Oxidative polymerization of 4-aminoazobenzene under the action of iodine

Article abstract of DOI:10.1134/S1070363209020145

Chemical oxidative polymerization of 4-aminoazobenzene under the action of iodine was studied for the first time. Samples of poly(4-aminoazobenzene) with different molecular mass depending on the reaction conditions were obtained. Their structures were st

Full text of DOI:10.1134/S1070363209020145

ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 2, pp. 252–257. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © A.A. Durgaryan, R.A. Arakelyan, N.A. Durgaryan, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79, No. 2, pp. 264–268.
Oxidative Polymerization of 4-Aminoazobenzene
under the Action of Iodine
A. A. Durgaryan, R. A. Arakelyan, and N. A. Durgaryan
Yerevan State University,
ul. A. Manukyana 1; Yerevan, 375025 Armenia
E-mail: durgaryan@ysu.am
Received May 26, 2008
Abstract―Chemical oxidative polymerization of 4-aminoazobenzene under the action of iodine was studied
for the first time. Samples of poly(4-aminoazobenzene) with different molecular mass depending on the
reaction conditions were obtained. Their structures were studied by means of the IR and 1H NMR spectroscopy
and viscometry. The polymers obtained contain mainly imino-1,4-phenylenazo-1,4-phenylene units. Together
with the polymers, 3-iodo-4-aminoazobenzene is also formed.
DOI: 10.1134/S1070363209020145
Polyaniline occupies special place among the
electroactive polyconjugated polymers due to its
stability to the action of the environmental conditions,
and because of the easy and cheap method of its
synthesis and the unique properties [1, 2]. It has a
broad spectrum of probable use as the anticorrosion
covering [3, 4], in the accumulator batteries [5–7], for
the separation of gases and hardly separable liquids [8–
10], as bio- and chemosensor [11–13], etc. [14–16].
sisting mainly of the repeating structural units I was
offered [23–25].
NH
N=N
I
Oxidative polymerization of aminoazobenzene under
the action of iodine was carried out in boiling ethanol
at the equimolar reagent ratio. Basing on the solubility
in petroleum ether the reaction products were separ-
ated to give two fractions. The soluble fraction con-
sisted of low molecular weight compounds, while the
insoluble one, PAAB-1, is a polymer partially soluble
in DMF and DMSO (characteristic viscosity 0.11 dl g–1
in DMF at 298 K). Acidity of the reaction mixture
alters in the course of the reaction due to formation of
hydrogen iodide. With the purpose of establishing the
dependence of the yield and the molecular mass of
polymer on the acidity of the medium oxidative poly-
merization of aminoazobenzene was studied in presence
of potassium hydrocarbonate at the aminoazoben-
zene:I2 1:1 and 1:1.5 molar ratio, and also in the presence
of calcium carbonate at the aminoazoben-zene:I2 1:1
molar ratio to give the polymers PAAB(K-1), PAAB
(K-1.5), and PAAB(Ca) respectively. Experimental
data show that in all the cases presence of salts
decreases the conversion of monomer to polymer. In
the case of PAAB-1 it is 87%, PAAB(K-1.5) 73.3%,
PAAB(K-1) 53.3%, PAAB(Ca) 40%. These polymers
In the series of polyconjugated electroactive poly-
mers the substances containing aromatic azo-groups in
the main chain and in the side groups [17] are studied
rather scarcely. Such polymers present certain interest
in connection with the possibility of their use in optical
devices, in optical computers, for writing information
on the polymer films [18], for conversion of the light
wavelength, as the electrode for the light-emitting
diode [19], etc. [20–22].
Synthesis of electroconducting polymer containing
the amino and the azo-groups in the main polymer
chain is actual because the polymers obtained combine
specific features of polyaniline and polyazo-arylenes
and may exhibit new valuable properties. With the
purpose of obtaining such polymers we for the first
time studied chemical oxidative polymerize-tion of 4-
aminoazobenzene under the action of iodine.
Electrochemical polymerization of aminoazobenzene
was studied previously, and on the basis of the IR and
Raman spectral data the structure of polymer con-
252

OXIDATIVE POLYMERIZATION OF 4-AMINOAZOBENZENE
253
completely dissolve in DMF, but their molecular mass
is low as compared to PAAB-1. For PAAB(K-1) and
PAAB(K-1.5) [η] is 0.1 dl g–1, and for PAAB(Ca) [η]
is 0.08 dl g–1 at 298 K.
secondary ones, while azo groups remain intact
(absorption at 1405 cm–1, see the table). Presence of
absorption band at 830–836 cm–1 (p-disubstituted
benzene ring 2H), and practically absence of absorp-
tion at 880 cm–1 (1H) shows that the amino group
occupies mainly para-position respectively to the azo
group.
In the IR spectra of obtained polymers PAAB-1,
PAAB(K-1), PAAB(Ca), and PAAB(K-1.5) absorption
bands of primary amino groups of the aminoazo-
benzene at 3400, 3450, and 1615 cm–1 are absent, and
the absorption bands of secondary amino groups at
3199–3380 cm–1 are observed. Hence, in the course of
the reaction primary amino groups are converted to
According to these data the oxidative polymerize-
tion of aminoazobenzene as well as its electrochemical
polymerization [23, 24] can be described by following
reaction.
Scheme 1.
a
b
a
b
I2
H
-
H_(N_
_N=N_
p C6H5N=N_C6H4NH2
_)nH
1
In the H NMR spectra of all the polymers the
signals of protons in DMSO are broadened (δ, ppm in
DMSO). Considering that the signals of protons of p-
diphenylenamine units in poly(diphenylamin-4,4'-diyl)
in trifluoroacetic acid are observed at 7.52 ppm [26],
and of [C6H4(BOC)NC6H4NH–]n in THF at 7 ppm as
two doublets [27], and also that the signals of protons
in o-position in relation to azo group are observed in
the monomer at 7.6–7.8 ppm, while in 7-(4-N,N-
dihydroxyethylaminophenylazo)-2-nitro-9-fluorene
ortho-proton of azophenyl group gives a signal at
8.01 ppm [28], following assinment of the signals can
be made. The signals at 7.34–7.66 ppm belong to the
ortho-protons in relation to amino groups and the amino
group protons, while the signals at 7.66–8.10 ppm
belong to the ortho-protons in relation to azo group.
Integral intensity of the latter is smaller as compared to
the signal at 7.34–7.66 ppm that is explained by the
presence of terminal groups in the polymer (Scheme 1).
1
To improve resolution in the H NMR spectrum of
PAAB-1 it was taken at different temperatures (Fig. 1)
Absorption bands in the IR spectra of polymers and the 4-aminoazobenzene monomer
PAAB(K-1)
PAAB(Ca)
PAAB(K-1.5)
PAAB-1
AAB
3380, 3310
3057
1588
1504
1462
1436
1409
1298
1230
1175
1138
1070
1018
925
3334, 3199
3059
3300
3060
1586
1500
1460
1420
3220; NH
3050
3400; 3450, NH
3050; 1613, NH
1587, benzene ring
1504, benzene ring
1460, N=N
1593
1590
1497
1502; 1475
1460
1420
1409
1408, N=N
1302
1300
1302
1299; =N–Ar
1235; =N–Ar
1220–1240
1180; 1150
1138
1180
1130
1070
1015
1180; 1150
1136
1070
1015
930
1136, C–N=
1100; 1070
1013
1111, –C–N, N–N
–C–N, N–N
950
833
831
766
689
834
830
833 (2H)
769 (5H)
690 (5H)
765
766
766
686
686
687
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 2 2009

254
DURGARYAN et al.
6.72
70
8.2 8.1 8.0 7.9 7.8 7.7 7.6 7.5 7.4
δ, ppm
6.71
6.70
60
50
1
Fig. 2. H NMR spectrum of PAAB-1 polymer [δ, ppm in
(D3C)2SO] at 70°C.
d, and 7.73 ppm, d, J 8.73 Hz respectively. Presence of
a large number of signals can be explained by slow
interconversion of monomers due to rotation about N–C
bond, for example as is shown in Scheme 2.
6.70
6.69
The fraction with low molecular mass soluble in
petroleum ether was also studied by means of 1H NMR
spectroscopy in DMSO-d6 (Fig. 3). The sample under
investigation was obtained parallel to PAAB-1 poly-
mer. It was found that it is an equimolar mixture of two
compounds, aminoazobenzene and 3-iodo-4-amino-
azobenzene. The elemental analysis data show that
nitrogen content in the obtained low molecular fraction
is 16.11; 15.93% that corresponds to the calculated
value 16.15% for the equimolar mixture of com-
pounds. It permits to conclude that in parallel to poly-
merization, the substitution of hydrogen with iodine in
the monomer slowly proceeds (Scheme 3).
40
30
?
7
δ, ppm
1
Fig. 1. H NMR spectrum of PAAB-1 polymer (δ, ppm in
DMSO-d6). Registration temperature, °C, is given above
each spectrum.
1H NMR and the elemental analysis data for the
soluble fraction obtained in the course of oxidative
polymerization of aminoazobenzene in presence of
potassium carbonate was considered analogously.
Composition of the obtained mixture of low molecular
compounds is presented in the Experimental. Perform-
ing the reaction of aminoazobenzene with iodine in the
presence of calcium carbonate leads to increase in the
in the range 30–70°C. Increase in temperature
improves the resolution, and for the spectrum obtained
at 70°C (Fig. 2) the following assignment can be
made: the protons a at 7.63 ppm, d, J 8.73 Hz; 7.64
ppm, d, J 8.73 Hz; 7.67 ppm, d, J 8.7 Hz; 7.62 ppm, d,
J 8.33 Hz; 7.66 ppm, d, J 4.76 Hz; protons b 7.97 ppm,
d, J 8.73 Hz; 7.89 ppm, d, J 8.33 Hz; 8.13 ppm, d, J
4.76 Hz; protons a and b of terminal groups: 6.69 ppm,
Scheme 2.
N
N
N
N
N
N
N
N
N
H
H
N
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 2 2009

OXIDATIVE POLYMERIZATION OF 4-AMINOAZOBENZENE
255
Scheme 3.
H
H
N
a
a'
N
b
b'
H
H
I2
c
c'
N
N
_HI
d
e
d'
e'
N
N
J
b''
EXPERIMENTAL
Aminoazobenzene was prepared according to the
yield of the iodine derivative that can be explained by
the fact that CaI2 obtained in the course of the reaction
acts as a Friedel–Krafts catalysts to favor the substitu-
tion with iodine. This effect may be used for the
preparing the iodine-substituted aminoazobenzene.
established procedure and purified by crystallization
from ethanol, mp 124–126°C [29]. IR spectra were
registered on a FT IR Nicolet Nexus spectrometer in
KBr pellets and by means of ATR technique on the
IR spectra of all low molecular fractions contain the
absorption bands common to aminoazobenzene as well
as to iodoaminoazobenzene, and also the absorption
bands of the 1,2,4-substituted benzene ring [δC–H
890 cm–1 (1H)]. The bands at 680 and 650 cm–1 belong
evidently to C–I bond and are characteristic only of the
iodine derivative.
1
ZnSe crystal. H NMR spectra were taken on a Varian
Mercury 300 spectrometer in DMSO-d6.
Synthesis of polyaminoazobenzene [PAAB-1]. A
mixture of 3.0 g of aminoazobenzene, 33 ml of
ethanol, and 3.87 g of iodine was refluxed with stirring
on a water bath for 63 h. The mixture obtained was
treated with a saturated water solution of 3.0 g of
sodium hydrocarbonate and left for 3 days. After that
reaction mixture was filtered, washed with water until
the disappearance of iodide anions and the neutral
reaction of the medium. Precipitate obtained was dried
in air, extracted with petroleum ether, and two frac-
Hence, a procedure for preparing PAAB by means
of chemical oxidative polymerization of the amino-
azobenzene is developed for the first time. The
structure of the polymers obtained is established. It is
shown that substitution with iodine in the molecule of
monomer leading to the iodine derivative proceeds
simultaneously.
6.9
6.1
3.8
2.0
1.0
0.9
8
0.2
9
7
6
5
δ, ppm
Fig. 3. 1H NMR spectrum (DMSO-d6), δ, ppm, of low molecular fraction formed with PAAB-1.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 2 2009

256
DURGARYAN et al.
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tions were separated. One of them, 0.42 g, was soluble
in petroleum ether, while another one, 2.6 g, was
insoluble. The last fraction is partially soluble in DMF
and DMSO (1.8 g), while 0.8 g remains undissolved.
1
According to H NMR data from 3 g of amino-
zobenzene 2.6 g (87%) converts to a polymer, 0.16 g
(5.3%) converts to 3-iodo-4-aminoazobenzene, and 0.16 g
(5.3%) remains unreacted. The fraction insoluble in
petroleum ether was purified by precipitation from
1
DMF solution with water. H NMR spectrum, δ, ppm
(J, Hz): aminoazobenzene: 5.52 s (NH2), 6.64 d (2Ha,
Jab 8.73 Hz), 7.65 d (2Hb, Jab 8.73 Hz); 3-iodo-4-
aminoazobenzene: 5.68 s (NH2), 6.87 d (1Ha', Jab'bd'
8.73 Hz), 7.70 d (1Hb', Jab'bd' 8.73 Hz, Jb'b" 2.37 Hz),
8.19 d (1Hb", Jb'b" 2.37 Hz), 7.74-7.78 m (4Hc,c'), 7.29–
7.47 m (6Нd,d',e,e').
11. Gerard, M., Chaubey, A., and Malhotra, B.D.,
Synthesis of polyaminoazobenzene [PAAB(K-1)]
was carried out analogously to PAAB-1. A mixture of
3.0 g of aminoazobenzene, 33 ml of ethanol, 3.85 g of
iodine, and 3.04 g of potassium hydrocarbonate was
refluxed for 23 h. After that reaction mixture was
treated with 60 ml of water to give 1.9 g of the fraction
soluble in petroleum ether and 1.6 g of the insoluble
one. Conversion to polymer 53.3%.
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Synthesis of polyaminoazobenzene [PAAB(K-
1.5)] was carried out analogously. A mixture of 1.5 g
of aminoazobenzene, 17 ml of ethanol, 2.9 g of iodine,
and 2.28 g of potassium hydrocarbonate was refluxed
for 40 h to give 0.38 g of the fraction soluble in petro-
leum ether and 1.1 g of the insoluble one. Conversion
to polymer 73.3%.
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Synthesis of polyaminoazobenzene [PAAB(Ca)]
was carried out analogously to PAAB-1. A mixture of
1.01 g of aminoazobenzene, 12 ml of ethanol, 1.3 g of
iodine, and 0.51 g of calcium carbonate was refluxed
for 110 h to give 0.69 g of the fraction soluble in
petroleum ether, and 0.4 g of the insoluble fraction.
19. Ramanujam, P.S., Hvilted, S., Ujhelyi, F., Koppa, P.,
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1
According to H NMR data recovery of aminoazo-
21. Schlz, B.M., Huber, M.R., Bieringer, T., Krausch, G.,
benzene 0.22 g (conversion 78%). Yield of the
polymer 0.40 g (40%), and of 3-iodo-4- aminoazo-
benzene 0.47 g (36%).
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