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 °C. From these data, the solute–solute enthalpic interactions, H AA E ≡N(∂H A E /∂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. Key words: excess partial molar enthalpies in aqueous solutions, methanol, ethanol, 1-propanol, 2-propanol, enthalpic interaction, transition of mixing scheme.