Handbook of Solvents - George Wypych - ChemTech - Ventech!

536 Y. Y. Fialkov, V. L. Chumak
Figure 9.8. Dependence of equilibrium constant for
the formation process of addition product DMSO to
o-cresol on permittivity in solution based on
heptylchloride (o), ethyl acetate (x) and nitromethane
(•):1 - resolvation of o-cresol solvated in ethyl acetate
in DMSO in mixed solvent CCl 4-ethyl acetate; 2 -
resolvation of DMSO solvated in nitromethane in
o-cresol in mixed solvent CCl 4-nitromethane; 3 - process
[9.84] in mixed solvent CCl 4-heptylchloride; 4 -
solvation of o-cresol in ethyl acetate; 5 - solvation of
DMSO in nitromethane.
C 6H 3(NO 2) 3 + C 6H 5N(CH 3) 2 ↔ C 6H 3(NO 2) 3•C 6H 5N(CH 3) 2
The data obtained for equilibrium [9.84]
in binary mixed solvents of different physical
and chemical nature are in need of some explanatory
notes.
First of all, if solvents are universal or
conditionally universal ones, in accordance
with general rules of equilibrium constants,
the dependence on permittivity and the dependence
of K= f(1/ε) in all cases is rectilinear.
As appears from the above, specific solvation
of one component decreases equilibrium
constants in comparison with
equilibrium constants in isodielectric universal
solvent.
The increase of K EF with permittivity increase
in DMSO - o-cresol system required
supplementary study. 33
The method of study of specific solvation
effect on the process of heteromolecular
association has been described in work, 34 devoted
to study of the following interaction:
[9.85]
in the binary liquid solvent formed from a solvate-inert component (heptane) and one of the
following solvate-active component: trifluoromethylbenzene, acetophenone or
p-chlorotoluene.
Therefore trinitrobenzene, TNB, is solvated in initial mixed solvents, so its interaction
with donor represents the resolvation process.
C 6H 3(NO 2) 3•A +C 6H 5N(CH 3) 2 ↔ C 6H 3(NO 2) 3•C 6H 5N(CH 3) 2 +(A) [9.85a]
Equation [9.62] applied to process of the heteromolecular association is written in the
form:
(cov)
[ ( solv, EF solv, E solv, F)
+σβ ε]
( v)
(cov)
(cov)
lnK
= ΔG + σG −σG −σG
solv / / RT [9.86]
(cov)
But for equilibrium [9.85a] in mixed solvents one can assume σGsolv,EF ≈ 0. That is why
equation [9.52] can be converted for the process in conditionally universal media:
( v ) (cov) [ solv, E solv ]
ln K = ΔG − σG + σβ / ε / RT
[9.86a]
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