Assembling of H5PW10V2O 40/MCM-48 and studying its superior catalytic performance in the synthesis of 14-aryl-14-H-dibenzo[a, j]xanthenes

Article abstract of DOI:10.1007/s12039-013-0372-3

A highly efficient, green, and reusable heterogeneous catalytic system is introduced for the preparation of aryl-14-H-dibenzo[a,j]xanthenes via one-pot condensation of β-naphthol with aryl-aldehydes by the mediation of a heterogeneous material composed of

Full text of DOI:10.1007/s12039-013-0372-3

c
J. Chem. Sci. Vol. 125, No. 2, March 2013, pp. 335–344. ꢀ Indian Academy of Sciences.
Assembling of H5PW10V2O40/MCM-48 and studying
its superior catalytic performance in the synthesis
of 14-aryl-14-H-dibenzo[a, j]xanthenes
REZA TAYEBEE∗ and BEHROUZ MALEKI
Department of Chemistry, School of Sciences, Hakim Sabzevari University, Sabzevar 96179-76487, Iran
e-mail: rtayebee@yahoo.com
MS received 3 January 2012; revised 28 July 2012; accepted 4 September 2012
Abstract. A highly efficient, green, and reusable heterogeneous catalytic system is introduced for the
preparation of aryl-14-H-dibenzo[a,j]xanthenes via one-pot condensation of β-naphthol with aryl-aldehydes
by the mediation of a heterogeneous material composed of Keggin-type tungsto-divanado-phosphoric acid,
H5PW10V2O40, supported on MCM-48 under solvent-free condition. Excellent yields (85–100%), short reac-
tion time (<60 min.), mild condition, simple work-up, and using a cheap and environmentally friendly cata-
lyst bearing remarkable reusability are advantages of the present methodology. The catalytic efficacy of
H5PW10V2O40/MCM-48 over some reported protocols are also overviewed.
Keywords. Xanthene; heteropolyacid; keggin; solvent-free; heterogeneous; MCM-48.
1. Introduction
an ideal support for various HPAs, because of its large
surface area and special pore structure, moreover, this
support is easier to be produced at a low cost.
The increasing applications of catalyst-based synthetic
methods in emerging industries have been favoured
by the continuous innovations observed over the last
decade for different catalytic processes.1 Catalysis
based on heteropolyacids (HPAs) and related com-
pounds, especially those comprising the strongest Keg-
gin-type HPAs, is an important field in which new
and promising developments are being carried out in
both academia and technological fields.2 The major
disadvantages of heteropolyacids lie in extremely low
surface area, water-solubility, hard recovery and recy-
cling which always limit their practical applications.3,4
Utilization of heterogeneous catalysts in organic syn-
thesis seems to be one of the most attractive ways
to avoid the above mentioned problems and referred
to as environmentally benign catalysts for their non-
polluting properties. In general, heterogeneous catalysts
offer higher surface area, lower coordinating sites, high
atom efficiency, easy product purification, and simple
reusability.
Xanthenes and benzoxanthene derivatives are bio-
logically important drug intermediates in the field
of medicinal chemistry for their biologically active
properties, such as antimalarial,7 antibacterial,8 antiin-
flammatory,9 and antiviral properties.8 Among them,
xanthenediones form the structural unit in many of the
natural product compounds10,11 and are used as versa-
tile synthons for their inherent reactivity12 due to the
presence of inbuilt pyran ring. Xanthenediones have
been synthesized by various procedures via conden-
sation of appropriate active methylene carbonyl com-
pounds with aldehydes.13 These compounds are usually
formed from condensation of active methylene carbonyl
compounds with aldehydes in the presence of various
Lewis acids. Furthermore, 14-H-dibenzo[a,j]xanthenes
and their analogues are synthesized from the reac-
tion of 2-naphthol with 2-naphthol-1-methanol,14
formamide,15 carbon monoxide,16 aldehydes17 and
aldehyde acetals.18 Although, most of the reported
homogeneous and heterogeneous catalytic systems
have exhibited acceptable efficacy, however, many of
them suffer from certain drawbacks including corrosive
and harmful nature, long reaction time, unsatisfactory
yield, harsh reaction condition, difficulty in reusability,
and excessive use of reagents and catalysts.
MCM-48 is a class of mesoporous silica tube-
like materials with uniformly sized three-dimensional
mesopores. These compounds have been of interest as
sorbent and solid support in catalysis.5,6 The meso-
porous silica material MCM-48 has been considered as
In order to overcome these common drawbacks, con-
siderable efforts have been achieved to the development
∗For correspondence
335

336
Reza Tayebee and Behrouz Maleki
H5PW10V2O40
X
O
C
H
OH
2
+
MCM-48
100o C
,
O
Solvent-free
X
Scheme 1. General formulation for the synthesis of aryl-14-H-dibenzo[a,j]xanthenes.
of heterogeneously catalysed organic reactions using with di-sodium hydrogen phosphate (Na2HPO4, 3.55 g,
solid acid catalysts such as zeolites,19 clays,20 and ion 25 mmol), dissolved in 50 ml of water. After the result-
exchange resins.21
ing solution was cooled to room temperature, con-
In continuation of our previous works to develop centrated sulphuric acid (5 mL, 17 M, 85 mmol) was
non-hazardous and eco-friendly synthetic methodolo- added to give a red solution. Sodium tungstate dihydrate
gies,22–25 here we wish to report a highly versatile, (Na2WO4. 2H2O, 82.5 g, 250 mmol) was dissolved in
eco-friendly, and efficient one pot heterogeneous proto- 100 ml of water and was added to a red solution with
col for the synthesis of aryl-14-H-dibenzo[a,j]xanthene vigorous stirring, followed by the slow addition of
derivatives from condensation of aldehydes and 2- concentrated sulphuric acid (42 ml, 17 M, 714 mmol).
naphthol catalysed by a catalytic amount of hetero- Extraction of the solution with diethyl ether (500 mL),
genized H5PW10V2O40/MCM-48 under solvent-free followed by evaporation in air, afforded H5PW10V2O40
condition (scheme 1). The experimental procedure for as a crystalline, orange-red solid (yield, 74%). Calcd
this reaction is remarkably simple and requires no toxic (Found): P, 0.98 (1.05); W, 58.24 (58.12); V, 3.22
organic solvents or inert atmosphere.
(3.16); H2O, 17.12 (17.26). FT-IR (KBr): 1070(s),
H5PW10V2O40/MCM-48 was prepared by loading 980(vs), 885(s), 788(vs) cm−1.
of H5PW10V2O40 on siliceous MCM-48 via the wet
impregnation method and was characterized by means
of spectroscopic instruments. The reactions were car-
ried out at 100◦C for <1 h by taking a 1:2 mol ratio mix-
ture of aldehyde: β-naphthol in the presence of 0.06 g
catalyst.
2.2 Synthesis of MCM-48, conventional hydrothermal
synthesis29
n-Hexadecyltrimethylammonium bromide (C16H33
(CH3)3NBr, template) was dissolved in deionized water,
and sodium hydroxide and tetraethoxysilane (TEOS)
2. Experimental
Reagents and starting materials were purchased from were added. The molar composition of the gel was 1 M
commercial resources and were used as received. All TEOS/0.25M Na2O/0.65 M C16H33(CH3)3NBr/62M
products were identified by comparison of their spectral H2O. The solution was stirred for about 1 h, charged
and physical data with those previously reported.26,27 into a polypropylene bottle and then heated at 383 K
Progress of the reactions was monitored by TLC. for 3 days. The product was filtered, washed with water
Infrared spectra were recorded (KBr pellets) on a and calcined at 823 K for 6 h.
8700 Shimadzu Fourier Transform spectrophotometer.
1H and 13C NMR spectra were recorded on a Bruker
AVANCE 100-MHz instrument using TMS as an inter-
2.3 Preparation of supported catalysts26
nal reference. Data for 1H NMR are reported as follows:
chemical shift (δ) and multiplicity (s: singlet, d: dou-
blet, t: triplet, q: quartet, m: multiplet, qt: quintuple, dq:
doublet of quartets, br: broad).
The MCM-48 supported H5PW10V2O40.30 H2O was
prepared by mixing the dried MCM-48 (1 g) with a
solution of H5PW10V2O40.30 H2O (0.25 g) in the min-
imum amount of deionized water. The resulting mix-
ture was stirred continuously with a magnetic stirrer
for 12 h. After removal of water, the solid powder was
2.1 Preparation of 10-Tungsto-2-vanadophosphoric
acid H5PW10V2O40.30H2O28
Sodium metavanadate (NaVO3, 12.2 g, 100 mmol) first dried at 100◦C for 4–5 h, then dried at 140◦C
was dissolved in 50 ml of boiling water and mixed for 2 h.

Synthesis of 14-aryl-14-H-dibenzo[a, j]xanthenes
337
2.4 General procedure for the synthesis of aryl-14-H- 2.5d 14-(4-Bromophenyl)-14-H-dibenzo[a,j]xanthenes:
dibenzo[a,j]xanthenes
1H NMR (CDCl3, δppm): 8.30 (s, 1H), 8.28 (s, 1H), 7.83
(s, 1H), 7.81 (s, 1H), 7.79 (s, 1H), 7.77 (s, 1H), 7.56
(t, J 6.96 Hz, 2H), 7.47 (s, 1H), 7.45 (s, 1H), 7.42
(s, 1H), 7.40 (s, 1H), 7.38 (s, 1H), 7.36 (s, 1H), 7.24
(d, J 2.93 Hz, 2H), 6.43 (s, 1H); 13C NMR: 148.66,
143.95, 131.55, 131.22, 131.03, 129.83, 129.07,
128.88, 126.88, 124.34, 122.36, 120.18, 117.97,
116.63, 37.41. IR (KBr, cm−1): 3030, 1624, 1586.
A mixture of 2-naphthol (2 mmol), aldehyde (1 mmol)
and 0.06 g MCM 48-H5PW10V2O40 was heated at
110◦C for an appropriate time (monitored by TLC,
2:1 petroleum ether:ethyl acetate). After cooling, the
reaction mixture was washed with CHCl3 (10 mL)
to remove the un-reacted aldehyde. The solvent was
evaporated and the crude product was re-crystallized
from EtOH to afford the pure product.
3. Results and discussion
2.5 Spectral data for selected
14-aryl-14-H-dibenzo[a, j]
xanthenes
3.1 Spectroscopic studies
The powdered small-angle X-ray scattering of calcined
mesoporous structure of MCM-48 was studied. This
compound showed an intense peak assigned to the
reflections at (100) and two-low intense peaks at (110)
and (200), which belong to a significant degree of long-
range ordering in the structure and well-ordered hexa-
gonal pore system. The 100 reflection of the MCM-
48 was still observed after the H5PW10V2O40 loading
(figure 1). This observation confirmed that the meso-
porous structure of the MCM-48 remained almost
unchanged upon the heteropolyacid loading. Accord-
ing to Scanning Electron Microscopy (SEM) images,
morphology of MCM-48 support has retained after
immobilization of H5PW10V2O40 (figure 2).
2.5a 14-(4-Chlorophenyl)-14H-dibenzo[a,j]xanthenes:
Brown solid; 1H NMR (CDCl3, δppm): 8.29 (d, J
8.46 Hz, 2H), 7.83–7.77 (m, 4H), 7.58–7.54 (m, 2H),
7.47 (s, 1H), 7.45–7.38 (m, 5H), 7.10–7.07 (m, 2H),
6.44 (s, 1H); 13C NMR: 156.0, 147.8, 132.8, 131.2,
129.3, 128.8, 128.3, 127.0, 126.8, 126.5, 124.7, 119.3,
118.2, 117.8, 33.5; IR (KBr, cm−1): 3050, 2925, 1620,
1595, 1456, 1431, 1396, 1242, 1060, 960, 824, 778,
695; EI-MS: m/z(%) = 392 (M+); Anal. Calcd for
C27H17ClO: C, 82.54; H, 4.36. Found: C, 82.46; H,
4.44.
2.5b 14-(4-Nitrophenyl)-14H-dibenzo[a,j]xanthenes:
1
Yellow solid; H NMR (CDCl3, δppm): 8.29 (2H, d,
J8.4 Hz),7.99 (2H, d, J8.7 Hz), 7.86 (2H, d, J4.1 Hz),
7.82 (2H,d, J5.4 Hz), 7.67 (2H, d, J8.8 Hz), 7.61 (2H,
t, J5.6 Hz),7.51 (2H, d, J8.9 Hz), 7.44 (2H, t, J7.9 Hz),
6.60 (1H, s); IR (KBr, cm−1): 3070, 2930, 1621, 1591,
1614, 1457, 1400, 1340, 1200, 1140, 1105, 1013, 964,
851, 827, 808, 742, 690. EI-MS:m/z(%) = 403 (M+);
Anal. Calcd for C27H17NO3: C, 80.38; H, 4.25; N, 3.47.
Found: C, 80.30; H, 4.35; N, 3.55.
2.5c 14-(3-Chlorophenyl)-14H-dibenzo[a. j]xanthenes:
Brown solid; 1H NMR (CDCl3, δppm): 8.30 (d, J 8.4 Hz,
2H), 7.86 (d, J 8.6 Hz, 2H), 7.76 (d, J 9.0 Hz, 2H),
7.60 (t, J7.0 Hz, 2H), 7.50 (d, J8.9 Hz, 2H), 7.48–7.43
(m, 4H), 7.10 (t, J 8.0 Hz, 1H), 6.96 (d, J8.7 Hz, 1H),
6.45 (1H, s); 13C NMR: 148.5, 146.8, 134.5, 131.2,
131.0, 129.7, 129.1, 128.8, 128.2, 127.1, 126.8, 126.4,
124.5, 122.4, 118.1, 116.4, 37.8; IR (KBr, cm−1): 3053,
2926, 1622, 1590, 1508, 1455, 1430, 1398, 1245, 1064,
959, 815, 775, 745, 690; EI-MS:m/z(%) = 392 (M+);
Anal. Calcd for C27H17ClO: C, 82.54; H, 4.36. Found:
C, 82.48; H, 4.42.
Figure 1. Low angle XRD patterns of calcined MCM-48
(up) and H5PW10V2O40/MCM-48 (bottom).

338
Reza Tayebee and Behrouz Maleki
Table 1. Effect of the kind of vanadium substituted hete-
ropolyacid catalyst in the synthesis of 14-(4-chlorophenyl)-
14H-dibenzo[a,j]xanthenes under homogeneous condition.
Time
(min.)
Yield
(%)
Heteropolyacid
Mol.%
H5PW10V2O40
H7SiW9V3O40
H5PMo10V2O40
H5SiW9Mo2VO40
HPA/MCM-48
0.5
0.5
0.5
0.5
0.06 g
80
90
90
180
60
95
86
92
96
99
the vanadyl species at the surface of the heteropolyan-
ion, which might be involved in the catalytic cycle. This
realm has to be taken into account for the evaluation
of the catalytic activity of H5PW10V2O40 and role of
vanadium in the catalytic system.30,31
Expectedly, the catalytic efficiency should be
affected by the catalyst amount. Thus, a set of
experiments using different amounts of HPA/MCM-
48 was taken into account in the reaction of 4-
bromobenzaldehyde and β-naphthol under solvent-free
condition at 100◦C (table 2). The synthetic route is dras-
tically dependent to the presence of the catalyst and no
conversion was attained in the absence of catalyst. The
optimum catalyst amont was 0.06 g to reach complete
conversion after 1 h. Lower amounts of catalyst resulted
in a pronounced decrease in the efficacy of the proto-
col, while higher amounts led to complete conversion
in short time, 0.5 h.
3.3 Condensation of different aromatic aldehydes
with β-naphthol
Figure 2. (a) SEM micrographs of MCM-48 and (b)
H5PW10V2O40/MCM-48.
The generality of this process was studied by a range of
substituted aryl aldehydes to synthesize the correspond-
ing dibenzo[a,j]xanthenes in high to excellent yields
3.2 Effect of the kind and concentration of vanadium
substituted heteropolyacid
Table 2. Effect of HPA/MCM-48 amount on the conden-
sation of 4-bromo-benzaldehyde with β-naphthol.
The catalytic activity of H5PW10V2O40 was com-
pared with other vanadium substituted heteropolyacid
catalysts in the preparation of 14-(4-chlorophenyl)-
14H-dibenzo[a,j]xanthene (table 1). According to our
previous findings,25 substitution of one and two vana-
dium atoms instead of Mo6+ and W6+ in H3PM12O40,
leading to an increase in the catalytic activity of the
heteropolyacid. Meanwhile, H5PW10V2O40 has been
a little more reactive than H5PMo10V2O40. Speculate
catalytic activity of H5PW10V2O40 would be due to spe-
cial coordination geometry of the complex metal oxo
species and far distance of the vanadyl oxygen double
bond from the heteropolyanion. This geometry exposed
Entry
Catalyst (g)
Time (h)
Yield (%)
Selec.%
1
2
3
4
5
—
10
6
3
1
0.5
<5
65
96
99
99
—
90
100
100
95
0.01
0.03
0.06
0.1
Reactions were carried out at 100◦C by using β-naphthol
(2 mmol), 4-bromo-benzaldehyde (1 mmol) and different
amounts of the heteropolyacid under solvent-free condition.
Progress of the reactions was monitored as described in the
experimental section by TLC. Yields refer to isolated yields

Synthesis of 14-aryl-14-H-dibenzo[a, j]xanthenes
339
Table 3. Synthesis of different xanthene derivatives catalysed by MCM-48/H5PW10V2O40.
Entry
Aldehyde
Product
Time (h) Yield (%) Mp (◦C) observed Mp (◦C) reported Ref.
1
1
99
95
295–297
289–290
296
32
32
2
3
0.6
289–290
1
70
309–310
310
33
4
5
1
90
85
212–213
213–214
211–212
32
34
0.8
215
6
7
1
1
90
85
182–183
190–191
181–183
190–192
32
34
Br
H
C
O

340
Reza Tayebee and Behrouz Maleki
Table 3. (continued)
Entry
Aldehyde
Product
Time (h) Yield (%) Mp (◦C) observed Mp (◦C) reported Ref.
Cl
H
C
8
1
87
189–190
210–211
35
O
Reactions were carried out at 100◦C by using β-naphthol (2 mmol), aromatic aldehyde (1 mmol) and 0.06 g MCM-
48/H5PW10V2O40 under solvent-free condition. Progress of the reactions was monitored as described in the experimental
section by TLC
(table 3). High yields were attained without any signifi- channels, whereas mesoporous MCM-48 contains a
cant amounts of undesirable side products. The present three-dimentional channel system with high hydropho-
protocol does not require toxic organic solvent to bicity and acidity, large surface area, and high ther-
produce aryl-14-H-dibenzo[a,j]xanthenes. All products mal and hydrothermal stability (figure 3).37 Although
were characterized by FT-IR and comparison of melt- table 4 reveals that textural and physicochemical pro-
ing points with literature. This general method tolerated perties of mesoporous MCM-41 and MCM-48 are com-
both electron-withdrawing and electron-donating con- parable, tunable mesoporous pore size distribution of
stituents and afforded the respective xanthene deriva- the latter, enabled this material as a potent support.38
tives in high yields. It was confirmed that aldehydes These structural features might be involved in the less
were stable toward oxidation under the reported strong catalytic activity of MCM-41/H5PW10V2O40 versus
acidic condition.
MCM-48/H5PW10V2O40.
To further investigate the efficacy of MCM-48 as sup-
port, some other well-known carriers such as SBA-15,
MCM-41, SiO2, and ZrO2 were evaluated to immo-
bilize H5PW10V2O40. All the catalysts were compared
under similar conditions in the reaction of β-naphthol
with 4-chlorobenzaldehyde (table 5). The comparison
was based on the product yield, recovery, and reusabil-
ity of the catalyst. MCM-48 was the best among the
examined supports and led to 95% yield after 1.3 h.
3.4 The excellence of MCM-48 over some
well-known carriers for H5PW10V2O40
The M41S family consists of three basic silicate struc-
tures, including hexagonal, cubic, and lamellar which
has been designated as MCM-41, MCM-48, and MCM-
50.36 MCM-41 consists of one-dimentional parallel
Figure 3. (a) Hexagonal channel arrangement of MCM-41 and (b) cubic
array of MCM-48 channels. Data are reproduced with permission from Kresge,
Bejblova et al.36–38

Synthesis of 14-aryl-14-H-dibenzo[a, j]xanthenes
341
HPA due to its interaction with the solid support. Using
0.015 g H5PW10V2O40 supported on 0.06 g MCM-48
led to the formation of 95% product after 0.6 h, whereas
the same amount of catalyst led to the same conver-
sion after 1.3 h in the homogeneous condition. These
findings clearly showed the activating role of the solid
support in the desired reaction.
Apparently, besides the surface area, particle size,
pore structure, and distribution of the protons in HPAs,
nature and interaction of supports with HPAs are very
influential on the catalytic activity. Silica as a con-
ventional, cheaply available supporting material has
attracted more attention among other supports. It is
well-established that physiochemical properties of sili-
ca has an important role in the final properties of grafted
materials. Clearly, the interaction of HPA with vari-
ous silicas depends on the type of silica and surface
characteristics.
Table 4. Textural and physicochemical properties for
mesoporous MCM-41 and MCM-48.
Pore
Pore
diameter
(A◦)
SBET
volume
Support
(M2/g)
(cm3/g)
MCM-41
MCM-48
1155
1096
0.88
0.71
30.5
26.1
Data are reproduced with permission from Kresge, Bejblova
et al.36–38
SBA-15 also produced the same conversion, but dur-
ing longer time 1.5 h. Although, MCM-41 has com-
parable structure as MCM-48, the former was less
effective and produced 75% of conversion after 2.5 h.
0.25 mol% H5PW10V2O40 embeded on 0.03 g of MCM-
48 and SBA-15 produced 95–97% of conversion after
1.3–1.5 h.
ZrO2 and SiO2 were inefficient compared to other
supporting materials, produced 60 and 37% of conver-
sions after 3 and 4 h, respectively. Although, all the
examined supports involve pores large enough to sca-
venge the heteropolyacid, however, different observed
reactivity pattern would be attributed to the influence
of internal backbone of the solid material on the reac-
tivity of the heteropolyacid. Interestingly, in compa-
rison with the unsupported homogeneous system, the
catalytic activity of H5PW10V2O40 was increased by
immobilization onto MCM-48. Thus, it seems that the
solid support would activate the catalyst molecules into
the desired synthesis route. However, for other supports,
the catalytic activity of HPA was declined as a result of
immobilization. These observations would be explained
considering changes occurred in the acid strength of the
3.5 Comparing the catalytic activity of solid acid
MCM-48/H5PW10V2O40 with other reported catalysts
The superiority of the present heterogeneous cata-
lytic system over reported methodologies was studi-
ed by comparing the obtained results with those
reported previously (table 6). The catalytic acti-
vity of catalysts was compared considering mol%
of the used catalyst, temperature, reaction time,
and percentage yields. Among the examined cata-
lysts, H5PW10V2O40/MCM-48 was the best. MCM-
48 activated the heteropolyacid such that 0.06 g of it
(including 0.015 g of H5PW10V2O40) led to the same
results as obtained for 1 mol% of catalyst (includ-
ing 0.03 g of H5PW10V2O40) under homogeneous
condition. This comparison revealed the reactivity pat-
tern of H5PW10V2O40/MCM-48 > H5PW10V2O40
>
Table 5. Comparison of the efficiency of MCM-48
with other well-known supports in synthesis of 14-(4-
chlorophenyl)-14H-dibenzo[a,j]xanthene.
SiO2/H6P2W18O62 > SiO2/H3PW12O40. Heterogeneous
nature and explicit catalytic activity of H5PW10V2O40/
MCM-48 are the two key features of the present
protocol. Comparison of the heteropolyacid systems
with other introduced catalytic routes, clearly, justified
the distinct higher activity of H5PW10V2O40/MCM-48
compared to other methods in the preparation of of
14-aryl-14H-dibenzo[a,j]xanthenes.
Amount Time Yield
Entry
Carrier
(g, mol%) (h)
(%)
1
2
3
4
5
6
7
8
9
H5PW10V2O40
H5PW10V2O40
H5PW10V2O40
MCM-48/H5PW10V2O40
MCM-48/H5PW10V2O40
SBA-15/H5PW10V2O40
MCM-41/H5PW10V2O40
ZrO2/H5PW10V2O40
SiO2/H5PW10V2O40
0.1 mol%
0.5 mol% 1.3
9
79
95
98
95
95
97
75
60
37
1 mol%
0.06 g
0.03 g
0.03 g
0.03 g
0.03 g
0.03 g
0.5
0.6
1.3
1.5
2.5
3
3.6 Reusability of the catalyst
4
Studying recoverability of H5PW10V2O40/MCM-48 has
been one of the most important parameters before
recommending it for industrial-scale use. To attain
this goal, the recycled catalyst was washed with
dichloromethane, activated at 130◦C for 5 h, and then
Reactions were carried out as described below table 2.
0.03 g of MCM-48/H5PW10V2O40 was included 0.0075 g
of H5PW10V2O40 . This amount was equal to 0.25 mol%
H5PW10V2 O40

342
Reza Tayebee and Behrouz Maleki
Table 6. Comparison of the efficiency of various reported catalysts in synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes.
Catalyst
[mol%] or (g)
Time
(h)
Yield
(%)
Condition
(◦C)
Catalyst
Ref.
H5PW10V2O40
[1]
0.06 g
0.15 g
0.2 g
0.1 g
0.08 g
0.1 g
[10]
[10]
1:4 (v:v)
[50]
0.3 g
0.5–0.8
0.6–1
0.5–1
0.5–1.5
0.1–0.4
0.25
0.1–0.5
2–5
6–12
73
82–98
70–99
84–95
84–96
73–98
82–97
75–98
85–95
90–95
60–90
82–91
75–89
S. F (100)
S. F (100)
S. F (100)
S. F (100)
S. F (125)
S. F (60)
S. F (110)
S. F (90)
S. F (125)
HOAc (80)
H2O (100)
S. F (120)
This work
This work
MCM-48/H5PW10V2O40
SiO2/H3PW12O40
SiO2/H6P2W18O62
NH4H2PO4/SiO2
37% BF3/SiO2
NaHSO4/SiO2
39
39
34
40
41
42
43
44
45
46
I2
Sulphamic acid
H2SO4:HOAc
KAl(SO4)2.12H2O
Montmorillonite K10
3–4
2–4
S.F. refers to solvent-free condition
subjected to a second run. The recovered catalyst was
Figure 5 shows the FT-IR spectra of H5PW10V2O40,
reused for several times and did not show considerable MCM-48, and MCM-48/H5PW10V2O40. The Keggin-
loss of activity after ten times. Thus, the reaction would type heteropolyacid has four characteristic peaks in
be carried out with the recovered and/or fresh catalyst the range of 750–1100 cm−1.47 It can be seen that
with equal efficacy. Stability of the catalyst was inves- peaks appeared at 778–784 cm−1 and 846–890 cm−1
tigated via studying the permanency of the character-
istic IR bands of Keggin structure at ca. 1070–1090,
947–955, 846–890, and 778–784 cm−1.47 These studies
confirmed that the mentioned structure should be intact
under the reaction condition reported here.
Reusability studies and high catalytic activity of
the recovered heterogeneous catalyst clearly confirmed
that the loaded heteropolyacid was firmly bound to
the MCM-48 surface. Moreover, spectroscopic analy-
sis proved that the morphology of MCM-48 is retained
after several reusing of the supported catalyst, similar to
those of pure catalyst (figure 4).38 Therefore, MCM-48
could be considered as one of the promising materials
to adsorb heteropolyacids for the catalytic purposes.
70
60
50
40
30
20
10
0
1
2
3
4
5
6
7
8
9
10
11
No of cycles
Figure 5. IR spectra of (A) H5PW10V2O40, (B) MCM-
48, (C) MCM-48/H5PW10V2O40 before reaction, and (D)
MCM-48/H5PW10V2O40 after reaction.
Figure 4. Studying reusability of H5PW10V2O40/MCM-
48 in the three component condensation of 4-nitro-
benzaldehyde and β-naphthol after 1 h.

Synthesis of 14-aryl-14-H-dibenzo[a, j]xanthenes
343
H
H+
O
OH
MCM
H
O
X
H
X
H
OH
OH
OH+
H
H+
MCM
H
Ar
H
X
H2O
O
H
OH
OH
OH
HO
OH
X
H
+
OH2
HO
X
H
+
OH2
OH
OH
H
H
X
H2O
Scheme 2. Suggested reaction pathway for the preparation of 14-aryl-14H-
dibenzo[a,j]xanthenes catalysed by H5PW10V2O40/MCM-48.
correspond to M–O–M and peaks at 947–955 cm−1 dibenzo[a,j]xanthenes. Condensation of aromatic alde-
and 1070–1090 cm−1 are related to M=O and P–O, hydes with β-naphthol in the presence of a catalytic
respectively. That explicitly indicates the neat struc- amount of H5PW10V2O40/MCM-48 under solvent-free
ture of Keggin-type heteropolyacid. In FT-IR spectrum conditions led to excellent yields. Low cost, easy work-
of HPW/MCM-48, these peaks overlap with MCM- up, short time, and using mild reaction condition are
48, therefore these informations cannot confirm that some advantages of the present protocol.
loading of heteropolyacid was occurred over MCM-48.
Acknowledgements
However, due to appearance of weak new peaks in the
FT-IR spectrum of HPW/MCM-48 in range of 850–
950 cm−1 in comparison with MCM-48, confirmed that
HPW actually existed in the pores of MCM-48.
Finally, a reasonable reaction pathway is proposed
for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes
by means of the heteropolyacid H5PW10V2O40 immobi-
lized on MCM-48 (scheme 2).28,30,43
Partial financial support from the Research Council of
Hakim Sabzevari University is appreciated. We thank
Ms Shima Tizabi for carrying out some of the reactions.
We also thank Dr. Mostafa M Amini for recording SEM
images.
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