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Thermodynamics and nucleation of the enantiotropic compound p-aminobenzoic acid
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.ORCID iD: 0000-0002-6647-3308
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
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2013 (English)In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 15, no 25, 5020-5031 p.Article in journal (Refereed) Published
Abstract [en]

In this work, the thermodynamic interrelationship of the two known polymorphs of p-aminobenzoic acid has been explored, and primary nucleation in different organic solvents investigated. The solubility of both polymorphs in several solvents at different temperatures has been determined and the isobaric solid-state heat capacities have been measured by DSC. The transition temperature below which form α is metastable is estimated to be 16°C by interpolation of solubility data and the melting temperature of form β is estimated to be 140°C by extrapolation of solubility data. Using experimental calorimetry and solubility data the thermodynamic stability relationship between the two polymorphs has been estimated at room temperature to the melting point. At the transition temperature, the estimated enthalpy difference between the polymorphs is 2.84 kJ mol-1 and the entropy difference is 9.80 J mol-1 K-1. At the estimated melting point of form β the difference in Gibbs free energy and enthalpy is 1.6 kJ mol-1 and 5.0 kJ mol-1, respectively. It is found that the entropic contribution to the free energy difference is relatively high, which explains the unusually low transition temperature. A total of 330 nucleation experiments have been performed, with constant cooling rate in three different solvents and with different saturation temperatures, and multiple experiments have been carried out for each set of conditions in order to obtain statistically significant results. All performed experiments resulted in the crystallization of the high-temperature stable α-polymorph, which is kinetically favoured under all evaluated experimental conditions. The thermodynamic driving force required for nucleation is found to depend chiefly on the solvent, and to be inversely correlated to both solvent polarity and to solubility.

Place, publisher, year, edition, pages
2013. Vol. 15, no 25, 5020-5031 p.
Keyword [en]
Interfacial-Tensions, Carboxylic-Acids, Polymorphs, Crystallization, History
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Other Chemistry Topics
URN: urn:nbn:se:kth:diva-134134DOI: 10.1039/c3ce26984aISI: 000319987700007ScopusID: 2-s2.0-84882377366OAI: diva2:665192
Swedish Research Council, 621-2010-5391

QC 20131119

Available from: 2013-11-19 Created: 2013-11-18 Last updated: 2016-10-24Bibliographically approved

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