Thermodynamic study of sulfanilamide polymorphism: (I). Monotropy of the alpha-variety.
OBJECTIVE
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 alpha-, beta-, and gamma-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 alpha- to gamma- and beta- to gamma-transitions were found to be + 10.2 and + 10.9 J g-1, respectively. The calculated enthalpy of the beta- to alpha-transition is consistent with the experimental one (+ 1 J g-1).


CONCLUSIONS
The monotropy of the alpha-form was ascertained over the explored temperature range at ordinary pressure.
Toscani
S
S
Laboratoire de Chimie Minérale Structurale, Faculté des Sciences Pharmaceutiques et Biologiques, Université René Descartes, Paris, France.
Thorén
S
S
Agafonov
V
V
Céolin
R
R
Dugué
J
J
D002152:Calorimetry, Differential Scanning; D003080:Cold Temperature; D003460:Crystallization; D013424:Sulfanilamides / Q000737:chemistry*; D013816:Thermodynamics; D014961:X-Ray Diffraction
D013424:Sulfanilamides