Thermodynamics of binary mixtures containing N-alkylamides

Abstract

N-alkylamide + organic solvent mixtures have been investigated in the framework of a purely physical theory [ dispersive- quasi chemical (DISQUAC)]. The amides considered are n-methylformamide (NMF), n-methylacetamide (NMA), n-ethylacetamide (NEA), n-methylpropanamide (NMPA), 2-pyrrolidone and caprolactam. The solvents are alkanes, benzene, toluene or 1-alkanols. The DISQUAC interaction parameters are reported. The model describes consistently thermodynamic properties such as vapor–liquid equilibria (VLE), excess molar Gibbs energies, G E, and excess molar enthalpies, H E, solid–liquid equilibria (SLE), or the concentration–concentration structure factor, S CC(0). DISQUAC improves results from other models, such as the extended real associated solution model (ERAS) or UNIFAC. Interactions present in the studied mixtures are discussed. Solutions with alkanes are characterized by strong dipole–dipole interactions between amide molecules. n-Methylformamide+aromatic compound mixtures behave similarly to associated systems. The heterocoordination observed in some solutions involving methanol where interactions between like molecules are almost cancelled by interactions between unlike molecules may partially be ascribed to size effects. For other alcoholic solutions, the ability of the alcohol for the breakage of the amide–amide interactions is prevalent over solvation effects.