Direct covalent attachment of Mn(III) salophen complex to the hydroxyapatite-encapsulated γ-Fe2O3 nanocrystallites: An efficient magnetic and reusable catalyst for oxidation of alcohols

Article abstract of DOI:10.1039/c5ra08594b

In the present work, the highly efficient oxidation of alcohols catalyzed by manganese(III) salophen acetate, [Mn(salophen)OAc], supported on hydroxyapatite coated magnetite nanoparticles, HAp-Fe₂O₃, is reported. First, the HAp-Fe₂O₃ nanoparticles were modified with 5-chloromethyl-2-hydroxybenzaldehyde and then using 1,2-diamino benzene, 2-hydroxybenzaldehyde and Mn(CH₃COO)₂·4H₂O, [Mn(salophen)OAc] was synthesized and attached to the support via covalent linkages. The prepared catalyst was characterized by FT-IR spectroscopy, X-ray diffraction, diffuse reflectance UV-Vis spectrophotometry and scanning electron microscopy. This new heterogeneous catalyst was used for efficient oxidation of alcohols with NaIO₄ at room temperature. This new heterogeneous catalyst is of high reusability in the oxidation reactions, in which the catalyst was reused several times without significant loss of its catalytic activity.

Full text of DOI:10.1039/c5ra08594b

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PAPER
Direct covalent attachment of Mn(III) salophen
complex to the hydroxyapatite-encapsulated g-
Fe O nanocrystallites: an efficient magnetic and
Cite this: RSC Adv., 2015, 5, 70577
2
3
reusable catalyst for oxidation of alcohols
Ali Saffar-Teluri
In the present work, the highly efficient oxidation of alcohols catalyzed by manganese(III) salophen acetate,
[
Mn(salophen)OAc], supported on hydroxyapatite coated magnetite nanoparticles, HAp–Fe
First, the HAp–Fe nanoparticles were modified with 5-chloromethyl-2-hydroxybenzaldehyde and then
using 1,2-diamino benzene, 2-hydroxybenzaldehyde and Mn(CH COO) $4H O, [Mn(salophen)OAc] was
2 3
O , is reported.
2
O
3
3
2
2
synthesized and attached to the support via covalent linkages. The prepared catalyst was characterized
by FT-IR spectroscopy, X-ray diffraction, diffuse reflectance UV-Vis spectrophotometry and scanning
electron microscopy. This new heterogeneous catalyst was used for efficient oxidation of alcohols with
Received 8th May 2015
Accepted 21st July 2015
DOI: 10.1039/c5ra08594b
4
NaIO at room temperature. This new heterogeneous catalyst is of high reusability in the oxidation
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reactions, in which the catalyst was reused several times without significant loss of its catalytic activity.
The use of nanostructured materials as support for different
versions of catalyst immobilization is increasing. In spite of the
1
. Introduction
Selective catalytic oxidation of alcohols to carbonyls is one of advantages of supported catalysts, the tedious recycling of
the most important chemical transformations in industrial catalysts by ltration and the inevitable loss of some solid
chemistry. Carbonyl compounds such as ketones and aldehydes catalyst in the separation process, especially with air sensitive
are the precursors for many drugs, vitamins, and fragrances and materials, are some of the drawbacks of the traditional proce-
they are also important intermediates for many complex dures. Therefore, there is more interest to introduce more effi-
1
,2
syntheses.
oxidation. Conventional methods for these transformations standpoint of green chemistry. Magnetic nanoparticles are
Numerous methods are available for alcohol cient manners for catalyst recovery, especially from the
6
–8
generally involve the use of stoichiometric or more than stoi- receiving increasing interest in recent years. The magnetic
chiometric quantities of inorganic oxidants such as chro- nature of these particles allows for easy recovery and recycling
mium(VI) and permanganates and also the use of toxic, of the catalysts by an external magnetic eld, which may opti-
3
corrosive and expensive oxidants. The search for new oxidation mize operational cost and enhance product's purity.
catalysts is one of the most important topics connected with
4 6 2
Hydroxyapatite (Ca10(PO ) (OH) , HAp) is a principal
both industrial and academic research.
component of animal bones and its synthetic form nds many
Manganese Schiff base complexes are known as powerful applications in bioceramics, chromatographic adsorbents,
homogeneous catalysts for oxidation of organic compounds lighting materials, powder carriers, chemical sensors, retardant
and various single oxygen atom donors such as NaClO, PhIO, of cancer cells, drug delivery agent, catalyst supports, catalysts
KHSO
the catalytic activity of manganese Schiff base complexes in oxidation, ion conductors and powders for articial teeth and
5 2 2 4
, H O and NaIO
have been used in these reactions. But, for dehydration and dehydrogenation of alcohols, methane
9–14
homogeneous conditions usually decreases with time due to the bones paste germicides.
These properties relate to various
oxidation of ligand or formation of dimeric oxo- and peroxo- surface characteristics of HAp. It has been found that HAp
15
bridged complexes. The heterogenization of these homoge- surface possesses P–OH groups acting as sorption sites. The
neous catalysts on solid supports displayed high recyclability sorption properties of HAp are of great importance for both
and stability, and also decreased the possibility of dimerization, environmental processes and industrial purposes.
4,5
and formation of undesired mono-oxo manganese(IV).
Covalent surface modication of inorganic materials using
organic compounds is an efficient way to obtain materials
having specic properties. Recently, the reaction between
Department of Chemistry, Faculty of Science, Najafabad Branch, Islamic Azad phenyl phosphonic dichloride (C
University, Najafabad 85141-43131, Isfahan, Iran. E-mail: a.saffar.t@iaun.ac.ir;
5 2
H P(O)Cl ) and calcium
6
hydroxyapatite has been investigated. From their results, a
a.saffar13@gmail.com
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cooled to room temperature and aged overnight. The dark
brown precipitate formed was ltered, washed repeatedly with
deionized water until neutral, and air dried under vacuum at
room temperature. The as-synthesized sample was calcined at
ꢁ
3
00 C for 3 h, giving a reddish-brown powder.
Fig.
1
Covalent surface modification of hydroxyapatite using
2
.2 Synthesis of manganese(III) salophen acetate supported
C
6
H
5
P(O)Cl
2
.
on hydroxyapatite coated Fe
OAc]
2 3 2 3
O [g-Fe O @HAp/Mn(salophen)
The procedures of the catalyst synthesis is shown in Fig. 3.
The HAp-encapsulated-g-Fe nanoparticles (3.0 g) were
2 3
O
dispersed in ethanol (50 ml) for 1 h. Then, 5-chloromethyl-2-
hydroxybenzaldehyde (30 mmol) was added and the reaction
mixture was reuxed for 24 h. At the end of this time, the
mixture was cooled to room temperature and a solution of 1,2-
diamino benzene (10 mmol) in ethanol (20 ml) was added
dropwise to the above solution. Aer stirring for 12 h, 2-
hydroxybenzaldehyde (10 mmol) was added to mixture. The
resulted mixture was heated under reux for 12 h. In order to
synthesize Mn(III) complex, Mn(CH COO) $4H O (10 mmol) was
4 2 3
Fig. 2 Oxidation of alcohols with NaIO catalyzed by g-Fe O @HAp/
Mn(salophen)OAc.
3
2
2
added to the suspension and stirred at reux temperature under
Ar for 8 h. Aer this time, the precipitate was collected with a
permanent magnet, and rinsed with ethanol three times. The
product was dried and stored under vacuum conditions.
The manganese(III) salophen loading on g-Fe O @HAp
2 3
support, determined by ICP analysis, was calculated from the
manganese content in the heterogenized catalyst.
mechanism has been proposed for the formation of covalent
P–O–P bonds as the result of a reaction between the C P(O)
and/or OH ions of the
6 5
H
ꢀ
2 4
organic reagent and HPO
ꢀ
Cl
hydroxyapatite (Fig. 1).
16–22
Herein, we report the attachment of Mn(salophen)OAc on
HAp-coated g-Fe O via a strong covalent interaction and
2
3
investigate its catalytic activity in alcohols oxidation as a
magnetically recyclable oxidation catalyst (Fig. 2).
2
.3 Typical procedure for oxidation of alcohols with NaIO4
2. Experimental
catalyzed by g-Fe O @HAp/Mn(salophen)OAc
2
3
All materials were commercial reagent grade. These materials All of the reactions were carried out at room temperature under
were obtained from Merck or Fluka chemical companies and air in a 25 ml ask equipped with a magnetic stirrer bar. A
used without further purication. The diffuse reectance UV- solution of NaIO4 (1 mmol) in H O (5 ml) was added to a
2
Vis spectra were recorded by a solid UV-Vis JASCO model V- mixture of alcohol (0.5 mmol) and g-Fe O @HAp/Mn(salophen)
2
3
6
70 spectrophotometer. FT-IR spectra were obtained with OAc (130 mg) in CH CN (5 ml). Progress of the reactions was
3
ꢀ1
potassium bromide pellets in the range 400–4000 cm with a monitored by thin layer chromatography (TLC) technique. At
JASCO 6300 spectrophotometer. A scanning electron micro- the end of the reaction, the catalyst was removed by a magnet.
graph of the catalyst was taken on a Philips XL 30 SEM instru- The catalyst was thoroughly washed with Et O and combined
2
ment. Information about the phase of catalyst was obtained by washings and ltrates were puried on a silica gel plate or a
ꢀ
the X-ray powder diffractometer (Cu Ka, k ¼ 1.54178 A; Philips) silica gel column to give the pure product. All of the products
ꢁ
ꢁ
in the Bragg angle ranging between 10 and 80 .
are known compounds and were identied by comparison of
their physical data with those of authentic samples. Blank
experimental with using the same experimental conditions in
the absence of catalyst or in the absence of oxidant were also
performed.
2
.1 Synthesis of HAp-encapsulated-g-Fe
2 3 2 3
O (g-Fe O @HAp)
Preparation of HAp-encapsulated-g-Fe O was according to the
2
3
23,24
previously reported method.
FeCl $6H O (3.7 mmol) were dissolved in deionized water (30
ml) under Ar atmosphere at room temperature, and the
resulting solution was added to a 25% NH OH solution (10 ml)
with vigorous mechanical stirring. A black precipitate Fe was The reusability of the g-Fe
produced instantly. Aer 15 min, 100 ml of Ca(NO ) $4H O lysts was investigated in the multiple sequential oxidation of 4-
2 2
FeCl $4H O (1.85 mmol) and
3
2
2.4 Catalyst reuse and stability
4
3
O
4
2 3
O
@HAp/Mn(salophen)OAc cata-
3
2
2
(
33.7 mmol, 0.5 M) and (NH ) HPO (20 mmol, 3.0 M) solutions methoxybenzyl alcohol as described above. At the end of each
4 2 4
adjusted to pH 11 were added drop-wise to the obtained reaction, the catalyst was separated from the reaction mixture
precipitate over 30 min with mechanical stirring. The resultant by a permanent magnet, washed and dried carefully before
ꢁ
milky solution was heated to 90 C. Aer 2 h, the mixture was using it in the next run.
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2 3
Fig. 3 Synthesis of g-Fe O @HAp/Mn(salophen)OAc.
ꢀ
1
new band at 422 cm region assignable to yMn–N for Mn(salo-
3
. Results and discussion
phen)OAc complex. The FT-IR bands of g-Fe
Mn(salophen)OAc at 1450–1550 cm are due to the stretch-
ing vibrations of C]C bonds of the phenyl ring. The presence of
2
O
3
@HAp-
3
.1 Preparation and characterization of the catalyst,
g-Fe @HAp-Mn(salophen)OAc
For identication of the structure of g-Fe
Mn(salophen)OAc, we studied FT-IR spectra of g-Fe
and g-Fe @HAp-Mn(salophen)OAc (Fig. 4). It was found that
all characteristic bands of g-Fe @HAp appeared in the FT-IR
spectrum of g-Fe @HAp-Mn(salophen)OAc. For example,
PO -derived bands at 481, 607, 641, 970, 1043, 1104 cm
ꢀ1
2 3
O
ꢀ1
2 3
O
2 3
O @HAp
@HAp- a new band at 1360 cm region assignable to the acetate ion
2 3
O
2 3
O
2 3
O
ꢀ
1
25,26
,
4
are observed in these spectra. Stretching mode of Fe–O appears
ꢀ
1
ꢀ1
at 573 cm . The band at 1644 cm reecting OH stretching is
27
also observed. In addition, it was noted that a new band at
ꢀ
1
1
2 3
610 cm appeared in the FT-IR spectrum of g-Fe O @HAp-
Mn(salophen)OAc, which was attributed to the vibration of
the azomethine group (C]N) of the salophen complex. The
vibration of the azomethine group (C]N) of the free ligand was
ꢀ
1
observed at 1627 cm . In the complex this band is shied to
the lower frequency, indicating that the nitrogen atom of the
azomethine group is coordinated to the metal ion. Coordina-
tion of azomethine nitrogen is conrmed with the presence of a
2 3 2 3
Fig. 4 FT-IR spectra of (a) g-Fe O @HAp and (b) g-Fe O @HAp-
Mn(salophen)OAc.
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Fig. 7 UV-Vis spectrum of Mn(salophen)OAc.
Fig. 5 FT-IR spectrum of Mn(salophen)OAc.
(
OAc) for this complex. Due to overlapping by the framework of
hydroxyapatite, some of vibration of the groups were absent in
the spectrum of g-Fe @HAp-Mn(salophen)OAc.
2 3
O
The above results are conrmed by the FT-IR spectrum of the
homogeneous Mn(salophen)OAc in Fig. 5.
The diffuse reectance spectra provide further evidence for
the presence of the Mn(salophen) complex on the support. The
diffusion reection UV-Vis spectra of g-Fe
@HAp-Mn(salophen)OAc are shown in Fig. 6. The diffusion
reection UV-Vis spectrum of g-Fe @HAp shows three bands
at 225, 270 and 345 nm which could be due to the ligand (O) to
2 3 2
O @HAp and g-Fe -
O
3
2 3 2 3
Fig. 8 XRD patterns of (a) g-Fe O @HAp and (b) g-Fe O @HAp-
Mn(salophen)OAc.
2 3
O
3
+
metal (Fe ) charge transfer transitions and the excitation of an
3
+
3+
Fe –Fe pair. The absorption spectrum of g-Fe O @HAp–
2
3
Mn(salophen)OAc exhibits three new bands near 220, 295 and
80 nm. The two bands near 220 and 295 nm are attributed to
3
the p–p* transition of the benzene ring of salicylaldehyde, and
the n–p* transition of the azomethine chromophore, respec-
28
tively, while the third band near 380 nm, as the most charac-
teristic adsorption band of Mn(III)salophen complex, is due to
29
metal to ligand charge transfer (MLCT), indicating that g-
Fe @HAp-Mn(salophen)OAc have been successfully in situ
2 3
O
synthesized by consecutive reactions. In this spectrum two
bands near 225 and 345 nm are attributed to support. The band
270 nm in spectrum was absent due to overlapping by adsorp-
tion band of Mn(III)salophen complex.
2 3
Fig. 6 Diffusion reflection UV-Vis spectra of (a) g-Fe O @HAp and (b)
g-Fe @HAp-Mn(salophen)OAc.
2
O
3
2 3
Fig. 9 SEM image of the g-Fe O @HAp-Mn(salophen)OAc.
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Table
1
Optimization of the g-Fe
2
O
3
@HAp-Mn(salophen)OAc
For further investigation, the UV-Vis spectrum of homoge-
neous Mn(salophen)OAc is shown in Fig. 7. Mn(salophen)OAc
shows an absorption peak at 380 nm. Since the g-Fe O @HAp
did not show any peak at 380 nm in its diffuse reectance
spectrum, therefore, it is conrmed that Mn(salophen)OAc has
a
amount in the oxidation of 4-methoxybenzyl alcohol with NaIO
4
b
2 3
Entry
Catalyst amount (mg)
Aldehyde yield (%) aer 1 h
1
2
3
4
5
0
90
110
130
145
10
45
63
95
95
been supported on g-Fe
The characterization of g-Fe
Mn(salophen)OAc was further carried out byXRD patterns
2 3
O @HAp.
2 3 2 3
O @HAp and g-Fe O @HAp-
(
(
Fig. 8). There was no obvious difference between the support
g-Fe O @HAp) and the catalyst (g-Fe O @HAp-Mn(salophen)
a
4
Reaction conditions: 4-methoxybenzyl alcohol (0.5 mmol), NaIO (1
b
2
3
2 3
3 2
mmol), catalyst, CH CN/H O (5/5 ml). Isolated yield.
OAc). This result indicates that supporting of Mn(salophen)
OAc on g-Fe O @HAp does not change the support structure.
2
3
2 3
Fig. 9 depicts the SEM image of the g-Fe O @HAp-
Table 2 The effect of oxidant on the oxidation of 4-methoxybenzyl
Mn(salophen)OAc nanocatalyst. The catalyst nanospheres
show a smooth surface and mean diameter of catalyst is less
than 100 nm.
alcohol catalyzed by g-Fe
temperature
O
2 3
@HAp-Mn(salophen)OAc at room
a
b
Entry
Oxidant
Aldehyde yield (%) aer 1 h
3
.2 Catalytic experiments
1
2
3
4
5
6
7
8
NaIO
Oxone (KHSO
4
95
85
80
35
20
50
45
10
5
)
The prepared catalyst was used for the oxidation of alcohols
with sodium periodate at room temperature. First, the reaction
parameters, such as catalyst amount, type of solvent and
oxidant, were optimized in the oxidation of 4-methoxybenzyl
alcohol.
H
H
2
O
O
2
2
2
/urea
tert-BuOOH
Bu NIO
NaOCl
No oxidant
4
4
3
.2.1 The effect of catalyst amount on the oxidation of 4-
(1 methoxybenzyl alcohol catalyzed by g-Fe O @HAp-Mn(salo-
4
a
Reaction conditions: 4-methoxybenzyl alcohol (0.5 mmol), NaIO
2
3
b
3 2
mmol), catalyst (130 mg), CH CN/H O (5/5 ml). Isolated yield.
phen)OAc. In order to optimize the catalyst amount, different
amounts of g-Fe @HAp-Mn(salophen)OAc were used in the
2 3
O
4 2 2
Fig. 10 The proposed intermediates for formation of manganese-oxo intermediate from t-BuOOH, NaIO and H O .
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Table 3 The effect of solvent on the oxidation of 4-methoxybenzyl solvents were checked in the oxidation of 4-methoxybenzyl
alcohol with NaIO
room temperature
4 2 3
catalyzed by g-Fe O @HAp-Mn(salophen)OAc at
alcohol with NaIO . Among the different mixtures of acetoni-
trile, acetone, ethanol (single phase systems), dichloromethane,
4
ab
chloroform (two phase systems with n-Bu NBr as a phase
Entry
Solvent
Aldehyde yield (%) aer 1 h
4
transfer catalyst) and water, a 1 : 1 mixture of acetonitrile/water
was chosen as the reaction medium, because a higher catalytic
activity was observed (Table 3). The higher catalytic activity in
the acetonitrile/water mixture is attributed to the polarity of
1
2
3
4
5
6
CH
CH
CH
3
3
3
CN/H
OCH
CH OH/H
/H
Cl
CHCl /H
2
O
/H O
2
95
50
45
10
30
20
3
2
2
O
CCl
CH
4
2
O
/H
4
solvent and solubility of NaIO in it. For six solvents acetonitrile,
2
2
2
O
O
acetone, ethanol, dichloromethane, chloroform and water, the
dielectric constants are 37.5, 20.7, 24.5, 8.93, 4.81 and 80.1,
respectively.
3
2
a
Reaction conditions: 4-methoxybenzyl alcohol (0.5 mmol), NaIO
4
(1
b
2
mmol), catalyst (130 mg), solvent/H O (5/5 ml). Isolated yield.
3
.3 Oxidation of alcohols with NaIO catalyzed by g-
4
oxidation of 4-methoxybenzyl alcohol (0.5 mmol) with NaIO
4
(1
2 3
Fe O @HAp-Mn(salophen)OAc
mmol). The best results were obtained with 130 mg of the
catalyst (Table 1).
First, in order to show the effect of Mn(salophen) in the
oxidation of alcohols, blank experiments in the presence of g-
Fe O or g-Fe O @HAp were carried out and the results showed
2 3 2 3
that only negligible amounts of oxidation products were
detected. Also, the same reaction was designed for the oxidation
3
.2.2 The effect of oxidant on the oxidation of 4-methoxy-
benzyl alcohol. The ability of different single oxygen donors,
such as NaIO , H , UHP (urea–H ) and tert-BuOOH, was
investigated in the oxidation of 4-methoxybenzyl alcohol. The
results, which are summarized in Table 2, showed that NaIO is
4
2
O
2
2 2
O
4-methoxybenzyl alcohol in the presence of Mn(salophen)OAc.
4
The results showed that only 50% of the corresponding alde-
the best oxygen source because of its good oxidation conversion,
inertness in the absence of catalyst and its high solubility in
CH CN/H O. Also, the high activity of NaIO can be attributed to
hyde is produced aer 60 min, while, by g-Fe O @HAp-
2
3
Mn(salophen)OAc, the reaction is almost completed (95%
yield). This can be related to the nanoparticle nature of g-Fe
@HAp, with a high isolation of catalytic active sites, which in
turn increases the catalytic activity. Therefore, g-Fe @HAp-
Mn(salophen)OAc was found as an efficient catalyst for the
oxidation of alcohols with NaIO at room temperature under air
Table 4).
3
2
4
2
-
the high tendency of this oxidant for formation of manganese-
oxo intermediate from the proposed intermediate because of
the steric hindrance of the bonds (Fig. 10).
O
3
2 3
O
3.2.3 The effect of solvent on the oxidation of 4-methoxy-
4
benzyl alcohol. In order to choose the reaction media, different
(
4 2 3
Table 4 Oxidation of alcohols with NaIO catalyzed by g-Fe O @HAp-Mn(salophen)OAc at room temperature
a
b
Entry
Alcohol
Product
Yield (%)
Time (min)
1
2
3
4
5
6
7
8
9
C
6
H
5
–CH
o-NO –C
m-NO –C
p-NO –C
o-Br–C
p-Br–C
o-Cl–C
p-Cl–C
p,o-Cl
o-F–C
o-H C–C
p-H C–C
2
OH
–CH
–CH
–CH
–CH
–CH
–CH
–CH
–CH
C
6
H
5
–CHO
o-NO –C
m-NO –C
p-NO –C
o-Br–C
p-Br–C
o-Cl–C
p-Cl–C
p,o-Cl
o-F–C
o-H C–C
p-H C–C
o-H CO–C
p-H CO–C
PhCH CHO
PhCOCH CH
PhCH CH CHO
92
85
86
90
92
94
90
90
92
93
95
95
95
95
85
89
84
78
76
75
78
80
150
135
120
85
80
80
78
75
78
75
65
70
2
6
H
4
2
OH
2
6 4
H –CHO
2
6
H
4
2
OH
OH
2
6
H
4
–CHO
–CHO
2
6
H
4
2
2
6
H
4
6
H
4
2
OH
OH
OH
6 4
H –CHO
6
H
4
2
6
H
4
–CHO
–CHO
6
H
H
–C
4
2
6
H
4
6
4
2
OH
6
H
4
–CHO
–CHO
–CHO
–CHO
–CHO
2
6
H
3
2
OH
2
–C
6
H
3
10
11
12
13
14
15
16
17
18
19
20
21
6
H
4
–CH
2
OH
6
H
4
3
6
H
4
–CH
–CH
–CH
–CH
OH
PhCH(OH)CH
PhCH CH CH
CH
2
OH
OH
OH
OH
3
6
H
H
4
3
6
H
4
2
3
6
4
o-H
p-H
3
CO–C
CO–C
CH
6
H
4
2
3
6
H
4
–CHO
–CHO
3
6
H
4
2
3
6
H
4
60
PhCH
2
2
2
140
100
150
155
140
145
140
2
CH
3
2
3
2
2
2
OH
OH
2
2
CH
CH
CH
CH
3
3
3
3
(CH
(CH
2
)
)
6
5
2
CH
CH
CH
CH
3
3
3
3
(CH
(CH
CH
CH
2
)
)
6
CHO
COCH
3
2
CH(OH)CH
CH OH
CH(OH)CH
3
2
5
CH
CH
2
CH
2
2
2
2
CH CHO
2
3
2
COCH
3
a
b
Isolated yield. All of the products are known compounds and were identied by comparison of their physical data with those of authentic
samples.
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This heterogeneous catalyst was applicable for the oxidation water and releases the catalyst for the next catalytic cycle
of a wide variety of primary and secondary alcohols to corre- (Fig. 11).
sponding aldehydes and ketones. As shown in Table 4, benzyl
alcohol and substituted benzyl alcohols are converted to their
corresponding aldehydes efficiently. The electron donor
3.5 Catalyst reuse and stability
substituted groups on benzene ring of alcohols, accelerate the The reusability of a heterogeneous catalyst is of great impor-
reaction and acceptors groups have the opposite effect. In this tance from synthetic and economical points of view. The
oxidation process, the aromatic primary alcoholic groups were homogeneous Mn(salophen)OAc cannot be recovered even
oxidized with faster rate and higher yields than the aliphatic
groups.
Table 5 The results of catalyst recovery and the amounts of manga-
nese leached in the oxidation of 4-methoxybenzyl alcohol with
a
3
.4 Proposed mechanism for oxidation of alcohols with
NaIO catalyzed by g-Fe @HAp-Mn(salophen)OAc
The exact mechanism for oxidation of alcohols with NaIO
sodium periodate
4
2 3
O
b
c
Run
Yield (%)
Mn leached (%)
4
in
the presence of Schiff bases was not reported in the literatures.
However, based on the solvents and substituents effects, a
plausible mechanism is that the manganese salophen 1 is rst
transformed to the manganese-oxo intermediate 5 in the pres-
1
2
3
4
5
6
95
95
92
90
90
87
0.28
0.10
0
0
0
ence of NaIO
4
. The oxo compound reacts with alcohol to afford
0
intermediates 7 and 8 by electrophilic oxygen of the oxo
compound. The intermediate 9 can be formed from 7 and 8 and
is nally converted to the desired product by elimination of
a
Reaction conditions: 4-methoxybenzyl alcohol (0.5 mmol), NaIO
4
(1
b
mmol), catalyst (130 mg), CH
3
CN/H
2
O (5/5 ml). Isolated yield.
c
Determined by ICP.
Fig. 11 The proposed mechanism for the oxidation of alcohols.
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3 2 2 3
Fig. 12 (A) Catalyst dispersed in CH CN/H O, (B) g-Fe O @HAp-Mn(salophen)OAc nanoparticles adsorbed on the magnetic stirring bar and (C)
catalyst separation by a magnet.
2 3
Table 6 Comparison of the results obtained for oxidation of alcohols catalyzed by g-Fe O @HAp-Mn(salophen)OAc with some of those
reported in the literature
Entry
Catalyst
Co@SiO
Oxidant/time(min)/yield(%)
Ref.
1
2
3
4
5
6
7
2
@Schiff base nickel complex
H
2
O
2
/50/94
tert-BuOOH/480/44
/180/33
30
31
32
33
34
35
[Co(salophen)]/bentonite
Cobalt salophen encapsulated in zeolite Y
O
2
CoFe
2
O
4
@SiO
2
@Co(II) salophen complex
H
H
2
O
O
2
/120/95
/120/66
Sulphonato-salen-chromium(III) hydrotalcites
Mn(salen)OAc
2
2
NaIO
NaIO
4
/30/91
/80/92
By g-Fe
2
O
3
@HAp–Mn(salophen)OAc
4
This work
once, in contrast, the g-Fe O @HAp magnetic nanoparticles catalyst showed excellent catalytic capability in the oxidation of
2
3
supported catalyst can be separated and reused several times alcohols and could be reused for at least 6 times without loss of
without signicant loss of its activity. The reusability of g-Fe
@HAp-Mn(salophen)OAc was investigated in the multiple
sequential oxidation of 4-methoxybenzyl alcohol with NaIO . At
2
-
its activity.
O
3
4
Acknowledgements
the end of the each reaction, the catalyst was separated by a
permanent magnet, washed with Et O and dried carefully
before using it in the next run. Aer using the catalyst for six
consecutive times, the aldehyde yield was 87% (Table 5)
2
We gratefully acknowledge for nancial support from the
Research Council of Islamic Azad University of Najafabad
Branch.
(Fig. 12). The ltrates were collected for determination of Mn
leaching. The results showed that aer two rst runs, no
remarkable manganese was detected in the ltrates by ICP References
analysis.
1
2
3
R. A. Sheldon and J. K. Kochi, Metal-catalyzed Oxidation of
The results obtained by this method were compared with
some of previously reported methods for the oxidation of alco-
hols with different catalysts. As can be seen in Table 6, the
presented method is more efficient and more acceptable in
term of yield, reaction time and reusability.
Organic Compounds, Academic Press, New York, 1981.
M. Hudlicky, Oxidations in Organic Chemistry, ACS,
Washington, DC, 1990.
W. P. Griffith and J. M. Joliffe, in Dioxygen Activation and
Homogeneous Catalytic Oxidation, ed. L. L. Simandi,
Elsevier, Amsterdam, 1991.
4
Q. H. Fan, Y. M. Li and A. S. C. Chan, Chem. Rev., 2002, 102,
4
. Conclusion
3385.
A novel catalytic system by direct covalent attachment of Mn(III)
salophen complex to the hydroxyapatite-encapsulated magnetic
g-Fe O nanocrystallites was synthesized. This heterogenized
2 3
5 C. E. Song and S. G. Li, Chem. Rev., 2002, 102, 3495.
6 Y. J. Wang, J. D. Chen, K. Wei, S. H. Zhang and X. D. Wang,
Mater. Lett., 2006, 60, 3227.
70584 | RSC Adv., 2015, 5, 70577–70585
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
7
8
Q. J. He and Z. L. Huang, J. Cryst. Growth, 2007, 300, 460.
H. Tanaka, M. Futaoka, R. Hino, K. Kandori and T. Ishikawa,
J. Colloid Interface Sci., 2005, 283, 609.
22 H. Roussiere, G. Montavon, S. Laib, P. Janvier, B. Alonso,
F. Fayon, M. Petit, D. Massiot, J.-M. Bouler and B. Bujoli, J.
Mater. Chem., 2005, 15, 3869.
9
L. Lopez and L. Troisi, Tetrahedron Lett., 1989, 30, 3097.
23 K. Mori, S. Kanai, T. Hara, T. Mizugaki, K. Ebitani,
K. Jitsukawa and K. Kaneda, Chem. Mater., 2007, 19, 1249.
24 T. Hara, T. Kaneta, K. Mori, T. Mitsudome, T. Mizugaki,
K. Ebitani and K. Kaneda, Green Chem., 2007, 9, 1246.
25 S. Kannan, A. F. Lemos and J. M. F. Ferreira, Chem. Mater.,
2006, 18, 2181.
10 J. Kagan, P. Y. Juang, B. E. Firth, J. Przyb, T. ytek and
S. P. Singh, Tetrahedron Lett., 1977, 18, 4289.
11 J. Delaunay, A. Lebouc, A. Tallaec and J. Sinonet, J. Chem.
Soc., Chem. Commun., 1982, 387.
12 H. Monma and T. Kamiya, J. Mater. Sci., 1987, 22, 4247.
13 S. V. Dorozhkin and M. Epple, Angew. Chem., Int. Ed., 2002, 26 J. B. Liu, X. Y. Ye, H. Wang, M. K. Zhu, B. Wang and H. Yan,
41, 3130.
Ceram. Int., 2003, 29, 629.
14 S. Bose and S. K. Saha, Chem. Mater., 2003, 15, 4464.
15 T. G. Kim and B. Park, Inorg. Chem., 2005, 44, 9895.
16 A. Aissaa, M. Debbabia, M. Gruselleb, R. Thouvenotb,
27 J. G. Morales, R. R. Clemente, B. Armas, C. Combescure,
R. Berjoan, J. Cubo, E. Martinez, J. G. Carmona, S. Garelik,
J. Murtra and D. N. Muraviev, Langmuir, 2004, 20, 5174.
P. Gredinc, R. Traksmaad and K. Tonsuaadud, J. Solid 28 B. Bosnich, J. Am. Chem. Soc., 1968, 90, 627.
State Chem., 2007, 180, 2273.
29 S. M. Crawford, Spectrochim. Acta, 1963, 19, 255.
30 A. R. Judy-Azar and S. Mohebbi, J. Mol. Catal. A: Chem., 2015,
397, 158.
31 M. H. Peyrovi, V. Mahdavi, M. A. Salehi and R. Mahmoodian,
Catal. Commun., 2005, 6, 476.
1
1
7 S. C. D'Andrea and A. Y. Fadeev, Langmuir, 2003, 19, 7904.
8 L. E. Hammari, A. Laghzizil, A. Saoiabi, P. Barboux and
M. Meyer, Colloids Surf., A, 2006, 289, 84.
9 H. W. Choi, H. J. Lee, K. J. Kim, H.-M. Kim and S. C. Lee, J.
Colloid Interface Sci., 2006, 304, 277.
1
32 A. Zsigmond, F. Notheisz, G. Csjernyik and J.-E. B ¨a ckvall,
Top. Catal., 2002, 19, 119.
2
0 G. H. Nancollas, R. Tang, R. J. Phipps, Z. Henneman,
S. Gulde, W. Wu, A. Mangood, R. G. G. Russell and 33 M. Afshari, M. Gorjizadeh, S. Nazari and M. Naseh, Orient. J.
F. H. Ebetino, Bone, 2006, 38, 617. Chem., 2013, 29, 1523.
1 J. Robinson, I. Cukrowski and H. M. Marques, J. Mol. Struct., 34 G. Wu, X. Wang, J. Li, N. Zhao, W. Wei and Y. Sun, Catal.
2
2006, 825, 134.
Today, 2008, 131, 402.
35 B. Bahramian, V. Mirkhani, M. Moghadam and A. H. Amin,
Appl. Catal., A, 2006, 315, 52.
This journal is © The Royal Society of Chemistry 2015
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