Chelating tendencies in the rows of polymeric sorbents and their copper(II) and lead(II) complexes

Article abstract of DOI:10.1134/S0036023607090288

The physicochemical properties of chelating polymer sorbents (CPSs), derivatives of poly(styrene-2-hydroxy-1-azo-1-2-hydroxybenzene), are studied with respect to copper and lead ions. The following sorption parameters are determined: the optimum acidity, temperature, and duration; the sorption capacity of the sorbent (SCS); and stability constants of polychelates. Quantitative correlations are found between the dissociation constants (pK _a) of the analytical functional group (AFG) of the sorbent, and the pH₅₀ of chelation of the tested metals; between p K_a and the stability of the complexes (logβ); and between pK_a and the charge of the oxygen atom of the complexing group (z); these correlations are intended for use in elucidating the effect of the structural features and acid-base properties of the AFG on the chemisorption parameters of copper(II) and lead(II). These correlations predict the physical-chemical properties of sorbents and the sorption parameters of trace elements for preconcentrating and separating them from biological, natural, and technical objects

Full text of DOI:10.1134/S0036023607090288

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2007, Vol. 52, No. 9, pp. 1474–1477. © Pleiades Publishing, Inc., 2007.
Original Russian Text © N.N. Basargin, E.R. Oskotskaya, A.V. Chebrova, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 9, pp. 1572–1576.
PHYSICAL CHEMISTRY
OF SOLUTIONS
Chelating Tendencies in the Rows of Polymeric Sorbents
and Their Copper(II) and Lead(II) Complexes
N. N. Basargina, E. R. Oskotskayab, and A. V. Chebrovab
a Institute of the Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences,
Staromonetnyi per. 35, Moscow, 119017 Russia
b Natural Sciences Department, Orel State University GOU VPO, ul. Komsomol’skaya 95, Orel, 302026 Russia
Received March 15, 2007
Abstract—The physicochemical properties of chelating polymer sorbents (CPSs), derivatives of poly(styrene-
2-hydroxy-〈1-azo-1'〉-2'-hydroxybenzene), are studied with respect to copper and lead ions. The following sorp-
tion parameters are determined: the optimum acidity, temperature, and duration; the sorption capacity of the
sorbent (SCS); and stability constants of polychelates. Quantitative correlations are found between the dissoci-
'
ation constants (Ka ) of the analytical functional group (AFG) of the sorbent, and the ç50 of chelation of the
'
'
tested metals; between Ka and the stability of the complexes ( logβ ); and between Ka and the charge of the
oxygen atom of the complexing group (z); these correlations are intended for use in elucidating the effect of the
structural features and acid–base properties of the AFG on the chemisorption parameters of copper(II) and
lead(II). These correlations predict the physical–chemical properties of sorbents and the sorption parameters of
trace elements for preconcentrating and separating them from biological, natural, and technical objects
DOI: 10.1134/S0036023607090288
Global pollution of the biosphere with inorganic
compounds is a result of the industrial and agricultural
activity of mankind. Heavy-metal pollution of water,
soil, and foodstuffs is most dangerous. Copper and lead
are classified as toxic elements. Their high abundance
in nature, toxicity, migration ability, and cumulating
ability necessitate the strict control of their level in
nature to maintain it far below their maximum permis-
sible concentrations [1].
Studying and comparing parameters such as the
'
acid–base ionization constants of the AFGs (Ka ), the
ç50 of chelation of the metal cations studied, the
charge of the oxygen atom of the complexing group (z),
and the stability constants of the resulting complexes
(logβ ), we derive the following correlation relations:
'
'
'
Ka – ç50, Ka – logβ , and Ka – z.
These correlation provide a theoretical basis for
synthesizing, choosing, and using CPSs with optimum
physical–chemical and sorption properties for use in
polychelate chemistry and the separation and precon-
centration of the trace elements studied.
In this context, the preconcetration, separation, and
determination of these elements are very topical. The
use of chelating polymer sorbents (CPSs) for these pur-
poses opens wide possibilities for researchers, namely
the individual and group separation of elements with
canceling matrix effects and providing high preconcen-
tration coefficient. A distinctive feature of the CPSs is
the existence of chemically reactive groups in their
polymer matrix, which react with metal ions in solution
forming chelates. The properties of the sorbents are
mostly dictated by the structure and physical–chemical
properties of analytical functional groups (AFGs) in the
matrix [2].
EXPERIMENTAL
Stock solutions of the metals with the concentration
equal to 1 mg/mL were prepared by dissolving an ali-
quot of a high-purity-grade metal in hydrochloric acid
as in work [3]. Working solutions were prepared by
diluting the stock solutions.
Chelating polymer sorbents were synthesized in the
Central Chemical Laboratory of the Institute of the
Geology of Ore Deposits, Petrography, Mineralogy,
and Geochemistry and purified by known methods to
reagent-grade purity. The AFG concentration ψ was
monitored through ultimate analysis for the key atoms
and through determining the sorption capacity of the
sorbent (SCS) [2]. Before use, spherical pellets of the
Here, we discuss the results of our study of the com-
plexing (chemisorption) of copper(II) and lead(II) by
CPSs that are derivatives of polystyrene-2-hydroxy-〈1-
azo-1'〉-2'-hydroxybenzene. We also find correlation
relations between the structure and properties of AFGs
and the physicochemical parameters of chemisorption
of the trace elements studied.
1474

CHELATING TENDENCIES IN THE ROWS OF POLYMERIC SORBENTS
1475
sorbent were pounded with an agate mortar, and
screened through a 200-mesh (0.074-mm) screen.
The structural formula of a fragment of the sorbent is
OH
HO
X
The solution pH was adjusted with weak HCl or a
sodium acetate solution and was measured on an I-500
Ionomer pH-meter accurate to 0.05. The trace-ele-
ment concentration in test solutions was determined by
inversion voltammetry on an Ecotest-VA instrument.
,
HC
H C
N
N
2
Y
n
The sorption parameters—time (τ, min), tempera-
ture (T, °ë), and optimum acidity (pHopt)—were stud-
ied as described in work [4]. Solutions 25 mL in vol-
ume containing 25 µg of a metal and 25 mg of a sorbent
were used in experiments. The ç50 of sorption was
determined graphically from R (%)–pH plots, where R
is the degree of sorption. The SCS was determined as
the amount of the metal (in mg) sorbed by 1 g of the
sorbent under the optimum sorption parameters.
where X and Y are substituents (H, SO3H, NO2, Cl, or
COOH).
The AFG in this class of sorbents is the o,o'-dihy-
droxyazo group. The ionization constants of theAFG of
sorbents were determined elsewhere [6].
The table lists the physicochemical and analytical
parameters of the sorption of trace copper(II) and
lead(II) by CPSs.
The number of protons replaced from the AFG dur-
ing the sorption of copper(II) and lead(II), n, was deter-
mined by the procedure developed for CPSs [2].
All test metals are quite rapidly (in 10–30 min) are
sorbed at room temperature (20 2°ë). A rise in tem-
perature to 60°ë makes the sorption time 5–10 min
shorter, but brings about a significant degradation of the
chelates. The SCSs for the test sorbents fall in the range
of 17.62–25.80 mg of copper(II) or lead(II) per gram of
the sorbent.
The stability constants of complexes of CPSs with
tested ions were determined potentiometrically at
20 2°ë [5].
The numbers of the protons displaced upon sorption
imply that the AFGs are involved in complexing. After
RESULTS AND DISCUSSION
The tested sorbents were brown spherical pellets matching of the pH and degree of extraction (R, %),
insoluble in water, acids, alkalis, and organic solvents. n was found graphically from the slope of the
Parameters of sorbents and chemisorption of copper(II) and lead(II) by CPSs. Determination conditions: T = 20 2°C, µ = 1,
and R = 98–100% (n = 5, P = 0.95)
Charge
'
Sorbent
no.
SCSM,
mg/g
pKa
Sorbent
M
on the
pHpt
pH50
τ, min
n
logβ
[6]
O atom, z
1
2
3
4
5
6
7
8
9
Polystyrene-2-hydroxy-〈1-azo-1'〉-2'-
Cu
Pb
Cu
Pb
Cu
Pb
Cu
Pb
Cu
Pb
Cu
Pb
Cu
Pb
Cu
Pb
Cu
Pb
3.5–5.5 2.5
5.5–7.4 2.1
3.1–5.0 1.9
5.7–7.1 1.9
2.5–5.5 1.5
5.3–7.7 1.7
2.9–5.1 1.3
5.5–7.5 1.4
3.7–5.4 1.8
5.0–7.3 1.9
2.8–5.1 1.5
6.0–8.0 1.5
3.0–5.3 1.1
5.3–7.7 1.4
2.7–5.3 1.1
5.3–7.0 1.2
3.8–5.6 1.8
5.3–7.0 2.2
17.62
19.85
21.05
21.22
23.20
20.70
25.15
21.67
20.82
25.10
22.68
25.80
27.76
25.40
29.40
25.65
19.13
20.57
25
30
25
25
20
25
10
15
30
25
20
25
10
15
15
15
25
30
8.2
8.1
8.0
7.9
7.5
7.5
7.3
7.2
7.7
7.6
7.5
7.4
7.2
7.1
7.1
6.9
8.1
8.0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
8.30
–0.227
hydroxybenzene
Polystyrene-2-hydroxy-〈1-azo-1'〉-2'-
8.10
7.75
7.50
7.90
7.70
5.40
7.30
8.20
–0.226
–0.223
–0.221
–0.224
–0.222
–0.220
–0.218
–0.221
hydroxy-5'-chlorobenzene
Polystyrene-2-hydroxy-〈1-azo-1'〉-2'-
hydroxy-5'-sulfobenezene
Polystyrene-2-hydroxy-〈1-azo-1'〉-2'-
hydroxy-5'-nitrobenzene
Polystyrene-2-hydroxy-〈1-azo-1'〉-2'-
hydroxy-3'-sulfo-5'-chlorobenzene
Polystyrene-2-hydroxy-〈1-azo-1'〉-2'-
hydroxy-3',5'-disulfobenzene
Polystyrene-2-hydroxy-〈1-azo-1'〉-2'-
hydroxy-3'-sulfo-5'-nitrobenzene
Polystyrene-2-hydroxy-<〈1-azo-1'〉-2'-
hydroxy-3',5'-dinitrobenzene
Polystyrene-2-hydroxy-<〈1-azo-1'〉-2'-
hydroxy-3'-carboxy-5'-sulfobenzene
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 9 2007

1476
BASARGIN et al.
pKa'
8.9
HO
O
(a)
X
Y
HC
N
8.5
8.1
7.7
7.3
6.9
1
;
9
N
H2C
2
n
3
7
8
5
where • denotes a metal ion (Cu2+ or Pb2+).
6
This structure of the complex suggests that the metal
cation forms a valence bond with a phenyl oxygen
atom, a coordination bond with the azo nitrogen atom,
and another coordination bond with the oxygen atom of
the phenyl group that remains undissociated under the
sorption conditions (äéç = 9.08–9.80; çopt 2.5–8.0).
The net positive charge of the cation is balanced by the
anions in the solution.
Comparing the ionization constants of the AFGs
with the stability constants and the charge of the oxy-
gen atom of the complexing group, we found correla-
tion relations between these parameters (Figs. 2, 3).
Mathematically, these correlations are described by the
following linear equations:
4
0.5
1.0
1.5
(b)
2.0
2.5
9
3.0
8.6
8.4
8.2
8.0
7.8
7.6
1
2
5
6
3
4
8
7
7.4
7.2
'
for the copper–sorbent system, Ka = 0.97 logβ +
6.25 (r = 0.9922);
1.0
1.5
2.0
2.5
pH50
'
for the lead–sorbent system, Ka = 0.84logβ +
6.95 (r = 0.9957).
'
The Ka – z correlation is based on the linear corre-
'
Fig. 1. Correlation between the acid–base properties (Ka )
lation between the acid–base properties of the AFG and
the electron charge induced by the substituent in the
para on the reactive site and neighboring atoms; the lat-
ter is revealed by quantum-chemical computations
using Hyper Chem Release 7.01 for Windows software.
From the correlation between the acid–base proper-
ties of the AFG and the charge of the oxygen atom of
the complexing group, it follows that the substituent is
in the effective position in which the electron density is
redistributed along the conjugated chain to the oxygen
atom of the AFG; ultimately, this is manifested as a
change in the acid–base properties of the AFG.
of the AFGs of sorbents and the ç for sorption of (a)
50
copper and (b) lead for sorbents 1–9.
logR (100 – R) versus pH plot. In the test systems, one
proton is replaced for copper and zinc.
A match between the ç50 of sorption for copper
'
and lead and the acid–base properties (Ka ) of the
AFG implies that there are correlation relations
between these quantities (Fig. 1); the correlations are
described by the following linear equations:
'
for the copper–sorbent system, ç50 = (Ka – 5.8)
0.75 (r = 0.9696);
'
The correlation between the Ka of the sorbents
studied, except for the carboxysulfo-substituted sor-
bent, and the charge of the oxygen atom of the com-
plexing group is
'
for the lead–sorbent system, ç50 = (Ka – 5.95)
1.19 (r = 0.9723).
'
z = 0.25Ka – 0.213,
'
The quantitative relation between the Ka of the
AFG and the ç50 of sorption verifies the direct
involvement of the 2'-hydroxy group of the AFG of the
test sorbents in chelation.
From the structure of the AFG introduced prepara-
tively into the polymer matrix, the numbers of the pro-
tons replaced upon sorption, and the quantitative rela-
'
or Ka = (z + 0.213)/0.25 (r = 0.9743).
These correlations quantitatively predict, proceed-
ing from Ka , the ç50 of sorption and the strength of
complexes formed by ions with this group of sorbents.
For example, let us have no a sorbent bearing an
arsono group AsO3H2. The tabulated Hammett constant
σÔ for this substituent is 0.460 [2]. The correlation rela-
'
'
tion between the Ka of the AFG and the ç50 of sorp-
tion, we suggest that the most likely structure of the
resulting chelate complex is
'
tion between σÔ and Ka for mono- and disubstituted
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 9 2007

CHELATING TENDENCIES IN THE ROWS OF POLYMERIC SORBENTS
1477
pKa'
8.8
pKa'
(a)
7.2 7.4 7.6 7.8 8.0 8.2 8.4 8.6 8.8
–0.216
8.6
8.4
–0.218
–0.220
–0.222
–0.224
–0.226
8
4
9
7
3
8.2
8.0
7.8
7.6
7.4
7.2
1
5
6
2
2
3
5
–0.228
–0.230
1
7
6
8
4
–0.232
z
7.0 7.25 7.50 7.75 8.0 8.25 8.50 8.75
'
Fig. 3. Correlation between the acid–base properties (Ka )
of the AFGs of sorbents and the charge of the oxygen atom
of the complexing group for sorbents 1–8.
9.0
(b)
1
8.5
8.0
7.5
7.0
2
5
Thus, the calculations show that the predicted sor-
bent is not superior to the existing one in its ç50 of
sorption (the pH shift is 0.76 (Cu) and 1.95 (Pb)), and
its synthesis for subsequent use in the development of a
new preconcentration method is impertinent in view of
the unavailability of the precursor.
9
6
7
8
3
4
6.5
7.0
7.5
8.0
8.5
REFERENCES
logβ
1. V. F. Protasov, Ecology, Health, and Environmental Pro-
tection in Russia (Finansy i Statistika, Moscow, 2001)
[in Russian].
'
Fig. 2. Correlation between the acid–base properties (Ka )
2. N. N. Basargin, Yu. G. Rozovskii, V. A. Golosnitskaya,
et al., Correlations and Prediction of the Analytical
Properties of Chelating Polymer Sorbents and Their
Complexes with Chemical Elements (Nauka, Moscow,
1986) [in Russian].
of the AFGs of sorbents and the stability constants ( logβ )
of the complexes formed with (a) copper and (b) lead ions
for sorbents 1–9.
'
3. P. P. Korostelev, Solution Preparation for Chemical
Analysis (Izd-voAN SSSR, Moscow, 1962) [in Russian].
4. N. N. Basargin, Yu. G. Rozovskii, V. A. Golosnitskaya,
et al., Organic Reagents and Chelating Sorbents in Mi-
neral Analysis (Nauka, Moscow, 1980) [in Russian].
5. K. M. Saldadze and V. D. Kopylova-Valova, Complexing
Ion Exchangers (Complexites) (Khimiya, Moscow,
1980) [in Russian].
6. N. N. Basargin, E. R. Oskotskaya, O. E. Simakova, and
E. A. Dorofeeva, Application of Poly(azostyrene) Sor-
bents with o,o'-Dihydroxyazo Group in Environmental
Analysis for Be, Cd, Sc, Y, Co, and Ni: Theory and Prac-
tice (OGU, Nauka, IGEM RAN, Izd–vo OOO Kartush,
Orel, 2006) [in Russian].
sorbents was derived previously: Ka = 8.29 – 0.29σÔ,
'
and Ka = 8.11 – 0.38σÔ + Ó [7]. We can use these corre-
lation relations to calculate Ka for the given model
'
monosubstituted sorbent:
'
Ka = 8.29 – (0.29 × 0.46) = 8.16.
Next, substituting this value to the correlation equa-
tion, we calculate ç50 and logβ as follows:
for copper, ç50 = (8.16 – 5.8)/0.75 = 3.15,
logβ = (8.16 – 6.25)/0.97 = 1.97;
for lead, ç50 = (8.16 – 5.95)/1.19 = 1.86,
7. N. N. Basargin, E. R. Oskotskaya, and A. V. Chebrova,
Zh. Fiz. Khim. 80 (12), 2260 (2006) [Russ. J. Phys.
Chem. 80 (12), 2016 (2006)].
logβ = (8.16 – 6.95)/0.84 = 1.44.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 9 2007