Carbamazepine polymorphs trigonal

The induction times of carbamazepine polymorphs [monoclinic, CBZ(M) and trigonal, CBZ(Trg)] were evaluated by optical microscopy. The polymorphs were identified by their crystal morphology where CBZ(M) crystallizes as prismatic crystals and CBZ(Trg) crystallizes as needles, which were confirmed by X-ray powder diffraction. It was determined that under constant supersaturation concomitant crystallization is favored in solvents that accept and donate hydrogen bonds (ethanol, methanol, isopropanol, etc.). However, the metastable CBZ(Trg) polymorph preferentially crystallized in solvents that primarily accept hydrogen bonds (ethyl acetate, methyl acetate, 2-butanone, etc.) with the stable CBZ(M) polymorph crystallizing at least an hour later. The induction times of CBZ polymorphs did not decrease with increases in solubility, suggesting that nucleation is not controlled by solubility differences. It was determined that CBZ polymorph nucleation was governed by the specific solute-solvent interactions that occurred in solution to... 

In the case of carbamazepine polymorphs, a similar approach has been adopted to calculate dPjdT for the transition from literature solubility data (7). At least three polymorphic forms of carbamazepine have been identified form I (trigonal or a form mp 174-176°C), form II (triclinic or y form mp 184-186°C), and form III (monoclinic or (5 form mp 189-191 °C). Polymorphs I and III are enantiotropically related with a transition temperature of 71 °C (8). The former polymorph has a significantly higher solubility in supercritical carbon dioxide than the latter at 55 °C and 350 bar (9). In contrast to the negative value of dPjdT observed for the salmeterol xinafoate polymorphs, Edwards et al. obtained a positive dPjdT value (-1-23.7 bar/K) based on calculations from the carbamazepine monoclinic ((3 form) and triclinic (y form) equilibrium curves (7). The transition temperature of the... 

Fig. 5 Packing diagrams of carbamazepine anhydrous polymorphs (A) monoclinic, form III and (B) trigonal, form II. (From Ref i°l)...

There has been some confusion in the literature on the nomenclature of carbamazepine anhydrous polymorphs. For this chapter, we will use the following nomenclature Form I (Triclinic), Form II (Trigonal), Form III (P-monoclinic), and Form IV (C-monoclinic). 

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