Chemistry Reference
In-Depth Information
tAbLe 4.33
Distribution Ratios for Am and eu from Aqueous solutions (3 M Hno
3
) into
Dichloromethane for Adamantyl-Calixarenes at Various Ligand
Concentrations
[
C
L
] mM
Ligands
D
0.25
0.5
1.0
2.0
3.0
4.0
5.0
10
20
CAd1
D
Am
0.27
1.0
2.1
D
Eu
0.19
0.62
1.7
CAd2
D
Am
0.29
0.60
1.9
6.6
17
17
32
240
920
D
Eu
0.19
0.44
1.2
4.1
9.0
14
26
125
570
CAd3
D
Am
0.11
0.39
0.66
1.08
5.2
10.5
D
Eu
0.08
0.25
0.47
1.03
2.6
6.1
CAd4
D
Am
0.15
0.33
0.86
3.3
D
Eu
0.12
0.24
0.61
2.3
CAd5
D
Am
0.58
1.4
2.4
8.8
22
D
Eu
0.49
1.1
2.8
7.0
16
CAd6
D
Am
0.06
0.11
0.27
0.71
1.2
D
Eu
0.04
0.08
0.25
0.48
0.8
CAd7
D
Am
0.11
0.22
0.44
1.1
1.6
D
Eu
0.08
0.14
0.38
0.64
1.0
CAd8
D
Am
0.32
0.70
1.2
4.9
14
D
Eu
0.19
0.45
1.8
3.0
9.2
•
The extraction percentage increases strongly with increasing length of the
spacer for all types of ligands, and best extraction results were found for
CAd2 and CAd7; the separation factor
S
Am/Eu
did not exceed 2, which is
close to the narrow rim CMPO calixarenes.
Variation of the spacer length between CMPO groups attached to the 1,3-
•
and 2,4-positions of the calixarene platform did not lead to appreciable
improvements, in terms of extraction or selectivity.
As on the wide-rim CMPO compounds, the plots of log
D
Am
versus log
C
L
for
several compounds suggests that the extracted complexes are a 1:2 cation/ligand
species. For all the ligands tested, americium is extracted slightly more efficiently
than europium, though the ratio
S
Am
/
Eu
does not exceed 2. Apparently, this is con-
nected with the weaker preorganization of adamantyl-calixarenes as well as CMPO-
calixarenes on the narrow rim in comparison with CMPO-calixarenes on the wide
rim. Preorganization of the ligating functions on a suitable platform (e.g.,
a calix-
arene) still remains the determining factor in increasing the extraction of americium
and europium in comparison with simple ligands.
All calixarenes bearing CMPO residues on the wide rim display a higher affinity
for thorium. The hexamer CAd4 is the most effective for thorium, while lanthanides
are better extracted by CAd2. Without spacers (CAd1), the ligating CMPO functions
