Enthalpy of Dilution of Tetra-n-Butylammonium Bromide in Mixtures of Water and N-Methylacetamide

The enthalpy of dilution of tetra-n-butylammonium bromide in mixtures of water and N-methylacetamide has been measured from approximately 0.1 to 1.0 m at 35 degrees C. The mole fraction of water in the solvent varied from 0.250 to 0.969. The results are strikingly nonlinear in the mole fraction of water. As the mole fraction of water varies from 0 to 0.7, there is only a small change in the enthalpy of dilution. At higher mole fractions of water, the excess enthalpy rises sharply to the unusually high values found in water. This indicates that the unusually high values of excess enthalpy associated with hydrophobic bonding in water are destroyed by relatively small amounts of N-methylacetamide.