Volumetric investigation of the ternary system ethanol + dimethylformamide + cyclohexane at 298.15 K

Abstract

Density measurements have been carried out by means of a vibrating tube densimeter for the ternary system ethanol (EtOH)+dimethylformamide (DMF)+cyclohexane (CyH) and for the binary mixture DMF+CyH. Molar excess volumes VE at 298.15K, as well as excess apparent molar volumes ΦV,iE of the components, have been obtained from the measured quantities. A large miscibility gap is exhibited by DMF+CyH and by the ternary mixtures in the region near this binary. The VE's are largely positive for DMF+CyH and EtOH+CyH, while slightly negative for EtOH+DMF. The VE's of the ternary mixtures are always positive except in a narrow strip in the proximity of the binary EtOH+DMF. The positive sign of VE (as well as of GE and HE) for EtOH+CyH and DMF+CyH, and of large portions of the ternary domain, can be qualitatively explained with a net destruction in the mixing process of H-bonding in EtOH and of dipolar interactions in DMF. The behavior of ΦV,iE of single components confirms that the self-association of EtOH or DMF is the largest in the pure liquids and the least in dilute solution, and that the unlike association EtOH–DMF in the ternary mixtures produces a volume contraction which increases with increasing content of each of the polar components.