- Email: [email protected]
Catalytic transfer hydrogenation of aromatic nitro compounds in presence of polymer-supported nano-amorphous Ni–B catalyst
Catalysis Communications 10 (2009) 1207–1211
Contents lists available at ScienceDirect
Catalysis Communications journal homepage: www.elsevier.com/locate/catcom
Catalytic transfer hydrogenation of aromatic nitro compounds in presence of polymer-supported nano-amorphous Ni–B catalyst Hongliang Wen a,*, Kaisheng Yao a, Yingdan Zhang a, Zhiming Zhou a, Andreas Kirschning b,1 a b
School of Chemical Engineering and Environment, Beijing Institute of Technology, Beijing 100081, PR China Institute of Organic Chemistry, Leibniz Universät Hannover, Schneiderberg 1B, D-30167 Hannover, Germany
a r t i c l e
i n f o
Article history: Received 24 July 2008 Received in revised form 7 January 2009 Accepted 15 January 2009 Available online 29 January 2009 Keywords: Catalytic transfer hydrogenation Aromatic nitro compounds Anilines Polymer-supported Nano-amorphous Ni–B
a b s t r a c t Polymer-supported nano-amorphous Ni–B particles prepared by ion-exchange-chemical reduction method exhibited good activity in the catalytic transfer hydrogenation of aromatic nitro compounds with hydrazine hydrate as hydrogen donor. The catalyst was characterized by ICP, SEM, TEM, XRD and XPS. The reusability experiments showed that the catalyst was stable and could be used three times with no decrease in activity. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction The reduction of aromatic nitro compounds is important synthetically both in the laboratory and in industry. Many methods have been developed for the reduction of aromatic nitro compounds [1–4]. One of the popular methods is catalytic transfer hydrogenation [4,5]. Catalytic transfer hydrogenation represents a special variation of catalytic hydrogenation in which a catalyst and hydrogen gas is replaced with a catalyst and hydrogen donor such as hydrazine hydrate, formic acid or propan-2-ol. In comparison with other methods catalytic transfer hydrogenation has potential advantages, including operational simplicity, high chemselectivity and yield, no highly diffusible, flammable hydrogen gas used and no special equipment required. Pt, Pd, Ru and Ni are classical catalysts employed in catalytic transfer hydrogenation [4,6]. Amorphous alloys have received much attention in the past two decades owing to their special physical and chemical properties [7–9]. With the combined characteristic of small particles size, short-range order and long-range disorder, the nano-amorphous alloys have attracted increasing attention in catalysis. However * Corresponding author. Tel.: +86 10 68912664; fax: +86 10 68412890. E-mail addresses: [email protected] (H. Wen), [email protected] (A. Kirschning). 1 Fax: +49 0511 762 4614. 1566-7367/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2009.01.030
nano-amorphous alloys tend to deactivate during the catalytic process due to the low crystallization temperatures which are associated with the metastable structure of amorphous alloys. Positioning nano-amorphous alloys on high-surface-area carriers is a promising route to improve their thermal stability [8]. Recently many new supported nano-amorphous Ni–B alloys with better thermal stability have been prepared, some of them showed higher activity and selectivity in catalytic hydrogenation of double bonds, triple bonds, nitro compounds and aromatic compounds [10–15]. However catalytic transfer hydrogenation with amorphous alloys has not been reported before. In the present work we describe the catalytic transfer hydrogenation of aromatic nitro compounds in presence of polymer-supported nano-amorphous Ni–B catalyst with hydrazine hydrate as hydrogen donor. The polymer is an anionic exchange resin incorporated inside a megaporous glass. The resulting monolithic glass–polymer composites are shaped as Raschig Rings. The highly porous polymeric material is chemically functionalized with sulfonate groups after precipitation polymerization of styrene in the presence of divinyl benzene (DVB; 5.3%) inside the megaporous glass followed by sulfonation. This procedure creates a polymeric matrix inside the glass which consists of small polymer bridged beads (1–5 lm diameters) [16,17]. By ion-exchange of Ni (II) chloride on this anionic exchange resin followed by reduction with NaBH4, highly dispersed nano-amorphous Ni–B particles supported on polymer were obtained.
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H. Wen et al. / Catalysis Communications 10 (2009) 1207–1211
2. Experimental 2.1. Preparation of catalyst In a typical procedure, these Raschig rings (10 g) were successively washed with CH2Cl2 (30 mL), MeOH (30 mL), water (50 mL). After treatment with 100 mL aq. HCl (2 mol/mL) for 10 min, the material was filtered and washed with water until pH 6 of the eluate was reached. Then, the rings were added to a solution of NiCl2 2H2O (0.5 g, 3 mmol) in 100 mL distilled water and shaken. When the pH reached 6 to 7, the rings were filtered and washed with water (100 mL). A solution of NaBH4 (1.07 g, 28 mmol) in 150 mL water was added to the Raschig rings at 5 °C until gas formation ceased. Filtration and washing with 100 mL water followed by 100 mL MeOH and drying in high vacuum terminated the preparation. 2.2. Characterization of catalysts Chemical analysis was performed by inductively coupled plasma spectroscopy (ICP) using LEEMAN Prodigy ICP-AES instrument. X-ray diffraction patterns were obtained with PANalytical X’Pert Pro MPD X-ray diffractometer using Cu Ka radiation (k = 0.15406 nm) at 40 kV and 40 mA (for annealing sample, a Raschig-Ring loaded nano-amorphous Ni–B particle was heated slowly
to the specific temperature and held at this temperature for 2 h under a stream of hydrogen, then cooled to room temperature before collecting the XRD data). SEM was recorded on a Hitachi, S-4700I instrument. TEM was recorded on a JOEL JEM-1200EX with an acceleration. XPS spectra were recorded on a ESCALAB 250 spectrometer, the XPS patterns were collected using Al Ka radiation at a current of 30 mA, during which the samples were in pure nitrogen atmosphere to avoid oxidation. 2.3. Reduction of aromatic nitro compounds General procedure for the reduction of aromatic nitro compounds: Nitroarenes (1.1 mmol), hydrazine hydrate (100% purity) 30 mmol, Raschig-Ring (attached nano-amorphous Ni–B, Ni:B = 19:10 and Ni0 is 0.011 g) and methanol 10 mL were charged into a 25 mL round bottom flask and heated to reflux under nitrogen. The reaction was monitored by TLC and GC using Varian CP-3800 gas chromatography equipped with flame ionization detector (FID) and a Supco-DE 120 column (30 m 0.25 mm 0.25 lm). The column temperature was programmed to start at 50 °C for
SO3 )2Ni2 SO3H
aq. NiCl2
SO3 Na
aq. NaBH4
or
Ni-B
SO3 NiCl
and
. BH4- + 2 H2O 2 BH4- + 2 H2O
BO2- + 4 H2 2 B + 2 OH- + 5 H2
Scheme 1. Preparation of polymer-supported nano-amorphous Ni–B particles.
NO2 R
NH2
SO3Na +
NH2-NH2. H2O
Ni-B
Scheme 2. Reduction of aromatic nitro compounds.
R Fig. 2. TEM images of Ni–B particles.
Fig. 1. (a) SEM image of Ni–B particles on the polymeric surface, and (b) SEM image of enlarged Ni–B particles.
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H. Wen et al. / Catalysis Communications 10 (2009) 1207–1211
Fig. 3. XRD patterns of Ni–B particles (a) reduced, (b) after annealed at 523 K, (c) after annealed at 573 K, (d) after annealed at 623 K.
The schematic presentation of polymer-supported nanometer Ni–B particles is depicted in Schemes 1 and 2. The H+ of sulfonic acid exchanged with Ni2+ in the solution and 2+ Ni was loaded on the polymer; then Ni2+ was reduced to Ni0 by
NaBH4, at the same time BH4 reacted with H2O to give B0 and nano-amorphous Ni–B particles formed on the surface of polymer. Inductively coupled plasma spectroscopy (ICP) showed that after several exchanges (until the pH of the solution was about 7), the Ni loading percentage was 93.2% with a Ni–B ratio of Ni19B10. Fig. 1 shows the SEM images of polymer-supported nano-amorphous Ni–B particles reduced under 5 °C. The Ni–B particles are uniform in size and homogeneously dispersed on the surface of the polymer. The TEM image shows that the Ni–B particles are spherical in shape and the size distribution is rather homogeneous (60–70 nm) (Fig. 2). The typical amorphous Ni–B XRD pattern is depicted in Fig. 3. No XRD peaks that are indicative of metallic Ni or their borides were observed in Fig. 4a, suggesting an amorphous nature of the particles. The diffraction peaks corresponding to Ni (2h = 45°) begin to appear after annealing the product in hydrogen at 250 °C and the Ni diffraction peaks become prominent when the annealing temperature is increased to 300 °C. However, no B diffraction peaks appear owing to decomposition of the amorphous Ni–B to crystalline Ni and gaseous B2H6.
Fig. 4. XPS spectra of Ni2p3/2.
Fig. 5. XPS spectra of B1s.
1 min followed by increasing to the final temperature of 200 °C at the rate of 10 °C/min. After completion of the reaction, the catalyst was separated by filtration, the filtrate was evaporated under vacuum and the crude product was purified by column chromatography to afford the pure products. In order to evaluate the recyclability of the catalyst, three consecutive hydrogenations of p-nitrotoluene were carried out. After each reaction, the catalyst was separated by filtration, washed with methanol, followed by drying under vacuum at 313 K. Then, the next reaction was carried out with recovered catalyst.
3. Results and discussion 3.1. Preparation and characterization of catalyst
1210
H. Wen et al. / Catalysis Communications 10 (2009) 1207–1211
The surface electronic states of nano-amorphous Ni–B catalyst was studied by XPS spectra, the XPS spectra of the sample are shown in Figs. 4 and 5. In the Ni2P3/2 level, two XPS peaks corresponding to the binding energy (BE) of 853.3 and 856.2 eV appeared, indicating the elementary and oxidative nickel were present in the catalyst. The oxidized Ni may come from partial oxidation during preparation and preservation. In B1s level there are two boron species on the surface of the catalyst. The peaks at 188.9 and 192.0 eV are assigned to elementary boron and oxidized boron. In comparison with the pure amorphous B, the BE of elementary B in the sample shifted positively by 1.8 eV, indicating that partial electrons transfer from B to Ni and making Ni electron-enriched and B electron-deficient.
Table 1 Reduction of aromatic nitro compounds with nano-amorphous Ni–B catalyst. Entry
Substrate
Product
NO2
Time (h)
NO2
CH 3
CH 3
NO2
NH2
3
OH
OH
NO2
NH2
4
NH2
NH2
NO2
NH2
5
NH2 NH2
NH2
99.6
8.8
100
97.7
9
100
81.7
17
100
100
17
100
97.5
17
100
97.9
18
100
83.3
15
100
76.1
NH2
NO2
NO2
CH3
CH3
NH2
NO2 8
NO2
NO2
CH3
CH3 NO2
O2N
Numerous reagents can be employed as hydrogen donors in catalytic transfer hydrogenation of aromatic nitro compounds. The catalytic performance of polymer-supported nano-amorphous Ni–B particles was evaluated with different hydrogen donor using nitrobenzene reduction as probe reaction. In the reduction with formic acid, ammonium formate, lithium formate and hydrazinium monoformate as hydrogen donor, the products were complicated and the Raschig-Rings turned white, the formic acid reacted with Ni and the catalysts were spoiled. When propan-2-ol as hydrogen donor, the reduction did not take place even took a very long time. The reduction did not take place with hydrazine hydrate and unsymmetrical dimethyl hydrazine as hydrogen donor in methanol at room temperature. When reaction temperature was raised to reflux, the reduction took place and after 8 h nitrobenzene conversed completely. The results of aromatic nitro compounds reduced with hydrazine hydrate in presence of polymer-supported nano-amorphous Ni–B particles are summarized in Table 1. Arenes, containing one nitro group could be reduced in presence of polymer-supported nano-amorphous Ni–B particles and gave excellent yields. For dinitro aromatic compounds, only one nitro group could be reduced and gave mild yields. The recycling experiments were carried out with p-nitrotoluene. After each reaction, the catalyst could be separated conveniently by filtration. The catalysts were recovered by rinsing with methanol which exhibited the same catalytic activity as before. The yields of anilines obtained from p-nitrotoluene were 97.7%, 90% and 96%, indicating that the catalyst was stable under the reaction conditions and well reusable. It is well known that surface electronic state has important effect on the catalytic property of a material. In amorphous Ni–B alloys partial electrons transfer from B to Ni and making Ni electronenriched and B electron-deficient, which promotes adsorption of electron-deficient nitrogen and electron-enriched oxygen in nitro group. When nitro group is reduced to electron-enriched amine group and it tends to leave the catalyst. The electronic character of amorphous Ni–B alloy can promote the reduction of nitro compounds effectively. On the other hand the catalytic decomposition of hydrazine plays a crucial role in the reaction. In this reaction hydrazine hydrate decomposes in contact with Ni–B catalyst and gives hydrogen to reduce the nitro group. However the detailed decomposition mechanism of hydrazine hydrate in presence of nano-amorphous Ni–B particles is under study. 4. Conclusion
NH2
7
O2N
100
NH2
NO2
9
8.
NH2
2
6
Yield (%)
NH2
1
NO2
Conv (%)
3.2. Reduction of aromatic nitro compounds
NH 2
12
100
72.4
Polymer-supported nano-amorphous Ni–B particles have been prepared by ion-exchange-chemical reduction protocol. The Ni–B particles are uniform in size and homogeneously dispersed on the surface of the polymer. In the catalytic transfer hydrogenation of aromatic nitro compounds they exhibited active, single nitro group aromatic compounds could be reduced smoothly and gave excellent yields. For dinitro aromatic compounds, only one nitro group could be reduced and gave mild yields. The catalyst is stable and reusable under this condition. References [1] F.D. Popp, H.P. Schultz, Chem. Rev. 62 (1962) 19. [2] R.A.W. Johnson, A.H. Wilby, Chem. Rev. 85 (1985) 129. [3] H.O. House, Modern Synthetic Reaction, second ed., Benjamin, New York, 1977, pp. 145. [4] P.N. Rylander, Hydrogenation Methods, Academic, New York, 1985, pp. 365. [5] R.E. Harmon, S.K. Gupta, D.J. Brown, Chem. Rev. 72 (1972) 21. [6] A. Furst, R.C. Berlo, S. Hooton, Chem. Rev. 65 (1965) 51. [7] J.V. Wonterghem, S. Morup, J.W. Christian, S. Charles, W.S. Wells, Nature 322 (1986) 622.
H. Wen et al. / Catalysis Communications 10 (2009) 1207–1211 [8] [9] [10] [11] [12] [13]
A. Molnar, G.V. Smith, M. Bartok, Adv. Catal. 36 (1989) 329. Y. Chen, Catal. Today 44 (1998) 3. A.Z. Ma, Chin. J. Catal. 20 (1999) 603. H. Li, H.X. Li, W.L. Dai, J.F. Deng, Appl. Catal. A 207 (2001) 151. R.B. Zhang, F.Y. Li, Q.Y. Shi, L.T. Luo, Appl. Catal. A 205 (2001) 279. Y.G. He, M.H. Qiao, H.R. Hu, J.F. Deng, K.N. Fan, Appl. Catal. A 228 (2002) 29.
[14] [15] [16] [17]
1211
Y. Lu, Z.T. Xiong, J.T. Li, J.Y. Lin, Catal. Lett. 78 (2002) 231. M.H. Wang, H.X. Li, Chin. J. Catal. 22 (2001) 287. U. Kunz, A. Kirschning, V. Hoffmann, US Patent 2004062941, 2004. U. Kunz, A. Kirschning, H.L. Wen, W. Solodenko, R. Cecilia, C.O. Kappe, T. Turek, Catal. Today 105 (2005) 318.
Contents lists available at ScienceDirect
Catalysis Communications journal homepage: www.elsevier.com/locate/catcom
Catalytic transfer hydrogenation of aromatic nitro compounds in presence of polymer-supported nano-amorphous Ni–B catalyst Hongliang Wen a,*, Kaisheng Yao a, Yingdan Zhang a, Zhiming Zhou a, Andreas Kirschning b,1 a b
School of Chemical Engineering and Environment, Beijing Institute of Technology, Beijing 100081, PR China Institute of Organic Chemistry, Leibniz Universät Hannover, Schneiderberg 1B, D-30167 Hannover, Germany
a r t i c l e
i n f o
Article history: Received 24 July 2008 Received in revised form 7 January 2009 Accepted 15 January 2009 Available online 29 January 2009 Keywords: Catalytic transfer hydrogenation Aromatic nitro compounds Anilines Polymer-supported Nano-amorphous Ni–B
a b s t r a c t Polymer-supported nano-amorphous Ni–B particles prepared by ion-exchange-chemical reduction method exhibited good activity in the catalytic transfer hydrogenation of aromatic nitro compounds with hydrazine hydrate as hydrogen donor. The catalyst was characterized by ICP, SEM, TEM, XRD and XPS. The reusability experiments showed that the catalyst was stable and could be used three times with no decrease in activity. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction The reduction of aromatic nitro compounds is important synthetically both in the laboratory and in industry. Many methods have been developed for the reduction of aromatic nitro compounds [1–4]. One of the popular methods is catalytic transfer hydrogenation [4,5]. Catalytic transfer hydrogenation represents a special variation of catalytic hydrogenation in which a catalyst and hydrogen gas is replaced with a catalyst and hydrogen donor such as hydrazine hydrate, formic acid or propan-2-ol. In comparison with other methods catalytic transfer hydrogenation has potential advantages, including operational simplicity, high chemselectivity and yield, no highly diffusible, flammable hydrogen gas used and no special equipment required. Pt, Pd, Ru and Ni are classical catalysts employed in catalytic transfer hydrogenation [4,6]. Amorphous alloys have received much attention in the past two decades owing to their special physical and chemical properties [7–9]. With the combined characteristic of small particles size, short-range order and long-range disorder, the nano-amorphous alloys have attracted increasing attention in catalysis. However * Corresponding author. Tel.: +86 10 68912664; fax: +86 10 68412890. E-mail addresses: [email protected] (H. Wen), [email protected] (A. Kirschning). 1 Fax: +49 0511 762 4614. 1566-7367/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2009.01.030
nano-amorphous alloys tend to deactivate during the catalytic process due to the low crystallization temperatures which are associated with the metastable structure of amorphous alloys. Positioning nano-amorphous alloys on high-surface-area carriers is a promising route to improve their thermal stability [8]. Recently many new supported nano-amorphous Ni–B alloys with better thermal stability have been prepared, some of them showed higher activity and selectivity in catalytic hydrogenation of double bonds, triple bonds, nitro compounds and aromatic compounds [10–15]. However catalytic transfer hydrogenation with amorphous alloys has not been reported before. In the present work we describe the catalytic transfer hydrogenation of aromatic nitro compounds in presence of polymer-supported nano-amorphous Ni–B catalyst with hydrazine hydrate as hydrogen donor. The polymer is an anionic exchange resin incorporated inside a megaporous glass. The resulting monolithic glass–polymer composites are shaped as Raschig Rings. The highly porous polymeric material is chemically functionalized with sulfonate groups after precipitation polymerization of styrene in the presence of divinyl benzene (DVB; 5.3%) inside the megaporous glass followed by sulfonation. This procedure creates a polymeric matrix inside the glass which consists of small polymer bridged beads (1–5 lm diameters) [16,17]. By ion-exchange of Ni (II) chloride on this anionic exchange resin followed by reduction with NaBH4, highly dispersed nano-amorphous Ni–B particles supported on polymer were obtained.
1208
H. Wen et al. / Catalysis Communications 10 (2009) 1207–1211
2. Experimental 2.1. Preparation of catalyst In a typical procedure, these Raschig rings (10 g) were successively washed with CH2Cl2 (30 mL), MeOH (30 mL), water (50 mL). After treatment with 100 mL aq. HCl (2 mol/mL) for 10 min, the material was filtered and washed with water until pH 6 of the eluate was reached. Then, the rings were added to a solution of NiCl2 2H2O (0.5 g, 3 mmol) in 100 mL distilled water and shaken. When the pH reached 6 to 7, the rings were filtered and washed with water (100 mL). A solution of NaBH4 (1.07 g, 28 mmol) in 150 mL water was added to the Raschig rings at 5 °C until gas formation ceased. Filtration and washing with 100 mL water followed by 100 mL MeOH and drying in high vacuum terminated the preparation. 2.2. Characterization of catalysts Chemical analysis was performed by inductively coupled plasma spectroscopy (ICP) using LEEMAN Prodigy ICP-AES instrument. X-ray diffraction patterns were obtained with PANalytical X’Pert Pro MPD X-ray diffractometer using Cu Ka radiation (k = 0.15406 nm) at 40 kV and 40 mA (for annealing sample, a Raschig-Ring loaded nano-amorphous Ni–B particle was heated slowly
to the specific temperature and held at this temperature for 2 h under a stream of hydrogen, then cooled to room temperature before collecting the XRD data). SEM was recorded on a Hitachi, S-4700I instrument. TEM was recorded on a JOEL JEM-1200EX with an acceleration. XPS spectra were recorded on a ESCALAB 250 spectrometer, the XPS patterns were collected using Al Ka radiation at a current of 30 mA, during which the samples were in pure nitrogen atmosphere to avoid oxidation. 2.3. Reduction of aromatic nitro compounds General procedure for the reduction of aromatic nitro compounds: Nitroarenes (1.1 mmol), hydrazine hydrate (100% purity) 30 mmol, Raschig-Ring (attached nano-amorphous Ni–B, Ni:B = 19:10 and Ni0 is 0.011 g) and methanol 10 mL were charged into a 25 mL round bottom flask and heated to reflux under nitrogen. The reaction was monitored by TLC and GC using Varian CP-3800 gas chromatography equipped with flame ionization detector (FID) and a Supco-DE 120 column (30 m 0.25 mm 0.25 lm). The column temperature was programmed to start at 50 °C for
SO3 )2Ni2 SO3H
aq. NiCl2
SO3 Na
aq. NaBH4
or
Ni-B
SO3 NiCl
and
. BH4- + 2 H2O 2 BH4- + 2 H2O
BO2- + 4 H2 2 B + 2 OH- + 5 H2
Scheme 1. Preparation of polymer-supported nano-amorphous Ni–B particles.
NO2 R
NH2
SO3Na +
NH2-NH2. H2O
Ni-B
Scheme 2. Reduction of aromatic nitro compounds.
R Fig. 2. TEM images of Ni–B particles.
Fig. 1. (a) SEM image of Ni–B particles on the polymeric surface, and (b) SEM image of enlarged Ni–B particles.
1209
H. Wen et al. / Catalysis Communications 10 (2009) 1207–1211
Fig. 3. XRD patterns of Ni–B particles (a) reduced, (b) after annealed at 523 K, (c) after annealed at 573 K, (d) after annealed at 623 K.
The schematic presentation of polymer-supported nanometer Ni–B particles is depicted in Schemes 1 and 2. The H+ of sulfonic acid exchanged with Ni2+ in the solution and 2+ Ni was loaded on the polymer; then Ni2+ was reduced to Ni0 by
NaBH4, at the same time BH4 reacted with H2O to give B0 and nano-amorphous Ni–B particles formed on the surface of polymer. Inductively coupled plasma spectroscopy (ICP) showed that after several exchanges (until the pH of the solution was about 7), the Ni loading percentage was 93.2% with a Ni–B ratio of Ni19B10. Fig. 1 shows the SEM images of polymer-supported nano-amorphous Ni–B particles reduced under 5 °C. The Ni–B particles are uniform in size and homogeneously dispersed on the surface of the polymer. The TEM image shows that the Ni–B particles are spherical in shape and the size distribution is rather homogeneous (60–70 nm) (Fig. 2). The typical amorphous Ni–B XRD pattern is depicted in Fig. 3. No XRD peaks that are indicative of metallic Ni or their borides were observed in Fig. 4a, suggesting an amorphous nature of the particles. The diffraction peaks corresponding to Ni (2h = 45°) begin to appear after annealing the product in hydrogen at 250 °C and the Ni diffraction peaks become prominent when the annealing temperature is increased to 300 °C. However, no B diffraction peaks appear owing to decomposition of the amorphous Ni–B to crystalline Ni and gaseous B2H6.
Fig. 4. XPS spectra of Ni2p3/2.
Fig. 5. XPS spectra of B1s.
1 min followed by increasing to the final temperature of 200 °C at the rate of 10 °C/min. After completion of the reaction, the catalyst was separated by filtration, the filtrate was evaporated under vacuum and the crude product was purified by column chromatography to afford the pure products. In order to evaluate the recyclability of the catalyst, three consecutive hydrogenations of p-nitrotoluene were carried out. After each reaction, the catalyst was separated by filtration, washed with methanol, followed by drying under vacuum at 313 K. Then, the next reaction was carried out with recovered catalyst.
3. Results and discussion 3.1. Preparation and characterization of catalyst
1210
H. Wen et al. / Catalysis Communications 10 (2009) 1207–1211
The surface electronic states of nano-amorphous Ni–B catalyst was studied by XPS spectra, the XPS spectra of the sample are shown in Figs. 4 and 5. In the Ni2P3/2 level, two XPS peaks corresponding to the binding energy (BE) of 853.3 and 856.2 eV appeared, indicating the elementary and oxidative nickel were present in the catalyst. The oxidized Ni may come from partial oxidation during preparation and preservation. In B1s level there are two boron species on the surface of the catalyst. The peaks at 188.9 and 192.0 eV are assigned to elementary boron and oxidized boron. In comparison with the pure amorphous B, the BE of elementary B in the sample shifted positively by 1.8 eV, indicating that partial electrons transfer from B to Ni and making Ni electron-enriched and B electron-deficient.
Table 1 Reduction of aromatic nitro compounds with nano-amorphous Ni–B catalyst. Entry
Substrate
Product
NO2
Time (h)
NO2
CH 3
CH 3
NO2
NH2
3
OH
OH
NO2
NH2
4
NH2
NH2
NO2
NH2
5
NH2 NH2
NH2
99.6
8.8
100
97.7
9
100
81.7
17
100
100
17
100
97.5
17
100
97.9
18
100
83.3
15
100
76.1
NH2
NO2
NO2
CH3
CH3
NH2
NO2 8
NO2
NO2
CH3
CH3 NO2
O2N
Numerous reagents can be employed as hydrogen donors in catalytic transfer hydrogenation of aromatic nitro compounds. The catalytic performance of polymer-supported nano-amorphous Ni–B particles was evaluated with different hydrogen donor using nitrobenzene reduction as probe reaction. In the reduction with formic acid, ammonium formate, lithium formate and hydrazinium monoformate as hydrogen donor, the products were complicated and the Raschig-Rings turned white, the formic acid reacted with Ni and the catalysts were spoiled. When propan-2-ol as hydrogen donor, the reduction did not take place even took a very long time. The reduction did not take place with hydrazine hydrate and unsymmetrical dimethyl hydrazine as hydrogen donor in methanol at room temperature. When reaction temperature was raised to reflux, the reduction took place and after 8 h nitrobenzene conversed completely. The results of aromatic nitro compounds reduced with hydrazine hydrate in presence of polymer-supported nano-amorphous Ni–B particles are summarized in Table 1. Arenes, containing one nitro group could be reduced in presence of polymer-supported nano-amorphous Ni–B particles and gave excellent yields. For dinitro aromatic compounds, only one nitro group could be reduced and gave mild yields. The recycling experiments were carried out with p-nitrotoluene. After each reaction, the catalyst could be separated conveniently by filtration. The catalysts were recovered by rinsing with methanol which exhibited the same catalytic activity as before. The yields of anilines obtained from p-nitrotoluene were 97.7%, 90% and 96%, indicating that the catalyst was stable under the reaction conditions and well reusable. It is well known that surface electronic state has important effect on the catalytic property of a material. In amorphous Ni–B alloys partial electrons transfer from B to Ni and making Ni electronenriched and B electron-deficient, which promotes adsorption of electron-deficient nitrogen and electron-enriched oxygen in nitro group. When nitro group is reduced to electron-enriched amine group and it tends to leave the catalyst. The electronic character of amorphous Ni–B alloy can promote the reduction of nitro compounds effectively. On the other hand the catalytic decomposition of hydrazine plays a crucial role in the reaction. In this reaction hydrazine hydrate decomposes in contact with Ni–B catalyst and gives hydrogen to reduce the nitro group. However the detailed decomposition mechanism of hydrazine hydrate in presence of nano-amorphous Ni–B particles is under study. 4. Conclusion
NH2
7
O2N
100
NH2
NO2
9
8.
NH2
2
6
Yield (%)
NH2
1
NO2
Conv (%)
3.2. Reduction of aromatic nitro compounds
NH 2
12
100
72.4
Polymer-supported nano-amorphous Ni–B particles have been prepared by ion-exchange-chemical reduction protocol. The Ni–B particles are uniform in size and homogeneously dispersed on the surface of the polymer. In the catalytic transfer hydrogenation of aromatic nitro compounds they exhibited active, single nitro group aromatic compounds could be reduced smoothly and gave excellent yields. For dinitro aromatic compounds, only one nitro group could be reduced and gave mild yields. The catalyst is stable and reusable under this condition. References [1] F.D. Popp, H.P. Schultz, Chem. Rev. 62 (1962) 19. [2] R.A.W. Johnson, A.H. Wilby, Chem. Rev. 85 (1985) 129. [3] H.O. House, Modern Synthetic Reaction, second ed., Benjamin, New York, 1977, pp. 145. [4] P.N. Rylander, Hydrogenation Methods, Academic, New York, 1985, pp. 365. [5] R.E. Harmon, S.K. Gupta, D.J. Brown, Chem. Rev. 72 (1972) 21. [6] A. Furst, R.C. Berlo, S. Hooton, Chem. Rev. 65 (1965) 51. [7] J.V. Wonterghem, S. Morup, J.W. Christian, S. Charles, W.S. Wells, Nature 322 (1986) 622.
H. Wen et al. / Catalysis Communications 10 (2009) 1207–1211 [8] [9] [10] [11] [12] [13]
A. Molnar, G.V. Smith, M. Bartok, Adv. Catal. 36 (1989) 329. Y. Chen, Catal. Today 44 (1998) 3. A.Z. Ma, Chin. J. Catal. 20 (1999) 603. H. Li, H.X. Li, W.L. Dai, J.F. Deng, Appl. Catal. A 207 (2001) 151. R.B. Zhang, F.Y. Li, Q.Y. Shi, L.T. Luo, Appl. Catal. A 205 (2001) 279. Y.G. He, M.H. Qiao, H.R. Hu, J.F. Deng, K.N. Fan, Appl. Catal. A 228 (2002) 29.
[14] [15] [16] [17]
1211
Y. Lu, Z.T. Xiong, J.T. Li, J.Y. Lin, Catal. Lett. 78 (2002) 231. M.H. Wang, H.X. Li, Chin. J. Catal. 22 (2001) 287. U. Kunz, A. Kirschning, V. Hoffmann, US Patent 2004062941, 2004. U. Kunz, A. Kirschning, H.L. Wen, W. Solodenko, R. Cecilia, C.O. Kappe, T. Turek, Catal. Today 105 (2005) 318.