Thermodynamic study of phase transitions in methyl esters of ortho- meta- and para-aminobenzoic acids |
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| Institution: | 1. Department of Electronic and Electrical Engineering, Sungkyunkwan University, Suwon 440-746, Republic of Korea;2. Research Institute for Cell and Gene Therapy, SAM Medical Center, 9-Samdeok-ro, Manan-gu, Anyang-si, Gyeonggi-do 430-733, Republic of Korea;3. Korea Institute of Machinery and Materials, 104, Sinseongno, Yuseong-Gu, Daejeon 305-343, Republic of Korea;1. R&D Center for Membrane Technology and Department of Chemical Engineering, Chung Yuan Christian University, Chung Li 32023, Taiwan, ROC;2. School of Chemical Engineering and Chemistry, Mapua Institute of Technology, Manila 1002, Philippines;1. College of Architecture and Environment, Sichuan University, Chengdu, 610065, China;2. College of Chemistry and Material Science, Sichuan Normal University, Chengdu 610068, China;3. Analytical & Testing Center, Sichuan University, Chengdu, 610064, China |
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| Abstract: | A static method based on capacitance gauges was used to measure the vapor pressures of the condensed phases of the methyl esters of the three aminobenzoic acids. For methyl o-aminobenzoate the vapor pressures of the liquid phase were measured in the range (285.4 to 369.5) K. For the meta and para isomers vapor pressures of both crystalline and liquid phases were measured in the ranges (308.9 to 376.6) K, and (332.9 to 428.0) K, respectively. Vapor pressures of the latter compound were also measured using the Knudsen effusion method in the temperature range (319.1 to 341.2) K.From the dependence of the vapor pressures on the temperature, the standard molar enthalpies and entropies of sublimation and of vaporization were derived. Differential scanning calorimetry was used to measure the temperatures and molar enthalpies of fusion of the three isomers. The results enabled the estimation of the enthalpy of the intermolecular (N−H…O) hydrogen bond in the crystalline methyl p-aminobenzoate. A correlation relating the temperature of fusion and the enthalpy and Gibbs energy of sublimation of benzene, methyl benzoates and benzoic acids was derived. |
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