Department of Chemistry and Biochemistry, University of Regina, Regina, Saskatchewan S4S 0A2, Canada.
J Chem Phys. 2018 Sep 7;149(9):094505. doi: 10.1063/1.5039623.
Explanations are provided for the first time for the historically known locations of electrical conductivity maxima versus mixing ratio (mole fraction of acid, x) in mixtures of (i) acetic acid with water and (ii) acetic acid with pyridine. To resolve the question for the second system, density-functional-based molecular dynamic simulations were performed, at 1:1, 1:2, 1:3, 1:5, and 1:15 mixing ratios, to gain vital information about speciation. In a zeroth-order picture, the degree of ionization (and hence conductivity) would be maximal at x = 0.5, but these two examples see this maximum shifted to the left (water/acetic acid, x = 0.06), due to improved ion stability when the effective dielectric constant is high (i.e., water-rich mixtures), or right (pyridine/acetic acid x = 0.83), due to improved acetate stability via "self-solvation" with acetic acid molecules (i.e., acid-rich mixtures) when the dielectric constant is low. A two-parameter equation, with theoretical justification, is shown to reproduce the entire 0 < x < 1 range of data for electrical conductivity for both systems. Future work will pursue the applicability of these equations to other amine/carboxylic acid mixtures; preliminary fits to a third system (trimethylamine/acetic acid) give curious parameter values.
首次对（i）乙酸与水以及（ii）乙酸与吡啶混合物中电导率最大值与混合比（酸的摩尔分数，x）的历史已知位置进行了解释。为了解决第二个系统的问题，在 1:1、1:2、1:3、1:5 和 1:15 的混合比下进行了基于密度泛函的分子动力学模拟，以获取有关形态的重要信息。在零阶图像中，电离度（因此电导率）最大的位置应为 x = 0.5，但这两个实例表明，由于有效介电常数较高时离子稳定性提高（即富水混合物），最大位置向左移动，或由于介电常数较低时通过与乙酸分子的“自溶剂化”提高乙酸盐稳定性（即富酸混合物），最大位置向右移动。展示了一个具有理论依据的双参数方程，可以重现两个系统的电导率在 0 < x < 1 整个范围内的数据。未来的工作将探索这些方程在其他胺/羧酸混合物中的适用性；对第三个系统（三甲胺/乙酸）的初步拟合给出了有趣的参数值。
