Thermodynamic and IR spectroscopic studies of solutions with simultaneous association and solvation

As part of a project on thermodynamic properties of H-bonding solutions, IR spectroscopic studies on mixtures were carried out, in which both association and solvation occur simultaneously. Three types of systems were studied at temperatures between 283 and 313 K: (a) binary mixtures of the type: alcohol + solvating solvent, (b) ternary mixtures of the type: alcohol + solvating solvent + inert solvent, and (c) ternary mixtures of the type: alcohol (1) + alcohol (2) + inert solvent. The systems of type (a) cover four alcohols (methanol, ethanol, I-butanol, I-hexanol) in two solvating solvents (tetrachloromethane, toluene). The systems of type (b) are: 1-hexanol + hexane + toluene and 1-hexanol + hexane + tetrachloromethane; those of type (c) are: methanol + 2-methyl-2-propanol + hexane and methanol + cyclohexanol + hexane. A recently published physicochemical model for associating mixtures, the UNIQUAC association model, which was developed based on IR spectroscopic data on associating systems, is extended to include solvation. Using that model, it is possible to reliably describe thermodynamic data, such as vapor-liquid equilibrium data and excess enthalpies, as well as the spectroscopic data. The present work is a case study on the benefits of including spectroscopic data on solvation in the development of thermodynamic models of H-bonding solutions. (C) 2002 Elsevier Science B.V. All rights reserved.