Abstract: As an important organic chemical intermediate, the determination of the solubility of α-amino-ε-caprolactam is a thermodynamic basis for the development of solution crystallization purification technology and product quality control. The solubility of α-amino-ε-caprolactam in various organic solvents such as N,N-dimethylformamide, acetone, 1,4-dioxane, trioctyl phosphate, toluene, p-xylene, 1,3,5-trimethylbenzene, methyl tert-butyl ether, cyclohexane, and n-hexane was measured by the static equilibrium method. The results indicated that within the temperature range of 278.15~323.15 K, the solubility of α-amino-ε-caprolactam in different solvents increased with the rise of temperature, and the solubility in different solvents generally followed the trend that it increased with the increase of the polarity of the solvent. However, there were also some exceptional cases. For instance, although methyl tert-butyl ether was polar and could form electrostatic interaction with the solute, the steric hindrance restricted its interaction with α-amino-ε-caprolactam, resulting in a relatively low solubility. In contrast, the delocalized π-electron clouds of aromatic molecules could generate π-π interactions with the conjugated regions of α-amino-ε-caprolactam, thereby enhancing the solubility. These observations indicated that dissolution behavior was influenced not only by solvent polarity but also by intermolecular interactions such as π-π stacking. The solubility data were fitted by the Apelblat, λh, quadratic polynomial, and Van't Hoff models. The correlation coefficients (R2) of all models were greater than 0.95. Among them, the quadratic polynomial model showed the best fitting effect, with an average relative deviation ranging from 0 to 1.8403% and a root mean square deviation ranging from 0 to 0.3190%. Thermodynamic parameters of the dissolution process were analyzed by the Van't Hoff equation. It was shown that ΔdisH, ΔdisS, and ΔdisG of α-amino-ε-caprolactam were positive values in both n-hexane and cyclohexane, two non-polar solvents. It indicated that the dissolution process was a non-spontaneous, endothermic process with an increase in entropy. The calculated relative contribution of enthalpy ζH was less than the relative contribution of entropy ζTS, indicating that ΔdisH contributed less to ΔdisG than ΔdisS during the dissolution process in these 10 solvents.

Key words: α-amino-ε-caprolactam, solubility, model fitting, dissolution thermodynamic properties

摘要： 氨基己内酰胺作为一种重要的有机化工中间体，其溶解度的测定是溶液结晶纯化技术开发和产品质量控制的热力学基础。本工作采用静态平衡法测定了氨基己内酰胺在N,N-二甲基甲酰胺、丙酮、1,4-二氧六环、磷酸三辛酯、甲苯、对二甲苯、1,3,5-三甲苯、甲基叔丁基醚、环己烷和正己烷等有机溶剂中的溶解度。结果表明，在278.15~323.15 K温度范围内，氨基己内酰胺在不同溶剂中的溶解度随温度升高而增大，且在不同溶剂中的溶解度基本符合随溶剂极性增大而增大的规律。但该规律存在个别例外，甲基叔丁基醚虽具有一定极性，理论上可与氨基己内酰胺形成静电相互作用，但其分子结构带来的空间位阻显著阻碍了溶质与溶剂间的有效相互作用，导致氨基己内酰胺在该溶剂中的溶解度偏低；而甲苯等芳香烃溶剂可通过离域π电子云与氨基己内酰胺的共轭区域形成电子云重叠，从而增强溶解性。这表明除极性外，溶质-溶剂电子云重叠等因素也会影响溶解行为。采用Apelblat、λh、二次多项式和Van't Hoff模型对溶解度数据进行拟合，所有模型的相关系数(R2)均大于0.95。其中二次多项式模型的拟合效果最佳，平均相对偏差ARD为0~1.8403%，均方根偏差RMSD为0~0.3190%。通过Van't Hoff方程分析溶解过程的热力学参数，显示在正己烷和环己烷两种非极性溶剂中氨基己内酰胺的ΔdisH, ΔdisS和ΔdisG均为正值，表明其溶解过程是非自发的吸热熵增过程。计算得出焓相对贡献ζH小于熵相对贡献ζTS，表明其在这10种溶剂的溶解过程中，ΔdisH对ΔdisG的贡献小于ΔdisS。

关键词: 氨基己内酰胺, 溶解度, 模型拟合, 溶解热力学性质