Abstract
In order to obtain wider knowledges on the physico-pharmaceutical properties of the molecular compounds of organic medicinals, the dissolution behaviors, solubility equilibrium and the nature of the bonding between components were investigated with the compound of homosulfanilamide and sulfathiazole. When the molecular compound was dissolved, the stable equilibrium, not the metastable one was rapidly attained. On the contrary, much differences in dissolution behaviors were observed with the corresponding physical mixture and the equilibrium was not reached even after 24 hours due to deposition of the compound on sulfathiazole particles. From the phase diagram constructed, it was confirmed that the system belongs to the type where the formed compound is not decomposed by water. By applying the solubility product principle, formation constants at various temperatures were obtained and the changes of enthalpy, free energy and entropy for the molecular compound formation in solutionwere calculated. It was supposed from these thermodynamic constants and the data of IR and electric conductance measurements that in the compound, the bonding between homosulfanilamide and sulfathiazole is caused by ionic interaction.
