Poly(4-vinylpyridine-co-divinylbenzene) supported iron(III) catalyst for selective oxidation of toluene to benzoic acid with H2O2

Article abstract of DOI:10.1016/j.tet.2012.09.004

Poly(4-vinylpyridine-co-divinylbenzene) supported iron(III) catalysts were developed for the selective oxidation of toluene to benzoic acid in the presence of H₂O₂. The influence of the DVB content on the capacity of immobilized Fe(I

Full text of DOI:10.1016/j.tet.2012.09.004

Tetrahedron 68 (2012) 9423e9428
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Poly(4-vinylpyridine-co-divinylbenzene) supported iron(III) catalyst for selective
oxidation of toluene to benzoic acid with H2O2
,
,
,b,
*
Weeranuch Karuehanon a b, Chinnapat Sirathanyarote a b, Mookda Pattarawarapan a
a Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand
b Center of Excellence for Innovation in Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 June 2012
Received in revised form 15 August 2012
Accepted 3 September 2012
Available online 10 September 2012
Poly(4-vinylpyridine-co-divinylbenzene) supported iron(III) catalysts were developed for the selective
oxidation of toluene to benzoic acid in the presence of H2O2. The influence of the DVB content on the
capacity of immobilized Fe(III) and on the catalytic activities of the polymeric complexes was in-
vestigated. The extent of Fe(III) uptake by the copolymers varied slightly with the concentration of DVB.
The catalytic activities generally increase with increasing degree of crosslinker from 2 to 10% and de-
crease further with increasing the DVB content. Under the optimal conditions (80 ꢀC, 6 h), the catalyst
containing 10% DVB was found to be highly efficient in conversion of toluene to benzoic acid with 90%
conversion and 96% selectivity.
Keywords:
Toluene oxidation
Heterogeneous catalyst
4-Vinylpyridine
Hydrogen peroxide
Iron(III)
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
The copper(II) chloride with 6-hydroxy-pyrrolo[3,4-b]pyrazine-
5,7-dione system could convert toluene to benzoic acid with 70.9%
The catalytic oxidation of hydrocarbons has been a topic of in-
terest in synthetic, industrial, and biological chemistry. Oxidation
of toluene to benzoic acid, for example, represents a highly signif-
icant reaction since benzoic acid is widely used in medicine, in dye,
plasticizer, and as a food preservative.1,2 It is also a key intermediate
in the preparation of fine chemicals. Industrially, benzoic acid is
produced from catalytic oxidation of toluene with molecular oxy-
gen using a cobalt(II) acetate or bromide promoter in acetic acid
under extreme reaction conditions (w200 ꢀC, 10 atm).3 However,
there are several drawbacks of this process such as low energy
efficiencies, low selectivity, and the generation of environmentally
hazardous waste.
Recently, there has been a considerable effort focusing on the
development of new catalysts for the selective oxidation of toluene.
Both homogeneous and heterogeneous catalysts based on transi-
tion metal complexes have so far been reported. For example, the
combination of MnO2 and N-hydroxyphthalimide was used as
a catalyst in aerobic oxidation of toluene to yield benzoic acid with
94% conversion and 98% selectivity at 110 ꢀC, 0.3 MPa.4
conversion and 93.5% selectivity at 90 ꢀC.5 Pt/ZrO2 oxidation of
toluene by molecular oxygen in liquid phase-solvent free condi-
tions (90 ꢀC, 101 kPa) produced benzoic acid with up to 60% se-
lectivity at 40% conversion within 3 h.6
In order to develop sustainable, inexpensive, and environmen-
tally friendly oxidation reactions, several bioinspired catalytic sys-
tems have also been investigated. Among those in particular are
biomimetic homogeneous catalytic systems based on iron salts, of-
ten complexed with nitrogen-containing ligands such as porphyrins,
phthalocyanines, and pyridine derivatives.7e13 These catalysts have
been applied in the oxidation of aliphatic and/or aromatic hydro-
carbons using either oxygen or hydrogen peroxide as an oxidant.
Nevertheless, many of these systems give low conversion and low
product selectivity. Difficulty in the catalyst preparation, recovery,
and reuse also further limit such systems from practical use.
To circumvent the problems related with homogeneous catalytic
systems, the catalysts can be anchored on the insoluble solid sup-
ports to make it heterogeneous.14e16 Polymeric materials are often
used for this purpose since they are typically non-toxic, non-volatile,
insoluble, and recyclable. Often metal ions are supported on the
surface of polymer using chelating ligands or using monomer con-
taining coordination sites in order to prevent leaching of the metals
from the polymer catalysts.17 Catalytic activity and catalyst stability
could be enhanced as a consequence of active site isolation.18
* Corresponding author. Department of Chemistry, Faculty of Science, Chiang Mai
University, Chiang Mai 50200, Thailand. Tel.: þ66 5394 3341; fax: þ66 5389 2277;
e-mail address: mookdap55@gmail.com (M. Pattarawarapan).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.09.004

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W. Karuehanon et al. / Tetrahedron 68 (2012) 9423e9428
So far, only precedent exists on hydrocarbon oxidations with
copolymers determined by BET analysis was also varied according
to the DVB content. The highest surface area was obtained with
PVPDVB10% containing 10% DVB. Lower surface area observed at 2%
DVB content is presumably attributed to the absence of porosity at
dry state in gel-type copolymer while that at 50% DVB is un-
doubtedly due to the highly rigid cross-linking polymeric network.
The degree of iron ions introduced into the polymer matrices
should be directly dependent on the relative content of the func-
tional groups in the polymers. It is thus expected that copolymer
with lower DVB content should exhibit higher loading of Fe(III) due
to their high ligand capacity. Surprisingly, according to Table 1, the
percentage of Fe(III) anchored on the polymeric complexes varied
slightly with the copolymer type and correlation with the DVB
content cannot be observed. The degree of swelling and fold
structure of the polymeric network may lead to various co-
ordination modes in complex formation, which in turn affect on the
degree of iron uptake.
The catalytic activities of the synthesized polymer metal com-
plexes were screened in the oxidation of toluene using H2O2 as an
oxidant in acetonitrile. Excess amount of H2O2 was used in this
study (1:9.4 mole ratio of toluene/H2O2) due to the possibility of its
decomposition in the presence of Fe(II/III) salts. Acetonitrile was
used as the solvent since it has been shown to provide high cata-
lytic activity in other iron catalytic systems due to a comparatively
good solubility power for both the organic substrate and the
aqueous H2O2.16,22,23 All oxidation reactions were carried out at
80 ꢀC for 1 and 6 h. It was found that the catalytic oxidation reaction
involved both the benzylic oxidation and the benzene ring hy-
droxylation, which yielded benzoic acid (PhCOOH), benzaldehyde
(PhCHO), benzyl alcohol (PhCH2OH), o-cresol, m-cresol, and p-
cresol as the oxidative products (Scheme 1). Nevertheless, in all
cases, benzoic acid was obtained as the predominant product.
The conversion of toluene and selectivity toward benzoic acid
formation are summarized in Table 2. Generally, the catalytic ac-
tivities of the Fe(III)ecopolymer complexes increase with in-
creasing the degree of DVB cross-linking from 2 to 10% and decrease
further with increasing the DVB content. When the oxidation re-
action was performed at 80 ꢀC for 1 h, the toluene conversions were
in the range between 13.3 and 32.6% while the selectivity to ben-
zoic acid was relatively high in all cases (72.8e88.1%). Increasing
the reaction time from 1 to 6 h resulted in enhancement in both
conversion (73.0e89.7%) and selectivity toward benzoic acid
(88.3e91.2%).
polymer supported iron catalysts.9,19,20 For example, poly(4-
vinylpyridine-co-divinylbenzene), 6% crosslinked iron salts com-
plexes have been used as co-catalysts with palladium in cyclo-
hexane oxidation in the presence of molecular oxygen and
hydrogen.19 Cyclohexanol and cyclohexanone were obtained in
2.5 mol % with the polymer supported FeCl2. In another work,
metalecopolymer complexes of poly-4-vinylpyridine grafted on
polymer films were used as catalysts in the oxidation of cyclo-
hexene with tert-butylhydroperoxide.20 With an Fe(III)-containing
complex, cyclohexene oxide and the side-product, 2-cyclohexene-
1-one, were produced in 41.6% and 54.2% yields, respectively.
In search for a simple and environmental friendly catalytic
system capable of catalyzing toluene oxidation efficiently, herein,
poly(4-vinylpyridine-co-divinylbenzene) copolymers containing
various amount of divinylbenzene (DVB) were synthesized and
used as supports to form polymer complexes with iron(III). The
catalytic activities of these complexes in the oxidation of toluene
with hydrogen peroxide (H2O2) were investigated. The best can-
didate complex was selected for further characterization and ap-
plied in the reaction optimization to improve conversion of toluene
and enhance the product selectivity. The catalyst reusability was
also investigated.
2. Results and discussion
In a preliminary study, various poly(4-vinylpyridine-co-divinyl-
benzene) copolymers containing different amounts of DVB cross-
linker, PVPDVB2e50%, were synthesized to be used as the polymer
supports for complexation with iron(III). The pyridine moiety in
4-vinylpyridine can act as nitrogen-donor ligand to bind iron species,
while DVB provides a porous structure in the polymeric network.
Iron(III) chloride was used as an iron(III) source to form complex
with the pyridine moiety in the synthesized copolymers. Since
iron(III) has the ability to coordinate from 3 to 8 ligands, depending
on the folded structure of the copolymers, complex formation in-
volving more than one pyridine unit per iron ion is likely to occur.
The synthesis parameters and physicochemical properties of the
synthesized copolymers were summarized in Table 1. The nitrogen
contents of the copolymers determined by elemental analysis were
in agreement with the theoretical values calculated from the feed
monomer contents. Swelling in both methanol and acetonitrile
decreased along with increasing the DVB content. A high concen-
tration of DVB is commonly known to create a more rigid polymeric
network having a lesser degree of swelling. The surface area of the
Since the loading of Fe(III) on the polymer complexes was al-
most invariable according to the polymer type, the low conversion
Table 1
Copolymers characteristics and iron content of the Fe(III)ecopolymer complexes
Fe(III)ecopolymer complex
Polymer characterization
Fe content (mmol/g)
Yield (%)
Na (%)
Swelling (%)
Surface areac (m2/g)
MeOH
CH3CN
Fe(III)ePVPDVB2%
Fe(III)ePVPDVB6%
Fe(III)ePVPDVB10%
Fe(III)ePVPDVB25%
Fe(III)ePVPDVB50%
75
75
96
73
97
12.4 [13.0]b
11.5 [12.4]b
10.7 [11.8]b
10.2 [10.1]b
8.4 [8.2]b
150
110
90
60
50
150
110
100
60
8.1
13.2
14.4
13.4
4.4
0.55
0.54
0.41
0.52
0.46
50
a
From elemental analysis (CHN).
[Theoretical value].
Determined by BET method.
b
c

W. Karuehanon et al. / Tetrahedron 68 (2012) 9423e9428
9425
CO2H
CHO
CH2OH
CH3
CH3
35% H2O2
OH
cresols
+
+
+
Fe(III)-PVPDVB (cat), CH3CN
Toluene
PhCOOH
PhCHO
PhCH2OH
Scheme 1. Catalytic oxidation of toluene with hydrogen peroxide.
Table 2
Toluene oxidation with the Fe(III)ecopolymer complexesa
Entry
Fe(III)ecopolymer complex
Reaction time
1 h
6 h
Conversion (mol %)
Selectivity to PhCOOH (mol %)
Conversion (mol %)
Selectivity to PhCOOH (mol %)
1
2
3
4
5
Fe(III)ePVPDVB2%
Fe(III)ePVPDVB6%
Fe(III)ePVPDVB10%
Fe(III)ePVPDVB25%
Fe(III)ePVPDVB50%
20.1
24.1
32.6
30.4
13.3
81.4
86.9
88.1
87.0
72.8
73.0
78.8
89.7
77.0
77.9
91.0
90.2
91.2
89.3
88.3
a
All reactions were carried out with toluene (1.46 mmol), 35% H2O2 (13.7 mmol) using 10 mg of the Fe(III)ecopolymer complex in CH3CN at 80 ꢀC.
observed when using the copolymer complexes with low DVB
content (entries 1 and 2) could be attributed to the saturation in the
Fe(III) coordination sphere, due to the high pyridyl/Fe(III) ratio and
highly flexible fold structures of the polymer complex, thus pre-
venting the coordination of hydrogen peroxide.20,24,25 On the other
hand, the low conversion of toluene when using the complexes
with higher DVB content (entries 4 and 5) could be associated with
the low surface area and low degree of swelling of the polymer
supports, which hinder mass transfer process in the heterogeneous
catalytic system.
vibrations of the
y(]CH) groups, while the d(CeC]C) vibration at
562 cmꢁ1 was also observed. For the iron(III)epolymer complex,
the corresponding y(C]N), y(C]C), and y(CeN) bands as well as
a band at 993 cmꢁ1 were shifted toward longer wavelength. These
shifts indicated the interaction of the nitrogen atom in the pyridyl
moiety with iron(III) ion.18
Since the Fe(III) is a very acidic cation with hydrolytic properties
above pH 2, the production of iron(III) hydroxide, Fe(OH)3, during
the complexation is therefore possible and can lead to the pre-
cipitation of Fe(OH)3 on polymer supports. To further confirm that
iron(III) was complexed with the nitrogen of the pyridyl moiety of
the support, the Fe(III)ePVPDVB10% catalyst was further in-
vestigated by FT-Raman spectroscopy. As shown in Fig. 2, no peaks
at 303, 387, and 698 cmꢁ1 (characteristic of Fe(OH)3) were observed
in the spectrum of the prepared catalyst, indicating that the pre-
cipitation of Fe(OH)3 on polymer support was not occurred.29 The
assignment of Raman spectrum was listed in Table 3.27,28
Unfortunately, at this point, it was unable to characterize the
exact structure of the catalyst due to its heterogeneity, though it
was believed that various coordination modes of Fe(III)eligand
complex may take place. From the FT-Raman result, since Fe(OH)3
was not observed in the ironepolymer complex, it was assumed
that Fe(OH)3 was not present as the active catalyst species. How-
ever, the presence of Fe(Py)Cl stretching at 330 cmꢁ1 further in-
dicated coordination complex between Fe(III) and the nitrogen
atom in the pyridyl moiety of the support.
The best conversion and selectivity were observed using the
Fe(III)ePVPDVB10% catalyst (entry 3). Though it should be noted
that the amount of Fe(III) incorporated in this catalyst was signifi-
cantly less than the estimated loading presuming that iron(III)
forms eight maximum coordinate bonds with pyridines
(0.41 mmol/g vs 0.95 mmol/g). This data indicated that some pyr-
idyl units may have limit accessibility, while the fold structures of
the polymeric chains can also affect on the degree of iron uptake.
Complex formation in the Fe(III)ePVPDVB10% catalyst was fur-
ther investigated by FTIR. The IR spectrum of PVPDVB10% (Fig. 1)
showed the characteristic absorption bands of pyridine ring at
1595, 1555, and 1413 cmꢁ1 attributed to
(CeN), respectively.26 A band at 993e819 cmꢁ1 is the out-of-plane
y(C]N), y(C]C), and
y
Fig. 1. FTIR spectra of (a) PVPDVB10% and (b) Fe(III)ePVPDVB10%
.
Fig. 2. Raman spectrum of Fe(III)ePVPDVB10%.

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W. Karuehanon et al. / Tetrahedron 68 (2012) 9423e9428
moisture. The polymer decomposition started at ca. 350 ꢀC and
virtually completed at 450 ꢀC for the support and at 500 ꢀC for the
Fe(III)ePVPDVB10% complex. The TGA results suggested that both
materials should be thermally stable under the applied reaction
conditions.
To optimize the reaction conditions, various parameters that
influence the outcome of toluene oxidation including reaction
temperature, the amount of the catalyst, and reaction time were
further investigated using the Fe(III)ePVPDVB10% complex as the
catalyst. The effect of temperature on the oxidation of toluene was
studied over the reaction temperature range from 25 to 80 ꢀC while
keeping other parameters constant. According to Fig. 4, at a re-
action temperature below 60 ꢀC, a slight increase in the toluene
conversion along with the selectivity toward benzoic acid was
observed with a sharp enhancement from 60 to 80 ꢀC. At elevated
temperature, the diffusion rate of the H2O2 and toluene molecules
to the catalytic sites of the polymeric complex is accelerated thus
causes the reaction to proceed at a faster rate.4
Table 3
Raman spectrum assignment of the Fe(III)ePVPDVB10% complex
Assignment of the pyridyl moiety and Fe(Py)Cl bond
Frequency (cmꢁ1
)
Ring stretching
Ring stretching
1631
1448
1201
1064
1005
648
In-plane CH bending
In-plane CH bending
Assym. ring breathing
In-plane ring deformation
Fe(Py)Cl stretching
330
The thermal stability of the Fe(III)ePVPDVB10% complex relative
to the corresponding copolymer support was examined using the
TGA technique, over the temperature range of 50e600 ꢀC. From the
TGA curves (Fig. 3), both the polymers degraded mainly in two
stages. The initial weight loss was attributed to the loss of adsorbed
The influence of the amount of the catalyst on the oxidation re-
action was then investigated at 80 ꢀC after 6 h over the catalyst
quantity range of 1e200 mg (0.03e5.62 mol %). No toluene oxida-
tion was observed when using 1 mg of the catalyst (Fig. 5). When
increasing the catalyst quantity from 1 to 10 mg, toluene oxidation,
as well as selectivity toward benzoic acid formation, increased sig-
nificantly and reached the highest values in this range. However,
both the conversion and the selectivity reduced considerably with
further addition of the catalyst. This observation could be due to low
capability of mass transfer in the reaction and the non-availability of
catalytic sites when using excessive amounts of the catalyst.16,30,31
Effect of the reaction time on the efficiency of the reaction was
further studied using 10 mg of the Fe(III)ePVPDVB10% catalyst at
80 ꢀC. As shown in Fig. 6, the degree of toluene oxidation increases
slightly at the beginning then increases rapidly from 4 to 6 h. After
6 h, no significant change in the conversion as well as the selectivity
toward benzoic acid was observed indicating the reaction was
completed within 6 h.
Fig. 3. TGA curves for PVPDVB10% and Fe(III)ePVPDVB10% complex.
It is notable that in control experiments where the reactions
were carried out under the optimal conditions (80 ꢀC at 6 h with
Fig. 4. Influence of reaction temperature on (a) the reaction conversion and (b) product selectivity after 6 h of reaction time using 10 mg (0.28 mol %) of Fe(III)ePVPDVB10% catalyst.
Fig. 5. Influence of the amount of the Fe(III)ePVPDVB10% catalyst on (a) the reaction conversion and (b) product selectivity after 6 h of reaction time at 80 ꢀC.

W. Karuehanon et al. / Tetrahedron 68 (2012) 9423e9428
9427
Fig. 6. Influence of reaction time on (a) the reaction conversion and (b) product selectivity at reaction temperature of 80 ꢀC using 10 mg of the Fe(III)ePVPDVB10% catalyst.
10 mg of the catalyst) but in the absence of the supported catalyst
or in the presence of free PVPDVB, no toluene oxidation was ob-
served. The oxygen released in the H2O2 decomposition should also
play no role in the toluene oxidation since no conversion was ob-
served when performing the reaction under similar conditions but
using atmospheric oxygen as oxidant. When FeCl3$6H2O was added
as a catalyst, less than 58% toluene conversion with up to 92% se-
lectivity toward benzoic acid was observed indicating higher cat-
alytic activity of the Fe(III)ePVPDVB10% complex than a simple salt.
The catalyst turnover number calculated from the mole ratio of
total products/catalyst was 319.
plausibly the coordination mode in the iron(III)ecopolymer com-
plexes. Using the catalyst containing 10% DVB, toluene can be con-
verted to benzoic acid with up to 96% selectivity and 90% conversion
within 6 h at 80 ꢀC. Since this heterogeneous catalyst can be simply
removed by filtration then recovered and reused, it also enhances
product purity, environmental friendly, and promises economic.
4. Experimental
4.1. Material and methods
According to the previous reports on the other ironenonheme
complexes catalyzed hydrocarbons oxidation,23,32,33 the reaction
between the catalyst and H2O2 is likely to start with the formation
of an Fe(III)ehydroperoxo species (LFeIIIOOH). Upon decomposition
by OeO bond heterolysis gives rise to a high-valent iron-oxo spe-
cies (LFeV]O), both of which could be involved in substrate oxi-
dation in a highly selective manner. However, homolytic cleavage of
All reagents were purchased from Fluka and Aldrich and were
used without further purification. Acetonitrile was analytical grade
and was purified prior use. The iron content of the polymer complex
was determined using atomic absorption spectrophotometer (Shi-
madzu, AA-670). Elemental analysis was performed using CHNS/O
ANALYSER, Perkin Elmer PE2400 Series II. Infrared (IR) spectra were
recorded in the range of 4000e400 cmꢁ1on a Shimadzu FT-IR 8900
spectrometer in KBr pellet. Raman spectra were recorded on FT-IR
Raman Spectrometer, Spectrum GX, Perkin Elmer, USA. BET surface
area measurement was performed by N2 adsorption on Autosorb-1-
MP (Quantachrome Corporation, Boynton Beach, Florida, USA).
Thermal gravimetric analysis (TGA) was carried out using a Perkin
Elmer Model TG-7 Instrument. TG sample was heated in air in the
range of 50e600 ꢀC at 20 ꢀC/min. Gas chromatographic (GC) mea-
surements were carried out on Agilent GC-6890A (G2163A), equip-
ped with a capillary column (column: innowax; column length:
30 m; column temperature: 40e260/270 ꢀC).
III
IV
ꢂ
LFe OOH will generate LFe ]O along with a highly reactive OH
radical, which are responsible for nonselective oxidation.
Interestingly, in all cases, selectivity toward the benzylic oxi-
dation was always accompanied by high toluene conversion
whereas ring hydroxylation products increased at low toluene
conversion. This observation suggested that the selectivity outcome
of Fe(III)ePVPDVB10% catalyzed oxidation of toluene could be gov-
erned by more than one of the oxidizing species described above
depending on the reaction conditions. In addition, ꢂOH radical
generated from H2O2 decomposition could also be able to oxidize
toluene non-selectively, especially when performing the reaction
under a short period of time at low temperature.
4.2. Preparation and characterization of the polymer support
The recyclability of Fe(III)ePVPDVB10% in toluene oxidation was
also investigated under the optimal reaction conditions. Pre-
liminary study showed a decrease in toluene conversion by 11%
after the first cycle, which could be due to leaching of iron ions from
the polymer support. It is possible that the reaction products such
as cresols and benzoic acid can act as a catalyst deactivator by
competing coordination against the pyridyl moiety of the co-
polymer and cause leaching of the iron ions. After each cycle, the
used catalyst was regenerated by treating the used material with
a saturated methanolic solution of FeCl3$6H2O before the sub-
sequent runs. With the pretreatment step, there was no significant
change in the conversion and selectivity after five consecutive re-
cycles. High substrate conversions (74e90%) and excellent benzoic
acid selectivity (88e96%) can be obtained.
Poly(4-vinylpyridine-co-divinylbenzene) crosslinked with vari-
ous mol % of DVB, PVPDVB, was synthesized by suspension co-
polymerization according to the reported procedure.21 The reaction
was carried out in 250 mL three-necked round bottom flask fitted
with reflux condenser. A solution of polyvinyl alcohol (PVA) (150 mg)
in water (50 mL) was stirred at 50 ꢀC under N2 for 15 min. Whilst the
mixture of 4-vinylpyridine (1.03 g, 10 mmol), divinylbenzene (as in-
dicated in Table 1), and benzoyl peroxide (0.025 g, 0.1 mmol) in test
tube was also bubbled by N2 for 15 min before adding to the PVA
solutionunder N2 atmosphere. The reaction mixturewas thenpurged
by N2 gas for 10 min and heated up to 85 ꢀC. After stirring for 16 h, the
obtained polymer was poured into 50 mL of water, filtered off, then
washed sequentially with water, THF, and methanol and dried at
80 ꢀC overnight. The polymer was characterized by elemental anal-
ysis, swelling degree, FTIR, and BET analysis.
3. Conclusions
Various Fe(III)ePVPDVB complexes were synthesized and applied
as catalysts in the oxidation of toluene in the presence of H2O2. The
degree of DVB in the polymer supports was found to have a direct
influence on the catalytic activities of the polymeric complexes by
controlling the catalyst surface area, degree of swelling, and
4.3. Preparation and characterization of the polymer support
iron(III)
PVPDVB (0.50 g) was stirred with a saturated solution of
FeCl3$6H2O in methanol (pH¼2) at reflux temperature for 16 h.20

9428
W. Karuehanon et al. / Tetrahedron 68 (2012) 9423e9428
After filtration, the polymer complex was washed repeatedly with
methanol to remove free iron ions and dried at 60 ꢀC to obtain
yellow-brown beads of the Fe(III)ecopolymer complex. AAS anal-
ysis was used to analyze the methanol filtrate in the final wash to
ensure no trace of iron ion was left in the solution. The complex-
ation between PVPDVB and iron(III) ion was investigated by FTIR
and FT-Raman techniques. The iron content in the Fe(III) supported
polymer was determined by atomic absorption spectroscopy (AAS)
using the standard AOAC method.
acknowledge the Center of Excellence for Innovation in Chemistry
(PERCH-CIC), and the National Research University Project under
Thailand’s Office of the Higher Education Commission for addi-
tional financial support to this research. Valuable discussion and
suggestions from and Associate Prof. Apinpus Rujiwatra and Dr.
Praput Thavornyutikarn (Chiang Mai University) are greatly
appreciated.
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each table and figure. Briefly, a mixture of toluene (1.46 mmol) and
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This research was supported by the grant under the program
Strategic Scholarships for Frontier Research Network for the Ph.D.
Program Thai Doctoral degree from the Commission on Higher
Education (CHE), Thailand (to W.K.). The authors also gratefully