Synthesis of Kaolin/Ag nanocomposite as an efficient and versatile reagent for the synthesis of 1,8-dioxo-octahydroxanthene derivatives

Article abstract of DOI:10.1080/15533174.2013.776598

Kaolin/Ag nanocomposite was synthesized in a nano reactor by the calcination of the precursor at high temperature, and shown to efficiently catalyze 1,8-dioxo-octahydroxanthene synthesis via condensation of aromatic aldehydes and 5,5-dimethyl-1,3- cyclohe

Full text of DOI:10.1080/15533174.2013.776598

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Synthesis and Reactivity in Inorganic, Metal-Organic,
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Synthesis of Kaolin/Ag nanocomposite as an efficient
and versatile reagent for the synthesis of 1,8-dioxo-
octahydroxanthene derivatives
Bahareh Sadeghi a
a Department of Chemistry, Yazd Branch , Islamic Azad University , P.O. Box 89195-155 ,
Yazd , Iran
Accepted author version posted online: 08 Oct 2013.
To cite this article: Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry (2013): Synthesis of
Kaolin/Ag nanocomposite as an efficient and versatile reagent for the synthesis of 1,8-dioxo-octahydroxanthene derivatives,
Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, DOI: 10.1080/15533174.2013.776598
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Synthesis of Kaolin/Ag nanocomposite as an efficient and versatile reagent for the synthesis
of 1,8-dioxo-octahydroxanthene derivatives
Bahareh Sadeghi
Department of Chemistry, Yazd Branch, Islamic Azad University, P.O. Box 89195-155, Yazd,
Iran
Corresponding author: E-mail: bsadeghia@gmail.com
Abstract:
Kaolin/Ag nanocomposite was synthesized in a nano reactor by the calcination of the precursor
at high temperature, and shown to efficiently catalyse 1,8-dioxo-octahydroxanthene synthesis via
condensation of aromatic aldehydes and 5,5-dimethyl-1,3- cyclohexanedione under mild reaction
conditions in good to excellent yields.
Keywords: nanocomposite, Ag nanoparticles, Kaolin, 1,8-dioxo-octahydroxanthenes, aromatic
aldehyde, 5,5-dimethyl-1,3- cyclohexanedione
1. Introduction
[1]
Nano reactor is a new technology
for preparing nanoparticles, which provides a relatively
simple method to adjust the particle size distribution with restricted growth of crystal nuclei in a
limited space. Silver is an important inorganic material that has wide applications as
[5,6]
superconductors [2], catalysts [3,4], photosensitive components
and etc. Among the various
methods of silver nanoparticle synthesis, silica substrate is considered to have the advantages of
structural and thermal stability and also show weak interactions with silver particles [7]. Nowday,
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the nanocomposite of Ag/SiO2 have been synthesized by various chemical and physical methods,
[12]
such as sol-gel [8], RF-sputtering [9,10], sono chemical deposition [11], thermal decomposition
[13]
and reverse micelle
techniques. In this paper, the kaolin has been used as adsorbent for the
preparation of Ag/kaolin nanocomposite, that the average size is small and well distributed. The
prepared composite was characterized using Fourier Transform Infrared (FT-IR), X-ray
diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope
(TEM), instruments. In continuation of previous research on the use of solid acids in organic
synthesis [14-17], the synthesis of Kaolin/Ag nanocomposite as a new catalyst have been
investigated and applied for the synthesis of 1,8-dioxo-octahydroxanthene derivatives.
2.Experimental
2.1. Material and instrumentation
Melting points were determined with an Electrothermal 9100 apparatus. IR spectra were
recorded on a Shimadzu IR-470 spectrometer. 1H NMR spectra were recorded on Bruker DRX-
400 Avance spectrometer for solutions in CDCl3 using TMS as an internal standard. The
morphologies of the products were observed using TEM of Philips CM10 and SEM of a
VEGA//TESCAN microscope with an accelerating voltage of 15 kV. X-ray diffraction (XRD),
patterns were taken on a Rigaku D=max-2500 instrument with Cu Ka radiation (40 kV, 100 mA)
to analyze crystalline structure. The chemicals for this work were purchased from Fluka (Buchs,
Switzerland) and were used without further purification.
2.2. Synthesis of Kaolin/Ag nanocomposite
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1.5 g Kaolin was dried at 120°C for 2 h and cooled at room temperature. Then 600 mL absolute
ethyl alcohol were added and well mixed. After 2 h water (3ml) and NaOH (0.162g) were added
into the reaction system under stirrer and room temperature conditions. Because of selective
adsorption capacity of Kaolin, NaOH/water-rich adsorption layer that is just several nanometers
thick and can be used as a nano phase reactor. After the adsorption equilibrium was attained (24
h), Silver nitrate in water (100 mL and 2.28 g) was added at a constant rate and reacts with
NaOH and reduced by ethanol. After reacting for a definite time, the product was gained by
centrifugation and dried at room temperature.
2.3. General procedure for the preparation of compounds 3a-m
Kaolin/Ag nanocomposite (0.001 g) was added to a stirred mixture of the aromatic
aldehyde (1 mmol) and dimedone (2 mmol) in EtOH (5 mL). The reaction mixture was then
stirred for appropriate time (Table 5) at reflux. The progress of the reaction was followed
by TLC (n-hexane:ethyl acetate). After completion of the reaction, the mixture was filtered
to remove the catalyst. After evaporation of the solvent, the crude product was re
crystallised from hot ethanol to obtain the pure compound.
3. Results and discussion
Herein, is attempted to synthesize Kaolin/Ag nanocomposite in a nano reactor and shown to
efficiently catalyse the synthesis of 1,8-dioxo-octahydroxanthene derivatives, by the
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condensation of an aromatic aldehyde 1, and 5,5-dimethyl-1,3- cyclohexanedione (dimedone) 2,
(Scheme 1).
Please insert Scheme 1
The stable catalyst is easily prepared and used for preparation of 1,8-dioxo-octahydroxanthene
derivatives.
In the experiment was first studied FT IR spectra of Kaolin and Kaolin/Ag nanocomposite
(Scheme 2). In both of them, OH stretching bond is observed in ~3621 cm-1. Comparison of the
infrared spectra of Kaolin and Kaolin/Ag show that, in both of them, the asymmetric stretching
vibrations for Al2O3 and SiO2 are appeared in ~914cm-1 and ~1114 cm-1, respectively. Also, the
symmetric stretching vibrations for Al2O3 and SiO2 are appeared in ~694cm-1 and ~789 cm-1,
respectively. In Kaolin/Ag spectrum, the absorption of nitrate is observed in 1369 and 1444 cm-1.
It is detected that Ag nanoparticles are distributed over the surface of Kaolin in the form of
massive agglomeration.
Please insert Scheme 2
The results of XRD are shown in Scheme 3. In both XRD patterns, peaks that appeared at 2θ= 10
and 25º are quartz crystals. The pattern of Kaolin shows at 2θ =30-40o no characteristic peaks
comes out but pattern of Kaolin/Ag nanocomposite shows at 2θ =30-40o intensities of peaks
increases, which demonstrates Kaolin/Ag nanocomposite is produced.
Please insert Scheme 3
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The dimensions of nanoparticles were observed with SEM. The size of commercial Kaolin/Ag
nanocomposite are about 36-53 nm and SEM images of Kaolin/Ag nanocomposite showed that
the Ag nanoparticles were homogeneously dispersed in Kaolin matrices (Scheme 4).
Please insert Scheme 4
It is clearly seen on the TEM images of Kaolin that the crystals size are 170-400 nm but TEM
images of Kaolin/Ag nanocomposite show crystals size decrease 50-55 nm and it is detected that
Ag nanoparticles are distributed over the surface of Kaolin in the form of massive agglomeration
(Scheme 5 and 6).
Please insert Scheme 5
Please insert Scheme 6
BET results are given in the table 1. This information includes the measurement of surface area,
total pore volume and the average pore diameter of Kaolin/Ag nanocomposite and Kaolin.
According to the obtained data, weight, surface area and the average pore diameter Kaolin/Ag
nanocomposite than to Kaolin were increased and the total pore volume were decreased.
Please insert Table 1
To optimize the reaction conditions, the reaction of benzaldehyde and dimedone was used as a
model reaction. In order to establish the better catalytic activity of Kaolin/Ag nanocomposite, the
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model reaction has compared with other catalysts reported in literature. As shown in Table 2, the
condensation of benzaldehyde with dimedone catalyzed by Kaolin/Ag nanocomposite in EtOH
offer corresponding product 3a in short time, excellent yield and mild conditions, while other
catalysts need harder conditions and longer reaction times[18-24] for synthesis of xanthenes 3a.
Please insert Table 2
The above reaction was also examined in various solvents (Table 3). The results indicated that
different solvents affected the efficiency of the reaction. Most of these solvents required a longer
time and gave moderate yields, and the best results were obtained when EtOH was used (Table 3,
entry 1).
Please insert Table 3
In order to determine the optimum quantity of Kaolin/Ag nanocomposite, the reaction of
benzaldehyde and dimedone was carried out under reflux in ethanol using different quantities of
Kaolin/Ag nanocomposite (Table 4). Kaolin/Ag nanocomposite of 0.001 g gave an excellent
yield in 30 min (Table 2, entry 4).
Please insert Table 4
To study the scope of the reaction, a series of aromatic aldehydes and dimedone catalysed by
Kaolin/Ag nanocomposite as catalyst were examined. The results are shown in Table 5. In all
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cases, aromatic aldehyde substituted with either electron-donating or electron-withdrawing
groups underwent the reaction smoothly and gave products in good yields. For further
investigation, the reaction of heterocyclic aldehydes were also studied. Thiophene-2-
carbaldehyde and picolinaldehyde reacted with dimedone under optimized reaction conditions,
and products 3l, 3m were produced with in a somewhat lower yields than other aldehydes (Table
5, entries 12, 13).
Please insert Table 5
An interesting feature of this method is that the reagent can be regenerated at the end of the
reaction and can be used several times without losing its activity. To recover the catalyst, after
completion of the reaction, the mixture was filtered and catalyst was washed with CHCl3 and
then dries the solid residue. This process repeated for three cycles and the yield of product 3a did
not change significantly (Table 6).
Please insert Table 6
4. Conclusions
In summary, by adsorption phase nano reactor technique, Kaolin/Ag nanocomposite material is
synthesized and have shown that it has advantages in the preparation of 1,8-dioxo-
octahydroxanthene derivatives such as shorter reaction times, simple work-up, and affords
excellent yield. The present method does not involve any hazardous organic solvent. Therefore,
this procedure could be classified as green chemistry.
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Acknowledgements
The research Council of the Islamic Azad University of Yazd is gratefully acknowledged for the
financial support for this work.
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O
O
Ar
O
O
Kaolin/Ag Nanocomposite
Reflux in EtOH
+
2
Ar
2a-n
H
O
O
1
3a-n
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Scheme 1: Synthesis of 1,8-dioxo-octahydroxanthene derivatives in the presence of
Kaolin/Ag nanocomposite as catalyst
Scheme 2: FT-IR spectrum of (a) Kaolin and (b) Kaolin/Ag nanocomposite
Scheme 3: XRD patterns of (a) Kaolin and (b) Kaolin/Ag nanocomposite
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Scheme 4: SEM images of Kaolin/Ag nanocomposite
Scheme 5: TEM images of (a) Kaolin 400nm and (b) Kaolin 170nm
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Scheme 6: TEM images of Kaolin/Ag nanocomposite 55nm and 50nm
Table1: Study of BET tests of Kaolin and Kaolin/Ag nanocomposite
Entry
Type of measurment
Sample weight (g)
Kaolin
0.1527
77
Silver/Kaolin
0.2412
77
1
2
3
4
5
6
Temperature (k)
Saturated vapor pressure (KPa)
Mean pore diameter (nm)
Total pore volume (cm3.g-1)
As, BET (m2.g-1)
89.013
41.65
0.1064
1.02
89.009
54.70
0.1013
7.41
Table 2: Evaluation of the activity of different catalysts for the synthesis of 3a
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Entry
Catalyst
TMSCl
Solvent/Condition
CH3CN-DMF/reflux
[bmim][BF4]/80ºC
Neat/120 ºC
Time(h)
Yield[Ref.]
84[18]
87[19]
98[20]
93[21]
90[22]
86[23]
85[24]
60
1
2
8
4
InCl3.4H2O
SmCl3
3
9
4
PPA.SiO2
Neat/140 ºC
0.5
3
5
BiCl3
Neat/80 ºC
6
ZnO-CH3COCl
In(OTf)3
CH3CN/reflux
Toluene/reflux
EtOH/reflux
5
7
4
8
KAl(SO4)2.12H2O
Kaolin
0.5
0.5
0.5
0.5
9
EtOH/reflux
83
10
11
Silver NPs
EtOH/reflux
92
Kaolin/Ag nanocomposite
EtOH/reflux
98
Table 3: Effect of the solvent on the synthesis of 3a by Kaolin/Ag nanocomposite catalyst
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Entry
Solvent
Yielda(%)
1
2
3
4
5
6
7
EtOH
THF
98
20
60
45
10
50
60
DMF
H2O
n-Hexane
Toluene
Solvent-freeb
a) 30 min at reflux temperature in 10 mL solvent.
b) 30 min at 70 °C.
Table 4: Optimisation amount of Kaolin/Ag nanocomposite catalyst for the synthesis of 3a
Entry
Catalyst
Yielda(%)
1
2
3
4
-
-
0.0005
0.0008
0.001
57
83
98
aReaction conditions: 30 min under reflux in EtOH.
Table 5: Condensation of an aromatic aldehyde and dimedone in the presence of Kaolin/Ag
nanocomposite catalyst
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Entry
Ar
Producta Time(min) Yield(%)b
m.p.(ºC)
found
m.p.(ºC)
Reported[21-
24]
1
2
C6H5
2-NO2C6H4
3-NO2C6H4
4-NO2C6H4
4-CH3C6H4
3-OMeC6H4
4-OMeC6H4
3,4-(OMe)2C6H3
4-OHC6H4
3-OMe-4-
3a
3b
3c
3d
3e
3f
3g
3h
3i
30
45
40
30
60
70
70
75
60
75
98
96
97
97
90
92
90
85
88
86
204-206
247-249
168-170
227-228
215-217
160-162
241-243
185-186
247-249
223-225
203-204
248-252
171-173
225-227
216-218
162-165
242-245
184-186
245-250
224-225
3
4
5
6
7
8
9
10
3j
OHC6H3
11
12
13
14
4-NMe2C6H4
2-thienyl
3k
3l
50
70
70
75
90
81
78
83
220-223
163-165
203-205
195-197
222-225
162-164
203-204
194-196
2-pyridyl
3m
3n
2-naphthyl
a All the products were identified by comparing of melting point and 1H NMR spectra with those
of authentic samples reported in the literature.
b Yields refer to pure isolated products.
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Table 6: Recycling studies of reaction between benzaldehyde and dimedone in the presence of
Kaolin/Ag nanocomposite to give product 3a
Entry
Cycle
Time (min)
Yield %a
1
2
3
4
fresh
30
30
30
30
98
92
89
85
1
2
3
a Yields refer to isolated products.
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