Excess partial molar enthalpies of alkane-mono-ols in aqueous solutions

Excess partial molar enthalpies, H-A(E), of methanol, ethanol, and 1- and 2-propanols in aqueous solutions were measured directly, accurately, and in small increments in mole fraction at 25 degrees C. From these data, the solute-solute enthalpic interactions, H-AA(E) = N(partial derivative H-A(E)/partial derivative n(A)), were evaluated for each alcohol. These data indicate that three distinctively different mixing schemes, I, II, and III exist, as was the case for aqueous 2-butoxyethanol previously studied in our laboratory. The transition from mixing scheme I to II appears to take place gradually within a small composition range. As the hydrophobic moiety becomes smaller from 2-butoxyethanol to methanol, the locus of the transition moves to a higher value in mole fraction of the alcohol. At the same time, the range of transition becomes wider and the solute-solute enthalpic interaction weaker.