Handbook of Solvents - George Wypych - ChemTech - Ventech!

9.4 Mixed solvent influence on the chemical equilibrium 537
It follows from equation [9.86a] that dependence of lnKus vs. 1/ε will be rectilinear.
Experimental data of equilibrium constants for process [9.85a] are in agreement with the
conclusion. Approximation of data by equation [9.65] is presented in Table 9.3.
It also follows from equation [9.86a] that RT, unlike in the cases of chemical equilibrium
in universal solvents, describes, not the vacuum component of the process free energy,
(v) (cov)
(el)
but the remainder ΔG −σGsolv,TNB and σGsolv,TNB . The values of the remainder as well as
electrostatic component of the free energy for the described chemical equilibrium are summarized
in Table 9.4.
Although the solvate-active components are weak bases, their differences influence
(v) (cov)
(el)
the values ΔG −σGsolv,TNB and σG ε=1
. The first value characterizes the difference between
the covalent components of solvation energy for trinitrobenzene in any solvate-active solvent.
It follows from the table, that contributions of the covalent and electrostatic components
are comparable in the whole concentration range of the mixed solvents. This indicates
the same influence of both donor property and permittivity of the solvent on the [9.85a] process
equilibrium.
Table 9.3. Coefficients of equation [9.65] equilibrium constants of the [9.85a] process
at 298.15K (r-correlation coefficient)
Solvent a b r
Heptane-trifluoromethylbenzene -0.80 5.50 0.997
Heptane-acetophenone -1.49 6.74 0.998
Heptane-chlorotoluene -2.14 7.93 0.998
Table 9.4. Free energy components (kJ/mol) of resolvation process [9.85a] in mixed
solvents at 298.15K
ε
-ΔG in system heptane - S, where S:
trifluoromethylbenzene acetophenone chlorotoluene
2 6.8 8.3 9.8
4 3.4 4.1 4.9
6 2.3 2.8 3.3
8 1.7 2.1 -
(v) (cov)
ΔG −σG -2.0 -3.7 -5.3
(el)
σG ε=1
solv,TNB
13.6 16.7 19.6
According to the above energy characteristics of the heteromolecular association process
(resolvation) in specific media, the solvent exchange affects the products’ output (the
relationship of output c M and K us is estimated from the equation [9.66]). This shows that the
product output (with initial concentration of reagents 0.1M) can be changed from 34% (pure
heptane) to 4 % (pure n-chlorotoluene) by changing the binary mixed solvent composition.
The processes [9.85a] and [9.85] can be eliminated completely when the solvate active
component (more basic then chlorotoluene) is used.