Enthalpies of solution of organic compounds in water/octan-1-ol mixtures. A rationale based an a model of structural organization of the solvent medium

Limiting enthalpies of solution Delta(soln)H(o)(oct/w) of several monofunctional compounds (tetrahydropyran, diethylamine, pyrrolidine, piperidine, 1-methylpiperidine) in water-octan-1-ol mixtures with water content ranging from zero to saturation have been determined at 25 degrees C. The observed phenomenology has been interpreted by supposing that the solvent medium undergoes a microphase transition at water mole fraction of about 0.08. In the water-poor region the experimental behavior is consistent with the presence of water molecules in prevailingly monodispersed form, while in the water-rich region the formation of organized pseudomicellar water aggregates is suggested. Two different simple models have also been proposed to describe quantitatively the observed trends of Delta(soln)H(o)(oct/w) vs. mole fraction of water.