Protolytic and complexing properties of hetarylhydrazones derived from o-tosylaminobenzaldehyde

Article abstract of DOI:10.1134/S1070363212070080

New ligand systems were synthesized by condensation of o- tosylaminobenzaldehyde with quinolin-2-ylhydrazine and 1-methyl-1H-benzimidazol- 2-ylhydrazine. Acid-base properties of the resulting hetarylhydrazones and their complexing power toward bivalent co

Full text of DOI:10.1134/S1070363212070080

ISSN 1070-3632, Russian Journal of General Chemistry, 2012, Vol. 82, No. 7, pp. 1233–1237. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © L.D. Popov, O.I. Askalepova, E.B. Kaimakan, Yu.P. Tupolova, I.N. Shcherbakov, S.I. Levchenkov, V.V. Lukov, O.V. Maevskii,
V.A. Kogan, A.S. Burlov, A.A. Zubenko, 2012, published in Zhurnal Obshchei Khimii, 2012, Vol. 82, No. 7, pp. 1129–1134.
Protolytic and Complexing Properties of Hetarylhydrazones
Derived from o-Tosylaminobenzaldehyde
L. D. Popova, O. I. Askalepovaa, E. B. Kaimakana, Yu. P. Tupolovaa, I. N. Shcherbakova,
S. I. Levchenkovb, V. V. Lukova, O. V. Maevskiia, V. A. Kogana, A. S. Burlovc, and A. A. Zubenkod
b Southern Federal University, ul. Zorge 7, Rostov-on-Don, 344090 Russia
e-mail: tup_u@mail.ru
b Southern Research Center, Russian Academy of Sciences, Rostov-on-Don, Russia
e-mail: s.levchenkov@gmail.com
c Research Institute of Physical and Organic Chemistry, Southern Federal University, Rostov-on-Don, Russia
d North Caucasian Zonal Research Veterinary Institute, Novocherkassk, Russia
Received June 9, 2011 g.
Abstract—New ligand systems were synthesized by condensation of o-tosylaminobenzaldehyde with quinolin-
2-ylhydrazine and 1-methyl-1H-benzimidazol-2-ylhydrazine. Acid–base properties of the resulting
hetarylhydrazones and their complexing power toward bivalent copper, nickel, and cobalt ions were studied.
The stability constants of the complexes were determined.
DOI: 10.1134/S1070363212070080
Hetarylhydrazones, i.e., condensation products of
heterocyclic hydrazines and carbonyl compounds,
having an acyclic moiety, have long attracted
researchers’ attention, primarily due to their strong
complexing power [1–7]. In addition, hetarylhydra-
zones exhibit diverse biological activity [8–12],
possess photochemical properties [13–15] and electriv
conductivity [16], and are efficient analytical reagents
for metal ions [17–21].
Schiff bases and hydrazones derived from o-
tosylaminobenzaldehyde, as well as their metal com-
plexes, were the subject of numerous studies [22–28];
however, hetarylhydrazones derived from o-tosyl-
aminobenzaldehyde were not reported. Therefore, the
goal of the present work was to synthesize new
hetarylhydrazones Ia and Ib by condensation of o-
tosylaminobenzaldehyde with quinolin-2-ylhydrazine
and 1-methyl-1H-benzimidazol-2-ylhydrazine and ex-
amine their physicochemical properties.
The structure of hydrazones Ia and Ib was
determined on the basis of their elemental composi-
tions (Table 1), IR, 1H NMR, and electronic absorption
spectra, and potentiometric titration data.
The IR spectra of Ia and Ib (Table 2) contained a
broad absorption band in the region 3100–3200 cm–1
due to stretching vibrations of NH groups in the
hydrazone and tosylamino fragments; stretching vibra-
tions of the azomethine C=N bond appeared at
1615 cm–1; and symmetric and antisymmetric stretching
vibrations of the sulfonyl group were observed at
1170–1160 and 1345–1325 cm–1, respectively
Compound Ia displayed the following signals in the
1H NMR spectrum (DMSO-d6), δ, ppm: 11.5 a and
11.1 s (1H each, NH, exchangeable with D2O), 2.2 s
and 3.3 s (3H each, CH3), 8.3 s (1H, N=CH), 7.0–7.9
NH
Ts
1
m (12H, Harom). The H NMR spectrum of Ib is
similar, δ, ppm: 11.57 11.05 (1H each, NH), 2.2 s (3H,
CH3), 8.25 s (1H, CH=N), 7.1–7.8 m (14H, Harom);
addition of D2O leads to complete disappearance of the
NH proton signals, indicating their acidic character.
N
NH
Het
Ia, Ib
Het = 1-methyl-1H-benzimidazol-2-yl (a), quinolin-2-yl
(b), Ts = 4-methylphenylsulfonyl.
In the electronic spectra of solutions of Ia and Ib in
ethanol and aqueous ethanol we observed long-wave
1233

1234
POPOV et al.
Table 1. Colors, melting points, and elemental analyses of compounds Ia, Ib, and IIIa–IIIf
Found, %
Н
Calculated, %
Comp.
no.
Color
mp, °C
Formula
С
N
С
Н
N
Yellow
Yellow
Green
Green
Brown
Green
Brown
Brown
197
196
60.5
66.3
57.0
57.3
57.1
61.0
61.9
62.0
5.3
16.5
13.3
15.6
15.9
16.5
12.3
12.4
12.2
C22H21N5O2S
60.1
66.4
57.5
57.9
57.9
61.8
62.1
62.1
5.0
4.8
4.6
4.6
4.6
4.3
4.3
4.3
16.7
13.5
16.0
16.1
16.1
12.5
12.6
12.6
Ia
4.5
C23H20N4O2S
Ib
>250
>250
>250
>250
>250
>250
4.1
C44H40N10O4S2Сu
C44H40N10O4S2Co
C44H40N10O4S2Ni
C46H38N8O4S2Сu
C46H38N8O4S2Сo
C46H38N8O4S2Ni
IIIa
IIIb
IIIc
IIId
IIIe
IIIf
4.3
4.1
4.0
4.1
3.9
absorption bands at λ 356–358 nm (logε ≈ 4) (Figs. 1, 2).
In going to acid medium, the absorption maximum of
Ia shifts to the blue region (Δλ = 53 nm) (Fig. 1).
Protonation of hydrazone Ib is accompanied by a red
shift (Δλ = 16 nm) and increase in the intensity of the
long-wave absorption maximum and appearance of a
new band at λmax 284 nm (Fig. 2). Variation of the
spectral pattern of Ib in going to acid medium is
related to n→π*-transitions with participation of the
nitrogen atom in the heteroring. Less basic hydrazone
Ia displayed appreciable variation of the spectral
pattern in going to alkaline medium.
With a view to estimate the basicity of particular
nitrogen atoms, we synthesized two model compounds
IIa and IIb and examined their protolytic properties.
Taking into account structural similarity of compounds
II and hydrazones I, the obtained pKa values were
assigned to different nitrogen atoms in molecules I as
shown below.
8.25
NH
Ts
4.1
N
The acid–base properties of hydrazones Ia and Ib
were studied by potentiometric titration [29] in
aqueous ethanol. Their structure suggests existence of
protonated, neutral, and deprotonated species, depend-
ing on the acidity of the medium. In acid medium,
molecules of both hydrazones Ia and Ib undergo
protonation at the endocyclic nitrogen atoms and
nitrogen atom of the azomethine group, which possess
the highest negative effective charge and electron
density. Ionization of Ia and Ib in alkaline medium
involves proton abstraction from the substituted amino
group and NH nitrogen atom in the hydrazone
fragment. The obtained pKa values are given below.
IIa
10.9
NH
Ts
>11.0
N
NH
IIb
Ts
10.6
NH
4.9
N
2.3
N
>11
NH
Table 2. Principal absorption bands (ν, cm–1) in the IR
spectra of compounds Ia, Ib, and IIIa–IIIe
N
CH3
Ia
Comp. no.
C=N
SO2as
SO2s
NH
9.43
NH
1615 m
1605 m
1605 m
1590 s
1325 m
1300 s
1310 m
1280 m
1160 m
1150 s
1150 s
1120 s
3200
–
–
Ia
Ts
IIIa
IIIc
IIIe
>11
NH
3.85
N
1.1
N
1615 s
1600 s
1595 s
1345 s
1312 w
1290 w
1170 s
1100 m
1105 s
3100
–
–
Ib
IIIb
IIId
Ib
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 7 2012

PROTOLYTIC AND COMPLEXING PROPERTIES OF HETARYLHYDRAZONES
1235
D
D
λ, nm
λ, nm
Fig. 1. Electronic absorption spectra of ethanolic solutions of
hetarylhydrazone Ia (cIa = 2.5×10–5 M): (1) aqueous
ethanol, (2) acid medium (cHCl = 0.1 M), and (3) alkaline
medium (cNaOH = 0.1 M).
Fig. 2. Electronic absorption spectra of ethanolic solutions of
hetarylhydrazone Ib (cIa = 2.5×10–5 M): (1) aqueous
ethanol, (2) acid medium (cHCl = 0.1 M), and (3) alkaline
medium (cNaOH = 0.1 M).
By reactions of hydrazones Ia and Ib with Cu(II),
Co(II), and Ni(II) salts we obtained the corresponding
1:2 (metal–ligand) complexes IIIa–IIIf. Their struc-
ture was determined on the basis of their elemental
compositions, IR spectra, and magnetochemical data.
Unlike the free ligands, complexes III were charac-
terized by reduced frequency of the C=N bond vibra-
tions (Table 2), indicating participation of the azo-
methine nitrogen atom in the coordination. Deprotona-
tion of the amino group upon complex formation was
confirmed by disappearance of NH absorption in the
region 3100–3200 cm–1. The low-frequency shift (by
10–20 cm–1) of absorption bands due to symmetric and
antisymmetric stretching vibrations of the SO2 group is
likely to reflect its coordination to the metal ion [28].
According to the magnetochemical data, complexes
IIIa–IIIf are mononuclear. Their effective magnetic
moments approach the corresponding purely spin
values, and they almost do not change as the
temperature was reduced down to 77 K.
Complexes IIIa–IIIf in solutions showed a strong
absorption band at λ 415–490 nm in the electronic
spectra. The spectral parameters of IIIa–IIIf are
collected in Table 3.
It is known that the yield depends on the acidity of
the medium, which is an important factor determining
the equilibrium state in complexation process [29]. In
the case of hydrolyzable metal ions, rise in pH
increases the concentration of anionic ligand, but the
concentration of metal ions simultaneously decreases
as a result of formation of mono- and dihydroxo
complexes. Therefore, to study the complexation
reaction for analytical purposes, it was necessary to
determine an optimal pH value which ensures the
maximal yield of colored product. We examined the
dependence of the absorbance of Cu(II), Co(II), and
Ni(II) complexes with hydrazones I in solution upon
pH. The most intense color developed in the pH ranges
indicated in Table 4.
Stability constant is an important physicochemical
parameter of coordination compounds. The stability
constants of complexes III were determined by spec-
trophotometry using the equilibrium displacement
technique, linear dependence (according to Rossoti),
and preliminarily calculated equilibrium constant [30,
31]. The resulting stepwise constants were refined by
approximating the sum of the partial mole fractions to
unity by the following equation:
Het
NH
N
Ts
N
M
N
Ts
N
NH Het
IIIa_IIIf
Het = 1-methyl-1H-benzimidazol-2-yl (a, c, e), quinolin-2-
yl (b, d, f); M = Cu (a, b), Co (c, d), Ni (e, f).
Ai/Amax + Ai/Amaxβ1[L] + (Ai/Amax – 1)β2[L]2 = 0.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 7 2012

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POPOV et al.
Table 3. Spectral parameters of solutions of complexes
IIIa–IIIe in aqueous acetone (c = 2×10–5 M)
for 4 h under reflux, and the precipitate was filtered
off, washed with hot methanol, and dried under
reduced pressure.
Comp. no.
IIIa
λmax, nm
430
ε, l mol–1 cm–1
9.75×103
1.11×104
1.11×104
9.75×103
8.13×103
The IR spectra were recorded on a Varian 1000 FT-
1
IR spectrometer. The H NMR spectra were measured
425
IIIc
on a Varian Unity-300 spectrometer using tetramethyl-
silane as internal reference and DMSO-d6 as solvent.
The magnetic susceptibilities of the complexes were
determined by the relative Faraday method in the
temperature range from 78 to 300 K using a setup
manufactured at the Physical and Colloidal Chemistry
Department, Southern Federal University; Hg[Co(CNS)4]
was used as calibration standard. The electronic
absorption spectra (λ range 200–800 nm) were deter-
mined on a Cary 50 Scan spectrophotometer.
430
IIIe
490
IIIb
470
IIId
Table 4. Optimal pH values for complex formation
Ligand no.
Metal
Cu(II)
Co(II)
Ni(II)
Cu(II)
Co(II)
рН
9.45
Iа
10.5
10.0
The acidity (pH) of solutions and ionization and
protonation constants were determined with the aid of
an I-120M ionometer. Potentiometric measurements
were performed as follows. Ligand Ia or Ib, 0.1 mmol,
was dissolved in aqueous acetone (1:1), 2 ml of 0.1 M
hydrochloric acid was added, and the mixture was
titrated with a 0.1 M solution of sodium hydroxide. All
experiments were run at a constant ionic strength
(0.1 M NaCl) under continuous stirring. The titrant
was added in 0.02-ml portions using a microburet, and
pKa values were calculated by the formula [29]
8.25
10.5
Ib
Table 5. Stability constants of complexes IIIa–IIIe
Comp. no.
IIIa
β1
β2
1.8×109
1.5×106
1.6×106
6.4×109
1.0×105
3.1×1017
4.5×1011
1.5×1012
1.7×1019
2.7×1010
IIIc
IIIe
IIIb
(1 – a)cL – [H+] + [OH–]
pKa = pH + log –—————————— .
acL + [H+] – [OH–]
IIId
Here, Ai amd Amax are, respectively, the intermediate
and maximal optical densities obtained from the
dependence A = f(pH), and [L] is the ligand concentra-
tion. The stability constants of complexes IIIa–IIIf are
given in Table 5.
Here, a is the degree of neutralization, and cL is the
ligand molar concentration. The optimal pH values for
complex formation and stability constants of the
complexes were determined from the dependences A =
f(pH) at cL = 4×10–4 M, cM = 2×10–5 M, l = 2 cm, A =
f(cL) for aqueous acetone (1:1) at a constant metal
concentration (cM = 2×10–5 M) and optimal pH value.
EXPERIMENTAL
Hydrazones Ia and Ib were synthesized accoring to
the following procedure. A solution of 0.001 mol of the
corresponding hetarylhydrazine in 10 ml of ethanol
was added to a hot solution of 0.001 mol of o-
tosylaminobenzaldehyde [32] in 10 ml of ethanol. The
mixture was heated for 4 h under reflux, and the
precipitate was filtered off, washed with ethanol, and
recrystallized from DMF–ethanol.
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