Control over Polymorph Formation of o-Aminobenzoic Acid

Control over the polymorph formation requires thermodynamic and kinetic knowledge and in situ analytical techniques. In this study, the crystallization behavior of o-aminobenzoic acid (o-ABA) in batch cooling crystallization as well as the transformation behavior in solution was monitored in situ. Raman spectroscopy was used to analyze the polymorphic content of o-ABA. Form II was always obtained as the initial polymorph in the cooling crystallization at a cooling rate of 3.3 degrees C/min between 25 and 65 degrees C. Solvent-mediated transformations were performed in ethanol/water mixtures (X-v,X-w= 0.5) and in pure water at temperatures between 25 and 80 degrees C. It was clearly observed from solvent-mediated transformations that form I was stable below 50 degrees C, form III was stable above 50 degrees C, while form II was metastable at all investigated temperatures. Ultimately, an experiment was designed and performed, in which successively all pure polymorphs were present. Thus, control over polymorphism of o-ABA has been established.