Enthalpies of Dilution of Bifunctional Alcohols in Concentrated Aqueous Solution of Urea at 298.15 K

The enthalpies of dilution of aliphatic bifunctionalalcohols were measured in 7 m ureaaqueoussolutions at 298.15K by flow microcalorimetry. The excess enthalpies were expressed as a power expansion series in the molality of the alcohol, referred to 1 kg of the mixed urea-water solvent. The values of the second and the third coefficients were all found to be positive and lower than the corresponding values in water. They show an approximately linear dependence on the square of the number of methylene groups. This fact suggests that in the presence of a large amount of urea excess enthalpies are determined primarily by methylene-methylene interactions. This is quite surprising and of remarkable interest on account of its obvious biological implications, since a kind of “lipophobic” or some modified hydrophobic effect seems still to be effective in concentratedureasolutions.