Physicochemical properties and complex formation of ethyl 2-aryl(methyl)sulfonylamino-4,5,6,7-tetrahydrobenzothiophene-3-carboxylates

Article abstract of DOI:10.1134/S1070363214060243

Acid-base properties, solubility, and chemical stability of ethyl 2-aryl(methyl)sulfonylamino-4,5,6,7-tetrahydrobenzothiophene-3-carboxylates have been studied. Complexes of Cu(II), Co(II), and Ni(II) with one of the ligands have been prepared and isolate

Full text of DOI:10.1134/S1070363214060243

ISSN 1070-3632, Russian Journal of General Chemistry, 2014, Vol. 84, No. 6, pp. 1202–1206. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © L.G. Chekanova, K.O. Manylova, P.T. Pavlov, Yu.B. El’chishcheva, A.S. Kandakova, 2014, published in Zhurnal Obshchei Khimii,
2014, Vol. 84, No. 6, pp. 1025–1029.
Physicochemical Properties and Complex Formation
of Ethyl 2-Aryl(methyl)sulfonylamino-4,5,6,7-
tetrahydrobenzothiophene-3-carboxylates
L. G. Chekanovaa, K. O. Manylovaa, P. T. Pavlovb,
Yu. B. El’chishchevab, and A. S. Kandakovab
a Institute of Technical Chemistry, Ural Branch, Russian Academy of Sciences,
ul. Akademika Koroleva 3, Perm, 614013 Russia
е-mail: larchek.07@mail.ru
b Perm State National Research University, Perm, Russia
Received October 17, 2013
Abstract—Acid-base properties, solubility, and chemical stability of ethyl 2-aryl(methyl)sulfonylamino-
4,5,6,7-tetrahydrobenzothiophene-3-carboxylates have been studied. Complexes of Cu(II), Co(II), and Ni(II)
with one of the ligands have been prepared and isolated; their solubility products were determined.
Keywords: Gewald thiophene, physicochemical properties, complex formation, nonferrous metal
DOI: 10.1134/S1070363214060243
The interest in chemistry of substituted thiophenes
is to a great extent due to the possibility of formation
of their oligo- and polymeric derivatives that possess
unusual properties and can therefore be used as
molecular switches, organic semiconductors, dyes, and
biologically active compounds [1, 2]. The composition
and structure of coordination compounds of thiophene
derivatives with metal ions have been studied [3, 4];
the application of thiophene derivatives for metals
concentration has been as well discussed, for instance,
for gold leaching in hydrometallurgy [5].
nonferrous metals has not been discussed in the
literature.
COOC2H5
O
S
NH
S
R
O
Iа−If
R = CH3 (а); C6H5 (b); C6H4(CH3-p) (c); C6H4Сl-p (d);
C6H4(NO2-p) (e); C6H4(NHCOCH3-p) (f).
The prepared compounds Ia–If were white
crystalline solids. Their yields and melting points are
collected in Table 1. The composition and the structure
of the products were confirmed by elemental analysis,
IR, and 1H NMR spectroscopy.
In this work we prepared ethyl 2-aryl(methyl)-
sulfonylamino-4,5,6,7-tetrahydrobenzothiophene-3-
carboxylates Ia–If and studied their physicochemical
properties and complex formation with Cu(II), Co(II),
and Ni(II) to estimate the potential of their application
in flotation technology.
The following characteristic absorption bands were
observed in IR spectra of the studied compounds:
stretching vibrations of secondary amino group at
3170–3340 cm–1, ester С=О stretching vibrations at
1655–1670 cm–1 (two bands were observed in the case
of compound If: at 1695, amide I band, and at
1660 cm–1), and SO2 stretching vibrations (symmetric
at 1160–1180 cm–1 and asymmetric at 1320–1340 cm–1);
the presence of NO2 group in compound Ie was
The N-substituted sulfonyl thiophene derivatives
Ia–If were chosen due to the presence of two
functional fragments: substituted amine and carboxy
groups that were anticipated to form chelates with non-
ferrous metals and thus extend possible applications of
the ligands. To the best of our knowledge, the
application of sulfonyl derivatives of the Gewald-type
thiophenes for concentration and separation of
1202

PHYSICOCHEMICAL PROPERTIES AND COMPLEX FORMATION
1203
Table 1. Selected parameters of compounds Ia–If
confirmed by the absorption band of the asymmetric
stretching vibrations at 1540 cm–1.
Comp.
R
mp, °C
Yield, % Rfa
no.
Iа
Ib
Ic
Singlet signal of the NH group proton was observed
in 1Н NMR spectra of the products at 10.35–
10.54 ppm (the spectrum of compounds If contained
two singlets at 10.30 and 10.32 ppm). Aromatic ring
protons resonated at 7.32–8.20 ppm, and multiplet
signals of methylene protons were found at 1.67–
1.70 ppm (the groups in positions 5 and 6) or at 2.54–
2.57 ppm (the groups in positions 4 and 7). Ethoxy
group signals appeared as quartets at 4.17–4.20 ppm
(СН2О) and triplets at 1.24–1.30 ppm (СН3). The
spectrum of compound If contained additionally a
singlet at 2.11 ppm assigned to acetyl СН3.
CH3
76–78
68
75
78
65
75
69
0.67
0.31
0.31
0.46
0.39
0.33
C6H5
113–115
125–127
109–110
133–135
p-C6H4(CH3)
p-C6H4Сl
Id
Ie
p-C6H4NO2
If
p-C6H4NHCOCH3 149–151
a
Mobile phases: benzene–diethyl ether 1 : 2 (Ia–Ic); benzene (Id,
If); benzene–diethyl ether–acetone 9 : 8 : 2 (Ie).
The compounds structure suggested that they
should be acidic. Electron absorption spectra of the
studied compounds confirmed the existence of
different ionization states at different pH (see example
in the figure). In particular, the spectra of their neutral
aqueous-ethanolic solutions contained absorption
bands at 208–210 nm (ester group), at 250 nm (р–π*
conjugated thiophene ring), and at 300 nm (due to the
electron density transfer from donor to acceptor). In
the alkaline medium, the band at 300 nm shifted to
longer wavelength by 25–30 nm and grew stronger.
The industrial application of compounds is often
determined by their solubility. For instance, the
solubility of flotation and extraction agents to be used
in hydrometallurgy processes should be reasonably
high (above 0.03–0.1 mol/L in the corresponding
solvents [6]). Experimental data collected in Table 2
show that compounds Ia–If can be applied as
precipitants or collectors for ionic flotation in the form
of solutions in ethanol or in 0.1 mol/L KOH; and they
should be extracted with chloroform or xylene.
Scheme 1.
COOC2H5
O
COOC2H5
KOH
H+
+ H2O
O
NH S R
O
S
S
N−
S R
K+
O
Table 2. Solubility of compounds Ia–If, mmol/L (g/L)
Comp.
no.
Ethanol 1 mol/L 1 mol/L KОН
Water
Hexane
Xylene
Isoamyl alcohol
Chloroform
>65 (>19)
18.0 (6.4)
25.0 (9.6)
18.0 (7.0)
3.4 (1.4)
40.0 (12.50)
8.0 (3.07)
0.9 (0.33)
0.15 (0.06)
1.8 (0.74)
1.1 (0.47)
0.3 (0.10)
1.4 (0.50)
0.4 (0.16)
1.1 (0.43)
0.73 (0.30)
0.2 (0.10)
13.0 (4.0)
6.8 (2.5)
7.0 (2.6)
6.0 (2.4)
1.2 (0.5)
0.2 (0.1)
>40 (>14)
21 (6.3)
12 (4.4)
21 (7.8)
20 (7.9)
3 (1.1)
>40 (>13)
1260 (459.7)
1950 (741.5)
1590 (637.7)
1190 (489.4)
66 (27.7)
Iа
Ib
Ic
Id
Ie
If
360 (132.0)
680 (258.6)
460 (184.8)
515 (211.3)
4 (1.6)
37.0 (15.6)
20 (8.3)
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CHEKANOVA et al.
ethanolic solutions with varied ratio of water to
A
ethanol. The determined acidity constants were then
extrapolated to zero concentration of ethanol (linear fit
of pKa with mass fraction of ethanol) to get рKа value
in aqueous solution [7].
The so determined рKа values of compounds Ia–If
are given in Scheme 2.
The studied compounds were weak acids; the
acidity constants of compounds Ib–If was linear with
the Hammett constant σ:
pKa = 7.55 – 1.41σpara (r = 0.978).
The determined acidity constants suggested that the
studied compounds should form complexes with
nonferrous metals in neutral and alkaline media. It was
therefore important to check the ligands stability in the
alkaline medium. It was found that they were stable
over 4 h at 60°С and over 24 h at 20°С (0.1 mol/L
KOH).
λ, nm
Electron absorption spectra of solutions of ethyl-2-mesyl-
amino-4,5,6,7-tetrahydrobenzothiophene-3-carboxylate (Ia,
10–5 mol/L) in aqueous ethanol at different pH: 6.6 (1), 9.0
(2), and 10.7 (3).
Following the procedure described elsewhere [8]
we prepared several complexes with compound Ic in
the form of precipitates (Table 3). The complexes were
insoluble in water, but soluble in ethanol, chloroform,
and hexane. The IR spectroscopy (Table 4) and
elemental analysis data suggested the complexes
composition to be [МL2] (Scheme 3).
The ionization of compounds Ia–If in alkaline
medium occurred as deprotonation of the sulfonamide
group (Scheme 1).
In order to determine the compounds acidity
constants, we studied the solutions absorbance at 320 nm
as a function of pH. However, the absorbance change
in the course of ionization was sufficiently high only in
the case of compound Ia; therefore, the acidity
constants of the rest of the products were determined
by means of potentiometric titration.
One of the requirements for a reagent to be used as
collector in ionic flotation is a low solubility of its
metal complex [9]. We calculated the solubility
products SP of the prepared complexes as described in
[8] (taking into account the metal ion and the ligand
ionization states above the precipitate). The elec-
As the studied compounds were poorly soluble in
water, their ionization was studied in aqueous-
Scheme 2.
Compound
рKа
Iа
Ib
7.64±0.04
Ic
Id
Ie
If
7.57±0.05
7.69±0.03 (SP)
7.77±0.05
7.10±0.06
6.45±0.04
7.58±0.05
Table 3. Selected properties of metal complexes with ethyl 2-tosylamino-4,5,6,7-tetrahydrobenzothiophene-3-carboxylate Ic
(HL)
Compound, color
[CuL2], dark-blue
pH range of formation
7.0–10.8
–log SP
17.08
13.86
16.02
Solubility, mol/L
1.28 × 10–6
cfMree a
2.5 × 10–4
3.3 × 10–2
1.0 × 10–2
[СоL2], light-brown
8.5–11
1.51 × 10–5
[NiL2], green
7.4–10.8
2.87 × 10–6
a As calculated from the dissociation constants of [M(NH3)4]2+ complexes.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 6 2014

PHYSICOCHEMICAL PROPERTIES AND COMPLEX FORMATION
1205
Table 4. Position of stretching vibrations bands (cm–1) in IR
spectra of ethyl 2-tosylamino-4,5,6,7-tetrahydrobenzothio-
phene-3-carboxylate Ic (HL) and its metal complexes
trolytes concentration was below 10–3 mol/L, and their
activity coefficients were therefore taken equal to unity.
The complexes solubility products were calculated
as follows:
SP = [М2+][L–]2,
where the equilibrium ligand concentration [L–]
determined as
Compound
HL (Ic)
[CuL2]
ν(N–H)
ν(C=O)
1657
ν(SO2)
3117
1160, 1323
1148, 1316
1145, 1317
1165, 1323
–
–
–
1595
[СоL2]
1587
[L–] = {K[cHL – 2cM(Si/100)]}/[H+],
[NiL2]
1563
where K, dissociation constant of the ligand НL; cМ
and cНL, initial concentrations of the metal ion and the
ligand, respectively, mol/L; Si, degree of the metal ion
precipitation at the observation point, %.
were recorded on a MERCURY plus 300 spectrometer
(Varian, USA). Melting points were determined using
the PTP instrument in standard capillaries. Elemental
analysis was performed with the CHNS-932
instrument (LECO Corporation, USA). Thin layer
chromatography was run with the Silufol UV-254
plates using iodine vapor as developer.
The calculated SP values are collected in Table 3.
The most efficient precipitation with compound Ic was
attained in the case of copper ions. Low solubility of
the complexes in water suggested that the studied
compounds were promising collectors to be used in
ionic flotation of nonferrous metals. Comparison of the
complexes solubility with concentration of the free
metal ion in equilibrium with ammonia complexes cMfree
[10] suggested that the complex formation reaction
should be efficient for the precipitation of the metal
ions from their ammonia solutions.
Compounds Ia–If were prepared via interaction of
ethyl 2-amino-4,5,6,7-tetrahydrobenzothiophene-3-
carboxylate with the corresponding sulfonyl chlorides
at room temperature in pyridine; the products were
crystallized from 2-propanol [11]. The parent ester was
prepared in a single stage from cyclohexanone,
cyanoacetic ester in alcoholic solution, and sulfur,
using diethanolamine as catalyst [12]. The products
purity was confirmed by IR and 1Н spectroscopy, TLC,
and elemental analysis.
EXPERIMENTAL
IR spectra (mineral oil suspension) were recorded
on
a
IFS-66/S Fourier spectrometer (Bruker,
The fraction of the major component in the product
was determined by potentiometric titration [13] of
0.1 g of the product in 30 mL of ethanol with 0.1 mol/L
ethanolic KОН. The major component fraction was in
all cases above 97%.
1
Germany), H NMR spectra (DMSO-d6 solutions)
Scheme 3.
w, % = (VKOHcKOHMI)/m × 10.
The products solubility was determined as des-
cribed elsewhere, by gravimetry [14], spectro-photo-
metry [14], and refractometry [15]. UV spectra were
registered with the SF-2000 spectrophotometer;
refractive index was measured using the IRF-22 refrac-
tometer. Acid dissociation constants were determined
either by means of spectrophotometry or by poten-
tiometry. рН and E of the solutions were measured
with the I-160M ionomer (ANTEKh, Belarus) equip-
ped with glass and silver chloride electrodes. The
measured рН values were corrected for the ethanol
presence as described elsewhere [16].
S
O
O
OC2H5
O
N
S
M
O
S
N
S
OC2H5
O
O
The рKа values were calculated from potentiometry
M = Cu, Co, Ni.
results as follows.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 6 2014

1206
CHEKANOVA et al.
istry of Thienopyridines and Related Systems),
(1 – α)cI – [H+] + [OH–]
αcI + [H+] – [OH–]
pKa = log
+ pH,
Moscow: Nauka, 2006.
5. Soul, K.S. and Skott, T.D., RF Patent no. 2114926,
1998.
6. Ritchi G.M., Eshbruk, A.V., Ekstraktsiya: Printsipy i
primenenie v metallurgii (Extraction: Principles and
Application in Metallurgy), Moscow: Metallurgiya, 1983.
where α, degree of neutralization of the studied com-
pound; cI, the total compound concentration, mol/L;
[Н+] and [OH–], concentrations of the respective ions,
mol/L.
7. Zheltvai, I.I. and Spinul, V.V., Russ. J. Inorg. Chem.,
Hydrolytic stability of the compounds was studied
by spectrophotometry as described elsewhere [14].
2010, vol. 55, no. 4, p. 634.
8. Radushev, A.V., Chekanova, L.G., and Shabalina, L.S.,
Russ. J. Inorg. Chem., 2004, vol. 49, no. 3, p. 426.
The content of the metal ions in the solutions was
determined using the iCE 3500 atomic absorption
spectrometer with flame atomization (Thermo Fisher
Scientific, USA).
9. Radushev, A.V., Chekanova, L.G., and Chernova, G.V.,
Tsvet. Met., 2005, no. 7, p. 34.
10. Lur’e, Yu.Yu., Spravochnik po analiticheskoi khimii
(Handbook on Analytical Chemistry), Moscow: Khimiya,
1979.
ACKNOWLEDGMENTS
11. Shvedov, V.I., Kharizomenova, I.A., Medvedeva, N.V.,
and Grinev, A.N., Khim. Geterotsikl. Soedin., 1977,
no. 2, p. 204.
This work was supported by the Russian Founda-
tion for Basic Research (project no. 14_03_00606_a).
12. Geval’d, K., Khim. Geterotsikl. Soedin., 1976, no. 10,
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