Solvatomorphism of the Antibacterial Dapsone: X-ray Structures and Thermal Desolvation Kinetics

Three non-isostructural solvates of the antibacterial dapsone (DDS) containing dichloromethane [DDS center dot 0.5(DCM)], 1,4-dioxane [DDS center dot DXN], and tetrahydrofuran [DDS center dot THF] were prepared and characterized by X-ray diffraction (XRD) and thermal analysis, the latter including hot stage microscopy (HSM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). In addition, their thermal desolvation was investigated by isothermal kinetic studies which indicated the A2 model as the best fit for desolvation of the DCM and DXN solvates, while the R2 model was indicated for the THE solvate. Activation energies for desolvation of these new species were in the range 141-173 kJ mol(-1). Attempts were made to reconcile the kinetic models with the observed HSM desolvation behavior and the modes of solvent inclusion within the solvate crystals determined by XRD (viz, isolated sites for the DCM solvate and channel-type for the others).