Efficient and selective oxidation of alcohols in water employing palladium supported nanomagnetic Fe3O4@hyperbranched polyethylenimine (Fe3O4@HPEI.Pd) as a new organic–inorganic hybrid nanocatalyst

Article abstract of DOI:10.1002/aoc.3908

Palladium immobilized magnetic nanoFe₃O₄@hyperbranched polyethylenimine (Fe₃O₄@HPEI.Pd) was prepared according to a simple and cost effective pathway and it was employed as a new efficient and selective organic–inorganic hybrid nanocatalyst for the aqueous oxidation of primary and secondary alcohols to their corresponding products in good yields applying oxone (potassium hydrogen monopersulfate) and H₂O₂ as an oxidant at room temperature. Moreover, the catalytic system was reused at least 13 times without significant loss of activity. The complete characterization of this efficient nanocatalyst was investigated by FTIR, UV–Vis, TEM, SEM, XRD, TGA, VSM, ICP and EDX techniques.

Full text of DOI:10.1002/aoc.3908

Received: 6 March 2017
DOI: 10.1002/aoc.3908
Revised: 28 April 2017
Accepted: 5 May 2017
F U L L PA P E R
Efficient and selective oxidation of alcohols in water employing
palladium supported nanomagnetic Fe3O4@hyperbranched
polyethylenimine (Fe3O4@HPEI.Pd) as a new organic–inorganic
hybrid nanocatalyst
Ali Ramazani1
| Mehdi Khoobi2,3 | Fariba Sadri4 | Roghayeh Tarasi1 | Abbas Shafiee2 |
Hamideh Aghahosseini1 | Sang Woo Joo5
1 Department of Chemistry, University of
Zanjan, P.O. Box 45195‐313 Zanjan, Iran
Palladium immobilized magnetic nanoFe3O4@hyperbranched polyethylenimine
2 Department of Medicinal Chemistry,
Faculty of Pharmacy and Pharmaceutical
Sciences Research Center, Tehran University
of Medical Sciences, Tehran 14176, Iran
3 Medical Biomaterials Research Center,
Tehran University of Medical Sciences,
Tehran, Iran
4 Department of Chemistry, Payame Noor
University, P.O. Box 19395‐3697 Tehran,
Iran
5 School of Mechanical Engineering,
Yeungnam University, Gyeongsan 712‐749,
Republic of Korea
(Fe3O4@HPEI.Pd) was prepared according to a simple and cost effective pathway
and it was employed as a new efficient and selective organic–inorganic hybrid
nanocatalyst for the aqueous oxidation of primary and secondary alcohols to their
corresponding products in good yields applying oxone (potassium hydrogen
monopersulfate) and H2O2 as an oxidant at room temperature. Moreover, the cata-
lytic system was reused at least 13 times without significant loss of activity. The
complete characterization of this efficient nanocatalyst was investigated by FTIR,
UV–Vis, TEM, SEM, XRD, TGA, VSM, ICP and EDX techniques.
KEYWORDS
alcohols, carbonyl compounds, nanomagnetic catalyst, oxidation, oxone
Correspondence
Ali Ramazani, Department of Chemistry,
University of Zanjan, PO Box 45195‐313,
Zanjan, Iran.
Email: aliramazani@gmail.com
Funding information
National Research Foundation of Korea,
Grant/Award Number: NRF‐2015‐002423
1 | INTRODUCTION
need expensive metals and/or other reagents. Traditional
methods utilizing stoichiometric quantities of inorganic oxi-
One of the significant transformations in organic chemistry is
the oxidation of alcohols. A wide variety of metal and non‐
metal‐based stoichiometric reagents has been developed in
order to oxidize primary and secondary alcohols to the
corresponding aldehydes, ketones and carboxylic acids.[1–4]
Catalytic oxidation of non‐activated aliphatic alcohols with
molecular oxygen is rather challenging, especially in an aque-
ous medium in the absence of an additional base.[5] Although
these processes are more environmentally friendly, they often
dants such as chromium (VI) reagents, permanganates, or
N‐chlorosuccinimide (NCS) are not environmentally benign.
Even grave recent developments of hypervalent iodine
reagents, which are popular in organic synthesis, also cause
severe environmental problems. Thus, the development of
greener oxidation systems continues using less poisonous
catalysts, oxidants, and solvents became a crucial aim for
the catalysis and the search for environmentally friendly as
well as economical oxidation processes.[6–9] The oxone is
Appl Organometal Chem. 2017;e3908.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3908

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RAMAZANI ET AL.
relatively stable compound at room temperature, readily
available, and a convenient and therefore is utilized for vari-
ous transformations in organic synthesis.[10–19] Selective oxi-
dation processes represent a large class of organic reactions,
which the improvement of green catalysts is a major concern
in the field of chemical reactions. Some defects have been
found regarding homogeneous catalysts. For example, diffi-
cult workup of the perilous metal residues, and lack of
recycling methods, which make them inconvenient for
large‐scale applications.[20]
effective for uniform reoxidation of Pd(0) in the cycle of
reaction[35] (Scheme 1). The prepared nanomagnet
(Fe3O4@HPEI.Pd) was employed as a high active and
reusable catalyst through magnetic separation for the selec-
tive oxidation of alcohols with oxone in the presence of water
at room temperature.
2 | EXPERIMENTAL
2.1 | Materials and methods
The use of palladium catalysts for the oxidation of alco-
hols to aldehydes and ketones in the presence of various
types of oxidants is well known. Recently, the advantages
of using molecular oxygen as the oxidant in the Pd‐catalyzed
oxidation of alcohols have been explored. The magnetic Pd
catalyst showed high activity in the oxidation of HMF to
FDCA in water.[21–23] In heterogeneous reaction, tedious
methods like centrifugation and filtration are utilized to
recover catalysts and end in loss of solid catalyst in the sepa-
ration process. The magnetic nanoparticles in a variety of
solid matrices allows the combination of well‐known proce-
dures for catalyst heterogenization and magnetic separation
that supplies a convenient method to remove and recycle
magnetized species by utilizing an appropriate magnetic
field.[24,25]
Iron oxide magnetic nanoparticles have attracted grow-
ing interest owing to their unique properties and potential
applications in various fields, such as magnetically assisted
drug delivery, magnetic resonance imaging (MRI) contrast
agents, hyperthermia, and magnetic separation of biomole-
cules.[26–28] Most of these utilizations require the nanopar-
ticles to be chemically stable, uniform in size, and well
scattered in liquid media. As a result of anisotropic dipolar
attraction, pristine nanoparticles of iron oxides tend to
aggregate into large groups and thus lose the particular
qualities associated with single‐domain, magnetic nano-
structures. Surfactants with relatively high concentrations
are often required to prevent such an aggregation. The
presence of large amounts of surfactants in these systems
may severely affect its utilizations. It has been illustrated
that the formation of a passive coating of inert materials
such as polymers, carbons, and silicas on the surfaces of
iron oxide nanoparticles could help prevent their aggrega-
tion in liquid and make their chemical stability better and
better.[29–34]
[3‐(2,3‐Epoxypropoxy)propyl]trimethoxysilane (EPO, 98%
purity), ferric chloride hexahydrate (FeCl3·6H2O), ferrous
chloride tetrahydrate (FeCl2·4H2O), palladium chloride and
alcohols were purchased from Merck (Darmstadt, Germany).
Hyperbranched polyethyleneimine (HPEI, Mw = 60,000)
was purchased from Sigma‐Aldrich.
The IR spectra were taken using Nicolet FT‐IR Magna
550 spectrographs (KBr disks). The UV–Vis spectrum of
catalyst (dispersed in ethanol) was recorded at room tem-
perature on
a UV–visible spectrophotometer (model:
dr5000). The thermogravimetric analyses were performed
using a TGA Q50 thermogravimetric analyzer of a TGA
instrument with a heating ramp of 10 °C min−1 under
argon flow from room temperature to 800 °C. The
structural properties of synthesized nanoparticles were ana-
lyzed by X‐ray powder diffraction (XRD) with a XPert
MPD advanced diffractometer using Cu (Kα) radiation
(wavelength: 1.5406 Å) at room temperature in the range
of 2θ from 4 to 120° with a scanning rate of 0.02° S−1
.
The magnetic properties of samples were detected at room
temperature using vibrating sample magnetometer (VSM,
Meghnatis Kavir Kashan Co., Kashan, Iran). The particle
size and morphology of the surfaces of the samples were
analyzed by a scanning electron microscopy (VEGAII
TESCAN) with an acceleration voltage of 15 kV. The disc
was pasted with copper tape, and the sample was dispersed
over the tape. The disc was coated with gold in an ioniza-
tion chamber. An EM208 Philips Company transmission
electron microscopy (TEM) was used. Samples were
prepared by placing a droplet 1 (μl) of nanocomposite dis-
persion latex, along with a droplet of water, on a copper
grid covered by Formvar foil (200 mesh), dried and ana-
lyzed. The concentration of Pd in the Fe3O4@HPEI.Pd
was analyzed by inductively coupled plasma emission spec-
troscopy (ICP) using an ICP‐OES (Model: VISTA‐PRO)
instrument. Energy dispersive X‐ray analysis (EDX) was
carried out on Rontec (Germany) electron microscope.
The parameters were as follows: accelerating voltage
In this work, the amine groups of hyperbranched
polyethylenimine (HPEI) were reacted with the epoxy groups
of [3‐(2,3‐Epoxypropoxy)propyl]trimethoxysilane (EPO) and
then the resulted polymer was grafted to the Fe3O4 magnetic
nanoparticles (MNPs) via the reaction of its trimethoxysilane
group with OH groups of MNPs. Finally, it is assumed that
the prepared Fe3O4@HPEI has good nitrogenous ligand for
palladium (or cobalt and copper) chelating and could be
1
15 kV. H–NMR spectra were recorded on a Bruker Ultra
shield‐300 MHz spectrometer. The aliphatic products
detected by GC‐FID (VARIAN C‐P‐3800 with FID detec-
tor, column CP‐Sil 5 CB30m × 0.32 mm).

RAMAZANI ET AL.
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SCHEME 1 (a) preparation of mangnetic
nano Fe3O4@HPEI; (b) palladium, cobalt
and copper chelation with the nitrogenous
ligands in Fe3O4@HPEI to prepare
Fe3O4@HPEI.M (b)
unreacted substrates and by products. It was magnetically
separated by an external magnet again and dried at 40 °C
for several days.[37]
2.2 | Preparation of catalyst
2.2.1 | Preparation of Fe3O4 MNPs
Iron oxide nanoparticles were synthesized by the co‐precipi-
tation of Fe2+ and Fe3+ ions (molar ratio 1:2) in ammonia
solution.[36] Briefly, FeCl2.4H2O (1.6 g) and FeCl3.6H2O
(4.32 g) were dissolved in deionized water (20 ml) under a
nitrogen atmosphere and vigorous stirring with mechanical
stirrer. Then, NH3.H2O (28 wt.%, 25 ml) was added dropwise
to the solution under vigorous stirring and the solution was
heated to 70 °C. The reaction proceeded for 2 h at 70 °C,
and then the temperature was increased to 85 °C to vapor
the residual ammonia. The resulting black dispersion was
magnetically separated by an external magnet and washed
repeatedly with deionized water.
2.3 | Preparation of nanomagnetic
hyperbranched polyethylenimine‐supported
palladium catalyst (Fe3O4@HPEI.Pd)
Fe3O4@HPEI (0.3 g) was charged into a round‐bottomed
flask containing an acetonitrile solution (10 ml) and soni-
cated for 20 minutes. Palladium chloride (0.6 mmol) was
charged into another round‐bottomed and sonicated for
20 minutes. Then, this mixture was added drop wise to
the above mixture under an argon atmosphere and soni-
cated for 30 minutes. Then, this mixture stirred under an
argon atmosphere for 48 h. The resultant catalyst was fil-
tered off and washed with acetonitrile followed by acetone.
The residue was dried in a vacuum oven for 24 h.[35] In
addition, the same procedure was used Co and Cu incorpo-
ration into the nanomagnetic catalyst by using cobalt and
copper chloride.
2.2.2 | Covalently grafting of HPEI to Fe3O4
MNPs (preparation of Fe3O4@HPEI)
To a stirred solution of 150 ml dry toluene containing 3 mmol
of HPEI, 1 mmol of EPO was added. The resulting mixture
was allowed to react at 80 °C for 24 h. To this solution,
2.5 g of dispersed Fe3O4 MNPs in 25 ml of ethanol were
added and the solution was then stirred at 80 °C for 24 h.
Fe3O4@HPEI was magnetically isolated by an external mag-
net and washed repeatedly with methanol and ethanol. Then,
it was soxheleted with ethanol during 24 h to remove the
2.4 | General procedure for the oxidation of
alcohols
Alcohol (1 mmol), water (2 ml) and catalyst (1 mol% of Pd,
30 mg) were added into a round‐bottomed flask. The reaction

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RAMAZANI ET AL.
mixture was stirred for two minutes, and then oxone
(0.6 mmol) was added in three portions during 15 minutes.
The reaction mixture was stirred at room temperature. Prog-
ress of the reaction was followed by TLC (EtOAc‐cyclohex-
ane, 2:10) in comparison with the standard samples of
corresponding alcohols and carbonyl compounds. After the
completion of the reaction, the product was extracted with
dichloromethane. The organic phase was evaporated under
reduced pressure to give the corresponding aromatic
products. Purification of the residue using flash
columnchromatography (silica gel) provided the pure car-
bonyl compounds. The products were characterized via com-
parison their spectral data (IR, 1H NMR) with authentic
samples. The aliphatic products in dichloromethane were
dried by using anhydrous MgSO4 and detected by GC‐FID
in comparison with the standard samples of corresponding
alcohols and carbonyl compounds. The GC yields of the ali-
phatic products were calculated based on their corresponding
gas chromatogram. The selectivity of the oxidized products
was determined from their 1H NMR spectra of corresponding
crude samples.
on the surfaces of Fe3O4 (Figure 1b). Comparing the IR
peaks of Fe3O4@HPEI with the FT‐IR spectra of metal
(Pd, Cu or Co) coated nanocatalysts (Supplementary data,
Figure S1), the similar bands suggest the presence of
Fe3O4@HPEI in the structure of metal (Pd, Cu or Co)
coated nanocatalysts.
The crystalline structures of the obtained Fe3O4,
Fe3O4@HPEI and Fe3O4@HPEI.Pd were determined by
XRD analysis (Figure 2). The position and relative intensity
of all diffraction peaks matched well with standard
Fe3O4.[39] The results indicate that the shape of the MNPs
is inverse spinel Fe3O4 with a face‐centered cubic (fcc)
structure, suggesting the sample has a cubic crystal system.
From comparing the diffraction patterns of Fe3O4 with
Fe3O4@HPEI and fe3o4@hpei.pd, the broadening of dif-
fraction peaks indicated that the prepared Fe3O4 is in poly-
crystalline form. All the diffraction peaks could be readily
indexed to (1 1 1), (2 2 0), (2 0 0) lattice planes of a face‐
centered cubic (fcc) Pd crystal structure and (2 2 0),
(3 1 1), (2 2 2), (4 0 0), (5 1 1), (4 4 0) lattice planes of
[40]
fcc Fe3O4.
3 | RESULTS AND DISCUSSION
3.1 | Characterization of the catalyst
Figure 1 shows the FT‐IR spectra of Fe3O4 MNPs and
Fe3O4@HPEI. HPEI grafted on the Fe3O4 by coupling
agent EPO can be seen clearly from the occurrence of the
strongly absorbing region of 1110–1000 cm−1 results from
the vibration of Si–O–H and Si–O–Si groups, 584 cm−1
corresponds to the Fe–O bond and the bands at around
2924 cm−1 and 2831 cm−1 which are attributed to the ali-
phatic C‐H bands.These values are in accord with the previ-
ously reported data.[38] The produced band 1581 cm−1 are
ascribed to the stretching vibration of the C–N bonds. The
appearances of these bands reveal covalently link of HPEI
FIGURE 2 XRD patterns of the Fe3O4 (a), Fe3O4@HPEI (b) and
FIGURE 1 FT‐IR spectra of the Fe3O4 (a) and Fe3O4@HPEI (b)
fe3o4@Hpei.pd (c)

RAMAZANI ET AL.
5 of 11
In the UV–Vis absorption spectra of Fe3O4@HPEI and
Magnetic behavior of the obtained Fe3O4 MNPs and
Fe3O4@HPEI is shown in Figure 3a. The superparamagnetic
behavior was reflected in the low residual magnetization (Mr)
fe3o4@hpei.pd (Supplementary data, Figure S2), position
and relative intensity of absorptions are matched well with
previously reported.[41,42] The absorption peaks observed
for Fe3O4@HPEI at λmax = 210 nm. The UV–vis spectrum
of Fe3O4@HPEI.Pd, displayed the characteristic absorption
band with decreasing absorptivity at 225 nm in the presence
of Pd2+
.
FIGURE 3 (a) magnetic behavior of Fe3O4 and Fe3O4@HPEI; (b)
fe3o4@Hpei.pd catalyst removing by an external magnet in an alcohol
oxidation reaction
FIGURE 5 SEM images of Fe3O4 (a) and Fe3O4@HPEI (b) and
FIGURE 4 TGA analyses of Fe3O4 and Fe3O4@HPEI
TEM images of Fe3O4 (c) and Fe3O4@HPEI (d,e)

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RAMAZANI ET AL.
and coercivity (Hc) values.[43] The coercive field (Hc),
which represents the required force to rotate the magnetiza-
tion vector of a magnet out of its equilibrium direction,
and specific saturation magnetization (σs) values for the pre-
pared MNPs were calculated as 32 Oe and 46.4 emu g−1
whereas for Fe3O4@HPEI were calculated as 30.2 Oe
and 33.8 emu g−1. The saturation magnetization of
Fe3O4@HPEI was less than that of Fe3O4, which might be
attributed to the silica and polymer coating on the surface
of the Fe3O4. Figure 3b shows Fe3O4@HPEI.Pd as a catalyst
was easily separated from the products by exposure of the
reaction vessel to an external magnet and decantation of
the reaction mixture.
The amount of EPO and HPEI groups on the MNPs
was measured by TGA analyses (Figure 4). The weight
loss in the first step (25–150 °C) was attributed to the
vaporization of water (about 10%). The second weight loss
observed at temperatures higher than 200 °C was
corresponded to the slow decomposition of the higher
molecular weight species that present in the magnetic
nanospheres. According to the TGA results, the percentage
of grafting density of the HPEI has been found to be about
20%.
harmony with the XRD analyses (Figure 2). The results show
that the diameter of pristine Fe3O4 nanoparticles is about 20–
30 nm. After the grafting of HPEI on the magnetic nano-
spheres, the morphology of the resulting Fe3O4@HPEI was
shown to resemble their original state.
The ICP analyzing shows that 3.44% of Fe3O4@HPEI.
Pd weight is palladium, Fe3O4@HPEI.Cu has 8.87% cop-
per and Fe3O4@HPEI.Co has 8.19% cobalt. The elemental
composition of the Fe3O4@HPEI.Pd was also analyzed by
the energy‐dispersive X‐ray (EDX) spectrum and the pres-
ence of palladium inside the catalyst was further confirmed
(Supplementary data, Figure S3). From the EDX spectrum,
it can be seen obviously the presence of Pd peaks, which
confirm the presence of Pd.
The electronic properties and surface chemical composi-
tions of Fe3O4@HPEI were investigated by XPS technique
(Supplementary data, Figure S4). The characteristic peaks
at 159 eV, 285 eV, 405 eV, and 536 eV corresponded to
S2p, C 1 s1/2, N 1 s1/2 and O1s1/2, respectively.[44]
3.2 | Optimization of alcohol oxidation
conditions
Figure 5 shows the SEM and TEM images of Fe3O4 and
Fe3O4@HPEI. The TEM analysis suggests that the MNPs are
almost spherical (Figure 5c‐e). These results are in good
For optimizing the reaction conditions, we tried to convert
benzyl alcohol (1 mmol) to benzaldehyde, as a model reac-
tion, in the presence of the Fe3O4@HPEI/Pd catalyst
TABLE 1 Oxidation of benzyl alcohol (1 mmol) in the presence of nanomagnetic catalyst
Catalyst
Entry
1
(mol% of metal)
Oxidizing agent (mmol)
Oxone (1.2)
Solvente
Water
Time (min)
Yield (%)
20
‐‐‐
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
65
120
2
Fe3O4@HPEI/Pd (1)
Fe3O4@HPEI/Pd (1)
Fe3O4@HPEI/Pd (1)
Fe3O4@HPEI/Pd (1)
Fe3O4@HPEI/Pd (1)
Fe3O4@HPEI/Pd (1)
Fe3O4@HPEI/Pd (1)
Fe3O4@HPEI/Pd (1)
Fe3O4@HPEI/Pd (1)
Fe3O4@HPEI/cu (1)
Fe3O4@HPEI/co (1)
Fe3O4@HPEI/Pd (1.5)
Fe3O4@HPEI/Pd (0.5)
Fe3O4@HPEI/Pd (0.25)
Fe3O4@HPEI/Pd (1)
Fe3O4@HPEI/Pd (1)
Fe3O4@HPEI/Pd (1)
Fe3O4@HPEI/Pd (1)
Fe3O4@HPEI/Pd (1)
H2O2 (1.2)
Cyclohexane
Acetonitrile
Ethanol
Dichloromethane
Dry toluene
Solvent free
Water
Trace
20
3
H2O2 (1.2)
4
H2O2 (1.2)
Trace
15
5
H2O2 (1.2)
6
H2O2 (1.2)
Trace
20
7
H2O2 (1.2)
8
H2O2 (1.2)
28
9
O2 atmosphere
Oxone (1.2)
Oxone (1.2)
Oxone (1.2)
Oxone (1.2)
Oxone (1.2)
Oxone (1.2)
Oxone (0.8)
Oxone (0.6)
Oxone (0.5)
Oxone (0.3)
Absence (under N2 atmosphere)
Water
12
10
11
12
13
14
15
16
17
18
19
20
Water
90
Water
55
Water
48
Water
90
Water
64
Water
30
Water
89
Water
90
Water
80
Water
55
Water
0
a Yields refer to isolated products.

RAMAZANI ET AL.
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TABLE 2 Oxidation of various alcohols using Fe3O4@HPEI.Pd catalyst in water with oxone
Entry
Substrate
Product
Time (min)
Yielda (%)
1
65
90
2
3
4
70
65
70
89
93
90
5
80
91
6
7
65
65
89
90
8
70
70
91
88
87
86
9
10
11
70
120
12
13
120
120
85
85
14
45
94
(Continues)

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RAMAZANI ET AL.
TABLE 2 (Continued)
Entry
Substrate
Product
Time (min)
Yielda (%)
15
70
91
16
120
88
17b
18
90
24 h
24 h
120
45
‐‐‐
‐‐‐
No product
No product
96.88
19
20c,d
21c
22c
120
120
88.9
99.6
aYields refer to isolated products. The products were characterized from their spectral data (IR, 1H NMR) and compared with authentic samples.
bThe reaction was followed by TLC (EtOAc‐cyclohexane,3:10).
cThe yields refer to GC analysis.
dThe yield was 95.02% with 1 mol% of catalyst in 6 hrs at 80 °C and that was 99.30% with 1 mol% of catalyst in 24 hrs at r.t.
(30 mg, 1% mol of metal) and hydrogen peroxide
(1.2 mmol was added in 3 steps) in various solvents
(2 ml) at room temperature and the results are given in
Table 1. The highest yield for benzaldehyde was achieved
in water (entry 8). We investigated the effect of different
oxidants on the oxidation of benzyl alcohol over
Fe3O4@HPEI/Pd catalyst (1%mol) at room temperature.
These results showed that the higher conversion was
achieved with oxone as oxidant (entry 10). We also studied
the oxidation of benzyl alcohol to benzaldehyde with other
nanomagnetic catalysts (1% mol of metals,) and oxone. The
results show that Fe3O4@HPEI/Pd is the best catalyst
(entries 10–12). In addition, we observed that in the
absence of catalyst the yield of oxidation with oxone
is 20%.
(1 mol% of Pd) and 0.6 mmol (60 mol%) of oxidant is the best
choice for the oxidation of 1 mmol of alcohol (entry 17). We
also observed that benzyl alcohol was not oxidized with this
system in the absence of oxidant under nitrogen atmosphere,
even for long period of time (entry 20).
The competing reaction such as over oxidation of
aldehydes to the corresponding carboxylic acids was not
observed in any of the cases under above conditions, but
the reaction produces by product corresponding carboxylic
acid at high temperatures (>40 °C).
3.3 | Application scope
The optimized conditions were used for various alcohols
to screen the generality of the work. As indicated in the
Table 2, Fe3O4@HPEI/Pd catalyst showed higher effi-
ciency than other nanomagnetic catalysts (Fe3O4@HPEI/
The amount of the catalyst and oxidant were also
optimized. The results showed that 30 mg of catalyst

RAMAZANI ET AL.
9 of 11
Co and Fe3O4@ PEI/Cu) for oxidation of a wide range of
alcohols. This evidence could be resulted from relatively
illustrated by the finding that the 13th consecutive oxida-
tion cycle was 86% complete after a reaction time of only
65 minutes. ICP analyzing showed that 3.36% of catalyst
weight is palladium in13th recycling. Therefore, it showed
that no obvious diminishing palladium of the catalyst
in13th recycling. The TEM analysis suggests that the
fe3o4@hpei.pd nanoparticles in13th recycling are almost
spherical shapes and it shows that there is no obvious
change of the catalyst in 13th recycling (Supplementary
data, Figure S5).
high redox potential of Pd in comparison with Co and
ꢀ
Cu E°Pdþ2
¼ þ0:951 V ; E°Coþ2
¼ −0:280 V and
=Pd
=Co
E°Cuþ2
¼ þ0:340 VÞ. In most cases, the aldehyde selec-
=Cu
tivity was very high (>99%). The oxidation of various
benzylic alcohols gave the carbonyl compounds in high
yields and short reaction times. However, heterocyclic or
heteroaromatic substrate containing oxygen or nitrogen
atom seems to be poisonous for the catalyst.[45] For
example, oxidation of piperonylalcohol has low yield even
in 24 hrs. (entry 17). In addition, 3‐pyridinemethanol and
2‐pyridinemethanol cannot produce corresponding alde-
hyde or carboxylic acid even for a long period of time
(entries 18 and 19) and the catalyst inactivates a little at
the end of the reaction. In comparison to benzylic alco-
hols, oxidation of aliphatic alcohols with this method
did occur with longer reaction times.
To show the chemoselectivity of this method, the com-
petitive reactions have been carried out in the presence of
two alcohols (Supplementary data, Table S1, Figure S4 and
Figure S5). The donor substituted group for example CH3O−
group on the benzene ring of alcohol accelerates the reaction
rate and the withdrawing groups (chloro‐ or carbonyl) reduced
the reaction rate.
3.5 | Proposed mechanism for the oxidation
Based on our experimental results and the related litera-
ture,[46,47] we propose the following reaction mechanism for
the oxidation of alcohols by using oxone in the water and in
the presence of Fe3O4@HPEI/Pd catalyst (Scheme 2). The
common feature is that the formation of real oxidant is inde-
pendent of catalyst Pd (II)‐catalyzed oxidation of alcohols
proceeds through a reduction of Pd (II) to Pd (0) by the
alcohol. It seems that in Fe3O4@HPEI/Pd, PEI ligand as
water soluble polymer which has several amine groups and
facilitates oxidation of Pd(0) to Pd(II),[34] and then oxone
(HSO5− in water) takes two electrons and the cycle continues
in this mechanism.[48–50] Since the catalyst is present in the
water phase, HSO5− takes electrons rapidly in contrast, when
the palladium catalyst resides are in the organic phase,
3.4 | Catalyst recycling
The catalyst was easily separated from the products by
exposure of the reaction vessel to an external magnet
and decantation of the reaction solution (Figure 3b). The
remaining catalyst was washed repeatedly with acetone
and water to remove undesired materials and dried to
reuse. The catalyst showed excellent catalytic activity for
more than 10 iterative cycles (Figure 6). The excellent
activity and recyclability of catalyst in this reaction is
FIGURE 6 Recyclability of the Fe3O4@HPEI.Pd catalyst for the
SCHEME 2 Proposed mechanism for the oxidation of alcohols with
oxidation of benzyl alcohol
oxone in the presence of fe3o4@Hpei.pd catalyst

10 of 11
RAMAZANI ET AL.
−
[14] L. A. Wozniak, M. Koziolkiewicz, A. Kobylanska, W. J. Stec,
HSO5 forms a separate aqueous phase, thus Pd(0) cannot
donate electron.
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In conclusion, we have introduced a direct and effective
method for the oxidation of alcohols to their corresponding
carbonyl compounds utilizing oxone in the presence of
Fe3O4@HPEI/Pd catalyst at room temperature in water. The
use of non‐toxic and inexpensive materials, stability of the
oxidative system, simple method, short reaction times, good
yields of the products and mild reaction conditions are the
advantages of this method. In comparison with the other oxi-
dants such as O2 or TBHP, oxidation with oxone accom-
plished at low temperatures and in short times.[51,52] The
extension of the application of this nanocatalyst to different
oxidation reactions is currently under investigation in our
laboratory.
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ACKNOWLEDGEMENT
3790.
This work is funded by the grant NRF‐2015‐002423 of the
National Research Foundation of Korea.
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How to cite this article: Ramazani A, Khoobi M,
Sadri F, et al. Efficient and selective oxidation of
alcohols in water employing palladium supported
nanomagnetic Fe3O4@hyperbranched
polyethylenimine (Fe3O4@HPEI.Pd) as a new
organic–inorganic hybrid nanocatalyst. Appl
Organometal Chem. 2017;e3908. https://doi.org/
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