Thermodynamics and nucleation kinetics of m-aminobenzoic acid polymorphs

The polymorphism of m-aminobenzoic acid has been investigated, Two polymorphs have been identified and characterized by X-ray powder diffraction (XRPD). Fourier transform IR (FTIR), microscopy, and thermal analysis. The melting properties and isobaric heat capacities of both polymorphs have been determined calorimetrically and the solubility each polymorph in several solvents at different temperatures has been determined gravimetrically. the solid-state activity i.e., the Gibs free energy of fusion) of each polymorph has been determined through a comprehensive heterodynamic analysis based oil experimental data. It is found that the polymorphs are enantiotropically related, with a stability transition temperature of 1-56.1 degrees C. Thc published crystal Structure belongs to the polymorph that is metastable at room temperature. Energy-temperature diagrams of both polymorphs have been established by determining the free energy. enthalphy, and entropy of fusion as a function of temperature. A total of 300 cooling crystallizations have been carried out at constant cooling rate using different saturation temperatures and solvents. and the visible Onset of primary nucleation was recorded. The results show that for this Substance the polymorph that will nucleatic depends chiefly on the solvent. In water and Methanol solutions the stable form I was obtained in all experiments, whereas in acetonitrile, a majority of nucleation experiments resulted in the isolation of the metastable form II. It is shown how this call be rationalized by analysis Of Solubility, solution speciation. and nucleation relationships. The importance of carrying out multiple experiments at identical conditions in nucleation Studies of polymorphic systems is demonstrated.