Selective hydrogenation of nitroarenes and olefins over rhodium nanoparticles on hydroxyapatite

Article abstract of DOI:10.1002/adsc.201200330

We have demonstrated a highly active and selective nanocatalyst, Rh/HAP (rhodium supported on hydroxyapatite), for the reduction of nitroarenes with hydrazine and for the hydrogenation of olefins with hydrogen gas under mild conditions. Nitroarenes were hydrogenated selectively to the corresponding anilines over the Rh/HAP catalyst with hydrazine as reducing agent, and reducible groups, such as halides (fluorine, chlorine, bromine and iodine), cyano and alkene were untouched. Moreover, olefins can be hydrogenated selectively to the corresponding alkanes in good yields over the Rh/HAP catalyst in the presence of reducible nitro, carbonyl and cyano groups when H ₂ was used.

Full text of DOI:10.1002/adsc.201200330

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DOI: 10.1002/adsc.201200330
Selective Hydrogenation of Nitroarenes and Olefins over
Rhodium Nanoparticles on Hydroxyapatite
a
a
a
a
a
a
Lei Huang, Pingfei Luo, Weige Pei, Xiaoyun Liu, Yong Wang, Jun Wang,
a
a,
Weihong Xing, and Jun Huang *
State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering,
Nanjing University of Technology, Nanjing 210009, Peopleꢀs Republic of China
Fax : (+86) 25-8317-2261; e-mail: junhuang@njut.edu.cn
a
Received: April 18, 2012; Revised: July 27, 2012; Published online: September 28, 2012
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201200330.
Abstract: We have demonstrated a highly active
and selective nanocatalyst, Rh/HAP (rhodium sup-
ported on hydroxyapatite), for the reduction of ni-
troarenes with hydrazine and for the hydrogenation
of olefins with hydrogen gas under mild conditions.
Nitroarenes were hydrogenated selectively to the
corresponding anilines over the Rh/HAP catalyst
with hydrazine as reducing agent, and reducible
groups, such as halides (fluorine, chlorine, bromine
and iodine), cyano and alkene were untouched.
Moreover, olefins can be hydrogenated selectively
to the corresponding alkanes in good yields over
the Rh/HAP catalyst in the presence of reducible
nitro, carbonyl and cyano groups when H2 was
used.
same molecules. Recently, we have reported on Pt
and Rh nanocatalysts for the selective hydrogenation
of nitroarenes with H and hydrazine (N H ), respec-
2
2
4
[
8]
tively.
On the other hand, the selective hydrogenation of
olefins in the presence of a nitro group is a demanding
task, since the nitro group is one of the most easily re-
ducible groups in transition metal-catalyzed processes.
Although the selective reduction of a double bond in
[9]
the presence of a nitro group with bakerꢀs yeast and
[
10]
metal hydride has been reported, very few transi-
tion metal-catalyzed processes have been described in
the literature. A homogeneous Rh complex (Wilkin-
sonꢀs catalyst) was reported as an efficient catalyst for
the selective reduction of double bonds in the pres-
[
11]
ence of nitro groups, but the application was limit-
ed as the homogeneous catalyst was air sensitive and
separation was hardly possible. In addition, the selec-
tive hydrogenation of olefins in the presence of other
functional groups (such as C=O and CN etc.) is useful
in industrial applications and in the academic labora-
Keywords: anilines; hydrogenation; nanoparticles;
nitroarenes; olefins; rhodium
[
12]
tory. Thereafter, the development of heterogeneous
Hydrogenation is one of the most important chemical catalysts for the selective hydrogenation of olefins in
processes because a lot of fine chemicals are pro- the presence of reducible groups is also highly desira-
[
1]
duced by hydrogenation processes. The reduction of ble.
nitroarenes to anilines is applied widely in industrial
Hydroxyapatites have attracted considerable inter-
processes since functional anilines are essential inter- est and have been widely used as biomaterials, ad-
[
13]
mediates for the production of agrochemicals, phar- sorbents, and ion exchangers. In addition, hydroxy-
[
2]
maceuticals, dyes, and pigments. Traditionally, the
ACHTUNGTRENNUNaG patites were also applied as catalysts or catalyst sup-
Bechamp reduction of nitroarenes which employs ports because of their several unique characteristics.
iron and hydrochloric produced a large amount of Some kinds of transition metal cations were readily
waste, which is not environmentally acceptable nowa- accommodated into the apatite framework based on
days. Green processes are highly favorable for the hy- their large cation exchange ability, and transition
drogenation of nitroarenes, and a number of transi- metal cation-exchanged hydroxyapatites were used as
[
13,14]
tion metal catalysts (based on Pt, Pd, Ru, Au, Rh effective heterogeneous catalysts.
Recently, Ru
etc.) were reported to be efficient for the transforma- nanoclusters supported on hydroxyapatite were re-
[
3–7]
tion.
However, the selective hydrogenation of ported as highly active catalysts for the hydrogenation
[15]
a nitro group is a challenging issue in organic synthe- of aromatics under mild conditions.
sis, when other reducible groups are present in the
Adv. Synth. Catal. 2012, 354, 2689 – 2694
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2689

Lei Huang et al.
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Herein, hydroxyapatite-supported Rh nanoparticles HAP were nearly identical with that of HAP (see the
are reported as a highly active and selective catalyst Supporting Information, Figure S3), which indicated
(
Rh/HAP) for the hydrogenation of nitroarenes and that the crystal structure of the HAP remained intact
olefins, respectively under mild conditions. When when Rh nanoparticles were supported on the HAP
N H was used as reducing agent, nitro groups were material.
2
4
hydrogenated selectively to the corresponding anilines
The reduction of nitrobenzene with N H was per-
2 4
with the Rh/HAP nanocatalyst, and reducible groups, formed as a model reaction, and the results are listed
such as halides (F, Cl, Br and I), CN and alkene were in Table S1 (Supporting Information). The Rh/HAP
untouched. Furthermore, olefins can be hydrogenated catalyst was highly active for the hydrogenation of ni-
selectively to alkanes with the Rh/HAP nanocatalyst trobenzene to aniline at room temperature in toluene.
in the presence of reducible groups (such as NO2, Cyclohexane, ethanol, and H O were also good sol-
2
C=O and CN etc.) when H is used (Scheme 1). Thus, vents, but THF and 1,4-dioxane were less effective
2
the selectivity of the hydrogenation of nitro or alkene solvents for the transformation (see the Supproting
groups can be tunable by selecting the reducing Information, Table S1, entries 1–6). The reduction of
agents with the Rh/HAP catalyst.
nitrobenzene afforded aniline in good yield also with-
The preparation of the Rh/HAP (2.01 wt% Rh de- out a solvent (see the Supporting Information,
termined by ICP-OES) catalyst is presented in the Table S1, entry 10). Rh catalysts with other supports,
Supporting Information. The Rh/HAP catalyst was such as Rh on TiO , HT (hydrotalcite) and Al O ,
2
2
3
characterized by TEM and the Rh particles were dis- were found to be less active for the transformation
persed well on the HAP (Figure 1), and the mean di- (see the Supporting Information, Table S1, entries 7–
ameter of the Rh particles was around 3–7 nm 9). No aniline was obtained without the catalyst
(
Figure 1, left). The BET (Brunauer–Emmett–Teller) under similar reaction conditions (see the Supporting
surface area of the Rh/HAP was found to be Information, Table S1, entry 11).
2
À1
À1
6
(
2 m g , which is similar to the parent HAP material
The reusability of the Rh/HAP nanocatalyst was
2
65 m g ), based on the nitrogen adsorption–desorp- tested and the results are shown in Table 1. The Rh/
tion analysis (see the Supporting Information, Fig- HAP nanocatalyst was easily recycled by filtration
ure S1 and Figure S2). The XRD patterns of Rh/ and reused for the next reaction cycle. The Rh/HAP
Scheme 1. Rh-catalyzed selective hydrogenation of nitro/alkene groups.
Figure 1. TEM images of the Rh/HAP nanocatalyst. The fresh Rh/HAP nanocatalyst (left); Rh/HAP nanocatalyst recovered
th
for the 5 time (right); scale bar=20 nm.
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Selective Hydrogenation of Nitroarenes and Olefins over Rhodium Nanoparticles on Hydroxyapatite
Table 1. Reusability of the Rh/HAP for the hydrogenation
of nitrobenzene.
Table 2. Rh/HAP-catalyzed hydrogenation of nitroarenes
[a]
[a]
with hydrazine.
Recycled
1
2
3
4
5
Conv./Yield [%] 100/99 100/99 100/99 100/99 100/99
[
a]
Entry
R
Time [h]
Conv./Yield [%]
100/98
Reaction conditions: nitrobenzene, 1.0 mmol; Rh/HAP
0.5 mol%); N H ·H O (2.0 mmol); toluene (2.0 mL); at
(
2
4
2
1
2
3
4
5
6
7
8
9
2-F
4-F
3
3
3
3
3
3
10
3
3
3
3
10
10
3
room temperature; in 3 h; the conversions and yields
were determined by GC (C H used as internal stan-
[b]
100/95
1
6
34
2-Cl
3-Cl
4-Cl
2-Br
3-I
100/99
100/99[
dard).
b]
100/95[
b]
100/97
[
b,c]
can be reused at least 5 times without loss of activity
(
100/90
100/97
th
Table 1). The Rh/HAP recovered for the 5 time was
4-NH2
2-NH
analyzed by TEM also and the mean diameter of the
recovered Rh nanoparticles had not increased evi-
dently (Figure 1, right). The filtrate was detected by
ICP-OES (inductively coupled plasma optical emis-
sion spectroscopy with detection limitation 7 ppb)
after removal of the Rh/HAP catalyst by filtration.
No Rh was detected in the filtrate, and the filtrate
was not active anymore for the hydrogenation of ni-
trobenzene, which indicated that no Rh was leached
into the reaction mixture and the Rh/HAP catalyst is
a heterogeneous catalyst.
Using hydrazine as reducing agent, the nitro group
was reduced selectively with the Rh/HAP nanocata-
lyst. Several nitrobenzenes were hydrogenated to the
corresponding anilines, and the results are shown in
Table 2. The Rh/HAP was highly active and selective
for the hydrogenation of nitro groups, and halides (F,
2
100/96[
d]
10
11
12
13
14
3-OH
4-OH
4-CN
2,6-CH3
3-C=C
100/95
[
d]
100/99[
d]
100/94[
100/92[
100/99
d]
d,e]
[a]
Reaction conditions: nitrobenzene (1.0 mmol); Rh/HAP
(0.5 mol%); N ·H O (2.0 mmol); toluene (2.0 mL); at
H
2
4
2
room temperature; in 3 hours; the conversions and yields
were determined by GC (C H used as internal stan-
1
6
34
dard).
[
b]
The by-product is aniline.
[c]
[d]
[e]
1
mol% metal used; at 1008C; N H ·H O (5.0 mmol).
2 4 2
At 508C;
N H ·H O (1.6 mmol); 2.0 mL ethanol used instead of
2
4
2
toluene as solvent; 3-vinylaniline yield.
Cl, Br and I), CN, OH and NH groups were tolerated (2-nitrovinyl)benzene gave (2-nitroethyl)benzene in
2
during the hydrogenation of NO . The corresponding 81% yield (Table 3, entry 5). To examine the olefin
2
anilines were obtained in good to excellent yields selectivity of the Rh/HAP over the C=O group, ben-
(
Table 2, entry 1–12). The hindered nitrobenzene, 2,6- zaldehyde and acetophenone were added in the hy-
dimethylnitrobenzene was hydrogenated to 2,6-dime- drogenation of styrene, respectively. Ethylbenzene
thylaniline in good yield also (Table 2, entry 13). In- was obtained quantitively without hydrogenation of
terestingly, the hydrogenation of 3-nitrostyrene gave the C=O group when benzaldehyde and acetophe-
3-aminostyrene quantitatively (Table 2, entry 14).
none were present in the reaction system (Table 3, en-
Using H gas, the Rh/HAP-catalyzed hydrogenation tries 6 and 7). Moreover, the Rh/HAP-catalyzed hy-
2
of olefins was tested and the results are listed in drogenation of crotonaldehyde and cinnamaldehyde
Table 3. With H gas, the hydrogenation of 3-nitrostyr- gave butyraldehyde and phenylpropylaldehyde, re-
2
ene gave 3-nitroethylbenzene quantitatively (Table 3, spectively, in good yield (Table 3, entries 8 and 9).
entry 1). The Rh/HAP catalyzed hydrogenation of The hydrogenation of cinnamonitrile was also per-
a mixture of styrene and nitrobenzene was tested with formed, and 3-phenylpropanenitrile was obtained in
H gas, and the styrene was hydrogenated completely good yield. The Rh/HAP catalyst was highly selective
2
into ethylbenzene without any aniline formed for the hydrogenation of olefins with H gas, and
2
(
Table 3, entry 2). Similarly, phenylacetylene was also other groups, such as NO , C=O and CꢀN groups
2
selectively hydrogenated with H gas to ethylbenzene were tolerated during the hydrogenation process.
2
without any aniline formed, when nitrobenzene was
In addition, the hydrogenation processes for reduc-
present in the reaction system (Table 3, entry 3). The ing the mixture of styrene and nitrobenzene with
CꢀC and C=C groups were reduced at the same time, N H and H gas were investigated, respectively, and
2
4
2
and styrene was detected as an intermediate and the the results are shown in Figure 2 and Figure 3. When
final product was only ethylbenzene. The Rh/HAP- N H was used as reducing agent, nitrobenzene was
2
4
catalyzed hydrogenation of cyclohexene gave cyclo- reduced selectively to aniline quickly (within 30 min),
hexane quantitively without hydrogenation of nitro- and only a trace of styrene was reduced into ethylben-
benzene (Table 3, entry 4). The hydrogenation of (E)- zene (Figure 2). When H gas was used as reducing
2
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Lei Huang et al.
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[a]
Table 3. Rh/HAP-catalyzed selective hydrogenation of olefins with H2.
Entry
Substrate/mixture
Time [h]
Product
Yield [%]
99
1
20
2
3
4
5
10
20
12
24
99, 0
99, 0
99, 0
[b]
81
6
7
10
10
99, 0
99, 0
99
8
9
12
60
[
c]
86
91
[d]
10
20
[
a]
Reaction conditions: substrate (1.0 mmol); Rh/HAP (0.5 mol%); with an H balloon; room temperature; 1,4-dioxane
2
(
2.0 mL); the conversions and yields were determined by GC (C H used as internal standard).
16 34
[
[
[
b]
Isolated yield.
Rh/HAP (2.0 mol%); at 1008C.
Rh/HAP (1 mol%); at 608C.
c]
d]
Figure 3. Rh/HAP-catalyzed selective hydrogenation of the
Figure 2. Rh/HAP -catalyzed selective hydrogenation of the
mixture of styrene and nitrobenzene with N H ·H O. Reac-
mixture of styrene and nitrobenzene with H . Reaction con-
2
2
4
2
ditions: nitrobenzene (1 mmol); styrene (1 mmol); with an
tion conditions: nitrobenzene (1 mmol); styrene (1 mmol);
N H ·H O (5 mmol); toluene (2.0 mL); Rh/HAP
0.5 mol%); at room temperature.
H balloon; 1,4-dioxane (2.0 mL); Rh/HAP (0.5 mol%); at
2
2
4
2
room temperature.
(
agent, styrene was hydrogenated slowly into ethylben- the hydrogenation of styrene was completed
zene (within 10 h), and no aniline was detected until (Figure 3).
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Adv. Synth. Catal. 2012, 354, 2689 – 2694

Selective Hydrogenation of Nitroarenes and Olefins over Rhodium Nanoparticles on Hydroxyapatite
Scheme 2. A possible pathway for the reduction of nitrobenzene with H NNH .
2
2
Using the Rh/HAP as catalyst, Rh is coordinated plied as a good support for the Rh nanoparticles. The
more strongly with the C=C bond than with NO2, selective hydrogenation of olefins to alkanes was real-
C=O and CꢀN groups, which allowed the preferential ized with the Rh/HAP nanocatalyst in the presence of
hydrogenation of the C=C bond with H gas. There- reducible NO , C=O and CN groups when H was
2
2
2
after, the reduction of nitrobenzene with N H does used, and the selectivity of the Rh/HAP was even
2
4
[
11,12]
not go through the traditional Rh/H way over the higher than that of homogeneous catalysts.
More-
Rh/HAP catalyst. A possible pathway was proposed over, these results confirmed that the Rh/HAP-cata-
Scheme 2). An intermediate is formed firstly through lyzed reduction of nitrobenzene with N H did not go
2
(
2
4
the condensation of the nitro group with N H , and through the traditional Rh/H pathway, thus a reasona-
2
4
2
then the decomposition of the intermediate by Rh/ ble condensation/decomposition pathway was pro-
HAP gives nitrosobenzene and N . The condensation posed.
2
of nitrosobenzene with N H is followed by H-trans-
In conclusion, we demonstrated an active and selec-
2
4
formation, and then the decomposition leads to ani- tive nanocatalyst Rh/HAP for the reduction of nitro-
line with N gas (Scheme 2). A trace of nitrosoben- arenes with N H and for the hydrogenation of olefins
2
2
4
zene was founded by GC-MS before the completion with H gas under mild conditions. Nitroarenes were
2
of the hydrogenation of nitrobenzene with N H . No hydrogenated selectively to the corresponding anilines
2
4
other intermediates were found by GC-MS, which over the Rh/HAP catalyst with N H as reducing
2
4
may be due to the instability of the intermediates. Al- agent, and reducible groups, such as halides (F, Cl, Br
though few intermediates were identified, the path- and I), CN and alkene were untouched. Moreover,
way was supported by the following reaction results. olefins can also be hydrogenated selectively to the
Firstly, Rh is coordinated more strongly with the C=C corresponding alkanes over the Rh/HAP catalyst in
bond than with NO group, which allowed the prefer- the presence of reducible NO , C=O and CN groups
2
2
ential hydrogenation of C=C bond with H gas. So the when H was used. Thus the selectivity is tuneable for
2
2
reaction of the NO group with H N should have oc- the hydrogenation of nitro and olefin groups over Rh/
2
4
2
curred before Rh is involved, otherwise the C=C HAP nanocatalyst. The possible condensation/decom-
bond should be reduced preferentially. Secondly, the position pathway was proposed for the reduction of
NO was reduced preferentially over the C=C bond nitroarenes with N H , and we believe that the path-
2
2
4
with N H , thus the condensation of the nitro group way will be useful for the selective reduction of the
2
4
with N H should have occurred before the decompo- nitrobenzenes in industrial applications and in aca-
2
4
sition of hydrazine to N /H . Figure S4 (Supporting demic research.
2
2
Information) shows that styrene can be hydrogenated
slowly to ethylbenzene after the transformation of ni-
trobenzene to aniline with more hydrazine being Experimental Section
added (Figure S4 in Supporting Information), since
Rh can catalyze the decomposition of hydrazine to Typical Procedure for the Reduction of Nitroarenes
[16]
N /H . Thirdly, nearly all the N H was used for the
2
2
2
4
A
nitroarene
(1.0 mmol),
hydrazine
monohydrate
reduction of the NO group (no N H for C=C bond).
2
2
4
(
2.0 mmol) and toluene (2.0 mL) were added to a Schlenk
Only 1.6 mmol of N H (1.5 mmol of N H needed
2
4
2
4
tube which contained Rh/HAP (Rh: 0.5 mol%) catalyst and
a stir bar under argon. The Schlenk tube was kept at room
theoretically) was needed for the hydrogenation of 3-
nitrostyrene to 3-aminostyrene quantitatively (as temperature with stirring for 3 hours. After the reaction was
shown in Table 2 entry 14).
completed, the Rh/HAP was separated by filtration, and the
The reduction of nitrobenzene with N H was com- products (in the filtrate mixture) were analyzed by GC/MS
2
4
and GC.
pletely different to the hydrogenation of styrene with
H gas, thus the selectivity was tuneable for the hy-
2
drogenation of nitro and olefin groups over Rh/HAP
nanocatalyst. In addition, the hydroxyapatite was ap-
Adv. Synth. Catal. 2012, 354, 2689 – 2694
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Lei Huang et al.
COMMUNICATIONS
Typical Procedure for the Selective Reduction of
Olefins
Srikanth, Catal. Lett. 2009, 128, 164–170; c) X. Cui, F,
Shi, Y. Deng, ChemCatChem 2012, 4, 333–336.
6] Au catalysts, see: a) A. Corma, P. Serna, Science 2006,
[
An olefin (1.0 mmol) and 1,4-dioxane (2.0 mL) were added
to a Schlenk tube which contained Rh/HAP (Rh: 0.5 mol%)
catalyst and a stir bar under argon. Then argon was removed
by H , and a balloon of H was connected to the Schlenk
3
13, 332–334; b) A. Corma, P. Serna, H. Garcia, J. Am.
Chem. Soc. 2007, 129, 6358–6359; c) A. Corma, P. Con-
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2
2
tube. The reaction mixture was stirred at room temperature
for 10 h. After the reaction was completed, the Rh/HAP
was separated by filtration, and the products (in the filtrate
mixture) were analyzed by GC/MS and GC.
6
3; e) L. He, L. C. Wang, H. Sun, J. Ni, Y. Cao, H. Y.
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[
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Acknowledgements
This work was supported by the National Natural Science of
Foundation of China (grant No. 21136005) and the Founda-
tion from State Key Laboratory of Materials-Oriented Chem-
ical Engineering (grant No. ZK201003, ZK201011).
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Adv. Synth. Catal. 2012, 354, 2689 – 2694