Application of highly sulfonated single-walled carbon nanotubes: An efficient heterogeneous catalyst for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under solvent-free conditions

Article abstract of DOI:10.1016/j.crci.2013.02.005

Highly sulfonated single-walled carbon nanotube-catalyzed synthesis of 14-aryl-14H- dibenzo[a,j]xanthenes in excellent yields and very short reaction times. Sulfonated single- walled carbon nanotubes are prepared using a chemical and simple process and it

Full text of DOI:10.1016/j.crci.2013.02.005

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Full paper/Memoire
Application of highly sulfonated single-walled carbon nanotubes:
An efficient heterogeneous catalyst for the one-pot synthesis
of 14-aryl-14H-dibenzo[a,j]xanthenes under solvent-free conditions
*
Reza Fareghi-Alamdari , Mohsen Golestanzadeh, Farima Agend, Negar Zekri
Department of Chemistry and Chemical engineering, Malek-Ashtar University of Technology, 16765-3454 Tehran, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
Highly sulfonated single-walled carbon nanotube-catalyzed synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes in excellent yields and very short reaction times. Sulfonated single-
walled carbon nanotubes are prepared using a chemical and simple process and it
characterized by Scanning electron microscopy (SEM), Fourier transform infrared
spectroscopy (FT-IR), Raman spectroscopy, Thermal gravimetric analysis (TGA) and
acid-base titration. The sulfonated single-walled carbon nanotube was easily separated by
simple filtration and was recycled eight consecutive times without any loss in its activity.
Received 7 October 2012
Accepted after revision 7 February 2013
Available online xxx
Keywords:
Heterogeneous catalyst
Dibenzoxanthene
Carbon nanotubes
Characterization
Solid acid
´
ß 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Reusable catalyst
1. Introduction
harsh conditions, use of toxic organic solvents, excess
amount of catalyst, non-reusable catalysts, and tedious
Over the years, xanthenes and 14-aryl-14H-diben-
zo[a,j]xanthene derivatives have emerged as a significant
class of heterocyclic compounds that have attracted much
synthetic interest due to their useful biological and
pharmacological properties such as antiviral [1], antibac-
terial [2], and anti-inflammatory activities [3]. These
compounds have also been used as luminescent sensors
[4], dyes [5] and in laser technology [6]. Therefore, the
synthesis of this class of heterocyclic compounds is
practically important. Various catalysts such as Bro¨nsted
acids [7–23], Lewis acids [24–33], molecular iodine [34],
nano-AgI [35], heteropolyacid [36,37], ionic liquids
[38–41], nano-ZnO [42] and resin [43] have been devel-
oped for the synthesis of dibenzoxanthenes. However,
several of these methodologies involve long reaction times,
work-up confine the usefulness of some reported meth-
odologies. Hence, introduction of new methods to over-
come these problems is still in demand.
Carbon nanotubes (CNTs) have attracted much attention
in the synthesis, characterization and other applications
because of their unique structural, mechanical, thermal,
optical and electronic properties [44–46]. Due to the high
specific surface area of CNTs and other unique surface
chemistry of them (e.g. activated carbons, silica, alumina,
TiO2. . .); they are effective supports forthe synthesis of solid
acid catalysts. The covalent functionalization of CNTs with
sulfonic groups provides stability, considerable solubility
[47] and strong surface acidity [48]. The sulfonated single-
walled carbon nanotube (SWCNT-SO3H) is useful as a solid
acid catalyst in organic transformations.
In continuation of our interest towards green meth-
odologies [49–53], we wish to report an efficient and
green method for the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes in the presence of reusable and
* Corresponding author.
E-mail address: reza_fareghi@yahoo.com (R. Fareghi-Alamdari).
1631-0748/$ – see front matter ß 2013 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.crci.2013.02.005
Please cite this article in press as: Fareghi-Alamdari R, et al. Application of highly sulfonated single-walled carbon
nanotubes: An efficient heterogeneous catalyst for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under
solvent-free conditions. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.02.005

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Scheme 1. Synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes in the presence of SWCNTs-SO3H.
Scheme 2. Preparation of the catalyst.
robust SWCNTs-SO3H under solvent-free conditions
(Scheme 1).
significant difference between SWCNTs and SWCNTs-
SO3H. It is possible that the presence of –OH,–COOH and
–SO3H groups on the side-wall of SWCNTs generate
hydrogen-bond-type interactions.
2. Result and discussion
2.1. Preparation of the catalyst
The characterization of the SWCNTs-SO3H was per-
formed by Fourier transform spectroscopy (FT-IR). As
shown in Fig. 2, the high symmetry presented on pristine
SWCNTs generates very weak infrared signals, due to the
weak difference of charge state and very small induced
electric dipole. After functionalization of SWCNTs, new
bands are clearly seen. One of them appears at approxi-
mately 1550 cmÀ1 and is ascribed to the C5C double bonds
of CNTs. Another bands that become more prominent is the
one at about 1720 cmÀ1, which can be assigned to the
carbonyl group of the carboxylic acid group present in
the SWCNTs-COOH. Although this band was present in the
SWCNTs-SO3H, resulting from carboxylic acid groups, now
it is much more intense. The presence of the sulfonic acid
group is also demonstrated by the bands at 1120, 1300 and
590 cmÀ1, which correspond to the symmetric, asymmet-
ric SO2 and C–S stretching modes, respectively.
Scheme 2 shows the preparation procedure of SWCNTs-
SO3H. As can be seen, first the SWCNTs, which are
commercially available, were converted to SWCNTs-COOH
with HCl (37%) and HNO3 (63%). This step was carried out
in order to increase the reactivity and purity of SWCNTs
and to remove the catalyst particles such as Fe, Co and Ni.
Then sulforic acid (98%) was reacted with SWCNTs-COOH
to afford the SWCNTs-SO3H.
2.2. Characterization of SWCNTs-SO3H
The scanning electron microscopy (SEM) images of
SWCNTs before and after H2SO4 treatment are shown in
Fig. 1. The morphology, as observed by SEM, shows
Fig. 1. SEM images of (a): SWCNTs; (b): SWCNTs-SO3H.
Please cite this article in press as: Fareghi-Alamdari R, et al. Application of highly sulfonated single-walled carbon
nanotubes: An efficient heterogeneous catalyst for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under
solvent-free conditions. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.02.005

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3
Fig. 2. FT-IR spectra of (a): SWCNTs; (b): SWCNTs-COOH; (c): SWCNTs-
SO3H.
Fig. 4. Thermograms of (a): SWCNTs-COOH; (b): SWCNTs-SO3H.
Raman spectroscopy was also used to characterize the
SWCNTs samples. Fig. 3 depicts the Raman spectra for
SWCNTs, SWCNTs-COOH and SWCNTs-SO3H. In the region
spectrum (1300–1600 cmÀ1); two bands are observed
showing the characteristic of CNTs. These bands point
the graphite band (G-band) and disorder or defects of
the structure, named (D-band) [54]. The ratio between the
intensity of the D-band and the G-band noted ID/G value
corresponds to a higher proportion of sp3 carbon [55]. The
large extent of CNTs functionalization is indicated by the
significant increase in the D-band at about 1350 cmÀ1
(Fig. 3, spectra b and c) over that of pristine SWCNTs. We
can calculate that ID/G values of SWCNTs, SWCNTs-COOH
and SWCNTs-SO3H are 0.22, 0.34 and 0.80, respectively.
This increasing value implies that a strong damage to the
side-wall of SWCNTs is due to the functionalization.
The thermal gravimetric analysis (TGA) thermograms
were used to determine the amount of sulfonic acid groups
onto the SWCNTs. As shown in Fig. 4, the attached SO3H
groups decomposed at ꢀ200 8C, while the SWCNTs remain
stable up to 550 8C, at which temperature oxidation starts.
Accordingly, these results indicate that about 30.3 wt% can
be ascribed to the covalently of sulfonic acid groups and
functionalization. Therefore, taking into account that the
covalently SO3H measurements indicated one functionali-
ty every ꢀ30 C atoms, results obtained by TGA showed
good agreement with those of FT-IR and Raman spectros-
copy.
The dispersibility of SWCNTs is remarkably changed
after functionalization. SWCNTs-SO3H is hydrophilic and
well dispersed in polar solvent, but in non-polar solvent,
SWCNTs-SO3H agglomerate and sediment at the bottom
(Fig. 5). Thus, the sulfonation process can be used as an
effective method to obtain dispersive CNTs for a variety of
applications, e.g. composites and catalysts. In addition, the
SWCNTs-SO3H act as a proton carrier; therefore, they can
be used as solid acid catalysts in organic synthesis. The
functional groups attached to SWCNTs are quantitatively
determined by acid-base titration (–SO3H) in SWCNTs-
SO3H 0.94 mmol gÀ1 (values calculated by the weight of
SWCNTs-SO3H) [56].
2.3. Synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes
catalyzed by SWCNTs-SO3H under solvent-free conditions
The SWCNTs-SO3H was investigated in the synthesis of
14-aryl-14H-dibenzoxanthenes. First, the reaction param-
eters such as solvent, temperature and catalyst amount
were optimized in the reaction of 4-nitrobenzaldehyde
Fig. 5. Dispersibility of SWCNTs in (solvent) after 120 days. A: SWCNTs
(CH3NO2). B: SWCNTs-COOH (CH3NO2). C: SWCNTs-SO3H (n-hexane). D:
SWCNTs-SO3H (H2O). E: SWCNTs-SO3H (CH3CN). F: SWCNTs-SO3H
(CH3NO2).
Fig. 3. Raman spectra of (a): SWCNTs; (b): SWCNTs-COOH; (c): SWCNTs-
SO3H.
Please cite this article in press as: Fareghi-Alamdari R, et al. Application of highly sulfonated single-walled carbon
nanotubes: An efficient heterogeneous catalyst for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under
solvent-free conditions. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.02.005

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Table 1
Optimization of the reaction conditions for the SWCNTs-SO3H catalyzed reaction of 2-naphthol with 4-nitrobenzaldehyde.
Entry
Solvent
T (8C)
SWCNTs-SO3H (mg)
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
9
10
Solvent-free
Solvent-free
Solvent-free
Solvent-free
n-hexane
50
50
50
50
50
50
50
50
55
45
0
15
15
5
60
91
96
96
35
50
90
96
88
5
60
70
80
5
Reflux
Reflux
Reflux
100
80
50
50
35
5
CH3CN
CH3NO2
Solvent-free
Solvent-free
Solvent-free
10
60
80
Reaction conditions: 2-naphthol (8 mmol), 4-nitrobenzaldehyde (4 mmol).
a
Isolated yields.
(2a) with 2-naphthol (1) in the presence of SWCNTs-SO3H
as a model reaction (Table 1). Initially, the condensation of
2-naphthol (1) with 4-nitrobenzaldehyde (2a) in the
presence of a catalytic amount of SWCNTs-SO3H under
solvent-free conditions at 50 to 80 8C was examined
(Table 1, entries 1–4). At 50 8C, the yield of the reaction was
60% and it increased to 91% at 60 8C (Table 1, entry 2). Entry
3 (70 8C) gave the best result. The effect of a higher
temperature on the product yield was also examined and
the reaction proceeded at 80 8C, but there was no
significant change in the yield of the desired product
and reaction time (Table 1, entry 4). In order to show the
effect of solvent on this reaction, the reaction was carried
out in different solvents such as n-hexane, CH3CN, CH3NO2
Table 2
Synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes in the presence of SWCNTs-SO3H.
Entry
RCHO
Product
Yield (%)a
Time (min)
Mp (8C)
Found
Reported [Ref.]
1
4-Nitrobenzaldehyde (2a)
3a
3b
3c
3d
3e
3f
96
91
94
98
85
93
90
89
80
92
94
87
60
55
91
5
7
312–313
214–215
338–339
290–291
213–214
182–183
197–198
226–228
240–241
263–264
204–205
258–259
210-211
219–221
310–311
309–310 [30]
213–214 [30]
336–338 [40]
289–290 [25]
214–216 [25]
184–185 [25]
197–198 [25]
227–229 [25]
240–241 [40]
262–263 [43]
203–205 [25]
258–259 [25]
–
2
3-Nitrobenzaldehyde (2b)
3
4-Cyanobenzaldehyde (2c)
4-Chlorobenzaldehyde (2d)
2-Chlorobenzaldehyde (2e)
Benzaldehyde (2f)
6
4
3
5
6
6
8
7
3-Methylbenzaldehyde (2 g)
4-Methylbenzaldehyde (2 h)
4-Isopropylbenzaldehyde (2i)
3-Hydroxybenzaldehyde (2j)
4-Methoxybenzaldehyde (2k)
2-Methoxybenzaldehyde (2l)
2-Hydroxy-4-methoxybenzaldehyde (2 m)
5-Bromo-2-hydroxybenzaldehyde (2n)
4-Formylbenzaldehyde (2o)
3 g
3 h
3i
8
8
10
15
10
6
9
10
11
12
13
14
15b
3j
3k
3l
15
15
15
7
3 m
3n
3o
–
308–310 [26]
Reaction conditions: 2-naphthol (8 mmol), aldehyde (4 mmol), catalyst 50 mg, solvent-free.
a
Isolated yields.
b
Reaction conditions: 2-naphthol (8 mmol), 4-formylbenzaldehyde (2 mmol).
Please cite this article in press as: Fareghi-Alamdari R, et al. Application of highly sulfonated single-walled carbon
nanotubes: An efficient heterogeneous catalyst for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under
solvent-free conditions. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.02.005

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5
Scheme 3. Proposed mechanism for the reaction.
and also under solvent-free conditons (Table 1, entries 5–
7). We observed that the best result was obtained under
solvent-free conditions. In order to optimize the amount of
the SWCNTs-SO3H, the model reaction was carried out in
the presence of different amounts of the catalyst (Table 1,
entries 3, 8–9). The maximum yield was obtained by the
use of 50 mg of the SWCNTs-SO3H (Table 1, entry 3).
Further increase in the amount of the catalyst did not affect
the desired product yield (Table 1, entry 8), whereas the
yield of the desired product was reduced by decreasing the
amount of the SWCNTs-SO3H (Table 1, entry 9). When the
same reaction was carried out in the absence of the
SWCNTs-SO3H, the desired product was obtained in only
5% yield.
After optimization of the reaction conditions, synthesis
of 14-aryl-14H-dibenzo[a,j]xanthenes was carried out
from the condensation of 2-naphthol (1) with different
aromatic aldehydes utilizing SWCNTs-SO3H under sol-
vent-free conditions at 70 8C. All reactions were completed
within 3 to 15 min, as can be seen in Table 2. The electron-
withdrawing substituents on the benzaldehyde afforded
the desired product in high yields with short reaction times
Scheme 4. Reaction of terephthaldehyde with 2-naphthol in the presence of SWCNTs-SO3H.
Please cite this article in press as: Fareghi-Alamdari R, et al. Application of highly sulfonated single-walled carbon
nanotubes: An efficient heterogeneous catalyst for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under
solvent-free conditions. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.02.005

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(Table 2, entries 1–5, 15), while electron-donating groups
on benzaldehyde increased the reaction time (Table 2,
entries 7–11). In addition, we observed that the steric
effects between ortho-substituents of benzene ring and
the xanthene ring decreased product yields (Table 2,
entries 13–14). The proposed reaction mechanism for
the SWCNT-SO3H-catalyzed synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes using 2-naphthol and aldehyde is
shown in Scheme 3. The aldehyde is first activated by
protonation with SWCNTs-SO3H to give I. Nucleophilic
attack of 2-naphthol on I affords II, which in turn was
activated by SWCNTs-SO3H to afford carbocation III.
Nucleophilic attack of second molecule of 2-naphthol to
carbocation III, gives the oxonium species IV and V,
respectively, which is subsequently converted to the
dibenzoxanthene VI and release SWCNTs-SO3H for the
next catalytic cycle.
As can be seen in Table 2 (entry 15), the practical
synthetic efficiency of this reaction was investigated
by the reaction of 4-formylbenzaldehyde (2o) (ter-
ephthaldehyde) with 2-naphthol (1). We expected that
both of the formyl groups on the aromatic ring of
terephthaldehyde (2o) would react with 2-naphthol (1).
But we observed that one of the formyl groups reacted
with 2-naphthol and another formyl group was
unreacted, because of the steric effects between ortho-
hydrogens of the benzene ring and the xanthene rings
(Scheme 4).
In order to show the efficiency and advantage of
the new method in the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes, we have compared the obtained
results in the synthesis of 14-(4-nitrophenyl)-14H-
dibenzo[a,j]xanthene catalyzed by SWCNTs-SO3H with
those of some works in the literature (Table 3). It seems
Table 3
Comparison of the results obtained for the synthesis of 14-(4-nitrophenyl)-14H-dibenzo[a,j]xanyhene catalyzed by SWCNTs-SO3H with those obtained by
the recently reported catalysts.
Entry
Catalyst
Catalyst (mol%)
T (8C)
Time
Yield (%)a
Ref.
1
SWCNTs-SO3H
Cellulose sulfonic acid
SBA-15-SO3H
Oxlic acid
12.5 mg
70
115
85
5 min
2 h
96
90
91
95
94
75
98
74
94
96
90
98
88
94
95
95
85
90
91
90
90
90
95
93
95
89
96
93
94
98
84
This work
[7]
2
80 mg
3
40 mg
24 h
[8]
4
100
80
35 min
60 min
20 min
2 h
[9]
5
Silica sulfuric acid
NH4H2PO4-SiO2
H3BO3
30 mg
80
[10]
[12]
[13]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[24]
[25]
[34]
[26]
[27]
[28]
[29]
[30]
[32]
[33]
[35]
[36]
[38]
[31]
[40]
[41]
[43]
6
100 mg
125
120
110
125
90
7
20
8
TCCA
5
50 min
11 h
9
Sulfamic acid
Saccharin sulfonic acid
Cyanuric chloride
SiO2-Pr-SO3H
[C4DABCOC4SO3H][BF4][HSO4]
HBF4-SiO2
20
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
15
100 min
45 min
40 min
10 min
1 h
10
110
125
100
120
120
60
20 mg
3
0.2 g (10)
ZrO (OTf)2
1
10
2 min
1.2 h
2.5 h
4 h
Fe (HSO4)3
I2
20
90
KAl (SO4)2.12 H2O
Yb (OTf)3
50
100
110
60
1
3 h
Mg (HSO4)2
Nano-TiO2
10
–
15
90
10 min
1 h
TaCl5
10
110
110
60
Sc [N(SO2C8F17)2]3
BF3-SiO2
1
2 h
80 mg
20
–
Nano-AgI
140
100
125
100
100
110
100
42 min
60 min
60 min
110 min
6 min
5 min
2 h
HPA
1
n-Bu4NBr
10
MPA-DAZY
0.6
5
[MIMPS]HSO4
SAFIS
10
Dowex-50 W
100 mg
All of the reactions were performed in thermal conditions. Reaction conditions: 2-naphthol (2 mmol), 4-nitrobenzaldehyde (1 mmol).
a
Isolated yields.
Please cite this article in press as: Fareghi-Alamdari R, et al. Application of highly sulfonated single-walled carbon
nanotubes: An efficient heterogeneous catalyst for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under
solvent-free conditions. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.02.005

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7
of 14-aryl-14H-dibenzo[a,j]xanthenes. In addition, short
reaction time, high yield of the desired product, solvent-
free and non-toxicity of the catalyst are other worth-
while advantages of the present work.
4. Experimental method
4.1. Materials
The CNTs used in this study (L = 20–30 mm, D = 1–3 nm)
have been purchased from Research Institute of Petroleum
Industry (RIPI-Iran). The chemicals used in this work were
purchased from Fluka and Merck companies.
Fig. 6. Reusability of the SWCNTs-SO3H in the synthesis of 14-(4-
4.2. Apparatus
nitrophenyl)-14H-dibenzo[a,j]xanthene.
Melting points were determined using melting point IA
8103 apparatus and are uncorrected. The thermal analysis
(C, H, N) was carried out using a Carlo ERBA Model EA 1108
analyzer. FT-IR spectra were obtained with KBr pellets in
that the presented new method is superior in terms of
catalyst amount, time of reaction, reaction temperature,
product yield and reusability of the catalyst.
the range of 400 to 4000 cmÀ1 with
a Nicolet-860
2.4. Reusability and stability of the catalyst
spectrometer. FT-NMR spectra were recorded in CDCl3
solvent on a Brucker-Avance 500 MHz spectrometer using
TMS as an internal standard. The Raman spectra were
recorded with an Almega Thermo Nicolet Dispersive
Raman spectrometer excited at 532 nm. TGA was per-
formed on a mettle TA 4000 instrument at a heating rate of
10 K minÀ1. SEM images of CNTs were taken on a Philips
XL30 SEM instrument.
The reusability of the SWCNTs-SO3H is of great
importance from synthetic and economical points of view.
Therefore, the reusability of the catalyst was checked by
separating the SWCNTs-SO3H from the reaction mixture by
simple filtration, washing with ethanol and chloroform,
and drying in a vacuum oven at 80 8C for 10 h prior to reuse
in subsequent reactions. The recovered catalyst can be
reused at least eight times in subsequent reactions without
significant loss in the product yield (Fig. 6).
4.3. Preparation of SWCNTs-SO3H
In a typical experiment; SWCNTs (1 g) and 100 ml of
deionized water were added in a well becher and were
sonicated for 15 min. After the sonication, the solvent was
removed under reduced pressure and the obtained
SWCNTs was transferred to another flask containing
(HCl [37%], 25 ml; HNO3 [63%], 25 ml) and stirred at
80 8C for 4 h under a nitrogen atmosphere. Then the
solution was filtered under reduced pressure and the
obtained materials were first washed thoroughly with
deionized water and then dried at 120 8C for 20 h. In this
step (I), the SWCNTs-COOH was obtained. After the step (I),
the SWCNTs-COOH (0.5 g) and 50 ml of deionized water
were sonicated for 15 min. Then, the water was filtered and
40 ml H2SO4 (98%) was added to the set-up at 250 to 270 8C
(the sulfuric acid boils at 335 8C) for 20 h under a nitrogen
atmosphere. After cooling the solution to room tempera-
ture, the liquid was filtered and washed completely with
deionized water for several times. The obtained solid
materials were dried at 120 8C for 24 h. After this step (II),
the SWCNTs-SO3H was obtained and used in the synthesis
of 14-aryl-14H-dibenzo[a,j]xanthenes as a catalyst.
2.5. A comparison study with MWCNTs-SO3H as catalyst
The catalytic properties of multi-walled and single-
walled carbon nanotubes were compared with the
synthesis of 14-(4-nitrophenyl)-14H-dibenzo[a,j]xanthene.
The results showed that there is no significant difference
between these two types of catalysts. For comparison,
multi-walled carbon nanotube was also used for the
reaction of 2-naphthol (1) with 4-nitrobenzaldehyde (2a).
Observations showed no improvement in the reaction
efficiency. But the time of the reaction was somewhat more
as compared to SWCNTs-SO3H (5 min vs 7 min).
3. Conclusions
In conclusion, in this research a heterogeneous and
stable SWCNTs-SO3H was prepared and characterized by
SEM, FT-IR spectroscopy, Raman spectroscopy, TGA and
acid-base titration. For the first time, we report a new
and efficient method for the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes via condensation of 2-naphthol
with different aromatic aldehydes using SWCNTs-SO3H.
To the best of our knowledge, the use of SWCNTs-SO3H
as a catalyst for the synthesis of 14-aryl-14H-diben-
zo[a,j]xanthenes has not been previously reported. We
4.4. General procedure for the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes in the presence of SWCNTs-SO3H under
solvent-free conditions
also introduced
reusable catalyst as an efficient catalyst for the synthesis
a
robust, stable, eco-friendly and
In a 25-ml flask equipped with a condenser and
magnetic stirring bar, a mixture of 2-naphthol (8 mmol),
Please cite this article in press as: Fareghi-Alamdari R, et al. Application of highly sulfonated single-walled carbon
nanotubes: An efficient heterogeneous catalyst for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under
solvent-free conditions. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.02.005

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R. Fareghi-Alamdari et al. / C. R. Chimie xxx (2013) xxx–xxx
aldehyde (4 mmol) and SWCNTs-SO3H (50 mg) was
heated at 70 8C under solvent-free conditions for the
appropriate time according to Table 2. The progress of
the reaction was monitored by TLC (EtOAc/n-hexane,
5:1). After completion of the reaction, the mixture was
cooled to the room temperature and 30 ml CHCl3 was
added. The catalyst was filtered by simple filtration. The
obtained liquid was heated by evaporation on a rotary
evaporator. The remained solid materials were recrys-
tallized from ethanol to afford the pure products. All of
the pure products were identified by FT-IR, 1H-NMR and
melting points.
14-(4-Chlorophenyl)-14H-dibenzo[a,j]xanthene (Table
2, entry 4, compound 3d): IR (KBr) (
cmÀ1): 3068, 3026,
1620, 1591, 1484, 1242, 1082, 961, 807. 1H-NMR
(500 MHz, CDCl3), (ppm): 6.50 (1H, s, CH), 7.13–7.15
(2H, d, 3J = 8 Hz, Ar-H), 7.44–7.52 (6H, m, Ar-H), 7.60–7.63
(2H, t, 3J = 7.9 Hz, Ar-H), 7.83–7.84 (2H, d, 3J = 7.9 Hz, Ar-H),
7.86–7.88 (2H, d, 3J = 8 Hz, Ar-H), 8.34–8.36 (2H, d,
3J = 7.8 Hz, Ar-H). Anal. Calcd for C27H17ClO: C, 82.54; H,
4.36%. Found: C, 82.59; H, 4.44%.
n
d
14-(2-Chlorophenyl)-14H-dibenzo[a,j]xanthene (Table
2, entry 5, compound 3e): IR (KBr) (
1591, 1400, 1243, 1030, 960, 808. 1H-NMR (500 MHz,
CDCl3), (ppm): 6.84 (1H, s, CH), 6.92–6.98 (2H, m, Ar-H),
n
cmÀ1): 3057, 1622,
d
4.5. Acidity of SWCNTs-SO3H
7.28–7.30 (1H, m, Ar-H), 7.41–7.48 (3H, m, Ar-H), 7.51–
7.53 (2H, d, 3J = 8 Hz, Ar-H) 7.64–7.67 (2H, t, 3J = 8 Hz, Ar-
H), 7.82–7.86 (4H, m, Ar-H), 8.77–8.79 (2H, d, 3J = 7.9 Hz,
Ar-H). Anal. Calcd for C27H17ClO: C, 82.54; H, 4.36%. Found:
C, 82.62; H, 4.04%.
The content of sulfonic acid groups in the SWCNTs-
SO3H was determined by acid-base titration according to
the literature [56]. The acid-base titration showed that the
amount of SO3H attached to SWCNTs is 0.94 mmol gÀ1
.
14-(Phenyl)-14H-dibenzo[a,j]xanthene (Table 2, entry
6, compound 3f): IR (KBr) (
1513, 1398, 1247, 1076, 960, 808, 696. 1H-NMR (500 MHz,
CDCl3), (ppm): 6.53 (1H, s, CH), 7.01–7.04 (1H, t,
n
cmÀ1): 3069, 3016, 1591,
4.6. Reusability of the catalyst
d
Recovery and reusability of the SWCNTs-SO3H is a very
important factor in practice and also from an economic
point of view. The reusability of the SWCNTs-SO3H was
investigated in the reaction of 2-naphthol (1) and 4-
nitrobenzaldehyde (2a). At the end of the reaction, the
catalyst was isolated by filtration, washed exhaustively
with chloroform and ethanol, and dried at 80 8C for 10 h
before being used with fresh 2-naphthol and aldehyde. The
catalyst can be reused eight times without any loss in its
catalytic activity.
3J = 7.8 Hz, Ar-H), 7.17–7.20 (2H, t, 3J = 7.9 Hz, Ar-H),
7.43–7.46 (2H, t, 3J = 7.8 Hz, Ar-H), 7.52–7.54 (2H, d,
3J = 8.1 Hz, Ar-H), 7.56–7.58 (2H, d, 3J = 8 Hz, Ar-H), 7.60–
7.63 (2H, t, 3J = 8.1 Hz, Ar-H), 7.82–7.84 (2H, d, 3J = 7.9 Hz,
Ar-H), 7.85–7.87 (2H, d, 3J = 8 Hz, Ar-H), 7.43–7.45 (2H, d,
3J = 8 Hz, Ar-H). Anal. Calcd for C27H18O: C, 90.47; H, 5.06%.
Found: C, 90.55; H, 4.94%.
14-(3-Methylphenyl)-14H-dibenzo[a,j]xanthene (Table
2, entry 7, compound 3 g): IR (KBr) (
1619, 1587, 1515, 1249, 809. 1H-NMR (500 MHz, CDCl3),
n
cmÀ1): 3047, 3016,
d
(ppm): 2.18 (3H, s, CH3), 6.46 (1H, s, CH), 6.80–6.82 (2H, d,
3J = 8 Hz, Ar-H), 7.05–7.08 (2H, d, 3J = 8.1 Hz, Ar-H), 7.40–
7.61 (6H, m, Ar-H), 7.79–7.84 (4H, m, Ar-H), 8.40–8.42 (2H,
d, 3J = 8 Hz, Ar-H). Anal. Calcd forC28H20O: C, 90.29;H, 5.41%.
Found: C, 90.35; H, 5.35%.
4.7. Spectroscopic and physical data
14-(4-Nitrophenyl)-14H-dibenzo[a,j]xanthene (Table 2,
entry 1, compound 3a): IR (KBr) (
1513, 1340, 1239, 961, 806. 1H-NMR (500 MHz, CDCl3),
n
cmÀ1): 3070, 1621, 1589,
d
14-(4-Methylphenyl)-14H-dibenzo[a,j]xanthene (Table
(ppm): 6.63 (1H, s, CH), 7.46–7.49 (2H, t, 3J = 8 Hz, Ar-H),
7.53–7.55 (2H, d, 3J = 7.8 Hz, Ar-H), 7.62–7.65 (2H, t,
3J = 8 Hz, Ar-H), 7.70–7.71 (2H, d, 3J = 7.8 Hz, Ar-H), 7.86–
7.89 (4H, m, Ar-H), 8.02–8.03 (2H, d, 3J = 8 Hz, Ar-H), 8.30–
8.32 (2H, d, 3J = 7.8 Hz, Ar-H). Anal. Calcd for C27H17NO3: C,
80.38; H, 4.25; N, 3.47%. Found: C, 80.40; H, 4.33; N, 3.41%.
14-(3-Nitrophenyl)-14H-dibenzo[a,j]xanthene (Table 2,
2, entry 8, compound 3 h): IR (KBr) (
1591, 1511, 1399, 1245, 962, 811, 741. 1H-NMR (500 MHz,
CDCl3), (ppm): 2.16 (3H, s, CH3), 6.49 (1H, s, CH), 6.97–6.99
n
cmÀ1): 3070, 3019,
d
(2H, d, 3J = 8 Hz, Ar-H), 7.42–7.45 (4H, m, Ar-H), 7.50–7.52
(2H, d, 3J = 7.8 Hz, Ar-H), 7.59–7.62 (2H, t, 3J = 8 Hz, Ar-H),
7.80–7.82 (2H, d, 3J = 7.8 Hz, Ar-H), 7.84–7.86 (2H, d,
3J = 8 Hz, Ar-H), 8.42–8.44 (2H, d, 3J = 7.8 Hz, Ar-H). Anal.
Calcd for C28H20O: C, 90.29; H, 5.41%. Found: C, 90.25; H,
5.15%.
entry 2, compound 3b): IR (KBr) (
1397, 1352, 1238, 1079, 958, 804, 745. 1H-NMR (500 MHz,
CDCl3),
(ppm):6.64(1H, s, CH), 7.30–7.34(1H, t, 3J = 7.9 Hz,
n
cmÀ1): 3066, 1590, 1519,
d
14-(4-Isopropylphenyl)-14H-dibenzo[a,j]xanthene
Ar-H), 7.46–7.49 (2H, t, 3J = 8 Hz, Ar-H), 7.54–7.56 (2H, d,
3J = 8 Hz, Ar-H), 7.63–7.66 (2H, t, 3J = 7.9 Hz,Ar-H), 7.83–7.89
(6H, m, Ar-H), 8.33–8.35 (2H, d, 3J = 8 Hz, Ar-H), 8.45 (1H, s,
Ar-H). Anal. Calcd for C27H17NO3: C, 80.38; H, 4.25; N, 3.47%.
Found: C, 80.45; H, 4.30; N, 3.37%.
(Table 2, entry 9, compound 3i): IR (KBr) (
1621, 1578, 1510, 1244, 806. 1H-NMR (500 MHz, CDCl3),
n
cmÀ1): 3048,
d
(ppm): 2.22 (6H, d, 2CH3), 3.1 (1H, m, CH), 6.46(1H, s, CH),
6.84–6.86 (2H, d, 3J = 8 Hz, Ar-H), 7.12–7.41(4H, m, Ar-H),
7.48–7.53 (4H, m, Ar-H), 7.68–7.71 (4H, m, Ar-H), 7.86–
7.88 (2H, d, 3J = 8 Hz, Ar-H). Anal. Calcd for C30H24O: C,
89.97; H, 6.04%. Found: C, 90.25; H, 5.85%.
14-(4-Cyanophenyl)-14H-dibenzo[a,j]xanthene (Table
2, entry 3, compound 3c): IR (KBr) (
1635, 1591, 1558, 1500, 1449, 1374, 1245, 1169, 960, 810.
1H-NMR (500 MHz, CDCl3),
(ppm): 6.54 (1H, s, CH), 7.12–
n
cmÀ1): 3026, 2221,
14-(3-Hydroxyphenyl)-14H-dibenzo[a,j]xanthene
d
(Table 2, entry 10, compound 3J): IR (KBr) ( cmÀ1): 3451,
n
7.15 (4H, m, Ar-H), 7.30–7.33 (4H, m, Ar-H), 7.55–7.58 (2H,
m, Ar-H), 7.84–7.87 (4H, t, 3J = 8.2 Hz, Ar-H), 8.27–8.30 (2H,
t, 3J = 8.2 Hz, Ar-H). Anal. Calcd for C28H17NO: C, 87.71; H,
4.47; N, 3.65%. Found: C, 87.55; H, 4.65; N, 3.64%.
3056, 1593, 1512, 1237, 813, 697. 1H-NMR (500 MHz,
CDCl3),
d (ppm): 4.55 (1H, s, OH), 6.47–6.50 (2H, m, CH,
Ar-H), 6.91 (1H, s, Ar-H), 7.04–7.07 (1H, t, 3J = 8.1 Hz, Ar-
H), 7.21–7.23 (1H, d, 3J = 8 Hz, Ar-H), 7.43–7.47 (2H, t,
Please cite this article in press as: Fareghi-Alamdari R, et al. Application of highly sulfonated single-walled carbon
nanotubes: An efficient heterogeneous catalyst for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under
solvent-free conditions. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.02.005

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9
3J = 7.8 Hz, Ar-H), 7.50–7.52 (2H, d, 3J = 8 Hz, Ar-H), 7.61–
7.63 (2H, t, 3J = 8.1 Hz, Ar-H), 7.79–7.81 (2H, d, 3J = 7.8 Hz,
Ar-H), 7.85–7.87 (2H, d, 3J = 8.1 Hz, Ar-H), 8.40–8.42 (2H,
d, 3J = 8 Hz, Ar-H). Anal. Calcd for C27H18O2: C, 86.61; H,
4.85%. Found: C, 87.01; H, 4.84%.
Industry (RIPI-Iran) for providing CNTs and SEM images of
the catalyst.
References
14-(4-Methoxyphenyl)-14H-dibenzo[a,j]xanthene
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1625, 1594, 1512, 1251, 1236, 811. 1H-NMR (500 MHz,
CDCl3), (ppm): 3.62 (3H, s, OCH3), 6.45 (1H, s, CH), 6.67–
n
cmÀ1): 3042,
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d
6.69 (2H, d, 3J = 7.9 Hz, Ar-H), 7.27–7.40 (4H, m, Ar-H),
7.42–7.44 (4H, m, Ar-H), 7.78–7.80 (2H, d, 3J = 8 Hz, Ar-H),
8.02–8.04 (2H, d, 3J = 8 Hz, Ar-H), 8.38–8.40 (2H, d,
3J = 7.9 Hz, Ar-H). Anal. Calcd for C28H20O2: C, 86.57; H,
5.19%. Found: C, 87.22; H, 4.79%.
14-(2-Methoxyphenyl)-14H-dibenzo[a,j]xanthene
(Table 2, entry 12, compound 3l): IR (KBr) (
3023, 1592, 1404, 1242, 1156, 1100, 960, 807, 744. 1H-
NMR (500 MHz, CDCl3), (ppm): 4.30 (3H, s, OCH3), 6.65–
n
cmÀ1): 3055,
d
6.68 (1H, t, 3J = 7.8 Hz, Ar-H), 6.89–6.91 (1H, d, 3J = 8 Hz, Ar-
H), 6.99 (1H, s, CH), 7.00–7.04 (1H, t, 3J = 7.8 Hz, Ar-H),
7.22–7.23 (1H, d, 3J = 8 Hz, Ar-H), 7.40–7.43 (2H, t,
3J = 8.1 Hz, Ar-H), 7.49–7.51 (2H, d, 3J = 8 Hz, Ar-H), 7.55–
7.58 (2H, t, 3J = 8.1 Hz, Ar-H), 7.78–7.84 (4H, m, Ar-H),
8.60–8.62 (2H, d, 3J = 7.9 Hz, Ar-H). Anal. Calcd for
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[18] M.A. Bigdeli, M.M. Heravi, G.H. Mahdavinia, Catal. Commun. 8 (2007)
1595.
C
28H20O2: C, 86.57; H, 5.19%. Found: C, 86.95; H, 5.55%.
14-(2-Hydroxy-4-methoxyphenyl)-14H-dibenzo[a,j]
[19] G.M. Ziarani, A.R. Badiei, M. Azizi, Sci. Iran. 18 (2011) 453.
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Baltork, M. Moosavifar, C. R. Chim. 14 (2011) 489.
xanthene (Table 2, entry 13, compound 3 m): IR (KBr)
cmÀ1): 3398, 3156, 3057, 1594, 1508, 1462, 1399, 1228,
1102, 1010, 812, 746. 1H-NMR (500 MHz, CDCl3),
(ppm):
4.30 (3H, s, OCH3), 5.90 (1H, s, OH), 6.65–6.68 (1H, m, Ar-
H), 6.89–6.91 (1H, m, Ar-H), 7.14 (1H, s, CH), 7.00–7.04 (1H,
m, Ar-H), 7.22–7.23 (1H, m, Ar-H), 7.40-–7.43 (2H, m, Ar-
H), 7.49–7.51 (2H, m, Ar-H), 7.55–7.58 (2H, m, Ar-H), 7.78–
7.84 (4H, m, Ar-H), 8.60–8.62 (1H, m, Ar-H). Anal. Calcd for
(
n
d
C28H20O3: C, 83.15; H, 4.98%. Found: C, 83.65; H, 4.15%.
14-(5-Bromo-2-hydroxyphenyl)-14H-dibenzo[a,j]-
xanthene (Table 2, entry 14, compound 3n): IR (KBr)
cmÀ1): 3535, 3431, 3057, 1603, 1460, 1405, 1253, 1189,
1120, 812. 1H-NMR (500 MHz, CDCl3),
(ppm): 5.98 (1H, s,
(
n
d
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dx.doi.org/10.1016/j.jscs.2012.05.007.
OH), 6.65–6.99 (2H, m, Ar-H), 6.89–6.93 (1H, m, Ar-H), 7.20
(1H, s, CH), 7.22–7.24 (1H, m, Ar-H), 7.26–7.28 (1H, m, Ar-
H), 7.40–7.43 (2H, m, Ar-H), 7.49–7.51 (2H, m, Ar-H), 7.55–
7.58 (2H, m, Ar-H), 7.78–7.82 (3H, m, Ar-H), 8.60–8.62 (1H,
m, Ar-H). Anal. Calcd for C27H17BrO2: C, 71.54; H, 3.78%.
Found: C, 70.98; H, 4.11%.
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323 (2007) 242.
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A443–444 (2012) 207.
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Catal. Commun. 9 (2008) 1575.
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zadeh, A. Hasaninejad, A. Khazaei, M. Mokhlesi, V. Khakyzadeh, F.
Derakhshan-panah, M.H. Beyzavi, E. Rostami, A. Arghoon, R. Roohan-
deh, J. Mol. Liq. 167 (2012) 69.
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Asgari, A. Hasaninejad, C. R. Chim. 15 (2012) 719.
14-(4-Formylphenyl)-14H-dibenzo[a,j]xanthene (Table
2, entry 15, compound 3o): IR (KBr) (
2852, 2765, 1691, 1595, 1513, 1243, 819. 1H-NMR
(500 MHz, CDCl3), (ppm): 6.58 (1H, s, CH), 7.17–7.19
n
cmÀ1): 3060, 2923,
d
(2H, d, 3J = 8 Hz, Ar-H), 7.42–7.45 (2H, t, 3J = 7.8 Hz, Ar-H),
7.50–7.68 (4H, m, Ar-H), 7.70–7.78 (4H, m, Ar-H), 7.82–
7.86 (2H, t, 3J = 7.6 Hz, Ar-H), 8.33–8.35 (2H, d, 3J = 8 Hz, Ar-
H), 9.79 (1H, s, CHO). Anal. Calcd for C28H18O2: C, 87.02; H,
4.69%. Found: C, 87.15; H, 4.65%.
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2741.
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1105.
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We gratefully acknowledge the financial support by the
Malek-Ashtar University of Technology (MUT). We thank
Dr. Rashidi from the Research Institute of Petroleum
Please cite this article in press as: Fareghi-Alamdari R, et al. Application of highly sulfonated single-walled carbon
nanotubes: An efficient heterogeneous catalyst for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under
solvent-free conditions. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.02.005

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Please cite this article in press as: Fareghi-Alamdari R, et al. Application of highly sulfonated single-walled carbon
nanotubes: An efficient heterogeneous catalyst for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under
solvent-free conditions. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.02.005