Centro de Investigação em Química (CIQUP), Department of Chemistry and Biochemistry, Faculty of Sciences, University of Porto, Rua do Campo Alegre, P-4169-007 Porto, Portugal.
Molecules. 2021 Dec 22;27(1):39. doi: 10.3390/molecules27010039.
The present work reports an experimental thermodynamic study of two nitrogen heterocyclic organic compounds, fenclorim and clopyralid, that have been used as herbicides. The sublimation vapor pressures of fenclorim (4,6-dichloro-2-phenylpyrimidine) and of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were measured, at different temperatures, using a Knudsen mass-loss effusion technique. The vapor pressures of both crystalline and liquid (including supercooled liquid) phases of fenclorim were also determined using a static method based on capacitance diaphragm manometers. The experimental results enabled accurate determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation for both compounds and of vaporization for fenclorim, allowing a phase diagram representation of the (,) results, in the neighborhood of the triple point of this compound. The temperatures and molar enthalpies of fusion of the two compounds studied were determined using differential scanning calorimetry. The standard isobaric molar heat capacities of the two crystalline compounds were determined at 298.15 K, using drop calorimetry. The gas phase thermodynamic properties of the two compounds were estimated through ab initio calculations, at the G3(MP2)//B3LYP level, and their thermodynamic stability was evaluated in the gaseous and crystalline phases, considering the calculated values of the standard Gibbs energies of formation, at 298.15 K. All these data, together with other physical and chemical properties, will be useful to predict the mobility and environmental distribution of these two compounds.
本工作报道了两种已用作除草剂的氮杂环有机化合物，芬氯苯和氯吡咯草，的实验热力学研究。采用克努森质量损失扩散技术，在不同温度下测量了芬氯苯（4,6-二氯-2-苯基嘧啶）和氯吡咯草（3,6-二氯-2-吡啶羧酸）的升华蒸气压。还使用基于电容膜压力计的静态方法，测定了芬氯苯的晶体和液体（包括过冷液体）各相的蒸气压。实验结果能够准确确定两种化合物的升华标准摩尔焓、熵和吉布斯自由能，以及芬氯苯的蒸发标准摩尔焓，允许在该化合物的三相点附近，用相图表示（，）结果。用差示扫描量热法测定了所研究的两种化合物的熔点和熔融摩尔焓。在 298.15 K 下，采用滴量热法确定了两种结晶化合物的标准等压摩尔热容。通过从头算计算，在 G3(MP2)//B3LYP 水平上估算了两种化合物的气相热力学性质，并考虑到在 298.15 K 下形成的标准吉布斯自由能的计算值，评估了它们在气相和晶体相中的热力学稳定性。所有这些数据，以及其他物理和化学性质，将有助于预测这两种化合物的迁移性和环境分布。
