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 degrees and 50 degrees C. Heat capacities of aqueous solutions of tetrabutylammonium butyrate were measured in order to obtain values of phi(cp) at 15 degrees, 25 degrees and 35 degrees C. These data were combined with the enthalpy of dilution data to obtain phi(cp) as a function of molality and temperature. The apparent molal heat content phi(L) decreased with increasing temperature in concentrated solutions but increased with increasing temperatures in dilute solutions (below 0.7 m). Over the temperature range studied phi(cp) shows a maximum as a function of molality at approximately 0.5 m. The decrease in phi(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 0.5 m, and that at higher molalities increased overlap of the hydration cages occurs.