Evidence for a New Crystalline Phase of Racemic Ibuprofen

Purpose. The aim of this work is to search for the existence of crystalline polymorphism for racemic Ibuprofen. Methods. The pharmaceutical material was studied by X-ray diffraction to identify crystalline phases, and by Differential Scanning Calorimetry to follow the thermodynamic evolution of these forms versus temperature. Results. Results presented here show that, in addition to the already known conventional crystalline phase, whose nucleation domain extends between 233 K and 263 K and which melts at 349 K, racemic Ibuprofen can crystallize in another polymorphic phase. The nucleation of this new polymorphic variety is triggered by a stay at least 60 degrees below the glass transition temperature Tg of Ibuprofen (Tg=228 K). This nucleation is probably of heterogeneous type. The new phase melts well below the conventional one, i. e. at 290 K. A schematic free energy diagram is provided allowing establishing the relative thermodynamic stability of the two polymorphs. Conclusions. These results establish, for the first time, that Ibuprofen can exist under two different crystalline phases which constitute a monotropic system, the new form being metastable.