Mechanochemically Induced Conversion of Crystalline Benzamide Polymorphs by Seeding

Benzamide has been known for its polymorphism for almost 200 years. Three polymorphic forms are described. To date, it was only possible to crystallize a metastable form in a mixture together with the thermodynamically most stable form I. A complete transformation of form I into the metastable form III by mechanochemical treatment has been achieved. Catalytic amounts of nicotinamide seeds were used to activate the conversion by mechanochemical seeding. NMR experiments indicated that the nicotinamide molecules were incorporated statistically in the crystal lattice of benzamide form III during the conversion. The transformation pathway was evaluated using in situ powder X-ray diffraction.