An exploration of the polymorphism of piracetam using high pressure

Abstract

High-pressure recrystallisation of aqueous and methanolic solutions of piracetam (2-oxo-pyrrolidineacetamide) contained in a diamond-anvil cell at pressures of 0.07–0.4 GPa resulted in the formation of a new high-pressure polymorph of piracetam that has been characterised by in situ X-ray diffraction. The molecular packing arrangement of the new form is very different from those of forms I, II, and III, and the piracetam molecules also adopt a very different conformation in this new phase. Depressurisation to ambient pressure resulted in the formation of form II via a single-crystal to single-crystal transition. By contrast, crystallisation of piracetam from water at ambient pressure resulted in the formation of a new monohydrate of piracetam, which has been characterised by single crystal X-ray diffraction.