Synthesis and Electrochemical Properties of 2,5-Disubstituted Derivatives of 1,4-Bis(4,5-diphenylidimidazol-2-yl)benzene

Article abstract of DOI:10.1134/S1070363220060055

Abstract: The data on the synthesis and electrochemical properties of 2,5-disubstituted derivatives of 1,4-bis(4,5-diphenyldimidazol-2-yl)benzene are reported. The effect of substituents on redox properties has been comprehensively investigated. The electrochemical reduction of quinones into the biradical occurs at positive potentials and is a result of two stages of single-electron transfer, through the stage of the monoradical formation. The correlation between the reduction potentials and the salts structure has been found.

Full text of DOI:10.1134/S1070363220060055

ISSN 1070-3632, Russian Journal of General Chemistry, 2020, Vol. 90, No. 6, pp. 961–967. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Obshchei Khimii, 2020, Vol. 90, No. 6, pp. 858–865.
Synthesis and Electrochemical Properties of 2,5-Disubstituted
Derivatives of 1,4-Bis(4,5-diphenylidimidazol-2-yl)benzene
A. V. Dolganova,*, O. Yu. Gantsa, S. G. Kostryukova, A. V. Balandinaa,
M. K. Pryanichnikovaa, A. Sh. Kozlova, Yu. I. Lyukshina, A. A. Akhmatovaa,
V. O. Zhirnovaa, A. D. Yudinaa, and A. S. Timoninaa
a N.P. Ogarev Mordovian National Research University, Saransk, 430005 Russia
*e-mail: dolganov_sasha@mail.ru
Received December 18, 2019; revised December 18, 2019; accepted December 22, 2019
Abstract—The data on the synthesis and electrochemical properties of 2,5-disubstituted derivatives of 1,4-bis(4,5-
diphenyldimidazol-2-yl)benzene are reported. The effect of substituents on redox properties has been comprehen-
sively investigated. The electrochemical reduction of quinones into the biradical occurs at positive potentials and
is a result of two stages of single-electron transfer, through the stage of the monoradical formation. The correlation
between the reduction potentials and the salts structure has been found.
Keywords: biradicals, monoradicals, cyclic voltammetry, 1,4-bis(4,5-diphenyldimidazol-2-yl)benzene
DOI: 10.1134/S1070363220060055
Monoradicals of the triarylimidazoles series are
convenient and widely used objects for the investigation
of correlation between structure and reactivity of stable
radicals, due to their high stability against atmospheric
oxygen [1–3]. However, biradicals of this series have
been scarcely studied so far.
derivatives of 1,4-bis(4,5-diphenylimidazol-2-yl)benzene
were extreme for 1,4-subtituted cyclohexadienes.
2,5-Disubstituted-1,4-bis(4,5-diphenylimidazol-2-yl)-
benzenes were synthesized as shown in Scheme 1.
Starting mono- and dibromo-substituted para-xylenes
required for the synthesis of dialdehydes 1b and 1c
were synthesized as described elsewhere [4, 5]. The
obtained dialdehydes 1a–1c were used for the synthesis
of diimidazoles 2a–2c which were oxidized into quinones
3a–3c.
We have earlier synthesized bisimidazole systems
with imidazole fragments at 1,4- positions of benzene
ring, oxidation of which have yielded quinones exhibiting
paramagnetic susceptibility at heating, due to the rupture
of quinoid bonds. It has been suggested that substitution
of the benzene ring at the o-position with respect to
imidazole moiety should prevent the formation of
quinoid systems, and the so obtained biradical products
should possess unusual redox properties. Herein we
present the approaches to the synthesis of 2-bromo and
2,5-dibromo derivatives of 1,4-bis(4,5-diphenylimidazol-
2-yl)benzene, the simplest diimidazoles. Electrochemical
properties of the obtained compounds were studied by
means of cyclic voltammetry. It was shown that steric
tension caused by two bromine atoms at the central
ring was responsible for the unusual redox properties,
in particular, the shift of the potential of the reduction
process to more positive potentials. The obtained
values of the reduction potentials for 2,5-disubstituted
Oxidation of imidazoles was performed using
potassium hexacyanoferrate(III) in a biphasic benzene–
water system in the presence of potassium hydroxide
(Scheme 2). Quinones were separated as precipitates
partially soluble in benzene. According to the results of
TLC (Silufol, benzene as eluent), imidazoles were not
completely oxidized under the process conditions, since
the oxidation products contained the starting imidazole
along with unidentified products.
To elucidate the influence of the substitution of the
central ring on the properties of quinones 3a–3c, we
studied their electrochemical behavior by means of cyclic
voltammetry. The measurements were conducted using
Pt electrode in СH3CN. Cyclic voltammogram (CV) of
compound 3a is shown in Fig. 1. A single two-electron
961

962
DOLGANOV et al.
Scheme 1.
Scheme 2.
R1
R1
H
N
Ph
Ph
Ph
Ph
Ph
Ph
Ph
N
N
N
N
N
K3[Fe(CN)6]
H2O, C6H6
N
N
H
Ph
R2
2a 2c
R2
3a 3c
ꢀ
ꢀ
R1 = R2 = H (a); R1 = H, R2 = Br (b); R1 = R2 = Br (c).
wave was observed over the range of potentials between
1 and –1 V (at Е = 0.17 V vs. Ag/AgCl/KCl) with
diffusion current limitation.An oxidation peak present at
the reverse semi-cycle indicated the reversibility of the
reduction process. The said peak was present even at low
scan rates, reflecting high stability of the formed specie.
Hence, the species particles formed upon electrochemical
reduction were stable over time and did not undergo any
chemical transformations.
It should be noted that the processes of electrochemical
reduction accompanied by the transfer of two electrons at
the same potential are rare, being possible in certain cases
only. For example, if the second electron is transferred at
more positive potential than the first one, it could look like
a two-electron process. Another option is the transfer of
the first electron directly followed by very fast chemical
reaction (in the case of quinone this is possible at certain
pH values of pH) [6]. In this case, the voltamperogram
shape is changed: the peak becomes narrower, the peak
potential difference of direct and reverse processes is up
to 28 mV, and the peak current is increased [6]. When
two identical redox centers are separated by a spacer,
mere addition of currents can be observed, and the curve
shape remains almost unchanged. The latter case was
observed for the CV shown in Fig. 1. Therefore, the
two-electron behavior of the reduction wave could be
explained as follows: the anion-radical formed at the
first stage quickly detached a proton from the solvent
ȿ, mV
Fig. 1. Cyclic voltammogram of compound 3a (1 mM, Pt,
CH2Cl2, 0.1 M Bu4NPF6, 100 mV/s).
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SYNTHESIS AND ELECTROCHEMICAL PROPERTIES OF 2,5-DISUBSTITUTED DERIVATIVES
963
ȿ, mV
ȿ, mV
Fig. 3. Cyclic voltammogram of compound 3c (1 mM, Pt,
CH2Cl2, 0.1 M Bu4NPF6).
Fig. 2. Cyclic voltammogram of compound 3b (1 mM, Pt,
CH2Cl2, 0.1 M Bu4NPF6).
(in other words, got protonated) and was immediately
reduced into the anion-radical at the same potential, the
latter undergoing various chemical transformation, for
example, protonation (Scheme 3).
data. Apparently, dianion of 3a compound which was
oxidized during the reverse CV scan should be formed
via a different mechanism. It could be suggested that
the anion-radical formed at the first stage was subject
to very fast disproportionation with the formation of a
dianion and the starting compound which was reduced
again (Scheme 4).
That series of sequential electrochemical and chemical
processes could be described as the ECEC mechanism
(electrochemical, chemical, electrochemical, and
chemical stages). However, such mechanism should lead
to irreversible reduction waves, since the electrochemical
stage is followed by the chemical one, whereas reversible
wave was observed during the CV scan in our study
(Fig. 1). Hence, the said scheme of electrochemical
process was not consistent with the obtained experimental
The latter mechanism should be manifested in a
formally two-electron wave in the CV curve, which
was in line with the experiment. The disproportionation
could be likely due to the instability of the anion-radical
formed at the first stage. However, that fact somehow
contradicted the reference data on the reduction of the
Scheme 3.
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
N
N
N
N
N
N
N
N
+eꢀ
Ph
Ph
3a
H
Ph
N
N
N
N
N
N
Solv
N
N
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
H
N
H
N
N
N
+eꢀ
N
N
N
N
Ph
Ph
Ph
Ph
H
N
H
N
N
N
N
Solv
N
N
N
H
Ph
Ph
2a
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964
DOLGANOV et al.
Scheme 4.
Ph
Ph
Ph
Ph
Ph
Ph
Ph
N
N
N
N
N
N
N
N
+eꢀ
Ph
3a
Ph
Ph
Ph
Ph
N
N
N
N
disproportionation
+
3a
Scheme 5.
Br
Br
Ph
Ph
Ph
Ph
Ph
Ph
Ph
+eꢀ
ꢀeꢀ
N
N
N
N
N
N
N
N
Ph
Br
Br
3c
Br
Ph
Ph
Ph
+eꢀ
N
N
N
ꢀ
ꢀ
e
N
Ph
Br
A
compounds with quinoid structure [6], since it is known
that such compounds are reduced via two sequential
single-electron stages. Most of the reference data on
the reduction of quinoid compounds have been reported
for the only solvent, and thus the role of solvent on the
stability of intermediate compounds cannot be elucidated.
Yet this in an important issue, since the solvent nature is
an extremely significant factor affecting the stability of
mixed-valence compounds. Therefore, we planning to
study electrochemical behavior of compounds 3a–3c in
other solvents.
the potential scan rate to 1 V/s (Fig. 2) did not allow the
detection of the anion-radical. Thus, electrochemical
behavior of compound 3b could be described by Scheme 4.
The introduction of the second bromine atom
at the central phenyl ring qualitatively changed the
electrochemical properties (Fig. 3): two reversible
reduction peaks were observed, at Е = 0.400 and Е =
0.275 V, even at low potential scan rates. In comparison
with compounds 3a and 3b, the reduction potential
was strongly shifted towards the anodic region. Such
strong shift could not be explained exclusively by the
electronic effects of an additional bromine atom, since
the reduction potential of compound 3b was only slightly
shifted in comparison with compound 3a. Moreover, the
second reduction potential of compound 3c was also
more negative than the first potential of compounds
3a and 3b. That fact indicated that even anion-radical
possessed higher accepting properties. It could be argued
that compound 3c formed a biradical specie in a solution,
in which two radical centers did not interact (or the
interaction was weak) and the reduction process occurred
at those radical centers. That could be due to disruption
Another possible factor enhancing the stability of
anion-radicals formed at first stage is the introduction of
acceptor substituents at the central ring. To investigate
that, we studied the behavior of compounds 3b and 3c.
CV of compound 3b is given in Fig. 2. As in the case
of compound 3a, one reversible wave at Е = 0.195 V
was observed. In comparison with compound 3a, the
reduction potential was shifted towards positive values,
in good accordance with the electronomer effect of the
substituent. However, disproportionation of anion-radical
formed at the first stage of reduction was not prevented
by the introduction of a bromine atom. The increase in
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SYNTHESIS AND ELECTROCHEMICAL PROPERTIES OF 2,5-DISUBSTITUTED DERIVATIVES
965
of the coplanarity of quinoid system of compound 3c by
cell. The oxygen was removed via bubbling with dry
argon. Cyclic voltammetry experiment was performed at
different scan rates using a standard platinum electrode
(S = 0.6 cm2) and saturated silver chloride reference
electrode (potential vs Fc/Fc+ –0.55 V in CH3CN). The
determined potential values were recalculated with
consideration of ohmic losses.
the bromine atoms in positions 2 and 5.
Hence, electrochemical behavior of compound 3c
could be expressed by Scheme 5. The reduction of
compound 3c occurring at the first stage gave a stable
anion-radical form. Since the introduction of two bromine
atoms at the central ring strongly lowered the energy
of HOMO at which reduction process was localized,
the potentials were strongly shifted towards the anodic
region.At the second stage, the anion-radical was reduced
into dianion A which was stable over time and did not
undergo any chemical transformations.
Terephthalaldehyde 1a, 2,5-dibromoterephthalal-
dehyde 1c [7], imidazoles 2a–2c, and quinones 3a–3c
were synthesized as described elsewhere [8, 9]
2-Bromoterephthalaldehyde (1b). 8.5 mL(0.15 mol)
of H2SO4 was added to a mixture of 3.7 g (0.02 mol) of
2-bromoxylene, 60 mL (0.95 mol) of glacial acetic acid,
and 56.5 mL (0.1 mol) of acetic anhydride at continuous
cooling and stirring, maintaining the reaction mixture
temperature at 6–12°С. 10 g (0.1 mol) of CrO3 was
added to the obtained reaction mixture in small portions
maintaining the reaction mixture temperature at 5–10°С.
After addition of CrO3, the stirring had been continued
for 1.5 h at 6–12°С; then the reaction mixture was poured
into icy water and kept at room temperature for 24 h. The
precipitate was filtered off, dried in air, and recrystallized
from ethanol.
In summary, the obtained CV data suggested that
compound 3c was readily transformed into the biradical
form in a solution. At the same time, it possessed strong
accepting properties in neutral as well as in anion-
radical forms. That was due to the introduction of the
substituents disrupting the coplanarity of the quinoid
system of compound 3c and favored localization of the
radicals at the imidazole fragments. That in turn led to the
biradical system formally exhibiting the properties of a
monoradical system. Expectedly, the reduction potential
of compound 3c was strongly shifted to the anodic region.
That fact coincided well with the reference data on the
reduction of monoradical compounds.
The mixture of 6.26 g (0.015 mol) of the acetoxy
derivative, 60 mL of ethanol, 10 mL of water and
8 mL of concentrated H2SO4 was refluxed for 1.5 h,
and then the reaction mixture was cooled to room
temperature and diluted with water (200 mL). Light-
yellow precipitate was filtered off and purified by
recrystallization from a CHCl3–petroleum ether mixture.
Yield 2.56 g (80.1%). IR spectrum, cm–1: 1696 s (С=О),
1199 m, 817 m, 694 m. 1Н NMR spectrum (CDCl3), δ,
ppm: 7.72–7.81 m (2H), 8.15 d. d (1H, J = 1.8, 0.4 Hz),
10.33 s (1H), 10.37 s (1H). 13С NMR spectrum (CDCl3),
δC, ppm: 125.3, 126.1, 130.5, 131.7, 135.4, 137.6, 189.5,
190.2 (С=О).
EXPERIMENTAL
The solvents were dried and distilled prior to the use.
Commercial chemicals (Sigma-Aldrich) were used as
received.
IR spectra were obtained using an InfraLYuM FT-
02 Fourier spectrometer (KBr pellets). Н and 13С
1
NMR spectra were registered using a JNM-ECX400
Jeol spectrometer (400.1 and 100.6 MHz, respectively;
solution in CDCl3 or DMSO-d6. Chemical shifts
were referenced to the residual signals of deuterated
solvents. Elemental analysis was performed using
a Vario MICRO СHNS-analyzer. The conditions of
analytical TLC were as follows: sorbent – Silufol UV-
245, eluent – methylene chloride–ethylacetate (2 : 1),
development in iodine chamber. Column chromatography
was performed using L40/100 μ silica gel, eluting with
benzene. Electrochemical reduction potentials were
measured in a 5 mL electrochemical cell using a Gamry
digital potentiostat–galvanostat (Canada), connected to
a personal computer. Voltammograms were registered
with 0.05 М of n-Bu4NBF4 in CH3CN as background
electrolyte at 20°С in a special 10 mL electrochemical
General procedure for the synthesis of compounds
2a–2c. Amixture of 0.7 mmol of aldehyde 1a–1c, 300 mg
(1.4 mmol) of benzene, 700 mg (1.9 mmol) of ammonium
acetate, and 20 mL of glacial acetic acid was refluxes for
2 h. The precipitate was dissolved during refluxing,
and the solution color turned golden. Then the reaction
mixture was cooled; 50 mL of water and 10 mL of
ammonia solution were added. The precipitate was
filtered off and dried in air. Fine-crystalline yellow
powder was obtained.
1,4-Bis(4,5-diphenylimidazol-2-yl)-benzene (2a).
Yield 270 mg (75%), bp > 300°С (decomp.). IR spectrum,
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DOLGANOV et al.
ν, cm–1: 3375 m (NH), 1659 m (C=CAr), 1509 s (C=CAr),
1339 m (С=N), 1126 m, 895 s. 1Н NMR spectrum, δ, ppm:
12.92 br. s (NH, 2Н), 7.29–7.52 m (12H), 7.62–7.71 m
(8H), 8.07 d. d (4H, J = 8.7, 1.9 Hz). 13C NMR spectrum,
δC, ppm: 124.2, 126.9, 127.1, 128.6, 128.9, 130.4, 133.3,
137.7, 148.2. Found, %: C 84.05; H 5.07; N 10.86.
C36H26N4. Calculated, %: C 84.02; H 5.09; N 10.89.
octane was added. The precipitate was filtered off and
dried in air. Fine-crystalline green powder was obtained.
3,6-Bis(4,5-diphenylimidazol-2-yliden)-1,4-
cyclohexadiene (3a). Yield 120 mg (25%), bp 135–137°С
(benzene–octane). IR spectrum, ν, cm–1: 1610 m (C=CAr),
1571 m (C=CAr), 1333 m (С=N), 1290 m, 895 s. 1Н NMR
spectrum (DMSO-d6), δ, ppm: 6.95 d (4H, J = 10.2 Hz),
7.52–7.62 m (12H), 8.07 d. d. d (8H, J = 7.9, 1.7, 1.5 Hz).
13C NMR spectrum (DMSO-d6), δС, ppm: 107.1, 128.2,
129.1, 131.2, 132.1, 133.2, 134.9, 140.1, 159.8. Found, %:
C 84.32; H 4.71; N 10.96. C36H24N4. Calculated, %: C
84.35; H 4.72; N 10.93.
1,4-Bis(4,5-diphenylimidazol-2-yl)-2-bromo-
benzene (2b). Yield 350 mg (84%), bp > 300°С
(decomp.). IR spectrum, ν, cm–1: 3360 m (NH), 1662 m
(C=CAr), 1504 s (C=CAr), 1343 m (С=N), 1130 m, 894 s,
1
698 s (С–Br). Н NMR spectrum, δ, ppm: 12.71 br. s
(NH, 2Н), 7.45–7.64 m (12H), 7.78 d. d (1H, J = 8.5,
1.9 Hz), 7.83–7.92 m (4H), 7.95–8.02 m (3H), 8.08 d. d
(1H, J = 1.9, 0.4 Hz). 13C NMR spectrum, δC, ppm: 122.7,
124.2, 126.3, 126.8, 126.9, 127.1, 127.8, 128.6, 129.0,
130.4, 130.7, 133.3, 137.7, 148.2. Found, %: C 72.66;
H 4.24; N 9.46. C36H25BrN4. Calculated, %: C 72.85; H
4.25; N 9.44.
3,6-Bis(4,5-dyphenylimidazol-2-yliden2)-2-bromo-
1,4-cyclohexadiene (3b). Yield 140 mg (23.6%), bp 157–
158°С (benzene–octane). IR spectrum, ν, cm–1: 1604 m
(C=CAr), 1566 m (C=CAr), 1326 m (С=N), 1280 m, 894 s,
1
694 s (С–Br). Н NMR spectrum (DMSO-d6), δ, ppm:
7.51–7.58 m (4H), 7.58–7.68 m (8H), 7.78–7.85 m (4H),
13
7.93–8.04 m (2H), 8.12 s (1Н), 8.20–8.26 m (4H). C
1,4-Bis(4,5-dyhenylimidazol-2-yl)-2,5-di-
brombenzene (2c). Yield 330 mg (70%), bp > 300°С
(decomp.). IR spectrum, ν, cm–1: 3325 m (NH), 1672 s
(C=CAr), 1594 m (C=CAr), 1344 m (С=N), 1284 s, 694 s
NMR spectrum (DMSO-d6), δС, ppm: 108.1, 114.2, 121.4,
127.2, 128.7, 128.9, 129.2, 132.2, 133.2, 134.9, 150.6,
158.9. Found, %: C 73.12; H 3.91; N 9.46. C36H23BrN4.
Calculated, %: C 73.10; H 3.92; N 9.47.
1
(С–Br). Н NMR spectrum (DMSO-d6), δ, ppm:
3,6-Bis(4,5-diphenylimidazol-2-yliden)2,5-dibromo-
1,4-cyclohexadiene (3c). Yield 270 mg (30.2%), bp 172–
174°С (benzene–octane). IR spectrum, ν, cm–1: 1609 m
(C=CAr), 1570 m (C=CAr), 1333 m (С=N), 1282 m, 896 s,
12.75 br. s (NH, 2Н), 7.45–7.63 m (12H), 7.87 d. d. d
(4H, J = 7.1, 2.0, 1.5 Hz), 7.93 d. d. d (4H, J = 7.7, 1.7,
1.5 Hz), 8.08 d (2H, J = 0.4 Hz). 13C NMR spectrum
(CDCl3), δC, ppm: 120.7, 124.2, 126.3, 126.9, 128.6,
128.9, 129.2, 130.4, 130.7, 133.3, 137.7, 148.2. Found,
%: C 64.32; H 3.61; N 8.36. C36H24Br2N4. Calculated,
%: C 64.30; H 3.60; N 8.33.
1
699 s (С–Br). Н NMR spectrum (DMSO-d6), δ, ppm:
7.55–7.67 m (12H), 7.78–7.85 m (8H), 8.02 s (2H). 13C
NMR spectrum (DMSO-d6), δC, ppm: 115.2, 120.4,
128.2, 129.2, 129.8, 131.9, 133.0, 133.2, 158.9. Found,
%: C 64.47; H 3.32; N 8.39. C36H22Br2N4. Calculated:
C 64.50; H 3.31; N 8.36.
General procedure for the synthesis of quinones
3a–3c. 100 mL of 20% solution of K3[Fe(CN)6] was
added to a mixture of 12.5 mL of 6% solution of KОН
and a suspension of 1 mmol of compound 2a–2c in
25 mL of dioxane at continuous stirring during 2 h
under argon atmosphere, maintaining temperature of
the reaction mixture at 5–7°С. When first drops of the
K3[Fe(CN)6] solution were added, the reaction mixture
turned purple and then became green. After the addition
of K3[Fe(CN)6], the reaction mixture was stirred under
argon atmosphere at 5–7°C for 30 min; the precipitate was
filtered off, washed with huge amount of water, and dried
in air. Fine-crystalline purple precipitate was obtained.
To remove the unreacted starting component, the product
was dissolved in 50 mL of benzene and separated from
the undissolved residue. The benzene solution was
evaporated in vacuum to 10 mL volume, and 5 mL of
FUNDING
This study was financially supported by the Ministry of
Science and Higher Education of the Russian Federation as
a part of the government task in the field of research (project
no. 4.4566.2017/8.9).
CONFLICT OF INTEREST
No conflict of interest was declared by the authors.
REFERENCES
1. Lu, N.-N.,Yoo, S.J., Li, L.-J., Zeng, C.-C., andLittle, R.D.,
Electrochim. Acta, 2014, vol. 142, p. 254.
https://doi.org/10.1016/j.electacta.2014.07.105
2. Francke, R. and Little, R.D., J. Am. Chem. Soc.,
2014, vol. 136, p. 427.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 6 2020

SYNTHESIS AND ELECTROCHEMICAL PROPERTIES OF 2,5-DISUBSTITUTED DERIVATIVES
967
https://doi.org/10.1021/ja410865z
2001.
7. Xia, C. and Advincula, R.C., Macromol., 2001, vol. 34,
p. 6922.
3. Zeng, C.-C., Zhang, N.-T., Lam, C.M., and Little, R.D.,
Org. Lett., 2012, vol. 14, p. 1314.
https://doi.org/10.1021/ma0100192
https://doi.org/10.1021/ol300195c
8. Maeda, K., Sakaino, Y., and Hayashi, T., Nippon
Kagaku Kaishi, 1972, p. 100.
4. Englander, F., US Patent 4465865, 1984.
5. Naylor, J.R., J. Chem. Soc., 1952, p. 4078.
https://doi.org/10.1246/nikkashi.1972.100
https://doi.org/10.1039/JR9520004839
9. Sakaino, Y., Kakisawa, H., Kusumi, T., and Maeda, K.,
J. Org. Chem., 1979, vol. 44, p. 1241.
6. Bard, A.J. and Faulkner, L.R. Electrochemical Methods:
Fundamentals and Applications, New York: John Wiley,
https://doi.org/10.1021/jo01322a010
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 6 2020