Mesoporous nickel-aluminosilicate nanocomposite: A solid acid catalyst for ether synthesis

Article abstract of DOI:10.1166/jnn.2013.7419

Mesoporous nickel aluminosilicate, a solid acid catalyst prepared by sol-gel technique was utilized as a heterogeneous catalyst for the synthesis of symmetrical ethers by dehydro-condensation of alcohols. The prepared catalysts were characterized by Fourier-transform infra red spectroscopy (FT-IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), N₂ adsorption-desorption analysis, temperature programmed desorption of ammonia (TPD) and X-ray photoelectron spectroscopic techniques. The presence of the catalyst assisted the etherification reaction in 30 minutes. Ethers formed in these reactions were quantified by gas chromatography (GC) and the identities of few of them were confirmed by nuclear magnetic resonance spectral data (NMR). Copyright

Full text of DOI:10.1166/jnn.2013.7419

Copyright © 2013 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 13, 2853–2863, 2013
Mesoporous Nickel–Aluminosilicate Nanocomposite:
A Solid Acid Catalyst for Ether Synthesis
N. Neelakandeswari1, R. Karvembu2, and N. Dharmaraj1ꢀ∗
1Inorganic and Nanomaterials Research Laboratory, Department of Chemistry,
Bharathiar University, Coimbatore 641046, India
2Department of Chemistry, National Institute of Technology, Tiruchirappalli 620015, India
Mesoporous nickel aluminosilicate, a solid acid catalyst prepared by sol–gel technique was utilized
as a heterogeneous catalyst for the synthesis of symmetrical ethers by dehydro-condensation of
alcohols. The prepared catalysts were characterized by Fourier-transform infra red spectroscopy
(FT-IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive
X-ray analysis (EDAX), N2 adsorption–desorption analysis, temperature programmed desorption of
ammonia (TPD) and X-ray photoelectron spectroscopic techniques. The presence of the catalyst
assisted the etherification reaction in 30 minutes. Ethers formed in these reactions were quantified
by gas chromatography (GC) and the identities of few of them were confirmed by nuclear magnetic
resonance spectral data (NMR).
Keywords: Mesoporous Materials, Nickel Aluminosilicate, Nanocomposites, Ether Synthesis,
Heterogenious Catalysis.
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1. INTRODUCTION
the direct condensation of alcohols in presence of an
organic or inorganic protic acid catalyst such as p-toluene
sulphonic acid or sulphuric acid has been employed.8–10
Bronsted acids have also been utilised for the direct con-
densation of alcohols to ethers but are limited to vapour
phase reactions alone.11 However, Lewis acids have been
applied for the preparation of ethers from alcohols in
both vapour and liquid phases12 but in stoichiometric
ratio. Later, to overcome the above mentioned difficul-
ties, organic resins (Nafion H) loaded with both Lewis
and Bronsted acids were used for the preparation of
methyl isobutyl ethers but with less selectivity.13–14 Inor-
ganic catalysts like sulfated zirconia, sulphonic acid loaded
MCM-41, HZSM-5 etc., were tested for the condensa-
tion of alcohols, in which case the yield of the ether
formed was very low.15–17 Sulfonic acid functionalized
mesoporous silica18 and SBA-15 were also active for ether
synthesis only under vapour phase conditions.19 Aluminum
dodecatungstophosphate was used for the condensation of
alcohols to ethers in liquid phase but the amount of cata-
lyst required is a limiting factor.20 Hence, it is necessary
to introduce a highly active catalyst system for ether syn-
thesis in liquid phase. Recent reports by some researchers
revealed that mesoporous materials register their role both
as catalyst and as support for various industrially impor-
tant reactions.21–24 Based on the belief that the incorpora-
tion of a bivalent cation like Ni2+ into the aluminosilicate
Some organic reactions catalyzed by mineral acids have
also been successfully carried out using solid acids like
clays, aluminosilicates, heteropolyacids and ion exchange
resins.1 Besides the strong acidity and heterogeneous
nature of solid acids, they do not require neutralization step
at the end of the reaction and also can be reused. From the
literature reports it is inferred that solid acid catalysts are
extremely useful for alkylation, isomerisation and cracking
reactions in petroleum industries.2–5 Among the available
solid acids, aluminosilicates are the promising materials
because of their tunable acidic properties. Negative charge
created on the surface during the incorporation of AlO45−
for SiO44− led to the surface acidity of these materials, the
concentration and strength of the acidic sites can be altered
by changing the Si/Al ratio.6
Ether preparation is one of the most important reactions
in chemical industries since long time. Though many meth-
ods available for ether synthesis, Williamson’s method7 is
the most commonly employed one and requires the con-
version of an alcohol to their corresponding halides or
tosylates followed by their displacement with more basic
alkoxides or phenoxides which causes some limitations in
their industrial applicability. Alternative strategy involving
∗Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2013, Vol. 13, No. 4
1533-4880/2013/13/2853/011
doi:10.1166/jnn.2013.7419
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Mesoporous Nickel-Aluminosilicate Nanocomposite: A Solid Acid Catalyst for Ether Synthesis
Neelakandeswari et al.
framework will alter the total acidity of the catalytic
system, we herein present the catalytic applications of
mesoporous nickel aluminosilicate nanocomposites for
the preparation of ethers from alcohols by dehydro-
condensation in liquid phase.
as a function of temperature with thermal conductivity
detector in a Micromeritics autochem II chemisorption
instrument. Gas chromatographic analysis of the alco-
hols and the products was done in Shimadzu-2010 gas
chromatograph (GC). Nuclear magnetic resonance (NMR)
spectra of selected products were recorded with BRUKER
AMX 500 at 500 MHz with tetramethyl silane as internal
standard in CDCl3 solvent.
2. MATERIALS
All the chemicals used were of reagent or analar grade.
Tetraethyl orthosilicate (TEOS) and aluminium nitrate
were purchased from Sigma-Aldrich and used as received
without any further purification. Absolute alcohol, nickel
chloride and ammonia were obtained from Merck India
Pvt. Ltd. and used as such.
2.2. Catalytic Experiments
0.5 mM substrate (alcohol) was added to suitable quantity
of nickel aluminosilicate catalyst and refluxed at 110 C
ꢀ
with 5 mL of toluene as solvent for 30 min. The reaction
mixture was centrifuged and the centrifugate was quanti-
fied by GC. After the completion of catalytic experiment
the useꢀd catalyst was filtered, washed with toluene, dried
at 100 C for one hour and utilized in reusability test.
Clear solutions of aluminium nitrate (0.32 M) and
TEOS (0.63 M) in ethanol were prepared separately and
mixed with continuous stirring and pH of the medium was
adjusted to 9 with ammonia. To the above aluminosilicate
sol, NiCl2 (0.05 M) in ethanol was added slowly with stir-
ring and the resulting nickel aluminosilicate sol obtained
was allowed to remain for 5 days at room temperature
to get the gel. Since the concentration of water affects
the rate of hydrolysis and condensation, ratio of TEOS to
water was maintained as 1:16. The gel obtained was dried
2.3. Product Analysis
Gas chromatograph equipped with 5% diphenyl and 95%
dimethyl siloxane, Restek capillary column (60 m length,
0.32 mm dia) and a flame ionization detector (FID) with
nitrogen as a carrier gas. The initial column temperature
ꢀ
at 100 C for one hour, calcined at various temperatures
was increased from 60 to 150 ꢀCꢀat a rate of 10 ꢀC/min and
such as 800 ꢀC, 1000 ꢀC and 1200 ꢀC to get the nickelalu-
ꢀ
then to 220 C at the rate of 40 C/min. The temperatures
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minosilicate nanocomposites and were labeled as NAS-A,
of the injection port and FID were kept constant at 150
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NAS-B and NAS-C respectively and were used as hetero-
ꢀ
Copyright: American Scientific Publishers
and 250 C, respectively during the product analysis.
geneous catalysts for the synthesis of a series of ethers
from respective alcohols.
3. RESULTS AND DISCUSSION
2.1. Catalyst Characterization
Thermogram of nickel aluminosilicate gel (Fig. 1) showꢀed
ꢀ
Thermal analysis and the TG-DTA of the samples were
recorded with PYRIS/DIAMOND thermal analyser. Infra-
red spectral studies of different samples were recorded
as KBr discs with Nicolet Avatar model FT-IR spec-
trophotometer between 400 and 4000 cm−1. Powder
X-ray diffraction patterns of the nanocomposites were
obtained using X’PERT PANALYTICAL X-Ray diffrac-
tometer (Cu-Kꢀ radiation ꢁ = 1ꢂ54056 Å) equipped
with a scanning rate of 0.02 ꢀ/sec in 2ꢃ range from
10ꢀ–90ꢀ. The textural properties of the materials were
analyzed by N2 adsorption/desorption measurements using
MICROMERITICS ASAP 2020 POROSIMETER instru-
ment. Pore size distribution was obtained by applying the
BJH pore analysis to the adsorption branch of the nitrogen
adsorption–desorption isotherms. Scanning electron micro-
scopic (SEM) images were recorded on JEOL JSM-6390
instrument equipped with an energy dispersive X-ray anal-
ysis (EDAX). Temperature programmed desorption (TPD)
of ammonia was carried out in a U-shaped quartz reac-
tor with 10% ammonia/Helium gas flow of 25 cm3/min,
the ꢀsample was pretreated with a constant heating rate of
10 /min to 500ꢀ. Ammonia consumption was monitored
a set of plateaus respectively around 80 C and 280 C
with corresponding endotherm and exotherm in the DTA
due to the loss of water molecules and the decomposi-
tion of organic moieties in the gel respectively. Another
ꢀ
endotherm appeared around 700 C in the DTA without
corresponding weight loss in the TGA suggested the occur-
rence of phase transformation of the formed nickel alumi-
nosilicate nanocomposite from amorphous to crystalline.
Based on the knowledge of TGA/DTA, the as-prepared gel
Fig. 1. Thermogram of nickel aluminosilicate gel.
2854
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Neelakandeswari et al.
Mesoporous Nickel-Aluminosilicate Nanocomposite: A Solid Acid Catalyst for Ether Synthesis
ꢀ
was calcined at three diꢀfferent temperatures with 800 C
ꢀ
as the lowest and 1000 C and 1200 C as the other two
temperatures.
The IR spectra of as-prepared nickel aluminosilicate
gel and the calcined samples NAS-A, NAS-B and NAS-C
were given in Figure 2. A broad band found around
3137 cm−1 due to the asymmetric stretching of free silanol
groups in the spectra of as-prepared gel was disappeared
in the case of calcined samples indicating the condensation
between them to form silicate structures upon calcinations.
However, a new broad band around 3410 cm−1 was found
in the spectra of calcined samples corresponding to the
surface hydroxyl groups even after calcination. In addition,
the band appeared around 1360 cm−1 due to the nitrate
vibrations in the gel was not seen in the calcined sam-
ples that can be due to the complete decomposition of the
organic residues during calcination. Absorptions occurred
between 1110 cm−1 and 1030 cm−1 and around 730 cm−1
in the infrared spectra of NAS-A, NAS-B and NAS-C were
respectively assigned as due to the stretching and bending
vibrations of internal tetrahedral units that are typical of
zeolites. Vibrational bands corresponding to the tetrahedral
Fig. 3. Powder X-ray diffraction of nickel aluminosilicate nanocompos-
ite calcined at different temperature.
powder XRD diffractions of the prepared NAS confirmed
the presence of Ni ion in the aluminosilicate framework.
Layered, porous morphology of the prepared samples
was identified from the SEM images (Fig. 4). The ele-
mental composition of the catalysts were analysed using
energy dispersive X-ray analysis technique and the results
were tabulated (Table I). It was observed from the elemen-
tal analysis that the ratio of Si/Al decreases slightly and
amount of nickel on the surface increases with an increase
in the calcination temperature. Though a constant quantity
linkage atoms appeared in the region of 498–550 cm−1
.
These IR spectral features were characteristic of zeolite
like structure in the calcined nickel aluminosilicates.6
An increase in the crystallinity of the aluminosilicate
nanocomposites, NAS-A, NAS-B and NAS-C as a func-
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of nickel was loaded during the sol preparation, variation
in its concentration on the surface of the catalytic system
was observed depending upon the calcination temperature
tion of calcination temperature was evidenced from the
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XRD patterns presented in Figure 3. Diffraction patterns
obtained were compared with the standard JCPDS file and
it was found that diffraction is similar to that of nickel
aluminium oxide (JCPDS No.: 78-2180), nickel silicate
(JCPDS No.: 83-1646) and also orthorhombic nickel alu-
minosilicate (JCPDS No.: 74-0731). Further, diffraction
lines corresponding to either alumina or silica have not
been observed suggesting that no phase separation of the
catalyst occurred during the crystallization. The observed
Copyright: American Scientific Publishers
350
300
250
200
150
100
50
Gel
Calcined at 800 ºC
Calcined at 1000 ºC
Calcined at 1200 ºC
Fig. 4. SEM images of nickel aluminosilicates calcined at (a) 800 ꢀC,
(b) 1000 ꢀC and (c) 1200 ꢀC.
Table I. Elemental composition of NAS.
Sample code O (mass %) Al (mass %) Si (mass %) Ni (mass %)
0
4000
3000
2000
1000
NAS-A
NAS-B
NAS-C
65.04
61.73
58.94
29ꢂ7
32ꢂ45
33ꢂ79
3.97
4.07
3.62
0.41
0.57
1.21
Frequency (cm–1
Fig. 2. FT-IR spectra of nickel aluminosilicate.
J. Nanosci. Nanotechnol. 13, 2853–2863, 2013
)
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Mesoporous Nickel-Aluminosilicate Nanocomposite: A Solid Acid Catalyst for Ether Synthesis
Neelakandeswari et al.
Table II. Sorption characteristics of nickel aluminosilicate
nanocomposites.
that can be ascribed to the sintering of the material at
higher temperature that changed the composition of the
constituent elements at the surface level.
Surface area, pore diameter, pore volume and pore
size distribution were determined using the nitrogen
adsorption–desorption isotherm and the results were sum-
marized in Table II. The BET isotherms (Fig. 5) of the
BET surface
BJH pore
volume (cm3 g−1
BJH pore
radius (nm)
Catalyst
area (m2 g−1
ꢄ
ꢄ
NAS-A
NAS-B
NAS-C
210ꢂ16
131ꢂ57
33ꢂ36
0.2862
0.3659
0.0902
1.8
4.0
3.0
250
200
(b)
Adsorption
Desorption
(a)
Adsorption
Desorption
180
160
140
120
100
80
200
150
100
50
60
40
20
0
0
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (P/P0)
Relative pressure (P/P0)
1.8
1.5
(d)
Adsorption
Desorption
(c)
60
50
40
30
20
10
0
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0.9
0.6
0.3
0.0
0.0
0.2
0.4
0.6
0.8
1.0
2
4
Relative pressure (P/P0)
Pore radius (nm)
2.0
1.5
1.0
0.5
0.0
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
(f)
(e)
2
4
6
8
10
2
4
6
Pore radius (nm)
8
10
Pore radius (nm)
Fig. 5. N2 adsorption–desorption isotherm of nickel aluminosilicates calcined at (a) 800 ꢀC, (b) 1000 ꢀC and (c) 1200 ꢀC, BJH pore volume distribution
(d) catalyst NAS-A, (e) catalyst NAS-B and (f) catalyst NAS-C.
2856
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Neelakandeswari et al.
Mesoporous Nickel-Aluminosilicate Nanocomposite: A Solid Acid Catalyst for Ether Synthesis
(a)
15000
10000
5000
0
1600
284.6
1400
1200
C1S
1000
800
600
400
282 284 286 288 290 292 294
Binding energy (e.V)
0
200
400
600
800
1000
1200
Binding energey (e.V)
(b)
855.7
4500
4000
3500
3000
2500
2000
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872.9
879.65
861.75
850
855
860
865
870
875
880
885
Binding energy (e.V)
Fig. 6. XPS spectra of nickel aluminosilicate calcined at 800 ꢀC (a) Survey plot (instet-C1S specrum) and (b) Ni 2P spectrum.
OH
O
Dehydro-condensation
NAS-A
O
Isopropylalcohol, KOH
Scheme 1. Transfer hydrogenation of acetophenone followed by dehydro-condensation.
J. Nanosci. Nanotechnol. 13, 2853–2863, 2013
2857

Mesoporous Nickel-Aluminosilicate Nanocomposite: A Solid Acid Catalyst for Ether Synthesis
Neelakandeswari et al.
samples, NAS-A, NAS-B and NAS-C were found to be
of type-IV in nature and confirmed the mesoporous nature
of these catalysts.25 Nickel aluminosilicate nanocompos-
ites experienced a decrease in surface area with rise in cal-
cinations temperature, whereas pore size and pore volume
Acidity of the prepared nickel aluminosilicate nanocom-
posites NAS-A, NAS-B and NAS-C was determined by
TPD of ammonia (figure not included). Ammonia TPD
of each sample exhibited three desorption peaks out of
which the low temperature peak appeared in the region
202 to 297 was ascribed to the weakly adsorbed ammonia
on the surface silanol ꢀgroups of the samples.28 Desorptions
ꢀ
is maximum for the sample calcined at 1000 C than the
other two samples. As observed in the case of TG/DTA
analysis, phase transformation occurred at 800 ꢀC and
hence above this temperature sintering takes place that
led to a decrease in the surface area of the catalysts.
Further, the broad distribution of the pore size obtained
(Figs. 5(d)–(f)) is attributed to the disordered pores formed
during the capillary evaporation of the solvent in the
absence of any external templates.
ꢀ
appeared around 397 C and 538 C in the case of sample
NAS-A were assigned to the chemisorbed ammonia on the
strong acidic sites formed by the incorporation of Al3+ and
Ni2+ in to the Si4+ framework respectively. However the
same peaks due to the desorption of adsorbed ammonia at
respective acidic sites in the samples NAS-B and NAS-C
appeared at little lower regions owing to the reason that
these samples possess less acidity than the other sample.
In general, a decrease in respective desorption tempera-
ture for the three peaks was observed with increase in
the calcination temperature of them because of both the
decreased acidic strength and concentration of acidic sites
of the catalyst.
Oxidation state of Ni in nickel aluminosilicate compos-
ite NAS-A was identified from the XPS spectra. Figure 6
depicts the XPS spectra of C1s, Ni 2p and survey plot
of the catalyst. Ni 2p3/2 peak appered at 855.7 eV and
872.9 eV with their corresponding shake up peaks at
861.75 eV and 879.65 eV respectively. Binding ener-
gies of these peaks are assigned to the oxidized form of
nickel.26 Further, the 2p binding energy of NiO obtained
for the nanocomposites NAS-A was higher than that of
the free NiO (853.5 eV), indicating a strong interaction
between NiO and the aluminosilicate support leading to
an enhanced binding energy of the NiO incorporated on to
the framework.27
3.1. Catalytic Reactions
In this study, an attempt was made for the transfer hydro-
genation of carbonyl compounds in presence of catalyst
NAS-A by choosing acetophenone as a model substrate and
isopropanol as a hydrogen donor to yield phenylethanol.
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H
Copyright: American Scientific Publishers
O
H
O
O
O
O
H
R
R
2
O H
Step I
Dryingat 100 ºC
O
–H 2
H
R
R
H
O
O
H
R
R
H
H
O
H
H
H
O
O
O
O
H
O
O
H
O
O
O
O
H
O
R
R
H
R
R
H
O
H
H
S t e p I I
S t e p I I I
O
H
O
O
O
O
H
R
R
R
R
O
H
Scheme 2. Mechanism for the etherification of alcohols.
2858
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Neelakandeswari et al.
Mesoporous Nickel-Aluminosilicate Nanocomposite: A Solid Acid Catalyst for Ether Synthesis
Table III. Transfer hydrogenation of acetophenone.
Table V. Effect of calcination temperature on the etherification of
phenylethanol.
Catalyst
quantity
(mg)
Reaction
time
(Hrs)
Yield
of phenyl
ethano (l%)
Yield of
unknown
product (%)
Calcination
S. no.
Base
temperature of
support (ꢀC)
Yield
(%)
S. no. Catalyst
Substrate
Selectivity
1
2
3
4
50
50
100
100
KOH
KOH
KOH
–
12
24
24
24
11ꢂ6
58ꢂ3
16ꢂ5
2ꢂ0
–
1
2
3
NAS-A
NAS-B
NAS-C
800
1000
1200
Phenylethanol 49ꢂ7
Phenylethanol 96ꢂ9
80.4
97.6
53.7
16.9
48.1
–
Phenylethanol
1ꢂ6
reported during the attempted oxidation of phenylethanol
using HAuCl4 as catalyst.29 However, to the best of our
knowledge, there is no report on the utility of nickel
aluminosilicate for ether synthesis. Hence, for the first time
we herein present a detailed investigation on the utility of
mesoporous nickel aluminosilicate as heterogeneous solid
acid catalyst system towards ether synthesis from alcohols.
But, during the course of the reaction, examination of thin
layer chromatography (TLC) revealed the formation of
phenylethanol in very low yield along with another low
polar compound as a major product. Analysis of the above
reaction mixture by GC registered a maximum intense
peak at 9.6 min as retention time corresponding to the
above said low polar product. Based on the knowledge
gained from the results of TLC and GC, the above reaction
mixture was subjected to column chromatography over sil-
ica gel and the low polar product was isolated with high
purity which did not answer any of the tests for alcohols.
In order to identify it, 1H and 13C NMR spectra were
recorded and interpreted. The spectral features revealed
that the product is bis(ꢀ-methylbenzyl)ether. Further proof
for the structure of bis(ꢀ-methylbenzyl)ether was also
derived from the 1H NMR spectrum of the same compound
reported by Kim et al. in a reaction using ZnCl as a Lewis
acid catalyst for ether synthesis.12 Hence, we believed
that the selected catalyst NAS-A initially promoted the
transfer hydrogenation reaction to afford the phenylethanol
which underwent insitu dehydro-condensation to afford
bis(ꢀ-methylbenzyl)ether as identified above (Scheme 2)
(Table III).
The formation of ether gave an idea that the phenyl-
ethanol formed by transfer hydrogenation of acetophenone
involved in intermolecular dehydration to yield bis(ꢀ-
methylbenzyl)ether. However, to ascertain whether the
catalyst promotes both transfer hydrogenation as well as
intermolecular dehydration of alcohols exclusively, the
later reaction was carried out by utilizing phenylethanol as
a substrate under various conditions (Table IV). From the
results obtained, it was evident that the reaction carried
out in toluene was more successful without the addition of
any base to promote the dehydration. Similar results were
3.2. Optimisation of Reaction Conditions
3.2.1. Selection of Catalyst
In order to identify the most efficient catalyst system for
the ether synthesis among the available three catalysts
NAS-A, NAS-B and NAS-C prepared at different calci-
nation temperatures, all of them were tested by refluxing
0.5 mM phenylethanol in toluene with 100 mg of the cat-
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alyst and the results obtained were given in Table V. From
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the results given in the table, it was evident that the cata-
Copyright: American Scientific Publishers
ꢀ
lyst obtained after calcination at 1000 C (sample NAS-B)
showed superior performance than the remaining two sam-
ples (NAS-A and NAS-C) indicating that not only the sur-
face area but also the dimension of pores of the catalyst
do have a significant contribution towards its efficiency in
the ether formation reaction.
To confirm the role of the catalyst in this reaction, sub-
strate (phenylethanol) alone was refluxed in toluene with-
out catalyst NAS-B, wherein the reaction did not proceed
highlighting the presence of the catalyst is vital for the
expected transformation. However, an increase in the quan-
tity of the catalyst had a linear correlation with the yield
of the product until the loading of 100 mg catalyst beyond
which no significant impact was observed (Table VI).
Further, with a view to know whether the reaction pro-
ceeds at room temperature, the same was carried out at
by stirring at room temperature with 100 mg of catalyst
in which case no ether formation was observed even after
Table IV. Etherification of phenylethanol.
Catalyst
Reaction
% yield
S. no. quantity (mg)
Additive
Solvent
time (Hrs) of ether
Table VI. Effect of catalyst quantity on the etherification of
phenylethanol.
1
2
3
4
5
6
7
50
100
100
100
100
100
100
H2O2
H2O2
KOH
−
Water
Water
Toluene
Toluene
Water
24
24
15
1
24
24
24
–
–
S. no.
Catalyst quantity (mg)
Substrate
Yield (%)
50ꢂ3
73ꢂ2
14ꢂ0
2ꢂ1
8ꢂ5
1
2
3
4
0
50
100
150
Phenylethanol
Phenylethanol
Phenylethanol
Phenylethanol
0
HIO4
−
88.6
96.9
98.2
Acetone
Acetone
KOH
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Mesoporous Nickel-Aluminosilicate Nanocomposite: A Solid Acid Catalyst for Ether Synthesis
Neelakandeswari et al.
Table VII. Etherification of alcohols.
S. no.
1
Substrate
OH
Product
Reaction time (min)
30
Yielda
96.9
Selectivityb
97.6
O
2
3
4
30
30
30
74.6
72.8
88.1
66.4
90.4
73.1
OH
O
H
Cl
Cl
Cl
OH
O
O
H
Br
Br
Br
OH
H3CO
OCH3
H3CO
5
30
3.7
97.0
OH
OH
O
Cl
Cl Cl
6
7
180
92.8
71.7
92.8
84.1
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O
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180
OH
O
H3CO
H3CO
OCH3
8
30
71.6
100
OH
O
O
9
30
30
30
98.3
93.7
99.1
96.6
94.9
99.8
OH
10
11
OH
O
O
OH
2860
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Neelakandeswari et al.
Mesoporous Nickel-Aluminosilicate Nanocomposite: A Solid Acid Catalyst for Ether Synthesis
Reaction
Table VII. Continued.
S. no.
12
Substrate
OH
Product
time (min)
Yielda
Selectivityb
30
52.5
100
O
13
14
30
30
98.8
70.9
98.6
96.6
OH
O
OH
O
Notes: aDetermined from GC; bDetermined from GC peak area; Selectivity = [(area of substrate+area of product)/total peak are ×100.
6 hrs of the reaction with or without a base. From these
facts, it became obvious that 0.5 mM substrate in 5 mL
of toluene was converted into its corresponding ether in
4-methoxy benzylalcohol as substrates in our experiment
was less, it appeared to be better than that reported using
ZnCl2 as a catalyst.12
Aliphatic alcohols have also been etherified under the
same experimental conditions in excellent to moderate
ꢀ
30 minutes using 100 mg of catalyst NAS-B at 110 C.
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yield using the selected catalyst NAS-B. Among them,
3.3. Extension of the Scope
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Copyright: American SccyiecnlotipfiecntPaunoblliswhaesrsconverted into its symmetrical ether in
The generality of the reaction was tested by extending the
reaction to various alcohols including both aliphatic and
aromatic classes. In all the reactions, a smooth conver-
sion of selected alcohols to respective ethers was realized
in 30 min (Entries 1–5 and 8–14, Table VII) except ben-
zyl alcohol or its derivative wherein it took 3 hrs (Entries
6 and 7, Table VII). The yield of ether decreased in the
order phenylethanol > para-substituted phenylethanols >
ortho-substituted phenylethanol. Generally, the presence
of both electron withdrawing and electron releasing sub-
stituents at the para position of the alcohol resulted in low
yield due to the fact that electron withdrawing substituents
can weaken the O H bond to make the substrates (alco-
hol) more acidic and thus became difficult to release –OH
group that is a partial requirement to get symmetrical
ethers by dehydro-condensation. In contrast, when electron
releasing group is available on the para position, alcohol
could behave better as a base to release –OH and conse-
quently proton release would become unfavoured. Hence,
there was a decrease in the yield of symmetrical ethers
from the alcohols containing both electron withdrawing
and electron releasing substituents at the para position
(Entries 2–4 and 7 in Table VII) compared to unsub-
stituted one. Substitutional effect was more pronounced
in the case of ortho position (Entry 5, Table VII) due
to the steric hinderance at ortho position. Though the
yield of respective ethers obtained with benzylalcohol or
higher yield than that of cyclohexanol (Entries 11 and 12,
Table VII), the fact that could be correlated to the reactiv-
ity of the aliphatic cyclic compounds based on the internal
ring strain that is more effective in the case of five mem-
bered cyclopentanol than the six membered cyclohexanol
that facilitates the former towards etherification at a faster
rate than the later.
3.4. 1H and 13C-NMR Spectral Data
1
Di(ꢀ-methyl benzyl)ether (Table VII, entry 1). H NMR
(CDCl3ꢄ: ꢅ = 1ꢂ45 (d, J = 6ꢂ5 Hz, 3 H, C1–CH3ꢄ, 1.54
(d, J = 6ꢂ5 Hz, 3 H, C8–CH3ꢄ, 4.32 (q, J = 6ꢂ5 Hz, 1 H,
C1–H), 4.60 (q, J = 6ꢂ5 Hz, 1 H, C8–H) and 7.28–7.43
(m, 10 H, Ar–H).
13C NMR (CDCl3ꢄ: ꢅ = 23ꢂ04 (C1–CH3ꢄ, 23.74 (C8–
CH3ꢄ, 74.46 (C1), 74.68 (C8), 126.26 (C3, C5), 126.35
(C12, C14), 127.17 (C7), 127.41 (C10), 128.27 (C4, C6),
128.49 (C11, C13), 144.21 (C2) and 144.29 (C9).
Di(4-methoxy benzyl)ether (Table VII, entry 7). 1H
NMR (CDCl3ꢄ: ꢅ = 3ꢂ84 (s, 6 H, –OCH3ꢄ, 4.50 (s, 4 H,
–CH2ꢄ, 6.92 (dd, J = 2 Hz, 6.5 Hz, 4 H, Ar–H) and 7.32
(d, J = 8ꢂ5 Hz, 4 H, Ar–H).
1
Dibenzylether (Table VII, entry 6). H NMR (CDCl3ꢄ:
ꢅ = 4ꢂ72 (s, 4 H, –CH2ꢄ and 7.32–7.4 (m, 10 H, Ar–H).
J. Nanosci. Nanotechnol. 13, 2853–2863, 2013
2861

Mesoporous Nickel-Aluminosilicate Nanocomposite: A Solid Acid Catalyst for Ether Synthesis
Neelakandeswari et al.
Table VIII. Results of reusability test using phenylethanol as
a
50
substrate.
Catalytic cycle no.
Yield (%)
1
2
3
4
5
97.7
97.6
96.9
96.2
95.3
alcohols on the surface of nickel aluminosilicate nanocom-
posite NAS-B is proposed and presented in Scheme 2.
In the first step, weak hydrogen bonds were formed
between the proton of a substrate alcohol and oxygen
available on the catalyst surface and also between the oxy-
gen or hydrogen of –OH group of silanol on the surface
of the catalyst with a hydrogen or oxygen atom of another
alcohol molecule. In the second step, interaction between
the oxygen atom of an alcohol moiety and the ꢀ–C atom
of the other alcohol occupying the neighbouring catalyst
site occurred. Consequently, C O bond formed in step 2
became much stronger with the cleavage of O H and
40
15
20
25
30
Reaction time (min)
Fig. 7. Heterogeneity test.
Di(diphenylcarbinyl)ether (Table VII, entry 9). 1H NMR
(CDCl3ꢄ: ꢅ = 5ꢂ69 (s, 2 H, CH), and 7.19–7.45 (m, 20 H,
Ar–H).
Diindanylether (Table VII, entry 13). 1H NMR (CDCl3ꢄ:
ꢅ = 2ꢂ16 (m, 2 H, C2–CH2ꢄ, 2.54 (m, 2 H, C13–CH2ꢄ,
3.01 (m, 2 H, C3–CH2ꢄ, 3.11 (m, 2 H, C12–CH2ꢄ, 3.36
(m, 1 H, C1–H), 4.39 (t, J = 8ꢂ0 Hz, 1 H, C14–H) and
7.15–7.43 (m, 8 H, Ar–H).
C
O bonds in the respective alcohols to form symmetri-
cal ethers. At the end of the catalytic cycle, the catalyst
ꢀ
was recovered and dried at 100 C for next cycle.
3.5. Heterogeneity Test
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In order to prove that the catalyst involved in the reaction
did not leach out during the course, heterogeneity test was
4. CONCLUSION
Copyright: American Scientific Publishers
A novel, mesoporous solid acid catalyst composed of
nickel aluminosilicate was prepared by a simple sol–
gel technique without employing any structure directing
agents. The effect of calcination temperature of the as-
prepared gel on the surface area, porosity and acidity of
the catalysts were analysed and the best one was applied
as a heterogeneous catalyst for the preparation of ethers
from both aliphatic and aromatic alcohols by dehydro-
condensation. Interestingly, the chosen catalyst effected
the dehydro-condensation of alcohols to the corresponding
symmetrical ethers with a maximum of 99.1% yield from
the cyclopentanol in 30 minutes. The effect of electron
with drawing and electron releasing substituents present
in the alcohols on the quantity of ether obtained was dis-
cussed in terms of the acidity or the basicity of the –OH
group. The catalyst applied was highly selective towards
the synthesis of symmetrical ethers and was reusable up to
five cycles. Hence, this new catalyst could be utilized to
prepare even complicated ethers at ambient reaction con-
ditions in short time.
performed by filtering the reaction mixture after 15 min-
utes of the commencement and the filtrate was allowed to
reflux at 110 C for another 15 minutes (Fig. 7). Ether
ꢀ
formed at the first 15 minutes and also at every 5 minutes
interval for another 15 minutes after filtering the catalyst
was quantified. Yield of symmetrical ether was found to
be 48.25% after 15 minutes and no appreciable increase
in the quantity of ether was noticed after the catalyst was
removed by filtration even allowing the reaction up to
30 minutes indicating the concept of heterogeneity in these
reactions.
3.6. Reusability
Main distinguishable property of solid acids than that
of mineral acids is their reusability. Catalyst NAS-B
almost retained its activity towards the etherification of
phenylethanol to yield bis(ꢀ-methylbenzyl)ether even after
five cycles. The corresponding yield obtained in each run
was also presented in Table VIII. The reusability test
proved that the nickel aluminosilicate nanocomposite is an
excellent, reusable catalyst system.
Acknowledgment: The authors wish to thank the
Department of Science and Technology (DST), Govern-
ment of India, New Delhi, for the financial support in the
form of a major research project (DST File No.: SR/SI/
IC-45/2007 dated 02-04-2008).
3.7. Plausible Mechanism for the Ether Formation
Based on the reports on dehydro-condensation of alco-
hols,6 a typical mechanism for the etherification of
2862
J. Nanosci. Nanotechnol. 13, 2853–2863, 2013

Neelakandeswari et al.
Mesoporous Nickel-Aluminosilicate Nanocomposite: A Solid Acid Catalyst for Ether Synthesis
References and Notes
16. A. S. Dias, M. Pillinger, and A. A. Valente, J. Catal. 229, 414
(2005).
17. R. Ohnishi, R. Kojima, Y. Shu, H. Ma, and M. Ichikawa, Studies
in Surface Science and Catalysis, edited by B. Xinhe and X. Yide,
Elsevier, China (2004), Vol. 147, p. 553.
18. J. G. C. Shen, R. G. Herman, and K. Klier, J. Phys. Chem. B
106, 9975 (2002).
19. R. G. Herman, F. H. Khouri, K. Klier, J. B. Higgins, M. R. Galler,
and C. R. Terenna, J. Catal. 228, 347 (2004).
20. H. Firouzabadi, N. Iranpoor, and A. A. Jafari, J. Mol. Catal., A
227, 97 (2005).
21. Y. Ren, Z. Ma, and P. G. Bruce, Chem. Soc. Rev. 41, 4909 (2012).
22. P. Yang, S. Gai, and J. Lin, Chem. Soc. Rev. 41, 3679 (2012).
23. K. Ariga, A. Vinu, Y. Yamauchi, Q. Ji, and J. P. Hill, Bull. Chem.
Soc. Jpn. 85, 1 (2012).
24. I. K. Nam, N. Dong, K. G. Pyo, P. Junsu, and Y, Jongheop,
J. Nanosci. Nanotechnol. 12, 5704 (2012).
25. S. Brunauer, L. S. Deming, W. S. Deming, and E. Teller, J. Am.
Chem. Soc. 62, 1723 (1940).
1. W. K. Gray, F. R. Smail, M. G. Hitzler, S. K. Ross, and M. Poliakoff,
J. Am. Chem. Soc. 121, 10711 (1999).
2. L. Fan, I. Nakamura, S. Ishida, and K. Fujimoto, In. Eng. Chem.
Research 36, 1458 (1997).
3. K. Tanabe and W. F. Hölderich, J. App. Catal., A 181, 399 (1999).
4. R. S. Drago and E. E. Getty, J. Am. Chem. Soc. 110, 3311 (1988).
5. M. A. Harmer, W. E. Farneth, and Q. Sun, J. Am. Chem. Soc.
118, 7708 (1996).
6. D. K. Chakrabarty and B. Viswanathan, Heterogenious Catalysis,
New Age Science, UK (2009), p. 148.
7. M. B. Smith and J. March, March’s Advanced Organic Chemistry:
Reactions, Mechanisms, and Structures, John Wiley & Sons, Inc.
Publications, New Jersey (2007).
8. H. E. van Dam, A. P. G. Kieboom, and H. van Bekkum, Starch-
Starke 38, 95 (1986).
9. S. Ramayya, A. Brittain, C. DeAlmeida, W. Mok, and M. J. Antal, Jr,
Fuel 66, 1364 (1987).
10. M. Bicker, D. Kaiser, L. Ott, and H. Vogel, J. Supercritical Fluids
36, 118 (2005).
26. Y. Koltypin, A. Fernandez, T. C. Rojas, J. Campora, P. Palma,
R. Prozorov, and A. Gedanken, Chem. Mater. 11, 1331 (1999).
27. J. S. Gonzalez, M. M. Lara, and A. J. Lopez, J. Chem. Society,
Faraday Trans. 93, 493 (1997).
28. C. V. Hidalgo, H. Itoh, T. Hattori, M. Niwa, and Y. Murakami,
J. Catal. 85, 362 (1984).
11. G. Larsen, E. Lotero, M. Marquez, and H. Silva, J. Catal. 157, 645
(1995).
12. S. Kim, K. N. Chung, and S. Yang, J. Org. Chem. 52, 3917 (1987).
13. M. A. Harmer and Q. Sun, App. Catal., A 221, 45 (2001).
14. H. Wang and B.-Q. Xu, App. Catal., A 275, 247 (2004).
15. X. Qi, M. Watanabe, T. M. Aida, and R. L. Smith, Jr, Catal.
Commun. 10, 1771 (2009).
29. X. Jiang, E. K. London, D. J. Morris, G. J. Clarkson, and M. Wills,
Tetrahedron 66, 9828 (2010).
Received: 30 October 2012. Accepted: 4 December 2012.
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J. Nanosci. Nanotechnol. 13, 2853–2863, 2013
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