Synthesis of new AB-type monomers for polybenzimidazoles from N-(4,5-dichloro-2-nitrophenyl)acetamide

Article abstract of DOI:10.1016/j.mencom.2015.03.022

S_NAr reaction between N-(4,5-dichloro-2-nitrophenyl)acetamide and 4-hydroxybenzoic acid gives 4-(5-acetylamino-2-chloro-4-nitro- phenoxy)benzoic acid and 4-{5-[(5-acetylamino-2-chloro-4-nitrophenyl)amino]-2-chloro-4-nitrophenoxy}benzoic acid wh

Full text of DOI:10.1016/j.mencom.2015.03.022

Mendeleev
Communications
Mendeleev Commun., 2015, 25, 140–141
Synthesis of new AB-type monomers for polybenzimidazoles
from N-(4,5-dichloro-2-nitrophenyl)acetamide
Roman S. Begunov* and Asya N. Valyaeva
P. G. Demidov Yaroslavl State University, 150000 Yaroslavl, Russian Federation.
Fax: +7 4852 797 751; e-mail: begunov@bio.uniyar.ac.ru
DOI: 10.1016/j.mencom.2015.03.022
SNAr reaction between N-(4,5-dichloro-2-nitrophenyl)acetamide and 4-hydroxybenzoic acid gives 4-(5-acetylamino-2-chloro-4-nitro-
phenoxy)benzoic acid and 4-{5-[(5-acetylamino-2-chloro-4-nitrophenyl)amino]-2-chloro-4-nitrophenoxy}benzoic acid which were
used for the synthesis of new AB-type monomers for polybenzimidazoles.
Chemistry of aromatic condensation polymers, containing hetero-
cyclic fragments in the main chain, is currently actively developed.1
Therefore, the synthesis of new monomers for their preparation
is an actual problem. The AB-type monomers are promising for
the synthesis of polybenzimidazoles because such polymers
have a well-ordered structure and possess good physicochemical
characteristics.2 Recently,3 weobtained4-(3,4-diaminophenoxy)-
benzoic acid and prepared poly-2-(4'-hydroxyphenylene)-5-benz-
imidazole on its basis, which exhibited good thermomechanical
properties.4 In this development, we intended to carry out the
synthesis of a new AB-type monomer containing a chlorine atom.
According to published data, the presence of halogens bound to
the benzene fragments of a main polymer chain in polybenz-
imidazoles improves polymer properties such as solubility, film
formation, incombustibility and capability for binding larger
dopant amounts5 without impairing other physicochemical charac-
teristics.6
Compound 3 was an expected one. The structure of compound
4 was confirmed by 1H, 13C NMR and {1H-1H} NOESY spectro-
scopy as well as mass spectrometry and elemental analysis.
Apparently, the formation of product 4 occurs due to aromatic
nucleophilic substitution involving N-nucleophile from N-acetyl-
aniline moiety (N-deprotonation–substitution–N-deacetylation,
or N-deacetylation–substitution). Special experiment in the absence
of substrate 2, regarding N-nucleophilic properties of compound
1 (Scheme 2) brought about 17% of diarylamino product 8.‡ Its
1H NMR spectrum exhibited four signals due to aromatic protons
as intense singlets and two signals of protons bound to nitrogen
atoms. In this case, the signal of a secondary amine proton observed
at d 9.35 appeared as a broadened singlet.7 Mass-spectrometric
data showed a molecular ion of m/z 418.
According to the 1H NMR and mass spectra, compound 9 was
a product of the replacement of a chlorine atom by the hydroxy
1
group. In its H NMR spectrum, the signal of a 6-positioned
The use of N-(4,5-dichloro-2-nitrophenyl)acetamide 1 instead
of N-(5-chloro-2-nitrophenyl)acetamide in the SNAr reaction
with 4-hydroxybenzoic acid 2 unexpectedly gave two products
3 and 4 at the first stage (Scheme 1), which were separated and
whose structures were established.†
proton of the benzene ring was upfield shifted (d 7.75) in com-
parison with the signal of this proton in initial compound 1 at
d 8.06; this can be explained by the presence of an electron-donor
substituent, the hydroxy group, in the ortho-position, whose proton
signal appears at d 11.88.
HO
COOH
H
H
H
3'
H
5
2
6''
3''
Ac
N
N
O
Ac
N
Cl
Cl
O
Ac
N
6
2
+
Cl
O2N
3
O2N
Cl
O2N
COOH
COOH
O2N
Cl
COOH
COOH
6'
1
3
4
7
H
N
H
N
H2N
H2N
H2N
O2N
O
O
O
Me
Cl
O2N
N
Cl
Cl
COOH
Cl
6
5
Scheme 1
†
The NMR spectra were recorded on a Bruker DRX500 instrument
the mixture was poured into water and filtered. The filtrate was treated
with acetic acid to pH 6; the precipitate formed was filtered off, dried
and recrystallized from a mixture of PriOH and DMF. Yield 87%,
(500 MHz for H and 125 MHz for 13C) using DMSO-d6 as a solvent
and TMS as an internal standard. The mass spectra were recorded on
FINNIGAN MAT INCOS 50 at an electron energy of 70 eV. Elemental
analysis was performed on a Carlo Erba 1106 CHN analyzer.
4-(5-Acetylamino-2-chloro-4-nitrophenoxy)benzoic acid 3. Compound
1 (2.5 g, 0.01 mol) in 50 ml of DMSO was added to 5.8 g (0.042 mol)
of K2CO3 and 1.9 g (0.014 mol) of 2 in 100 ml of DMSO at 100°C for
1.5 h. The reaction mass was stirred at 100°C for 1 h. After cooling,
1
mp 270–276°C. 1H NMR, d: 2.05 (s, 3H, Me), 7.25 (d, 2H, H3',5'
,
J 8.72 Hz), 7.42 (s, 1H, H6), 8.04 (d, 2H, H2',6', J 8.77 Hz), 8.29 (s, 1H,
H3), 10.31 (s, 1H, NH), 13.05 (s, 1H, COOH). MS, m/z (%): 350 [M]+ (7),
308 (22), 304 (16), 227 (3), 183 (15), 76 (5), 65 (12), 43 (100). Found (%):
C, 51.34; H, 3.05; N, 8.05. Calc. for C15H11ClN2O6 (%): C, 51.36; H, 3.14;
N, 7.99.
© 2015 Mendeleev Communications. Published by ELSEVIER B.V.
on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.
– 140 –

Mendeleev Commun., 2015, 25, 140–141
phile 2. Meantime, when the molar ratio 1: 2 was 2:1, only com-
H
N
3'
6'
H
N
H
6
3
Ac
Cl
Cl
Ac
N
OH
Cl
pound 4 was formed. With the gradual introduction of electrophile
1 into the reaction mass for 1.5 h, only a 1.4-fold molar excess of
the nucleophile was required for obtaining 3 in 87% yield.
Finally, compound 3 was converted into required monomer 6
in accordance with a procedure2 developed for the synthesis of
4-(3,4-diaminophenoxy)benzoic acid.§ Compound 4 was reduced
with SnCl2 in acetic acid in the presence of catalytic amounts
of HCl to give benzimidazole derivative 7.¶
i
+
1
Cl
O2N
O2N
O2N
8, 17%
9, 68%
Scheme 2 Reagents and conditions: i, K2CO3, DMSO, 100°C.
Thus, more than 60% compound 1 was converted into hydrolysis
product 9, which was not observed as a by-product in the main
reaction. Furthermore, the formation of binuclear product 8 in
only 17% suggests that initial compound 1 cannot serve as an
active nucleophilic agent. Most probably, trinuclear product 4 is
formed during the reaction of compound 3 with parent substance 1.
This is facilitated by an increase in the basicity of the nitrogen
atom in the NHAc group of compound 3 as a result of the replace-
ment of the electron-acceptor chlorine atom by the aryloxy group
as an electron-donor substituent. This assumption was confirmed
by the preparation of compound 4 from substrate 1 and product 3
under the reaction conditions of (K2CO3, DMSO, 100°C, 2 h) in
82% yield.
In summary, we obtained two new AB-type monomers for the
synthesis of polybenzimidazoles.
This work was supported by the Ministry of Education and
Science of the Russian Federation (project no. 178).
References
1 (a) V. A. Kostyanovsky, D. K. Susarova, G. Adam, R. N. Lyubovskaya
and P. A. Troshin, Mendeleev Commun., 2013, 23, 26; (b) A. Parhamia,
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Materials), Khimiya, Moscow, 1976 (in Russian).
To obtain individual compounds 3 and 4, we studied the
influence of a reactant ratio on the course of the main and side
reactions. Only one product 3 was detected in the reaction mass
after the synthesis performed with a 2.4-fold excess of nucleo-
4-{5-[(5-Acetylamino-2-chloro-4-nitrophenyl)amino]-2-chloro-4-nitro-
phenoxy}benzoic acid 4. Compound 1 (12.5 g, 0.05 mol) was added to
10.4 g (0.075 mol) of K2CO3 and 3.5 g (0.025 mol) of compound 2 in
200 ml of DMSO. The reaction mass was stirred at 100°C for 3 h. After
cooling, the reaction mixture was poured into water. The precipitate formed
was filtered off, washed with water several times, dried and recrystallized
from a mixture of PriOH and DMF. Yield 88%, mp 292–306°C. 1H NMR,
d: 2.11 (s, 3H, Me), 7.13 (s, 1H, H6'), 7.22 (d, 2H, H3,5, J 8.76 Hz), 7.80 (s,
1H, H6''), 7.97 (d, 2H, H2,6, J 8.74 Hz), 8.25 (s, 1H, H3''), 8.48 (s, 1H, H3'),
9.39 (s, 1H, NH), 10.26 (s, 1H, NHCOMe), 13.00 (s, 1H, COOH). 13C NMR,
d: 23.98 (MeCO), 111.28 (C6''), 112.04 (C6'), 117.58 (C2'), 117.78 (C2''),
118.31 (C3,5), 126.83 (C3''), 127.81 (C1), 128.49 (C3'), 131.68 (C2,6), 132.99
(C1''), 133.83 (C5''), 134.76 (C5'), 137.28 (C4'), 143.11 (C4''), 156.18 (C1'),
157.88 (C4'), 166.66 (COOH), 168.77 (COMe). MS, m/z (%): 521 [M]+
(79), 480 (3), 474 (12) [M–NO2]+, 461 (4), 460 (21), 458 (42), 456 (100),
443 (6), 427 (18), 413 (6), 399 (4), 397 (9), 365 (3), 353 (4), 351 (7), 306 (4),
244 (4), 140 (3), 44 (12), 43 (30). Found (%): C, 48.28; H, 2.82; N, 10.59.
Calc. for C21H14Cl2N4O8 (%): C, 48.37; H, 2.69; N, 10.75.
6 J. Varga, A. A. Izyneev, V. P. Mazurevskij, J. P. Mazurevskaya and I. S.
Novak, Periodica Polytechnica, 1985, 29, 51.
7 (a) A. V. Gulevskaya, I. N. Tyaglivaya, S. Verbeeck, B. U. W. Maes and
A. V. Tkachuk, Arkivoc, 2011, ix, 238; (b) M. A. Carroll and R. A. Wood,
Tetrahedron, 2007, 63, 11349.
Received: 5th June 2014; Com. 14/4390
§
4-(4,5-Diamino-2-chlorophenoxy)benzoic acid 6. Compound 5 (9.3 g,
0.03 mol) and SnCl2·2H2O (22.6 g, 0.10 mol) were stirred in 100 ml of
36% HCl at 90°C for 1 h. After cooling, the reaction mixture was treated
with a 25% aqueous ammonia solution to pH 7–8. The precipitate was
filtered off and dried at 60°C. Then, the precipitate was added to 400 ml of
anhydrous isopropanol, and the mixture was heated to boiling with stirring
for 0.5 h. The hot alcohol was separated by filtration. The precipitate formed
was filtered off after cooling the alcohol. Yield 90%, mp 231–232°C.
1H NMR, d: 6.38 (s, 1H, H6'), 6.64 (s, 1H, H3'), 6.86 (d, 2H, H3,5, J 9.5 Hz),
7.88 (d, 2H, H2,6, J 10.0 Hz). Signals due to the protons of NH2 and
COOH groups were absent from the 1H NMR spectrum because of rapid
deuterium exchange. MS, m/z (%): 279 [M]+ (73), 242 (17), 226 (27), 198
(15), 166 (100), 110 (68), 92 (9), 74 (28). Found (%): C, 55.58; H, 3.95;
N, 10.07. Calc. for C13H11ClN2O3 (%): C, 56.01; H, 3.95; N, 10.05.
4
-(5-Amino-2-chloro-4-nitrophenoxy)benzoic acid 5. Compound 3 (14.0 g,
0.04 mol) in 200 ml of a 20% aqueous solution of KOH was stirred at
60°C for 1 h. The precipitate formed was filtered off and treated with
acetic acid to pH 6. Yield 98%, mp 226–228°C. 1H NMR, d: 6.57 (s, 1H,
H6'), 7.20 (d, 2H, H3,5, J 9.5 Hz), 7.46 (s, 2H, NH2), 8.04 (d, 2H, H2,6
,
J 10.0 Hz), 8.12 (s, 1H, H3'), 13.00 (s, 1H, COOH). MS, m/z (%): 308 [M]+
(7), 292 (4), 256 (11), 188 (26), 136 (100), 90 (7). Found (%): C, 51.54;
H, 2.95; N, 9.06. Calc. for C13H9ClN2O5 (%): C, 51.57; H, 2.92; N, 9.08.
‡
Compounds 8 and 9. Potassium carbonate (3.1 g, 0.023 mol) and com-
¶
pound 1 (3.7 g, 0.015 mol) were stirred in 150 ml of DMSO at 100°C
for 2 h. After cooling, the mixture was poured into water. The resulting
precipitate was filtered off, repeatedly washed with water and dried. The
yield of compound 8 was 17%. The filtrate was treated with acetic acid to
pH 5–6 and the resulting precipitate was filtered off, washed with water
and dried. The yield of compound 9 was 68%.
4-{4-Amino-2-chloro-5-[(5-chloro-2-methyl-1H-benz[d]imidazol-
6-yl)amino]phenoxy}benzoic acid 7. Compound 4 (15.6 g, 0.030 mol),
SnCl2·2H2O (44.1 g, 0.195 mol) and 36% HCl (2 ml) were stirred in
200 ml of glacial acetic acid at 100°C for 1 h. Then, 190 ml of acetic acid
was distilled off and the residue was treated with a 25% aqueous ammonia
solution to pH 7–8. The precipitate was filtered off and dried at 60°C.
Thereafter, the precipitate was added to 400 ml of anhydrous isopropanol
and the mixture was heated to boiling with stirring for 0.5 h. The hot
alcohol was separated by filtration.After cooling the alcohol, the resulting
precipitate was filtered off.Yield 86%, mp > 300°C. 1H NMR, d: 2.43 (s,
3H, Me), 6.42 (s, 1H, H6’), 6.67 (s, 1H, H3’), 6.86 (d, 2H, H3,5, J 9.03 Hz),
6.91 (s, 1H, H7’’), 6.98 (s, 1H, H4’’), 7.89 (d, 2H, H2,6, J 8.77 Hz), 8.34 [s,
1H, NH(Ph)2], 12.11 (s, 1H, NH). Signals due to the protons of NH2 and
COOH groups were absent from the 1H NMR spectrum because of rapid
deuterium exchange. MS, m/z (%): 443 [M]+ (69), 407 (45), 371 (32), 276
(74), 230 (63), 166 (19), 136 (23), 130 (47), 74 (39), 41 (32). Found (%):
C, 56.73; H, 3.58; N, 12.67. Calc. for C21H16Cl2N4O3 (%): C, 56.88;
H, 3.61; N, 12.64.
N-{4-Chloro-5-[(4,5-dichloro-2-nitrophenyl)amino]-2-nitrophenyl}-
acetamide 8: mp 208–210°C. 1H NMR, d: 2.10 (s, 3H, Me), 7.78 (s, 1H,
H6), 7.80 (s, 1H, H6'), 8.24 (s, 1H, H3), 8.44 (s, 1H, H3'), 9.35 (br.s, 1H,
NH), 10.32 (s, 1H, NHCOMe). MS, m/z (%): 418 [M]+ (7), 372 (22),
325 (5), 295 (6), 262 (3), 25 (7), 97 (19), 73 (37), 30 (76). Found (%):
C, 40.15; H, 2.07; N, 13.33. Calc. for C14H9Cl3N4O5 (%): C, 40.05;
H, 2.15; N, 13.35.
N
-(4-Chloro-5-hydroxy-2-nitrophenyl)acetamide 9: mp > 300°C. 1H NMR,
d: 2.13 (s, 1H, Me), 7.75 (s, 1H, H6), 8.10 (s, 1H, H3), 10.28 (s, 1H, NH),
11.88 (s, 1H, OH). MS, m/z (%): 230 [M]+ (6), 183 (26), 182 (10), 158
(9), 142 (9), 43 (100). Found (%): C, 41.45; H, 3.12; N, 12.17. Calc. for
C8H7ClN2O4 (%): C, 41.65; H, 3.04; N, 12.15.
– 141 –