Poly(4-vinylpyridinium)hydrogen sulfate: A novel and efficient catalyst for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under conventional heating and ultrasound irradiation

Article abstract of DOI:10.1016/j.ultsonch.2011.12.004

A simple and convenient procedure for the synthesis of 14-aryl-14H- dibenzo[a,j]xanthenes is described through a one-pot condensation of 2-naphthol with aryl aldehydes in the presence of poly(4-vinylpyridinium)hydrogen sulfate as an efficient, cheap, read

Full text of DOI:10.1016/j.ultsonch.2011.12.004

Ultrasonics Sonochemistry 19 (2012) 736–739
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Short Communication
Poly(4-vinylpyridinium)hydrogen sulfate: A novel and efficient catalyst for the
synthesis of 14-aryl-14H-dibenzo[a, j]xanthenes under conventional heating
and ultrasound irradiation
⇑
Nader Ghaffari Khaligh
Department of Chemistry, College of Science, University of Guilan, Rasht, P.O. Box 41335-19141, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 June 2011
Received in revised form 24 July 2011
Accepted 14 December 2011
Available online 23 December 2011
A simple and convenient procedure for the synthesis of 14-aryl-14H-dibenzo[a, j]xanthenes is described
through a one-pot condensation of 2-naphthol with aryl aldehydes in the presence of poly(4-vinylpyrid-
inium)hydrogen sulfate as an efficient, cheap, readily synthesized and eco-friendly catalyst in a solvent
free media using conventional heating and ultrasound irradiation.
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Poly(4-vinylpyridinium)hydrogen sulfate
Xanthenes
Ultrasound irradiation
One-pot reactions
1. Introduction
zoxanthenes including cyclodehydrations [10], alkylations c to the
heteroatoms [11], trapping of benzynes by phenols [12], cyclocon-
densation between 2-hydroxyaromatic aldehydes and 2-tetralone
[13], the reaction of 2-naphthol with aldehydes or acetals under
acidic conditions and intramolecular phenyl carbonyl coupling
reactions of benzaldehydes and acetophenones [14]. In addition,
14H-dibenzo[a, j]xanthenes and related products are prepared by
reaction of b-naphthol with formamide [15], 2-naphthol-1-metha-
nol [16], carbon monoxide [17] and sulfomic acid [18].
Even though various procedures are reported, disadvantages
including low yields, prolonged reaction times, use of an excess
of reagents/catalysts and use of toxic organic solvents necessitate
the development of an alternative route for the synthesis of xan-
thene derivatives.
Ultrasonic-assisted organic synthesis (UAOS) as a green syn-
thetic approach is a powerful technique that is being used more
and more to accelerate organic reactions [19,20]. UAOS can be ex-
tremely efficient and it is applicable to a broad range of practical
syntheses. The notable features of the ultrasound approach are en-
hanced reaction rates, formation of purer products in high yields,
easier manipulation and considered a processing aid in terms of
energy conservation and waste minimization which compared
with traditional methods, this technique is more convenient taking
green chemistry concepts into account [21–23]. However, the use
of ultrasound in heterocyclic system is not fully explored [24–
37]. In order to expand the application of ultrasound in the synthe-
sis of heterocyclic compound, we wish to report a general, efficient
and eco-friendly method for the synthesis of aryl-14-H-
dibenzo[a, j]xanthenes.
Solid acids have many advantages over liquid acids in organic
catalysis. They do less harm to environment and have no corrosion
or disposal of effluent problems. They are reusable and easy to be
separated from liquid products. As economically and ecologically
benign catalysts, their research and application have attracted
much attention in chemistry and industry. There are more than
100 industrial processes using over 103 solid acids as catalysts at
the end of last century [1]. The replacement of traditional homoge-
neous catalysts with solid acids is becoming an inevitable trend.
Solid acid can be mainly divided into eight categories: oxides
(Al2O3, SiO2, etc.), sulfides (CdS, ZnS, etc.), metal salts (AlPO4,
CuSO4, etc.), zeolites (HZSM-5, HY, H-b, etc.), heteropolyacids
(H3PW12O40, etc.), natural clays (kaolin, montmorillonite K10 and
KSF, etc.), supported solid acids (BF3/Al2O3, SO2À=ZrO2; etc.) and
4
cationic ion-exchange resins (Amberlyst-15, Nafion NR 50, etc.).
The synthesis of xanthenes, especially benzoxanthenes, has
emerged as a powerful tool in organic synthesis due to their wide
range of biological and therapeutic properties such as antibacterial
[2], antiviral [3] and anti-inflammatory activities [4] as well as in
photodynamic therapy [5] and for antagonism of the paralyzing ac-
tion of zoxazolamine [6]. Furthermore, due to their useful spectro-
scopic properties, they are used as dyes [7], in laser technologies
[8], and in fluorescent materials for visualization of biomolecules
[9]. Many procedures describe the synthesis of xanthenes and ben-
⇑
Tel.: +98 21 66431738; fax: +98 21 66934046.
E-mail addresses: ngkhaligh@gmail.com, ngkhaligh@guilan.ac.ir
1350-4177/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ultsonch.2011.12.004

N.G. Khaligh / Ultrasonics Sonochemistry 19 (2012) 736–739
737
In this paper, we investigated the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes in the presence of poly(4-vinylpyridini-
um)hydrogen sulfate under normal heating and sonication
conditions. The reported route is an efficient, convenient and novel
method for condensation of aldehydes with 2-naphthol in the pres-
ence of poly(4-vinylpyridinium)hydrogen sulfate as solid acid
(Scheme 1).
rectly for the next run. As shown in Table 3, the solid acid P(4-
VPH)HSO4 can be recycled at least five times without significant de-
crease in catalytic activity, the yields ranged from 97% to 92%.
3. Experimental
All chemicals were purchased from Merck or Fluka Chemical
Companies. Products were identified by comparison of their melt-
ing points, IR and 1H NMR data with those reported in the litera-
ture. Progress of the reactions was monitored by TLC using silica
gel SIL G/UV 254 plates. The reaction conversions were measured
by GC on a Shimadzu model GC-16A instrument using a 25 m
2. Results and discussion
In an initial study, in order to examine the catalytic activity of
catalyst and the amount of catalyst in this condensation reaction,
benzaldehyde was first reacted with 2-naphthol in solvent free
conditions at 100 °C and in ethanol under ultrasound irradiation
in the presence 0, 5, 10, 15 and 20 mg catalyst separately. The best
results were obtained using 10 mg of P(4-VPH)HSO4. Using lower
amounts of catalyst resulted in lower yields, while higher amounts
of catalyst did not affect the reaction times and yields and in the
absence of catalyst, nearly no product could be detected (Table 1).
The condensation of 2-naphthol and aryl aldehydes (carrying
both electron-withdrawing and electron-donating groups), in the
presence of P(4-VPH)HSO4 0.010 g as a solid acid catalyst in a solvent
free media using conventional heating at 100 °C (method A) and
ultrasound irradiation with a frequency of 35 kHz and a nominal
power 200 W (method B) yielded desired 14H-dibenzo[a, j]xanth-
enes in high purity with excellent yields. The reactions required
45–78 min with conventional heating at 100 °C, and 20 min with
ultrasound irradiation with a frequency of 35 kHz. We initially
investigated the catalytic activity of P(4-VPH)HSO4, which promotes
the condensation reaction between 1:2 ratio of benzaldehyde and 2-
naphthol in the presence of P(4-VPH)HSO4 0.010 g catalyst in a sol-
vent free media using conventional heating at 100 °C and ultrasound
irradiation with a frequency of 35 kHz. We found that under the best
reaction conditions in the presence of 0.010 g of P(4-VPH)HSO4 full
conversion into the 14-(phenyl)-14H-dibenzo[a, j]xanthene oc-
curred in 55 min and 20 min. P(4-VPH)HSO4 in excess of 20 mg did
not help to increase the yield to any greater extent (Table 1, entry
5). The nature of the functional group on the aromatic ring of the
aldehyde exerted a strong influence on the reaction time. An in-
crease of the reaction rate was observed with arylaldehyde bearing
electron-withdrawing (such as –NO2) group in the para-position
(Table 2, entry 7), in comparison to the unsubstituted arylaldehyde.
The presence of a electron-donating (such as –OCH3) group (Table 2,
entry 10) decreased both the rate and the yield.
CBPI-S25 (0.32 mm ID, 0.5 l
m coating) capillary column. The 1H
NMR (250 or 300 MHz) and 13C NMR (62.5 or 75 MHz) were run
on a Bruker Avance DPX-250 FT-NMR spectrometer (d in ppm).
Microanalyses were performed on a Perkin–Elmer 240-B microan-
alyzer. Melting points were recorded on a Büchi B-540 B.V.CHI
apparatus in open capillary tubes. BANDELIN Sonorex (with a fre-
quency of 35 kHz and a nominal power 200 W) ultrasonic bath
was used for ultrasonic irradiation. Built-in heating, 30–80 °C ther-
mostatically adjustable. The reaction vessel placed in side the
ultrasonic bath containing water.
3.1. Catalyst synthesis
H2SO4 (0.3 mL, 5.3 mmol, as a 96% standard solution) was added
to the suspension of powdered poly(4-vinyl pyridine) (1.0 g) in
10 mL dry methanol. The mixture was stirred at room temperature
for 8 h then methanol was removed under reduced pressure to
form P(4-VPH)HSO4 catalyst. The excessive sulfuric acid were
washed by deionized water until the sulfate anions were absent
in the liquid (checked by reaction with BaCl2). The solid powder
was dried under vacuum at 65 °C for 48 h to afford P(4-VPH)HSO4
(0.5 mmol gÀ1) as a pale yellow powder. The catalyst is washed
with solvent and dried then reused for subsequent reactions.
3.2. General procedure for the synthesis of aryl-14H-
dibenzo[a, j]xanthenes
3.2.1. Conventional heating method (method A)
A mixture of 2-naphthol (2 mmol), aldehyde (1 mmol) and P(4-
VPH)HSO4 (0.010 g) was heated at 100 °C. The progress of the reac-
tion was followed by TLC. After completion of the reaction, the
reaction mixture was diluted with ethanol (10 mL) and stirred
for 10 min in 80 °C. The solid (catalyst) were collected by filtration
and the residue was kept at room temperature and the resulting
crystalline product was collected by filtration. The product was
found to be pure and no further purification was necessary.
Table 3, compares our results (time, yield, reaction conditions)
with results obtained by other groups. As can be seen, our method
is simpler, more efficient, and uses no toxic solvents.
Compared with traditional solvents and catalysts, it is easy for
this catalyst to be reused, which is prior to the conventional solvents
and catalysts [28]. Hence, we decided to study the catalytic activity
of recycled solid acid P(4-VPH)HSO4 for the synthesis of 14-(Phe-
nyl)-14H-dibenzo[a,j]xanthene (Table 4). After the separation of
product, the catalyst was washed with dichloromethane and vacu-
umed to remove CH2Cl2 and the resulting catalyst was reused di-
3.2.2. Ultrasound irradiation method (method B)
In a two-necked flask, a mixture of 2-naphthol (2 mmol), alde-
hyde (1 mmol), P(4-VPH)HSO4 (0.010 g) and ethanol (10 mL) was
irradiated in an BANDELIN Sonopuls HD 3200 ultrasonic apparatus
at 40 °C for 20 min. The mixture was filtered to recover the catalyst
and the residue was crystallized. The pure products were obtained
in 87–95% yields.
3.3. Representative spectral data
3.3.1. 14-(Phenyl)-14H-dibenzo[a, j]xanthene (Table 1, entry 1)
Colorless crystals; m.p. 184–185 °C; 1H NMR (CDCl3, 300 MHz):
d = 6.46 (s, 1H, CH), 6.96 (t, J = 7.2 Hz, 1H, ArH), 7.12 (t, J = 7.2 Hz,
2H, ArH), 7.36–7.58 (m, 8H, ArH), 7.74–7.81 (m, 4H, ArH), 8.37
(d, J = 8.4 Hz, 2H, ArH) ppm; IR (KBr): 3070, 3020, 1620, 1590,
Scheme 1. Synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes in the presence of
poly(4-vinylpyridinium) hydrogen sulfate under normal heating and sonication
conditions.
1430, 1400, 1250, 1150, 1075, 825, 740 cmÀ1
.

738
N.G. Khaligh / Ultrasonics Sonochemistry 19 (2012) 736–739
Table 1
Comparison of the amount of catalyst and yields using conventional heating and ultrasound irradiation for the synthesis of 14
(phenyl)-14H-dibenzo[a,j]xanthene.
Entry
Amount of
catalyst (mg)
Method A
Yield (%)a
Method B
Yield (%)a
Time (min)
Time (min)
1
2
3
4
5
0
5
10
15
20
–
360
120
60
60
60
–
120
40
20
20
20
65
94
94
92
92
95
95
96
a
Isolated yields.
Table 2
P(4-VPH)HSO4 catalyzed synthesis of aryl-14H-dibenzo[a,j]xanthenes.a
Entry
1
Aldehyde
Method A
Time (min)
55
Method B
Mp (°C)
Yield (%)b
Time (min)
20
Yield (%)b
97
94
184–185
230–231
2
3
4
5
72
45
65
72
93
20
20
20
20
90
92
95
92
94
96
94
239–240
297–298
295–260
6
7
72
70
92
96
20
20
90
95
213–215
312–314
8
9
78
76
94
92
20
20
87
94
259–260
179–180
10
11
12
72
57
54
90
92
93
20
20
20
94
88
88
204–205
214–216
210–213
13
52
96
20
92
290–292
a
Products were characterized by 1H NMR, IR and melting point and also by comparison with the reported in literature data [10].
Isolated yields.
b

N.G. Khaligh / Ultrasonics Sonochemistry 19 (2012) 736–739
739
Table 3
Comparison of our results with results obtained by other groups.a
Acknowledgement
Catalyst
Conditions
Time
(h)
Yield
(%)
References
The author is thankful to the Guilan University Research Coun-
cil for partial support of this work.
K5CoW12O40Á3H2O
I2
p-TsOH
Neat/125 °C
Neat/90 °C
2
2.5
4
1
2
8
1.5
55 min
20 min
91
90
89
82
94
93
81
94
97
29
30
10
31
32
18
33
This work
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Neat/125 °C
Neat/130 °C
Neat/125 °C
Neat/125 °C
Neat/110 °C
Neat/100 °C
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4. Conclusion
We described herein solid acid P(4-VPH)HSO4 catalyzed highly
efficient, one-pot, green protocol for the synthesis of aryl-14-H-
dibenzo[a, j]xanthenes by the condensation of an aldehyde and 2-
naphthol under ultrasound irradiation in excellent yields. The pres-
ent methodology offers several advantages such as simple proce-
dure, low cost, easy work-up, short reaction times and milder
conditions.