One-pot cascade reactions catalyzed by acid-base mesoporous MCM-41 materials

Article abstract of DOI:10.1016/j.materresbull.2011.11.055

Acid-base bifunctional mesoporous materials (AB-MCM-41) with aminopropyl and propanesulfonic acid in the same mesoporous material have been synthesized by two different methods: postsynthetic grafting and direct synthesis. AB-MCM-41-g was gained by the modification of SO₃H-MCM-41 surfaces with organic amine functional groups, while AB-MCM-41-co was prepared through co-condensation of trialkoxyorganosilanes with tetraethyl orthosilicate. The bifunctional samples possess hexagonal arrays of uniform pores, large surface area, high pore volume and excellent acid-basic properties. One-pot acid-base cascade reactions were wonderfully achieved in the presence of the efficient acid-base catalysts, which demonstrate the coexistence of acid and base sites in the same material. In addition, the AB-MCM-41-g possesses higher activity for one-pot deacetalization-Knoevenagel and deacetalization-nitroaldol (Henry) reactions in contrast to AB-MCM41-co and this outcome is achieved under simpler synthetic conditions utilizing less time and less material.

Full text of DOI:10.1016/j.materresbull.2011.11.055

Materials Research Bulletin 47 (2012) 801–806
Contents lists available at SciVerse ScienceDirect
Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
One-pot cascade reactions catalyzed by acid–base mesoporous MCM-41 materials
a,
Fanpeng Shang a,b, Jianrui Sun a, Heng Liu a, Chunhua Wang a, Jingqi Guan a, , Qiubin Kan
*
*
a College of Chemistry, Jilin University, Changchun 130023, PR China
b High Middle School attached to Jilin University, PR China
A R T I C L E I N F O
A B S T R A C T
Article history:
Acid–base bifunctional mesoporous materials (AB-MCM-41) with aminopropyl and propanesulfonic acid
in the same mesoporous material have been synthesized by two different methods: postsynthetic
grafting and direct synthesis. AB-MCM-41-g was gained by the modification of SO3H-MCM-41 surfaces
with organic amine functional groups, while AB-MCM-41-co was prepared through co-condensation of
trialkoxyorganosilanes with tetraethyl orthosilicate. The bifunctional samples possess hexagonal arrays
of uniform pores, large surface area, high pore volume and excellent acid–basic properties. One-pot acid–
base cascade reactions were wonderfully achieved in the presence of the efficient acid–base catalysts,
which demonstrate the coexistence of acid and base sites in the same material. In addition, the AB-MCM-
41-g possesses higher activity for one-pot deacetalization–Knoevenagel and deacetalization–nitroaldol
(Henry) reactions in contrast to AB-MCM41-co and this outcome is achieved under simpler synthetic
conditions utilizing less time and less material.
Received 10 March 2011
Received in revised form 11 November 2011
Accepted 22 November 2011
Available online 29 November 2011
Keywords:
B. Chemical synthesis
B. Sol–gel chemistry
C. X-ray diffraction
D. Catalytic properties
ß 2011 Elsevier Ltd. All rights reserved.
1. Introduction
amine and different acid centers (sulfonic acid, phosphoric or
carboxylic acid) [8,9]. These antagonist functions exhibit
a
It is well known that since acids and bases neutralize each other
when brought together. Therefore, one needs to separate acidic
steps from basic ones in reaction sequences. In recent years, some
scientists have solved this problem by incorporating acid and base
functional groups onto solid supports [1–6]. One of the best-known
supports is mesoporous material, which is a structurally well-
ordered material with narrow pore size distribution between 2 and
50 nm, depending on the surfactant and a very high surface area up
to 1500 m2 gÀ1. Since the mesoporosity of these materials may be
easily tuned, many organic reactions may be carried out selectively
and diffusion problems are minimized. In general, functional
groups have been incorporated into mesoporous silica by either
postsynthetic grafting or co-condensation of trialkoxyorganosi-
lanes with tetraethyl orthosilicate. The later approach, also
referred to direct synthesis, has been the preferred route for most
researchers because of the easier single-pot synthetic protocol and
better control of organosilane loading and distribution. There are
several successful preparations of acid–base bifunctional catalysts
through co-condensation method [7–11]. Davis et al. described the
formation of bifunctional mesoporous SBA-15 containing primary
cooperative effect in nitro-aldol condensation. However, those
mesoporous materials were unable to give rise to high activities
due to mutual neutralization of acids with amines in the one-pot
synthetic process. In order to avoid mutual neutralization of
antagonist functions, some researchers reported a method to
synthesize mesoporous catalysts that contain organic amines and
organic acids through protection of amino group [12,13]. Although
the resultant catalysts exhibit excellent acid–basic properties, the
preparation process seems redundant and time-consuming. As an
alternative approach for the design of acid–base bifunctional
catalyst surfaces, Motokura et al. have reported immobilization of
organic amines as bases onto inorganic solid–acid surfaces by post
grafting afforded highly active acid–base bifunctional catalysts,
which enabled various organic transformations including C–C
coupling reactions and also performed one-pot acid–base reactions
[14–17]. Although these types of materials may lack uniform and
controlled porosity, this method is really simple and efficient to
create bifunctional catalysts.
Enlightened by this method, in this paper, acid–base bifunc-
tional AB-MCM-41-g was gained by modification of SO3H-MCM-
41 surfaces with organic amine functional groups. For compari-
son, AB-MCM-41-co was also synthesized through co-condensa-
tion using an amino-protected reagent [13]. Their catalytic
activities for one-pot cascade reactions were comparatively
investigated.
* Corresponding authors at: Jiefang Road 2519, Changchun 130023, PR China.
Tel.: +86 431 88499140; fax: +86 431 88499140.
E-mail addresses: guanjq@jlu.edu.cn (J. Guan), qkan@mail.jlu.edu.cn (Q. Kana).
0025-5408/$ – see front matter ß 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2011.11.055

802
F. Shang et al. / Materials Research Bulletin 47 (2012) 801–806
2. Experimental
2.1. Chemicals and materials
tetraethoxysilane (4.74 ml) and MPTMS (0.37 ml) was added into it
after the solution was stirred for 30 min at 80 8C. The molar
composition of the reaction mixture was 1 TEOS:0.05 MPTMS:0.11
CTAB:0.28 NaOH:527 H2O. The mixture was stirred moderately at
80 8C for 2 h to get SH-MCM-41. After solvent extraction, the thiol
group was oxidized to sulfonic acid by H2O2 in the presence of
methanol at 50 8C for 24 h (2.38 ml of 30% H2O2 in 7.14 ml
methanol for 1 g of thiol-functionalized material). The oxidized
material was suspended in 25 ml of 1 wt% H2SO4 for 4 h, washed
with water, and then dried in vacuo (120 8C, 3 h). The sample was
designated as SO3H-MCM-41. After the sample was dried over
night at 150 8C to remove the physisorbed water, 1 g SO3H-MCM-
41 was stirred vigorously in 80 ml dry toluene containing
0.84 mmol 3-aminopropyltriethoxysilane at 80 8C for 10 h (N/
Si = 0.05). The solution was filtered and the resultant solid was
washed with dichloromethane, followed by ethanol. The solid
material was allowed to dry under ambient conditions, resulting in
a sample named AB-MCM-41-g. For comparison, AB-MCM-41-co
Cetyltrimethylammonium bromide (Aldrich), tetraethyl ortho-
silicate (Aldrich), H2O2 (30%, A.R), ethanol (A.R), 3-aminopropyl-
trimethoxysilane (APTMS) (Aldrich), di-tert-butyl dicarbonate
(Acros), 3-mercaptopropyltrimethoxysilane (MTPMS) (Aldrich),
benzaldehyde dimethylacetal (Alfa), nitromethane (A.R), ethyl
cyanoacetate (Acros), benzene (A.R) were commercially available
and used as received.
2.2. Sample preparation
Preparation of the bifunctionalized catalyst AB-MCM-41-g is
shown in Scheme 1. Typically, 1.0 g (5.5 mmol) cetyltrimethy-
lammonium bromide (CTAB) was mixed with 240 g (13.35 mmol)
of millipore water and 7 ml 1.0 M NaOH solution. The premixed
A
O
O
Si
SH
O
template
Si(OEt)
4
OH
OH
OH
OH
OH
template extraction
HS
Si(OMe)
3
H O
2
50 °C
2
O
O
O
OH
OH
O
O
O
O
OH
OH
OH
OH
OH
Si
Si
SO3H
Si
SO3H
toluene
H N
Si(OEt)
3
2
O
O
NH2
B
Si(OEt)
4
O
O
Si
SH
O
+
O
template
HS
Si(OMe)
O
OH
OH
O
3
template extraction
+
C(CH )
3 3
Si
N
H
O
O
O
C(CH )
3 3
(EtO) Si
N
H
O
3
H O
2
50 °C
2
O
O
O
OH
OH
O
O
Si
SO3H
Si
SO3H
O
O
250 °C , N
4h
2
OH
OH
O
O
O
O
C(CH3)3
Si
O
O
NH2
Si
N
O
H
Scheme 1. Preparations of the bifunctionalized catalysts by grafting (A) or co-condensation (B).

F. Shang et al. / Materials Research Bulletin 47 (2012) 801–806
803
was obtained through co-condensation using an amino-protected
reagent [13]. Pure MCM-41 and NH2-MCM-41 (only use of APTES
as organosilane) were also prepared according to a previous
literature [13].
2.3. Characterization
Powder X-ray diffraction patterns (XRD) were collected using a
Siemens D5005 (0.28/min) with Cu Ka radiation (40 kV, 30 mA).
Transmission electron microscopy (TEM) was performed on a
Hitachi H-8100 electron microscopy, operating at 200 kV. N2
adsorption–desorption isotherms were obtained on a Micromeri-
tics ASAP 2020 system at liquid N2 temperature (À196 8C). Before
measurements, the samples were outgassed at 100 8C for 24 h. The
specific surface area was calculated by using Brunauer–Emmett–
Teller (BET) method and the pore size distributions were measured
by using Barrett–Joyner–Halenda (BJH) method analyzed from the
adsorption curve of the isotherms. N elemental analyses (EA) were
performed on a VarioEL CHN elemental analyzer. A back titration
method was used to measure the amounts of acid–base centers of
the materials according to the modified procedure in a literature
[10,18]. 0.2 g of the sample was added to a conical beaker, and then
20 mL 0.01 M HCl (or 10 mL 0.01 M Li2CO3) solution was added.
The mixture was stirred at room temperature for an hour;
afterwards, the mixture was filtered and rinsed repeatedly for four
times with 25 mL distilled water. The resulting filtrate was titrated
with 0.01 M NaOH (or HCl) solution using phenolphthalein (or
dimethylcarbinol) as an indicator. The solid state 29Si was recorded
on a Varian Unity-400 spectrometer with a 4 mm zirconia rotors
spun at 4 kHz. X-ray photoelectron spectra (XPS) were recorded on
a VG ESCA LAB MK-II X-ray electron spectrometer using AlKa
radiation (1486.6 eV). The measurement error of the spectra was
Æ0.2 eV.
a
b
c
d
0
2
4
6
8
10
2θ / degree
Fig. 1. Powder XRD patterns of the synthesized samples: (a) MCM-41, (b) NH2-
MCM-41, (c) AB-MCM-41-g and (d) AB-MCM-41-co.
(5 ml). The resulting mixture was vigorously stirred at 90 8C
under nitrogen. The products were analyzed with a BEIFEN-3420A
gas chromatograph (GC) equipped with an OV-101 capillary
column and FID detector.
3. Results and discussion
3.1. Characterization of the catalysts
The XRD patterns of the synthesized samples are shown in
Fig. 1. The XRD results are consistent with the literature results
[13,19], indicating that all the prepared materials contain well-
ordered hexagonal arrays of one dimensional channel structure. It
indicates that the immobilization of acid and base sites do not
destroy well-ordered mesoporous structure of MCM-41. Compared
with AB-MCM-41-g, the (1 0 0) peak intensity of AB-MCM-41-co
weakens and the higher order diffraction peaks do not become
well-resolved, indicating the formation of less ordered mesos-
tructure in materials prepared through co-condensation. The
mesostructure ordering and symmetry inferred from the XRD
patterns can also be confirmed by the TEM images (Fig. 2). N2
adsorption–desorption isotherms and pore size distribution of AB-
MCM-41-g and AB-MCM-41-g are shown in Fig. 3. It shows that
both the samples display a type IV isotherm. It is the case of blind
cylindrical, cone-shaped and wedge-shaped pores [20]. The
texture properties are shown in Table 1.
2.4. Catalytic experiments
Typical examples for the tandem reactions of benzaldehyde
dimethylacetal with ethyl cyanoacetate or nitromethane are as
follows.
2.4.1. One-pot deacetalization–Knoevenagel reaction
Into a reaction vessel were placed the catalyst (0.15 g), toluene
(12 ml), benzaldehyde dimethylacetal (4.0 mmol) and ethyl
cyanoacetate (4.0 mmol). The resulting mixture was vigorously
stirred at 80 8C under nitrogen for 1 h. Then the catalysts were
separated by filtration. The products were analyzed with a BEIFEN-
3420A gas chromatograph (GC) equipped with an OV-101 capillary
column and FID detector.
Besides the FTIR study and DTA-TG analysis [21], the XPS
technique is proved to be extremely useful not only to discriminate
between the –SH and –SO3H, whose chemical shifts differ by 5 eV,
but also to quantify the proportion of these species. S2p core-level
spectra of SH-MCM-41 and SO3H-MCM-41 are given in Fig. 4. By
2.4.2. One-pot deacetalization–Henry reaction
Into
a reaction vessel were placed the catalyst (0.05 g),
benzaldehyde dimethylacetal (1.0 mmol) and nitromethane
Fig. 2. TEM images of (a) AB-MCM-41-g and (b) AB-MCM-41-co.

804
F. Shang et al. / Materials Research Bulletin 47 (2012) 801–806
a
b
a
b
0.0
0.2
0.4
0.6
0.8
1.0
0
2
4
6
8
10
ralative pressure (p/p0)
pore distribution / nm
Fig. 3. N2 adsorption–desorption isotherms and pore size distribution of (a) AB-MCM-41-g and (b) AB-MCM-41-co.
Table 1
Texture properities, acid and base amounts of the samples.
Sample
SBET (m2 gÀ1
)
Pore size (nm)
Vt (cm3 gÀ1
)
N content (mmol gÀ1
)
Acid amount (mmol gÀ1
)
Base amount (mmol gÀ1
)
MCM-41
1134
1023
935
3.27
2.47
2.07
2.03
0.91
0.85
0.67
0.64
NH2-MCM-41
AB-MCM-41-g
AB-MCM-41-co
0.66
0.65
0.56
0.60
0.57
0.46
0.44
0.42
957
comparing between the spectra of the samples, it can be found that
only a peak appeared at 163.6 eV due to –SH groups in unoxidized
sample. This peak became weak and a new strong peak at higher BE
(168.6 eV) associated with –SO3H groups was present. This result
reveals that most of the precursor thiol (–SH) groups were oxidized
to the sulfonic acid (–SO3H) groups by H2O2 at 50 8C.
Si(OSi)4 (Q4, Qn = Si(OSi)n(OH)4Àn, n = 1–4) and Si(OH)(OSi)3
structural units, respectively. The resonance peaks from À60 to
À80 ppm can be attributed to Tm(Tm = RSi(OSi)3(OH)3Àm, m = 1–3),
confirming trialkoxysilanes adsorbed generally forming mainly
one single bridge or two bridges on the surface [13].
Quantification of acid and base functional groups loaded in
catalysts was performed for bifunctional materials using elemental
analysis (N) and back titration. The results were listed in Table 1.
Those results confirm the coexistence of the acid and base in the
catalysts, however, the amount of base centers in AB-MCM-41-g is
slightly higher than that in AB-MCM-41-co while the amount of
acid centers remains roughly constant.
Solid-state 29Si MAS NMR spectroscopy has been proven to be
the most useful technique for providing chemical information
regarding the condensation of organosilica. As shown in Fig. 5, the
chemical shifts at À110 and À100 ppm are attributed to the
3.2. Catalytic properties
The acid–basic properties of the catalysts were evaluated in the
acid-catalyzed deprotection of benzaldehyde dimethyl acetal (1)
and nucleophilic amine-catalyzed Knoevenagel reaction of benz-
aldehyde with ethyl cyanoacetate into benzylidene ethyl cyanoa-
cetate (3), and the results were listed in Table 2. Almost complete
hydrolysis of the benzaldehyde dimethylacetal was observed
during the course of 1 h when the reaction was performed with
bifunctional catalysts (entry 1–4), and at the end of the experiment
96.2% or 68.5% of the aldehyde had been converted into
benzylidene ethyl cyanoacetate over AB-MCM-41-g (entry 1) or
AB-MCM-41-co (entry 4). These results illustrate the coexistence
of acidic and basic sites for this one-pot reaction on bifunctional
catalysts and the AB-MCM-41-g showed better catalytic property
than AB-MCM-41-co. To determine whether leaching and/or
deactivation of the catalysts occur, AB-MCM-41-g was reused
three times. It is observed that the material can be recycled with
only slight loss in activity (entry 2 and 3). As control experiments,
S2p
a
b
160
165
170
175
Binding Energy (eV)
Fig. 5. 29Si MAS NMR spectra of AB-MCM-41-g.
Fig. 4. S 2p core-level spectra of samples of (a) SH-MCM-41 and (b) SO3H-MCM-41.

F. Shang et al. / Materials Research Bulletin 47 (2012) 801–806
805
Table 2
One-pot deacetalization–Knoevenagel reaction over different catalysts.
CN
CO2Et
O
base catalyst
OMe
OMe
acid catalyst
H2O
H
NC
CO2Et
2
3
1
Entry
Catalyst
Conv. of 1 (%)
Yield of 2 (%)
Yield of 3 (%)
Selectivity to 3 (%)
1
2
3
4
5
6
7
AB-MCM-41-g1st
AB-MCM-41-g2nd
AB-MCM-41-g3rd
AB-MCM-41-co
MCM-41
ꢀ100
ꢀ100
95.5
3.8
96.2
92.8
88.3
68.5
Trace
0
96.2
92.8
92.4
71.4
7.2
7.2
95.9
27.4
Trace
50.6
Trace
Trace
50.6
HSO3-MCM-41
NH2-MCM-41
0
Trace
Trace
Reaction conditions: 1 (4 mmol), ethyl cyanoacetate (4 mmol), catalyst (0.15 g), toluene (12 ml), 1 h, 80 8C.
Table 3
One-pot deacetalization–Henry reaction over different catalysts.
NO2
O
base catalyst
CH3NO2
OMe
OMe
acid catalyst
H2O
H
4
2
Entry
Catalyst
Reaction time (h)
Conv. of 1 (%)
Yield of 2 (%)
Yield of 4 (%)
Selectivity to 4 (%)
1
2
3
4
5
6
7
8
HSO3-MCM-41
1.5
1.5
1.5
1.5
5
61.6
59.7
Trace
1.1
1.9
3.2
NH2-MCM-41
Trace
ꢀ100
57.4
Trace
98.9
31.2
69.9
94.5
Trace
2.5
AB-MCM-41-g
98.9
54.3
69.9
94.5
AB-MCM-41-co
26.2
30.1
5.5
AB-MCM-41-co
ꢀ100
ꢀ100
Trace
49.6
AB-MCM-41-co
7
AB-MCM-41-g + ethylamine
AB-MCM-41-g + sulfonic acid
1.5
1.5
Trace
47.1
5.04
Reaction conditions: 1 (1 mmol), nitromethane (5 ml), catalyst (0.05 g), 90 8C.
reactions were also performed with pure MCM-41, with mono-
functional HSO3-MCM-41 and with NH2-MCM-41(entry 5–7). Only
a negligible formation (<1%) of 3 was formed over NH2-MCM-41
and MCM-41. The production of the intermediate benzaldehyde
was achieved only in 50.6% yield when HSO3-MCM-41 was applied
alone, since the missing second aldol condensation step did not
provide the necessary amount of water needed for complete
hydrolysis. Thus the pure MCM-41 and monofunctional catalyst on
its own cannot perform the one-pot cascade reaction. The one-pot
reaction system did not need the addition of water probably due to
the presence of adsorbed water in the internal pore channels of
materials and/or the successive aldol reaction produced water to
efficiently accelerate the deprotection of 1.
Similar results (Table 3) were got when we used the acid–base
bifunctional materials to catalyze Deacetalization–nitroaldol
(Henry) reaction, which also involve two separate steps: an
acid-catalyzed deprotection to give the intermediate benzalde-
hyde (2) and the subsequent base-catalyzed nitroaldol (Henry)
reaction to yield 2-nitrovinyl benzene (4). This One-pot reaction
sequence has been employed to evaluate the acid–base bifunctio-
nalized catalyst MSN-NH2-SO3H by Thiel et al. [9], and it afforded 4
in 37.4% yield after 5 h. Remarkably, under the same reaction
conditions, AB-MCM-41-g converts 1 to 4 in high yields of 98.9%
after 1.5 h (entry 1). Although AB-MCM-41-co shows lower
activities for this reaction in comparison with AB-MCM-41-g,
and gives 94.5% yield of 4 after 7 h, which is also comparable to the
previous reports [9,10]. Addition of equivalent amounts of
structurally similar free acid (p-toluenesulfonic acid) or base
(ethylamine) to bifunctionalized catalysts cannot catalyze the
tandem reaction sufficiently, as these homogeneous species diffuse
into the pore channels and destroy the catalytic sites by formation
of ion pairs (entry 7 and entry 8).
Of particular interest is the comparison of the catalytic
efficiency for one-pot deacetalization–Knoevenagel and deaceta-
lization–nitroaldol (Henry) reactions performed in the presence of
the two bifunctional catalysts under the same experimental
conditions (entry 1 vs 4 in Table 2, entry 3 vs 4 in Table 3).
Obviously, the AB-MCM-41-g materials possess higher catalytic
activity for the two one-pot tandem reactions in contrast to AB-
MCM41-co. One can speculate that the higher catalytic activity of
AB-MCM-41-g might be due to the fact that the higher amount of
acid and base sites on this catalyst, as shown in Table 1. Although
this factor causes some differences in catalytic efficiency, it alone
could not explain the significant difference in catalytic efficiency
between the two samples. As a possible explanation of the
dramatic difference in reaction rate, we propose that in the grafting
procedure, the aminopropyl groups are linked onto the surface of
the material and the majority of them are easily reachable; on the
contrary, in the materials prepared by co-condensation method,
the propylamine are incorporated within the siliceous framework.
As a result, it is difficult for reagents to reach the active sites and
thus it leads to a relatively low reaction rate.

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F. Shang et al. / Materials Research Bulletin 47 (2012) 801–806
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Acknowledgments
This work was supported by Jilin province (20090591 and
201105006), Jilin University (450060445017), Specialized Re-
search Fund for the Doctoral Program of Higher Education
(20100061120083).
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