Solubility Parameter-Based Methods for Predicting the Solubility of Sulfapyridine in Solvent Mixtures

Abstract

Sulfapyridine is used to test the extended Hildebrand approach for predicting solubility in dioxane-water mixtures. The method provided good agreement with the experimental data. A modification of this method, that directly relates the logarithm of the mole fraction solubility with the solubility parameter of the solvent mixture (δ1) gave results comparable to that of the extended Hildebrand approach. This suggests that the volume fraction of the solvent can be disregarded in the solubility equation. The modified method does not require the knowledge of the ideal solubility of the drug. A single equation based on the solubilities of several sulfonamides is able to accurately calculate the solubility profile of sulfapyridine from 0 to 70% water in dioxane. Beyond 70% water, the extended Hildebrand method or its simplified form provide less errors, but these methods require 12-14 experimental solubilities, whereas the single equation only needs two experimental solubilities.