Targett, J.J.; (2009) The polymorphs and solvates of phenylbutazone and their phase transition behaviour. Masters thesis , UCL (University College London).

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Abstract

In this study, which was conducted between March 2007 and December 2008, the crystal structure of the alpha polymorph of phenylbutazone has been determined by single crystal X-ray diffractometry. The present findings support those of Singh & Vijayan (1977) and Paradies (1987). Efforts to grow single crystals of the beta and delta polymorphs of phenylbutazone did not locate specimens of adequate quality for structure determination. Nonetheless it was possible to isolate high purity powder samples of these two forms. The powder diffraction pattern of the delta polymorph was measured with improved accuracy at the Diamond synchrotron, and reveals a number of peak overlaps in previously published diffraction patterns of this crystal form. The improved diffraction data have enabled the crystal system of the delta form to be identified as orthorhombic, and space-group selection has been narrowed down to Pnn2 or Pnnm. Four new solvated forms of phenylbutazone have been identified. The crystal structures of two of these new solvates have been determined by single crystal diffractometry. Both have space-group C2/c, and may be considered isostructural with five formerly identified solvates, whose structures were published by Hosokawa et al. in 2004. Previously phenylbutazone has been found to change polymorphic forms at above-ambient temperatures. This behaviour has been examined both in a differential scanning calorimeter and on a powder X-ray diffractometer equipped with isothermal sample heating, where the transition of the alpha and beta polymorphs to the delta polymorph was observed. Thermodynamic methods of predicting the transition temperatures of polymorphs are discussed, particularly those derived from dissolution data. In the case of phenylbutazone, a substantial amount of dissolution data has been collected elsewhere, and these data are used to generate computational predictions of the polymorphic transition temperatures for comparative purposes.

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