Phosphoryl-containing acidic podands as extractants for recovery of f-elements: 1. Synthesis and comparison of podands different in polyether chain length and structure

Article abstract of DOI:10.1007/s11172-015-0837-2

The extraction efficiency of uranium(vi), thorium(iv), and lanthanum(iii) from nitric acid solutions to 1,2-dichloroethane was compared for a series of phosphoryl podands of the acidic type different in polyether chain length and number of oxygen atoms: 2

Full text of DOI:10.1007/s11172-015-0837-2

Russian Chemical Bulletin, International Edition, Vol. 64, No. 1, pp. 161—168, January, 2015
161
Phosphorylꢀcontaining acidic podands as extractants for recovery of fꢀelements
1. Synthesis and comparison of podands different in polyether chain length and structure
A. M. Safiulina,a A. G. Matveeva,b D. V. Ivanets,c E. M. Kudryavtsev,c,d
M. S. Grigor´ev,e V. E. Baulin,e,f and A. Yu. Tsivadzee
aOJSC Uralchem Joint Chemical Company,
10 Presnenskaya nab., 123317 Moscow, Russian Federation.
Fax: +7 (495) 721 8585. Еꢀmail: alfiya.safiulina@uralchem.com
bA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5085. Eꢀmail: matveeva@ineos.ac.ru
cOJSC Leading Research Institute of Chemical Technology,
33 Kashirskoe sh., 115409 Moscow, Russian Federation
dNational Research Nuclear Institute MIFI,
31 Kashirskoe sh., 115409 Moscow, Russian Federation
eA. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences,
4/31 Leninsky prosp., 119071 Moscow, Russian Federation.
Fax: +7 (495) 952 5308
fInstitute of Physiologically Active Substances, Russian Academy of Sciences,
1 Severnyi proezd, 142432 Chernogolovka, Moscow Region, Russian Federation
The extraction efficiency of uranium(VI), thorium(IV), and lanthanum(III) from nitric acid
solutions to 1,2ꢀdichloroethane was compared for a series of phosphoryl podands of the acidic
type different in polyether chain length and number of oxygen atoms: 2ꢀ[(HO)(EtO)(O)P]—
C6H4—(OCH2CH2)m—OC6H4—2ꢀ[P(O)(EtO)(OH)] (1—3, where
m = 1—3) and
2ꢀ[(HO)(EtO)(O)P]—C6H4—O(CH2)5O—C6H4—2ꢀ[P(O)(EtO)(OH)] (4). The synthesis of
podands 1 and 4 obtained for the first time is described. The molecular and crystal structures of
podand 1 were determined by Xꢀray diffraction analysis, and the formation of a strong intraꢀ
molecular hydrogen bond was observed. Podand 2 is the most efficient extractant for the
selective recovery of ThIV in the presence of UVI and LaIII among the studied podands. Micellar
aggregates 3—5, 6—90, 3—70, and 7—10 nm in size were found by the dynamic light scattering
data in thorium extracts of podands 1—4, respectively.
Key words: phosphoryl podands, diphosphonic acids, synthesis, extraction, thorium, uranꢀ
ium, lanthanum, micelles.
Phosphorus acids (RO)2P(O)OH, R(RO)P(O)OH,
The main regularities of the influence of alkylenediphosꢀ
phonic acid structure on the extraction of sꢀ, pꢀ, dꢀ, and
fꢀelements from nitric acid solutions were established. The
detailed study of the extraction processes showed that both
diphosphonic acids themselves and extracted metal comꢀ
plexes exist as aggregates in the organic phase, and the
degree of aggregation depends on both the acid structure
(alkylene bridge length) and nature of extracted metal (the
dependence of the degree of aggregation on the experiꢀ
mental conditions was studied separately).3,4,6 In addiꢀ
tion, very important and practically useful property of
diphosphonic acids (unlike carboxylate analogs and the
most part of neutral extractants) was discovered: their
unique ability to strongly bind actinides in highly acidic
solutions.2
and R2P(O)OH (R are various linear and branched alkyl
or aryl substituents) are widely used as extractants for the
group extraction of lanthanides and actinides from highly
active waste of radiochemical industry and irradiated nuꢀ
clear fuel processing. Primarily they were developed for
the TALSEPAK (USA) and DIDPA (Japan) processes,
and their use has recently started in the DIAMEXꢀSANꢀ
EX process (France).1 It was found later than diphosꢀ
phonic acids (HO)(RO)(O)P—(CH2)n—P(O)(OR)(OH)
(R is 2ꢀethylhexyl; n = 1, 2, and 4) and related polymer
sorbents have very strong affinity to cations of 5fꢀeleꢀ
ments.2—4 In this connection, they were patented as reꢀ
agents for extraction and chromatographic separation and
concentrating of triꢀ, tetraꢀ, and hexavalent actinides.5
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 0161—0168, January, 2015.
1066ꢀ5285/15/6401ꢀ0161 © 2015 Springer Science+Business Media, Inc.

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Safiulina et al.
Up to presently, these results stimulate the preparation
The synthesis of podands 2 and 3 was described earliꢀ
er.9 Podands 1 and 4 were synthesized in this work for the
correct evaluation of the influence of the polyether bridge
structure on the properties of the extractant.
of new modified diphosphonic acids and study the extracꢀ
tion properties of both newly synthesized and known comꢀ
pounds of this class.7
The group of phosphorylꢀcontaining podands of the
acidic type in which two phosphonic —P(O)(OR)(OH)
fragments are linked by the polyether chain with oꢀphenyl
substituents as terminal groups is also referred to diphosꢀ
phonic acids.8 Although the first phosphoryl podands of
the acidic type were synthesized rather long ago,9 data on
their coordination properties are few10 and the study of the
extraction properties has started only recently. However,
already the first results showed high efficiency of some of
them for the selective extraction of ThIV in the series of
UVI and LaIII from nitric acid media.11
Continuing our studies on search for efficient and seꢀ
lective extractants for the extraction and separation of lanꢀ
thanides and actinides, it seemed reasonable to establish
the main regularities of the influence of the structures of
phosphoryl podands of the acidic type on the extraction of
fꢀelements.
Results and Discussion
Neutral phosphorylated podands with oꢀdiethoxyphosꢀ
phorylphenyl terminal groups 1´ and 4´ were used as the
starting substances for the synthesis of phosphorylꢀconꢀ
taining podands of the acidic type 1 and 4. Compounds 1´
and 4´ were synthesized by the alkylation of oꢀdiethoxyꢀ
phosphorylphenol with ethylene glycol ditosylate or 1,5ꢀdiꢀ
bromopentane in anhydrous dioxane at 80—100 С in the
presence of sodium hydride as a base. The target diphosꢀ
phonic acids were obtained by the alkaline hydrolysis of
the corresponding neutral podands 1´ and 4´ in an aqueꢀ
ousꢀalcohol medium (Scheme 1).
The Xꢀray diffraction study of podand 1 showed that its
structure is built of molecules with two strong intramolecꢀ
ular hydrogen bonds (Fig. 1).
The purpose of this work is to compare the properties
of a series of acidic phosphorylꢀcontaining podands 1—4 difꢀ
ferent in length and number of oxygen atoms in the polyꢀ
ether chain for UVI, ThIV, and LaIII recovery and to choose
the most promising extraction system for thorium(IV) exꢀ
traction from nitric acid solutions to dichloroethane.
The geometric parameters of the molecule of podand 1
(bond lengths and bond angles, Table 1) lie in the ranges
characteristic of compounds of this class12 and are close
to those found earlier for related phosphorylꢀsubstitutꢀ
ed acidic podands.13,14 The Р=О and P—OH bond lengths
vary within 1.500(3)—1.522(3) Å. The P—C bond
lengths are nearly equal: 1.781(4) and 1.786(5) Å. In the
PO3C tetrahedra, the О—Р—С angles lie in the range
104.6(2)—111.2(2), and the О—Р—О angles are
106.0(2)—115.7(2). The average bond lengths and bond
angles of the ОСН2СН2О unit have usual values characꢀ
teristic of podands and crown ethers.14
The acidic groups of podand P(O)OH form two strong
intramolecular hydrogen bonds Р—OН...O=P (Table 2)
linking two ends of the podand molecule to form three
1: n = 0; 2: n = 1, X = O; 3: n = 2, X = O; 4: n = 1, X = CH2
Scheme 1

Acidic phosphoryl podands as extractants
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 1, January, 2015
163
Table 2. Geometric parameters of intramolecular hydrogen bonds
in the structure of podand 1
C(6)
C(4)
C(3)
O(5)
O(3)
O(7)
H(7)
Bond
D—H...А
d/Å
Angle D—H—А
/deg
O(8)
P(2)
C(21)
O(5)
P(1)
C(11)
D—H
H...А
D...A
H(4)
C(16)
C(15)
C(26)
C(25)
O(4)
O(4)—H(4)...O(6) 1.10(5) 1.43(5) 2.519(5)
O(7)—H(7)...O(3) 1.11(5) 1.39(5) 2.483(4)
170(5)
167(6)
O(5)
O(2)
C(13)
C(23)
C(12)
O(1)
C(22)
C(14)
C(24)
C(2)
in structures of related phosphorylꢀcontaining acidic
podands.13
Fig. 1. Molecular structure of podand 1. Thermal vibration ellipꢀ
soids are presented with 20% probability. Hydrogen atoms are
shown by spheres of arbitrary radius. Hydrogen bonds are shown
by dashed lines.
In crystal, molecule 1 has a Cꢀlike conformation, where
the atoms of the phenyl rings, P atoms, and O atoms of
the ethoxy groups lie almost in one plane Р(1)С(11)—
С(16)О((1)О(2)С(21)—С(26)Р(2)О(8) and the rootꢀ
meanꢀsquare deviation of the atoms from this plane is
0.03 Å. The carbon atoms of the СН2СН2 bridge deviate
from the considered plane to one side, whereas the carbon
atoms of both EtO substituents at the P atom deviate to
another side. The whole molecule possesses intrinsic (nonꢀ
crystallographic) symmetry Cs (m), from which only the
Н(7) and Н(4) atoms deviate substantially. The plane of
the mirror reflection is perpendicular to the plane of Fig. 1.
Note that all the three planes indicated above are almost
perpendicular to each other.
Extraction properties of phosphoryl podands 1—4 toꢀ
ward fꢀelements were studied for the extraction of uranꢀ
ium(VI), thorium(IV), and lanthanum(III) from nitric acid
solutions to the organic phase at the varied concentration
of nitric acid and constant concentrations of the salt in the
aqueous phase and ligand in 1,2ꢀdichloroethane.
Hꢀrings: eightꢀmembered P(1)O(3)H(7)O(7)P(2)O(6)ꢀ
H(4)O(4) ring and two 13ꢀmembered rings P(1)C(11)ꢀ
C(12)O(1)C(1)C(2)O(2)C(22)C(21)P(2)O(6)H(4)O(4)
and P(1)C(11)C(12)O(1)C(1)C(2)O(2)C(22)C(21)P(2)ꢀ
O(7)H(7)O(3) (see Fig. 1). The eightꢀmembered Hꢀring
is planar, and the rootꢀmeanꢀsquare deviation of the
atoms from the Р(1)О(3)О(7)Р(2)О(6)О(4) plane (igꢀ
noring H atoms) is 0.005 Å. The parameters of hydroꢀ
gen bonds (distances and bond lengths) in crystal 1 (see
Table 2) are close to those found for strong intermolecuꢀ
lar hydrogen bonds in cyclic dimers of diphosphinic acꢀ
ids Me2P(O)OH and Ph2P(O)OH (see Ref. 15) and
Table 1. Selected bond lengths (d) and bond
angles () in the structure of podand 1
When analyzing the data, it was taken into account
that the crystal structures of podands 1 and 2 differ basiꢀ
cally. According to the Xꢀray diffraction data, in crystal
molecules of podand 1 form strong intramolecular bonds
(this work), whereas the data of powder Xꢀray diffraction
analysis and IR spectroscopy show that molecules 2 in
crystal are bonded exclusively by intermolecular hydrogen
bonds.13 It can be assumed that in solutions of 1,2ꢀdichloroꢀ
ethane this difference will retain to a significant extent
and will appear as different degrees of selfꢀaggregation of
podands 1 and 2 and also as different complexation and
extraction abilities of these compounds.
The structures of the extracted complexes of phosꢀ
phoryl podands 1—4 are unknown. There are preliminary
data on the structure of the solid copper complex of
ligand 2 [CuL(H2O)2]0 (here L is the deprotonated anion
of podand 2). The elemental analysis and IR spectral data
suggest that complex [CuL(H2O)2]0 is mononuclear with
the chelate coordination of the dianion closing the poꢀ
dand to form a pseudoꢀmacrocycle.13 However, it should be
mentioned that the structures of the solid complexes isoꢀ
lated from neutral solutions and the complexes extracted
from real strongly acidic solutions do not always coincide.
Parameter
Bond
Value
d/Å
P(1)—O(3)
P(1)—O(4)
P(1)—O(5)
P(1)—C(11)
P(2)—O(6)
P(2)—O(7)
P(2)—O(8)
P(2)—C(21)
1.506(3)
1.507(3)
1.584(3)
1.781(4)
1.500(3)
1.522(3)
1.566(4)
1.786(5)
Angle
/deg
O(3)—P(1)—O(4)
O(3)—P(1)—O(5)
O(4)—P(1)—O(5)
O(3)—P(1)—C(11)
O(4)—P(1)—C(11)
O(5)—P(1)—C(11)
O(6)—P(2)—O(7)
O(6)—P(2)—O(8)
O(7)—P(2)—O(8)
O(6)—P(2)—C(21)
O(7)—P(2)—C(21)
O(8)—P(2)—C(21)
115.7(2)
109.6(2)
106.0(2)
110.2(2)
110.0(2)
104.8(2)
114.9(2)
106.9(2)
109.6(2)
111.2(2)
109.2(2)
104.6(2)

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Safiulina et al.
DTh
It is known that the polyether chain length exerts difꢀ
ferent effects on the complexation ability of some classes
of podands.16 For example, in the case of neutral phosꢀ
phoryl podands, the dependence of the complexation conꢀ
stants on the polyether chain length is extreme for some
cations (Li, Na), whereas the complexation constants for
other cations (K, Rb, Cs) monotonically increase with an
increase in the chain length.16 The complexation ability of
the podands with the —Р(О)(ОН)2 terminal groups toꢀ
ward doublyꢀcharged cations decreases nonuniformly with
the polyether chain elongation.10
80
60
40
20
1
2
3
4
In organic media, alkylenediphosphonic acids related
to the studied podands form aggregates of different comꢀ
position and structure, and the extracted complexes are
also aggregates of different composition.3,4 In the simpliꢀ
fied form, the composition of the extracted complexes, for
example, for the doublyꢀcharged cation М2+, can be preꢀ
sented as M[(HA)2(H2A)n]0 and M[(A)(H2A)n]0, where
H2A is a dibasic alkylenediphosphonic acid. The differꢀ
ences in the efficiency of extraction by acids with alkylene
linkers are mainly determined by different degrees of agꢀ
gregation of acids and their complexes, which depends, in
turn, on the linker length in a complicated way.2
The results of liquid extraction of fꢀelements at the
same concentrations of podands 1—4 in dichloroꢀ
ethane (0.01 mol L–1) and salt in the aqueous phase
(2.5•10–5 mol L–1) are presented in Figs 2—4.
It follows from the data on uranium (see Fig. 2) that
podands 1—4 demonstrate a similar dependence of the
distribution ratios (DU) on the HNO3 concentration.
The DU values remain almost unchanged in a range of
HNO3 concentrations of 0.04—2.64 mol L–1 and decrease
very insignificantly (on the average, by 0.20 0.07) with an
increase in the HNO3 concentration to 3.86 М. The effiꢀ
ciency of uranium extraction for podands 1, 3, and 4 is
1
2
3
C(HNO3)/mol L–1
Fig. 3. Distribution ratios of ThIV vs HNO3 concentration for
extraction by phosphoryl podands 1—4 (0.01 М solution in
1,2ꢀdichloroethane).
almost the same and low (average DU = 1.10 0.08), and
the extraction by podand 2 is more efficient (DU = 1.43).
Unlike UVI extraction, the efficiency of extraction of
ThIV by ligands 1—4 differs substantially (see Fig. 3).
The most efficient extraction of ThIV is observed for
phosphoryl podand 2, and in the concentration range of
HNO3 0.04—2.64 mol L–1 the distribution ratios remain
almost unchanged: DTh = 63 2. The distribution ratio
decreases to 32 only for the HNO3 concentration equal to
3.86 mol L–1. Podand 1 with the shortest ethylene glycol
chain extracts ThIV worse than all other studied reagents,
and the DTh values remain almost unchanged in the whole
acidity range of the aqueous phase: DTh = 0.39 0.04. Poꢀ
dand 3 with the longest chain extracts ThIV much better:
the DTh values are 10 0.07 on the average in the whole
range of HNO3 concentrations. Podand 4, whose polyꢀ
ether chain differs from that in podand 2 by the presence
of the СН2 group instead of the O atom, exhibits rather
high efficiency in the extraction of ThIV, but it is twice as
DU
1.6
DLa
1.2
1.2
1
1.0
2
0.8
0.4
3
4
1
2
3
0.8
0.6
0.4
0.2
1
2
3
C(HNO3)/mol L–1
Fig. 2. Distribution ratios of UVI vs HNO3 concentration for
extraction by phosphoryl podands 1—4 (0.01 М solution in 1,2ꢀdiꢀ
chloroethane).
Note. Figures 2—4 are available in full color in the onꢀline verꢀ
sion of the journal (http://www/springerlink.com).
1
2
3
C(HNO3)/mol L–1
Fig. 4. Distribution ratios of LaIII vs HNO3 concentration for
extraction by phosphoryl podands 1—3 (0.01 М solution in 1,2ꢀdiꢀ
chloroethane).

Acidic phosphoryl podands as extractants
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 1, January, 2015
165
lower than that for podand 2. Note that the distribution
ratios DTh decrease smoothly with an increase in the HNO3
concentration only in this case.
In fact, according to the Xꢀray diffraction data, the neuꢀ
tral phosphoryl podand having the same linker as podand 4
in a complex with uranyl manifests bidentateꢀbridging
coordination due to the O atoms of two Р(О) groups, and
the ether O atoms are not involved in coordination.17 In
principle, coordination involving the ether O atoms can
be expected for the complexes of acidic podands with alꢀ
kaline metal cations by analogy to the complexes of neuꢀ
tral phosphoryl podands.*
The efficiency of LaIII extraction (see Fig. 4) for poꢀ
dands 1—3 also differs. Podands 1 and 2 nearly do not
extract lanthanum in the whole range of HNO3 concenꢀ
trations (DLa are 0 and 0.02, respectively). Unlike them,
podand 3 (with the longest polyether chain) noticeably
extracts lanthanum in the range of low HNO3 concentraꢀ
tions (DLa = 0.99—0.92), but the efficiency of extraction
decreases sharply (DLa = 0.2—0.1) in highly acidic media
(see Fig. 4).
However, there is very interesting example of the crysꢀ
talline complex of erbium nitrate with neutral podand
Ph2P(O)(CH2CH2O)3CH2CH2P(O)Ph2 (L), viz.,
[ErL(H2O)(NO3)3], in which the ligand is bound to the
cation by the bidentate mode through the phosphoryl oxyꢀ
gen atoms and the coordinated H2O molecule forms hyꢀ
drogen bonds with two ether oxygen atoms of the ligand.20
It can be assumed that for extraction during complex forꢀ
mation of the acidic phosphoryl podands (H2L) with the
cations having large charges and radii the ether O atoms of
the podand can form similar hydrogen bonds with coordiꢀ
nated H2O molecules, whereas the coordination bonds
with the cation are formed by the terminal РОО– groups
of the podand anion (L2–). In terms of this assumption,
the complexes of podand 3 should be stronger than those
of podand 4, and their lipophilicity, which depends on the
number of carbon atoms in the molecule, should be nearly
equal. Therefore, the extraction efficiency of the comꢀ
plexes of podand 3 will be higher than that for podand 4
(see Fig. 5, b, c).
As already mentioned, the consecutive increase in the
number of ОСН2СН2 units in the chain binding the terꢀ
minal groups of the podands from one to three (poꢀ
dands 1—3) is accompanied by the monotonic enhanceꢀ
ment of the efficiency of LaIII extraction (Fig. 5, a),
although the DLa values themselves in the compared
of HNO3 concentrations (>0.74 mol L–1) are very low
(0, 0.02, and 0.1 for podands 1, 2, and 3, respectively). In
the first approximation, for lanthanum extraction, this
effect can be related to an increase in the lipophilicity of
the extracted complexes with the polyether chain elonꢀ
gation.
For uranium and thorium cations, the dependence of
DМ on the number of ОСН2СН2 units in the chain is
substantially different. In both cases, some maximum at
m = 2 (podand 2) is observed. However, for uranium this
maximum is low: the whole range of changing DU is only
0.3 (Fig. 5, b), whereas it is very significant for thorium:
the range of changing DTh is 65 (Fig. 5, с). Note that the
DU and DTh values for podand 4 is lower than those for
podand 2, i.e., the replacement of the СН2 group in the
linker of podand 4 by the O atom (on going to the strucꢀ
ture of podand 2) increases the efficiency of uranium and
thorium extraction. It is difficult to understand that this
effect is caused by the participation of the ether oxygen
atom (atoms) in coordination with the uranyl cation
(O=U=O2+), whose coordination sphere assumes the coꢀ
ordination of the ligands on the equatorial plane only.
The difference in extraction efficiency of ThIV by poꢀ
dands 1—3 is unusually high compared to the extraction
* The cooperative interaction of all donor atoms of the podand
with the central metal cation was observed in the solid complexꢀ
es of the neutral phosphoryl podands with NaI, LiI, and
Ba(NCS)2,18 whereas in the complexes with ZnI2, LiCl, LiBr,
and LiI the podands are bidentateꢀbridging coordinated only
through the oxygen atoms of the Р(О) groups.18,19 It was found
that the neutral phosphoryl podands exhibit different dentate
modes, depending on the metal nature.
DLa
DTh
DU
1.6
a
b
c
0.12
0.08
0.04
80
1.2
40
1
2
3
4
m
1
2
3
4
m
1
2
3
4
m
Fig. 5. Distribution ratios DМ (М = LaIII (a), UVI (b), and ThIV (c)) for extraction by 2ꢀ[(HO)(EtO)(O)P]—C6H4—(OCH2CH2)m—
OC6H4—2ꢀ[P(O)(EtO)(OH)] (1—3) vs number of —OСН2СН2— units (m) in the polyether chain (extraction from 1.66 М HNO3,
concentration of podands in 1,2ꢀdichloroethane 0.01 mol L–1, initial concentration of metal nitrates in the aqueous phase
2.5•10–5 mol L–1). The values for podand 4 are put on plots b and c as particular points (circles).

166
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Safiulina et al.
of LaIII and UVI. An assumption about different composiꢀ
tions of the extracted complexes (considered in detail in
Ref. 21) as the main reason for the difference does not
seem exhausting. Evidently, the neutral intracomplex salts
[ThL2]0, [UO2L]0, and [LaL(NO3)]0 with chelate coordiꢀ
nation of the dianion L2– of one acidic podand Н2L should
possess different lipophilicities because of the different
numbers of lipophilic, chelateꢀcoordinated anions L2– and
the presence or absence of the hydrophilic nitrate ion.
Then (assuming that the stability of the intracomplex salt
differs insignificantly), the extraction efficiency should
decrease in the series Th > U > La. However, an assumpꢀ
tion about the same (or similar) structures of particles
extracted by podands 1—4 is quite reasonably consistent
with the results of extraction of LaIII and UVI nitrates,
whereas for ThIV this assumption is explicitly insufficient:
the extraction coefficients of thorium by ligands 2—4 are
much higher than the values expected by prediction on the
basis of DTh for ligand 1. By analogy to related alkyleneꢀ
diphosphonic acids, one can assume that the effect obꢀ
served for ThIV extraction is mainly determined by differꢀ
ent degrees of aggregation (m) of both podands 1—4
((H2L)m) themselves and their complexes (in the simpliꢀ
fied form, [ThL2(H2L)n]0, [ThL(HL)2(H2L)n]0, etc.). Acꢀ
cording to the Xꢀray diffraction data on the structures of
molecules 1 and 2 (see above), it can be expected that in
the organic phase podands 2—4 with a longer polyether
chain would form larger aggregates due to intermolecular
hydrogen bonds, unlike podand 1, whose molecules are
stabilized by a strong intramolecular hydrogen bond. To check
this assumption, we used the dynamic light scattering
method to study thorium extracts by podands 1—4. In accord
with expectations, they contain micellar aggregates of difꢀ
ferent sizes: 3—5, 6—90, 3—70, and 7—10 nm for extracts
of podands 1, 2, 3, and 4, respectively. These data are well
consistent with a change in the efficiency of ThIV extracꢀ
tion in the series of the studied podands: 2 > 3 > 4 > 1.
To compare the efficiency and selectivity of podands
1—4 depending on their structure, the distribution ratios
of fꢀelements for extraction from 1.66 М solutions of
HNO3 were compared (Fig. 6).
DM
80
60
40
20
0
1
Th
U
2
3
La
4
Fig. 6. Comparison of the distribution ratios of LaIII, UVI, and
ThIV for extraction by podands 1—4 (0.01 М solutions in 1,2ꢀdiꢀ
chloroethane) from 1.66 М HNO3; initial concentration of metal
nitrates in the aqueous phase 2.5•10–5 mol L–1
.
Experimental
1
Н and 31P NMR spectra were recorded on a BrukerꢀСPXꢀ200
instrument (1H, 200 MHz; 31P, 81 MHz) relative to tetramethylꢀ
silane (1Н) and 85% Н3РО4 as an external standard (31P).
1,2ꢀBis(2ꢀdiethoxyphosphorylphenoxy)ethane (1´). A 55%
suspension of NaH in (1.2 g, 27.0 mmol) in Nujol was added by
portions to a solution of 2ꢀdiethoxyphosphorylphenol9 (6.2 g,
27.0 mmol) in anhydrous dioxane (75 mL), the mixture was
stirred for 0.5 h, ethylene glycol ditosylate (5.0 g, 13.5 mmol)
was added, and the mixture was heated to boiling and stirred for
15 h. After cooling, the mixture was poured to water (150 mL),
acidified to pH 1 by concentrated HCl, and extracted with CHCl3
(3×25 mL). The extract was washed with water (3×25 mL), and
the solvent was evaporated in vacuo. The residue was chromatoꢀ
graphed on a column with silica gel L (particle size 100—160 m,
CHCl3 and CHCl3—PriOH (1 : 50) as eluents). The yield was
3.6 g (57%), m.p. 62—64 C (benzene—pentane). Found (%):
С, 54.33; Н, 6.62, Р, 12.75. С22Н32О8Р2. Calculated (%): С, 54.32;
Н, 6.63, Р, 12.74. 1Н NMR (CDCl3), : 1.28 (t, 12 H,
4 CH3CH2O, 3JН—Н = 7.0 Hz); 5.16 (m, 8 Н, 4 MeCH2O); 5.50
(s, 4 Н, ОСН2СН2); 8.08 (m, 4 Н, ArH); 8.50 (m, 2 Н, ArH);
8.82 (m, 2 Н, ArH). 31Р NMR (CDCl3), : 17.8 (s).
1,2ꢀBis(2ꢀhydroxyethoxyphosphorylphenoxy)ethane (1). Comꢀ
pound 1´ (5.9 g, 12.2 mmol) was added to a solution of NaOH
(1.5 g, 37.0 mmol) in aqueous (1 : 1) ethanol (20 mL). The mixꢀ
ture was refluxed for 5 h, and the solvent was removed in vacuo.
Dilute (1 : 3) HCl (15 mL) was added to the residue, the mixture
was extracted with CHCl3 (2×15 mL), and the extract was evapꢀ
orated in vacuo. Methyl ethyl ketone (15 mL) was added to the
residue, and the precipitate formed was filtered off. The yield
was 3.4 g (65%), m.p. 195—196 C (ethanol). Found (%): С, 50.18;
Н, 5.64, Р, 14.40. С18Н24О8Р2. Calculated (%): С, 50.24; Н, 5.62,
All studied podands 1—4 almost do not extract LaIII
(DLa = 0—0.1) and extract UVI with moderate efficiency
(DU = 1.10—1.41). However, podands 2—4 are of certain
interest with respect to the extraction of ThIV (DTh = 10—65).
Among them podand 2 is most efficient (DTh = 65) and
can be recommended as an extractant for the selective
extraction of ThIV from nitric acid solutions containing
LaIII, ThIV, and UVI.
Thus, the study performed makes it possible to deterꢀ
mine the direction of design of promising extractants for
the extraction of actinides in the group of phosphorylꢀ
containing acidic dipodands. Diethylene glycol chain
—(OCH2CH2)2O— is the optimum linker for the producꢀ
tion of extractants of this type.
1
Р, 14.40. Н NMR (DMSOꢀd6), : 1.22 (t, 6 H, 2 CH3CH2O,
3JН—Н = 7.0 Hz); 4.00 (m, 4 Н, 2 CH3CH2O); 4.20 (s, 4 Н,
ОСН2СН2); 7.08 (m, 4 Н, ArH); 7.48 (m, 2 Н, ArH); 7.67 (m, 2 Н,
ArH). 31Р NMR (DMSOꢀd6), : 14.0 (s). The structure of podand 1
was confirmed by the Xꢀray diffraction method.
1,5ꢀBis(2ꢀhydroxyethoxyphosphorylphenoxy)ꢀ3ꢀoxapentane
(2) and 1,8ꢀbis(2ꢀhydroxyethoxyphosphorylphenoxy)ꢀ3,6ꢀdiꢀ

Acidic phosphoryl podands as extractants
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 1, January, 2015
167
oxaoctane (3) were synthesized using a previously described
procedure.9
99.4%, the number of refined parameters was 260, and the maximꢀ
um and minimum residual electron density peaks were 0.214 and
–0.291 e Å–3, respectively. The Flack parameter x equal to 0.15(15)
shows that the absolute structure was determined correctly.26
The full tables of atomic coordinates, bond lengths, and anꢀ
gles were deposited with the Cambridge Crystallographic Data
Centre (CCDC 1006221).
1,5ꢀBis(2ꢀdiethoxyphosphorylphenoxy)pentane (4´). A 55%
suspension of NaH (0.4 g, 10.0 mmol) in Nujol was added to
a solution of 2ꢀdiethoxyphosphorylphenol9 (2.3 g, 10.0 mmol) in
anhydrous dioxane (25 mL). The reaction mixture was stirred for
0.5 h, 1,5ꢀdibromopentane (1.2 g, 5.0 mmol) was added, and the
mixture was heated to boiling and stirred for 15 h. After cooling,
the mixture was poured to water (75 mL), acidified with concenꢀ
trated HCl to рН 1, and extracted with CHCl3 (3×25 mL). The
extract was washed with water (3×25 mL), and the solvent was
removed in vacuo. The residue was chromatographed on a colꢀ
umn with silica gel L using CHCl3 and CHCl3—PriOH (1 : 50)
as eluents. The yield was 2.1 g (79%), viscous oil. Found (%):
С, 56.79; Н, 6.27; Р, 11.70. C25H38O8P2. Calculated (%):
С, 56.81, Н, 6.25; Р, 11.72. 1Н NMR (CDCl3), : 1.12 (t, 12 Н,
Study of extraction. Bidistilled water, 1,2ꢀdichloroethane (reꢀ
agent grade), arsenazo III (analytical grade), HNO3 (high purity
grade), UO2(NO3)2•6H2O (reagent grade), Th(NO3)4•4H2O
(reagent grade), and La(NO3)3•6H2O (reagent grade) were used
to prepare solutions. Solutions were prepared by the volumetric
gravimetric method. Solutions of actinide and lanthanum
nitrates were prepared by the dissolution of a weighed sample of
the corresponding nitrate in a 0.01 М solution of HNO3. The
concentration of solutions of metal nitrates (0.1 mmol L–1) was
refined by spectrophotometry according to an earlier described
procedure27 using a Cary50 Scan spectrophotometer (Varian).
The concentration of solutions of HNO3 was determined by
potentiometric titration with 0.1 М NaOH using a pH/ion Analꢀ
yser Radelkisꢀ125 pH meter (model OPꢀ300) with an accuracy
of 0.01 рН units. The electrode pair was calibrated by standard
buffer solutions with рН 1.68, 4.01, and 9.22 (the values of pH at
20 C). The concentration of a solution of NaOH was refined by
potentiometric titration with 0.1 М HCl (fixanal).
The extraction of metal cations was studied as follows.
A solution of nitric acid (1.5 mL), whose concentration was varied
from 0.053 to 5.15 mol L–1, 0.5 mL of 0.1 mМ solution of metal
nitrate, and 2 mL of a 0.01 М solution of the ligand in 1,2ꢀdiꢀ
chloroethane was placed in a tube with a ground stopper.
A 0.006 М solution of podand 2 was used because of its restricted
solubility. The phases were stirred for 20 min in a Multi RSꢀ60
BioSan multirotator (80 rpm). The time of extraction equilibraꢀ
tion was checked by increasing the duration of phase contact to
120 min, and distribution ratios remained unchanged during this
process. Phases were separated by centrifugation. After phase
separation, the concentration of metals in the aqueous phase
was determined by spectrophotometry.27 To enhance the sensiꢀ
tivity of the analysis, the content of actinides in the organic
and aqueous phases were monitored radiometrically using an
LSꢀ6500 Beckman Instruments liquid scintillation counter
(WSꢀBECKLS65) (Beckman LS 6500 Liquid Scintillation Counꢀ
ter). For this purpose, 233UVI (104 pulse s–1) and 239PuIV
(104 pulse s–1) labels were introduced into solutions of uranyl
and thorium nitrates during extraction. At least three indepenꢀ
dent experiments were carried out for each concentration. All
experiments were conducted at 20 1 С.
3
4 ОСН2СН3, JН—Н = 7.5 Hz); 1.30 (m, 8 Н, 4 ОСН2СН2ꢀ
СН2СН3); 1.54—1.79 (m, 14 Н, 4 ОСН2СН3 + ОСН2(СН2)3Оꢀ
СН2О); 7.08 (m, 4 Н, ArH); 7.30 (m, 2 Н, ArH); 7.37 (m, 2 Н,
ArH). 31Р NMR (CDCl3), : 17.4 (s).
1,5ꢀBis(2ꢀhydroxyethoxyphosphorylphenoxy)pentane (4).
solution of NaOH (1.2 g, 30.0 mmol) in 40% aqueous ethanol
(5 mL) was added to a solution of compound 4´ (2.4 g, 5.1 mmol)
in EtOH (5 mL). The mixture was refluxed for 5 h and cooled,
dilute (1 : 3) HCl (15 mL) was added, the mixture was stored for
~14 h, and the precipitate was filtered off. The yield was 1.6 g
(69%), m.p. 109—111 C (ethanol—water). Found (%): С, 53.29;
Н, 6.39; Р, 13.18. C25H38O8P2. Calculated (%): С, 53.39, Н, 6.40;
1
Р, 13.11. Н NMR (DMSOꢀd6), : 1.16 (t, 6 Н, 2 ОСН2СН3
3JН—Н = 7.5 Hz); 1.73 (m, 6 Н, ОСН2(СН2)3ОСН2О); 4.11
(m, 4 Н, 2 ОСН2СН3); 4.21 (m, 4 Н, ОСН2(СН2)3ОСН2О);
7.09—7.43 (m, 8 Н, ArH). 31Р NMR (DMSOꢀd6), : 16.3 (s).
XꢀRay diffraction study. Colorless crystals of podand 1 suitꢀ
able for Xꢀray diffraction analysis were obtained by the isotherꢀ
mal evaporation at ~20 C of a solution of compound 1 in
1,2ꢀdichloroethane. The crystals of C18H24O8P2 (1) (M = 430.31)
are orthorhombic, at 293(2) K a = 7.0603(13) Å, b = 14.480(3) Å,
3
c = 20.119(4) Å, V = 2056.8(7) Å , space group P212121, Z = 4,
dcalc = 1.390 g cm–3. The experimental set of 13 791 reflections
was obtained on a Bruker Kappa Apex II automated fourꢀcircle
diffractometer with a twoꢀdimensional detector22 (MoꢀK radiꢀ
ation, graphite monochromator,  and  scan modes) from s
single crystal 0.32×0.10×0.08 mm in size. The unit cell parameꢀ
ters were refined over the whole data massive.23 Absorption corꢀ
rections were applied using the SADABS programs.24 After avꢀ
eraging equivalent reflections, 4698 independent reflections were
obtained (Rint = 0.0934) and used for structure decoding
and refinement. The structure was solved by a direct method
(SHELXS97)25 and refined by the fullꢀmatrix leastꢀsquares methꢀ
od (SHELXL97)25 against F2 for all data in the anisotropic apꢀ
proximation for all nonꢀhydrogen atoms. The H atoms of the
CH, CH2, and CH3 groups were placed in geometrically calcuꢀ
lated positions and refined with isotropic temperature parameters
equal to 1.2Ueq of the C atom for the CH and CH2 groups and
1.5Ueq of the C atoms for the CH3 group. The H atoms of the
POOH groups were localized from the difference Fourier synꢀ
thesis and refined isotropically with constraints of equality of the
temperature parameters and O—H distances. The final values of
R factors are R1 = 0.0605 (calculated by Fhkl for 2177 reflections
with I > 2(I)), wR2 = 0.1383 (calculated by F2hkl for all reflecꢀ
tions), GOOF = 0.962. The completeness of data collection was
The distribution ratios (D = [M]org/[M]aq) were determined
at constant concentrations of the extractant (0.01 mol L–1
in 1,2ꢀdichloroethane) and metal (0.025 mmol L–1 in the aqueꢀ
ous phase).
A Malvern Zetasizer Nano analyzer of particle size (NanoꢀZS)
was used to establish the presence of nanosized aggregates in the
organic phase. Extracts were studied after contact of a solution
of the ligand (1 mmol L–1 in 1,2ꢀdichloroethane) with a 0.025 mM
solution of thorium nitrate in 0.04 М HNO3. The choice of
concentrations was determined by the necessity of comparison
with experimental results for other podands (see Ref. 21).
This work was financially supported by the Presidium
of the Russian Academy of Sciences (Program Pꢀ8 "Deꢀ

168
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 1, January, 2015
Safiulina et al.
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Received June 5, 2014