Synthesis and evaluation of novel water-soluble ligands for the complexation of metals during the partitioning of actinides

Article abstract of DOI:10.1039/c1nj20523d

Different types of water-soluble ligands were synthesized and their capability was evaluated by solvent extraction studies to complex trivalent actinides and suppress their extraction by a strong lipophilic ligand, such as TODGA. The back extraction efficiency of hydrophilic diglycolamide (DGA) derivatives with a varying number of ethylene glycol groups, or containing sodium acetate moieties on the amidic nitrogen shows a decrease in back-extraction efficiency with increasing number of ethylene glycol units on the amidic nitrogen at various pH values of the aqueous phase. Among the PS donating ligands only the ligand with a malonamide backbone exhibits a high reverse extraction efficiency, although, with no selectivity for americium. Within the water-soluble tripodal ligands, i.e. the amide derivatives of nitrilotriacid with N,N-dimethyl and N,N-bis(hydroxyethyl) moieties, the first one shows a pronounced selectivity for Am(iii) over Eu(iii), with a maximum separation factor of 11.1, while the latter one more efficiently complexes the radionuclides in the aqueous phase with a maximum separation factor of 5. Isothermal microcalorimetry experiments of the complexation of Eu(iii) by a selected series of ligands confirm the observed trend in the back extraction properties.

Full text of DOI:10.1039/c1nj20523d

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PAPER
Synthesis and evaluation of novel water-soluble ligands for the
complexation of metals during the partitioning of actinidesw
Mudassir Iqbal,a Jurriaan Huskens,a Michal Sypula,b Giuseppe Modolob and
Willem Verboom*a
Received (in Gainesville, FL, USA) 14th June 2011, Accepted 4th August 2011
DOI: 10.1039/c1nj20523d
Different types of water-soluble ligands were synthesized and their capability was evaluated by
solvent extraction studies to complex trivalent actinides and suppress their extraction by a strong
lipophilic ligand, such as TODGA. The back extraction efficiency of hydrophilic diglycolamide
(DGA) derivatives with a varying number of ethylene glycol groups, or containing sodium acetate
moieties on the amidic nitrogen shows a decrease in back-extraction efficiency with increasing
number of ethylene glycol units on the amidic nitrogen at various pH values of the aqueous
phase. Among the PQS donating ligands only the ligand with a malonamide backbone exhibits
a high reverse extraction efficiency, although, with no selectivity for americium. Within the
water-soluble tripodal ligands, i.e. the amide derivatives of nitrilotriacid with N,N-dimethyl and
N,N-bis(hydroxyethyl) moieties, the first one shows a pronounced selectivity for Am(III) over
Eu(III), with a maximum separation factor of 11.1, while the latter one more efficiently complexes
the radionuclides in the aqueous phase with a maximum separation factor of 5. Isothermal
microcalorimetry experiments of the complexation of Eu(III) by a selected series of ligands
confirm the observed trend in the back extraction properties.
Within the current European project ACSEPT7 (Actinide
Introduction
reCycling by SEParation and Transmutation) the so-called
‘‘innovative SANEX’’ (Selective ActiNide EXtraction)
concept is studied. In this strategy, the trivalent actinides are
recovered from the PUREX raffinate by means of one organic
solvent, thus reducing the cycles and minimizing the waste.
The process consists of an An(III)/Ln(III) co-extraction step at
high acidity and then, the loaded solvent is subjected to several
stripping steps. The first one concerns selective stripping
of trivalent actinides with a selective water-soluble agent
followed by the subsequent stripping of trivalent lanthanides.
N,N,N0,N0-Tetraoctyl-3-oxapentanediamide (TODGA) is
currently one of the innovative-SANEX reference molecules
due to its high distribution ratios for An and Ln from highly
acidic media,8 high stability in aliphatic diluents,9 composition
allowing destruction by combustion (C, H, O, N principle), and
easy synthesis.10 Since it shows a slightly higher affinity towards
trivalent lanthanides compared to trivalent actinides, the
implementation of a selective water-soluble ligand forming
stronger complexes with An(III) than Ln(III) would significantly
increase the Ln/An separation factor. The most well-known
hydrophilic ligand EDTA has been studied for the stripping of
Am(III) and Cm(III) in the TALSPEAK (Trivalent Actinide
Lanthanide Separations by Phosphorus-reagent Extraction
from Aqueous Komplexes) process.11,12 A number of other
carboxylic and polycarboxylic acids have been described by
Sasaki et al.13 However, EDTA and other carboxylic acids have
The P&T (Partitioning and Transmutation) strategy aims at
decreasing the radiotoxicity of the nuclear waste thereby
minimising the cost and the time of its storage. After the
recovery of U and Pu in the PUREX process (Plutonium
Uranium Recovery by Extraction) the main contribution to
the total radiotoxicity of the remaining waste is given by the
minor actinides (Np, Am, and Cm). These elements must be
separated from the neutron-absorbing elements such as the
lanthanides (Ln(III)) before being properly transmuted.1
A demand exists for the design of new extracting agents
for the recovery of An(III). Due to the very similar physico-
chemical properties of An(III) and Ln(III), i.e. trivalent oxida-
tion state in solution, close ionic radii, their partitioning is one
of the most challenging issues.2
Numerous selective extractants containing nitrogen3 or sulfur4
functionalities, which are softer than oxygen donors, have been
developed to favor An(III) over Ln(III) complexation.5,6
a Laboratory of Molecular Nanofabrication, MESA+ Institute for
Nanotechnology, University of Twente, P.O. Box 217,
7500 AE Enschede, The Netherlands. E-mail: w.verboom@utwente.nl
b Forschungszentrum Juelich GmbH, Institute of Energy and Climate
Research-Nuclear Waste Management (IEK-6), 52425 Juelich,
Germany
w Electronic supplementary information available: ITC thermograms
of Eu(III)–ligand interaction. See DOI: 10.1039/c1nj20523d
c
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a limited solubility and the solubility also greatly depends on
the HNO3 concentration of the aqueous solution. During the
stripping process there is always a competition between the
organic and the aqueous phase to bind the metals, therefore
strong ligands with a high solubility are required to selectively
strip the actinide ions. Some water-soluble diglycolamides (tetra-
alkyl diglycolamide) have been studied by Sasaki et al.,13,14
however, their water solubility is limited. Water-soluble N-donor
ligands, containing pyridine and pyrazine rings described by
Heitzmann et al.,15,16 demonstrate a correlation of the selectivity
for trivalent actinides (e.g. Am) over Ln with the N-donor groups
coordinated to the cation (softness of the molecule).
Scheme 2
1
in acetone using K2CO3 as a base (Scheme 1). In the H NMR
spectra the peak for the methylene protons was shifted from
4.57 ppm in 1 to 4.28 ppm in 2.
Herein we describe new water-soluble diglycolamides with
varying lengths of ethylene glycol chains on the amidic nitro-
gens, and two novel water-soluble ligands with the backbone
similar to diglycolamide10 and malonamide,17 but with the
softer sulfur as a coordinating atom instead of oxygen to study
their back-extraction properties.
To extend the glycol chain in ligand 2 benzylamine (3) was
reacted with 2-(2-chloroethoxy)ethanol (4a) and 2-(2-(2-chloro-
ethoxy)ethoxy)ethanol (4b) in the presence of K2CO3 and KI in
DMF at 110 1C to give 5a21 and 5b, respectively. Removal of
the benzyl group in 5a and 5b by hydrogenolysis with 10%
Pd/C in methanol afforded 6a and 6b, which subsequently were
reacted with diglycolyl dichloride (1) in acetone to give the
desired ligands 7a and 7b in 62% and 63% yield, respectively
(Scheme 1). In the 1H NMR spectra the peak for the methylene
protons was shifted from 4.57 ppm in 1 to 4.31 and 4.29 ppm in
7a and 7b, respectively.
In
a
previous study of lipophilic ligands18 2,20,200-
nitrilotris(N,N-dialkylacetamides) proved to be selective ligands
for Am(III), however, only at lower nitric acid concentrations.
Since back-extractions of An(III) and Ln(III) are performed
at low nitric acid concentrations, we also synthesized water-
soluble derivatives of these ligands to study their applicability for
selective back extraction.
The next target molecule was ligand 10 containing four
sodium acetate groups connected to the amidic nitrogen to
induce water solubility. Diglycolyl dichloride (1) was reacted
with dimethyl 2,20-azanediyldiacetate (8) in the presence of
triethylamine to get tetraester 9 in 80% yield. Subsequent
hydrolysis of the ester groups in 9 using NaOH in methanol
gave N,N,N0,N0-tetrasodium acetate diglycolamide (10) in
Results and discussion
Synthesis of water-soluble TODGA derivatives
The synthesis of water-soluble TODGA derivatives 2, 7a,b, and
10 is summarized in Schemes 1 and 2. First diglycolyl dichloride
(1) was reacted with diethanolamine in the presence of triethyl-
amine in THF according to a literature procedure.19 However, a
1 : 1 mixture was obtained of the desired 2,20-oxybis(N,N-bis(2-
hydroxyethyl)acetamide) (2) and the HCl salt of diethanolamine
1
quantitative yield (Scheme 2). In the H NMR spectrum the
methyl ester peaks at 3.72 and 3.75 ppm of 9 completely
disappeared upon hydrolysis.
Synthesis of S/O-containing ligands
1
as followed from H NMR spectroscopy, which could not be
separated in our hands.20 Ligand 2 could be synthesized in 67%
Water-soluble O-containing ligand with a diglycolamide
yield by reaction of diglycolyl dichloride (1) with diethanolamine
backbone. (Diethoxyphosphoryl)methyl trifluoromethane-
Scheme 1
c
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Scheme 3
sulfonate (11), prepared from diethyl(hydroxymethyl)-
phosphonate according to a literature procedure,22 reacted
with diethyl(hydroxymethyl)phosphonate in the presence of
NaH as
a base to give the desired tetraethyl(oxybis-
(methylene))bis(phosphonate) (12) in 74% yield. In the 1H
NMR spectra the doublet for the methylene hydrogens at
4.62 ppm in 11 shifted to 3.85 ppm in 12. The PQO groups in
12 were converted into PQS moieties using Lawesson’s
Scheme 5
1
reagent to afford 13 in 80% yield. In this case in the H NMR
appeared at 3.62 ppm in 21. For the synthesis of tripodal
ligand 23 the known triester 22 was reacted neat with diethanol-
1
amine to give the desired ligand 23 in 81% yield. In the H
spectrum the methylene protons appeared at 4.10 ppm. Subse-
quent hydrolysis of 13 with conc. HCl gave the hydrophilic
oxybis(methylene)diphosphonic acid (14) in 70% yield and not
the expected diphosphonothioic acid (Scheme 3). Apparently,
during the acid treatment the PQS moieties were transformed
to PQO groups. The 1H NMR spectrum of 14 shows the
methylene protons as a doublet at 3.62 ppm. All compounds
showed characteristic M + 1 peaks in their mass spectra. The
coupling reaction to give PQO ligand 12 was also performed
with a tosylate instead of a triflate group as a leaving group.
However, it gave rise to a much lower yield (34%) of 12.
NMR spectrum of 23 the peak for the methoxy groups in 22 at
3.67 ppm completely disappeared and characteristic triplets for
the amidic CH2 protons were found at 3.31 and 3.39 ppm.
All these ligands showed infinite solubility in water.
Extraction results
Preliminary solvent extraction experiments were carried out to
determine the back extraction ability of the new water-soluble
ligands. An organic solution containing TODGA + 5 vol%
1-octanol in TPH (Total Petroleum Hydrocarbon/hydro-
genated tetrapropene) was used as solvent for the evaluation
and comparison of the new ligands.
S-containing water-soluble ligand with a malonamide backbone.
For the synthesis of ligand 17, with a malonamide backbone,
first bis(dichlorophosphino)methane (15) was quantitatively
converted into bis(dichlorophosphorothioyl)methane (16) upon
treatment with PSCl3 (Scheme 4). In contrast to a literature
procedure, AlCl3 was not used as a Lewis acid catalyst.23
Subsequently, 16 was reacted with aqueous acetone and
complete hydrolysis occurred to give methylenediphosphono-
thioic O,O-acid (17). In the 1H NMR spectra the signal for the
methylene hydrogens shifted from 4.48 ppm in 16 to 2.99 ppm
in 17. The electrospray mass spectrum of 17 exhibited the
correct M + H peak at m/z 208.9.
A certain concentration of the ligand was dissolved in an
aqueous NH4NO3 (0.5 mol Lꢀ1) solution followed by pH
adjustment and addition of traces of Am(III) + Eu(III). The
nitrate ion was used as a salting-out agent to compensate the
metal charge, since TODGA extracts metals only as neutral
species (solvating extraction mechanism).24,25 The metal
distribution ratio DM was calculated according to eqn (1)
and the percentage of metal ions retained in the water phase
after extraction using eqn (2). Therefore, the smaller DM is, the
more efficient the back-extraction is.
Synthesis of tripodal ligands
DM = [M]org/[M]aq
(1)
Different methods were employed for the synthesis of the
tripodal ligands 21 and 23 (Scheme 5). For the synthesis of
ligand 21 2-chloro-N,N-dimethylacetamide (18) was reacted
with benzylamine in acetonitrile to get 19 in 81% yield. The
methylene protons next to chlorine shifted from 4.06 in 18 to
3.74 ppm in 19 in the 1H NMR spectra. The benzyl group of 19
was cleaved by hydrogenation using 10% Pd/C to give 20,
which was subsequently reacted with 18 to afford ligand 21 in
75% yield. In the 1H NMR spectra the methylene protons
1
%Meq;aq
¼
ꢁ 100%
ð2Þ
1 þ DM
The separation factor (SF) between Eu(III) and Am(III) was
calculated using eqn (3).
SFEu/Am = DEu/DAm
(3)
The higher the SFEu/Am is, the better the selectivity of the
water-soluble ligand for Am(III) versus Eu(III) is.
Water-soluble TODGA derived ligands. The four aliphatic
groups of TODGA were substituted by four glycol chains of
different lengths in order to increase its hydrophilicity to give
the three new highly water-soluble diglycolamide ligands 2, 7a,
and 7b. Since they are neutral ligands, it can be anticipated
Scheme 4
c
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that their utility for reverse-extraction experiments in principle
is pH independent.13 In contrast, the solubility of (poly)-
carboxylic acids such as EDTA greatly depends on the
HNO3 concentration of the aqueous solution.
aqueous phase). As expected, no significant separation
between Eu(III) and Am(III) was observed (SFEu/Am o 2).
Moreover, the discrimination between both radionuclides
decreased further with increasing pHini (Table 1). Decreasing
the ligand 2 concentration below 0.1 mol Lꢀ1 decreased
the metals complexation in the aqueous phase and thus
increased the extraction of Am(III) and Eu(III) into the organic
phase (Fig. 1). Only at pH = 4 and a low concentration of
0.01 mol Lꢀ1 ligand 2 it was sufficient to keep most of Am(III)
and Eu(III) in the aqueous phase. A lower initial pH resulted
in D-values more than 1 (o 50% metal kept in the aqueous
phase).
The extraction kinetics of Am(III) and Eu(III) by 0.1 mol Lꢀ1
ligand 2 at pH 3 with formation of aqueous Am– and
Eu–ligand 2 complexes is very fast. Only a mixing time of
5 minutes was required to suppress the Am + Eu extraction
by TODGA (Fig. S1, ESIw). The equilibrium values reached
after 5 minutes did not further change up to 60 minutes mixing
time, indicating the formation of strong and stable metal
complexes.
Since TODGA shows only a slightly higher affinity for
Ln(III) than An(III), no significant separation factor between
these two element groups was expected from its hydrophilic
derivatives studied in this paper. The distribution ratios of
ligand 2 for Am(III) and Eu(III) as a function of initial pH are
shown in Fig. 1. The results of our reference extraction system
(TODGA) without the presence of the hydrophilic ligand in
the aqueous phase are expressed by the dotted lines in Fig. 1
for comparison. It can be seen that high distribution ratios for
Am(III) and Eu(III) were obtained and they were not affected
by the initial pH of the aqueous phase due to the salting-out
effect of NO3ꢀ. The D-values for Am were between 34 and 76,
whereas higher D-values (250–323) were obtained for Eu,
resulting in separation factors SFEu/Am between 4.5 and 7.2.
Ligand 2 with the shortest glycol chain at the N-amide of the
DGA showed a very strong complexation for 241Am + 152Eu
with increasing ligand concentration. At a fixed ligand con-
centration of 0.1 mol Lꢀ1, the extraction of Am(III) and Eu(III)
was progressively more suppressed with increasing pH of the
aqueous solution (Fig. 1). Even at pHini = 1 the distribution
ratios DAm and DEu were 0.2 and 0.5, respectively (DM less
than 1 expresses that 450% of the metal is retained in the
Compared to ligand 2, the chains of ligands 7a and 7b
contain one and two more ethylene glycol units, increasing
the hydrophilicity. Both new water-soluble DGA ligands 7a and
7b do not complex Am(III) and Eu(III) as effectively as ligand 2
(Fig. 2). Only at pHini = 4 ligand 7a kept most of the radio-
nuclides in the aqueous phase (DAm = 0.5 and DEu = 0.92).
Fig. 1 Initial pHaq and ligand (2) concentration dependency for the extraction of 241Am and 152Eu. Organic phase: 0.2 mol Lꢀ1 TODGA +
5 vol% 1-octanol in TPH. Aqueous phase: 0.5 mol Lꢀ1 NH4NO3, variable pHini, variable concentrations of ligand 2, tracers: 241Am, 152Eu, mixing
time: 60 min; T = 22 1C ꢂ 1 1C.
Table 1 Percentages of retained ions in the aqueous phase and Eu/Am separation factors using ligands 2 and 17a
Ligand 2
Ligand 17
Ligand conc./mol Lꢀ1
0
pHini
%Amaq,eq
%Euaq,eq
SFEu/Am
%Amaq,eq
%Euaq,eq
SFEu/Am
1
2
3
4
1
2
3
4
2.83
2.38
1.64
1.31
83.45
95.01
99.63
99.96
0.40
0.39
0.37
0.31
68.78
91.78
99.68
99.97
7.2
6.3
4.5
4.3
2.3
1.7
0.9
0.7
2.83
2.38
1.64
1.31
95.16
99.42
99.75
99.74
0.40
0.39
0.37
0.31
90.70
99.47
99.73
99.78
7.2
6.3
4.5
4.3
2.0
0.9
1.0
0.8
0.1
a
Calculated using eqn (2) and (3) on the distribution ratios from Fig. 1 and 4, respectively.
c
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Fig. 2 Initial pHaq dependency for the extraction of 241Am and 152Eu. Organic phase: 0.2 mol Lꢀ1 TODGA + 5 vol% 1-octanol in TPH.
Aqueous phase: 0.5 mol Lꢀ1 NH4NO3, variable pHini, 0.1 mol Lꢀ1 ligand 7a, 7b (0.01 mol Lꢀ1 ligand 10), tracers: 241Am, 152Eu, mixing time:
60 min; T = 22 1C ꢂ 1 1C.
Fig. 3 Initial pHaq dependency for the extraction of 241Am and 152Eu. Organic phase: 0.2 mol Lꢀ1 TODGA + 5 vol% 1-octanol in TPH.
Aqueous phase: 0.5 mol Lꢀ1 NH4NO3, variable pHini, ligand 14 o 0.03 mol Lꢀ1, tracers: 241Am, 152Eu, mixing time: 60 min; T = 22 1C ꢂ 1 1C.
Surprisingly, higher distribution ratios were observed for
ligand 7b in comparison with the TODGA reference extraction
system (dotted lines) at pH o 2. At pH 3 they are comparable
and only at pH 4, they are lower than in the absence of the
ligand.
of 2–4 the DAm and DEu values remain nearly constant around
10 and 40, respectively, indicating only poor complexation
properties for reverse extraction. In addition, no increased com-
plexation for the trivalent Am(III) was observed in comparison
to the extraction system without the ligand, since the curves for
Eu/Am are nearly overlapping one another.
Finally, water-soluble diglycolamide derivative 10 was
tested in which the aliphatic chains connected to the amidic
nitrogen of the parent TODGA are substituted by four sodium
acetate groups. The solubility of this ligand was poorer than
that of the three ligands with glycol chains and a clear solution
was obtained at a ligand concentration of 0.01 mol Lꢀ1
in the aqueous phase. The distribution ratios DAm and DEu
decreased with increasing pHini. However, the complexes
formed were not strong enough to prevent the metals extrac-
tion (Fig. 2) by TODGA.
Sulfur containing ligands. In order to increase the selectivity
for the trivalent actinides over the lanthanides two hydrophilic
ligands containing sulfur bearing groups were synthesised to
study the impact of S-donors on their complexation proper-
ties. Sulfur containing ligand 17, having a malonamide back-
bone, has a good solubility and allowed the preparation of a
0.1 mol Lꢀ1 solution. At this high ligand concentration, both
Am(III) and Eu(III) were strongly complexed in the aqueous
phase in the entire pHini range studied, thus their extraction by
TODGA was significantly prevented (Fig. 4). Over 90% of
each metal stayed in the aqueous phase at pHini = 1, while
over 99% at pHini = 2–4 (Table 1).
Ligand 14, with a diglycolamide backbone, has a poor solu-
bility in 0.5 mol Lꢀ1 NH4NO3 solution. After adjusting the
ligand concentration to 0.03 mol Lꢀ1, still small un-dissolved
residues were visible in the solution. After centrifugation, the
clear supernatant was used for the subsequent extraction
experiment (see Fig. 3). The distribution ratios of Am and Eu
do not significantly decrease with increasing pHini. There is
only a drop between pHini = 1 and 2. In the initial pH range
Decreasing the ligand 19 concentration, the distribution
ratios of Am(III) and Eu(III) increased, although in comparison
with ligand 2 (cf. Fig. 1), the S-containing ligand seems
to form more stable complexes, especially at lower pHini
.
c
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Fig. 4 Initial pHaq and ligand 17 concentration dependency for the extraction of 241Am and 152Eu. Organic phase: 0.2 mol Lꢀ1 TODGA +
5 vol% 1-octanol in TPH. Aqueous phase: 0.5 mol Lꢀ1 NH4NO3, variable pHini, variable concentration of ligand (17), tracers: 241Am, 152Eu,
mixing time: 60 min; T = 22 1C ꢂ 1 1C.
The separation factor SFEu/Am decreased from 2.0 to 0.8 with
increasing pHini (Table 1).
Ligand 17 exhibits a fast complexation kinetics and distri-
bution ratios close to the equilibrium value are reached within
5 minutes of mixing time (Fig. S2, ESIw). Longer mixing times
up to 60 minutes did not show any change, indicating the
formation of strong and stable metal complexes.
Tripodal ligands. The extraction results for the new tripodal
ligands 21 and 23 are shown in Fig. 6 and 7, respectively. The
SFEu/Am for ligand 21 decreases upon raising the pHini of the
aqueous phase. However, a higher selectivity for Eu(III) over
Fig. 5 Structure of 2,20,20 0-nitrilotris(N,N-bis(2-ethylhexyl)acetamide).
Am(III) was obtained at a pHini range of 1–3 compared to
the SFEu/Am of the TODGA system without ligand (dotted
line in Fig. 6). The SFEu/Am = 11.1 (ligand 21 at pHini = 2)
is comparable with the SFAm/Eu = 11.8 obtained for the
lipophilic ligand 2,20,20 0-nitrilotris(N,N-bis(2-ethylhexyl)-
ligands 2, 7a,b, 21, and 23 towards Eu(III) in water at pH 3.
The binding constants and the thermodynamic data are
summarized in Table 2. Dilution experiments with ligands 2,
7a,b, 21 showed negligible heat effects indicating that no
aggregation of the ligands takes place under the conditions
used. For ligand 23 some dilution effect was observed,
however, correcting the DH complexation values for it, no
significant change was observed in the DH versus molar ratio
plot (see ESIw).
From Table 2 it is clear that ligands 2, 7a, and 7b show a
complexation affinity towards Eu(III) in the order 2 4 7a 4 7b.
The stripping efficiency in the back extraction experiments
described above can be explained by the binding efficiency of
the different ligands towards Eu(III). Ligand 2 is the most
efficient ligand as follows from both the extraction results as
well as the ITC experiments. Ligand 2 shows an already
sufficiently good fit for 2 : 1 (ligand: metal) complexation,
however, ligands 7a and 7b show an already sufficiently good
fit for a 1 : 1 stoichiometry, probably due to the lower affinity
observed for these ligands. More importantly and noticeably,
the 1 : 1 complex of ligand 2 shows a relatively low binding
enthalpy compared to ligands 7a and 7b, which is fully
compensated by a strongly positive entropy of binding for
ligand 2. This is attributed partially to co-coordination of the
hydroxyl groups of ligand 2 to the Eu center (associated with a
negative enthalpy and a positive entropy of complexation
acetamide) (24; see Fig. 5) at [HNO3] = 0.01 mol Lꢀ1 18
At
.
these conditions 72% of 241Am and only 19% of 152Eu
remained in the aqueous phase. Over 98 and 92 percent of
radionuclides were not extracted by TODGA at the highest
tested pHini = 4 (241Am and 152Eu, respectively).
The results of the tripodal ligand 23 reveal a similar com-
plexing behavior as ligand 21. Increase of the initial pH of the
aqueous phase increased the metals complexation (Fig. 7),
however, low distribution ratios indicate that more metals
retained in the aqueous phase compared to ligand 21 for
pHini = 3 and 4. This can be partly explained by the different
concentrations of the two ligands, resulting from a poorer
solubility of ligand 21.
The Eu/Am separation factors were almost the same as those
of TODGA in the absence of the ligand. As a matter of fact the
SFEu/Am at pHini = 1 and 2 is even lower than in the reference
experiment (dotted line). In conclusion, ligand 21 shows a good
discrimination for Am(III), while ligand 23 is more efficient in
stripping of Am(III) and Eu(III) simultaneously.
Microcalorimetry
Isothermal microcalorimetry (ITC) experiments were per-
formed to study the difference in the binding strengths of
c
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Fig. 6 Initial pHaq dependency for the extraction of 241Am and 152Eu. Organic phase: 0.2 mol Lꢀ1 TODGA + 5 vol% 1-octanol in TPH.
Aqueous phase: 0.5 mol Lꢀ1 NH4NO3, variable pHini, 0.07 mol Lꢀ1 ligand 21, tracers: 241Am, 152Eu, mixing time: 60 min; T = 22 1C ꢂ 1 1C.
Fig. 7 Initial pHaq dependency for the extraction of 241Am and 152Eu. Organic phase: 0.2 mol Lꢀ1 TODGA + 5 vol% 1-octanol in TPH.
Aqueous phase: 0.5 mol Lꢀ1 NH4NO3, variable pHini, 0.1 mol Lꢀ1 ligand 23, tracers: 241Am, 152Eu, mixing time: 60 min; T = 22 1C ꢂ 1 1C.
observed by Rao et al.26 for malonamide ligands by changing
Table 2 Binding constants and thermodynamic parameters of the
binding of ligands 2, 7a, 7b, 21, and 23 with Eu(III) determined with
microcalorimetry in water at 25 1Ca
the substituents on the amidic nitrogen in acetonitrile. The ITC
experiments performed here indicate that the poorer perfor-
mance of ligand 7b is due to a more negative entropy effect of
binding for ligand 7b compared to 7a.
Ligand K/molꢀ1 DG/kcal molꢀ1 DH/kcal molꢀ1 TDS/kcal molꢀ1
2b
6.4 ꢁ 105 ꢀ7.3 ꢂ 0.7
7.3 ꢁ 103 ꢀ4.9 ꢂ 0.4
2.2 ꢁ 103 ꢀ4.3 ꢂ 0.3
7.1 ꢁ 102 ꢀ3.9 ꢂ 0.1
1.4 ꢁ 103 ꢀ4.2 ꢂ 0.1
3.5 ꢁ 102 ꢀ3.4 ꢂ 0.1
1.5 ꢁ 104 ꢀ5.5 ꢂ 0.2
ꢀ1.0 ꢂ 0.1
ꢀ4.0 ꢂ 0.1
ꢀ3.6 ꢂ 0.4
ꢀ4.1 ꢂ 0.2
4.2 ꢂ 0.1
6.3 ꢂ 0.8
0.9 ꢂ 0.5
0.7 ꢂ 0.7
ꢀ0.2 ꢂ 0.4
8.4 ꢂ 0.3
7.3 ꢂ 0.2
9.1 ꢂ 0.5
The tripodal ligands 21 and 23 show the best fit for 2 : 1 and
1 : 1 (ligand : metal) complexation, respectively, in an endo-
thermic process.27 Ligand 23 has a stronger binding affinity for
Eu(III) than ligand 21 as clearly corresponds with the back
extraction data (vide supra). The ITC data indicate that ligand
21 binds Eu in a 2 : 1 fashion, which is logical because of its
tetradentate nature. The facts that ligand 23 binds stronger but
only shows a 1 : 1 stoichiometry indicate that in this case several
of the ethylene glycol moieties are involved in binding. This is
also witnessed by the more endothermic enthalpy of binding
and more positive entropy of binding, both in agreement with a
higher loss of water from the first coordination sphere.
7a
7b
21b
3.9 ꢂ 0.1
23
3.6 ꢂ 0.3
a
Ligand conc. = 10 mmol L:1, Eu(III) conc. = 0.166 mmol L:1
.
Ligands 2 and 21 show the best fit for 2 : 1 (L : M) complexation, so
b
the thermodynamic parameters are given for both the 1 : 1 (first row)
and 2 : 1 (second row) complexes.
owing to release of first coordination sphere water molecules)
and partially to more negative entropies of binding for ligands
7a and 7b due to restricted degrees of conformational freedom
of the ethylene glycol chains upon complexation. Ligand 7b has
a lower K-value than ligand 7a, which apparently is not high
enough for back extraction (vide supra). The longer glycol
chains on the amidic nitrogens in 7b compared to 7a weaken
the binding capacity of the ligand. A similar effect was
Conclusion
Different types of water-soluble ligands, partly based on
the well-known TODGA and malonamide skeletons, have
successfully been prepared. In most cases they show very good
c
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back extraction properties of Am(III) and Eu(III) from a
TODGA-containing organic phase, dependent on the pH,
however, without selectivity. However, only water-soluble
tripodal ligands 21 and 23 exhibit a promising SFEu/Am
of 11.1 and 5, respectively. It is clearly demonstrated that
microcalorimetry is an efficient method to determine the (trend
in the) extraction efficiency of different ligands.
(2.50 g, 14.4 mmol), benzylamine (0.82 g, 7.7 mmol), K2CO3
(4 g, 29 mmol) and KI (2.5 g) afforded 5b (2.14 g, 75%) as an
oil. dH(300 MHz; CDCl3) 2.90 (4H, t, J 6.0, N(CH2)2),
3.50–3.84 (22H, m, OCH2 and NCH2Ph), 7.20–7.36 (5H, m,
ArH). dC(75 MHz; CDCl3) 50.7, 56.1, 57.9, 66.2, 67.0, 69.5,
122.2, 125.1, 126.0, 135.7; m/z 372.2 (M + H)+. HRMS m/z
372.2046, calculated 372.2386.
2,20-((Azanediylbis(ethane-2,1-diyl))bis(oxy))diethanol
Experimental
(6a)32. A solution of 5a (1.70 g, 6.0 mmol) in methanol (30 mL)
in the presence of 10% Pd/C (0.5 g) was kept under a H2
atmosphere overnight. After removal of the catalyst by filtra-
tion the solvent was evaporated under reduced pressure to
afford 6a (1.03 g, 93%) as an oil. dH(300 MHz; CDCl3)
2.83 (4H, t, J 6.0, N(CH2)2), 3.56–3.63 (8H, m, OCH2), 3.71
(4H, t, J 6.0, CH2OH), 4.04 (2H, br s, OH); m/z 194.1 (M + H)+.
General
All moisture-sensitive reactions were carried out under an
argon atmosphere. The solvents and all reagents were
obtained from commercial sources and used without further
purification. All known compounds viz. 1,28 11,22 18,29
and 2230 were prepared according to literature procedures.
Solvents were dried according to standard procedures and
stored over molecular sieves. 1H NMR and 13C NMR spectra
were recorded on a Varian Unity INOVA (300 MHz) spectro-
meter. 1H NMR (300 MHz) and 13C NMR (75 MHz) chemical
shift values are reported as d using the residual solvent signal
as an internal standard. The IR spectrum was recorded on
a Perkin Elmer Spectrum BX2 spectrometer. Electrospray
Ionization (positive mode) mass spectra and high resolution
mass spectra were recorded on a WATERS LCT mass spectro-
meter. Elemental analyses were performed using a Flash 200
CHN analyzer of Thermo Scientific/Interscience. Analytical
TLC was performed using Merck prepared plates (silica gel 60
F-254 on aluminium). Column chromatography was carried
out on Merck silica gel 60 (230–400 mesh).
3,6,12,15-Tetraoxa-9-azaheptadecane-1,17-diol (6b)33. Com-
pound 6b was synthesized by a similar procedure as described
for 6a. Starting from 5b (1.80 g, 4.8 mmol) and 10% Pd/C
(0.5 g) gave 6b (1.18 g, 87%) as an oil. dH(300 MHz; CDCl3)
2.89 (4H, t, J 6.0, N(CH2)2), 3.56–3.74 (20H, m, OCH2), 4.09
(2H, br s, OH); m/z 282.1 (M + H)+; HRMS 282.1928,
calculated 282.1917.
2,20-Oxybis(N,N-bis(2-(2-hydroxyethoxy)ethyl)acetamide)
(7a). The same procedure was adopted as described for 2.
Starting from 6a (0.80 g, 4.1 mmol), diglycolyl dichloride (1)
(0.35 g, 2.1 mmol), and K2CO3 (1.1 g, 8 mmol) afforded 7a
(0.61 g, 62%). dH(300 MHz; D2O) 3.37 (4H, t, J 6.0,
CONCH2), 3.42–3.47 (12H, m, NCH2 and OCH2), 3.49–3.58
(16H, m, CH2OH), 4.31 (4H, s, OCH2); dC(75 MHz; D2O)
60.6, 67.8, 68.1, 68.5, 71.8, 72.2, 171.7; HRMS m/z 485.2742
(M + H)+, calculated 485.2710.
2,20-Oxybis(N,N-bis(2-hydroxyethyl)acetamide) (2). To a
solution of diethanolamine (0.86 g, 8.2 mmol) in acetone
(50 mL) containing K2CO3 (2.26 g, 16.4 mmol) was added
diglycolyl dichloride (1) (0.68 g, 3.9 mmol) dropwise at 0 1C
and the resulting mixture was stirred overnight at room
temperature, filtered and the solvent was evaporated. The
residue was dissolved several times in CHCl3 (25 mL) and
decanted to remove the excess of diethanolamine to afford 2
(0.85 g, 67%) as an oil. dH(300 MHz; D2O) 3.28 and 3.36
(4H, t, J 6.0, NCH2), 3.56 (8H, m, CH2OH), 4.29 (4H, s, OCH2);
dC(75 MHz; D2O) 48.9, 58.6, 68.5, 171.7; m/z 309.2 (M + H)+.
HRMS 331.1418, calculated 331.1481 (M + Na)+.
2,20-Oxybis(N,N-bis(2-(2-(2-hydroxyethoxy)ethoxy)ethyl)-
acetamide) (7b). The same procedure was adopted as described
for the synthesis of 2. Starting from 7a (0.90 g, 3.2 mmol),
diglycolyl dichloride (1) (0.27 g, 1.6 mmol), and K2CO3 (1.0 g,
7.2 mmol) gave 7b (0.66 g, 63%). dH(300 MHz; D2O) 3.36 (4H, t,
J 6.0, NCH2), 3.42–3.47 (12H, m, NCH2 and CH2OH),
3.49–3.59 (32H, m, OCH2), 4.29 (4H, s, OCH2); dC(75
MHz; D2O) 60.5, 67.8, 68.1, 69.7, 70.2, 71.8, 171.5; HRMS
m/z 661.3782 (M + H)+, calculated 661.3759.
2,20-(((Benzylazanediyl)bis(ethane-2,1-diyl))bis(oxy))diethanol
(5a)31. A mixture of 2-(2-chloroethoxy)ethanol (4a) (2.00 g,
16 mmol), benzylamine (0.86 g, 8.0 mmol), K2CO3 (4 g,
29 mmol), and KI (2.5 g) in DMF (30 mL) was heated at
110 1C overnight. The solvent was evaporated and the residue
was dissolved in ethyl acetate (50 mL) and filtered. The filtrate
was washed with 5% HCl (2 ꢁ 30 mL) and water (2 ꢁ 30 mL),
dried over anhydrous MgSO4, and concentrated under reduced
pressure to give 5a (2.0 g, 77%) as an oil. dH(300 MHz; CDCl3)
2.76–2.86 (4H, m, N(CH2)2), 3.56 and 3.64 (4H, t, J 6.0, OCH2),
3.70 (4H, t, J 6.0, CH2OH), 3.83 (2H, s, NCH2Ph), 7.27–7.45
(5H, m, ArH); m/z 283.9 (M + H)+.
Tetramethyl 2,20,20 0,20 00-((2,20-oxybis(acetyl))bis(azanetriyl))-
tetraacetate (9). To a solution of dimethyl 2,20-azanediyldi-
acetate (1.50 g, 9.3 mmol) in THF (50 mL), containing
triethylamine (1.0 g, 9.9 mmol) as a base was added diglycolyl
dichloride (1) (0.79 g, 4.6 mmol) in THF (15 mL) dropwise at
0 1C. The mixture was stirred at room temperature overnight,
whereupon the solvent was evaporated. The residue was dis-
solved in dichloromethane (50 mL), washed with 10% HCl
(2 ꢁ 40 mL), sat. aq. NaHCO3 (2 ꢁ 40 mL), and water (50 mL)
to afford 9 (1.51 g, 80%) as an oil. dH(300 MHz; CDCl3)
3.72 and 3.75 (6H, s, C(O)OMe), 4.19 and 4.21 (4H, s, NCH2),
4.27 (4H, s, OCH2); dC(75 MHz; CDCl3) 48.2, 49.5, 52.4, 52.5,
52.8, 69.5, 169.5; HRMS m/z 421.1495 (M + H)+, calculated
421.1458.
9-Benzyl-3,6,12,15-tetraoxa-9-azaheptadecane-1,17-diol
(5b). Compound 5b was synthesized by a similar procedure as
described for 5a. 2-(2-(2-Chloroethoxy)ethoxy)ethanol (4b)
c
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Sodium 2,20,20 0,200 0-((2,20-oxybis(acetyl))bis(azanetriyl))tetra-
acetate (10). To a solution of 9 (1.00 g, 2.4 mmol) in a mixture
of MeOH : water (8 : 2) (50 mL) was slowly added NaOH
(0.38 g, 9.5 mmol) and the mixture was stirred at room
temperature for 2 days. The mixture was concentrated to
dryness under reduced pressure to afford pure 10 (1.07 g,
quant.) as a white solid. Mp 284–286 1C. dH(300 MHz; D2O)
3.67 and 3.74 (4H, s, NCH2), 4.18 (4H, s, OCH2); dC(75 MHz;
D2O) 51.6, 68.4, 171.3, 175.7, 176.4; HRMS m/z 453.0160
(M + H)+, calculated 453.0110.
CH6O4P2S2 requires C, 5.8; H, 2.9%). Mp 131–133 1C;
dH(300 MHz; CD3C(O)CD3) 2.99 (2H, t, J 16.5, PSCH2PS),
7.02 (4H, br s, OH); dC(75 MHz; D2O) 57.7; HRMS m/z
208.9297 (M + H)+, calculated 208.9261.
2,20-(Benzylazanediyl)bis(N,N-dimethylacetamide) (19).
A
mixture of 2-chloro-N,N-dimethylacetamide (18) (2.30 g,
18.9 mmol), benzylamine (1.00 g, 9.5 mmol), K2CO3 (5.2 g,
38 mmol) and KI (3 g) in acetonitrile (50 mL) was refluxed for
6 h. The acetonitrile was evaporated and the residue was
dissolved in ethyl acetate (50 mL). The resulting solution
was washed with dil. HCl (3 ꢁ 50 mL) and water (3 ꢁ 50 mL).
The organic layer was dried over anhydrous MgSO4 and con-
centrated under reduced pressure. The residue was purified by
chromatography (SiO2, EtOAc) to afford 21 (4.20 g, 81%) as
an oil. dH(300 MHz; CDCl3) 2.91 and 2.95 (6H, s, NMe2), 3.74
(4H, s, NCH2), 4.02 (2H, s, NCH2Ph); dC(75 MHz; CDCl3) 35.6,
36.9, 55.6, 59.1, 127.5, 128.5, 129.4, 138.3, 170.3; HRMS m/z
278.1875 (M + H)+, calculated 278.1869.
O,O,O0,O0-Tetraethyl(oxybis(methylene))diphosphonothioate
(13). To a solution of diethyl(hydroxymethyl)phosphonate
(0.73 g, 4.3 mmol) in THF (40 mL) was slowly added NaH
at 0 1C portion wise. After stirring at this temperature for 1 h,
a solution of (diethoxyphosphoryl)methyl trifluoromethane-
sulfonate (11) (1.30 g, 4.3 mmol) in THF (15 mL) was added and
stirring was continued overnight at room temperature. The
solvent was evaporated under reduced pressure and the residue
was dissolved in chloroform (30 mL). The resulting solution was
washed with 10% HCl (3 ꢁ 50 mL) and water (3 ꢁ 50 mL). The
organic layer was dried over anhydrous MgSO4 and concen-
trated under reduced pressure, followed by purification of the
residue with chromatography (SiO2, dichloromethane) to afford
12 (1.02 g, 74%) as an oil. dH(300 MHz; CDCl3; Me4Si) 1.32
(12H, t, J 7.0, CH3), 3.85 (4H, d, J 6.0, OCH2P), 4.16 (8H,
pentet, J 7.0, OCH2).34 A solution of 12 (1.00 g, 3.1 mmol) and
Lawesson’s reagent (2.54 g, 6.2 mmol) was refluxed in toluene
for 2 h. After removal of the solvent the residue was separated
by chromatography (SiO2, dichloromethane) to afford 13
(0.87 g, 80%) as an oil. dH(300 MHz; CDCl3) 1.33 (12H, t,
J 7.0, CH3), 4.10 (4H, d, J 3.0, OCH2P), 4.12–4.25 (8H, m,
OCH2); dC(75 MHz; CDCl3) 16.5, 63.3, 72.5, 74.2; HRMS m/z
351.0631 (M + H)+, calculated 351.0619.
2,20-Azanediylbis(N,N-dimethylacetamide) (20). A mixture
of 19 (1.20 g, 4.3 mmol) and 10% Pd/C (0.5 g) in ethanol
(40 mL) was kept under a H2 atmosphere overnight. After
removal of the catalyst by filtration, the solvent was evapo-
rated under reduced pressure to afford 20 (0.80 g, quant.) as a
solid (found C, 51.3; H, 9.0; N, 22.6. C8H17N3O2 requires C,
51.3; H, 9.15; N, 22.4%). Mp 58–60 1C. dH(300 MHz; CDCl3)
2.98 and 3.02 (6H, s, NMe2), 4.22 (4H, s, NCH2); dC(75 MHz;
CDCl3) 35.6, 36,3, 50.1, 170.5; HRMS m/z 188.1411 (M + H)+,
calculated 188.1399.
2,20,200-Nitrilotris(N,N-dimethylacetamide) (21). A mixture
of 20 (0.70 g, 3.7 mmol), 2-chloro-N,N-dimethylacetamide (18)
(0.45 g, 3.7 mmol), K2CO3 (1 g, 7.4 mmol), and KI (0.5 g) in
acetonitrile (30 mL) was refluxed overnight. The acetonitrile
was evaporated and the residue dissolved in ethyl acetate
(50 mL). The resulting solution was filtered and the solvent
evaporated. The residue was dissolved in water (50 mL) and
the solution was extracted with dichloromethane (3 ꢁ 50 mL).
Removal of the water afforded pure 21 (0.74 g, 75%) as an oil.
dH(300 MHz; CDCl3) 2.92 and 3.04 (18H, s, NMe2), 3.62 (6H,
s, NCH2); dC(75 MHz; CDCl3) 35.6, 37.2, 55.9, 60.1, 169.8;
HRMS m/z 295.1741 (M + Na)+ calculated 295.1746.
(Oxybis(methylene))diphosphonic acid (14). A suspension of
13 (0.90 g, 2.5 mmol) in conc. HCl (20 mL) was heated in
a sealed tube at 100 1C overnight. The HCl was evaporated
under reduced pressure. The residue was dissolved in water
(25 mL), and the solution was extracted with chloroform (2 ꢁ
25 mL) to remove non-water soluble impurities. Removal of
the solvent under reduced pressure gave 14 (0.46 g, 70%) as
a dense oil. dH(300 MHz; D2O) 3.62 (4H, d, J 9.0, OCH2);
dC(75 MHz; D2O) 66.9, 69.1; m/z 207.0 (M + H)+; HRMS
m/z 206.9833 (M + H)+, calculated 206.9824.
2,20,200-Nitrilotris(N,N-bis(2-hydroxyethyl)acetamide) (23).
A mixture of triester 22 (2.00 g, 8.5 mmol) and diethanolamine
(2.70 g, 25.7 mmol) was heated as neat at 120 1C for 5 h to give
23 (3.14 g, 81%) as an oil. dH(300 MHz; D2O; Me4Si) 3.31 and
3.39 (6H, t, J 6.0, CONCH2), 3.51–4.01 (18H, m, NCH2 and
CH2OH); dC(75 MHz; D2O); 48.1, 50.1, 55.6, 58.9, 173.0;
HRMS m/z 453.2618 (M + H)+, calculated 453.2561.
Methylenediphosphonothioic dichloride (16). A mixture of
thiophosphoryl chloride (15 mL) and bis(dichlorophosphino)-
methane (1.00 g, 4.5 mmol) was refluxed for 5 h at 115 1C. The
excess of PSCl3 was evaporated under reduced pressure to
afford 16 (1.3 g, quant.). dH(300 MHz; CDCl3) 4.48 (4H, t,
J 15.0, PSCH2PS). In the ESI+ mass spectrum a characteristic
pattern was observed at m/z 278.8, 281.8, 283.8, 285.8
for [M + H]+ that corresponds to the calculated isotopic
abundance of four chlorides.
Microcalorimetry experiments
Calorimetric measurements were carried out in water at pH 3
and 25 1C using a Microcal VP-ITC microcalorimeter with a
cell volume of 1.4115 mL. The pH of the solution was adjusted
by 65% HNO3. For studying the complexation of Eu(III) to
the ligands 2, 7a, 7b, 21, and 23, aliquots of a 10.0 mM
aqueous solution of the ligands in the buret were added to a
0.166 mM solution of Eu(NO3)3 in the calorimetric cell,
Methylenediphosphonothioic O,O-acid (17). A mixture of 16
(1.00 g, 3.5 mmol) in acetone : water (1 : 1) (50 mL) was stirred
at room temperature for 1 h. The solvent was evaporated to
give pure 17 (0.70 g, quant.) as a solid (found C, 5.95; H, 2.65.
c
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monitoring the heat change after each addition. Dilution
experiments showed that at the experimental concentrations
none of the species described above showed significant
aggregation behavior.
5 Z. Kolarik, Chem. Rev., 2008, 108, 4208.
6 H. H. Dam, D. N. Reinhoudt and W. Verboom, Chem. Soc. Rev.,
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7 See: www.acsept.org.
8 Y. Sasaki and S. Tachimori, Solvent Extr. Ion Exch., 2002, 20, 21.
9 Y. Sasaki, Y. Sugo, S. Suzuki and S. Tachimori, Solvent Extr. Ion
Exch., 2001, 19, 91.
Extraction procedure
10 Y. Sasaki and G. R. Choppin, Anal. Sci., 1996, 12, 225.
11 A. Facchini, L. Amato and R. Nannicini, Sep. Sci. Technol., 1996,
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Chem. Lett., 2006, 35, 256.
15 M. Heitzmann, F. Bravard, C. Gateau, N. Boubals, C. Berthon,
All the aqueous solutions were prepared by dissolution of
weighted amounts of the ligand in ultrapure water (resistivity,
18 M O cmꢀ1) containing 0.5 mol Lꢀ1 NH4NO3 (salting-out
agent). The initial pHini of the aqueous phase was adjusted
using ammonia or diluted nitric acid. The organic solvent
consisted of 0.2 mol Lꢀ1 TODGA (extractant) and 5 vol%
1-octanol dissolved in TPH.
The organic phase was not loaded with Am and Eu followed
by stripping as TODGA extracts significant amounts of HNO3
which would prevent obtaining reasonable results at pH 4 1
without using a buffer. Instead each of the aqueous phases
(500 mL) were spiked with 10 mL of radiotracer (241Am, 152Eu,
approx. 25 KBq mLꢀ1) and contacted with the organic solvent
(500 mL) by shaking for 60 min at 22 1C ꢂ 1 1C using an IKA
Vibrax Orbital Shaker Model VXR (2,200 rpm). After phase
separation by centrifugation, 200 mL aliquots of each phase were
withdrawn for radio analysis. The kinetics extraction experi-
ments were performed similarly as described above, except the
phases contact time (mixing time). Activity measurements of the
g-ray emitters were performed with a HPGe spectrometer,
EG–G Ortec using the g-lines at 59.5 keV, and 121.8 keV for
241Am and 152Eu, respectively. The distribution ratio DM was
measured as the ratio between the radioactivity in the organic
and the aqueous phase (eqn (1)). Distribution ratios between
0.01 and 100 exhibit a maximum error of ꢂ5%. The error may
be up to ꢂ20% for smaller and larger values. The acidities of the
initial and final aqueous solutions were determined using a 691
Metrohm pH meter (3 mol Lꢀ1 KCl).
J. Pecaut, M. C. Charbonnel and P. Delangle, Inorg. Chem., 2009,
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19 J. S. Bradshaw, H. An, K. E. Krakowiak, T. Wang, C. Zhu and
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20 In a second attempt diglycolic acid was reacted with diethanol-
amine in THF using DCC as a coupling reagent, however, no
reaction occurred.
21 Reaction of N-benzyl protected diethanolamine with 2-bromo-
ethanol in the presence of NaH as a base was not successful.
22 Y. Xu, M. T. Flavin and Z. Q. Xu, J. Org. Chem., 1996, 61,
7697.
23 M. Fild and W. Handke, Z. Anorg. Allg. Chem., 1987, 555, 109.
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25 T. Yaita, A. W. Herlinger, P. Thiyagarajan and M. P. Jensen,
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26 L. Rao, P. L. Zanonato, P. D. Bernardo and A. Bismondo,
J. Chem. Soc., Dalton Trans., 2001, 1939.
27 Endothermic lanthanide complexes are well known in the
literature: (a) L. Rao, P. L. Zanonato, P. D. Bernardo and
A. Bismondo, Inorg. Chim. Acta, 2000, 306, 49; (b) R. G. de
Carvalho and G. R. Choppin, J. Inorg. Nucl.Chem., 1967, 29, 737.
28 C. Louis, D. M. Christine, P. Claude and T. Pierre, Tetrahedron
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29 J. R. Green, M. Majewski and V. Snieckus, Can. J. Chem., 2006,
84, 1397.
30 L. H. Wei, Y. B. He, J. L. Wu, H. J. Qin, K. X. Xu and L. Z. Meng,
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Acknowledgements
The authors gratefully acknowledge the financial support from
the EU ACSEPT (Actinide reCycling by SEParation and
Transmutation) project (FP7 collaborative project 211267)
and HEC (higher education commission) Pakistan.
31 For another synthetic method see: N. G. Luk’yanenko,
A. V. Lobach, N. Yu. Nazarova, L. P. Karpenko and
L. N. Lyamtseva, Khim. Geterotsikl. Soedin., 1988, 687.
32 For another synthetic method see: A. V. Bordunov, P. C. Hellier,
J. S. Bradshaw, N. K. Dalley, X. Kou, X. X. Zhang and R. M.
Izatt, J. Org. Chem., 1995, 60, 6097.
33 For another synthetic method see: H. Maeda, S. Furuyoshi,
Y. Nakatsuji and M. Okahara, Tetrahedron, 1982, 38, 3359.
34 For a related synthesis and more spectral data see: A. R. P. M.
Valentijn, O. van den Berg, G. A. van der Marel, L. H. Cohen and
J. H. van Boom, Tetrahedron, 1995, 51, 2099.
Notes and references
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2 B. A. Moyer, Ion Exchange and Solvent Extraction: A Series of
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3 C. Musikas, Proceedings of Symposium on Americium and Curium
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This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011