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首页> 外文期刊>Crystal growth & design >M-hydroxybenzoic acid: Quantifying thermodynamic stability and influence of solvent on the nucleation of a polymorphic system
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M-hydroxybenzoic acid: Quantifying thermodynamic stability and influence of solvent on the nucleation of a polymorphic system

机译：M-羟基苯甲酸：定量热力学稳定性和溶剂对多晶型体系成核的影响

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Nucleation of m-hydroxybenzoic acid crystals in different pure solvents has been investigated, and the thermodynamic interrelationship between two polymorphs was analyzed. The melting properties and specific heat capacities of both polymorphs have been determined by differential scanning calorimetry, and the solubility in several solvents at different temperatures was measured gravimetrically. Absolute values of the Gibbs free energy, enthalpy and entropy of fusion, and the activity of the polymorphs have been determined as functions of temperature. It is established that the polymorphs are monotropically related, with differences in enthalpy and Gibbs free energy of approximately 1 kJ/mol at room temperature. In a total of 539 nucleation experiments, in six solvents and with different cooling rates, the visible onset of nucleation was recorded and the nucleating polymorph was isolated. It is found that the degree of supersaturation required for nucleation and the polymorphic outcome depend strongly on the solvent. The metastable polymorph is kinetically favored under all evaluated experimental conditions, and for most of the conditions it is also statistically the most probable outcome. Nucleation of the stable polymorph is increasingly promoted in solvents of increasing solubility. It is shown how this can be rationalized by analysis of solubility and rate of supersaturation generation.
机译：研究了不同纯溶剂中间羟基苯甲酸晶体的成核现象，并分析了两种多晶型物之间的热力学相互关系。两种多晶型物的熔融性质和比热容已通过差示扫描量热法测定，并且通过重量分析法测量了在不同温度下在几种溶剂中的溶解度。吉布斯自由能，熔化的焓和熵以及多晶型物的活性的绝对值已经确定为温度的函数。已确定多晶型物是单向相关的，在室温下焓和吉布斯自由能的差异约为1 kJ / mol。在总共539次成核实验中，在六种溶剂中以不同的冷却速率记录了可见的成核现象，并分离出了有核多晶型物。发现成核所需的过饱和度和多晶型产物在很大程度上取决于溶剂。在所有评估的实验条件下，亚稳态多晶型在动力学上都是有利的，并且在大多数条件下，从统计学上讲，它也是最可能的结果。在溶解度增加的溶剂中，稳定多晶型物的成核作用日益增强。它显示了如何通过分析溶解度和过饱和生成速率来使其合理化。

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