Excess partial molar enthalpy of 1-propanol in 1-propanol–acetone (or tetramethyl urea)–H 2O at 25°C: effect of acetone (or tetramethyl urea) on H 2O

Abstract

Excess partial molar enthalpies of 1-propanol, H 1P E, were measured at 25°C in ternary 1-propanol–acetone (or tetramethyl urea)–H 2O, with various initial compositions of acetone (or tetramethyl urea). They were determined accurately and in small increments in mole fraction of 1-propanol. It was therefore, possible to take a derivative of H 1P E with respect to the amount of 1-propanol, n 1P, H 1P–1P E≡ N( ∂H 1P E/ ∂n 1P). The changes in the mole fraction dependence of H 1P E and hence, H 1P–1P E caused by adding a third component, acetone or tetramethyl urea, were compared with the results of analogous earlier studies with urea and 2-propanol as a third component. The effects of acetone and tetramethyl urea were found qualitatively the same. The CH 3 group in each compound works as a typical hydrophobic moiety and enhances the hydrogen bond network of H 2O in the immediate vicinity of solute molecule (“iceberg formation”) with concomitant reduction of the hydrogen bond probability of H 2O. The CO group on the other hand, seems to reduce the degree of fluctuation in the hydrogen bond strength in the bulk H 2O away from the solute.