Ionic liquid-type crown ether as a novel medium for a liquid/liquid extraction of radioactive metal ion85Sr2+

Article abstract of DOI:10.1246/cl.2006.1024

1,13-Dichloro-4,7,10-trioxatridecane (2-[2-(1-chloro-2-ethoxy)ethoxy]ethyl chloride) (3a) was synthesized by a chlorination of 1,13-dihydroxy-4,7,10- trioxatridecane (triethylene glycol). And it was treated with imidazole and sodium ethoxide to give the 1N,1N′(oxoethylene)-diimidazole (3b), which was then converted to ionic liquid-type crown ether (ILCE) 3 with a reaction with 1,9-dichloro-3,6-trioxaoctane (2a). Further, the anion of ILCE was exchanged by an anion-exchange method. Ultimately, we developed a very efficient synthetic pathway for ILCEs 1-4 which have various physical and chemical characteristics by a modification of the polyethylene glycol chain length and anions. ⁸⁵Sr²⁺ was successfully extracted into the [(3,2)O_EtIm][Cl] (3) phase, but it was not extracted into the [(2,2)O_EtIm][Cl] (1), [(3,3)O_EtIm][Cl] (2), and [(4,3)O_EtIm][Cl] (4) phases. Copyright

Full text of DOI:10.1246/cl.2006.1024

1024
Chemistry Letters Vol.35, No.9 (2006)
Ionic Liquid-type Crown Ether as a Novel Medium for a Liquid/Liquid Extraction
of Radioactive Metal Ion 85Sr2þ
Sang Hyun Park,ꢀ1 Dorjnamjin Demberelnyamba,2 Seung Ho Jang,1 and Myung Woo Byun1
1Korea Atomic Energy Research Institute, 1266 Sinjeong-dong, Jeongeup, Jeonbuk 580-185, Korea
2Pai Chai University, 14 Yeonja-1-gil, Seo-gu, Daejeon, 302-735, Korea
(Received June 19, 2006; CL-060696; E-mail: parksh@kaeri.re.kr)
1,13-Dichloro-4,7,10-trioxatridecane (2-[2-(1-chloro-2-
attracted much attention as recyclable media for an organic syn-
thesis and a solute–solvent interaction.3,11–13 They are consid-
ered as green solvents since they are non-volatile, non-flamma-
ble, non-toxic, thermally stable, and recyclable. Limited solubil-
ity of ionic species in nonionic organic solvents is the main prob-
lem associated with conventional solvent extractions. Therefore,
a synthesis of new ionic liquid-type crown ethers was performed
for a liquid/liquid extraction of metal ions. The new crown
ethers have a large polyoxyethylene ring, which is capable of in-
teracting with metal ions to produce a complex of associates.
Certain modifications can be made to produce a molecule
designed for optimal results for specific applications. The goal
is a development of novel sequestering agents to achieve the
extreme selectivity required to extract specific radionuclides.
Polyethylene glycol in benzene was treated with pyridine
and thionyl chloride to give compounds 1a–4a. A solution of
imidazole (0.20 mol) in 100 mL of absolute ethanol was treated
with compounds 1a–4a (0.10 mol) and sodium ethoxide. The
mixture was stirred and refluxed for 6 h to give compound 1b–
4b. And compound 1b–4b (0.20 mol) in 250 mL of anhydrous
acetonitrile was treated with 0.20 mol of compounds 1a–4a to
give compound 1–4 in good yields (Scheme 1). Instrumental
analyses confirmed the chemical structure of the target com-
pounds 1a and 3.14
ethoxy)ethoxy]ethyl chloride) (3a) was synthesized by a chlori-
nation of 1,13-dihydroxy-4,7,10-trioxatridecane (triethylene
glycol). And it was treated with imidazole and sodium ethoxide
to give the 1N,1N0-tris(oxoethylene)-diimidazole (3b), which
was then converted to ionic liquid-type crown ether (ILCE) 3
with a reaction with 1,9-dichloro-3,6-trioxaoctane (2a). Further,
the anion of ILCE was exchanged by an anion-exchange method.
Ultimately, we developed a very efficient synthetic pathway
for ILCEs 1–4 which have various physical and chemical chara-
cteristics by a modification of the polyethylene glycol chain
length and anions. 85Sr2þ was successfully extracted into the
[(3,2)OEtIm][Cl] (3) phase, but it was not extracted into the
[(2,2)OEtIm][Cl] (1), [(3,3)OEtIm][Cl] (2), and [(4,3)OEtIm][Cl]
(4) phases.
The interest for radiopharmaceuticals for the treatment of
serious illness such as cancer and rheumatism has increased
during the last decade. Radioisotopes of 90Sr, 186Re, 153Sm,
90Y, and 166Ho are currently used in the routine practice of
medical clinics. 89Sr1 is a radionuclide which has been used
for a palliative treatment of bone cancers and a treatment of
prostate cancer. 90Sr is a parent nuclide of 90Y-generator which
is being used as a radiotherapeutic nuclide.2 Accordingly, many
methods for these radioisotope extractions have been proposed
with the growth of nuclear medicine. The 89=90Sr can be extract-
ed by using crown ethers. The crown ethers 18-crown-6 (18C6),
dicyclohexano-18-crown-6 (DCH18C6), and 4,40-(50)-di-(tert-
butylcyclohexano)-18-crown-6 (Dtb18C6) have been studied
for an extraction of Sr2þ from aqueous solutions.3 In the absence
of an extractant, the distribution ratio for the metal ion indicates
a strong preference for the aqueous phase. In a typical liquid/
liquid extraction experiment, the crown ether resides in the hy-
drophobic extraction phase and serves to dehydrate and complex
the metal ions while removing them from the aqueous phase.4,5
To enhance the efficiency of such a process, an organic solvent is
selected to sustain the biphasic system while maximizing the hy-
drophobic and complexing properties of the extracting phase.
However, the volatile organic compounds (VOCs) commonly
employed in traditional liquid/liquid separations can have high
hazard ratings and low flash points, indicating associated health
and safety concerns. While liquid/liquid separations by utilizing
VOC diluents have extensive applications in industry from
chemical synthesis to an hydrometallurgy, the end result of
such practices often generates volumes of contaminated solvent.
Ending the reliance on separations that consume large quantities
of VOCs has become a target area for an emphasis in the devel-
opment of ‘‘Green’’ industrial processes that are inherently safer
and are less polluting.6–10 In recent years, ionic liquids have
The ring size of the ILCEs can be regulated by an increase of
the ether chain length.
Physical characteristics of ILCE can be regulated by the
anion-exchange reactions. Sodium trifluoroacetate was added
to a solution of the [(2,2)OEtIm][Cl] (1) prepared above in
acetone. This mixture was stirred at room temperature for
O
O
SOCl2
EtONa
EtOH
a
a
+
N
N H
2
Pyridine
OH
HO
Cl
Cl
1a£- 4a
O
a
CH3CN
N
N
N
+
1a£- 4a
N
1b£- 4b
O
a
1 : a, b = 2, 2 ; X- = Cl-
2 : a, b = 3, 3 ; X- = Cl-
3 : a, b = 3, 2 ; X- = Cl-
4 : a, b = 4, 3 ; X- = Cl-
Cl-
N
Cl-
N
+
+
N
N
O
b
[(a,b)OEtIm] [Cl]
Scheme 1. Synthesis of [(a,b)OEtIm][Cl].
Copyright ꢀ 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.9 (2006)
1025
D
Table 1. Distribution of 85Sr (Bq)
O
O
O
O
O
O
Distribution of 85Sr (Bq)
-
-
'-
'-
Cl
N
+
Cl
N
+
X
N
X
N
ILCE
MX'
+
+
Aqua layer
ILCE layer
N
N
N
N
[(2,2)OEtIm][Cl] (1)
[(3,3)OEtIm][Cl] (2)
[(3,2)OEtIm][Cl] (3)
[(4,3)OEtIm][Cl] (4)
390
323
17
No detection
No detection
356
0
0
21
0
O
O
1
5
369
No detection
Scheme 2. Synthesis of ILCE by anion-exchange reaction.
other radionuclides or heavy metals. The ionic liquid-type crown
ethers obtain their selectivity through their ability to fine-tune
and reorganize their crown ether structure and the resulting
properties of the crown by changing their ring size and rigidity,
changing their number and type of donor atoms, appending
ionizable groups, and modifying their lipophilicity.
24 h. Other anion substituted ILCEs can be prepared in the same
ꢁ
way as 5 from AlCl4ꢁ, Al2Cl7ꢁ, BF4ꢁ, SbF6ꢁ, NO3ꢁ, HSO4
CF3SO3ꢁ, and (CF3SO3)2Nꢁ (Scheme 2).
,
85Sr was produced at the HANARO research reactor
(30 MW) installed at the Korea Atomic Energy Research Insti-
tute by a neutron irradiation of a capsulated 84SrCO3 target for
24 min at a neutron flux (2:5 ꢂ 1013 n/cm2ꢃs). And it was cooled
for 24 h and dissolved in deionized water and 1 M nitric acid.
The radionuclidic purity of the 85Sr was estimated by a ꢀ-ray
spectrometry (GEM-10175 HPGe Detector coupled to a Multi-
Channel Analyzer, ORTEC, Oak Ridge, TN, U.S.A.). A typical
ꢀ-ray spectrum obtained from the HPGe detector shows photo-
peaks due to the ꢀ-rays of 85Sr and 87mSr. The 514.0 and 388.4
keV photopeaks were used for the assay. The initial specific
activity of 85Sr was 189 Bq/mg. The radioactivity was measured
by using an ionizing chamber (Capintec 15R, BIODEX Atomlab
200, NY, U.S.A.) by setting the calibration value for 85Sr which
was corrected and calibrated by the manufacturer.
Metal ion distribution ratios were determined by mixing
1 mL of ILCE and 1 mL of aqueous phase followed by vortexing
(2 min) and centrifuging (2000 g, 2 min) to equilibrate the phas-
es. Addition of the metal ion tracer (ca. 407 Bq, 5 mL) was fol-
lowed by two intervals of a vortexing (2 min) and a centrifuging
(2000 g, 2 min) to ensure that the phases were fully mixed and
separated. The phases were separated and dispensed into shell
vials from which 100 mL of each phase was removed for a
radiometric analysis. Because equal volumes of both phases
were removed for an analysis, the distribution ratio (D) for the
metal ions was determined as follows:
This work was supported from the Korean Ministry of
Science and Technology.
References and Notes
`
1
2
3
4
C. Cipriani, G. Atzei, G. Argiro, S. Boemi, S. Shukla, G.
Rossi, A. F. Sedda, Eur. J. Nucl. Med. 1997, 24, 1356.
D. J. Wood, S. Elshani, H. S. Du, N. R. Natale, C. M. Wai,
Sep. Anal. Chem. 1993, 65, 1350.
A. E. Visser, R. P. Swatloski, W. M. Reichert, S. T. Griffin,
R. D. Rogers, Ind. Eng. Chem. Res. 2000, 39, 3596.
J. S. Bradshaw, R. M. Izatt, A. V. Bordunov, C. Y. Zhu,
J. K. Hathaway, Comprehensive Supramolecular Chemistry,
Oxford, 1996, Vol. 1, Molecular Recogition, 39.
B. A. Moyer, Comprehensive Supramolecular Chemistry,
Oxford, 1996, Vol. 1, Molecular Recogition, 377.
S. Adler, E. Beaver, P. Bryan, J. E. L. Rogers, S. Robinson,
C. Russomanno, Vision 2020: 1998 Separations Roadmap,
American Institute for Chemical Engineers, New York,
1998.
5
6
7
8
Green Chemistry: Theory and Practice, ed. by P. T. Anastas,
J. Warner, Oxford University Press, 1998.
Synthesis and Processing with Alternative Resources Road-
mapping Workshop Report, Department of Energy, Office
of Industrial Technologies, Washington DC, 2000.
T. E. Long, M. O. Hunt, Solvent-Free Polymerizations and
Processes: Minimization of Conventional Organic Solvents,
ACS Symposium Series 713, American Chemical Society,
Washington DC, 1998.
Activity in the ILCE lower phase
D ¼
:
ð1Þ
Activity in the aqueous upper phase
9
Each experiment was done in duplicate and the results
agreed to within 5%.
85Sr2þ was successfully extracted into cyclo-{1N,1N0-[(3,
6,9-trioxa)-1,11-undecyl]}-{3N,3N0-[(3,6,-dioxa)-1,8-octyl]}di-
imidazolium chloride {[(3,2)OEtIm][Cl] (3)} phase, but it was
not extracted into [(2,2)OEtIm][Cl] (1), [(3,3)OEtIm] [Cl] (2)
and [(4,3)OEtIm][Cl] (4) phases (Table 1).
10 J. Sherman, B. Chin, P. D. T. Huibers, R. Garcia-Valls, T.
Alan Hatton, Environ Health Perspect. 1998, 106, 253.
11 D. Sheng, Y. H. Ju, C. E. Barnes, J. Chem. Soc., Dalton
Trans. 1999, 1201.
´ `
12 O. B. Helene, M. Lionel, J. Mol. Catal. A: Chem. 2002, 182–
183, 419.
Novel ILCEs which are non-toxic, recyclable, and econom-
ical are synthesized and employed for an efficient extraction of
85Sr. The new imidazolium ionic liquid-type crown ethers de-
scribed here posses polyoxyethylene (POE) substituent groups.
Their increased density should a1low the imidazolium cores to
adhere more tightly in order to maximize an interaction. ILCEs
have been found to behave like a multifunctional compound
which discriminates a metal cation according to its ring size.
Also, the ILCEs are expected to be used for an extraction of
13 A. E. Visser, R. P. Swatloski, W. M. Reichert, R. Mayton, S.
Sheff, A. Wierzbicki, J. H. Davis, Jr., R. D. Rogers, Environ.
Sci. Technol. 2002, 36, 2523.
14 1H NMR (CDCl3) of 1a: 3.56–3.58 (m, 4H, OCH2), 3.64–
3.78 (m, 8H, OCH2), 3.78 (t, 4H, J ¼ 4:5 Hz, CH2Cl).
1H NMR (CDCl3) of 3: 3.48–4.01 (m, 20H), 4.61 (t, 8H,
J ¼ 4:5 Hz), 6.91 (d, 4H, J ¼ 1:8 Hz), 7.41 (s, 2H).
Published on the web (Advance View) August 12, 2006; doi:10.1246/cl.2006.1024