Novel approach to synthesizing polymer-functionalized Fe3O4/SiO2-NH2via an ultrasound-assisted method for catalytic selective oxidation of alcohols to aldehydes and ketones in a DMSO/water mixture

Article abstract of DOI:10.1039/c5ra19093b

N-(2-Oxotetrahydrothiophen-3-yl)acrylamide was successfully polymerized on the surface of amine functionalized magnetic silica nanocomposites via an ultrasound-assisted method. Then, MnO₂ nanoparticles were formed on the surface of the polymer

Full text of DOI:10.1039/c5ra19093b

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Novel Approach to Synthesis PolymerꢀFunctionalized Fe O /SiO ꢀNH via Ultrasonicꢀ
3
4
2
2
Assisted Method as a Catalyst to Selective Oxidation of Alcohols to Aldehydes and Ketones
in the Mixture of DMSO and Water
b
c
d
a
Mahsa Dehghan , Atieh Motaharinejad , Mostafa Saadat , Reza Ahdenov , Mirzaagha Bab
a,
a
azadeh * and Rahim HosseinzadehꢀKhanmiri
a
Department of Chemistry, Tabriz Branch, Islamic Azad University, Tabriz, Iran. E-mail:
babazadeh@iaut.ac.ir, Fax: +98-491-2231616
b
Department of Organic Chemistry, Faculty of Chemistry, Razi University, Kermanshah 67149-
6
7346, Iran
c
Department of physical chemistry, Faculty of chemistry, Kashan University, Kashan, Iran
d
Department of Chemistry, Faculty of Science, Urmia University, Urmia 57154, Iran
Abstract
Nꢀ(2ꢀoxotetrahydrothiophenꢀ3ꢀyl)acrylamide was successfully polymerized onto surface of
amine functionalized magnetic silica nanocomposites via ultrasonicꢀassisted method. Then,
MnO nanoparticles were formed on surface of polymer functionalized magnetic nanocomposites
2
leading to a magnetically recoverable MNO catalyst, which exhibits high catalytic activity in the
2
selective aerobic oxidation of alcohols to aldehydes and ketones in the mixture of DMSO and
water in 30 min. The catalyst can be separated from the reaction mixture by applying a
permanent magnet externally and can be reused for several times without significant loss of
activity.
Keywords: Polymer, Ultrasonic, Magnetic Silica Nanocomposites, MnO , Aerobic Oxidation.
2
1. Introduction
Nanoscience and nanotechnology have attracted great interest from the scientific community due
1
to the new technological possibilities offered by the properties of nanomaterials. A wide variety
2
3,4
of applications have been suggested, in field ranging from electronic, nanocatalysis,
5
magnetiteꢀsupported catalysis, etc. Rapid development of nanotechnology over the past few
decades has allowed researchers to view conventional heterogeneous catalysts from a new
perspective. In particular, catalytic materials can now be prepared with greater precision via
nanotechꢀenabled processes. Combining properties of NPs with polymers, aiming at the

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production of hybrid multifunctional nanoparticles (NPs) and nanostructures, presents several
6
advantages and opportunities. Hybrid NPs containing polymer, which often serve as active
catalytic components, can now be routinely synthesized with wellꢀdefined sizes, shapes, crystal
7
facets, structure and composition. Such controllability over materials’ structures could
potentially lead to the development of new technologies for applications in green, sustainable
and economicallyꢀviable chemical processes, which are currently regarded as among the most
desirable yet challenging areas in chemistry.
8
Magnetic nanomaterials stand out for their novel properties. The most widely studied
superparamagnetic NPs is magnetite (Fe O ), which offers a large variety of applications, such as
3
4
9
10
11
12
13
information storage, color imaging, microwave absorption, medical diagnosis, catalyst,
and so on. However, naked Fe O NPs are very sensitive to oxidation for their high chemical
3
4
reactivities and prone to aggregate for their large ratio of surface area to volume and thus result
in poor magnetism and dispersibility. Those defects limit their further applications. One of the
main approaches to overcome these limitations is to protect naked magnetic NPs with polymers
1
4
or inorganic shell such as metals or oxides. These protective layers not only prevent the Fe3O4
NPs from aggregating but also provide a useful platform for further functionalization. Several
ways for the functionalization of this hybrid nanomaterials have been reported, for example
1
5
immobilization of metal, anchoring the organic species, reducing metal ion onto the surface of
1
6,17
the nanocomposites via different methods.
Threeꢀcomponent magnetic nanocomposites have
been paid much attention. Stoeva et al. assembled magnetic NPs into a core/shell/shell structure
1
8
with a silica core with Fe O and gold as the inner and outer shells, respectively. These
3
4
core/shell/shell magnetic NPs have excellent DNA binding properties as well as magnetic
properties. Yu et al. prepared Fe O @Au/polyaniline (PANI) nanocomposites by in situ
3
4
polymerization in the presence of mercaptocarboxylic acid with integrated and stable optical,
1
9
electrical, and magnetic properties. These species of nanocomposites exhibited promising
application in many catalytic process.
Selective oxidation of alcohols to their corresponding carbonyl compounds is of significant
importance in organic chemistry, both for fundamental research and industrial manufacturing.
This transformation is traditionally carried out using stoichiometric quantities of inorganic
2
0
oxidants, which are relatively expensive, highly toxic and environmentally polluting.
Therefore, introducing green, selective and efficient aerobic oxidation systems for alcohols are of

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prime importance for both economic and environmental reasons. From both environmental and
economic viewpoints, heterogeneous catalysts have attracted considerable interest for catalytic
2
1
systems. Various materials have been employed as the support to produce heterogeneous
2
2
23
24
catalytic systems, such as mesoporous silica, activated carbon, (bio)polymer and biomass.
In this paper, a new kind of threeꢀcomponent magnetic nanocomposite, Fe O /SiO /PATL was
3
4
2
synthesized. First, uniform Fe O nanospheres with a diameter of 10 nm were prepared. Then,
3
4
Fe O /SiO ~NH nanospheres with wellꢀdefined core/shell nanocomposite structures were
3
4
2
2
obtained through polymerization of (3ꢀAminopropyl)triethoxysilane (APTES) over the group of
Fe O NPs. Finally, Nꢀ(2ꢀoxotetrahydrothiophenꢀ3ꢀyl)acrylamide (ATL) was polymerized onto
3
4
the surface of the Fe O /SiO ~NH . The obtained threeꢀcomponent magnetic nanocomposite was
3
4
2
2
used to immobilizing of MnO nanoparticles as heterogeneous catalyst for selective oxidation of
2
alcohols.
2. Experimental Section
Iron(III) chloride hexahydrate (FeCl ·6H O), (3ꢀAminopropyl)triethoxysilane (99%), DLꢀ
3
2
homocysteine thiolactone hydrochloride (CTH), acryloyl chloride, methacryloyl chloride,
dimethylphenylphosphine (DPP) and all amines were purchased from SigmaꢀAldrich and used as
received.
2
.1. Preparation of organosilica coated magnetite NPs (Fe O /SiO –NH )
3 4 2 2
Magnetite (Fe O ) nanoparticles (NPs) were prepared according to the reported method (coꢀ
3
4
precipitation) and coated with organosilane in the presence of 2ꢀpropanol (sol–gel method). In
brief, 0.036 mol of FeCl .6H O and 0.018 mol of FeCl .4H O were dissolved in 20 mL deionized
3
2
2
2
water under nitrogen gas with vigorous stirring. Then, NH (25%) was added into the solution
3
o
until the pH of the solution reached. Stirring was continued for 1 h at 60 C. The color of the
bulk solution turned from orange to black immediately. The magnetite precipitate was separated
from the solution using a magnet, washed several times with deionized water and ethanol, and
left to dry in air. Then, the obtained MNP powder (300 mg) was dispersed in 2ꢀpropanol (150
mL) and water (15 mL) by sonication before APTES (99%, 120 µL) was added to the mixture.
After mechanically agitation for 7 h, the suspended substance was separated from the solution
using a magnet. The settlement product was reꢀdispersed in ethanol by sonication and isolated

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with magnetic decantation for 5 times. The precipitated product (Fe O /SiO –NH ) was dried at
3
4
2
2
room temperature under vacuum.
2
.2. Preparation of Fe O /SiO /PATL nanocomposites.
3
4
2
Nꢀ(2ꢀoxotetrahydrothiophenꢀ3ꢀyl)acrylamide (ATL) was synthesized according to previously
reported by the amidation of DLꢀhomocysteine thiolactone hydrochloride with acryloyl chloride
in dichloromethane (DCM) using triethylamine (TEA) as base. Then, to solution of 17.1 mg (0.1
mmol) ATL and 0.05 equivalent DPP (0.70 mg, 0.005 mmol) in 5 mL of ethanol, 300 mg of
Fe O /SiO –NH was added and the mixture was sonicated at r.t. for 2 h. Finally, the precipitated
3
4
2
2
solid was separated using external magnet and several time washed by ethanol. The precipitated
o
product (Fe O /SiO /PATL) was dried at 80 C for 12 h.
3
4
2
2
.3. Preparation of MnO NPs on surface of Fe O /SiO /PATL nanocmposites.
2 3 4 2
A mixture of Fe O /SiO /PATL (1.00 g) in 20 mL of H O at 60 °C, a solution of KMnO (0.01
3
4
2
2
4
M, 80 mL) at 60 °C, and a solution of MnCl (0.02 M, 60 mL) at 70 °C were prepared,
2
separately. In continue, the solutions of KMnO and MnCl were added dropwise to the mixture
4
2
of Fe O /SiO /PATL for 12 h at 60 °C. The mixture was stirred at room temperature; after 24 h,
3
4
2
it was separated using external magnet, and the residue (Fe O /SiO /PATL/MnO ) washed
3
4
2
2
successively with H O (3 × 5 mL) and EtOH (3 × 10 mL) and dried at 80 °C. The loading of
2
−
1
manganese was measured to be 0.80 mmol g by inductively coupled plasmaꢀoptical emission
spectrometry (ICPꢀOES).
2.4. Characterization techniques
Infrared spectra were recorded using a Ray Leigh Wqfꢀ510 fourier transform infrared (FTIR)
spectrophotometer. Morphological studies measurements were performed using a transition
electron microscopy (TEM, Philips CM10) operated at an 80 kV electron beam accelerating
voltage. Scanning electron microscopy (SEM) and EDX were performed on a PhilipsXLꢀ300
instrument. The sample was sputtered by gold to avoid undesirable electron charging. Xꢀray
diffraction was conducted using a Philips X'pert Pro (PW 3040) Xꢀray diffractometer with
monochromatic CuꢀKaradiation (k¼1.54056˚ A, 40 kV, 30 mA). Thermogravimetric analyses
o
ꢀ1
were investigated using a TG/DTA6300 instrument, at a heating rate of 20 C min under
nitrogen flow. Elemental analysis was performed with a CHN machine (Perkin Elmer Series II,

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2
400). The concentration of manganese was estimated using Shimadzu AAꢀ680 flame atomic
absorption spectrophotometer and inductively coupled plasma optical emission spectrometer
ICPꢀOES) Varian Vista PRO Radial.
(
2
.5. Oxidation of alcohols in presence of Fe O /SiO /PATL/MnO ; General procedure
3 4 2 2
In a general process, an alcohol (1 mmol) was added to a twoꢀnecked flask containing
Fe O /SiO /PATL/MnO (0.06 g, 4.8 mol%), K CO (0.5 mmol) and mixture 1:1(v/v) of
3
4
2
2
2
3
DMSO:deionized water (5 mL). The reaction mixture was stirred under air blowing for 30ꢀ50
min at room temperature. The progress of the reaction was followed by thin layer
chromatography (TLC). Upon completion, the catalyst was collected using external magnet and
the reaction solution was analyzed by GC method.
3. Results and discussion
3.1. Preparation and characterization of the catalyst
The Fe O /SiO /PATL/MnO nanocatalyst was prepared with a multiꢀstep reaction, initially by
3
4
2
2
preparing iron oxide as a magnetic core for coating by organosilica through solꢀgel method. It is
known that organosilanes can act as a linker between the organic catalyst and the support. In this
work, APTES was used. Scheme 1 illustrates the process of catalyst preparation. The ATL
(monomer) was synthesized according to previously reported by the amidation of DLꢀ
2
5
homocysteine thiolactone hydrochloride with acryloyl chloride. The polymerization was
carried out by thiobutyrꢀolactone aminolysis via a part of the linker's amine and consequent
thiolꢀ(meth)acrylate addition. Finally, MnO NPs was formed onto surface of nanocomposites
2
through the reaction of KMnO with MnCl The sulfide groups in structure of the polymer layer
4
2.
was oxidated to sulfoxide through the formation of MnO NPs. Each step of the catalyst
2
preparation procedure was monitored using techniques such as FTIR to ensure the presence of
new functional groups.

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O
O
O
NH
3
Cl
NEt , CH Cl
2
S
S
3
2
Cl
N
R.T.
H
O
ATL
O
H
S
O
N
O
HN
S
HN
S
NH
3
H
N
H
O
N
O
Fe3++ Fe2+
HO Si
Si
O
N
O
H
O O
O
O
Si
O
O
O
Si
H
HN
OH
OH
S
O
O
N
HO
OH
O
HN
OH
Si
O
O
O
O
OH
O
HO
HO
O
O
S
Si
OH
O Si
S
O
OH
NH
NH
NH
H
OH
NH
OH
NH
O
O
N
O
O
O
O
O
O
O
S
NH
2
S
S
N
NH
2
H
MnCl2 + KMnO4
NH
2
O
O
HO Si
Si
H
2
N
O O
O
O
O
NH
2
O
Si
OO
Si
H
S
O
N
O
O
O
O
O
O
Si
O
O
S
HN
O
H
2
N
O
HN
S
O
O
O
Si
H
Si
N
O
OH
NH2
N
H
O
HO Si
Si
N
H
O
O O
O
O
Si
O
O
O
O
H
2
N
H
HN
S
O
O
Si
N
O
Si
H
O
O
N
O
O
O
O
O
O
O
Si
Si
S
O
NH
OH
NH
NH
NH
H
N
O
O
O
O
S
S
O
O
O
Scheme 1 The schematic pathway for synthesis of Fe O /SiO /PATL/MnO nanocatalyst.
3
4
2
2
The stages of the catalyst formation were tracked by FTIR spectroscopy. Fig. 1 shows the FTIR
spectra of the Fe O /SiO –NH Fe O /SiO /PATL and Fe O /SiO /PATL/MnO . The peaks
3
4
2
2,
3
4
2
3
4
2
2
ꢀ1
appearing at 645, 591 and 445 cm are ascribed to the stretching vibrations of Fe–O bonds,
ꢀ1
while the absorption peak at 3253 cm is the OH stretching vibration characteristic peak,
2
+
indicating the presence of some amount of ferric hydroxide in Fe O . At room temperature, Fe
3
4
3
+
and Fe are converted into hydroxide compounds with a pH above 10 (required pH for
o
magnetite preparation is 11), while at elevated temperature (e.g.60 C within magnetite
preparation) they are crystallized to Fe O slowly. Silicaꢀcoated Fe O is expected to produce a
3
4
3
4
ꢀ1
corresponding peak of Fe–O–Si bonds at 584 cm resulting from the adsorption of silica on the
magnetite surface, while this band was overlapped with the Fe–O vibration. In other words, the

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formation of Fe–O–Si bonds upon silica coating affected the position of Fe–O bands, and a peak
ꢀ1
shift occurred. The Si–O–Si stretching and bending vibrations appeared at 1088 and 463 cm ,
2
6
ꢀ1
respectively. The absorption bands at 3460, 1100 and 960 cm are attributed to the stretching,
asymmetric stretching, and bending of silanol groups (Si–OH) on the silica surface, respectively.
ꢀ1
Vibrations at 3500–3400, 1637 and 800 cm correspond to the adsorbed water (H–OH, stretching
vibration), residual intermolecular water (H–OH, bending), and moisture (H–OH, bending) in the
ꢀ
1
ꢀ1
samples. The spectrum of the Fe O @SiO –NH shows peaks at 2847 cm and 2926 cm due to
3
4
2
2
C–H bonds of aliphatic chain stretching vibrations, while the two broad bands at 1580 and 3403
ꢀ1
27
cm are attributed to the N–H stretching and bending vibrations, respectively. For the
ꢀ1
Fe O /SiO /PATL sample, the bond in the range of 1670ꢀ1690 cm was assigned to the C=O of
3
4
2
the amide. After immobilization of MnO NPs onto surface of NPs, the position of C=O and NꢀH
2
bands was changed due to interaction of MnO NPs with amide’s nitrogen. The C=O stretching
2
ꢀ1
ꢀ
vibration was observed to shift to 1706 cm and the NꢀH bending vibration appeared at 1530 cm
1
28
.
The spectrum of Fe O /SiO /PATL/MnO shows a new peak at 1030, which was confirmed
3
4
2
2
29
the S=O bonds. Therefore, CHN, EDX and TGA analyses were required to confirm the
functionalization processes and the presence of polymer layers and MnO NPs on the surface.
2
a
b
c
S=O
C=O
N-H
Figure
1
FTIR spectra of the (a) Fe O /SiO –NH
(b) Fe O /SiO /PATL and (c)
3
4
2
2,
3
4
2
Fe O /SiO /PATL/MnO .
3
4
2
2

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Figure 2 shows the XRD spectra of Fe O /SiO /PATL and Fe O /SiO /PATL/MnO . The
3
4
2
3
4
2
2
appearance of Fe O peaks at 30.1, 35.4, 43.2, 53.6, 57.2 and 62.9 in both spectra indicates the
3
4
3
0
retention of the crystalline structure of Fe O through the functionalization steps. As for the
3
4
XRD patterns of Fe O /SiO /PATL/MnO , a characteristic peaks at 2θ of, 25.77 and 34.57 are
3
4
2
2
3
1
also observed that corresponded to manganese oxide NPs.
Fe O
3
4
MnO2
b
a
1
0
20
30
40
50
60
70
2Ө (degree)
Figure 2 XRD patterns of (a) Fe O /SiO /PATL and (b) Fe O /SiO /PATL/MnO .
3
4
2
3
4
2
2
The corresponding TEM image of the magnetite nanoparticles is presented in Figure 3aꢀd. As
seen in this figure, magnetite nanoparticles are spherical with diameter from 70 to 80 nm. The
Fe O particles have a diameter ranged from 10 to 15 nm and possess regular sphere shape. After
3
4
coating the magnetite clusters cores with SiO layer, core–shell nanocomposite structured
2
Fe O @SiO ꢀNH nanospheres with a thin silica layer of 20 nm in thickness were obtained.
3
4
2
2
These images reveal that the magnetic silica nanoparticles and Fe O /SiO /PATL are similar in
3
4
2
size and are spherical in shape. A comparison between TEM images of Fe O /SiO /PATL/MnO
2
3
4
2
and previous step revealed that dispersion of MnO NPs is excellent onto the surface of
2
nanocomposites. These particles have a diameter ranged from 10 to 15 nm. In the SEM images,
the MnO NPs cannot be clearly seen due to the lower particle size of the MnO NPs than
2
2
nanocomposites sphere. These SEM images show the granular and spherical morphology for
these nanoparticles and the average size of 70 to 80 nm obtained by SEM analysis is consistent
with the TEM results (Figure 3e, f).

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a
b
c
d

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e
MnO2
Fe O
3
4
f
g
Figure
Fe O /SiO /PATL/MnO (f, g) the SEM images of Fe O /SiO /PATL/MnO
2
3
TEM images of (a) Fe O /SiO –NH (b, c) Fe O /SiO /PATL and (d, e)
3 4 2 2, 3 4 2
3
4
2
2
3
4
2
From the elemental analysis (CHN) in Table 1, it is observed that there is an increase in carbon
content and also in hydrogen and nitrogen content after functionalization of the Fe O /SiO –NH
2
3
4
2
through the polymerization process. This indicates the successful attachment of organic
fragments onto the surface of the nanocomposites. However, the Fe O /SiO /PATL/MnO shows
3
4
2
2

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a slightly decrease in the carbon content and also in hydrogen and nitrogen content than
Fe O /SiO /PATL due to increase the inorganic content of nanocomposites after formation of
3
4
2
MnO NPs on the surface (Table 1). Furthermore, the Energy dispersive Xꢀray spectroscopy
2
(
EDX) in Figure 4 confirmed the presence of polymer layers and MnO NPs on the surface with
2
elemental analysis Fe (60.41%), Si (8.13%), O (17.86%), C (4.26%), N (1.91%), Mn (6.30%),
and S (1.13%).
Table 1 the elemental analysis (CHN) result
Elements (mg/g)
Fe O /SiO –NH
Fe O /SiO /PATL
Fe O /SiO /PATL/MnO
3
4
2
2
3
4
2
3
4
2
2
N
C
H
4.124
26.232
2.071
8.734
6.652
30.916
3.804
36.547
4.731
Figure 4 EDX analysis of Fe O /SiO /PATL/MnO .
3
4
2
2
Thermogravimetric analysis (TGA) of Fe O /SiO –NH
Fe O /SiO /PATL and
3 4 2
3
4
2
2,
o
Fe O /SiO /PATL/MnO are presented in Figure 5. The initial wt% losses below 150 C are
3
4
2
2
related to the adsorbed moisture in the samples. The decomposition temperature, which started at
o
o
4
12 C, and continued until 550 C, is associated with the decomposition of the organic chains.
o
The organic species decomposed completely at temperatures higher than 600 C and the residual
weights of Fe O /SiO –NH Fe O /SiO /PATL and Fe O /SiO /PATL/MnO were 90% and
3
4
2
2,
3
4
2
3
4
2
2

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o
8
5% and 87%, respectively, at 700 C. In other words, the results demonstrate percentages of
%, 10% and 8% for organic groups on the surface of nanocomposites. The differences between
4
Fe O /SiO –NH and Fe O /SiO /PATL confirm the successful plolymerization of ATL on the
3
4
2
2,
3
4
2
surface of Fe O /SiO ꢀNH NPs. Also, the TGA curve of Fe O /SiO /PATL/MnO shows a
3
4
2
2
3
4
2
2
decrease in loss of weight because the inorganic content of NPs increased after formation of
MnO NPs on surface of Fe O /SiO /PATL.
2
3
4
2
1
02
00
1
9
9
9
9
9
8
8
8
8
6
4
2
0
8
6
4
a
c
b
3
0
130
230
330
430
530
630
Temperature oC
Figure 5 TGA analysis of (a) Fe O /SiO –NH (b) Fe O /SiO /PATL and (c) Fe O /SiO /PATL/MnO .
3
4
2
2,
3
4
2
3
4
2
2
3
.2. Evaluation of the catalytic activity of Fe O /SiO /PATL/MnO through the selective
3 4 2 2
oxidation alcohols to corresponding aldehydes and ketones.
In order to optimize the reaction conditions, oxidation of benzylalcohol was selected as a model
reaction and various medium such as catalyst amount, solvent and base amount applied to
investigate the best medium for selective oxidation primary alcohols to aldehydes. (Table 2). The
comparison of the results related to the use of polar and nonpolar solvents that the efficiency of
o
DMSO was higher than other solvents; the reaction yield was 70% after 30 min at 60 C. It was
found that addition of water to the DMSO solution can improve the reaction outcome and
interestingly (entries 10, 11) when the reaction was performed in DMSO/water mixture (1:1) the
corresponding product was obtained qualitatively (entry 11) The order of activity of different
solvents have been shown in Table 2 (Entries 1ꢀ9). It is important to note that the aerobic
oxidation of benzylalcohol did not proceed well efficiently without air blowing and the

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benzaldehyde was produced about 56% after 3 h stirring at room temperature. Furthermore,
effect of various inorganic base was examined on the reaction yields, as well. Based on these
experiments K CO was found as the preferred inorganic base. Also, different amount of the
2
3
K CO was used to obtain the preferred amount of it (Entries 13ꢀ17). To illustrate the need for
2
3
catalyst, the feasibility of model reaction is checked in the absence of catalyst. No product was
o
obtained at 60 C after 12 h. The desired product was scarcely obtained in the presence of
Fe O /SiO ꢀNH /PATL as catalyst. However, the MnO NPs and MnO ꢀimmobilized
3
4
2
2
2
2
Fe O /SiO ꢀNH were employed in model reaction under optimum conditions, which were
3
4
2
2
obtained moderate yields within 1h. This further confirms the effect of the polymer layer on the
catalytic activity of MnO NPs. The main benefit of the polymeric shell seems to come from
2
increased the interaction of nanocomposites with substrates by the hydrogen bands and dipoleꢀ
dipole interactions. The results showed that the Fe O /SiO /PATL/MnO had high dispersibility
3
4
2
2
in compared to MnO and Fe O /SiO ~NH under reaction conditions. Additionaly, interactions
2
3
4
2
2
between metal d orbital and πꢀlevel of part of polymer’s amide can effect on the delocalization of
the electron density over both metal and ligand. These interactions may change the
3
2,33
electrochemical properties of metal.
a
Table 2 Optimization of the reaction conditions for aerobicoxidation of alcohols
b
Entry
Catalyst
Amount of catalyst (mol%)
0.06 g (4.8)
Solvent
Toluene
Base (mmol)
Yield (%)
37
1
2
3
4
5
6
7
8
9
Fe
Fe
Fe
Fe
Fe
Fe
Fe
Fe
Fe
Fe
3
3
3
3
3
3
3
3
3
3
O
O
O
O
O
O
O
O
O
O
4
4
4
4
4
4
4
4
4
4
/SiO
2
2
2
2
2
2
2
2
2
2
/PATL/MnO
2
2
2
2
2
2
2
2
2
2
K
K
K
K
K
K
K
K
K
K
2
2
2
2
2
2
2
2
2
2
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
3
3
3
3
3
3
3
3
3
3
(0.5)
(0.5)
(0.5)
(0.5)
(0.5)
(0.5)
(0.5)
(0.5)
(0.5)
(0.5)
/SiO
/SiO
/SiO
/SiO
/SiO
/SiO
/SiO
/SiO
/SiO
/PATL/MnO
/PATL/MnO
/PATL/MnO
/PATL/MnO
/PATL/MnO
/PATL/MnO
/PATL/MnO
/PATL/MnO
/PATL/MnO
0.06 g (4.8)
nꢀHexane (r.t.)
Acetonitrile
Dichloroethan
oꢀXylene
DMF
trace
46
0.06 g (4.8)
0.06 g (4.8)
50
0.06 g (4.8)
58
0.06 g (4.8)
60
0.06 g (4.8)
Water
30
0.06 g (4.8)
Ethanol
35
0.06 g (4.8)
DMSO
70
1
1
1
0
1
2
0.06 g (4.8)
DMSO/Water
78
(
2:1)
DMSO/Water
1:1)
DMSO/Water
Fe
Fe
O
O
/SiO
/SiO
/PATL/MnO
/PATL/MnO
0.06 g (4.8)
0.03 g (2.4)
K
K
CO
CO
(0.5)
(0.5)
92
54
3
3
4
4
2
2
2
2
2
2
3
3
(

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(
1:1)
DMSO/Water
1:1)
DMSO/Water
1:1)
DMSO/Water
1:1)
DMSO/Water
1:1)
DMSO/Water
1:1)
DMSO/Water
1:1)
DMSO/Water
1:1)
DMSO/Water
1:1)
1
1
1
1
1
1
1
2
3
4
5
6
7
8
9
0
Fe
Fe
Fe
Fe
Fe
3
3
3
3
3
O
O
O
O
O
4
4
4
4
4
/SiO
/SiO
/SiO
/SiO
/SiO
2
2
2
2
2
/PATL/MnO
/PATL/MnO
/PATL/MnO
/PATL/MnO
/PATL/MnO
2
2
2
2
2
0.1 g (8)
0.06 g (4.8)
0.06 g (4.8)
0.06 g (4.8)
0.06 g (4.8)
0.006 g (7)
0.06 g
K
K
K
2
2
2
CO
CO
CO
3
3
3
(0.5)
(0.1)
(0.3)
88
92
81
50
58
43
68
(
(
(
NaOAc (1)
(
Et N (1)
3
(
MnO
NPs
K
K
K
CO
CO
CO
(0.5)
(0.5)
2
2
2
2
3
3
3
(
Fe O /SiO ꢀNH / MnO
3 4 2 2 2
(
Fe
O
/SiO
/PATL
0.06 g
(0.5)
trace
3
4
2
(
a
o
b
Reaction conditions: benzylalcohol (1.0 mmol), solvent (5 mL), air oxidant, 60 C, 30 min. Yield
determined by GC analysis.
Subsequently, to investigate the efficiency and applicability of this catalyst in the aerobic
oxidation of alcohols to aldehydes and ketones, the reaction was extended to other primary and
o
secondry alcohols at 60 C in mixture of DMSO/Water (1:1) in presence of K CO (0.5 mmol),
2
3
as base (Table 3).
Table 3 Selective aerobic oxidation of variuos alcohols to corresponding aldehydes and ketones
a
Entry
Alcohol
Time (min)
Yield (%)
1
30
92
OH
2
3
30
30
90
89
MeO
F
OH
OH

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4
5
6
7
30
30
50
50
90
93
93
92
Cl
OH
OH
O N
2
OH
OH
OH
30
50
94
89
8
9
HO
1
0
1
2
50
50
50
82
84
80
OH
OH
1
1
OH
1
3
OH
50
90
a
Yield determined by GC analysis.
3
.3. Recyclability of the Fe O /SiO /PATL/MnO
3 4 2 2
Recyclability of the Fe O /SiO /PATL/MnO was examined in the oxidation reaction of
3
4
2
2
benzylalcohol. For this reason, catalyst which was recovered from reaction using external
magnet and reused in the reaction after washed by ethanol and drying under vacuum at 80 °C to
12 h. This procedure was carried out for five repetitive cycles. The results showed that only
minor decreases in the reaction yields were observed (Figure 6) and the activity of the catalyst
was saved during successive uses.

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−
1
The concentration of manganese after 5th run measured to be 0.72 mmol g by ICPꢀOES. The
TEM micrographs of Fe O /SiO /PATL/MnO recycled after 5th run shows the surfaces of
3
4
2
2
nanocomposites are covered with MnO NPs with an average size of 12 nm (Figure 7).
2
Reusability of catalyst
9
8
8
7
7
0
5
0
5
0
1
2
3
4
5
Run
Figure 6 Reusability of the catalyst for the oxidation of the alcohols in 5 run.
Fe O
3
4
MnO2
Figure 7 TEM images of recycled Fe O /SiO /PATL/MnO after 5th run.
3
4
2
2

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DOI: 10.1039/C5RA19093B
4. Conclusions
In this study, synthesis of Fe O /SiO /PATL/MnO core/shell nanocomposite was reported. The
3
4
2
2
catalyst was prepared by polymerization of ATL on surface of Fe O /SiO ꢀNH NPs via
3
4
2
2
ultrasonicꢀassisted method and formation of MnO NPs on this surface. The prepared catalysts
2
was characterized via FTꢀIR, XRD, TEM, SEM, EDX, CHN and TGA. The catalytic activity of
these catalysts were evaluated in the aerobic oxidation of alcohols to aldehydes and ketones in
mixture of DMSO/Water (1:1). The results showed that the Fe O /SiO /PATL/MnO had high
3
4
2
2
catalytic activity and selectivity for these reaction.
Acknowledgements
The authors gratefully acknowledge the financial support and technical support from Tabriz Branch,
Islamic Azad University, Razi University and Urmia University for the financial support of this research.
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1