Green synthesis of 4-methoxybenzophenone from anisole and benzoic acid catalyzed by tungstophosphoric acid supported on MCM-41

Article abstract of DOI:10.1007/s11164-014-1772-9

Abstract An efficient method was established for the green synthesis of 4-methoxybenzophenone using benzoic acid as acylating agent catalyzed by tungstophosphoric acid (HPW) supported on MCM-41 (HPW/MCM-41). The conversion of benzoic acid reached 97.2 % and the selectivity for 4-methoxybenzophenone was 87.4 % under the optimum conditions over a 50 wt.% HPW/MCM-41 catalyst. HPW is proven to be well deposited on MCM-41, which leads to dealumination of MCM-41 and then offers more active centers, as demonstrated by inductively coupled plasma analysis and NH₃ temperature-programmed desorption, accounting for the high catalytic activity of HPW/MCM-41.

Full text of DOI:10.1007/s11164-014-1772-9

Res Chem Intermed
DOI 10.1007/s11164-014-1772-9
Green synthesis of 4-methoxybenzophenone
from anisole and benzoic acid catalyzed
by tungstophosphoric acid supported on MCM-41
Huanhuan Zhang
•
•
Jie Han
Chunzheng Wang
•
Fei Tian
•
•
Qingzhi Chen
Guoyi Bai
Hui Jin
•
Received: 18 April 2014 / Accepted: 23 July 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract An efficient method was established for the green synthesis of
-methoxybenzophenone using benzoic acid as acylating agent catalyzed by tung-
4
stophosphoric acid (HPW) supported on MCM-41 (HPW/MCM-41). The conver-
sion of benzoic acid reached 97.2 % and the selectivity for 4-methoxybenzophenone
was 87.4 % under the optimum conditions over a 50 wt.% HPW/MCM-41 catalyst.
HPW is proven to be well deposited on MCM-41, which leads to dealumination of
MCM-41 and then offers more active centers, as demonstrated by inductively
coupled plasma analysis and NH temperature-programmed desorption, accounting
3
for the high catalytic activity of HPW/MCM-41.
Keywords 4-Methoxybenzophenone Á Green synthesis Á Tungstophosphoric acid Á
MCM-41 Á Benzoic acid Á Dealumination
Introduction
Benzophenone and its derivatives are important fine chemical intermediates, and
widely used in the synthesis of UV-absorbers, dyes, drugs, fragrances and
insecticides [1–4]. For example, 4, 4-dihydroxybenzophenone is frequently used
as a UV-absorber in sunscreen cream [1]. Benzophenone and its derivatives are
usually prepared by the following three methods: Suzuki reaction [5], oxidization of
H. Zhang Á J. Han Á F. Tian Á Q. Chen Á C. Wang Á H. Jin Á G. Bai (&)
Key Laboratory of Chemical Biology of Hebei Province, College of Chemistry and Environmental
Science, Hebei University, No.180 Wusi East Road, Baoding 071002, Hebei, People’s Republic of
China
e-mail: baiguoyi@hotmail.com
Q. Chen
Hebei Geological Laboratory, Baoding 071051, Hebei, People’s Republic of China
123

H. Zhang et al.
benzhydrol [6], and Friedel–Crafts acylation [7], which is regarded as the most
important one.
Friedel–Crafts acylation is generally performed using acid anhydrides or acid
chlorides [8, 9] as the acylating agents and catalyzed by Lewis acids, such as AlCl3,
ZnCl , BF , or Br o¨ nsted acids, typically H SO or HF [10–13]. However, the
2
3
2
4
equimolar amounts of hydrogen halides or carboxylic acids concomitantly formed
from acid chlorides or acid anhydrides not only pollute the environment but also
markedly reduce the atom utilization. Meanwhile, the above catalysts also suffer
from severe environmental pollution hazards, and the catalyst amounts employed
are sometimes much more than the stoichiometric amount required, as the catalysts
have a tendency for complex formation with reactants or products. As is well
known, green chemistry has attracted special attention in recent years due to the
urgent demand of environmental protection. It aims to avoid or eliminate using
poisonous and harmful reagents in the chemical reactions so as to protect the
environment. Thus, there has been great demand to develop a novel method using
both green acylating agents and catalysts in Friedel–Crafts acylation.
Carboxylic acids are regarded as green acylating agents in the Friedel–Crafts
acylation because water is the only byproduct derived from carboxylic acid after the
reaction [14–16]. However, considering the low activity of carboxylic acids, it is
desirable to develop an efficient catalyst for this kind of Friedel–Crafts acylation.
Recently, solid acid catalysts, such as clays, zeolites, mesoporous molecular sieves,
and Nafion-H [17–21], have attracted much attention due to their eco-friendly
properties. Among them, mesoporous molecular sieves, especially MCM-41,
provide an attractive possibility for the development of highly active solid acid
catalysts due to their large surface area, large pore size and high thermal stability
[
18]; whereas lack of acidic sites restricts its wide application. On the other hand,
heteropoly acids (HPAs), including tungstophosphoric acid (HPW), phosphomo-
lybdic acid (HPMo) and silicotungstic acid (HSiW), are regarded as eco-friendly
catalysts due to their nontoxic and non-corrosive properties and have been widely
applied in a variety of reactions. However, high solubility in polar solvents, low
thermal stability and small surface area limit their practical applications;
fortunately, the application of suitable supports can overcome these drawbacks [20].
In continuation of our previous work [22], we herein report our recent research on
the green synthesis of benzophenone and its derivates over solid acid catalysts with the
synthesis of 4-methoxybenzophenone from anisole and benzoic acid being chosen as a
model reaction. A tungstophosphoric acid supported on MCM-41 (HPW/MCM-41)
showed good catalytic performance in this reaction. The catalytic behaviors of the
catalysts were correlated with their structures based on necessary characterizations.
Experimental
Catalyst preparation
Unless otherwise stated, all chemicals were purchased from Baoding Huaxin
Reagent and Apparatus, and were used without further purification. The zeolites
1
23

Green synthesis of 4-methoxybenzophenone
were first calcined at 500 °C for 4 h before usage. HPW/MCM-41 was prepared by
adding 0.4 g calcined MCM-41 to 5 mL of an aqueous solution of 0.08 g/mL HPW,
and then the resulting suspension was stirred vigorously at 80 °C for 1 h and
subsequently at room temperature for 24 h. After that, the sample was filtrated,
dried at 120 °C, and then calcined at 250 °C for 4 h. Moreover, HPW/Hb and HPW/
HY were prepared by the same method but using Hb (Si/Al = 25) and HY (Si/
Al = 8) zeolite, respectively, instead of MCM-41.
Catalyst characterization
X-ray diffraction (XRD) patterns were tested on a Bruker D8 advance diffractom-
eter with Cu Ka radiation. Brunauer–Emmett–Teller (BET) surface area and total
pore volume were measured on a Micromeritics Tristar II 3020 surface area and
pore analyzer. Bulk compositions were confirmed by inductively coupled plasma
analysis (ICP) on a Thermo Vista-MPX spectrometer. NH3 temperature-pro-
grammed desorption (NH -TPD) experiments were carried out on a TP-5000
3
instrument with a thermal conductivity detector.
Catalyst activity test
Synthesis of 4-methoxybenzophenone from anisole and benzoic acid, as shown in
Scheme 1, was carried out in a 50-mL three-necked flask equipped with a condenser.
In a typical run, benzoic acid (0.30 g, 2.5 mmol), anisole (2.16 g, 20 mmol), and
catalyst (0.1 g) were charged into the flask and stirred at 155 °C for 6 h. Reaction
mixtures were analyzed by gas chromatography using a 30-m SE-30 capillary column,
and the identities of the products were confirmed by GC–MS (Agilent 5975C).
Results and discussion
Catalysts selection and optimization
It is well known that benzoic acid is not active enough as an acylating agent in the
Friedel–Crafts acylation. Thus, it is crucial to select an active catalyst for this
transformation [23]. A series of commercial solid acid catalysts were first tested
(
Table 1, entries 1–4). As can be seen, these catalysts showed different catalytic
performance. The defective structure of Hb zeolite generates mesoporous, which
makes it more active with higher benzoic acid conversion (80.4 %) than HY zeolite
(
4.5 %), but the selectivity for 4-methoxybenzophenone was poor (30.8 %) over Hb
zeolite. In contrast, the highest selectivity for 4-methoxybenzophenone (86.0 %)
was obtained over MCM-41, together with poor benzoic acid conversion (7.8 %). It
is clear that HPW was the most efficient catalyst among them, with 98.1 %
conversion of benzoic acid and 71.9 % selectivity for 4-methoxybenzophenone, but
still lower than our expectation. Considering the difficulty in recycling due to the
high solubility of HPW, a series of supported HPW catalysts were prepared and
tested in this reaction (Table 1, entries 5–8). It was found that all the supported
123

H. Zhang et al.
O
OH
OCH3
O
Catalysts
+
OCH3
Scheme 1 Synthesis of 4-methoxybenzophenone from anisole and benzoic acid
Table 1 Results of different catalysts for Friedel–Crafts acylation of anisole with benzoic acid
Catalyst
Conversion of
benzoic acid (%)
Selectivity (%)
-Methoxybenzophenone
4
Phenyl benzoate
Hb
80.4
4.5
30.8
76.3
86.0
71.9
88.3
66.5
91.9
80.5
31.5
6.6
HY
MCM-41
HPW
7.8
1.0
98.1
91.6
57.8
6.7
10.3
3.2
HPW/MCM-41
HPW/Hb
HPW/HY
17.5
3.5
HPW/SiO
2
93.4
9.1
Catalysts preparation conditions: calcination temperature 300 °C, HPW loading amount 50 wt.%
Reaction conditions: benzoic acid-to-anisole molar ratio: 1:8, reaction time: 6 h, catalyst amount: 0.1 g,
reaction temperature: 155 °C
catalysts showed better selectivity for 4-methoxybenzophenone than the supports,
and the conversion of benzoic acid was over 90.0 % catalyzed by HPW/MCM-41
and HPW/SiO . HPW/MCM-41 showed the best catalytic performance among these
2
supported catalysts, with 91.6 % conversion of benzoic acid and 88.3 % selectivity
for 4-methoxybenzophenone, even better than the pure HPW. Thus, there should be
some synergistic effect between HPW and MCM-41 [20], probably due to the
proper acidic properties of HPW and the mesoporous structure of MCM-41 [24, 25].
Finally, HPW/MCM-41 was chosen as the catalyst for further investigation.
The loading amount of the active species and the calcination temperature are
believed as two important factors on the catalytic performance of the supported
catalysts [26]. Thus, the effect of the HPW loading amount was first studied
(
Table 2). It was found that the conversion of benzoic acid increased from 80.7 to
3.1 % with the increase of the HPW loading amount from 30 to 60 wt.%, whereas
the selectivity for 4-methoxybenzophenone simultaneously decreased from 90.0 to
9.4 %. Considering that HPW benefits the efficient conversion of benzoic acid, but
9
7
reduces the selectivity for 4-methoxybenzophenone (Table 1), it is reasonable that
the selectivity for 4-methoxybenzophenone decreased with the increase of HPW
loading amount and benzoic acid conversion. The best yield of 4-methoxybenz-
ophenone was obtained while the HPW loading amount was 50 wt.% and it was
then selected as the appropriate HPW loading amount.
1
23

Green synthesis of 4-methoxybenzophenone
Table 2 Effect of HPW loading amount on the catalytic performance of HPW/MCM-41
HPW loading
amount (wt.%)
Conversion of
benzoic acid (%)
Selectivity (%)
-Methoxybenzophenone
4
Phenyl benzoate
3
5
6
0
0
0
80.7
91.6
93.1
90.0
88.3
79.4
2.7
3.3
8.2
Catalysts preparation condition: calcination temperature 300 °C
Reaction conditions: benzoic acid-to-anisole molar ratio: 1:8, reaction time: 6 h, catalyst amount: 0.1 g,
reaction temperature: 155 °C
Table 3 Effect of calcination temperatures on the catalytic performance of HPW/MCM-41
Calcination
temperature (°C)
Conversion of
benzoic acid (%)
Selectivity (%)
-Methoxybenzophenone
4
Phenyl benzoate
2
2
3
4
5
00
50
00
00
00
87.9
97.2
91.6
48.4
2.3
78.3
87.4
88.3
84.8
79.9
6.2
4.3
3.2
4.9
3.4
Catalysts preparation condition: HPW loading amount 50 wt.%
Reaction conditions: benzoic acid-to-anisole molar ratio: 1:8, reaction time: 6 h, catalyst amount: 0.1 g,
reaction temperature: 155 °C
Subsequently, the effect of calcination temperature was investigated and the
results are listed in Table 3. As can be seen, the conversion of benzoic acid first
increased from 87.9 to 97.2 % while the calcination temperature increased from 200
to 250 °C, whereas it decreased with further increase of the calcination temperature
and dropped sharply to 2.3 % as the calcination temperature increased to 500 °C,
ascribed to the decomposition of the Keggin structure of HPW at high temperatures
[
21]. In contrast, the selectivity for 4-methoxybenzophenone retained in a relatively
high level during the whole process, and the best yield of 4-methoxybenzophenone
was obtained over a HPW/MCM-41 catalyst calcined at 250 °C. Thus, 250 °C was
chosen as the appropriate calcination temperature for further study.
The reusability of HPW/MCM-41 was finally investigated under the optimized
conditions. It was found that the HPW/MCM-41 catalyst kept relatively stable in the
first two recycles with 89.2 and 87.4 % benzoic acid conversion, but the benzoic
acid conversion markedly decreased to 56.9 % in the third recycle. Considering
1
.02 lg/mL W being detected by ICP in the reaction mixture, the leaching of the
active species into the reaction mixture is believed to be the main reason for the
catalyst deactivation. Thus, improving the stability of HPW/MCM-41 will be a big
challenge for further application of this system.
123

H. Zhang et al.
(a)
a
b
b
2
4
6
8
10
2
Theta (degree)
(b)
c
b
a
1
0
20
30
40
2
Theta (degree)
Fig. 1 (a) Low-angle XRD diffraction patterns of a MCM-41 and b 50 wt.% HPW/MCM-41. (b) Wide-
angle XRD diffraction patterns of a MCM-41, b 50 wt.% HPW/MCM-41, and c HPW
Catalysts characterization
XRD patterns of MCM-41, 50 wt.% HPW/MCM-41 and HPW are shown in Fig. 1.
In the low-angle XRD diffraction patterns of MCM-41 and 50 wt.% HPW/MCM-41
(Fig. 1a), the two peaks could be indexed to (100) and (110) reflections, which
correspond to a hexagonal pore system. These reflections of MCM-41 are still
1
23

Green synthesis of 4-methoxybenzophenone
Table 4 Textural properties of MCM-41 and 50 wt.% HPW/MCM-41
a
Catalyst
Bulk Si/Al
BET surface
2
area (m /g)
Pore
volume (cm /g)
Pore
size (nm)
3
MCM-41
87
976
342
0.79
0.27
3.3
3.1
HPW/MCM-41
205
a
Calculated from the ICP results
6
5
4
3
2
1
00
00
00
00
00
00
0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
MCM-41
HPW-MCM-41
0
5
10
15
20
Pore Diameter (nm)
MCM-41
HPW/MCM-41
-0.2
0.0
0.2
0.4
0.6
0.8 1.0
Relative presure (P/P0)
Fig. 2 N
and 50 wt.% HPW/MCM-41
2
adsorption–desorption isotherms and corresponding pore size distribution curves of MCM-41
observed after the HPW loading although the intensity of the diffraction peaks
becomes a little weaker. This suggests that the mesoporous structure of MCM-41
remains almost unchanged upon the HPW loading. Furthermore, 50 wt.% HPW/
MCM-41 possesses the characteristic peaks of both MCM-41 and HPW, but with
lower intensity. The peaks at 10.3°, 20.7°, 23.2°, 25.4°, 29.5°, 31.2°, 34.7° and 37.8°
3
-
were attributed to HPW of the Keggin structure (PW O
2 40
) [26]. This result
1
indicated that HPW had been deposited onto MCM-41 and aggregated to form HPW
crystallites in high loading HPW/MCM-41 catalysts, as also reported by Khder [20],
whereas, no characteristic peaks related to HPW was detectable in low loading
HPW/MCM-41 catalysts, such as 30 wt.% HPW/MCM-41.
The compositions, BET surface areas, and pore volumes of MCM-41 and
0 wt.% HPW/MCM-41 were measured, and the results are listed in Table 4. As
5
calculated from the ICP results, the Si/Al molar ratio increased from 87 to 205 while
HPW was supported on MCM-41, indicating that the dealumination of MCM-41
occurred. The strong acidity of HPW may dissolve parts of aluminum in the MCM-
4
1 framework, and the removal of octahedrally coordinated aluminum may offer
123

H. Zhang et al.
b
a
100
200
300
400
500
600
700
o
Temperature of desorption ( C)
3
Fig. 3 NH -TPD profiles of a MCM-41 and b 50 wt.% HPW/MCM-41
more active centers in HPW/MCM-41, as also reported in previous literatures [27–
2
2
9]. In contrast, the BET surface area decreased markedly from 976 to 342 m /g and
3
the pore volume from 0.79 to 0.27 cm /g during this process, indicating that HPW is
well deposited inside the mesoporous channels of MCM-41 [20]. Furthermore, the
N adsorption–desorption isotherms of both MCM-41 and 50 wt.% HPW/MCM-41
2
(
Fig. 2) exhibit a type IV isotherm and a type H2 hysteresis loop, which is
characteristic of a mesoporous structure. However, the hysteresis loop of HPW/
MCM-41 shifted to lower relative pressure, indicating the decrease of pores in this
catalyst, as confirmed by the corresponding pore size distribution curve (inset), and
in agreement with previous reports [30, 31].
NH -TPD analyses were then carried out to determine the type and amounts of
3
acidic sites of MCM-41 and 50 wt.% HPW/MCM-41, and the results are shown in
Fig. 3. There is only one large peak, centered at approximately 240 °C, in the NH
3
desorption profile of the parent MCM-41, ascribed to the weakly acidic sites,
whereas there are two peaks at approximately 260 and 410 °C in HPW/MCM-41,
which are assigned to the weakly acidic sites and moderately-strong acidic sites,
respectively [32]. Compared with MCM-41, the amount of weakly acidic sites in
HPW/MCM-41 markedly increased, together with a notable shift to higher
temperatures. This indicated that more acidic sites were generated due to HPW
loading and responsible for the good catalytic performance of HPW/MCM-41.
Conclusions
In summary, a green method was established for the efficient synthesis of
4
-methoxybenzophenone via the Friedel–Crafts acylation of anisole with benzoic
1
23

Green synthesis of 4-methoxybenzophenone
acid catalyzed by a novel 50 wt.% HPW/MCM-41 catalyst. The conversion of
benzoic acid reached 97.2 % and the selectivity for 4-methoxybenzophenone was
8
7.4 % under the optimum conditions. HPW is proven to be finely deposited and
aggregated on MCM-41 in the 50 wt.% HPW/MCM-41, which leads to the
dealumination of MCM-41 and then offers more active centers, accounting for the
high catalytic activity of HPW/MCM-41.
Acknowledgments Financial support by the National Natural Science Foundation of China (20806018
and 21376060) and the Natural Science Foundation of Hebei Province (B2014201024) are gratefully
acknowledged.
References
1. A. Zenker, H. Schmutz, K. Fent, J. Chromatogr. A 1202, 64 (2008)
2. C.M. Sousa, J. Berthet, S. Delbaere, P.J. Coelho, Dyes Pigments 92, 537 (2011)
3. H.A.M. Hejaz, L.W.L. Woo, A. Purohit, M.J. Reed, B.V.L. Potter, Bioorg. Med. Chem. 12, 2759
(2004)
4
5
6
7
8
9
. D. Kishore, A.E. Rodrigues, Catal. Commun. 10, 1212 (2009)
. B.W. Xin, Y.H. Zhang, K. Cheng, J. Org. Chem. 71, 5725 (2006)
. S. Farhadi, A. Zabardasti, Z. Babazadeh, Tetrahedron Lett. 47, 8953 (2006)
. M.H. Sarvari, H. Sharghi, J. Org. Chem. 69, 6953 (2004)
. K. Bachari, R. Chebout, R.M. Guerroudj, M. Lamouchi, J. Porous Mater. 19, 615 (2012)
. C. Anand, B. Sathyaseelan, L. Samie, A. Beitollahi, R.P. Kumar, M. Palanichamy, V. Murugesan,
E.R. Kenawy, S.S. Al-Deyab, A. Vinu, Microporous Mesoporous Mater. 134, 87 (2010)
1
1
1
1
1
1
1
1
1
1
2
2
2
0. D. Basavaiah, M. Krishnamacharyulu, R.S. Hyma, S. Pandiaraju, Tetrahedron Lett. 38, 2141 (1997)
1. J.B. Baek, C.B. Lyons, L.S. Tan, J. Mater. Chem. 14, 2052 (2004)
2. X. Wang, Y.K. Wang, D.M. Du, J.X. Xu, J. Mol. Catal. A Chem. 255, 31 (2006)
3. H. Naeimi, L. Moradi, J. Mol. Catal. A Chem. 256, 242 (2006)
4. S.G. Wagholikar, P.S. Niphadkar, S. Mayadevi, S. Sivasanker, Appl. Catal. A Gen. 317, 250 (2007)
5. G. Bond, J.A. Gardner, R.W. McCabe, D.J. Shorrock, J. Mol. Catal. A Chem. 278, 1 (2007)
6. J. Kaur, I.V. Kozhevnikov, Chem. Commun. (21), 2508 (2002)
7. A.X. Li, T.S. Li, T.H. Ding, Chem. Commun. (15), 1389 (1997)
8. A. Corma, Chem. Rev. 97, 2373 (1997)
9. M. Alvaro, A. Corma, D. Das, V. Forn e´ s, H. Garc ´ı a, J. Catal. 231, 48 (2005)
0. A.E.R.S. Khder, H.M.A. Hassan, M.S. El-Shall, Appl. Catal. A Gen. 411–412, 77 (2012)
1. J. Kaur, K. Griffin, B. Harrison, I.V. Kozhevnikov, J. Catal. 208, 448 (2002)
2. G.Y. Bai, Z. Ma, L.J. Shi, T.Y. Li, J. Han, G.F. Chen, N. Li, P.D. Liu, Res. Chem. Intermed. 38, 2501
(2012)
2
2
2
2
3. H. Yamashita, Y. Mitsukura, H. Kobashi, J. Mol. Catal. A Chem. 327, 80 (2010)
ˇ
4. M. Bejblov a´ , D. Proch a´ zkov a´ , J. Cejka, ChemSusChem 2, 486 (2009)
5. H. Ishitani, H. Naito, M. Iwamoto, Catal. Lett. 120, 14 (2008)
6. K.M. Su, Z.H. Li, B.W. Cheng, L. Zhang, M.L. Zhang, J. Ming, Fuel Process. Technol. 92, 2011
(2011)
27. G.Y. Bai, T.Y. Li, Y.H. Yang, H.H. Zhang, X.W. Lan, F. Li, J. Han, Z. Ma, Q.Z. Chen, G.F. Chen,
Catal. Commun. 29, 114 (2012)
28. A.E.W. Beers, J.A. Bokhoven, K.M. Lathouder, F. Kapteijn, J.A. Moulijn, J. Catal. 218, 239 (2003)
2
9. M. M u¨ ller, G. Harvey, R. Prins, Microporous Mesoporous Mater. 34, 135 (2000)
30. J. Liu, B. Sun, J.Y. Hu, Y. Pei, H.X. Li, M.H. Qiao, J. Catal. 274, 287 (2010)
31. W.R. Zhao, J.L. Gu, L.X. Zhang, H.R. Chen, J.L. Shi, J. Am. Chem. Soc. 127, 8916 (2005)
32. W.L. Chu, X.G. Yang, Y.K. Shan, X.K. Ye, Y. Wu, Catal. Lett. 42, 201 (1996)
123