Chemistry Reference
In-Depth Information
Under the same conditions, in contrast to what is observed for calix[4]arene-
bearing CMPO moieties, with CPi12, distribution ratios of lanthanides increase
from the lightest lanthanide, lanthanum, to europium. Americium can be easily
separated from the lightest lanthanides (separation factor
D
Am/La
> 20,
D
Am/Ce
= 15,
D
Am/Nd
= 10,
D
Am/Sm
= 7. 5,
D
Am/Eu
= 6), which are the most abundant lanthanides
in fission-product solution. Cavitands bearing picolinamide (Cv5) or thiopicolin-
amide (Cv6) residues seems much less selective than their calixarene counterparts,
giving
S
Am/Eu
< 2.
18
4.5.4 e
X t r a C t i o n
b y
CmPo C
a l i X a r e n e S
w i t H
m
i X e d
f
u n C t i o n a l i t i e S
4.5.4.1 extraction by Wide-Rim Calixarenes bearing one to
three CMPo Residues
Böhmer et al. synthesized calix[4]arenes fixed in the cone conformation and sub-
stituted at their wide rim by one to three CMPO residues and hydrogen atoms in
the remaining positions: CPw23 (with one CMPO unit), CPw24 (with two CMPO
units in opposite positions), and CPw25 (with three CMPO units).
191
These calix-
arenes were tested with their counterpart bearing four CMPO groups (CPw3) and
the linear trimer for the extraction of La, Eu, and Th from 1 M HNO
3
in dichlo-
romethane and for Sm, Eu, Gd, Er, Pm, and Am from solutions containing 10
−2
M
HNO
3
, 4 M NaNO
3
. CPw3 is much more efficient than the four other calixarenes
even the calixarene bearing three CMPO residues CPw25. It definitively reveals
that all four CMPO groups are required to obtain excellent extraction ability. In
spite of the fact that the fixed cone conformation of the calixarene orients the
CMPO ligands in one direction, inducing a better preorganization, CPw25
is less
effective than the linear trimer. This phenomenon can be explained by an easier
formation of a 2:1 M:calix complex in the case of the trimer (Table 4.37) (see
Section 4.7).
4.5.4.2 extraction by Wide-Rim Calixarenes bearing Malonamide or
Carboxylate Residues
Böhmer et al. also synthesized calixarenes bearing one or more CMPO moi-
eties and another functionality (malonamide or carboxylate). These calixarenes
display lower extracting ability than CPw3, and contrary to expectations, these
functions do not lead to a new order of selectivity. Calix[4]arenes bearing one
or two adjacent malonic acid groups (NH-C(O)-CH
2
-COOH) adjacent to CMPO
functions at the wide rim were unstable and decomposed during the complex-
ation studies.
4.5.4.3 extraction by Wide-Rim Calixarenes bearing Amide Residues
Quite unexpectedly, the tris-CMPO monoacetamide CPw26, the bis-CMPO
diamides CPw27 and CPw28 and, to a lesser extent, the monoamine CPw25 show
much better Am/Eu selectivity than the corresponding tetrakis-CMPO derivatives.
The mono- and tris-CMPO derivatives CPw23
and CPw24 were synthesized in
order to gain a deeper insight into the structural requirements for an efficient
