Spherical Agglomerates of m-Aminobenzoic Acid: Solvent Selection, Preparation, Mechanism, and Characterization

Solvents for spherical agglomerates preparation are usually selected according to the Lifshitz–van der Waals acid–base theory with negative adhesion free energies. However, some solvents with positive adhesion free energies in which spherical agglomerates can be obtained are easily ignored. This work proposes that solvents should be screened comprehensively by theoretical calculation combined with experiments using m-aminobenzoic acid (m-ABA) as a model compound. According to the Lifshitz–van der Waals acid–base theory, water, isopropyl alcohol, and ethylene glycol with negative adhesion free energies were screened out as the possible solvents for the preparation of m-ABA spherical agglomerates. Crystallization experiments showed that in addition to the three solvents, methanol and ethanol with positive adhesion free energies were also appropriate for spherical crystallization of m-ABA. A common feature of the five solvents which can form spherical agglomerates is that they have both hydrogen-bond-donating and hydrogen-bond-accepting capabilities. The single-factor analysis method was used to systematically investigate the effects of stirring speed, terminal temperature, and supersaturation on spherical agglomerates of m-ABA. The formation mechanism of m-ABA spherical agglomerates was elucidated with the help of the in situ Pixact Crystallization Monitoring system. Comparative experiments proved that the obtained spherical agglomerates exhibit better chemical stabilities and crystal form stability than needle-like crystals.