Handbook of Solvents - George Wypych - ChemTech - Ventech!

1010 An Li
Figure 14.21.2.2c. Deviations from log-linear model (equation [14.21.2.2], triangle) and the extended log-linear
model (equation [14.21.2.10], circle) for solute benzoic acid in various water cosolvent systems. Experimental
data are from Refs. 61 and 86.
the UNIFAC group interaction parameters involved in these systems are incorrect. With all
the systems tested in this study with solute naphthalene, benzocaine, or benzoic acid, it is
also found that replacing f i in the last term of equation [14.21.2.11] with mole fraction x i offers
slight improvement in only a few cases. Dropping the logarithm conversion constant
2.303 results in larger estimation errors for most systems.
An apparent limitation of this modification is the exclusion of any active role the solute
may play on the observed deviation. Little understanding of the influence of solute
structure and properties on deviations from the log-linear equation has been obtained. Although
the patterns of deviations tend to be similar among solutes, as mentioned above, the
extent of deviation is solute-dependent. For instance, C 1~C 4 alkyl esters of
p-hydroxybenzoates and p-aminobenzoates demonstrated similar characteristics of
solubilization by propylene glycol, with a negative deviation from the log-linear pattern occurring
when f is low, followed by a positive one when f increases. 91 The magnitude of the
negative deviation, however, was found to be related to the length of the solute alkyl chain
in each group, while that of the positive deviation to the type of the polar groups attached. 91