Apparent and partial molar volumes of 18-Crown-6 ether in the mixture of N,N-dimethylformamide with water

The density of 18-Crown-6 ether (18C6) in the mixture of N,N-dimethylformamide (DMF) and water (H2O) was measured within the temperature range: T = (293.15, 298.15, 303.15, 308.15) K. The apparent molar volumes (VΦ) and partial molar volumes (Vm0) of 18C6 in the mixture of DMF + H2O within the whole concentration range of mixed solvent were calculated. Based on the calculations, the excess partial molar volumes (Vm0E) of 18C6 were determined and the changes in the solute volume were analyzed when it was transferred to solvent. The results obtained for 18C6 that shows hydrophobic properties were compared with the analogous results for hydrophilic urea. The analysis of the partial molar volume revealed the clear changes and differences in the volumes of the two tested compounds which result from the differences of their properties (hydrophilic and hydrophobic). As a result, this paper explains how the content of each component of the mixed solvent, influences the solvation of the solute. The obtained data allow to demonstrate that the crown ether is hydrophobically hydrated in the water rich region.