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 °C/min between 25 and 65 °C. Solvent-mediated transformations were performed in ethanol/water mixtures ( x v,w = 0.5) and in pure water at temperatures between 25 and 80 °C. It was clearly observed from solvent-mediated transformations that form I was stable below 50 °C, form III was stable above 50 °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.