Zirconia-incorporated mesoporous silica nanoparticles as an efficient and reusable catalyst for the synthesis of octahydroxanthene-1,8-diones

Article abstract of DOI:10.1007/s11164-014-1883-3

Zr-containing mesoporous silica with high loading amount of zirconia efficiently catalyzes the reaction of dimedone with aldehydes under solvent-free conditions to afford the corresponding octahydroxanthene-1,8-diones in good-to-excellent yields. Zr-conta

Full text of DOI:10.1007/s11164-014-1883-3

Res Chem Intermed
DOI 10.1007/s11164-014-1883-3
Zirconia-incorporated mesoporous silica nanoparticles
as an efficient and reusable catalyst for the synthesis
of octahydroxanthene-1,8-diones
•
Mohammad Abdollahi-Alibeik Gohar Ahmadi
Received: 27 June 2014 / Accepted: 20 November 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract Zr-containing mesoporous silica with high loading amount of zirconia
efficiently catalyzes the reaction of dimedone with aldehydes under solvent-free
conditions to afford the corresponding octahydroxanthene-1,8-diones in good-to-
excellent yields. Zr-containing mesoporous silica samples with a high loading
amount of Zr were prepared by sol–gel method and results show that the catalyst
with 20 mol% of Zr has better activity than the catalyst with 10 and 30 mol% of Zr.
The catalyst can be recovered and reused with moderate loss of activity.
Keywords Octahydroxanthene-1,8-diones Á Zr-MCM-41 Á Mesoporous silica Á
Nanoparticles Á Zirconia Á Reusability
Introduction
Xanthene derivatives are an important class of heterocyclic compounds because of
their useful biological and pharmacological properties such as antiviral, antibacte-
rial, and anti-inflammatory activities [1]. These compounds are also used as
luminescent sensors [2], in laser technologies [3], in fluorescent materials for the
visualization of biomolecules [4], and in photodynamic therapy [5]. Therefore,
the development of a convenient and efficient method for the synthesis of these
heterocycles is of practical importance. Several methods for the synthesis of
these compounds have been reported. Among them, the general method includes the
condensation reaction of aldehydes with dimedone in the presence of acid catalysts.
M. Abdollahi-Alibeik (&)
Department of Chemistry, Yazd University, 89158-13149, Yazd, Iran
e-mail: abdollahi@yazd.ac.ir
G. Ahmadi
Department of Chemistry, Payame Noor University, PO BOX 19395-3697, Tehran, Iran
123

M. Abdollahi-Alibeik, G. Ahmadi
A variety of catalysts such as [Hbim]BF4 [6], H3PW12O40/MCM-41 [7],
HClO4-SiO2 [8], PPA-SiO2 [8], Fe3?-montmorillonite [9], amberlyst-15 [10],
diammonium hydrogen phosphate [11], ZnO nanoparticles [12], starch sulfate
[13], and acetic acid [14] are utilized for this condensation reaction. However, the
use of many of these catalysts is associated with one or more disadvantages such as
long reaction times, low yields, the use of excess reagents/catalysts, harsh reaction
conditions, the use of special equipment, and difficulty in recovery and reusability
of the catalysts. Hence, there is a need to develop a convenient, efficient, and
practically useful protocol for the synthesis of octahydroxanthene-1,8-diones.
In recent years, the use of solid acid catalyst has received considerable attention
in organic transformations. This is mainly due to the advantages of solid acid
catalysts such as non-toxicity, non-corrosiveness, less expensive, ease of handling,
recovery, and reusability [15].
MCM-41 belongs to the family of mesoporous molecular sieves [16] and has
been used alone and also in surface or framework-modified form as a catalyst in
some organic transformations [17–20]. Some other mesoporous catalysts containing
acid/base functionalized sites or mixed oxides were also improved as solid acid
catalysts [21–23]. Among the various types of modified MCM-41, zirconia-
modified MCM-41 (Zr-MCM-41) has been widely used as a catalyst or catalyst
support in some acid-catalyzed reactions [24–26].
In this communication, we wish to report the efficient synthesis of octahydrox-
anthene-1,8-diones by the reaction of dimedone with aldehydes in the presence of
catalytic amounts of zirconia containing mesoporous silica (Zr-MS) as reusable
solid acid catalyst (Scheme 1).
Experimental
Materials and methods
All of the chemicals were commercial products. All reactions were monitored by
TLC (thin-layer chromatography) and all yields refer to isolated products. Melting
points were obtained with a Thermo Scientific-9200 apparatus and are uncorrected.
1H NMR spectra were recorded in CDCl3 on a Bruker DRX-500 AVANCE
spectrometer. Infrared spectra were recorded on a Shimadzu FT-IR Prestige-21
spectrophotometer in KBr pellets. The X-ray diffraction (XRD) patterns were
recorded on a Bruker D8 ADVANCE X-ray diffractometer using nickel-filtered
˚
Cu-Ka radiation (k = 1.5406 A). Scanning electron micrographs (SEM) were
O
O
Ar
O
Zr-MCM-41
+
ArCHO
1
2
Solvent-free
100 oC
O
O
3
2
Scheme 1 Synthesis of octahydroxanthene-1,8-diones in the presence of zirconia incorporated
mesoporous silica
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Zirconia-incorporated mesoporous silica
obtained on a Philips XL-30 microscope. Transmittance electron microscopy was
performed with a Zeiss-EM10C at 80 kV. The BET surface area was performed
using a BELSORP instrument (BELSORP-mini JAPAN INC).
Catalyst preparation
The synthesis of zirconia-containing mesoporous silica samples (Zr-MS) was carried out
using tetraethylorthosilicate (TEOS) as the Si source, cetyltrimethylammonium bromide
(CTAB) as the template, and ammonia as the pH control agent with the gel composition of
SiO2:ZrO2:CTAB:NH4OH:H2O = 1:n:0.115:1.85:460 (n = 0.11 for sample containing
10 mol% Zr, 0.25 for 20 mol% Zr and 0.428 for 30 mol% Zr). In a typical procedure for
the synthesis of Zr-MS samples, 0.25 g of CTAB and an appropriate amount of ZrCl4 (243,
553, and 944 mg for sample containing 10, 20, and 30 mol% of Zr, respectively) dissolved
in 50 ml of deionized water at 70 °C; 1.25 g of TEOS was added to above solution for the
20 min. The mixture was further stirred at room temperature for 2 h. A solution of NH4OH
was slowly added into the resulting mixture until a gelatinous solution was obtained, while
the pH value of the mixed solution was adjusted to 10.5. The gel was stirred for 24 h and
then was centrifuged and washed with distilled water until the supernatant liquid was
neutralized. The sample was placed in an oven at 120 °C for 12 h and calcined at 550 °C
for4 hto obtain white-solidZr-MS samplesdenoted as10Zr-MS, 20Zr-MS, and 30Zr-MS,
with 10, 20, and 30 mol% loading amount of Zr in the samples, respectively.
General procedure for synthesis of octahydroxanthene-1,8-diones (4a-k)
In a 5-ml round-bottom flask, a mixture of dimedone (2 mmol), aldehyde (1 mmol) and
20Zr-MS (50 mg) was stirred (100 rpm) at 100 °C for 10–85 min. After completion of
the reaction (monitored by TLC, eluent; EtOAc:n-hexane, 20:80), the mixture was
cooled to room temperature and EtOH (15 ml) was added. The resulting solid material
was filtered and recrystallized from EtOH/H2O (2/1) to give the pure product.
Physical and spectroscopic data for selected compound
9-(3-Nitrophenyl)-3,3,6,6-tetramethyl-1,2,3,4,5,6,7,8-octahydroxanthene-1,8-dione
(4 g): Yield: 91 %, white solid, m.p. 191–193 °C (Lit. [23] 163–164 °C); FT-IR:
tmax (KBr) = 2,960, 1,595, 1,527, 1,377, 1,346 cm-1 1H NMR (500 MHz,
;
CDCl3): d = 0.91 (s, 6H), 1.05 (s, 6H), 2.11 (d, J = 12.8 Hz, 2H), 2.29 (d,
J = 12.0 Hz, 2H), 2.51–2.59 (m, 4H), 4.65 (s, 1H), 7.56 (t, J = 6.5 Hz, 1H), 7.70
(d, J = 4.0 Hz, 1H), 8.00 (s, 2H) ppm.
Results and discussion
Catalyst characterization
The powder XRD patterns of mesoporous materials usually exhibit the diffraction
peaks in the low-angle region. Figure 1 presents the low-angle XRD patterns of the
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M. Abdollahi-Alibeik, G. Ahmadi
Fig. 1 Low-angle XRD
patterns of MCM-41 (a) and
20Zr-MS (b)
(a)
(b)
2
4
6
8
10
2θ (°)
synthesized MCM-41 and 20Zr-MS samples. As shown in Fig. 1, MCM-41 shows a
diffraction peak (100) at 2h value of ca. 2.3, and has small and weak diffraction
peaks (110 and 200, respectively) at 2h value ranging from 4 to 5, which is
consistent with hexagonal mesoporous structure of MCM-41 [27]. Figure 1b shows
that incorporation of Zr into the MCM-41 framework causes broadening of the main
peaks of MCM-41 due to decrease in long-range ordering of the mesostructure of
Zr-MS with high loading amount of Zr.
The high-angle XRD patterns of the 20Zr-MS and the nanosized ZrO2 calcined at
550 °C are shown in Fig. 2. As shown in Fig. 2a, ZrO2 pattern shows characteristic
peaks of both tetrahedral and monoclinic phases. However, absence of these peaks
in the Zr-MS pattern (Fig. 2b) confirms that ZrO2 did not form crystalline phase in
the mesoporous silica framework and is dispersed in the framework.
Mesostructure of the 20Zr-MS sample was further studied by TEM, as shown in
Fig. 3. Porosity of the sample is clear and disordered mesoporous system is due to
the incorporation of Zr into the MCM-41 framework that also confirms by XRD
data.
To confirm the presence of Zr in the structure of MCM-41, FT-IR spectra of
MCM-41 and 20Zr-MS are shown in Fig. 4. Figure 4a shows main peak of
MCM-41 at 459 cm-1 (Si–O-Si bending vibration), 795 cm-1 (Si–O–Si symmetric
123

Zirconia-incorporated mesoporous silica
Fig. 2 High-angle XRD patterns of the nanosized ZrO2 (a) and 20Zr-MS (b)
Fig. 3 TEM image of 20Zr-MS
stretching) and 1,100 cm-1 (Si–O–Si asymmetric stretching). In the spectrum of
20Zr-MS (Fig. 4b), broadening of the main peak of silica confirms the presence of
Zr in the framework due to overlap of Zr–O bands with this peak.
The SEM image of 20Zr-MS (Fig. 5) shows spherical nanoparticles with the size
of \100 nm.
In order to compare the acidic strength of Zr-MS samples, potentiometric
titration method was used (Fig. 6). According to this method, the initial potential
123

M. Abdollahi-Alibeik, G. Ahmadi
Fig. 4 FT-IR spectra of the Zr-MS (a) and MCM-41 (b)
Fig. 5 SEM image of the 20Zr-MS
electrode (Ei) shows the strength of surface acid sites and the range where a plateau
is reached (meq/g solid) indicates the total number of acid sites. As shown in Fig. 6,
very low initial potential shows that MCM-41 is very weak acid relative to 20Zr-MS
123

Zirconia-incorporated mesoporous silica
Fig. 6 Potentiometric titration
curve of 10Zr-MS (open circle),
20Zr-MS (filled circle),
30Zr-MS (filled square) and
MCM-41 (asterisk)
200
100
0
'10Zr-MS'
'20Zr-MS'
'30Zr-MS'
'MCM-41'
-100
0.0
0.2 0.4
0.6 0.8
1.0
1.2 1.4
meq/g
Table 1 Surface area of MCM-
Entry
Catalyst
SBET (m2 g-1
)
41 and Zr-MS samples
1
2
3
4
MCM-41
10Zr-MS
20Zr-MS
30Zr-MS
900
610
560
350
and 10Zr-MS. However, initial potential of 20Zr-MS is higher and thus has higher
acidity strength. The pattern of 30Zr-MS shows lower acidity strength and also
lower number of acid sites.
To show the effect of Zr loading on the surface of mesoporous materials, specific
surface areas were measured by BET calculation. As shown in Table 1, surface area
was decreased by the incorporation of Zr onto the framework of silica from 610 to
350 with increase in Zr loading. Although, according to acidity measurement
results, 20Zr-MS shows the better catalytic activity, this is not in contrast with the
results of BET. The lower acidity in 10Zr-MS sample may be due to lower loading
of Zr and also lower acidity of 30Zr-MS may be due to serious reduction of surface
and also mesoporosity because of very high incorporation of Zr onto the silica
framework.
123

M. Abdollahi-Alibeik, G. Ahmadi
Catalyst activity
Initially, the reaction of dimedone and benzaldehyde was selected as the model
reaction for optimization experiments and results are summarized in Table 2. To
optimize the effect of Zr/Si mole ratio on the catalytic activity of Zr-MS, the model
reaction was performed in the presence of Zr-MS prepared by different Zr/Si mol%.
As shown in Table 2, the catalyst activity was increased by increase in the amount
of Zr from 10 up to 20 % and then was decreased after increase in amount of Zr up
to 30 %. The results show that 20Zr-MS has the best activity in term of reaction
time and yield of the product (Table 2, entry 2). This is in agreement with the
obtained results of acid strength by potentiometric titration. To optimize the amount
of the catalyst, the model reaction was carried out in the presence of various
amounts of 20Zr-MS (Table 2, entries 2, 4, 5) and results show that the use of
100 mg catalyst for 1 mmol of aldehyde has the best results. To show efficiency of
Zr in the framework of silica, the model reaction was also carried out in the
presence of 100 mg MCM-41 and ZrO2. The results show low activity for these
catalysts (Table 2, entries 6, 7).
Following the obtained results, the reaction of dimedone and benzaldehyde was
carried out in the presence of 100 mg of 20Zr-MS in solvent-free conditions at
100 °C and the corresponding octahydroxanthene-1,8-diones was obtained in 90 %
yield (Table 3, entry 3a). The scope and generality of this method was investigated
in the reaction of various types of aldehydes with dimedone. Aldehydes with both
electron-donating and electron-withdrawing substituents were reacted with dime-
done at the same reaction conditions and the corresponding octahydroxanthene-1,8-
diones were obtained in the 80–92 % yields (Table 3, entries 3b–k).
To investigate reusability of the catalyst, the recovered catalyst from the model
reaction (run 1, Table 4), was washed with EtOH and dried at 120 °C and then
reused at the same reaction conditions (run 2, Table 4). This was repeated for a third
run. The results show a moderate decrease in activity after recovering. This may be
due to partial blocking of active sites of the catalyst in the reaction media and/or
partial leaching of nanoparticles. In order to clean the surface of the active sites, the
Table 2 Optimization of the catalyst condition in the reaction of benzaldehyde and dimedone
Entry
Catalyst
Catalyst amount (mg)
Substrate:Zr (molar ratio)
Time (min)a
Yield (%)b
1
2
3
4
5
6
7
a
10Zr-MS
20Zr-MS
30Zr-MS
20Zr-MS
20Zr-MS
MCM-41
ZrO2
100
100
100
75
0.13
0.21
0.27
0.16
0.11
–
180
40
75
90c
80
81
81
72
76
145
100
135
35
50
100
100
0.43
28
Time of complete conversion of reactant or stop of reaction
Isolated yield
TON and TOF was obtained 3.34 and 5 h-1, respectively
b
c
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Zirconia-incorporated mesoporous silica
Table 3 Synthesis of
octahydroxanthene-1,8-diones in
the presence of 20Zr-MS at
100 °C under solvent-free
conditions
Entry
a
Aldehyde (1)
Product (3)
Time (min) Yielda (%)
O
H
40
90
O
H
b
65
87
Cl
Cl
O
O
O
Cl
c
30
25
80
87
H
O
Cl
O
d
H
OH
O
O
O
O
H
e
10
92
HO
O
H
f
35
70
85
88
91
85
F
O
H
g
h
NO2
O
H
O2N
OMe
O
O
O
i
j
40
60
60
81
80
84
a
Isolated yields
Reaction conditions: aldehyde
(1 mmol), dimedone (2 mmol),
20Zr-MS (100 mg), substrate:Zr
molar ratio: 0.27, temp.
(100 °C)
k
recycled catalyst after the third run was calcined at 300 °C for 4 h. Then again, the
catalyst was used in the model reaction. Enhancement in the activity after
calcination of recovered catalyst confirms that some of the deactivation is due to
partial blockage of active sites of the catalyst (run 4, Table 4). It should be noted
that at 300 °C the calcination may be incomplete and partial blockage may remain.
To investigate leaching, the model reaction was carried out using fresh catalyst and
123

M. Abdollahi-Alibeik, G. Ahmadi
Table 4 Reusability of 20Zr-
MS in the reaction of
benzaldehyde and dimedone
Run
Time (min)
Yield (%)
1
2
3
4
40
45
50
45
90
80
79
86
Table 5 Comparison of 20Zr-MS with other catalysts for the synthesis of octahydroxanthene-1,8-diones
Entry
Catalyst
Solvent
Condition
Time (min.)
Yield (%)
1
2
3
4
5
6
20Zr-MS
–
90 °C
Ultrasound
40
45
90 [this work]
85 [6]
[Hbim]BF4
–
H3PW12O40/MCM-41
HClO4-SiO2
EtOH
–
90 °C
300
30
94 [7]
140 °C
140 °C
100 °C
32 [8]
PPA-SiO2
Fe3?-montmorillonite
–
30
93 [8]
EtOH
360
94 [9]
after 10 min the reaction was stopped by cooling to r.t. and then the catalyst was
filtered by dilution with EtOH. The solvent was evaporated at low temperature and
the reaction was continued at 100 °C (without catalyst). Slight progress of the
reaction may be due to presence of trace amounts of leached nanoparticles in the
reaction media.
Reactivity of 20Zr-MS was compared with other reported catalysts for the
synthesis of octahydroxanthene-1,8-diones (Table 5). With an overall look at
Table 5, we can say that our method is comparable with other catalytic systems in
terms of yield and reaction time. In addition to this, reusability and absence of
solvent are some obvious benefits with respect to the other mentioned catalysts.
Conclusions
In this work, we reported a modified simple method for the preparation of
Zr-MCM-41 and its application as catalyst for the synthesis of octahydroxanthene-
1,8-diones. The reusability, solvent-free conditions, simple workup, and
non-toxicity of the catalyst are some advantages of the method.
Acknowledgments We are thankful to the Payame Noor University of Ardakan for support of this
work.
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