Nucleophilic substitution in nitrofluorenones

Article abstract of DOI:10.1134/S1070428013020097

The reaction of 2,4,5,7-tetranitrofluorenone with amines, thiols, and phenol in a polar aprotic solvent led to the preferable substitution of the nitro group in the position 2, and in the reaction of 2,4,7-trinitrofluorenone first the nitro group in the position 4 was replaced. The different regioselectivity is due evidently to the steric hindrances to the nucleophilic attack on the atom C⁴ caused by the nitro group in the position 5 of tetranitrofluorenone.

Full text of DOI:10.1134/S1070428013020097

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 2, pp. 228−232. © Pleiades Publishing, Ltd., 2013.
Original English Text © A.M. Andrievskii, M.K. Grachev, O.V. Chelysheva, 2013, published in Zhurnal Organicheskoi Khimii, 2013, Vol. 49, No. 2, pp. 232−237.
Nucleophilic Substitution in Nitrofluorenones
A. M. Andrievskiia, M. K. Grachevb, and O. V. Chelyshevaa
aResearch Istitute of Organic Semiproducts and Dyes, Moscow,123995 Russia
e-mail: info@cemess.ru
bMoscow State Pedagogical University, Moscow, Russia
Received June 25, 2012
Abstract—The reaction of 2,4,5,7-tetranitrofluorenone with amines, thiols, and phenol in a polar aprotic solvent led
to the preferable substitution of the nitro group in the position 2, and in the reaction of 2,4,7-trinitrofluorenone first
the nitro group in the position 4 was replaced. The different regioselectivity is due evidently to the steric hindrances
to the nucleophilic attack on the atom C4 caused by the nitro group in the position 5 of tetranitrofluorenone.
DOI: 10.1134/S1070428013020097
Polynitrofluorenones are used as efficient sensitizers
for electrophotography [1]. The nucleophilic substitution
of nitro groups in nitrofluorenones is a simple way to the
modification of their structure. The comparison of the
reactions of tetranitro- and trinitrofluorenones with O-,
N-, and S-nucleophiles provides a possibility to conclude
on the dependence of the substitution regioselectivity on
the structure of the reagent and the substrate.
As a result of the reaction with dimethylamine in DMF
without heating within 3 days 2-dimethylamino-4,5,7-
trinitrofluorenone (Va) was obtained with insignificant
impurity of 4-dimethylamino-2,5,7-trinitrofluorenone.At
the use of the appropriate secondary amines 2-diethyl-
amino-4,5,7-trinitrofluorenone (Vb) and 2-dibutylamino-
4,5,7-trinitrofluorenone (Vc) were synthesized.
The reaction of 2,4,5,7-tetranitrofluorenone (I) with
butane-1-thiol in DMSO at heating or in HMPA at room
temperature gave 2-butylsulfanyl-4,5,7-trinitrofluorenone
(VIb) [4]. At boiling tetranitrofluorenone (I) in DMSO
2-methylsulfanyl-4,5,7-trinitro-fluorenone (VIa) formed
because of the thermal decomposition of the solvent [5].
In the reaction of fluorenone I with thiophenol also the
nitro group in the position 2 suffered the substitution to
afford 2-phenylsulfanyl-4,5,7-trinitrofluorenone (VIc)
in a 78% yield. At heating compound I with phenol in
HMPAat 100°C 2-phenoxy-4,5,7-trinitrofluorenone (VII)
was obtained. The reactions with thiols and phenol do not
require the presence of a base usually added to increase
the nucleophilicity. This fact demonstrates the high
electron-deficiency of the polynitrofluorenones.
It was formerly established that in 2,4,5,7-tetra-
nitrofluorenone (I), 2,4,7-trinitrofluorenone (II) [2],
and also in the 2,4,7-trinitrofluorenone-5-carbonitrile
[3] in HMPA at room temperature the nitro group in the
position 4 is replaced by the hydroxy group with the
formation of 4-hydroxy-2,5,7-trinitro-fluorenone (III),
4-hydroxy-2,7-dinitrofluorenone (IV), and 4-hydroxy-
2,7-dinitrofluorenone-5-carbonitrile respectively. The
heating of tetranitrofluorenone I in HMPA results in the
formation alongside 4-hydroxy-substituted (III) of the
isomeric 2-hydroxy-4,5,7-trinitrofluorenone, and the
heating of the 2,4,7-trinitrofluorenone-4-carbonitrile
provides only the 4-hydroxy derivative. Presumably
the nucleophilic agent attacking the nitro group is
water contained in HMPA. Adding water to dry HMPA
accelerates the reaction.
Compounds Va, VIa possess the properties of sensi-
tizers for the organic electrophotographic layers [6, 7].
The boiling of 2,4,7-trinitrofluorenone (II) in DMSO
led to the formation of a mixture of 4-methylsulfanyl-
2,7-dinitrofluorenone (VIIIa) and 2-methylsulfanyl-
4,7-dinitrofluorenone (IXa) in the ratio ~4:1. Treating
2,4,7-trinitrofluorenone (II) with excess butanethiol
Whereas at the hydrolysis in HMPAat room tempera-
ture in 2,4,5,7-tetranitrofluornone (I) only the nitro group
in the position 4 is exchanged for the hydroxy group, at
the action of amines, thiols, phenol in the polar aprotic
solvents the nitro group in the position 2 is substituted.
228

NUCLEOPHILIC SUBSTITUTION IN NITROFLUORENONES
O
229
O
O
O2N
NO2
O2N
NO2
O2N
NR2
HMPA, H2O
R2NH
PhOH
NO2
OH
NO2
NO2
NO2
NO2
III
Vа_Vc
I
R'SH
O
O
O
O2N
SR'
O2N
OPh
O2N
NO2
NO2
NO2
NO2
NO2
SR'
NO2
II
VII
VIа_VIc
HMPA,
H2O
R'SH
O
O
O
O2N
NO2
O2N
NO2
O2N
+
OH
SR'
VIIIа_VIIIc
V, R = Me (a), Et (b), Bu (c); VI, VIII, IX, R' = Me (a), Bu (b), Ph (c).
NO2
IXа, IXb
IV
in DMSO at room temperature in the course of 2 days
resulted in the formation of a mixture of 4-butylsulfanyl-
2,7-dinitrofluorenone (VIIIb) and 2-butylsulfanyl-4,7-
dinitrofluorenone (IXb) in the ratio 3:1 and an overall
yield 74%. In the reaction of trinitrofluorenone II with
thiophenol exclusively the nitro group in the position 4
underwent the substitution, and the sole reaction product
was 4-phenylsulfanyl-2,7-dinitrofluorenone (VIIIc)
(yield 87–89%).
and 8.35 ppm. The doublet signals from the protons in the
position 3 for these isomeric pairs are observed at 7.67 and
7.79, 8.30 and 8.42, 8.31 and 8.51 ppm respectively. In the
combination with the interpretation of the other signals in
the 1H NMR spectra (see Experimental) it is possible to
distinguish between the substitution in the position 2 or 4.
The structure of 4-phenylsulfanyl-substituted compound
VIIIc was established by X-ray analysis [8].
Therefore in 2,4,5,7-tetranitrofluorenone (I) the hy-
droxy group substituted predominantly the nitro group
in the position 4, and dialkylamino-, alkylsulfanyl-,
phenylsulfanyl-, and phenoxy groups replace the nitro
group in the position 2. In 2,4,7-trinitrofluorenone (II)
prevailingly the nitro group in the position 4 is substituted.
The regioselectivity of the nucleophilic substitution in the
polynitrofluorenones depends on the relative reactivity
of the certain position occupied by the nitro group, and
on its spatial accessibility which in its turn is governed
by the extent of shielding of the site of the attack and by
the volume of the attacking species. In the absence of
steric hindrances the position 4 is obviously more active,
and the substitution with water occurs just in this place
The position of the substituent arising at the replace-
ment of the nitro group by the nucleophile was established
from the 1H NMR spectra.At the exchange in the position
2 for an electron-donor group the doublet signals of the
protons located in the position 1 appear in essentially
stronger field than the signals of the same protons at the
substitution in the position 4 when in the ortho-position
to them remains the electron-acceptor nitro group. The
corresponding chemical shifts in 2-dimethylamino-substi-
tuted Va and its 4-dimethylamino-substituted isomer are
observed at 7.38 and 7.55 ppm, in 2-methylsulfanyl-sub-
stituted IXa and its isomer VIIIa, at 7.98 and 8.32 ppm,
in 2-butyl-substituted IXb and its isomer VIIIb, at 7.99
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 2 2013

ANDRIEVSKII et al.
230
By chromatography also 0.63 g (2%) of 4-dimethyl-
amino derivative was isolated. Violet crystals, Rf 0.36
(benzene), mp 192–194°C (acetonitrile). IR spectrum,
ν, cm–1: 1720 (C=O), 1535, 1520, 1335 (NO2). 1H NMR
spectrum, δ, ppm: 2.83 s (6H, CH3), 7.55 d (1H, H1,
since water does not find any hindrances due to its small
molecule. The X-ray analysis data for 2,4,5,7-tetranitro-
fluorenone [9] and 2,4,5-trinitrofluorenone [10] confirm
the existence of the steric hindrances because of the nitro
groups in the positions 4 and 5 of the fluorenone. At the
attack of a bulky species of dialkylamine or thiophenol
in 2,4,5,7-tetranitrofluorenone (I) the less hindered nitro
group in the position 2 undergoes the exchange. At the
lack of a nitro group in the position 5 the hindrance to
the attack decreases, therefore in 2,4,7-trinitrofluorenone
(II) the substitution in the position 4 becomes possible.
4
4J 2.1 Hz), 7.79 d (1H, H3, J 2.1 Hz), 8.55 d (1H, H8,
4J 1.8 Hz), 8.85 d (1H, H6, 4J 1.8 Hz). Found, %: C 50.18;
H 2.76; N 15.59. C15H10N4O7. Calculated, %: C 50.29;
H 2.81; N 15.64.
2-Diethylamino-4,5,7-trinitro-9H-fluoren-9-one
(Vb). To a solution of 3 mmol of compound I in 10 ml of
DMF was added dropwise at 20–25°C while stirring 2 ml
of diethylamine. The mixture was stirred for 20 min and
poured into 50 ml of 5% hydrochloric acid. The separated
dark brown precipitate was filtered off, washed with wa-
ter, dried, and recrystallized from acetonitrile. Yield 0.79 g
(73%). Violet crystals, Rf 0.25 (benzene), mp 261–263°C
(acetonitrile). IR spectrum, ν, cm–1: 1730 (C=O), 1535,
EXPERIMENTAL
1H NMR spectra were registered on a spectrometer
Jeol ECX-400 (operating frequency 400.13 MHz) in
DMSO-d6, chemical sifts are reported with respect to
TMS. IR spectra were recorded on a spectrophotometer
Perkin Elmer-598 from pellets with KBr. The reaction
progress was monitored and the homogeneity of com-
pounds obtained was checked by TLC on aluminum
plates with a fixed layer of silica gel (Silufol UV-254),
development with a mixture of solutions of SnCl2 and
4-dimethylaminobenzaldehyde in aqueous ethanol con-
taining HCl. The preparative column chromatography
was performed using Silicagel L40/100μ and L100/160μ
(Chemapol, Czechia). Melting points were measured on
a Boёtius heating block.
1
1335 (NO2). H NMR spectrum, δ, ppm: 1.15 t (6H,
CH3, 3J 7.2 Hz), 3.36 q (4H, CH2, 3J 7.2 Hz), 7.40 d (1H,
4
4
H1, J 2.1 Hz), 7.69 d (1H, H3, J 2.1 Hz), 8.58 d (1H,
4
4
H8, J 1.8 Hz), 8.85 d (1H, H6, J 1.8 Hz). Found, %:
C 52.78; H 3.57; N 14.56. C17H14N4O7. Calculated, %:
C52.85; H 3.63; N 14.51.
2-Dibutylamino-4,5,7-trinitro-9H-fluoren-9-
one (Vc) was obtained similarly by the reaction with
dibutylamine. Yield 0.92 g (69%). Violet crystals,
Rf 0.47 (benzene), mp 168–169°C (acetonitrile).
IR spectrum, ν, cm–1: 1730 (C=O), 1530, 1330
2-Dimethylamino-4,5,7-trinitro-9H-fluoren-9-one
(Va) and 4-dimethylamino-4,5,7-trinitro-9H-fluoren-
9-one. To a solution of 36.0 g (100 mmol) of compound
I in 75 ml of DMF was added at 20–25°C and while
stirring 40 ml of 20% water solution of dimethylamine.
After 3 days the solution was poured into 300 ml of 5%
hydrochloric acid, the separated dark brown precipitate
was filtered off, washed with water, and dried. We ob-
tained 23.85 g of compound Va.Additional 0.71 g of this
compound was isolated by evaporation of the filtrate to
dryness, dissolution of the residue in benzene and chro-
matographing this solution (eluent benzene). Overall
yield 24.56 g (69%). Violet crystals, Rf 0.25 (benzene), mp
272–272.5°C (acetonitrile). IR spectrum, ν, cm–1: 1735
(C=O), 1540, 1530, 1340 (NO2). 1H NMR spectrum, δ,
ppm: 2.81 s (6H, CH3), 7.38 d (1H, H1, 4J 2.1 Hz), 7.67 d
1
(NO2). H NMR spectrum, δ, ppm: 0.97 t (6H, CH3,
3J 7.2 Hz), 1.36 m (4H, CH2CH3), 1.57 m (4H,
3
CH2CH2CH3), 3.40 q (4H, NCH2, J 7.8 Hz), 7.38 d
4
4
(1H, H1, J 2.2 Hz), 7.67 d (1H, H3, J 2.2 Hz), 8.56 d
(1H, H8, 4J 1.8 Hz), 8.83 d (1H, H6, 4J 1.8 Hz). Found,
%: C 56.92; H 5.02; N 12.64. C21H22N4O7. Calculated,
%: C 57.01; H 4.98; N 12.67.
2-Methylsulfanyl-4,5,7-trinitro-9H-fluoren-9-one
(VIa). A solution of 3.6 g (10 mmol) of compound I in
30 ml of DMSO was boiled for 9 h, cooled to room tem-
perature, and poured into 200 ml of 3% hydrochloric acid.
The separated dark brown precipitate was filtered off,
treated with a mixture of 50 ml of acetone and 150 ml of
benzene, the obtained solution was chromatographed on
a column packed with silica gel (eluent acetone–benzene,
1 : 3). Yield 1.86 g (52%), bright yellow crystals. Rf 0.7
(benzene), mp 214–215°C (acetic acid). IR spectrum, ν,
4
4
(1H, H3, J 2.1 Hz), 8.53 d (1H, H8, J 1.8 Hz), 8.82 d
4
(1H, H6, J 1.8 Hz). UV spectrum (benzene), λmax, nm
1
cm–1: 1730 (C=O), 1560, 1540, 1340 (NO2). H NMR
(log ε): 485 (4.09). Found, %: C50.02; H 2.90; N 15.47.
C15H10N4O7. Calculated, %: C 50.29; H 2.81; N 15.64.
spectrum, δ, ppm: 2.81 s (3H, CH3), 8.07 d (1H, H1,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 2 2013

NUCLEOPHILIC SUBSTITUTION IN NITROFLUORENONES
231
4
4J 1.8 Hz), 8.30 d (1H, H3, J 1.8 Hz), 8.70 d (1H, H8,
4J 2.3 Hz), 8.94 d (1H, H6, 4J 2.3 Hz). Found, %: C 46.78;
H 2.05; N 11.49; S 8.83. C14H7N3O7S. Calculated, %:
C 46.54; H 1.91; N 11.63; S 8.86.
matographed on a column packed with silica gel (eluent
benzene).
Compound VIIIa. Yield 0.51 g (51%). Light yellow
crystals. Rf 0.25 (benzene), mp 245–246°C (acetic acid).
IR spectrum, ν, cm–1: 1728 (C=O), 1520, 1345 (NO2).
1H NMR spectrum, δ, ppm: 2.47 s (3H, CH), 8.13 d (1H,
H5, 3J 8.7 Hz), 8.32 d (1H, H1, 4J 1.8 Hz), 8.37 d (1H, H8,
4J 2.3 Hz), 8.42 d (1H, H3, 4J 1.8 Hz), 8.63 d.d (1H, H6,
3J 8.7, 4J 2.3 Hz). Found, %: C 53.58; H 2.94; N 8.23;
S 9.68. C14H8N2O5S. Calculated, %: C 53.16; H 2.53;
N 8.86; S 10.13.
2-Phenylsulfanyl-4,5,7-trinitro-9H-fluoren-9-one
(VIc). To a solution of 3.6 g (10 mmol) of compound I
in 25 ml of DMSO was added dropwise at 20–25°C 2.2 g
(20 mmol) of thiophenol, and the mixture was stirred for
8 h till disappearance of initial compound I from the reac-
tion mixture (TLC monitoring, benzene). The separated
precipitate was filtered off, washed with water, dried in
air, and crystallized from acetic acid. Yield 3.30 g (78%),
orange crystals. Rf 0.53 (benzene), mp 190–191°C (acetic
acid). IR spectrum, ν, cm–1: 1730 (C=O), 1535, 1340
(NO2). 1H NMR spectrum, δ, ppm: 7.25 d.d (1H, Hп, 3J 8.5,
4J 2.0 Hz), 7.43 d.d (2H, HO, 3J 8.5, 4J2.0 Hz), 7.47 d.d
(2H, Hm, 3J 8.5, 4J 2.0 Hz), 7.70 d (1H, H1, 4J 2.2 Hz),
Compound IXa. Yield 0.14 g (14%). Yellow crystals.
Rf 0.42 (benzene), mp 192–193°C (acetic acid). IR spec-
trum, ν, cm–1: 1725 (C=O), 1530, 1340 (NO2). 1H NMR
spectrum, δ, ppm: 2.49 s (3H, CH), 7.88 d (1H, H5,
4
3J 8.7 Hz), 7.98 d (1H, H1, J 1.8 Hz), 8.03 d (1H, H8,
4J 2.3 Hz), 8.30 d (1H, H3, 4J 1.8 Hz), 8.52 d.d (1H, H6,
7.92 d (1H, H3, J 2.2 Hz), 8.58 d (1H, H8, J 1.8 Hz),
8.85 d (1H, H6, 4J 1.8 Hz). Found, %: C 53.82; H 2.09;
N 9.91; S 7.92. C19H9N3O7S. Calculated, %: C 53.90;
H 2.13; N 9.93; S 7.56
4
4
4
3J8.7, J 2.3 Hz). Found, %: C 53.18; H 2.61; N 8.82;
S 9.97. C14H8N2O5S. Calculated, %: C 53.16; H 2.53;
N 8.86; S 10.13.
4-Butylsulfanyl-2,7-dinitro-9H-fluoren-9-one
(VIIIb) and 2-butylsulfanyl-4,7-dinitro-9H-fluoren-
9-one (IXb). To a solution of 1.0 g (3.17 mmol) of
compound II in 10 ml of DMSO was added 1.0 ml of
butane-1-thiol at room temperature. After 2 days the
mixture was poured into 50 ml of 5% hydrochloric acid.
The separated precipitate was filtered off, washed with
water, dried, dissolved in benzene, and chromatographed
on a column packed with silica gel (eluent benzene).
2-Phenoxy-4,5,7-trinitro-9H-fluoren-9-one (VII).
To a solution of 2.0 g (5.5 mmol) of compound I in
20 ml of HMPA was added 1.5 g (15.9 mmol) of phenol,
the mixture was heated to 100°C and stirred at this tem-
perature for 4 h. The solution was cooled and poured on
a mixture of 50 g of ice and 100 ml of 5% hydrochloric
acid. The separated precipitate was filtered off, washed
with water, dried, treated with benzene, the obtained solu-
tion was chromatographed on a column packed with silica
gel (eluent benzene). Yield 1.04 g (46%), yellow crys-
tals. Rf 0.56 (benzene), mp 180–181°C (acetic acid). IR
spectrum, ν, cm-1: 1735 (C=O), 1530, 1365, 1355 (NO2).
1H NMR spectrum, δ, ppm: 7.13 d.d (2H, HO, J 8.3,
4J 2.2 Hz), 7.18 d.d (1H, Hп, 3J 8.3, 4J 2.2 Hz), 7.45 d.d
(2H, Hm, 3J 8.3, 4J 2.2 Hz), 7.72 d (1H, H1, 4J 2.2 Hz),
7.92 d (1H, H3, J 2.2 Hz), 8.57 d (1H, H8, J 1.8 Hz),
8.85 d (1H, H6, 4J 1.8 Hz). Found, %: C 55.92; H 2.52;
N 9.93. C19H9N3O8. Calculated, %: C 56.02; H 2.21;
N 10.32.
Compound VIIIb. Yield 0.63 g (55%). Yellow crys-
tals. Rf 0.64 (benzene), mp 151–152°C (acetic acid).
IR spectrum, ν, cm–1: 1725 (C=O), 1520, 1345 (NO2).
1H NMR spectrum, δ, ppm: 1.03 t (3H, CH3, 3J 7.2 Hz),
1.35 m (2H, CH2CH3), 1.61 m (2H, CH2CH2CH3), 2.78 q
(2H, SCH2, 3J 7.8 Hz), 8.13 d (1H, H5, 3J 8.7 Hz), 8.35 d
3
4
4
(1H, H1, J 1.8 Hz), 8.38 d (1H, H8, J 2.3 Hz), 8.51 d
(1H, H3, 4J 1.8 Hz), 8.62 d.d (1H, H6, 3J 8.7, 4J 2.3 Hz).
Found, %: C 56.80; H 3.74; N 7.58; S 8.89. C17H14N2O5S.
Calculated, %: C 56.98; H 3.91; N 7.82; S 8.94.
4
4
Compound IXb. Yield 0.21 g (18%). Orange crystals.
Rf 0.73 (benzene), mp 146–147°C (acetic acid). IR spec-
trum, ν, cm–1: 1730 (C=O), 1525, 1340 (NO2). 1H NMR
4-Methylsulfanyl-2,7-dinitro-9H-fluoren-9-one
(VIIIa) and 2-methylsulfanyl-4,7-dinitro-9H-fluoren-
9-one (IXa). A solution of 1.0 g (3.17 mmol) of trini-
trofluorenone II in 10 ml of DMSO was heated for 8 h
at 185–190°C, cooled to room temperature, and poured
into 200 ml of 3% hydrochloric acid. The separated
dark brown precipitate was filtered off, washed with
water, dried, dissolved in 150 ml of benzene, and chro-
3
spectrum, δ, ppm: 0.98 t (3H, CH3, J 7.2 Hz), 1.35 m
(2H, CH2CH3), 1.60 m (2H, CH2CH2CH3), 2.79 q (2H,
SCH2, 3J 7.8 Hz), 7.90 d (1H, H5, 3J 8.7 Hz), 7.99 d (1H,
H1, 4J 1.9 Hz), 8.06 d (1H, H8, 4J 2.3 Hz), 8.31 d (1H, H3,
4J 1.9 Hz), 8.52 d.d (1H, H6, 3J 8.7, 4J 2.3 Hz). Found,
%: C 56.78; H 3.80; N 7.81; S 9.06. C17H14N2O5S. Cal-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 2 2013

ANDRIEVSKII et al.
Obshch. Khim., 1987, vol. 57, p. 415.
232
culated, %: C 56.98; H 3.91; N 7.82; S 8.94.
4. Perepichka, I.F., Popov,A.F., Orekhova, T.V., Bryce, M.R.,
Andrievskii, A.M., Batsanov, A.S., Howard, J.A.K., and
Sokolov, N.I., J. Org. Chem., 2000, vol. 65, p. 3053.
4-Phenylsulfanyl-2,7-dinitro-9H-fluoren-9-one
(VIIIc). To a solution of 2 g (3.65 mmol) of trinitrofluo-
renone III in 20 ml of DMSO was slowly added within
20 min 1.1 g (10 mmol) of thiophenol, and the mixture
was stirred at room temperature for 1 h. The separated
precipitate was filtered off, washed with water, dried,
and crystallized from acetic acid. Yield 2.09 g (87%),
mp 218.5–219.5°C. Rf 0.58 (benzene). IR spectrum, ν,
cm–1: 3440, 3080, 1725 (C=O), 1520, 1340 (NO2). Found,
%: C 60.61; H 2.67; N 7.32; S 8.36. C19H10N2O5S. Calcu-
lated, %: C 60.32; H 2.65; N 7.41; S 8.47. The structure of
compound VIIIc was established by X-ray analysis [8].
5. Martin, D. and Hauthal, H.G., Dimethylsulfoxide, Berlin:
Academic Verlag, 1971, p. 324.
6. Andrievskii, A.M., Kokosova, A.S., Dyumaev, K.M.,
Balabanov, E.M., Klokov, V.A., Bogachev, Yu.S., Bere-
stova, S.S., and Perov, A.A., USSR Inventor’s Certificate
1330989, 1987; SSSR Byull. Izobr., 2011, no. 17.
7. Andrievskii, A.M., Balabanov, E.M., Bespalov, B.P.,
Grachev, V.T., Dyumaev, K.M., Klokov, V.A., Kokoso-
va, A.S., Poplavskii, A.N., and Semidetko, O.V., USSR
Inventor’s Certificate 1482143, 1989; SSSR Byull. Izobr.,
2011, no. 17.
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