Enthalpy of dilution and heat capacity of aqueous solutions of tetrabutylammonium butyrate as a function of temperature

Enthalpies of dilution of tetrabutylammonium butyrate are reported as a function of temperature between 10° and 50°C. Heat capacities of aqueous solutions of tetrabutylammonium butyrate were measured in order to obtain values of _cp at 15°, 25°, and 35°C. These data were combined with the enthalpy of dilution data to obtain _cp as a function of molality and temperature. The apparent molal heat content _L decreased with increasing temperature in concentrated solutions but increased with increasing temperatures in dilute solutions (below0.7 m). Over the temperature range studied _cp shows a maximum as a function of molality at approximately 0.5m. The decrease in _cp with increasing concentration of hydrophobic solute is consistent with the view that the hydrophobic hydration cages, formed under the influence of the tetrabutylammonium and butyrate ions, are saturated at about 0.5m, and that at higher molalities increased overlap of the hydration cages occurs.