Controlling the Crystal Morphology and Polymorphism of 2,4-Dinitroanisole

Nitroaromatic 2,4-dinitroanisole (DNAN) was used as a model compound for the study of surface-poisoning effects in crystallization. In addition to the expected solvent effect, it was found that the concentration of solutions and presence of additives control the formation of polymorphs and forms. In some cases, aromatic and/or nitro-containing additives interact with DNAN, probably competing with intrinsic intermolecular interactions that allow the formation and growth of DNAN crystals. It was also found that single-crystal-to-single-crystal phase transitions take place between two β forms and from the β form to the α form. This β-to-α transformation is most probably possible because of a similarity between the two crystal structures. Hence, the barrier for this transformation is rather low. Nevertheless, the formation of α-DNAN in the typically β morphology introduces strain in the crystals, causing defects. It was also found that the orientations of the molecules against the unit cell faces for the two α forms (blocks and needles) are markedly different.