Mild hydrogenation of quinoline to decahydroquinoline over rhodium nanoparticles entrapped in aluminum oxy-hydroxide

Article abstract of DOI:10.1016/j.catcom.2012.11.015

An Rh/AlO(OH) catalyst was prepared by a sol-gel method. This catalyst showed an excellent catalytic performance for the complete hydrogenation of quinoline to decahydroquinoline at relatively mild conditions. The growth of Rh-particle size and the decrease in the number of surface hydroxyl groups during heat treatment resulted in a significant decrease in catalytic properties. The excellent catalytic performance of the fresh Rh/AlO(OH) was attributed to the cooperation between the hydroxyl groups on the support and on the active metal centers.

Full text of DOI:10.1016/j.catcom.2012.11.015

Catalysis Communications 31 (2013) 81–85
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Mild hydrogenation of quinoline to decahydroquinoline over rhodium nanoparticles
entrapped in aluminum oxy-hydroxide
Guang-Yin Fan ⁎, Jie Wu
Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, College of Chemistry and Chemical Engineering, China West Normal University, Nanchong, P. R. China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 August 2012
Received in revised form 14 November 2012
Accepted 15 November 2012
Available online 23 November 2012
An Rh/AlO(OH) catalyst was prepared by a sol–gel method. This catalyst showed an excellent catalytic
performance for the complete hydrogenation of quinoline to decahydroquinoline at relatively mild condi-
tions. The growth of Rh-particle size and the decrease in the number of surface hydroxyl groups during
heat treatment resulted in a significant decrease in catalytic properties. The excellent catalytic performance
of the fresh Rh/AlO(OH) was attributed to the cooperation between the hydroxyl groups on the support
and on the active metal centers.
Keywords:
Quinoline
©
2012 Elsevier B.V. All rights reserved.
Hydrogenation
Rhodium
Decahydroquinoline
1
. Introduction
of quinoline [7]. Subsequent studies by evaluating hydroxyapatite-
supported Ru revealed that Ru catalysts are also highly effective for
the hydrogenation of quinoline to produce DHQ [8]. However, one
critical limitation of these Ru- and Rh-based catalyst systems is that
The manufacture of decahydroquinoline (DHQ) from quinoline is
one of the most challenging reactions in synthetic organic chemistry.
The resulting decahydroskeleton is widely employed in the synthesis
of petrochemicals [1], fine chemicals, and pharmaceuticals [2–4].
Although it has been extensively studied, the production of DHQ
promoted by catalytic hydrogenation rather than stoichiometric
reduction remains a big challenge. The complete hydrogenation of
quinoline to DHQ occurs in two different reaction steps. Quinoline is
the reaction conditions are harsh (T=150 °C to 200 °C; PH2
=
2.0 MPa to 4.0 MPa). In addition, publications that address the
recycling of supported metal catalysts for producing DHQ from
quinoline are few because the catalysts are deactivated, which is
caused by the adsorption of intermediates during the hydrogenation
process. The manufacture of alternative simple and efficient catalysts
that would enable the complete hydrogenation of quinoline at mild
conditions remains a big challenge in terms of an industrial applica-
tion. In this paper, we reported an Rh/AlO(OH) catalyst that has an
exceptionally high selectivity for the hydrogenation of quinoline to
DHQ at relatively mild conditions. Our results show that the fresh
Rh/AlO(OH) catalyst exhibited a DHQ yield of 99.3% at 125 °C and a
hydrogen pressure of 0.8 MPa. Moreover, the catalyst could be reused
three times. The foregoing values are the best results obtained at
relatively mild conditions among the reported catalyst systems.
1
first hydrogenated to 1,2,3,4-tetrahydroquinoline ( THQ) and 5,6,7,8-
tetrahydroquinoline ( THQ), and both the intermediates are subse-
5
quently hydrogenated to DHQ. The synthesis of supported transition
and noble metal catalysts for the hydrogenation of quinoline to DHQ
has gained increasing interest [5–11], but the catalytic activities of the
investigated catalysts are not high. Moreover, a relatively high temper-
ature and hydrogen pressure are still needed as essential conditions of
2
the reaction [12,13] (T >200 °C and P >11.0 MPa H ). Nevertheless,
directly obtaining DHQ from quinoline is not feasible because of the
rapid deactivation of catalysts. Therefore, great efforts have been
made to overcome this problem, either by using a strong Brönsted
acid as a solvent [5] or tuning the particle sizes of the catalysts [7].
Recently, supported Ru and Rh nanoparticles have received
considerable attention as new hydrogenation materials because of
their intrinsic catalytic performance in the production of DHQ. This
interest was prompted by Campanati and coworkers' discovery of
an Rh/PLC (PLC: pillared layered clay) catalyst for the hydrogenation
2. Experimental
2.1. Catalyst preparation
All aromatic compounds (A.R.), solvents (A.R.), and reagents (A.R.)
were used as received. According to the literature [14], Rh/AlO(OH)
was prepared with a one-pot procedure from RhCl
some modifications. RhCl ·xH O (Rh content: 38 wt.%) (200 mg),
-butanol (1.6 g), and Al(O-Sec-Bu)3 (4.3 g) were added into a
50 mL round-bottom flask equipped with a condenser. When the
3
hydrates with
3
2
2
⁎
Corresponding author. Tel./fax: +86 817 2568081.
E-mail address: fanguangyin@cwnu.edu.cn (G.-Y. Fan).
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2012.11.015

82
G.-Y. Fan, J. Wu / Catalysis Communications 31 (2013) 81–85
reaction mixture turned to a black suspension after 3 h, excess water
10 mL) was added. The reaction mixture was further stirred for
0 min at 100 °C and cooled to room temperature. The black solid
was filtered, washed with acetone, and dried in air at 100 °C for 1 h
to obtain a bluish-gray powder.
were detected as the intermediates in the hydrogenation process.
For the reaction carried out at 100 °C and an H pressure of
(
3
2
0.8 MPa, the Rh/AlO(OH) catalyst achieved a 99.4% conversion of
quinoline within 0.5 h with a selectivity of 88.2 % toward 1THQ
(entry 1). Furthermore, the selectivity to DHQ increased from 7.9%
to 87.4% when the reaction time was increased to 5.0 h (entries
2–4). The increase in the amount of DHQ was equal to the decrease
in the amount of 1THQ, which indicates that the hydrogenation of
quinoline first occurred in the N-heterocycle of quinoline to yield
2
.2. Characterization of the catalyst
The content of the metal was determined by inductively coupled
1
plasma (ICP) (IRIS Intrepid). The morphology of the catalysts was
determined with a transmission electron microscope (JEM-2010) at
an accelerating voltage of 200 kV. X-ray diffraction patterns (XRD)
were recorded on a PHILIPHS X'Pert MPD. X-ray photoelectron
spectroscopy (XPS) spectra were obtained with Kratos XSAM800.
The Fourier transform-infrared spectra (FT-IR) of the sample were
obtained on a Nicolet 510SX FTIR spectrometer using the KBr wafer
technique.
THQ, and then further hydrogenated to DHQ.
The effect of the catalyst amount on quinoline hydrogenation
shows that the yield of DHQ increased from 50.4% to 99.6% when
the catalyst amount was increased from 30 mg to 50 mg (entries 3,
5–6). Moreover, the results of the tests illustrate that hydrogen
pressure has a great effect on the yield of DHQ. When the hydrogen
pressure was increased from 0.4 MPa to 1.4 MPa at a reaction
temperature of 100 °C, the selectivity towards DHQ increased from
2
0.9% to 87.5% (Entry 3, 7–8) because of the rapid hydrogenation
1
2
.3. Activity tests
of the partial hydrogenated product THQ to form DHQ. In addi-
tion, the yield of DHQ increased from 15.9% to 99.3% when the
reaction temperature elevated from 75 °C to 125 °C (entry 3,
9–10). Consequently, the optimum reaction conditions were a
reaction temperature of 125 °C, a hydrogen pressure of 0.8 MPa,
a substrate/catalyst mole ratio of 120, and a reaction time of
3.5 h. on the basis of our experimental data, this is the optimum
conditions compared with those reported in the Ru and Rh catalyst
systems. For example, Sánchez-Delgado [10] only reported a 1THQ
yield of a 92% over a Ru/P4VPy catalyst with a quinoline/Rh ratio of
The hydrogenation of quinoline was carried out in a 60 mL steel
autoclave equipped with a glass liner and a magnetic stirrer. The
desired amounts of the catalyst, quinoline, and the solvent were
introduced to the reactor. The autoclave was flushed with pure
hydrogen for five times. When the designated reaction temperature
was reached, hydrogen was fed to the desired pressure, the stirring
rate was adjusted to 1500 rpm, and the reaction time was measured.
Parallel experimental data were obtained by repeating the reaction
two or three times, and they had good repeatability. All liquid
samples were analyzed by gas chromatography (GC-960) with an
FID detector and OV-17 Supelco column (30 m×0.25 mm, 0.25 μm
film).
84 at 200 °C and an H
obtained a maximum DHQ yield of 41.9% over Rh/PLC at a quino-
line/Rh ratio of 560 at 200 °C and an H pressure of 2.0 MPa for
2
pressure of 4.0 MPa for 1 h, Campanati only
2
2.5 h. On the other hand, Fache obtained a 100% yield of DHQ with
a quinoline/Rh ratio of 40 in expensive hexafluoroisopropanol for
19 h.
3
. Results and discussion
3
.1. Catalyst characterization
3.3. Effect of calcination temperature
The ICP results indicate that the rhodium loading was 5.0 wt.%.
The transmission electron microscopy (TEM) images of Rh/AlO(OH)
Fig. 1) show nanofiber morphologies that are characteristic of the
The effects of calcination temperature of Rh/AlO(OH) on the
hydrogenation of quinoline were also investigated, and the results
are listed in Table 2. From Table 2, the calcination temperature has a
significant influence on the catalytic properties of the Rh/AlO(OH)
catalyst for the hydrogenation of quinoline. When the calcination
temperature was increased from 100 °C to 350 °C, a sharp decrease
in the conversion of quinoline from 100% to 23.6% was observed,
and the selectivity to DHQ decreased from 50.4% to 0%. A contrary
trend was found for the selectivity to 1THQ, which increased from
47.3% to 99.3%. Fig. 2 shows the XRD pattern of Rh/AlO(OH) calcined
at different temperatures. The corresponding mean Rh particle sizes
are listed in Table 2. When the reduction temperature was increased
from 100 °C to 350 °C, the mean Rh particle sizes increased from
2.9 nm to 7.5 nm (entries 1–3). TEM results of the fresh and calcined
catalysts indicate that the Rh particle size was consistent with the
XRD results. The aggregation of Rh particles of the Rh/AlO(OH) cata-
lyst during the heat treatment may account for the decrease in the
conversion of quinoline.
(
aluminum oxyhydroxide matrix [14–16]. The mean particle size of
Rh was estimated to be 3.2 nm based on a high-resolution transmis-
sion electron microscopy (HRTEM). XRD pattern of the fresh Rh/
AlO(OH) (Fig. 2a) shows an existence of metallic Rh. The Rh particle
size was calculated to be 2.9 nm from the half-width of the diffraction
line (111), which is consistent with the HRTEM results. The binding
energy values at 308.1 and 312.4 eV in XPS assigned to the Rh3d5/2
and Rh3d3/2 peaks, indicating that Rh (III) was reduced to a
low-oxidation state (Fig. 3). The infrared spectrum of Rh/AlO(OH)
−
1
(
Fig. 4) indicates that the O―H stretching band at 3439 cm
the O―H bending mode at 1630 cm
and
−
1
[7] are rather strong, which
implies the presence of structure water and surface hydroxyl groups
on the surface of the catalyst.
3
.2. Optimization of reaction conditions
It should be noted that this remarkable decrease in reaction activ-
ity and selectivity of the Rh/AlO(OH) catalyst could be attributed to
not only the aggregation of Rh particles but also other reasons. The
results listed in Table 2 indicate a drastic loss of water when the
calcination temperature of the Rh/AlO(OH) catalyst was increased
from 100 °C to 350 °C. As the calcination temperature increased
from 100 °C to 250 °C, the loss of water, which is expressed as weight
percent of the fresh catalyst, was 23.3% (entry 2 in Table 2). This
result is attributed to the reversible elimination of physisorbed
water [17]. Furthermore, a water loss of about 6.7 % was observed
when the calcination temperature was increased to 350 °C because
The catalytic properties of the Rh/AlO(OH) catalysts were investi-
gated using the hydrogenation of quinoline as a model reaction. The
results are presented in Table 1. The conversion of quinoline was neg-
ligible without catalyst or in the presence of Rh-free AlO(OH) at the
same conditions, which shows that the presence of Rh is indis-
pensable for high catalytic activity. The Rh/AlO(OH) catalyst was
extremely catalytically active for quinoline hydrogenation at relative-
ly mild conditions. Special attention was given to distinguish the
intermediate products of the reaction with gas chromatography–
mass spectrometry (GC–MS). 1THQ and a small amount of 5THQ

G.-Y. Fan, J. Wu / Catalysis Communications 31 (2013) 81–85
83
Fig. 1. TEM morphology of the fresh Rh/AlO(OH) (a, b), dried at 250 °C (c, d), at 350 °C (e, f) and the reused catalyst (g, h).

84
G.-Y. Fan, J. Wu / Catalysis Communications 31 (2013) 81–85
(111)
(200)
(
220)
(311)
(
c)
(
b)
(
a)
Fig. 4. The FTIR morphology of Rh/AlO (OH).
10
20
30
40
50
60
70
80
90
2θ/degree
higher than that in methanol, ethanol, i-propanol, and water at the
Fig. 2. XRD pattern of Rh/AlO(OH).(a)dried at 100 °C, (b) 250 °C, (c) 350 °C.
same conditions. A DHQ yield of 99.8% was obtained in n-hexane
when the reaction was conducted at 125 °C and an H
0.8 MPa for 3.0 h.
2
pressure of
of the irreversible dehydration caused by the condensation of
H-bonded basal OH groups [18]. Taken together, the decreases in
the conversion of quinoline with increasing catalyst calcination tem-
perature can be due to two reasons: (1) the growth of Rh particle
sizes caused by the heating treatment led to the reduction of active
sites of the catalyst; (2) loss of structure water and surface hydroxyl
groups of the fresh catalyst. These phenomena are valuable observa-
tions that are not previously reported in literature.
3.5. Hydrogenation of other substrates
Following the catalytic hydrogenation of quinoline over the Rh/
AlO(OH) catalyst presented above, we have studied hydrogenations
of other substituted quinolines. The results are presented in Table 4.
The Rh/AlO(OH) catalyst remained highly efficient in the investigated
substrates. The reusability of the fresh Rh/AlO(OH) was tested using
quinoline as a substrate at the optimal reaction conditions identified
above. The catalyst was separated from the reaction system by centri-
fugation at the end of one hydrogenation run, and the supernatant
liquid was removed. The black solid catalyst was thoroughly washed
for three times with ethanol to remove the adsorbed species, dried
in vacuum, and then reused for the same reaction. Reusing the cata-
lyst in three consecutive cycles (entries 1–3, Table 4) showed that
the conversion of the substrate remained at 100% with minimal
leaching of Rh (0.26‰, assessed by ICP). However, the selectivity to
DHQ decreased to 71% after the third reaction cycle because of the
growth of the Rh particle sizes (the mean Rh particle size is estimated
to be 5.2 nm by TEM analysis).
3
.4. Effect of solvent
It has been reported that the formation of hydrogen bonds be-
tween the hydroxyl group in protic solvent and the π electrons of
the aromatic cycle in quinoline may inhibit the adsorption of the aro-
matic cycle on the surface of the catalysts [8]. Therefore, obtaining
DHQ is difficult because the hydrogenation of quinoline in protic
1
solvents generally stops at the stage of THQ, as reported by
Sánchez-Delgado [10] and Zhang [11]. Our results confirm this argu-
ment. As shown in Table 3, the hydrogenation of quinoline can only
1
achieve selectivity to THQ in the protic solvent methanol. On the
contrary, the selectivity to DHQ in the aprotic solvent n-hexane was
3.6. Possible hydrogenation mechanism
The effect of the hydroxyl group of the support on the formation of
DHQ was investigated. Although the exact reaction mechanism of the
hydroxyl group for quinoline hydrogenation was difficult to achieve,
Table 1
Quinoline hydrogenation catalyzed by Rh/AlO(OH) at different reaction conditions.
Entry
Cat.
Temp.
(°C)
P
H2
Time
(h)
Conv.
(%)
Selectivity (%)
(mg)
(Mpa)
DHQ
1THQ
5THQ
1
2
3
4
5
6
7
8
9
30
30
30
30
40
50
30
30
30
30
100
100
100
100
100
100
100
100
75
0.8
0.8
0.8
0.8
0.8
0.8
0.4
1.4
0.8
0.8
0.5
1.5
3.5
5.0
3.5
3.5
3.5
3.5
3.5
3.5
99.4
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
7.9
39.3
50.4
87.4
93.3
99.6
20.9
87.5
15.9
99.3
88.2
58.1
47.3
12.1
6.7
3.9
2.6
2.3
0.5
0
0
3.9
0
0.4
75.4
12.5
80.3
0
316
314
312
310
308
306
304
302
3.8
0.7
binding energy(eV)
1
0
125
Fig. 3. XPS pattern of Rh/AlO (OH) catalyst.
Reaction conditions: quinoline: 0.2 mL, solvent i-PrOH 2.0 mL.

G.-Y. Fan, J. Wu / Catalysis Communications 31 (2013) 81–85
85
Table 2
Table 4
a
a
Effect of calcination temperature on quinoline hydrogenation.
Hydrogenation of different substituted quinolines catalyzed by the Rh/AlO(OH).
Entry
Calcined
temp.(°C)
Loss of
water
Rh particle
size (nm)
Conv.
(%)
Selectivity (%)
Entry
Substrates
Time (h)
Conversion (%)
Yieldc (%)
1
2
100
100
99
97
XRDb
TEMc
DHQ
1THQ
5THQ
3.0
1
2
3
100
250
350
–
2.9
5.3
7.5
7.5
3.2
4.9
7.2
7.2
100.0
54.1
23.6
32.4
50.4
0.6
0
47.3
97.5
99.3
97.0
2.3
1.9
0.7
3.0
3
4
100
100
71
73
23.3
30.0
b
3.0
3.0
3.0
3.0
d
4
0
5
6
7
100
100
100
84
96
99
a
Reaction conditions: catalyst 30 mg, temperature: 100 °C, PH2: 0.8 MPa, solvent:
i-propanol (2.0 mL), time: 3.5 h.
b
The mean Rh particle sizes estimated by XRD.
The mean Rh particle sizes estimated by TEM.
.0 mL water used as solvent.
c
d
2
a
The Reaction conditions are same as shown in Table 1 entry 6 except that 2.0 mL
n-hexane was used as solvent.
b
The catalyst was Rh/C prepared by impregnation method.
Yield of DHQ.
several useful information were obtained by analyzing the reaction
results. We prepared a Rh/C catalyst that did not have any surface
hydroxyl group for quinoline hydrogenation. The result indicates
that the yield of DHQ could reach 100% over the fresh Rh/AlO(OH)
catalyst, whereas the yield to DHQ was only 73 % over the Rh/C cata-
lyst at the same conditions. Furthermore, the fresh Rh/AlO(OH) cata-
lyst with a large amount of structure water and surface hydroxyl
groups exhibited a much higher activity and selectivity to DHQ than
the Rh/AlO(OH) catalysts calcined at 250 °C and 350 °C. The catalytic
activity of the Rh/AlO(OH) catalyst calcined at 350 °C increased when
the hydrogenation was conducted in an aqueous medium. The con-
version of quinoline increased to 32.4% in water. The removal of the
surface hydroxyl groups became irreversible when the catalyst was
calcined at 350 °C [18]. Thus, the yield of DHQ was unsuccessful
although the reaction was conducted in an aqueous medium. More-
over, the Rh particle sizes of the catalyst reused for three consecutive
cycles were similar to those of the calcined Rh/AlO(OH) catalyst (cal-
cined at 250 °C). However, the conversion of quinoline remained at
c
4
. Conclusion
The complete hydrogenation of quinoline was carried out over Rh/
AlO(OH) catalyst at relatively mild conditions. The catalyst showed
excellent catalytic properties for the hydrogenation of quinoline to
DHQ, which was attributed to the formation of a hydrogen bond
between the surface hydroxyl group on AlO(OH) and the aromatic
compound. The hydrogen bonding reduced the interaction of the
active center and the nitrogen atom, and the deactivation of the cata-
lyst was inhibited. The hydrogenation rate was also promoted by the
hydrogen bond between the surface hydroxyl group and the π elec-
trons in the aromatic cycle of 1THQ or 5THQ in the aprotic solvent.
Acknowledgments
This work was financially supported by the National Natural
Science Foundation of China (21207109), Scientific Research Fund of
SiChuan Provincial Education Department (11ZA034), the Program
for Scientific and Technological Innovative Team in Sichuan Provincial
Universities (2010008), Program for Scientific Research Innovation
Team of China West Normal University and the funds provided by
China West Normal University (09B006 and 10A018).
1
00% with a selectivity of 71% to DHQ after the third cycle, whereas
the conversion of quinoline was 54.1% with a selectivity of 0.6% to
DHQ when the catalyst was calcined at 250 °C. The results suggest
that the growth of the Rh particle size is attributed to the reduction
of selectivity to DHQ, but is not the main reason for the decrease in
the conversion of quinoline. In summary, our results suggest that
the presence of structure water and surface hydroxyl groups is impor-
tant in the catalytic activity of the Rh/AlO(OH) catalyst. Therefore, we
propose that the formation of a hydrogen bond with the surface
hydroxyl group of Rh/AlO(OH) and the nitrogen atom of quinoline
promotes the first hydrogenation of the N-heterocycle of quinoline
to THQ [8]. On the other hand, the aromatic cycle of 1THQ is easily
adsorbed on the surface of Rh/AlO(OH) by the hydrogen bond
between the surface hydroxyl group and the aromatic cycle. Thus,
quinoline is quickly hydrogenated to DHQ.
References
[
[
1] G. Perot, Catalysis Today 10 (1991) 447.
2] R.T. Shuman, P.L. Ornstein, J.W. Paschal, P.D. Gesellchem, Journal of Organic
Chemistry 55 (1990) 738.
1
[3] J.M. Schaus, D.L. Huser, R.D. Titus, Synthetic Communications 20 (1990) 3553.
[
4] P. Bouyssou, C. Le Goff, J. Chenault, Journal of Heterocyclic Chemistry 29 (1992)
95.
5] F. Fache, Synlett 15 (2004) 2827.
8
[
[6] C. Bianchini, V. Dal Santo, A. Meli, S. Moneti, M. Moreno, W. Oberhauser, R. Psaro,
L. Sordelli, F. Vizza, Journal of Catalysis 213 (2003) 47.
[
[
[
7] M. Campanati, M. Casagrande, I. Fagiolino, M. Lenarda, L. Storaro, M. Battagliarin,
A. Vaccari, Journal of Molecular Catalysis A: Chemical 184 (2002) 267.
8] Y.P. Sun, H.Y. Fu, D.L. Zhang, R.X. Li, H. Chen, X.J. Li, Catalysis Communications 12
Table 3
(
2010) 188.
9] M. Campanati, A. Vaccari, O. Piccolo, Journal of Molecular Catalysis A: Chemical
79 (2002) 287.
a
Effect of solvent on quinoline hydrogenation.
1
Entry
Solvent
Conversion (%)
Selectivity (%)
[
[
10] R.A. Sánchez-Delgado, N. Machalaba, N. Ng-a-qui, Catalysis Communications
8 (2007) 2115.
11] R.M. Zhang, G.Y. Fan, C. Li, R.X. Li, C. Chen, X.J. Li, Acta Physico-Chimica Sinica 24
DHQ
1THQ
5THQ
1
2
3
4
methanol
Ethanol
i-propanol
n-hexane
99.0
100.0
100.0
100.0
100.0
98.0
1.9
32.7
50.4
60.8
99.8
49.8
93.1
65.7
47.3
38.2
0.2
5.0
1.6
2.3
1.0
0
(2008) 965.
[12] M. Freifelder, Advances in Catalysis 14 (1963) 203.
[13] S. Tsushima, S. Sudzuki, Journal of the Chemical Society of Japan 64 (1943) 1295.
[14] I.S. Park, M.S. Kwon, K.Y. Kang, J.S. Lee, J. Parka, Advanced Synthesis and Catalysis
349 (2007) 2039.
[15] S.C. Kuiry, E. Megen, S.D. Patil, S.A. Deshpande, S. Seal, The Journal of Physical
Chemistry. B 109 (2005) 3868.
b
5
n-hexane
c
6
H
2
O
50.2
0
a
The reaction conditions were same as shown in Table 1 entry 3.
[
16] L. Ji, J. Lin, K.L. Tan, H.C. Zeng, Chemistry of Materials 12 (2002) 931.
b
The reaction conditions were same as shown in Table 1 entry 6 except that time
for 3h.
[17] H. Liu, J. Deng, W. Li, Catalysis Letters 137 (2010) 261.
[18] J.J. Fitzgerald, G. Pedra, S.F. Dec, M. Seger, G.E. Maciel, Journal of the American
Chemical Society 119 (1997) 7832.
c
2.0 mL water was used as solvent.