Highly selective aldol condensation using amine-functionalized SiO2-Al2O3 mixed-oxide under solvent-free condition

Article abstract of DOI:10.1002/cjoc.201090346

A series of amine catalysts supported on mesoporous molecular sieves SiO₂/Al₂O₃ with trimethoxysilylpropylamine [(CH₃O)₃Si(CH₂)₃NH₂] loading varying from 3 mmol to 6 mmol were synthesized by impregnation method. The aldol condensation of various aromatic aldehydes and 1-heptanal was used to test the acid-base cooperativity of amine-functionalized SiO₂/Al₂O₃. The effects of solvent, reaction temperature, benzaldehyde to 1-heptanal molar ratio, different supports (SiO₂, Al₂O₃ and SiO₂-Al₂O₃), catalyst amount and recyclability of the catalyst were investigated. Sample containing 5 mmol amine loaded showed highest benzaldehyde conversion (100%) and selectivity (97%) for jasminaldehyde.

Full text of DOI:10.1002/cjoc.201090346

FULL PAPER
Highly Selective Aldol Condensation Using
Amine-functionalized SiO2-Al2O3 Mixed-
oxide under Solvent-free Condition
Abbaspourrad, Alireza*,a
Javad Kalbasi, Roozbeh*,b
Zamani, Farzadb
a Department of Chemistry, Islamic Azad University, Shahryar-Qods City Branch, 37515-374,
Qods City, Tehran, Iran
b Department of Chemistry, Islamic Azad University, Shahreza Branch, 311-86145, Shahreza, Isfahan, Iran
A series of amine catalysts supported on mesoporous molecular sieves SiO2/Al2O3 with trimethoxysilylpro-
pylamine [(CH3O)3Si(CH2)3NH2] loading varying from 3 mmol to 6 mmol were synthesized by impregnation
method. The aldol condensation of various aromatic aldehydes and 1-heptanal was used to test the acid-base coop-
erativity of amine-functionalized SiO2/Al2O3. The effects of solvent, reaction temperature, benzaldehyde to
1-heptanal molar ratio, different supports (SiO2, Al2O3 and SiO2-Al2O3), catalyst amount and recyclability of the
catalyst were investigated. Sample containing 5 mmol amine loaded showed highest benzaldehyde conversion
(100%) and selectivity (97%) for jasminaldehyde.
Keywords aldol reaction, jasminaldehyde, 1-heptanal, organic-inorganic hybrid composites, solvent-free
Introduction
liquid alkali (NaOH or KOH) taken in more than
stoichiometric amounts as a homogeneous catalyst.12
A
Aldol condensation is a well-known reaction in or-
ganic chemistry.1,2 Many valuable bulk, intermediate
and fine chemicals, such as isophorone, calcium antago-
nists, cinnamaldehyde and ionones, are produced via al-
dol condensation reactions. particularly, the aldol con-
densation reactions of aldehydes and ketones are widely
used in organic synthesis for preparing chemicals con-
taining a double bond conjugated with a carbonyl group.
By properly choosing the operating conditions the C— C
bond formation proceeds by condensation between a
molecule having a carbonyl group and another which
contains an activated methylenic group. After subse-
quent dehydration the product is an α,β-unsaturated
compound. Aldol condensation is generally catalyzed by
weak bases like primary, secondary, tertiary amines,
ammonium or ammonium salts3,6 under homogeneous
conditions. Later, inorganic solids and solid-supported
reagents, such as amino group immobilized on silica
gel,7 clays,8 magnesium and aluminium oxides,9,10 zeo-
lites,11 were used because they provided operational
simplicity and higher selectivity with the chance of re-
usability. Attention to solid basic catalysts is increased
in recent years as they facilitate a variety of organic re-
actions that take place via carbanionic intermediates.
Among α,β-unsaturated compounds, jasminaldehyde
or α-pentylcinnamaldehyde is a perfumery chemical of
commercial interest and is synthesized by the condensa-
tion of 1-heptanal with benzaldehyde in the presence of
limitation of this condensation reaction is the formation
of by-products which reduce the yield of jasminalde-
hyde. The most abundant undesired product comes from
the self condensation of heptanal to form 2-n-pentyl-2-
n-nonenal. Moreover, the main drawbacks of homoge-
neous process for synthesis of jasminaldehyde include
lack of reusability of the catalyst, hazardous nature of
liquid base like KOH or NaOH and post reaction
work-up of spent liquid bases. Therefore, it is desirable
to develop solid base catalysts which would overcome
these disadvantages and provide a commercial process
having easy handling of the catalyst, easy separation of
products, decreased corrosion of the reactor, producing
jasminaldehyde with high selectivity and possible re-
generation and reuse of the catalyst. The applicability of
various solid acids and base catalysts has been reported
for the synthesis of jasminaldehyde in the literature such
as mesoporous MCM-41 aluminosilicates,13 amorphous
aluminophosphate (ALPO),14 beta zeolites,15 Al-MCM-
41 supported magnesium oxide,16 hydrotalcite17 and
magnesium organo silicates.18
The earliest studies of aldol condensation have fo-
cused on the single oxide and zeolite composite, but few
studies on binary and ternary oxides composite have
been reported. Binary composite may exhibit different
pore structures and separation performance in compari-
son with the single oxide because of the different
chemical compositions and preparation conditions. For
*
E-mail: rkalbasi@iaush.ac.ir (R. J. Kalbasi); abbaspour@alumni.iut.ac.ir (A. Abbaspurrad); Fax: 0098-321-3293095; Tel.: 0098-321-3292072
Received January 5, 2010; revised May 17, 2010; accepted May 24, 2010.
2074
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Chin. J. Chem. 2010, 28, 2074— 2082

Highly Selective Aldol Condensation using Amine-functionalized SiO2-Al2O3 Mixed-oxide
example, SiO2-Al2O3 mixed oxide could have the de-
sired combination of the features of both the Al2O3 and
SiO2 components. The Al2O3 moiety usually offers good
mechanical stability as well as catalytic properties and
the SiO2 species would provide the composite with com-
paratively large surface area.
Herein, we report the preparation of amine-func-
tionalized SiO2-Al2O3 mixed oxide by grafting trimeth-
oxysilylpropylamine moiety on calcined SiO2-Al2O3
mixed oxide and its successful application in aldol con-
densation reaction of some aromatic aldehydes with
1-heptanal under solvent-free condition. These catalysts
show very high activities and can be reused several
times.
deionized water (11.0 mol of H2O/mol of alkoxide). The
solutions were left overnight to hydrolyze the alkoxides,
yielding transparent gels. The transparent gels were
dried at 110 ℃ to remove water and solvent, and then
calcined at 500 ℃ for 5 h to remove the organics. The
supports with different SiO2/Al2O3 molar ratios donated
as SiO2-Al2O3 (1/1), SiO2-Al2O3 (3/1) and SiO2-Al2O3
(1/3).
Amine-functionalized SiO2-Al2O3 mixed oxide ob-
tained by grafting was synthesized according to the
procedure previously reported.19 5.2 g of SiO2-Al2O3
with various volumes of trimethoxysilylpropylamine (3,
4, 5 and 6 mmol) were refluxed in dry dichloromethane
(100 mL) for 24 h. Then the solid was filtered off,
washed with anhydrous methanol and dried at 100 ℃
(Scheme 1). These synthesized amine-functionalized
SiO2-Al2O3 mixed-oxides with different SiO2/Al2O3
molar ratios are donated as SiO2-Al2O3 (1/1)-TMSPA,
SiO2-Al2O3 (3/1)-TMSPA and SiO2-Al2O3 (1/3)-TMSPA.
Experimental
Materials
The chemicals used in this work include: alumini-
umtri-sec-butylate (Merck), trimethoxy silyl propyl
amine (Merck), silica gel (Merck), 2,4-pentandione
(Merck), tetraethylorthosilicate (Acros), 1-heptanal
(Sigma-Aldrich) and benzaldehyde (Sigma-Aldrich). All
the solvents and aromatic aldehydes were purchased
from Merck and deionized double distilled water was
used throughout.
Scheme 1 Synthesis of SiO2-Al2O3-TMSPA
Catalyst preparation
Nitrogen content of amine-grafted samples was es-
timated by back titration using NaOH (0.1 mol/L).20,21
First, the known amount of the catalyst was stirred in
HCl (0.5 mol/L) for 30 min. Then, the mixture was fil-
trated and titrated with NaOH (0.1 mol/L). Nitrogen
content of catalysts was 3.1, 3.3, 3.5, 3.9 and 3.2 mmol•
SiO2-Al2O3 was used as the support. This support
was prepared by the sol-gel method.19 Aluminum
tri-sec-butylate (97%) and tetraethylorthosilicate (98%)
were used as the precursors, and 2,4-pentandione
(H-acac) as the complexing agent. Appropriate amounts
of aluminum tri-sec-butylate and tetraethylorthosilicate
were dissolved in the solvent, n-butanol. The solution
was heated to 60 ℃. The components were thoroughly
mixed. Then the solution was cooled down to room
temperature, and the H-acac was added as the complex-
ing agent. This clear solution was hydrolyzed with
g－ using 5 mmol trimethoxysilylpropylamine for the
1
supports with various SiO2/Al2O3 molar ratios (Table 1).
According to the data, SiO2-Al2O3 (3/1)-TMSPA con-
tains higher basic sites for the aldol condensation.
Table 1 Structural and textural properties
1
1
1
Catalyst
SiO2-TMSPA
BET surface area/(m2•g－
)
Pore volume/(cm3•g－
)
Pore diameter/Å
N content/(mmol•g－
)
520
276
352
411
315
580
335
427
496
381
0.44
0.18
0.26
0.30
0.22
0.53
0.27
0.36
0.43
0.31
31
50
40
37
33
38
56
49
45
40
3.1
Al2O3-TMSPA
3.3
SiO2-Al2O3 (1/1)-TMSPA
SiO2-Al2O3 (3/1)-TMSPA
SiO2-Al2O3 (1/3)-TMSPA
SiO2
3.5
3.9
3.2
—
—
—
—
—
Al2O3
SiO2-Al2O3 (1/1)
SiO2-Al2O3 (3/1)
SiO2-Al2O3 (1/3)
Chin. J. Chem. 2010, 28, 2074— 2082
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Abbaspourrad, Javad Kalvasi & Zamani
FULL PAPER
Characterization of catalysts
minosilicate powder before and after modification with
TMSPA. Notable changes associated with TMSPA
modification include weakening of free silanol O—H
stretch at 3744 cm－ 1, consistent with formation of
TMSPA-silicate siloxane bonds, and appearance of pri-
The crystalline phase composition of calcined sam-
ples was characterized by X-ray diffraction with a
Bruker D8ADVANCE diffractometer, using nickel fil-
tered Cu Kα radiation. Thermal gravimetric analysis
(TGA) data were obtained by a Mettler TGA-50 under
air atmosphere at a rate of 10 ℃/min. Elemental analy-
sis was performed by a CHNO-Rapid Heraeus elemental
analyzer (Wellesley, MA). Fourier transform infrared
spectra (FT-IR) were recorded by an FT-IR spectropho-
tometer (Jasco-680, Japan). The spectra of solids were
obtained using KBr pellets and the vibrational transition
－
1
mary amine stretches at 3303 and 3370 cm , C—H
stretch bands in the 2800—3000 cm－ region and, less
1
－
1
prominently, NH2 bend at 1600 cm , CH2 bend at 1470
－
－
1
1
cm , and Si-CH2 bend at 1412 cm .
－
1
frequencies are reported in wave numbers (cm ). The
specific surface areas of the samples were calculated
from the N2 adsorption-desorption isotherms using Se-
ries BEL SORP 18 at 77 K. The morphology of the
catalyst surface was performed by scanning electron
microscopy (SEM) (SERON, AIS-2100) and the amount
of nitrogen content in the synthesized catalysts was
－
1
measured by back titration using NaOH (0.1 mol•L ).
Aldol condensation reaction
In a typical procedure, 0.09 g of catalyst [SiO2-Al2O3
(3/1)-TMSPA] and 2 mmol of distilled benzaldehyde
were taken in a round-bottomed flask. To this mixture, 1
mmol of 1-heptanal was added slowly and the mixture
was stirred at 110 ℃ for 4 h under solvent-free condi-
tions (Scheme 2). The reaction was monitored by TLC.
After completion of the reaction, the catalyst was fil-
tered; the filtrate was concentrated and purified by col-
umn chromatography (hexane/ethylacetate) on silica gel.
Figure 1 FT-IR spectra of (a) SiO2-Al2O3 mixed oxide, (b)
SiO2-Al2O3 (3/1)-TMSPA (5 mmol) and (c) SiO2-Al2O3 (3/1)-
TMSPA (6 mmol)
The TG and DTG curves of SiO2-Al2O3 (3/1)-
TMSPA are shown in Figure 2, which show three sepa-
rate weight loss steps. The first, small (around 3%, w)
step appearing at temperature ＜150 ℃ corresponds to
the release of water (i.e., adsorbed water on the inner
and outer surface). The second step (about 150—350 ℃)
can be attributed to the water loss from the condensation
of adjacent Si—OH groups to form siloxane bonds
(around 5%, w). The third weight-loss (about 360—590
℃) amounts around 11% (w) is related to the decompo-
sition of the TMSPA moiety. The main oxidative de-
sorption of the TMSPA takes place in the range of 350
to 600 ℃.
1
The product was then analyzed by IR, H NMR, 13C
NMR and mass spectroscopy. The conditions of aldol
condensation were optimized for benzaldehyde, and
consequently those of some other aromatic aldehydes
were performed in optimum conditions.
Scheme 2 Synthesis of jasminaldehyde
Results and discussion
Catalyst characterization
Samples, SiO2-Al2O3 (1/1)-TMSPA, SiO2-Al2O3
(3/1)-TMSPA, SiO2-Al2O3 (1/3)-TMSPA and unmodi-
fied SiO2-Al2O3, were characterized by XRD and all the
samples showed amorphous phase.
Figure 2 Thermal analysis of the samples: TG figures of (a)
SiO2-Al2O3 (3/1), (c) SiO2-Al2O3 (3/1)-TMSPA and (b) DTG
figure of SiO2-Al2O3 (3/1)-TMSPA.
Figure 1 shows characteristic mid-IR spectra of alu-
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Chin. J. Chem. 2010, 28, 2074— 2082

Highly Selective Aldol Condensation using Amine-functionalized SiO2-Al2O3 Mixed-oxide
Figures 3a and 3b show the SEM micrographs of
SiO2-Al2O3 and modified SiO2-Al2O3, respectively, with
the same magnification. After the modification, it was
obvious that the particles divided to smaller pieces with
narrow size distribution (Figure 3b).
Table 2 Synthesis of SiO2-Al2O3 (3/1)-TMSPA using various
amount of trimethoxysilylpropylamine
1
Entry
Used amine/mmol
N content/(mmol•g－
)
1
2
3
4
3
4
5
6
2
2.5
3.91
3.92
Effect of solvent
The aldol condensation of 1-heptanal with benzal-
dehyde was carried out at reflux temperature using
various solvents such as n-hexane, acetonitrile, toluene,
ethanol, dichloromethane, water and also under sol-
vent-free condition over SiO2-Al2O3 (3/1)-TMSPA. The
results are summarized in Table 3. The highest conver-
sion (100%) and selectivity to jasminaldehyde (97%)
were obtained under solvent-free condition, indicating
the effect of solvent on the reaction product.
Effect of reaction temperature
Temperature is another important parameter which
can affect the selectivity for a given reaction. In order to
study the influence of the temperature, the condensation
reaction was carried out in the range of 25—160 ℃, by
keeping other reaction parameters constant. The results
are reported in Table 4. The conversion of 1-heptanal
was observed to increase from 63% to 100% by in-
creasing the reaction temperature from 25 to 110 ℃. On
further increase in the temperature to 160 ℃, the con-
version was constant and the selectivity of jasminalde-
hyde was slightly decreased. The aldol condensation is
an endothermic reaction, which indicates that a higher
temperature can promote the reaction. With further in-
crease in temperature, the conversion remained constant,
but the selectivity decreased due to formation of more
condensation products.
Figure 3 SEM images of samples: (a) SiO2-Al2O3 and (b)
SiO2-Al2O3-TMSPA with the same magnification.
Catalytic activity
The effect of different parameters on aldol condensa-
tion of benzaldehyde with 1-heptanal was investigated
and the results are as follows.
Synthesis of SiO2-Al2O3 (3/1)-TMSPA using various
amount of trimethoxysilylpropylamine
In order to achieve high basic activity, SiO2-Al2O3
(3/1)-TMSPA was synthesized with various amounts of
trimethoxysilylpropylamine. Then, nitrogen content was
measured by back titration for all the catalysts. The re-
sults are summarized in Table 2. As can be seen, the syn-
thesized catalyst using 5 mmol of amine is suitable for the
aldol condensation because of its high basic sites.
Effect of benzaldehyde to 1-heptanal molar ratio
The effect of benzaldehyde to 1-heptanal molar ratio
was studied using various molar ratios from 1 to 6,
keeping other parameters fixed (Table 5). At benzalde
Table 3 Effect of solvent on the aldol condensation of benzaldehydea
Selectivity/%
Solvent
Conversionb/%
Jasminaldehyde
2-Pentyl-non-2-enal
CH3CN
n-Hexane
CH2Cl2
75
63
85
81
85
87
91
95
97
15
19
15
13
9
56
Toluene
EtOH
61
83
H2O
Solvent-freec
100
100
5
3
a Reaction conditions: SiO2-Al2O3 (3/1)-TMSPA (0.09 g), benzaldehyde (2 mmol), 1-heptanal (1 mmol), reflux, reaction time＝4 h;
b conversion of 1-heptanal; c reaction temperature＝110 ℃.
Chin. J. Chem. 2010, 28, 2074— 2082
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FULL PAPER
Table 4 Effect of reaction temperature on the aldol condensation of benzaldehyde with heptanala
Selectivity/%
Temperature/℃
Conversionb/%
Jasminaldehyde
2-Pentyl-non-2-enal
25
50
63
80
100
99
97
97
90
—
1
80
92
3
110
160
100
100
3
10
a Reaction conditions: SiO2-Al2O3 (3/1)-TMSPA (0.09 g), benzaldehyde (2 mmol), 1-heptanal (1 mmol), solvent-free, reaction time＝4 h;
b conversion of 1-heptanal.
Table 5 Effect of molar ratio of benzaldehyde to heptanal on product distributiona
Selectivity/%
Benzaldehyde/heptanal molar ratio
Conversionb/%
Jasminaldehyde
2-Pentyl-non-2-enal
1
2
4
6
100
100
100
100
81
97
97
98
19
3
3
2
a Reaction conditions: SiO2-Al2O3 (3/1)-TMSPA (0.09 g), 110 ℃, solvent-free, reaction time＝4 h; b conversion of 1-heptanal.
hyde to 1-heptanal molar ratio of 1, 100% conversion
with 81% selectivity to jasminaldehyde was observed.
The jasminaldehyde selectivity was observed to increase
up to 97% with 100% conversion of 1-heptanal at molar
ratio of 2. This is probably due to lower 1-heptanal car-
banion concentration compared with benzaldehyde,
which prevents self condensation of the former.
hyde with increasing Si-content in SiO2-Al2O3 mixed
oxide is explained in terms of increased basicity of the
catalyst which aids aldol condensation reaction. The ba-
sicity of the amine-functionalized SiO2-Al2O3 is mainly
due to their amine functions and it can be adjusted by
changing the SiO2/Al2O3 molar ratio of mixed oxide.
Moreover, according to Table 1, SiO2-Al2O3 (3/1)-
TMSPA is more suitable for aldol condensation as
compared to SiO2-TMSPA and Al2O3-TMSPA, both in
terms of N-content and surface area.
Effect of support
Table 6 shows the obtained results of benzaldehyde
condensation using SiO2, Al2O3 and SiO2-Al2O3 mixed
oxide as supports in this work. Moreover, the synthesis
of jasminaldehyde was carried out using SiO2-Al2O3 of
varied Si/Al molar ratio as supports. 1-Heptanal conver-
sion in the range of 93%—100% was observed for the
studied catalysts. The maximum conversion of 1-heptanal
was observed to be 100% with selectivity to jasminalde-
hyde 97% in case of SiO2-Al2O3 (3/1)-TMSPA.
For any base catalyzed reaction, maximum catalytic
activity occurs at an optimum SiO2/Al2O3 molar ratio
and depends upon the base strength required to activate
the particular reactant molecule. The increase in the
conversion of 1-heptanal and selectivity of jasminalde-
Effect of amine functionalization
The catalytic activity of SiO2-Al2O3 (3/1)-TMSPA
was improved by optimizing the amount of amine func-
tionalization. As can be seen in Table 7, the change of the
amount of TMSPA (3—6 mmol) has no significant effect
on the selectivity of the aldol condensation. A maximum
1-heptanal conversion (100%) and jasminaldehyde selec-
tivity (97%) appears on the catalyst which synthesized
with 5 mmol amine. It should be mentioned that all of the
SiO2-Al2O3 (3/1)-TMSPA catalysts are far superior to the
support (without TMSPA) for the aldol condensation be-
cause of their Brønsted basic sites (NH2).
Table 6 Effect of support on the aldol condensation of benzaldehyde with 1-heptanala
Selectivity/%
2-Pentyl-non-2-enal
Catalyst
Conversionb/%
Jasminaldehyde
SiO2-TMSPA
93
97
87
96
91
97
94
13
4
Al2O3-TMSPA
SiO2-Al2O3 (1/1)-TMSPA
SiO2-Al2O3 (3/1)-TMSPA
SiO2-Al2O3 (1/3)-TMSPA
100
100
95
9
3
6
a Reaction conditions: catalyst (0.09 g), benzaldehyde (2 mmol), 1-heptanal (1 mmol), 110 ℃, solvent-free, reaction time＝4 h; b conver-
sion of 1-heptanal.
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Highly Selective Aldol Condensation using Amine-functionalized SiO2-Al2O3 Mixed-oxide
In addition, at this point, it is known that SiO2-Al2O3
mixed oxide has Lewis acid and Lewis base sites, while
amine-functionalized SiO2-Al2O3 mixed oxide has
Brønsted basic sites that are stronger than those of
SiO2-Al2O3 mixed oxide. Thus, if only the Brønsted
basic sites of the catalyst were responsible for the cata-
lytic behavior of this material in the synthesis of jasmi-
naldehyde, it could be expected that SiO2-Al2O3 mixed
oxide (without TMSPA) is not an active catalyst for this
reaction. However, the presented results in Table 7 in-
dicate that SiO2-Al2O3 mixed oxide gives an activity
(23%) and selectivity (95%) to jasminaldehyde. Thus, it
can be concluded that both Lewis acid and Brønsted
base sites in the amine-functionalized SiO2-Al2O3 mixed
oxide would be effective for the aldol condensation.
self condensation of 1-heptanal to 2-pentyl-non-2-enal
under studied experimental conditions. The self con-
densation of 1-heptanal is catalyzed by the active basic
sites available on the surface of catalyst. By increasing
the amount of catalyst, the number of active basic sites
increases significantly. Therefore, 0.09 g of the catalyst
was taken as optimized amount for the aldol condensa-
tion.
Aldol condensation of various aromatic aldehydes
with 1-heptanal over SiO2-Al2O3 (3/1)-TMSPA
After setting optimized reaction conditions, the cata-
lytic activity of SiO2-Al2O3 (3/1)-TMSPA was investi-
gated for the aldol condensation by employing various
aromatic and hetero-aromatic aldehydes with 1-heptanal
as an active methylene compound (Table 9). Hetero-
aromatic aldehydes, such as 2-pyridine carbaldehyde
and furfural (Entries 7, 8), provided excellent conver-
sion (100%). Aromatic aldehyde with electron with-
drawing groups (Entry 5) also offered very good con-
version and selectivity and the reaction was completed
in the reasonable time. Also in the case of electron do-
nating groups (Entries 2, 3, 4), reasonably good conver-
sion and selectivity were observed but demanded more
reaction time. Moreover, moderately inactivated aro-
matic compound (Entry 6) provided good selectivity and
conversion. Therefore, as can be seen, this synthesized
catalyst shows excellent conversion and high selectivity
in aldol condensation of aromatic aldehydes under sol-
vent-free condition.
Effect of catalyst amount
The effect of catalyst amount on conversion and se-
lectivity of jasminaldehyde was studied by varying the
amount of catalyst from 0.03 to 0.12 g at constant con-
centration of 1-heptanal and benzaldehyde (Table 8).
The conversion of 1-heptanal was found to be 100%
with 97% selectivity of jasminaldehyde at 0.09 g of the
catalyst. On further increase in the amount of catalyst to
0.12 g, the conversion did not change significantly.
However, the selectivity of jasminaldehyde was ob-
served to decrease from 97% to 90% on increasing the
amount of catalyst from 0.05 to 0.12 g under identical
reaction conditions. The decrease in the selectivity of
jasminaldehyde at higher catalyst amount is due to the
Table 7 Effect of amine functionalization on aldol condensation of benzaldehyde with 1-heptanala
Selectivity/%
2-Pentyl-non-2-enal
Catalyst
Used amine/mmol
Conversionb/%
Jasminaldehyde
SiO2-Al2O3 (3/1)
—
3
23
65
95
96
97
97
95
5
4
3
3
5
SiO2-Al2O3 (3/1)-TMSPA
SiO2-Al2O3 (3/1)-TMSPA
SiO2-Al2O3 (3/1)-TMSPA
SiO2-Al2O3 (3/1)-TMSPA
4
82
5
100
6
100
a Reaction conditions: catalyst (0.09 g), benzaldehyde (2 mmol), 1-heptanal (1 mmol), 110 ℃, solvent-free, reaction time＝4 h; b conver-
sion of 1-heptanal.
Table 8 Effect of catalyst amount on the aldol condensation of benzaldehyde with 1-heptanala
Selectivity/%
Catalyst amount/g
Conversionb/%
Jasminaldehyde
2-Pentyl-non-2-enal
0.03
0.05
0.07
0.09
0.12
68
81
98
100
98
2
—
2
90
100
97
3
100
90
10
a Reaction conditions: SiO2-Al2O3 (3/1)-TMSPA, benzaldehyde (2 mmol), 1-heptanal (1 mmol), 110 ℃, solvent-free, reaction time＝4 h;
b conversion of 1-heptanal.
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Abbaspourrad, Javad Kalvasi & Zamani
FULL PAPER
Table 9 Aldol condensation of some aromatic aldehydes with 1-heptanal over SiO2-Al2O3-TMSPAa
M.p./℃
Entry Substrate Conversion/%
Product distribution
Time/h
Ref.
22
Found Reported
1
2
100
4
82
80
3%
8%
97%
195—
91
5
199b
23
200b
92%
90%
94%
3
4
90
93
7
120b
124b
24
26
10%
4.5
48
—
6%
5
6
100
100
—
2.5
162
—
—
27
28
100%
3
66
1%
99%
100%
98%
7
8
100
100
—
2.5
3
85
—
29
25
150b
151.5b
2%
5%
9
98
2.5
114
—
30
95%
a Reaction conditions: catalyst (0.09 g), substrate (2 mmol), 1-heptanal (1 mmol), 110 ℃; b boiling point.
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© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 2074— 2082

Highly Selective Aldol Condensation using Amine-functionalized SiO2-Al2O3 Mixed-oxide
Reusability of catalyst
solvent-free condition. The conversion of 1-heptanal
was observed to increase with an increase in basic char-
acter of the studied catalysts. The results show that
SiO2/Al2O3 molar ratio plays an important role for con-
version and selectivity of the product. SiO2-Al2O3
(3/1)-TMSPA showed excellent 1-heptanal conversion
and high selectivity to jasminaldehyde in aldol conden-
sation under optimized reaction conditions. Moreover,
the catalyst was recycled up to 4 cycles without signifi-
cant loss of activity.
The recyclability of the catalyst was studied by using
SiO2-Al2O3 (3/1)-TMSPA in recycling experiments. For
this purpose, at the end of each reaction, the catalyst was
recovered from the reaction mixture by filtration and
washing with anhydrous methanol (10 mL×3), then
dried in air and then reused in the aldol condensation.
Table 10 shows that the catalyst can be reused 4 cycles
without significant loss in its activity for the aldol con-
densation.
Acknowledgements
Conclusion
Support from Islamic Azad University, Shahreza
Branch (IAUSH) Research Council and Center of Ex-
cellence in Chemistry is gratefully acknowledged.
The amine-functionalized SiO2-Al2O3 mixed-oxide
samples with various SiO2/Al2O3 molar ratios were
synthesized and used as a catalyst for aldol condensation
of 1-heptanal with different aromatic aldehydes under
Table 10 Reusability of the catalysta
Selectivity/%
Reaction cycles
Conversionb/%
Jasminaldehyde
2-Pentyl-non-2-enal
Fresh
100
100
99
97
97
97
93
96
3
3
3
7
4
1
2
3
4
97
95
a Reaction conditions: SiO2-Al2O3 (3/1)-TMSPA (0.09 g), benzaldehyde (2 mmol), 1-heptanal (1 mmol), 110 ℃, solvent-free, reaction
time＝4 h; b conversion of 1-heptanal
References and notes
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23 Knorr, A.; Weissenborn, A. US 1716822, 1929.
24 Isikawa, S.; Seiiti, O. Science Repts. Tokyo Bunrika Dai-
gaku 1939, 3, 291.
1
2
3
4
5
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6
7
8
9
25 Mastagli, P.; Pierre, J. I. Compt. Rend. 1952, 235, 1402.
26 The new product obtained in this study was characterized by
1
1
GC-mass, H NMR and 13C NMR. M.p. 48 ℃; H NMR
(CDCl3, 90 MHz) δ: 9.87 (s, 1H, CHO,), 7.41 (d, J＝7.26
Hz, 1H, ArH), 7.30 (s, 1H, C＝C—H), 7.14 (t, J＝7.26 Hz,
1H, ArH), 7.11 (d, J＝7.26 Hz, 1H, ArH), 7.09 (s, 1H, ArH),
2.41 (t, J＝1.37 Hz, 2H, CH2), 2.34 (s, 3H, CH3), 1.29 (m,
6H, CH2), 0.9 (t, J＝0.86 Hz, 3H, CH3,); 13C NMR (CDCl3,
62.9 MHz) δ: 14.4, 21.7, 22.8, 24.8, 26.9, 31.9, 125.5, 126.6,
128.2, 128.8, 135.1, 138.2, 143.4, 149.7, 195.6; GC (EI) m/z
(%): 216.15 (100), 217.15 (16.2), 218.16 (1.5). Anal. calcd
for C15H20O: C 83.28, H 9.32, O 7.40; found C 82.92, H
9.08, O 7.28.
10 Muzart, J. Synthesis 1982, 60.
11 Sharma, S. K.; Parikh, P. A.; Jasra, R. V. J. Mol. Catal. A:
Chem. 2007, 278, 135.
12 Payne, L. S. EP 0392579 A2, 1990.
13 Climent, M. J.; Corma, A.; Garcia, H.; Guil-Lopez, R.;
Ibora, S.; Fornes, V. J. Catal. 2001, 197, 385.
14 Climent, M. J.; Corma, A.; Guil-Lopez, R.; Ibora, S.; Primo,
J. J. Catal. 1998, 175, 70.
15 Climent, M. J.; Corma, A.; Fornes, V.; Guil-Lopez, R.;
Ibora, S. Adv. Syn. Catal. 2002, 344, 1090.
16 Yu, J. I.; Shiau, Y.; Ko, A. N. Catal. Lett. 2001, 77, 165.
27 The new product obtained in this study was characterized by
Chin. J. Chem. 2010, 28, 2074— 2082
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
2081

Abbaspourrad, Javad Kalvasi & Zamani
FULL PAPER
GC-mass, H NMR and 13C NMR. M.p. 162 ℃; H NMR
(CDCl3, 90 MHz) δ: 9.87 (s, 1H, CHO), 8.21 (d, J＝7.26 Hz,
2H, ArH), 8.03 (d, J＝7.26 Hz, 2H, ArH), 7.44 (s, 1H, C＝
C—H), 2.41 (t, J＝1.37 Hz, 2H, CH2), 1.29 (m, 6H, CH2),
0.9 (t, J＝0.86 Hz, 3H, CH3); 13C NMR (CDCl3, 62.9 MHz)
δ: 14.1, 22.7, 24.8, 26.9, 31.9, 123.8, 129.0, 141.2, 143.2,
147.1, 149.7, 195.6; GC (EI) m/z (%): 247.12 (100), 248.12
(15.5), 249.13 (1.7). Anal. calcd for C14H17NO3: C 68.00, H
6.93, N 5.66, O 19.41; found C 67.87, H 6.71, N 5.44, O
19.27.
(CDCl3, 90 MHz) δ: 9.87 (s, 1H, CHO), 8.45 (d, J＝8.59 Hz,
1H, ArH), 7.51 (s, 1H, C＝C—H), 7.43 (d, J＝7.38 Hz, 1H,
ArH), 7.41 (t, J＝7.75 Hz, 1H, ArH), 7.29 (t, J＝7.38 Hz,
1H, ArH), 2.41 (t, J＝1.37 Hz, 2H, CH2), 1.29 (m, 6H, CH2),
0.9 (t, J＝0.86 Hz, 3H, CH3); 13C NMR (CDCl3, 62.9 MHz)
δ: 14.1, 22.7, 24.8, 26.9, 31.9, 122.7, 124.3, 137, 138.2,
148.8, 149.1, 154.7, 195.6; GC (EI) m/z (%): 203.13 (100.0),
204.13 (14.4), 205.14 (1.2). Anal. calcd for C13H17NO: C
76.81, H 8.43, N 6.89, O 7.87; found C 76.71, H 8.17, N
6.75, O 7.76.
1
1
28 The new product obtained in this study was characterized by
30 The new product obtained in this study was characterized by
GC-mass, H NMR and 13C NMR. M.p. 66 ℃; H NMR
(CDCl3, 90 MHz) δ: 9.87 (s, 1H, CHO), 7.57 (s, 1H, C＝
C—H), 7.44 (d, J＝7.26 Hz, 1H, ArH), 7.32 (d, J＝7.26 Hz,
1H, ArH), 7.28 (t, J＝7.26 Hz, 1H, ArH), 7.27 (t, J＝7.26
Hz, 1H, ArH), 2.41 (t, J＝1.37 Hz, 2H, CH2), 1.29 (m, 6H,
CH2), 0.9 (t, J＝0.86 Hz, 3H, CH3); 13C NMR (CDCl3, 62.9
MHz) δ: 14.1, 22.9, 24.8, 26.7, 31.8, 126.7, 127.8, 129.3,
129.9, 133, 134, 143.4, 145.4, 195.6; GC (EI) m/z (%):
236.10 (100), 238.09 (32), 237.10 (15.4), 239.10 (4.9),
238.10 (1.3). Anal. calcd for C14H17ClO: C 71.03, H 7.24,
Cl 14.98, O 6.76; found C 70.86, H 7.02, Cl 14.68, O 6.55.
29 The new product obtained in this study was characterized by
GC-mass, H NMR and 13C NMR. M.p. 114 ℃; H NMR
(CDCl3, 90 MHz) δ: 9.87 (s, 1H, CHO), 8.08 (d, J＝7.67 Hz,
1H, ArH), 7.96 (d, J＝7.67 Hz, 1H, ArH), 7.93 (d, J＝7.67
Hz, 1H, ArH), 7.78 (d, J＝7.32 Hz, 1H, ArH), 7.55 (t, J＝
7.32 Hz, 2H, ArH), 7.50 (t, J＝7.32 Hz, 1H, ArH), 7.30 (s,
1H, C＝C—H), 2.41 (t, J＝1.37 Hz, 2H, CH2), 1.29 (m, 6H,
CH2), 0.9 (t, J＝0.86 Hz, 3H, CH3); 13C NMR (CDCl3, 62.9
MHz) δ: 14.1, 22.7, 24.8, 26.9, 31.9, 122.9, 124, 126, 126.3,
126.9, 128.3, 128.8, 132, 133.5, 135.6, 143.4, 145.4, 195.6;
GC (EI) m/z (%): 252.15 (100), 253.15 (19.5), 254.16 (2.0).
Anal. calcd for C18H20O: C 85.67, H 7.99, O 6 34; found C
85.51, H 7.83, O 6.19.
1
1
1
1
1
1
GC-mass, H NMR and 13C NMR. M.p. 85 ℃; H NMR
(E0912303 Ding, W.; Zheng, G.)
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© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 2074— 2082