S(ae

ESa

b

c

d

a

ARR2A

KPSL4p

1

aaqepcl[c[gt

1d

Separation and Purification Technology 64 (2008) 170–175

Contents lists available at ScienceDirect

Separation and Purification Technology

journa l homepage: www.e lsev ier .com/ locate /seppur

ynthesis of octa(1,1,3,3-tetramethylbutyl)octakisdimethylphosphinoylmethyleneoxy)calix[8]arenend its application in the synergistic solventxtraction and separation of lanthanoids

mil Tasheva,∗, Maria Atanassovab, Sabi Varbanovc, Tania Toshevaa,toycho Shenkova, Anne-Sophie Chauvind, Ivan Dukovb

Institute of Polymers, Bulgarian Academy of Sciences, Acad. G. Bonchev str., bl. 103A, Sofia 1113, BulgariaUniversity of Chemical Technology and Metallurgy, Department of General and Inorganic Chemistry, 8 Kl. Okhridski bl, Sofia 1756, BulgariaInstitute of Organic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev str., Bl. 9, Sofia 1113, BulgariaEcole Polytechnique Federale Lausanne, Laboratory of Lanthanide Supramolecular Chemistry, BCH 1401, 1015 Lausanne, Switzerland

r t i c l e i n f o

rticle history:eceived 14 July 2008eceived in revised form3 September 2008ccepted 25 September 2008

a b s t r a c t

A new lower rim substituted calix[8]arene bearing eight phosphine oxide moieties has been syn-thesized. The structure of 5,11,17,23,29,35,41,47-octa(1,1,3,3-tetramethylbutyl)-49,50,51,52,53,54,55,56-octakis(dimethylphosphinoylmethyleneoxy)calix[8]arene (S) was identified and confirmed by elementalanalysis, IR-, 1H, 13C and 31P-{1H} NMR spectroscopy as well as by ES-mass spectrometry.

The synergistic solvent extraction of five selected lanthanoid ions (La3+, Nd3+, Eu3+, Ho3+ and Lu3+) with

eywords:hosphorus-containing calix[8]areneynergistic solvent extractionanthanoids-Benzoyl-3-methyl-1-phenyl-5-yrazolone

4-benzoyl-3-methyl-1-phenyl-5-pyrazolone (HP) and S in chloroform has been studied. It was foundthat in the presence of this phosphorus-containing calix[8]arene the lanthanoids have been extractedas LnP3·S. On the basis of the experimental data, the values of the equilibrium constants have beencalculated. The influence of the synergistic agent (S) on the extraction process has been discussed.A synergistic effect of about three orders of magnitude occurs in the extraction of Ln(III) with themixture of HP and S. The values of the separation factors between the adjacent elements have been

snefall

bs

evaluated.

. Introduction

In the last years the calix[n]arenes are of particular interests metal ion receptors [1]. They possess excellent coordinationnd extraction capabilities [2–5] in addition to being ade-uate platforms for the design of catalysts [1]. Because of theirasy functionalization both at the wide and narrow rims withhosphorus-containing moieties, calixarenes continue to attractonsiderable attention, especially in view of their potential use asigands for extraction and recovery of metals from nuclear wastes6–8]. The use of calixarenes in analytical chemistry and separation

hemical technology has been discussed in the review of Ludwig9]. It was noted that the cavity size, the position and kind of donorroups and the molecular flexibility have a pronounced impact onhe complexation properties as well as the extraction power and

∗ Corresponding author.E-mail address: tashev@polymer.bas.bg (E. Tashev).

itp55aoL

383-5866/$ – see front matter © 2008 Elsevier B.V. All rights reserved.oi:10.1016/j.seppur.2008.09.011

© 2008 Elsevier B.V. All rights reserved.

electivity. The solvent extraction of trivalent lanthanoid and acti-oid ions has been investigated by Ludwig et al. [10,11], Arnaud-Neut al. [5,12–15] and Roundhill and Shen [16]. The influence of variousactors on the extraction process has been discussed. Kuznetsova etl. [17–19] have studied the synergistic solvent extraction of someanthanoid ions with calix[4]resorcinarene or its alkylaminomethy-ated derivatives in the presence of 1,10-phenanthroline.

Using mixtures of conformers of tetrathiocalixarene and dicar-ollide, Kyrs et al. [20,21] have observed synergistic effect in theolvent extraction of Eu(III).

It is therefore of interest to test various extractant combinationsncluding calix[n]arenes in order to determine the factors governinghe extraction efficiency and selectivity of the lanthanoid ions. Theresent work is devoted to the synthesis and characterization of

,11,17,23,29,35,41,47-octa(1,1,3,3-tetramethylbutyl)-49,50,51,52,3,54,55,56-octakis(dimethylphosphinoylmethyleneoxy)calix[8]rene (S) and to its use as synergistic agent in the solvent extractionf five representative lanthanoid ions (La3+, Nd3+, Eu3+, Ho3+ andu3+) with 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone, HP. It

rificati

ip

2

2

eoiK

p

ppAr

2

P

s

soCfN

u4w

MmG

sf

2

acecuowtrd2

m

---

2bm

msmawwrpwrtrN1ntI129

3

3

sIiAw25o

(v

wd(w

m

g

3nsstr

t

E. Tashev et al. / Separation and Pu

s a part of systematic investigations on syntheses [22–25] androperties of phosphorus-containing calix[n]arenes.

. Experimental

.1. Reagents

The starting calix[8]arene I was synthesized according to the lit-rature procedures [26,27]. Xylene was distilled over Na and storedver molecular sieves 4 Å (Merck). Methanol was distilled after dry-ng by a procedure with Mg. TLC was done using plates coated withieselgel 60 F254 (Merck).

The commercial product 4-benzoyl-3-methyl-1-phenyl-5-yrazolone, HP (purity > 99%, Fluka) was used as received.

Stock solutions of La(III), Nd(III), Eu(III), Ho(III) and Lu(III) wererepared by dissolving appropriate amounts of their oxides (Fluka,uriss) in hydrochloric acid. The diluent was CHCl3 (Merck, p.a.).rsenazo III (Fluka) was of analytical grade purity as were the othereagents used.

.2. Apparatus

Melting point (uncorrected) was determined on a BoetziusHMK05 microheating plate apparatus.

The IR spectrum was measured on Mattson Alpha Centaury FTpectrometer as KBr pellet.

1H NMR spectrum was recorded on DRX Avance Bruker 400pectrometer in DMSO-D6, 31P{1H} NMR spectrum was registeredn the same instrument at 161.9 MHz in DMSO-D6 as solvent.hemical shifts were measured relative to TMS as internal standard

or 1H and 13C or H3PO4 (85%) as external standard for 31P{1H}. 13CMR spectrum was recorded at 100.6 MHz in CDCl3.

The ES-MS was performed on a Finnigan SSQ 710C spectrometersing a capillary temperature of 200 ◦C and acceleration potential of.5 kV. The solution of the substance in methanol (10−4 mol dm−3)as infused in a mixture of CH3OH/H2O/HCOOH (50:50:1, v/v).

The elemental analysis was carried out by Dr. H. J. Eder from theicrochemical Laboratory of the University of Geneva (for deter-ination of C and H) and by Ilse Beetz Laboratory (96301 Kronach,ermany) for determination of the phosphorus content.

S-20 Spectrophotometer Boeco (Germany) was used for mea-uring absorbances. A pH 211 HANNA digital pH meter was usedor the pH measurements.

.3. Extraction procedure

The experiments were carried out using 10 cm3 volumes ofqueous and organic phases. The samples were shaken mechani-ally for 45 min at room temperature which was sufficient to reachquilibrium. After the separation of the phases, the metal con-entration in the aqueous phase was determined photometricallysing Arsenazo III [28]. The concentration of the metal ion in therganic phase was obtained by mass balance. These concentrationsere used to calculate the distribution coefficient. The acidity of

he aqueous phase was measured by a pH meter with an accu-acy of 0.01 pH unit. The ionic strength was maintained at 0.1 molm−3 with (Na, H)Cl. The initial concentration of the metal ions was.5 × 10−4 mol dm−3 in all experiments.

The distribution coefficients of the lanthanoid ions were deter-

ined in three series of experiments, viz.:

with fixed HP and S concentrations, and varied pH;with fixed pH and S concentration, and varied HP concentration;with fixed pH and HP concentration, and varied S concentration.

2wP1

on Technology 64 (2008) 170–175 171

.4. Synthesis of 5,11,17,23,29,35,41,47-octa(1,1,3,3-tetramethyl-utyl)-49,50,51,52,53,54,55,56-octakis(dimethylphosphinoyl-ethyleneoxy)calix[8]arene

To a solution of NaOCH3 (Na, 0.317 g, 13.8 mmol, in 30 ml dryethanol) at room temperature, under argon atmosphere and

tirring was added at once 5,11,17,23,29,35.41,47-octa(1,1,3,3-tetra-ethylbutyl)-49,50,51,52,53,54,55,56-octakis(hydroxy)calix[8]

rene (I) (2.61 g, 1.5 mmol) and 50 ml dry xylene. The solutionas stirred 30 min at room temperature and then the methanolas removed via distillation. The resulting mixture was heated to

eflux and then a warm solution of chloromethyldimethylphos-hineoxide (CMDMPO) (2.28 g, 18 mmol) in 30 ml dry xyleneas added via a dropping funnel by drops for 10 min. After 20-h

eflux, the reaction mixture was cooled to room temperaturehen NaCl was filtered off, the filtrate was evaporated and theesulting product was dissolved in chloroform. The residualaCl was filtered off again, the filtrate was washed twice withmol dm−3 HCl solution followed by washing with water to theeutral reaction. The chloroform solution was dried over Na2SO4,hen was evaporated on a rotary evaporator and a crude productI yielded was obtained (3.2 g, 86%). It was recrystallized from a:5 dichloromethane/hexane mixture giving white crystals (m.p.95–300 ◦C). Calc. for C144H232O16P8·3H2O; C, 68.60; H, 9.51; P,.83; found: C, 68.51; H, 9.66; P, 9.42.

. Results and discussion

.1. Characterization of the phosphorylated calix[8]arene

The phosphorylated calix[8]arene S was obtained in a two-tep procedure. First, the OH groups of the initial calix[8]arene(Scheme 1) were deprotonated by a base, sodium methox-

de (NaOCH3) in methanol followed by addition of xylene.fter removing the methanol and subsequent phosphorylationith chloromethyldimethylphosphineoxide the new 5,11,17,23,

9,35,41,47-octa(1,1,3,3-tetramethylbutyl)-49,50,51,52,53,54,55,6-octakis(dimethylphosphinoylmethoxy)calix[8]arene II wasbtained.

Thin layer chromatography of II on Silica gel 60 F254 platesMerck) showed only one spot, Rf = 0.61 (CHCl3/CH3OH/H2O, 13:5:1,/v).

The recrystallized product is a white crystalline substance,hich melts at 295–300 ◦C and is soluble in alcohols, chloroform,ichloromethane, toluene, xylene, acetone, dimethylsulfoxideDMSO), dimethylformamide (DMFA) and insoluble in hexane andater.

The structure was confirmed by IR-, NMR-spectroscopy and ES-ass spectrometry.The IR spectrum of the compound contains band for phosphoryl

roups at 1169 cm−1.The 1H NMR spectrum shows a broad doublet at 4.04 and

.94 ppm overlapped for both CH2 P(O) and Ar CH2 Ar. The sig-al (singlet) for the aryl protons is observed at 6.97 ppm, a broadinglet at 1.28 ppm—corresponds to (O)P(CH3)2 protons, singletignals at 0.68, 1.13 and 1.56 ppm and their integrals referred tohe protons of the t-octyl group (1,1,3,3-tetramethylbutyl group),espectively C(CH3)3, C(CH3)2 and C CH2 C .

There is a singlet signal at 27.2 ppm for the methylene bridges inhe 13C NMR spectrum, singlets for the C atoms from t-octyl groups

C(CH3)3, C(CH3)3, C(CH3)2, C(CH3)2 and C CH2 C at 29.3, 29.7,9.8, 35.6 and 54.1 ppm and doublets for CH2–P(O) at ı = 69.3 ppmith 2JPC = 66.1 Hz and at ı = 11.8 ppm with 2JPC = 75.2 Hz for (CH3)2

. The signals for the C atoms of the aryl rings are at ı = 150.5, 143.6,28.8 and 124.5 ppm.

172 E. Tashev et al. / Separation and Purification Technology 64 (2008) 170–175

eme 1

3

pa

icc

3

F

Sch

Only one singlet is observed at ı = 36.08 ppm for P atom in the1P{1H} NMR spectrum, which indicates that the eight P O phos-horus atoms are equivalent and that no other type of phosphorus

tom is present.

The ES-MS displays peaks at m/z = 1234.3 (100%), correspond-ng to the [M+2H]2+/2 mass (calc. 1234.6), at m/z = 822.9 (44%)orresponding to the [M+3H]3+/3 mass (calc. 823.4) and no peaksorresponding to the lower substituted products (Fig. 1).

Cm

L

ig. 1. ESI-mass spectrum (positive mode) of 5,11,17,23,29,35,41,47-octa(1,1,3,3-tetramethy

.

.2. Synergistic solvent extraction of lanthanoids(III) ions

The solvent extraction of the lanthanoid(III) ions with HP in

HCl3 has been studied previously [29]. It has been found that theetal extraction can be represented by the following equation:

n3+(aq) + 4HP(o)

KP�LnP3 · HP(o) + 3H+(aq) (1)

lbutyl)-49,50,51,52,53,54,55,56-octakis(dimethylphosphinoylmethyleneoxy)calix[8]arene.

rification Technology 64 (2008) 170–175 173

w“

sii“DfeetaeSDcTtocpot

taloe

L

aK

l

Fm(

Fop

d

L

Tt

l

E. Tashev et al. / Separation and Pu

here Ln3+ denotes a lanthanoid ion and the subscripts “aq” ando” denote aqueous and organic phases, respectively.

The synergistic solvent extraction of the lanthanoids wastudied using a traditional and effective means of obtaining sto-chiometric coefficients, the composition of the extracted speciesn the organic phase and equilibrium constants information, calledslope analysis”. It is based on an examination of the variation ofP,S (the distribution coefficient due to the synergistic effect) as a

unction of the relevant experimental variables. As the lanthanoidxtraction with the calix[8]arene, S, alone is negligible under thexperimental conditions of the present study, the values of the dis-ribution coefficient D obtained experimentally are the sum of DP,Snd DP (DP is the distribution coefficients due to the lanthanoidxtraction with HP alone under the same experimental conditions).o, the values of DP,S were calculated as D − DP. A log–log plot ofP,S vs. one of the variables [H+], [HP] and [S] keeping the other twoonstant, indicates the stoichiometry of the extractable complex.his leads to the derivation of a suitable equilibrium expression andhen to the calculation of the equilibrium constant. If the variationf concentration of the extractants during the metal extraction isonstant and the hydrolysis in the aqueous phase as well as theolymerization in the organic phase occur to a negligible extentnly, then the plots will be straight lines and their slopes will givehe number of the ligands in the adducts.

The experimental data for the extraction of Ln(III) with mix-ure of HP and S are given in Figs. 2–4. The plots of log DP,S vs. pHnd log[HP] are linear with slope close to three and the plots ofog DP,S vs. log[S] with slope close to one. Therefore, in the presencef HP–S the lanthanoid extraction can be expressed by the followingquilibrium:

n3+(aq) + 3HP(o) + S(o)

KP,S� LnP3 · S(o) + 3H+(aq) (2)

Taking into account that the partition of HP [30] and S toward the

queous phase is very low, the overall equilibrium constant valuesP,S can be determined by the equation:

og KP,S = log DP,S − 3 log[HP] − log[S] − 3pH (3)

ig. 2. log DP,S vs. pH for the extraction of lanthanoid elements withixtures of [HP] = 2 × 10−2 mol dm−3 and [S] = 2 × 10−4 mol dm−3. Slopes:

3.01–3.32) ± (0.01–0.07).

fco

FHp

ig. 3. log DP,S vs. [HP] for the extraction of lanthanoid elements with mixturesf HP–S at [S] = 2 × 10−4 mol dm−3: La, pH = 3.20; Nd, pH = 2.80; Eu, pH = 2.70; Ho,H = 2.50; Lu, pH = 2.20. Slopes: (2.79–2.97) ± (0.02–0.13).

The formation of mixed complexes in the organic phase can beescribed by the equation:

nP3 · HP(o) + S(o)ˇP,S� LnP3

•S(o) + HP(o) (4)

he equilibrium constant ˇP,S for the organic phase synergistic reac-ion can be determined as

og ˇP,S = log KP,S − log KP (5)

The values of the equilibrium constants KP,S and ˇP,S calculatedrom the experimental data are given in Table 1. The equilibriumonstants are based on the assumption that the activity coefficientsf the species do not change significantly under the experimental

ig. 4. log DP,S vs. [S] for the extraction of lanthanoid elements with mixtures ofP–S at [HP] = 2 × 10−2 mol dm−3: La, pH = 3.30; Nd, pH = 2.85; Eu, pH = 2.60; Ho,H = 2.35; Lu, pH = 2.25. Slopes: (0.96–1.04) ± (0.02–0.06).

174 E. Tashev et al. / Separation and Purification Technology 64 (2008) 170–175

Table 1Values of the equilibrium constants KP, KP,S, ˇP,S and synergistic coefficients ([HP] = 2 × 10−2 mol dm−3, [S] = 2 × 10−4 mol dm−3), pH50 and separation factors for the Ln3+

extraction from 0.1 M (Na, H)Cl medium with HP–S mixtures in CHCl3.

Ln3+ log KP [29] log KP,S log ˇP,S S.C. S.F. pH50

HP HP–S HP HP–S

La3+ −5.84 −0.73 5.11 3.11 Nd/La 30.9 14.2 4.21 3.17Nd3+ −4.35 0.42 4.77 2.77 Eu/Nd 8.51 4.46 3.72 2.80Eu3+ −3.42 1.07 4.49 2.49 Ho/Eu 1.52 2.57 3.40 2.59HL

N xperim

citKci[

bc

S

wwTiTeaopses[[saftboiwamvtobAtppl

adasd

uLcirstti

4

4cbaELcoapi

A

Fa2W

R

o3+ −3.24 1.48 4.72 2.72u3+ −2.83 1.94 4.77 2.77

ote: The values of the equilibrium constants are calculated on the basis of the 36 e

onditions i.e. they are concentration constants. The data presentedn Table 1 show that the introduction of the used calix[8]arene intohe system Ln3+–HP leads to a significant increase of the values ofP,S in comparison with those of KP as well as that the values of thisonstant increase from La3+ to Lu3+ as expected from their decreas-ng ionic radii. A similar trend was observed in other investigations24,29,31,32].

The synergistic enhancement produced by HP–S mixtures cane determined using the synergistic coefficients (S.C.). They werealculated according to [33]

.C. = log(

D1,2

D1 + D2

)

here D1, D2 and D1,2 are the distribution coefficients of the metalith the two extractants taken separately and with their mixture.

he values of the synergistic coefficients are listed in Table 1. Its seen that the lanthanoids are extracted synergistically (S.C. > 0).he addition of the synthesized calix[8]arene to the chelatingxtractant improves the extraction efficiency of the lanthanoid ionsnd produces rather large synergistic effects (about three ordersf magnitude). The synergistic enhancement established in theresent study is higher (2–3 times) as compared to those found inome of our previous investigations dealing with the lanthanoidxtraction with the same chelating extractant (HP) and variousynergistic agents as dibenzo-18-crown-6, dibenzo-24-crown-831], 1-(2-pyridylazo)-2-naphtol [32], 4-(2-pyridylazo)-resorcin34] and the perchlorate form of the quaternary ammoniumalt Aliquat 336 [35]. But the overall equilibrium constantsnd the synergistic coefficients are smaller to those foundor the phosphorus-containing 5,11,17,23-tert-butyl-25,26,27,28-etrakis(dimethylphosphinoylmethoxy)calix[4]arene [24], proba-ly because of the larger size, the steric constraint and the flexibilityf the calix[8]arene macrocycle. The overall explanation of thenfluence of calix[n]arenes of various n, on the synergistic process

ill be given in further studies. To compare the extraction efficiencyt low pH of the aqueous phase, appreciable for industrial uses, ofixture HP–S to that of a chelating extractant HP alone, the pH50

alues (values of pH where log D = 0), corresponding to the extrac-ion of the studied lanthanoids in the absence and in the presencef calix[8]arene, are gathered in Table 1. A significant differenceetween the pH50 values (approximately one pH unit) is observed.nother advantage of this extractants mixture to similar combina-

ions [18], including calix[4]resorcinarene or its dimethylamino-,iperidyl- or trimethylammoniummethylated derivatives and 1,10-henanthroline is that the extraction process is carried out at rather

ower pH values of the aqueous phase.The separation of the lanthanoids using HP–S mixtures can be

ssessed by the separation factors (S.F.) calculated as a ratio of theistribution coefficients of two adjacent lanthanoids (the heaviernd the lighter one). When the metal ions form complexes of theame type (as in the present case), the separation factors can beetermined as a ratio of the equilibrium constants KP,S. Their val-

[[[

Lu/Ho 2.57 2.88 3.34 2.433.20 2.28

ental points, statistical confidence 95% and standard deviation ≤ ±0.07.

es are also given in Table 1. The selectivity for the Ho/Eu andu/Ho pairs obtained with the synergistic mixture is improved asompared to that obtained with the extraction by HP alone butt is lower for Nd/La and Eu/Nd pairs. So, the synergist amelio-ates the selectivity for heavier lanthanoid pairs. A comparableelectivity is observed using 5,11,17,23-tert-butyl-25,26,27,28-etrakis(dimethylphosphinoylmethoxy)calix[4]arene as a synergis-ic agent in combination with HP although the extraction efficiencys different [24].

. Conclusions

A new 5,11,17,23,29,35,41,47-octa(1,1,3,3-tetramethylbutyl)-9,50,51,52,53,54,55,56-octakis(dimethylphosphinoylmethoxy)alix [8]arene (S) was synthesized and its structure was confirmedy elemental analysis, IR-, 1H, 13C and 31P-{1H} NMR spectroscopynd ES-mass spectrometry. Selected lanthanoid (III) ions (La, Nd,u, Ho, Lu) were synergistically extracted by HP–S combination asnP3·S species. The addition of this new phosphorus-containingalix[8]arene S produces a large synergistic effect. The valuesf the overall equilibrium constant KP,S increase with increasingtomic numbers of the metals. The synergistic mixture used in theresent study combines the higher extraction efficiency with the

mproved selectivity for heavier lanthanoid ions.

cknowledgements

The financial support from the Bulgarian National Scienceoundation—Project’VU X 13/2007 (Atanassova, Dukov) as wells from the Swiss National Science Foundation—Project SCOPES000–2003: 7BUPJ062293.00/1 is acknowledged with gratitude.e thank Prof. Jean-Claude G. Bünzli for his contribution.

eferences

[1] C.D. Gutsche, Calixarenes, in: J.F. Stoddart (Ed.), Monographs in SupramolecularChemistry, The Royal Society of Chemistry, Cambridge, 1998.

[2] G.J. Lumetta, R.D. Rogers, A. Gopalan (Eds.), Calixarenes for SeparationsACSSymp. Ser., American Chemical Society, Washington, DC, USA, 2000, p. 757,Chapter 12.

[3] Z. Asfari, V. Bohmer, J.M. Harrowfield, J. Vincens (Eds.), Calixarenes, KluwerAcademic Publishers, Dordrecht, 2001.

[4] F. Sansone, M. Fontanella, A. Casnati, R. Ungaro, V. Bohmer, M. Saadioui, K. Liger,J.F. Dozol, Tetrahedron 62 (2006) 6749–6753.

[5] F. Arnaud-Neu, J.K. Browne, D. Byrne, D.J. Marrs, M.A. McKervey, P. O’Hagan,M.-J. Schwing-Weill, A. Walker, Chem. Eur. J. 5 (1999) 175–186.

[6] M. Baaden, M. Burgard, C. Boehme, G. Wipff, Phys. Chem. Chem. Phys. 3 (2001)1317–1325.

[7] S.E. Mattews, P. Parzuchowski, A. Garcia-Carrera, C. Gruttner, J.F. Dozol, V.Bohmer, Chem. Commun. (2001) 417–418.

[8] L. Le Saulnier, S. Varbanov, R. Scopelliti, M. Elhabiri, J.-C.G. Bunzli, J. Chem. Soc.,

Dalton Trans. (1999) 3919–3928.

[9] R. Ludwig, Fresenius J. Anal. Chem. 367 (2000) 103–128.10] R. Ludwig, K. Kunogi, N. Dung, S. Tachimori, Chem. Commun. (1997) 1985–1986.11] R. Ludwig, D. Lentz, T. Nguyen, Radiochim. Acta 88 (2000) 335–342.12] F. Arnaud-Neu, M. Anthony, M.A. McKervey, M.-J. Schwing-Weill, Metal-ion

complexation by narrrow rim carbonyl derivatives, in: Z. Asfari, V. Böhmer,

rificati

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[[[

14.

E. Tashev et al. / Separation and Pu

J. Harrowfield, J. Vincens (Eds.), Calixarenes 2001, Kluwer, Dordrecht, 2001, p.385.

13] F. Arnaud-Neu, M.-J. Schwing-Weill, J.F. Dozol, Calixarenes for nuclear wastetreatment, in: Z. Asfari, V. Böhmer, J. Harrowfield, J. Vincens (Eds.), Calixarenes2001, Kluwer, Dordrecht, 2001, pp. 642–662.

14] F. Arnaud-Neu, S. Cremin, S. Harris, M.A. McKervey, M.J. Schwing-Weill, P.Schwinte, A. Walker, J. Chem. Soc., Dalton Trans. (1997) 329–334.

15] F. Arnaud-Neu, S. Barboso, V. Böhmer, F. Brisach, L. Delmau, J. Dozol, O. Mogck,E. Paulus, M. Saadioui, A. Shivanyuk, Aust. J. Chem. 56 (2003) 1113–1119.

16] D. Roundhill, J. Shen, Phase transfer extraction of heavy metals, in: Z. Asfari, V.Böhmer, J. Harrowfield, J. Vincens (Eds.), Calixarenes 2001, Kluwer, Dordrecht,2001, pp. 407–420.

17] L. Kuznetsova, A. Mustafina, C. Podjatchev, E. Kazakova, A. Buzirilova, M.Pudovik, Russ. Coord. Chem. 24 (1998) 623–626.

18] L. Kuznetsova, A. Mustafina, A. Ziganshina, E. Kazakova, A. Konovalov, J. Incl.Phenom. 39 (2001) 65–69.

19] L. Kuznetsova, G. Pribylova, A. Mustafina, I. Tananaev, B. Myasoedov, A. Kono-valov, Radiochemistry 46 (2004) 277–281.

20] M. Kyrs, K. Svoboda, P. Lhotak, J. Alexova, J. Radioanal. Nucl. Chem. 254 (2002)455–464.

21] M. Kyrs, K. Svoboda, P. Lhotak, J. Alexova: J. Radioanal. Nucl. Chem. 258 (2003)497–509.

[[[[[

on Technology 64 (2008) 170–175 175

22] E. Tashev, T. Tosheva, S. Shenkov, A.-S. Chauvin, V. Lachkova, R. Petrova, R.Scopelliti, S. Varbanov, Supramol. Chem. 19 (2007) 447–457.

23] V. Videva, T. Tosheva, A.-S. Chauvin, S. Shenkov, R. Petrova, R. Scopelliti, E.Tashev, S. Varbanov, M. Miteva, Polyhedron 25 (2006) 2261–2268.

24] M. Atanassova, V. Lachkova, N. Vassilev, S. Varbanov, I. Dukov, J. Incl. Phenom.Macrocycl. Chem. 58 (2007) 173–179.

25] L.N. Puntos, A.S. Chauvin, S. Varbanov, J.C.G. Bünzli, Eur. J. Inorg. Chem. 16 (2007)2315–2326.

26] C.D. Gutsche, B. Dhawan, K.H. No, R. Muthukrishnan, J. Am. Chem. Soc. 103(1981) 3782–3792.

27] V. Bocchi, D. Fiona, A. Pochini, R. Ungaro, G.D. Andretti, Tetrahedron 38 (1982)373–378.

28] S.B. Savvin, Arsenazo III, Atomizdat, Moskva, 1966, p. 172.29] M. Atanassova, I. Dukov, Sep. Purif. Technol. 40 (2004) 171–176.30] Yu. Zolotov, N. Kuzmin, Ekstraktsia acylpirazolonomi, Nauka, Moskva, 1977, p.

31] M. Atanassova, I. Dukov, Acta Chim. Slovenika 53 (2006) 457–463.32] M. Atanassova, I. Dukov, Sep. Purif. Technol. 49 (2006) 101–105.33] J.N. Mathur, Solvent Extr. Ion Exch. 1 (1983) 349–412.34] M. Atanassova, Proc. Est. Acad. Sci. Chem. 55 (2006) 202–211.35] I. Dukov, M. Atanassova, Sep. Sci. Technol. 39 (2004) 227–239.