Racemic species of sodium ibuprofen: characterization and polymorphic relationships.

Racemic and homochiral sodium ibuprofen were characterized by thermal analysis and powder X-ray diffractometry. The melting point phase diagram was constructed and thermodynamic calculation was performed. In contrast to racemic ibuprofen, which is a racemic compound, racemic sodium ibuprofen forms both a racemic conglomerate (termed the gamma-form) as well as two polymorphic racemic compounds, alpha and beta, which are less stable monotropes. From the supercooled liquid, alpha and beta crystallized along with the original gamma-form. Forms alpha and beta are "enantiotropically related" with a transition temperature between 75 degrees and 113 degrees C, but can be considered to be metastable monotropes of the racemic conglomerate, the stable gamma-form.