Enthalpies and heat capacities of interaction of tetraalkylammonium bromides with hexamethylphosphoric triamide in water, methanol and ethylene glycol: The comparative analysis of aqueous and non-aqueous systems

This paper focuses on the interaction between familiar hydrophobic solutes – tetraalkylammonium ions and hexamethylphosphoric triamide (HMPT) in water and H-bonded non-aqueous solvents such as methanol (MeOH) and ethylene glycol (C2H4(OH)2). Enthalpic and heat capacity parameters of electrolyte–amide and methylene group–amide pair interaction have been extracted from the enthalpies of solution for Et4NBr and Bu4NBr in the mixtures of MeOH or C2H4(OH)2 with HMPT at 298 and 313 K and compared with those in water. We have found that for tetraalkylammonium ions of moderate size solvophobic interaction with apolar groups of HMPT molecule is much weaker pronounced in non-aqueous media than in water.

► Enthalpies of Et4NBr and Bu4NBr solution in mixtures of methanol or ethylene glycol with hexamethylphosphoric triamide have been measured at 298 and 313 K.
► Enthalpy and heat capacity parameters of electrolyte–amide and methylene group–amide pair interaction have been computed and compared with those in water.
► The behaviour of hydrophobic solutes of moderate size in aqueous and non-aqueous hexamethylphosphoric triamide solutions is found to differ strongly.