A simultaneous X-ray diffraction–differential scanning calorimetry study into the phase transitions of mefenamic acid

DOI: 10.1107/S1600576719012500

Authors: Yuying Pang (University College London) , Asma Buanz (University College London) , Richard Telford (University of Bradford) , Oxana V. Magdysyuk (Diamond Light Source) , Simon Gaisford (University College London) , Gareth Williams (University College London)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Applied Crystallography , VOL 52

State: Published (Approved)
Published: December 2019
Diamond Proposal Number(s): 187201

Abstract: In this study, the polymorphic transitions of mefenamic acid (MA) were studied by synchrotron X-ray powder diffraction combined with differential scanning calorimetry (XRD-DSC). The initial material was found to be phase-pure form I which, when heated, produces two endotherms that can be observed by DSC at 162.72 and 219.55°C. The former was found to correspond to a solid–solid enantiotropic transition from form I to a mixture of forms II and III. The latter is the melting point of form II. As form I is heated, significantly greater unit-cell expansion is seen in the a direction than in b and c, which can be explained by the stronger intermolecular interactions in the bc plane. Refinements of the reported MA structures against the patterns collected during heating revealed that at 175°C there exists a mixture of forms I, II and III, whereas only forms II and III remain at 205°C. However, reflections are observed at both temperatures which cannot be fitted with the known forms of MA. It is hypothesized that a new form of MA is produced upon heating. The stability of MA after the enantiotropic transition temperature is II > III > I, which differs from the previously reported II > I > III.

Journal Keywords: synchrotron X-ray diffraction; differential scanning calorimetry; hyphenated techniques; mefenamic acid; polymorphic transitions; solid–solid transitions

Subject Areas: Biology and Bio-materials, Chemistry


Instruments: I12-JEEP: Joint Engineering, Environmental and Processing