Reaction Profiles of High Silica MOR Zeolite Catalyzed Friedel–Crafts Acylation of Anisole Using Acetic Anhydride in Acetic Acid

Article abstract of DOI:10.1007/s10562-018-2530-1

Friedel–Crafts reaction of anisole over high silica mordenite zeolite was investigated. Detailed reaction profiles were obtained using various reaction conditions. In particular, the behavior of acetic anhydride during the reaction and the effect on the h

Full text of DOI:10.1007/s10562-018-2530-1

Catalysis Letters
https://doi.org/10.1007/s10562-018-2530-1
Reaction Profiles of High Silica MOR Zeolite Catalyzed Friedel–Crafts
Acylation of Anisole Using Acetic Anhydride in Acetic Acid
Makoto Makihara1 · Hisakazu Aoki2 · Kenichi Komura1,2
Received: 21 May 2018 / Accepted: 20 August 2018
© Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
Friedel–Crafts reaction of anisole over high silica mordenite zeolite was investigated. Detailed reaction profiles were obtained
using various reaction conditions. In particular, the behavior of acetic anhydride during the reaction and the effect on the
hydrophilicity of the mordenite zeolite catalyst were investigated.
Graphical Abstract
Keywords Friedel–Crafts acylation · Anisole · Mordenite zeolite
1 Introduction
pigments, and engineering plastics [1]. Friedel–Crafts acety-
lation is generally performed using activated acid or acetic
anhydride as acetylating agents in the presence of a stoichio-
metric amount of Lewis acid catalysts, such as AlCl3 and
BF3, in toxic solvents such as dichloroethane and nitroben-
zene. Therefore, this reaction has critical drawbacks, in that
large amounts of waste are produced during the work-up
steps, especially in the neutralization of the activated acid
and the catalyst.
Friedel–Crafts acylation is one of the pivotal synthetic tools
to introduce acetyl moieties into aromatic compounds, and
almost all such products are widely used as key interme-
diates such as medicines, cosmetics, flavors and perfumes,
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-018-2530-1) contains
supplementary material, which is available to authorized users.
Since understanding the essential functions of zeolite such
as the solid acid properties over 30 years ago, many devel-
opments over the zeolite catalyzed Friedel–Crafts acylation
of anisole (AN) to selectively produce 4-methoxyacetophe-
none (4-MA) have been reported (Scheme 1), and these are
well summarized in reviews and books [1–4]. In particular,
the use of BEA zeolites (*BEA-type) and modified ZSM-5
zeolites (MFI-type) has attracted much attention because
of their three-dimensional pore systems [5]. For recent
* Kenichi Komura
kkomura@gifu-u.ac.jp
1
Department of Materials Science and Technology,
Faculty of Engineering, Gifu University, Yanagido 1-1,
Gifu 501-1193, Japan
2
Graduated School of Materials Science and Possessing
Division, Faculty of Engineering, Gifu University, Yanagido
1-1, Gifu 501-1193, Japan
Vol.:(0123456789)
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M. Makihara et al.
Scheme 1 Friedel-Crafts acyla-
MeO
O
MeO
MeO
tion of anisole
Zeolite
Ac O
∆
,
2
+
AcOH,
anisole
(AN)
O
4-methoxyacetophenone 2-methoxyacetophenone
(4-MA) (2-MA)
examples within the last decade, attempts have been made
to use modified BEA zeolites for fixed-bed continuous flow
reactions [6, 7], microwave irradiation [8] and for metal dop-
ing of the zeolite [9]. Wu et al. recently reported a reaction
using hierarchical nanosized BEA zeolite, which resulted
in 66% conversion of AN and > 99% selectivity of 4-MA
[10]. In 2008, Selvin et al. pointed out that nano-scale range
ZSM-5 zeolite exhibited excellent catalytic activity due to
enhancement of its surface area [11]. Serrano et al. reported
a ZSM-5 zeolitic mesostructured hybrid catalyst [12] and
a hierarchical ZSM-5 zeolite in nitrobenzene solvent [13].
Selvin and co-workers also reported efficient acylation using
the hierarchical ZSM-5 zeolite with 65% conversion of AN
and 99.5% selectivity of 4-MA [14]. Ryoo and co-workers
recently reported the same reaction using a ZSM-5 zeolitic
nanosponge catalyst, where ca. 80% conversion of AN and
98% selectivity of 4-MA was achieved for 20 h in nitroben-
zene solvent [15]. The interest in this reaction has triggered
the use of unique zeolite catalysts such as MWW zeolite
or its precursors, MCM-22 and MCM-49. Tatsumi and co-
workers [16] reported the reaction using Al-MWW (MWW-
type) zeolite, and Tatsumi and co-workers also applied an
interlayer-expanded zeolite Al-MWW (IEZ–MWW) [17].
Further Xu and co-workers recently attempted fixed-bed
continuous flow systems using modified MCM-49 zeolites
and claimed that the reaction proceeds at external pockets
[18, 19], and Nunes and co-workers reported a kinetic study
of this reaction over hierarchical MWW zeolite [20]. As
other approaches, Wu and co-workers reported the alumi-
nosilicate IEZ-PLS-3, designated as ECNU-8, where PLS-3
is a layered zeolitic material possessing FER sheets [21],
which resulted in the moderate conversion of AN [22, 23].
The use of an aluminophosphate molecular sieve containing
Sn(II) with AIF-type topology, denoted as Sn(II)AlPO4-5,
reported by Sànchez et al. [24]. The Friedel–Crafts acyla-
tion of AN has been used as an index for the elucidation
of zeolite properties, particularly of their Brønsted acidity;
therefore, almost all recent reports have been focused on new
materials, their preparation strategies and modification. The
use of mordenite (MOR) zeolite has been reported by Tomar
and co-workers however, the reaction was performed using
propionic anhydride as an acylating agent [25]. The straight
one-dimensional 12-ring pore channels of MOR zeolite
mean that the diffusion of participating molecules into the
zeolite is more restricted than that of BEA and ZSM-5 zeo-
lites, which are three-dimensional pore systems. Therefore,
investigations on Friedel–Crafts acylation over MOR-type
zeolites have been limited. Recently, our group has reported
on high-silica MOR zeolite catalyzed Friedel–Crafts acyla-
tion of 2-methoxynaphthalene using acetic anhydride in
acetic acid to afford 2-methoxy-6-acetylnaphthalene with
excellent conversion and shape-selectivity [26]. This reac-
tion system can also be successfully applied to anisole (AN),
which revealed that high silica MOR zeolite with SiO2/
Al2O3 =110, designated as MOR(110), showed the highest
conversion of AN and perfect selectivity of 4-MA (>99.9%)
within 2 h. The MOR zeolite catalyst was also reusable at
least 30 times without loss of conversion of AN and selectiv-
ity of 4-MA, and no leaching of Al after reuse of zeolite was
observed, even in the acidic reaction medium [27].
Here we report the reaction profiles of the Friedel–Crafts
acylation of anisole over a high silica MOR zeolite catalyst
using acetic anhydride in an acetic acid medium. In particu-
lar, the effects of the Ac2O/AN ratio on the catalysis and
hydrophilicity of the MOR zeolite catalyst were investigated
to understand the detailed reaction system and catalysis.
2 Experimental
2.1 Characterization and Materials
Powder X-ray diffraction (XRD; Shimadzu XRD-6000) was
measured using Cu Kα radiation (λ=1.5418 Å). Elemental
analyses were performed using X-ray fluorescence spectros-
copy (XRF; Bruker S8 TIGER). Nitrogen adsorption and
desorption isotherm measurements were performed using
an absorption analyzer (Bel Japan Belsorp 28SA). Acid
properties were determined using ammonia temperature-
programmed desorption (NH3-TPD; Bel Japan TPD-66).
Solid-state 29Si magic angle spinning (MAS) nuclear mag-
netic resonance (NMR) and 27Al MAS NMR spectra were
recorded at ambient temperature using a 4 mm diameter
zirconia rotor with a spinning rate of 6 kHz (JEOL ECA-
500 NMR spectrometer). The SiO2/Al2O3 ratio of 110, des-
ignated as MOR(110), is almost the limit of measurement;
therefore, NH3 was adsorbed on MOR(110) using aque-
ous ammonia to enhance the intensity. Thermogravimetric
1 3

Reaction Profiles of High Silica MOR Zeolite Catalyzed Friedel–Crafts Acylation of Anisole…
(TGA) and differential thermal analysis (DTA) were con-
ducted using an apparatus (Shimadzu DTG-50) with the
ramp rate at 10 °C/min under an air stream. The crystallite
size and morphology were measured using field emission
scanning electron microscopy (FE-SEM; Hitachi High-
Technologies Co. S-4800). Products were analyzed using gas
chromatography (GC; Shimadzu GC-18) with a flame ioni-
zation detector (FID) and an Agilent Technologies Ultra-1
capillary column. MOR-type zeolites were received from
Tosoh Corp. and used after calcination at 500 °C for 5 h
under air flow. Organic reagents such as anisole, acetic anhy-
dride and acetic acid were purchased from Tokyo Chemical
Industry, Co., Ltd. and were used as-received without further
purification.
high silica zeolite does not have sufficient Brønsted acid sites
than in often used conventional zeolite catalysts [4]. Figure 1
shows the reaction profiles over the commercial MOR(110)
zeolite at different reaction temperatures. Decreasing the
reaction temperature caused a decline in the catalytic activ-
ity. At 170 °C, a slight decrease in catalytic activity was
observed, and the best catalytic performance was at 150 °C.
This is because the boiling point of Ac2O is 140 °C, and thus
vigorous reflux conditions would inhibit interaction between
the MOR zeolite and Ac2O. The quantities of Al in the MOR
catalysts before and after the reaction did not change, which
indicates that the reaction system does not damage the MOR
zeolite catalyst, and the selectivity of 4-MA was >99.5% in
every case, which is attributed to the shape-selective char-
acteristics of the MOR zeolite catalyst with its straight pore
channels. Further the reaction never occur in the absence of
zeolite catalyst at 150 °C [27]. The activation energy (Ea)
was estimated from the initial slopes of Fig. 1, except for the
value at 170 °C, and it was 1.5 kcal/mol, which is very low
when compared with the 11 kcal/mol reported by Derouane
et al. under neat conditions over the BEA zeolite catalyst
[29]. These results infer that the role of the solvent (AcOH)
is also critical to decrease the activation energy in this reac-
tion system.
2.2 Preparation of Dealuminated Mordenite
Dealuminated MOR-type zeolite with SiO2/Al2O3 =110 was
prepared according to a previously reported procedure [28].
Commercially available MOR(25) was added to 8 M HCl
solution and stirred for 3 h at 80 °C. The resulting prod-
uct was washed with distilled water thoroughly and dried
at 90 °C for 12 h. The SiO2/Al2O3 ratio was estimated from
XRF measurements.
2.3 Reaction
3.2 Effect of Ac2O/AN Ratio
A typical reaction procedure involved dissolving a pre-
scribed amount of anisole (1.0 mmol), an acetylating agent
(acetic anhydride, 10 mmol) and the zeolite catalyst (0.50 g)
in AcOH (5 mL), and then stirring the mixture at 150 °C.
The product yield and selectivity of the isomers were esti-
mated by GC and compared with authentic samples. It
should be noted that under these conditions, no formation
of Ac2O from the AcOH solvent occurred.
Reaction profiles were obtained by varying the Ac2O/AN
ratios over commercially available MOR(110), and the
results are given in Fig. 2. As the Ac2O/AN ratio increased,
100
80
3 Results and Discussion
60
To understand the zeolite-catalyzed Friedel–Crafts acyla-
tion of AN in AcOH, the fundamental reactions and condi-
tions were investigated. The reaction rate is dependent on
the amount of MOR zeolite catalyst, which indicates that an
increased amount of catalyst increases the reaction rate (see
Supporting Information).
40
R
ꢀꢁꢂꢄꢃꢁ &
R
20
ꢀꢁꢂꢅꢃꢁ &
R
ꢀꢁꢂꢆꢃꢁ &
R
ꢀꢁꢂꢂꢃꢁ &
3.1 Effect of Reaction Temperature
0
0
2
4
6
In the most of the reported Friedel–Crafts acylation reac-
tions over zeolite catalysts, the reactions are typically per-
formed at around 80 °C. However, the reaction system we
have developed requires higher temperature and is typically
promoted at 150 °C over the MOR(110) zeolite because a
Time (h)
Fig. 1 Reaction profiles at different reaction temperature. Reaction
conditions: MOR(110) (0.5 g), anisole (1.0 mmol), Ac2O (7.0 mmol)
and AcOH (5 mL)
1 3

M. Makihara et al.
and 4.0. The excess amount of Ac2O was almost instantly
consumed by the zeolite catalyst (Ac2O/AN ratio from 10 to
around 1.0, Fig. 3, filled circles). When there was a sufficient
amount of Ac2O in the reaction medium, the conversion of
AN was increased and 4-MA was produced with >99.5%
selectivity due to the shape-selective manner of the zeolite
catalyst (Fig. 3, open circles), whereas Ac2O was fully con-
sumed (Fig. 3, filled squares), no increase of conversion was
observed from 2 h with a ratio of Ac2O/AN = 4.0 (Fig. 3,
open squares). These results indicate that the conversion of
AN is compatible with the amount of Ac2O in the reaction
solution, and it is also considerable that non-polar Ac2O
can be rapidly adsorbed into the high silica zeolite catalyst
for activation.
100
80
60
40
20
0
3.3 Effect of Hydrophilicity of MOR Catalyst
0
2
4
6
Time (h)
One of the factors for the success of this system is the
hydrophobicity of the MOR zeolite catalyst. The developed
Friedel–Crafts acylation system is sufficiently promoted
by high silica MOR zeolite catalyst; however, the catalytic
activity and shape-selectivity in the Friedel–Crafts acyla-
tion of 2-methoxynaphthalene were severely affected by
the SiO2/Al2O3 ratio, where the use of a low silica MOR
zeolite with hydrophilic property declined the catalytic per-
formance [26]. The purpose here is to elucidate the effect of
the hydrophilicity of the MOR zeolite; therefore, dealumi-
nated MOR zeolite with SiO2/Al2O3 =110 [deMOR(110)]
was prepared from a commercially available MOR (SiO2/
Al2O3 =25) zeolite by intentionally introducing nest silanol
into the zeolite framework, which has more hydrophilic
property due to formation of Si–OH moieties. The charac-
terization results are given in the Supporting Information.
FE-SEM revealed that deMOR(110) had a slightly aggre-
gated morphology with small rugby-ball-like grains, and
29Si MAS NMR spectra showed an ca. 10% increase in the
amount of Q3 silicon (SiOH) in deMOR(110) compared
with commercially available MOR(110), which indicates the
formation of nest silanol in the zeolite. NH3-TPD profiles
of the MOR(110) and deMOR(110) zeolites are shown in
Fig. 4. In the profile for the commercial MOR(110) zeo-
lite, a l-peak corresponding to physically adsorbed NH3
was detected at around 150 °C, and a h-peak was detected
at around 400 °C, which corresponds to chemisorbed NH3
(Fig. 4a). The NH3-TPD profile for deMOR(110) showed the
two distinct l- and h-peaks at 180 °C and 400 °C, respec-
tively (Fig. 4b). The desorption peak of NH3 in the middle
range temperature was observed for deMOR(110) zeolite,
which is attributed to weak acid–base interaction of NH3
molecules at nest silanol groups, and also reflects the amount
of acid, as given in Table 1. Other estimated parameters
such as the Brunauer–Emmett–Teller (BET) surface area
and pore volume were similar for these samples. In the
Fig. 2 Reaction profiles with different Ac2O/AN ratios (open circles:
10, filled circles: 7, filled squares: 4, filled triangles: 1). Reaction con-
ditions: MOR(110) (0.5 g), anisole (1.0 mmol) and AcOH (5 mL)
100
80
60
40
20
0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0
0
2
4
6
Time (h)
Fig. 3 Reaction profiles and Ac2O/AN ratio during reactions. Conver-
sion of AN (Ac2O/AN; open circles: 10, open squares: 4). Ac2O/AN
ratios (filled circles; 10, filled squares; 4)
the conversion of AN was increased, and a satisfactory ratio
was determined to be over 7.0. However, the reaction did
not proceed at a ratio of Ac2O/AN=1.0, which implies that
not only the consumption and/or activation of Ac2O into
the zeolite should be significantly fast, but also the reac-
tion is severely affected by the amount of Ac2O. Therefore,
the reaction was conducted with respect to the behavior of
Ac2O during the reaction. Figure 3 shows the profiles of AN
conversion and Ac2O/AN ratios for Ac2O/AN ratios at 10
1 3

Reaction Profiles of High Silica MOR Zeolite Catalyzed Friedel–Crafts Acylation of Anisole…
100
(B)
80
60
(A)
40
20
0
0
1
2
3
Time (h)
0
200
400
600
Fig. 5 Reaction profiles over MOR(110) (open circles) and
deMOR(110) (open squares) zeolites. Reaction conditions: zeolite
(0.5 g), anisole (1.0 mmol), Ac2O (7.0 mmol) and AcOH (5 mL)
temperature (oC)
Fig. 4 NH3-TPD profiles of MOR(110) (a) and deMOR(110) (b)
with a 10% enhanced quantity of Q3 silicon, the reaction
was severely affected by the hydrophilic environment of
the zeolite catalyst.
Table 1 Textural parameters of MOR(110) and deMOR(110)
Zeolite
BET surface
areaa (m2 g−1
Pore volumea
Acid
)
(mL g−1
)
amountb
(mmol g−1
)
MOR(110)
deMOR(110)
579
566
0.35
0.32
0.233
0.302
4 Conclusion
aEstimated by nitrogen isotherm
bEstimated by NH3-TPD analysis
The high silica MOR zeolite catalyzed Friedel–Crafts acyla-
tion of anisole was investigated under various conditions.
This reaction system required an appropriate temperature
and amount of acetic anhydride. In particular, during the
reaction, acetic anhydride was almost instantly consumed
over the hydrophobic MOR zeolite, in which the adsorption
of participating molecules would compete in a polar solvent.
Reaction over a hydrophilic zeolite, dealuminated MOR zeo-
lite, decreased the reaction rate. High silica MOR zeolite is
known to have hydrophobic property, i.e. the amount of cata-
lytic active sites (Brønsted acid sites) is insufficient. There-
fore, this reaction requires high temperature for sufficient
promotion; however, the reason why a large amount of acetic
anhydride is required has yet to be clarified. Further research
with this reaction system is ongoing in our laboratory.
deMOR(110) zeolite, N2 isotherms using Horvath–Kawazoe
(HK) and Barrett–Joyner–Halenda (BJH) analyses indicated
no meso- and macroporous pores (data not shown), which is
reasonable for MOR-type zeolite with 12-ring straight pore
channels.
Figure 5 shows reaction profiles for the Friedel–Crafts
acylation of AN over commercially available MOR(110)
and deMOR(110) catalysts. The commercially available
MOR(110) exhibited excellent catalytic performance, i.e.
the reaction was completely finished within 2 h. In con-
trast, the deMOR(110) zeolite with nest silanol groups
showed only moderate catalytic activity. This result indi-
cates that the hydrophilic zeolite catalyst is not prefer-
able for the developed reaction system. The reason for
this can be considered to be that the participating mol-
ecules such as Ac2O and AN are hydrophobic and could
not easily enter into the MOR zeolite in a highly polar
solvent AcOH. Therefore, the catalytic activity declined
over the deMOR zeolite. These results suggest that even
Acknowledgements This work was partially supported JSPS KAK-
ENHI Grant Number 15K05586, 18K05200 and the OGAWA Science
and Technology Foundation.
Compliance with Ethical Standards
Conflict of interest The authors declare no competing financial inter-
est.
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M. Makihara et al.
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