Preparation, Characterization, and Desolvation of 5-Sulfoisophthalic Acid Sodium Salt Solvates

5-Sulfoisophthalic acid sodium salt (5-SSIPA) is a crucial intermediate for pharmaceuticals, pesticides, and polyesters. Several acidic groups lead to an unstable crystal structure. Two new polymorphs and three novel solvates were identified during the solvent screening. These crystals were characterized by powder X-ray diffraction, Fourier transform infrared, and scanning electron microscopy. The desolvation temperature of solvates was found to be higher than the boiling point of pure solvents, which tentatively indicated the existence of an interaction between solvents and 5-SSIPA molecules. The phenomenon that the three solvates gradually darkened with desolvation in the hot-stage microscopic images proved the occurrence of crystal desolvation. The non-isothermal desolvation kinetics of the 5-SSIPA solvates was analyzed and discussed.