Hyperbranched aromatic poly(ether ketone) functionalized with TEMPO as a heterogeneous catalyst for aerobic oxidation of alcohols

Article abstract of DOI:10.1039/c4ra12126k

A hyperbranched aromatic poly(ether ketone) functionalized with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO/HBPEK) was investigated as a novel heterogeneous catalyst for aerobic oxidation of alcohols. The TEMPO/HBPEK contained 2 mmol g^-1 TEMPO and had a turnover number (TON) of 46 compared to commercial TEMPO with a TON of 60, indicating good catalytic activity and selectivity for the aerobic oxidation of benzyl alcohol. This material can be used as a recyclable heterogeneous catalyst by grafting it onto insoluble supports such as carbon black (TEMPO/HBPEK/CB) or polyimide nanoparticles (TEMPO/HBPEK/PI), whereas the bare TEMPO/HBPEK acts as a homogeneous catalyst. These heterogeneous catalysts had TONs of 27 and 22, respectively, indicating greater catalytic activity than the commercially available heterogeneous catalyst, TEMPO immobilized on polystyrene, which had a TON less than 1.

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ARTICLE
Hyperbranched Aromatic Poly(ether ketone)
Functionalized with TEMPO as a Heterogeneous
Catalyst for Aerobic Oxidation of Alcohols
Cite this: DOI: 10.1039/x0xx00000x
Ying Shi, a Yuta Nabae, a* Teruaki Hayakawa, a and Masaꢀaki Kakimoto a
Received 00th January 2012,
Accepted 00th January 2012
A
hyperbranched
aromatic
poly(ether
ketone)
functionalized
with
2,2,6,6ꢀ
DOI: 10.1039/x0xx00000x
tetramethylpiperidineꢀ1ꢀoxyl (TEMPO/HBPEK) was investigated as a novel heterogeneous
catalyst for aerobic oxidation of alcohols. The TEMPO/HBPEK contained 2 mmol gꢀ1 TEMPO
and had a turnover number (TON) of 46 compared to commercial TEMPO with a TON of 60,
indicating good catalytic activity and selectivity for the aerobic oxidation of benzyl alcohol.
This material can be used as a recyclable heterogeneous catalyst by grafting it onto insoluble
supports such as carbon black (TEMPO/HBPEK/CB) or polyimide nanoparticles
(TEMPO/HBPEK/PI), whereas the bare TEMPO/HBPEK acts as a homogeneous catalyst.
These heterogeneous catalysts had TONs of 27 and 22, respectively, indicating greater
catalytic activity than the commercially available heterogeneous catalyst, TEMPO immobilized
on polystyrene, which had a TON less than 1.
www.rsc.org/
fibers.21 The supported TEMPO can be collected easily after
each cycle by filtration. However, most of these immobilized
1. Introduction
TEMPO systems possess low catalytic activity or poor
chemical stability of the polymer backbone under severe
oxidative conditions.
The oxidation of primary alcohols to aldehydes is an important
basic procedure for the synthesis of chemicals and
intermediates.1,2 The aerobic oxidation of alcohols is of interest
because of its potential for environmentally friendly (“green”)
chemistry, because the reaction consumes pure oxygen or air as
the oxidant and produces only water as the byproduct.3 For this
purpose, a nitroxyl radical with low toxicity and reversible
Therefore, chemically and thermally stable polymers, such
as poly(ether ketone), have been investigated as backbones to
immobilize the TEMPOꢀbased terminals. In addition,
hyperbranched structures have the potential to maximize the
catalytic activity of the TEMPOꢀbased terminals. Since
hyperbranched structures have a low degree of entanglement,
the endꢀgroups are exposed and sufficiently accessible for
reactants. The catalytic performance of sulfonic acid terminals
on hyperbranched poly(ether sulfone)22 and carboxylic acid
terminals on hyperbranched poly(ether ketone)23 has been
demonstrated.
redox
behavior,
2,2,6,6ꢀtetramethylpiperidineꢀ1ꢀoxyl
(TEMPO), has been studied for its catalytic ability.4,5 Several
studies utilized catalytic systems involving TEMPO and salts of
transition metals such as Cu6,7 and Fe8; these systems possessed
good catalytic performance under mild reaction conditions. In
addition, Hu and coworkers9 reported the transitionꢀmetalꢀfree
system,
TEMPO/Br2/NaNO2
and
derivatives,
as
This reports describes a novel catalyst, hyperbranched
environmentally friendly. In this system, TEMPO oxidizes the
alcohol, and the reduced form of TEMPO is reꢀoxidized by O2
via intermediation of the Br2/Brꢀ and NO2/NO redox
couples.10,11 However, this system has the disadvantages of Brꢀ
containing byproducts and contamination from the NOx
species.12 A nitric acidꢀassisted carbonꢀcatalyzed oxidation
system (NACOS) using carbonꢀbased materials as metalꢀfree
catalysts has also been reported13 and it was demonstrated that
TEMPO enhanced the oxidation.14 This oxidation protocol did
poly(ether
ketone)
functionalized
with
TEMPO
(TEMPO/HBPEK), for the aerobic oxidation of benzyl alcohol.
Since HBPEK is fairly soluble under the reaction conditions,
immobilization of TEMPO/HBPEK on carbon black
(TEMPO/HBPEK/CB)
or
polyimide
particles
(TEMPO/HBPEK/PI) has also been studied in order to utilize
this polymer as a heterogeneous catalyst.
not involve halogenꢀcontaining byproducts and resulted in good 2. Experimental
yield and selectivity for various alcohols under solventꢀfree or
minimalꢀsolvent conditions.
The high cost of TEMPO and the purity of the products
necessitate the development of heterogeneous TEMPOꢀbased
2.1 Materials synthesis
The synthetic
routes
to
TEMPO/HBPEK,
catalysts.
A typical strategy involved immobilization of
TEMPO/HBPEK/CB, and TEMPO/HBPEK/PI are shown in
Scheme 1. Preparation of a symmetrical AB2 monomer, 4,4’ꢀ
(mꢀphenylenedioxy)ꢀbis(benzenecarboxylic acid),24,25 and its
TEMPO onto a support such as mesoporous silica,15,16 silica
solꢀgels,17,18 crossꢀlinked polystyrene resins,19,20 or polyolefin
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polycondensation to form HBPEK23 have been reported dichloromethane and then added to the previous mixture. After
previously; this procedure was used with slight modifications.
stirring at 40°C for 24 h, the solvent was removed by
evaporation and the product washed with water and acetone.
Polyimide particles were synthesized by the precipitation
polymerization method.27 A solution of PMDA in acetone was
added to a solution of ODA in acetone (1:1 molecular ratio of
PMDA:ODA) all at once under vigorous stirring at 0°C. After 2
h, the solvent was evaporated and the product heated in a
vacuum at 220°C overnight. To immobilize HBPEK on
polyimide particles, HBPEK (300 mg), polyimide particles (60
mg), and PPMA (10 mL) were mixed with nitrobenzene (20
mL) and heated at 110°C under N2 for 24 h, followed by reflux
in THF for 24 h twice to remove polymer that was not
immobilized.
To immobilize TEMPO on HBPEK/PI, the HBPEK/PI
(921 mg, corresponding to 1.0 mmol of terminal COOH
groups) was mixed with 1ꢀ(3ꢀdimethylaminopropyl)ꢀ3ꢀ
ethylcarbodiimide (EDCI) (186 mg, 1.2 mmol) in 5 mL
dichloromethane and stirred for 30 min. The 4ꢀaminoꢀTEMPO
(188 mg, 1.1 mmol) and 4ꢀdimethylaminopyridine (DMAP) (13
mg, 0.1 mmol) were dissolved in 3 mL dichloromethane and
then added to the previous mixture, followed by stirring at 40°C
for 24 h. After reaction, the solvent was removed by
evaporation and the product washed with water and acetone.
To determine the inductive effect by the polymer
backbone on the catalytic activity of TEMPO, a model
compound, 4ꢀbenzylaminoꢀTEMPO, also was prepared from
benzoic acid (122 mg, 1.0 mmol), and purified using column
chromatography, with 1:3 CH2Cl2:ethyl acetate as the eluent to
yield an orange powder.
CN
OH
K2CO3
O
O2N
CN
+
DMF
120oC, 48h
90%
CN
OH
O
4,4'-(m-phenylenedioxy)-
bis benzenenitrile
resorcinol
4-nitrobenzonitrile
COOH
COOH
PPMA
84%
KOH
O
O
O
C
COOH
H2O/glycol
136oC, 4h
96%
O
O
4,4'-(m-phenylenedioxy)-
bis(benzenecarboxyl acid)
HBPEK
O
N
O
C
N
H
EDCI, DMAP
O
O
C
CH2Cl2
40 °C, 24h
93%
O
TEMPO/HBPEK
O
N
HOOC
O
C
Ketjen Black
EDCI, DMAP
N
O
H
CO
PPMA, DMF
110 °C, 24h
30%
CH2Cl2
40 °C, 24h
92%
O
CO
O
HBPEK/CB
O
TEMPO/HBPEK/CB
O
N
HOOC
CO
O
C
N
Polyimide
EDCI, DMAP
O
H
Nitrobenzene
PPMA, 110 °C, 24h
CH2Cl2
40 °C, 24h
92%
O
CO
13%
O
O
HBPEK/PI
TEMPO immobilized on polymer (1% crossꢀlinked with
divinylbenzene, TEMPO/PS) with a TEMPO loading of 1.00
mmol gꢀ1 was purchased from Aldrich and used as received.
TEMPO/HBPK/PI
Scheme 1. Synthesis of TEMPO/HBPEK,
HBPEK/TEMPO/CB, and TEMPO/HBPEK/PI
2.2 Measurements
To immobilize TEMPO on the HBPEK, the HBPEK (350
mg, 1.0 mmol) was mixed with 1ꢀ(3ꢀdimethylaminopropyl)ꢀ3ꢀ
ethylcarbodiimide (EDCI) (186 mg, 1.2 mmol) in 5 mL
dichloromethane and stirred for 30 min. The 4ꢀaminoꢀTEMPO
(188 mg, 1.1 mmol) and 4ꢀdimethylaminopyridine (DMAP) (13
mg, 0.1 mmol) were dissolved in 3 mL dichloromethane and
then added to the previous mixture, followed by stirring at 40°C
for 24 h. After reaction, the solvent was removed by
evaporation and the product washed with water and acetone.
To immobilize HBPEK on carbon black, HBPEK (300
mg) was dissolved in 20 mL DMF in the presence of Ketjen
Black (EC600JD, 60 mg) and PPMA26 (10 mL), stirred under
N2 at 110°C for 24 h, and then filtered. The product was stirred
in DMF at 100°C for 24 h, and then filtered. This washing
process was repeated to obtain HBPEK/CB.
To immobilize TEMPO on HBPEK/CB, the HBPEK/CB
(777 mg, corresponding to 1.0 mmol of terminal COOH
groups) was mixed with 1ꢀ(3ꢀdimethylaminopropyl)ꢀ3ꢀ
ethylcarbodiimide (EDCI) (186 mg, 1.2 mmol) in 5 mL
dichloromethane, followed by stirring for 30 min. The 4ꢀaminoꢀ
TEMPO (188 mg, 1.1 mmol) and 4ꢀdimethylaminopyridine
(DMAP) (13 mg, 0.1 mmol) were dissolved in 3 mL
Thermogravimetric analysis (TGA) was performed under
nitrogen using a SII TGA 6200 system at a heating rate of 10°C
minꢀ1. The CHN elemental analysis was performed using a
Perkin Elmer 2400ꢀII analyzer. Fourierꢀtransform infrared (FTꢀ
IR) spectroscopy was performed using a spectrophotometer
(Jasco, 6100) on KBr pellets. Scanning electron microscopy
(SEM) was performed using a Hitachi SU9000 microscope
operated at 6.0 kV. Gel permeation chromatography (GPC) was
performed using a Viscotek GPCꢀ1000 system equipped with a
TDA 302 triple detector and a TSKꢀGEL αꢀM column.
Dimethylformamide (DMF) with 0.05 M LiBr were used as the
eluent. The weight average molecular weight (Mw) was
calculated based on the lightꢀscattering data.
The ion exchange capacity (IEC) of HBPEK and
HBPEK/CB was determined by titration as follows. Sample
powder (30 mg) was stirred in 0.1 M NaOH (3 mL) overnight,
and then filtered. The filtrate was diluted to 10 mL with
deionized water, and titrated with 0.05 M HCl.
2.3 Catalytic reaction
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loading /
The catalytic performance of the materials was determined
using a Shibata Chemist Plaza CP100 multiꢀreactor system
equipped with 6ꢀmL reactors. Benzyl alcohol (10 mmol), nitric
acid (67%, 0.2 mmol), and the catalyst (TEMPO content:
0.08mmol) were stirred at 90°C for 2 h with an oxygen balloon.
The products were quantified using a Shimadzu GCMSꢀ
QP2010 Plus instrument equipped with a TCꢀFFAP column
(0.25 mmφ × 30 m). The conversion was calculated based on
the peak area ratio of benzyl alcohol against the internal
standard (naphthalene). The product yield was calculated based
on the peak area ratio of benzaldehyde against the internal
standard.
C
H
N
mmol gꢀ1
HBPEK
68.8
69.1
4.2
5.3
0.2
5.9
ꢀ
TEMPO/HBPEK
2.04
3.2 Synthesis of TEMPO/HBPEK/CB
HBPEK was immobilized on CB using the FriedelꢀCrafts
reaction. The IEC of HBPEK/CB was determined by titration to
be 1.5 mmol gꢀ1, whereas that of HBPEK was 2.5 mmol gꢀ1.
This IEC value corresponds to 60 wt% of the polymer loading
on CB, which represents a 30% yield of the grafted polymer. It
was found to be difficult to obtain FTꢀIR spectra for
HBPEK/CB and TEMPO/HBPEK/CB. The CHN elemental
analysis results for CB, HBPEK/CB, and TEMPO/HBPEK/CB
are shown in Table 2. Both the CB and HBPEK contained a
low level of nitrogen. The TEMPO loading was 1.32 mmol gꢀ1.
Figure 2 shows SEM images of carbon black and HBPEK/CB.
The surfaces of the HBPEK/CB and carbon black are clearly
different. Compared to carbon black, HBPEK/CB had a smooth
surface, probably formed by the polymer layer covering the
rough surface of the carbon black. These experimental results
suggest that HBPEK was successfully grafted onto carbon
black, and its terminals were converted to TEMPO units.
For catalyst recycling, the reaction mixture was diluted to
40 mL with acetone, filtered, and washed with acetone, and
then the residue used for the next cycle after drying and
weighing.
3. Results and discussion
3.1 Synthesis of TEMPO/HBPEK
The synthesized HBPEK had a weightꢀaverage molecular
weight (Mw) of 74000, as measured by GPC, and an ion
exchange capacity (IEC) of 2.5 mmol gꢀ1 as calculated by
titration. The FTꢀIR spectra of HBPEK and TEMPO/HBPEK
are shown in Figure 1. After loading TEMPO, the OH broad
band (2500ꢀ3000 cmꢀ1) decreased and the CH3 stretching band
(2900ꢀ3000 cmꢀ1) appeared, which suggests a decrease in the
number of terminal carboxylic acid groups and the inclusion of
TEMPO. The CHN elemental analysis results for HBPEK and
TEMPO/HBPEK are shown in Table 1. The TEMPO loading
rate was calculated from the nitrogen content of the catalyst.
The TEMPO/HBPEK had a TEMPO loading of more than 2
mmol gꢀ1.
Table 2. CHN elemental analysis of CB, HBPEK/CB, and
TEMPO/HBPEK/CB
Elemental analysis wt%
TEMPO
loading /
mmol gꢀ1
Catalyst
C
H
N
CB
90.2
86.3
81.1
0.3
1.5
2.5
0.3
0.2
3.9
ꢀ
HBPEK/CB
HBPEK
TEMPO/HBPEK/CB
1.32
TEMPO/HBPEK
C=O
CH3 stretching
Fig. 2. SEM images of (a) carbon black and (b) HBPEK/CB.
4000
3000
2000
1000
3.3 Synthesis of TEMPO/HBPEK/PI
Wavenumber / cm-1
Fig. 1. FTꢀIR spectra of HBPEK and TEMPO/HBPEK
The CHN elemental analysis for CB, HBPEK/CB, and
TEMPO/HBPEK/CB are shown in Table 3. A comparison of the
nitrogen content in PI and in HBPE/PI indicated that the HBPEK
loading rate was 40 wt%, which corresponds to a 13% yield of the
grafted polymer. The TEMPO loading of TEMPO/HBPEK/PI was
0.96 mmol gꢀ1, calculated by comparing the nitrogen content before
and after loading TEMPO. The FTꢀIR spectra of PI, HBPEK/PI, and
TEMPO/HBPEK/PI are shown in Figure 3. Compared to PI, an OH
broad band (2500ꢀ3000 cmꢀ1) was observed in the spectra of
Table 1. CHN elemental analysis results for HBPEK and
TEMPO/HBPEK
Catalyst
Elemental analysis wt%
TEMPO
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HBPEK/PI. For TEMPO/HBPEK/PI, a CH3 stretching band (2900ꢀ showed a sharp weight loss beginning at 550°C. The initial
3000 cmꢀ1) appeared, which suggests the presence of TEMPO. weight losses were likely due to decomposition of the terminal
Figure 4 shows SEM images of polyimide particles and HBPEK/PI. functional groups, resulting in a weight loss near 400ꢀ600°C
The surfaces of HBPEK/PI and polyimide particles were different. due to the backbone of poly(ether ketone). Because the TEMPO
The polyimide particles had a diameter of 150ꢀ200 nm with a group is heavier than a carboxylic acid group, the weight loss of
smooth surface, while the surface of HBPEK/PI appeared rough. TEMPO/HBPEK was more rapid than that of HBPEK during
This difference suggests the successful grafting of HBPEK onto the initial stage.
polyimide particles.
HBPEK
TEMPO/HBPEK
TEMPO/HBPEK/CB
TEMPO/HBPEK/PI
100
Table 3. CHN elemental analysis result of PI, HBPEK/PI, and
TEMPO/HBPEK/PI
90
80
70
60
50
40
30
Elemental analysis wt%
TEMPO
loading /
mmol gꢀ1
Catalyst
C
H
N
PI
65.5
67.2
66.5
1.9
2.9
4.0
6.5
4.0
6.7
ꢀ
ꢀ
HBPEK/PI
TEMPO/HBPEK/PI
0.96
200
400
600
800
Temperature(oC)
PI
Fig. 5. TG curves for the catalysts HBPEK, TEMPO/HBPEK,
TEMPO/HBPEK/CB, and TEMPO/HBPEK/PI
3.5 Catalytic performance
HBPEK/PI
The prepared catalysts were tested for activity in the aerobic
oxidation of benzyl alcohol. Table 4 compares the performance
of several TEMPOꢀbased catalysts. The turnover number
(TON) of the TEMPO unit was calculated from the yield of
benzaldehyde. A control test without catalyst resulted in a low
yield, while HBPEK showed slight catalytic activity.
Commercial TEMPO, which is a homogeneous system, showed
the highest activity with a TON of 60. 4ꢀBenzylaminoꢀTEMPO
showed similar catalytic activity (TON of 56), suggesting little
influence of the inductive effect by aromatic amide backbone
on the catalytic activity of the TEMPO unit. Another control
experiment with a mixture of TEMPO and HBPEK yielded a
result similar to that with TEMPO, suggesting that the presence
of HBPEK does not affect the catalytic activity of the TEMPO
unit. The catalytic activity of TEMPO/HBPEK, which is a
homogenous system, was slightly lower, likely due to the lower
mobility of the TEMPO terminal units on HBPEK compared to
those of molecular TEMPO. The TEMPO/PS, which is a
commercial heterogeneous catalyst, did not possess good
catalytic activity. In contrast, two synthesized heterogeneous
catalysts, TEMPO/HBPEK/CB and TEMPO/HBPEK/PI,
possessed much stronger catalytic activity than the control test
and TEMPO/PS, although the catalytic activities were still less
than those of the homogeneous systems. The performance of
TEMPO/HBPEK/CB was slightly better than that of
TEMPO/HBPEK/PI, perhaps due to synergy between TEMPO
and CB. Kuang et al. proposed that CB absorbs and activates
HNO3 in the nitric acidꢀassisted carbonꢀcatalyzed oxidation
system (NACOS).14 Note that TEMPO/HBPEK/CB and
TEMPO/HBPEK/PI showed much better catalytic activity than
TEMPO/PS, likely due to high reactivity of the hyperbranched
polymer terminals, which have good affinity toward the
reactant phase.
TEMPO/HBPEK/PI
CH3 stretching
3000
4000
2000
1000
Wavenumber / cm-1
Fig. 3. FT
-
IR spectra of PI, HBPEK/PI, and
TEMPO/HBPEK/PI
Fig. 4. SEM images of (a) polyimide particles and (b)
HBPEK/PI
3.4 Thermal stability
The thermal stability of HBPEK, TEMPO/HBPEK,
TEMPO/HBPEK/CB, and TEMPO/HBPEK/PI was examined
using TGA under a nitrogen atmosphere (Figure 5). The weight
loss of those materials began at 150°C, and was maintained up
to 600°C. The weight loss of TEMPO/HBPEK occurred most
rapidly in the first stage. Meanwhile, TEMPO/HBPEK/PI
4 | J. Name., 2012, 00, 1-3
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Table 4. Catalytic performance of various TEMPOꢀbased catalystsa
Entry
Catalyst
TEMPO unit / mmol Yield / % Conversion / % TON
1
2
3
4
5
6
7
8
9
Blank
0
1.0
2.0
ꢀ
HBPEK
0
5.4
5.7
ꢀ
TEMPO
0.08
0.08
0.08
0.08
0.08
0.08
0.08
47.7
32.1
47.8
1.23
36.7
22.9
18.4
48.6
31.9
49.8
4.15
37.5
26.7
17.4
60
56
60
<1
46
27
22
4ꢀBenzylaminoꢀTEMPO
HBPEK + TEMPO
TEMPO/PS
TEMPO/HBPEK
TEMPO/HBPEK/CB
TEMPO/HBPEK/PI
a
Benzyl alcohol (10 mmol), nitric acid (67%, 0.2 mmol) and catalyst (TEMPO content: 0.08 mmol), 90°C, 2 h, with an oxygen
balloon.
The collected yield of TEMPO/HBPEK/CB was excellent
even after the sixth run. The yield of TEMPO/HBPEK/CB
gradually decreased in the first 3 runs; however, it remained
steady after that.
3.6 Recycling tests
Recyclability of TEMPO/HBPEK, TEMPO/HBPEK/CB,
TEMPO/HBPEK/PI, and TEMPO/PS was tested by repeating
the catalytic reactions. The conversion of each run was
controlled to less than 50% to avoid TEMPO unit overꢀdose.
Recycling of the catalyst of TEMPO/HBPEK was attempted by
precipitation into acetone because HBPEK is insoluble in
acetone. The other catalysts were collected by filtration and
used for the next run after washing with acetone. Figure 6
shows catalyst yields after each run of the recycling tests, and
Figure 7 shows the benzaldehyde yield of each run.
40
TEMPO/HBPEK/PI
TEMPO/HBPEK/CB
TEMPO/HBPEK
TEMPO/PS
30
20
10
0
100
80
1
2
3
4
5
6
TEMPO/HBPEK/PI
60
Run
TEMPO/HBPEK/CB
TEMPO/HBPEK
TEMPO/PS
Fig. 7. Yield of benzaldehyde with the fresh catalyst (1st run)
and the recycled catalysts (2ꢀ6th run)
40
The collected yield of TEMPO/HBPEK/PI gradually
decreased throughout the 6 runs, similar to that of TEMPO/PS.
However, this decrease was not due to an inherent instability of
TEMPO/HBEPK/PI, but from collection loss during the
experimental procedure because this catalyst powder tended to
stick to glassware, making it difficult to collect. The yield of
20
0
1
2
3
4
5
6
Run
TEMPO/HBPEK/PI showed
TEMPO/HBPEK/CB, but the degradation was not significant;
therefore, the yield after
TEMPO/HBEPK/PI.
a trend similar to that of
Fig. 6. Collected yield after runs 1 through 6 against initial
amount
3
runs was better with
As shown in Figure 6, TEMPO/HBPEK was difficult to
collect at a high yield. The catalytic activity of the recycled
TEMPO/HBPEK in the second run was still high; however, it
decreased significantly in the third run. These experimental
results suggest that TEMPO/HBPEK, as a heterogeneous
catalyst or an easily recyclable homogeneous catalyst, is
difficult to recycle.
Figure
8 shows SEM images of fresh and recycled
TEMPO/HBEPK/CB and TEMPO/HBEPK/PI after the sixth
run. The surface of recycled TEMPO/HBEPK/CB (Fig. 8c)
appeared smooth with a cover layer, similar to that of
TEMPO/HBPEK/CB (Fig. 8a). The surface of recycled
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TEMPO/HBEPK/PI (Fig. 8d) was rough, similar to that of
TEMPO/HBPEK/PI (Fig. 8b). These results indicate that the
catalyst did not change after the recycling reaction.
4
5
6
7
8
9
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Fig. 8. SEM images of (a) fresh TEMPO/HBPEK/CB, (b) fresh
TEMPO/HBPEK/PI, (c) recycled TEMPO/HBPEK/CB, and (d)
recycled TEMPO/HBPEK/PI after the sixth run
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TEMPO
materials,
TEMPO/HBPEK/CB
and
TEMPO/HBPEK/PI exhibit good durability.
17
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4. Conclusions
18
19
A
novel hyperbranched aromatic poly(ether ketone)
functionalized with TEMPO was synthesized as a catalyst for
aerobic oxidation of benzyl alcohol. The TEMPO/HBPEK
possessed good catalytic activity in the selective oxidation, but
could not be collected after the reaction. After immobilizing it
onto carbon black and polyimide particles, it formed a
heterogeneous system and became recyclable. These
heterogeneous catalysts showed much better catalytic activity
than the commercially available heterogeneous catalyst,
TEMPO immobilized on polystyrene
20
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Acknowledgements
This study was supported by JSPS KAKENHI (26870183). The
SEM analysis was performed in the Center for Advanced
Materials Analysis at the Tokyo Institute of Technology. M.K.
was supported by a Visiting Professorship for Senior
International Scientists from the Chinese Academy of Science.
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Notes and references
a
Department of Organic and Polymeric Materials, Graduate School of
Science and Engineering, Tokyo Institute of Technology, 2ꢀ12ꢀ1 S8ꢀ26
Ookayama, Meguroꢀku, Tokyo 152ꢀ8552, Japan. Tel: +81ꢀ3ꢀ5734ꢀ2429.
Eꢀmail: nabae.y.aa@m.titech.ac.jp
1
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Compounds, Academic Press, New York, 1981.
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6 | J. Name., 2012, 00, 1-3
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