子相同时,变换阴离子会影响离子液体的蒸发焓,顺序为:氨基酸咪唑类>羧酸咪唑类>卤素咪唑类。结合三者的结构差异,推断上述顺序与分子间氢键有关。

关键词: 1-烷基-3-甲基咪唑氯化物离子液体, 热重法, 表征, 蒸发焓, 氢键

Abstract:

The structures of ionic liquids (ILs) based on 1-alkyl-3-methylimidazolium chloride [Cnmim]Cl (n = 2, 4, 6), (1-ethyl-3-methylimidazolium chloride [C2mim]Cl, 1-butyl-3-methylimidazolium chloride [C4mim]Cl, and 1-hexyl-3-methylimidazolium chloride [C6mim]Cl) were elucidated by 1H NMR and 13C NMR experiments. The vaporization characteristics of these ILs were studied by thermogravimetric analysis. Dynamic and isothermal thermogravimetric experiments were conducted in this study. The purpose of the dynamic experiments was to determine the initial decomposition temperature of the experimental sample and the temperature range for the isothermal thermogravimetric experiments. The purpose of the isothermal experiments was to record the mass dependence of the sample on time in the experimental temperature range. The Langmuir equation and Clausius-Clapeyron equation were used to fit the experimental data and obtain the vaporization enthalpies of these ILs at the average temperature within the experimental temperature range. However, in order to expand the applicability of the estimated values and to compare them with the literature data, the vaporization enthalpy ΔHvap(Tav) measured at the average temperature was converted into vaporization enthalpy ΔHvap(298) at ambient temperature. The difference between the heat capacities of the ILs in the gaseous and liquid states at constant pressure, ΔlgCpmө proposed by Verevkin, was used in this conversion process. The experimental data for substance density and surface tension at other temperatures were obtained by referring to the literature. In addition, the data for density and surface tension at T = 298.15 K were obtained by applying the extrapolation method to the literature values for other temperatures. The vaporization enthalpy of the 1-octyl-3-methylimidazolium chloride IL [C8mim]Cl was estimated by using the new vaporization model we had proposed in our previous work and compared with the reference value. The estimated value for [C8mim]Cl was on the same order of magnitude as the reference value. We compared the vaporization enthalpies in the present study with those for the carboxylic acid imidazolium and amino acid imidazolium ILs ([Cnmim]Pro (n = 2-6) and [Cnmim]Thr (n = 2-6), respectively in our previous work. The results revealed that a change in the anion type affects the vaporization enthalpy of the ILs in the order amino acid imidazolium > carboxylic acid imidazolium > halogen imidazolium, when the cation is the same. Considering the structural differences between the three kinds of ILs, the abovementioned order may be related to the intermolecular hydrogen bonds. There were no intermolecular hydrogen bonds in the [Cnmim]Cl (n = 2, 4, 6) ILs studied here. Therefore, the vaporization enthalpy of [Cnmim]Cl (n = 2, 4, 6) was the lowest among the three kinds of ILs considered.

Key words: 1-Alkyl-3-methylimidazolium chloride ionic liquids, Thermogravimetry, Characterization, Vaporization enthalpy, Hydrogen bonds

MSC2000: 

  • O642