Amine functionalized K10 montmorillonite: A solid acid-base catalyst for the Knoevenagel condensation reaction

Article abstract of DOI:10.1039/c3dt32495h

Different amine functionalized K10 montmorillonites were hydrothermally fabricated by a simple method of treatment of the neat clay with different amine solutions and used as heterogeneous catalysts towards the Knoevenagel condensation reaction. Catalytic results show that the di-amine functionalized K10 montmorillonite exhibits high efficacy for promoting this reaction at room temperature and in the absence of a solvent. The solid catalyst was characterized using a variety of different techniques; including Fourier transform infrared spectroscopy (FT-IR), nitrogen physisorption measurements, ²⁹Si CP MAS NMR spectroscopy, NH₃-temperature programmed desorption (NH₃-TPD), X-ray powder diffraction (XRD), and field emission scanning electron microscopy (FESEM). The catalyst could be recycled and reused for several runs without any loss of inherent catalytic activity.

Full text of DOI:10.1039/c3dt32495h

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Amine functionalized K10 montmorillonite: a solid
acid–base catalyst for the Knoevenagel condensation
reaction
Cite this: Dalton Trans., 2013, 42, 5122
G. Bishwa Bidita Varadwaj, Surjyakanta Rana and K. M. Parida*
Different amine functionalized K10 montmorillonites were hydrothermally fabricated by a simple
method of treatment of the neat clay with different amine solutions and used as heterogeneous catalysts
towards the Knoevenagel condensation reaction. Catalytic results show that the di-amine functionalized
K10 montmorillonite exhibits high efficacy for promoting this reaction at room temperature and in the
absence of a solvent. The solid catalyst was characterized using a variety of different techniques; includ-
Received 19th October 2012,
Accepted 14th January 2013
29
ing Fourier transform infrared spectroscopy (FT-IR), nitrogen physisorption measurements, Si CP MAS
3 3
NMR spectroscopy, NH -temperature programmed desorption (NH -TPD), X-ray powder diffraction (XRD),
DOI: 10.1039/c3dt32495h
and field emission scanning electron microscopy (FESEM). The catalyst could be recycled and reused for
www.rsc.org/dalton
several runs without any loss of inherent catalytic activity.
condense with compounds containing active methylene
groups, which is usually catalyzed by weak bases like primary,
1. Introduction
Montmorillonite is a ubiquitous, inexpensive and eco-friendly secondary, tertiary amines and ammonium salts under homo-
1
,2
12,13
support, preferred in heterogeneous catalysis.
Therefore, geneous conditions.
Other Lewis acids have also been
substantial efforts in research have been made on modified reported as catalysts in the Knoevenagel condensation, includ-
1
4–16
montmorillonites by our group, like pillaring with metal ing ZnCl , Al O and KF–Al O , etc.
2
2
3
2 3
oxides by different techniques, complex immobilization and
K10 montmorillonite is known to behave as an acid catalyst
3
–9
surface modification with heteropoly acids, etc.
Since in organic reactions. Therefore, we thought to employ a new
surface functionalization on inorganic supports with many type of solid acid–base catalyst, where the base is covalently
organic moieties provides organo-inorganic hybrids, where the grafted onto a solid acidic support towards the desired reac-
inorganic and organic components are linked via strong-type tion. Hence, we did mono and di-amine functionalization on
interactions (i.e. covalent or iono-covalent bonds), we now K10 montmorillonite and compared their activities towards
directed our study to the surface functionalization of clays to the Knoevenagel condensation reaction. In our early reports,
fabricate some stable catalysts. This approach enables robust we carried out the reaction in the absence of a solvent using
1
7,18
immobilization of the reactive organic groups by strong amine functionalized zirconia and MCM-41.
However, we
binding on the clay surfaces, preventing therefore their leach- are getting better results using the present system for a shorter
ing in the surrounding medium when used in solutions. Con- period of time. This may be due to the interlayer acid sites pro-
sequently, these materials can act as active heterogeneous moting the base catalyzed reactions in amine functionalized
1
9
liquid-phase catalysts without further alteration and also give acidified montmorillonite as reported by Motokura et al.
access to a large variety of potential catalysts by successive They varied various solvents and found n-heptane as the best
chemical derivatization. solvent for the functionalization. However, taking water as the
Knoevenagel condensation is one of the most useful and solvent they observed a high amine loading on acid activated
widely employed methods for carbon–carbon bond formation montmorillonite. Therefore, water can be taken as a green
with numerous applications in the synthesis of fine chemi- alternative solvent for the functionalization of amines on acid
1
0,11
cals.
In Knoevenagel condensation, the aldehydes activated montmorillonite. Hence in this work, we have
chosen a water medium to prepare amine functionalized
K10 montmorillonite.
The objective of the present work is to explore the possi-
bility of utilizing K10 montmorillonite as an inexpensive raw
material for the preparation of organo-inorganic hybrids by
C&MC Department, Institute of Minerals & Materials, Technology, Bhubaneswar-
51013, Orissa, India. E-mail: paridakulamani@yahoo.com;
Fax: +91 674 2581637; Tel: +91 674 2581636 (Extn.9425)
7
5
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grafting them with amino propyl triethoxysilane (APTES) and temperature, NH
3
(20% NH
3
balanced with helium) gas was
N-(2-amino ethyl)-3-amino propyl trimethoxysilane (AAPTMS), passed over the sample while it was heated at a rate of 10 °C
−1
and to evaluate the resulting materials towards the Knoevena- min and the profile was recorded. The low and broad angle
gel condensation reaction. The di-amine functionalized cata- XRD patterns of powdered samples were taken in the 2θ range of
lyst is found to be robust enough to achieve high catalytic 5–80° at a rate of 2° min− in steps of 0.01° (Rigaku Miniflex set
activity toward the Knoevenagel condensation reaction at room at 30 kV and 15 mA) using Cu Kα radiation. The FTIR spectra of
temperature and also under solvent free conditions in 12 h; i.e. the samples were recorded using a Varian 800-FTIR spectrophoto-
1
−1
beneficial for industry as well as environment, particularly meter in a KBr matrix in the range of 4000–400 cm . The
29
from the viewpoint of green chemistry.
FE-SEM was performed with a ZEISS 55 microscope. Si CP MAS
spectra were recorded at 79.49 MHz applying 90° pulses, 300 s
pulse delays and 5.0 ms contact time. Both the spectra were
obtained by using a Bruker Avance 400 MHz spectrometer.
2. Experimental
2
.1 Preparation of the catalyst
2.3 Catalytic reaction
1
3
g K10 montmorillonite was added to 15 ml of a solution of The Knoevenagel condensation between benzaldehyde and
-amino propyl triethoxysilane (2.32 mmol) using water as a diethyl malonate using the amine functionalized
solvent and stirred at room temperature for 2 h. The sus- K10 montmorillonite samples was carried out in a magnetically
pended solution was transferred into a teflon bottle and hydro- stirred round-bottom flask. About 10 mmol of benzaldehyde
thermally aged at 100 °C for another 10 h. The solid products (1.01 ml), 10 mmol of diethyl malonate (1.51 ml) and 0.05 g of
were filtered; three times washed with deionized water and catalyst were taken in the reactor and were stirred at room temp-
dried subsequently in a vacuum at 80 °C for 8 h. It is named erature. After 12 h of the reaction, 50 ml of methanol was added
as APTES@K10. AAPTMS@K10 is also prepared using the in order to solubilize all the organic compounds and again
same procedure, taking N-(2-amino ethyl)-3-amino propyl tri- stirred for 10 min. The catalyst was recovered by centrifugation
methoxysilane as the amine source as shown in Scheme 1.
for reuse and the reaction mixture was analyzed off-line on a
Shimadzu gas chromatograph (GC-2010).
2
.2 Characterization techniques
The BET surface area, average pore diameter, mesopore distri-
bution, total pore volume of all the samples were determined
by a multipoint N adsorption–desorption method at liquid N
2 2
3
. Results and discussion
3
.1 Characterization
.1.1 Elemental analysis. The results of nitrogen elemental
analysis of the prepared materials suggest that it was loaded
temperature (−196 °C) using an ASAP 2020 (Micromeritics)
3
surface area analyser. Prior to analyses, all the samples were
−
6
onto the clay at 0.92 mmol g− and 1.84 mmol g for APTES
and AAPTMS respectively. These amines may be present as
non-linked amines or covalently grafted amines on the surface
of montmorillonite. The covalent grafting of amines can be
confirmed from various studies given below.
1
−1
degassed at 300 °C and 10 Torr pressure for 5 h to evacuate
the physically adsorbed moisture. The acid character of the
3
samples was studied by an NH -TPD Auto Chem-II chemisorp-
tion analyzer (Micromeritics) equipped with a thermal conduc-
tivity detector (TCD). About 1 g of the powdered sample
contained in a quartz “U” tube was degassed at 250 °C for 1 h
with ultra-pure nitrogen gas. After cooling the sample to room
3.1.2 FTIR. The FTIR spectra of K10 montmorillonite,
APTES@K10 and AAPTMS@K10 are presented in Fig. 1. The
Scheme 1 Mechanism
of
di-amine
immobilization
on
the
Fig. 1 FTIR spectra of K10 montmorillonite (a), APTES@K10 (b), and
K10 montmorillonite surface.
AAPTMS@K10 (c).
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2
9
Fig. 3
Si CP MAS NMR spectrum of AAPTMS@K10.
supported by the appearance of silicon peaks associated with
3
2
the silanes in the so-called T region. The presence of T and T
peaks confirmed the existence of the covalent linkage between
the organic silane moieties of the amine group and the silicate
3
layers of the clay. The high intensity of the T peak reveals the
high degree of condensation of the diamine moiety with the
clay surface. This confirms the successful covalent attachment
of AAPTMS on the surface of the clay.
2
3.1.4 Nitrogen physisorption studies. N adsorption–deso-
rption is a common method to characterize porous materials,
which can provide information about the specific surface area,
average pore diameter and pore volume, etc. N adsorption–
2
desorption isotherms of K10 montmorillonite, APTES@K10
and AAPTMS@K10 samples are shown in Fig. 4. According to
the BDDT classification, all the samples are of type IV with a
typical hysteresis loop, featuring mesoporous materials with
2
1
highly uniform pore size distribution.
BET surface area, pore size and pore volume for different
Fig. 2 (A) Enlarged view of the FTIR spectra of K10 montmorillonite (a), materials are presented in Table 1. The BET surface areas for
1
2
−1
APTES@K10 (b), and AAPTMS@K10 (c) showing NH
2
vibrations at 1536 cm−
.
the APTES@K10 and AAPTMS@K10 samples are 153.15 m g
(
(
B) Enlarged view of the FTIR spectra of K10 montmorillonite (a), APTES@K10
2
−1
and 140.89 m
g
respectively, with corresponding pore
b), and AAPTMS@K10 (c) showing NH
2
vibrations at 690 cm−
1
.
3
−1
volumes 0.30 and 0.29 cm g respectively. While a decrease
in the surface area and pore volume was observed, we also
observed an increase in pore diameter in the case of
APTES@K10 (7.9 nm) and AAPTMS@K10 (8.6 nm) than the
FTIR spectrum of the entire sample shows bands at 3416 and
1
1
636 cm− for –OH stretching and bending vibrations respect-
ively. The –CH stretching and –CH bending vibrations from
2
2
grafted APTES and AAPTMS can be seen in the range
−
1
20
2
970–2845 and 1470–1415 cm respectively. The presence of
−
1
N–H bending vibration at around 690 cm and of NH sym-
metric bending vibration at 1536 cm
2
−1
(Fig. 2A and 2B)
suggests the presence of the organosilanes on the clay surface.
2
9
29
3
.1.3
Si CP MAS NMR spectroscopy. The Si CP MAS
NMR spectrum (Fig. 3) provides important information about
the degree of functionalization and the coordination environ-
ments of the amine moiety with the clay surface. From the
solid state NMR spectra, three resonance peaks up-field corre-
4
3
sponding to Q (δ = −112 ppm), Q (δ = −101 ppm), and
2
Q (δ = −94 ppm), and two peaks down-field corresponding to
T (δ = −68 ppm) and T (δ = −61 ppm), where Q = Si(OSi) −
OH)4−n, n = 2–4 and T = RSi(OSi) − (OH)3−m, m = 1–3 can
be observed. The Q , Q and Q peaks are the characteristic
3
2
n
n
m
(
m
2
3
4
peaks of the silicate layers present in the clay. The grafting of
Fig. 4
2
N ads–des isotherms of K10 montmorillonite (a), APTES@K10 (b), and
silane molecules onto the silicate layer of the clay is also AAPTMS@K10 (c).
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Table 1 Textural data of various samples
Surface
Pore
volume
Pore
Total
area
diameter acidity
2
3
(mmol g−1)
Catalyst
(m g−1) (cm g−1) (nm)
K10 montmorillonite 242.21
0.41
0.30
0.29
6.5
7.9
8.6
4.3
2.9
2.5
APTES@K10
153.15
140.89
AAPTMS@K10
parent K10 montmorillonite (6.7 nm). A considerable decrease
in the BET surface area, and pore volume than the parent
K10 montmorillonite suggests the possibility that the organic
moieties might have been anchored on the inner surface of
the mesopores.
3
.1.5 NH -TPD. Ammonia TPD is a commonly used
3
method to determine the total acidity of solids, though this
method lacks selectivity because ammonia can titrate acid
sites of any strength and type. The amount of ammonia des-
orbed at some characteristic temperatures is taken as a
measure of the number of acid centres while the temperature
range in which ammonia is desorbed is an indicator of the
strength of such acid sites. However, the total acidity values,
determined by the temperature programmed desorption of
ammonia, are lower for APTES@K10 and AAPTMS@K10, than
that of neat K10 montmorillonite (Table 1). The decrease in
acidity may be interpreted as: grafting of the organosilane
lowers the number of free surface Si–OH groups as well as the
Fig. 5 Broad angle XRD spectra of K10 montmorillonite (a), APTES@K10 (b),
and AAPTMS@K10 (c).
+
strong acidic H ions present in the interlayer space, which are
responsible for the acidity in the neat K10 montmorillonite.
3
.1.6 XRD. XRD analysis was carried out directly on the
raw K10 montmorillonite as well as on the organofunctional
clays (Fig. 5 and 6). The corresponding patterns are indicative
of a chief contribution of the mineral family corresponding to
a typical smectite “montmorillonite”. The hkl and two dimen-
sional hk reflections for montmorillonite can be clearly visual-
ized in all the samples. Apart from these peaks, several peaks
due to many impurities like quartz, cristobalite and feldspar
can be seen in the diffractograms. A similar nature in the spec-
trum of the three samples suggests no structural change in the
clay matrix.
Fig. 6 Low angle XRD spectra of K10 montmorillonite (a) and AAPTMS@K10
(b).
The suggestive indication of the presence of the organosi-
lanes in the interlayer space cannot be envisaged from the low
angle XRD patterns because of the absence of the (001) peak
in the neat K10 montmorillonite itself. The poor long range
ordering may be due to the damage to the clay layers caused
during acid treatment of the synthetic clay. The peak observed
at 9° creating doubt about the (001) peak is due to the illite The
impurity present in the clay.
3
micrographs of APTES@K10 and AAPTMS@K10 clearly show
highly porous morphology.
3
.2. Catalytic activity
catalytic activity
K10 montmorillonite was assessed for the Knoevenagel con-
.1.7 FESEM. Field emission scanning electron micro- densations of benzaldehyde with diethyl malonate to produce
of
the
amine
modified
2
2
graphs of K10 montmorillonite, APTES@K10 and cinnamic acid as the major product. Earlier, Romero et al.
AAPTMS@K10 are shown in Fig. 7. FESEM observation reveals reported amine-functionalized SBA-15 giving 98% conversion
that the parent K10 montmorillonite is a layered material con- at 105 °C towards the Knoevenagel condensation reaction.
sisting of many parallel arrays of cleaved plates. The mor- However, at room temperature amine-functionalized MCM-41
2
3
phologies of the final products were quite similar to that of showed 81% conversion as reported by Sugi et al. In our
the parent clay, as can be seen from the inset of Fig. 7(a). The earlier studies with amine functionalised zirconia, we observed
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Table 2 Conversion and selectivity of various catalysts towards the Knoevena-
gel condensation reaction
Selectivity (%)
Catalyst
Conversion (%)
Cinnamic acid
Other
K10 montmorillonite
APTES@K10
AAPTMS@K10
39
93
97
97
98
99
3
2
1
temperature or longer reaction time. However, in this study we
got better results due to the co-operative effect of the acidic
and basic sites present in the amine grafted montmorillonite.
As motivated by the principles of green chemistry, it was
decided to carry out the reaction under room temperature and
solvent free conditions. Initially it was found that no reaction
occurred in the absence of any catalyst, whereas
K10 montmorillonite grafted with amines or di-amines effec-
tively catalyzed Knoevenagel condensation reactions producing
cinnamic acid in high yields, whereas a lower conversion but
good selectivity was achieved by unpromoted pure
K10 montmorillonite (Table 2). This may be due to the pres-
ence of some Lewis acidic sites in neat K10 montmorillonite,
which is responsible for the activity. In comparison to the
monoamine functionalized K10 montmorillonite, the di-
amine functionalized catalyst showed highest conversion
(
97%) due to the presence of more basic sites or increase in
nitrogen content. Recently, Park et al. demonstrated the use of
high nitrogen containing mesoporous carbon nitride as a base
catalyst for Knoevenagel condensation of ethylcyanoacetate
2
4
with aromatic aldehydes.
With such results in hand, we then decided to investigate
the effects of various reaction parameters on the condensation
of benzaldehyde with diethyl malonate to produce cinnamic
acid using AAPTMS@K10 as a catalyst.
The effect of a benzaldehyde to diethyl malonate molar
ratio on the reaction conversion was studied by carrying out
the reaction at molar ratios of 1 : 4, 1 : 3, 1 : 2, and 1 : 1 respecti-
vely (Fig. 8). At a benzaldehyde : diethyl malonate molar ratio
of 1 : 2, the catalyst gave the best conversion of 97% in 12 h.
The selectivity towards cinnamic acid was 99%. However, on
further increasing the diethyl malonate concentration, though
the conversion remains almost the same, the product selectiv-
ity towards cinnamic acid decreased. This suggests that the
self-condensation of diethyl malonate takes place when its
concentration in the reactant mixture increases.
In our next move, we then decided to study the influence of
the catalyst amount from 0.02 to 1.00 g (Fig. 9). As expected,
increasing the amount of AAPTMS@K10 from 0.02 to 0.05 g
could lead to a significant enhancement of the conversion
Fig. 7 FESEM images of AAPTMS@K10 (a), APTES@K10 (b), and
K10 montmorillonite (c).
(
from 76%–97%). It can be clearly seen that the selectivity was
meanwhile largely influenced by the catalyst amount, and
9% conversion with 98% selectivity for cinnamic acid and in increasing the catalyst concentration would give higher selec-
the case of amine functionalized MCM-41, we got 92% conver- tivity. The phenomenon could be attributed to the suppression
8
1
6,17
sion and 98% selectivity in 24 h.
The inherent disadvan- of the by-product of cinnamic acid with the increase in basicity
tages associated with these reports were either higher of the reaction system.
5
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Fig. 8 The effect of molar ratios of benzaldehyde : diethyl malonate towards
Knoevenagel condensation. Reaction conditions: room temperature; catalyst
amount 0.05 g; time 12 h.
Fig. 10 Influence of reaction time on Knoevenagel condensation. Catalyst
amount, 0.05 g; room temperature; benzaldehyde : diethyl malonate 1 : 2.
Fig. 9 The effect of catalyst amount towards Knoevenagel condensation. Reac-
tion conditions: room temperature; benzaldehyde : diethyl malonate 1 : 2; time
1
2 h.
Results showing the influence of reaction time on conver-
sion and product selectivity in the condensation reaction over
the AAPTMS@K10 catalyst are presented in Fig. 10. As can be
seen from the figure, the conversion and selectivity are increas-
ing with time up to 12 h. Then the reaction became slower and
reached a plateau. The conversion and selectivity values show
no appreciable change with further rise in reaction time.
The AAPTMS@K10 catalyst was employed in the reaction, Scheme 2 A plausible reaction mechanism for the Knoevenagel condensation
by AAPTMS@K10.
where the catalyst activity is mainly due to the structural
basicity of the amine group. The reaction pathway can be
rationalized by the possible mechanism illustrated in
Scheme 2. The scheme shows a co-operative effectiveness of a
single clay based system containing acid and basic sites in it.
In order to demonstrate the versatility of AAPTMS@K10 for
Knoevenagel condensation, we submitted various substituted
2
5
The acid sites present in the clay activate the carbonyl (benz- aldehydes and substrates containing active methylene groups
aldehyde), and the basic sites activate the diethyl malonate, with the molar ratio 1 : 2.
this on subsequent steps of the Knoevenagel condensation
produces cinnamic acid and condensation products of diethyl donating groups (–CH
malonate.
In the case of substituted benzaldehyde containing electron
, etc.), the conversion decreased while
the electron withdrawing substituents (NO , –CN, etc.) on the
3
2
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Table 3 Knoevenagel condensation of various aldehydes with diethyl malo-
nate under solvent free conditions
Selectivity (%)
Sl. no
R1
R2
R3
Conversion (%)
Major
Minor
1
2
3
4
5
OH
—
—
—
H
—
—
NO
—
H
—
CH
—
CN
H
85
81
98
99
97
91
87
99
99
99
9
13
1
1
1
3
2
Conditions: room temperature, catalyst – 0.05 g, time – 12 h,
substituted benzaldehyde: substrates possessing active methylene
groups 1 : 2.
Fig. 11 Results of recycling tests.
Table 4 Effect of various active methylene groups towards Knoevenagel
condensation
Selectivity (%)
Sl. no
X
Y
Conversion (%)
Major
Minor
1
2
3
4
COOEt
CN
CN
COOEt
CN
COOEt
COOMe
97
99
93
82
99
99
95
87
1
1
5
Fig. 12 FT-IR spectra of fresh AAPTMS@K10 (a) and reused AAPTMS@K10 (b).
COOMe
13
Conditions: room temperature, catalyst – 0.05 g, time – 12 h,
benzaldehyde: compounds containing active methylene groups 1 : 2.
Fig. 11 shows the recycling test of the AAPTMS@K10 catalyst
towards the Knoevenagel condensation. The catalyst was separ-
ated by centrifugation after the reaction, washed several times
with distilled water, dried, and used in the reaction with a
fresh reaction mixture. No significant decrease in either
activity or selectivity was observed after being used repetitively
for 6 times. This can be attributed to the strong covalent
bonding of the amine moiety with the clay surface. Compari-
son of the FTIR spectra of the fresh and reused catalyst persua-
sively validates that the structural reliability of the
AAPTMS@K10 remains unchanged after the Knoevenagel con-
densation reaction (Fig. 12).
aromatic ring substantially increased the conversion (Table 3).
In the case of electron withdrawing groups the possibility of
attack of the carbanion (generated from the active methylene
group) on the carbonyl carbon is more when compared to that
of electron donating groups.
Condensation of benzaldehyde with various substrates pos-
sessing active methylene groups is shown in Table 4. The sub-
stituents with electron withdrawing nature stabilize the
carbanion (due to resonance) compared to those having elec-
tron donating nature. So malononitrile displays the maximum
conversion among all other substrates.
4. Conclusion
3
.2.1 Recycling test. To reduce the cost of production in
chemical industries, now-a-days researchers are keener We have synthesized two catalytic systems APTES@K10 and
towards the development of effective heterogenized catalytic AAPTMS@K10 based on the functionalization of K10 mont-
systems, which can be reused for several cycles. In this context, morillonite. Furthermore, such systems require minimum
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effort for preparation using a simple approach. Under very
benign reaction conditions without the help of any solvent,
9 G. B. B. Varadwaj, S. Rana and K. M. Parida, Chem. Eng. J.,
2013, 215–216, 849.
AAPTMS@K10 showed intrinsic high reactivity with 97% con- 10 G. Marciniak, A. Delgado, G. Leclerc, J. Velly, N. Decker and
version and 99% product selectivity in 12 h towards the Knoe- J. Schwartz, J. Med. Chem., 1989, 32, 1402.
venagel condensation reaction. Application of this stable 11 D. Enders, E. Muller and A. S. Demir, Tetrahedron Lett.,
catalyst will be more desirable in industries, since it can be 1988, 29, 6437.
recycled many times without appreciable loss of catalytic 12 E. Knoevenagel, Chem. Ber., 1894, 27, 2345.
activity. A thorough understanding of the behaviour of acidic 13 G. Jones, Org. React., 1967, 15, 204.
and basic sites in a single material will open innovative poten- 14 P. S. Rao and R. V. Venkataratnam, Tetrahedron Lett., 1991,
tials of the material towards one-pot reaction sequences,
which is our future prospect.
32, 5821.
15 F. Texier-Boullet and A. Foucaud, Tetrahedron Lett., 1982,
2
3, 4927.
6 G. Dai, D. Shi, L. Zhou and Y. Huaxue, Chin. J. Appl. Chem.,
995, 12, 104.
7 K. M. Parida, S. Mallick, P. C. Sahoo and S. K. Rana, Appl.
Catal., A, 2010, 381, 226.
1
1
1
1
2
Acknowledgements
1
The authors are extremely thankful to Professor B. K. Mishra,
Director, CSIR-IMMT, Bhubaneswar 751013, Odisha, India, for
his constant encouragement and permission to publish this
work. GBBV and SKR are obliged to CSIR for a senior research
fellowship.
8 K. M. Parida and D. Rath, J. Mol. Catal. A: Chem., 2009, 310,
9
3.
9 K. Motokura, M. Tada and Y. Iwasawa, J. Am. Chem. Soc.,
009, 131, 7944.
2
0 E. T. Vandenberg, L. Bertilsson, B. Liedberg, K. Uvdal,
R. Erlandsson, H. Elwing and I. Lundstrom, J. Colloid Inter-
face Sci., 1991, 147, 103.
Notes and references
1
2
3
4
5
P. Laszlo, Science, 1987, 235, 1473.
A. Vaccari, Catal. Today, 1998, 41, 53.
T. Mishra and K. M. Parida, J. Mater. Chem., 1997, 7, 147.
T. Mishra and K. M. Parida, Appl. Catal., A, 1998, 174, 91.
T. Mishra, P. Mohapatra and K. M. Parida, Appl. Catal., B,
21 S. Brunauer, L. S. Deming, W. E. Deming and E. Teller,
J. Am. Chem. Soc., 1940, 62, 1723.
22 M. D. Gracia, M. J. Jurado, R. Luque, J. M. Campelo,
D. Luna, J. M. Marinas and A. A. Romero, Microporous
Mesoporous Mater., 2009, 118, 87.
2
008, 79, 279.
23 Y. Kubota, Y. Nishizaki, H. Ikeya, M. Saeki, T. Hida,
S. Kawazu, M. Yoshida, H. Fujii and Y. Sugi, Microporous
Mesoporous Mater., 2004, 70, 135.
6
7
8
K. M. Parida, G. B. B. Varadwaj, S. Sahu and P. C. Sahoo,
Ind. Eng. Chem. Res., 2011, 50, 7849.
G. B. B. Varadwaj, S. Sahu and K. M. Parida, Ind. Eng. 24 M. B. Ansari, H. Jin, M. Parvin and S.-E. Park, Catal. Today,
Chem. Res., 2011, 50, 8973. 2012, 185, 211.
G. B. B. Varadwaj and K. M. Parida, Catal. Lett., 2011, 141, 25 M. Zhang, P. Zhao, Y. Leng, G. Chen, J. Wang and
476. J. Huang, Chem.–Eur. J., 2012, 18, 12773.
1
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Dalton Trans., 2013, 42, 5122–5129 | 5129