Hydration of dioxaalkanes in aqueous solutions

The interactions between water and linear dioxaalkane molecules were investigated by water-heptane partition. Two homologous series: dimethoxyalkanes and diethoxyalkanes were studied, with the oxygen atoms separated by a number of methylene groups (changing from 1 to 5). Free energy and enthalpy of partition were calculated from partition constants and from their temperature dependence. Hydration of these amphiphilic solutes in the aqueous phase was evaluated. The separation between the oxygen atoms in the molecule affects hydrophilic-hydrophobic properties of dioxaalkanes. The effect is due not only to a different number of hydrophobic groups in the molecule, but also to different degrees of their hydrophobicity as well as of hydrophilicity of the oxygen atoms at different separations. The contribution from different parts of the molecules is, therefore, not additive and the group-contribution model cannot be used to describe physicochemical properties of aqueous solutions of dioxaalkanes without taking into account the structure of the solute molecules. (C) 2000 Elsevier Science B.V. All rights reserved.