The cellulose aluminum oxide composite-supported imidazolium chloroaluminate ionic liquid as a novel and stable heterogeneous catalyst

Article abstract of DOI:10.1080/24701556.2017.1284103

1-Methyl-3-(triethoxysilylpropyl)imidazolium chloroaluminate ionic liquid anchored on a composite of cellulose and aluminum oxide was easily synthesized and tested for its catalytic activity in one-pot Knoevenagel condensation, Michael addition, and cyclo

Full text of DOI:10.1080/24701556.2017.1284103

Inorganic and Nano-Metal Chemistry
ISSN: 2470-1556 (Print) 2470-1564 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt21
The Cellulose Aluminium Oxide Composite-
Supported Imidazolium Chloroaluminate Ionic
Liquid as a Novel and Stable Heterogeneous
Catalyst
Kaveh Parvanak Boroujeni & Parisa Tahani
To cite this article: Kaveh Parvanak Boroujeni & Parisa Tahani (2017): The Cellulose
Aluminium Oxide Composite-Supported Imidazolium Chloroaluminate Ionic Liquid as a
Novel and Stable Heterogeneous Catalyst, Inorganic and Nano-Metal Chemistry, DOI:
10.1080/24701556.2017.1284103
To link to this article: http://dx.doi.org/10.1080/24701556.2017.1284103
Accepted author version posted online: 13
Mar 2017.
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Date: 14 March 2017, At: 23:45

ACCEPTED MANUSCRIPT
The Cellulose Aluminium Oxide Composite-Supported Imidazolium Chloroaluminate
Ionic Liquid as a Novel and Stable Heterogeneous Catalyst
Kaveh Parvanak Boroujeni* and Parisa Tahani
Department of Chemistry, Shahrekord University, P.O. Box 88186-34141 Shahrekord, Iran
*
Corresponding author. E-mail: parvanak-ka@sci.sku.ac.ir;
Abstract
-Methyl-3-(triethoxysilylpropyl)imidazolium chloroaluminate ionic liquid anchored on a
1
composite of cellulose and aluminium oxide was easily synthesized and tested for its catalytic
activity in one-pot Knoevenagel condensation, Michael addition, and cyclodehydration of 5,5-
dimethyl-1,3-cycloheanedione (dimedone) with aromatic aldehydes. The catalyst was
characterized by Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis
(
TGA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), elemental
analysis, and atomic absorption technique. It is non-hygroscopic (as a bench top catalyst),
reusable, and environmentally compatible heterogeneous catalyst.
Keywords cellulose coated aluminium oxide, chloroaluminate ionic liquid, heterogeneous
catalysis; 1,8-dioxo-octahydroxanthene, aldehyde
1
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INTRODUCTION
In promotion of Green Chemistry, synthetic organic chemistry has played an important
role, and it has changed many synthetic processes to environmentally friendly ones. In this
regard, the use of bio-supported and solid heterogeneous catalysts for the synthesis of fine
[
1]
chemicals have attracted considerable interest. Cellulose is the most abundant biopolymer and
has gained increasing attention because it is biodegradable material and a renewable resource. Its
[
2]
unique properties make it a promising support material for heterogeneous catalysis.
Within oxygen heterocycles, xanthene derivatives have gained much attention in medicinal
[
3]
chemistry because of their biological and pharmaceutical properties such as anti-inflammatory,
[
4]
[5]
anti-depressant, and anti-cancer activities. Also, they were used as antagonists for the
[
6]
paralyzing action of zoxazolamine,
fluorescent markers for the visualization of bio-
[
7]
[8]
molecules,
and photostable laser dyes.
Among xanthene derivatives, 1,8-dioxo-
octahydroxanthenes become more popular and are usually prepared by the condensation reaction
of dimedone with aromatic aldehydes. Several types of catalysts were introduced previously for
[
9]
[10]
this reaction such as NaHSO
4
-SiO
2
or silica chloride,
polyphosphoric acid–SiO
2
,
[
11]
[12]
[13]
In(OTf)
3
,
H
2
4
SO ,
InCl
3
or P
2
O
5
,
ceric ammonium nitrate (CAN) under ultrasound
[
14]
[15]
[16]
[17]
irradiation, succinimide-N-sulfonic acid, CaCl
2
,
Fe
3
O nanoparticles, CAN supported
4
[
18]
[19]
[20]
HY-zeolite,
Fe
3
O
4
@SiO
2
-Imid-H
3
PMo12
O
40
nanoparticles,
piperidine,
Mg-Al
[
21]
[22]
[23]
hydrotalcite,
thiourea dioxide,
ZnO nanoparticles,
and hydroxylamine-O-sulfonic
[
24]
acid. Each of the above methods has its own merits, while some of these methods are plagued
by limitations of low yields, high reaction temperature, long reaction times, tedious work-up, the
2
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formation of the uncyclized product 2,2'-aryl-methylene bis(3-hydroxy-2-cyclohexene-1-one)
derivatives, and the use of unrecyclable, hazardous or difficult to handle catalysts.
Chloroaluminate ionic liquids were the first to be studied because of their electrochemical
[
25]
properties. Following this, many researchers have been showing interest in the development
and use of these compounds as catalysts or dual catalyst-solvents for organic transformations due
to their manifest Lewis acidity, negligible vapour pressure, and tunable solubility for many
[
26,27]
organic substrates.
However, it is well known that the use of conventional chloroaluminate
ionic liquids pose significant risks in handling, containment, disposal, and regeneration due to
their hygroscopic and corrosive nature. Thus, several attempts have been done by organic
chemists for the substitution of homogeneous chloroaluminate ionic liquids with heterogeneous
[
28,29]
ones.
Also, we recently introduced polystyrene and poly(4-vinylpyridine) supported
chloroaluminate ionic liquids as heterogeneous catalysts for the Knoevenagel condensation
[
30,31]
reaction and the synthesis of biscoumarins, respectively.
Along this line and in continuation
of our works on the synthesis and applications of heterogeneous catalysts, we now wish to
introduce cellulose aluminium oxide composite-supported chloroaluminate ionic liquid as a non-
hygroscopic (as a bench top catalyst), reusable, inexpensive, and biodegradable catalyst for the
synthesis of 1,8-dioxo-octahydroxanthenes.
EXPERIMENTAL
Materials and Methods
All chemicals were either prepared in our laboratory or were purchased from
Merck and Fluka. Reaction monitoring and purity determination of the products were
3
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accomplished by GLC or TLC on silica-gel polygram SILG/UV254 plates. Gas
chromatography was recorded on Shimadzu GC 14–A. IR spectra were obtained by a
1
Shimadzu model 8300 FT-IR spectrophotometer. H NMR spectra were recorded on 400
MHz spectrometer in CDCl . Capacity of the catalyst was determined by atomic
3
absorption technique using a Philips atomic absorption instrument. Elemental analysis
was performed with an Elementar Vario EL. TGA was carried out on a Stanton Redcraft
o
STA–780 with a 20 C/min heating rate. SEM images were taken with a MIRA3 FEG–
SEM and EDS analysis was studied by LEO–1455 VP microscope. Melting points were
determined on a Fisher–Jones melting–point apparatus.
Synthesis of 1-Methyl-3-(triethoxysilylpropyl)imidazolium chloride ([mpIm]Cl)
A mixture of (3-chloropropyl)triethoxysilane (20 mmol, 3.97 g) and 1-methylimidazole (20
mmol, 1.64 g) was stirred for 30 h at 80°C under nitrogen atmosphere. The reaction mixture was
concentrated on a rotary evaporator under reduced pressure to afford the [mpIm]Cl (viscous oil;
[
32]
yield: 96%).
Synthesis of Cellulose Aluminium Oxide Composite (Cell/Al
In a round bottomed flask (50 mL) equipped with a reflux condenser, 5 g of AlCl
and 5 g of cellulose was added to distilled water (20 mL) and the mixture was stirred at 38 °C for
2
O
3
)
3
.6H O
2
4
8 h, filtered, washed with distilled water (10 mL), and dried at 80 °C overnight to give
[
33]
Cell/Al
2
3
O composite as a white precipitate.
4
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Synthesis of Cellulose Aluminium Oxide Composite-Supported Imidazolium
Chloroaluminate Ionic Liquid (Cell/Al
The above obtained [mpIm]Cl was added to a solution of Cell/Al
ethanol (20 mL) and the mixture was stirred under reflux condition for 48 h, filtered, washed
with ethanol, and dried at 80 °C overnight to give Cell/Al -[mpIm]Cl. Then, the Cell/Al
mpIm]Cl was added to a solution of AlCl (2 g) in toluene (30 mL) and refluxed under nitrogen
atmosphere for 24 h. Afterwards, AlCl (1 g) was added again and the mixture was stirred under
2
O
3
-[MeIm]Cl-XAlCl
3
)
2
3
O composite (2 g) and
2
O
3
2
3
O -
[
3
3
reflux condition for 12 h and filtered and then the excess of AlCl
3
was removed by extraction
with ethanol (95%) in an Soxhlet apparatus for 72 h.
Typical Procedure for the Preparation of 1,8-Dioxo-octahydroxanthene Using Cell/Al
2
O
3
-
[
MeIm]Cl-XAlCl
Dimedone (2 mmol) was added to a solution of 4-nitrobenzaldehyde (1 mmol), Cell/Al
MeIm]Cl-XAlCl
3
2
O
3
-
[
3
(0.08 mmol), and ethanol (3 mL) and the resulting mixture was magnetically
stirred at room temperature. Progress of the reaction was monitored by TLC and GC. After
completion of the reaction, the catalyst was filtered off and washed with ethanol (2×10 mL).
Then, the filtrate was concentrated on a rotary evaporator under reduced pressure and the crude
product recrystallized from ethanol to afford the pure product 9-(4-Nitrophenyl)-3,3,6,6-
1
tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8-(2H)-dione in 93% yield: H NMR (400
MHz, CDCl
s, 2 CH ), 4.91 (1H, s, CH), 7.45–8.11 (4H, m, Ar-H); IR (KBr, cm ) 2966, 2930, 2870, 1730,
670, 1600, 1350, 1192, 860.
3
) δ = 0.93 (6H, s, 2 CH
3
), 1.11 (6H, s, 2 CH
3
), 2.16–2.25 (4H, m, 2 CH ), 2.51 (4H,
2
–
1
2
1
5
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RESULTS AND DISCUSION
The synthesis of Cell/Al
formation of [MeIm]Cl through reaction of (3-chloropropyl)triethoxysilane with 1-
methylimidazole, (2) reaction of the Cell/Al with [mpIm]Cl to form Cell/Al -[mpIm]Cl,
and (3) treatment of the Cell/Al -[mpIm]Cl with anhydrous AlCl
Cell/Al -[mpIm]Cl and Cell/Al -[MeIm]Cl-XAlCl were analyzed by elemental
2
O
3
-[MeIm]Cl-XAlCl
3
as shown in Scheme 1 involves (1)
2
O
3
2
O
3
2
O
3
3
.
2
O
3
2
O
3
3
analysis to quantify the percentage loading of the imidazolium moieties by measuring the
nitrogen content, giving 0.70 and 0.69 mmol/g, respectively. The aluminium content of the
Cell/Al
2
O
3
-[mpIm]Cl and Cell/Al
2
O
3
-[MeIm]Cl-XAlCl
3
obtained by atomic absorption
technique were 0.87 and 2.55 mmol/g, respectively. Considering the Al and imidazolium moiety
content of Cell/Al
2
O
3
-[MeIm]Cl-XAlCl
3
, it is clear that the AlCl
3
mole fraction in this catalyst is
−
larger than 0.5 and thus we can imagine that it is the Lewis acid Al
2
Cl
7
(as the predominant
[
30,31]
aluminium species) that plays an important role in the catalytic activity in this ionic liquid.
Figure 1 shows the FT-IR spectra of Cell/Al and Cell/Al -[MeIm]Cl-XAlCl . In the
spectrum (B) a broad band of absorption is observed in the 3100–3650 cm region due to the
remained OH groups of cellulose aluminium oxide composite (Cell/Al ) after the
2
O
3
2
O
3
3
−
1
2
O
3
−
1
functionalization processes. The weak absorption around 2930 cm is assigned to C–H
stretching vibration, which confirms the presence of the propyl groups of the ionic liquid.
−
1
Vibration peaks at 1660 and 1570 cm are attributed to the characteristic vibration of the
[
30]
−1
aromatic ring of imidazole. The absorption bands at about 1060 and 1040 cm are assigned to
[34]
−1
C–O–Si stretching bands.
The appearance of peaks at 450, 475, 550, and 625 cm are
6
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−
[30,31]
assigned to Al−Cl stretching modes of the Al
the Cell/Al -[MeIm]Cl-XAlCl cannot be observed in the IR spectrum of Cell/Al
spectrum (A)).
The TGA analysis clearly confirmed immobilization of imidazolium chloroaluminate ionic
liquid on the pore surface of Cell/Al (Figure 2). In TGA curves of Cell/Al and Cell/Al
MeIm]Cl-XAlCl a first weight loss step (about 4%) at <150 °C may be due to removal of
surface adsorbed water. The second step weight loss (about 25%) in TGA curve of Cell/Al
MeIm]Cl-XAlCl at 200–290 °C is probably due to the decomposition of the immobilized
chloroaluminate ionic liquid ([MeIm]Cl-XAlCl ) moieties. The last weight losses (about 55-
-[MeIm]Cl-XAlCl were observed at about
30 °C and 380 °C, respectively, which are attributed to the degradation of cellulose. The results
-[MeIm]Cl-XAlCl
2
Cl
7
anion.
All of these characteristic peaks of
2
O
3
3
2
O
3
(
2
O
3
2
O
3
2
3
O -
[
3
2
3
O -
[
3
3
7
3
0%) in TGA curves of Cell/Al
2
O
3
and Cell/Al
2
O
3
3
indicated that the decomposition temperature and char yield of the Cell/Al
is higher than that of the parent Cell/Al
In this work, we also studied SEM analysis of our catalyst. Figure 3 shows the SEM
micrographs of cellulose and Cell/Al -[MeIm]Cl-XAlCl . It can be seen in Figure 3 that
cellulose has a smooth surface, while the surface of Cell/Al -[MeIm]Cl-XAlCl is somewhat
coarse and is completely covered with the supporting materials.
EDS analysis of Cell/Al and Cell/Al -[MeIm]Cl-XAlCl
of Cell/Al -[MeIm]Cl-XAlCl shows that there is no impurities in this catalyst and confirms
the presence of Si, Al, and Cl elements (spectrum (B)). Also, with comparison of EDX spectra of
Cell/Al and Cell/Al -[MeIm]Cl-XAlCl together it is clear that the percentage of Al
2
O
3
3
2
3
O .
2
O
3
3
2
O
3
3
2
O
3
2
O
3
3
are shown in Figure 4. EDS
2
O
3
3
2
O
3
2
O
3
3
7
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element within the Cell/Al
2
3
O was increased after functionalization with chloroaluminate ionic
liquid.
In order to evaluate the catalytic activity of Cell/Al
2
O
3
-[MeIm]Cl-XAlCl , the reaction of
3
4
-nitrobenzaldehyde with dimedone was chosen as a model and its behavior was studied under a
variety of conditions (Table 1). We observed that this reaction was performed smoothly in
ethanol in the presence of 0.08 mmol of catalyst at room temperature and the desired product 9-
(
4-nitrophenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione
was
obtained in 95% isolated yield after 20 min (entry 4). After optimizing the experimental
conditions, a variety of other aromatic aldehydes having electron-donating as well as electron-
withdrawing substituents were smoothly converted into the corresponding products in good to
excellent yields (Table 2, entries 1–13). The method is also suitable for the preparation of 1,8-
dioxo-octahydroxanthenes from acid sensitive aldehydes such as cinnamaldehyde, thiophene-2-
carbaldehyde, and pyridine-2-carbaldehyde (entries 14–16). In this case, all reactions proceed
[
16]
smoothly, without formation of any polymeric by-product. Notably, when the reaction of 4-
nitrobenzaldehyde with dimedone was performed in the absence of catalyst in ethanol at room
temperature, only the uncyclized product 4-nitrophenyl-2,2'-methylene bis(3-hydroxy-5,5-
1
dimethyl-2-cyclohexene-1-one) was formed after 7 h in 84% isolated yield. H NMR spectra of
the 4-nitrophenyl-2,2'-methylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) and 9-(4-
nitrophenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8-(2H)-dione are shown
in Figure 5. Finally, it is worth mentioning that the synthesis of 1,8-dioxo-octahydroxanthenes
from the reaction of aldehydes with dimedone at room temperature has very rarely been
8
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explored. Usually, this reaction was carried out at high temperatures or needs to an additional
[
35–37]
energy (ultrasound or microwave).
Scheme 2 shows a possible mechanism for the preparation of 1,8-dioxo-
octahydroxanthenes using Cell/Al -[MeIm]Cl-XAlCl . First, the acidic nature of catalyst may
facilitate the enolization step of dimedone. Second, the aldehyde was activated by coordination
of Cell/Al -[MeIm]Cl-XAlCl catalyst to the carbonyl group which is then attacked by
2
O
3
3
2
O
3
3
dimedone to yield intermediate I. Then, dehydration of intermediate I in the presence of the
catalyst gives the other intermediate II as a Knoevenagel product, which undergoes Michael
addition with a second molecule of dimedone to gives intermediate III. Finally, intermediate III
undergoes intramolecular cyclodehydration in the presence of Cell/Al
2
O
3
-[MeIm]Cl-XAlCl to
3
give the 1,8-dioxo-octahydroxanthene. Based on this mechanism, it is clear that in the cases of
electron withdrawing groups substituted on aromatic aldehyde (Table 2, entries 9–12) the 1,4-
nucleophilic addition of a second molecule of dimedone on activated intermediate II is more
possible which can finally cause decrease of reaction time of these type of aldehydes with
[
38]
dimedon.
The reusability of recovered Cell/Al
2
O
3
-[MeIm]Cl-XAlCl catalyst was examined by
3
performing reactions using the same amount of catalyst again and again and observed that the
yields remains almost same. The results for the reaction of 4-nitrobenzaldehyde with dimedone
were depicted in Figure 6.
Finally, we presented a comparison of the efficiency of Cell/Al
2
O
3
-[MeIm]Cl-XAlCl
3
catalyst with selected previously known protocols in the synthesis of 1,8-dioxo-
octahydroxanthenes (Table 3). As it is seen in addition to having the general advantages
9
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attributed to the solid catalysts, Cell/Al
2
O
3
-[MeIm]Cl-XAlCl has a good efficiency compared to
3
many of those reported catalysts.
CONCLUSION
In summary, we have introduced a novel heterogeneous chloroaluminate ionic liquid salt
based on cellulose aluminium oxide composite as a catalyst for the synthesis of 1,8-dioxo-
octahydroxanthenes. The catalyst favorably combines the properties of ionic liquids and
advantages of a solid support. It is cheap, noncorrosive, biodegradable, and environmentally
benign compounds. The easy handling and reusability of catalyst, high yields, mild reaction
conditions, and short reaction times are other obvious advantages of the present method.
ACKNOWLEDGEMEBNTS
The author thanks the Research Council of Shahrekord University for partial support of this
work.
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a
Table 1. Optimization of reaction condition.
b
Entry
Solvent
Amount of catalyst (mmol)
Time (min) Yield (%)
1
2
3
4
5
6
7
8
9
Solvent-free
EtOH
0.08
-
70
120
30
20
20
30
35
30
35
45
55
7
EtOH
0.05
0.08
0.1
70
95
95
70
70
80
85
70
EtOH
EtOH
Toluene
Benzene
1,2-Dichloroethane
0.08
0.08
0.08
0.08
0.08
CH
3
2
CN
Cl
1
0
CH
2
a
Reaction of 4-nitrobenzaldehyde (1 mmol) with dimedone (2 mmol) in the presence of
Cell/Al
2
O
3
-[MeIm]Cl-XAlCl . All reactions were carried out at room temperature.
3
b
Isolated yield.
17
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Table 2. Synthesis of 1,8-dioxo-octahydroxanthenes.
O
O
Ar
O
O
Cell/Al O -[MeIm]Cl-XAlCl
3
2
3
(
0.08 mmol)
2
+
ArCHO
EtOH / r.t.
O
a,b
o
Entry Aldehyde
Time (min) Yield (%)
Mp ( C) (Lit.)
[
[
[
[
13]
13]
10]
11]
1
2
3
4
5
6
7
8
9
1
1
1
Benzaldehyde
25
25
30
30
30
27
24
26
22
20
20
22
91
92
91
92
91
92
95
94
95
95
93
93
201–205 (204–205)
208–212 (213–215)
161–166 (162–165)
235–240 (242–244)
4-Methylbenzaldehyde
3-Methoxybenzaldehyde
4-Methoxybenzaldehyde
4-Hydroxybenzaldehyde
4-Chlorobenzaldehyde
2,4-Dichlorobenzaldehyde
2-Bromobenzaldehyde
4-Cyanobenzaldehyde
4-Nitrobenzaldehyde
3-Nitrobenzaldehyde
2-Nitrobenzaldehyde
[
13]
240–244(249–251)
[
[
19]
225–230 (231–233)
245–250 (248–250)
10]
[16]
224–227 (226-229)
[
22]
13]
16]
11]
217–221 (218–220)
219–223 (223–224)
173–176 (171–173)
254–260 (259–261)
[
[
[
0
1
2
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[11]
[21]
[13]
[14]
1
1
1
3
4
5
6
1-Naphthaldehyde
37
60
26
25
94
90
92
93
227–231 (232–234)
174–176 (177–178)
160–165 (161–162)
190–193 (189–190)
Cinnamaldehyde
Thiophene-2-carbaldehyde
Pyridine-2-carbaldehyde
1
a
Isolated yield.
b
All products are known compounds and were identified by comparison of their physical and
spectral data with those of the authentic samples.
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Table 3. Comparison of the efficiencies of a number of different reported catalysts with that of
Cell/Al
2
O
3
-[MeIm]Cl-XAlCl
3
in the reaction of benzaldehyde with dimedone.
Time (min)
a
Entry
Reaction conditions
Yield (%)
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
9]
1
2
3
4
5
6
7
8
9
Silica chloride, MeCN, reflux
Polyphosphoric acid–SiO , neat, reflux
In(OTF) , toluene, reflux
SO , water, 70-80 ºC
InCl , solvent-free, 100 ºC
360
30
93
92
85
90
83
98
92
85
89
88
82
85
96
94
92
89
10]
11]
12]
13]
14]
15]
16]
17]
18]
19]
21]
22]
23]
24]
35]
2
3
240
120
36
H
2
4
3
CAN under ultrasound irradiation, 2-propanol, 50 ºC 35
Succinimide-N-sulfonic acid, solvent-free, 80 ºC
35
CaCl
2
, DMSO, 85-90 ºC
240
30
Fe
3
O
4
nanoparticles, solvent-free, 100 ºC
1
1
1
1
1
1
1
0
1
2
3
4
5
6
CAN supported HY-zeolite, solvent-free, 80 ºC
Fe @SiO -Imid-H 40, EtOH, reflux
Mg-Al hydrotalcite, H O or EtOH, reflux
Thiourea dioxide, H O, 50-60 ºC
ZnO, H O, reflux
90
3
O
4
2
3
PMo12
O
150
180
45
2
2
2
20
Hydroxylamine-O-sulfonic acid, solvent-free, 90 ºC 35
p-Dodecylbenzenesulfonic acid under ultrasound 60
irradiation, H
Ionic liquid [Hbim]BF
in an atmosphere of argon, MeOH, 30 ºC
2
O, 25-30 ºC
[
36]
1
1
7
8
9
4
under ultrasound irradiation, 45
85
86
91
+
–
[37]
Ionic liquid [H-NMP] [HSO
irradiation, H O, r.t.
Cell/Al -[MeIm]Cl-XAlCl
4
] under ultrasound 50
2
1
2
O
3
3
, EtOH, r.t.
25
a
Isolated yield.
20
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Cl
CH3
CH3
Cl
30 h
N
N
(
EtO) Si
+
N
N
(EtO) Si
3
3
o
80 C
([mpIm]Cl)
EtOH
Reflux / 48h
OH
OH
OH
(
AlCl ) Cl
O
O
O
3 x
O
O
O
CH3
Cl
CH3
N
Si
AlCl3
Si
Cell/Al2O3
N
2
N
N
2
Toluene
Reflux / 36 h
(
Cell/Al O -[MeIm]Cl-XAlCl )
(Cell/Al O -[MeIm]Cl)
2 3
2
3
3
Scheme 1. Synthetic pathways for Cell/Al
2
O
3
-[MeIm]Cl-XAlCl .
3
21
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Cat
O
Cat
H
O
O
O
O
Ar
(II)
Ar
H
H
Ar - H O
2
O
O
O
O
HO
(I)
Cat
Cat
O
Ar
O
O
Ar
O
O
Ar
O
O
O
H
H
O
- H O
2
O
OH O
HO
(
III)
Cat
Cat: Cell/Al O -[MeIm]Cl-XAlCl
3
2
3
Scheme 2. Suggested mechanism for the preparation of 1,8-dioxo-octahydroxanthenes catalyzed
by Cell/Al -[MeIm]Cl-XAlCl
2
O
3
3
.
22
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Figure 1. FT-IR spectra of Cell/Al
2
O
3
(A) and Cell/Al
2
O
3
-[MeIm]Cl-XAlCl (B).
3
23
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Figure 2. TGA curves of Cell/Al
2
O
3
(A) and Cell/Al
2
O
3
-[MeIm]Cl-XAlCl (B).
3
24
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Figure 3. SEM photographs of Cell/Al
2
O
3
(A) and Cell/Al
2
O
3
-[MeIm]Cl-XAlCl (B).
3
25
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Figure 4. EDX spectra of Cell/Al
2
O
3
(A) and Cell/Al
2
O
3
-[MeIm]Cl-XAlCl (B).
3
26
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1
Figure 5. H NMR spectra of 9-(4-nitrophenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-
xanthene-1,8-(2H)-dione (A) and 4-nitrophenyl-2,2'-methylene bis(3-hydroxy-5,5-dimethyl-2-
cyclohexene-1-one) (B).
27
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Figure 6. Recyclability of Cell/Al
2
O
3
-[MeIm]Cl-XAlCl (0.08 mmol) in the reaction of 4-
3
nitrobenzaldehyde (1 mmol) with dimedone (2 mmol) at room temperature. Reaction time 20
min.
28
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