Host (nanocavity of dealuminated zeolite-Y)-guest (12-molybdophosphoric acid) nanocomposite material: An efficient and reusable catalyst for synthesis of 14-substituted-14-H-dibenzo[a,j] xanthenes under thermal and microwave irradiation conditions

Article abstract of DOI:10.1016/j.crci.2010.10.006

12-Molybdophosphoric acid (MPA) encapsulated in the supercages of dealuminated zeolite Y (DAZY) was used as an efficient and reusable catalyst for green synthesis of biologically active 14-substituted-14-H-dibenzo[a,j] xanthene derivatives via three-compo

Full text of DOI:10.1016/j.crci.2010.10.006

C. R. Chimie 14 (2011) 489–495
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´
Full paper/Memoire
Host (nanocavity of dealuminated zeolite-Y)-guest
(12-molybdophosphoric acid) nanocomposite material: An efficient and
reusable catalyst for synthesis of 14-substituted-14-H-dibenzo[a,j]
xanthenes under thermal and microwave irradiation conditions
a
a
Majid Moghadam a,b, , Shahram Tangestaninejad , Valiollah Mirkhani ,
*
Iraj Mohammadpoor-Baltork a, Maryam Moosavifar a
a Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan 81746-73441, Iran
b Department of Nanotechnology Engineering, University of Isfahan, Isfahan 81746-73441, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
12-Molybdophosphoric acid (MPA) encapsulated in the supercages of dealuminated
zeolite Y (DAZY) was used as an efficient and reusable catalyst for green synthesis of
biologically active 14-substituted-14-H-dibenzo[a,j] xanthene derivatives via three-
component reaction under conventional heating and microwave irradiation conditions.
The prepared catalyst, MPA-DAZY, was characterized by infrared spectroscopy (FT-IR), X-
ray diffraction (XRD) and elemental analysis techniques. The catalyst, MPA-DAZY, was
reused several times without significant loss of its catalytic activity.
Received 18 March 2010
Accepted after revision 20 October 2010
Available online 28 December 2010
Keywords:
12-Molybdophosphoric acid
Dealuminated zeolite Y
Xanthenes
ß 2010 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
2-Naphthol
Aldehyde
1. Introduction
times, the use of toxic solvents, special apparatus and the
use of toxic catalysts. Therefore, introduction of new and
In recent years, the synthesis of xanthenes has been of
considerable interest because these compounds have a
wide range of biological and pharmaceutical properties
such as antiviral [1], antibacterial [2], antiflammatory [3],
as well as in photodynamic therapy and as antagonism for
the paralyzing action of zoxazolamine [4]. Also, these
compounds can be used as dyes [5] in laser technologies
[6] and fluorescent material for visualization of biomole-
cules [7]. A variety of the reagents and catalysts [8–29]
have been reported for the preparation of these com-
pounds. However, some of the reported methods suffer
from drawbacks such as low yields, prolonged reaction
environmentally benign catalytic methods for the prepa-
ration of xanthene derivatives is highly desirable.
Heteropoly acids (HPAs) with Keggin type structure are
known to be very active catalysts for both acid-catalyzed
and redox reactions [30–32]. In the modern era of catalyst
design, heteropoly acids offer a unique opportunity to tune
solids at the atomic level since they have well-defined local
structures in which the constituent elements can be easily
varied. However, these catalysts have drawbacks such as
short lifetime under reaction conditions, low surface area
(<10 m2/g) and insufficient thermal stability [33,34]. To
overcome these disadvantages, many efforts including
immobilization of HPA on a support have been devoted.
Silica, silica-alumina, alumina, titania, zirconia, resins,
polymers, clay, MCM-41 and zeolites have been reported
as support for immobilization of these compounds
[34–39]. Amongst them, zeolite Y has been employed by
* Corresponding author.
E-mail addresses: moghadamm@sci.ui.ac.ir (M. Moghadam),
stanges@sci.ui.ac.ir (S. Tangestaninejad).
1631-0748/$ – see front matter ß 2010 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.crci.2010.10.006

[()TD$FIG]
490
M. Moghadam et al. / C. R. Chimie 14 (2011) 489–495
R
O
hydrochloric acid, and analyzing the obtained solution
using atomic absorption spectroscopy.
O
OH
MPA-DAZY
R
H
+
Δ or MW
2.2. General procedure for synthesis of 14-substituted-14-H-
dibenzo[a,j] xanthenes in the presence of MPA-DAZY under
thermal and under MW irradiation conditions
Scheme 1.
2-Naphthol (2 mmol), aldehyde (1 mmol) and catalyst
(300 mg, 0.0125 mmol) were mixed and heated at 100 8C
or irradiated at 800 W for an appropriate time. The
progress of the reaction was monitored by TLC. At the
end of the reaction, Et2O (15 mL) was added and MPA-
DAZY was filtered. The organic layer was dried over Na2SO4
to give the crude xanthene. The solvent was evaporated
and the product was recrystallized from ethanol to yield
the pure produce.
several researchers as support for immobilization of HPAs
because of its supercage diameter [40,41].
In continuation on our previous works on the encapsu-
lation of catalysts in the zeolites [42–44], here, we describe
the application of dealuminated zeolite Y-encapsulated
molybdophosphoric acid (MPA-DAZY) in the synthesis of
xanthene derivatives under solvent-free conditions by
conventional heating and under microwave irradiation
(Scheme 1).
3. Results and discussion
2. Experimental
3.1. Preparation and characterization of MPA-DAZY
All materials were of the commercial reagent grade and
obtained from Merck or Fluka. FT-IR spectra were obtained
in the range 400–4000 cmÀ1 with a Nicolet Impact 400D
spectrometer. 1H NMR spectra were recorded on a Bruker-
Arance AQS 300 MHz spectrometer. The microwave
system used for these experiments includes the following
items: micro-SYNTH labstation, complete with glass door,
dual magnetron system with pyramid-shaped diffuser,
1000 W delivered power, exhaust system, magnetic stirrer,
‘‘quality pressure’’ sensor for flammable organic solvents,
ATCFO fiber optic system for automatic temperature
control.
The prepared catalyst was characterized by infrared
spectroscopy (FT-IR), X-ray diffraction (XRD), differential
thermal gravimetry (DTG) and elemental analysis techni-
ques.
The content of MPA in the synthesized sample, which
was measured based on the Mo content of the MPA-DAZY,
was obtained 0.0875 g (0.043 mmol) per gram of the
supported catalyst. The FT-IR spectra confirm the existence
of MPA in the zeolite matrix. In the IR spectra of MPA, six
characteristic peaks are observed at 1627, 1063, 963, 871,
782, 595 cmÀ1. When the MPA is encaged into USY zeolite,
these peaks are observed at 1634, 1412, 1043 (P–O), 919
(Mo Ot), 724 (Mo–Oe–Mo) (Ot: terminal oxygen, Oe: edge-
sharing oxygen) 564 cmÀ1. The shift in the position of
peaks reveals that the Keggin structure interacts with Y
zeolite mostly through corner-shared [40,46] (Fig. 1).
Since all of the MPA, which have been absorbed on the
surface, was washed away in the washing process;
therefore, the presence of MPA bands in the IR spectra
clearly proves the presence of MPA in the zeolite cages.
The XRD patterns indicated that the calcinated Y zeolite
and MPA-DAZY have crystallinity almost identical to the
parent NaY zeolite. Upon calcination of NaY zeolite, the
intensity of the main peaks of the zeolite only slightly
reduces, which indicates that the framework of zeolite is
still maintained after dealumination of zeolite by hydro-
thermal treatment. In the XRD pattern of MPA-DAZY, the
disappearance of the corresponding peaks of pure
2.1. Preparation of catalyst (MPA-DAZY)
The modified DAZY, as support, was prepared by
hydrothermal treatment according to the reported proce-
dure [40]. In order to inhibit the decomposition of MPA by
basic Na zeolite, dealumination of NaY zeolite should be
carried out under hydrothermal conditions. This not only
increases the zeolite stability but also yields a secondary
pore system in zeolite matrix for deposition of the large
MPA species [35,45].
The method reported by Mukai et al. was used for the
synthesis of H3PMo12O40 (MPA) encapsulated into DAZY
[40]. In a typical procedure, DAZY (2.0 g) and molybdenum
(VI) oxide (7.2 g) were mixed in deionized water (70 mL)
and stirred at room temperature for 24 h. Then, phosphoric
acid (0.48 g, 85%) was added, and the mixture was stirred
for 3 h at 368 K. The synthesized sample (MPA-DAZY) was
filtered and dried at 383 K and then individually immersed
into hot water (363 K). After agitation for 1 h, the sample
was filtered and dried at 363 K. Then, the unreacted species
of metal cations in the lattice were exchanged with
aqueous 1 M solution of NaCl. Therefore, the sample was
suspended in a solution of NaCl (1 M) for 4 h under
vigorous stirring. Then, the catalyst was filtered, washed
thoroughly with distilled water and dried. The amount of
MPA into zeolite Y obtained by dissolving a small amount
of sample in hydrofluoric acid and hot concentrated
H3PMo12O40 (2u = 7.2) proves the encapsulation of Keggin
structure in the dealuminated zeolite matrix [32,46,47]
(Fig. 2).
Thermogravimetric analysis showed that when the
MPA is formed into supercage of zeolite, the thermal
stability of MPA increases and the decomposition temper-
ature of MPA-DAZY is higher than pure MPA. This behavior
can be attributed to the difficulty of O2 access inside the
supercage of zeolite for decomposition of MPA. Mean-
while, the strong interaction between MPA and zeolite
framework through corner-shared can confirmed this
occurrence [48].

[()TD$FIG]
M. Moghadam et al. / C. R. Chimie 14 (2011) 489–495
491
Fig. 1. FT-IR spectra of: (A) DAZY; (B) MPA and (C) MPA-DAZY.

[()TD$FIG]
492
M. Moghadam et al. / C. R. Chimie 14 (2011) 489–495
Fig. 2. XRD patterns of: (A) NaY zeolite; (B) calcinated NaY zeolite; (C) HMP-DAZY and (D) MPA.
3.2. Synthesis of xanthenes catalyzed by MPA-DAZY under
thermal conditions
800 W. At this power, the temperature of the reaction
vessel was measure to be 40 8C for liquid aldehydes and
70 8C for solid aldehydes.
First, the amount of catalyst was optimized in the
condensation reaction of 2,4-dichlorobenzaldehyde
(1 mmol) with 2-naphthol (2 mmol) under conventional
heating at 100 8C. The results showed that the highest yield
obtained in the presence of 0.0125 mmol (0.3 g) of catalyst,
whereas the yield of the product is reduced by decreasing
the amount of the catalyst or decreasing the temperature.
When the same reaction was performed in the absence of
the catalyst, the corresponding product was obtained in
only 5% yield.
The dependency of MPA amount in the catalysts on the
catalytic activity was also investigated. In this manner,
catalysts with different MPA loading were prepared and
used in the conversion of 4-nitrobenzaldehyde to its
corresponding xanthene. The results showed that the
catalyst with 0.043 mmol/g of catalyst was more efficient
than the others (Table 1).
Under the optimized reaction conditions, a wide range
of aromatic aldehydes with electron-withdrawing and
electron-donating substituents were reacted with 2-
naphthol in the presence of 0.0125 mmol (0.3 g) of MPA-
DAZY under solvent-free conditions to afford the corre-
sponding dibenzoxanthene derivatives in high yields
(Table 2, entries 1–13).
Under the optimized reaction conditions, different
aromatic aldehydes were reacted with 2-naphthol in the
presence of this catalyst under microwave irradiation to
afford the corresponding xanthene in high yields (Table 2).
The results showed that the reaction times are consider-
ably shorter under microwave irradiation. The acceleration
of reactions by microwave mainly results from two effects:
thermal effect and a specific microwave effect. Thermal
effect (dielectric heating) resulting from material–micro-
wave interaction, which allows fast and uniform distribu-
tion, and conversion of microwave energy into heat.
A specific microwave effect can be expected for the
polar mechanism, when the polarity is increased during
the reaction from the ground state (GS) towards the
transition state (TS) [49,50].
When HY zeolite was used as support, the same results
were obtained. These results were expected because NaY
zeolite is converted to HY zeolite during the dealumination
process [40].
Table 1
The effect of catalyst loading in synthesis of 14-substituated-14H-
dibenzo[a,j] xanthenes under conventional heatinga.
Entry
Catalyst loading (mmol/g)
Time (min)
Yield(%)b
1
2
3
4
0.025
0.03
110
110
110
110
45
60
93
93
3.3. Synthesis of xanthenes catalyzed by MPA-DAZY under
MW irradiation
0.043
0.055
The synthesis of xanthenes was also investigated in the
presence of MPA-DAZY under microwave irradiation. The
highest yield of the product was obtained at the power of
a
Reaction conditions: 4-nitrobenzaldehyde (1 mmol),
(2 mmol), catalyst (0.3 g).
b-naphthol
b
Isolated yield.

M. Moghadam et al. / C. R. Chimie 14 (2011) 489–495
493
Table 2
MPA-USZY catalyzes the synthesis of 14-substituated-14H-dibenzo[a,j] xanthenes under conventional heating and microwave irradiationa.
R
O
OH
MPA-DAZY
R
H +
Δ or MW
O
Entry
Aldehyde
Xantene
Thermal conditions
Yield (%)b,c
Microwave irradiation
Yield (%)b,c
Time (min)
Time (min)
O
H
1
2
85
75
120
95
90
3
2
Cl
O
H
80
Cl
O
H
3
4
95
98
120
120
78
93
4
3
Cl
Cl
O
H
OH
O
O2N
H
5
6
95
87
90
80
95
88
3
3
OH
O
H
NO2
O
H
7
8
9
93
88
93
110
130
120
92
82
85
6
4
6
O2N
O
H
H3C
O
H
OMe

494
M. Moghadam et al. / C. R. Chimie 14 (2011) 489–495
Table 2 (Continued )
R
O
OH
MPA-DAZY
R
H +
Δ or MW
O
Entry
Aldehyde
Xantene
Thermal conditions
Yield (%)b,c
Microwave irradiation
Yield (%)b,c
Time (min)
Time (min)
O
H
10
78
120
88
7
OMe
O
H
11
12
90
86
130
150
82
90
4
MeO
O
H
35
OMe
OMe
O
H
13
95
90
93
6
MeO
OMe
a
Reaction condition: aldehyde (1 mmol),
Isolated yield.
b-naphthol (2 mmol), catalyst (0.3 g, 0.0125 mmol).
b
c
The products were identifide by m.p. and IR and NMR spectroscopic data.
3.4. Catalyst recovery and reused
which means that MPA is still present in the supercages of
zeolite. The filtrates were used for measuring the amount
of Mo leached by ICP. The results, which are summarized in
Table 3, showed that only small amounts of initial Mo is
leached in three first runs and in the fourth run, no Mo is
leached. The yields of corresponding xanthene after fourth
run were 85% and 87% under thermal conditions and under
MW irradiation, respectively.
The reusability of the encaged MPA-DAZY, both under
thermal conditions and under MW irradiation, was tested
using 4-nitrobenzaldehyde as a model substrate. At the
end of the reaction, the catalyst was filtered and activated
by washing with ethyl acetate and drying at 120 8C for 3 h.
No appreciable loss in the catalytic activity was observed,
Table 3
The results obtained in the reusability of HMP-DAZY catalyst recovery and the amount of molybdenum leached in the formation of xanthenes from 4-
nitrobenzaldehydea.
Run
Microwave irradiation
Time (min)
Thermal conditions
Time (min)
Yield (%)b
Mo leached (%)c
Yield (%)b
Mo leached (%)c
1
2
3
4
120
120
120
120
93
87
86
85
2
1
1
0
3
3
3
3
92
90
88
87
1.8
1.0
0.9
0
a
Reaction condition: 4-nitrobenzaldehyde (1 mmol),
Isolated yield.
b-naphthol (2 mmol), catalyst (0.3 g, 0.0125 mmol).
b
c
Determined by ICP.

M. Moghadam et al. / C. R. Chimie 14 (2011) 489–495
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aromatic aldehydes with b-naphthol using MPA-DAZY as
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The financial support of this work by the Strategies
Research Council of New Technologies of Isfahan Province
is acknowledged.
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