Chemistry Reference
In-Depth Information
results were reported qualitatively, in that mixtures of ethanol with B = toluene and
chlorobenzene resemble those with B = benzene, those with B =
n-
hexane resemble
those for B =
n-
heptane, those with B =
c-
hexane resemble those with B = acetonitrile,
those with B = triethylamine and B = acetone resemble those with A = methanol and
B = acetone, and those with B = 1,4-dioxane resemble those with A = methanol and B
= acetonitrile described above. Mixtures of A = ethanol and B = pyridine do not have
any appreciable preferential solvation. For the two alcohols as solvents A, there exists
an approximately linear correlation of
G
BB
for solutes B with their Kamlet-Taft elec-
tron pair donation parameters β
B
.
Acetone and cosolvents
. Preferential solvation curves δ
x
AA
and δ
x
AB
(not volume-
corrected) for A = acetone and several cosolvents, B, were obtained (Marcus 1991).
The preferences vary among the systems, some showing preferential mutual sol-
vation, others preferential self-association of the acetone. For B = chloroform,
δ
x
AB
(max) = 0.048 and δ
x
AA
(min) = -0.01, that is, small preferences are manifested.
For B = methanol, the δ
x
AA
curve is S-shaped but with very small values, <0 in
methanol-rich mixtures and >0 in acetone-rich ones, and the mutual δ
x
AB
(min) -
-0.042. For B = toluene, curves qualitatively similar to those for B = methanol were
obtained. For B =
n-
heptane, δ
x
AA
(max) = 0.23 and δ
x
AB
(min) = -0.15 and qualita-
tively similar curves were obtained for B =
n-
hexane, B =
c-
hexane, and B = 1,2 =
ethanediol. For B = benzene, δ
x
AB
is small and positive, δ
x
AA
is small and negative;
for B = chlorobenzene, δ
x
AB
is small and positive, δ
x
AA
is near zero. For B = pyridine
and B =
N
,
N
-diethylformamide, both parameters are near zero, and for B = for-
mamide both parameters are negative, δ
x
AB
moderately and δ
x
AA
less so.
Triethylamine and cosolvents.
Preferential solvation curves δ
x
AA
and δ
x
AB
(not
volume-corrected) for A = triethylamine and two cosolvents, B, were shown by
Marcus (1991), but qualitative results for other cosolvents were also mentioned there.
For B = chloroform, δ
x
AB
(max) = 0.020 and δ
x
AA
(min) = -0.25, that is, mutual sol-
vation is somewhat preferred. For B = methanol, δ
x
AB
(min) = -0.05 and δ
x
AA
(min)
= -0.02, meaning that self-association of the methanol δ
x
BB
= -δ
x
AB
(min) = 0.05 is
preferred. Qualitative results are that for B =
n-
heptane no appreciable preferential
solvation occurs; for B = benzene and chlorobenzene, both δ
x
AA
and δ
x
AB
are nega-
tive and small; for B = 1-butanol, δ
x
AB
is positive and small, but δ
x
AA
is near zero; for
B = 1-propanol and B =
t-
butanol, δ
x
AB
is small and negative and δ
x
AA
is near zero.
Values of both the infinite dilution KBIs,
G
AA
and
G
BB
of these systems have been
calculated (Marcus 1991).
Tetrahydrofuran and cosolvents.
A detailed study of the preferential solvation in
mixtures of tetrahydrofuran, A, and cosolvents, B, was reported by Marcus (2006a).
For B =
n-
hexane and
c-
hexane at 303 K,
n-
heptane and
i-
octane at 298 K, the self-
association of tetrahydrofuran is preferred: δ
x
′
AA
(max) = 0.025, 0.030, 0.025, and
0.034, respectively. The mutual interaction is small: the extrema in δ
x
′
AB
are: -0.010,
0, 0.004, and 0.004, that is, hardly significant. For B = benzene, toluene, ethylben-
zene, dichloromethane, chloroform, tetrachloromethane, and 1-chlorobutane at 303
K, there is essentially no preferential solvation, both δ
x
′
AA
and δ
x
′
AB
being less than
0.01. The smallness of the preferential solvation parameters for mixtures of tetra-
hydrofuran and tetrachloromethane has already been noted by Ben-Naim (1990b)
