Thermochemical behaviour of crown ethers in the mixtures of water with organic solvents. Part III. Hydrophobic hydration and preferential solvation of crown ethers in water-amide mixtures at 298.15 K

Abstract

Enthalpies of solution of 15-crown-5 (15C5) and benzo-15-crown-5 ether (B15C5) in the mixture of water with formamide (F) and N-methylformamide (NMF) have been measured at 298.15 K. The values of standard enthalpies of solution of 15C5 are negative and those of B15C5 are positive in the mixtures. The results of calorimetric measurements of dissolution enthalpies of 15C5 and B15C5 in the mixture of water and organic solvents at 298.15 K are discussed with regard to the intermolecular interactions that occur in the solution. Considering the properties and molecular structure of the examined crown ethers, particular attention is given to the hydrophobic hydration and preferential solvation of solute in the mixed solvents. The preferential solvation in the examined systems was analysed using the Covington model developed by Balk and Somsen. The relative importance of the solvation mechanism appeared to depend on co-solvent properties.