Thermodynamic Aspects of Solubility and Solvation of Bioactive Bicyclic Derivatives in Organic Solvents

The solubility of eight biologically active nonaromatic compounds with a common 3-thia-1-aza-bicyclo fragment in 1-octanol and hexane was determined in the temperature range of T = 293.15–315.15 K. The solubility of the substances in alcohol is approximately 2 orders of magnitude higher than in alkane and varies within 3.0 × 10^–3 to 2.1 × 10^–1 and 7.1 × 10^–5to 13.5 × 10^–3 mol. fractions, respectively. In accordance with the structure of the substituent at the para position of the phenyl ring, the studied compounds are arranged in the following order of decreasing solubility in both solvents: methyl- > fluoro- > ethyl- > trifluoromethyl- > cyano- > acetyl-. The ideal solubility of the substances in 1-octanol, calculated from thermophysical parameters was found to correlate with the reported experimental data. The activity coefficients of the substances in saturated solutions of organic solvents are determined by the method of distribution between two liquid phases. The thermodynamic aspects of the relationship between the processes of dissolution, melting, sublimation, and solvation of the substances are discussed.