Excess Gibbs Energies and Volumes of the ternary system ethanol + dimethylformamide + tetrahydrofuran at 298.15 K

Density measurements have been carried out by means of a vibrating tube densimeter for the ternary system ethanol (EtOH) + dimethylformamide (DMF) + tetrahydrofuran (THF) and for the binary mixtures containing DMF. For the same ternary system and for the binary DMF + THF vapour-liquid equilibrium data have been collected by head-space gas-chromatographic analysis of the vapour phase directly withdrawn from an equilibration apparatus. All experiments have been conducted at 298.15 K. Molar excess Gibbs energies GE and volumes VE, as well as activity coefficients gammai and excess apparent molar volumes of the components, have been obtained from the measured quantities. Both binaries involving THF show positive deviations from ideality for GE, while slightly negative deviations are exhibited by EtOH + DMF. The GE's and ln gammi iof the ternary system are positive almost throughout due to destruction upon mixing of H-bonding in EtOH and dipolar interactions in DMF and THF pure liquids. Feeble negative VE's are displayed by the binaries involving DMF, whereas EtOH + THF shows an S-shaped curve with verysmall VE values. As a consequence, the VE's and the excess apparent molar volume of the ternary system, differently from GE and ln gammai are negative nearly over the whole composition domain suggesting a more ordered structure in solution,namely that EtOH.DMF association prevails on EtOH and DMF self-association.