Efficient and selective green oxidation of alcohols by MOF-derived magnetic nanoparticles as a recoverable catalyst

Article abstract of DOI:10.1039/c6ra01617k

A simple and highly efficient synthesis strategy for the green oxidation of alcohols to corresponding carbonyl products is developed using a heterogeneous non-noble magnetic Fe₃O₄@C catalyst. The magnetic nanocomposites were prepared by one-pot thermal decomposition of a Fe-containing MOF and fully characterized by powder X-ray diffraction (PXRD), N₂ physical adsorption, atomic absorption spectroscopy (AAS), element analysis, scanning electronic microscopy (SEM), and transmission electron microscopy (TEM). The catalytic activities of Fe₃O₄@C materials were investigated in the selective oxidation of alcohols in neat water using hydrogen peroxide as a green oxidant under base-free conditions. Besides the high activity and selectivity to the target products, the proposed catalytic system features a broad substrate scope for both aryl and alkyl alcohols. Moreover, the magnetically catalyst could be easily separated by using an external magnetic field and reused for at least four times without significant loss in catalytic efficiency under the investigated conditions.

Full text of DOI:10.1039/c6ra01617k

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: X. Yao, C. Bai, J.
Chen and Y. Li, RSC Adv., 2016, DOI: 10.1039/C6RA01617K.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Please do not adjust margins
RSC Advances
Page 1 of 9
View Article Online
DOI: 10.1039/C6RA01617K
Journal Name
ARTICLE
Efficient and selective green oxidation of alcohols by MOF-
derived magnetic nanoparticles as recoverable catalyst
Received 00th January 20xx,
Accepted 00th January 20xx
Xianfang Yao, Cuihua Bai, Junying Chen,* Yingwei Li*
A simple and highly efficient synthesis strategy for green oxidation of alcohols to corresponding carbonyl products is
developed using a heterogeneous nonꢀnoble magnetic Fe3O4@C catalyst. The magnetic nanocomposites were prepared by
oneꢀpot thermal decomposition of a Feꢀcontaining MOF and fully characterized by powder Xꢀray diffraction (PXRD), N2
physical adsorption, atomic absorption spectroscopy (AAS), element analysis, scanning electronic microscopy (SEM), and
transmission electron microscopy (TEM). The catalytic activities of Fe3O4@C materials were investigated in the selective
oxidation of alcohols in neat water using hydrogen peroxide as green oxidant under baseꢀfree conditions. Besides the high
activity and selectivity to the target products, the proposed catalytic system features a broad substrate scope for both aryl
and alkyl alcohols. Moreover, the magnetically catalyst could be easily separated by using an external magnetic field and
reused for at least four times without significant loss in catalytic efficiency under the investigated conditions.
DOI: 10.1039/x0xx00000x
ww.rsc.org/
nonꢀnoble catalysts, even in term of the scope and functional group
tolerance of substrates.9 Besides, there are still persistent problems in
this field: on one hand, a large excess of base additives or
stoichiometric amounts of hazardous oxidizing agents (e.g., metal
Introduction
The oxidation of alcohols to the corresponding aldehydes, ketones
and carboxylic acids is commonly recognized as one of the most
widely used and important oxidation reactions in organic synthesis.
Typically, the chemoselective oxidation of alcohols to aldehydes or
ketones without traceable overoxidation products (i.e., carboxylic
acids) is attractive for the preparation of fine chemicals owing to the
nature of aldehydes or ketones as an intermediate for producing
carbonyl products, which are of great importance and versatility for
the chemical industry and pharmaceutical synthesis.1 Numerous
efforts on developing efficient catalysts towards these oxidations
have been progressed and reported a lot. In most cases, nobleꢀmetalꢀ
based (e.g., Au, Pd and Ru) catalysts show excellent activities and
selectivities for this chemical proceses.2ꢀ4 However, the high price
and shortage of noble metals resources limit the usage of these
noble–metal–based catalyst. Therefore in recent years, there has
been increasing demand for catalysts with less cost though high
efficiency and selectivity towards the desired products, as well as
environmentally benign. Some nonꢀnoble transitionꢀmetalꢀbased
catalyst systems (e.g., Co, Fe, Cu, and Mn) have been successfully
developed for the oxidation of alcohols.5ꢀ8 Nevertheless, in
competition with nobleꢀmetalꢀcatalysts, the activity or selectivity in
the reactions of aerobic alcohol oxidation is somehow lower for the
oxidants and peroxy acids) are conventionally utilized aiming to
promote the activity and selectivity of this transformation,10ꢀ13 which
would cause drawbacks such as high cost, waste, byꢀproducts, and
serious environmental issues. More importantly, liquid phase
oxidation of alcohols by dioxygen or hydrogen peroxide is highly
desired since they are relatively convenient and acceptable; the
oxidants having high contents of active oxygen are cheap, mild and
environmental friendly owing to the producing of water as the sole
byꢀproduct. On the other hand, some of these reported oxidation
reactions were carried out in organic solvents, for instance, toluene,9
acetonitrile,11,14 dimethyl sulfoxide (DMSO),15 which would cause
the environmental pollution and the waste of resources. In general,
the development of highlyꢀefficient heterogeneous catalytic systems
for the selective green oxidation of alcohols attracts keen interest
continuously in both organic synthesis and green chemistry.
In addition, carbon nanocomposites containing inorganic
oxides have become one kind of preferred functional materials
attributed to their extensive applications covering diverse fields,
among which magnetic nanomaterials have been invoked as an
easyꢀrecoverable material thus received increasing attentions.
The unique physical and chemical properties of magnetic
nanomaterials make them of great potential in various
applications such as electrochemical,16,17 removal of
wastewater,18 oils and dyes,19,20 magnetic storage media, drug
delivery and cell separation etc.21ꢀ24 In particular, the special
magnetic characteristic plays decisive role in the separation
procedure after usage by addition of external magnetic field,
which have been proved to be simple and convenient. Over the
past decade, functionalized magnetic nanoparticles have been
State Key Laboratory of Pulp and Paper Engineering, School of Chemistry and
Chemical Engineering, South China University of Technology, Guangzhou 510640,
China. E-mail: cejychen@scut.edu.cn, liyw@scut.edu.cn
†
Electronic Supplementary Information (ESI) available: Experimental details of
catalyst characterization and additional reaction results. See
DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 2 of 9
View Article Online
DOI: 10.1039/C6RA01617K
ARTICLE
Journal Name
utilized as efficient and recoverable catalyst for various organic Commercially available chemicals and regents involved in this
transformations, which represent excellent catalytic activities.25ꢀ study were used without further purification unless otherwise
29
A
commonlyꢀused method to synthesize these indicated. Powder Xꢀray diffraction patterns of the MILꢀ88B and Bꢀ
nanocomposites is to utilize metalꢀorganic frameworks (MOFs) x were recorded on a Rigaku diffractometer (D/MAXꢀIIIA, 3 kW)
as one component or precursors. In the recent two decades, using Cu Kα radiation (40 kV, 30 mA, 0.1543 nm). Elemental
MOFs have emerged as a new class of porous materials that can analysis was performed on an Elementar Vario EL III equipment by
undergo selfꢀassembly with metal ions and organic ligands. weighing samples of 0.2ꢀ0.3 mg and packing with aluminium foil for
Owing to the highlyꢀordered structures, relatively huge surface the measurement. BET surface area and pore sizes were obtained
areas and large pore volumes, MOFs have been widely utilized from N2 adsorption/desorption isotherms at 77K with
a
in a variety of fields such as gas storage/separation,30,31 Micromeritics ASAP 2020M instrument. The Fe contents of the Bꢀx
catalysis,32 sensing,33,34 biomedical field,35,36 etc. However, the samples were measured by atomic adsorption spectroscopy (AAS)
stability of MOFs is normally lower than the traditional porous with a Hitachi Zꢀ2300 instrument. The stability of MILꢀ88B was
materials such as zeolites and active carbons considering the evaluated by TGA at a heating rate of 10 ºC·minꢀ1 under N2
low coordination bond energy between the ligands and metal atmosphere. The surface topography of MILꢀ88B and Bꢀx as well as
ions of MOFs, which would likely led to the collapse of the the elemental mapping were investigated by scanning electron
framework during reactions thus impede the practical microscope (SEM, MERLIN of ZEISS) and transmission electron
applications to the extent. Hence researchers thought from microscope (TEM, JEOL, JEMꢀ2010HR).
another side that to utilize this soꢀcalled “disadvantage” of
MOFs to prepare more stable nanoporous materials. As a Preparation of MIL-88B
consequence, MOFs being considered as one component or
The Feꢀcontaining MOF precursor, MILꢀ88B, was prepared
alternative precursors to construct nanocomposites including
according to the literature reports.47 In a typical synthesis procedure,
metal/carbon hybrids has become the focus in the MOFꢀbased
a
mixture of FeCl3•6H2O (0.748 g, 2.77 mmol), 1,4ꢀ
chemistry. This new approach that to utilize MOFs in
preparation of metal oxides or metal/carbon nanomaterials via a
simple thermolysis procedure has been aroused in recent years.
From a theoretical perspective, metal oxides are expected as
products when the pyrolysis takes place in air and metal/carbon
composites could be the produced in an inert atmosphere.
Great progress has been made in the synthesis of porous
carbon,37 metal/metal oxides38 and metal/metal oxide@C
composites with various structures and compositions39 ever
since the development of this new approach to functional
benzenedicarboxylic acid (0.460 g, 2.77 mmol) in N,Nꢀ
Dimethylformamide (DMF, 120 mL) were transferred to a Teflonꢀ
lined autoclave, in which the mixture was then heated at 150 °C for
7 days. After cooling down to room temperature, the solid was
collected by centrifugation, followed by washing with DMF and
ethanol, then dried under vacuum at 60 °C to afford orange colour
powder.
Preparation of B-x by thermolysis of MIL-88B
materials; the corresponding applications are also widely The typical thermolysis procedure for the preparation of the
investigated especially in electrochemistry, including magnetic particleꢀembedded porous carbon materials is described as
supercapacitors, batteries, fuel cells, sensing and catalysis. To follows: the asꢀsynthesized MILꢀ88B was heated at a heating rate of
date, efforts for such MOFꢀderived materials in liquidꢀphase 1 °C/min from room temperature to 150 °C and maintained at this
catalytic oxidation reactions have been rarely done.40ꢀ44 Our temperature for 2 h under argon atmosphere. Then increasing
research work aimed to fill up this field starting with temperature to the target (i.e., 500 °C, 600 °C, 700 °C or 800 °C)
developing this nonꢀnoble magnetic heterogeneous catalystꢀ lead to the formation of the hybrid composites. After calcination, the
based system for selective oxidation of alcohols with green sample was cooled down to room temperature and collected. The
oxidants.
obtained black powder was denoted as Bꢀx (where x represents the
In continuation with recent research endeavours from the temperature for thermolysis procedure).
group,2c,40ꢀ42,44ꢀ46 here we report the design and synthesis of
novel nonꢀnoble magnetic heterogeneous catalysts, Fe3O4@C
(Bꢀx, where x indicates the temperature for preparing the
General procedures for the catalytical oxidation of alcohols
catalyst) for selective oxidation of alcohols in neat water using A mixture of alcohol (0.5 mmol), H2O2 30 wt.% (1.5 mmol), H2O (3
hydrogen peroxide as green oxidant under baseꢀfree conditions. mL) and catalyst (Fe 10 mol%) was placed in a Schlenk tube. The
The proposed catalytic system features a good substrate scope reaction solution was stirred at 110 °C for a certain course. At the
for a variety of aryl and alkyl alcohols with a high selectivity end of a reaction, the catalyst was isolated and a sample of the liquid
for the target oxidation products. Moreover, the catalysts could mixture was subjected to GCꢀMS analysis after extraction with ethyl
be easily recovered and reused for a number of times without acetate. (Shimadzu GCMSꢀQP5050A equipped with a 0.25 mm × 30
significant loss in activity and selectivity.
m DBꢀWAX capillary column).
Recycling of catalyst
Experimental
The recyclabilities of the catalysts were examined in the optimized
reaction system. The catalyst was firstly reꢀcollected after the former
General information
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 3 of 9
View Article Online
DOI: 10.1039/C6RA01617K
Journal Name
ARTICLE
catalytic reaction by placing a magnet close to the Schlenk tube. The
powders were adsorbed on the wall near the magnet side of the tube
in seconds. After removing the supernatant solution from the
mixture, the collected powders were thoroughly washed with
ethanol, dried under vacuum to remove the residual solvent, and then
reutilized as catalyst for subsequent runs under the identical reaction
conditions as described above, except using the recycled catalyst.
Table 1 Properties of Feꢀbased materials
Pore
Pore
Content (wt%)
SBET
Sample
Volume
(cm3 gꢀ1)
Size
(Å)
(m2 gꢀ1)
Ca
Ha
Feb
Oc
MILꢀ88B
Bꢀ500
1104
237
0.41
0.15
0.5
2.3
38.6
62.1
4.0
0.5
19.2
20.1
37.8
16.9
Results and discussion
Characterization of MIL-88B and B-x
2.4 and
4.1
Bꢀ600
214
0.65
66.2
0.4
23.8
9.3
The powder Xꢀray Diffraction (XRD) patterns of MILꢀ88B (Fig. 1)
matched well with the simulated and also the reported XRD
patterns,48 confirming the structure of the asꢀsynthesized MOF
material in this work. Thermogravimetric Analysis (TGA) curves of
MILꢀ88B indicated that the MOF structure began to decompose
when the temperature was increased to 400 °C under nitrogen
(Fig.S1, ESI†). Therefore, the calcination temperatures for
carbonization of MILꢀ88B were varied from 500 °C to 800 °C. The
resulting composite was denoted as Bꢀx, where x indicates the MOF
thermolysis temperature. XRD patterns of Bꢀx materials (Fig. 2)
exhibited five diffraction peaks at around 30.1°, 35.4°, 53.1°, 56.9°
and 62.5°, respectively, which were characteristics of Fe3O4 (JCPDS
No. 19ꢀ0629). In addition, we have performed XPS measurements
on the Bꢀ600 catalyst. The XPS survey spectrum of Bꢀ600 (Fig. S2a,
ESI†) mainly showed the peaks of three elements present in the
composite (i.e., Fe, O, C). Two strong peaks at 724.5 and 711.0 eV,
assigned to Fe 2p1/2 and Fe 2p3/2 of Fe3O4,49 respectively, were
observed in the XPS spectrum (Fig. S2b, ESI†). As shown in the N2
adsorption/desorption isotherms, micropores were only present in
MILꢀ88B (Fig. S3, ESI†, and Table 1); after thermolysis, the
observation of hysteresis loops at higher P/P0 indicated the presence
of mesopores in Bꢀx materials (Fig. 2, and Table 1). Significant
reduces in the specific surface areas of the Bꢀx composites varied
from around 237 m2 gꢀ1 (Bꢀ500) to 198 m2 g−1 (Bꢀ800) were
observed as compared with 1104 m2 gꢀ1 of MILꢀ88B, probably
owing to the collapse of crystal structure. The chemical
compositions of the resulting Bꢀx materials were characterized by
elemental analysis and AAS. Contents of Fe, C, and O elements
were mainly detected and summarized in Table 1.
Bꢀ700
Bꢀ800
204
198
0.42
0.59
2.6
30.7
22.2
0.7
0.2
45.0
42.9
23.4
34.5
2.8
a Measured by elemental analysis. b Measured by AAS. c Calculated.
The surface morphology of Bꢀx was subsequently investigated
by SEM (Scanning Electron Microscopy). As shown in Fig. 3, all Bꢀ
x exhibited similar particle shapes to those of the parent MILꢀ88B.
However, the composite surface was distorted to rough when the
calcination started, indicating the decomposition and carbonization
of the MOF frameworks. Elemental mapping (Fig. 3, C1ꢀC3)
Fig. 2 (a) The powder XRD patterns of the Bꢀx materials. All samples
show six wellꢀresolved peaks which are identified as Fe3O4 (JCPDS
No. 19ꢀ0629). (b) Nitrogen adsorption/desorption isotherms at 77 K for
Bꢀx materials. Black for Bꢀ500, red for Bꢀ600, blue for Bꢀ700, purple
for Bꢀ800.
Fig. 1 Powder XRD patterns of asꢀsynthesized MILꢀ88B: (a) simulated, (b)
asꢀsynthesized.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 4 of 9
View Article Online
DOI: 10.1039/C6RA01617K
ARTICLE
Journal Name
Table 2 Optimization of reaction conditions for oxidation of benzyl
alcohol to benzaldehyde.
Entry
Catalyst
Solvent
Con. (%)a
Sel. (%)a
Fig. 3 SEM images of (a) MILꢀ88B, (b) Bꢀ500, (c) Bꢀ600, (d) Bꢀ700, (e) Bꢀ
800, and elemental mapping of Bꢀ600: (C1) Fe, (C2) C, (C3) O.
1
2
No
Toluene
Toluene
Toluene
Toluene
Toluene
Acetonitrile
DMF
5
99
99
99
99
99
96
95
94
95
95
99
99
99
95
95
95
92
91
91
Bꢀ500
Bꢀ600
Bꢀ700
Bꢀ800
Bꢀ600
Bꢀ600
Bꢀ600
Bꢀ600
Bꢀ600
Bꢀ600
Bꢀ600
Bꢀ600
Bꢀ600
Bꢀ600
Bꢀ600
Bꢀ600
Bꢀ600
Bꢀ600
14
21
12
9
3
4
5
6
22
13
19
39
18
7
7
8
DMA
9
H2O
10
11
12
13
14
15b
16c
17d
18e
19f
Acetone
DMSO
Dimethylbenzene
nꢀHexane
Ethanol
H2O
8
7
30
70
71
91
93
99
Fig. 4 (a)–(c) TEM images of Fe3O4 nanoparticles of Bꢀ600. (d) The
corresponding size distribution of Fe3O4 particles for Bꢀ600.
H2O
revealed a uniform distribution of Fe, C, and O in the material. The
high dispersion nature of Fe3O4 in the porous carbons was further
demonstrated by highꢀresolution transmission electron microscopy
(HRTEM) (Fig. 4). It was obvious that Fe3O4 was dispersed on the
carbon in Bꢀ600 with a uniform particle size of 12.5±3.6 nm. A
highꢀresolution TEM image of Bꢀ600 confirmed the existence of
crystallized Fe3O4 nanoparticles which were tightly surrounded by
graphitized carbon. Moreover, no significant aggregation of Fe3O4
nanoparticles was observed, which could be attributed to the
isolation effect of carbons formed from carbonization of the
terephthalic acid linkers in MILꢀ88B. As the pyrolysis temperature
increased, the Fe3O4 nanoparticles tended to aggregate gradually, as
shown in Figure S3. Transmission Electron Microscopy (TEM)
H2O
H2O
H2O
Reaction conditions: benzyl alcohol (0.5 mmol), catalyst (10 mol%
a
Fe), solvent (3 mL), H2O2(1.5 mmol), 80 °C, 15 h. Conversion and
selectivity were based on the yield determined by GCꢀMS with an
b
external standard. Benzoic acid was detected as byꢀproduct. 50 °C ,
48 h. c 70 °C , 48 h. d 90 °C , 48 h. e 100 °C , 48 h. f 110 °C , 48 h.
The catalytic activities of these magnetic nanopraticles
materials were subsequently tested in alcohol oxidation using benzyl
alcohol transforming to benzaldehyde as a model reaction, hydrogen
peroxide as the oxidant; reactions were performed under moderate
baseꢀfree condition. As illustration in Table 2, blank test (without
catalyst) showed almost no reactivity (Table 2, entry 1). To our
delight, the asꢀsynthesized magnetic nanocomposites showed
promising activity in this transformation. First, the Bꢀx materials
were examined as catalysts for the aerobic oxidation of benzyl
alcohol in toluene at 80 °C. Although the conversions were
somewhat low under these conditions, it was noteworthy that the
aldehyde selectivities achieved by the Bꢀx composites were all
micrographs (Fig.
4 and Fig. S4, ESI†) revealed magnetic
nanoparticles homogeneously dispersed in Bꢀx materials. Magnetic
nanoparticles obtained at higher thermolysis temperatures exhibited
relatively larger sizes. These results suggested that the thermolysis
temperature and organic ligands played important roles in reducing
the particle size of Fe3O4 particles.
Catalytic activity in aerobic oxidations of alcohols under base-
free conditions
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Page 5 of 9
RSC Advances
View Article Online
DOI: 10.1039/C6RA01617K
Journal Name
ARTICLE
Table 3 Oxidation of various alcohols by Bꢀ600 in water.
Table 3 (Contd.)
Con.
Con.
(%)a
Entry
1
Substrate
Sel. (%)a
Entry
18b
Substrate
Sel. (%)a
(%)a
99
86
99
99
99
90
76
86
19c
20d
2
3
93
91
99
95
21c
22c
69
70
4
5
>99
88
99
99
99
99
Reaction conditions: substrate (0.5 mmol), Bꢀ600 (10 mol% Fe), H2O (3 mL),
a
H2O2 (1.5 mmol), 110 °C, 48 h.
Conversion and selectivity were
6
7
8
84
96
94
99
99
99
determined by GCꢀMS with an external standard. b 60 h. c 72 h. d 96 h.
nearly 100% (Table 2, entries 2–5). Among all the Bꢀx materials, Bꢀ
600 (i.e., the material prepared at 600 °C) was most active (Table 2,
entry 3), therefore was selected as catalyst for further optimization
and investigation. The Bꢀ600 catalyst for the alcohol oxidation was
then tested under different solvent systems, among which water was
revealed to be the best (Table 2, entry 9). It appears that solvation
effect might hugely influence the conversion of benzyl alcohol to the
desired products. H2O, which possesses the strongest polarity of all
the investigated solvents, was preference to this reaction system.
Although, the role of water for benefiting this reaction system is
unclear, it is reasonable to consider water as a safe, cheap and green
solvent if this reaction system could be performed in water.
9
83
>99
81
99
99
99
10
11
12
13
82
89
99
99
Inspired by these intriguing results, we further optimized the
oxidation reaction conditions. It is well known that the reaction
temperature would affect the transformation in the term of both
conversion and selectivity. As revealed in Table 2 (entries 15–19),
slightly increase of temperature 50 °C to 110 °C led to an obvious
increase of the conversion from 70.16% to an almost quantitative
transformation with the reaction time prolonged to 48 h (Table 2,
entry 19); in addition, the selectivities seemed satisfactory with a
faintest decrease, probably owing to the producing of a very small
amount of byꢀproducts at high temperatures. Thus after screening the
reaction parameters and taking the balance between conversion and
selectivity into consideration, the optimized reaction conditions
could be obtained as follows: 10 mol% Bꢀ600 as the catalyst, H2O as
the solvent, hydrogen peroxide as the green oxidant, and reaction
temperature at 110 °C for 48 h.
14
15
91
81
99
99
16
91
98
90
96
17b
The substrate scope and the functional group tolerance of the
selective green alcohol oxidation over the Bꢀ600 materials was then
investigated under the optimized reaction environment (Table 3).
First, different primary and secondary benzylic alcohols bearing
electronꢀdonating or ꢀwithdrawing functional groups afforded the
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 6 of 9
View Article Online
DOI: 10.1039/C6RA01617K
ARTICLE
Journal Name
time without any obvious reduces in selectivities. For example, 2ꢀ
hexanol was efficiently oxidized in excellent yield (86 %) with a 95
% selectivity towards 2ꢀhexanone after 96 h of reaction (entry 20).
Notably, the excellent selectivity to the target oxidation products
could be obtained for all the investigated substrates.
Finally, we investigated the reusability of the highly active Bꢀ
600 catalyst in the green oxidation of benzyl alcohol to
benzaldehyde in aqueous medium. After the former run, the catalyst
was dispersed in water, it can be easily separated out in a solid form
with the assistance of an external magnet (Fig. 5). AAS analysis of
the separating solution confirmed that the content of Fe in the
solution was under the detection limit, indicating that no significant
leaching of the active Fe3O4 was detected during the reaction
process. The used catalyst was washed several times with acetic
ester and methanol, and then dried in vacuum. Results included in
Fig. 5 revealed no appreciable loss of conversion after at least four
reaction runs. Powder XRD characterization proved that the
structure of the catalyst was mostly preserved (Fig. S5, ESI†),
indicating the stability of the material under the investigated
conditions. Moreover, at ca. 60% conversion, the reaction solution
was quickly filtrated at the reaction temperature, the resulting
solution would undergo a slow conversion and reach to a conversion
of 65% when the total reaction time was extended to 60 h, probably
owing to the oxidation of substrates by H2O2, strongly suggesting
that the reaction proceeded mostly on the heterogeneous surface
(Fig. S6, ESI†).
Fig. 5 (a) Magnetic separation of the Fe3O4@C catalyst after reaction; (b)
recycling of the Bꢀ600 in the oxidation of benzyl alcohol to benzaldehyde.
Reaction conditions: benzyl alcohol (0.5 mmol), Bꢀ600 (10 mol% Fe), H2O
(3 mL), H2O2 (1.5 mmol), 110 ℃, 48 h.
corresponding substituted aldehyde or ketones in good to excellent
yields within 48 h (entries 1–14). As shown in Table 3, studies with
substituted benzyl alcohols reveal that the conversion to aldehydes
or ketones are not significantly controlled by the electronꢀdonating
and electronꢀwithdrawing abilities of the substituents, nor sensitive
to the substituent position on the benzene ring, which could be
explained by the proposed mechanism for this transformation: the
oxidation of benzyl alcohol derivatives proceeds via a hydrogen
atom abstraction procedure of CꢀH bond activation, which should be
the rateꢀdetermining step in the alcohol oxidation as demonstrated in
the kinetic studies in other systems for alcohol oxidation.2c,50 The
difference in activities between these alcohols could be ascribed to
their compositions and structures. For the secondary benzylic
alcohols such as 1ꢀphenylethanol and its derivatives as well as
diphenylmethanol, the convertions to the corresponding ketones
were found in good yet relatively smaller yields comparing with
those of primary benzylic alcohols (entry 11–15), which were likely
caused by the steric effect of the secondary alcohols at the ɑꢀCH
position. This is consistent with the proposed mechanism that
hydrogen atom abstraction reaction requires significant interaction
Conclusions
In summary, we have developed a nonꢀnoble, highly efficient, and
reusable magnetic heterogeneous catalyst for selective green
oxidation of alcohols. The Fe3O4@C composites, synthesized by
oneꢀstep thermolysis of cheap metalꢀcontaining organic framework
of MILꢀ88B under an inert atmosphere, were proved to be highly
active and selective in the oxidation of a broad substrate scope for
both aryl and alkyl alcohols in the absence of any base additives in
neat water. Moreover, the catalysts are magnetically separable and
reusable, maintaining its high performance in this transformation for
at least four recycles. Although the explanation of the solvation
effect and the exact mechanism for the oxidation of alcohols over
this catalytic system is still unclear, the combination of cheap, green
and efficient, versatility and recyclability, as well as mild reaction
conditions (in the absence of bases in neat water) makes this system
an attractive alternative pathway for various oxidation processes.
Further investigations to better understand the precise mechanism of
this catalytic system in alcohol oxidation as well as in other
oxidation processes are currently in progress.
between the target C−H bond and the active centre of the catalyst,
which is likely hindered by the other group in the secondary benzylic
alcohols, thus end up with a decreased activity. Besides, 1,4ꢀ
Benzenedimethanol could also undergo oxidation to 1,4ꢀBenzene
dicarboxaldehyde in 91% yield (entry 16).
In addition, we also investigated the oxidation reactions with
heterocyclic alcohols such as 1ꢀpyridinemethanol, furfuryl alcohol.
The activities were well if prolonging reaction time to 60 h (entries
Acknowledgements
We thank the National Natural Science Foundation of China
(21322606, 21436005, and 21576095), the State Key Laboratory of
Pulp and Paper Engineering (2015TS03), the Doctoral Fund of
Ministry of Education of China (20120172110012), Fundamental
Research Funds for the Central Universities (2015ZP002 and
2015PT004), and Guangdong Natural Science Foundation
17ꢀ18). Moreover,
a range of aliphatic alcohols were also
demonstrated suitable for the formation of the corresponding
products, achieving moderate to good yields within 72 h (entries 19,
21ꢀ22). For the cases in which the conversion was not satisfying, it
could be remarkably improved by simply prolonging the reaction
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 7 of 9
View Article Online
DOI: 10.1039/C6RA01617K
Journal Name
ARTICLE
(2013B090500027) for financial support.
Zeng, C. Shao, J. Wang, J. Mater. Chem., 2012, 22, 1033.
21. H. Gu, K. Xu, C. Xu, B. Xu, Chem. Commun., 2006, , 941.
9
22. S. J. Son, J. Reichel, B. He, M. Schuchman, S. B. Lee, J. Am.
Chem. Soc., 2005, 127, 7316.
Notes and references
23. S. Guo, S. Dong, E. Wang, Chem. Eur. J., 2009, 15, 2416.
24. I. Willner, E. Katz, Angew. Chem. Int. Ed., 2003, 42, 4576.
25. V. V. Costa, M. J. Jacinto, L. M. Rossi, R. Landers, E. V.
Gusevskaya, J. Catal., 2011, 282, 209.
1.
(a) R. A. Sheldon, J. K. Kochi, Metal-Catalyzed Oxidation of
Organic Compounds; Academic Press: New York, 1981; (b)
M. Hundlucky, Oxidations in Organic Chemistry, American
Chemical Society, Washington, DC, 1990.
26. M. Esmaeilpour, A. R. Sardarian, J. Javidi, Appl. Catal. A-Gen
2012, 445, 359.
27. M. Zhang, Q. Sun, Z. Yan, J. J. Jing, W. Wei, D. Jiang, J. Xie,
M. Chen, Aust. J. Chem., 2013, 66, 564.
28. A. Heidarnezhad, F. Zamani, Catal. Commun., 2015, 60, 105.
29. D. Wang, C. Deraedt, L. Salmon, C. Labrugère, L. Etienne, J.
Ruiz, D. Astruc, Chem. Eur. J., 2015, 21, 6501.
30. M. O'Keeffe, Chem. Soc. Rev., 2009, 38, 1215.
31. D. J. Tranchemontagne, J. L. MendozaꢀCortés, M. O'Keeffe,
O. M. Yaghi, Chem. Soc. Rev., 2009, 38, 1257.
2.
(a) C. Shang, Z.ꢀP. Liu, J. Am. Chem. Soc., 2011, 133, 9938;
(b) H. Miyamura, R. Matsubara, Y. Miyazaki, S. Kobayashi,
Angew. Chem., 2007, 119, 4229; (c) H. Liu, Y. Liu, Y. Li, Z.
Tang, H. Jiang, J. Phys. Chem. C, 2010, 114, 13362; (d) M.
Mahyari, A. Shaabani, M. Behbahani, A. Bagheri, Appl.
Organometal. Chem., 2014, 28, 576.
(a) B. Karimi, M. Khorasani, H. Vali, C. Vargas, R. Luque,
ACS Catal., 2015, 5, 4189; (b) G. Chen, S. Wu, H. Liu, H.
Jiang, Y. Li, Green Chem., 2013, 15, 230.
3.
4.
5.
(a) S. Wu, L. Chen, B. Yin, Y. Li, Chem. Commun., 2015, 51
,
32. (a) T. W. Goh, C. X. Xiao, R. V. MaligalꢀGanesh, X. L. Li, W.
Y. Huang, Chem. Eng. Sci., 2015, 124, 45; (b) X. L. Li, Z.
Y.Guo, C. X. Xiao, T. W. Goh, D. Tesfagaber, W. Y. Huang,
9884; (b) H.ꢀB. Ji, Q.ꢀL. Yuan, X.ꢀT. Zhou, L.ꢀX. Pei, L.ꢀF.
Wang, Bioorg. Med. Chem. Lett., 2007, 17, 6364.
(a) J. Zhu, K. Kailasam, A. Fischer, A. Thomas, ACS Catal.,
Acs Catal., 2014, 4, 3490; (c) O. K. Farha, C. E. Wilmer, I.
2011,
1, 342; (b) G. Zhang, K. V. Vasudevan, B. L. Scott, S. K.
Eryazici, B. G. Hauser, P. A. Parilla, K. O'Neill, A. A.
Sarjeant, S. T. Nguyen, R. Q. Snurr, J. T. Hupp, J. Am. Chem.
Soc., 2012, 134, 9860.
Hanson, J. Am. Chem. Soc., 2013, 135, 8668; (c) J. Zhu, J. L.
Faria, J. L. Figueiredo, A.Thomas, Chem. Eur. J., 2011, 17
,
7112.
33. L. E. Kreno, K. Leong, O. K. Farha, M. Allendorf, R. P. Van
Duyne, J. T. Hupp, Chem. Rev., 2012, 112, 1105.
34. N. Yanai, K. Kitayama, Y. Hijikata, H. Sato, R. Matsuda, Y.
Kubota, M. Takata, M. Mizuno, T. Uemura, S. Kitagawa, Nat.
Mater., 2011, 10, 787.
35. P. Horcajada, R. Gref, T. Baati, P. K. Allan, G. Maurin, P.
Couvreur, G. Férey, R. E. Morris, C. Serre, Chem. Rev., 2012,
112, 1232.
36. P. Horcajada, T. Chalati, C. Serre, B. Gillet, C. Sebrie, T.
Baati, J. F. Eubank, D. Heurtaux, P. Clayette, C. Kreuz, J.ꢀS.
Chang, Y. K. Hwang, V. Marsaud, P.ꢀN. Bories, L. Cynober,
6.
(a) W. Qi, D. Su, ACS Catal., 2014, 4, 3212; (b) D. Obermayer,
A. M. Balu, A. A. Romero, W. Goessler, R. Luque, C. O.
Kappe, Green Chem., 2013, 15, 1530.
L. Liu, J. Ma, L. Ji, Y. Wei, J. Mol. Catal. A-Chem., 2008, 291,
1.
(a) M. T. Räisänen, A. AlꢀHunaiti, E. Atosuo, M. Kemell, M.
Leskelä, T. Repo, Catal. Sci. Technol., 2014, 4, 2564; (b) H.ꢀY.
Sun, Q. Hua, F.ꢀF. Guo, Z.ꢀY. Wang, W.ꢀX. Huang, Adv. Synth.
Catal., 2012, 354, 569.
L. Geng, M. Zhang, W. Zhang, M. Jia, W. Yan, G. Liu, Catal.
Sci. Technol., 2015, 5, 3097.
7.
8.
9.
S. Gil, G. Férey, P. Couvreur, R. Gref, Nat. Mater., 2010, 9,
10. Y. Yan, X. Tong, K. Wang, X. Bai, Catal. Commun., 2014, 43
,
172.
112.
37. B. Liu, H. Shioyama, T. Akita, Q. Xu, J. Am. Chem. Soc.,
2008, 130, 5390.
38. F.ꢀX. Qin, S.ꢀY. Jia, Y. Liu, X. Han, H.ꢀT. Ren, W.ꢀW. Zhang,
J.ꢀW. Hou, S.ꢀH. Wu, Mater. Lett., 2013, 101, 93.
11. M. Jafarpour, A. Rezaeifard, V. Yasinzadeh, H. Kargar, RSC
Adv., 2015, , 38460.
12. J. Yu, Y. Luan, Y. Qi, J. Hou, W. Dong, M. Yang, G. Wang,
RSC Adv., 2014, , 55028.
5
4
39. A. Banerjee, R. Gokhale, S. Bhatnagar, J. Jog, M. Bhardwaj,
13. G. C. Behera, K. M. Parida, Appl. Catal. A-Gen., 2012, 413
,
B. Lefez, B. Hannoyer, S. Ogale, J. Mater. Chem., 2012, 22
,
245.
19694.
14. B. Liu, Z. Zhang, K. Lv, K. Deng, H. Duan, Appl. Catal. A-
Gen., 2014, 472, 64.
40. C. Bai, X. Yao, Y. Li, ACS Catal., 2015, 5, 884.
41. J. Long, Y. Zhou, Y. Li, Chem. Commun., 2015, 51, 2331.
42. W. Zhong, H. Liu, C. Bai, S. Liao, Y. Li, ACS Catal., 2015,
1850.
43. Y.ꢀX. Zhou, Y.ꢀZ. Chen, L. Cao, J. Lu, H.ꢀL. Jiang, Chem.
Commun., 2015, 51, 8292.
44. C. Bai, A. Li, X. Yao, H. Liu, Y. Li, Green Chem., 2016. DOI:
10.1039/c5gc02082d.
45. K. Shen, L. Chen, J. Long, W. Zhong, Y. Li, ACS Catal., 2015,
15. S. Wang, Z. Zhang, B. Liu, ACS Sustainable Chem. Eng.,
5,
2015, 3, 406.
16. W.ꢀM. Zhang, X.ꢀL. Wu, J.ꢀS. Hu, Y.ꢀG. Guo, L.ꢀJ. Wan, Adv.
Funct. Mater. 2008, 18, 3941.
17. X. Du, C. Wang, M. Chen, Y. Jiao, J. Wang, J. Phys. Chem. C,
2009, 113, 2643.
18. Y. Zhang, S. Xu, Y. Luo, S. Pan, H. Ding, G. Li, J. Mater.
Chem., 2011, 21, 3664.
5
, 5264.
19. Q. Zhu, F. Tao, Q. Pan, ACS Appl. Mater. Inter., 2010, 2,
46. X. Wang, W. Zhong, Y. Li, Catal. Sci. Technol., 2015,
5
, 1014.
3141.
47. X. Xu, R. Cao, S. Jeong, J. Cho, Nano Lett., 2012, 12, 4988.
20. G. Xie, P. Xi, H. Liu, F. Chen, L. Huang, Y. Shi, F. Hou, Z.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 8 of 9
View Article Online
DOI: 10.1039/C6RA01617K
ARTICLE
Journal Name
48. S. Surblé, C. Serre, C. MellotꢀDraznieks, F. Millange, G.
Férey, Chem. Commun., 2006, 284.
49. T. Yamashita, P. Hayes, Appl Surf Sci., 2008, 254, 2441.
50. (a) M. P. Chaudhari, S. B. Sawant, Chem. Eng. J., 2005, 106
,
111; (b) N. Y. Oh, Y. Suh, M. J. Park, M. S. Seo, J. Kim, W.
Nam, Angew. Chem., 2005, 117, 4307ꢀ4311. (c) Y. Zhang, C.
Huang, J. Wang, Q. Sun, C. Wang, Chin. J. Catal., 2012, 33
,
360.
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 9 of 9
View Article Online
DOI: 10.1039/C6RA01617K
Journal Name
ARTICLE
Graphical Abstract
A magnetic Fe3O4@C heterogeneous catalyst derived from MOFs is
highly efficient and selective in oxidation of alcohols with neat water
and baseꢀfree conditions.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins