Volumetric investigation of the ternary system ethanol plus dimethylformamide plus cyclohexane 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)+ cyclohexane (CyH) and for the binary mixture DMF + CyH. Molar excess volumes V-E at 298.15 K, as well as excess apparent molar volumes Phi(E)(V,t) 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 V(')(E)s are largely positive for DMF + CyH and EtOH + CyH, while slightly negative for EtOH + DMF. The V-E'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 V-E (as well as of G(E) and H-E) 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 Phi(E)(V,t) 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. (C) 2014 Elsevier B.V. All rights reserved.