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Microporous and Mesoporous Materials 81 (2005) 343–355
Synthesis of 2-acetyl-6-methoxynaphthalene using mesoporousSO2�
4 /Al-MCM-41 molecular sieves
M. Selvaraj a,*, K. Lee a, K.S. Yoo b, T.G. Lee a,*
a Department of Chemical Engineering, Yonsei University, Seoul 120-749, Koreab Environment & Process Technology Division, KIST, Seoul 136-791, Korea
Received 15 May 2004; received in revised form 17 February 2005; accepted 18 February 2005
Available online 11 April 2005
Abstract
The mesoporous molecular sieves Al-MCM-41 with Si/Al ratio equal to 16, was synthesized under hydrothermal conditions using
cetyltrimethylammonium bromide (CTMA+Br�) as surfactant. The SO2�4 /Al-MCM-41(Si/Al = 16) material was synthesized using
sulfuric acid under impregnation method, and the resulting material is sulfated Al-MCM-41 (SO2�4 /Al-MCM-41). The mesoporous
materials viz. Al-MCM-41 and SO2�4 /Al-MCM-41 were characterized using several techniques e.g. ICP-AES, Nephelometer, XRD,
FT-IR, TG/DTA, N2-adsorption, solid-state-NMR, SEM, TEM and TPD-pyridine. By impregnating of sulfuric acid on silica sur-
face, crystallinity, surface area, pore diameter and pore volume of SO2�4 /Al-MCM-41 decreased except wall thickness. While the
Lewis acidity is increased because of the expelling aluminum from the Al-MCM-41 framework by impregnating sulfuric acid.
The SO2�4 /Al-MCM-41 has been used for synthesis of 2-acetyl-6-methoxynaphthalene using 2-methoxynaphthalene with acetic
anhydride as acylating agent and 1,2-dichloroethane as solvent. The catalytic results were compared with those obtained using
0.8 N sulfuric acid, amorphous silica–alumina, H-b, USY and H-ZSM-5 zeolites. From the catalytic results it was concluded that
the conversion of 2-methoxynaphthalene and selectivity of 2-acetyl-6-methoxynaphthalene in the SO2�4 /Al-MCM-41 is higher than
that in other catalysts due to higher number of Lewis acid sites. Thus the SO2�4 /Al-MCM-41 is found to be a highly active and recy-
clable heterogeneous catalyst while the catalyst is a very suitable for the synthesis of 2-acetyl-6-methoxynaphthalene.
� 2005 Elsevier Inc. All rights reserved.
Keywords: Al-MCM-41; SO2�4 /Al-MCM-41; Lewis acidity; Conversion of 2-methoxynaphthalene; Selectivity of 2-acetyl-6-methoxynaphthalene
1. Introduction
Friedel-crafts acylation of aromatics is one of the
most important reactions to produce aromatic ketones,
which are useful intermediates for the synthesis of fine
chemicals such as pharmaceutical ((S)-naproxen), fra-grances and dye stuffs [1,2]. The conventional processes
for the preparation of these aromatic ketones employ
metal halides (AlCl3, FeCl3, etc.) or mineral acids (HF
or polyphosphoric acid) as homogeneous catalysts [3].
1387-1811/$ - see front matter � 2005 Elsevier Inc. All rights reserved.
doi:10.1016/j.micromeso.2005.02.017
* Corresponding authors. Tel.: +82 2 2123 5751; fax: +82 2 312 6401.
E-mail addresses: [email protected] (M. Selvaraj), teddy.
[email protected] (T.G. Lee).
Such process, however, consume near stoichiometric
quantities of catalysts, and the recovery of products
from reaction mixture is difficult. Most of these catalysts
cannot be recycled and pose serious waste disposal
problems. Because of current environmental restrictions,
many research groups have tried to develop environ-mentally benign acylation processes using solid acid cat-
alysts [4–10].
The acylation of 2-methoxynaphthalene (2MN) has
been investigated over HY, ZSM-12 and BEA [11,12]
and mordenite [13], and ZSM-5 [14]. In the acylation
reaction, one of the major products is 2-acetyl-6-meth-
oxynaphthalene (2A-6MN), the intermediate for an
important anti-inflammatory drug, (S)-(+)-6-methoxy-a-methyl-2-naphthaleneacetic acid, known as Naproxen.
344 M. Selvaraj et al. / Microporous and Mesoporous Materials 81 (2005) 343–355
During the acylation of 2MN with acetic anhydride the
linear 2A-6MN and the bulky 1-acetyl-2-methoxy-
naphthalene (1A-2MN) can be formed. 2A-6MN can
be created at the inner and outer surfaces of zeolites.
1A-2MN is too bulky and cannot enter the micropores
[11]. Harvey et al. [11,15] reported that zeolite beta wasthe most effective catalysts among various zeolites in
the acylation of 2MN. According to their results, the
external surface played an important role in the catalytic
activity for synthesis 1A-2MN. A disadvantages of zeo-
lite catalysts are their limited pore (up to 1.0 nm), which
renders useless as catalysts in the conversion of larger
sized reactants.
The discovery of the mesoporous material MCM-41[16,17] has greatly enlarged the window of porous mate-
rials applicable as catalyst for organic reactions. The
typical characteristics of the materials, viz. highly or-
dered mesoporosity, large surface area, high hydrother-
mal stability and mild acidity, allude to the possibility of
applying these materials as catalysts in the synthesis and
conversion of large organic molecules. Unfortunately,
the acid strength of MCM-41 resembles that of theamorphous silica aluminas rather than that of the more
strongly acidic zeolites [18]. Although the materials are
valuable for many organic conversions [19–24], enhance-
ment of its acidity is desirable for extension of its
applicability.
Gunnewegh et al. [25] studied the acylation of 2MN
catalysed by mesoporous molecular sieve such as
MCM-41. They concluded that the higher selectivity of1A-2MN is formed with small amount of undefined high
molecular products at 100 �C over H-MCM-41. How-
ever, the molecular size of 1A-2MN is higher than that
of 2A-6MN. So this catalyst is very suitable to 1A-
2MN due to the catalyst pore size with the higher num-
ber of mild Bronsted acid sites.
Chen et al. (1999) first reported the details of the syn-
thesis and characterization of sulfuric acid impregnatedmesoporous Al-MCM-41 materials for synthesis of b-naphthyl methyl ether [26] and later, we also reported
the synthesis, characterization of mesoporous materials
with different Si/Al ratios for synthesis of neroline
[27,28] and dypnone [29]. Herein we report the synthesis
and characterization of Al-MCM-41 with aluminum
isopropoxide under hydrothermal conditions [29]. The
synthesized Al-MCM-41 materials were modified withsulfuric acid and the resulting materials are known as
sulfated Al-MCM-41 (SO2�4 /Al-MCM-41) materials.
From the physicochemical characterization and some
catalytic experimental results of the materials it was con-
cluded that the SO2�4 /Al-MCM-41 have the higher num-
ber of Lewis acid sites, have good recyclability and
suitable pore size to the synthesis of 2A-6MN. So the
materials have used as catalyst for highly selective syn-thesis of 2A-6MN. The catalytic reaction was carried
out under various reaction conditions using SO2�4 /Al-
MCM-41 as catalyst. The catalytic results are correlated
and compared with those of 0.8 N sulfuric acid solution
and other solid acid catalysts such as Al-MCM-41,
amorphous silica–alumina, H-b, USY and H-ZSM-5
zeolite.
2. Experimental
2.1. Materials
The syntheses of Al-MCM-41 and SO2�4 /Al-MCM-41
materials were carried out hydrothermally and by
impregnation methods respectively and using tetra-ethylorthosilicate (TEOS), aluminum isopropoxide
(Al–[O–CH–(CH3)2]3), cetyltrimethylammonium bro-
mide (C16H33(CH3)3N+Br), tetraethylammonium hy-
droxide ((C2H5)4NOH), sulfuric acid (H2SO4). The
synthesis of 2A-6MN was carried out by liquid phase
reaction and using 2-methoxynaphthalene (2MN) and
acetic anhydride (AC2O) as reactants, and cyclohexane,
dichloromethane, 1,2-dichloroethane, nitrobenzene, sul-folane, nitromethane as solvents. All chemicals (AR
grade) were purchased from Aldrich & Co., USA.
2.2. Commercial catalytic materials
Amorphous silica–alumina (Si/Al = 5.7, Strem), H-b(Si/Al = 25.7, Strem), USY (Si/Al = 27.5, PQ) and H-
ZSM-5 (Si/Al = 25.5, PQ) were obtained from commer-cial sources. These catalysts were calcined at 500 �C for
6 h in air before catalytic reaction.
2.3. Synthesis of Al-MCM-41 and SO2�4 /Al-MCM-41
2.3.1. Synthesis of Al-MCM-41
For the synthesis of the Al-MCM-41 (Si/Al = 16)
material, 22.3 mL (1 mol) of tetraethylorthosilicate wasmixed with 0.68 g (0.033 mol) of aluminum isopropox-
ide (dissolved in 5 mL of deionized water). The mixture
solution was stirred for 30 min at a speed of about
250 rpm and tetraethylammonium hydroxide solution
(10% water) was added with continuous stirring for
another 30 min. at a speed of about 250 rpm until the
gel formation (pH = 11). After that, 7.2 g (0.2 mol) of
cetyltrimethylammonium bromide was added dropwise(30 mL/h) via a dual syringe pump so that the gel
changed into suspension after further stirring for 1 h
the resulting synthesis gel of composition 1SiO2;
0.033Al2O3:0.2CTMABr:100H2O, it was transferred
into Teflon-line steel autoclave and heated at 150 �Cfor 48 h. After cooling to room temperature, the mate-
rial was recovered by filtration, washed with deionized
water and ethanol, dried in air at 100 �C for 1 h andfinally calcined at 540 �C for 6 h in the presence of air
(calcination ramp rate is 100 �C/h).
M. Selvaraj et al. / Microporous and Mesoporous Materials 81 (2005) 343–355 345
2.3.2. Synthesis of SO2�4 /Al-MCM-41
The SO2�4 /Al-MCM-41 was prepared by impregnat-
ing 1 g of calcined Al-MCM-41 with 50 mL (0.8 N) of
sulfuric acid with stirring 500 rpm for 3 h in room
temperature. Then the sample was dried at 110 �C for
12 h.
2.4. Characterization
The Al content in SO2�4 /Al-MCM-41 and Al-MCM-
41 was recorded using ICP-AES with allied analytical
ICAP 9000.
The SO2�4 content in SO2�
4 /Al-MCM-41 with barium
chloride was recorded using Nephelometer withCL52D (Elico Limited, India).
The crystalline phase identification and phase purity
determination of the calcined samples of Al-MCM-41
(Si/Al = 16) and SO2�4 /Al-MCM-41 were carried out by
x-ray diffraction (XRD, Philips, Holland) using nickel
filtered CuKa radiation (k = 1.5406 A). The samples
were scanned from 1� to 5� (2h) angle in steps of 0.5�,with a count of 5 s at each point. In order to protectthe detector from the high energy of the incident and dif-
fracted beam, slits were used in this work.
N2-adsorption isotherms were measured at �197 �Cusing a Micromeritics ASAP 2000. Prior to the experi-
ments, the samples dried at 130 �C and evacuated over-
night for 8 h in flowing argon at a flow rate of 60 mL/
min at 200 �C until the vacuum pressure was below
8 mmHg. Surface area, pore size, pore volume and wallthickness was obtained from these isotherms using the
conventional BET and BJH equations.
Infrared spectra were recorded with a Nicolet Impact
410 FTIR Spectrometer in KBr pellet (0.005 g sample
with 0.1 g KBr) scan number 36, resolution 2 cm�1.
Thermo gravimetric–differential thermal analysis was
carried out in Rheometric Scientific (STA H+) thermo
balance. Ten to 15 mg of as-synthesized Al-MCM-41and SO2�
4 /Al-MCM-41 were loaded, and the airflow
used was 50 mL/min. The heating rate was 20 K/min
and the final temperature was 1000 �C.The 27Al MAS NMR spectra were recorded at a fre-
quency of 75.512 MHz and a spinning rate of 8 kHz
with a pulse length of 4 ls, a pulse interval of 1 s and
approximately 1000 scans. 27Al chemical shifts are re-
ported relative to 1 M Al(NO3)3.The SEM micrographs of a typical sample of MCM-
41 materials were obtained on a JEOL 2010 microscope
operated at 200 kV from a thin film dispersed on a holly
carbon grid in ethanol solvent.
TEM images were recorded using a JEOL JEM-
200CX electron microscope operating at 200 kV with
modified spectrum stage with objective lens parameters
Cs = 0.41 mm and Cc = 0.95 mm, giving an interpretablepoint resolution of �ca�, 0.185 nm. Samples for analysis
were prepared by crushing the particles between two
glass slides and spreading them on a holly carbon film
supported on a Cu grid. The samples were briefly heated
under tungsten filament light bulb in air before transfer
into the specimen chamber. The images were recorded at
magnifications of 100,000·.Temperature programmed desorption of pyridine
was studied on Al-MCM-41 and SO2�4 /Al-MCM-41
samples under chromatograph conditions [30].
2.5. Experimental for synthesis of
2-acetyl-6-methoxynaphthalene
2.5.1. Catalytic reaction
The catalyst (0.2 g) was added to 2MN, acetic anhy-dride as acylating reagent and 1,2-dichloroethane as
solvent while the reaction was performed in a stirred
(600 rpm) and sealed batch autoclave reactor (100 mL,
Autoclave Engineers) at reaction temperatures namely,
40, 80, 120, and 140 �C with atmospheric pressure, dif-
ferent time (h), AC2O/2MN ratio, different solvent and
different catalysts. The reaction products were recovered
from the reactor after cooling to 0 �C.After reusing the MCM-41 its activity decreases and
the catalyst needs to be regenerated by calcination. It
can be reused after washing with dichloromethane and
ethyl acetate at 40 �C followed by hot water to remove
the organics and unreacted 2MN. The recycled SO2�4 /
Al-MCM-41 catalyst was washed 5 times with dichloro-
methane and ethyl acetate. It was drying at 140 �C for
overnight.
2.5.2. Analysis of reaction products
After the reaction, the catalyst (if a solid was used)
was separated from the reaction solution and washed
with small amount of dichloromethane and ethyl acetate
using a centrifuge. Again small amount of above re-
agents was added to separate the catalyst. The catalyst
solution centrifuge tube was tightly sealed and magneticstirred at 25 �C for 1 h. This step was repeated 2–3
times. The supernatant solutions collected in the above
steps were maintained at 0 �C for 1 h. The solution
was evaporated to give a crude oil. This crude product
was purified by preparative TLC (dichloromethane/ethyl
acetate = 10/1) to afford 2A-6MN. 1A-2MN could also
be purified by preparative TLC. The clear product solu-
tions were analyzed with a GC (HP 5890 series II) usinga flame-ionization detector on a 30-M HP-5 column.
The products were also identified by GC-MS (Shima-
dzu, QP 2000 a).
Spectroscopic data of 2-acetyl-6-methoxynaphtha-
lene: 1H NMR (CDCl3) d: 2.72 (s, 3H), 3.95 (s, 3H)
7.17 (d, J = 2.6 Hz, 1H), 7.22 (dd, J = 8.7, 2.6 Hz, 1H),
7.77 (d, J = 8.7 Hz, 1H), 7.86 (d, J = 8.8 Hz, 1H), 8.02
(dd, J = 8.7, 1.9 Hz, 1H), 8.40 (d, J = 1.7 Hz, 1H). 13CNMR (CDCl3) d: 26.5, 55.5, 105.8, 119.8, 124.7, 127.2,127.9, 130.1, 132.2, 132.7, 137.31, 159.7, 197.9.
(b)
200110
100
Inte
nsit
y
346 M. Selvaraj et al. / Microporous and Mesoporous Materials 81 (2005) 343–355
Spectroscopic data of 1-acetyl-2-methoxynaphtha-
lene: 1H NMR (CDCl3) d 2.64 (s, 3H), 3.99 (s, 3H),
7.28 (d, J = 9.1 Hz, 1H), 7.38 (ddd, J = 8.2, 6.9,
1.2 Hz, 1H), 7.48 (ddd, J = 8.1, 6.9 1.5 Hz, 1H), 7.77
(d, J = 8.1 Hz, 1H), 7.80 (d, J = 8.1 Hz, 1H), 7.89 (d,
J = 9.2 Hz, 1H). 13C NMR (CDCl3) d: 32.8, 56.4,112.8, 123.6, 124.2, 125.2, 127.8, 128.2, 128.7, 130.3,
131.5, 153.9, 205.3.
2.6. Leaching of sulfate experiment studies
from SO2�4 /Al-MCM-41
After the catalyst reaction, catalyst was equilibrated
with distilled water for 1 week at 100 �C (pH < 5), andkept in water bath and the supernatant was checked
for SO2�4 using barium chloride. The experiment was re-
peated to verify reproducibility before reporting the
results.
1 2 3 4 5
(a)
200110
2θ
Fig. 1. XRD patterns of (a) calcined Al-MCM-41 and (b) SO2�4 /Al-
MCM-41.
3. Results and discussion
3.1. ICP-AES
The Al content in both catalysts was found to be
0.28 g containing Si/Al = 16 using ICP-AES. The SO2�4
content was found to be 1960 ppm in the SO2�4 /Al-
MCM-41 using a Nephelometer.
3.2. X-ray diffraction
The X-ray diffractograms of the Al-MCM-41 and
SO2�4 /Al-MCM-41 materials are illustrated (Fig. 1), after
calcination at 540 �C for 6 h in air, contain, in addition
to sharp d100 reflection line near 2h = 1.93�, broad peaks
near 2h = 3.33� (110) and 3.83� (200). The SO2�4 /Al-
MCM-41 material after having been dried at 110 �Cfor 12 h, contains, in addition to the sharp d100 reflectionline near 2h = 2.0�, broad peaks near 2h = 3.48� (110)
and 3.98� (200). The broadening effects of higher reflec-
tion lines can be due to small crystallites [31]. Physico-
chemical properties of these mesoporous materials are
summarized in Table 1. The XRD patterns of calcined
Al-MCM-41 with characteristic peaks of hexagonal
symmetry and with d100 = 45.73 A are shown in Fig.
1(a). The unit cell parameter (a0) was 52.8 A. The hexag-onal unit cell parameter (a0) was calculated using 2d100/p3 from d100, which was obtained from the peak in the
XRD pattern by Bragg�s equation (2d sinh = k, where
k = 1.5406 A for the CuKa line). The value of a0 was
equal to the internal pore diameter plus one pore wall
thickness. In general, in the synthesis condition used,
the crystallization reaction is non-stoichiometric and
the crystal�s Si/Al ratio is always greater than in thehydrogel containing aluminum [32]. Incorporation of
aluminum into the silicate framework decreases the size
of the unit cell when the source of Al is Al-isopropoxide.
The data obtained for the calcined materials are in good
agreement with those reported by Beck et al. [17]. Excess
incorporation of aluminum (low Si/Al ratio) might lead
to the collapse of the structure, as reported by Kim et al.
(1997) for Al-MCM-41 (Si/Al = 10) prepared at a pH of
11 [33]. Impregnation of Al-MCM-41 with sulfuric acid
results in the decrease of crystallinity, d-spacing valueand unit cell parameter [26–29] and is as shown in
Table 1.
3.3. Nitrogen adsorption isotherm
Fig. 2 shows the isotherm of nitrogen adsorption on
the calcined Al-MCM-41 and SO2�4 /Al-MCM-41 mea-
sured at liquid nitrogen temperature (�197 �C). Threewell-defined stages may be identified: (1) A slow increase
in nitrogen uptake at low relative pressure, correspond-
ing to monolayer–multilayer adsorption on the pore
walls; (2) a sharp step at intermediate relative pressures
indicative of capillary condensation within mesopores;
and (3) a plateau with a slight inclination at high relative
pressures associated with multilayer adsorption on the
external surface of the crystals [34]. A fourth stage, char-acterized by a sharp rise in N2 uptake as the pressure
reaches saturation (P/P0 = 1), may be identified in some
Table 1
Physicochemical characterization of Al-MCM-41 and SO2�4 /Al-MCM-41
Samples d-spacing valuea
(A)
Unit cell parametera
(A)
BET surface area
(m2/g)bPore diameter
(A)bPore volume
(cm3/g) b
Wall thickness
(A)cAcidity
(mmol g�1)d
Al-MCM-41 45.7 52.8 1099 28.3 1.48 24.5 0.082
SO2�4 /Al-MCM-41 44.1 50.92 698 25.8 0.84 25.1 0.093
a Values obtained from XRD studies.b Values obtained from N2-adsorption results.c Wall thickness (t) = unit cell parameter (a0) � pore size (D).d Pyridine adsorbed beyond 100 �C.
0.0 0.2 0.4 0.6 0.8 1.00
100
200
300
400
500
600
700
800
900
1000
Vol
ume
adso
rbed
(cm
3 /g S
TP)
Relative pressure (P/P0)
adsorption (SO42 - /Al-MCM-41)
desorption (SO42-/Al-MCM-41)
adsorption (Al-MCM-41)
desorption (Al-MCM-41)
Fig. 2. N2-adsorption isotherms of Al-MCM-41 and SO2�4 /Al-MCM-
41.
M. Selvaraj et al. / Microporous and Mesoporous Materials 81 (2005) 343–355 347
isotherms. Mesoporous materials with high Al content
generally raise the isotherm lines at high pressure, which
is attributed to the condensation of nitrogen within
voids formed by crystal aggregates. It is worthwhile to
note that the sharpness and height of the capillary con-
densation (pore filling) step in the isotherms is a measureof the pore size uniformity. Departures from a sharp
and clearly defined pore-filling step are usually an
indication of increase in pore size heterogeneity (i.e.,
widening of pore size distribution). The samples exhibit
isotherms with a well-developed step in the relative pres-
sure (P/P0) range corresponding from 0.3 to 0.36 for Al-
MCM-41 and from 0.26 to 0.32 for SO2�4 /Al-MCM-41.
A characteristic hysteresis loop observed for both sam-ples in the region of P/P0 above 0.4 is assigned to capil-
lary condensation in the mesopores [35]. However, the
capillary condensation step is much higher and steeper
for the Al-MCM-41 than that for the SO2�4 /Al-MCM-
41. In general the isotherms indicate that all of the sam-
ples possess good mesopore structural ordering and
a narrow pore size distribution, and any structural
changes resulting from Al incorporation are not neces-sarily at the expense of pore uniformity. The surface area,
pore diameter and pore volume are given in Table 1.
The pore diameter of Al-MCM-41 is higher than that
of SO2�4 /Al-MCM-41 due to the presence of textural
mesoporosity. Sulfuric acid treatment of Al-MCM-41
sample results in a decrease of surface area from 1099to 698 m2/g which is consistent by lower relative pres-
sure (P/P0 < 0.3). Thus, in the SO2�4 /Al-MCM-41 the
surface area, pore diameter and pore volume are lower
than that of Al-MCM-41 material while the sulfation
of Al-MCM-41 results in a decrease of the pore volume
from 1.48 to 0.84 cm3/g. (Since the Kelvin equation is
not valid for pores below 18 A only the BJH approach
can be used for mesoporous material.) This could bedue to structure collapse due to arrangement of tetrahe-
dral Al in non-frame work with impregnation of sulfuric
acid.
3.4. Fourier transform infra red spectroscopy
Infra red spectroscopy had been used extensively for
the characterization of zeolites. In the FTIR spectrumof calcined siliceous MCM-41, the asymmetric and sym-
metric stretching vibration bands of framework Si–O–Si
bands, assigned by Sohn et al. [36] for zeolites, appeared
at 1123 and 814 cm�1. In as-synthesized Al-MCM-41,
the IR spectrum was measured in 400–4000 cm�1 range
in a few steps during sample preparation and is shown in
Fig. 3(a). The as-synthesized sample exhibits absorption
bands around 2921 and 2851 cm�1 corresponding to n-C–H and d-C–H vibrations of the surfactant molecules.
The broad bands around 3650–3800 cm�1 may be attrib-
uted to surface silanols and adsorbed water molecules,
while deformational vibrations of adsorbed molecules
cause the adsorption bands at 1623–1640 cm�1 [37].
The absorption band at 1069 and 1223 cm�1 are due
to asymmetric stretching vibrations of Si–O–Si bridges,
but in the opposite direction are observed for the962 cm�1 bands due to „Si–OH or „Si–O� vibrations
in aluminum incorporation. When various metals are
incorporated, the intensity of this band increases. This
is generally considered to be proof of the incorpora-
tion of the heteroatom into the framework. Cambler
et al. (1993) have reported similar stretching vibra-
tions of Si–OH groups present at defect sites [38]. From
disappearance of bands at 2851 and 2921 cm�1, wecan conclude that calcination of the original framework
O-
Si
O
OO-
Al-
O
Si
O-
O
O-
S
O
O-
O
O-
2-
LA
LA
BA
O-
O
Si
O
O O-
Si
O-
O
O O
Al
S+
O-
Fig. 4. Scheme proposed for the sulfate containing Al-MCM-41
material showing possible Lewis acid sites (LA—Lewis acid sites and
BA—Bronsted acid sites).
4000 3500 3000 2500 2000 1500 1000 500
(c)
(b)
(a)
Wave number (cm-1)
Tra
nsm
itta
nce
Fig. 3. FTIR absorption spectra of (a) as synthesized Al-MCM-41, (b)
calcined Al-MCM-41 and (c) SO2�4 /Al-MCM-41.
Table 2
Thermogravimetric results (in air) for the Al-MCM-41 and SO2�4 /Al-
MCM-41
Samples Weight loss (wt%)
Total 50–150 �C 150–350 �C 350–550 �C
Al-MCM-41 44.11 4.100 34.21 5.80
SO2�4 /Al-MCM-41 67.51 45.21 22.3 –
348 M. Selvaraj et al. / Microporous and Mesoporous Materials 81 (2005) 343–355
was completed. The vibration bands of calcined
Al-MCM-41 can be shifted from 1 to 3 or 5 cm�1. An
FTIR spectrum of calcined Al-MCM-41 is shown in
Fig. 3(b).
IR spectrum was measured in 400–4000 cm�1 range
for SO2�4 /Al-MCM-41 and is shown in Fig. 3(c). The sul-
fated sample exhibits absorption bands around
3500 cm�1, which may be attributed to surface silanol
groups and adsorbed water molecules [36]. The adsorp-
tion bands at 1186, 876 and 585 cm�1 are due to strong
stretching vibrations of HSO�4 [39]. The SO2 deformation
frequency has been assigned in the region 876 and
585 cm�1. The proposed structure to the SO2�4 /Al-
MCM-41 material showing possible Lewis acid sites isshown in Fig. 4. If the aluminum-ions are non-frame-
work by impregnating sulfuric acid while the sulfate
groups are also having inductive effect with aluminum-
ions, the strong Lewis acid sites (LA) can be generated
on its surface. From the infrared analysis, the asymmet-
ric and symmetric stretching of the S@O bond were
determined in the 1215–1125 cm�1 and 1060–995 cm�1,
respectively. The adsorption a band at 1186 cm�1 isdue to symmetric vibrations of S–O–Si-bridges, but in
the opposite direction are observed for the 963 cm�1
bands due to „Si–O� silanols. The absorption band at
799 cm�1 is due to the symmetric Si–O stretching vibra-
tion and band at 876 cm�1 is due to the symmetric S–O
stretching vibrations.
3.5. Thermal analysis
Thermogravimetric analysis [40] of the crystals shows
distinct weight losses that depend, on the framework
composition (Table 2). Representative thermogram is
given in Fig. 5(a). The minor weight loss below 150 �Ccorresponds to the desorption of physisorbed water (or
ethanol) in the voids formed by crystal agglomeration
and in the mesopores. Weight losses in the temperaturerange 150–350 �C are attributed to the decomposition
and removal of occluded organics. Weight losses in this
temperature range are not as large as in the parent sili-
cate because of stronger sorbate–sorbent interactions
at the aluminosilicate surface. In the temperature range
280–340 �C, the oxidative decomposition of residual or-
ganic compounds occurs which is accompanied by exo-
therms whose number and intensity depends on the
200 400 600 800 10000
10
20
30
40
50
60
70
80
90
100
Wei
ght l
oss
(%)
TGA
(b)
(a)
Temperature (˚C)
200 400 600 800 1000
DTA
(b)
(a)∆T (m
icro
vol
t)
Temperature (˚C)
Fig. 5. TG–DTA curves of as-synthesized (a) Al-MCM-41 and (b)
SO2�4 /Al-MCM-41.
100 80 60 40 20 0 -20 -40
Tetrahedral aluminum
Octahedral aluminum
Octahedral aluminum
Inte
nsit
y
Chemical shift / ppm
(b)
(a)
Fig. 6. 21Al-MAS-NMR spectra of (a) calcined Al-MCM-41 and
(b) SO2�4 /Al-MCM-41.
M. Selvaraj et al. / Microporous and Mesoporous Materials 81 (2005) 343–355 349
aluminum content of the crystal. The 350–550 �C was
the region of surfactant associated with Al–O. There
was almost no exothermal peak after 550 �C, which indi-
cated the surfactant, had been removed completely. The
total weight loss at 1000 �C of the Al-MCM-41 sample isin 44.11%.
Representative thermograms for SO2�4 /Al-MCM-41
are given in Fig. 5(b). The major endothermic reac-
tion peak is assigned the minor weight loss below
150 �C corresponds to the desorption of physisorbed
water in the voids formed by crystal agglomeration
and also the minor endothermic peak occurring at the
200–300 �C is attributed to the decomposition of SO2�4
into SO2 gas by absorption of entropy. Thus the total
weight loss at 1000 �C of the SO2�4 /Al-MCM-41 sample
is 67.51%.
3.6. Solid-state NMR spectroscopy
Fig. 6 shows solid-state 27Al-MAS-NMR spectra of
calcined Al-MCM-41 and SO2�4 /Al-MCM-41 with Si/
Al = 30. Chemical shift peak spectrum shows a strong
and sharp signal at 53 ppm as well as a weak and broadsignal at around 0 ppm regardless of the Al content in
the Al-MCM-41 (Fig. 6(a)), but a sharp signal at around
0 ppm shows in the SO2�4 /Al-MCM-41 (Fig. 6(b)). The
structure collapse consequent upon the disappearance
of tetrahedral aluminum after impregnation of sulfate
in the reduction in the physical parameters is only
resulted. The signal at around 53 ppm could be as-
signed to tetrahedrally coordinated framework alumi-num (Td -Al), which was observed in aluminosilicate
zeolites [41]. The signal at around 0 ppm was ascribed
to octahedrally coordinated (Oh) non-framework alumi-
num [41].
It is important to bear in mind these results when
considering the use of these materials for acid-catalyzed
reactions, in which the Bronsted acidity should be
attributed to the presence of tetrahedral aluminum andalso Lewis acidity should be attributed to the presence
of octahedral aluminum. From the results it is con-
cluded to the acid sites, however, the number of Lewis
acid sites is higher in SO2�4 /Al-MCM-41 than in Al-
MCM-41 due to higher number of aluminum octahedral
coordination on the silica surface by impregnation of
sulfuric acid.
Fig. 8. Transmission electron microscope images for SO2�4 /Al-MCM-
41.
350 M. Selvaraj et al. / Microporous and Mesoporous Materials 81 (2005) 343–355
3.7. Scanning electron microscopy
Al-MCM-41 materials are having micellar rod-like
shape hexagonal or spherical edges as shown in Figs.
7(a) and (b). In materials synthesized using cetyltri-
methylammonium bromide as surfactant, Steel et al.(1994) postulated that CTMABr surfactant molecules
assembled directly into the liquid crystal phase upon
addition of the silicate species, based on 14NMR spec-
troscopy [42]. The size of micellar rod like shape and
hexagonal phase is smaller in SO2�4 /Al-MCM-41 than
that of Al-MCM-41 materials because tetrahedral alu-
minum is forced into non-framework positions during
impregnation with sulfuric acid.
3.8. Transmission electron microscopy
The TEM image of SO2�4 /Al-MCM-41 (Fig. 8) exhib-
its ordered hexagonal arrays of mesopores with uniform
pore size [16]. While the distance between mesopores are
estimated by TEM image of the sample.
Fig. 7. Scanning electron microscope images for (a) Al-MCM-41 and
(b) SO2�4 /Al-MCM-41.
Both pore channels and hexagonal symmetry can be
clearly identified in the TEM image for SO2�4 /Al-
MCM-41 samples which indicate that the MCM-41samples have only one uniform phase as inferred from
the XRD results. The pore sizes are observed by TEM
analysis while the results are in agreement with the re-
sults obtained from N2-adsorption measurements. The
pore size is smaller in SO2�4 /Al-MCM-41 than that in
Al-MCM-41.
3.9. TPD-pyridine analysis
The acidities of the Al-MCM-41 and SO2�4 /Al-MCM-
41 samples were characterized by the TPD of pyridine.
The strength appears to be rather moderate as nearly
all the pyridine desorbed below 300 �C. The acidities
(mmol/g) based on the pyridine desorbed by the samples
beyond 100 �C are presented in Table 1. The number of
acid sites is higher in the SO2�4 /Al-MCM-41 than in Al-
MCM-41 due to the impregnation of sulfuric acid on the
Al-MCM-41.
3.10. Acylation of 2-methoxynaphthalene
In our experiments it was observed that the yield of
2A-6MN was higher than that of 1A-2MN, 1-acetyl-8-
methoxynaphthalene and diacetylmethoxynaphthalene.The mechanism proposed by Guisnet et al. [43] for the
formation of 2A-6MN from 2MN in strong acid med-
ium involves the acylation of 2MN with acetic anhy-
dride as acylating agent.
The acylation of 2-MN with acetic anhydride over
SO2�4 /Al-MCM-41 leads to a complex mixture of prod-
ucts, in which 2A-6MN is primary stable and 1A-2MN
is primary unstable. It is well known that the presenceof an electron-donating group like methoxy activates
M. Selvaraj et al. / Microporous and Mesoporous Materials 81 (2005) 343–355 351
the 1, 6 and 8 positions of the naphthalene ring. The 1-
position is more active than the other two positions,
and acylation of 2-methoxynaphthalene generally occurs
at this kinetically controlled position. However, migra-
tion of the acyl group from 1 to 8 positions [2] and pro-
tiodeacylation of the acyl group at the 1-position [44]results in the formation of the thermodynamically most
stable 6-acylated isomer. Steric hindrance to acylation
is in the order 1- > 8- > 6-position. Hence, the isomeriza-
tion of the sterically hindered ketones like 1A-2MN to
sterically less hindered isomers like 6- and 8-acetyl-2-
methoxynaphthalene will be favored. 1A-2-MN can
follow an intramolecular transacylation to yield other
acetyl-methoxynaphthalenes (i.e.,1-acetyl-8 methoxyna-phthalene) [43], while consecutive acylation of the prod-
ucts is also possible [45] providing different isomers of
the diacetylmethoxynaphthalene and is shown in Fig. 9.
3.10.1. Influence of conversion of 2MN and selectivity
of 2A-6MN
When the reaction was carried out at 120 �C in the
presence of SO2�4 /Al-MCM-41, the conversion of 2MN
was 60.1% and selectivity of 2-acetyl-6-methoxynaph-
thalene was highest at 72.1%. Hence, all the subsequent
OCH3 H+ - SO4
2-/A l-MCM-41 -
CH3
O
O CH3
O
H+ - SO42-/Al-MCM-41 -
O
OCH3
H+ SO4CH3
O
O CH3
O
H+ - SO42- /A l-MCM-41 -
2-methoxynaphthalene 1-acetyl-2-methoxy
2-acetyl-6-methoxynaphthalene
1 2
3
1-direct acylation; 2-intermolecular transacylation of 1-a3 - protodecylation of 1-acetyl-2-methoxynaphthalene;1-acetyl-2-methoxynaphthalene; 5 - consecutive acylati
1
-
most activated position for the electrophillic sub
activated position
*
* low activated position
CH3
O
O
H
O
H3C
Fig. 9. Reaction of 2MN and AC2O in
experiments in different conditions were carried out only
with SO2�4 /Al-MCM-41 catalyst; the results are com-
pared with that of various catalysts to synthesis of 2A-
6MN, which resulted into higher yield (Table 3).
The rate of acylation of 2MN depends upon the pore
structure and acidity behavior of the catalyst. The acid-ity of SO2�
4 /Al-MCM-41 and Al-MCM-41 are given in
Table 1. As it was reported, the acidity is higher in the
SO2�4 /Al-MCM-41 than that of Al-MCM-41. Hence
the yield of the final product 2A-6MN depends on the
rate of acylation of conversion, which in turn depends
on substrate and catalyst features (pore structure and
acidity). This observation indicates that number of
Lewis acid sites in SO2�4 /Al-MCM-41 is higher but Bron-
sted acid sites is lower than that in Al-MCM-41 due to
the higher number octahedral Al-ions coordinated on
the silica surface. Thus, the selectivity of 2A-6MN is
higher in SO2�4 /Al-MCM-41 than that of other catalysts
(Table 3).
3.10.2. Effects of reaction time
Acylation of 2MN was carried out with acetic anhy-dride to 2MN molar ratio = 2 and 50 mL of 1,2-dichlo-
roethane as solvent on SO2�4 /Al-MCM-41 catalyst at
OCH3
CH3
2- /Al-MCM-41 -
naphthalene
OCH3
H+ - SO42-/Al-MCM-41 -
OCH3
4
5
cetyl-2-methoxynaphthalene;4- intramolecular transacylation of on of monoacylated products.
diacetylmethoxynaphthalene
stitution on 2- methoxynaphthalene
CH3
O
O CH3
O
H+ - SO42-/Al-MCM-41 -
5
CH3
O
+ - SO42-/Al-MCM-41 -
1-acetyl-8-methoxynaphthalene
O CH3
CH3
OO
O
presence of SO2�4 /Al-MCM-41.
Table 3
Acylation of 2MN: Variation with different catalysts
Catalysts 1 h 12 h 24 h
X S1 S2 Others X S1 S2 Others X S1 S2 Others Yield of 6A-2MN (%)
SO2�4 /Al-MCM-41 33.4 60.6 38.1 1.3 48.3 34.7 64.2 1.1 60.1 25.7 72.1 2.2 43.33
Al-MCM-41 19.5 85.1 13.6 1.3 34.4 89.0 9.6 1.4 35.2 97.1 1.8 1.1 0.63
USY 26.8 84.2 14.7 1.1 41.7 74.3 24.7 1.0 42.4 82.9 15.3 15.3 6.49
H-b 27.9 78.1 20.8 1.1 42.8 71.9 26.8 1.3 43.4 45.9 54.7 1.4 23.73
H-ZSM-5 22.2 78.1 18.4 3.5 37.1 75.2 22.4 2.4 38.4 85.8 13.4 1.1 5.14
Silica–alumina 20.5 82.7 16.3 1.0 35.4 76.2 21.7 2.1 36.3 83.6 13.1 3.3 4.75
H2SO4 25.4 83.5 15.5 1.0 40.3 84.1 13.7 2.2 41.3 84.9 14.5 3.5 5.98
Reaction conditions: Catalyst, 2 g; reaction time, 24 h; reaction temperature, 120 �C; solvent, 50 mL of 1,2-dichloroethane; AC2O/2MN ratio = 2; 1A-
2MN, 1-acetyl-2-methoxynaphthalene; 6A-2MN, 6-acetyl-2-methoxynaphthalene, X, conversion of 2MN (%); S1, selectivity of 1A-2MN (%); S2, selec-
tivity of 6A-2MN (%); others, 1-acetyl-8-methoxynaphthalene, diactylmethoxynaphthalene.
0 10 20 30 40 500
10
20
30
40
50
60
70
80
conv
ersi
on o
f 2M
N a
ndis
omer
s se
lect
ivity
(%
)
Reaction time (h)
conversion of 2MN selectivity of 1A-2MN
selectivity of 2A-6MN selectivity of others
Fig. 10. Variation of conversion of 2MN and selectivity of isomers
with reaction time over SO2�4 /Al-MCM-41 at 120 �C (50 mL of 1,2-
dichloroethane and AC2O/2MN = 2).
0 10 20 30 40 500
20
40
60
80
(b)
sele
ctiv
ity o
f 1A
-2M
N (
%)
Reaction time (h)
40°C
80°C
120°C
140°C
0
10
20
30
40
50
60
70
(a)
conv
ersi
on o
f 2M
N (
%)
0 10 20 30 40 50Reaction time (h)
40°C
80°C
120°C
140°C
0 10 20 30 40 50Reaction time (h)
40°C
80°C
120°C
140°C
0
10
20
30
40
50
60
70
80
(c)
sele
ctiv
ity o
f 2A
-6M
N (
%)
Fig. 11. Variation of conversion of 2MN (a), selectivity 1A-2MN (b),
and selectivity of 2A-6MN (c) with reaction time over SO2�4 /Al-MCM-
41 at different temperature (50 mL of 1,2-dichloroethane and AC2O/
2MN = 2).
352 M. Selvaraj et al. / Microporous and Mesoporous Materials 81 (2005) 343–355
120 �C in the range of time between 1–48 h and is as
shown in Fig. 10. 2MN is mainly transformed into1A-2MN, and 2A-6MN. Small amounts of the other
monoacylated methoxynaphthalene isomers (1-acetyl-
8-methoxynaphthalene) are produced. As the reaction
progresses, traces of diacylated compounds (i.e. diac-
teylmethoxynaphthalene) are formed. The conversion
of 2MN is 33.4% at 1 h and then slowly levels off to a
final value 60.1% at 24 h. Initially, 1A-2MN is formed
with a slight selectivity over 2A-6MN. With longer reac-tion times, the opposite selectivity (2A-6MN) is ob-
served (Fig. 10).
3.10.3. Effects of reaction temperature with reaction time
The acylation of 2MN over SO2�4 /Al-MCM-41 at var-
ious reaction temperature (40–140 �C) and reaction time
(1–48 h) were carried out with acetic anhydride to 2MN
molar ratio = 2 and 50 mL of 1,2-dichloroethane as sol-
vent and the results are shown in Fig. 11. The conver-
sion of 2MN and selectivity of 2A-6MN increases, but
the 1A-2MN selectivity decreases significantly when
the reaction time (24 h) was increased up to 120 �C.
0 10 20 30 40 500
10
20
30
40
50
60
70
(a)
conv
ersi
on o
f 2M
N (
%)
Reaction time (h)
AC2O/2MN = 1 AC2O/2MN = 2
AC2O/2MN = 4
AC2O/2MN = 1 AC2O/2MN = 2
AC2O/2MN = 4
0 10 20 30 40 500
10
20
30
40
50
60
70
(b)
sele
ctiv
ity o
f 1A
-2M
N (
%)
Reaction time (h)
AC2O/2MN = 1 AC2O/2MN = 2
AC2O/2MN = 4
0 10 20 30 40 50
Reaction time (h)
0
10
20
30
40
50
60
70
80
(c)
sele
ctiv
ity o
f 2A
-6M
N (
%)
Fig. 12. Variation of conversion of 2MN (a), selectivity 1A-2MN (b),
and selectivity of 2A-6MN (c) with reaction time over SO2�4 /Al-MCM-
41 at AC2O/2MN ratio (50 mL of 1,2-dichloroethane and 120 �C).
M. Selvaraj et al. / Microporous and Mesoporous Materials 81 (2005) 343–355 353
After 120 �C, when the reaction temperature was in-
creased, the conversion of 2MN increases but the selec-
tivity of 1A-2MN and 2A-6MN slightly decreases at
48 h. However, the small amounts of the other monoa-
cylated methoxynaphthalene isomers and traces of dia-
cylated compounds are formed and may be due to theprotiodeacylation of the acyl group. The increase in
the temperature leads also to catalyst samples becoming
darker in color after reaction and likely indicates
increasing carbonaceous residue contents.
3.10.4. Effect of acetic anhydride (AC2O)/2MN molar
ratio with reaction time
The acylation of 2MN over SO2�4 /Al-MCM-41 at var-
ious volume of acetic anhydride to 2MN molar ratio
and 50 mL of 1,2-dichloroethane as solvent was carried
out at 120 �C reaction temperature. The results are
shown in the Fig. 12. The ratio of acetic anhydride to
2MN was varied while a constant amount of 2MN
and total reaction solution volume was maintained. At
early reaction times, the concentration of the acylating
agent has practically no influence on the conversion of1A-2MN and 2A-6MN. Thus, the reaction order is close
to zero order. At longer reaction time, the effect of the
ratio of acetic anhydride to MN is different for the for-
mation of 1A-2MN and 2A-6MN (Fig. 12). At longer
reaction times, the conversion of 2MN and selectivity
of 2A-6MN increases but the 1A-2MN decreases when
the ratio of AC2O/2MN was increased. After AC2O/
2MN ratio = 2, when the AC2O/2MN ratio was in-creased, the conversion of 2MN and selectivity of 2A-
6MN decreases. This may be due to the catalyst rapidly
turns into dark solid that is indicative of a large forma-
tion of heavy products and also small amounts of diacy-
lated compounds are formed.
3.10.5. Effect of different zeolites and Al-MCM-41
as catalysts
Both the catalytic activity and the yield and selectivity
of 2A-6MN follow: SO2�4 /Al-MCM-41 > H-b > USY >
H2SO4 > H-ZSM-5 > silica–alumina > Al-MCM-41 from
the catalytic results in Table 3. Based on the results from
FTIR of adsorbed pyridine, TPD of the ammonia and
those reported elsewhere [46], the catalyst acid strength
also exhibits a similar trend, except H-ZSM-5 zeolite.
As the acylation of 2MN is an acid-catalyzed reaction;the conversion of 2MN is correlated to the catalyst acid
strength and the conversion of 2MN with various cata-
lysts was shown in Table 3. Although the acid strength
of H-ZSM-5 is the highest among all solid catalysts, its
low catalytic activity is due to the small pore size that hin-
ders both the entry of 2MN and the formation of 2A-
6MN. The 2A-6MN selectivity with various catalysts is
shown in Table 3. The selectivity of 2A-6MN increasesfrom 14.5 to 72.1 wt% when Al-MCM-41 is impregnated
with 0.8 N H2SO4, while, a value is so much higher than
that obtained from sulfuric acid. Therefore, sulfuric acid
modification of Al-MCM-41 enhances the catalyst activ-
ity. To investigate the reasons for such a result, the
sulfated Al-MCM-41 was stirred and washed with deion-
ized water. The filtrate was found via atomic absorptionspectroscopy to contain aluminum cation. Therefore the
non-framework aluminum existing in the intrachannel
space is supposed to increase the catalyst activity due to
the increase of Lewis acidity [47].
Table 4
Acylation of 2MN: Variation with different solvents
Solvents 1 h 12 h 24 h
X S1 S2 Others X S1 S2 Others X S1 S2 Others
Cyclohexane 22.1 72.6 26.0 1.4 24.3 43.2 52.1 4.7 29.4 42.3 53.8 3.9
Dichloromethane 30.1 59.5 37.7 2.8 46.3 32.1 63.8 4.1 56.3 29.7 68.3 2.0
1,2-dichloroethane 33.4 60.6 38.1 1.3 48.3 34.7 64.2 1.1 60.1 25.7 72.1 2.2
Nitrobenzene 32.1 67.4 30.3 2.3 44.3 40.8 56.4 2.8 45.6 36.4 58.2 5.4
Sulfolane 30.4 85.6 11.4 3.0 46.4 75.0 19.4 5.6 49.3 72.3 21.9 5.8
Nitromethane 29.4 83.3 13.7 3.0 32.3 56.6 39.8 3.6 34.4 54.3 41.1 4.6
Reaction conditions: Catalyst, 2 g of SO2�4 /Al-MCM-41; reaction temperature, 120 �C; AC2O/2MN ratio = 2; 1A-2MN, 1-acetyl-2-methoxynaph-
thalene; 6A-2MN, 6-acetyl-2-methoxynaphthalene; X, conversion of 2MN (%); S1, selectivity of 1A-2MN (%); S2, selectivity of 6A-2MN (%); others,
1-acetyl-8-methoxynaphthalene, diactylmethoxynaphthalene.
Table 5
Regenerability of SO2�4 /Al-MCM-41 in the acylation of 2MN with
AC2O at 120 �C
Cycle
(catalyst
used)
Conversion of
2-methoxynaphthalene
(wt%)
Selectivity (wt%)
1A-2MN 6A-2MN Others
1 60.1 25.7 72.1 2.2
2 60.2 25.5 72.3 2.2
3 60.1 25.3 72.4 2.3
4 60.3 25.1 72.2 2.7
Catalyst, 2 g of SO2�4 /Al-MCM-41; reaction time, 24 h; reaction
temperature, 110 �C; solvent, 50 mL of 1,2-dichloroethane; 1A-2MN,
1-acetyl-2-methoxynaphthalene; 6A-2MN, 6-acetyl-2-methoxynaphtha-
lene; others, 1-acetyl-8-methoxynaphthalene, diactylmethoxynaphthalene.
354 M. Selvaraj et al. / Microporous and Mesoporous Materials 81 (2005) 343–355
3.10.6. Effect of solvents
The solvents employed for acylation of 2MN exerted
a significant effect of conversion and selectivity of 2A-
6MN with acetic anhydride as acylating agent and
AC2O/2MN = 2 at 120 �C for 24 h over SO2�4 /Al-
MCM-41 and the results is shown in the Table 4. The
selectivity of 2A-6MN follow: 1,2-dichloroethane >
dichloromethane > nitrobenzene > cyclohexane > nitro-methane > sulfolane from the catalytic results in Table
4. 1,2-dichloroethane and dichloromethane showed the
higher activity and selectivity of 2A-MN, because the
solvents can compete with reactants for adsorption on
the surface acidic sites. A non-polar solvent (cychlohex-
ane) or a very polar solvent (nitromethane) showed
slightly lower selectivity of 2A-6MN compared with
1,2-dichloroethane and dichloromethane. Sulfolaneshowed unusually high selectivity toward 1A-2MN
over SO2�4 /Al-MCM-41. Herein SO2�
4 /Al-MCM-41 did
not change its Si/Al ratio and sulfate content after
acylation of 2MN with acetic anhydride in both
sulfolane and 1,2-dichloroethane solvents. Conse-
quently, it was concluded that the low selectivity of
2A-6MN in sulfolane was not due to the modified cata-
lytic species but due to the properties of the solventitself.
3.10.7. Recyclability
After the initial use, the SO2�4 /Al-MCM-41 usually
suffers from the activity loss and hence the catalyst needs
to be regenerated by calcination. In contrast, SO2�4 /Al-
MCM-41 is excellent catalyst for the acylation of
2MN with acetic anhydride as acylating agent to 2A-6MN. It can be recycled by washing with dichlorometh-
ane and ethyl acetate at 40 �C followed by hot water to
remove the organics and unreacted 2MN. The recycled
SO2�4 /Al-MCM-41 catalyst was washed 5 times with
dichloromethane and ethyl acetate. It was dried at
140 �C overnight. No loss of activity was observed after
4 runs. Instead, its selectivity is to remain constant with
each cycling (Table 5). It was verified that the reactiondid not occur in the absence of catalyst. Also, the sulfate
ion in recycled samples confirmed that SO2�4 /Al-MCM-
41 was resistant to leaching under reaction conditions
tested in this study.
3.11. Leaching studies of SO2�4 /Al-MCM-41
From the experiments on leaching studies carried out
using SO2�4 impregnated Al-MCM-41 it was observed
no leaching of SO2�4 from the catalyst after catalytic
reaction.
4. Conclusions
Mesoporous Al-MCM-41 and SO2�4 /Al-MCM-41
were synthesized under hydrothermal and sulfuric acid
impregnation conditions, respectively. The materials
were characterized using ICP-AES, Nephelometer,
XRD, N2-adsorption, FT-IR, TG-DTA, Solid-State-
MAS-NMR, SEM, TEM and TPD-Pyridine techniques.
Sulfuric acid treatment of Al-MCM-41 sample results ina decrease of surface area from 1099 to 698 m2/g and
pore volume from 1.48 to 0.84 cm3/g. The number of
Lewis acid sites is higher in SO2�4 /Al-MCM-41 than that
Al-MCM-41 due to higher number of aluminum octahe-
dral coordination on the silica surface. The size of micel-
lar rod like shape and hexagonal phase is smaller in
SO2�4 /Al-MCM-41 than that of Al-MCM-41 materials.
The materials were evaluated for their efficiency with re-spect to acylation of 2MN in the liquid phase for the
M. Selvaraj et al. / Microporous and Mesoporous Materials 81 (2005) 343–355 355
production of 2A-6MN. The SO2�4 /Al-MCM-41 catalyst
has much higher activity than other catalysts tested due
to the higher catalytic activity. After the catalytic reac-
tion, no leaching of SO2�4 was detected.
Acknowledgment
The authors gratefully acknowledge the Korea Re-
search Foundation for sponsoring this work (KRF-2004-003-D00135).
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