Enhanced activity of nanocrystalline Beta zeolite for acylation of veratrole with acetic anhydride

Article abstract of DOI:10.1166/jnn.2016.11613

Friedel-Craft acylation of veratrole using homogeneous acid catalysts such as AlCl₃, FeCl₃, ZnCl₂, and HF etc. produces acetoveratrone, (3′ ,4′-dimethoxyacetophenone), which is the intermediate for synthesis of papavarine alkaloids. The problems associated with these homogeneous catalysts can be overcome by using heterogeneous solid catalysts. Since acetoveratrone is a larger molecule, large pore Beta zeolites with smaller particle sizes are beneficial for the liquid-phase acylation of veratrole, for easy diffusion of reactants and products. The present study aims in the acylation of veratrole with acetic anhydride using nanocrystalline Beta Zeolite catalyst. A systematic investigation of the effects of various reaction parameters was done. The catalysts were characterized for their structural features by using XRD, TEM and DLS analyses. The catalytic activity of nanocrystalline Beta zeolite was compared with commercial Beta zeolite for the acylation and was found that nanocrystalline Beta zeolite possessed superior activity.

Full text of DOI:10.1166/jnn.2016.11613

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Nanoscience and Nanotechnology
Vol. 16, 4247–4251, 2016
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Enhanced Activity of Nanocrystalline Beta Zeolite for
Acylation of Veratrole with Acetic Anhydride
Aisha Mahmood Abdulkareem Al-Turkustani∗ and Rosilda Selvin
Chemistry Department, Faculty of Science-Al Faisaliah Branch, King Abdulaziz University,
P.O. Box: 55075, 21534, Jeddah, Saudi Arabia
Friedel-Craft acylation of veratrole using homogeneous acid catalysts such as AlCl3, FeCl3, ZnCl2,
and HF etc. produces acetoveratrone, (3ꢀ,4ꢀ-dimethoxyacetophenone), which is the intermediate for
synthesis of papavarine alkaloids. The problems associated with these homogeneous catalysts can
be overcome by using heterogeneous solid catalysts. Since acetoveratrone is a larger molecule,
large pore Beta zeolites with smaller particle sizes are beneficial for the liquid-phase acylation of
veratrole, for easy diffusion of reactants and products. The present study aims in the acylation of
veratrole with acetic anhydride using nanocrystalline Beta Zeolite catalyst. A systematic investiga-
tion of the effects of various reaction parameters was done. The catalysts were characterized for
their structural features by using XRD, TEM and DLS analyses. The catalytic activity of nanocrys-
talline Beta zeolite was compared with commercial Beta zeolite for the acylation and was found that
nanocrystalline Beta zeolite possessed superior activity.
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Keywords: Friedel-Craft Acylation, Veratrole, Nanocrystalline Beta Zeolite, Catalyst.
Copyright: American Scientific Publishers
1. INTRODUCTION
and environmentally friendly. In this context, catalysts
based on zeolites are more promising for the acylation of
veratrole.
The Friedel-Crafts acylation of aromatics is one of the
most important reactions for the production of interme-
diates in the pharmaceutical, fragrance, flavor, and agro-
chemical industry.1 Conventionally, the method used to
prepare aromatic ketones is the acylation of aromatics
with activated derivatives of carboxylic acids, such as acid
halides and anhydrides, in presence of soluble Lewis acids
such as AlCl3, FeCl3 or ZnCl2 as catalysts. This method
poses several problems such as toxicity, potential danger
in handling, disposal of spent catalyst and difficulties in
product isolation. In recent years, the need to replace tradi-
tional catalysts with solid catalysts is one of the demands
of the society. Hence, the use of heterogeneous catalysis
has become attractive for the acylation of veratrole.
In recent years, several solid acid catalysts based on
metal triflates,2–4 dodecatungstophosphoric acid supported
on hexagonal mesoporous silica,5 carboxylic acid or trisub-
stituted silyl carboxylates in presence of trifluoromethyl-
benzoic acid anhydride6 and zeolites,7 have been used for
acylation of veratrole. Despite substantial progress, it is
still a challenge to develop a satisfactory solid catalyst
that makes the acylation of veratrole economically feasible
Zeolites are crystalline aluminosilicates that have gained
attention due to their ability to catalyze many organic
reactions.8 Zeolites are promising solid-acid catalysts for
the Friedel–Crafts reactions.9–15 without the drawbacks of
traditional Fredel-Crafts catalysts. The BEA type crys-
talline structure of zeolite Beta attracts much attention
because of the three-dimensional large-pore channel sys-
tem 12-membered ring (MR) with helical channels.16
An important potential benefit of zeolite molecular sieve
is high thermal stability, shape selectivity, regenerability
properties and tunable acidity. Due to its special pore
structure and surface acidity, Beta zeolite was attracted in
the synthesis of fine chemicals.17–24 It has been shown that
the particle size of zeolite used is a critical factor in the
performance of the catalyst. Nanocrystalline zeolite par-
ticles possess large external surface areas thereby expos-
ing the active surface for reaction and shortening of the
diffusion distances in the channels of the particles, thus
reducing deactivation. In addition, nanozeolites possess a
considerably higher mesopore volume compared with ref-
erence microcrystalline samples.25
The major problem of using the bulk zeolite for acyla-
∗Author to whom correspondence should be addressed.
tion is the catalyst deactivation.26 Hence, there has been
J. Nanosci. Nanotechnol. 2016, Vol. 16, No. 4
1533-4880/2016/16/4247/005
doi:10.1166/jnn.2016.11613
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Enhanced Activity of Nanocrystalline Beta Zeolite for Acylation of Veratrole with Acetic Anhydride
Al-Turkustani and Selvin
interest in using nanocrystalline Beta zeolite for acylation
of veratrole, for which it is expected to have less deacti-
vation due to open channels and smaller particle size.
The present study deals with the efficacy of nanocrys-
talline Beta zeolite for the acylation of veratrole with
acetic anhydride. The catalysts were characterized for
their structural features by using DLS, XRD and TEM
analyses.
2. EXPERIMENTAL DETAILS
2.1. Chemicals
Tetraethoxysilane (TEOS), aluminium iso-propoxide
10
20
30
40
50
(AlP), tetraethyllammonium hydroxide (TEAOH, 35%
aq), veratrole, 1,2-dichloroethane and acetic anhydride
were commercial samples from Merck and were used
without further purification. Beta (bulk, commercial) was
purchased from Zeolyst International.
2 Theta (degrees)
Figure 1. Diffraction pattern of the NPs (a) CP0 (b) NC-Beta.
drop of ethanol and dried before placing sample) on car-
bon coated copper grid for TEM examination.
2.2. Synthesis of Nanocrystalline Zeolite Beta
In order to synthesize nanocrystalline zeolite Beta, a
hydrolysed clear sol of TEAOH-AlP-TEOS-H2O was pre-
pared at room temperature. In a typical procedure, 1.30 g
of aluminium iso-propoxide (AlP) was transferred to a
polypropylene (PP) bottle containing 24 g of tetraethylam-
monium hydroxide (TEAOH, 35% aq.). The solution was
stirred on a magnetic stirrer for about 30 min to get a clear
2.4. Catalytic Studies
Acylation of veratrole by acetic anhydride over nanaocrys-
talline Beta zeolite catalysts was carried out in a magnet-
ically stirred glass reactor (capacity 100 cm3ꢃ fitted with
a reflux condenser and a thermometer for measuring the
reaction temperature. The reactor was kept in a constant
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temperature oil bath.
solution. To this 62 g of DI water was added. Then 33 g
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In a typical experiment, the reaction mixture consisted
of 120 mmol veratrole and 12 mmol acetic anhydride.
of tetraethoxysilane (TEOS) was added to the above solu-
Copyright: American Scientific Publishers
tion. The resulting solution was stirred vigorously at 25 ꢁC
for about 2 h to hydrolyze the TEOS. The clear sol was
The total volume of the reaction mixture was made up to
50 ml with 1,2-dichloroethane as a solvent. The freshly
activated catalyst (0.15 g) was added and the flask with
its contents was heated at a constant temperature (100 ꢁC)
in an oil bath for 160 minutes and stirred magnetically.
The progress of the reaction was monitored by withdraw-
ing samples from the reactor and subjecting them to gas
chromatographic analysis (Hewlett-Packard 5890), using
a 10% OV-17 column and a FID detector. The prod-
uct, 3ꢀ,4ꢀ-dimethoxyacetophenone was confirmed by gas
chromatography–mass spectroscopy (GC-MS).
ꢁ
concentrated in a rotary evaporator at 80 C as reported
in the literature.25 The concentrated precursor (CP0) was
aged at 90 ꢁC forꢁ48 hrs (CP48) followed by hydrothermal
treatment at 175 C for ꢁ12 h. The ꢁsamples were calcined
(NC-Beta) in air at 550 C (5 h, 2 C/min).
2.3. Characterization
The size of the nanocrystalline Beta zeolite produced after
hydrothermal reaction was analyzed by a ZetaSizer-3000
dynamic light scattering (DLS) instrument (Malvern, ZS).
Powder X-ray diffraction patterns were recorded on a Shi-
madzu LAB-X-700 diffractometer using Cu–Kꢀ radiation
from 2ꢁ = 1ꢂ5 to 30 at a scan rate of 2ꢁ/min with a step
size of 0.04ꢁ. Morphology of the zeolite nanocrystals was
examined with TEM (JEM-2010, 200 kV). A drop of the
diluted solution (0.003 wt% g/water) was placed (placed a
Table I. Dynamic light scattering (DLS) and zeta potentials
measurements.
Sample
Particle size (nm)
Polyindex
CP(0)
CP48
NC-Beta
4ꢂ5
38ꢂ2
41ꢂ1
0.56
0.24
0.011
Figure 2. TEM micrographs of nanocrystalline Beta zeolite.
J. Nanosci. Nanotechnol. 16, 4247–4251, 2016
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Al-Turkustani and Selvin
Enhanced Activity of Nanocrystalline Beta Zeolite for Acylation of Veratrole with Acetic Anhydride
60
50
40
60
0.05 g
0.10 g
0.15 g
0.20 g
50
40
30
20
10
0
30
20
10
0
0
20
40
60
80
100
120
1:2
1:4
1:5
1:8
1:10
1:12
Time (min)
Mole ratio (Acetic anhydride : Veratrole)
Figure 3. Effect of catalyst weight on the conversion of acetic anhy-
dride for the acylation of veratrole with acetic anhydride.
Figure 4. Effect of acetic anhydride to veratrole mole ratio on the con-
version of acetic anhydride for the acylation of veratrole with acetic
anhydride.
3. RESULTS AND DISCUSSION
3.4. Catalytic Activity Studies
3.1. Dynamic Light Scattering (DLS) Measurements
The concentrated precursor sol (CP0), 48 hh aged precur-
sor sol (CP48) and hydrothermally treated CP48 sol (NC-
Beta), were evaluated by DLS analysis after seven folds
dilution. The results shown in Table I represents that the
particle size increases with the ageing period and the appli-
cation of hydrothermal treatment, due to the aggregation
of primary units.25
Acylation of veratrole with acetic anhydride was car-
ried out over the nanocrystalline Beta catalyst. In the
first step the influence of time-on-stream (TOS) on the
conversion was studied using the catalyst nanocrystalline
Beta zeolite catalyst. It was found that the conversion
first increases with increasing TOS but remains practi-
cally constant after 160 min (Fig. 3). Hence all further
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experiments were carried out for 160 min. The reac-
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tion parameters such as, reaction temperature; veratrole/
acetic anhydride molar ratio and catalyst quantity were
optimized. Under the optimized reaction condition, the
catalytic activity of nanocrystalline Beta zeolite and
commercial bulk Bera zeolite were compared. The
product, 3ꢀ,4ꢀ-dimethoxyacetophenone was confirmed by
gas chromatography–mass spectroscopy. Ethylene chloride
was used as a solvent in all experiments. The reaction
scheme is represented as follows (Scheme 1).
Copyright: American Scientific Publishers
3.2. XRD of Hydrothermally Treated Aged NPs
The XRD patterns of the hydrothermally treated aged con-
centrated NPs is shown in Figure 1. The hydrothermally
treated aged nanoprecursors showed that the diffraction
reflections and the interplanar spacings calculated from the
XRD patterns are comparable and well matched with the
reported values for zeolite Beta. Compared to the standard
diffraction patterns of micrometer-sized zeolite Beta, the
diffraction peaks of nanocrystal samples are broadened.
3.3. TEM Analysis
50 ºC
60
50
40
30
20
10
0
75 ºC
The TEM micrographs of the nanocrystalline Beta zeolite
sample is presented in Figure 2. The size of the crystal
is about 40 nm nanocrystals are made up of sub-nanosize
crystals.
100 ºC
125 ºC
OMe
OMe
OMe
(CH3CO)2O
OMe
CH3COOH
0
20
40
60
80
100
120
Time (min)
COCH3
Figure 5. Effect of temperature on the conversion of acetic anhydride
Scheme 1. Acylation of veratrole with acetic anhydride.
J. Nanosci. Nanotechnol. 16, 4247–4251, 2016
for the acylation of veratrole with acetic anhydride.
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Enhanced Activity of Nanocrystalline Beta Zeolite for Acylation of Veratrole with Acetic Anhydride
Al-Turkustani and Selvin
Table III. Influence of ZSM-5 particle size on acylation of anisole with
acetic anhydride.
100
80
60
40
20
0
S. no.
Catalyst
Ac2O conversion (%)
1
2
Beta zeolite (nano)
Beta zeolite (bulk)
85
66ꢂ6
Notes: (Reaction Condition: TOS, 160 min.; Catalyst: 0.15 g; Mole ratio of
AC2O:Veratrole-1:10-; Reaction temperature: 100 ꢁC).
3.5. Reusability of Catalyst
The catalyst reusability was studied three times, including
the use of fresh catalyst. The used catalyst was centrifuged,
ꢁ
washed with CH2Cl2 and subsequently dried at 120 C
0
20 40 60 80 100 120 140 160 180 200
Time-on-stream
for 6 hrs before being reused in subsequent batches. It
was found that there was no appreciable change in the
conversion of the catalytic activity up to three runs. Thus it
is concluded that the catalyst is stable, hence, the catalyst
was reusable (Table II).
Figure 6. Time-on-stream versus conversion of acetic anhydride for the
acylation of veratrole with acetic anhydride.
3.6. Comparison of Nano and Bulk Beta Zeolite
3.4.1. Effect of Catalyst Weight
Table III compares the performance nano and bulk Beta
zeolite catalysts having different particle sizes in the con-
version of acetic anhydride for acylation of veratrole. The
purpose of using these catalysts was to study the effect
of particle size of zeolites for acylation of veratrole. The
experiments were carried out under identical set of condi-
tions. It was found that nanocrstalline Beta showed higher
The effect of catalyst weight was studied over a range of
0.05–0.2 g (Fig. 4). The conversion of acetic anhydride
was found to increase with increase in catalyst weight and
the increase becomes less significant beyond 0.15 g. The
increase in conversion is due to the increase in active sites
for the reaction during the increase in catalyst loading
and more active sites are available for the reaction when
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conversions compared to bulk Beta catalysts (Table III).
increasing catalyst loading. In further experiments the cat-
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The catalyst after reaction turned into brown in the case of
nanocrystalline Beta catalyst and chnaged into black while
using bulk Beta catalyst. This indicated that nanocrstalline
Beta zeolite catalyst is not deactivated much during the
reaction due to the smaller particle size and shorter diffu-
sion channels. The higher activity of nanocrystalline Beta
catalyst is probably due to the increased external surface of
smaller crystal and shorter diffusion length which makes
the easy diffusion of .the larger acylated product 3ꢀ,4ꢀ-
dimethoxyacetophenone.
Copyright: American Scientific Publishers
alyst loading of 0.15 g was used.
3.4.2. Effect of Mole Ratio
The effect of acetic anhydride to veratrole mole ratio was
studied at 1:2 to 1:12 under otherwise similar reaction con-
ditions (Fig. 5). The conversion of acetic anhydride was
found to increase with an increase in concentration of vera-
trole up to 10 and thereafter remained constant. Therefore,
all reactions were studied by using a acetic anhydride: ver-
atrole mole ratio of 1:10.
4. CONCLUSION
3.4.3. Effect of Temperature
The present study indicates that the acylation of veratrole
with acetic anhydride over nanocrystalline Beta zeolite is
advantages over the AlCl3-promoted acylation of veratrole.
The catalysts were characterized for their structural fea-
tures by using XRD, SEM and DLS analyses. High conver-
sion in the acylation of veratrole with acetic anhydride was
achieved under mild conditions using nanocrytalline Beta
zeolite catalys. The decrease in particle size of nanopar-
ticles of Beta zeolite enhances the density of acidic sites
and surface area, which are essential factors to increase the
activity of the acylation reaction. The catalytic activity of
nanocrystalline Beta zeolite was compared with commer-
cial bulk Beta zeolite and the nanocrystalline beta zeolite
possessed superior performance for the acylation of verat-
role due smaller particle size.
The effect of temperature on conversion acetic anhydride
under otherwise similar reaction conditions was studied
over a range of 50–125 C (Fig. 6). The conversion was
ꢁ
found to increase substantially on increasing the tempera-
ꢁ
ture upto 100 C.
Table II. Effect of reusability of the catalyst.
Conversion of cyclohexanone oxime (%)
Catalyst
NC-Beta
Fresh use
85
First reuse
83.7
Second reuse
83
Notes: (Reaction Condition: TOS, 160 min.; Catalyst: 0.15 g of NC-Beta; Mole
ratio of AC2O:Veratrole-1:10-; Reaction temperature: 100 ꢁC).
4250
J. Nanosci. Nanotechnol. 16, 4247–4251, 2016

Al-Turkustani and Selvin
Enhanced Activity of Nanocrystalline Beta Zeolite for Acylation of Veratrole with Acetic Anhydride
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Received: 16 March 2015. Accepted: 21 April 2015.
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J. Nanosci. Nanotechnol. 16, 4247–4251, 2016
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