Selective Synthesis of Primary Amines from Nitriles under Hydrogenation Conditions

Article abstract of DOI:10.1002/adsc.201800102

The hydrogenation of aliphatic nitriles over Pd/C, Pd/Al₂O₃, and Pd?Au/Al₂O₃ catalysts were evaluated for the selective hydrogenation of aliphatic nitriles to the corresponding primary amines. The highest selectivity (>99%) toward primary amines was achieved when the reaction was carried out in acetic acid using 10 mol% of 25% Pd-5% Au/Al₂O₃ under relatively low hydrogen pressure (0.8 MPa). Characterization of the catalysts by XRD, CO adsorption experiments, and EXAFS revealed that the excellent selectivity of 25% Pd-5% Au/Al₂O₃ toward the synthesis of primary amines is determined by the electronic properties and/or the surface structure resulting from alloying Pd with Au. (Figure presented.).

Full text of DOI:10.1002/adsc.201800102

Title: Selective Synthesis of Primary Amines from Nitriles under
Hydrogenation Conditions
Authors: Masayoshi Yoshimura, Akira Komatsu, Masaru Niimura,
Yukio Takagi, Tohru Takahashi, Shun Ueda, Tomohiro
Ichikawa, Yutaka Kobayashi, Hiroki Okami, Tomohiro Hattori,
Yoshinari Sawama, Yasunari Monguchi, and Hironao Sajiki
This manuscript has been accepted after peer review and appears as an
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201800102
Link to VoR: http://dx.doi.org/10.1002/adsc.201800102

10.1002/adsc.201800102
Advanced Synthesis & Catalysis
UPDATE
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Selective Synthesis of Primary Amines from Nitriles under
Hydrogenation Conditions
Masatoshi Yoshimura,a* Akira Komatsu,a Masaru Niimura,a Yukio Takagi,a
Tohru Takahashi,b Shun Ueda,b Tomohiro Ichikawa,b Yutaka Kobayashi,b Hiroki
Okami,b Tomohiro Hattori,b,c Yoshinari Sawama,b Yasunari Monguchi,b,d*and Hironao
Sajikib*
a
Catalysts Development Center, N.E. Chemcat Corporation, 678 Ipponmatsu, Numazu 410-0314, Japan
Fax: (+81) 55-967-9607; e-mail: masatoshi.yoshimura@ne-chemcat.co.jp
Laboratory of Organic Chemistry, Gifu Pharmaceutical University, 1-25-4 Daigaku-nishi, Gifu 501-1196, Japan
b
Fax: (+81) 58-237-5979; e-mail: sajiki@gifu-pu.ac.jp
Current address: Molecular Catalyst Research Center, Chubu University, 1200 Matsumoto-cho, Kasugai 487-8501,
c
Japan
d
Current address: Laboratory of Organic Chemistry, Daiichi University of Pharmacy, 22-1 Tamagawa-cho, Minami-ku,
Fukuoka 815-8511, Japan
Fax: (+81) 92-553-5698; e-mail: monguchi@daiichi-cps.ac.jp
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
hexamethylenediamine. It is industrially produced
Pd/C, Pd/Al2O3, and Pd-Au/Al2O3 catalysts were evaluated over 2 million tons a year as a raw material of nylon
Abstract. The hydrogenation of aliphatic nitriles over
for the selective hydrogenation of aliphatic nitriles to the
corresponding primary amines. The highest selectivity
(>99%) toward primary amines was achieved when the
reaction was carried out in acetic acid using 10 mol% of
25% Pd-5% Au/Al2O3 under relatively low hydrogen
pressure (0.8 MPa). Characterization of the catalysts by
XRD, CO adsorption experiments, and EXAFS revealed
that the excellent selectivity of 25% Pd-5% Au/Al2O3
toward the synthesis of primary amines is determined by
the electronic properties and/or the surface structure
resulting from alloying Pd with Au.
66, which is utilized in fibers and textiles, by the
hydrogenation of adiponitrile in the fixed bed high-
pressure process using promoted cobalt catalyst under
100—200 °C and 28—41 MPa or by the slurry phase
low-pressure process using Raney nickel or cobalt
under 60 — 100 °C and 2 — 5 MPa. The yields of
hexamethylenediamine by each method are 98–99%
and 85%, respectively.[3] In spite of such successful
industrial applications, a relatively limited number of
practical methods for the hydrogenation of aliphatic
nitriles to the corresponding primary amines have
been reported in the literature.[4,5] In a recent example,
Hegedus evaluated palladium on carbon (Pd/C) for
the hydrogenation of benzyl cyanide under 6 bar of
H2, while the selectivity of the primary amine was
only 45%.[5b] Although the hydrogenation of aliphatic
nitriles catalyzed by Pd/Mobil Crystalline Material-
41 (MCM-41, a mesoporous material) in supercritical
carbon dioxide proceeded selectively, the reaction
was never completed under 2 MPa H2 conditions.[5c]
Apesteguía et al. reported the highly selective
hydrogenation of butylonitrile under 25 bar H2
conditions with Co/SiO2 as the catalyst.[5d] Beller et al.
reported the excellent primary amine selective
hydrogenation of aliphatic nitriles catalyzed by a
combination of Co/Al2O3–1,10-phenanthroline in the
presence of ammonia under 40 bar H2.[5f] As
summarized above, relatively harsh and complex
reaction conditions are required in such reported
methods. Therefore, the development of a simple,
mild, and highly selective method for the
hydrogenation of aliphatic nitriles to the
Keywords: amines; chemoselectivity; gold; heterogeneous
catalysis; hydrogenation; nitriles; palladium
Introduction
The hydrogenation of nitrile functionalities is an
attractive method for the synthesis of primary amines,
which are common intermediates of functional
materials such as pharmaceuticals, agrichemicals, and
raw materials of polymers and resins.[1] The
development of selective hydrogenation reactions to
convert nitriles into primary amines is a challenging
task; the yield of primary amines is usually very
small compared to the considerable formation of the
corresponding secondary and tertiary amines,
especially in the case of the hydrogenation of
aliphatic nitriles.[2] One of the largest applications of
hydrogenation of nitriles is the production of
1
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10.1002/adsc.201800102
Advanced Synthesis & Catalysis
corresponding primary amines under mild conditions
is eagerly desired.
Influence of the solvent, catalyst support, and
additional immobilization of Au on the catalyst
In this paper, we demonstrate the effective use of
Pd-Au bimetallic catalysts supported on alumina, on
which relatively large quantity of Pd species were
loaded, for the selective hydrogenation of aliphatic
nitriles to primary amines under relatively mild
conditions. As reported in the literature, the addition
of acids is known to improve the selectivity of
primary amine formation[2] due to the in-situ
conversion of the generated primary amines into the
corresponding non-nucleophilic ammonium salts,
resulting in the simple neutralization of the
hydrogenation network of aliphatic nitriles (Scheme
1).[6] In the present work, excellent yields were also
obtained when acetic acid was used as the solvent.
The effect of the Pd and Au metals on the selectivity
is also discussed on the basis of the catalyst
characterization data.
When
10%
Pd/C
(0.5
mol%)-catalyzed
hydrogenation of valeronitrile (1a) was carried out in
MeOH or tetrahydrofuran, the corresponding
secondary (3a) and tertiary amines (4a) were
generated as products without the formation of
primary amines (2a) (Table 1, entries 1 and 2).[2]
Such a mixture arises from the comparable stability
(lifetime) of the corresponding imine intermediate
toward hydrogenation and the nucleophilic attack by
amine products (Scheme 1). The selectivity toward
primary amines (2a) was greatly improved using
acetic acid as the solvent due to the quick trapping of
the initially generated primary amines as ammonium
acetate species (entry 3). Such amine trap would also
be effective against catalyst poisoning effects by the
amine products (2a–4a). Palladium on alumina (5%
Pd/Al2O3) exhibited better selectivity toward the
formation of 2a in comparison with Pd/C (entries 3
and 4), probably based on differences in the number
of acidic sites on the surface of activated carbon and
alumina. In the gas phase Pd-catalyzed hydrogenation
of butyronitrile, Hao et al. reported that, since
activated charcoal possesses a greater number of
acidic sites than alumina, tertiary amines could be
more smoothly formed on these acid sites.[7]
Au has been previously used as a modifier for
metallic catalysts to change the inherent nature of
their active sites through alloy formation,[8] e.g., the
synthesis of vinyl acetate from ethylene and acetic
acid is effectively catalyzed by active Pd monomers
released from alloyed Au clusters in Pd-Au/SiO2.[8b]
In the case of the present hydrogenation of aliphatic
nitriles, the addition of Au to Pd/Al2O3 was found to
be quite effective for the enhancement of the primary
amine selectivity (entries 5 vs. 7 and 6 vs. 11).
Furthermore, the use of Pd-Au/Al2O3 catalysts with
larger Pd-Au content at a fixed 5:1 Pd/Au weight
ratio (equivalent to a 9:1 Pd/Au molar ratio) led to the
more selective formation of 2a (entries 7–11).
Scheme 1. Reaction scheme for the catalytic
hydrogenation of nitriles.
Results and Discussion
Table 1. Hydrogenation of valeronitrile (1a).a)
Entry
Catalyst
X (mol%)
Solvent
1a : 2a : 3a : 4ab)
1
2
3
4
5
6
7
8
10% Pd/C
10% Pd/C
10% Pd/C
5% Pd/Al2O3
5% Pd/Al2O3
25% Pd/Al2O3
5% Pd-1% Au/Al2O3
10% Pd-2% Au/Al2O3
15% Pd-3% Au/Al2O3
20% Pd-4% Au/Al2O3
25% Pd-5% Au/Al2O3
0.5
0.5
0.5
0.5
1
1
1
1
1
MeOH
THF
76 : 0 : 3 : 16
36 : 0 : 3 : 57
0 : 56 : 29 : 7
0 : 66 : 20 : 3
0 : 61 : 17 : 1
0 : 81 : 4 : 0
0 : 70 : 17 : 0
0 : 79 : 12 : 0
0 : 76 : 7 : 0
0 : 79 : 8 : 0
0 : 89 : 7 : 0
AcOH
AcOH
AcOH
AcOH
AcOH
AcOH
AcOH
AcOH
AcOH
9
10
11
1
1
2
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10.1002/adsc.201800102
Advanced Synthesis & Catalysis
a) The reaction was carried out at 50 °C under 0.15 MPa H2 for 5 h. b) Determined by GC. The generation of a small
amount of byproducts including secondary imines was observed.[8]
Optimization of the reaction conditions
Further optimization was conducted using
decanenitrile (1b, 0.5 mmol) as the substrate since
amines derived from valeronitrile would be difficult
to isolate owing to their low boiling point (Table 2).
When the hydrogenation of 1b was carried out in
AcOH (1 mL) in the presence of 25% Pd-5%
Au/Al2O3 (1 mol% based on Pd content) under
atmospheric H2, the starting nitrile compound was not
completely consumed at room temperature or even at
50 °C after 6 h (entries 1 and 2). The reaction was
completed by increasing the catalytic loading to 5
mol% of Pd content (entry 3), and the application of
pressurized hydrogen at 0.2 MPa was found to be
effective to increase the selectivity toward the
formation of primary amines (2b) (entry 4). The
selectivity was then further improved to 98% by
increasing the catalyst loading and hydrogen pressure
to 10 mol% and 0.8 MPa, respectively (entries 5–7).
Finally, the best selectivity (>99%) was achieved
when the reaction was carried out in 2 mL of AcOH
(entry 8),[9] while no further positive effects were
observed upon increasing the temperature (entry 9).
The reaction in the absence of solvent resulted in the
drastic reduction in conversion and selectivity (entry
10). The observed effects upon increasing the catalyst
loading and hydrogen pressure in a larger volume of
AcOH could be attributed to the acceleration of the
hydrogenation of the imine intermediate before
nucleophilic attack by the amine products.
7
10
10
10
10
RT
RT
50 °C 0.8
RT 0.8
0.8
0.8
0 : 98 : 2 : 0
trace : >99 : trace : 0
0 : 96 : 4 : 0
8c)
9
10d)
11 : 1 : 68 : 20
a) The hydrogenation of decanenitrile (1b) (0.5 mol) was
carried out in AcOH (1 mL) at room temperature or 50 °C
using 25% Pd-5% Au/Al2O3 (1, 5, or 10 mol% based on
the Pd content) as the catalyst under H2 pressure (0.1, 0.2,
0.4, or 0.8 MPa) for 6 h. b) The ratio was determined by 1H
NMR spectroscopy. c) The volume of AcOH was 2 mL. d)
The reaction was carried out in the absence of solvent.
The 25% Pd-5% Au/Al2O3-catalyzed hydrogenation
of other kinds of nitriles was further investigated for
the selective synthesis of primary amines (Table 3).
Cyclohexanecarbonitrile (1c) as a secondary alkyl-
substituted nitrile also underwent
a
smooth
hydrogenation to the corresponding primary amine
with a 98% selectivity (entry 2). The complete
selectivity for the primary amine synthesis was
achieved in the hydrogenation of aromatic nitriles (1d
and 1e), although a slight formation of deaminated
toluenes (5) based on the hydrocracking of desired
benzylamines (2) was observed in each case (<5%)
(entries 3 and 4).[11]
Table 3. Hydrogenation of various nitriles (1) using 25%
Pd-5% Au/Al2O3.a)
Both Pd and Au concentrations in the reaction
mixture of the hydrogenation of decanenitrile under
the optimal conditions (Table 2, entry 8) after the
removal of the catalyst by a filtration were analyzed
to evaluate the metal leaching from the catalyst by
inductively
coupled
plasma-optical
emission
spectrometry (ICP-OES). As the result, no leaching
of either Pd or Au was observed within the detection
limits (<0.1 ppm).[10]
Table 2. Hydrogenation of decanenitrile (1b) using 25%
Pd-5% Au/Al2O3.a)
X
H2
(MPa)
Entry
Temp.
1b : 2b : 3b : 4bb)
(mol%)
1
2
3
4
5
6
1
1
5
5
10
10
50 °C 0.1
52 : 42 : 6 : trace
69 : 28 : 3 : 0
0 : 93 : 7 : 0
0 : 95 : 5 : 0
0 : 92 : 8 : trace
0 : 91 : 9 : 0
RT
RT
RT
RT
RT
0.1
0.1
0.2
0.1
0.4
a) The hydrogenation of nitrile (1) (0.5 mol) was carried
out in AcOH (2 mL) at room temperature using 25% Pd-
3
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10.1002/adsc.201800102
Advanced Synthesis & Catalysis
5% Au/Al2O3 (10 mol% based on the Pd content) as the
catalyst under 0.8 MPa for 6 h. In the case of benzonitrile
derivatives, the formation of deaminated products (5) was
observed. b) The ratio was determined by 1H NMR
spectroscopy. Trace amount is indicated as t. c) Isolated
yield. d) Yield as a mixture of 2c and 3c is given. e) 1 h. f)
50 °C, 1 h.
Pairing factor = CN(Ru-Pt) / [CN(Ru-Ru) + CN(Ru-
Pt)]
where CN(Ru-Pt) is the number of Pt atoms around a
Ru metal and CN(Ru-Ru) is the number of Ru atoms
around a Ru atom.[13] As shown in Table 3, the
alloying degree of Au in the Pd-Au/Al2O3 catalysts
was calculated based on CN(Au-Pd) / [CN(Au-Pd) +
CN(Au-Au)], and it was found that Au-Pd alloying
increased with the increasing metal loading of Pd-
Au/Al2O3. Furthermore, the total coordination
number of Au atoms [CN(Au-Pd) + CN(Au-Au)] in
highly Pd-Au-loaded catalysts did not reach 12,
which is the coordination number of Au atoms in
face-centered cubic structures. These observations
suggest that the Au atoms of the highly metal-loaded
catalysts are preferentially located on the surface of
the Pd-Au alloy particles rather than in the inside,
since metal atoms on the surface of particles do not
have coordinating atoms in the outside of the
particles.
Characterization of the Pd-Au/Al2O3 structure by
EXAFS, XRD, and CO adsorption
Using the extended X-ray absorption fine structure
(EXAFS) data for the Pd-Au/Al2O3 catalysts with
varying Pd-Au contents at a 5:1 weight % ratio
(Figure 1), the coordination environment around the
Au atoms was analyzed employing the concept of the
coordination number (CN) (Table 3). Nitani et al.
estimated the degree of Ru alloyed in PtRu/C
catalysts as the 'pairing factor' using the following
equation:
(f) Au foil (ref.)
(e) 25%Pd-5%Au
(d) 20%Pd-4%Au
(c) 15%Pd-3%Au
(b) 10%Pd-2%Au
(a) 5%Pd-1%Au
0
1
2
3
4
5
R (Å)
Figure 1. Au LIII-edge EXAFS spectra of (a) 5% Pd-1% Au/Al2O3, (b) 10% Pd-2% Au/Al2O3, (c) 15% Pd-3% Au/Al2O3,
(d) 20% Pd-4% Au/Al2O3, (e) 25% Pd-5% Au/Al2O3, and (f) Au foil (reference).
Table 3. EXAFS data of the Au-LIII edge of the Pd-Au/Al2O3 catalysts.
R/Åa)
Coordination Number (CN)
Degree of alloying of Au in
the catalyst (%)d)
Catalyst
Au–Au
Au–Pd
Au-Aub)
Au-Pdc)
5% Pd-1% Au/Al2O3
10% Pd-2% Au/Al2O3
15% Pd-3% Au/Al2O3
20% Pd-4% Au/Al2O3
25% Pd-5% Au/Al2O3
2.84
2.82
2.83
2.83
2.76
2.75
2.75
2.76
2.75
2.75
8.7
7.1
5.5
5.2
3.7
3.4
3.0
3.0
3.3
5.8
28
29
36
38
61
4
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10.1002/adsc.201800102
Advanced Synthesis & Catalysis
a) Distance between two metal atoms. b) The number of Au atoms around an Au atom. c) The number of Pd atoms around
an Au atom. d) The degree of alloying is defined as CN(Au-Pd) / [CN(Au-Pd) + CN(Au-Au)], as reported in the
literature.[12]
Table 4. Physical properties of Pd-Au/Al2O3 catalysts and their selectivity toward primary amine generation.
Pd metal surface area
(m2/g-Pd)a)
Selectivity
toward
the
Catalyst
Pd particle size (Å)b)
primary amine (%)c)
5% Pd/Al2O3
234
120
104
92
104
65
N.D.d)
49
42
41
43
61
70
79
76
79
89
5% Pd-1% Au/Al2O3
10% Pd-2% Au/Al2O3
15% Pd-3% Au/Al2O3
20% Pd-4% Au/Al2O3
25% Pd-5% Au/Al2O3
37
a) Determined by CO adsorption experiments. b) Determined from the peak data of Pd(311) at 2θ = 82° on the X-ray
diffraction (XRD) spectra using Scherrer’s equation. c) From Table 1. d) The XRD peak was too broad to determine the
crystal size.
Table 5. Acid amount on the Pd-Au/Al2O3 catalysts, Pd black and Al2O3 powder determined by NH3-TPD.
Total
NH3 desorbed
100–500 °C
(mmol/g)
NH3 desorbed
500–800 °C
(mmol/g)
Total
NH3 desorbed
500–800 °C
(mmol/g-Pd)
Catalyst
NH3 desorbed
(mmol/g)
NH3 desorbed
(mmol/g-Pd)
5% Pd/Al2O3
0.010
0.019
0.026
0.028
0.043
0.025
0.065
0.183
0.010
0.012
0.010
0.012
0.009
0.011
0
0
0.20
0.38
0.26
0.18
0.22
0.10
0.065
–
0
5% Pd-1% Au/Al2O3
10% Pd-2% Au/Al2O3
15% Pd-3% Au/Al2O3
20% Pd-4% Au/Al2O3
25% Pd-5% Au/Al2O3
Pd black
0.007
0.016
0.016
0.034
0.014
0.065
0.003
0.14
0.16
0.11
0.17
0.056
0.065
–
Al2O3
0.180
While the Pd crystalline size of Pd-Au/Al2O3, as
determined by their X-ray diffraction (XRD) profiles,
was not affected by the Pd-Au loading on the
catalysts, the Pd metal surface area estimated by CO
adsorption experiments generally became smaller
with the increasing Pd-Au content (Table 4). Since
Au atoms have no ability to adsorb CO gas, the Au
atoms on the highly metal-loaded catalysts must be
preferentially located on the surface rather than the
inside of the particles. This observation is consistent
with the above-mentioned conclusion regarding the
degree of alloying and coordination number of Au
based on the EXAFS data provided in Table 3. The
positive correlation between the Pd-Au loading on the
catalysts and the selectivity toward primary amine
generation might be based on differences on the
electronic properties and/or the surface structure of
the Pd clusters alloyed with Au, including the Pd
concentration on the alloyed cluster surface.
indicating that there are weaker and stronger acidic
sites on the catalysts, respectively. While the total
amount of desorbed NH3 per gram of Pd-Au/Al2O3
catalyst was virtually the same irrespective of the Pd
and Au content, the NH3 amount desorbed from the
stronger acidic sites per Pd unit weight of each
catalyst in particular 25% Pd-5% Au/Al2O3 was
nearly comparable to that of Pd black, although the
corresponding peak was not observed in the case of
5% Pd/Al2O3. Assuming no Pd metal dispersion and
considering the extremely low metal surface area of
Pd black, such similarity between the Pd-Au/Al2O3
catalysts and Pd black suggests that these bimetallic
catalysts exhibit distinct properties on their surface
and these properties are characterized by the alloying
of Pd with Au.
Conclusion
The differences on the surface structure of the Pd-
Au/Al2O3 catalysts were also confirmed by measuring
their acidic properties based on NH3 temperature
programmed desorption (TPD) experiments on the
catalyst surface (Table 5). Two NH3 desorption peaks
were observed at approximately 200 °C and 650 °C
in the NH3-TPD profiles of all Pd-Au/Al2O3 catalysts,
The best catalyst among Pd/C, Pd/Al2O3, and Pd-
Au/Al2O3 for the selective hydrogenation of aliphatic
nitriles to the corresponding primary amines was
found to be 25% Pd-5% Au/Al2O3. Excellent
conversions (>99%) and selectivity (>99%) were
achieved in acetic acid at room temperature under
5
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10.1002/adsc.201800102
Advanced Synthesis & Catalysis
column chromatography on silica gel pretreated by MeOH
relatively low hydrogen pressure (0.8 MPa). Such
excellent selectivity arises from the distinctive
surface properties of the bimetallic catalyst,
characterized by the alloying of Pd with Au.
1
(EtOAc to MeOH). 98%. H NMR (500 MHz, CDCl3) δ
1.67 (2H, br s), 3.92 (2H, s), 7.34 (1H, t, J = 8.0 MHz),
7.39 (2H, d, J = 8.0 Hz), 7.58 (2H, dd, J = 8.0, 8.0 Hz),
7.56–7.60 (4H, m); 13C NMR (125 MHz, CDCl3) δ 46.1,
127.0, 127.2, 127.3, 127.5, 128.7, 139.8, 140.9, 142.3; MS
(EI) m/z (%) 183 (M+, 45), 182 (100).
4-Methoxybenzylamine (2e)[17] The reaction was carried
out at 50 °C for 1 h. The product was purified by a short
column chromatography on silica gel pretreated by MeOH
Experimental Section
Materials
1
(EtOAc to MeOH). 64%. H NMR (500 MHz, CDCl3) δ
2.50 (2H, br s), 3.81–3.81 (5H, m), 6.87 (2H, d, J = 7.0
Hz), 7.23 (2H, d, J = 7.0 Hz); 13C NMR (125 MHz,
CDCl3) δ 45.6, 55.3, 113.9, 128.4, 134.7, 158.6; MS (EI)
m/z (%) 137 (M+, 48), 136 (100).
10% Pd/C, Pd/Al2O3s, and Pd-Au/Al2O3s are obtained
from N.E. Chemcat Co., Tokyo, Japan. Valeronitrile and
decanonitile were purchased from Wako Pure Chemicals
and Tokyo Kasei Co., respectively and used without
purification.
Pentylamine,
dipentylamine,
and
tripentylamine were purchased from Wako Pure Chemicals
as standard materials.
Analysis of Leached Metals
After the hydrogenation of decanenitrile (0.500 mmol) was
carried out under the optimal conditions (Table 2, Entry 8)
as described in the general procedure, the reaction mixture
was passed through a membrane filter (0.45 μm), and the
catalyst on the filter was washed with CHCl3 (5 × 2 mL).
The combined filtrates were concentrated in vacuo. The
residue was extracted with CHCl3 (100 mL) and water
(100 mL). CHCl3 and aqueous phases were separated and
separately treated for ICP measurement. Each phase was
dried up and then treated with the mixture of HNO3 and
H2SO4. Aqua regia and additional HCl were added to the
mixture. By the addition of Te solution, Pd and Au were
separated as Pd-Te and Au-Te. Pd-Te and Au-Te were
filtered and dissolved with aqua regia and then dried up.
The residue was dissolved with aqueous HCl and small
amount of HNO3. Pd and Au concentrations in the solution
were analyzed by Thermo Fisher Scientific ICP-OES
iCAP6500.
Hydrogenation Procedure
General procedure for hydrogenation of valeronitrile
(1a) (Table 1): A suspension of valeronitrile (1a) (20
mmol) and catalyst [Pd/Al2O3 or Pd-Au/Al2O3 (0.2 mmol
based on Pd metal)] in specific solvent (50 mL) was stirred
at 50 °C under 0.15 MPa H2. After five hours, the catalyst
was removed from the reaction mixture by filtration.
NaOH was added at 0 °C with ice to the reaction mixture
till the pH of the mixture reached 7. CHCl3 (50 mL) is
added, and the organic layer was separated. Nitrobenzene
was added as an internal standard and then analysed by gas
chromatography (Shimadzu GC-2010 equipped with a
flame ionization detector) to determine the ratio of
valeronitrile (1a), pentylamine (2a), dipentylamine (3a),
and tripentylamine (4a).
General procedure for the hydrogenation of
decanenitrile (1b) (Table 2, Entry 8): A suspension of
decanenitrile (1b) (76.6 mg, 0.500 mmol) and 25% Pd-5%
Au/Al2O3 (21.3 mg, 50 μmol, 10 mol%) in AcOH (2 mL)
in a 50 mL stainless sealed tube was stirred at RT under 8
atm H2 pressure. After 6 h, the mixture was passed through
a membrane filter (0.45 μm), and the catalyst on the filter
was washed with CHCl3 (5 × 2 mL). The combined
filtrates were concentrated in vacuo. CHCl3 (10 mL) and
saturated aqueous NaHCO3 solution (10 mL) were added
to the residue, and the layers were separated. The aqueous
layer was extracted with CHCl3 (10 × 2 mL). The
combined organic layers were dried over MgSO4 and
concentrated in vacuo to give 1-decanamine (2b) (70.9 mg,
Catalyst Characterization
Metal surface area measurement: Palladium surface area
of each catalyst was calculated from the amount of CO by
the CO adsorption test using MicrotracBEL BEL-METAL-
3. The catalyst was purged with hydrogen gas at 40 °C,
then treated with CO gas pulses at room temperature. The
palladium surface area was calculated assuming that CO
was adsorbed on palladium surface in bridging manner (i.e.,
CO:Pd molar ratio is 1:2).
The X-ray diffraction measurements were conducted using
PANalytical X'Pert PRO-MPD at N.E. Chemcat. The
crystal sizes of Pd and Pd-Au particles were determined by
using Scherrer’s equation from the peak data from Pd(311)
at 2θ =82° by X-ray diffraction.
1
90%) with >99% purity without any purification. H and
13C NMR spectra were recorded on a JEOL AL-400
spectrometer (400 MHz for 1H NMR and 100 MHz for 13
C
1
NMR) or JEOL ECA500 spectrometer (500 MHz for H
NMR and 125 MHz for 13C NMR). Chemical shifts (δ) are
expressed in ppm based on internal standard [TMS (0
ppm)] for 1H NMR and residual solvent [CDCl3 (77.0
ppm)] for 13C NMR. The 1H NMR and 13C NMR spectra of
products were identical with those in literature.[14–17]
Surface acidity measurement: Acidity was measured by
NH3 adsorption coupled with temprature programmed
desorption (TPD) using the combination of MicrotracBEL
BELCAT and BELMass. The catalysts were pretreated at
500 °C under He and cooled, treated with 2.5% v/v
NH3/He at 100 °C, and flushed in He with TPD at
10 °C/min to 800 °C.
1
1-Decanamine (2b)[14] 90%. H NMR (400 MHz, CDCl3)
δ 2.68 (2H, t, J = 6.2 Hz), 1.44 (2H, m), 1.28–1.26 (18H,
m), 0.88 (3H, t, J = 7.0 Hz); 13C NMR (100 MHz, CDCl3)
δ 42.2, 33.8, 31.8, 29.6, 29.5, 29.5, 29.3, 26.8, 22.6, 14.0;
MS (EI) m/z (%) 156 [(M–H)+, 4], 55 (100).
EXAFS experiment: The Pd K-edge and Au L-edge X-ray
absorption spectra were recorded at BL14B2 station
attached to Si(311) monochromator at SPring-8 (JASRI),
Harima, Japan (Proposal No. 2010B1774). Data analyses
were performed using REX2000 program ver. 2.5.9
(RIGAKU). Coordination number (CN) and interatomic
distance (R) were estimated by curve-fitting analysis using
Pd-Pd and Au-Au shell parameters extracted from Pd foil
and Au foil as reference samples, respectively.
Cyclohexylmethylamine (2c)[15] The reaction was carried
out at RT for
6
h. 69% as
a
mixture with
bis(cyclohexylmethyl)amine in the ratio of 98 : 2. 1H NMR
(500 MHz, CDCl3) δ 2.51 (2H, d, J = 6.0 Hz), 1.75–1.65
(5H, m), 1.31–1.11 (6H, m), 0.88 (2H, m); 13C NMR (125
MHz, CDCl3) δ 48.9, 41.3, 30.7, 26.6, 26.0; MS (EI) m/z
(%) 113 (M+, 44), 67 (100).
Acknowledgements
4-Phenylbenzylamine (2d)[16] The reaction was carried
out at RT for 1 h. The product was purified by a short
6
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10.1002/adsc.201800102
Advanced Synthesis & Catalysis
The synchrotron radiation experiments were performed at the
BL14B2 of SPring-8 with the approval of the Japan Synchrotron
Radiation Research Institute (JASRI) (Proposal No. 2010B1774).
We thank the staffs at SPring-8 for their support upon conducting
EXAFS experiments.
Surkus, L. He, K. Junge, M. Beller, J. Am. Chem. Soc.
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10.1002/adsc.201800102
Advanced Synthesis & Catalysis
UPDATE
Selective Synthesis of Primary Amines from
Nitriles under Hydrogenation Conditions
Adv. Synth. Catal. Year, Volume, Page – Page
Masatoshi Yoshimura,* Akira Komatsu, Masaru
Niimura, Yukio Takagi, Tohru Takahashi, Shun
Ueda, Tomohiro Ichikawa, Yutaka Kobayashi,
Hiroki Okami, Tomohiro Hattori, Yoshinari
Sawama, Yasunari Monguchi,* Hironao Sajiki*
8
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