Characterization of the Polymorphic Behavior of an Organic Compound Using a Dynamic Thermal and X-ray Powder Diffraction Technique

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Abstract

The crystalline polymorphic forms of several samples of an organic compound produced by Dowpharma were characterized using differential scanning calorimetry (DSC); X-ray powder diffraction (XRPD); combined, simultaneous, and dynamic differential scanning calorimetry/X-ray powder diffraction (DSC/XRPD); and high performance liquid chromatography (HPLC). A total of 10 crystalline polymorphs were identified, six of which are anhydrous. Form l is a heptahydrate that reversibly converts to anhydrous Form I under dry conditions and also undergoes a reversible solid–solid phase transition at about 110 °C to convert to Form II. Form Il is anhydrous and melts at approximately 220 °C. Form III crystallizes as a hexahydrate, which reversibly converts to the monohydrate Form III and then to an anhydrous Form III above 120 °C. Anhydrous Form III melts at approximately 200 °C. Form IV crystallized as a hydrous material, which was converted to the anhydrous Form IV above approximately 60 °C, in a reversible process. Form IV appears to be unstable in high humidity conditions (e.g., 90% relative humidity at 25 °C) and slowly converts to Forms I and III. Form IV also undergoes a nonreversible solid–solid phase transition at approximately 180 °C, to form anhydrous Form V. Form V melts at approximately 245 °C. Form VI is observed only in the anhydrous state and melts at approximately 245 °C. The anhydrous nature of Form VI makes this material the most ideal crystalline material for subsequent formulation work.

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