Silica-coated magnetite nanoparticles stabilized simple Mn-tetraphenylporphyrin for aqueous phase catalytic oxidations with tert-butyl hydroperoxide

Article abstract of DOI:10.1039/c3ra47288d

An economic and environmentally friendly system for efficient and selective oxidation of industrially and biologically important substrates in water using tert-butyl hydroperoxide catalyzed by a new magnetically recoverable Mn-porphyrin was developed. The easily prepared heterogeneous catalyst was characterized by powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, FT-IR and UV-vis spectroscopy. The size of the catalyst was estimated to be about 10 nm. The thermal gravimetric analysis demonstrated that the nanocatalyst was thermally stable up to almost 300 °C. The reactivity, selectivity and scope of the reaction were investigated with a variety of olefins, saturated hydrocarbons, alcohols and organosulfur compounds. The reactions proceeded smoothly in the absence of surfactants, organic co-solvents and thus take place "on water". The separation and recycling of nanocatalyst as well as isolation of water-insoluble products were simple, effective and economical in this clean oxidation method.

Full text of DOI:10.1039/c3ra47288d

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Silica-coated magnetite nanoparticles stabilized
simple Mn-tetraphenylporphyrin for aqueous
phase catalytic oxidations with tert-butyl
hydroperoxide
Cite this: RSC Adv., 2014, 4, 9189
*
*
Abdolreza Rezaeifard, Parisa Farshid, Maasoumeh Jafarpour
and Gholamreza Kardan Moghaddam
An economic and environmentally friendly system for efficient and selective oxidation of industrially and
biologically important substrates in water using tert-butyl hydroperoxide catalyzed by new
a
magnetically recoverable Mn-porphyrin was developed. The easily prepared heterogeneous catalyst was
characterized by powder X-ray diffraction, transmission electron microscopy, scanning electron
microscopy, FT-IR and UV-vis spectroscopy. The size of the catalyst was estimated to be about 10 nm.
The thermal gravimetric analysis demonstrated that the nanocatalyst was thermally stable up to almost
300 ꢀC. The reactivity, selectivity and scope of the reaction were investigated with a variety of olefins,
saturated hydrocarbons, alcohols and organosulfur compounds. The reactions proceeded smoothly in
the absence of surfactants, organic co-solvents and thus take place “on water”. The separation and
recycling of nanocatalyst as well as isolation of water-insoluble products were simple, effective and
economical in this clean oxidation method.
Received 4th December 2013
Accepted 10th January 2014
DOI: 10.1039/c3ra47288d
www.rsc.org/advances
support can counteract this problem, enabling the easier
recovery and reuse of the catalysts, which makes them cost-
Introduction
effective. Moreover, the support can also reduces signicantly
the oxidative degradation of porphyrin ligands and conse-
quently the difficulties in separating the products and
contamination by residual catalyst.8 Various approaches to
metalloporphyrin immobilization have been considered to
minimize catalyst self destruction and dimerization of unhin-
dered metalloporphyrins.8 However, progress is still required to
further improve metalloporphyrin-based catalytic systems for
using in industries regarding the green chemistry context.9
Major drawbacks of conventional supported catalysts such as
low stability, catalyst leaching, and restricted accessibility of the
reactants to the reactive centers, as well as catalyst recovery and
reuse, must be overcome. Catalyst stability is essential to recy-
cling procedures and to the recovery of valuable
metalloporphyrins.10
Recently, the use of nanomaterials whose activity is very high
under mild conditions extended because of their very large
surface area.11–15 The control of chemical reactions by changing
the size, dimensionality, chemical composition and
morphology of the reaction center and by changing the kinetics
using nanopatterning of the reaction centers is the central aim
of nanocatalysis.16 However, the small size of nanoparticles
make their separation from the reaction solution and recycling
difficult, which impedes their use in industrial processes.17 In
Oxidation reactions are among the most important trans-
formations in applied synthetic chemistry and offer important
methodology for the introduction and modication of func-
tional groups. In the area of oxidative transformations one
major goal is the replacement of stoichiometric procedures,
using classical toxic waste-producing oxidants, with catalytic
procedures using environmentally benign oxidant. Oxidants
whose use is being contemplated include molecular oxygen,
hydrogen peroxide, and tert-butyl hydroperoxide (TBHP) where
there is either no by-product, the by-product is environmentally
benign, or the by product can be easily recovered and recycled.1
tert-Butanol, a useful high-octane oxygenate, is formed as the
by-product when tert-butyl hydroperoxide is used as the
oxidant.2 Furthermore, an extreme challenge is to accomplish
industrial processes in non-toxic solvents, particularly in
aqueous media.3–6
The applicability of the porphyrin complexes as bio-relevant
catalysts in oxidation chemistry has been widely reported in the
literature.7 However, the synthesis of metalloporphyrins is
challenging and low-yielding. Immobilization onto a solid
Catalysis Research Laboratory, Department of Chemistry, Faculty of Science,
University of Birjand, Birjand, 97179-414 Iran. E-mail: rrezaeifard@birjand.ac.ir;
rrezaeifard@gmail.com; mjafarpour@birjand.ac.ir; Fax: +98 561 2502515; Tel: +98
561 2502516
order
to
circumvent
such
recycling
problems,
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 9189–9196 | 9189

View Article Online
RSC Advances
Paper
superparamagnetic nanoparticles, whose occulation and 1076 cmꢁ1 could be assigned to the deformation vibration of
dispersion can be controlled reversibly by applying a magnetic the pyrrole fragments of the porphyrin molecule (Fig. 1A).32
eld, were recently employed as a recyclable support matrix.
The XRD of Mn(TPP)OAc@SMNP (Fig. 1B) shows similar
Regardingly, magnetic nanoparticles are one of the most widely pattern with the Fe3O4 nanoparticles,22,23 which indicates the
studied materials in multi-disciplinary research including stability of the crystalline phase of the magnetic nanoparticles
biotechnology, biomedicine, magnetic resonance imaging during the subsequent surface modication. The size of particles
(MRI), separation and catalysis.11–15
were estimated to be 8.50 nm using the Debye–Scherrer equation
In continuation of our research on the development of according to the (311) reection. Inductively coupled plasma
greener oxidation protocols and nanocatalysis,18–27 herein, we atomic emission (ICP) analysis revealed that the contents of
would like to describe a new environmentally benign method supported Mn was 6.02 wt%. Therefore, each gram of heteroge-
for economic production of epoxides, carbonyl compounds and neous catalyst contains 85 mmol of Mn or Mn(TPP)OAc complex.
sulfoxides, all of which are invaluable precursors in industry as
The UV–vis absorption spectra of Mn(TPP)OAc@SMNP is
well as pharmaceutical synthetic chemistry.1 The reactions presented in Fig. 1C. Supported Mn(TPP)OAc exhibits charac-
proceed in water using tert-butyl hydroperoxide (TBHP, 70%) teristic absorption peak at 470 nm (Soret band) demonstrating
under catalytic inuence of new synthesized Mn(TPP) that the structure of Mn(TPP)OAc (Soret band at 478 nm in
OAc@SMNP as a magnetically recoverable porphyrin nano- dichloromethane) remains the same aer being adsorbed by
catalyst. The surfactants, organic co-solvents and additives the SMNP (a) and also aer many recoveries (b). It demonstrates
removed in this method, therefore, the reactions take place “on the strong adsorption of Mn(TPP)OAc on to SMNP.
water”.28
Fig. 2A shows the transmission electron microscopy (TEM) of
Mn(TPP)OAc@SMNP in water with size range of 10–20 nm
(including the SiO2 shell and porphyrin complex). The SEM
image of the supported porphyrin catalyst shows uniformity and
spherical morphology of nanoparticles (Fig. 2B). Nevertheless,
aggregation gives rise to increase the size of observed nano-
particles as can be seen in the some parts of the SEM image.33
The thermal behavior of Mn(TPP)OAc@SMNP (Fig. 3a)
shows its thermal stability up to around 300 ꢀC in which the
degradation of Mn(TPP)OAc occurred (Fig. 3b). A decrease in
Results and discussion
Preparation and characterization of the Mn(TPP)OAc@SMNP
The magnetically recoverable catalyst Mn(TPP)OAc@SMNP, was
prepared by immobilization of the simple and easily prepared
manganese(III) acetate meso-tetraphenylporphyrinato on the
functionalized nanosized Fe3O4 (Scheme 1). We used magnetic
nanoparticles (MNP) of approximately 8–10 nm diameter which
were prepared by the co-precipitation method.29,30 The particles
were subsequently coated with a dense silica layer, using tet-
raethoxysilane (TEOS) as the silica source and ammonia solu-
tion as the hydrolysing agent. The silica layered system (SMNP)
then offers the binding sites (Si–OH units) for the hetero-
genization of the molecular catalysts. For the graing on the
surface we used (3-aminopropyl) triethoxysilane (APS) as
chelating ligands.29,30 It was reacted with Mn(TPP)OAc in
ethanol to yield the desired nanocatalyst Mn(TPP)OAc@SMNP
according to FT-IR, XRD and UV-vis spectra (Fig. 1).
ꢀ
the weight percentage at about 100 C related to desorption of
water molecules from the catalyst surface. The organic parts
were decomposed completely at 500 ꢀC. The nal weight loss at
900 ꢀC can be related to the formation of metal oxides. It should
be noted that the color and the magnetic properties of the
Mn(TPP)OAc@SMNP remained almost unchanged aer six
months storage when exposed to air at room temperature. The
coating of Fe3O4 with SiO2 layer containing Mn(TPP)OAc
attached to surface, shielded the nanomagnetite surface from
oxygen and improved greatly their stability.34,35
The presence of the magnetite core in the prepared nano-
materials was conrmed by observation of two bands at 470 and
Epoxidation of olens in water
650 cmꢁ1 31 The stretching vibration band of the phenyl rings in The synthesized and characterized Mn(TPP)OAc@SMNP was
.
the meso positions appears at 1625 cmꢁ1. The signal at explored for the epoxidation of cyclooctene as a model reaction.
Scheme 1 Preparation of SMNP, ASMNP and Mn(TPP)OAc@SMNP
9190 | RSC Adv., 2014, 4, 9189–9196
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
Fig. 1 FT-IR [A], XRD [B] and UV-vis spectra [C, fresh (a) and after 7 times reuses (b)] of Mn(TPP)OAc@SMNP.
Under aerobic conditions no activity was observed. Using H2O2
(30%) as the oxidant and in the presence of 0.1–0.5 mol% of
Mn(TPP)OAc@SMNP the yield of cyclooctene oxide was <10% at
60 ꢀC aer 4 h. Blank experiment using TBHP (70%) as oxidant,
under ambient temperature gave the starting material aer very
long reaction times. When the aqueous mixture was heated at
ꢀ
60 C, cyclooctene oxide was appeared in low yield (24%/12 h).
Mn-free nanoparticles (MNP, SMNP, ASMNP) showed no activity
under this condition. When only a few minute of heterogeneous
Mn(TPP)OAc@SMNP (0.05 mol%) was used at 60 ꢀC, cyclo-
octene was consumed completely (Table 1, entry 4). However,
Fig. 3 TGA diagram of Mn(TPP)OAc@SMNP (a) and Mn(TPP)OAc (b).
more catalyst amounts led to less efficiency of oxidation system
and lower yields of epoxide were obtained (Table 1, entries 5–7).
The addition of additives (10 times vs. catalyst) namely imid-
azole and pyridine to the reaction mixture and the use of
standard buffered solutions (pH ¼ 2, 4, 6, 7, 9) did not improve
the conversion rate. The good dispersity of a low concentration
of Mn(TPP)OAc@SMNP in aqueous solution may be a good
reason for such an activity compared with that having a higher
catalyst concentration showing fairly high levels of aggregation
in aqueous media (compare Fig. 2A and B for TEM images of
magnetic catalyst). This claim was supported by sonication of
the mixture before the reaction. The yield of cyclooctene oxide
increased to 48% in the presence of 1.0 mol% (120 mg) of
Mn(TPP)OAc@SMNP when the aqueous mixture was sonicated
for 5 min before the reaction (entry 8). Moreover, when the
catalyst was replaced by free Mn(TPP)OAc, only 40% epoxide
yield was achieved at the same conditions demonstrating the
signicant improvement in activity of manganese porphyrin
aer deposition on magnetic nanoparticles. However, high
aggregation tendency of free Mn(TPP)OAc catalyst in aqueous
media should be taken into account for such an deciency.22,24
The systematic investigations of reaction temperature and
oxidant amounts demonstrated that aqueous mixture of
Fig. 2 TEM images of 6.0 (A) and 120 mg (B) of Mn(TPP)OAc@SMNP in water. “C” represents a SEM image of the nanocatalyst with some
aggregation. A particle with 12 nm size was illustrated.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 9189–9196 | 9191

View Article Online
RSC Advances
Paper
Table 1 Screening of quantity of the catalyst in the epoxidation of
cyclooctane with TBHP in watera
Entry
Catalyst mol%
Cyclooctene oxideb %
1
2
3
4
5
6
7
8c
0.0
24
55
65
100
85
70
0.02
0.04
0.05
0.1
0.15
1.0
26
48
1.0
a
Reaction condition: 1.0 mmol cyclooctene, 2.5 mmol TBHP (70%) and
Mn(TPP)OAc@SMNP as catalyst in 1 mL water. The reactions were
b
run at 60 ꢀC for 4.5 h except for entry 1 which was run for 12 h. GC
Fig. 5 The screening of quantity of the oxidant in the oxidation of
cyclooctene. The reactions were run under air at 60 ꢀC for 4.5 h and
the molar ratio of olefin/oxidant/catalyst was 2000 : X : 1.
yield. c The reaction sonicated for ve min before addition of oxidant.
ꢀ
cyclooctene should be heated at 60 C (Fig. 4) with 2.5 equiva-
under the inuence of the catalyst, producing the pertinent
epoxides in good yields (Table 1, entries 9,10). We veried our
claim by performing competitive reactions between cyclooctene
lents of TBHP (Fig. 5) to achieve the best epoxidation
performance.
Having proved the activity of Mn(TPP)OAc@SMNP in the
model reaction, the scope of protocol was subsequently
extended to a range of olens as shown in Table 2. Desired
conversions and excellent selectivities to epoxides were
obtained for different olens. It led to complete conversion of
cyclooctene, norbornene and cyclohexenes with the formation
of the corresponding epoxides as sole products (entries 1–4). No
allylic oxidation products were observed in the oxidation of
cyclohexene. Epoxidation of C]C double bond conjugated with
phenyl ring such as styrene, trans-b-methyl styrene and indene
took longer reaction times (entries 5–7). However, no carbonyl
products resulting from ring opening of acid-sensitive epoxides
were detected contrary to other related catalytic systems.22,23,36–38
Another salient feature of title epoxidation methodology is
moderate yields of 1,2-epoxyoctane obtained in the oxidation of
terminal linear aliphatic olen (entries 8) which showed actu-
ally no activity in our previous reports in the presence of
magnetically recoverable catalysts.22,23 The method possesses
novelty regarding to chemoselectivity. The hydroxyl group
which is sensitive to oxidation remained completely intact
Table 2 Epoxidation of olefins using TBHP catalyzed by Mn(TPP)
OAc@SMNP in watera
Entry
1
Substrate
Yieldb %
Productc
Time (h)
4.5
95
2
3
4
92
93
88
4.5
4.5
4.5
5
6
91
85
6
6
7
8
71
6
46d
12
9
74d
61d
8
8
10
a
The reactions were run under air at 60 ꢀC and the molar ratio of
b
substrate/TBHP/catalyst was 2000 : 5000 : 1.
Yield of isolated
c
products. The products were identied by NMR spectral data and by
comparison with authentic samples GC retention times. The
selectivity of products were >99%. d GC yield.
Fig. 4 The screening of temperature on the epoxidation of cyclo-
octene. The reactions were run under air for 4.5 h and the molar ratio
of olefin/TBHP/catalyst was 2000 : 5000 : 1.
9192 | RSC Adv., 2014, 4, 9189–9196
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
and benzyl alcohol as well as cyclohexanol. Aer 4.5 h, cyclo-
octene oxide was obtained quantitatively as the only product.
Table 3 Oxidation of hydrocarbons and alcohols using TBHP cata-
lyzed by Mn(TPP)OAc@SMNP in watera
Entry
Substrate
Product
Yieldb,c
%
Oxidation of saturated hydrocarbons and alcohols in water
When the same procedure was used for oxidation of saturated
benzylic hydrocarbon, promising results were obtained. Ethyl-
benzene was converted to acetophenone in 83% yield contam-
inated with ve percentage of pertinent alcohol within 4.5 h
(Table 3, entry 1). The same catalyst loading of 0.05 mol% was
enough to perform the reaction equally well at the same
conditions (2.5 equiv. TBHP at 60 ꢀC). The high yields (84–90%
yields) and excellent selectivity (100%) of ketones were also
achieved in the oxidation of 4-methoxyethylbenzene, indane
and tetralin (entries 2, 4 and 5). Electron-decient 4-nitro-
ethylbenzene (entry 3), however, gave a low yield of the related
acetophenone at the same time. Moreover, cyclooctane as an
inactive saturated aliphatic hydrocarbon was converted exclu-
sively to pertinet ketone in moderate yield (41%, entry 6) which
is a promising result in modern oxidation methods from an
industrial point of view.1
The desired yields and selectivities of the ketones obtained
in the oxidation of saturated hydrocarbons prompted us to
apply this catalytic system for oxidation of alcohols to carbonyl
compounds. The results were summarized in Table 3 (entries 7–
14). As expected, excellent yields of the related ketones were
obtained in the oxidation of secondary benzylic alcohols (Table
3, entries 7, 8). Nevertheless, primary benzylic alcohols (entries
9–11) and saturated aliphatic alcohols (entries, 12, 14) gave
moderate/good yields of the pertinent carbonyl compounds
using 4 equiv. TBHP. These results, once again conrmed the
selective epoxidation of allylic and homoallylic alcohols (Table
2, entries 10,11). It should be noted that no trace of ester and
benzoic acide was observed resulting from overoxidation of
secondary and primary alcohols, respectively.
1
83
2
3
84
25d
4
5
6
7
90
87
41d
90
8
9
92
73d
Aqueous oxidation of suldes in water
A large number of methods are available for the oxidation of
suldes to sulfoxides and access to high selectivity for sulfoxide
over sulfone is the most challenging issue.1,39 Promising selec-
tivity obtained in the oxidation of hydrocarbons and alcohols,
induce us to extend the scope of this clean catalytic system
toward oxidation of organosulfur compounds. Preliminary
experiments on the oxidation of thioanisole as a model
substrate led to the same conditions used in previous sections
except that the reaction proceeded smoothly at room tempera-
ture within 1 h and the sole product was the related sulfoxide.
For example, using 2.5 equiv. of TBHP, the conversion of thio-
anisole was complete within 1 h in the presence of 0.05 mol% of
Mn(TPP)OAc@SMNP, and lesser catalyst concentration such as
0.025 and 0.04 mol% gave 60 and 85% yield of methyl phenyl
sulfoxide, respectively.
10
11
56
35d
12
13
37d
15d
14
10d
a
The reactions were run under air at 60 ꢀC for 4.5 h and the molar ratio
of substrate/TBHP/catalyst was 2000 : 5000 : 1 except for entries 9–14
b
c
Next, different suldes were subjected to the reaction system which was 2000 : 8000 : 1. Yield of isolated products. The products
at 25 ꢀC. All substrates could be smoothly converted to the
related sulfoxides with high/excellent yields and excellent
selectivities were obtained under mild conditions (Table 4). A
salient feature of the present oxidation system is its excellent
were identied by NMR spectral data and by comparison with
authentic samples GC retention times. The selectivity of products
were >99% except for entry 1 which was 95% (5% 1-phenyl ethanol).
d
GC yield.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 9189–9196 | 9193

View Article Online
RSC Advances
Paper
selectivity toward sulfoxide and the formation of sulfone as a good alternative for sulfoxide production. Finally, the oxida-
overoxidation product completely controlled. To conrm this tion of phenyl disulde and p-methyl thiophenol was examined
claim, an experiment was carried out using diphenyl sulfoxide and thiosulnates, biologically and medicinally important
as a substrate and no sulfone product was detected under the compounds,40 were produced exclusively under the same
same condition. The chemoselectivity of the method was also conditions.
notable. Suldes having a benzylic C–H bond (entry 3), carbon–
carbon double bond (entries 4,5) and hydroxyl group (entry 8)
The catalyst reuse and stability
were cleanly transformed into the corresponding sulfoxides in
The stability of the catalyst and its activity were investigated by
excellent yield without formation of any epoxide, alcohol and
recycling experiments for the oxidation of cyclooctene per-
carbonyl by-products. These advantages make the title method
formed over Mn(TPP)OAc@SMNP nanocatalyst under the
conditions used. In each cycle the catalyst was separated
magnetically and washed with ethanol or ethyl acetate and
nally dried. Nanocatalyst could be reused at least seven times
without any signicant loss of the initial catalytic activity (94%
cyclooctene oxide aer 7th run). Standard leaching experiments
(using the hot ltration method and ICP-AES) provided negli-
gible quantities of Mn in the ltrate (0.28, 0.16 and 0.07% aer
three rst runs respectively) conrming that the complex was
rmly anchored to the SMNP support. No conversion evolution
was observed in the absence of catalyst even aer 18 h. The
comparison of UV-vis (Fig. 1C) and TEM image of used Mn(TPP)
OAc@SMNP (Fig. 6) with the fresh catalyst (Fig. 2A) showed the
fact that the structure and morphology of the nanocatalyst
remained almost intact aer recovering. The additional
advantage of reported nanocatalyst relates to use of low-cost
commercially available and simple Mn(TPP)OAc which can also
be prepared easily as compared with the related magnetically
recoverable systems using tetra(4 N-pyridyl)porphyrinato
[TPyP],36 and 5,10,15,20 tetrakis(pentauorophenyl)porphyrin
[TF20PP].37 Further, additives, surfactants and organic co-
solvents were removed.36–38 Also, no trace of carbonyl products
resulting from ring opening of acid-sensitive poxides were
detected contrary to other related catalytic systems.22,23,36–38
Moreover, the possibility to use neat water as a standard “green”
reaction medium is a salient feature especially due to the very
low solubility of organic compounds in water providing easy
separation of products. It is worth to mention that, the desired
conversion rate in this oxidation system can be rationalized in
terms of the reaction conditions as a heterogeneous suspension
of organic droplets in water (‘‘on-water’’).28
Table 4 Oxidation of organosulfur compounds using TBHP catalyzed
by Mn(TPP)OAc@SMNP in watera
Entry Substrate
Product
Yield%bc
1
91
2
3
4
88
92
95
5
6
92
90
7
8
89
94
Therefore, title methodology is cost effective and sustainable
because of using water as reaction media, TBHP as an economic
9
93
90
10
a
The reactions were run under air at 25 ꢀC for 1 h and the molar ratio of
b
substrate/TBHP/catalyst was 2000 : 5000 : 1.
Yield of isolated
c
products. The products were identied by NMR spectral data and by
comparison with authentic samples GC retention times. The
selectivity of products were >99%.
Fig. 6 TEM image of Mn(TPP)OAc@SMNP after seven times reuses in
the oxidation of cyclooctene.
9194 | RSC Adv., 2014, 4, 9189–9196
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
oxidant, low concentration of a magnetically recoverable and orthosilicate (TEOS) was added slowly to the mixture and
reusable catalyst, lack of toxic reagents or solvents.
sonicated for 10 min. Then aqueous ammonia (10%, 1.4 mL)
was added slowly over 10 min under mechanical stirrer. The
mixture was heated at 40 ꢀC for 12 h. The iron oxide nano-
particles with a thin layer of silica (Fe3O4@SiO2) were separated
by an external magnet and washed three times with ethanol and
dried under vacuum.30
Conclusion
In summary, a robust magnetically separable biomimetic
nanocatalyst (10–20 nm) with high thermostability (300 C) for
ꢀ
oxidation of olens, saturated hydrocarbons, alcohols and
suldes using aqueous TBHP was designed. It was synthesized
by coordinative anchoring of simple Mn(TPP)OAc complex on
silica coated magnetic nano-particles via amine functionality.
Our results demonstrated well that the efficiency, selectivity and
oxidative stability of porphyrin catalyst improved greatly by
attaching to magnetite nanoparticles. Selected processes
successfully provided target products in high/excellent isolated
yields in water by using a very low catalyst loading (0.05 mol%).
However, the magnetically separable system was very stable
under the investigated conditions, preserving almost intact its
initial activity aer many runs regardless of the type of selected
reaction. Thus, our method is cost effective and enables indus-
trially important reactions to be carried out efficiently under
environmentally benign and practically attainable conditions.
Silanation of silica-coated magnetite nanoparticles (ASMNP)
10.0 g of dry SMNP powder were mixed with 200.0 mL of toluene
to produce a homogeneously mixed solution, followed by
sonication the mixture for 30 min. Then 2.5 mL of (3-amino-
propyl) triethoxysilane (APS) was added under mechanical
stirring and the mixture was slowly heated to 105 ꢀC and kept at
this temperature for 20 h. The nal sample was separated by an
external magnet and washed three times with methanol or
ethanol and dried under vacuum. The concentrated product
stored in refrigerator to use.30
Synthesis of magnetite nanoparticles supported catalyst
(Mn(TPP)OAc@SMNP)
4.0 g of dry ASMNP powder were mixed with 200.0 mL ethanol to
produce a homogenously mixed solution, followed by sonica-
tion the mixture for 30 min. 0.3 g of Mn(TPP)OAc complex was
added under mechanical stirring and the mixture was heated to
80 C for 8 h. The free Mn-porphyrins were removed through
soxhlet extraction with ethanol. The concentrated product
stored in refrigerator to use.22
Experimental section
General remarks
ꢀ
Conversion and yields of the products were accomplished by GC-
FID on a Shimadzu GC-16A instrument using a 25 m CBP1–S25
(0.32 mm ID, 0.5 mm coating) capillary column. IR spectra were
recorded on a Perkin Elmer 780 instrument. UV-Vis spectra were
recorded on a V670 JASCO spectrophotometer. NMR spectra were
recorded with a Brucker Avance DPX FT-NMR 400 MHz instrument.
Mass spectra were recorded on a Shimadzu GC-MS-QP5050A. SEM
micrographs were obtained by SEM instrumentation (SEM, XL-30
FEG SEM, Philips, at 20 kV), TEM images were obtained by TEM
instrumentation (Philips CM 10). X-ray diffraction (XRD, D8,
Advance, Bruker, axs), TGA (Shimadzu 50) and ICP (Varian, visa-pro)
were employed for characterization of the heterogeneous catalyst.
The free base porphyrin: TPPH2 and its manganese complex were
synthesized as reported in the literature.41,42
General procedure for hydrocarbon oxidation
To 1 mL aqueous suspension of olen (or saturated hydro-
carbon) (1.0 M), containing 6.0 mg of Mn(TPP)OAc@SMNP
(0.05 mol% of Mn-porphyrin catalyst) was added 2.5 mmol (320
ml) aqueous tert-butyl hydroperoxide solution (TBHP 70%) and
ꢀ
the mixture stirred at 60 C, for an appropriate time (Tables 2
and 3 entries 1–6). Aer completion of the reaction, the catalyst
removed by an external magnet and then ethyl acetate (5 mL)
was added to the reaction mixture. Organic phase was separated
and dried over sodium sulfate. The organic solvents (ethyl
acetate and residual tert-butanol) were evaporated under
vacuum giving the pure products. If necessary, further puri-
cation was carried out by column chromatography on silica gel
using n-hexane and ethyl acetate as eluent (90/10).
Large-Scale synthesis of nanomagnetite particles (Fe3O4)
A solution of FeCl2 (5.4 g) and FeCl3 (2.0 g) in aqueous hydro-
chloride acid (2.0 M, 25.0 mL) at room temperature, was soni-
cated until the salts dissolved completely. Aqueous ammonia
(25%, 40.0 mL) was added slowly over 20 min to the mixture
under Ar atmosphere at room temperature followed by stirring
about 30 min with mechanical stirrer. The Fe3O4 nanoparticles
were separated by external magnet and washed three times with
deionized water and ethanol. The nal product was obtained
aer drying under vacuum. Also it could be re-suspension in
ethanol and stored in refrigerator to use.30
General procedure for alcohol oxidation
To 1 mL aqueous suspension of alcohol (1.0 M), containing 6.0
mg of Mn(TPP)OAc@SMNP (0.05 mol% of Mn-porphyrin cata-
lyst) was added 2.5 mmol (320 ml) aqueous tert-butylhydroper-
oxide solution (TBHP 70%) (Table 3 entries 7,8) [and 4.0 mmol
(512 ml) TBHP for entries 9–14] and the mixture stirred at 60 ꢀC,
for an appropriate time. Aer completion of the reaction, the
catalyst removed by an external magnet and then ethyl acetate
(5 mL) was added to the reaction mixture. Organic phase was
Synthesis of silica-coated magnetite nanoparticles (SMNP)
The synthesized Fe3O4 suspended in 35.0 mL ethanol and 6 mL separated and dried over sodium sulfate. The organic solvents
deionized water and sonicated for 15 min. 1.5 mL of tetraethyl (ethyl acetate and residual tert-butanol) were evaporated under
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 9189–9196 | 9195

View Article Online
RSC Advances
Paper
vacuum giving the pure products. If necessary, further puri- 15 V. Polshettiwar, R. Luque, A. Fihri, H. Zhu, M. Bouhrara and
cation was carried out by column chromatography on silica gel
using n-hexane and ethyl acetate as eluent (90/10).
J.-M. Basset, Chem. Rev., 2011, 111, 3036–3075.
16 D. Astruc, Nanoparticles and Catalysis, Wiley-VCH Verlag
GmbH & Co. KGaA, 2008, pp. 1–48.
17 F. Raimondi, G. G. Scherer, R. Kotz and A. Wokaun, Angew.
Chem., Int. Ed., 2005, 117, 2228–2248.
18 A. Rezaeifard, M. Jafarpour, A. Naeimi and S. Kaa, Catal.
Commun., 2011, 12, 761–765.
19 A. Rezaeifard, M. Jafarpour and A. Naeimi, Catal. Commun.,
2011, 16, 240–244.
20 A. Rezaeifard, M. Jafarpour, A. Naeimi and M. Salimi, Inorg.
Chem. Commun., 2012, 15, 230–234.
21 A. Rezaeifard, M. Jafarpour, A. Naeimi and K. Mohammadi,
J. Mol. Catal. A: Chem., 2012, 357, 141–147.
22 A. Rezaeifard, M. Jafarpour, P. Farshid and A. Naeimi, Eur.
J. Inorg. Chem., 2012, 5515–5524.
23 A. Rezaeifard, M. Jafarpour, A. Naeimi and R. Haddad, Green
Chem., 2012, 14, 3386–3394.
24 A. Rezaeifard, V. Soltani and M. Jafarpour, Eur. J. Inorg.
Chem., 2013, 2657–2664.
General procedure for sulde oxidation
To 1 mL aqueous suspension of an organosulfur compound
(1.0 M), containing 6.0 mg of Mn(TPP)OAc@SMNP (0.05 mol%
of Mn-porphyrin catalyst) was added 2.5 mmol (320 ml) aqueous
tert-butylhydroperoxide solution (TBHP 70%) and the mixture
stirred at 25 ꢀC, for an appropriate time (Table 4). Aer
completion of the reaction, the catalyst removed by an external
magnet and then ethyl acetate (5 mL) was added to the reaction
mixture. Organic phase was separated and dried over sodium
sulfate. The organic solvents (ethyl acetate and residual tert-
butanol) were evaporated under vacuum giving the pure prod-
ucts. If necessary, further purication was carried out by
column chromatography on silica gel using n-hexane and ethyl
acetate as eluent (90/10).
25 A. Rezaeifard, R. Haddad, M. Jafarpour and M. Hakimi,
J. Am. Chem. Soc., 2013, 135, 10036–10039.
26 M. Jafarpour, M. Ghahramaninezhad and A. Rezaeifard, RSC
Adv., 2014, 4, 1601–1608.
Acknowledgements
Support for this work by Research Council of University of Bir-
jand is highly appreciated.
27 A. Rezaeifard and M. Jafarpour, Catal. Sci. Technol., 2014,
DOI: 10.1039/c3cy00554b.
References
28 S. Narayan, J. Muldoon, M. G. Finn, V. V. Fokin, H. C. Kolb and
K. B. Sharpless, Angew. Chem., Int. Ed., 2005, 44, 3275–3279.
29 Y. C. Chen, C. T. Chen, W. Y. Chen, C. Y. Lo, H. Y. Lin and
C. C. Liu, National Chiao Tung University, US Pat.,
2526258, 2009.
1 J. E. Backvall, Modern Oxidation Methods, WILEY-VCH,
Weinheim, 2004.
2 J. Yanowitz, E. Christensen, R. L. McCormick, Utilization of
Renewable Oxygenates as Gasoline Blending Components,
Technical Report NREL/TP, 2011, pp. 5400–50791.
30 B. Karimi and E. Farhangi, Chem.–Eur. J., 2011, 17, 6056–6060.
3 M. B. Gawande, V. D. B. Bonifacio, R. Luque, P. S. Branco and 31 Z. Zhang, F. Zhang, Q. Zhou, W. Zhao, B. Ma and Y. Ding,
R. S. Varma, Chem. Soc. Rev., 2013, 42, 5522–5551.
J. Colloid Interface Sci., 2011, 360, 189–194.
4 N. Parikh, D. Kumar, S. Raha Roy and A. K. Chakraborti, 32 N. Z. Mamardashivili and O. A. Golubchikov, Russ. Chem.
Chem. Commun., 2011, 47, 1797–1799.
Rev., 2001, 70, 577–606.
5 R. Butler and A. G. Coyne, Chem. Rev., 2010, 110, 6302–6337. 33 M. Masteri-Farahani and N. Tayyebi, J. Mol. Catal. A: Chem.,
6 C.-J. Li and T.-H. Chan, Comprehensive Organic Reactions in 2011, 348, 83–87.
Aqueous Media, John Wiley & Sons, Inc, Hoboken, New 34 J. Huang, C. Liu, H. Xiao, J. Wang, D. Jiang and E. Gu, Int.
Jersey, 2007. J. Nanomed., 2007, 2, 775–784.
7 K. M. Kadish, K. M. Smith, R. Guilard, The Porphyrin 35 J. G. Guan, J. Haung, S. L. Zhao and R. Z. Huan, Int. J. Mod.
Handbook, Academic Press, 2002, vol. 6.
Phys. B, 2001, 15, 599–609.
8 E. Brule and Y. R. De Miguel, Org. Biomol. Chem., 2006, 4, 36 M. S. Saeedi, S. Tangestaninejad, M. Moghadam,
599–609.
V.
Mirkhani,
I.
Mohammadpoor-Baltork
and
9 S. Ribeiro, A. C. Serra and A. M. d' A. Rocha Gonsalves,
ChemCatChem, 2013, 5, 134–137.
10 J. R. L. Smith, Metalloporphyrins in Catalytic Oxidations, ed.
R. A. Sheldon and M. Dekker, New-York, 1994, ch. 11, pp.
350–368.
11 M. B. Gawande, P. S. Branco and R. S. Varma, Chem. Soc.
Rev., 2013, 42, 3371–3393.
12 R. G. Chaudhuri and S. Paria, Chem. Rev., 2012, 112, 2373–
2433.
A. R. Khosropour, Polyhedron, 2013, 49, 158–166.
37 J. S. dos Santos, A. L. Faria, P. M. da Silva Amorin, F. M. La
Luna, K. L. Caiado, D. O. C. e Silva, P. P. C. Sartoratto and
M. D. Assis, J. Braz. Chem. Soc., 2012, 23, 1411–1420.
38 S. Rayati and P. Abdolalian, Comptes Rendus Chimie, 2013,
16, 814–820.
39 A. Rezaeifard, M. Jafarpour, H. Raissi, E. Ghiamati and
A. Tootoonchi, Polyhedron, 2011, 30, 592–598.
40 N. Benkeblia and V. Lanzotti, Food, 2007, 1, 193–201.
13 L. Guerrini and D. Graham, Chem. Soc. Rev., 2012, 41, 7085– 41 A. D. Adler, F. R. Longo, J. D. Finarelli, J. Goldmacher,
7107. J. Assour and L. J. Korsakoff, J. Org. Chem., 1967, 3, 476.
14 L. H. Reddy, J. L. Arias, J. Nicolas and P. Couvreur, Chem. 42 A. D. Adler, F. R. Longo, F. Kampas and J. J. Kim, Inorg. Nucl.
Rev., 2012, 112, 5818–5878.
Chem. Lett., 1970, 32, 2443–2445.
9196 | RSC Adv., 2014, 4, 9189–9196
This journal is © The Royal Society of Chemistry 2014