Evidence for a new crystalline phase of racemic Ibuprofen

Abstract

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.