Chemistry Reference
In-Depth Information
∆ps
1
23
∆ps
1
21
∆ps
3
12
0.15
0.015
0.06
0.04
0.1
0
0.02
0.05
1
0
3
0
-0.015
2
FIGURE 4.7
Preferential solvation (Δpsi
i
j,k
, Equation 4.31) in the system trichloromethane(1)
+ tetrahydrofuran(2) + cyclohexane(3) at 298.15 K.
Δps
1,3
is positive over the whole domain, and shows very large values in a wide region
near binary 1+3 with a maximum at
x
1
≈ 0.2,
x
3
≈ 0.8. This preference of Et to be
solvated by Et molecules is also evident with respect to THF, except in a small com-
position area in and near binary 2+3, due to the high dilution of Et. THF as solvatant
is instead preferred by Et, compared with cyH, except in the binary 1+2 mixture.
To determine the preferences of THF as solvaton, the three surfaces of the second
row should be compared. The first and third frames indicate a preference for Et with
respect to cyH (Δps
1,3
>> 0), except in the area near the binary Et+cyH, where Δps
1,3
≤ 0. The same preference is shown with respect to THF, but not in and near binary
1+2 and part of 2+3. It is only when the rival solvatant is cyH that THF prefers to
be solvated by the same species. In fact, Δps
2,3
>> 0 almost in the whole domain.
By comparing the three surfaces in the bottom row, we can determine the solvation
preferances of cyH: Δps
3,
i
(
i
= 1,2) >> 0 practically at any composition indicates that
cyH prefers to be solvated by cyH with respect to Et and THF. When the solvatant
capabilities of THF and Et are compared, it is the less polar, THF, that is preferred
(Δps
1,2
<< 0).
System II behaves exactly like system I, but with more marked features, as we
have found for the KBI and local composition, suggesting again a stronger alcohol-
alcohol association than in system I.
System III is characterized by the large preferential solvation of TCM and THF
for THF and TCM, respectively, with regard to cyH: Δps
2,3
, Δps
1,3
>> 0 in the whole
domain. Less pronounced are the values of Δps
2,1
and Δps
1,2
, which are positive except
in small areas near the binaries 1+3 and 2+3, respectively, and those of Δps
1,3
and
Δps
2,3
. These results suggest the following order of preferential solvation by THF:
TCM>THF>cyH and by TCM: THF>TCM>cyH. This latter behavior is clearly evi-
dent from the left and central panels of Figure 4.7. As regards to cyH as a solvaton,
both Δps
1,3
and Δps
2,3
are negative for almost the whole domain, whereas Δps
1,2
(third
picture in Figure 4.7) is practically zero except in and very near the binaries 1+3 and
2+3, where its values are anyway very small in magnitude. This indicates that cyH
prefers, or we would say is compelled, to be solvated by cyH and that is not capable
of distinguishing the solvation properties of TCM and THF.
