OCCURRENCE, STABILITY, KINETICS OF CRYSTALLIZATION AND POLYMORPHIC TRANSITION OF THE A-MODIFICATION, B-MODIFICATION AND C-MODIFICATION OF ABECARNIL - INFLUENCE OF SUPERSATURATION, TEMPERATURE, SOLVENTS AND IMPURITIES

Abecarnil is a beta-carboline derivative that occurs in three modifica tions, A, B and C, and shows a special type of polymorphism. Two therm odynamically unstable but closely related modifications with nearly th e same solubility and a stable polymorph are known. The polymorph nucl eated is in most cases one of the two unstable forms, its type is dete rmined by the type of solvent and crystallization kinetics, While not entirely dry, the modifications readily undergo a solution mediated ph ase transformation, which is, in the case of the two unstable forms, o f the contact model type. The kinetics of the transformation is drasti cally reduced in the presence of trace amounts of an acid. It is shown by microcalorimetry and sampling of mother liquor, that the system ex tremely rapidly reaches the saturation curve, i.e. Abecarnil crystalli zes very easily, Due to this phenomenon, Abecarnil can be crystallized by spray drying and a novel form of direct contact cooling with the s ame solvent, The modification obtained in these cases is always the mo st unstable B form, which is attributed to the extremely high supersat urations during nucleation.