Hydrophobic hydration and hydrophobic interaction in tetraalkylammonium salt solutions: The cation size effect

The heats of solution of tetrahexylammonium and tetraheptylammonium bromides in water and aqueous solutions of formamide and hexamethylphosphoric triamide have been measured at 318 and 338 K. The standard enthalpies and heat capacities of solution and the enthalpic and heart capacity parameters of amide-electrolyte pair interaction have been determined. It has been confirmed that the standard heat capacities of solution and the amide-electrolyte interaction parameters as a function of the cation size pass through an extremum. The hydrophobic hydration effect is weaker for large tetraalkylammonium cations.