Extraction of technetium(VII) by calix[4]arene tetraketones and tetraesters from acidic and basic media

Article abstract of DOI:10.1023/B:RUCB.0000024840.85337.48

Tetrasubstituted on the lower rim calix[4]arenes, containing carbonyl and ester groups, and existing in a cone conformation are selective and efficient extracting agents for Tc^VII extraction from both acidic and basic solutions.

Full text of DOI:10.1023/B:RUCB.0000024840.85337.48

Russian Chemical Bulletin, International Edition, Vol. 53, No. 1, pp. 127—132, January, 2004
127
Extraction of technetium(VII) by calix[4]arene tetraketones
and tetraesters from acidic and basic media
I. S. Antipin,ꢀa,b S. E. Solovieva,a I. I. Stoikov,b I. S. Vershinina,b
G. A. Pribylova,c I. G. Tananaev,c and B. F. Myasoedovc
aA. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center of the Russian Academy of Sciences,
8 ul. Akad. Arbuzova, 420088 Kazan, Russian Federation.
Fax: +7 (843 2) 73 2253. Eꢀmail: Igor.Antipin@ksu.ru
bKazan State University,
18 ul. Kremlevskaya, 420008 Kazan, Russian Federation.
cV. I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences,
19 ul. Kosygina, 119991 Moscow, Russian Federation.
Fax: +7 (095) 137 6891. Eꢀmail: tananaev@geokhi.ru
Tetrasubstituted on the lower rim calix[4]arenes, containing carbonyl and ester groups, and
existing in a cone conformation are selective and efficient extracting agents for TcVII extraction
from both acidic and basic solutions.
Key words: calix[4]arenes, extraction, technetium.
The intensive development of nuclear energetics and
broadening the scope of exhausted nuclear fuel processꢀ
ing compel the treatment of the radiochemical industrial
wastes. The highly active wastes contain both longꢀlived
β/γꢀemitters (99Тс, 129I, 135Cs, 137Сs, 90Sr) and αꢀemitꢀ
ters (transuranium elements). The development of nuclear
energetics in the Russian Federation assumes to perform
the fractionation of the liquid radioactive wastes containꢀ
ing isotopes of Cs, Sr, Тс, and longꢀlived actinides for
their subsequent separate solidification and disposal. One
of the ways for their extraction from highly active acidic
wastes with a complicated salt composition is extractional
concentrating.1 The data on the selective extraction of
both transuranium elements2—4 and artificial radionuclides
Cs and Sr 4—6 by calixarenes are available from the literaꢀ
ture. The most efficient extracting agents, viz., dicarbolꢀ
lides, crown ethers, and functionalized calixarenes, were
compared7 to show that the latter are more preferential
for cesium extraction from strongly acidic media.
The calixarene molecules provide unique possibilities
for the selective functionalization of the upper and lower
rims of the macrocycle by heteroatomic groups to form a
molecular system with several binding sites and for selecꢀ
tive binding of various ions. The selectivity of ion binding
by calix[4]arenes also depends on the macrocycle conforꢀ
mation: cone, partial cone, or 1,3ꢀ and 1,2ꢀalternate.8
A series of complexation agents based on calix[4]arenes
capable of binding the most diverse cations was syntheꢀ
sized.2,3 The tetrasubstituted on the lower rim calixarenes
containing donor groups, such as the carbonyl, ester, or
amide group, were shown to manifest a high ionophoric
activity toward alkaline metal cations,2,9—12 and the bindꢀ
ing selectivity can change dramatically.11,12 For example,
being in the cone conformation, these compounds effiꢀ
ciently extract Na+ and very poorly extract Cs+, whereas
the 1,3ꢀalternate conformation is characterized by the
strictly opposite properties. The highest Cs+/Na+ selecꢀ
tivity (>30000) was demonstrated by calix[4]crownꢀ6
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 124—129, January, 2004.
1066ꢀ5285/04/5301ꢀ0127 © 2004 Plenum Publishing Corporation

128
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 1, January, 2004
Antipin et al.
ethers 1—3, which combine both the calixarene and crown
ether structures in one molecule.6,13,14 These macrocycles
are presently used for the extraction of the 137Сs isotope
from radioactive wastes in which the Na+ content exceeds
that of the extracted Cs+ ion by several orders of magꢀ
nitude.
on the lower rim for technetium(VII) extraction from acidic
and basic media.
Experimental
1
H NMR spectra of functionalized calix[4]arenes in CDCl3
were recorded on a VarianꢀXLꢀ300 spectrometer, and chemical
shifts were measured relatively to Me4Si as the external stanꢀ
dard. Molecular mass spectra were obtained on a MALDIꢀTOF
Dynamo Finnigan mass spectrometer (1,8,9ꢀtrihydroxyꢀ
anthracene was used as matrix). Solutions of 99Тс and 241Am
in nitric acid, nitric acid (special purity grade), and sodium
hydroxide and nitrate (reagent grade) were used. 1,2ꢀDiꢀ
chloroethane (DCE), the solvent for extraction, was purified
using a known procedure.17 Solutions of reagents in organic
solvents were prepared using exact weighed samples.
5,11,17,23ꢀTetraꢀtertꢀbutylꢀ25,26,27,28ꢀtetrakis[(ethoxyꢀ
carbonyl)methoxy]ꢀ2,8,14,20ꢀcalix[4]arene (4). A mixture of
pꢀtertꢀbutylcalix[4]arene (5 g, 7.7 mmol), ethyl chloroacetate
(9.8 g, 80 mmol), and anhydrous К2CO3 (8.28 g, 60 mmol) in
anhydrous acetone (100 mL) was refluxed under argon for 60 h.
The reaction course was monitored by TLC. Then the precipiꢀ
tate was filtered off and washed with chloroform (2×25 mL).
The solvent and excess ethyl chloroacetate from the joint filꢀ
trates were removed under a reduced pressure. A mixture of
dichloromethane (5 mL) and methanol (35 mL) was added to
the residue. The mixture was left in a refrigerator until crystals
formed (10—12 h). The precipitate was filtered off, washed with
hexane (50 mL), and dried in vacuo. The product as a white
crystalline substance was obtained in 81% yield (6.2 g).
Compound 4, cone conformation, m.p. 154—155 °C (Ref. 9:
154—155 °C). 1Н NMR (CDCl3), δ: 1.07 (s, 36 H); 1.31 (t,
12 H, J = 7.6 Hz); 3.19 (d, 4 H, J = 13.3 Hz); 4.21 (q, 8 H, J =
7.6 Hz); 4.80 (s, 8 H); 4.85 (d, 4 H, J = 13.3 Hz); 6.77 (s, 8 H).
MALDI TOF MS: 1016.3 [M + Na]+. Found (%): С, 72.91;
H, 8.11. C60H80O12. Calculated (%): С, 72.58; Н, 8.06.
5,11,17,23ꢀTetraꢀtertꢀbutylꢀ25,26,27,28ꢀtetrakis(methylꢀ
carbonyl)methoxycalix[4]arene (5). A mixture of pꢀtertꢀbutylꢀ
calix[4]arene (1 g, 1.54 mmol) and anhydrous К2СО3 (1.28 g,
9.25 mmol) in CH3CN was refluxed with stirring for 1 h. Then
αꢀbromoacetone (0.8 mL, 9.25 mmol) was added with vigorous
stirring. The reaction mixture was stirred for 9.5 h at the boiling
point of the solvent. The mixture was filtered through a 1.5ꢀcm
zeolite layer, and the precipitate was washed with chloroform
(3×20 mL). The solvent was removed at a reduced pressure,
1 М HCl (20 mL) and CHCl3 (30 mL) were added to the resiꢀ
due, and the resulting mixture was extracted for 30 min. The
organic layer was separated and dried with MgSO4, and the
solvent was removed. The dry residue was recrystallized from a
CHCl3—EtOH mixture. The product as a white crystalline subꢀ
stance was obtained in 90% yield (1.21 g).
Alkalineꢀearth metal cations (Ca2+, Sr2+, Ba2+) do
not bind with calixarenes functionalized by ester and keꢀ
tone groups,2,3 although they efficiently interact with the
corresponding tetramide.2,5 However, the latter are siꢀ
multaneously efficient extracting agents for sodium catꢀ
ions, which leads to a low Sr2+/Na+ selectivity. The latter
increases sharply on going to calix[6]ꢀ and calix[8]areneꢀ
amides15,16 and, in several cases, exceeds 30000 (for comꢀ
parison, the Sr2+/Na+ selectivity of dicyclohexylꢀ18ꢀ
crownꢀ6 is 47).
Compound 5, cone conformation, m.p. 216—217 °C (Ref. 9:
204—207 °C). 1Н NMR (CDCl3), δ: 1.07 (s, 36 Н); 2.21
(s, 12 Н); 3.18 (d, 4 Н, J = 13 Hz); 4.81 (d, 4 Н, J = 13 Hz);
4.88, 6.80 (both s, 8 Н each). MALDI TOF MS: 896.2
[M + Na]+. Found (%): С, 77.30; H, 8.18. C56H72O8. Calcuꢀ
lated (%): С, 77.03; Н, 8.31.
Procedure of extraction experiments. Solutions of TcVII and
AmIII in nitric acid were placed in tubes with groundꢀglass
stoppers. The concentrations of 99Тс and 241Am were
Published data on the extraction of technetium(VII) by
calixarene derivatives are lacking. In this work, we studꢀ
ied the application of the calix[4]arenes tetrasubstituted

Technetium(VII) extraction by calix[4]arenes
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 1, January, 2004
129
1•10–8—1•10–10 mol L–1. Extraction was carried out by shakꢀ
ing of prepared aqueous solutions with an equal volume (as a
rule, these were 1 cm3 each) of an extracting agent solution in an
organic solvent for 3 min (this time was sufficient for equilibraꢀ
tion). After the phases were separated by centrifuging, aliquots
were taken from each phase to measure the βꢀactivity on a
Protoka installation. These data were used for the calculation of
the partition coefficients (D) of the elements under study. No
formation of a third phase, violation of the activity balance, and
scattering of results were observed in experiments on contact of
solutions of calixarenes in organic solvents with nitric acid.
plane formed by methylene bridges. In this case, the coꢀ
operative interaction of the four binding sites of the host
and guest molecules can occur.
Ligand 4 was synthesized according to a described
procedure9 using cheaper ethyl chloroacetate instead of
ethyl bromoacetate. This replacement did not virtually
change the yield of the product (88 and 81%, respecꢀ
tively). Compound 5 was synthesized in a considerably
higher yield (90%) than that described in the literature9
(51%). This was achieved by the introduction of substanꢀ
tial changes in the procedure of synthesis. Instead of unꢀ
stable iodoacetone formed in situ in acetone from a mixꢀ
ture of chloroacetone and NaI, we used a less active bromo
derivative but the higherꢀboiling solvent (acetonitrile inꢀ
stead of acetone). In addition, to prevent bromoacꢀ
etone decomposition in a basic medium, a mixture of
calix[4]arene with the K2CO3 base was preliminarily stored
at the boiling point, and only then bromoacetone was
added. The conformational structures of macrocycles 4
Results and Discussion
The purpose of this work was to study an application
of calix[4]arenes tetrasubstituted on the lower rim for
technetium(VII) extraction from acidic and basic media.
For this purpose, two ligands containing four beforehand
spatially organized groups on the calix[4]arene platform
were synthesized: 5,11,17,23ꢀtetraꢀtertꢀbutylꢀ25,26,27,28ꢀ
tetrakis[(ethoxycarbonyl)methoxy]ꢀ2,8,14,20ꢀcalix[4]areꢀ
ne (4) and 5,11,17,23ꢀtetraꢀtetraꢀbutylꢀ25,26,27,28ꢀ
tetrakis[(acetyl)methoxy]ꢀ2,8,14,20ꢀcalix[4]arene (5).
1
and 5 were proved by H NMR spectroscopy. The presꢀ
ence of two doublets of the methylene bridging proꢀ
tons indicates unambiguously that compounds 4 (δ 3.19
and 4.85) and 5 (δ 3.18 and 4.81) exist in the cone conforꢀ
mations.8
The extraction ability of the synthesized macrocycles
–
toward the TcVII ion, which exists as the TcO4 perꢀ
technetate anion in aqueous solutions, was studied by the
twoꢀphase extraction in a water—1,2ꢀdichloroethane
(DCE) system. Earlier, technetium was isolated from the
liquid waste of uranium fission products by the extraction
–
of TcO4 by dipolar aprotic solvents (ethyl methyl keꢀ
tone,18 pyridine19). Therefore, a high extraction ability
could be expected for ligands 4 and 5 bearing four carboꢀ
nyl groups on the lower rim of the macrocycle. Logaꢀ
rithms of the partition constants of TcVII (logDTc) beꢀ
tween water or the organic phase, which is a 0.0025 М
solution of ligands 4 and 5 in DCE, at different concenꢀ
trations of acid and base in the extracted solution are
presented in Table 1.
Both synthesized ligands demonstrated a high extracꢀ
tion ability toward the pertechnetate ion. The data obꢀ
tained (Fig. 1) show that in weakly acidic media the exꢀ
traction ability of ligand 5 containing carbonyl groups on
the lower rim is much higher than that of ligand 4. The
partition constants differ more than 50ꢀfold. Thus, the
replacement of the ethoxy group by methyl enhances the
efficiency of TcVII extraction by the calixarene derivatives.
For understanding of this effect, one has to consider
the donor ability of carbonyl and ester groups. To estiꢀ
mate quantitatively this ability, we used the Lewis basiciꢀ
ties of acetone and ethyl acetate, which can simulate the
donor properties of the functional groups present in
the macrocycles under study. For their estimation, the
Kamlet—Taft solvatochromic basicity parameter (β)20
Of possible calix4]arene conformations (cone, partial
cone, and 1,2ꢀ and 1,3ꢀalternates), for extraction studies
we chose the cone conformation in which all four funcꢀ
tional groups are arranged on one side from the macrocycle
along with the Gutman (DN or ∆H 0
(donor numꢀ
SbCl
5

130
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 1, January, 2004
Antipin et al.
Table 1. Logarithms of the partition constants
of TcVII (logDTc) in the system of water and a
0.025 М solution of ligands 4 and 5 in DCE at
different concentrations of acid and base
logDTc
1.2
1.0
0.8
0.6
0.4
0.2
0
[HNO3]
[NaOH]
logDTc
mol L–1
4
5
0.001
0.01
0.1
0.5
1
3
5
—
—
—
—
—
—
—
—
—
0.001
0.028
0.01
1
0.51
0.26
0.02
0.004
–0.07
–0.32
–0.72
0.39
—
1.22
—
0.928
0.658
–0.11
–0.7
0.67
1.29
2.31
>4
–0.2
–2.5
–2.0
lg[5]/[mol L–1
]
Fig. 2. Extraction of TcVII from 0.01 М solutions of HNO3 by
solutions of calix[4]arene 5 in dichloroethane as a function of
the ligand concentration.
0.4
0.97
2.56
from 10–3 М to 5 М the partition coefficients DTc deꢀ
crease and become the same at the 5 М acid concentraꢀ
tion (Fig. 2). This behavior can be explained in the frameꢀ
work of the following scheme of interaction. Extraction
proceeds via the protonation of one of the carbonyl groups
of macrocycles 4 and 5, and the other donor sites are
likely also involved in the coordination of the perꢀ
technetate anion. This conclusion seems valid, because
—
—
ber))21 and Maria—Gal22 (∆H 0 ) calorimetric scales
BF
were used. The latter characterize 3the energy of donorꢀ
acceptor interactions and are determined as a change in
the enthalpy upon the formation of the 1 : 1 adduct beꢀ
tween the Lewis acid (SbCl5 or BF3) and an electron pair
of the donor compound. The Lewis basicities of acetone
and ethyl acetate determined relatively to the soft acid
aliphatic ketones in this concentration (0.025 mol L–1
)
do not extract TcVII to the organic phase. In other words,
the ionꢀpair mechanism of extraction can take place in
which the protonated form of the extracting agent acts as
a cation capable of additional binding the anion due to
the interaction with the beforehand organized donor sites.
The influence of acidity can be related to two factors.
First, the pertechnetate ion concentration decreases beꢀ
cause of the transition to the HTcO4 molecule with an
increase in the medium acidity. Second, the protonation
of the donor sites of the ligands begins with an increase in
the acid concentration, and their ability to bind TcVII
decreases gradually. The more donor methyl ketone group
is protonated more efficiently and, as a result, the differꢀ
ence in the DTc constants decreases and becomes zero at a
concentration of 5 mol L–1. In this case, all donor sites of
the macrocycles under study are completely protonated,
and their complexation ability becomes equally low.
To reveal the composition of complexes formed in the
organic phase, we determined the dependence of the DTc
values on the concentration of ligand 5 at [HNO3] =
0.01 mol L–1. In the interval of ligand concentrations
from 0.0025 to 0.025 mol L–1, the DTc values change
from 0.63 to 16.6. In the logDTc—log[L] coordinates, this
dependence is described by a straight line with the slope
close to 1, which indicates that the 1 : 1 complex between
macrocycle 5 and ТсVII is formed in the organic phase.
This result is quite expected, because the cone conformaꢀ
tion is mostly characterized by 1 : 1 complexes with ions.
The extraction of americium(III) as a representative of
a transuranium element was studied for the estimation of
SbCl5 (∆H 0
5) are virtually the same (–71.3 and
SbCl
–71.5 kJ mol–1, respectively).21 The published data20,22
show that the ethoxycarbonyl group interacts with the
Lewis acid much more weakly than the methylcarbonyl
group does. Both the β (0.48 and 0.45) and ∆H 0
BF
3
(–76.03 and –75.55 kJ mol–1, respectively) parameters
for acetone are somewhat higher than those for ethyl acꢀ
etate. Thus, the increase in the extraction ability of comꢀ
pound 5 over that of compound 4 can be attributed to an
increase in the donor ability of the ligand groups arranged
on the lower rim of calix[4]arene.
The study of the influence of the nitric acid content in
the aqueous phase on technetium(VII) extraction by soluꢀ
tions of calix[4]arenes 4 and 5 showed that in the region
logDTc
1.0
4
5
0.5
0
–0.5
1
2
3
[HNO3]/mol L–1
Fig. 1. Partition coefficients of Тс (DTc) for extraction by 0.025 М
solutions of calix[4]arenes 4 and 5 in dichloroethane as funcꢀ
tions of the HNO3 concentration in the aqueous phase.

Technetium(VII) extraction by calix[4]arenes
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 1, January, 2004
131
Table 2. Extraction of TcVII as a
concentration of ligand 5 in DCE
counterion formed due to the complexation of the lipoꢀ
phylic cation. Our data on the influence of the salt backꢀ
ground on ТсVII extraction confirm the proposed extracꢀ
tion mechanism. The introduction of the competitive niꢀ
trate anion into the aqueous phase decreases the partition
coefficients. For example, for the extraction of techꢀ
netium(VII) by solutions of ligand 4 from (1 М NaOH +
+ 1 M NaNO3) solutions DTc = 142, while for the extracꢀ
tion from (1 М NaOH + 2 M NaNO3) solutions DTc = 102.
For ligand 5, DTc are 118 and 108, respectively, under the
same conditions. As can be seen, the influence of nitrate
anion on DTc is not too significant. Even with a manifold
excess of nitrate anions (>8—10 orders of magnitude), the
partition coefficients remain high (>100). In both basic
and acidic media, AmIII is not extracted by compounds 4
and 5 (DAm < 0.02).
[5]
/mol L–1
log[5] logDTc
0.0025
0.005
0.01
0.02
0.025
–2.6
–2.3
–2.0
–1.7
–1.6
–0.2
0.32
0.68
1.05
1.22
the selectivity of extraction of radioactive waste by
ligands 4 and 5. It turned out that AmIII is not extracted at
all under these conditions. Taking into account the availꢀ
able published data on the extraction of cesium and stronꢀ
tium,5,6,13—16 one can assert that the calix[4]arene derivaꢀ
tives under study are selective and efficient extracting
agents for TcVII extraction from radioactive solutions with
the acid content below 1 М.
Our experiments showed that in a basic medium both
reagents under study are characterized by the extremely
high extraction ability toward pertechnetate ions. For exꢀ
ample, for compound 4 containing the ester group an
increase in the NaOH concentration from 0.001 to 1 М
during Tc extraction increases DTc from 2.4 to 360,
whereas for compound 5 bearing the methyl ketone group
DTc increases from 4.6 to 100% (DTc > 4) of extraction
under the same conditions (Fig. 3).
The increase in the DTc partition coefficients with an
increase in the alkali concentration in the aqueous phase
can indicate the ionꢀpair mechanism of pertechnetate
anion extraction by the ligands studied. These macrocycles
in the cone conformation are known to efficiently bind
the sodium cation9 due to the inclusion of the sodium
cation suitable in size into the pseudoꢀcavity formed by
eight oxygen atoms on the lower rim of the macroꢀ
cycle. Therefore, calixarenes 4 and 5 bind Na+, and the
pertechnetate anion moves to the organic phase as a
Thus, the present studies showed that the calix[4]areꢀ
nes tetrasubstituted on the lower rim and containing carꢀ
bonyl and ester groups are selective and efficient extractꢀ
ing agents for TcVII extraction from both acidic and basic
radioactive solutions.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 02ꢀ03ꢀ
32934), the President of the Russian Federation (Proꢀ
gram for Support of the Leading Scientific Schools, Grant
NShꢀ2030.2003.3), the Program "Fundamental Research
and Higher Education" (Grant RECꢀ007), the Program
of Fundamental Research of the Presidium of the Russian
Academy of Sciences "Fundamental Problems of Physics
and Chemistry of Nanodimensional Systems and Nanoꢀ
materials," and the Welfare Foundation for Support of
Domestic Science.
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Received November 4, 2003;
in revised form January 14, 2004