Thermodynamic properties, intermolecular interaction parameters, and structure of aqueous amide solutions of ammonium and tetraalakylammonium bromides

The thermal effects of dissolution of ammonium bromide in water and its mixtures with formamide (FA) at 277-328 K were studied by the calorimetry method in the region of small additions of the nonaqueous component. The standard values of enthalpy and heat capacity of solution, as well as the temperature changes in the solution entropy and reduced dimensionless Gibbs energy, were calculated. The parameters of electrolyte-amide pair interactions were calculated using the McMillan-Mayer formalism. The contributions of the cation and anion to the pair interaction parameters were determined by the group additivity method. The results are compared with the data obtained previously for solutions of tetrabutyl- and tetraethylammonium bromides in aqueous solutions of FA and hexamethylphoshotriamide (HMPT). At elevated temperatures the system becomes less structured in amide solutions of tetraalkylammonium bromides (except solutions of Et4NBr in aqueous HMPT) but more structured in solutions of ammonium bromide and in aqueous FA and HMPT.