Excess partial molar enthalpies of <i>tert</i>-butanol in water–<i>tert</i>-butanol mixtures

Abstract

Excess partial molar enthalpies of tert-butanol (TBA) in water–tert-butanol mixtures were measured at 20.00, 26.90, 45.17, and 59.49 °C in the water-rich region, and at 30.00 °C for the entire range. The results together with those of the previous work, (Y. Koga. Can. J. Chem. 64, 206 (1986)), appear to support the following views: At X TBA ≈ 0, TBA molecules form hydrogen bonds with H 2 O molecules, and they enhance the structure of the hydrogen bond network of H 2 O. The latter effect is of very long range; the enthalpic repulsion between solutes is already operative via enhancement of hydrogen bond network when two TBA molecules are separated by 12 H 2 O molecules. This enthalpic repulsion becomes stronger as the concentration of TBA increases. At a certain threshold, X TBA ≈ 0.03 at 30.00 °C for example, the new scheme in which solutes tend to associate sets in, and for X TBA &gt; 0.06 this scheme becomes predominant. The effect of higher temperature is to shift this threshold to the lower values of X TBA . Therefore, it is probable that a lower critical solution temperature may exist at a temperature higher than the boiling points of the solution. It was also shown that if species of TBA(H 2 O) k type persist, they exhibit a hard-sphere nature in terms of enthalpic interaction among themselves.