Multisulfonate hyperbranched polyglycerol functionalized graphene oxide as an efficient reusable catalyst for green synthesis of benzo[a]pyrano-[2,3-c]phenazines under solvent-free conditions

Article abstract of DOI:10.1039/C8RA10180A

A novel acid catalyst was prepared based on growing hyperbranched polyglycerol (HPG) on the surface of graphene oxide. Then, the hydroxyl groups of HPG on graphene oxide were functionalized by sulfonate groups to form an acid catalyst. The catalyst displayed a good loading level of acidic groups on the surface because of coating graphene oxide with HPG. This new catalyst is demonstrated to be highly effective in the preparation of benzo[a]pyrano[2,3-c]phenazine dyes.

Full text of DOI:10.1039/C8RA10180A

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PAPER
Multisulfonate hyperbranched polyglycerol
functionalized graphene oxide as an efficient
reusable catalyst for green synthesis of benzo[a]
pyrano-[2,3-c]phenazines under solvent-free
conditions†
Cite this: RSC Adv., 2019, 9, 7400
*
Hossein Naeimi
and Maryam Farahnak Zarabi
A novel acid catalyst was prepared based on growing hyperbranched polyglycerol (HPG) on the surface of
graphene oxide. Then, the hydroxyl groups of HPG on graphene oxide were functionalized by sulfonate
groups to form an acid catalyst. The catalyst displayed a good loading level of acidic groups on the
surface because of coating graphene oxide with HPG. This new catalyst is demonstrated to be highly
effective in the preparation of benzo[a]pyrano[2,3-c]phenazine dyes.
Received 11th December 2018
Accepted 15th February 2019
DOI: 10.1039/c8ra10180a
rsc.li/rsc-advances
groups, so the GO-HPG-SO3H can be scalably and cost-
effectively produced.11 It is expected that the GO-HPG-SO3H
Introduction
would show great performance as an acid catalyst because the
HPG molecule has a hyperbranched structure and numerous
sulfonate groups.
Graphene, a at monolayer of carbon atoms tightly packed into
a two-dimensional (2D) honeycomb lattice, has been used in
a wide range of applications such as electronic devices, solar
cells, nano-catalysts, nanocomposites, molecular sensing, and
chemical and biological sensors.1–8 Graphene oxide (GO) is an
oxidized form of graphene which is the most versatile and easily
scalable. It is well-known that the presence of oxygen containing
groups in GO including hydroxyl, epoxide and carbonyl groups
provides reactive sites for chemical modication.9 The catalysts'
activity strongly depended on the loading amount of their
immobilized compounds. For these reasons, a rationalized
choice for solving this problem in heterogeneous catalysts is
immobilization of polymers on the solid surface. A class of
hyperbranched polymers is polyglycerol with a tree-like struc-
ture and a large number of hydroxyl functional groups in its
backbone and environs.10 The chemical graing of HPG onto
the surface of graphene oxide also supplies a suitable surface
for their functionalization with organic compounds to obtain
novel nanostructures. In this paper, we explored a novel catalyst
based on multisulfonate hyperbranched polyglycerol modied
graphene oxide (GO-HPG-SO3H). Graphene oxide possesses
a large surface area which provides a good platform for graing
HPG. In addition, HPG can be readily graed to the surface of
graphene oxide by a one-step ring opening polymerization. Also,
it is simple to alter the hydroxyl groups of HPG into sulfonate
The natural occurrence of phenazine pigments has been
known for a long time. Phenazine-based compounds are
nitrogen-containing heterocycles that are the main core of many
natural and synthetic organic materials12 and they are structural
components of various kinds of bacteria species.13,14 These
molecules are commonly employed in many elds such as
antimalarial,15 trypanocidal,16 fungicidal,17 antiplatelet,18 anti-
tumor, and antiphrastic.15 In addition, uorescent phenazine
compounds are used as photo-sensitizers in photodynamic
therapy (PDT).19 Also, chromenes have attracted great attention
due to their widespread pharmaceuticals20,21 properties such as
antifungal22,23 and antimicrobial activities.24 Although mole-
cules with phenazines and chromenes moieties have attracted
a lot of attention in drug discovery but functionalized benzo[a]
pyrano[2,3-c]phenazine derivatives have seldom been
described.
In recent years, designs of multi-component reactions
(MCRs) because of their advantages in comparison with multi-
step reactions according to environmental and economic
considerations have received signicant attention for the
synthesis of biologically interesting compounds. A number of
methods have been reported for the synthesis of benzo[a]pyrano
[2,3-c]phenazine. The synthesis of benzo[a]pyrano[2,3-c]phena-
zine is carried out with various catalysts such as acetic acid,25
nano copper(II) oxide,26 ionic liquid,27 theophylline,28 and
DABCO.12 Most of these catalysts have drawbacks, such as
corrosive, non-reusable, and non-recoverable.
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Kashan,
87317, Islamic Republic of Iran. E-mail: naeimi@kashanu.ac.ir; Fax: +98-
03155912397; Tel: +98-03155912388
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c8ra10180a
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Herein, we wish to describe a highly efficient method for the
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preparation of functionalized benzo[a]pyrano[2,3-c]phenazine
derivatives via one-pot, two-step condensation reaction in the
presence of GO-HPG-SO3H as an efficient and reusable catalyst
under solvent-free conditions.
Results and discussion
The process for the preparation of GO-HPG-SO3H catalyst is
schematically described in Scheme 1. First, graphene oxide
nanosheets were prepared using a modied Hummer's method.
There was a great amount of active hydrogen-containing
functional groups including hydroxyl and carboxylic acid
groups on graphene oxide nanosheets surface. Hyperbranched
polymerization of glycidol was initiated by these active surface
groups on graphene oxide nanosheets, producing a high
hydrophilic PG layer on graphene oxide surface.29 In the next
step, GO-HPG-SO3H was easily prepared by reaction of GO-HPG
with 1,4-butane sultone and acidication. Aer successful
preparation of the GO-HPG-SO3H, the catalyst was character-
ized by FT-IR, TGA, XRD, AFM, and FESEM.
Fig. 1a–d shows the FT-IR spectra of graphite, GO, GO-HPG,
and GO-HPG-SO3H respectively. The FT-IR spectrum of graphite
powder shows peaks characteristic of C]C groups at 1573 cmꢀ1
which the peak is not sharp (Fig. 1a). Fig. 1b shows the FT-IR
spectrum of graphene oxide powder. The absorption band at
1578 cmꢀ1 is related to C]C double bonds which this peak is
sharper than graphite due to the unsymmetry of GO. The
absorption peaks at 1064, 1720 and 3410 cmꢀ1 are assigned to
C–O, carbonyl, and hydroxyl stretching mode of functional
groups attachment to GO, respectively. Fig. 1c shows the FT-IR
spectrum of the GO-HPG. The vibrational bands at 2922 cmꢀ1
and 2853 cmꢀ1 are attributed to C–H stretching, which
conrmed that the HPG has been successfully graed on the
surface of graphene oxide. In the FT-IR spectrum of the GO-
HPG-SO3H, the peaks at 1175 cmꢀ1 and 1286 cmꢀ1 are the
symmetric and asymmetric stretching vibrations of the SO2
group, which indicate the presence of covalent –SO3H groups on
the surface of nanosheets and conrms the structure of GO-
HPG-SO3H (Fig. 1d).
Fig. 1 FT-IR spectra of (a) graphite, (b) GO, (c) GO-HPG, and (d) GO-
HPG-SO3H.
Fig. 2 depicts XRD patterns of graphite, GO and GO-HPG-
SO3H, respectively. The XRD pattern of graphite exhibits a peak
at approximately 2q ¼ 26.5ꢁ, corresponding to the interlayer
distance of 0.335 nm (Fig. 2a). In Fig. 2b, the peak at 2q ¼ 12.7ꢁ
represented graphene oxide. The interlayer spacing (d-spacing)
of GO is calculated 0.78 nm which indicated the formation of
oxygen-containing functional groups between the layers of the
graphite. As to the GO-HPG-SO3H, the strong peak at 12.7ꢁ
disappeared, which clearly demonstrates the HPG was
successfully graed on the GO surface, leading to a fully exfo-
liated structure of GO sheets and disappearance of the regular
and periodic structure of graphene (Fig. 2c).9,30
In Fig. 3, the TGA thermograms of (a) GO, (b) GO-HPG and (c)
GO-HPG-SO3H are displayed. As seen from Fig.ꢁ3a, TGA curve of
GO shows a weight loss about 10% below 140 C which can be
assigned to trapped water between GO nanosheets. Also, there
ꢁ
ꢁ
is a major weight loss between 140 C and 210 C due to the
decomposition of the labile oxygen-containing functional
groups on the GO.31 As shown in Fig. 3b and c, the GO-HPG and
Scheme 1 Preparation of GO-HPG-SO3H nanocatalyst.
Fig. 2 XRD patterns of (a) graphite, (b) GO and (c) GO-HPG-SO3H.
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Fig. 3 TGA graph of (a) GO, (b) GO-HPG and (c) GO-HPG-SO3H.
Fig. 4 FE-SEM images of (a) GO and (b) GO-HPG-SO3H.
GO-HPG-SO3H are more stable than GO, which demonstrates
the HPG has been successfully graed on to the GO surface. For
ꢁ
the GO-HPG curve, the weight loss below 100 C is assigned to
removal of physically adsorbed water. The second weight loss
ꢁ
about 33% occur at the temperatures ranging from 260 C to
370 ꢁC, and it is attributed to the chemical graing of HPG on to
the GO surface (Fig. 3b).9 Aer reacting with butane sultone, the
ꢁ
weight loss of the curve in Fig. 3c between 250-420 C increase
to 40%, conrmed the sulfonation of hydroxyl groups.
The FE-SEM images of GO and GO-HPG-SO3H are shown in
Fig. 4a and b. In Fig. 4a observed well-ordered two-dimensional
and ake-like sheets of the GO nanosheets. Different
morphologies were showed for GO and prepared catalyst. The
image of the GO-HPG-SO3H shows that the PEGylated nano-
sheets became wrinkled and folded during the sample prepa-
ration (Fig. 4b).32,33
Fig. 5 AFM images of (a) GO nanosheets and (b) GO-HPG-SO3H.
spectrum clearly exhibit the presence of carbon, oxygen, and
sulfur elements in the sample, which further conrm successful
preparation of the nanocatalyst.
Investigation of catalyst activity of GO-HPG-SO3H in the
synthesis of benzo[a]pyrano-[2,3-c]phenazine derivatives
Fig. 5 displays atomic force microscopy (AFM) images of GO
and GO-HPG-SO3H. In Fig. 5a, we clearly detect individual
single-layer GO sheets with average thickness of 1 nm, coinci- The prepared GO-HPG-SO3H were employed in the synthesis of
dent with the typical thicknesses reported previously.33,34 Aer benzo[a]pyrano-[2,3-c]phenazine dyes. Initially, the reaction
the surface functionalization, the thickness of sheets is parameters were optimized in the one-pot four-component
increased to 9 nm (Fig. 5b). The increase in the thickness of reaction of 2-hydroxy-1,4-naphthoquinone, benzene-1,2-
functionalized GO nanosheets can be attributed to the hyper- diamine, 4-chlorobenzaldehyde, malononitrile in the presence
branched polyglycerol, which is uniformly graed on the of GO-HPG-SO3H as the model reaction (Scheme 2). To choose
surface of GO nanosheets. EDS analysis was also used to char- the reaction medium, the reaction was carried out in various
acterize the GO and GO-HPG-SO3H (Fig. 6a and b). The solvents such as H2O, EtOH, CH3CN, PhCH3, and without any
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In order to obtain the optimal amount of the catalyst, the
reaction was carried out in the presence of different amounts of
catalyst (Table 2). The best result was observed with 10 mg of the
catalyst and the product yield afforded 95% at 30 min. Also, the
reaction was performed in the absence of catalyst and no
product was formed.
For optimization of reaction temperature, an increase in
temperature of the reaction (50 to 110 ꢁC) led to increased rate
of reaction and yields of product. At temperature of 100 ꢁC, the
yield of the reaction was 95% and it similar at 110 ꢁC (Table 3,
entries 4 and 5).
The best result was obtained with 10 mg of GO-HPG-SO3H as
catalyst at 100 ꢁC under solvent-free conditions afforded 3-
amino-2-cyano-1-(4-chlorophenyl)-1H-benzo[a]pyrano[2,3-c]
phenazine in 30 min with 95% yield. Aer optimization of the
reaction conditions, synthesis of benzo[a]pyrano-[2,3-c]phena-
zine derivatives were performed for a series of different
aromatic aldehydes containing electron-releasing and electron-
withdrawing substituents to investigate the versatility of the
protocol under GO-HPG-SO3H catalysis. As shown in Table 4,
aromatic aldehydes containing electron-withdrawing groups
reacted rapidly and gave higher yields, while substitutions of
electron-rich groups on the benzene ring required longer reac-
tion times and got lower yields. Furthermore, the structures of
1
these products were supported by H NMR spectra.
The reaction of benzo[a]pyrano-[2,3-c]phenazine derivatives
has been investigated with various catalysts in literature and
compared with the present method (Table 5). It was found that
our reported method, using GO-HPG-SO3H as the catalyst, is
simple, effective, applicable and comparable with many cata-
lytic systems for the synthesis of benzo[a]pyrano-[2,3-c]phena-
zine derivatives.
Fig. 6 EDS patterns of (a) GO and (b) GO-HPG-SO3H.
Table 2 The optimization of GO-HPG-SO3H catalyst amounta
Entry
Catalyst (mg)
Time (min)
Yieldb (%)
1
2
3
4
5
0
2
5
10
15
120
50
35
30
30
—
75
87
95
95
Scheme
2 Synthesis of 3-amino-1-(4-chlorophenyl)-1H-benzo[a]
pyrano[2,3-c]phenazine-2-carbonitrile.
solvent (Table 1, entries 1–5). As shown in Table 1, entry 2, the
yield of reaction under solvent free conditions is more than
other solvents. Therefore, the solvent free conditions were
chosen as the reaction medium.
a
Reaction conditions: 2-hydroxy-1,4-naphthoquinone (1 mmol),
benzene-1,2-diamine (1 mmol), aldehyde (1 mmol), malononitrile (1
mmol), solvent free, 100 ꢁC. b Isolated yields.
Table 1 Optimization of the reaction in the presence of different Table 3 Temperature optimization for the synthesis of benzo[a]pyr-
solventsa
ano-[2,3-c]phenazine derivativesa
Entry
Solvent
Temp.
Time (min)
Yieldb (%) Entry
T (ꢁC)
Time (min)
Yieldb (%)
1
2
3
4
5
H2O
Solvent free
EtOH
CH3CN
PhCH3
Reux
60
30
35
60
75
Trace
95
90
70
35
1
2
3
4
5
50
80
90
100
110
60
60
40
30
30
50
75
90
95
95
100 ꢁ
C
Reux
Reux
Reux
a
a
Reaction conditions: 2-hydroxy-1,4-naphthoquinone (1 mmol),
Reaction conditions: 2-hydroxy-1,4-naphthoquinone (1 mmol),
benzene-1,2-diamine (1 mmol), aldehyde (1 mmol), malononitrile (1 benzene-1,2-diamine (1 mmol), aldehyde (1 mmol), malononitrile (1
mmol), GO-HPG-SO3H (10 mg). b Isolated yields.
mmol), solvent free, GO-HPG-SO3H (10 mg). b Isolated yields.
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Table 4 Synthesis of benzo[a]pyrano-[2,3-c]phenazine derivatives catalyzed by GO-HPG-SO3Ha
Entry
1
Aldehyde
Product
T (min)
Yieldb (%)
TONc
114
TOFd (hꢀ1
)
45
91
152
2
3
40
45
87
89
109
111
165
148
4
30
95
119
238
5
6
30
45
93
89
116
111
232
148
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Table 4 (Contd.)
Entry
Aldehyde
Product
T (min)
Yieldb (%)
TONc
112
TOFd (hꢀ1
)
7
40
90
170
8
35
60
50
60
93
86
91
86
116
107
114
107
200
107
137
107
9
10
11
12
30
95
119
238
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Table 4 (Contd.)
Entry
13
Aldehyde
Product
T (min)
Yieldb (%)
TONc
112
TOFd (hꢀ1
)
40
90
170
14
45
85
106
141
15
16
50
45
87
85
109
106
131
141
17
40
87
109
165
a
Reaction conditions: 2-hydroxy-1,4-naphthoquinone (1 mmol), benzene-1,2-diamine (1 mmol), aldehyde (1 mmol), malononitrile (1 mmol), GO-
HPG-SO3H (10 mg), solvent free, 100 ꢁC. b Isolated yields. c TON: mole of formed benzo[a]pyrano-[2,3-c]phenazine derivatives per mole of catalyst.
d
TOF (hꢀ1): (mmol of product/mmol of active site of catalyst)/time of the reaction (h).
As shown in Fig. 7, we studied the reusability of GO-HPG- ethanol and drying at 80 ꢁC in an oven for 24 h for subsequent
SO3H as heterogeneous catalyst for the same reactants. Aer experiments to check its reusability under similar reaction
completion of the reaction, the catalyst was isolated by ltra- conditions. It was observed that the recovered catalyst could be
tion, washed exhaustively with acetone, chloroform, and reused ve times without signicant loss of its catalytic activity.
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Table 5 Comparison of the efficiencies of various catalysts used in the synthesis of benzo[a]pyrano-[2,3-c]phenazines
Entry
Catalyst
Condition
Time (min)
Yield (%)
Ref.
1
2
3
4
5
HOAC
CuO
Basic ionic liquids
Theophylline
GO-HPG-SO3H
HOAC/r.t.
10
7
6
180
30
89
94
94
89
95
25
35
27
36
Solvent free/75 ꢁ
C
75 ꢁ
C
Water/70 ꢁ
Solvent free/100 ꢁ
C
C
This work
GO-HPG-SO3H catalyst give intermediate (V). The intermediate
(V) undergo tautomerization and intramolecular cyclization
using GO-HPG-SO3H catalyst to form intermediate (VI). Ulti-
mately, aer tautomerization of intermediate (VI), benzo[a]
pyrano-[2,3-c]phenazines are formed in high yield and short
reaction times.
Conclusion
In this research, we have prepared an acid heterogeneous
catalyst for the synthesis of benzo[a]pyrano-[2,3-c]phenazines
under green condition. Aer optimization of the reaction
conditions, the catalytic reaction was performed with 10 mg of
GO-HPG-SO3H as a catalyst at 100 ꢁC under solvent-free
conditions in high to excellent yields and short times. In this
reaction, multisulfonate hyperbranched polyglycerol modied
graphene oxide has been used as a highly efficient, inexpensive
and non-toxic catalyst. The catalyst was characterized by FT-IR,
TGA, XRD, AFM, and FESEM techniques. Furthermore, the
products can be easily separated from the reaction mixture by
a simple purication process. Also, the catalyst was recycled
and reused for ve times without remarkable loss of catalytic
activity.
Fig. 7 The reusability of the catalyst GO-HPG-SO3H in the synthesis
of benzo[a]pyrano-[2,3-c]phenazine derivatives.
The proposed reaction mechanism
A plausible mechanism for the synthesis of benzo[a]pyrano-[2,3-
c]phenazines according the previously reported works26,27 is
depicted in Scheme 3. Firstly, 2-hydroxy-1,4-naphthoquinone
tautomerizes to intermediate (I). The primary condensation of
intermediate (I) with benzene-1,2-diamine obtain benzo[a]
phenazin-5-ol (II). On this mechanism, the GO-HPG-SO3H
catalyst activates the carbonyl group of the aromatic aldehyde to
afford intermediate (III). The Knoevenagel condensation of
intermediate (III) and malononitrile forms the arylidene malo-
nonitrile (IV). Subsequently, the Michael addition of 6H-benzo
[a] phenazin-5-ol (II) with intermediate (IV) in the presence of
Experimental
Materials and apparatus
The chemicals were purchased from Fluka and Merck Chemical
Companies and used without purication. IR spectra were ob-
tained as KBr pellets on a Perkin-Elmer 781 spectrophotometer
and on an impact 400 Nicolet FT-IR spectrophotometer. 1H
NMR was recorded in DMSO-d6 solvent on a Bruker DRX-400
spectrometer with tetramethylsilane as internal reference.
XRD patterns were obtained by an X'PertPro (Philips) instru-
ment with 1.54 ꢁA wavelengths of X-raꢀy1beam and Cu anode
material, at a scanning speed of 2ꢁ min from 10ꢁ to 80ꢁ (2q).
Thermogravimetric analysis (TGA) was performed on a mettler
TA4000 system TG-50 at a heating rate of 10 K minꢀ1 under N2
atmosphere. The SEM images of catalysts were recorded on
a FE-SEM Hitachi S4160 instrument. The AFM image of cata-
lysts was investigated using scanning probe microscopy (SPM-
9600, Shimadzu). Melting points were measured with a Yanagi-
moto micro melting point apparatus. The purity determination
of the substrates and reaction monitoring were accomplished
by TLC on silica-gel polygram SILG/UV 254 plates (from Merck
Company).
Scheme 3 Proposed mechanism for synthesis of benzo[a]pyrano-
[2,3-c]phenazine derivatives.
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Preparation of graphene oxide
General procedure for the preparation of benzo[a]pyrano-[2,3-
c]phenazine derivatives catalyzed by GO-HPG-SO3H under
thermal conditions
The graphene oxide nanosheets were synthesized by a modied
Hummer's method. Typically, in a 1000 mL round-bottom ask
equipped with a magnetic bar, a mixture of 5.0 g of natural A mixture of 2-hydroxy-1,4-naphthoquinone (1 mmol) and
graphite powder and 2.5 g of sodium nitrate and 115 mL of benzene-1,2-diamine (1 mmol) were heated at 100 ꢁC and
sulfuric acid (98%) were placed in an ice bath. Then, 15.0 g of solvent free conditions until in less than 5 min an orange solid
potassium permanganate was slowly added to obtained solu- of benzo[a]phenazine was formed. Aerward, aldehydes (1
tion and stirred for 2 h. The mixture solution was taken to mmol), malononitrile (1 mmol), and GO-HPG-SO3H (10 mg)
a water bath (35 ꢁC) and stirred for 30 min. Then, deionized were added into the reaction system and this mixture was stir-
water (230 mL) was slowly added and the solution temperature red at 100 ꢁC for the appropriate time according to Table 4. Aer
ꢁ
was about 98 C and stirred for 15 min. Aerward, 700 mL of completion of the reaction, monitored by TLC, the reaction
deionized water and 50 mL of H2O2 (30%) was added to the mixture was allowed to cool to room temperature. Then, the
solution respectively. The resulting materials were ltered and mixture was diluted with dichloromethane and the catalyst was
washed by diluted HCl (5%) and deionized water for several ltered and washed with chloroform and EtOH (2 ꢂ 5 mL) for
times. Then graphite oxide powder was obtained aer drying for checking the reusability. The solution was recovered via evap-
12 h at 60 ꢁC under vacuum. The graphite oxide powder was oration using a rotary evaporator. The solid was recrystallized
dispersed in distilled water to make concentration of 0.5 mg with hot ethanol to give the pure solid. The analytical and
mLꢀ1 and exfoliated by ultrasonication to obtain GO spectroscopic data for products:
nanosheets.
3-Amino-1-phenyl-1H-benzo[a]pyrano[2,3-c]phenazine-2-
carbonitrile (6a). Yellow solid, mp: 300–303 ꢁC (lit. 25: 298–300
ꢁC); IR (KBr, n, cmꢀ1): 3443, 3312, 3174, 3055, 2188, 1659, 1623,
Graing of hyperbranched polyglycerol on GO nanosheets
1
1593, 1493, 1397; H NMR (400 MHz, DMSO-d6) (d, ppm): 5.49
The hyperbranched polyglycerol modied GO nanosheets were
prepared according to the reported protocol with minor revi-
sion.37 A saturated solution of potassium methoxide in meth-
anol was mixed with 0.2 g of graphene oxide nanosheets. The
mixture was sonicated in an ultrasonic bath for 30 min and
stirred at room temperature for 2 h. Then, mixture was reuxed
at 80 ꢁC for 4 h. Aer completion of the reaction, graphene oxide
nanosheetsꢁwere washed with methanol and dried in a vacuum
oven at 60 C. The glycidol (4 mL) was added slowly to depro-
tonated nanosheets at 100 ꢁC and the mixture was stirred at
100 ꢁC for 8 h. Then it was cooled and the mixture was dissolved
in methanol. Aer repeated wash by methanol followed by
drying overnight under vacuum, HPG graed on graphene oxide
nanosheets (GO-HPG) was obtained. The synthesis of hyper-
branched polyglycerol functionalized graphene oxide was
conrmed by IR and TGA.
(s, 1H), 7.08 (t, J3 ¼ 8.0 Hz, 1H), 7.21 (t, J3 ¼ 8.0 Hz, 2H), 7.28 (m,
NH2), 7.39 (d, J3 ¼ 8.0 Hz, 2H), 7.90–7.94 (m, 3H), 7.98 (t, J3 ¼
8.0 Hz, 1H), 8.13–8.15 (m, 1H), 8.24–8.26 (m, 1H), 8.43 (d, J3 ¼
8.0 Hz, 1H), 9.21 (d, J3 ¼ 8.0 Hz, 1H).
3-Amino-1-(4-(dimethylamino)phenyl)-1H-benzo[a]pyrano
[2,3-c]phenazine-2-carbonitrile (6b). Orange solid, mp: 259–
263 ꢁC (lit. 25: 261–263 ꢁC); IR (KBr, n, cmꢀ1): 3463, 3310, 3061,
2208, 1628, 1594, 1533, 1458, 1351; 1H NMR (400 MHz, DMSO-
d6) (d, ppm): 3.38 (s, 6H), 6.84 (m, NH2), 7.19 (s, 1H), 7.80–7.91
(m, 6H), 8.15 (d, J3 ¼ 8.0 Hz, 1H), 8.28 (d, J3 ¼ 8.0 Hz, 1H), 8.30–
8.32 (m, 2H), 9.25–9.27 (m, 1H), 11.55 (s, 1H).
3-Amino-1-(2-chlorophenyl)-1H-benzo[a]pyrano[2,3-c]
phenazine-2-carbonitrile (6c). Yellow solid, mp: 300–304 ꢁC; IR
(KBr, n, cmꢀ1): 3464, 3312, 3170, 3057, 2191, 1658, 1623, 1590,
1470, 1387; 1H NMR (400 MHz, DMSO-d6) (d, ppm): 5.92 (s, 1H),
7.08–7.10 (m, 2H), 7.18–7.19 (m, 1H), 7.33 (m, NH2), 7.38–7.40
(m, 1H), 7.89–8.02 (m, 5H), 8.22–8.24 (m, 1H), 8.44 (d, J3
8.0 Hz, 1H), 9.21 (d, J3 ¼ 8.0 Hz, 1H).
¼
Preparation of GO-HPG-SO3H
3-Amino-1-(4-chlorophenyl)-1H-benzo[a]pyrano[2,3-c]
In a round-bottomed ask GO-HPG (0.2 g) was dispersed in
toluene at room temperature and 1,4-butane sultone (0.2 mL)
was slowly added. The mixture was stirred at 50 ꢁC for 24 h. The
resulting solid was isolated by ltration, washed with ethanol,
and dried under vacuum at 55 ꢁC. Aer that, excess sulfuric acid
solution in water was slowly added, and the mixture was stirred
at 60 ꢁC for 12 h to complete the reaction. Subsequently formed
mixture was washed several times with deionized water and
phenazine-2-carbonitrile (6d). Yellow solid, mp: 285–290 ꢁC (lit.
25: 288–291 ꢁC); IR (KBr, n, cmꢀ1): 3464, 3311, 3173, 3057, 2188,
1659, 1623, 1593, 1489, 1402, 1385; 1H NMR (400 MHz, DMSO-
d6) (d, ppm): 5.45 (s, 1H), 7.26 (d, J3 ¼ 8.0 Hz, 2H), 7.32 (s, NH2),
7.41 (d, J3 ¼ 8.0 Hz, 2H), 7.89–7.93 (m, 2H), 7.96–8.0 (m, 2H),
8.08–8.10 (m, 1H), 8.22–8.23 (m, 1H), 8.41 (d, J3 ¼ 8.0 Hz, 1H),
9.18 (d, J3 ¼ 8.0 Hz, 1H).
ꢁ
3-Amino-1-(2,4-dichlorophenyl)-1H-benzo[a]pyrano[2,3-c]
phenazine-2-carbonitrile (6e). Brown solid, mp: 307–310 ꢁC (lit.
39: 308–310 ꢁC); IR (KBr, n, cmꢀ1): 3478, 3313, 3168, 3069, 2186,
1659, 1624, 1589, 1468, 1403, 1385; 1H NMR (400 MHz, DMSO-
d6) (d, ppm): 5.84 (s, 1H), 7.14 (d, J3 ¼ 8.0 Hz, 1H), 7.20 (d, J3 ¼
8.0 Hz, 1H), 7.40 (s, NH2), 7.54 (s, 1H), 7.88–8.0 (m, 5H), 8.21–
8.23 (m, 1H), 8.41 (d, J3 ¼ 8.0 Hz, 1H), 9.19 (d, J3 ¼ 8.0 Hz, 1H).
dried under vacuum at 55 C for 24 h.
Determination of the acidity of the GO-HPG-SO3H catalyst
For evaluation of the acidity of the GO-HPG-SO3H, 25 mL
aqueous NaCl (1 M, pH 6.7) was prepared and 20 mg GO-
HPG-SO3H was added and stirred for 4 h.38 The pH of
solution decreased to 3.2, which is equivalent to 0.8 mmol
gꢀ1 H+.
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3-Amino-1-(2-bromophenyl)-1H-benzo[a]pyrano[2,3-c]
RSC Advances
(lit. 39: 240–242 C); IR (KBr, n, cmꢀ1): 3420, 3340, 3215, 2193,
1666, 1596, 1492, 1385; 1H NMR (400 MHz, DMSO-d6) (d, ppm):
3.67 (s, 3H), 5.48 (s, 1H), 6.67 (d, J3 ¼ 8.0 Hz, 1H), 6.91 (d, J3 ¼
8.0 Hz, 1H), 7.01 (s, 1H), 7.13 (t, J3 ¼ 8.0 Hz, 1H), 7.40 (s, NH2),
7.93–7.94 (m, 2H), 7.99 (t, J3 ¼ 8.0 Hz, 2H), 8.15–8.18 (m, 1H),
8.25–8.28 (m, 1H), 8.43 (d, J3 ¼ 8.0 Hz, 1H), 9.21 (d, J3 ¼ 8.0 Hz,
1H).
3-Amino-1-(4-methoxyphenyl)-1H-benzo[a]pyrano[2,3-c]
phenazine-2-carbonitrile (6n). Yellow solid, mp: 270–272 ꢁC; IR
(KBr, n, cmꢀ1): 3431, 3314, 3194, 3047, 2194, 1667, 1596, 1508,
1386; 1H NMR (400 MHz, DMSO-d6) (d, ppm): 3.61 (s, 3H), 5.50
(s, 1H), 6.77 (d, J3 ¼ 8.0 Hz, 2H), 7.19–7.21 (m, NH2), 7.33 (d, J3 ¼
8.0 Hz, 2H), 7.95–8.0 (m, 4H), 8.20–8.22 (m, 1H), 8.30–8.31 (m,
1H), 8.46 (d, J3 ¼ 8.0 Hz, 1H), 9.26 (d, J3 ¼ 8.0 Hz, 1H).
3-Amino-1-(2,3-dimethoxyphenyl)-1H-benzo[a]pyrano[2,3-c]
phenazine-2-carbonitrile (6o). Yellow solid, mp: 287–291 ꢁC (lit.
25: 292–294 ꢁC); IR (KBr, n, cmꢀ1): 3426, 3312, 3174, 3051, 2187,
ꢁ
ꢁ
phenazine-2-carbonitrile (6f). Brown solid, mp: 284–286 C; IR
(KBr, n, cmꢀ1): 3464, 3311, 3169, 3055, 2191, 1659, 1623, 1589,
1467, 1387; 1H NMR (400 MHz, DMSO-d6) (d, ppm): 5.88 (s, 1H),
6.97–7.01 (m, 1H), 7.10 (m, 2H), 7.36 (s, NH2), 7.57 (d, J3
¼
8.0 Hz, 1H), 7.87–7.89 (m, 2H), 7.93 (t, J3 ¼ 8.0 Hz, 2H), 7.99–
8.01 (m, 1H), 8.18–8.20 (m, 1H), 8.42 (d, J3 ¼ 8.0 Hz, 1H), 9.17 (d,
J3 ¼ 8.0 Hz, 1H).
3-Amino-1-(3-bromophenyl)-1H-benzo[a]pyrano[2,3-c]
phenazine-2-carbonitrile (6g). Brown solid, mp: 268–269 ꢁC; IR
(KBr, n, cmꢀ1): 3486, 3302, 3171, 3060, 2197, 1662, 1627, 1591,
1471, 1385; 1H NMR (400 MHz, DMSO-d6) (d, ppm): 5.51 (s,
1H), 7.19–7.23 (m, 1H), 7.29–7.33 (m, 1H), 7.40–7.44 (m, 1H),
7.46–7.49 (m, NH2), 7.61–7.63 (m, 1H), 7.95–8.02 (m, 4H), 8.14–
8.17 (m, 1H), 8.27–8.31 (m, 1H), 8.43–8.48 (m, 1H), 9.22–9.26
(m, 1H).
3-Amino-1-(4-bromophenyl)-1H-benzo[a]pyrano[2,3-c]
phenazine-2-carbonitrile (6h). Yellow solid, mp: 280–285 ꢁC (lit.
25: 283–285 ꢁC); IR (KBr, n, cmꢀ1): 3467, 3320, 3173, 3056, 2187,
1660, 1623, 1591, 1485, 1401, 1384; 1H NMR (400 MHz, DMSO-
d6) (d, ppm): 5.44 (s, 1H), 7.35 (d, J3 ¼ 8.0 Hz, 2H), 7.40 (d, J3 ¼
8.0 Hz, 2H), 7.43 (s, NH2), 7.92–7.98 (m, 4H), 8.09–8.10 (m, 1H),
8.22–8.23 (m, 1H), 8.42 (d, J3 ¼ 8.0 Hz, 1H), 9.19 (d, J3 ¼ 8.0 Hz,
1H).
1
1659, 1624, 1592, 1491, 1387; H NMR (400 MHz, DMSO-d6) (d,
ppm): 3.84 (s, 3H), 3.88 (s, 3H), 5.83 (s, 1H), 6.73 (t, J3 ¼ 8.0 Hz,
1H), 6.95 (d, J3 ¼ 8.0 Hz, 1H), 7.05–7.11 (m, 1H), 7.19 (s, NH2),
7.89–8.02 (m, 5H), 8.25–8.27 (m, 1H), 8.46 (d, J3 ¼ 8.0 Hz, 1H),
9.24 (d, J3 ¼ 8.0 Hz, 1H).
3-Amino-1-(o-tolyl)-1H-benzo[a]pyrano[2,3-c]phenazine-2-
carbonitrile (6p). Yellow solid, mp: 256–260 ꢁC; IR (KBr,
n, cmꢀ1): 3486, 3309, 3174, 3061, 2194, 1662, 1627, 1595, 1386;
1H NMR (400 MHz, DMSO-d6) (d, ppm): 2.18 (s, 3H), 5.44 (s, 1H),
6.89 (d, J3 ¼ 8.0 Hz, 1H), 7.10 (t, J3 ¼ 8.0 Hz, 1H), 7.19 (m, 2H),
7.36 (s, NH2), 7.91–7.92 (m, 2H), 7.97–8.0 (m, 2H), 8.13–8.14 (m,
1H), 8.23–8.25 (m, 1H), 8.43 (d, J3 ¼ 8.0 Hz, 1H), 9.20 (d, J3 ¼
8.0 Hz, 1H).
3-Amino-1-(2-uorophenyl)-1H-benzo[a]pyrano[2,3-c]
phenazine-2-carbonitrile (6i). Yellow solid, mp: 270–272 C; IR
ꢁ
(KBr, n, cmꢀ1): 3449, 3312, 3058, 2189, 1661, 1625, 1591, 1490,
1406, 1387; 1H NMR (400 MHz, DMSO-d6) (d, ppm): 5.75 (s, 1H),
7.0–7.16 (m, 2H), 7.26–7.34 (m, 2H), 7.38 (s, NH2), 7.90–8.0 (m,
4H), 8.26–8.29 (m, 1H), 8.32–8.36 (m, 1H), 8.46 (d, J3 ¼ 8.0 Hz,
1H), 9.24 (d, J3 ¼ 8.0 Hz, 1H).
3-Amino-1-(p-tolyl)-1H-benzo[a]pyrano[2,3-c]phenazine-2-
carbonitrile (6q). Yellow solid, mp: 295–297 ꢁC (lit. 25: 293–294
ꢁC); IR (KBr, n, cmꢀ1): 3441, 3311, 3177, 3054, 2187, 1659, 1623,
1594, 1496, 1387; 1H NMR (400 MHz, DMSO-d6) (d, ppm): 2.13
3-Amino-1-(4-uorophenyl)-1H-benzo[a]pyrano[2,3-c]
phenazine-2-carbonitrile (6j). Yellow solid, mp: 275–280 ꢁC (lit.
25: 274–276 ꢁC); IR (KBr, n, cmꢀ1): 3459, 3315, 3174, 3052,
(s, 3H), 5.45 (s, 1H), 7.01 (d, J3 ¼ 8.0 Hz, 2H), 7.27 (d, J3
¼
1
2190, 1660, 1623, 1593, 1502, 1402, 1385; H NMR (400 MHz,
DMSO-d6) (d, ppm): 5.49 (s, 1H), 7.03 (t, J3 ¼ 8.0 Hz, 2H), 7.41–
7.45 (m, 2H–Ar and 2H–NH2), 7.91–8.0 (m, 4H), 8.12–8.14 (m,
1H), 8.23–8.26 (m, 1H), 8.42 (d, J3 ¼ 8.0 Hz, 1H), 9.20 (d, J3 ¼
8.0 Hz, 1H).
8.0 Hz, 2H), 7.34 (m, NH2), 7.91–8.0 (m, 4H), 8.14–8.16 (m, 1H),
8.25–8.27 (m, 1H), 8.43 (d, J3 ¼ 8.0 Hz, 1H), 9.22 (d, J3 ¼ 8.0 Hz,
1H).
3-Amino-1-(2-nitrophenyl)-1H-benzo[a]pyrano[2,3-c]
phenazine-2-carbonitrile (6k). Brown solid, mp: 279–283 ꢁC; IR
(KBr, n, cmꢀ1): 3437, 3063, 2194, 1664, 1629, 1594, 1526, 1388,
1351; 1H NMR (400 MHz, DMSO-d6) (d, ppm): 6.11 (s, 1H), 7.31
(t, J3 ¼ 8.0 Hz, 1H), 7.40 (d, J3 ¼ 8.0 Hz, 1H), 7.47 (t, J3 ¼ 8.0 Hz,
1H), 7.52 (s, NH2), 7.86–7.98 (m, 4H), 8.19 (d, J3 ¼ 8.0 Hz, 1H),
8.24–8.26 (m, 1H), 8.28–8.31 (m, 1H), 8.42 (d, J3 ¼ 8.0 Hz, 1H),
9.13 (d, J3 ¼ 8.0 Hz, 1H).
Conflicts of interest
There are no conicts to declare.
Acknowledgements
The authors are grateful to University of Kashan for supporting
this work by Grant No. 159148/89.
3-Amino-1-(4-nitrophenyl)-1H-benzo[a]pyrano[2,3-c]
phenazine-2-carbonitrile (6l). Yellow solid, mp: 277–280 ꢁC (lit.
25: 281–283 ꢁC); IR (KBr, n, cmꢀ1): 3440, 3318, 3204, 3068, 2197,
1672, 1628, 1593, 1514, 1385, 1346; 1H NMR (400 MHz, DMSO-
d6) (d, ppm): 5.61 (s, 1H), 7.53–7.55 (m, NH2), 7.67–7.71 (m, 2H),
7.93–8.01 (m, 4H), 8.08–8.12 (m, 2H), 8.25–8.29 (m, 2H), 8.44–
8.46 (m, 1H), 9.21–9.24 (m, 1H).
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phenazine-2-carbonitrile (6m). Yellow solid, mp: 238–243 ꢁC
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