Heat capacity of six glymes in N,N-dimethylformamide + water mixtures. Solvation of glymes

Abstract

The paper presents the heat capacities of glyme solutions: monoglyme, diglyme, triglyme, tetraglyme, pentaglyme and hexaglyme, in binary solvents N,N-dimethylformamide + water at four temperatures (293.15 K, 298.15 K, 303.15 K, 308.15 K) obtained using differential calorimeter Micro DSC III, Setaram – France. The concentration of glymes was approximately 0.25 mol/kg. On the basis of the obtained experimental results, the apparent isobaric heat capacities of the glymes were calculated. It was noted that the larger the glyme molecule was, the more pronounced the increase in the value of the apparent molar heat capacity function with the increase in water content in the two-component solvent. The observed changes in apparent isobaric heat capacity as a function of the water content in the mixed solvent are discussed in terms of the hydrophobic nature of the glymes. Moreover, it was shown that the apparent molar isobaric heat capacity of the glymes in pure solvents, i.e. in water and in N,N-dimethylformamide, increases linearly with the increase in the number of oxygen atoms in the glyme molecules i.e. with the size of glyme molecules. Furthermore, a linear correlation was observed between the apparent isobaric molar heat capacity and the enthalpic effect of the hydrophobic hydration of the studied glymes at 298.15 K. The results obtained in this paper are compare with the same obtained for selected cyclic ethers.