Thermodynamics of amide+amine mixtures. 4. Relative permittivities of N,N-dimethylacetamide+N-propylpropan-1-amine, +N-butylbutan-1-amine, +butan-1-amine, or +hexan-1-amine and of N,N-dimethylformamide+aniline mixtures

Abstract

Relative permittivities at 1 MHz, $\varepsilon_{\text{r}}$, and at (293.15-303.15) K are reported for the binary systems N,N-dimethylacetamide (DMA) + N-propylpropan-1-amine (DPA), + N-butylbutan-1-amine (DBA), + butan-1-amine (BA) or + hexan-1-amine (HxA) and for N,N-dimethylformamide (DMF) + aniline. The excess permittivities, $\varepsilon_{\text{r}}^{\text{E}}$, are large and negative for systems with DMA, whereas they are large and positive for the aniline mixture. From the analysis of these $\varepsilon_{\text{r}}^{\text{E}}$ data and of measurements previously reported, it is concluded: (i) the main contribution to $\varepsilon_{\text{r}}^{\text{E}}$ in systems with linear amines arises from the breaking of interactions between like molecules; (ii) in the DMF + aniline mixture, interactions between unlike molecules contribute positively to $\varepsilon_{\text{r}}^{\text{E}}$, and such a contribution is dominant; (iii) longer linear amines are better breakers of the amide-amide interactions; (iv) interactions between unlike molecules are more easily formed when shorter linear amines, or DMF, participate. These findings are confirmed by a general study conducted in terms of excess values of molar orientational and induced polarizabilities and of the relative Kirkwood correlation factors for systems and components. The ERAS model is also applied to amide + amine mixtures. ERAS represents rather accurately the excess enthalpies and volumes of the mentioned systems. The variation of the cross-association equilibrium constants, determined using ERAS, with the molecular structure is in agreement with that observed for $\varepsilon_{\text{r}}^{\text{E}}$.