Thermoynamic properties (Hm, CP,m, Vm, κT) of binary mixtures {x1,3-Dioxane + (1−x)Cyclohexane} at 298.15 K

Molar excess enthalpies H_m^E, isobaric heat capacities C_P,m^E, volumes V_m^E and isothermal compressibilities κT^E for the 1,3-dioxane(3DX) + cyclohexane mixture were measured at 298.15 K, in order to compare to those of the 1,4-dioxane(4DX) + cyclohexane mixture. H_m^E is endothermic and the maximum value about 1.5 kJ mol⁻¹ at x ≈ 0.45, and lower than that of the 4DX mixture by about 80 J mol⁻¹. V_m^E is positive over the whole concentration and the maximum value is about 0.85 cm³ mol⁻¹ at x ≈ 0.45, and lower than that of the 4DX mixture. The above results suggest the energetic unstabilization, resulting in the volume expansion in the mixture. C_P,m^E shows the characteristic W-shaped concentration dependence, which has maximum at x ≈ 0.45 and two minima at x ≈ 0.1 and 0.9. The maximum C_P,m^E value for 3DX mixture shifts toward the positive side, compared to that of 4DX mixture. κT^E were estimated from speeds of sound, densities, thermal expansion coefficients and isobaric heat capacities of the pure component liquids and the mixtures. The κT^E result shows the positive concentration dependence over the whole composition range. The 3DX mixture has the similar thermodynamic properties to the 4DX mixture, despite that 4DX is the nonpolar solvent and 3DX is the dipolar liquid. this means that there exists the local dipolar interaction between 4DX molecules, and the prevalence of “microheterogeneity” in the both mixtures.