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Thermodynamic Study of Sulfanilamide Polymorphism: (I) Monotropy of the α-Variety

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Abstract

Purpose. Sulfanilamide was chosen as a model compound in order to gain insights on the stability hierarchy of drug polymorphs from structural and thermodynamic criteria. Despite numerous studies, disagreements remained on the reported enthalpies associated with the mutual interconvertions of the α-, β-, and γ-forms of sulfanilamide. Therefore, the unambiguous determination of these enthalpies was the purpose of this work.

Methods. Samples, free of solvent inclusions and made of only one form, were prepared, and analyzed combining X-ray powder diffraction and Differential Scanning Calorimetry (DSC).

Results. The enthalpy values associated with the α- to γ- and β- to γ-transitions were found to be + 10.2 and + 10.9 J g−1, respectively. The calculated enthalpy of the β- to α-transition is consistent with the experimental one ( + 1 J g−1).

Conclusions. The monotropy of the α-form was ascertained over the explored temperature range at ordinary pressure.

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Toscani, S., Thorén, S., Agafonov, V. et al. Thermodynamic Study of Sulfanilamide Polymorphism: (I) Monotropy of the α-Variety. Pharm Res 12, 1453–1456 (1995). https://doi.org/10.1023/A:1016271017802

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  • DOI: https://doi.org/10.1023/A:1016271017802

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