Chemistry Reference
In-Depth Information
formation as a proton acceptor. Components 1 are strongly polar molecules, Et and
MEt being able to form H-bonds either as donor or acceptor of protons, while TCM
can act only as donor. The experimental data for ln γ and for
V
E
were all deter-
mined in our laboratory (Lepori and Matteoli 1997; Lepori and Matteoli 1998;
Lepori et al. 1998; Conti et al. 2003; Gianni, Lepori, and Matteoli 2010; Matteoli,
Gianni, and Lepori 2010). The experiments were planned to cover the whole ter-
nary domain in detail, and sufficient care in their treatment was exercised to assure
high accuracy during the fitting.
We start this chapter with a description of the experimental techniques used and
the equations that we have found to best fit the data. We then outline the mathemati-
cal derivation, from the basic equations of KB theory, to the operative equations
to calculate the KBIs and the local composition. The algorithms for translating the
whole calculation procedure into a software application are also described. Finally,
we examine and discuss the information that the KBI and the local composition
results convey on the role played by the different interactions (H-bond, dipole-
dipole, dipole-induced dipole, dispersion) in determining the local composition in
the neighborhood of a molecule of each species. Issues that will be discussed are:
(1) the capability of THF to perturb the strong self-association feature of the alcohol-
hydrocarbon binary mixtures; (2) the influence of the additional ether oxygen of MEt
on the alcohol self-association due to the possibility of MEt forming an intramo-
lecular H-bond or enhancing intermolecular H-bonding; and (3) the interplay of the
TCM-THF hetero-association, shown in the binary mixture, and the TCM and THF
respective self-associations evident in their binary mixtures with cyH.
4.2
EXPERIMENTAL TECHNIQUES
4.2.1
G
e
d
eTerminaTion
As hinted in the Introduction, and explained in detail in Chapter 3 and in a previous
paper (Matteoli and Lepori 1984), in order to obtain reliable values of the KBIs,
very precise data for ln γ (or
G
E
) are necessary. At the same time, an empirical or
model equation that accurately describes or fits these experimental data is also
necessary in order to be able to calculate significant values of all the derivatives
with respect to concentrations of the chemical potentials required by the operative
equations. In an effort to fulfill these requirements, during the last decades we have
developed, tested, and applied a technique for determining ln γ based on the mea-
surement, via gas chromatography, of the composition of the vapor in equilibrium
with a liquid mixture of known composition (Gianni, Lepori, and Matteoli 2010;
Matteoli, Gianni, and Lepori 2010, and references therein). To be able to carry
out a large number of experiments in a reasonable time, a device, which provides
consecutive additions of small aliquots of a pure component to another component,
or to a known stock mixture, was implemented. Those areas of the composition
domain where ln γ displayed a strong dependence on concentration were covered
with a higher density of experimental points. Each experimental point in this tech-
nique is a vector of five numbers:
x
1
,
x
2
,
A
1
,
A
2
,
A
3
, the liquid composition, and
the areas of the three gas-chromatographic peaks of the vapor components. Each
