Catalytic behavior of surfactant-containing-MCM-41 mesoporousmaterials for cycloaddition of 4-nitrophenyl azide

Article abstract of DOI:10.1016/j.apcata.2014.10.022

Si-MCM-41, Ga-MCM-41 and Al-MCM-41 mesoporous catalysts (with Si/Al = 80 and Si/Ga = 80) were pre-pared by direct synthesis under hydrothermal crystallization method using sodium aluminate or galliumsulfate and tetraethyl orthosilicate (TEOS) as aluminum

Full text of DOI:10.1016/j.apcata.2014.10.022

Applied Catalysis A: General 489 (2015) 131–139
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Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Catalytic behavior of surfactant-containing-MCM-41 mesoporous
materials for cycloaddition of 4-nitrophenyl azide
Bouhadjar Boukoussaa, Sarah Zeghadab, Ghenia Bentabed Ababsab, Rachida Hamachaa,∗
,
Aïcha Derdourb, Abdelkader Bengueddacha, Florence Monginc
a Laboratoire de Chimie des Matériaux L.C.M, Université d’Oran, BP 1524 El-Mnaouer, 31000 Oran, Algeria
b Laboratoire de Synthèse Organique Appliquée L.S.O.A, Université d’Oran, BP 1524 El-Mnaouer, 31000 Oran, Algeria
c Equipe Chimie et Photonique Moléculaires CPM, Institut des Sciences Chimiques de Rennes, UMR 6226, Université de Rennes 1—CNRS, Bâtiment 10A,
Case 1003, Campus Scientifique de Beaulieu, 35042 Rennes Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Si-MCM-41, Ga-MCM-41 and Al-MCM-41 mesoporous catalysts (with Si/Al = 80 and Si/Ga = 80) were pre-
pared by direct synthesis under hydrothermal crystallization method using sodium aluminate or gallium
sulfate and tetraethyl orthosilicate (TEOS) as aluminum or gallium and silica sources, respectively. The
structural features of the materials were determined by various physico-chemical techniques such as X-
ray diffraction (XRD), nitrogen sorption at 77 K, Fourier transform infrared spectroscopy (FTIR), scanning
and transmission electronic microscopy (SEM, TEM) and thermogravimetric analysis ATG. The catalytic
activity of the calcined and as-synthesized catalyst was evaluated through the cycloaddition reaction of 4-
nitrophenyl azide with activated alkenes at room temperature under liquid-phase conditions. High yields
of 1,2,3-triazole were obtained. For comparison purpose, mixtures of homogeneous and heterogeneous
catalyst Et3N/M-MCM-41 (M = Al or Ga) are also tested. The catalyst was used in five consecutive exper-
iments without important loss of activity, confirming its stability. Finally, a new method for preparing
triazoles in short reaction times was developed.
Received 5 August 2014
Received in revised form
27 September 2014
Accepted 13 October 2014
Available online 23 October 2014
Keywords:
Mesoporous silica
MCM-41
Cycloaddition reaction
Triazoles synthesis
Surfactant
Catalyst re-use
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
for typical acid–base or oxido-reduction catalysis such as
dehydrogenation of n-butane [17], hydrodesulfurization of 4,6-
The discovery of ordered mesoporous materials M41S by Mobil
in 1992 [1] has attracted intense interest due to their large surface
areas, well-defined pore structures, inert framework, non toxicity
and high biocompatibility [2]. These catalysts are completely recov-
ered after reaction by filtration and are also easily regenerated [3].
The lack of hydrothermal stability of the mesoporous materials has
been overcome by the incorporation of heteroatoms such as Al, Ga,
Ti, Fe, V, W and Cr [4–7]. These properties allow these mesoporous
materials to be used in a wide range of applications such as catalysis
[4–7], adsorption [8,10], extraction [11], energy [12], drug delivery
systems [13], and for their luminescent character [14].
dimethyldibenzothiophene [18], synthesis of benzo[␣]xanthenone
derivatives [19], oxidation of alcohols and toluene [20], tert-
butylation of hydroquinone [21], Beckmann rearrangement
reaction [22], and cyclohexanone oxime rearrangement [23].
Recently several approaches have been proposed to develop
basicity in mesoporous materials by dispersing alkali metal oxides
in the channel [24,25]. Kloetstra et al. [26] initially proposed to dis-
perse cesium oxide particles in Si-MCM-41 pores. However, due
to the treatments used throughout the preparation, its structure
was extensively damaged [26]. Another way to get basic Si-MCM-
41 sites is by functionalizing its surface with organic compounds,
particularly with those containing terminal amines in their compo-
sition [27,28]. These procedures, which are used to generate basic
sites on Si-MCM-41, are hard to process and not always lead to
the planned basic sites, stable enough for catalysis application. Roy
et al. [29] have synthesized a new pyridine-imine functionalized
mesoporous silica (SBA-15) followed by the grafting of Cu(II) for
obtaining a new Cu-PyIm-SBA-15 material and they used these
solids like basic catalysts for synthesis of 1,4-disubstituted 1,2,3-
triazole.
MCM-41 mesoporous materials have drawn the attention
of researchers because of their rapid and easy synthesis [15].
Possessing regular pore structure, uniform pore diameter and
high surface area [16], they have successfully been employed
∗
Corresponding author. Tel.: +213 0557675408.
E-mail addresses: hamacha.rachida@univ-oran.dz, rachidahamacha@gmail.com
(R. Hamacha).
http://dx.doi.org/10.1016/j.apcata.2014.10.022
0926-860X/© 2014 Elsevier B.V. All rights reserved.

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B. Boukoussa et al. / Applied Catalysis A: General 489 (2015) 131–139
The material is functionalized by anchoring organic bases at the
CTAB (2.91 g, 98%, Alfa Aesar), distilled water (110 mL) and ethanol
(6 mL, 99.5%, Riedel-de-Haën) and stirring for 15 min at 308 K, and
the second solution by mixing NaOH (0.66 g, 98% Sigma-Aldrich),
distilled water (10 mL), and the appropriate amount of sodium alu-
minate (54% Al2O3, 41% Na2O, 5% H2O, Aldrich) or gallium sulfate
(Ga2(SO4)3, 99.99%, Sigma-Aldrich). TEOS (7.4 mL, 98%, Aldrich) and
the second solution were added dropwise to the first solution. After
ageing at 308 K for 3 h, the obtained mixture was transferred to an
autoclave and hydrothermally treated under autogenous pressure
at 423 K for 10 h. The obtained product was then removed from the
oven and cooled to room temperature. After filtration and washing
several times with distilled water, the obtained solid was dried at
333 K for at least 24 h. The powder was then calcined in air at 823 K
for 12 h to remove the template.
silanol groups, thereby forming a covalent bond. Unfortunately,
these organic–inorganic hybrid materials are less basic than the
corresponding free organic amine molecule. This fact has been
explained as involving the interaction of the amine function with
residual silanol groups [30].
Mesoporous solids may be used without calcination, the pres-
ence of surfactant inside the pores showing interesting and
remarkable basic properties. Thus, these attractive catalysts have
also been tested in different reactions which require basic cata-
lysts such as Knoevenagel and Claisen–Schmidt condensations [31],
Michael additions [32], and cycloaddition reactions of CO2 with
epoxides [33].
Kubota et al. [32,34] achieved excellent results during Knoeve-
nagel condensation by using Si-MCM-41 molecular sieve while
keeping the surfactant inside the pores called [CTA]Si-MCM-41. In
this catalyst, active sites are high basicity SiO− sites, which are in the
channels. Oliveira et al. [35] used a series of as-synthesized molec-
ular sieves containing several Si/Al ratio and they have been tested
as basic catalysts for Knoevenagel condensation, they showed that
increasing the content of Si/Al ratio increases the amount of siloxy
anion and increases conversion of benzaldehyde.
1,2,3-Triazoles have found widespread applications as
pharmaceuticals and industrial compounds such as dyes, anti-
corrosive agents, photostabilizers, photographic materials, and
agrochemicals [36]. In addition, compounds containing 1,2,3-
triazoles have shown a broad spectrum of biological activities such
as antibacterial against Gram positive bacteria [37], herbicidal and
fungicidal [38], antiallergic [39], anticonvulsant [40], ␤-lactamase
inhibitive [41] and anti-HIV [42]. Several synthetic methods for
preparing triazole derivatives have been developed. Among them,
we can cite Huisgen 1,3-dipolar cycloaddition [43] and its recent
development toward click chemistry [44].
2.2. Characterization
The XRD powder diffraction patterns of the Si-MCM-41, Ga-
MCM-41 and Al-MCM-41 mesoporous materials were obtained
with a Bruker AXS D-8 diffractometer using Cu-K␣ radiation. Nitro-
gen adsorption was performed at 77 K in a TriStar 3000 V6.04
A volumetric instrument. The samples were outgassed at 353 K
prior to the adsorption measurement until a 3 × 10−3 Torr static
vacuum was reached. The surface area was calculated by the
Brunauer–Emmett–Teller (BET) method [48]. The pore size distri-
butions were obtained from the adsorption branch of the isotherm
using the Barrett–Joyner–Halenda (BJH) method [49]. FTIR spec-
tra of the mesoporous Al, Ga or Si-MCM-41 molecular sieves in the
range 400–4000 cm−1 were collected on a JASCO (4200) instrument
using KBr pellet technique. Thermogravimetric analysis (LABSYS
Evo SETARAM) was carried out under air atmosphere in the temper-
ature range 20–800 ◦C with a heating rate of 10 ◦C/min. The energy
dispersive X-ray analysis (EDX) jointed to a XL-30 scanning elec-
tron microscope was used to calculate the Si/Al and Si/Ga ratios of
the aluminum- or gallium-containing MCM-41. The surface topog-
raphy of the different solids was observed using SEM on a Hitachi
4800S microscope and TEM was performed on a JEOL 1200 EXII
device.
In this paper, we report a facile and rapid pathway for the syn-
thesis of 1,2,3-triazoles through 1,3-dipolar cycloaddition reactions
between 4-nitrophenyl azide and activated alkenes [36] using a
heterogeneous catalytic system.
In previously reported works concerning MCM-41-catalyzed
Knoevenagel condensation reactions, as-synthesized Si-MCM-41
was studied as basic catalyst [31–33]. Generally the catalysts for the
cycloaddition of azide are solids which contain copper [29,45–47],
to our best knowledge, mesoporous Si- Ga- or Al-MCM-41 have
never been studied for cycloaddition of aryl azides. Thus the aim
of the present research is to compare the catalytic properties
of a series of mesoporous catalyst including: (1) Si-MCM-41, (2)
Ga-MCM-41, (3) Al-MCM-41, (4) and a mixture between homoge-
neous/heterogeneous catalysts.
2.3. Reaction procedures for the cycloaddition of 4-nitrophenyl
azide with activated alkenes
2.3.1. Procedure 1
To the required methylene-activated compound (2 mmol) and
Et3N (2 mmol) in DMF (2 mL) was added 4-nitrophenyl azide (1,
1 mmol), and the mixture was stirred at room temperature for 24 h.
The precipitate formed upon addition of H2O (5 mL) was filtrated,
washed with H2O, dried, and recrystallized from iPrOH.
These mesoporous materials are used as-synthesized or calcined
like catalysts for the cycloaddition of aryl azides with activated
alkenes in liquid phase at room temperature.
2.3.2. Procedure 2
To the required methylene-activated compound (2 mmol) and
Et3N (2 mmol) in DMF (2 mL) was added 4-nitrophenyl azide (1,
1 mmol) and calcined or as-synthesized mesoporous Si- Ga- or Al-
MCM-41 catalyst (10 mol%), and the mixture was stirred at room
temperature (TLC monitoring). The precipitate formed upon addi-
tion of H2O (5 mL) was filtrated, washed with H2O and dried. To
remove the catalyst, the precipitate was extracted with acetone.
After removal of the solvent, the crude product was recrystallized
from iPrOH. Characterization data associated with this article have
been previously described [50], except in the case of 3c.
2. Experimental
2.1. Synthesis of Ga-MCM-41 and Al-MCM-41
Si-MCM-41, Ga-MCM-41 and Al-MCM-41 mesoporous mate-
rials were prepared by direct hydrothermal synthesis using
cetyltrimethylammonium bromide (CTAB) as structure-directing
template, gallium sulfate or sodium aluminate and TEOS as the gal-
lium or aluminum and silica source, respectively. The procedure for
the catalysts preparation was thoroughly described elsewhere [8].
The gel composition was: 1 TEOS, 0.12 CTAB, 0.25 NaOH, 1.5
EtOH, 100 H2O and 0.00625 Ga2(SO4)3 (case of Ga-MCM-41) or
0.00625 Al2O3 (case of Al-MCM-41) (for the case of Si-MCM-41 the
Si/Al or Ga ≈ ∞). We first prepared two solutions, the first by mixing
2.3.3. The characterization data for the 3c is as fellow Ethyl
5-methyl-1-(4-nitrophenyl)-1H-1,2,3-triazole-4-carboxylate (3c)
Yield: 93% (Section 2.3.1). Yellow powder, mp 185 ◦C. 1H NMR
(300 MHz, CDCl3): 1.45 (t, 3H, H1, J = 7.1 Hz), 2.68 (s, 3H, H6), 4.47 (q,
2H, H2, J = 7.1 Hz), 7.73 (d, 2H, J = 9.1 Hz), 8.46 (d, 2H, J = 9.1 Hz).13
C

B. Boukoussa et al. / Applied Catalysis A: General 489 (2015) 131–139
133
Fig. 1. XRD patterns of as-synthesized and calcined Si- Ga- or Al-MCM-41, (a) Ga-MCM-41 and (b) Al-MCM-41. (c) Si-MCM-41.
NMR (75 MHz, CDCl3): 10.4 (CH3), 14.5 (CH3), 61.5 (CH2), 125.3 (2
CH), 126.0 (2 CH), 137.6 (C), 139.0 (C), 140.4 (C), 148.4 (C), 161.5
(C O).
consistent with the literature, where it has been showed that the
incorporation of a heteroatom in the structure of MCM-41 increases
the unit cell parameter [9]. This difference is probably due to the
bond length of Ga O, Al O and Si O, Ga O being higher than Al
O
2.3.4. Procedure 3
and Si O as consequence of the larger ionic radius of Ga3+ than
Al3+ and Si4+ [54]. The change in d-spacing and unit cell parameter
compared to siliceous MCM-41 proved the incorporation of gallium
or aluminum in the framework.
To the required methylene-activated compound (2 mmol) in
DMF (2 mL) was added 4-nitrophenyl azide (1, 1 mmol) and as-
synthesized mesoporous MCM-41 catalyst (25 mol%), the mixture
was stirred at room temperature (TLC monitoring). The next steps
are as above (Section 2.3.2).
An increase of peak intensity is systematically visible after calci-
nation, assessing more ordered structure after surfactant removal.
The (1 0 0) reflection becomes sharper and more intense upon cal-
cination, although the (1 1 0), (2 0 0) and (2 1 0) reflections are not
well defined and overlap to give a single broad band. A lattice con-
traction is also observed after calcination due to surfactant removal
and to the condensation of silanol (SiOH) groups in the walls.
Quantitative data for the estimation of gallium and aluminum
incorporation was obtained by EDX analysis. According to the
chemical composition used for the synthesis of Ga-MCM-41 and
Al-MCM-41, a nominal value of Si/Ga or Si/Al = 80 was expected.
However, the Si/Ga and Si/Al ratios, as determined by EDX in the
calcined MCM-41, are a little higher, indicating that the amount of
heteroatom incorporated in the structure is a little less than the
expected one (Table 1). For the same ratios of Si/Ga or Si/Al, the
percentage of aluminum in Al-MCM-41 is much more than gallium
in Ga-MCM-41. This difference of the gallium content in the start-
ing gel and in the final product has already been revealed by Lin
et al. when studying the effect of gallium content in the synthesis
of hexagonal silicas. In fact, the yield of Ga in the synthesized solids
decreased to around 60% [55].
In Table 1, are also given the BET surface area, pore size, wall
thickness and pore volume of the calcined Si- Ga- or Al-MCM-41
catalysts. There was a slight increase of the wall thickness in the
Ga or Al containing materials, when compared with Si-MCM-41.
These results could suggest that there was a modification of the
structure, probably due to the introduction of these elements in the
framework [56]. Fig. 2 shows the nitrogen adsorption–desorption
isotherms of the different solids. All the isotherms are of type IV and
exhibit three stages. The first stage is due to monolayer adsorp-
tion of nitrogen to the walls of the mesopores at a low relative
pressure (P/P0 < 0.25). The second stage is characterized by a steep
increase in adsorption (0.25 < P/P0 < 0.4). As the relative pressure
3. Results and discussion
3.1. Characterization of the catalysts
The diffraction patterns of the as-synthesized and calcined Si-
MCM-41, Ga-MCM-41 and Al-MCM-41 catalysts are given in Fig. 1.
The main peaks of the XRD patterns of all the samples are consis-
tent with the characteristic peaks of the hexagonal structure of the
MCM-41 mesoporous molecular sieves. Si-MCM-41 and Al-MCM-
41 exhibits a strong peak, respectively, at 2ꢀ = 2.27–2.13 due to
(1 0 0) reflection lines and three weak signals around 3.94–3.65,
4.56–4.18 and 6.01–5.50 (2ꢀ) corresponding to (1 1 0), (2 0 0) and
(2 1 0) reflections, indicating the formation of well-ordered meso-
porous materials with hexagonal regularity [51].
For Ga-MCM-41 materials, peaks of XRD are broadened as a
result of the insertion of amount of Ga. This suggests a more dis-
ordered arrangement of channels for the Ga-MCM-41, but keeping
a hexagonal structure with good regularity. Similar observations
have been shown by Campos et al. where they studied the influence
of Si/Ga on the structure of MCM-41 [9].
The decrease of structure order for Al MCM-41 and particularly
for Ga-MCM-41 can be explained by the isomorphous substitution
of Ga or Al in MCM-41 framework carried out by a direct synthesis
method [52,53].
√
The unit cell parameter a0 is calculated from a0 = 2d100
/
3,
where the d-spacing values are calculated by n ꢁ = 2d sin ꢀ. The
observed d spacing and unit cell parameter results (Table 1) are
well-matched with the hexagonal p6mm space group.
We notice that the calculated cell parameters are 43, 47 and
˚
48 A for Si- Al- or Ga-MCM-41 solids, respectively; these results are

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B. Boukoussa et al. / Applied Catalysis A: General 489 (2015) 131–139
Table 1
Physical characteristics of mesoporous catalysts.
Catalyst (calcined)
Si/Ma
Si/M (EDX)b
d100 (Å)
a0 (Å)c
Surface area (m2/g)
Dd (Å)
he (Å)
Pore volume (cm3/g)
Si-MCM-41
Al-MCM-41
Ga-MCM-41
–
80
80
–
37.54
41.24
42.42
43.34
47.61
48.98
1430
1440
1030
35.2
35.7
36.7
8.14
11.91
12.28
1.071
1.097
0.973
90.74
100.01
a
Molar ratio in the initial gel. M = Ga or Al.
b
c
Molar ratio determined by EDX analysis.
√
a0 means lattice parameter: a0 = 2d100
/
3.
d
e
Pore diameter determined by the BJH method.
h: Wall thickness: h = a0 − D.
Fig. 2. Nitrogen adsorption–desorption isotherms of calcined Si- Ga- or Al-MCM-41
materials.
Fig. 3. TGA analysis curves for as-synthesized Si- Ga- or Al-MCM-41 mesoporous
materials photomicrographs of calcined (a) Ga-MCM-41 and (b) Al-MCM-41.
increases, the isotherm exhibits a sharp inflection, characteristic
of capillary condensation within the uniform mesopores. The third
stage (P/P0 > 0.4) in the adsorption isotherm is the gradual increase
in volume with P/P0, due to multilayer adsorption on the outer sur-
face of the particles. The BJH pore size distribution curves for Si- Al-
or Ga-MCM-41 are shown in Fig. S1 (see Supporting information).
The mesoporous materials Si- or Al-MCM-41 have narrow meso-
pore size distribution; in the case of Ga-MCM-41, the BJH pore size
distribution further indicates the presence of irregular mesopores.
These results are well correlated to the XRD data which already
revealed less ordered structure for Ga-MCM-41 solids.
It could be seen from Table 1 that the pore diameter of
samples increased gradually in the following sequence Si-MCM-
41 < Al-MCM-41 < Ga-MCM-41, which suggested generally that
heteroatoms incorporation would result in a shift to higher pore
size [9].
On the other hand, the pore volume and BET surface area
decreased basically for Ga-MCM-41. Such decrease in the SSA when
gallium was introduced could be partly related to the presence of
extra-framework gallium species with lower specific surface area
and thus lowering the overall surface area of the final material [57].
The FTIR spectra of the calcined and as-synthesized samples
are given in Fig. S2 (see Supporting information). The presence
of absorption bands around 2921 and 2851 cm−1 for the as-
synthesized materials corresponds to asymmetric and symmetric
CH2 vibrations of the surfactant molecules. The infrared spec-
trum of the calcined samples indicates a broad envelop around
3500 cm−1, due to O H stretching of surface hydroxyl groups,
bridged hydroxyl groups and adsorbed water molecules, while
deformational vibrations of adsorbed molecules cause the adsorp-
tion bands at 1626–1638 cm−1. The peaks between 1247 and
1072 cm−1 are attributed to the asymmetric stretching of T
O T
(T = Ga or Al). Other groups are observed around 800 and 544 cm−1
and the peak at 460 cm−1 is due to the bending mode of T
O
T.
The thermal properties of the samples were investigated by TGA
(Fig. 3). The initial weight loss up to 120 ◦C is due to desorption of
physically adsorbed water. The weight loss from 120 to 350 ◦C is
due to organic template. The oxidative desorption of the organic
template takes place at 180 ◦C and the minute quantity of weight
loss above 350–550 ◦C is related to water loss from the conden-
sation of adjacent Si OH groups to form siloxane bonds. The loss
in mass varies according to the following order Si-MCM-41 > Ga-
MCM-41 > Al-MCM-41.
From the TGA results, one can deduce that the organic template
associated with the silanol groups in pure silica MCM-41 can be
easily removed at lower temperatures whereas, for the Al-MCM-41
samples, the template has to be removed at higher temperatures
due to the stronger interaction of the organic template with the
aluminum species.
SEM and TEM images of the calcined samples Si- Al- or Ga-
MCM-41 are shown in Fig. 4. This information could be required
to assess any relationship between catalytic activity and their

B. Boukoussa et al. / Applied Catalysis A: General 489 (2015) 131–139
135
Fig. 4. SEM and TEM images of calcined Si- Ga- or Al-MCM-41 mesoporous materials: (a–c) SEM images, (d–f) TEM images.
morphologies. The SEM pictures of the samples are typical of sili-
cate mesoporous materials and show a different morphology with
some large elongated agglomerates.
3.2.1. Cycloaddition reaction using a mixture of homogeneous
and heterogeneous catalysis
Table 3 depicts the results using both homogeneous (Et3N) and
heterogeneous (MCM-41) basic catalysts. When compared with
triethylamine alone (Table 2), the evaluated mixtures exhibit a
very important activity, with very high yields and, except for 3d,
shorter reaction times (0.5 to 2 h, Table 3). In the case of homoge-
nous/heterogeneous catalysis using the calcined or as-synthesized
mesoporous materials Si- Ga- or Al-MCM-41, 4-nitrophenyl azide
(1) was simply added to the activated alkenes 2 (2 Eq) in the
presence of both triethylamine (2 Eq) and a catalytic amount
(10 mol%) of Si- Ga- or Al-MCM-41, using DMF as solvent. The
products were collected and washed with water. To remove the
catalyst, the precipitate was extracted with acetone, and the sol-
vent was then removed. Good results were obtained under these
conditions from 4-nitrophenyl azide (1) and all the activated
alkenes 2 using Et3N/calcined mesoporous material Si-MCM-41
(Table 3, entries 21–25). By using Et3N/calcined Ga- or Al-MCM-41
(Table 3, entries 1–5 and 11–15), Et3N/as-synthetized Si-MCM-41
(Table 3, entries 26–30) and Et3N/as-synthetized Ga- or Al-MCM-
41 (Table 3, entries 6–10 and 16–20), good yields were still
observed using acetylacetone (2a), methyl acetoacetate (2b) and
Whereas Ga-MCM-41 exhibits particles irregular shape
between 0.5 and 2 ␮m, Si- or Al-MCM-41 have particle size
between 1 and 2.5 ␮m.
The TEM images show that the Si- or Al-MCM-41 mesoporous
catalysts display highly ordered honeycomb-like regular arrange-
ment of hexagonal pores. The TEM pictures of the calcined catalysts
are presented in Fig. 4. In the case of Ga-MCM-41, the TEM analysis
shows pores of irregular form. These results are in agreement with
nitrogen sorption measurements and XRD analysis.
3.2. Catalytic experiments
By reaction of 4-nitrophenyl azide (1, 1 Eq) with the activated
alkenes 2 (2 Eq) in the presence of triethylamine (2 Eq), and using
DMF as the solvent, the 1,2,3-triazoles 3a–e were isolated in mod-
erate to high yields after 24 h reaction time at room temperature
(Table 2). The reaction proved regioselective. The assignment of
the stereochemistry was established by NMR (NOESY, HMBC, and
HMQC) and was confirmed by XRD [50].

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B. Boukoussa et al. / Applied Catalysis A: General 489 (2015) 131–139
Table 2
Cycloaddition reaction of 4-nitrophenyl azide (1) with the activated alkenes 2 performed at room temperaturea.
R'
R"
N3
N
Et3N, DMF
rt, 24 h
N
R
R'
N
+
O2N
O2N
1
2
3
Entry
2
R, Rꢀ
3
Rꢀꢀ
Yield (%)b
1
2
3
4
5
2a
COMe, COMe
COMe, CO2Me
COMe, CO2Et
COPh, COPh
CN, CN
3a
3b
3c
3d
3e
Me
Me
Me
Ph
98
80
93
40
61
2b
2c
2d
2e
NH2
a
Reaction conditions: 4-nitrophenyl azide (1, 1 mmol), activated alkene (2, 2 mmol), Et3N (2 mmol), DMF (2 mL), room temperature, 24 h (see Section 2.3.1).
Isolated yields.
b
Table 3
Cycloaddition reaction of 4-nitrophenyl azide (1) with the activated alkenes 2 catalyzed under homogeneous/heterogeneous catalysisa.
R'
R"
N
N 3
N
N
Et 3 N, X/MCM-41
DMF, rt, 0.5-24h
R
+
R'
O
2 N
NO2
X= calcined or uncalcined
Entry
2
Catalyst
3
T (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
2a
2b
2c
2d
2e
2a
2b
2c
2d
2e
2a
2b
2c
2d
2e
2a
2b
2c
2d
2e
2a
2b
2c
2d
2e
2a
2b
2c
2d
2e
3a
3b
3c
3d
3e
3a
3b
3c
3d
3e
3a
3b
3c
3d
3e
3a
3b
3c
3d
3e
3a
3b
3c
3d
3e
3a
3b
3c
3d
3e
1.5
1.5
1.5
24
2
1.5
1.5
1.5
24
2
1.5
1.5
1.5
24
2
1.5
1.5
1.5
24
2
97
94
51
53
71
90
98
54
47
97
98
91
95
84
88
98
97
55
59
78
98
93
95
88
92
98
90
97
79
98
Calcined
Ga-MCM-41
As-synthesized
Ga-MCM-41
Calcined
Al-MCM-41
As-synthesized
Al-MCM-41
0.5
0.5
0.5
Calcined
Si-MCM-41
24
0.5
0.5
0.5
0.5
24
0.5
As-synthesized
Si-MCM-41
a
Reaction conditions: 4-nitrophenyl azide (1, 1 mmol), activated alkene (2, 2 mmol), Et3N (homogeneous catalyst, 2 mmol), heterogeneous catalyst (10 mol%), DMF (2 mL),
room temperature (see Section 2.3.2), 0.5–24 h.
b
Isolated yields.

B. Boukoussa et al. / Applied Catalysis A: General 489 (2015) 131–139
137
existence of the ionic pair ( SiO−, CTA+) has been demonstrated
by many researchers [35,58,59]. For instance, Oliveira and al stud-
ied a variety of as-synthesized molecular sieves and assessed that
they have basic sites and can be employed as catalysts for Kno-
evenagel condensation under mild conditions [35]. Their catalytic
activity is mostly dependent on the fraction of silicon framework.
Pure siliceous molecular sieves are suggested to contain the high-
est number of siloxy anions, which are the strong basic sites. The
occluded organic cations can interact with the molecular sieves
framework, providing the high catalytic activity. Calcined siliceous
molecular sieves, which have only silanol groups, show a lower
activity. The catalytic activity difference between Si- Ga- or Al-
MCM-41 could be caused by a higher concentration of siloxy anions
in Si-MCM-41 since it has more silica than Ga- or Al-MCM-41 (see
EDX results).
Fig. 5. Effect of the catalyst amount (as-synthesized Ga-MCM-41) on the yield of
3a.
malonodinitrile (2e). However, when using ethyl acetoacetate (2c)
and ␣-benzoylacetophenone (2d), moderate yields were noted.
After recourse to a 24 h contact in the case of 2d, the product 3d was
purified by column chromatography and isolated in yields ranging
from 47 to 84%. The use of the mixtures Et3N/as-synthesized or
calcined Si-MCM-41 catalyst led to higher yields than the other
catalysts.
For the products 3d and 3e, if we compare the results obtained
using the mixture of basic catalysts (Table 3) with those obtained
by homogeneous basic catalysis (Table 2), we can note that the
reaction times are reduced and that the yields are always improved
using the mixtures of Si- Ga- or Al-MCM-41 (10 mol%) with the
Et3N homogeneous catalyst (2 mmol). These results suggest that
the triethylamine is entrapped in the mesoporous materials [57],
and acts as a supported catalyst for this reaction.
Koller et al. [60] have also synthesized MFI zeolites with dif-
ferent amounts of silicon and showed that increasing the content
of this element increases the amount of siloxy anion. The same
remarks were pointed out by Oliveira et al. [35]. Srivastava et al.
also noticed similar behavior in their work, using Si, Al-BEA and
Si-MCM-41 [33]. When they carried out their reaction over as-
synthesized Si, Al-BEA catalyst, they had to use three times the
amount of the catalyst than that used for siliceous Si-MCM-41 to
achieve comparable conversions.
From the three tested catalysts, Si-MCM-41 mesoporous silica
showed to have the highest catalytic activity in the cycloaddition
reaction. This result is well correlated to the physico-chemical char-
acterizations of these materials (DRX, EDX, N2 sorption) and also
to their range of features: (1) they are siliceous materials con-
taining a high number of siloxy anion, (2) capacity of the large
pores to hold higher amounts of surfactant, which are cationic
CTA+ in concert with siloxy anions [58], (3) CTA+ cations are bulky
organic cations (low charge/volume ratio) and this means that
their interaction with the catalytic active sites, i.e. siloxy anions, is
weaker.
3.2.2. Cycloaddition reaction using a heterogeneous catalysis
As-synthesized M-MCM-41 (M = Si Ga or Al) materials were also
used as base catalysts without adding triethylamine (Fig. 5 and
Table 4).
We have demonstrated using TGA analysis that removal of the
surfactant (CTA+) in the Si-MCM-41 is easier compared to Ga or
Al-MCM-41, which means that the interaction between the silica
matrix and CTA+ is low whereas in the case of Ga or Al-MCM-41 the
interaction between the heteroatom-containing matrix and CTA+
is important. EDX analysis also shows that the incorporation of
aluminum is more important compared to the gallium thus the Ga-
MCM-41 has a high number of siloxy compared to Al-MCM-41 (see
Table 1).
Otherwise, triethylamine is at the origin of the irreversible water
elimination step [50]. The latter may displace the reaction toward
the formation of the final triazole, and thus help to perform more
difficult reactions such as that giving 3e (absence of intramolecular
hydrogen bond to favor the enimine form).
Using triethylamine alone leads to an efficient reaction,
except from ␣-benzoylacetophenone (2d) and malonodinitrile
(2e). Whereas for the former steric hindrance can be proposed to
rationalize the low yield, the absence of intramolecular hydrogen
bond to favor the enimine form can be advanced for the latter.
Using triethylamine in the presence of 10% of MCM-41 allowed
the yields of 3d and 3e to be improved. In the case of 3d, cal-
cined Si-MCM-41, which possesses a larger surface area, proved
the most efficient catalyst. The presence of surfactant inside
the mesopores, by decreasing the available surface, reduces the
catalyst activity. In the case of 3e, the yield is increased what-
ever the catalyst employed. The latter can either favor the
formation of the enimine form or the 1,3-dipolar cycloaddition
through coordination of the dipolarophile nitrogen to the catalyst
metal.
3.2.2.1. Effect of the amount of catalyst. In order to understand
the influence of the heterogeneous catalysts on the cycloaddi-
tion reaction, reactions between 4-nitrophenyl azide (1, 1 Eq) and
acetylacetone (2a, 1 Eq) were performed using different amounts
of as-synthesized Ga-MCM-41 (Fig. 5). Using 10 mol% of as-
synthesized Ga-MCM-41 led to a very low 5% yield for 24 h reaction
time. This result contrasts with the 90% yield obtained using the
same amount of catalyst in the presence of triethylamine for a
shorter 1.5 h reaction time (Table 3, entry 6), and suggests a synergic
effect between triethylamine and the as-synthesized mesoporous
material. One can notice in Fig. 5 that increasing the amount of
catalyst has an impact on the reaction yield. Indeed, a 24 h reaction
time led to a 75% yield using 20 mol% (and 92% yield using 25 mol%)
of as-synthesized Ga-MCM-41. The yield obtained after one hour of
reaction in the presence of 20% of catalyst is low about 7%. Thus,
the reaction time can been minimized due to an increased reactivity
using both catalysts Et3N and as-synthesized Ga-MCM-41.
3.2.2.2. Cycloaddition reaction using Si-, Ga- or Al-MCM-41 catalysts.
As expected no products were detectable by using 25 mol% of cal-
cined Si-, Ga- or Al-MCM-41 as catalyst for the reaction between
4-nitrophenyl azide (1, 1 Eq) and acetylacetone (2a, 1 Eq) (results
not shown). In contrast, very high yields were obtained for the prod-
ucts 3a–c with a reaction time not more than 0.25 h (15 min) when
using 25 mol% of as-synthesized Si-MCM-41 (Table 4). The latter is
more active than as-synthesized Ga- or Al-MCM-41, Et3N and the
mixed catalyst in these three reactions (results not shown).
The basic properties exhibited by as-synthesized Si- Ga- or
Al-MCM-41 are due to the presence of siloxy anions ( SiO−),
which exist in combination with the cationic surfactant. Indeed, the
Without triethylamine, using as-synthesized MCM-41 catalysts
in a sufficient amount (25 mol%) provides the triazoles 3a–c (for

138
B. Boukoussa et al. / Applied Catalysis A: General 489 (2015) 131–139
Table 4
Cycloaddition reaction of 4-nitrophenyl azide (1) with the activated alkenes 2 catalyzed by as-synthesized Si- Ga- or Al-MCM-41a.
R'
R"
N
N
3
N
N
S i- G a o r A l- M C M - 4 1
a s - s y n t h e s iz e d
R
+
R'
D M F , r t, 0 .2 5 -2 4 h
O
2 N
NO
2
2
3
Entry
2
Catalyst
3
T (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
2a
2b
2c
2d
2e
2a
2b
2c
2d
2e
2a
2b
2c
2d
2e
3a
3b
3c
3d
3e
3a
3b
3c
3d
3e
3a
3b
3c
3d
3e
1
1
1
92
93
94
47
9
89
61
71
48
8
94
97
90
69
55
As-synthesized
Ga-MCM-41
24
24
24
24
24
24
24
0.25
0.25
0.25
24
18
As-synthesized
Al-MCM-41
As-synthesized
Si-MCM-41
a
Reaction conditions: 4-nitrophenyl azide 1 (1 mmol), activated alkene 2 (1 mmol), as-synthesized Si- Ga- or Al-MCM-41 (25 mol%), DMF (2 mL), room temperature (see
Section 2.3.4), reaction time 0.25–24 h
b
Isolated yields.
which the enol forms are favored due to intramolecular hydrogen
bond) in good yields. In this case, the triethylamine effect can be
restored by the siloxy anions contained in as-synthesized MCM-41
catalysts. Substrate and intermediate product size seems to be a
limit of the system (products 3d and 3e), with better yields noted
for Si-MCM-41.
If we compare our materials with others catalysts, the as-
synthesized Si-MCM-41 catalyst seems to be the best for the
reactions of cycloaddition [29,45]. In fact, not only the reaction time
is decreased (around 15 min), but also the Si-MCM-41 is used as
synthesized thus no further preparation is needed.
3.2.2.3. Catalyst reusability. Reusability of the catalysts has been
studied in the cycloaddition of 4-nitrophenyl azide (1) under the
following conditions: 4-nitrophenyl azide (1, 1 mmol), acetylac-
tone (2a, 1 mmol), as-synthesized Si- Ga- or Al-MCM-41 (25 mol%),
DMF (2 ml), room temperature, 0.25 h reaction time for Si-MCM-
41, 1 h for Ga-MCM-41 and 24 h for Al-MCM-41. The catalysts were
filtered, washed with DMF and dried before use in the following
cycles, the results are represented in Fig. 6.
The catalyst could be reused up to five times with little loss
of activity, confirming its stability as seen by TGA and XRD data
(Figs. 3S and 4S see Supplementary data).
Indeed, the results obtained by the TGA analysis (Fig. 3S see Sup-
plementary data) indicate that there is a weak CTA+ leaching from
the reaction medium (for example ca. 0.2%, after five use of as-
synthesized Si-MCM-41). This mass loss is probably responsible for
the slight reduction of the catalyst activity. Concerning the results
obtained by XRD analysis (Fig. 4S see Supplementary data) we note
that there was a small decrease in the intensity of all characteristic
peaks of MCM-41, may be due to the influence of the solvent on the
CTA containing mesoporous materials [56].
4. Conclusion
Si- Ga or Al-MCM-41 molecular sieves have been successfully
prepared by a direct synthesis method. The samples exhibited high
structural regularity and surface area values, EDX results showed a
more important incorporation of aluminum into the framework of
MCM-41 compared to gallium.
Three types of catalysts were compared in the course of
the thermal cycloaddition of aryl azides with activated alkenes,
i.e. homogeneous [50], heterogeneous and mixed homoge-
neous/heterogeneous catalysts. Concerning the latter two catalysts,
the reaction time and product yields of 3a–c have been improved
Fig. 6. Catalyst reusability. Reaction conditions: 4-nitrophenyl azide (1, 1 mmol),
acetylacetone (2a, 1 mmol), catalyst (25 mol %), DMF (2 mL), room temperature,
reaction time: 0.25 h (15 min) for Si-MCM-41, 1 h for Ga-MCM-41 and 24 h for Al-
MCM-41 (at the end of the reaction, the catalyst is dried and reused).

B. Boukoussa et al. / Applied Catalysis A: General 489 (2015) 131–139
139
in the following order: heterogeneous catalyst > mixed cata-
lyst > homogeneous catalyst and, for the products 3d and 3e, the
homogeneous/heterogeneous catalysis was superior than the cat-
alysts used individually. This later result may be explained by a
synergic effect between Et3N and the mesoporous material.
The as-synthesized Si-MCM-41 is particularly efficient for the
cycloaddition reaction at room temperature due to its higher num-
ber of ionic pairs SiO− CTA+.
The incorporation of moderate amount of heteroatoms such
as Al or Ga in the silica framework would allow the mesoporous
solids to benefit from enhanced hydrothermal stability a feature
particularlyneeded in reactions operating in aqueous media. Unfor-
tunately, heteroatom incorporation reduces the number of siloxy
and decreases the basic character.
In conclusion, we have developed a convenient method for the
synthesis of 1,2,3-triazoles, which can serve as useful building
blocks for useful targets, by Si-MCM-41-catalyzed cycloaddition of
aryl azides with activated alkenes in very high yields. This one-pot
synthesis of 1,2,3-triazoles using a heterogeneous catalytic sys-
tem benefits from considerable synthetic advantages, such as mild
reaction conditions, easy availability of starting materials, short
durations of reaction (15 min), simplicity of the reaction procedure,
efficient catalyst regeneration and reuse for new reaction cycle.
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