Handbook of Solvents - George Wypych - ChemTech - Ventech!

9.4 Mixed solvent influence on the chemical equilibrium 555
Figure 9.19. Dependence of equilibrium constants for
triphenylchloromethane methanolysis on 1/ε of mixed
solvent at 298.15K: 1 - hexane-nitrobenzene; 2 - toluene-nitromethane;
3 - toluene-acetonitrile.
The dependence of equilibrium constant
for reaction [9.116] on ε is similar in a
concentration range from 0.5 to 1.0 molar
fraction of aldehyde, if the degrees of
homomolecular association for aldehydes
and acetals are smaller than for alcohol and
water.
K ch increase with increasing ε of media
is a general property of all processes of
exchange interaction presented in the Table
9.13. Dependence of lnK ch -1/εfor process
[9.111] is not linear in all mixed solvents
(Figure 9.19).
Extreme K ch dependence on 1/ε is explained
by chemical effect of solvation (it is
explained in detail elsewhere 60 ). Correlations
with different empirical parameters of
individual solvent parameters are held true
for this process. The best of them is correlation
(r=0.977) with parameter E T.
Table 9.13. Characteristics of some processes of exchange interaction
Reaction
Coefficients of equation [9.122] Free energy components, kJ/mol
a00 -a01 -σ cov
σG at max. ε σGat min. ε
[9.111] 2.40 97.6 5.9 241 5.2 19.0
[9.115], a, (F) 1.72 19.6 4.3 48.5 3.1 6.3
[9.115], b, (Cl) 2.55 17.1 6.3 42.3 5.1 7.0
[9.116], a 1.24 47 3.1 116.4 7.5 9.9
[9.116], b 2.47 16.7 6.1 41.3 3.4 4.1
The influence of molecular state of participants of exchange interaction on the process
equilibrium is reflected in K ch dependence (processes [9.113]) on the mixed solvent composition
(Figure 9.20). The change of K dim for acetic acid is less pronounced than for
monochloroacetic acid, when CCl 4 is replaced by chlorobenzene. Thus K ch should increase
for reaction [9.113a] and it should decrease for reaction [9.113b], with εincreasing in accordance
to equation [9.121].
Correlation of K dim for acetic and monochloroacetic acid is obtained when chlorobenzene
is replaced by nitrobenzene. This leads to decrease of K dim when ε increases in the case
of reaction [9.113a], and the opposite is the case for reaction [9.113b]. That is why a maximum
is observed in the first process (see Figure 9.20 on the left hand side), and a minimum
is observed for the second process.
el
σε=1