Catalytic Performance of Al-MCM-41 Catalyst for the Allylation of Aromatic Aldehydes with Allyltrimethylsilane: Comparison with TiCl4 as Lewis acid

Article abstract of DOI:10.1016/j.molcata.2016.06.004

Mesoporous Al-MCM-41 molecular sieve with Si/Al ratio equal to 12.5 was synthesized under hydrothermal condition using cetyltrimithylammonium bromide (CTAB) as surfactant. This solid was characterized using several techniques e.g. powder X-ray diffraction (XRD), N₂ adsorption-desorption, FT-IR, TG/DTG and pyridine adsorption-desorption followed by IR spectroscopy. The catalytic performance of Al-MCM-41 catalyst as Lewis acid was used without treatment and was compared with TiCl₄ in the allylation of aromatic aldehydes with allyltrimethylsilane. The results showed that in presence of Al-MCM-41, homoallyl silyl ether is obtained regardless of the nature of aromatic aldehydes at a temperature of 35?°C. When TiCl₄ was used, the reactions require temperature of ?85?°C and all the products obtained were due to the diallylation. To explain this different allylation in the presence of the Al-MCM-41 or TiCl₄, two plausible reaction mechanisms are proposed. The Al-MCM-41 was used in four consecutive experiments without important loss of activity, confirming it stability. Finally, a new method for preparing single allylation in the short timeframe and mild conditions are presented.

Full text of DOI:10.1016/j.molcata.2016.06.004

Accepted Manuscript
Title: Catalytic Performance of Al-MCM-41 Catalyst for the
Allylation of Aromatic Aldehydes with Allyltrimethylsilane:
Comparison with TiCl4 as Lewis acid
Author: Lamia Brahmi Tewfik Ali-Dahmane Rachida
Hamacha Salih Hacini
PII:
S1381-1169(16)30217-5
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2016.06.004
MOLCAA 9910
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
8-5-2016
1-6-2016
2-6-2016
Please cite this article as: Lamia Brahmi, Tewfik Ali-Dahmane, Rachida Hamacha, Salih
Hacini, Catalytic Performance of Al-MCM-41 Catalyst for the Allylation of Aromatic
Aldehydes with Allyltrimethylsilane: Comparison with TiCl4 as Lewis acid, Journal of
Molecular Catalysis A: Chemical http://dx.doi.org/10.1016/j.molcata.2016.06.004
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Catalytic Performance of Al-MCM-41 Catalyst for the Allylation of
Aromatic Aldehydes with Allyltrimethylsilane: Comparison with TiCl4 as
Lewis acid
Lamia Brahmi a,*, Tewfik Ali-Dahmane b,c, Rachida Hamacha b, Salih Hacini a .
aLaboratoire de Chimie fine L.C.F., Université d'Oran, BP-1524 El-Mnaouer, 31000 Oran,
Algeria.
bLaboratoire de Chimie des Matériaux L.C.M, Université d'Oran, BP-1524 El-Mnaouer,
31000 Oran, Algeria.
cÉcole Supérieure en Sciences Appliquées de Tlemcen (ESSAT), BP 165 RP Bel horizon,
13000 Tlemcen, Algerie.
* Corresponding author. E-mail address: brahmilam@gmail.com

Graphical Abstract
O
O
O
O
Al
Si
OSiMe3
Si

O
H

Al-MCM-41
+
C
1
4
-
R
R
M
C
M
-
l
Single Allylation
Reusable
A
C
°
5
3
O
H
R
O
-
8
T
NCH3
5
i
C
4
°
O
C
l
,
C
Cl
Cl
Cl
H
Si
Ti
Cl

3
N
O
O
TiOCl2
2
+

R
H
R
Diallylation
Not Reusable
Highlights
 Mesoporous Al-MCM-41 molecular sieve with Si/Al ratio equal to 12.5 was
synthesized under hydrothermal condition.
 Pyridine coupled FT-IR spectroscopy analysis showed the existence of a high
concentration of Lewis acid sites in Al-MCM-41.
 In presence of Al-MCM-41 using mild conditions, homoallyl silyl ether is obtained.
With TiCl4, the reactions require temperature of -85 °C and the products obtained are
the diallylation.
 To explain this different allylation in the presence of the Al-MCM-41 or TiCl4, two
plausible reaction mechanisms are proposed.

Abstract
Mesoporous Al-MCM-41 molecular sieve with Si/Al ratio equal to 12.5 was synthesized
under hydrothermal condition using cetyltrimithylammonium bromide (CTAB) as surfactant.
This solid was characterized using several techniques e.g. powder X-ray diffraction (XRD),
N2 adsorption-desorption, FT-IR, TG/DTG and pyridine adsorption-desorption followed by IR
spectroscopy. The catalytic performance of Al-MCM-41 catalyst as Lewis acid was used
without treatment and was compared with TiCl4 in the allylation of aromatic aldehydes with
allyltrimethylsilane. The results showed that in presence of Al-MCM-41, homoallyl silyl ether
is obtained regardless of the nature of aromatic aldehydes at a temperature of 35 °C. When
TiCl4 was used, the reactions require temperature of -85 °C and all the products obtained were
due to the diallylation. To explain this different allylation in the presence of the Al-MCM-41
or TiCl4, two plausible reaction mechanisms are proposed. The Al-MCM-41 was used in four
consecutive experiments without important loss of activity, confirming it stability. Finally, a
new method for preparing single allylation in the short timeframe and mild conditions is
presented.
Keyword:
Al-MCM-41, TiCl4, aromatic aldehydes, allyltrimethylsilane, Lewis acid.

1. Introduction
Allylation of aromatic aldehydes with allylmethylsilane reactions is an important tool for the
formation of different carbon-carbon bond, using homogeneous Lewis acids such as BF3 [1],
Sc(OTf3) [2], InCl3 [3], YbCl3 [4], FeCl3 [5] and TiCl4 [6-9] as catalysts, which and is
commonly practiced in organic synthesis.
However, the commonly used homogeneous Lewis acids pose several problems, such as
difficulty in separation and recovery, disposal of spent catalyst, corrosion, high toxicity and
they are not reused for catalytic runs. For these reasons, more recyclable or environmentally
benign catalysts have been developed. The replacement of homogeneous acids by easily
separable heterogeneous solids in the allylation of aromatic aldehydes reactions is, therefore,
of great practical importance for the production of industrially important chemicals [10-12],
from the standpoint of so-called “green chemistry”.
Although zeolitic materials have important catalytic properties for use in different reactions
[13], they are not used when the size of the reactants is greater than pore size. For this reason,
in the past, efforts were directed towards the synthesis of similar structures which led to the
discovery of a novel family of materials called M41S [14,15]. Thus the discovery of
mesoporous materials MCM-41 belonging to the M41S family of catalysts opens new
possibilities for using uniform mesopores, whose access is possible for large molecules such
as those commonly used in the production of fine chemicals and petroleum chemistry. The
obvious advantage of these materials compared to zeolites is in the size of their pores which
can be adjusted from 20 to 100 Å in diameter, a surface area that can reach 1500 m2/g and a
pore volume which is of the order of 1.2 cm3/ g.
MCM-41 pure silica possesses a neutral framework, which limits its application as a
catalyst. However, the isomorphous substitution of silicon by a variety of metals such as
Al, Ga or Fe [16,17] gives rise to acidic properties. The catalytic activity of Al-MCM-41 is
attributed to the presence of the acid sites resulting AlO4 tetrahedral units in the structure.
These acid sites are Brönsted or Lewis according to the nature of the treatment. The acid sites
of these solids were used in several applications as acetalization [18,19], alkylation [20-22],
esterification [23], Mukaiyama aldol reactions [24], Strecker-type synthesis [25] and
Beckmann rearrangement [26]. The Lewis acid sites of Al-MCM-41 were tested in different
reactions, such as in the synthesis of diphenylmethane [27], Michael addition of indole to α,β-
unsaturated ketones [28], gas phase m-cresol alkylation with methanol [29], production of 5-
hydroxymethylfurfural from glucose [30], etc.

In our preliminary communication [7], the TiCl4 was used as Lewis acid in the reaction of the
allylation of aromatic aldehyde using allyltrimethylsilane to afford the corresponding
diallylation. In this work the efficiency of the Al-MCM-41 as catalyst Lewis acid in the
allylation of aldehyde aromatic by allyltrimethylsilane is explored and a comparison with
TiCl4 is discussed.
2. Experimental
2.1. Catalyst preparation
2.1.1. Starting materials
Sodium aluminate (54%Al2O3; 41%Na2O; 5%H2O; Aldrich) was used as the aluminium
source, colloidal silica (ludox 40%, Prolabo) served as
a
silicon source,
cetyltrimethylammonium bromide (C19H42NBr; CTAB, Merck; 99%) as a surfactant,
tetramethylammonium hydroxide (TMAOH.5H2O, 97%, Aldrich) was utilized as a base and
the demineralized water as a solvent.
2.1.2. Synthesis of Si-MCM-41
Sample of Si-MCM-41 was prepared by using the direct synthesis method hydrothermal [31].
The molar chemical composition was: 1SiO2:0.25CTABr:0.2TMAOH:40H2O. The mixtures
were prepared by adding an amount of the surfactant (CTAB) under continuous stirring to a
basic solution tetramethylammonium hydroxide. After 30 min, Ludox was slowly added,
giving rise to white slurry. The reaction mixture was continuously stirred for 2 h. Afterwards
the obtained hydrogel was transferred into a Teflon autoclave vessel for the crystallization,
which lasted 48 h at 100 °C. Thereafter, the product was washed several times with
demineralized water, filtered and dried at 100 °C overnight, afterwards calcined under air at
550 °C for 12 h.
2.1.3. Synthesis of Al-MCM-41
The Al-MCM-41 was synthesized according to the procedure described in a previous paper
[32]. For this method three solutions were prepared, the first one contains a source of
aluminum mixed with an organic hydroxide of quaternary ammonium type (S1), the second
one a source of silica (S2) and a surfactant agent for the last one (S3). The solvent used in the
three
solutions
is
demineralized
water.
The
molar
composition
was
1SiO2:0.25CTAB:0.2TMAOH: 0.04Al2O3:40H2O. The obtained gel was kept in a Teflon-
lined stainless steel autoclave and heated at 100 °C for two days for crystallization. The solid
product obtained was washed, filtered and dried overnight at 100 °C. The as-synthesized
samples were calcined at 550 °C in air for 12 h.
2.2. Catalyst characterization

Powder X-ray diffraction (XRD) patterns were carried out using a Bruker D5005
diffractometer using Cu Kradiation (wavelength =1.15406 Å), with scanning step 0.0358
2theta between 1° and 10° 2theta. N2 gas sorption measurements were performed at -196 °C
with a Nova 1000e. For the N2 adsorption–desorption, the sample was degassed under vacuum
at 200 °C over 24 hours prior to adsorption. The specific surface area was determined by the
BET formula [33] from data in the relative pressure range from 0.04 to 0.2. The transmission
infrared spectra was recorded on a Nicolet Avartar 360 spectrometer, and the sample content
in KBr wafers was 1%. The thermogravimetric analysis of the as-synthesized Si-MCM-41 and
Al-MCM-41 were obtained in the air from 20 °C to 800 °C at the heating rate of 10 °C/min in
SDT Q600 Instruments apparatus. The energy dispersion X-ray analysis (EDX) jointed to
Philips ESEM XL 30 FEG scanning electron microscope was used to calculate the Si/Al
ratio of the aluminum containing MCM-41. The surface acidity of the Al-MCM-41 was
characterized by in situ pyridine adsorption FT-IR spectroscopy. A self-supporting wafer with
20 mg catalyst was put into the in situ cell and was activated at 200 °C for 4 hours under
0.267 Pa. The sample was cooled to room temperature, and pyridine adsorption was
performed in excess pure pyridine for 15 min followed by evacuation. FT-IR spectra were
then recorded at room temperature of 50, 150, 250 and 350 °C respectively. To determine the
concentration of both types of acid sites, the extinction coefficients [34] used were B = 0.73
cm µ mol-1 and L = 1.11 cm µ mol-1, for Brönsted and Lewis acid sites, respectively.
2.3. General procedure for the allylation of aromatic aldehydes with allyltrimethylsilane
2.3.1. In the presence of TiCl4
A flame-dried, three-necked, round-bottomed flask equipped with a magnetic stirring bar, a
thermometer and an argon outlet were charged with anhydrous CH2Cl2 (20 mL) and MeNO2
(1.2 mL, 20 mmol). The solution was cooled at-60 °C, TiCl4 (1 mL, 8.1 mmol) and aldehyde
(5.0 mmol) in CH2Cl2 (2 mL) was then added. After 15 min of stirring, the mixture was
cooled at -90 °C and allyltrimethylsilane (2.4 mL, 15 mmol, 3 equiv.) in CH2Cl2 (2 mL) was
slowly added. The mixture was stirred at -85°C for 3 h and then warmed to -60 °C. After
completion of the reaction (TLC; 5–15 h), the mixture was poured into a saturated solution of
NH4Cl. After the usual workup, the crude product was purified by flash chromatography on
silica-gel (petroleum ether then petroleum ether–ether 25:1). The product gave a satisfactory
1H NMR and 13C NMR spectra.
2.3.2. In the presence of Al-MCM-41

In a two-necked, round-bottomed flask equipped with a magnetic stirring bar, under an
atmosphere of argon was charged with aldehyde (0.106 g, 1.0 mmol, 1 equiv.) and Al-MCM-
41 (25 mol%, dried prior to use at 300 °C for 1h under vacuum) in dichloromethane (2
mL),the mixture was stirred at 35 °C. After 5 min of stirring, the allyltrimethylsilane (0.228 g,
2 mmol, 2 equiv.) in CH2Cl2 (0.5 mL) was slowly added, the reaction mixture was stirred at
35°C. Upon completion of the reaction (TLC; 25min–24 h), the catalyst was removed by
filtration. After the filtrate was concentrated under reduced pressure, only pure homoallyl silyl
ether was obtained, thus further purification by silica-gel column chromatography (petroleum
1
ether then petroleum ether–ether 28:1) was necessary. The product gave a satisfactory H
NMR and 13C NMR spectra.
2.3.3. Analytical data for compounds 3a, 3c, 3e, 3l
Proton nuclear magnetic resonance (1H) spectra and carbon-13 (13C) spectra were recorded at
400 and 100 MHz, respectively. The proton signal of residual, non-deuterated solvent ( 7.26
1
13
ppm for CHCl3) was used as an internal reference for H spectra. For C spectra, chemical
shifts are reported relative to the  77.23 ppm resonance of CDCl3. Coupling constants are
1
reported in Hz. Trimethyl(1-phenylbut-3-enyloxy)silane (3a): colorless oil; H NMR (300
MHz, CDCl3) 7.39–7.28 (m, 5H), 5.84 (m, 1H), 5.11 (t, J = 9 Hz, 2H), 4.75 (dd, J = 5.41,
7.42 Hz, 1H), 2.50 (m, 2H), 0.11 (s, 9H); 13C NMR (75MHz, CDCl3)  144.90, 135.33,
128.12, 127.08, 125.94, 116.86, 74.95, 45.18, 0.18.
1
1-Chloro-4-[1-[(trimethylsilyl)oxy]-3-buten-1-yl]benzene (3c): colorless oil; H NMR (300
MHz, CDCl3)  7.31 (m, 4H), 5.78 (m, 1H), 5.09-5.05 (m, 2H), 4.70 (m, 1H), 2.45 (m, 2H),
13
0.11 (s, 9H); C NMR (75MHz, CDCl3)  143.50, 134.79, 132.70, 128.31, 127.30, 117.28,
74.26, 45.19, 0.16.
1
4-[1-[(trimethylsilyl)oxy]-3-buten-1-yl]benzonitrile (3e): colorless oil; H NMR (300 MHz,
CDCl3)  7.60 (d, J = 8.43Hz, 2H), 7.42 (d, J = 8.06 Hz, 2H), 5.71 (m, 1H), 5.01 (m, 2H),
13
4.74 (dd, J = 5.15, 7.35 Hz, 1H), 2.39 (m, 2H), 0.05 (s, 9H); C NMR (75MHz, CDCl3) 
150.29, 134.06, 131.98, 126.57, 118.91, 117.72, 110.80, 73.98, 44.78, 0.02.
1
1,3-bis(1-(trimethylsilyloxy)but-3-enyl)benzene (3l): pale yellow oil; H NMR (300 MHz,
CDCl3)  7.31–7.23 (m, 4H), 5.81 (m, 2H), 5.06 (m, 4H), 4.70 (m, 2H), 2.58-2.41 (m, 4H),
13
0.07 (s, 18H); C NMR (75MHz, CDCl3)  144.74, 135.23, 127.88, 124.71, 123.66, 116.81,
75.07, 45.27, 0.16.
3. Results and discussion
3.1. Catalyst characterization

3.1.1.X-ray diffraction analysis
The diffraction patterns of the as-synthesized and calcined Si-MCM-41and Al-MCM-41
catalysts are given in Fig. 1. The main peaks of the XRD patterns of all the samples are
consistent with the characteristic peaks of the hexagonal structure of the MCM-41
mesoporous molecular sieves [35-37]. The as-synthesized Si-MCM-41 material (Fig. 1a)
exhibit a strong peak, at 2theta = 2.21 due to (100) reflection lines and three weak signals
around 3.79, 4.35 and 5.72 (2theta) corresponding to (110), (200) and (210) reflections,
indicating the formation of well-ordered mesoporous materials with hexagonal regularity [38].
For the as-synthesized Al-MCM-41 (Fig. 1b), the characteristic reflection (100) is broadened
as a result of the insertion of amount of Al. This suggests more disordered arrangement of
channels for the Al-MCM-41, but keeping a hexagonal structure with good regularity.
However, when the MCM-41 mesoporous molecular sieves are submitted to the calcinations
process, the (100) reflection becomes sharper and more intense.
In the case of Si-MCM-41, we can observe the disappearance of peak (210); this is probably
due to reduction of the order of the structure. After calcinations, the 2theta positions for all
samples are shifted to a higher value, which indicated a contraction of the unit cell parameter
a used by template removal and subsequent condensation of the silanol groups. The unit cell
parameter a0is calculated from a0= 2d100/√3, where the d-spacing values are calculated by n λ
= 2d sin. The observed d spacing and unit cell parameter results (Fig. 1) are well-matched
with the hexagonal p6mm space group. We notice that the calculated cell parameters are 42
and 44 Å for Si- or Al-MCM-41 solids, respectively; these results are consistent with the
literature, where it has been shown that the incorporation of a heteroatom in the structure of
MCM-41 increases the unit cell parameter [32,39]. This difference is probably due to the
bond length of Al-O (183.6 pm) being higher than Si-O (158 pm) as consequence of the larger
ionic radius of Al3+ than Si4+ [32]. The change in d-spacing and unit cell parameter compared
to siliceous MCM-41 proved the incorporation of aluminum in the framework. It is important
to note that after the calcinations process of the samples an expected contraction of the unit
cell parameter (a0) is observed (Table 1).
Higher degree of lattice contraction has occurred when the aluminum is incorporated in the
framework. According to Gaydhankar et al. [40], this indicates that the population of Si-OH
units in the channel wall increases in the order: Al-MCM-41 > Si-MCM-41. The quantity of

aluminum incorporated in the framework was obtained by EDX analysis. According to the
chemical composition used for the synthesis of Al-MCM-41, a nominal value of Si/Al = 12.5
was expected. However, the Si/Al ratio, as determined by EDX in the calcined MCM-41, is a
little higher, indicating that the amount of heteroatom incorporated in the structure is a little
less than expected (Table 1).
3.1.2.N2 adsorption–desorption
Fig. 2 shows the N2 adsorption–desorption isotherms of the calcined Si- or Al-MCM-41and
Table 1 summarizes the textural proprieties of theses catalysts. The obtained isotherms are
typical for MCM-41 phase. The corresponding isotherm is of type IV, characteristic of the
mesoporous solids according to the IUPAC nomenclature [41].
The type IV isotherm is defined by three stages: at low relative pressures, a slow increase of
nitrogen corresponding to monolayer-multilayer adsorption on the pore walls (P/P0 < 0.24). At
intermediate relative pressures, a sharp step indicates capillary condensation with in
mesopores (0.24 < P/P0 < 0.40). In the last stage (P/P0 > 0.40), a final plate with a slight
inclination associated with multilayer adsorption on external surface of the particles. It could
be seen from Table 1 that the pore diameter of Al-MCM-41is higher than Si-MCM-41, on the
other hand, the pore volume and BET surface area decreased for Al-MCM-41, which
suggested generally that heteroatoms incorporation would result in a shift to higher pore size
and decreased in specific surface areas [39]. The wall thickness in the case of Al-MCM-41 is
around (8.4Å) and higher than that found for Si-MCM-41 (ca. 7.6Å). This can be explained
by the incorporation of aluminium species (Si/Al = 13.47) [42].
3.1.3.FT-IR analysis
The IR spectra in the 500-1600 cm-1 range, named the fingerprint zone of the materials for the
KBr-pelletized calcined Si-MCM-41 and Al-MCM-41 samples are shown in Fig. 3. The main
bands described in the literature for MCM-41 are found in our samples [43,44]. The peaks
between 1244 and 1081 cm−1are attributed to the asymmetric stretching of the T-O-T (T is Al
or Si) groups. The symmetric stretching mode of the T-O-T (T is Al or Si) groups is observed
at approximately 802 cm-1. The pure silica MCM-41 presents a band at 964 cm−1attributed to
the Si-O stretching vibration in the Si-OH groups at the defect sites present in the mesoporous
structure [45].
3.1.4.TG-DTG analysis

Thermogravimetric analysis of uncalcined samples prepared with CTAB as template,
presented typical MCM-41 TG-DTG curves. The thermograms of the samples are presented
in Fig. 4. The TGA curves show three weight losses at 30-120 °C, 120-350 °C and 350-600
°C. The weight loss in the first step is due to desorption of physically adsorbed water. The
second mass loss is caused by the oxidative decomposition of organic surfactant. The final
step is mainly due to the water loss formed by the condensation of adjacent silanol groups to
form siloxane bonds.
The loss in mass varies according to the following order Si-MCM-41 > Al-MCM-41. From
the TGA results, the peaks of surfactant removal for the Al-MCM-41 are shifted towards
higher temperature compared to the pure silica MCM-41. According to Hui and Chao [42],
Al-MCM-41 has a much stronger interaction of the organic template cations with aluminium
species than with SiO-.
3.1.5.Pyridine FT-IR analysis
The acidity of Al-MCM-41 was measured by adsorption of pyridine coupled FT-IR
spectroscopy, for detect the presence and nature of acid sites. The corresponding FT-IR
spectra (Fig. 5) shows the presence of both types of acid sites, as inferred from the intense
bands at 1454 cm-1 and 1545 cm−1 due to Lewis and Brönsted acid sites respectively. The
integration of the area under these bands quantified the concentration of the acid sites [46].
The concentrations were determined after evacuation at different temperatures (Table 2), thus
corroborates that the catalyst is strong acid solid. It can be seen that Al-MCM-41 gave priority
to with Lewis acid and the concentration of this site still remained even after evacuation at
350 °C.
3.2. Allylation of aromatic aldehydes with allyltrimethylsilane catalyzed by TiCl4 or Al-MCM-
41
In our previous communication, TiCl4 was used to catalyze the allylation of aromatic
aldehydes with allyltrimethylsilane [7]. We have observed that benzaldehyde,
naphthaldehydes and benzaldehydes substituted by electron- donor and electron withdrawing
groups twice undergo allylation by treatment with allylsilane and titanium tetrachloride,
giving rise to 1,6-heptadien-4-yl-substituted arene compounds (Table 3). In contrast, the use
of phthalaldehyde gives a single allylation of each carbonyl moiety in modest yield (Table 3,

entry 10). This moderate yield is explained by the instability in a reaction condition of the
product.

In the presence of the Al-MCM-41(Table 4), we have used the same conditions, namely the
temperature and the amount of allyltrimethylsilane in the condensation reactions of
allyltrimethylsilane with benzaldehyde and 2,4-dichlorobenzaldehyde, and TiCl4 was replaced
by Al-MCM-41. At low temperature (-85 °C to -10 °C), the condensation reaction does not
give any product (Table 4, entries 1 and 8), while in the presence of TiCl4 excellent yields
were obtained (Table 3, entries 1-7).When we increased the reaction temperature from 0 to 24
°C, only trace amount of the product were obtained (Table 4, entry 2),whereas at a higher
temperature of 35 °C, the best yields were obtained (Table 4, entries 3 and 9). NMR analysis
H1 and C13 confirmed that these products are the result of a single allylation. Increasing the
amount of allyltrimethylsilane to 5 equivalent (Table 4, entry 4) does not yield the diallylated
product, however, when TiCl4 was used as the Lewis acid and in the presence of only 3
equivalent of allyltrimethylsilane, the diallylated products were obtained regardless the
substituted aromatic aldehydes (Table 3).
A reaction of various aldehydes with allyltrimethylsilane using Al-MCM-41 at 35°C gives
rise to a single allylation (homoallyl silyl ether) (Table 5). We have observed that electron-
deficient aromatic aldehydes are allylated in excellent yields (Table 5, entries 1-7, 10-13).
However, in aromatic aldehydes bearing electron-donating groups such as p-anisaldehyde and
p-tolualdehyde, the desired products were obtained in moderate yields (Table 5, entries 8 and
9).
On the other hand, when the heteroaromatic aldehydes were used as allylation with
allyltrimethylsilane no reaction occurred (Table 5, entries 14 and 15). This may be due to the
low stability of the furfural ring and thiophene ring when exposed to Lewis acids. Whereas,
the reaction of crotonaldehyde gave the allylated products in moderate yields (Table 5, entry
16).
To explain this difference allylation in the presence of the MCM-41 or TiCl4, two plausible
reaction mechanisms are proposed, involving the role of Lewis acid sites of Al-MCM-41 and
the role of TiCl4 in allylation of different benzaldehydes in the presence of
allyltrimethylsilane (scheme 1). Upon the addition of benzaldehyde to the different catalysts,
a strong chelation is created between the oxygen of the aldehyde and the Lewis acid site of
Al-MCM-41 (A), the appearance of the brown color indicates that chelation O-TiCl4 (A’) has

occurred [47], which makes the addition of allyltrimethylsilane easier and thereby forming a
carbon-carbon bond (Scheme 1, B and B'). The reorganization of the electrons in the
intermediate (C) gives rise to a formation of an allylic motif for obtaining homoallyl silyl
ethers (D), thereby freeing the Lewis site of Al-MCM-41 for the following cycle. The stage
between (C) and (D), shows that the attack of the second allyltrimethylsilane is not permitted,
it is for this reason that diallylated products were not detected in this catalytic system.
However, the reorganization of the electrons in the intermediate (C’), is first made by the
expulsion of the chloride anion of the intermediate (B') due to the coordination of
nitromethane with TiCl4. The chloride anion will be captured by trimethylsilane for
regeneration of allyl motif [48]. The intermediate (D’) reacts rapidly with excess allyl
trimethylsilane via the formation of gem-diallyl derivative (E) and the expulsion of the
catalyst in the form of titanium oxychloride [49]. The condensation in the presence of Al-
MCM-41 of allyltrimethylsilane is very rapid, compared to the first allylation catalyzed TiCl4,
which is known to be a slow step [50]. This can be observed by comparing the time of the
reaction of terephthalaldehyde with allyltrimethylsilane. Using Al-MCM-41, the homoallyl
silyl ethers (100% yield) was obtained after only 25 minutes (Table 5, entry 7), whereas the
diallylation of the same aldehyde was obtained after 5 hours of reaction at low temperature
with a 85% yield (Table 3, entry 5).
3.3. Catalyst reusability
Reusability of the catalyst has been studied in the reaction of benzaldehyde with
allyltrimethylsilane in the presence of Al-MCM-41. Upon completion of the reaction, Al-
MCM-41 is recovered by simple filtration, washed by dichloromethane three times to confirm
the complete removal of any residual material, then dried and activated before use for the next
cycle. The catalyst could be reused three times with-out a significant loss of catalytic activity
(Fig. 6).
4. Conclusion
The solid catalyst Al-MCM-41 was synthesized by hydrothermal method with Si/Al atomic
ratio of 12.5. The structural and textural properties of this catalyst were measured using
various analytical instruments.
Pyridine coupled FT-IR spectroscopy analysis showed the existence of a high concentration
of acid sites, with both Brönsted and Lewis sites. The concentrations determined after
evacuation at different temperatures gave priority to Lewis acid. The site acids of Lewis of
Al-MCM-41 are highly efficient for the allylation of various aldehydes with

allyltrimethylsilane. Similar to TiCl4 the Lewis acid promotes the formation of the
diallylation, whereas in the presence of Al-MCM-41, the single allylation was obtained using
mild conditions. To explain this different allylation in the presence of the MCM-41 or TiCl4, a
reaction mechanism is proposed. The catalyst can be regenerated and reused for three times
without significant loss of activity.
Acknowledgments
The authors are very grateful to the Laboratory of Catalysis and Synthesis in Organic
Chemistry (LCSCO), faculty of Science - Abu Bakr Belkaid University of Tlemcen (Algeria).

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(100)
Si-MCM-41
As-synthesized
2 theta (100) : 2,21
d
a
: 39,94Å
100
: 46,12Å
0
Calcined
Calcined
2 theta (100) : 2,45
As-synthesized
d
: 36,03Å
100
: 41,60Å
(110)
a
0
(200)
(210)
(a)
1
2
3
4
5
6
7
8
9
10
2 theta
(100)
Al-MCM-41
As-synthesized
2 theta (100) : 2,04
d
a
: 43,27Å
100
: 49,96Å
0
Calcined
Calcined
2 theta (100) : 2,32
d
: 38,05Å
100
: 43,94Å
a
as-synthesized
0
(b)
1
2
3
4
5
6
7
8
9
10
2 theta
Fig.1. XRD patterns of as-synthesized and calcined Si-or Al-MCM-41. (a) Si-MCM-41, (b)
Al-MCM-41.

700
600
500
400
300
200
100
Si-MCM-41
Al-MCM-41
0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0
Relative pressure (P/P0)
Fig.2. Nitrogen adsorption–desorption isotherms of calcined Si- or Al-MCM-41 mesoporous
materials.

Si-MCM-41
Al-MCM-41
1500
1250
1000
750
500
Wavenumber (cm-1)
Fig.3. FT-IR spectra of calcined Si- or Al-MCM-41 mesoporous materials.

100
90
80
70
60
50
40
30
20
10
0
0,00
Si-MCM-41
TG
-0,05
-0,10
-0,15
-0,20
-0,25
-0,30
DTG
(a)
100
200
300
400
500
600
700
800
Temperature (°C)
100
90
80
70
60
50
40
30
20
10
0
Al-MCM-41
0,00
DTG
-0,04
-0,08
-0,12
-0,16
TG
(b)
100
200
300
400
500
600
700
800
Temperature (°C)
Fig.4. TG and DTG curves of as-synthesized Si- or Al-MCM-41. (a) Si-MCM-41, (b) Al-
MCM-41.

Py-L
1456
Py-L
1622
Py-(B+L)
1490
Py-B
1545
(d)
Py-B
1635
(c)
(b)
(a)
1650
1600
1550
1500
1450
1400
Wavenumber (cm-1)
Fig.5. FTIR spectra of pyridine desorbed on calcined Al-MCM-41 under vacuum 3 Torr
pressure at (a) 50 °C, (b) 150 °C, (c) 250 °C, (d) 350 °C.

100
90
80
70
60
50
98 %
97 %
95 %
92 %
1
2
3
4
Number of cycles
Fig. 6. Reusability of Al-MCM-41. Reaction conditions: benzaldehyde (1 mmol),
allyltrimetylsilane (1.5 mmol), Al-MCM-41 (25 mol%), CH2Cl2 (2 mL), 35 °C, reaction
period = 4h.

(a)
OSiMe3
O
H
C
O
O
O
O
R
Al
Si
R
(D)
O
O
O
O
O
O
O
Al
Si
Al
Si
O

O(-)
O
H

C
(A)
C
(+)
R
O
R
SiMe3
(C)
O
O
Al
Si
O
O(-)
Si
C
(+)
R
SiMe3
)
(B
O
O
O
NCH3
NCH3
(b)
O
(-) Cl
O
Cl
Cl
Cl
Cl
Cl
Ti
Cl
Si
Ti
Cl
O
H
TiCl4 , CH3NO2

O

R
R
R
H
(+)
' )
(A
B' )
(
SiMe3
Cl(-)
O
O
O
NCH3
NCH3
O
Cl
Cl
Cl
Cl
O
Cl
Cl
Si
Ti
Ti
O
TiOCl2
+
R
R
R
(+)
ClSiMe3
ClSiMe3
(-)SiMe3
Cl
)
(E)
(D
' )
(C'
Scheme 1. Plausible mechanism of role of Al-MCM-41 as a Lewis acid (a) catalyst in
allylation of various aldehydes with allyltrimethylsilane in compared with TiCl4 as a Lewis
acid (b).

Table 1
Physical characteristics of calcined mesoporous catalysts.
d
e
f
Si/Ala Si/Alb
(EDX)
a0
SBET
Vm so
Dp
Wtg
(Å)
c
Catalysts
a0
e
(Å)
(m2/g) (cm3/g) (Å)
(%)
Si-MCM-41
Al-MCM-41
-
-
41.60 9.8
1154
983
0.84
0.76
34.0 7.6
35.6 8.4
12.50
13.47
43.94 12.0
a Molar ratio in the initial gel.
b Molar ratio determined by EDX analysis.
c a0 (%) = ([a0 (as-synthesized)- a0 (calcined)]/a0 (as-synthesized)).100
d Specific surface area.
e Mesoporous volume.
f Pore diameter determined by BJH.
g Wall thikness, a0 – Dp.

Table 2
Brönsted (CB) and Lewis (CL) acidity of the Al-MCM-41 sample measured by FTIR
spectroscopy combined with pyridine adsorption and desorption at different temperatures.
Acid proprieties (mol.g-1)
50 °C
150 °C
250 °C
350 °C
Total
acidity
Total acidity
295.62
92.13
203.49
2.21
372.21
124.79
247.42
1.98
402.52
142.78
259.74
1.82
344.42
85.89
258.53
3.01
1414.77
445.59
969.18
2.17
Brönsted acidity (CB)
Lewis acidity (CL)
CL/ CB

Table 3
Allylation of various aldehydes with allyltrimethylsilane catalysed byTiCl4 .
a
O
H
TiCl4
SiMe3
+
R
R
CH2Cl2 - CH3NO2
-85°C to -10°C
Entry
1
Aldehyde
Product
Yieldb (%)
74
O
H
O
H
Me
Me
2
3
4
5
85
85
95
85
O
H
MeO
Br
MeO
Br
O
H
O
H
O
H
O
H
6
7
8
88
75
35
O
H
O
H
O
O
H
9
76
MeO
MeO
O
O
H
H
O
10
30
O
a Reaction conditions: aldehyde (5 mmol), allyltrimethylsilane (15 mmol), TiCl4 (8.1
mmol), CH2Cl2 (20 mL) and MeNO2 (1.2 mL), -85 to -10 °C, 5-15 h.
b Isolated yield after column chromatography.

Table 4
The effect of reaction temperature in the presence of Al-MCM-41 as catalysta.
OSiMe3
O
Al-MCM-41
SiMe3
R'
R'
+
H
R
R
Yieldb
(%)
SiMe3
Entry
R,R’
Temperature
(°C)
Time
(h)
(equiv)
1
H, H
H, H
H, H
H, H
H, H
H, H
H, H
Cl, Cl
Cl, Cl
Cl, Cl
-85 to -10
3
-
n.r.
Traces
99
2
0 to 24
3
24
3
35
3
4
4
35
5
4
99
5
35
1.5
1.5
1.5
3
4
99
6c
7d
8
35
4
54
35
4
35
-85 to -10
-
n.r.
100
100
9
35
35
3
45 min
45 min
10
1.5
a Reaction conditions: aldehyde (1 mmol), Al-MCM-41 (25 mol%), CH2Cl2 (2 mL).
b Isolated yield after column chromatography.
c 10 mol% of Al-MCM-41 is used.
d 5 mol% of Al-MCM-41 is used.

Table 5
Allylation of various aldehydes with allyltrimethylsilane catalysed by Al-MCM-41a.
OSiMe3
O
Al-MCM-41
SiMe3
R
+
R
CH2Cl2 , 35°C
H
1
2
3a-3n
Entry
1
Aldehyde
Time (h) Product
Yieldb (%)
O
H
OSiMe3
4
3a
99
O
H
OSiMe3
OSiMe3
OSiMe3
OSiMe3
OSiMe3
Br
Br
2
3
4
5
6
3
3b
3c
3d
3e
3f
98
99
99
98
99
O
H
Cl
Cl
2
O
F
F
H
< 2
1
O
H
NC
O2N
NC
O2N
O
H
0.5
O
H
O
OSiMe3
OSiMe3
H
7
8
25 min
4
3g
3h
100
40
O
OSiMe3
Me
H
Me
O
H
OSiMe3
MeO
O2N
MeO
O2N
9
4
1
3i
3j
36
98
O
OSiMe3
H
10