The Phase Diagram of the API Benzocaine and Its Highly Persistent, Metastable Crystalline Polymorphs

Ivo B. Rietveld (1, 2, 3) , Hiroshi Akiba (3) , Osamu Yamamuro (3) , Maria Barrio (4) , René Céolin (4) , Josep-Lluís Tamarit (4)

1 SMS - Sciences et Méthodes Séparatives
2 UPCité - Université Paris Cité
3 ISSP - Institute for Solid State Physics [Tokyo]
4 UPC - Universitat Politècnica de Catalunya = Université polytechnique de Catalogne [Barcelona]

The availability of sufficient amounts of form I of benzocaine has led to the investigation of its phase relationships with the other two existing forms, II and III, using adiabatic calorimetry, powder X-ray diffraction, and high-pressure differential thermal analysis. The latter two forms were known to have an enantiotropic phase relationship in which form III is stable at low-temperatures and high-pressures, while form II is stable at room temperature with respect to form III. Using adiabatic calorimetry data, it can be concluded, that form I is the stable low-temperature, high-pressure form, which also happens to be the most stable form at room temperature; however, due to its persistence at room temperature, form II is still the most convenient polymorph to use in formulations. Form III presents a case of overall monotropy and does not possess any stability domain in the pressure–temperature phase diagram. Heat capacity data for benzocaine have been obtained by adiabatic calorimetry from 11 K to 369 K above its melting point, which can be used to compare to results from in silico crystal structure prediction.

Mots clés: active pharmaceutical ingredient; phase behaviour; pressure-temperature phase diagram; thermodynamics; crystal structure; thermal expansion; adiabatic calorimetry

Domaines: Chimie; Physique [physics]

Ivo B. Rietveld, Hiroshi Akiba, Osamu Yamamuro, Maria Barrio, René Céolin, et al.. The Phase Diagram of the API Benzocaine and Its Highly Persistent, Metastable Crystalline Polymorphs. Pharmaceutics, 2023, 15 (5), pp.1549. ⟨10.3390/pharmaceutics15051549⟩. ⟨hal-04102022⟩