Handbook of Solvents - George Wypych - ChemTech - Ventech!

556 Y. Y. Fialkov, V. L. Chumak
Figure 9.20. Dependence of K ch on the mixed solvent composition for processes [9.113a] and [9.113b] at 298.15K:
1-tetrachloromethane-nitrobenzene; 2- tetrachloromethane-chlorobenzene.
At equilibrium [9.114] (with three associated participants), association degree of associated
participants decreases with media polarity increasing. It leads to Kch increasing and to
Kadd decreasing in the process of heteromolecular association of acid and alcohol.
Thus, Kch depends to a low extent on the composition of studied mixed solvents. Vacuum
component of free energy of processes of exchange interaction (Table 9.13) is low;
σG el values are low, too. This indicates, that εchange does not lead to the change of the reaction
output. Solvent replacement leads to essential change of reaction output in process
[9.111], characterized by the high value of σ el (see Table 9.13), from 6% in pyridine to 60%
in DMSO (in 0.1M solutions). Kch increase in pyridine solution to its value in DMSO requires
cooling to -140 o C.
9.4.7 MIXED SOLVENT EFFECT ON PROCESSES OF COMPLEX
FORMATION
Non-aqueous solvent effect on equilibrium and thermodynamic of complexation processes
are summarized in monographs. 67-69
The solvent effect on complex formation processes has two aspects. The first is a
change of coordination sphere composition, changing participation of solvent as a chemical
regent:
p+ + A
p
[ ] ←⎯ →[
] + ←⎯→ ← →[
]
+ p+
MLm MLm−1AL � ⎯ MAn + mL [9.123]
where:
Lm a ligand in initial complex
A, B components of binary solvent
If both components of the mixed solvent are solvate-active, equilibrium [9.123] may
be presented as:
p+ + A+ B
p+
[ m ] ← →[
m−
] [ n−q q]
ML ⎯⎯ ML 2AB + 2L↔� ↔ MA B + mL [9.123a]
p+