Sulfonic acid functionalized hyperbranched poly(ether sulfone) as a solid acid catalyst

Article abstract of DOI:10.1039/c4gc00188e

Sulfonic acid functionalized hyperbranched poly(ether sulfone) (SHBPES) was studied as a novel type of solid acid catalyst. Various molecular weights of SHBPESs were tested for the esterification reaction between acetic acid and 1-butanol. The SO₃H terminal groups of the SHBPESs work as catalytically active sites, but all tested SHBPESs are totally or partially soluble under the current reaction conditions. To overcome the solubility problem, SHBPES was grafted onto carbon black, and this material, SHBPES/CB, shows fairly good catalytic activity and promising recyclability. The turnover frequency of SHBPES decreased upon grafting it onto carbon black, but it was still much better than that of Amberlyst-15. SHBPES/CB was also tested for the Friedel-Crafts alkylation of anisole and its durability seems to be much better than that of Amberlyst-15 under the operating conditions at 130°C. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4gc00188e

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: Y. Nabae, J. Liang,
X. Huang, T. Hayakawa and M. Kakimoto, Green Chem., 2014, DOI: 10.1039/C4GC00188E.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/greenchem

Page 1 of 7
Green Chemistry
A Novel Solid Acid Catalyst
SHBPES
Carbon

Green Chemistry
Page 2 of 7
View Article Online
DOI: 10.1039/C4GC00188E
Journal Name
RSCPublishing
ARTICLE
Sulfonic Acid Functionalized Hyperbranched
Poly(ether sulfone) as a Solid Acid Catalyst
Cite this: DOI: 10.1039/x0xx00000x
Yuta Nabae,*a Jie Liang,a Xuhui Huang,a Teruaki Hayakawaa and Masaꢀaki
Kakimotoa
Received 00th January 2012,
Accepted 00th January 2012
Sulfonic acid functionalized hyperbranched poly(ether sulfone) (SHBPES) was studied as a
novel type of solid acid catalyst. Various molecular weights of SHBPESs were tested for the
esterification reaction between acetic acid and 1ꢀbutanol. The SO3H terminal groups of the
SHBPESs work as catalytically active sites but all tested SHBPESs are totally or partially
soluble in the current reaction condition. To overcome the solubility problem, SHBPES was
grafted onto a carbon black and this material, SHBPES/CB, shows fairly good catalytic activity
and promising recyclability. The turn over frequency of SHBPES decreased by grafting it onto
a carbon black, but it is still much better than that of Amberlyst®ꢀ15. SHBPES/CB was also
tested for the FriedelꢀCrafts alkylation of anisole and its durability seems to be much better
than that of Amberlyst®ꢀ15 under an operating condition at 130 ˚C.
DOI: 10.1039/x0xx00000x
www.rsc.org/
active catalyst material with such aromatic polymers, our
research group is now interested in the hyperbranched structure.
Introduction
Hyperbranched polymers have a large number of endꢀgroups
and
dendriticꢀlike structure.8ꢀ10 Unlike dendrimers,
hyperbranched polymers can be synthesized in one step process
from ABxꢀtype monomers, where is two or more. It means
Acid catalyzed chemical reactions are widely used in the
current society to produce various chemicals. In terms of green
chemistry, it is quite important to replace liquid acid catalysts
such as HF and H2SO4 with solid acid catalysts.1ꢀ3 Ion
exchanging polymers such as Amberlyst®ꢀ15 is one of typical
solid acid catalysts; however, they are available only at ambient
operating temperature, typically below 120 ˚C, because of low
thermal stability of the vinyl based polymers.4,5 Developing ion
exchanging polymers with higher thermal stability will largely
expand the applicability of polymerꢀbased solid acid catalyst in
various chemical processes.
a
x
that a large number of catalytically active sites can be
introduced if the endꢀgroups are converted into catalytically
active functional groups. Other properties of hyperbranched
polymers might also contribute to the catalytic activity of the
endꢀgroups. The endꢀgroups of hyperbranched polymer would
be well exposed and accessible for the reactants of catalytic
reactions because of a low degree of entanglement. Besides, a
large free volume of hyperbranched polymer would enhance
mass transport of the reactants and products. For the case of
solid acid catalyst, sulfonic acid functionalized hyperbranched
polymer could be a good catalyst material.
To develop a stable polymerꢀbased solid acid catalyst,
employing aromatic polymers such as poly(arylene ether
sulfone) would be a reasonable approach because they are
chemically and thermally stable.6,7 Besides, to develop a highly
Scheme 1. Synthetic route of SHBPES and SHBPES/CB.
This journal is © The Royal Society of Chemistry 2013
J. Name., 2013, 00, 1-3 | 1

Page 3 of 7
Green Chemistry
View Article Online
DOI: 10.1039/C4GC00188E
Journal Name
RSCPublishing
ARTICLE
In this context, we hereby propose sulfonic acid
functionalized hyperbranched poly(ether sulfone)
0.1 M NaOH (3 ml) solution at room temperature and stirred
overnight. The mixture was filtrated and the remaining filtrate
was titrated with 0.1 M HCl.
(SHBPES)11,12 as a novel material for solid acid catalysts. This
paper discusses the catalytic performance of SHBPESs for 1)
the esterification between acetic acid and 1ꢀbutanol and 2) the
FriedelꢀCrafts alkylation of anisole with benzyl alchol. In
additions, since SHBPES itself will have a solubility problem
as a solid catalyst, SHBPES immobilized onto a carbon black
(SHBPES/CB) has also been studied.
CHS elemental analysis was performed using
Perkinelmer 2400ꢀII analyzer.
a
Transmission electron microscopy (TEM) was performed
using a Hitachi Hꢀ7650 microscope operated at 100 kV. The
sample was stained using a Gd based stainer (EM stainer,
Nisshin EM) before the measurement.
Experimental
Catalytic reaction
Material synthesis
The catalytic performance of the materials was tested using a
Shibata Chemist Plaza CP100 multiꢀreactor equipped with 100
mL reactors. The esterification over the prepared catalyst was
performed by stirring acetic acid (20 mmol), 1ꢀbutanol (20
mmol) and the catalyst (20 mg) at 65 ˚C for 0.5ꢀ2.5 h. The
FriedelꢀCrafts alkylation over the prepared catalyst was
performed by stirring anisole (18.5 mmol), benzyl alcohol (1.25
mmol) and the catalyst (75 mg) at 130 ˚C for 20 h. The reaction
products were quantified with a Shimadzu GCMSꢀQP2010 Plus
equipped with a TCꢀFFAP column (0.25 mmφ × 30 m). The
conversion was calculated based on the peak area ratio of 1ꢀ
butanol or benzyl alcohol against the internal standard:
naphthalene (esterification) or dodecane (FriedelꢀCrafts
alkylation). The product yields were calculated based on the
peak area ratios of the reaction products against the internal
standard.
Scheme
1 shows the synthetic routes of SHBPES and
SHBPES/CB. All reagents were used as received. Preparation
of the AB2 monomer, 4,4'ꢀ(mꢀphenyleneꢀdioxy)ꢀbisꢀ
(benzenesulfonyl chloride), has been previously reported and
the procedure was used with a slight modification.11,12 The
prepared AB2 monomer (0.30 g, 0.65 mmol) was dissoloved in
nitrobenzene (1 mL) with FeCl3 (0.003 g, 0.018 mmol) and
heated under N2 at 130 ˚C for 3ꢀ20 h. The mixture was poured
into methanol with a small amount of HCl. The precipitate was
washed with methanol, and then dried in vacuo at 80 ˚C.
SHBPES was obtained by hydrolyzing the chloride form
polymer in water at 80 ˚C for 20 h. To immobilize the polymer
onto a carbon black, the chrolide form polymer (0.2 g) was
dissolved in N,Nꢀdimethylformamide (DMF) with FeCl3 (0.01
g) and Ketjen Black (EC600JD, 0.1 g) and heated under N2 at
130 ˚C for 60 h. The resulting powder was stirred in DMF for
two nights to remove unimmobilized polymer. SHBPES/CB
was obtained by hydrolyzing the polymer/carbon sample in 0.5
M H2SO4 at 80 ˚C for 20 h.
Catalyst recycling tests were performed by the following
manner. The reaction mixture was filtered after each run of the
esterification, and then the residue was used for the next run
after drying and weighing.
To elucidate the effect of the chemical structure of the
backbone, the catalytic performances of pꢀtoluenesulfonic acid
Results and discussion
(PTSA) and 4ꢀ(phenoxy)benzenesulfonic acid (PBSA) were
also studied. PTSA was purchased in a monohydrate form
(TCI) and used as obtained. PBSA was prepared by
hydrolyzing 4ꢀ(phenoxy)benzenesulfonyl chloride, which was
synthesized by the literature method.12
Preparation of SHBPES
SHBPESs with various molecular weights were prepared
by polymerizing the AB2 monomer, 4,4'ꢀ(mꢀphenyleneꢀdioxy)ꢀ
bisꢀ(benzenesulfonyl chloride) for 3ꢀ20 h.11 Table 1 shows Mw
and IEC of the SHBPESs prepared with different reaction
periods. The results suggest that the molecular weight of
SHBPES was successfully controlled in the range of 3.6 × 104
to 2.06 × 105 g molꢀ1. SHBPES1 shows the highest IEC, 2.2
mmol gꢀ1, whilst the theoretical value is 2.8 mmol gꢀ1; and the
IEC slightly decreases as the molecular weight increases. This
is probably due to a crossꢀlinking reaction between the SO3Cl
terminals and aromatic rings during the polymerization.
Measurements
Gel permeation chromatography (GPC) was performed for the
chloride form polymer using a Viscotek GPCꢀ1000 system
equipped with a TDA 302 triple detector and a TSKꢀGEL αꢀM
column. DMF with 0.05 M LiBr was used for eluent. The
weight average molecular weight (
the light scattering data.
Mw) was calculated based on
The ion exchange capacity of the prepared samples was
determined by neutralization titration. The equivalent point was
determined based on the primary differential of the pHꢀtitration
curve. For SHBPESs, a polymer powder (20mg) was treated in
a 5 M NaCl solution (10 ml) at room temperature and stirred
overnight to exchange the protons on the sulfonic acid groups.
Then the mixture was titrated with 0.013M NaOH. For
SHBPES/CB samples, a sample powder (50mg) was treated in
Catalytic performance of SHBPES
The SHBPESs were tested as a catalyst for the esterification
reaction between acetic acid and 1ꢀbutanol. Figure 1 shows the
results of the esterification reaction with the SHBPESs. The
results with Amberlyst®ꢀ15 and H2SO4 are also shown for
comparison. H2SO4 showed the highest catalytic activity since
this is a homogenous catalyst. Amberlyst®ꢀ15, SHBPES4 and
This journal is © The Royal Society of Chemistry 2013
J. Name., 2013, 00, 1-3 | 2

Green Chemistry
Page 4 of 7
ViewAArRticTleICOLnEline
Journal Name
DOI: 10.1039/C4GC00188E
SHBPES5 showed similar catalytic performances, whilst such as ester and amide to graft polymers. To develop a reliable
SHBPES1, SHBPES2 and SHBPES3 showed better catalytic solid acid catalyst, however, such hydrolyzable bonds are not
performances than Amberlyst®ꢀ15.
suitable because the materials will be used in strongly acidic
conditions. In contrast, the present material, SHBPES, can be
directly grafted onto carbon surfaces via the FriedelꢀCrafts
reaction since the polymer can afford numerous sulfonyl
chloride terminals.22 This will result in an aromatic polymer
based solid acid catalyst without any hydrolyzable bond and
quite high durability can be expected in acidic conditions.
Table 1 Molecular weight and ion exchanging capacity of SHBPES prepared
with different polymerization period
a
Polymer
SHBPES1
SHBPES2
SHBPES3
SHBPES4
SHBPES5
Reaction period / h
Mw
IECb / mmol gꢀ1
3
6
8
14
20
36,000
66,000
91,000
134,000
206,000
2.2
2.2
2.1
1.2
1.1
70
a Chloride form polymer was analyzed by GPC with a light scattering
detector. b Determined by titration.
Amberlyst 15
SHBPES1
SHBPES2
SHBPES3
SHBPES4
SHBPES5
60
50
40
30
20
10
0
Figure 2 shows the results of recycling tests. After the first
runs, Most of SHBPES1, SHBPES2 and SHBPES3 could not
be collected because the majority of polymer dissolved in the
liquid phase. This is the reason why these SHBPESs showed
better catalytic performances than Amberlyst®ꢀ15. These
SHBPESs work as homogenous catalysts in the current reaction
condition. The SHBPESs with higher molecular weights,
SHBPES4 and SHBPES5, showed better collectability, but the
recycled weight gradually decreased as the run number
increased, whereas the recycle weight of Amberlyst®ꢀ15 was
almost 100%. These experimental results suggest that the
sulfonic acid terminals on SHBPESs can work as a solid
catalyst but the SHBPESs themselves are not suitable for a
solid acid catalyst because of the solubility problem.
(a)
100
80
60
40
20
0
Amberlyst 15
SHBPES1
SHBPES2
SHBPES4
SHBPES5
a
H2SO4
SHBPES3
70
60
50
40
30
20
10
0
(b)
1
2
3
4
5
Run
Figure 2. (a) Esterification yields with the fresh catalyst (1st run) and the recycle
catalysts (2-5nd run), and (b) the relative amounts of used catalyst which were
collected from the previous run. Conditions: idem as Fig 1 but the reaction
period was 2.5 h.
Table 2 Results of the immobilization of SHBPESs onto a carbon black
Elemental analysis
wt%
Polymer loading
wt%
IEC
Catalyst
mmol gꢀ1
C
H
S
IECa
38
EAb
35
35
SHBPES1/CB
SHBPES2/CB
SHBPES3/CB
0.87
0.73
0.89
77.3
76.7
75.9
2.2
2.1
2.3
5.1
5.1
5.3
0
0.5
1
1.5
2
2.5
32
39
Reaction time / h
36
a Evaluated from the change in IEC before and after the immobilization. b
Calculated from the S content of elemental analysis.
Figure 1. Time course of the esterification yield with various catalysts.
a
Conditions: T 65 ˚C, acetic acid 0.02 mol, 1-butanol 0.02 mol, catalyst 20 mg.
H2SO4 equivalent to Amberlyst®-15 was used.
Table 2 summarizes the results of immobilization of
SHBPESs onto a carbon black via the FriedelꢀCrafts reaction as
illustrated in Scheme 1. SHBPES1, SHBPES2 and SHBPES3
were selected for the immobilization considering the affinity
between the polymer and the reaction phase for catalytic
reactions. The IECs became 0.73ꢀ0.89 mmol gꢀ1, whereas they
were 2.08ꢀ2.20 mmmol gꢀ1 before the immobilization. These
IECs correspond to the polymer loading of 31.7ꢀ38.7 %. The
Immobilization of SHBPES onto Carbon Black
Since the SHBPESs themselves have a solubility problem to
consider them as solid acid catalysts, we hereby discuss the
immobilization of SHBPES onto a carbon black. Numerous
reports have been published about grafting polymers from
carbon surfaces.13ꢀ21 Many of them employ hydrolyzable bonds
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 3

Page 5 of 7
Green Chemistry
View Article Online
Journal Name
ARTICLE
DOI: 10.1039/C4GC00188E
polymer loading was also evaluated by CHS elemental analysis particle size of SHBPES3/CB seems slightly large. In the
and the results are in good agreement with the values from the enlarged images, SHBPES3/CB seems to have a uniform
IECs. Although the polymer loading was not quite different polymer layer with
a thickness of 10ꢀ20 nm. These
among three samples, SHBPES3/CB showed the highest experimental results suggest that SHBPES can be successfully
polymer loading. Thus obtained SHBPES3/CB was analyzed by grafted onto carbon black by the FriedelꢀCrafts reaction.
TEM. Figure 3 shows TEM images of SHBPES3/CB and
pristine carbon black. Compared to pristine carbon black, the
(a)
(b)
(c)
200 nm
(d)
100 nm 100 nm
(f)
(e)
100 nm
200 nm
100 nm
Figure 3. TEM images of (a-c) pristin carbon black and (d-e) SHBPES3/CB.
Table 3 Comparison of the ion exchanging capacity and catalytic performance between SHBPES3/CB and other control samplesa
Catalyst
IEC mmol gꢀ1
Catalyst amount / mg
Reaction period / h
Conversion / %
Yield / %
TOFb minꢀ1
blank
Ketjen black
PTSAc
‒
‒
2.5
2.5
0.5
0.5
0.5
2.5
2.5
3
4
4
4
‒
‒
20
10
10
20
20
20
5.3
4.0
2.1
0.89
4.7
33
26
20
13
20
26
21
18
13
21
3.21
3.56
2.85
0.97
0.30
PBSAd
SHBPES3
SHBPES3/CB
Amberlyst®ꢀ15
a Reaction conditions: idem as Fig 1 but the reaction period and catalyst amount. b Calculated from the IEC and the esterification yield. cpꢀToluene sulfonic
acid. d4ꢀ(Phenoxy)benzenesulfonic acid.
SHBPES3/CB was studied as a solid acid catalyst for the terminals on HBPES. The catalytic performance of
esterification between acetic acid and 1ꢀbutanol. Table 3 SHBPES3/CB against other stateꢀofꢀtheꢀart catalysts could be
compares the IEC and catalytic performance of several catalysts. supposed based on the comparison against that of Amberlyst®ꢀ
The IEC of SHBPES3/CB was 0.89 mmol gꢀ1 whereas that of 15. Liu et al. compared various catalysts for the esterification
SHBPES3 was 2.1 mmol gꢀ1. SHBPES3/CB shows a fairly between acetic acid and 1ꢀbutanol at 90 ˚C, and reported that Hꢀ
good catalytic activity: 13 % of esterification yield against PDVBꢀ1.5ꢀSO3H (IEC: 1.86 mmol gꢀ1), SBAꢀ15ꢀSO3H (1.26
46 % by SHBPES3. The turn over frequency (TOF) of mmol gꢀ1), Hꢀbeta zeolite (1.21 mmol gꢀ1) and HꢀUSY zeolite
SHBPES3/CB is smaller than that of SHBPES3, but still better (2.06 mmol gꢀ1) showed 9.3, 7.6, 6.7 and 4.1 minꢀ1 of TOFs
than that of Amberlyst®ꢀ15. The higher TOF against whereas Amberlyst®ꢀ15 showed 3.0 minꢀ1.23 Considering the
Amberlyst®ꢀ15 is probably due to the flexibility of the SO3H TOF of SHBPES3/CB in Table 3, which is three times better
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Green Chemistry
Page 6 of 7
ViewAArRticTleICOLnEline
Journal Name
DOI: 10.1039/C4GC00188E
than that of Amberlyst®ꢀ15, it can be presumed that the
inherent catalytic activity the acidic terminal groups on HBPES
are as good as the active sites of the stateꢀofꢀtheꢀart catalysts,
although the mass catalytic activity is not because of the lower
IEC.
One might wonder if the chemical structure of the polymer
backbone significantly affects the catalytic activity of the
terminal functional groups. To elucidate the effect of the
backbone, the homogenous catalysis of model compounds was
studied. Table 3 shows the catalytic performances of PTSA and
PBSA for the esterification between acetic acid and 1ꢀbutanol.
PBSA showed a slightly better TOF but the catalytic activities
of these two compounds were not very different. Therefore, the
better TOF of SHBPES3/CB compared to that of Amberlyst®ꢀ
15 presumably derives from good flexibility of the terminals on
the hyperbranched strucutre rather than their chemical
structures.
Recycling of SHBEPS3/CB was tested in the same
manner as the experiments for SHBPESs and the results are
shown in Figure 4. Although the collecting yield of
SHBPES3/CB is not 100%, SHBPES3/CB over 90 % was
successfully collected even after 5 runs. In the meantime, the
catalytic activity of SHBPES3/CB seems fairly stable. It could
be concluded that the stability of SHBPES3/CB are quite
promising.
Scheme 2. Friedel-Crafts alkylation of anisole with benzyl alcohol.
Figure 5 summarizes the results of the FriedelꢀCrafts
alkylation of anisole with benzyl alcohol over SHBPES3/CB
and Abmerlyst®ꢀ15. A blank test under the same reaction
condition but without the catalyst showed only trace amounts of
reaction products. In contrast, SHBPES3/CB showed a certain
catalytic activity for this reaction. Furthermore, the catalyst was
successfully collected after the reaction and used for the
following four runs, although the performance slightly
degraded as the run number increased. Amberlyst®ꢀ15 also a
catalytic activity under the same condition, but the reaction
mixture became turbid immediately at the early stage of the
reaction, and it was impossible to collect the catalyst. Probably,
Amberlyst®ꢀ15 was decomposed in the present reaction
condition and worked as a homogenous catalyst. These
experimental results clearly suggest that the stability of the
SHBPES/CB catalyst is much better than that of Amberlyst®ꢀ
15 under such a high temperature.
70
100
Interestingly, the product selectivities are slightly
different between SHBPES3/CB and Amberlyst®ꢀ15.
SHBPES3/CB produced dibenzyl ether whereas Amberlyst®ꢀ
15 did not. This different selectivity might derive from the
difference in the solubility of the reactants into the polymer
matrix. This result suggests that the HBPES derived solid acid
catalyst might exhibit a molecular sieving effect if the polymer
matrix and the reaction were appropriately designed.
60
80
50
40
30
20
10
0
60
40
20
0
o-Benzyl anisole
p-Benzyl anisole
1
2
3
4
5
Run
Dibenzyl ether
100
Figure 4 Esterification yields with the fresh catalyst (1st run) and the recycle
catalysts (2-5nd run), and the relative amounts of catalyst against the 1st run.
Conditions: idem as Fig 1 but the catalyst amount was 60 mg and the reaction
period was 2.5 h.
(a) SHBPES3/CB
80
60
40
20
Catalytic Reaction at High Temperature
One advantage of the SHBPESs as a polymerꢀbased solid acid
catalyst is the thermal stability of the poly(ether sulfone)
backbone; therefore, a higher operating temperature can be
expected compared to Amberlyst®ꢀ15. In this context, the
FriedelꢀCrafts alkylation of anisole with benzyl alcohol was
studied using the SHBPES3/CB as illustrated in Scheme 2.
0
Run 1 Run 2 Run 3 Run 4 Run5
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 5

Page 7 of 7
Green Chemistry
View Article Online
Journal Name
ARTICLE
DOI: 10.1039/C4GC00188E
A. Takagaki, M. Okamura, J. N. Kondo, S. Hayashi, K. Domen, M.
Hara, Nature, 2005, 438, 178.
100
4
5
M. A. Harmer, Q. Sun, Appl. Catal., A, 2001, 221, 45.
(b) Amberlyst-15
80
60
40
20
0
T. Okayasu, K. Saito, H. Nishide, M. T. W. Hearn, Chem. Commun.
,
2009, 4708; T. Okayasu, K. Saito, H. Nishide, M. T. W. Hearn,
Green Chem., 2010, 12, 1981.
6
7
M. A. Hickner, H. Ghassemi, Y. S. Kim, B. R. Einsla, J. E. McGrath,
Chem. Rev., 2004, 104, 4587.
F. Wang, M. Hickner, Y. S. Kim, T. A. Zawodzinski, J. E. McGrath,
J. Membr. Sci., 2002, 197, 231.
8
9
C. Gao, D. Yan, Prog. Polym. Sci., 2004, 29, 183.
M. Jikei, M. Kakimoto, Prog. Polym. Sci., 2001, 26, 1233.
Run 1 Run 2 Run 3 Run 4 Run5
10 M. Kakimoto, S. J. Grunzinger, T. Hayakawa, Polymer Journal
2010, 42, 697.
,
Figure 5. The results of the Friedel-Crafts alkylation over the (a) SHBPES3/CB and
(b) Amberlyst®-15. Conditions: anisole 18.5 mmol, benzyl alcohol 1.25 mmol,
catalyst 75 mg, 130 ˚C, 20 h. Inset: the reaction mixture after the 1st run with
Amberlyst®-15.
11 K. Matsumoto, M. Ueda, Chem. Lett., 2006, 35, 1196.
12 S. J. Grunzinger, T. Hayakawa, M. Kakimoto, J. Polym. Sci., Part A:
Polym. Chem., 2008, 46, 4785; S. J. Grunzinger, M. Watanabe, K.
Fukagawa, R. Kikuchi, Y. Tominaga, T. Hayakawa; M. Kakimoto,
J. Power Sources, 2008, 175, 120.
Conclusions
Sulfonic acid functionalized hyperbranched poly(ether sulfone)
(SHBPES) has been investigated as a novel type of solid acid
catalyst. Various molecular weights of SHBPESs were tested
for the esterification reaction between acetic acid and 1ꢀ
butanol. The SO3H terminal groups of the HBPESs works as
catalytically active sites for the esterification but all tested
SHBPESs are totally or partially soluble in the current reaction
condition. To overcome the solubility problem, SHBPES was
grafted onto a carbon black and those materials show fairly
good catalytic activity and promising recyclability. It should be
noted that SHBPES has been immobilized without any
hydrolyzable bonds, which will contribute to high chemical
stability in acidic conditions. As a model reaction at a high
operating temperature, the FriedelꢀCrafts alkylation of anisole
at 130 ˚C was studied and it has been revealed that
SHBPES3/CB exhibits much better stability than Amberlyst®ꢀ
15. Indeed the mass catalytic activity of the current material is
not as good as those of the stateꢀofꢀtheꢀart catalysts; however, it
will be much improved if the concentration of acidic sites could
be more increased. Further studies require to be done to
increase the concentration acidic sites and expand the
applicability of these catalysts to other acid catalyzed chemical
reactions.
13 C. Gao, S. Muthukrishnan, W. W. Li, J. Y. Yuan, Y. Y. Xu, A. H. E.
Muller, Macromolecules, 2007, 40, 1803.
14 C. M. Homenick, G. Lawson, A. Adronov, Polym. Rev., 2007, 47
,
265.
15 R. K. Layek, A. K. Nandi, Polymer, 2013, 54, 5087.
16 P. Liu, Eur. Polym. J., 2005, 41, 2693.
17 T. Q. Liu, R. CasadoꢀPortilla, J. Belmont, K. Matyjaszewski, J.
Polym. Sci., Part A: Polym. Chem., 2005, 43, 4695.
18 N. G. Sahoo, S. Rana, J. W. Cho, L. Li, S. H. Chan, Prog. Polym.
Sci., 2010, 35, 837.
19 G. Sakellariou, D. Priftis, D. Baskaran, Chem. Soc. Rev., 2013, 42
,
677.
20 Z. Spitalsky, D. Tasis, K. Papagelis, C. Galiotis, Prog. Polym. Sci.
2010, 35, 357.
,
21 C. C. Wang, Z. X. Guo, S. K. Fu, W. Wu, D. B. Zhu, Prog. Polym.
Sci., 2004, 29, 1079.
22 H.J. Lee, S.W. Han, Y.D. Kwon, L.S. Tan, J.B. Baek, Carbon, 2008,
46, 1850.
23 F. Liu, W. Kong, C. Qi, L. Zhu, F.ꢀS. Xiao, ACS Catal., 2012, 2, 565
.
Acknowledgements
This study was supported by JSPS KAKENHI (26870183). The
TEM analysis was performed in the Center for Advanced
Materials Analysis in Tokyo Institute of Technology. The
authors thank Dr Atsushi Takagaki (The University of Tokyo)
for valuable instruction about solid acid catalysts and Mr
Masatomo Mikuni and Mr Masaki Tomita for technical
assistance. M.K. was supported by Visiting Professorship for
Senior International Scientists from Chinese Academy of
Science.
Notes and references
a
Department of Organic and Polymeric Materials, Tokyo Institute of
Technology, 2ꢀ12ꢀ1 S8ꢀ26 Ookayama, Meguroꢀku, Tokyo 152ꢀ8552,
Japan. Tel: +81
3 5734 2429, Fax: +81 3 5734 2433, Eꢀmail:
nabae.y.aa@m.titech.ac.jp
1
2
3
Y. B. Huang, Y. Fu, Green Chem., 2013, 15, 1095.
T. Okuhara, Chem. Rev., 2002, 102, 3641.
M. Hara, T. Yoshida, A. Takagaki, T. Takata, J. N. Kondo, S.
Hayashi, K. Domen, Angew. Chem., Int. Ed., 2004, 43, 2955; S.
Suganuma, K. Nakajima, M. Kitano, D. Yamaguchi, H. Kato, S.
Hayashi, M. Hara, J. Am. Chem. Soc., 2008, 130, 12787; .M. Toda,
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012