Oxidative polymerization of p-phenylenediamine

Article abstract of DOI:10.1134/S1070363214060073

Oxidative polymerization of p-phenylenediamine in a hydrochloric acid solution yields not a polyquinoxaline polymer as described in the literature but a modified poly(1,4-benzoquinonediimine-N,N′-diyl-1,4-phenylene) analogous to polyaniline known as pernigraniline. A new scheme of oxidative polymerization of p-phenylenediamine was suggested.

Full text of DOI:10.1134/S1070363214060073

ISSN 1070-3632, Russian Journal of General Chemistry, 2014, Vol. 84, No. 6, pp. 1095–1100. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © A.A. Durgaryan, R.A. Arakelyan, N.A. Durgaryan, 2014, published in Zhurnal Obshchei Khimii, 2014, Vol. 84, No. 6, pp. 912–917.
Oxidative Polymerization of p-Phenylenediamine
A. A. Durgaryan, R. A. Arakelyan, and N. A. Durgaryan
Yerevan State University, ul. A. Manukyana 1, Yerevan, 375025 Armenia
e-mail: durgaran@ysu.am
Received October 10, 2013
Abstract—Oxidative polymerization of p-phenylenediamine in a hydrochloric acid solution yields not a
polyquinoxaline polymer as described in the literature but a modified poly(1,4-benzoquinonediimine-N,N'-diyl-
1,4-phenylene) analogous to polyaniline known as pernigraniline. A new scheme of oxidative polymerization
of p-phenylenediamine was suggested.
Keywords: oxidative polymerization, p-phenylenediamine, polyquinoxaline, polyaniline, pernigraniline,
1,4-benzquinonediimine
DOI: 10.1134/S1070363214060073
Polymers derived from aromatic amines have
attracted considerable interest due to their easy
preparation and suitability for various technical
applications [1–4]. In particular, much research has
been done on oxidative polymerization and copoly-
merization of p-phenylenediamine, but there are still
widely differing views on the structure of the resulting
polymer. Cataldo [5] assumed that the polymer has a
structure analogous to that of polyaniline known as
pernigraniline (fully oxidized polyaniline) and
assigned structure Ι to the resulting poly(p-phenyl-
enediamine). The same structure was reported for this
polymer by Li et al. [6].
Lakard et al. [7] carried out an ab initio study of
electrochemical polymerization of p-phenylenediamine
and suggested the following polymerization me-
chanism: The oxidation of p-phenylenediamine leads
to formation of a cation radical, followed by cleavage
of the C–N bond to produce a p-aminophenyl car-
bocation which attacks another p-phenylenediamine
molecule to form 4,4'-diaminodiphenylamine II
(Scheme 1), with leucopolyaniline, i.e., poly(imino-p-
phenylene) being the end product of oxidative
polymerization of p-phenylenediamine.
The oxidative copolymerization of o-xylidine with
p-phenylenediamine yields copolymer III [6], and its
copolymerization with aniline, copolymer IV [8]
(Scheme 2).
H
NH2
N
N
A careful comparison of data reported in [5, 6]
revealed some inconsistencies with the supposed
quinoxaline structure of the resulting polymer. The IR
spectrum of the polymer contains an absorption band
at 830 cm–1, which corresponds to para-disubstituted,
H2N
N
N
H
n
I
Scheme 1.
+
+
+
NH2
H2N
H2N
NH2
+
H2N
NH2
H2N
H
N
+
H2N
NH2
H2N
NH2
_H+
II
1095

1096
*
DURGARYAN et al.
Scheme 2.
H
N
H
H
N
N
N
N
N
H3C
CH3
H
N
H
N
N
H
N
N
H
N
N
N
*
H
9
III
H
*
N
N
NH
HN
N
NH
n
HN
N
NH
IV
Scheme 3.
H
N
N
N
N
N
N
K2S2O6
N
H
N
N
H
N
N
V
N
rather than to 1,2,4,5-tetrasubstituted benzene ring.
According to published data [9], the bands charac-
teristic of two and one C–H bonds are those at 800–
860 and 860–900 cm–1, respectively (830 and 880 cm–1,
on the average, respectively [10]). For example,
absorption bands are observed for leucopolyaniline at
816, for emeraldine at 834 [11], and for pernigraniline
at 830 cm–1 [12]. Poly(diphenylamine) exhibits
absorption at 803 cm–1 characteristic of p-phenylene
compounds [13]. In the IR spectrum of the quinoxaline
polymer obtained by oxidative polymerization of
o-phenylenediamine there are absorption bands of
1,2,4,5-tetrasubstituted benzene ring at 858–868 cm–1
[14], and no band is observed in the 800–835 cm–1
region. These data confirm that the oxidative
polymerization of p-phenylenediamine does not yield a
polymer having a quinoxaline structure.
intensities of the signals from the remaining protons, which
contradicts the polymer structure proposed in [5].
1
In the H NMR spectrum of the polymer presented
in [6] the signal at 4.5 ppm is lacking, but there is a
signal in the upfield region at 3.4 ppm. The assignment
of the broadened signal at 5.84 and four doublets at
6.60, 6.82, 7.10, and 7.16 ppm to the protons of the
amine groups [6] is questionable for two reasons.
Firstly, these signals are more intense than those from
aromatic protons, but the proposed structure of the
polymer has twice as many aromatic protons as the
protons in the NH groups. Secondly, the signals from
the NH protons appear as broadened singlets and
triplets with coupling constants J of 49–60 Hz [15].
The doublet signals with J of 7.0–9.2 Hz presumably
belong to the nonequivalent ortho protons of the
benzene ring [15] (Scheme 2, structure III).
1
The structure suggested in [5] does not correspond
to the fully oxidized state of the polymer. However,
the fully oxidized form V of polymer I results from
subsequent oxidation, like in the case of oxidative
polymerization of o-phenylenediamine [14] (Scheme 3).
The H NMR spectra presented in [5, 6] possess
fairly strong differences. The reason is that, in [5], a
salt form, and in [6], a base form of the polymer was
obtained, and the signal at 4.5 ppm, which was
attributed to the NH and NH2 protons [5], actually
corresponds to the water protons from DMSO. The
intensity of this signal strongly exceeds the sum of the
Theoretically, the formation of the polymer with
structure I requires the use of 2.5 mol of persulfate per
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OXIDATIVE POLYMERIZATION OF p-PHENYLENEDIAMINE
Scheme 4.
H2N
NH2
K2S2O8
NH2
+
+
+
H2N
NH2
H2N
NH2
H2N
+
H2N
NH2
+
NH3
NH3
+
+
+
H2N
N
NH2
H2N
H
HN
NH2
+
H2N
N
NH2
_H+
K2S2O8
2n + 1
H2N
H2N
NH2
N
N
NH2 + 2n NH3
n
VI
Scheme 5.
2NH3
+
HN
NH + 2H2O
O
O
Scheme 6.
O
O
O
H
N
+
2
NH2
N
H
O
1 mol of p-phenylenediamine; in [5, 6], there was
1 mol of persulfate. Consequently, the maximum yield
as calculated with respect to p-phenylenediamine may
be 40%, whereas the experimental yield of the polymer
prepared in [5] was 85%.
However, ammonia can be formed via hydrolysis of
quinonediimine as well (Scheme 5).
To check this possibility, we carried out extraction
of benzoquinone from the resulting substance with
diethyl ether. After evaporation of the solvent, an
insignificant amount of residue was left.
Based on published data [5, 6], we concluded that
oxidative polymerization of p-phenylenediamine yields
not a polyquinoxaline polymer but poly(1,4-benzoqui-
nonediimine-N,N'-diyl-1,4-phenylene) VI analogous to
polyaniline known as pernigraniline [16] (Scheme 4).
If the reaction leads to formation of benzoquinone,
there exists a possibility that the latter will react with
the terminal amino groups of the oligomers to form a
polymer containing benzoquinone moieties [17, 18]
(Scheme 6).
The comparison of the formation schemes for com-
pounds VI and I [5] shows that, if oxidative poly-
merization of p-phenylenediamine proceeds by
Scheme 4, ammonia should be eliminated during the
reaction. To test this assumption, we reproduced the
experiment described in [5] and detected ammonia in
the filtrate. In polymerization of 9 mmol of p-
phenylenediamine, 8.96 mmol of ammonia was found.
In the IR spectrum of the resulting polymer,
however, there are no absorption bands of benzo-
quinone carbonyl groups at 1630–1670 cm–1. Thus, the
above-mentioned findings suggest that hydrolysis of
benzoquinonediimine proceeds to insignificant extent
and, therefore, ammonia is formed mainly by Scheme 4.
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DURGARYAN et al.
by the above-described techniques the content of 1,4-
D
benzoquinonediimine-N,N'-diyl-1,4-phenylene groups
is only 75%. Cao [12] and Albuquerque et al. [19]
prepared pernigraniline by oxidation of emeraldine,
base form of polyaniline with ammonium persulfate
and the spectra presented in those studies obviously
correspond to ammonium bisulfate partial salt.
MacDiarmid et al. [20] obtained pernigraniline by
oxidation of free emeraldine with an acetic acid
solution of m-chloroperbenzoic acid. Consequently,
the compound involved in oxidation was a partial salt
of acetic acid. As to the compound obtained by us, this
is a modified poly(1,4-benzoquinonediimine-N,N'-diyl-
1,4-phenylene).
The 1H NMR spectrum of the polymer in DMSO-d6
fully coincides with that presented in [6]. It contains
signals from the protons of the terminal NH2 groups
(5.1–5.9 ppm) and those from the phenylene and
quinonediimine protons (6.4–8.0 ppm). The signals at
8.8–10.0 ppm are probably associated with the protons
of water coordinated to the sulfonate groups, which
were revealed by subsequent analysis of the polymer
that we obtained.
λ, nm
UV spectrum (DMSO) of the polymer obtained at a
1 : 1 molar ratio of p-phenylenediamine to K2S2O8.
According to Scheme 4, oxidative polymerization
of 1 mol of p-phenylenediamine requires 0.5 mol of
persulfate. Our studies showed that, at the 1 : 0.55 and
1 : 1 molar ratios of p-phenylenediamine to persulfate,
the reaction yields were identical.
The quinonediimine groups are responsible for
reactivity of pernigraniline. It is known [20] that the
reaction of pernigraniline with hydrochloric acid
proceeds via 1,4-addition followed by ring aromatize-
tion. Pernigraniline reacts in a similar way with
sulfuric acid, or with potassium bisulfate which is
formed from potassium persulfate during polymeriza-
tion (Scheme 7).
As indicated in [5], the UV spectra of the HCl salt
of the polymer prepared from p-phenylenediamine in
DMF and in water are similar to those of
pernigraniline. In the UV spectrum of the polymer in
DMSO (see figure) the absorption at 405 nm is lower
than that reported in the literature for pernigraniline
[12, 19, 20].
To prove the presence of sulfonate groups, the
polymer was heated for 5 h on a water bath with a 5%
These differences may be due to several factors.
Kang et al. [21] reported that in the polymers obtained
Scheme 7.
N
N
N
N
HCl
H
H
N
N
N
N
Cl
N
N
N
N
KHSO4
H
H
N
N
N
N
OSO3K
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OXIDATIVE POLYMERIZATION OF p-PHENYLENEDIAMINE
KOH solution, the sulfate ions were precipitated by
barium chloride, and sulfonate groups were determined
semiquantitatively (7.17 %). The sulfonate groups in
the polymer can affect its UV spectrum.
water. The distillate and the Tishchenko flask contents
were titrated with 0.1 N HCl. Found: 8.96 mmol of
ammonia. After distillation, the contents of the
distillation flask were filtered, and the precipitate was
washed with distilled water until neutral pH and then
treated with ether, the result being that 0.003 g of the
substance was dissolved in ether. To the air-dried
precipitate, a 10% KHCO3 solution was added (to pH
10), and the mixture was stirred for 8 h. The resulting
precipitate was filtered off, washed with distilled water
until neutral pH and to the absence of SO42– ions in
washings. The resulting polymers were vacuum-dried
at 60°C (2 kPa) to constant weight. Yield 0.72 g
(86%).
For obtain more data, the reaction was carried out
at a 1:0.25 molar ratio of the monomer to potassium
persulfate under the conditions of oxidative
polymerization of p-phenylenediamine.
1
According to the H NMR spectrum, the reaction
gives N,N'-bis(4-aminophenyl)-1,4-benzoqiunonedi-
imine (Scheme 4, n = 1) which subsequently reacts
with potassium bisulfate to form 1,4-di(4-amino-
1
anilino)benzene-2-sulfonate. The H NMR spectrum
(DMSO-d6) contains signals from the NH2 protons at
5.2–6.0 ppm and those from the aromatic protons and
NH protons at 6.4–8.0 ppm [6.6 d, 6.9 d (6H); 6.75 d,
7.1 d (4H), 7.3–8.2 ppm (3H)]. The signals at 9–
10.4 ppm are apparently due to the protons of water
coordinated to the sulfonate groups. At a 1 : 0.25 molar
ratio in glacial acetic acid the reaction of p-
phenylenediamine with persulfate gives N,N'-bis(4-
aminophenyl)-1,4-benzquinonediimine [22].
b. Molar ratio 1 : 0.55. The reaction was carried out
in a similar way. In 105 mL (0.15 mol) of HCl, 1.00 g
(9.3 mmol) of p-phenylenediamine was dissolved.
Next, 1.38 g (5.1 mmol) of potassium persulfate was
dissolved in 26 mL of distilled water, and the resulting
solution was added dropwise within 5–6 min into the
solution of p-phenylenediamine. In the distillate,
6.4 mmol of ammonia was found. Yield 0.74 g (88%).
c. Molar ratio 1 : 0.25. In a flat-bottomed flask,
1.00 g (9.3 mmol) of p-phenylenediamine was placed,
and 105 mL (0.15 mol) of HCl was added, after which
the content of the flask was stirred until dissolution of
p-phenylenediamine. Next, a con-centrated solution of
0.63 g (2.65 mmol) of potassium persulfate in 12 mL
of water was added at 20°C under permanent stirring
within 5 min. The reaction mixture was stirred for
14 h, and the resulting precipitate was filtered off, air-
dried, and treated with a 10% aqueous KHCO3
solution (to pH 10), after which the mixture was stirred
for 8 h. The resulting precipitate was filtered off,
washed with water until neutral pH and to the absence
of SO42– ions in washings. Yield 0.11 g (10%).
Thus, the above data confirm that oxidative
polymerization of p-phenylenediamine proceeds by
Scheme 4, and the structure of the resulting polymer is
analogous to that of pernigraniline which, under the
reaction conditions, undergoes certain transformations.
EXPERIMENTAL
In our experiments, p-phenylenediamine was
purified by sublimation (mp 143–145°C), and analy-
tically pure grade potassium persulfate was used. The
IR spectra were recorded on a Nicolet/Nexus FT-IR
spectrometer, the electronic spectra, on a Specord 65
1
spectrometer, and the H NMR spectra, on a Mercury
300 Varian NMR spectrometer.
REFERENCES
1. Handbook of Conducting Polymers, Skorheim, T.A.,
Elsenbaumer, R.L., and Reynolds, J.R., Eds., 2nd ed.,
New York: Marcel Dekker, 1998, p. 823.
2. Wei, Y., Focke, W.W., Wnek, G.E., Ray, A., and
MacDiarmid, A.G., J. Phys. Chem., 1989, vol. 93, p.
495. DOI: 1021/j100338a095.
3. Strounina, E.V., Shepherd, R., Kane-Maguire, L.A.P.,
and Wallace, G.G., Synth. Met., 2003, vols. 135–136,
p. 289. DOI: 10.1016/S0379-6779(02)00923-2.
4. Thiemann, C. and Brett, C.M.A., Synth. Met., 2001, vol. 125,
no. 3, p. 445. DOI: 10.1016/S0379-6779(01)00502-1.
5. Cataldo, F., Eur. Polym J., 1996, vol. 32, p. 43. DOI:
10.1016/0014-3057(95)00118-2.
Oxidative polymerization of p-phenylenediamine
under the action of potassium persulfate [5]. a.
Molar ratio 1 : 1. To a solution of 1.00 g (9.3 mmol) of
p-phenylenediamine in 102 mL (0.15 mol) of HCl, a
solution of 2.51 g (9.3 mmol) of potassium persulfate
in 47 mL of distilled water was added within 5–6 min,
and the resulting mixture was stirred for 16 h at room
temperature. Next, the solution was filtered, and the
precipitate was air-dried. The filtrate after alkalization
with concentrated KOH was distilled on an apparatus
equipped with a liquid trap, a receiver filled with water
for ammonia absorption, and a Tishchenko flask with
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 6 2014

1100
DURGARYAN et al.
6. Li, Xin-Gui, Huang, Mei-Rong, Chen, Run-Feng, Jin, Yi,
and Yang, Yu-Liang, J. Appl. Polym. Sci., 2001, vol. 81,
p. 3107. DOI: 10.1002/app.1762.
troscopy, Emsley, J.W., Feeney, J., and Sutcliffe, L.H.,
Eds., Oxford: Pergamon, 1965. Translated under the
title Spektroskopiya yadernogo magnitnogo rezonansa
vysokogo razresheniya, Moscow: Mir, 1969, vol. 2, p. 145.
7. Lakard, B., Herlem, G., Lakard, S., and Fahys, B.,
J. Mol. Struct. (THEOCHEM), 2003, vol. 638, p. 177.
DOI: 10.1016/S0166-1280(03)00567-0.
16. Durgaryan, N.A., Arakelyan, R.H., and Durgaryan, A.H.,
in Conducting Polymers: Formation, Structure,
Properties, and Application, Prague, 2011, SL02, p. 46.
17. Parini, V.P., Kazakova, Z.S., Okorokova, M.N., and
Berlin A.A., Polym. Sci. USSR, 1962, vol. 3, p. 750.
DOI: org/10.1016/0032-3950(62)90374-X.
8. Rani, M., Ramachandran, R., and Kabilan, S., Synth.
Met., 2010, vol. 160, nos. 7–8, p. 678. DOI: 10.1016/
j.synthmet.2010.01.001.
9. Bellamy, L.J., The Infrared Spectra of Complex
Molecules, New York: Wiley, 1958. Translated under
the title Infrakrasnye spektry slozhnykh molekul,
Moscow: Inostrannyaya Literatura, 1963, p. 97.
18. Nithianandam, V.S., Kaleem, K., Chertok, F.S., and
Erhan, J., Appl. Polym. Sci., 1991, vol. 42, p. 2899.
DOI: 10.1002/app.1991.070421106.
19. Albuquerque, J.E., Mattoso, L.H.C., Baligh, D.T.,
Faria, R.M., Masters, J.G., and MacDiarmid, A.G.,
Synth. Met., 2000, vol. 113, p. 19. DOI: org/10.1016/
S0379-6779(99)00299-4.
10. Günxler, H. and Gremlich, H.-U., IR Spectroscopy: An
Introduction, New York: Wiley, 2002, p. 195.
11. Zeng, Xing-Rong and Ko, Tze-Man, Polymer, 1998,
vol. 39, no. 5, p. 1187. DOI: 10.1016/S0032-3861(97)
00381-9.
20. MacDiarmid, A.G., Manohar, S.K., Masters, J.G., Sun, Y.,
Weiss, H., and Epstein, A.J., Synth. Met., 1991, vol. 41,
p. 621. DOI: org/10.1016/0379-6779(91)91145-Z.
12. Cao, Y., Synth. Met., 1990, vol. 35, p. 319. DOI:
10.1016/0379-6779(90)90216-8.
21. Kang, E.T., Neoh, K.G., and Tan, K.L., Surf. Interface
Аnal., 1993, no. 20, p. 833. DOI: 10.1002/
sia.740201006.
13. Yamamoto, T., Kim, S.-B., and Maruyama, T., Chem.
Lett., 1996, p. 413. DOI: 10.1246/cl.1996.413.
14. Permasiri, A.H. and Euler, W.B., Macromol. Chem.
Phys., 1995, vol. 196, p. 3655. DOI: 10.1002/
macp.1995.021961118.
22. Martikyan, N.Sh., Durgaryan, N.A., Arakelyan, R.H.,
and Durgaryan, A.H., Abstracts of Papers, Second Int.
Conf. of Young Chemists, Tbilisi (Georgia), April 21–
23, 2012, p. 105.
15. High Resolution Nuclear Magnetic Resonance Spec-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 6 2014