Excess Chemical Potentials and Partial Molar Enthalpies in Aqueous 1,2- and 1,3-Propanediols at 25°C

Abstract

Excess chemical potentials and excess partial molar enthalpies of 1,2- and 1,3-propanediols (abbreviated as 12P and 13P), μEi, and HEi (i = 12P or 13P) were determined in the respective binary aqueous solutions at 25°C. For both systems, the values of μEi are almost zero, within ±0.4 kJ-mol−1. However, the excess partial molar enthalpies, HEi show a sharp mole fraction dependence in the water-rich region. Thus, the systems are highly nonideal, in spite of almost zero μEi. Namely, the enthalpy-entropy compensation is almost complete. From the slopes of the HEi against the respective mole fraction xi we obtain the enthalpic interaction functions between solutes, Hi−iE, (i = 12P or 13P). Using these quantities and comparing them with the equivalent quantities for binary aqueous solutions of 1-propanol (1P), 2-propanol (2P), glycerol (Gly), and dimethyl sulfoxide (DMSO), we conclude that there are three composition regions in each of which mixing schemes are qualitatively different. Mixing Schemes II and III, operative in the intermediate and the solute-rich regions, seem similar in all the binary aqueous solutions mentioned above. Mixing Scheme I in the water-rich region is different from solute to solute. 12P shows a behavior similar to that of DMSO, which is somewhat different from typical hydrophobic solute, 1P or 2P. 13P, on the other hand, is less hydrophobic than 12P, and shows a behavior closer to glycerol, which shows hydrophilic behavior.