Enthalpies of solution of some tetraalkylammonium bromides in binary mixtures of water and some amides

Enthalpies of solution of tetraethylammonium bromide in mixtures of N,N-dimethylformamide (DMF) and water and of tetramethylammonium bromide in mixtures of DMF and water, N-methylformamide (NMF) and water, formamide (F) and water, and of NMF and F have been measured calorimetrically at 25°C in the whole mole-fraction range. The enthalpies of solution of tetraethylammonium bromide in DMF-water reach a maximum value while the enthalpies of solution of tetraethylammonium bromide in this mixture show a flat, broad maximum and a minimum. A similar behavior is found in NMF-water and F-water mixtures. In the NMF-F system the enthalpies of solution display a nearly ideal behavior. The results are compared with those of tetra-n-butylammonium bromide and of tetra-n-propylammonium bromide.