Chemistry Reference
In-Depth Information
tAbLe 4.10
thermodynamic Functions of the Complexation of Alkali Cations by
Dioctyloxycalix[4]arene-dibenzocrown-6 MC14 in Acetonitrile at 25°C
thermodynamic Functions
k
+
Rb
+
Cs
+
5.47
5.7
5.7
Log β
−∆
G
(kJ mol
−1
)
31.2
32.5
32.5
17.4
29
42
−∆
H
(kJ mol
−1
)
13.8
4
T
∆
S
(kJ mol
−1
)
−10
46
13
∆
S
(J K
−1
kJ mol
−1
)
−34
bis-C6
octyloxy
10
3
bis benzo
bis naphto
isopropoxy
10
2
bis dibenzo
octyl dibenzo
10
1
10
0
10
-1
10
-2
10
-3
10
-2
10
-1
10
0
10
1
HNO
3
FIGURe 4.2
Distribution ratios of cesium at trace level as a function of HNO
3
concentra-
tion. Organic phase: calixarene 10
−2
M in NPHE.
Very high distribution ratios are obtained with ligands including one and two benzo
units in the polyethylene chain,
D
Cs
= 45 and
D
Cs
= 56, respectively. This enhance-
ment of distribution ratios is explained by a lesser extraction of sodium, linked to a
better complementarity of these ligands with cesium (Table 4.6).
46
One goal of the project was the removal of cesium from highly acidic solutions of
fission products arising from the PUREX process (3 M HNO
3
). Cesium distribution
ratios, much higher than those of two dibenzo 21-crown-7 ethers, strongly increase
with the increasing concentration of nitric acid, to a value ranging between 2 and 3
M. The presence of benzene units on the crown bridge reduces the nitric acid extrac-
tion, strongly enhances that of cesium, and shifts the maximum of cesium extraction
toward higher acidity (
D
Cs
= 200 for 3-4 M HNO
3
in NPHE). The EC goal is reached
with these compounds, especially those including benzo and naphtho units in the
crown (Figure 4.2).
47
For the calix[4]arene-bis(crown-6), the trends are the same on adding a benzo
(BC5) or a naphtho group (BC10) in improving the extraction efficiency and the
selectivity for cesium over sodium. However, the distribution ratios, although higher
