Thermodynamics and Nucleation Kinetics of m-Aminobenzoic Acid Polymorphs

The polymorphism of m-aminobenzoic acid has been investigated. Two polymorphs have been identified and characterized by X-ray powder diffraction (XRPD), Fourier transform IR (FTIR), microscopy, and thermal analysis. The melting properties and isobaric heat capacities of both polymorphs have been det...

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Bibliographic Details
Published in:	Crystal growth & design Vol. 10; no. 1; pp. 195 - 204
Main Authors:	Svärd, Michael, Nordström, Fredrik L, Jasnobulka, Tanja, Rasmuson, Åke C
Format:	Journal Article
Language:	English
Published:	Washington,DC American Chemical Society 06-01-2010
Subjects:	AMINO-ACIDS Chemical engineering Condensed matter: structure, mechanical and thermal properties Crystalline state (including molecular motions in solids) Crystallographic aspects of phase transformations; pressure effects DISSOCIATION-CONSTANTS Equations of state, phase equilibria, and phase transitions Exact sciences and technology General studies of phase transitions Kemiteknik META Nucleation Physics Solubility, segregation, and mixing; phase separation Structure of solids and liquids; crystallography Structure of specific crystalline solids TECHNOLOGY TEKNIKVETENSKAP ZWITTERION Fourier transform spectroscopy Nucleation Metastable states Entropy XRD Temperature effects Alcoholic solution Crystal structure Temperature dependence Gibbs free energy Transition temperature Experimental data Cooling rate Crystallization Solubility Heat capacity Free enthalpy Heat treatments Free energy Powder pattern Acetonitrile Thermodynamic analysis Thermal analysis Thermodynamic properties Polymorphism
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Summary:	The polymorphism of m-aminobenzoic acid has been investigated. Two polymorphs have been identified and characterized by X-ray powder diffraction (XRPD), Fourier transform IR (FTIR), microscopy, and thermal analysis. The melting properties and isobaric heat capacities of both polymorphs have been determined calorimetrically, and the solubility of each polymorph in several solvents at different temperatures has been determined gravimetrically. The solid-state activity (i.e., the Gibbs free energy of fusion) of each polymorph has been determined through a comprehensive thermodynamic analysis based on experimental data. It is found that the polymorphs are enantiotropically related, with a stability transition temperature of 156.1 °C. The published crystal structure belongs to the polymorph that is metastable at room temperature. Energy-temperature diagrams of both polymorphs have been established by determining the free energy, enthalpy, and entropy of fusion as a function of temperature. A total of 300 cooling crystallizations have been carried out at constant cooling rate using different saturation temperatures and solvents, and the visible onset of primary nucleation was recorded. The results show that for this substance the polymorph that will nucleate depends chiefly on the solvent. In water and methanol solutions, the stable form I was obtained in all experiments, whereas in acetonitrile, a majority of nucleation experiments resulted in the isolation of the metastable form II. It is shown how this can be rationalized by analysis of solubility, solution speciation, and nucleation relationships. The importance of carrying out multiple experiments at identical conditions in nucleation studies of polymorphic systems is demonstrated.
ISSN:	1528-7483 1528-7505 1528-7505
DOI:	10.1021/cg900850u