Polymorphism of paracetamol: Relative stabilities of the monoclinic and orthorhombic phases inferred from topological pressure‐temperature and temperature‐volume phase diagrams

• Published in: Journal of pharmaceutical sciences Vol. 94; no. 3; pp. 524 - 539
• Main Authors: Espeau, Philippe, Céolin, René, Tamarit, Josep‐Lluis, Perrin, Marc‐Antoine, Gauchi, Jean‐Pierre, Leveiller, Franck
• Format: Journal Article
• Language: English
• Published: Hoboken Elsevier Inc 01.03.2005; Wiley Subscription Services, Inc., A Wiley Company; Wiley; American Pharmaceutical Association
• Subjects: Acetaminophen - analysis; Acetaminophen - chemistry; Biological and medical sciences; calorimetry (DSC); Calorimetry - methods; Chemistry, Pharmaceutical - methods; Computer Science; crystallography; Drug Stability; General pharmacology; materials science; Mathematics; Medical sciences; Pharmaceutical technology. Pharmaceutical industry; Pharmacology. Drug treatments; Phase Transition; physical characterization; physical stability; polymorphism; Pressure; solid state; solid state, X‐ray powder diffractometry; Temperature; Thermodynamics; X-ray powder diffractometry; calorimetry (DSC); crystallography; physical characterization; materials science; thermodynamics; polymorphism; physical stability; solid state, X‐ray powder diffractometry; Differential scanning calorimetry; Temperature; Stability; Pharmaceutical technology; Phase diagram; Antimigrainous agent; Pressure; Physical properties; Powder; Solid state; Thermodynamics; Paracetamol; Analgesic; calorimetry (DSC); crystallography; thermodynamics; polymorphism; physical stability; materials science; physical characterization; solid state; Antipyretic; X-ray powder diffractometry; X ray diffractometry; Physicochemical properties; Polymorphism; stabilité physique; cristallographie; calorimétrie (DSC); solid state, X-ray powder diffractometry; science des matériaux; PHARMACOLOGIE
• ISSN: 0022-3549; 1520-6017
• DOI: 10.1002/jps.20261

The thermodynamic relationships between the two known polymorphs of paracetamol have been investigated, and the subsequent pressure‐temperature and temperature‐volume phase diagrams were constructed using data from crystallographic and calorimetric measurements as a function of the temperature. Irrespective of temperature, monoclinic Form I and orthorhombic Form II are stable phases at ordinary and high pressures, respectively. The I and II phase regions in the pressure‐temperature diagram are bordered by the I‐II equilibrium curve, for which a negative slope (dp/dT ≈ −0.3 MPa · K−1) was determined although it was not observed experimentally. This curve goes through the I‐II‐liquid triple point whose coordinates (p ≈ 234 MPa, T ≈ 505 K) correspond to the crossing point of the melting curves, for which dp/dT values of +3.75 MPa · K−1 (I) and +3.14 MPa · K−1 (II) were calculated from enthalpy and volume changes upon fusion. More generally, this case exemplifies how the stability hierarchy of polymorphs may be inferred from the difference in their sublimation curves, as topologically positioned with respect to each other, using the phase rule and simple inferences resorting to Gibbs equilibrium thermodynamics. © 2004 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:524–539, 2005