A green and efficient oxidation of alcohols by amphiphilic resin-supported gold nanoparticles in aqueous H2O2

Article abstract of DOI:10.3184/174751911X13098760894063

A green and highly efficient oxidation of alcohols in aqueous H ₂O₂ using amphiphilic resin (PS-PEG-NH2)-supported gold nanoparticles is described. The reaction proceeded with excellent yields and selectivities, in particular, for nonactivated alcohols without base. The catalyst, in addition, could be readily recovered by simple work-up and reused several times without significant loss of its catalytic activity.

Full text of DOI:10.3184/174751911X13098760894063

JOURNAL OF CHEMICAL RESEARCH 2011
RESEARCH PAPER 397
JULY, 397–399
A green and efficient oxidation of alcohols by amphiphilic
resin-supported gold nanoparticles in aqueous H2O2
Ting Xiea*, Min Lua, Wenwen Zhangb and Jun Lic
aDepartment of Pharmacy, Changzhou Institute of Engineering andTechnology, Changzhou 213000, P. R. China
bDepartment of Chemical Engineering, Changzhou Institute of Engineering andTechnology, Changzhou 213000, P. R. China
cChangzhou Huari New Material Co., Ltd, Changzhou 213000, P. R. China
A green and highly efficient oxidation of alcohols in aqueous H2O2 using amphiphilic resin (PS-PEG-NH2)-supported
gold nanoparticles is described. The reaction proceeded with excellent yields and selectivities, in particular, for non-
activated alcohols without base. The catalyst, in addition, could be readily recovered by simple work-up and reused
several times without significant loss of its catalytic activity.
Keywords: oxidation, heterogeneous catalysis, gold nanoparticles, hydrogen peroxide, aqueous medium
The selective oxidation of alcohols to their corresponding car-
bonyl compounds is an important and challenging processes in
organic chemistry.1 Current methods for alcohol oxidation are
mainly based on the use of stoichiometric amounts of toxic or
corrosive reagents such as heavy metal salts.2 Hence there is a
desire for their replacement by environmentally more benign
approaches. Recently, numerous efforts have been made to
develop new catalytic protocols for the green oxidation of
alcohols due to the evergrowing concerns over green chemical
processes. Among these studies, oxidation of alcohols using
green oxidants such as H2O2 is notable since it leads to water
as the sole by-product.3–8 Also, the high content of oxygen and
simplicity of handling make it more advantageous than its
counterparts. Most importantly, it has been found to be partic-
ularly effective for non-activated alcohols, such as aliphatic
and alicyclic alcohols, without employing base additives
(e.g. KOH, Na2CO3).9 Although several facile and economical
oxidations of alcohols using H2O2 as oxidant have been devel-
oped, these protocols are invariably associated with one or
more disadvantages, such as non-recyclability of the catalyst,
long reaction time, low selectivity as well as the use of organic
solvents.
Since the discovery that gold nanoparticles can be very
active for alcohol oxidation reactions by Haruta and
coworkers,10,11 a series of protocols have been established.12–15
Of particular interest is the use of supported gold nanoparticles
due to the obvious advantages of these catalysts in product iso-
lation, product selectivity and catalyst recycling. However,
organic solvents and/or bases are generally required to achieve
high yield and selectivity. While acknowledging the pioneer-
ing work in this area, we believe the development of a novel
catalyst system exhibiting a wide range of substrate tolerance
under mild and aqueous conditions remains a major challenge.
Here we report a successful oxidation protocol in aqueous
H2O2 under base-free conditions with reusable amphiphilic
resin (PS-PEG-NH2)-supported gold nanoparticles.
ICP analysis. The catalyst was also characterised by high-
resolution transmission electron microscopy (TEM) and X-ray
diffraction (XRD). The TEM analysis revealed that the gold
nanoparticles have a mean diameter of 2.7 nm with a narrow
size distribution throughout the resin (Fig. 1a). Also, the char-
acteristic diffraction peaks at (111), (200), (220) and (311)
indicate the successful formation of gold nanoparticles on the
support (Fig. 1b).
Using the amphiphilic resin-supported gold nanoparticles,
we conducted the oxidation of a variety of primary and sec-
ondary alcohols to the corresponding carbonyl compounds.
The representative data are summarised in Table 1. The results
showed that all the reactions took place smoothly to afford the
corresponding products in excellent yields and selectivities.
The benzylic alcohols were much more active, providing the
products in excellent yields and selectivities in short times
with only a slight excess of H2O2 (entries 11–14). The nonacti-
vated alcohols, such as aliphatic and alicyclic alcohols could
also be efficiently oxidised (Table 1, entries 1–10). For cyclo-
pentanol, a conversion of 93% (99% selectivity) was obtained
within 6 h in presence of 1 equiv. of H2O2 (entry 1). By increas-
ing the amounts of H2O2, the reaction proceeded faster
and nearly full conversion and selectivity was obtained when
a five-fold molar excess of H2O2 was employed within 1 h
(entry 3). Although cyclopentanol was very active in this cata-
lytic system, the control experiment clearly showed that no
product was detected without adding catalyst (entry 4). The
effect of temperature was also studied. When the reaction was
conducted at room temperature, only 23% of conversion was
obtained after 6 h (entry 5), which could be explained by the
fact that the H2O2 decomposed slowly at low temperature. For
comparison, it was found that linear aliphatic alcohols were
more difficult to oxidise than alicyclic alcohols, so more H2O2
and longer reaction times were generally required for the
oxidation process (entries 7–10). The selective oxidation of
primary alcohols was then investigated. The results clearly
showed that a lower amount of H2O2 benefitted the formation
of aldehyde. For example, 1-octanol and benzyl alcohol were
oxidised to the corresponding aldehydes with 2 equiv. and
1.2 equiv. of H2O2, respectively (entries 9 and 11). When a
Catalyst 2 was readily accessible by complexation of
commercially available PS-PEG-NH2 (TentaGel S NH2) with
HAlCl4.3H2O in water followed by reduction with NaBH4
(Scheme 1). The Au loading was 2.28 wt % according to the
Scheme 1 Preparation of polymer-supported gold nanoparticles.
* Correspondent. E-mail: txie_czie@126.com

398 JOURNAL OF CHEMICAL RESEARCH 2011
Fig. 1 Characterisation of catalyst 2: (a) TEM image; (b) XRD pattern.
Table 1 Selective oxidation of various alcohols with catalyst 2 in aqueous H2O2a
Entry
1
Substrate
Product
H2O2/substrate molar ratio
1
Time /h
6
Conversion /%
93
Selectivity /%
99
2
3
2
2
1
2
6
3
3
3
6
6
1
2
95
>99
0
99
99
0
5
4b
5c
6
2
2
23
99
99
99
97
96
99
94
99
2
96
7
5
95
8
5
93
9
2
91
10
11
12
5
>99
>99
>99
1.2
2.5
13
14
1.2
1.2
2
2
>99
>99
99
99
a Reaction conditions: substrate (1 mmol), catalyst (0.5 mol%%, 30% H2O2, water (3 mL), 90°C; Conversion was based on GC and
GC-MS analysis.
b No catalyst was added.
c Room temperature.

JOURNAL OF CHEMICAL RESEARCH 2011 399
794 charge-coupled device (CCD) camera. XRD patterns of samples
were recorded on a Bruker AXS D8 ADVANCE X-ray diffractometer.
All the products are known compounds and were identified by com-
paring of their physical and spectra data with those reported in the
literature.
Preparation of catalyst 2: A mixture of PS-PEG-NH2 (3.9 g, total
amino capacity: 1 mmol) and HAuCl4.3H2O (0.197 g, 0.5 mmol) in
water (20 mL) was shaken at room temperature for 2 h. The polymer
beads turned from light yellow to intense yellow and then gradually
turned into red, which indicated the stabilisation of Au3+ in the resin
beads. Then a solution of NaBH4 (38.7 mg, 1 mmol) in water (2 mL)
was added dropwise over a period of 1 h. The resulting solution was
stirred for another 2 h at room temperature. After the reduction of
Au3+, the red colour of the beads had completely turned into dark
brown and the product was separated by filtration, washed with meth-
anol, water, and acetone and dried to give 2 (4.0 g, 0.12 mmol g−1).
The size of the nanoparticles was 2.7 nm, as determined by TEM.
Au analysis (ICP): 2.28 wt %.
Fig. 2 Recycling experiment.
Catalytic oxidation of alcohols in aqueous H2O2; general proce-
dure: The catalytic reactions were performed in a 10 mL two-necked
round-bottomed flask equipped with a septum, a magnetic stirring bar,
and a reflux condenser. The oxidation was carried out as follows:
substrate (1 mmol), water (3 mL), H2O2 (30% aq.) and catalyst
(0.005 mmol) were charged in the reaction flask. The reaction was
carried out at 90 °C and monitored by GC. When the reaction was
over, the organic products were separated from the aqueous phase by
extraction and then analysed by GC with the internal standard method.
The catalyst was removed by simple filtration, washed with methanol,
water and acetone, and then dried for next use. Assignments of
products were made by comparison with authentic samples. Selected
products were also analysed by GC/MS, 1H NMR and 13C NMR.
larger excess of H2O2 was employed, the acids were the only
products (entries 10 and 12).
Recycling studies were then performed using cyclopentanol
as substrate (Fig. 2). Considering the normal loss of catalyst in
the recycling and washing processes, the reaction was scaled
up to 10 mmol. After reaction, the supported catalyst could be
easily recovered by filtration and showed good reusability with
slight decrease in its activity after seven runs (1: 99%; 2: 99%;
3: 99%; 4: 97.5%; 5: 94.2; 6: 84.1%; and 7: 72.7%). The selec-
tivity of the reaction, however, was not affected during the
recycling processes. The recovered catalyst was also charac-
terised by ICP analysis. It was found that over 99% of Au was
retained in the resin. Meanwhile, the Au leaching in the crude
mixture of each recycling process was negligible (<10 ppm)
according to the ICP analysis, and the aqueous filtrate did not
show any catalytic activity. These observations indicated that
the oxidation proceeded in a heterogeneous fashion.
Received 25 February 2011; accepted 9 June 2011
Paper 1100592 doi: 10.3184/174751911X13098760894063
Published online: 5 August 2011
References
1
2
3
4
M. Hudlicky, Oxidation in organic chemistry, ACS Monograph Series,
American Chemical Society, Washington, DC, 1990.
W.J. Mijs, C.R.H. de Jonge, Organic synthesis by oxidation with metal
compounds, Plenum Press, New York, 1986.
K. Kamata, K. Yonehara, Y. Sumida, K. Yamaguchi, S. Hikichi and
N. Mizuno, Science, 2003, 300, 964.
R. Anderson, K. Griffin, P. Johnston and P.L. Alsters, Adv. Synth. Catal.,
2003, 345, 517.
H.R. Mardani and H. Golchoubian, Tetrahedron Lett., 2006, 47, 2349.
M.L. Guo and H.Z. Li, Green Chem., 2007, 9, 421.
J. Ni, W.J. Yu, L. He, H. Sun, Y. Cao, H.Y. He and K.N. Fan, Green Chem.,
2009, 11, 756.
In conclusion, we have successfully demonstrated that
amphiphilic resin (PS-PEG-NH2)-supported gold nanoparti-
cles show excellent activity and selectivity for environmentally
benign oxidation of various alcohols, especially for nonacti-
vated alcohols, to the corresponding carbonyl compounds. The
reaction could be conducted in aqueous medium without any
additives using hydrogen peroxide as oxidant to give only
water as the by-product. Moreover, the stability and reusability
of the catalyst have also been evaluated by conducting six suc-
cessive runs, which gave only a slight decrease in its activity.
5
6
7
8
9
Q.J. Zhu, W.L. Dai and K.N. Fan, Green Chem., 2010, 12, 205.
B.C. Ma, Y.S. Zhang, Y. Ding and W. Zhao, Catal Commun., 2010, 11,
853.
Experimental
10 M. Haruta, T. Kobayashi, H. Sano and N. Yamada, Chem. Lett., 1987,
The TentaGel S-NH2 resin was purchased from Aldrich (amine load-
ing: 0.26 mmol/g; average diameter: 90 µm). All other reagents were
obtained from local commercial suppliers and used without further
405.
11 M. Haruta, N. Yamada, T. Kobayashi and S. Iijima, J. Catal., 1989, 115,
301.
1
purification. H and 13C NMR spectra were recorded on a Bruker
12 A.S.K. Hashmi and G.J. Hutchings, Angew. Chem. Int. Ed., 2006, 45,
Advance RX300 analyser. GC and MS analyses were performed on a
Saturn 2000GC/MS instrument. The gold content was measured by
inductively coupled plasma (ICP) on a Varian AA240 analyser. TEM
images were collected on a JEOL-2100 transmission electron micros-
copy at 200 kV and the images were recorded digitally with a Gatan
7896.
13 A. Arcadi, Chem. Rev., 2008, 108, 3266.
14 C.D. Pina, E. Falletta, L. Prati and M. Rossi, Chem. Soc. Rev., 2008, 37,
2077.
15 G.J. Hutchings, Chem. Commun., 2008, 1148.

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