Enthalpies of solution of urea in water-alkanol mixtures and the enthalpic pair interaction coefficients of urea and several nonelectrolytes in water

Abstract

Enthalpies of solution of urea in binary mixtures of isopropanol, s-butanol, and ethoxyethanol with water have been measured at high water content. Those in the binaries isopropanol + water and ethoxyethanol + water show endothermic maxima at 8 and 4mol% alkanol, respectively. Enthalpic pair interaction coefficients are calculated for the interactions between urea and the alkanols and discussed in connection with these coefficients for interactions between urea and other nonelectrolytes and between A^N-dimethylformamide and several nonelectrolytes. The enthalpic pair interaction coefficients correlate linearly with the heat capacity change on hydration of the nonelectrolytes and with the enthalpy of hydrophobic hydration of the alkanols.