Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

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

Version 1 : Received: 7 April 2023 / Approved: 10 April 2023 / Online: 10 April 2023 (02:51:15 CEST)

A peer-reviewed article of this Preprint also exists.

Rietveld, I.B.; Akiba, H.; Yamamuro, O.; Barrio, M.; Céolin, R.; Tamarit, J.-L. The Phase Diagram of the API Benzocaine and Its Highly Persistent, Metastable Crystalline Polymorphs. Pharmaceutics 2023, 15, 1549. Rietveld, I.B.; Akiba, H.; Yamamuro, O.; Barrio, M.; Céolin, R.; Tamarit, J.-L. The Phase Diagram of the API Benzocaine and Its Highly Persistent, Metastable Crystalline Polymorphs. Pharmaceutics 2023, 15, 1549.

Abstract

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 with form III stable at low-temperature and high-pressure, while form II is stable at room temperature. Using adiabatic calorimetry data, it can be concluded, that form I is the stable low-temperature, high-pressure form, which also happens to be stable at room temperature; however, form II, due to its persistence at room temperature, 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 up to 369 K above its melting point, which can be used to compare to results from in-silico crystal structure prediction.

Keywords

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

Subject

Chemistry and Materials Science, Physical Chemistry

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