Friedel-crafts hydroxyalkylation of anisole over oxalic acid modified Hβ zeolite

Article abstract of DOI:10.1007/s10562-010-0387-z

Oxalic acid modified Hβ (OA-Hβ) zeolite is found to have better catalytic performance than Hβ zeolite in the Friedel-Crafts hydroxyalkylation of anisole with chloral. This is attributed to the increase of weak and moderately-strong acid sites, caused by oxalic acid modification. Furthermore, it is believed that the carbonaceous deposits on the acid sites and the blockage of the pores, together with poisoning by chlorinated materials, are responsible for the deactivation of OA-Hβ zeolite, as indicated by NH₃-TPD, BET, SEM, TG and XPS measurement results. Moreover, partial regeneration of OA-Hβ zeolite can be achieved via subsequent calcination.

Full text of DOI:10.1007/s10562-010-0387-z

Catal Lett (2010) 138:187–192
DOI 10.1007/s10562-010-0387-z
Friedel–Crafts Hydroxyalkylation of Anisole Over Oxalic Acid
Modified Hb Zeolite
•
Guoyi Bai Haiyang Dou Mande Qiu
•
•
•
Xinxin Fan Fei He Libo Niu Zheng Ma
•
•
Received: 3 March 2010 / Accepted: 2 June 2010 / Published online: 18 June 2010
Ó Springer Science+Business Media, LLC 2010
¨
Abstract Oxalic acid modified Hb (OA-Hb) zeolite is
found to have better catalytic performance than Hb zeolite in
the Friedel–Crafts hydroxyalkylation of anisole with chloral.
This is attributed to the increase of weak and moderately-
strong acid sites, caused by oxalic acid modification.
Furthermore, it is believed that the carbonaceous deposits on
the acid sites and the blockage of the pores, together with
poisoning by chlorinated materials, are responsible for the
deactivation of OA-Hb zeolite, as indicated by NH3-TPD,
BET, SEM, TG and XPS measurement results. Moreover,
partial regeneration of OA-Hb zeolite can be achieved via
subsequent calcination.
such as AlCl3, or mineral Bronsted acids, typically H2SO4.
However, in view of the current environmental restrictions,
there is an increasing demand for the replacement of con-
ventional catalysts due to problems with disposal of spent
catalysts, corrosion, toxicity and product isolation. Zeo-
lites, with their unique acid properties and pore structures,
are increasingly regarded as environmentally-friendly solid
acid catalysts instead of traditional liquid acid catalysts in
Friedel–Crafts type reactions [2–4]. Furthermore, acid
modifications have been proven to be important for
improving the activity of zeolites in these reactions [5, 6].
On the other hand, the selective synthesis of arylcarbi-
nols directly from Friedel–Crafts hydroxyalkylation with
aldehydes in the presence of zeolite is difficult because the
arylcarbinol thus obtained can easily react with another
aromatic compound to yield the corresponding bisarylal-
kane derivative under the same reaction conditions [7, 8].
Barthel and colleagues investigated the influence of zeo-
lites and other reaction parameters on the hydroxyalkyla-
tion of aromatic compounds with chloral to furnish the
arylcarbinol [9, 10], but few results have been reported on
the stability of zeolite under hydroxyalkylation conditions.
In this paper, we report our recent studies on the effect
of oxalic acid modification on the catalytic performance of
Hb zeolite in Friedel–Crafts hydroxyalkylation of anisole
with chloral. The activity and stability of the oxalic acid
modified Hb zeolite were investigated and defined.
Keywords Hydroxyalkylation Á Oxalic acid
modification Á Hb zeolite Á Stability Á Deactivation
1 Introduction
Friedel–Crafts hydroxyalkylation of aromatic compounds
by carbonyl derivates is of great industrial importance for
the synthesis of commodities such as methylenedianiline
and bisphenol A [1]. Presently, Friedel–Crafts hydrox-
yalkylation is carried out commercially using Lewis acids,
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-010-0387-z) contains supplementary
material, which is available to authorized users.
G. Bai (&) Á H. Dou Á M. Qiu Á X. Fan Á L. Niu Á Z. Ma
College of Chemistry and Environmental Science, Hebei
University, Baoding 071002, Hebei, People’s Republic of China
e-mail: baiguoyi@hotmail.com
2 Experimental
2.1 Materials
F. He
School of Chemical Engineering and Technology, Tianjin
University, Tianjin 300072, People’s Republic of China
All chemicals were of reagent grade and were used without
further purification. The zeolites, Hb (Si/Al = 25), ZSM-5
123

188
G. Bai et al.
2.4 Catalytic Tests
(Si/Al = 38), MCM-41 (Si/Al = 25), HY (Si/Al = 4.5),
were commercial samples purchased from Nankai Uni-
versity Catalyst Co., Ltd.
The hydroxyalkylation of anisole with chloral (Scheme 1)
was carried out in a 50 mL round bottom flask equipped
with a reflux condenser and a CaCl2 tube. In a typical run,
40 mmol anisole and 40 mmol chloral were charged to the
flask and heated to 40 °C. Then 1.0 g zeolite was added
and the reaction continued at this temperature for 8 h with
vigorous stirring. The OA-Hb zeolite was isolated after the
reaction by washing and drying at 120 °C. The regenerated
OA-Hb zeolite was obtained after calcination of the iso-
lated OA-Hb zeolite at 750 °C for 5 h. The reaction mix-
tures were analyzed by a gas chromatography using a 30 m
SE-30 capillary column. The products were confirmed by
GC–MS (Agilent 5975C) and 1H NMR (Bruker Avance III
600 MHz).
2.2 Catalyst Preparation
5.0 g Hb zeolite was subjected to acid treatment by stirring
with 20 mL oxalic acid (1.0 mol/L) at 50 °C for 1 h. After
that, the samples were dried at 120 °C and then calcined
at 550 °C for 5 h. The prepared zeolite was classified
as OA-Hb. Moreover, hydrochloric acid, tartaric acid,
phosphoric acid and sulfuric acid modified Hb zeolites
were prepared in the same method and classified HA-Hb,
TA-Hb, PA-Hb, SA-Hb, respectively.
2.3 Characterization of the Catalysts
3 Results and Discussion
X-ray diffraction (XRD) analysis was recorded on a Bruker
D8 advance diffractometer with Cu Ka radiation. The BET
surface area and total pore volume were determined using a
Micromeritics Tristar II 3020 surface area and pore ana-
lyzer. Ammonia temperature-programmed desorption
(NH3-TPD) experiments were carried out in a TP-5000
instrument with a thermal conductivity detector. The sur-
face acidity was monitored by FT-IR spectroscopy after
adsorption of pyridine (Py-IR), using a Bruker Vector 22
spectrometer coupled to a conventional high vacuum sys-
tem. The sample was compacted to a self-supporting wafer
and was calcined at 400 °C for 1.5 h in an in situ IR gas
cell under vacuum prior to pyridine adsorption. Pyridine
was adsorbed at room temperature, and then the samples
were heated to 200 °C and evacuated to remove physically
adsorbed and weakly chemisorbed pyridine. The mor-
phology of the samples was investigated using a JEOL
JSM-7500 scanning electron microscopy (SEM) micro-
scope. Thermogravimetric (TG) analysis was conducted on
a NETZSCH QMS 403C TG/DSC/MS instrument in an
argon gas flow. X-ray photoelectron spectroscopy (XPS)
measurements were performed on a PHI 1600 spectrometer
using a MgKa X-ray source for excitation.
3.1 Catalyst Selection and Characterization
As selection of a suitable catalyst is crucial for the efficient
hydroxyalkylation of anisole, commercial zeolites were first
examined in this reaction (Table 1, entries 1–4). It was
found that Hb zeolite was the most effective catalyst among
them with an anisole conversion of 13.1% and a 1-(4-
methoxyphenyl)-2,2,2-trichloroethanol (4-MPE) selectivity
of 93.5%, accompanied by a trace of ortho-isomer. This can
be attributed to the steric effect of the intermediate and
product, consistent with the results discussed by Barthel
[10]. A few bisaryl-product was detected as the main by-
product. Considering the benefit of acid modification [5, 6],
a series of acid-modified Hb zeolites was prepared and
investigated under the same reaction conditions (Table 1,
entries 5–9). Just as we expected, some acid-modified zeo-
lites, especially the OA-Hb zeolite, exhibited higher activ-
ities than parent Hb zeolite, the conversion of anisole
catalyzed by OA-Hb zeolite is nearly twice that of the Hb
zeolite. Thus, the OA-Hb zeolite was chosen as the catalyst
for further investigation and optimization.
Scheme 1
O
O
O
O
O
Cl
Cl
zeolite
Cl
Cl
O
+
+
+
H
Cl
Cl
OH
Cl
Cl
HO
Cl
Cl
Cl
Cl
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Friedel–Crafts Hydroxyalkylation of Anisole
189
Table 1 Effects of different zeolites on conversion and chemose-
lectivity of the Friedel–Crafts hydroxyalkylation of anisole with
chloral
Table 2 Textural properties of zeolites
Zeolite
BET surface area (m2/g) Pore volume (cm3/g)
Hb
331
408
13
0.26
0.30
0.05
0.29
Entries
Zeolite
Conversion of
anisole (%)
Selectivity
of 4-MPE (%)
OA-Hb
Used OA-Hb
1
2
3
4
5
6
7
8
9
MCM-41
ZSM-5
HY
9.3
0.5
88.8
100
Regenerated OA-Hb 370
7.1
79.1
93.5
94.2
94.3
91.2
91.1
79.7
Hb
13.1
25.2
15.6
16.1
8.4
OA-Hb
HA-Hb
TA-Hb
PA-Hb
SA-Hb
8
7
b
6
d
12.0
5
Reaction conditions—anisole: 40 mmol, chloral: 40 mmol, reaction
temperature: 40 °C, catalyst amount: 1.0 g, reaction time: 8 h
4
a
3
c
2
The crystalline structure of Hb and OA-Hb zeolites are
characterized by XRD, and XRD patterns are given in
Fig. 1. The XRD patterns at 7.5° and 22.5° of OA-Hb
zeolite are weaker than that of Hb zeolite. This suggests
that the crystallinity of OA-Hb zeolite decreases as a result
of modification with oxalic acid, and this may favor the
desired transformation.
1
0
-1
100
200
300
400
500
600
700
800
Temperature of desorption (
)
Fig. 2 NH3-TPD profiles of Hb (a), OA-Hb (b), used OA-Hb (c) and
regenerated OA-Hb (d) zeolites
N2 adsorption and desorption results of Hb and OA-Hb
zeolites are listed in Table 2. It was found that the OA-Hb
zeolite had higher BET surface area and pore volume than
Hb zeolite, possibly due to the dealumination of the zeolite
after oxalic acid modification [11], which could result in
production of more active sites for the reactants to adsorb
and react, resulting in the observed higher activity of
OA-Hb zeolite.
NH3-TPD profiles of Hb and OA-Hb zeolites are pre-
sented in Fig. 2 (curve a and b). The strong peaks centered
at 180–260 °C are assigned to the weak acid sites in both
zeolites and the peak centered approximately at 360 °C is
assigned to the moderately-strong acid sites according to
the literature [12]. It is clear that the amounts of both weak
and moderately-strong acid sites in OA-Hb zeolite are
higher than those in Hb zeolite. Thus, the catalyst activity
appears to increase proportionally with the increase of
the amounts of acid sites resulting from oxalic acid
modification.
The results of Py-IR analysis of Hb and OA-Hb zeolites
are listed Table 3. We conclude that OA-Hb zeolite
Table 3 Acidic properties of Hb and OA-Hb zeolites from pyridine
adsorption
a
Lewisa
Total aciditya
L/B ratio
¨
Bronsted
Zeolite
Hb
12.27
17.01
3.12
2.38
0.64
1.47
14.64
17.65
4.59
5.16
26.41
2.12
OA-Hb
Used OA-Hbb
a
Relative concentration
b
The used sample was preliminary treated and then heated to remove
pyridine both at 120 °C
Fig. 1 XRD patterns of Hb (a) and OA-Hb (b) zeolites
123

190
G. Bai et al.
contains more Lewis acid sites (1,450 cm-1) than Hb
3.2 Stability of OA-Hb Zeolite
¨
zeolite, while the amount of Bronsted acid sites
(1,540 cm-1) decreases remarkably after the oxalic acid
modification. Therefore, the Lewis acid component of the
zeolite promotes the conversion of anisole.
The preparation parameters of the OA-Hb zeolite and the
Friedel–Crafts hydroxyalkylation reaction parameters were
both optimized to improve the activity of the catalyst.
Finally, the stability of the optimized OA-Hb zeolite was
investigated under the optimum reaction conditions
(Table 4). A marked deactivation occurs with the reused
OA-Hb zeolite with a conversion of anisole dropping from
79.0% in the first run to 4.3%. In contrast, on regenerating
the re-isolated OA-Hb zeolite after each run, the conver-
sion of anisole first decreases to 58.7% and then stabilizes
at about 50% in eight subsequent cycles all of which are
better than the unmodified Hb zeolite with a conversion of
30.9% under the same reaction conditions. Moreover, the
selectivity for production of 4-MPE with the regenerated
catalyst was retained at roughly 94%; whereas that of the
re-isolated catalyst used without regeneration dropped to
64.8%. Therefore, the OA-Hb zeolite shows enhanced
activity and selectivity in this reaction in comparison with
the unmodified Hb zeolite as well as possessing the
capacity for regeneration and recycling without loss of the
Table 4 Stability of OA-Hb zeolite
OA-Hb Zeolite
Conversion
of anisole (%)
Selectivity
of 4-MPE (%)
Fresh
79.0
4.3
93.7
64.8
92.2
94.7
94.2
93.4
96.2
94.8
96.4
95.5
Used
Regenerated 1st cycle
Regenerated 2nd cycle
Regenerated 3rd cycle
Regenerated 4th cycle
Regenerated 5th cycle
Regenerated 6th cycle
Regenerated 7th cycle
Regenerated 8th cycle
58.7
48.1
51.7
50.0
51.8
48.6
52.6
51.5
Reaction conditions—anisole: 40 mmol, chloral: 40 mmol, reaction
temperature: 50 °C, catalyst amount: 5.0 g, reaction time: 8 h
Fig. 3 SEM images of fresh OA-Hb zeolite: a 98,000 and b 9100,000; used OA-Hb zeolite: c 98,000 and d 9100,000
123

Friedel–Crafts Hydroxyalkylation of Anisole
191
selectivity and retention of about two-thirds of its original
catalytic activity.
of the used OA-Hb zeolite and the detection of carbon
dioxide in the gas phase, based on TG-MS, support this
conclusion. Gratifyingly, the regenerated OA-Hb zeolite
has a relatively lower BET surface area (370 m2/g) than the
fresh one (408 m2/g), but still higher than Hb zeolite
(331 m2/g). We propose this to be due to the presence of
irreversible carbonaceous deposition inside the pores, even
after the regeneration by calcination.
In order to find the reason for the above results, the
fresh, used and regenerated OA-Hb zeolites were charac-
terized and compared with the unmodified Hb zeolite. As
can be seen from Table 2, BET surface area and pore
volume of the used OA-Hb zeolite decrease remarkably to
13 m2/g and 0.05 cm3/g, which we propose to be caused by
carbonaceous deposits on the surface and within the pores
of the used OA-Hb zeolite, and which are responsible for
its deactivation [13]. SEM analyses on the fresh and used
OA-Hb zeolites show the differences directly (Fig. 3), with
carbonaceous deposits detectable on the surface of the used
OA-Hb zeolite. Furthermore, the almost 17% weight loss
XPS spectra of the used OA-Hb zeolite also provide
evidence for carbonaceous deposits on the surface, com-
pared to the fresh and regenerated ones (Fig. 4), in total
agreement with the BET and SEM results. On the other
hand, chlorinated deposits are detected on the surface of
the used OA-Hb zeolite; whereas no chlorine is found on
Fig. 4 XPS spectra of fresh OA-Hb (a), used OA-Hb (b) and regenerated OA-Hb (c) zeolites
123

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G. Bai et al.
Acknowledgments The authors thank Professor L. M. Harwood for
his assistance. Financial support by the National Natural Science
Foundation of China (20806018), the Natural Science Foundation of
Hebei Province (B2007000156), the Science Project of the Hebei
Education Department (ZD200910) are gratefully acknowledged.
the surface of the regenerated one. We can thus deduce that
the adsorption of chlorinated compounds may result in
poisoning of a proportion of the Lewis acid sites, which
further induces the catalyst deactivation.
The NH3-TPD profile of the used OA-Hb zeolite (Fig. 2,
curve c) shows that the amount of acid sites decreases
sharply, especially for the moderately-strong acid sites,
compared to the fresh catalyst. However, the amount of
weak and moderately-strong acid sites on the regenerated
OA-Hb zeolite only partially decreases (Fig. 2, curve d).
Moreover, the amount of Lewis acid sites of the used
OA-Hb zeolite was also found to decrease significantly
compared to the fresh OA-Hb zeolite (Table 3). Thus, the
decrease of acid sites due to carbonaceous deposition is
believed to be the major source of deactivation.
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4 Conclusions
The OA-Hb zeolite, with a greater proportion of Lewis acid
sites, exhibits better catalytic performance than Hb zeolite
in hydroxyalkylation of anisole, with an anisole conversion
of 79.0% and a 93.7% selectivity of 4-MPE under the
optimized reaction conditions. The increased weak and
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