Activity of amino-functionalised mesoporous solid bases in microwave-assisted condensation reactions

Article abstract of DOI:10.1016/j.catcom.2012.12.005

Aminopropylated functionalised hexagonal mesoporous silicas (HMS) and SBA-15 materials with different amino-loadings (5-30 wt.% NH₂)were synthesized, characterised and their catalytic activitieswere subsequently investigated in the microwave-assisted Knoevenagel condensation of cyclohexanone and ethyl cyanoacetate as well as in the Michael reaction between 2-cyclohexen-1-one and nitromethane. The effects of the quantity of the catalyst in the reaction as well as a variety of microwave parameters including the power, temperature and time of microwave irradiation were optimised. High activities and selectivities to the condensation product could be achieved at short times of microwave irradiation for both base-catalysed processes. The low loaded HMS-5%NH₂ and higher loaded SBA-15-20%NH₂ were found to give the best activities in the reactions. This observation seems to be related to the significant deterioration observed in textural properties of HMS materials at amino-loadings larger than 10%.

Full text of DOI:10.1016/j.catcom.2012.12.005

Catalysis Communications 33 (2013) 1–6
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Activity of amino-functionalised mesoporous solid bases in microwave-assisted
☆
condensation reactions
,
1
Antonio Pineda, Alina Mariana Balu ⁎ , Juan Manuel Campelo, Antonio Angel Romero, Rafael Luque
Departamento de Química Orgánica, Universidad de Córdoba, Campus de Rabanales, Edificio Marie Curie, E-14014-Córdoba, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Aminopropylated functionalised hexagonal mesoporous silicas (HMS) and SBA-15 materials with different
Received 5 September 2012
Received in revised form 4 December 2012
Accepted 6 December 2012
Available online 14 December 2012
2
amino-loadings (5–30 wt.% NH ) were synthesized, characterised and their catalytic activities were subsequent-
ly investigated in the microwave-assisted Knoevenagel condensation of cyclohexanone and ethyl cyanoacetate
as well as in the Michael reaction between 2-cyclohexen-1-one and nitromethane. The effects of the quantity
of the catalyst in the reaction as well as a variety of microwave parameters including the power, temperature
and time of microwave irradiation were optimised. High activities and selectivities to the condensation product
could be achieved at short times of microwave irradiation for both base-catalysed processes. The low loaded
Keywords:
Knoevenagel condensation
Michael addition
2 2
HMS-5%NH and higher loaded SBA-15-20%NH were found to give the best activities in the reactions. This
SBA-15
observation seems to be related to the significant deterioration observed in textural properties of HMS materials
HMS
at amino-loadings larger than 10%.
Mesoporous functionalised silica catalyst
©
2012 Elsevier B.V. All rights reserved.
1
. Introduction
[11], hydrotalcites [12] and, more recently, aminopropylated func-
tionalised silicas [13–17]. These catalysts have been reported as high
efficient materials for condensation reactions, providing quantitative
conversions of starting materials in a few hours of reaction.
The development of more environmentally friendly methodologies
has stimulated the search for solid bases in substitution of homogenous
bases currently employed in many industrial processes [1,2]. In this
sense, important C\C coupling organic reactions including Michael ad-
ditions [3], Heck [4,5], Sonogashira [6] and Knoevenagel condensations
Microwaves have been proved to be a very useful tool to accelerate
conventionally heated reaction experiments which can be efficiently
performed at reduced times of reaction under milder reaction condi-
tions [18,19], often with the additional advantage of tuning the selectivity
to product distribution by controlling different microwave parameters
[20]. We have recently reported an efficient microwave assisted protocol
for the Knoevenagel condensation reaction using alkali-modified SBA-1
materials as compared to a conventionally heated protocol. Quantitative
conversion in the system could be achieved in less than 45 min reaction
(around 3 h for the more challenging substrates) as compared to 4–24 h
required under conductive heating [21].
[7–12] have been reported to be catalysed by solid bases.
Among them, the Knoevenagel condensations are interesting base-
catalysed processes for the preparation of high added-value chemicals
2,7–12]. The reaction involves a nucleophilic addition of an active hy-
[
drogen compound to a carbonyl group followed by a dehydration reac-
tion that generates an α,β-unsaturated carbonyl compound (Scheme 1).
The Michael addition is another relevant reaction for the preparation of
high-added value chemicals [13,14]. In this reaction, the nucleophilic
addition of a carbanion to an alpha, beta unsaturated carbonyl com-
pound takes place to give the cross-coupled product (Scheme 2).
A wide variety of heterogeneous catalysts have been reported for
In continuation with the development of designer catalysts for het-
erogeneous catalysed processes, we report here the effect of microwave
irradiation in the Knoevenagel condensation of cyclohexanone and
ethyl cyanoacetate over amino-functionalised silica-based materials as
well as in the Michael reaction between 2-cyclohexen-1-one and nitro-
methane (Schemes 1 and 2). Parameters such as the power irradiation,
the exposure time and the temperature were monitored in order to ob-
tain the optimum conditions leading to high yields for the condensation
product. Different silica-based materials, with varying loadings of
aminopropylated groups, were characterised by a number of tech-
4 2 3
these particular reactions including AlPO –Al O catalysts [10], clays
☆
In memoriam of Prof. Juan Manuel Campelo, inspiration and friend, who passed away
in October 2012.
⁎
Corresponding author. Tel.: +34 957211050; fax: +34 957212066.
E-mail addresses: alina.balu@aalto.fi, z82babaa@uco.es (A.M. Balu).
Current address: Department of Forest Products Technology, Aalto University, P.O.
niques including N
sequently investigated in the aforementioned reaction.
adsorption, DRIFTS, XRD, and CP-MAS 13C and sub-
2
1
Box 16300, FI-00014 Helsinki, Finland.
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2012.12.005

2
A. Pineda et al. / Catalysis Communications 33 (2013) 1–6
O
COOEt
COOEt
CN
+
CN
Scheme 3. General pathway of mesoporous silica functionalisation via classical grafting
method.
cyclohexanone ethyl cyanoacetate
Scheme 1. Knoevenagel reaction of cyclohexanone and ethyl cyanoacetate.
DRIFTS spectra for the catalysts were recorded in a Bomen MB-Series
100 FTIR spectrophotometer equipped with an environmental chamber
Spectra Tech, P/N 0030-100) that includes a diffuse reflectance device
2
. Experimental
(
−
1
2
.1. Preparation of supports
(Spectra Tech, Collector) at a resolution of 8 cm and 256 scans. Sam-
ples were prepared by mixing the powdered solids with KBr (15 wt.%).
All materials were evacuated for 1 h at 150 °C in the environmental
chamber prior to spectra adquisition at temperatures ranging from 50
to 150 °C. In all cases the spectra were obtained starting with the lowest
temperature and subtracting the corresponding reference signal.
Thermogravimetric (TG) experiments were carried out in a Setaram
Setsys 12 or Netzsch 409 STA derivatograph in a static air atmosphere.
n-Dodecylamine and Pluronics P123 were utilised as structure
directing agents for the synthesis of hexagonal mesoporous silica
HMS) and SBA-15 mesoporous materials, respectively. The synthesis
(
of HMS materials was performed following a previously reported meth-
odology by Macquarrie et al. [22]. Briefly, 20.80 g of TEOS was added
under stirring to a solution containing 5.10 g n-dodecylamine in 1:1
2
ACN/H O (50 g/50 g) at room temperature. After 18 h of stirring the
2 3
The sample was loaded in ceramic crucibles with α-Al O as reference
solid formed is filtered off and dried for 1 h in an oven at 100 °C. In
order to remove the template the sample was purified by extraction
with ethanol for 8 h using an automatic FexIKA extractor. The solid
resulted was oven dried for 16 h at 100 °C.
SBA-15 materials were prepared following the previously reported
methodology by Bonardet et al. [23]. The triblock copolymer Pluronic
P123 surfactant (0.41 mmol) was dissolved in water (1.25 mol) and
HCl (2 M, 1.23 mol) with stirring at RT. On complete dissolution TEOS
compound and a Pt/Pt-Rh (10%) thermocouple. The heating rate em-
ployed was 10 K min in all cases.
TG-IR measurements were conducted to quantify the amounts of
aminopropyl loading in the materials. These were carried out on a
Netsch STA409 interfaced to a Bruker Equinox-55 FTIR instrument
−
1
2
equipped with a liquid N cooled MCT detector.
Nitrogen adsorption measurements were carried out at 77 K using
an ASAP 2000 volumetric adsorption analyzer from Micromeritics. Sam-
ples were previously degassed for 24 h at 110 °C before performing ad-
sorption measurements. Surface areas were calculated according to the
BET (Brunauer–Emmet–Teller) equation. Pore volumes (VBJH) and pore
(
25 mmol) is added drop wise to the above solution. The mixture was
then allowed to be stirred for 24 h at RT. After that was subjected to a
hydrothermal treatment at 100 °C for 48 h in an oven. The solid formed
was filtered off and dried at 60 °C. The template was removed by calci-
nation at 550 °C for 8 h.
2
size distributions (DBJH) were obtained from the N adsorption branch.
CP-MAS 13C experiments were conducted on a Bruker Avance
00 MHz, WB with a resonance frequency of 100.6 MHz. The spin rate
4
2
.2. Synthesis of functionalised materials
of the sample was 8 kHz, the proton pulse length 2.5 μs (90 flip) a
2
.4 ms contact time and a 3 s repetition time.
The synthesis of functionalised silicates was carried out by a grafting
Microwave experiments were carried out in a CEM-DISCOVER
method using the amino reactant aminopropyltriethoxysilane (APTES)
in different concentrations (5, 10, 20 and 30 wt.%) over the silica-based
support. The required amounts of APTES to achieve these loadings were
dissolved in 50 mL of toluene, stirred for 1 min for a better mixing and
finally added to a round bottom flask containing the mesoporous mate-
rial (1.5 g). The mixture was refluxed at 110 °C for 10 h under stirring,
cooled to room temperature and filtered under vacuum to obtain the
grafted solid. The final catalysts were washed at RT with acetone and
toluene to ensure the removal of any physisorbed species on the mate-
rials prior to reaction. The schematic representation of the grafting of
amino-moieties on the surface of HMS and SBA-15 materials has been
included in Scheme 3.
model with PC control. Experiments were performed on a closed vessel
(pressure controlled) under continuous stirring. The microwave meth-
od was generally power-controlled where reactions mixture were irra-
diated with the maximum power output (300 W), achieving different
temperatures in the 70–90 °C range, as measured by an infra-red probe.
In a typical Knoevenagel condensation reaction, 10 mmol (1.036 mL)
of cyclohexanone and 1.2 mmol (0.123 mL) ethyl cyanoacetate were
stirred together with the solid base (0.25–0.1 g) in 2 mL toluene for up
to 30–45 min at 300 W. This reaction was selected on the basis of a chal-
lenging substrate (e.g. cyclohexanone as compared to more reactive
aldehydes) for the formation of the Knoevenagel condensation product
as test reaction for the synthesized solid base catalysts. Reaction reached
completion for most catalysts after 30 min of microwave irradiation.
Conversions at 15 min reaction have been included to establish a com-
parison of activities between catalysts.
2
.3. Characterisation and kinetic experiments
The structure regularity of the samples was determined by XRD on
a Siemens D-5000 (40 kV, 30 mA) using CuKα radiation. Scans were
performed over the 2θ range from 0.5 to 10.
Table 1
Textural properties of the HMS materials functionalised with various quantities of
aminopropyl groups.
Sample
Mean pore size
Pore
S
BET
2
Amino propyl
loading
(wt.%, TG-IR)
(nm)
volume
(m g−1
)
(
mL g−1)
HMS
2.8
2.6
2.6
b2.0
b2.0
0.80
0.45
0.36
0.39
0.28
736
496
407
550
332
–
HMS-5%APTES
HMS-10%APTES
HMS-20%APTES
HMS-30%APTES
7
9.6
8.2
11.5
Scheme 2. Michael reaction of 2-cyclohexen-1-one and nitromethane.

A. Pineda et al. / Catalysis Communications 33 (2013) 1–6
3
Table 2
Textural properties of the SBA-15 materials functionalised with various amounts of
aminopropyl groups.
Sample
Mean pore
size
Pore
S
BET
2
Aminopropyl
loading
(wt.%)
volume
(m g−1
)
(
nm)
(mL g−1)
SBA-15
5.4
2.4
b2.0
b2.0
b2.0
0.54
0.21
0.35
0.32
0.21
706
221
256
226
239
–
SBA-15-5%APTES
SBA-15-10%APTES
SBA-15-20%APTES
SBA-15-30%APTES
5.4
7.0
9.0
8.6
In a typical Michael reaction, 10 mmol 2-cyclohexen-1-one and
mL nitromethane (35 mmol) were microwaved with the solid base
2
(
0.05–0.2 g) for 15-30 min at 300 W (100 °C, maximum temperature
reached). Reaction reached completion for most catalysts after 45 min
a
b
1
2
3
4
5
6
7
8
2
θ (º)
Fig. 2. DRIFT spectra of functionalised HMS (HMS-APTES-10%) as compared to the par-
−
1
ent HMS support (top image), clearly showing the disappearance of the 3747 cm
band. SBA-15-10%APTES spectra acquired at 473 K (reference KBr, bottom image).
a
b
2
3
4
5
6
7
8
2
θ (º)
Fig. 1. XRD patterns of: a) SBA-15; and b) SBA-15-10%APTES (top) and a) HMS and
b) HMS-10%APTES (bottom).
Fig. 3. Representative 13C CP-MAS NMR spectra of HMS-10%APTES, displaying the char-
acteristic peaks of the C atoms in the aminopropyl groups (δ C=42, 22 y 11 ppm).
1
3

4
A. Pineda et al. / Catalysis Communications 33 (2013) 1–6
Fig. 4. Representative example of a CP-MAS 13C NMR spectrum of an uncalcined P123-containing APTES functionalised SBA-15 material, showing the characteristic peaks of APTES
1
3
(
2 2
δ C=42, 21 y 10 ppm) as well as bands correlated to the presence of P123 (CH \CH\ and \CH \ at 67-77 ppm and ~15 ppm, respectively).
of microwave irradiation. Conversions at 15 min reaction have been
included to establish a comparison of activities between catalysts and
conditions.
Sampling aliquots for both chemistries were subsequently analyzed
by GC/GC–MS using an Agilent 6890N GC model equipped with a 7683B
series autosampler fitted with a DB-5 capillary column and an FID
detector.
produced a decrease in BET surface from 706 to 211 m2 g−1 along
with a drop in the mean pore size from 5.4 to 2.4 nm). These findings
will have an important implication in terms of catalytic activity of
SBA-functionalised materials (with generally reduced activities) com-
pared to those of functionalised HMS (improved activities), as described
in the section on catalytic results.
XRD patterns of the prepared HMS and SBA-15 materials are typical
of hexagonal mesoporous silicas. As an example, Fig. 1 shows the XRD
pattern of SBA-15 support vs SBA-15 functionalised materials (and
their HMS analogues) with 10 wt.% amino groups. We note that
diffractograms of HMS materials prepared by a neutral route using
dodecylamine as template are not well resolved as compared to those
of SBA-15, although patterns indicate that the materials present a hexag-
onal symmetry. SBA-15 showed broad diffraction peaks in the low angle
region (2θ 0–5°) which is indicative of the long range hexagonal order.
These include three well-resolved XRD diffraction peaks in the region
of 2θ=0.5–2.5°, which can be indexed to the (100), (110) and (200) re-
flections, respectively [24]. As shown in Fig. 1, the peak intensity of the
functionalised SBA-15 materials decreases at increasing amino loadings,
implying a partial structural deterioration due to the aminopropyl
groups bound to the surface (see also supporting information for all
XRD patterns). This partial structure deterioration could also explain
the severe change in textural properties observed for SBA-15 materials
upon functionalisation (Table 2). In some cases, materials with over
20%APTES exhibited very low intensity and broad bands which correlat-
ed well with the reduction observed in both textural and surface proper-
ties (see Tables 1 and 2).
3
. Results and discussion
N
2
adsorption–desorption isotherms of the synthesized materials
(
not shown) exhibited the characteristic type IV isotherms correspond-
ing to mesoporous materials. Textural properties as well as aminopropyl
loading (obtained by thermogravimetric analysis) of both HMS and
SBA-15 functionalised materials have been summarised in Tables 1
and 2, respectively. It can be seen that, based on thermal analysis, the
maximum content of amino groups in the samples reached around
10 wt.% of aminopropyl groups. The discrepancy between the nominal
and actual aminopropyl content could be explain on the basis of satura-
tion of the functionalisable groups on the surface and within the pores of
the materials (free silanols) which may not allow a further chemical
functionalisation in the materials. Aminopropyl moieties will be surely
physisorbed in the materials during the functionalisation step but
these are subsequently removed in the washing and filtration step as
observed by the presence of N-containing groups in the washings
(
results not shown).
Results included in Tables 1 and 2 indicate that the grafting of
aminopropyl groups also caused a partial blocking of the porosity in
HMS and SBA-15 materials, as suggested by the simultaneous decrease
in BET surface area and pore volume with aminopropyl loading.
Interestingly, this decrease was generally more severe in the case of
SBA-15-based materials (5 wt.% loading of aminopropyl already
We performed Diffuse Reflectance Infrared Fourier Transform (DRIFT)
and 13C CP-MAS NMR experiments aiming to check the efficiency of the
grafting methodology used herein to functionalise HMS and SBA-15 ma-
terials. The DRIFT spectra of the HMS and SBA-15 supports exhibited in all
cases the characteristic bands of amorphous silicas (not shown) with an
−
1
intense band at 3747 cm
corresponding to the O\H stretching due
Table 3
to the superficial Si\OH groups. Remarkably, this band disappears
completely in the case of functionalised materials (Fig. 2) confirming
Catalytic activity [total conversion (X
product (S , %)] of basic mesoporous HMS–APTES type materials in the condensation of
cyclohexanone and ethyl cyanoacetate under microwave irradiation.
T
, mol%) and selectivity to Knoevenagel condensation
K
a
Table 4
Entry
Catalyst
Amount of catalyst
g)
X
T
S
K
(mol%)
Catalytic activity [total conversion (X
product (S , %)] of basic mesoporous SBA-15–APTES type materials in the condensation of
cyclohexanone and ethyl cyanoacetate under microwave irradiation.
T
, mol%) and selectivity to Knoevenagel condensation
(
(mol%)
K
a
1
2
3
4
5
6
7
8
9
HMS-5%APTES
0.025
0.05
0.1
0.025
0.05
0.1
0.025
0.05
0.1
0.025
0.05
0.1
35
64
>99
26
59
77
12
29
62
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
Entry
Catalyst
Amount of catalyst
g)
X
T
S
K
(mol%)
(
(mol%)
HMS-10%APTES
HMS-20%APTES
HMS-30%APTES
1
2
3
4
5
6
7
8
SBA15-5%APTES
SBA15-10%APTES
SBA15-20%APTES
SBA15-30%APTES
0.05
0.1
0.05
0.1
0.05
0.1
0.05
0.1
30
54
29
70
31
80
27
57
>99
>99
>99
>99
>99
>99
>99
>99
1
1
1
0
1
2
38
61
>90
a
a
1
0 mmol cyclohexanone, 1.2 mmol ethyl cyanoacetate, 2 mL toluene, 300 W and
10 mmol cyclohexanone, 1.2 mmol ethyl cyanoacetate, 2 mL toluene, 300 W and
15 min (max. temperature set at 150 °C).
1
5 min (max. temperature set at 150 °C).

A. Pineda et al. / Catalysis Communications 33 (2013) 1–6
5
Table 6
Total conversion (X
T
) and selectivity to Michael addition product (S
M
) of APTES
functionalised HMS materials in the microwave-assisted Michael addition of
a
2-cyclohexen-1-one and nitromethane.
Entry
Catalyst
Quantity of catalyst
g)
X
T
S
M
(mol%)
(
(mol%)
1
2
3
4
5
6
7
8
9
Blank (no catalyst)
Blank (HMS support)
HMS-5%APTES
–
–b
–
0.1
0.05
0.1
0.2
0.05
0.1
0.2
0.05
0.1
0.2
0.05
0.1
0.2
b5
b10
35
69
b5
12
40
b10
26
–
>99
>99
>99
>99
>99
>99
>99
>99
>99
–
Fig. 5. Conversion of cyclohexanone as a function of time for HMS-5%APTES (front,
white columns) and SBA-15-20%APTES (back, black columns) materials. Reaction con-
ditions: 10 mmol cyclohexanone, 1.2 mmol ethyl cyanoacetate, 2 mL toluene, 300 W
and 0.1 g catalyst.
HMS-10%APTES
HMS-20%APTES
HMS-30%APTES
10
11
12
13
14
63
b
–
the grafting of aminopropyl groups on the mesoporous material. The
b
–
–
presence of aminopropyl groups was further confirmed by the presence
b15
>99
−
1
of bands at 2925 and 2870 cm
which correspond to stretching of
a
−
1
Reaction conditions: 10 mmol 2-cyclohexen-1-one, 35 mmol (2 mL) nitromethane,
C\H groups along with bands at 1664–1589 cm
ascribed to the
3
00 W and 15 min.
N\H bending, which are more clearly observed operating at higher tem-
b
No reaction.
peratures, in good agreement with previous literature results (Fig. 2) [25].
13
C CP MAS NMR spectrum of SBA-15 and HMS functionalised sam-
ples (Fig. 3 shows a representative spectrum for HMS-10%) clearly
displayed three peaks at 10–11, 21–22 and 42 ppm respectively, corre-
sponding to the C atoms on the Si\CH \CH \CH \NH chain in
2 2 2 2
not be correlated directly with activity in the case of HMS materials
since, for example, HMS-5%APTES (aminopropyl content 7 wt.%) and
HMS-30%APTES (aminopropyl content 11.5 wt.%) showed similar activ-
ities at comparable conditions. In the case of SBA-15 based materials,
whilst a catalyst loading of 0.05 g showed similar activity for all the ma-
terials, a positive trend of the activity with the aminopropyl content was
found at catalyst loadings of 0.1 g, except for the material SBA-15-30%
APTES. An excessive loading of aminopropyl groups that are not grafted
to the surface (as indicated before) could lead to excessive blocking of
porosity in this sample leading to the observed decrease in activity. For
these samples, SBA-15-20%APTES exhibited the best catalytic results.
A variety of microwave parameters including power and time of mi-
crowave irradiation were investigated for the most active catalysts
(HMS-5%APTES and SBA-15-20%APTES) in order to find the optimal
conditions to run this condensation. As expected, an increase in power
produced an enhancement of activity in all cases without affecting the
selectivity to the condensation product, although a power increase
above 200 W did not significantly improve conversion In the case of re-
action time, 15 min allowed to reach very high activity for both samples
(Fig. 5), with slight increases at 30 min. Interestingly, an increase of the
time of reaction above this time did not produce significant increase in
conversion (Fig. 5). A comparison of our system with related literature
reports showed the possibility to work under mild reaction conditions
and low quantities of catalyst to achieve good conversions with com-
plete selectivity to the target product under the investigated conditions.
Similar reports gave as much as comparable yields under slightly milder
conditions (entry 3, Table 5).
sequence from left to right [26,27]. These results are relevant in that
they demonstrate that the aminopropyl groups were not decomposed
during the synthesis procedure and confirm the incorporation of such
functionalities in the materials. The absence of any additional bands re-
lated to the surfactant indicated its complete removal upon calcination.
In fact, a comparative spectrum of an unextracted template containing
amino-functionalised SBA-15 material (Fig. 4) shows distinctive peaks
in the 67–77 ppm range corresponding to the C species from P123 [28].
Tables 3 and 4 summarise the main catalytic data for the condensa-
tion of cyclohexanone with ethyl cyanoacetate under microwave irradia-
tion using different loadings of amino moieties grafted on mesoporous
silicas. Most catalysts provided quantitative conversion to the target
Knoevenagel product after 30 min microwave irradiation (see supporting
information) and results at 15 min reaction were only selected to estab-
lish an activity comparison between catalysts.
The use of microwave irradiation is beneficial in that it reduces reac-
tion times (from over 12 h typically reported in literature [10–12,15] up
to 15 min upon microwave heating) and increases at the same time con-
versions to products. Importantly, the blank reaction (in absence of the
catalyst) gave no conversion in the systems under the investigated
conditions. At optimised conditions, the microwave irradiated protocol
afforded moderate to very good conversions of cyclohexanone with
almost complete selectivites to the principal product of reaction. By
comparison of Tables 3 and 4 it can be seen that, in general, aminopropyl
functionalised-HMS materials showed higher activity than their coun-
terparts supported on SBA-15 at the same conditions of power, temper-
ature and catalyst loading. This result could be correlated with the
higher surface area and pore volume of the HMS materials after
functionalisation, as reported in Table 1. Aminopropyl loading could
The base catalysts were subsequently investigated in another
important base-catalysed process such as the Michael addition of 2-
cyclohexen-1-one to nitromethane under microwave irradiation
(Scheme 2). Optimised results for both HMS and SBA-15 functionalised
materials have been summarised in Tables 6 and 7. In general, short
Table 5
Comparison between our solid base system and related literature work of the same reaction under similar conditions.
Catalyst
Reaction conditions
Temp.
°C)
Reaction time
(h)
Product yield
(%)
Reference
(
HMS-5%APTES
SBA-15-20%APTES
Diamine-MCM-41
Mg–Al-HT
Silica gel-APTMS
γ-Aminopropyl silica
AMS–HMS
10 mmol cyclohexanone, 1 mmol ethyl cyanoacetate, 0.1 g cat., toluene (solvent)
10 mmol cyclohexanone, 1 mmol ethyl cyanoacetate, 0.1 g cat., toluene (solvent)
2 mmol cyclohexanone, 2 mmol ethyl cyanoacetate, 0.02 g cat., toluene (solvent)
2 mmol cyclohexanone, 2 mmol ethyl cyanoacetate, 0.05 g cat., DMF (solvent)
10 mmol cyclohexanone, 10 mmol ethyl cyanoacetate, 10 g cat., toluene (solvent)
20 mmol cyclohexanone, 20 mmol ethyl cyanoacetate, 0.25 g cat., cyclohexane (solvent)
20 mmol cyclohexanone, 20 mmol ethyl cyanoacetate, 0.25 g cat., toluene (solvent)
80
70
50
RT
RT
82
110
0.3
0.3
0.3
1
>99
80
81
33
66
Current work
Current work
[29]
[30]
[31]
–
1
0.5
98
98
[32]
[33]

6
A. Pineda et al. / Catalysis Communications 33 (2013) 1–6
Table 7
4. Conclusions
T M
Total conversion (X ) and selectivity to Michael addition product (S ) of APTES
functionalised SBA-15 materials in the microwave-assisted Michael addition of
a
Aminopropyl functionalised silica mesoporous materials have been
found to be effective catalysts in the Knoevenagel condensation of
cyclohexanone with ethyl cyanoacetate. Mild reaction conditions and
short reaction times (typically 30–45 min) are the obvious advantages
of the presented method which allowed excellent yields to target prod-
ucts with a complete selectivity. The investigated materials have been
also found to be useful for a series of related chemistries (e.g. Michael
additions) providing also excellent conversion and selectivities to target
products under microwave-assisted conditions.
2-cyclohexen-1-one and nitromethane.
Entry
Catalyst
Quantity of catalyst
g)
X
T
S
M
(mol%)
(
(mol%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
Blank (no catalyst)
Blank (SBA-15 support)
SBA-15-5%APTES
–
–
–
0.2
0.05
0.1
0.2
0.05
0.1
0.2
0.05
0.1
0.2
0.05
0.1
0.2
b5
b10
b20
39
b5
b10
28
b20
45
72
–
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
SBA-15-10%APTES
SBA-15-20%APTES
SBA-15-30%APTES
Acknowledgements
0
1
2
3
4
RL gratefully acknowledges support from Ministerio de Ciencia e
Innovacion, Gobierno de España through a Ramon y Cajal contract (ref.
RYC-2009-04199) and funding from Consejeria de Ciencia e Innovacion,
Junta de Andalucia (project P10-FQM-6711). Funding from projects
CTQ-2010-18126 and CTQ2011-28954-C02-02 (MICINN) and are also
gratefully acknowledged. The group is grateful to Dr. Juan Carlos
Serrano-Ruiz for his useful comments and revisions in the preparation
of this manuscript.
b5
22
39
a
Reaction conditions: 10 mmol 2-cyclohexen-1-one, 35 mmol (2 mL) nitrometh-
ane, 300 W and 15 min.
times of reaction (typically 15 min) were selected to compare the activ-
ities between the different functionalised solid bases. Results clearly
demonstrate HMS-5%APTES (69%) and SBA-15-20%APTES (72%) were
once again the most active catalysts in the base-catalysed process,
with remarkably different activities to those obtained for the other
functionalised materials, with the exception of comparable activities ob-
served for HMS-20%APTES (63% conversion). Both an increase in the
quantity of catalyst (from 0.05 to 0.2 g) and time of reaction (from 15
to 45 min) had a dramatic increase in the activity of the systems
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.catcom.2012.12.005.
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