Determination of Thiourea Solubility in 12 Different Monosolvents and Its Comparison with Structurally Similar Substances: Solvent Effect Analysis, Molecular Simulation, and Model Correlation

Thiourea exhibits many biological activities, and the study of the solubility behavior of thiourea in monosolvents is necessary for its crystallization and isolation processes. The mole fraction solubility of thiourea in 12 monosolvents was determined by the static gravimetric method from 283.15–323.15 K at 101.2 kPa. The solubility increased with the temperature. X-ray powder diffraction analysis was used to characterize the crystal form of thiourea before and after the dissolution equilibrium, and molecular electrostatic potentials were utilized to study the intermolecular interactions. Solubility was also evaluated by the interaction energy. The solvation behavior is primarily influenced by solvent polarity (E_T(30)), with additional contributions from cohesive energy density and hydrogen-bonding (HBD/HBA) effects. The relationship between the solubility of different solutes in the same solvent is then discussed by comparing the solubility behavior of N,N′-diphenyl thiourea and thiourea in monosolvents. The solubility data were fitted with the modified Apelblat and Yaws models; both show better results. These findings are relevant for thiourea purification, crystallization, and industrial applications and for structurally related compounds. Therefore, it is necessary to study the solvation behavior of thiourea in different monosolvents to provide sufficient data for the design of its crystallization process.