Handbook of Solvents - George Wypych - ChemTech - Ventech!

9.4 Mixed solvent influence on the chemical equilibrium 527
tion. Often, it can be achieved by combination of solvate active and solvate inert
components. For example, it is obvious that in all compositional range of mixture DMSO-
CCl4 (except 100% CCl4) specific solvation of acid dissolved in this mixture is realized by
DMSO. Similarly in mixed solvent formic acid-chlorobenzene, solvation of the dissolved
donor substance is performed exclusively by formic acid.
Selection of the second (indifferent) component’s ε also provides means to control the
universal solvation ability of mixed solvent. In the above mentioned examples, increasing
the solvate inert component concentration results in the decrease of mixed solvent ε .Onthe
contrary, addition of indifferent component (propylene carbonate) into the systems such as
acetic acid-propylene carbonate or propylene carbonate-aniline causes ε to rise. Because in
the last two systems acetic acid and aniline were chosen as solvate active components, it
was obviously intended to use these mixtures for specific solvation of the dissolved donor
and acceptor compounds respectively.
9.3.3.3 Donor-acceptor properties
As was demonstrated, 17
the parameters ET and Z of the binary mixed solvent
1,2-dibromoethane - 1,2-dibromopropane are strictly additive function of molar composition.
For the mixed solvents, having components engaged into specific interaction, dependencies
ET=f(x) and Z=F(x) are non-linear and even extremal, as can be seen from the
examples in Figure 9.7.
The method was proposed 18 to linearize polarity index of mixed solvent by introducing
a parameter, which connects the ET and Z values with fractional concentrations of components.
9.4 MIXED SOLVENT INFLUENCE ON THE CHEMICAL EQUILIBRIUM
9.4.1 GENERAL CONSIDERATIONS 7
The chemical process established in a solvent can be represented in a general form:
E ↔ F
[9.45]
where:
E all chemical forms of reaction reagents
F all chemical forms of reaction products
Considering the traditional thermodynamic cycle, we can use the general equation of
Gibbs’ energy variation because of the process [9.45]:
ΔG = ΔG −ΔG −ΔG
solv, E solv, F
( v )
[9.46]
where:
ΔGsolv,E, ΔGsolv,F Gibbs’ solvation energy of [9.45] equilibrium members
ΔG (v)
Gibbs’ energy of process [9.45] in vacuum
The process [9.45] takes place in mixed solvent A-B. Solvation energies of equilibrium
members are the algebraic sum of those for each of the mixed solvent components (this
sum also takes into account the energy of mixed solvates such as EAxBy and FAzBt): ΔG = ΔG + ΔG
=σ [9.47]
solv, i solv, A solv, B solv, i
Therefore the equation [9.46] can be represented in the form