Graphene oxide promoted synthesis of p-phenylenediamine antioxidants

Article abstract of DOI:10.1134/S1070363216020262

Three p-phenylenediamine antioxidants (p-phenylenediamine-N,N,N′,N′-tetrapropionic acid tetramethyl ester, p-phenylenediamine-N,N,N′-tripropionic acid trimethyl ester, and p-phenylenediamine-N, N′-dipropionic acid dimethyl ester) were successfully synthes

Full text of DOI:10.1134/S1070363216020262

ISSN 1070-3632, Russian Journal of General Chemistry, 2016, Vol. 86, No. 2, pp. 356–359. © Pleiades Publishing, Ltd., 2016.
Graphene Oxide Promoted Synthesis of p-Phenylenediamine
Antioxidants1
Yin-Tao Li, Quan-Ping Zhang, Feng Xiao, and Yuan-Lin Zhou
State Key Laboratory Cultivation Base for Nonmetal Composite and Functional Materials,
Southwest University of Science and Technology, Mianyang, 621010 China
e-mail: liyintao@swust.edu.cn; zhouyuanlin@swust.edu.cn
Received May 28, 2015
Abstract—Three p-phenylenediamine antioxidants (p-phenylenediamine-N,N,N′,N′-tetrapropionic acid tetra-
methyl ester, p-phenylenediamine-N,N,N′-tripropionic acid trimethyl ester, and p-phenylenediamine-N, N′-
dipropionic acid dimethyl ester) were successfully synthesized via atom-economic aza-Michael addition of p-
phenylenediamine to methyl acrylate promoted by graphene oxide in water. The synthesized compounds were
characterized by NMR, ESI-MS spectra, and elemental analyses. The effects of the solvent and graphene oxide
on the reaction were investigated.
Keywords: p-phenylenediamine antioxidants, graphene oxide, aza-Michael addition, atom economy.
DOI: 10.1134/S1070363216020262
Rubber materials are omnipresent and are
indispensable in our daily life due to their unique
properties [1] such as good mechanical strength and
electrical insulation. However, unsaturated bonds in
rubber chains are likely to be damaged by the action of
environmental factors, e.g., oxygen, ozone, heat and/or
dynamic stress, etc. [2–5], which induce discoloration,
cracking, stiffening, impairment of physicomechanical
and chemical properties, and so on. As a result, the
service life of rubber is definitely shortened [6], and it
negative affects the environment. A possible way to
circumvent these problems is to add a small amount of
special organic compounds known as antioxidants to
natural or synthetic rubber [7, 8].
product designers in rubber industry have turned to p-
phenylenediamine (PPD) which can protect rubber not
only from ozone cracking but also from autooxidation
and mechanical fatigue [12–14]. The antiozonant
effect of N-substituted p-phenylenediamines decreases
in going from N,N-dialkyl to N-alkyl-N-aryl and then
N,N-daryl derivatives. The reactivity toward ozone
decreases in the order N,N,N′,N′-tetraalkyl > N,N,N′-
trialkyl > N,N′-dialkyl [14]. Consequently, the design
of new efficient p-phenylenediamine antioxidants will
improve the atom economy of raw materials and
prolong the lifetime of products.
In order to achieve this goal, Michael addition of p-
phenylenediamine to methyl acrylate using graphene
oxide as organocatalyst was studied (Scheme 1).
Michael addition (also known as conjugate addition)
has attracted much attention among synthetic methods
due to its mildness, operability, and atom economy. In
recent years, due to cost effectiveness and easy
workup, organocatalysts have been used for efficient
syntheses of various compounds [15–17]. Graphene
oxide (GO) has a two-dimensional sheet-like structure
and large open surface area [18] which is readily
accessible to reactants with negligible mass transfer
resistance; therefore, it could be efficient in one-pot
multistep reactions due to more facile transportation of
intermediates. It is also important that GO possesses a
large number of hydroxy and epoxy groups on the
basal planes and carboxy groups along the sheet edges
Derivatives of diarylamine and phenols are most
widely used as radical-trapping antioxidants in rubber
industry [9, 10]. The antioxidation mechanism involves
donation of a labile hydrogen to peroxy radicals for
interrupting the propagation step [11]. Phenolic
antioxidants become increasingly ineffective at tem-
peratures above 100°C because peroxycyclohexa-
dienone is thermally unstable, which is controlled by
coupling of phenoxyl and peroxyl radicals. In contrast,
diarylamine antioxidants show a good antioxidant
effect at both high and low temperatures. However,
diarylamine derivatives are very intensely colored,
which restricts their further application [9]. Therefore,
1 The text was submitted by the authors in English.
356

357
GRAPHENE OXIDE PROMOTED SYNTHESIS OF p-PHENYLENEDIAMINE ANTIOXIDANTS
Scheme 1.
O
O
O
O
O
O
Graphene oxide, N2, H2O,
60°C, 24 h
O
N
NH2
N
+
H2N
O
O
O
1
O
O
O
O
O
O
+
N
N
O
O
HN
N
O
H
H
3
O
2
[19]. Therefore, GO proved to be a good organo-
catalyst for aza-Michael addition of amines to
activated alkenes [20].
6.50 ppm (aromatic protons) and a singlet at
δ 5.06 ppm which was assigned to the NH proton. The
singlet at δ 3.33 ppm (NCH2) was overlapped by the
signal of water present in the solvent. When the
solvent was changed to CDCl3, the NH singlet
disappeared, whereas the NCH2 signal was clearly
seen. In the 13C NMR spectrum of 2, four signals from
aromatic carbons were observed in the range from δC =
The Michael addition reaction of p-phenylene-
diamine with methyl acrylate is a consecutive reaction.
The formation of the tetrasubstituted product requires
appropriate conditions, primarily sufficiently long
reaction time. We examined the effect the solvent on
the reaction. For this purpose, the reaction of p-phenyl-
enediamine (10 mmol) with methyl acrylate (60 mmol)
was carried out in different solvents (10 mL), namely
chloroform, tetrahydrofuran, ethanol, and water, as
well under solvent-free conditions, in the presence of a
small amount of hydroquinone (60°C, 12 h). The results
are given in table. The reactions in chloroform and
tetrahydrofuran gave only the monosubstituted
product; mono- and disubstituted derivatives were
formed in the solvent-free system. Tri- and tetra-
substituted compounds 2 and 1 (together with mono-
and disubstituted derivatives) were obtained in ethanol
and water, respectively. The yield of tetrasubstituted
product 1 in water was 34% in the presence of GO and
21% in the absence of GO. Thus, GO can promote the
reaction.
1
114.79 to 141.21 ppm. Compound 3 showed in the H
NMR spectrum signals at δ = 6.40 ppm due to the
aromatic protons and at δ = 4.77 ppm due to the NH groups.
A possible mechanism of the catalytic aza-Michael
addition reaction is illustrated by Scheme 2. Hydrogen
bonding between water molecules and carbonyl oxygen
atom of methyl acrylate enhances polarization of the
C=C double bond thus favoring the addition of amine
to the Michael, while hydrogen bonds formed by
oxygen-containing functional groups on the GO sheet
facilitate proton transfer from the nitrogen to oxygen
atom.
In summary, we have successfully synthesized three
p-phenylenediamine antioxidants via aza-Michael
addition of p-phenylenediamine to methyl acrylate
promoted by GO under mild conditions, which is
promising from the viewpoint of atom economy. The
reaction in water was faster than in weakly polar
solvents, and the yield of the tetrasubstituted product
was 34% in the presence of GO against 21% without
GO. The prepared products can be used not only as
efficient antioxidants for macromolecular compounds
but also as important intermediates for further design
of new substances.
1
The structure of 1–3 was confirmed by H and 13C
NMR, FT-IR, and ESI MS spectra and elemental
analyses. The 1H NMR spectrum of 1 in CDCl3
showed a singlet at δ = 6.72 ppm corresponding to the
aromatic protons. In the 13C NMR spectrum of 1, two
kinds of aromatic carbons were observed at δC
=
116.74 and 140.02 ppm. The 1H NMR spectrum of 2 in
DMSO-d6 displayed two doublets at δ = 6.63 and
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 2 2016

358
YIN-TAO LI et al.
Scheme 2. Single-sheet graphene oxide (GO).
COOH
OH
OH
OH COOH
OH
OH
COOH
O
HO
HOOC
HO
O
O
O
HO
OH HO
OH
OH
HO
O
OH
O
O
OH
HO
COOH
COOH
O
O
H
R'
O
H
O
H
H
O−
H+
R'
−GO
GO
R'
−H2O
RHN
GO
N
R
H
..
RNH2
EXPERIMENTAL
a 1200L triple quadrupole mass spectrometer equipped
with an electrospray ionization source. Varian MS
workstation version 6.3 software was used for data
acquisition and processing. When the reaction was
complete, the mixture was extracted with ethyl acetate,
and the extract was dried over anhydrous sodium
sulfate and concentrated on a rotary evaporator. The
residue was initially analyzed by thin-layer chromato-
graphy and was then subjected to column chromato-
graphy on silica gel (200–300 mesh) using chloroform–
ethyl acetate as eluent to isolate pure compounds 1–3.
All chemicals and solvents were used as received
unless otherwise specified. p-Phenylenediamine was
purified by recrystallization from hot ethanol.
Graphene oxide was provided by our laboratory and
was finely dispersed in water under ultrasonic
irradiation.
Michael addition of p-phenylenediamine to
methyl acrylate in the presence of graphene oxide.
A three-necked flask was charged with a solution of
1.08 g (10 mmol) of p-phenylenediamine in 2 mL of
ethanol, 0.025 g of graphene oxide ultrasonically
dispersed in 10 mL of water was added, and a small
amount of hydroquinone was then added. Methyl
acrylate, 5.17 g (60 mmol) was added in portions, and
the mixture was heated to 60°C and magnetically
stirred for 24 h under a nitrogen atmosphere. NMR
was recorded by a Bruker AVANCE 600 pectrometer
[1H (600 MHz), 13C (151 MHz)], Switzerland, in
CDCl3 with TMS as an internal standard. The
elemental analysis was performed on a Vario EL cube
(Elementar Analysensysteme, Germany). TLC was
performed on GF254 glass-backed silica gel plates and
visualized in an iodine chamber. A Varian HPLC–ESI-
MS system (Palo Alto, CA, USA) consisted of a
ProStar 410 autosampler, two ProStar 210 pumps, and
p-Phenylenediamine-N,N,N′,N′-tetrapropionic
acid tetramethyl ester (1). Mass spectrum: m/z 474.9
[M + Na]+. Found, %: C 58.61; H 7.06; N 6.01; O
28.32. C22H32N2O8. Calculated, %: C 58.39; H 7.13; N
6.19; O 28.29. M 452.22.
p-Phenylenediamine-N,N,N′-tripropionic acid
trimethyl ester (2). Mass spectrum: m/z 389.0 [M +
Na]+. Found, %: C 58.73; H 7.09; N 7.84; O 26.34.
C18H26N2O6. Calculated, %: C 59.00; H 7.15; N 7.65;
O 26.20. M 366.18.
p-Phenylenediamine-N,N′-dipropionic acid
dimethyl ester (3). Mass spectrum: m/z 281 [M + H]+.
Found, %: C 59.78; H 7.08; N 10.06; O 23.08.
C14H20N2O4. Calculated, %: C 59.99; H 7.19; N 9.99;
O 22.83. M 280.14.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 2 2016

359
GRAPHENE OXIDE PROMOTED SYNTHESIS OF p-PHENYLENEDIAMINE ANTIOXIDANTS
Graphene oxide-catalyzed Michael addition of p-phenylene-
diamine to methyl acrylate in different solvents
ACKNOWLEDGMENTS
The authors thank the Platform Foundation of State
Key Laboratory Cultivation Base for Nonmetal
Composites and Functional Materials for financial
support (grant nos. 13zxfk07, 14zx7170, 14tdfk04).
No
b
Product
CHCl3 THFc EtOH H2Od
solventa
38.2
23.5
0.5
Mono substituted
Di substituted
43.8 53.3 33.7 11.9
6.6
0.0
0.0
9.5 18.9 20.8
0.4 11.5 19.1
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