Research Centre in Chemistry (CIQUP), Institute of Molecular Sciences (IMS), Department of Chemistry and Biochemistry (DQB), Faculty of Sciences, University of Porto (FCUP), Rua do Campo Alegre, 4169-007 Porto, Portugal.
Molecules. 2023 Feb 7;28(4):1590. doi: 10.3390/molecules28041590.
This work reports an experimental study aiming to determine the thermodynamic properties of five chlorinated compounds with environmental impact. The vapor pressures of the crystalline phases of three isomers of dichlorobenzoic acid (2,4-, 2,5-, and 2,6-) and 2,6-dichlorobenzonitrile were measured at several temperatures using the Knudsen effusion technique. Another technique (a static method based on capacitance diaphragm manometers) allowed the measurement of the vapor pressures of both the crystalline and liquid phases of 2,4-dichlorobenzonitrile between 303.0 and 380.0 K. This latter technique also enabled the measurement of sublimation vapor pressures of 2,6-dichlorobenzonitrile over a larger range interval of temperatures, = 328.7 and 391.8 K. The standard molar enthalpy, entropy, and Gibbs energy of sublimation (for all the compounds studied) and vaporization (for 2,4-dichlorobenzonitrile) were derived, at reference temperatures, from the experimental vapor pressure results. The temperatures and enthalpies of fusion and the isobaric heat capacities of the five crystalline-substituted benzenes were determined using differential scanning calorimetry. The contributions of the three substituents (-COOH, -CN, and -Cl) to the sublimation thermodynamic properties of the compounds studied were discussed.
本工作报道了一项旨在确定五种具有环境影响的氯代化合物热力学性质的实验研究。采用克努森扩散技术在多个温度下测量了三种邻二氯苯甲酸异构体（2,4-、2,5-和 2,6-）和 2,6-二氯苯甲腈的晶相蒸气压。另一种技术（基于电容膜压力计的静态方法）允许在 303.0 至 380.0 K 之间测量 2,4-二氯苯甲腈的晶相和液相蒸气压。后一种技术还能够在更大的温度间隔内测量 2,6-二氯苯甲腈的升华蒸气压， = 328.7 和 391.8 K。在参考温度下，从实验蒸气压结果推导出了所有研究化合物的标准摩尔焓、熵和升华焓（对于所有研究的化合物）以及蒸发焓（对于 2,4-二氯苯甲腈）。使用差示扫描量热法确定了五种取代苯的晶体的融解温度和融解热以及等压热容。讨论了三个取代基（-COOH、-CN 和 -Cl）对所研究化合物升华热力学性质的贡献。
