CRYSTALLINE FORMS OF 11 ~-(4-ACETYLPHENYL)-20,20,21,21,21-PENTAFLUORO-17-HYDROXY-19-NOR-17A-PREGNA-4,9-DIEN-3-ONE

The present invention relates to crystalline forms of 11 ß-(4-acetylpheny l)-20,20,21,21,21-pentafluor-17-hydroxy-19-nor-17.alpha.-pregna-4,9-dien-3-o ne. In particular, the invention relates to two crystalline ansolvate/anhydr ate forms of this compound, polymorphs I and II. However, the present invent ion also relates to crystalline solvates, for example, methanol and ethanol solvates of 11 ß-(4-acetylphenyl)- 20,20,21,21,21-pentafluor-17-hydroxy-19-n or-17.alpha.-pregna-4,9-dien-3-one, as precursors for the preparation of the se two polymorphs I and II. Processes are described for the preparation of p olymorph I by means of displacement crystallization or by means of extractio n. The choice of the last solvent, before the ansolvate formation can take p lace, on the basis of the differences in the purification ratios of the indi vidual solvates of 11 ß-(4-acetylphenyl)-20,20,21,21,21-pentafluor-17-hydrox y-19-nor-17.alpha.-pregna-4,9-dien-3-one is described. Polymorph I, accordin g to the invention, is particularly suitable for the preparation of drugs.