Handbook of Solvents - George Wypych - ChemTech - Ventech!

9.4 Mixed solvent influence on the chemical equilibrium 549
A similar phenomenon is observed in conditionally-universal media A-B (A is
solvate-active component, B is solvate-inert component). Association constant can be calculated
from equations [9.56] or [9.104] for LiBr and KCNS solutions. 55,57
Table 9.10. Coefficients of equations [9.56] and [9.106] for association constants of
salts
Solvent
a00 [9.56]
a10 a01 [9.106] (296K)
a11 a00 a01 Lithium bromide (298.15-323.15K)
Propylene carbonate-o-dichlorobenzene 3.38 -808 -361 1.53×10 5
0.67 152.4
Propylene carbonate-pyridine -5.56 2040 135 -6923 1.29 111.8
Propylene carbonate-acetic acid -3.55 1617 70.1 -6160 1.87 49.4
Potassium thiocyanate (298.15-348.15K)
Acetonitrile-chlorobenzene 3.80 -521 -25.4 3.26×10 4
2.05 84.0
Propylene carbonate-chlorobenzene 1.88 -229 -1.53 2.60×10 4
1.11 85.7
DMSO-chlorobenzene 6.18 -1580 -16.7 2.73×10 4
0.88 74.9
Figure 9.16. Dependence of lnK a for lithium bromide
on 1/ε in the mixed solvent based on propylene carbonate
at 298.15K.
( )
cov v
σ = σ + σ −σ −σ
correspondingly:
Δ Cat⋅Ansol, Cat⋅ An + −
sol, Cat sol, An
( )
el
σ = β −β −β
ε
Cat⋅ An + − /
Cat An
The dependence of lnK a and 1/ε for
LiBr in mixed solvent [9.53] shows an influence
of solvate-active component on K a. The
difference of LiBr solvation energy in the
presence of pyridine and acetic acid may be
evaluated in accordance to [9.53], assuming
low solvation energy of Li + by propylene
carbonate in comparison with pyridine and
negligible value of solvation energy of anion
in solvents containing dichlorobenzene
(DCB) and pyridine.
The data presented in Table 9.10 permit
us to calculate the components of free energy
for ion association processes. To
interpret the data, one must take into account:
cov