Gold nanoparticles supported on supramolecular ionic liquid grafted graphene: A bifunctional catalyst for the selective aerobic oxidation of alcohols

Article abstract of DOI:10.1039/c3ra44696d

Gold nanoparticles supported on supramolecular ionic liquid grafted graphene have been synthesized and used as a bifunctional, efficient and recyclable heterogeneous catalyst for the aerobic oxidation of various primary and secondary aliphatic and aromatic alcohols to the corresponding aldehyde and ketone derivatives in water as a green solvent at room temperature. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3ra44696d

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Graphical Abstract
Gold nanoparticles supported on supramolecular ionic liquid
grafted graphene: a bifunctional catalyst for the selective aerobic
oxidation of alcohols

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DOI: 10.1039/C3RA44696D
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ARTICLE TYPE
Gold nanoparticles supported on supramolecular ionic liquid grafted
graphene: a bifunctional catalyst for the selective aerobic oxidation of
alcohols
Mojtaba Mahyari, Ahmad Shaabani,* and Yasamin Bide
5
Received (in XXX, XXX)Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
50 Faculty of Chemistry, Department of Polymer, Shahid Beheshti University, G.C.,
P.O. Box 1983963113 Tehran, Iran. E-mail: a-shaabani@sbu.ac.ir
Gold nanoparticles supported on supramolecular ionic liquid
grafted graphene have been synthesized and used as an
bifunctional, efficient and recyclable heterogeneous catalyst
The heterogeneous oxidation of alcohols with noble metals has
10 for the aerobic oxidation of various primary and secondary
aliphatic and aromatic alcohols to the corresponding
aldehyde and ketone derivatives in water as a green solvent at
room temperature.
been exponentially improved since their first report in 150 years
ago. Gold was thought to be an ineffective noble metal for the
55 oxidation reaction due to its chemical inertness.41ꢀ44 Interactions
of gold and support affect on the size of the encapsulated gold
nanoparticles (Au NPs), and dispersity of catalyst in the reaction
media which is very important in the performance of the catalyst
to achieve the best results in the selective oxidation.41,45ꢀ53 In
60 aerobic oxidation of alcohols with Au NPs, in order to activate
the reactant inorganic bases such as NaOH and K2CO3 was
usually employed which produced byꢀproducts.51ꢀ55
15 Introduction
Selective oxidation of alcohols has major importance in both
organic synthesis and industrial applications.1ꢀ8 The world annual
production of carbonyl compounds is more than 1×107 tones
which most of them were produced from the oxidation of
20 alcohols using traditional stoichiometric amounts of oxidants and
aerobic oxidation under heterogeneous and homogeneous
catalytic strategy.9,10 One of the most important aspects of green
chemistry is the aerobic oxidation of alcohols into the
corresponding carbonyl derivatives. Another three important
25 aspects are the development the aerobic oxidation transformative
in a greener solvent such as water, avoiding the addition
activators such as inorganic bases and carrying the reaction
without any activation at ambient temperature. The combination
of these four aspects is highly challenging and will provide the
30 more benefits for chemical transformations in industry.11ꢀ14
Graphene as the high specific heterogeneous support has gained
more attention in recent years and due to extraordinary thermal
In continuation of our efforts to introduce new and efficient
catalysts for various organic transformations,56ꢀ64 herein we wish
65 to report the synthesis of Au NPs in supramolecular ionic liquids
grafted on graphene (Au NPs@SILꢀgꢀG), which upon dispersion
into water allows the aqueous aerobic oxidation of various
primary and secondary aliphatic and aromatic alcohols to the
corresponding aldehyde and ketone derivatives in the absence of
70 inorganic base at room temperature. To the best of our
knowledge, this is the first report that Au nanoparticles supported
by graphene covalently functionlized with SILs was synthesized
and used as a powerful catalyst for the aerobic selective oxidation
of alcohols in water as a green solvent without using bases as
75 activator. The synthesized catalyst exhibited excellent high
and mechanical properties, and high stability in different
15ꢀ24
conditions are ideal support for noble metals.
However, the
35 stabilization of nanoparticles, and achievement of uniform
distributions are two barriers to overcome which affect the
metal−graphene interaction due to the chemical inertness of
graphene. There are different methods to deal with these issues.
One of the most important methods consists of functionalizing
40 graphene, which also allows one to obtain chemically processable
graphene.25ꢀ29 Recently, due to the importance of poly ionic
liquids, several pioneer groups published reviews about this hot
topic.30ꢀ34 Graphene nanoꢀcomposite functionalized with poly
ionic liquid has several advantages such as high dispersity,
45 functionality, and high surface charge density.35,36.Therefore, this
system can cause highly dispersive and long term stable graphene
sheets in reaction media.36ꢀ38 Poly ionic liquid functionalized on
particle surface due to liquidꢀlike appearance called
supramolecular ionic liquids (SILs).39,40
dispersion and hydrophilicity properties.
Scheme 1 Oxidation of alcohols by Au NPs@SILꢀgꢀG hybrid materials
Experimental
Materials and instruments
80 All chemicals were purchased from Aldrich and used without
further purification. IR spectra were recorded on a Bomem MBꢀ
Series FTꢀIR spectrophotometer. Transmission electron
microscopy (TEM) analyzes were performed by LEO 912AB
electron microscope. Identification and quantification were
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carried out on a Varian model 3600 gas chromatograph (Varian 35 solution) and deionized water (140 mL) were added to the
Iberica, Madrid, Spain) equipped with a split/splitless capillary
injection port and flame ionization detector (FID). A CPꢀSilꢀ8
fused silica capillary column (25 m _ 0.32 mm i.d. and 0.52 mm
film thickness) from Chrompack was employed. Ultrasonic bath
(EUROSONIC® 4D ultrasound cleaner with a frequency of 50
kHz and an output power of 350 W) was used to disperse
materials in solvent. Xꢀray powder diffraction (XRD) data were
collected on an XDꢀ3A diffractmeter using Cu Kα radiation.
mixture. Then resulting precipitate was centrifuged and washed
repeatedly with HCl (5%, 3 × 15 mL) and EtOH and dried under
the vacuum at 60 oC. The GO was obtained as a brown powder.
5
Preparation
of
functionalized
graphene
oxide
by
40 tris(hydroxymethyl)aminomethane
GOꢀtris(hydroxymethyl)aminomethane
(GOꢀTris)
was
synthesized by an epoxide ringꢀopening reaction between
graphene oxide (GO) and tris(hydroxymethyl)aminomethane
(Tris or THAM). Firstly, 10 mL GO dispersion in water
45 (0.5mg/mL), Tris (20 mg), and KOH were added into a 100 mL
flask, and then the mixture was subjected to ultrsonication for 30
minutes. After the ultrsonication, the solution was vigorously
stirred at 80 °C for 24 h. Finally, the functionalized GO was
centrifuged, washed with ethanol and water, and airꢀdried to
10 Hitachi FEꢀSEM model Sꢀ4160 was used for surface imaging.
Preparation of 1-methyl-3-(oxiran-2-ylmethyl)-1H-imidazol-3-
ium chloride (3)
2ꢀ(Chloromethyl)oxirane (1) (3.9 mL or 50 mmol) and 1ꢀ
methylimidazole (2) (4.0 mL or 50 mmol) were added to a 100
15 mL roundꢀbottomed flask equipped with a reflux condenser and
reacted for 24–72 h at 70 °C with stirring to the formation of a 50 obtain a black powder (Scheme 2).66
twoꢀphase mixture under nitrogen atmosphere. The upper layer,
Synthesis of SIL-g-GO
which contained mostly the unreacted precursors, was decanted
and washed with ethyl acetate for three times and product as a
20 brown liquid was finally obtained. H NMR (300 MHz, CDCl3):
1
GOꢀTris (0.5 g) and cesium hydroxide monohydrate (3.0 g) were
placed in a 250 mL Schlenk flask, and 20 mL toluene was added.
The mixture was stirred at 60 °C under an argon atmosphere for 1
55 h and evacuated at 60 °C for 12 h to remove toluene and water to
generate the corresponding cesium alkoxide. Subsequently, 20
mL dry THF was transferred into the Schlenk flask. Compound 3
was transferred to a graduated ampoule and then transferred into
the reaction flask containing the above mixture. The mixture was
δH (ppm) 3.84 (3H, s, NCH3), 4.05ꢀ 4.31 (3H, m,
NCH2CHCH2O), 4.40ꢀ4.46 (2H, m, NCH2CHCH2O), 7.38ꢀ7.40
(1H, m, CH3NCHCHN), 7.42ꢀ7.43 (1H, m, CH3NCHCHN), 8.70
(1H, s, NCHN), (Scheme 2).
25 Preparation of graphene oxide
Graphene oxide (GO) was synthesized by Hummer method.65 60 heated to 60 °C and stirred for at least 12−24 h. The polymer
Graphite powder (1.00 g, 325 mesh) and concentrated H2SO4 (23
mL) were added to a 250 mL conical flask and the mixture was
stirred. Sodium nitrate (0.50 g) was added and the resulting
30 mixture was cooled to 0 °C. Under vigorous agitation, KMnO4
solution was dried under the vacuum and dialyzed against
deionized water. Finally a highly viscous black liquidꢀlike
product was obtained.67 Solid potassium hydroxide was used for
replacing chloride ion with hydroxide ion on SILꢀgꢀGO that both
(3.00 g) was added slowly and the mixture was stirred for 1h 65 were added to water (50 mL), and the mixture was stirred
while the temperature was kept below 35 °C. Then, H2O (45 mL)
was added slowly to the reaction mixture and the solution was
stirred for 30 min at 90 °C. Next, H2O2 (10 mL of a 30%
vigorously at room temperature for 24 h. Then the mixture was
centrifuged and washed with water and was dried under reduced
pressure to give the supported basic SILꢀgꢀGO (Scheme 2).
N
s.f.
70 o
N
Cl
O
O
N
N
+
Cl
C
1
2
3
OH
Cl
HO
OH
HO
O
N
N
O
1.MeO Na
N
NH2
HN
O
N
HN
2.
N
O
O
OH
OH
N
O
Cl
Cl
OH
OH
O
Cl
Cl
N
Cl
N
N
O
N
N
N
OH
OH
N
HO
O
N
N
Cl
N
HN
N
N
O
O
OH
O
OH
O
KOH
Anion exchange
OH
N
OH
OH
N
N
O
N
N
N
OH
N
N
OH
2
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Scheme 2. Synthesis route of SILꢀgꢀGO
Preparation of Au NPs@SIL-g-G hybrid materials
General procedure for the catalytic aerobic oxidation of alcohols
Aqueous solution of HAuCl4 (0.2 g in 3.0 mL) and SILꢀgꢀGO 15 A mixture of an alcohol (1.0 mmol) and Au NPs@SILꢀgꢀG (0.2
(0.2 g in 10.0 mL) were mixed and placed in an ultrasonic bath
(50 KHz) for 30 min to well disperse metal ions in the
functionalized graphene oxide sheets. Then 10.5 mL of a 1.0 M
NaBH4 solution in 0.3 M aqueous NaOH was added to mixture to
mmol% Au, 0.005 g) was added in portions to a twoꢀnecked vial
containing H2O (4.0 mL) as solvent under bubbling of air or O2 at
atmospheric pressure at room temperature. The progress of the
reaction was followed by gas chromatography (GC). After the
5
reduced and form gold nanoparticles. In the second step, another 20 reaction, the catalyst was removed via centrifuge and washed
10.5 mL of 1M NaBH4 solution was added into the solution under
twice with CH2Cl2 (6.0 mL) to separate the absorbed organic
compounds. Then the organic phase was combined, extracted
twice. Finally the solvent was removed under vacuum to give the
pure product.
10 constant stirring for converting functionalized GO to
functionalized reduced graphene oxide. After stirring for 4 h, it
was filtered under vacuum, washed well with ethanol and water
and dried under vacuum at 50 °C for 12 h (Scheme 3).
HAuCl4
OH
HO
OH
HO
HN
HN
N
N
O
O
N
N
O
n
n
O
O
O
N
N
O
O
OH
N
N
OH
O
OH
OH
N
N
O
OH
OH
OH
N
n
OH
N
n
n
O
n
O
N
N
OH
OH
OH
N
OH
N
N
N
N
N
N
N
N
N
OH
OH
NaBH4
OH
N
HO
N
O
HN
n
O
N
N
O
OH
O
OH
N
O
OH
OH
n
N
n
OH
O
N
N
N
N
N
OH
N
OH
25
Scheme 3. Synthesis route of Au NPs@SILꢀgꢀG
Results and discussion
Our approach was guided by four imperatives: (i) the synthesized
system should have gold nanoparticles and basic centers to act as
30 bifunctional catalyst for organic reaction (ii) the support should
encapsulate metal nanoparticles to control the size and uniform
distributions of nanoparticles; (iii) the catalyst should be
hydrophilic to have good dispersity in water as reaction solvent
and iv) developing an efficient, environmentalꢀfriendly and
35 benign synthetic process for the facile conversion of selective
aerobic oxidation reaction.
GO was synthesized by Hummer method.44 Typical scanning
electron microscopy 5 image of the suspended GO sheets are
shown in Fig. 1. The exfoliated graphene sheets with lateral
40 dimensions of several micrometers were observed by SEM
image.
Fig. 1 SEM image of GO
Basic supramolecular ionic liquid grafted graphene and
45 subsequent loading of gold have been outlined in Schemes 2 and
3. Briefly, based on nucleophilic substitution of epoxides groups
on graphene oxide sheets with aminoꢀgroups of Tris, GO was
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covalently functionalized by Tris. Supramolecular ionic liquid,
polyether polyol, was synthesized by a triꢀbranch initiator on 35 Functionalized GO with Tris indicates a peak around 2900 cmꢀ1,
cmꢀ1 (ν CꢀO), 1220 cmꢀ1 (ν phenolic), and 1720 cmꢀ1 (ν C=O).
graphene oxide and then the chloride ions exchanged with
hydroxide ions and finally, gold nanoparticles were encapsulated
on SILꢀgꢀGO.
which corresponds to C–H stretching of CH2 group of Tris that
there is not in GO spectrum. After the synthesis of SIL on the
GOꢀTris, due to the introduction of imidazolium groups, the
peaks in 1430–1640 cm−1 region were appeared that shows
40 formation of the poly ionic liquid on graphene.
5
As expected due to the hydrophilic properties of catalyst, Au
NPs@SILꢀgꢀG shows high despersity and stability in aqueous
solution (Fig. 2). In short, covalently functionalization of
graphene with SIL can be improved its despersity in a wide range
10 of solvents. The super dispersion of Au NPs@SILꢀgꢀG in water
makes it ideal candidate for environmentallyꢀfriendly oxidation
reaction.
Fig. 4 FTꢀIR spectrum of GO (A), GOꢀTris (B), and SILꢀgꢀGO (C)
As shown in Fig. 5, the XRD pattern of Au NPs@SILꢀgꢀG
indicated a peak for rGO with a 2θ value of about 20.17° and
45 wellꢀdefined peaks of the Au NPs with 2θ values of 38.21°,
44.38°, 64.61, 77.62° related to (111), (200), (220) and (311)
Bragg's reflection based on the fcc structure of gold nanoparticles.
The broadening of Bragg's peaks confirms the formation of
nanoparticle. The Debye–Scherrer's equation was used to
50 calculate the mean size of gold nanoparticles by determining the
width of the (111) Bragg reflection.68 The size of the
nanoparticles was thus obtained to be about 3 nm for gold
nanoparticles.
Fig. 2 Dispersity of GO (A), graphene (B), Au NPs@SILꢀgꢀG (C) in H2O
15 TGA is a powerful technique for identification of polymer
attached on support. Also, the percent of polymer connected to
support can be reasonably calculated. The result showed that
graphite is highly stable up to 700 oC. For GO, there are two
o
weight loss from ∼25 to ∼130 C and∼150 to ∼205 °C that are
20 related to weight loss of water and pyrolysis of the oxygenꢀ
containing functional groups, generating CO and CO2,
respectively. Reduced graphene (rGO) is stable up to 700 oC.
SILꢀgraphene shows the weight loss from ∼380 to ∼480 °C,
which is in accordance with decomposition of the surfaceꢀbound
25 SIL. So it can be concluded that the weight % of SIL supported
on graphene is about ∼30% (Fig. 3).
55
Fig. 5 Xꢀray diffraction (XRD) pattern of Au NPs@SILꢀgꢀG hybrid
material
TEM is one of the most powerful techniques used to investigate
single layers and the level of the dispersion of graphene sheets in
60 aqueous solution. Fig. 6A shows that thin graphene oxide sheets
which can be well dispersed in aqueous solution. It is important
to note, in addition to the above mention advantages,
functionalization graphene with SIL causes well stabilizing,
uniformly dispersing, and controlling size of gold nanoparticles
65 which is clearly shown in Fig. 6B. TEM analysis, indicated that
the range of nanoparticles sizes is 2ꢀ3 nm.
Fig. 3 TGA graph of pristine graphite (A), rGO (B), GO (C), and SILꢀgꢀ
GO (D) obtained under nitrogen
30 FTꢀIR has been used to analyze the presence of functional groups
in the synthesized catalyst. In Fig. 4, spectra of GO, GOꢀTris and
SILꢀgraphene have been shown after background subtraction for
each spectrum. The spectrum of GO shows bands around 1060
4
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A
Fig. 6 HRꢀTEM images of graphene oxide (A), and Au NPs SILꢀgꢀgraphene (B)
intermediate, since the formation of metal–alcoholate species is
50 recognized for such selective oxidation of primary hydroxy
groups.69,70
To investigate the effect of catalyst loading on the catalytic
activity, different weight ratios of HAuCl4:SILꢀgꢀGO, 1:1, 1:2
and 2:1, were employed to synthesis of catalyst. The weight
percents of metal to supported catalyst was obtained by AAS data
and it was tabulated in Table 1.The supported catalysts with
different amounts of metal loading but with the same amounts of
catalyst in the reaction (0.2 mmol%), to have a correct
5
Table 1. Effect of catalyst loading on the catalytic activity.
Au (g)/Au
NPs@SILꢀgꢀG (g)
HAuCl4:SILꢀgꢀGO
weight ratio
Conversion Yieldb
(%)
Entry
(%)a
4.5
7.9
11.4
10 comparison, were tested for oxidation reaction of benzyl alcohol
as a model reaction. The results were shown in Table 1, that
indicated increasing the catalyst reactivity for HAuCl4:SILꢀgꢀGO
1:1 compared to 1:2, but decreasing the catalytic activity with
changing the ratio to 2:1, maybe due to the aggregation of metal
15 nanoparticles because of high metal loading. To evaluate the
catalytic properties of this catalyst, oxidation reaction of benzyl
alcohol was performed as a model reaction. The reaction was
carried out in the presence of various amounts of catalyst (Table
2, entries 1ꢀ4). The optimized catalyst amount was 0.2 mol%
20 (with respect to benzyl alcohol). In order to obtain the best
solvent, various solvents, such as THF, DMF, DMSO, H2O,
CH3CN, toluene and solventꢀfree conditions were tested. As
indicated in Table 2 (Entries 4 ꢀ10), the H2O is the most suitable
solvent for this reaction in terms of yield, easy workꢀup and
25 coincidence to green chemistry principle. The reaction was
studied under O2 instead of air atmosphere, too, so that the
reaction time and yields for O2 are relatively better under the
same conditions. But the air due to its lower cost and availability
is preferred than O2. The optimization of aerobic oxidation of
30 benzyl alcohol is 0.2 mol% of catalyst in water in the absence of
additive inorganic bases such as NaOH, K2CO3, and KOH under
the atmosphere of oxygen at room temperature (Table 2, entry 4).
1
2
3
1:2
1:1
2:1
79
>99
81
a Obtained with AAS
Reaction conditions: benzyl alcohol (1mmol), solvent (5mL), at 25 C,
55 air (1 atm), Au NPs@SILꢀgꢀG (0.20 mmol% Au, x g), 1 h. Yield
determined by GC analysis.
b
o
Table 2 Optimization of the reaction conditions on oxidation reaction of
benzyl alcohola
Entry
Amount of catalyst
(Au content /mol %)
Solvent
Conversion
Yieldb (%)
1
2
None
0.05
0.10
0.20
0.20
0.20
0.20
0.20
0.20
0.20
H2O
H2O
11
30
3
H2O
75
4
H2O
>99
>99
>99
82
5
DMF
DMSO
THF
To show the efficiency of the prepared catalyst for the oxidation
reaction, a large variety of primary and secondary cyclic and
35 aromatic alcohols to the corresponding carbonyl compounds were
subjected to the optimized conditions. All products were obtained
in high yields and excellent selectivities (Table 3). Almost no
carboxylic acids or esters were observed for all substrates
investigated. Allyl alcohols such as cinnamyl alcohols were also
40 oxidized to the corresponding cinnamic aldehydes with high
selectivity (Table 3, entry 10ꢀ12). No epoxy, carboxylic acid or
ester as side products were observed. When a mixture of benzyl
alcohol and 1ꢀphenylethanol was employed as the reaction
substrates, primary alcohol was selectively oxidized even in the
45 presence of secondary one. Actually, this aerobic oxidation gave
a mixture of benzaldehyde and acetophenone in 91% and 19%
yields, respectively. These faster oxidations of primary alcohols
show that Au–alcoholate I (see scheme 4) is formed as an
6
7
8
None
CH3CN
toluene
70
9
40
10
55
a Reaction conditions: benzyl alcohol (1mmol), solvent (5mL), at 25 oC,
air (1 atm), 1 h. b Yield determined by GC analysis.
To evaluate the efficiency of catalyst in the presence of air, some
60 of the derivatives were examined and the results showed that
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good yields were obtained which are comparable with the yields 20 Long reaction time is another drawback of these reports. Using
of those reactions in the presence of oxygen but in longer reaction
times.
toxic solvents such as DCM and toluene make these reports
unfavorable from green chemistry point of view. In addition,
most of these examples required an equivalent of bases (Table 4,
entries 2ꢀ4). Recently, Liu and coꢀworkers48 reported
a
Gold NPs have attracted much interest in aerobic oxidation of
alcohols; however the mechanism of oxidation reaction with gold
NPs is still not fully understood. According to our experimental
results as well as the literature reports, we propose possible
mechanism for the catalytic oxidation of alcohols over
bifunctional catalytic system (Au nanoparticles and OH‾ as base)
10 which has been illustrated in Scheme 4. Deprotonation of alcohol
was promoted at the basic sites of OH‾ to from alkoxide on the
Au surfaces. Gold catalyzes the βꢀhydride elimination to produce
corresponding aldehyde along with the formation of O2 and H2O.
5
25 bifunctional catalysts containing Au NP and a solid base support,
Au/MgCr–HT, for the oxidation of alcohols (Table 4, entry 5);
however, the catalytic performance is limited by the use of toxic
solvent (toluene) and high temperature (100 oC). To overcome the
mentioned deficiencies, a new bifunctional catalytic system was
30 introduced based on functionalized graphene sheets with basic
supramolecular ionic liquid. In the presented catalyst, a task
specific ionic liquid containing Au NPs, and hydroxyl ions were
immobilized on the graphene. This structure omits any external
use of basic activators. The catalyst is usable on water as reaction
35 medium at room temperature. These properties and also high
reaction yields are the most important advantages of the
synthesized catalyst.
To understand the unique promotional effect of Au NPs@SILꢀgꢀ
15 G, its catalytic activity was compared with that of other supported
Au catalysts used in oxidation reaction of benzyl alcohol with
respect to their yields, solvents, additive base, temperature, and
time required for the reaction (Table 4). It is evident from Table 4
(Entries 3 and 4) that the high reaction temperatures are needed.
Table 3 Aerobic oxidation of alcohols using Au NPs@SILꢀgꢀGraphenea
40
Entry
R1
R2
Time (h)
O2
Conversion/Isolated
yield (%)
Selectivity,b (%)
Air
2.5
Air
O2
1
2
Ph
4ꢀClC6H4
H
H
1
98/97
>99/99
>99
>99
>99
>99
>99
>99
98
3
2.2
3.4
3
1.2
1
98/98
95/94
93/92
94/92
97/96
91/88
92/90
92/92
95/90
92/89
91/86
95/94
97/97
95/93
96/94
93/93
>99/98
>99/98
>99/99
98/96
>99/99
96/92
98/98
98/98
95/90
96/94
98/95
97/95
98/98
97/96
99/99
97/95
3
4ꢀMeC6H4
H
4
2ꢀMeC6H4
H
1.5
1.3
1.7
2
5
4ꢀMeOC6H4
4ꢀNO2C6H4
CH3(CH2)4
H
6
H
3.5
4
7
H
8
CH3(CH2)6
H
4.5
4.2
2.5
3
2
>99
>99
97
9
PhꢀCH2
H
1.5
1.4
1.5
1.8
1
10
11
12
13
14
15
16
17
PhCH=CHꢀ
4ꢀMeC6H4CH=CHꢀ
4ꢀMeOC6H4CH=CHꢀ
Ph
H
H
98
H
3
96
Me
Ph
Me
2
99
PhꢀCO
2.5
3
1
99
PhCH=CHꢀ
Cyclohexanol
4ꢀtertꢀbutylcyclohexanol
1.5
1.2
1.5
99
2.8
2.5
99
99
6
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16
2,3ꢀdihydroꢀ1Hꢀindenꢀ1ꢀol
2
1
98/96
>99/96
98
17
18
Cyclooctanol
Ph
3.5
6.3
2
98/94
92/90
>99/97
95/91
98
97
Ph
4.2
a Reaction conditions: alcohol (1.0 mmol), Au NPs@SILꢀgꢀG (0.20 mmol% Au, 0.005 g), H2O (4.0 mL), O2 or Air (1 atm), 25 oC. b Se
air.
5
Scheme 4. Plausible pathways for the oxidation of alcohols over Au NPs@SILꢀgꢀG
Table 4 Comparison of the results obtained from Au NPs@SILꢀgꢀG with other supported Au catalysts for the oxidation of benzyl alcohol.
Entry
Cat.
Solvent
Temp.
(oC)
25
Time
(h)
1
Base
Yield (%)
Selectivity
Ref.
(%)
>99
ꢀ
1
2
AuNPsꢀSILꢀgꢀgraphene
PS–PAMAM–Au NPsa
H2O
ꢀ
>99
99
ꢀ
71
DCM/H2O
25
16
K2CO3
35
72
73
3
4
5
Fe3O4/Au
toluene
H2O
100
25
6
6
1
K2CO3
K2CO3
ꢀ
100
94
100
5
Fe3O4:PVPb/Au
Au/MgCr–HTc
toluene
100
96
99
a Polystyrene–polyamidoamineꢀsupported gold nanoparticles
b Poly(Nꢀvinylꢀ2ꢀpyrrolidone)
10 c Layered double hydroxide hydrotalcite
The organic product phase was monitored for the presence of
recyclability. But catalysis is a totally kinetic phenomenon, so
ppm amount of gold. The atomic absorption spectroscopy of the 20 one can argue that only kinetic data should be considered to
filtrate showed that the Au content in the solution was below the
15 detection limit (0.1 ppm).
prove recyclability, stability and deactivation. Measurement of
initial rates obtained from kinetic plots is a good approach to
investigate recyclability and deactivation. Since if a single data
point was taken in each run after long reaction time, one might
25 incorrectly conclude that the catalyst is completely stable and
recyclable.74 So, we investigated conversion yields for every run
Many reports of stable and recyclable supported homogeneous
catalysts are based on a single data point in each run, often a
reaction yield at a long time, to prove catalyst stability and
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after 1h (The reaction proceed was monitored by GC) for
6. R. Liu, X. Liang, C. Dong and X. Hu, J. Am. Chem. Soc., 2004,
126, 4112ꢀ4113.
oxidation reaction of benzyl alcohol in air atmosphere as a model
reaction. After carrying out the reaction, the reaction mixture was
filtered off and Au NPs@SILꢀgꢀG separated as a black solid,
washed with EtOH (2× 5 mL) and reused. The results showed in
Fig. 7 Au NPs@SILꢀgꢀG showed good stability and recyclability
as the conversion yields after 1h for five runs didn’t decrease
significantly.
7. A. Rahimi, A. Azarpira, H. Kim, J. Ralph and S. S. Stahl, J.
45 Am. Chem. Soc., 2013, 135, 6415ꢀ6418.
5
8. D. Obermayer, A. M. Balu, A. A. Romero, W. Goessler, R.
Luque and C. O. Kappe, Green Chem., 2013, 15, 1530ꢀ1537.
9. K. Weissermel and H.ꢀJ. Arpe, In Industrial Organic
Chemistry, 3rd ed; Lindley, C. R., Ed.; VCH: New York, 1997.
50
40
30
20
10
0
50 10. C. Parmeggiani and F. Cardona, Green Chem., 2012, 14, 547ꢀ
564.
11. B.ꢀZ. Zhan and A. Thompson, Tetrahedron, 2004, 60, 2917ꢀ
2935.
12. R. C. Larock, Comprehensive Organic Transformations: a
55 Guide to Functional Group Preparations, VCH New York, 1989.
1
2
3
4
5
No. of recycling
13. R. A. Sheldon, J. K. Kochi and J. Richardson, Metal-
Catalyzed Oxidations of Organic Compounds: Mechanistic
Principles and Synthetic Methodology Including Biochemical
Processes, Academic Press New York, 1981.
10 Fig. 7 The reusability of the catalyst in the oxidation of benzyl alcohol.
In this work, we have found several important achievements; (i)
providing a suitable support for stabilizing and encapsulating
gold nanoparticles to control their size and uniform distributions
by grafting supramolecular ionic liquid to graphene (ii) having a
15 heterogeneous graphene based catalyst with good dispersity in
water as reaction solvent and (iii) removing the need for an
additive base by synthesis of a new efficient bifunctional
heterogeneous catalyst, gold nanoparticles and basic centers (iv)
developing an efficient, environmentalꢀfriendly and benign
20 synthetic process for the facile conversion of selective aerobic
oxidation reaction of various primary, secondary and allyl
alcohols into their corresponding aldehydes and ketones in water
at room temperature with excellent yield and selectivity. Also the
catalyst has good chemical stability in the reaction media proved
25 by investigating the recyclability of the catalyst.
60 14. B. M. Trost, M. F. Semmelhack and I. Fleming,
Comprehensive Organic Synthesis: Selectivity, Strategy,
&
Efficiency in Modern Organic Chemistry, Pergamon, 1991.
15. M. J. Allen, V. C. Tung and R. B. Kaner, Chem. Rev., 2009,
110, 132ꢀ145.
65 16. D. Chen, H. Feng and J. Li, Chem. Rev., 2012, 112, 6027ꢀ
6053.
17. V. Georgakilas, M. Otyepka, A. B. Bourlinos, V. Chandra, N.
Kim, K. C. Kemp, P. Hobza, R. Zboril and K. S. Kim, Chem.
Rev., 2012, 112, 6156ꢀ6214.
70 18. F. Schedin, A. Geim, S. Morozov, E. Hill, P. Blake, M.
Katsnelson and K. Novoselov, Nat. Mater., 2007, 6, 652ꢀ655.
Acknowledgements
19. Y. Si and E. T. Samulski, Nano Lett., 2008, 8, 1679ꢀ1682.
20. S. Bai and X. Shen, RSC Adv., 2012, 2, 64ꢀ98.
We gratefully acknowledge financial support from the Research
Council of Shahid Beheshti University and Catalyst Center of
Excellence (CCE).
21. L. J. Wu, Y. Wang, Y. P. Wang, X. Du, F. Wang, Y. Y. Gao,
75 T. Qi and C. M. Li, RSC Adv., 2013, 3, 5196ꢀ5203.
30 Reference
22. K. S. Novoselov, Z. Jiang, Y. Zhang, S. Morozov, H.
Stormer, U. Zeitler, J. Maan, G. Boebinger, P. Kim and A. Geim,
Science, 2007, 315, 1379ꢀ1379.
1. Z. Shi, C. Zhang, C. Tang and N. Jiao, Chem. Soc. Rev., 2012,
41, 3381ꢀ3430.
2. C. P. Vinod, K. Wilson and A. F. Lee, J. Chem. Technol. Biot.,
2011, 86, 161ꢀ171.
23. A. Chen, J. Qi, Q. Zhao, Y. Li, G. Zhang, F. Zhang and X.
80 Fan, RSC Adv., 2013, 3, 8973ꢀ8977.
35 3. B. Guan, D. Xing, G. Cai, X. Wan, N. Yu, Z. Fang, L. Yang
and Z. Shi, J. Am. Chem. Soc., 2005, 127, 18004ꢀ18005.
24. X. An and J. C. Yu, RSC Adv., 2011, 1, 1426ꢀ1434.
25. P. V. Kamat, J. Phys. Chem. Lett., 2009, 1, 520ꢀ527.
4. X.ꢀM. Zeng, J.ꢀM. Chen, A. Yoshimura, K. Middleton and V.
V. Zhdankin, RSC Adv., 2011, 1, 973ꢀ977.
26. R. Muszynski, B. Seger and P. V. Kamat, J. Phys. Chem., C,
2008, 112, 5263ꢀ5266.
5. S. R. Hall, A. M. Collins, N. J. Wood, W. Ogasawara, M.
40 Morad, P. J. Miedziak, M. Sankar, D. W. Knight and G. J.
Hutchings, RSC Adv., 2012, 2, 2217ꢀ2220.
85 27. K. Jasuja, J. Linn, S. Melton and V. Berry, J. Phys. Chem.
Lett., 2010, 1, 1853ꢀ1860.
8
| RCS Adv, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

RSC Advances
Page 10 of 11
View Article Online
DOI: 10.1039/C3RA44696D
28. P. A. Pandey, G. R. Bell, J. P. Rourke, A. M. Sanchez, M. D.
Elkin, B. J. Hickey and N. R. Wilson, Small, 2011, 7, 3202ꢀ3210.
51. T. Ishida, M. Nagaoka, T. Akita and M. Haruta, Chem. Eur.
J., 2008, 14, 8456ꢀ8460.
29. P. Kundu, C. Nethravathi, P. A. Deshpande, M. Rajamathi, G. 45 52. H. Liu, Y. Liu, Y. Li, Z. Tang and H. Jiang, J. Phys. Chem. C,
Madras and N. Ravishankar, Chem. Mater., 2011, 23, 2772ꢀ2780.
2010, 114, 13362ꢀ13369.
5
30. J. Yuan, D. Mecerreyes and M. Antonietti, Prog. Polym. Sci.,
2013, 38, 1009ꢀ1036.
53. R. L. Oliveira, P. K. Kiyohara and L. M. Rossi, Green Chem.,
2010, 12, 144ꢀ149.
31. D. Mecerreyes, Prog. Polym. Sci., 2011, 36, 1629ꢀ1648.
54. L. Prati and M. Rossi, J. Catal., 1998, 176, 552ꢀ560.
32. J. Lu, F. Yan and J. Texter, Prog. Polym. Sci., 2009, 34, 431ꢀ 50 55. B. N. Zope, D. D. Hibbitts, M. Neurock and R. J. Davis,
448.
Science, 2010, 330, 74ꢀ78.
10 33. M. Xie, H. Han, L. Ding and J. Shi, Polym. Rev., 2009, 49,
56. A. Shaabani and M. Mahyari, J. Mater. Chem. A, 2013, 1,
315ꢀ338.
9303ꢀ9311.
34. M. D. Green and T. E. Long, Polym. Rev., 2009, 49, 291ꢀ314.
57. A. Shaabani and M. Mahyari, Catal. Lett., 2013 (DOI:
55 10.1007/s10562ꢀ013ꢀ1063ꢀx).
35. S. P. Lonkar, A. Bobenrieth, J. D. Winter, P. Gerbaux, J.ꢀM.
Raquez and P. Dubois, J. Mater. Chem., 2012, 22, 18124ꢀ18126.
58. A. Shaabani, M. Mahyari and F. Hajishaabanha, Res. Chem.
Intermediat., 2013 (DOI:10.1007/s11164ꢀ013ꢀ1129ꢀ9).
15 36. Q. Ji, I. Honma, S.ꢀM. Paek, M. Akada, J. P. Hill, A. Vinu
and K. Ariga, Angew. Chem. Int. Ed., 2010, 49, 9737ꢀ9739.
59. S. Keshipour, S. Shojaei and A. Shaabani, Cellulose, 2013,
20, 973ꢀ980.
37. K. Ul Hasan, M. O. Sandberg, O. Nur and M. Willander,
Nanoscale Res. Lett., 2011, 6, 1ꢀ6.
60 60. A. Shaabani and E. Farhangi, Appl. Catal., A, 2009, 371, 148ꢀ
152.
38. X. Zhou, T. Wu, K. Ding, B. Hu, M. Hou and B. Han, Chem.
20 Commun., 2010, 46, 386ꢀ388.
61. A. Shaabani, A. Maleki, A. H. Rezayan and A. Sarvary,
Molec. Divers., 2011, 15, 41ꢀ68.
39. J. Texter, Z. Qiu, R. Crombez, J. Byrom and W. Shen, Polym.
Chem., 2011, 2, 1778ꢀ1788.
62. A. Shaabani, E. Farhangi and A. Rahmati, Appl. Catal., A,
65 2008, 338, 14ꢀ19.
40. C. Zeng, Z. Tang, B. Guo and L. Zhang, PCCP., 2012.
63. A. Shaabani and A. Maleki, Appl. Catal., A, 2007, 331, 149ꢀ
151.
41. A. S. K. Hashmi and G. J. Hutchings, Angew. Chem. Int. Ed.,
25 2006, 45, 7896ꢀ7936.
64. A. Shaabani, A. Rahmati and Z. Badri, Catal. Commun.,
2008, 9, 13ꢀ16.
42. S. Biella, L. Prati and M. Rossi, J. Catal., 2002, 206, 242ꢀ
247.
70 65. W. S. Hummers and R. E. Offeman, J. Am. Chem. Soc., 1958,
80, 1339ꢀ1339.
43. A. Abad, C. Almela, A. Corma and H. García, Tetrahedron,
2006, 62, 6666ꢀ6672.
66. H. Yang, C. Shan, F. Li, D. Han, Q. Zhang and L. Niu, Chem.
Commun., 2009, 0, 3880ꢀ3882.
30 44. P. Haider and A. Baiker, J. Catal., 2007, 248, 175ꢀ187.
45. C. Della Pina, E. Falletta, L. Prati and M. Rossi, Chem. Soc.
Rev., 2008, 37, 2077ꢀ2095.
67. C. Tonhauser, A. Alkan, M. Schömer, C. Dingels, S. Ritz, V.
75 Mailänder, H. Frey and F. R. Wurm, Macromolecules., 2013, 46,
647ꢀ655.
46. A. Corma and H. Garcia, Chem. Soc. Rev., 2008, 37, 2096ꢀ
2126.
68. H. Borchert, E. V. Shevchenko, A. Robert, I. Mekis, A.
Kornowski, G. Grübel and H. Weller, Langmuir, 2005, 21, 1931ꢀ
1936.
35 47. A. Abad, P. Concepción, A. Corma and H. García, Angew.
Chem. Int. Ed., 2005, 44, 4066ꢀ4069.
80 69. K. B. Sharpless, K. Akashi and K. Oshima, Tetrahedron Lett.,
1976, 17, 2503ꢀ2506.
48. A. Abad, A. Corma and H. García, Chem. Eur. J., 2007, 14,
212ꢀ222.
70. S. Kanemoto, S. Matsubara, K. Takai, K. Oshima, K. Utimoto
and H. Nozaki, Bull. Chem. Soc. Jpn., 1988, 61, 3607.
49. V. R. Choudhary, A. Dhar, P. Jana, R. Jha and B. S. Uphade,
40 Green Chem., 2005, 7, 768ꢀ770.
71. J. Zheng, S. Lin, X. Zhu, B. Jiang, Z. Yang and Z. Pan, Chem.
85 Commun., 2012, 48, 6235ꢀ6237.
50. V. R. Choudhary, R. Jha and P. Jana, Green Chem., 2007, 9,
267ꢀ272.
72. H. W. Chen, A. Murugadoss, T. Hor and H. Sakurai,
Molecules, 2010, 16, 149ꢀ161.
This journal is © The Royal Society of Chemistry [year]
RSC Adv, [year], [vol], 00–00 | 9

Page 11 of 11
RSC Advances
View Article Online
DOI: 10.1039/C3RA44696D
73. P. Liu, Y. Guan, R. A. v. Santen, C. Li and E. J. M. Hensen,
Chem. Commun., 2011, 47, 11540ꢀ11542.
74. C. Jones, Top. Catal., 2010, 53, 942ꢀ952.
10 | RCS Adv, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]