Thermodynamics of Amide + Amine Mixtures. 1. Volumetric, Speed of Sound, and Refractive Index Data for N,N-Dimethylformamide +N-Propylpropan-1-amine, +N-Butylbutan-1-amine, +Butan-1-amine, or +Hexan-1-amine Systems at Several Temperatures

Values of density ($\rho$), speed of sound ($c$) and refractive index ($n_{\text{D}}$) for N,N-dimethylformamide (DMF) + N-propylpropan-1-amine (DPA) or + butan-1-amine (BA) mixtures at (293.15-303.15) K, and for DMF + N-butylbutan-1-amine (DBA) or hexan-1-amine (HxA) mixtures at 298.15 K are reported. $\rho$ and $c$ measurements were conducted using a vibrating-tube densimeter and sound analyzer, Anton Paar model DSA5000; $n_{\text{D}}$ values were obtained by means of a RFM970 refractometer from Bellingham+Stanley. The experimental $\rho$, $c$ and $n_{\text{D}}$ values have been used to determine excess molar volumes, $V_{\text{m}}^{\text{E}}$, excess adiabatic compressibilities, $\kappa_S^{\text{E}}$, excess speeds of sound, $c^{\text{E}}$, excess thermal expansion coefficients, $\alpha_p^{\text{E}}$, and excess refractive indices, $n_{\text{D}}^{\text{E}}$. This set of data shows the existence of interactions between unlike molecules and of structural effects in the mixtures under study. $V_{\text{m}}^{\text{E}}$ values of solutions including linear secondary amines are lower than those of mixtures with linear primary amines. In fact, the contribution to $V_{\text{m}}^{\text{E}}$ from the breaking of amine-amine interactions is larger for the latter systems. Calculations on Rao's constant point out that there is no complex formation between the mixture components. Dispersive interactions have been analyzed by means of the molar refraction. It is shown that solutions with DPA or HxA are characterized by similar dispersive interactions and that they mainly differ in dipolar interactions.