Phosphine-functionalized ionic liquid-stabilized rhodium nanoparticles for selective hydrogenation of aromatic compounds

Article abstract of DOI:10.1016/j.apcata.2015.04.015

Phosphine-functionalized, ionic liquid-stabilized rhodium nanoparticles with an average size of about 3.5 nm are very active catalysts for the selective hydrogenation of aromatic compounds, including quinoline and its analogues, and aromatic nitro compounds. Their catalytic performance complements that of classic homogeneous and heterogeneous rhodium catalysis.

Full text of DOI:10.1016/j.apcata.2015.04.015

Accepted Manuscript
Title: Phosphine functionalized ionic liquids stabilized
rhodium nanoparticles for selective hydrogenation of aromatic
compounds
Author: He-yan Jiang Xu-xu Zheng
PII:
S0926-860X(15)00248-3
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2015.04.015
APCATA 15352
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
5-1-2015
21-3-2015
9-4-2015
Please cite this article as: H.-y. Jiang, X.-x. Zheng, Phosphine
functionalized ionic liquids stabilized rhodium nanoparticles for selective
hydrogenation of aromatic compounds, Applied Catalysis A, General (2015),
http://dx.doi.org/10.1016/j.apcata.2015.04.015
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Phosphine functionalized ionic liquids
stabilized rhodium nanoparticles for
selective hydrogenation of aromatic
compounds
He-yan Jiang, and Xu-xu Zheng
Highlights
 Highly regioselective hydrogenation of aromatic compounds.
 Phosphine functionalized ionic liquids stabilized rhodium nanoparticles as
catalysts.
 H2 and NaBH4 as reducing agents in the preparation of rhodium nanoparticles.
 Mild reaction conditions and high recoverability of catalysts.
1
Page 1 of 24

Phosphine functionalized ionic liquids
stabilized rhodium nanoparticles for
selective hydrogenation of aromatic
compounds
He-yan Jiang, and Xu-xu Zheng
Graphical abstract
R2
R1
R1
R2
Rh nanoparticles catalyst
H2, ionic liquid, 50oC
N
N
H
high yields
high regioselectivity
high reusability
mild conditions
2
Page 2 of 24

Phosphine functionalized ionic liquids
stabilized rhodium nanoparticles for
selective hydrogenation of aromatic
compounds
He-yan Jianga,*, and Xu-xu Zhenga
a Key Laboratory of Catalysis Science and Technology of Chongqing Education
Commission, Chongqing Key Laboratory of Catalysis and Functional Organic
Molecules, Chongqing Technology and Business University, Chongqing 400067, P.R.
China
* Corresponding author. Tel./fax: +86 23 6276 9652; E-mail: orgjiang@163.com.
Abstract
Phosphine functionalized ionic liquids stabilized rhodium nanoparticles with an
average size about 3.5 nm are very active catalysts for the selective hydrogenation of
aromatic compounds, including quinoline and its analogues, and aromatic nitro
compounds. Their catalytic performance complements that of classic homogeneous
and heterogeneous rhodium catalysis.
Keywords: Selective hydrogenation; Nanoparticles; Ionic liquid; Quinoline; Rhodium
1. Introduction
Heterogeneous catalytic reactions performed by transition-metal nanoparticles have
gained increasing interest in both academic and industrial research in the last decade
[1-4]. As a result of the high surface/volume ratios and the quantum size effects,
3
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transition-metal nanoparticles have unique electronic, optical, and catalytic properties.
Catalysis by soluble metal nanoparticles is considered as “quasi-homogeneous”
catalysis, which is a significant bridge between homogeneous and heterogeneous
catalysis.
Ionic liquids have been employed as useful media for the preparation of
transition-metal nanoparticles with various sizes and shapes. When used as catalysts,
purely ionic liquid stabilized transition-metal nanoparticles may trend to agglomerate
under strict reaction conditions [5-6]. Additional stabilizers, including functionalized
ionic liquids with specific stabilizing groups, polymers, or solid supports, can improve
the lifetime of the catalyst [7-11].
Up to now, ionic liquid stabilized metal nanoparticles were tested as catalysts
mainly in the hydrogenation of alkenes or arenes [12-15]. 1,2,3,4-tetrahydroquinoline
and related structures are ubiquitous in numerous biologically active natural products
and pharmacologically relevant therapeutic agents [16-17]. Direct hydrogenation of
quinoline and its analogues is regarded as an efficient and straightforward approach to
access 1,2,3,4-tetrahydroquinoline and related structures. Both homogeneous and
heterogeneous catalysis based on Ru, Rh, Pd, Pt, and Ir [18-22] have been studied
extensively with H2 but suffer from high temperatures (>60 oC). Moreover, the strong
adsorption of quinolines and their hydrogenated products on heterogeneous catalysts
influences the catalytic activity and selectivity. In continuation of our interest in
nanometal catalysis [23-24], herein, we report originally the highly regioselective
hydrogenation of quinoline and its analogues catalyzed by the phosphine
4
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functionalized ionic liquids (PFILs) stabilized rhodium nanoparticles (Rh NPs) under
mild conditions, affording the corresponding 1,2,3,4-tetrahydroquinoline and related
structures in high yield and high chemoselectivity.
2. Experimental
2.1. Materials
All manipulations involving air-sensitive materials were carried out using standard
.
Schlenk line techniques under an atmosphere of nitrogen. RhCl3 3H2O and Rh/C were
purchased from Acros. Various substrates and other reagents were analytical grade.
The purity of hydrogen was over 99.99%. Phosphine-functionalized ionic liquids were
synthesized according to literature [25-26]. [BMIM][tppm]: 1HNMR (300M, CDCl3),
δ 0.81-1.00 (m, 3H), 1.17-1.31 (m, 2H), 1.71-1.87(m, 2H), 2.70(s, 3H), 3.81(s, 3H),
31
4.14-4.30 (m, 2H), 7.03-7.65 (m, 14H), 7.92-8.10 (m, 2H). PNMR (300M, CDCl3),
δ -5.40. [BMIM][tppt]: 1HNMR (300M, CDCl3), δ 0.70-0.96 (m, 9H), 1.15-1.45 (m,
6H), 1.71-1.97(m, 6H), 2.68-3,15(m, 9H), 3.68-3.94(m, 9H), 4.15-4.32 (m, 6H),
31
7.20-7.58 (m, 12H), 7.90-8.26 (m, 6H). PNMR (300M, CDCl3), δ -5.93. Products
were analyzed by GC instrument with an FID detector and HP-5 column (30 m × 0.25
mm). Products were confirmed by GC–MS and NMR ((J) in Supplementary material).
The TEM analyses were performed in a JEOL JEM 2010 transmission electron
microscope operating at 200 kV with nominal resolution of 0.25 nm. The X-ray
photoelectron spectroscopy (XPS) measurements were performed on a Thermo
ESCALAB 250 spectrometer. The XRD analysis was performed in a D/MAX 2550
VB/PC using a graphite crystal as monochromator.
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2.2. Synthesis of Rh NPs
.
Preparation of nanocatalysts 1, 2 or 5 (Fig. 1): In a typical experiment, RhCl3 3H2O
(0.018 mmol) and PFIL (0.018 mmol for 1 and 2, no ligand for 5) were dispersed in
[BMIM]PF6 (1 mL) (BMIM=1-butyl-2,3-dimethylimidazolium) and the reaction
mixture was placed in a 20 mL stainless-steel high pressure reactor. After stirring the
mixture at room temperature under an atmosphere of argon for 30 min, a constant
pressure of H2(g) (1 MPa) was admitted to the system and the content was stirred for
24 h at 55 oC. The reactor was cooled to ambient temperature and carefully vented. A
dark solution was obtained. The Rh NPs embedded in [BMIM]PF6 were employed for
hydrogenation studies (see below). Isolation of the Rh NPs for TEM, XPS and XRD
analysis was achieved by dissolving the mixture in acetone (5 mL), centrifuging
(8000 rpm for 10 min), washing with acetone (3 × 5 mL) and drying under vacuum.
.
Preparation of nanocatalysts 3 or 4 (Fig. 1): In a typical experiment, RhCl3 3H2O
(0.018 mmol) and PFIL (0.018 mmol) were dispersed in a mixture of THF (2 mL) and
[BMIM]PF6 (1 mL). NaBH4 (0.054 mmol) dissolved in water (two drops) was quickly
added under vigorous stirring to the mixture. Then, THF was removed under reduced
pressure and the colloidal suspension was dried under vacuum for 2 h. The reduction
occurs instantaneously and is characterized by a color change from red to black. The
dark solution was obtained that was used for the hydrogenation reaction (see below).
Isolation of the Rh NPs for TEM analysis was achieved by dissolving the mixture in
acetone (5 mL), centrifuging (8000 rpm for 10 min), washing with acetone (3 × 5 mL)
and drying under vacuum.
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2.3. General procedure for the heterogeneous selective hydrogenation
The stainless steel autoclave containing previously prepared PFIL-stabilized Rh(0)
catalysts was charged with the appropriate substrate, then the autoclave was sealed
and purged with pure hydrogen several times. After the reactants were heated to
predetermined temperature, the reaction timing began. After completion of the
reaction and cooling to ambient temperature, the products were isolated by
liquid-liquid extraction with diethyl ether and analyzed by gas chromatography.
3. Results and discussion
3.1. Characterization of Rh NPs
.
The synthesis of Rh NPs was achieved through the reduction of RhCl3 3H2O in
[BMIM]PF6 or a mixture of THF and [BMIM]PF6 in the presence of 1.0 equivalent of
PFILs [BMIM][tppm] or [BMIM][tppt] (Fig. 1), which afforded a dark suspension.
Both H2 and NaBH4 were employed as reducing agents in this work. For comparison,
Rh NPs were also synthesized in the absence of any additional stabilizer. A black
powder could be isolated from the black suspension by adding acetone and then
centrifuging (8000 rpm for 10 min). Washed three times with acetone and dried under
reduced pressure, the isolated powder was analyzed by transmission electron
microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD)
and infrared spectroscopy (IR).
TEM analysis was employed to characterize the obtained Rh NPs and determine
their mean diameter (Fig. 2, Fig. 1s-6s in Supplementary material). Generally, Rh NPs
prepared with H2 (Fig. 2, images 1-2) showed better dispersion than Rh NPs prepared
7
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with NaBH4 (Fig. 2, images 3-4), and the TEM image showed an obvious trend
toward agglomeration of the particles in the absence of PFILs (Fig. 2, image 5). The
TEM image of nanoparticles 1 exhibited a regular spherical shape and a narrow size
distribution, with an average diameter of 3.5 nm (Fig. 1s in Supplementary material).
The XPS analysis of the Rh NPs 1 was employed to elucidate the nature of the
stabilizing layer of the particles. XPS analysis of Rh NPs stabilized by [BMIM][tppm]
showed the presence of rhodium, phosphorus, nitrogen, carbon and chloride anions,
which signified the presence of the [BMIM][tppm] in the ligand sphere of the Rh NPs
(Fig. 7s in Supplementary material). The binding energies for Rh, 307.1 eV and 311.7
eV, which indicated the Rh NPs were composed of Rh(0) (Fig. 8s in Supplementary
material). As showed in Fig. 3, the XRD pattern of the obtained Rh NPs 1 featured
characteristic reflections corresponding to the (111), (200), (220), and (311) planes of
crystals of Rh(0) (JCPDS 22-0700).
IR and 31P solid state NMR (31PMAS NMR) spectra are effective for the
investigation of the mutual ligand-metal interactions of nanometal catalysts [24, 27].
Information on the interaction between the nanometal and the phosphine was first
confirmed by FTIR methods in which the red shift of the P-C6H5 deformation around
1469 cm-1 in Rh NPs 1 was an indication of the coordination of [BMIM][tppm] to the
metal Rh(0) (Fig. 9s in Supplementary material). Furthermore, the interactions
between [BMIM][tppm] and Rh NPs in [BMIM]PF6 were detected by 31PMAS NMR
spectroscopy (Fig. 4); the signal at δ=-5.4 ppm in Fig. 4a was assigned to
[BMIM][tppm]. The broad signals at δ=17.32 ppm and δ=24.86 ppm in Fig. 4b are
8
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new, and appear during the catalyst (Rh NPs 1) preparation. We speculate that the
signals at δ=17.32 ppm and δ=24.86 ppm in Fig. 4b represent the coordination
between [BMIM][tppm] and Rh in [BMIM]PF6. In short, the TEM, XPS, XRD, IR
and 31PMAS NMR results indicated that the rhodium (III) species was completely
reduced to Rh NPs, and these Rh NPs could be protected by the PFILs without any
change of valence.
3.2. Catalytic hydrogenation
We first chose styrene as a model substrate to explore the catalytic performance of
Rh NPs 1 under mild conditions. Fig. 5 showed the effect of reaction time on the
product yield. The hydrogenation of styrene produced only ethylbenzene in this
system. It was found that the yield increased linearly with time with no induction
period. A CS2 poisoning test was also carried out on the Rh NPs 1 to determine
whether a homogeneous mechanism was involved during the hydrogenation of
styrene [28]. In such an experiment, the conversion was 52.8 % after the initial 10
minutes; CS2 was then added under argon atmosphere and the reaction was
completely terminated as evidenced by no change in the conversion after an additional
reaction time of 50 minutes. This result supported a heterogeneous mechanism for the
hydrogenation of styrene employing Rh NPs and removed the possibility of active
homogeneous species in the system. In addition, it was found that the amount of
leaching from catalyst Rh NPs 1 was negligible by ICP-AES analysis in consecutive
catalytic cycles. The catalyst could be reused by simple liquid-liquid extraction after
reaction. The procedure was repeated ten times and the results indicated that Rh NPs
9
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1 could be recycled without any loss of catalytic activity (Fig. 6). The average
diameter of the spent Rh NPs 1 after ten recycles of styrene hydrogenation was 8.76
nm (Fig. 2, image 6 and Fig. 6s in Supplementary material). When Rh NPs 5 was used
as a catalyst for the catalytic cycles, it showed poor activity. Furthermore, Rh NPs 5
suffered 49.8% deactivation throughout only three continuous hydrogenation
recycling steps, and was almost inactive after four recycling steps.
Hydrogenation of quinoline and its analogues is of considerable industrial interests
for the production of petrochemicals, fine chemicals, and pharmaceuticals [18-19].
The effect of different catalysts on the chemoselective hydrogenation of quinoline is
listed in Table 1. Generally, similar reaction activity was achieved with Rh NPs
reduced by H2 or NaBH4 (Table 1, entries 1-4). Complete chemoselectivity to
1,2,3,4-tetrahydroquinoline could be attained with PFILs stabilized Rh NPs reduced
by H2 (Table 1, entries 1-2). Rh NPs stabilized by [BMIM][tppm] showed higher
activity and chemoselectivity to 1,2,3,4-tetrahydroquinoline than Rh NPs stabilized by
[BMIM][tppt] (Table 1, entries 3-4). Without the stabilizer, the hydrogenation resulted
in a conversion of 90.0% to 1,2,3,4-tetrahydroquinoline with the chemoselectivity of
98.0% (Table 1, entry 5). Both the recycle test (Fig. 6) and chemoselective
hydrogenation of quinoline catalyzed by Rh NPs 5 indicated that the
phosphine-functionalized ionic liquid stabilizers were important in the catalytic
system. In comparison, triphenylphosphine was also tested as the stabilizer (Table 1,
entry 6), poor activity and moderate chemoselectivity was obtained. These results
indicated that PFILs not only stabilized the metal particles in the preparation of the
10
Page 10 of 24

catalyst, but also served to additionally modify the Rh NPs in the chemoselective
hydrogenation. Additionally, the commercially available Rh/C was utilized as a
catalyst for the selective hydrogenation of quinoline, showing poor activity and
chemoselectivity to 1,2,3,4-tetrahydroquinoline (Table 1, entry 7). After reducing
procedure for Rh/C before catalytic hydrogenation of quinoline (Table 1, entry 8),
reaction activity could be greatly enhanced.
In heterogeneous selective catalysis, catalytic activity and chemoselectivity are
always very sensitive to the solvent used [6,29-30]. The effect of different solvents
was investigated and the data is listed in Table 2. In general, the results indicated that
ionic liquid solvents were more suitable than traditional organic solvents. Considering
the activity and chemoselectivity, [BMIM]PF6 was the most suitable solvent for the
chemoselective hydrogenation of quinoline (Table 2, entry 1).
We investigated the catalytic performance of Rh NPs 1 for the hydrogenation of
quinoline and its analogues (Table 3). Quinoline could be easily hydrogenated to
1,2,3,4-tetrahydroquinoline with 100.0% chemoselectivity in [BMIM]PF6 (Table 3,
entry 1). The hydrogenation activity of 2-, 3- or 8-methylquinoline was close to
quinoline. Interestingly, the presence of substituent in quinoline had no influence on
the hydrogenation chemoselectivity (Table 3, entries 2-4). Indole, 2,3-benzofuran and
1-benzothiophene were also tested. In comparison to quinoline, indole and
2,3-benzofuran exhibited lower catalytic activity. Indole could be hydrogenated with a
single complete hydrogenation product (Table 3, entry 5). 2,3-benzofuran could be
hydrogenated with absolute chemoselectivity to 2,3-dihydrobenzofuran (Table 3,
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entry 6). 1-benzothiophene was not reduced (Table 3, entry 7), the absence of activity
may be attributed to the affinity of sulfur atoms for its classical η1-S adsorption onto
the surface of Rh NPs 1 catalysts [31-32].
Selective hydrogenation of aromatic nitro compounds, being a major challenge for
chemists, is commonly used to manufacture aniline and its derivatives, which are
significant intermediates for dyes, polyurethanes, pharmaceuticals, explosives, and
agrochemicals [28-29]. We also investigated the hydrogenation of aromatic nitro
compounds over PFILs stabilized Rh NPs catalysts. As shown in Table 4, with the
superior Rh NPs 1 as the catalyst, almost all the substrates could be efficiently
converted into the corresponding substituted amino aromatic compounds under mild
conditions except o-methoxylnitrobenzene (Table 4, entry 10). The methyl- or
chloro-substituted nitrobenzene afforded the corresponding amino aromatic
compounds and showed comparable reactivity as that of unsubstituted nitrobenzene.
Rh NPs 1 showed promising activity for chemoselective hydrogenation of
nitrobenzene and its derivatives, which was not apparently affected by the steric effect,
but possibly by the electric effect. In comparison, commercially available Rh/C
catalyst was also tested under similar reaction conditions in the hydrogenation of
nitrobenzene (Table 4, entry 6). However, Rh/C catalyst showed low activity towards
aniline. Further reducing procedure for Rh/C before catalytic hydrogenation (Table 4,
entry 7), nitrobenzene could be completely hydrogenated to aniline.
4. Conclusion
PFILs are effective stabilizers in the formation of Rh NPs catalysts. This class of
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ligands improved the catalytic activity, chemoselectivity and lifetime of the Rh NPs
catalysts in the highly heterogeneous chemoselective hydrogenation of challenging
substrates including quinoline and its analogues, and aromatic nitro compounds under
very mild conditions. The catalytic performance is complementary to both classical
homogeneous and heterogeneous catalysts. Additional work is currently in progress in
this and related areas.
Acknowledgements
This work was financially supported by National Natural Science Foundation of
China (No. 21201184), Natural Science Foundation Project of CQ (No.
cstc2014jcyjA10105), Ministry of Education of Chongqing (No. KJ1400601) and 100
leading scientists promotion project of Chongqing.
-
-O3S
SO3
-
SO3
nBu
N
P
N
nBu
P
N
N
3
-
SO3
[BMIM] [tppm]
[BMIM]3 [tppt]
13
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N
nBu
PF6
N
Functionalized ionic liquid
RhCl3
Rh
Reduction
[BMIM] [tppm]
[BMIM]3 [tppt]
[BMIM] [tppm]
H2
1
2
3
H2
NaBH4
[BMIM]3 [tppt]
no ligand
NaBH4
H2
4
5
Fig. 1 Synthesis of Rh NPs in [BMIM]PF6
14
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Fig. 2 TEM images of Rh NPs 1, 2, 3, 4 and 5. 1*: TEM characterization of the spent
Rh NPs 1 after ten recycles of styrene hydrogenation.
15
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Fig. 3 X-Ray diffraction pattern of isolated Rh NPs 1
Fig. 4. 31P NMR spectra of a) [BMIM][tppm]; and 31PMAS NMR spectra of b) Rh
NPs 1 in [BMIM]PF6.
.
16
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Fig. 5 Reaction profiles for hydrogenation of styrene and CS2 poisoning of the Rh
o
NPs 1. Reaction conditions: styrene (8.9 × 10-3 mol; styrene/Rh=500), 25 C, H2 at
1MPa.
17
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Fig. 6 Recyclability of Rh NPs 1 and 5 for the hydrogenation of styrene. Reaction
conditions: styrene (8.9 × 10-3 mol; styrene/Rh=500), 25 oC, H2 at 1MPa.
Table 1. Different Rh catalysts for the chemoselective hydrogenation of quinoline. a
N
H
A a
N
N
H
A
A c
N
A b
Entry
Catalyst
Yield
(%)
Selectivity (%)
Aa Ab
Ac
1
2
3
4
5
6
7
8
1
96.0 100.0 0.0 0.0
93.0 100.0 0.0 0.0
2
3
98.3 99.5
97.4 98.7
90.0 98.0
34.4 95.1
41.2 96.3
81.9 97.2
0.5 0.0
1.3 0.0
0.9 1.1
4.9 0.0
3.7 0.0
2.8 0.0
4
5
Rh-tpp b
Rh/C
Rh/C c
a
Reaction was carried out at 50°C. Substrate: in a 1 ml [BMIM]PF6 at [1.8M],
PH2:3.0MPa. Reaction time: 5 h. Substrate/Rh=100:1, Rh/C (5 wt%, 37 mg). Products
b
were analyzed by a GC instrument with an FID detector and HP-5 column.
Triphenylphosphine as the stabilizer, the reduction conditions are the same as Rh NPs
c
o
1. Stirred under a constant pressure of H2(g) (1 MPa) for 24 h at 55 C before
catalytic hydrogenation of quinoline.
Table 2. Effect of different solvents on selective hydrogenation of quinoline catalyzed
by Rh NPs 1. a
Entry
Solvent
Yield
(%)
Selectivity (%)
Aa
Ab
Ac
1
[BMIM]PF6
93.9
100.0
0.0
0.0
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2
[BMIM]BF4
[BMIM]OTf
[BMIM]NTf2
[BMIM]OAc
MeOH
96.8
75.5
97.2
98.1
39.5
96.1
46.9
92.2
44.6
20.0
98.3
89.0
97.5
98.3
95.4
97.4
97.6
98.9
97.0
97.0
1.7
11.0
2.5
1.7
4.6
2.6
2.4
1.1
3.0
3.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
3
4
5
6
7
EtOH
8
iPrOH
9
H2O
10
11
THF
cyclohexane
a The reaction conditions are the same as in Table 1 except the solvent, Rh NPs 1 was
isolated by adding acetone and then centrifuging (8000 rpm for 10 min), washed three
times with acetone, dried under reduced pressure, and redispersed in different
solvents.
Table 3. Hydrogenation of quinoline and its analogues catalyzed by 1. a
A :
B :
C :
D :
N
N
N
N
E :
F :
G :
N
O
S
H
Entry
Substrate
Yield (%)
Selectivity (%)
A-Ga A-Gb
A-Gc
1
A
B
C
D
E
F
96.0
100.0
82.3
81.3
30.9
48.0
0.0
100.0 0.0
100.0 0.0
100.0 0.0
100.0 0.0
0.0
0.0
0.0
0.0
100.0
0.0
-
2
3
4
5 b
6
0.0
0.0
100.0 0.0
7
G
-
-
a The reaction conditions are the same as in Table 1. b Reaction time: 10 h.
Table 4. Hydrogenation of aromatic nitro compounds by Rh NPs. a
Entry Substrate
Catalyst Product
Yield (%)
1
2
3
4
5
nitrobenzene
1
2
3
4
5
aniline
aniline
aniline
aniline
aniline
100.0
99.0
83.0
95.4
97.0
nitrobenzene
nitrobenzene
nitrobenzene
nitrobenzene
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6
nitrobenzene
Rh/C
aniline
89.9
7
nitrobenzene
Rh/C b
aniline
100.0
100.0
100.0
83.4
8
m-methylnitrobenzene
p-methylnitrobenzene
o-methoxylnitrobenzene
p-methoxylnitrobenzene
p-fluoronitrobenzene
o-chloronitrobenzene
p-chloronitrobenzene
1
1
1
1
1
1
1
m-methylaniline
p-methylaniline
o-methoxyaniline
p-methoxyaniline
p-fluoroaniline
o-chloroaniline
p-chloroaniline
9
10
11
12
13
14
100.0
100.0
100.0
100.0
a
Reaction was carried out at 50°C. Substrate: in a 1 ml [BMIM]PF6 at [1.8M],
PH2:3.0MPa. Substrate/Ru=100:1, Rh/C (5 wt%, 37 mg). Reaction time: 5 h. Products
were analyzed by a GC instrument with an FID detector and HP-5 column. Only
corresponding amino aromatic products were detected during all the catalytic
reactions. b Stirred under a constant pressure of H2(g) (1 MPa) for 24 h at 55 oC before
catalytic hydrogenation of nitrobenzene.
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