One-pot synthesis of magnetically recyclable mesoporous silica supported acid-base catalysts for tandem reactions

Article abstract of DOI:10.1039/c3cc43568g

We report one-pot synthesis of magnetically recyclable mesoporous silica catalysts for tandem acid-base reactions. The catalysts could be easily recovered from the reaction mixture using a magnet, and the pore size of the catalysts could be controlled by introducing a swelling agent, resulting in the significant enhancement of the reaction rate.

Full text of DOI:10.1039/c3cc43568g

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One-pot synthesis of magnetically recyclable
mesoporous silica supported acid–base catalysts for
Cite this: DOI: 10.1039/c3cc43568g
tandem reactions†
Received 13th May 2013,
Accepted 26th June 2013
ab
ab
Samuel Woojoo Jun,z Mohammadreza Shokouhimehr,z Dong Jun Lee,ab
Youngjin Jang,ab Jinkyung Parkab and Taeghwan Hyeon*ab
DOI: 10.1039/c3cc43568g
www.rsc.org/chemcomm
We report one-pot synthesis of magnetically recyclable mesoporous immobilization of acidic and basic catalytic species,10 and many
silica catalysts for tandem acid–base reactions. The catalysts could be research groups have tried to improve the catalytic performance by
easily recovered from the reaction mixture using a magnet, and the controlling the morphology11 and structure of the catalysts.12
pore size of the catalysts could be controlled by introducing a Herein, we report a facile one-pot synthesis of a magnetically
swelling agent, resulting in the significant enhancement of the recyclable mesoporous silica catalyst for acid–base tandem reactions.
reaction rate.
We also present results of the effect of pore size on the catalytic
activity of the mesoporous materials.
Magnetic mesoporous nanocomposite materials have attracted
We synthesized magnetic mesoporous silica nanocomposite
tremendous scientific and technological interest because magnetic materials by combining the Massart method13 for magnetite
characteristics can be incorporated into mesoporous structures with nanoparticles and the previously reported synthetic procedure
large pore volume, high surface area, and easy functionalization for mesoporous acid–base catalysts (the detailed synthetic
capability.1 Such nanocomposite materials have been extensively procedures are described in the ESI†).14 First, iron(II) chloride
applied in various biomedical areas,2 including separation of tetrahydrate, iron(III) chloride hexahydrate, and cetyltrimethyl-
biomolecules,3 magnetically guided targeted delivery,4 and ammonium bromide (CTAB) were dissolved in distilled water.
theragnostics.5 Magnetic mesoporous nanocomposite materials This solution was stirred for 5 min at 70 1C, and 2 M aqueous
immobilized with catalytic species have also been extensively sodium hydroxide was rapidly added. The color of the solution
investigated as magnetically recyclable catalysts for organic immediately changed from light yellow to black, indicating the
reactions.6 General synthesis of the magnetic mesoporous formation of the magnetite nanoparticles upon reaction with
materials requires extra work to synthesize and purify the hydroxide ions. Without any purification or drying, tetraethyl
uniform sized magnetic nanoparticles beforehand. Otherwise, orthosilicate (TEOS) and a swelling agent, mesitylene, were
the method involves a high temperature process or strong slowly added to the resulting solution, followed by addition
chemical environments to form magnetic species on the surface of ethyl acetate. Subsequently, 2-(4-chlorosulfonylphenyl)ethyl-
of the mesoporous materials. Despite their many potential trimethoxysilane (CESE) dissolved in dichloromethane and
applications, one-step synthesis of the magnetic mesoporous [3-(2-aminoethylamino)propyl]trimethoxysilane (AAPS) were added
functional materials has been rarely proposed.7
with vigorous stirring, and the resulting mixture was aged for 6 h
Acid–base site-isolated catalysts, which were inspired by at 70 1C. Because of the presence of residual hydroxide ions after
enzymes that can effectively perform multistep catalytic reactions the magnetite synthesis, addition of extra aqueous sodium hydrox-
through cooperative interactions of isolated catalytically active ide was not necessary to accelerate the condensation of the silanol
sites, have been intensively investigated as single-site hetero- groups. The powdery product was retrieved by centrifugation,
geneous catalysts.8 Several silica nanostructured materials have and was further treated with a mixture of hydrochloric acid and
been employed as heterogeneous supports9 for the site-isolated ethanol to remove CTAB and to activate the sulfonic acid groups,
thereby producing the final magnetic mesoporous silica nano-
a Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul 151-742,
composite with immobilized acidic (sulfonic acid) and basic
(diamine) groups.
Republic of Korea
b School of Chemical and Biological Engineering, Seoul National University,
Seoul 151-742, Republic of Korea. E-mail: thyeon@snu.ac.kr; Fax: +82-2-886-8457;
Tel: +82-2-880-7150
Transmission electron microscope (TEM) images of the
synthesized nanocomposite materials revealed that B9 nm Fe3O4
nanoparticles were enveloped by mesoporous silica shells (Fig. 1).
The average pore size and surface area were found to be 5.4 nm and
327 m2 gꢀ1, respectively, and the material is designated as MMAB
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c3cc43568g
‡ These two authors contributed equally to this work.
c
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Scheme 1 Conversion of benzaldehyde dimethyl acetal (1) to 1-nitro-2-phenyl-
ethyelene (3) by MMAB catalysis. Benzaldehyde (2) is the intermediate of the
tandem reaction.
Table 1 Catalytic deacetalization and Henry reaction using various magnetic
Fig. 1 TEM images of the magnetic mesoporous acid–base catalyst prepared
mesoporous materialsa
(a) without a swelling agent and (b) with a swelling agent.
Entry
Catalyst
Reactant
Product
Yield (%)
1
2
3
4
5
MMAB
N/A
MMB
MMB
MMA
1
1
1
2
1
2 and 3
2 (2)/96 (3)
—
—
3
—
—
98
93
2
a
Reaction conditions: benzaldehyde dimethyl acetal (1 mmol), nitro-
methane (5 mL), catalyst (30 mg), 90 1C, 5 h.
The catalyst showed excellent performance with very high yield and
selectivity (entry 1), and as expected, the reaction did not proceed
without the catalyst (entry 2). Comparative catalytic reactions were
conducted to demonstrate the importance of both the acidic and
basic functional groups. When a magnetic mesoporous silica
catalyst with only basic groups (MMB) was used, the reaction
did not proceed owing to the absence of the acid catalyzed
deacetalization reaction that converts benzaldehyde dimethyl acetal
to benzaldehyde (entry 3). However, when benzaldehyde was used
as a starting material, 1-nitro-2-phenylethylene was produced nearly
quantitatively (entry 4). Meanwhile, the catalyst derivatized only
with acidic groups (MMA) did transform benzaldehyde dimethyl
acetal to benzaldehyde, but could not catalyze the final reaction to
Fig. 2 The N2 adsorption–desorption isotherms and the corresponding pore
size distributions of the catalysts with large pore size (MMAB) and small pore size
(MMAB-SP).
(Fig. 2). When we performed the synthesis without using the form 1-nitro-2-phenylethylene (entry 5).
swelling agent (mesitylene), mesoporous material with a pore
Lifetime and recyclability of a catalyst are very important for
size of 2.4 nm and a surface area of 285 m2 gꢀ1 was generated large-scale industrial applications. The MMAB catalyst showed
(designated as MMAB-SP). The X-ray diffraction (XRD) pattern excellent recyclability, maintaining high activity for up to five
revealed that the embedded iron oxide nanoparticles were runs (Table 2). In addition, MMAB could be easily recovered
magnetite, Fe3O4 (Fig. S1, ESI†). The synthesized nanocomposite using a magnet after each reaction, and could be reused for
showed superparamagnetic characteristics with a high saturation subsequent reactions without regeneration or further addition
magnetization of 78 emu gꢀ1 of Fe at 300 K (Fig. S2 and S3, ESI†). of a catalyst.
This superparamagnetic property is advantageous for the efficient
Next, we compared the catalytic activities of mesoporous
recycling of catalysts because the residual magnetic moment in silica catalysts with different pore sizes. We ran the catalytic
ferromagnetic materials prevents rapid redispersion.15 For the reactions with the 5.4 nm MMAB and 2.4 nm MMAB-SP under
catalyst characterization, we performed Fourier-transform infra- identical reaction conditions, and aliquots were drawn from the
red spectroscopy (FT-IR) and X-ray photoelectron spectroscopy reaction mixtures at 15 min intervals. The yield of product 3 in
(XPS) analysis of MMAB (Fig. S4 and S5, ESI†), and we confirmed each sample was measured and the results are shown in Fig. 3.
that the amine and sulfonic acid moieties were properly loaded on
With MMAB, the reaction was completed within 4.5 h, while
the magnetic mesoporous material. Furthermore, we confirmed the reaction with MMAB-SP took more than 7 h for the
that both acid and base functions were properly working in the
catalysts by monitoring NH3 and CO2 temperature programmed
Table 2 Magnetic separation and recycling results for the MMAB catalyst in the
tandem reaction of 1 to yield 3a
desorption (NH3-TPD, CO2-TPD) profiles (Fig. S6 and S7, ESI†).
To examine the catalytic activity of MMAB, we performed a
one-pot tandem reaction that converts benzaldehyde dimethyl
acetal (1) to benzaldehyde (2) via acid-catalyzed deacetalization,
followed by conversion of 2 to 1-nitro-2-phenylethylene (3)
via the base-catalyzed Henry reaction (Scheme 1 and Table 1).
Cycle
1st
95
2nd
94
3rd
93
4th
91
5th
91
Yield (%)
a
Reaction conditions: benzaldehyde dimethyl acetal (1 mmol), nitro-
methane (5 mL), MMAB nanocatalyst (30 mg), 90 1C, 5 h.
c
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Notes and references
1 (a) J. Liu, S. Z. Qiao, Q. H. Hu and G. Q. M. Lu, Small, 2011, 7, 425; (b) A.-H.
Lu, E. L. Salabas and F. Schu¨th, Angew. Chem., Int. ed., 2007, 46, 1222.
2 (a) K. M. L. Taylor-Pashow, J. D. Rocca, R. C. Huxford and W. Lin,
Chem. Commun., 2010, 46, 5832; (b) J. Liu, S. Z. Qiao, J. S. Chen,
X. W. Lou, X. Xing and G. Q. Lu, Chem. Commun., 2011, 47, 12578.
3 (a) T. Sen, A. Sebastianelli and I. J. Bruce, J. Am. Chem. Soc., 2006,
128, 7130; (b) Y. Deng, D. Qi, C. Deng, X. Zhang and D. Zhao, J. Am.
Chem. Soc., 2008, 130, 28.
4 (a) J. Kim, H. S. Kim, N. Lee, T. Kim, H. Kim, T. Yu, I. C. Song,
W. K. Moon and T. Hyeon, Angew. Chem., Int. ed., 2008, 47, 8438;
(b) W. Zhao, J. Gu, L. Zhang, H. Chen and J. Shi, J. Am. Chem. Soc.,
2005, 127, 8916; (c) W. Zhao, H. Chen, Y. Li, L. Li, M. Lang and J. Shi,
Adv. Funct. Mater., 2008, 18, 2780.
5 (a) M. W. Ambrogio, C. R. Thomas, Y.-L. Zhao, J. I. Zink and
J. F. Stoddart, Acc. Chem. Res., 2011, 44, 903; (b) J. E. Lee, N. Lee,
T. Kim, J. Kim and T. Hyeon, Acc. Chem. Res., 2011, 44, 893;
(c) S. Giri, B. G. Trewyn, M. P. Stellmaker and V. S.-Y. Lin, Angew.
Chem., Int. ed., 2005, 44, 5038; (d) J. E. Lee, N. Lee, H. Kim, J. Kim,
S. H. Choi, J. H. Kim, T. Kim, I. C. Song, S. P. Park, W. K. Moon and
T. Hyeon, J. Am. Chem. Soc., 2010, 132, 552.
Fig. 3 Time-dependent product yield of the tandem deacetalization–Henry reaction
using MMAB and MMAB-SP catalysts. Reaction conditions: benzaldehyde
dimethyl acetal (1 mmol), nitromethane (5 mL), MMAB (30 mg) or MMAB-SP
(30 mg), 90 1C, 5 h.
¨
6 (a) A.-H. Lu, W. Schmidt, N. Matoussevitch, H. Bonnemann,
B. Spliethoff, B. Tesche, E. Bill, W. Kiefer and F. Schu¨th, Angew.
Chem., Int. Ed., 2004, 116, 4403; (b) M. Shokouhimehr, Y. Piao,
J. Kim, Y. Jang and T. Hyeon, Angew. Chem., Int. ed., 2007, 46, 7039.
7 L. Han, H. Wei, B. Tu and D. Zhao, Chem. Commun., 2011, 47, 8536.
8 (a) J. M. Thomas, R. Raja and D. W. Lewis, Angew. Chem., Int. ed.,
2005, 44, 6456; (b) F. Gelman, J. Blum and D. Avnir, Angew. Chem.,
Int. Ed., 2001, 40, 3647.
completion. This dramatic increase in the reaction rate for the
larger pore-sized silica materials can be explained by internal
pore diffusion.16,17 Internal pore diffusivity, which is a function of
Knudsen diffusivity, is known to increase as pore sizes increase for
diffusion-controlled reactions.16 Because we synthesized MMAB
and MMAB-SP using nearly identical procedures with a similar
loading of the catalytic functional groups (Table S1, ESI†), the
different catalytic activity can be explained solely by the difference
in pore size.
9 (a) B. Kesanli and W. Lin, Chem. Commun., 2004, 2284; (b) C. Perego
and R. Millini, Chem. Soc. Rev., 2013, 42, 3956.
10 (a) E. L. Margelefsky, R. K. Zeidan and M. E. Davis, Chem. Soc. Rev.,
2008, 37, 1118; (b) N. R. Shiju, A. H. Alberts, S. Khalid, D. R. Brown
and G. Rothenberg, Angew. Chem., Int. Ed., 2011, 50, 9615.
11 (a) L. Zhang, Y. Guo, J. Peng, X. Liu, P. Yuan, Q. Yang and C. Li,
Chem. Commun., 2011, 47, 4087; (b) Y. Li, H. Xia, F. Fan, Z. Feng,
R. a. van Santen, E. J. M. Hensen and C. Li, Chem. Commun., 2008,
774; (c) Y. Yang, X. Liu, X. Li, J. Zhao, S. Bai, J. Liu and Q. Yang,
Angew. Chem., Int. ed., 2012, 51, 9164.
In conclusion, we have successfully synthesized a magnetically
separable mesoporous site-isolated acid–base catalyst using a one-
pot reaction. The catalyst showed excellent performance with very
high yield and selectivity for the conversion of benzaldehyde
dimethyl acetal to 1-nitro-2-phenylethylene via benzaldehyde
using tandem acid-catalyzed deacetalization and base-catalyzed
Henry reaction. The catalyst could be easily recovered by using a
magnet and dispersed in subsequent reaction mixtures, enabling
recycling of the catalyst for up to five uses without losing catalytic
activity. Furthermore, comparative studies revealed that the
larger-pore-sized materials exhibited higher catalytic activity
than the smaller-pore-sized materials. We believe that the
current synthetic approach for this magnetic mesoporous
acid–base site-isolated catalyst will contribute to the practical
applications of tandem catalysts.
12 (a) K. K. Sharma, A. Anan, R. P. Buckley, W. Ouellette and T. Asefa,
J. Am. Chem. Soc., 2008, 130, 218; (b) J. D. Bass, A. Solovyov,
A. J. Pascall and A. Katz, J. Am. Chem. Soc., 2006, 128, 3737;
(c) K. Motokura, N. Fujita, K. Mori, T. Mizugaki, K. Ebitani and
K. Kaneda, J. Am. Chem. Soc., 2005, 127, 9674; (d) F. Shang, J. Sun,
S. Wu, H. Liu, J. Guan and Q. Kan, J. Colloid Interface Sci., 2011,
355, 190.
13 R. Massart, IEEE Trans. Magn., 1981, 17, 1247.
14 (a) R. Zeidan, V. Dufaud and M. Davis, J. Catal., 2006, 239, 299;
(b) S. Shylesh, A. Wagner, A. Seifert, S. Ernst and W. R. Thiel,
Chem.–Eur. J., 2009, 15, 7052.
15 C. T. Yavuz, J. T. Mayo, W. W. Yu, A. Prakash, J. C. Falkner, S. Yean,
L. Cong, H. J. Shipley, A. Kan, M. Tomson, D. Natelson and
V. L. Colvin, Science, 2006, 314, 964.
16 (a) M. Shimura, Y. Shiroto and C. Takeuchi, Ind. Eng. Chem.
Fundam., 1986, 25, 330; (b) H. Takahashi, B. Li, T. Sasaki,
C. Miyazaki, T. Kajino and S. Inagaki, Chem. Mater., 2000,
12, 3301; (c) M. Iwamoto, Y. Tanaka, N. Sawamura and S. Namba,
J. Am. Chem. Soc., 2003, 125, 13032.
17 (a) J. T. Richardson, Principles of Catalyst Development, Plenum
Press, New York, 1989; (b) H. S. Fogler, Elements of Chemical Reaction
Engineering, Prentice-Hall, New Jersey, 3rd edn, 1999.
We acknowledge financial support from the Research Center
Program of Institute for Basic Science (IBS) in Korea.
c
This journal is The Royal Society of Chemistry 2013
Chem. Commun.