Selective gas-phase hydrogenation of benzonitrile into benzylamine over Cu-MgO catalysts without using any additives

Article abstract of DOI:10.1039/c3nj00453h

A clean and mild gas-phase hydrogenation of benzonitrile to benzylamine has been accomplished using Cu-MgO catalysts prepared by impregnating a freshly prepared MgO support using Cu(NO₃)₂·3H₂O as a Cu precursor with Cu loading of 4, 8, 12 and 16%, of which 12% Cu-MgO catalyst exhibited superior activity with 98% conversion of benzonitrile and 70% selectivity of benzylamine even in the absence of any additives at atmospheric pressure. Under these optimized conditions, the selectivity of benzylamine has been significantly elevated to nearly 100% with considerable conversion.

Full text of DOI:10.1039/c3nj00453h

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Selective gas-phase hydrogenation of benzonitrile into
benzylamine over Cu–MgO catalysts without using
any additives
Cite this: DOI: 10.1039/c3nj00453h
Ravi Kumar Marella, Kumara Swamy Koppadi, Yadagiri Jyothi,
Kamaraju Seetha Rama Rao and David Raju Burri*
A clean and mild gas-phase hydrogenation of benzonitrile to benzylamine has been accomplished using
Received (in Montpellier, France)
3
0th April 2013,
Cu–MgO catalysts prepared by impregnating a freshly prepared MgO support using Cu(NO
3
)
2
Á3H
2
O as a
Accepted 23rd July 2013
Cu precursor with Cu loading of 4, 8, 12 and 16%, of which 12% Cu–MgO catalyst exhibited superior
activity with 98% conversion of benzonitrile and 70% selectivity of benzylamine even in the absence of
any additives at atmospheric pressure. Under these optimized conditions, the selectivity of benzylamine
has been significantly elevated to nearly 100% with considerable conversion.
DOI: 10.1039/c3nj00453h
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tertiary by-products through ammonium salt formation. Under
these conditions, benzonitrile was gently reduced to benzylamine
Introduction
13
Hydrogenation of nitriles to amines is an industrially impor- over Pd–C. Addition of CH COOH in hydrogenation of benzo-
3
tant reaction, because amines have found widespread utility as nitrile over Pd on BaSO gave over 80% yield of benzylamine.
4
solvents, disinfectants, corrosion inhibitors, textile additives, Hydrogenation of phenylacetonitrile gave best results when the
1
4
rubber stabilizers, raw materials for resins, intermediates for CH COOH contained H SO or dry HCl.
3
2
4
pharmaceuticals, and in the manufacture of detergents and
Generally, additives are being used to increase the selectivity
plastics. For the synthesis of amines, reductive amination of of primary amine, but the use of additives creates new problems
1
2
3
carbonyl compounds, hydroamination of olefins and alkynes
like their separation and reuse. Additives make the process more
and hydrogenation of nitriles have been established. However, expensive by involving product separation and some cases
hydrogenation of nitriles is recognized as an atom efficient additives lead to catalyst deactivation. Hence, it is difficult to
4
,5
process.
implement such a process at an industrial scale.
Indeed, the conversion of nitrile to primary amine is facile,
Apart from adding either base or acid, high-pressure operation
but the selectivity for primary amines strongly decreases due to with molecular hydrogen is one of the important strategies for the
6
,7
15–17
the formation of secondary and tertiary amines as by-products
improvement of primary amine selectivity,
wherein, handling
8
via imine intermediates as proposed by von Braun et al. Hence, risks and use of high-pressure equipment are unavoidable process
selectivity control is one of the most important issues in the limitations. To avoid these limitations, transfer hydrogenation of
hydrogenation of nitriles. For the enhancement of primary amine nitriles have been studied using a mixture of formic acid and
selectivity various possibilities are being explored. The addition amines or formate salts, as well as alcohols in combination with a
of bases to the reaction medium has been found to enhance the base are used as suitable hydrogen sources.
In this process
by decreasing the formation of separation problems are also unavoidable. It is reported that
18,19
4
,9
primary amine selectivity
secondary and tertiary amines through poisoning the acidic molecular hydrogen is undoubtedly the cleanest reducing agent
sites, which are responsible for the coupling reactions. Recently, for catalytic hydrogenation in synthetic organic chemistry both on
1
0,11
6,20
instead of using ammonia, less toxic bases like NaOH
and the laboratory and the production scale.
Hence, atmospheric
s
LiOH are also being used effectively with RANEY Ni and Co pressure operation using molecular hydrogen would be the best
catalysts, wherein, OH ions block the active sites responsible option if a selective catalyst is available.
À
1
2
s
s
for by-product formation.
For the hydrogenation of nitriles RANEY Ni, RANEY Co,
2
1
It has also been reported that the addition of HCl solution Pd–C, Pt–C, Ru–C, and Rh–C are frequently used catalysts. The
prevents the subsequent reactions that lead to secondary and same metals supported on SiO or Al O are also often employed
2
2 3
22
as catalysts. Though Cu is inexpensive and abundant compared
to noble metals, only few reports are available on Cu based
Catalysis Laboratory, Indian Institute of Chemical Technology, Hyderabad, India.
23,24
E-mail: david@iict.res.in; Fax: +91-40-27160921; Tel: +91-40-27193232
catalysts for the hydrogenation of nitriles.
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It is well known that the physico-chemical characteristics of
NJC
The X-ray diffraction (XRD) patterns were recorded at room
the catalyst support, such as surface area, pore volume, acidity temperature using a Rigaku Ultima-IV diffractometer with nickel
and basicity, can affect significantly the activity and selectivity. filtered Cu-Ka radiation of wavelength 1.5418 Å at a power of
For instance, the selectivity of supported nickel-based catalysts 40 kV and a current of 20 mA in the 2y range of 10–801 to
in acetonitrile hydrogenation demonstrates that the basic sup- confirm the crystalline phases of copper species present in
ports favour the formation of primary amines, while the acidic reduced Cu–MgO catalysts.
2
5
sites favour the formation of secondary and tertiary amines.
To get higher selectivity of primary amine, it is important to use X-ray photoelectron spectroscopy (XPS) on a KRATOS AXIS 165
the basic support. with a DUAL anode (Mg and Al) apparatus using the Mg-Ka anode.
Furthermore, gas-phase hydrogenation of nitriles would be The non-monochromatized Al-Ka X-ray source (hn = 1486.6 eV)
The oxidation state of the surface atoms were examined by
2
2–25
an alternative method to produce amines,
with different was operated at 12.5 kV and 16 mA. Before acquisition of the
results than obtained in liquid-phase reactions, namely control data the sample was out-gassed for about 3 h at 100 1C under a
À7
of the product selectivity. The development of new catalysts for vacuum of 10 /760 bar to minimize surface contamination.
the efficient and selective hydrogenation of nitriles using The instrument was calibrated using Au as standard. For energy
molecular hydrogen is still a challenging goal.
calibration, the carbon 1s photoelectron line was used. The
The purpose of this contribution is to achieve high selectivity carbon 1s binding energy was taken as 285 eV. Charge neutra-
of benzylamine through gas-phase hydrogenation of benzonitrile lization of 2 eV was used to balance the charge up of the
over Cu–MgO catalysts at 1 atmosphere pressure without using sample. Prior to the XPS studies, all the catalysts were reduced
any additives. Herein, the catalyst preparation, characteriza- in a H flow at 523 K for 4 h, followed by passivation in a N2
2
tion and the details of benzonitrile hydrogenation have been atmosphere.
delineated.
The temperature-programmed reduction of hydrogen (H -TPR)
2
was conducted in a home-made TPR system. Typically, about
5
0 mg of calcined CuO–MgO sample was loaded in a quartz
Experimental section
Materials and methods
reactor initially treated at 473 K for 1 h under argon gas flow
À1
(30 ml min ). After being cooled to room temperature, the
À1
All the chemicals and reagents were obtained from commercial sample was heated to 973 K at a rate of 10 K min with the flow
sources and were used without further purification. Freshly of a 5 vol% H –argon mixture gas (30 ml min ). The hydrogen
À1
2
prepared MgO was used as a support for the preparation of consumption was monitored using GC equipped with a thermal
Cu–MgO catalysts. For the preparation of the MgO support, Mg conductivity detector (TCD).
(
NO
3
)
2
Á6H
2
O (Alfa-Aesar, USA, 99%) and K
2
CO
3
(M/s Sd fine-
The total basicity of the catalysts was measured by tempera-
. In a typical experiment,
chem. Ltd., India, 99.5%) were used as a precursor and hydro- ture programmed desorption of CO
2
lyzing agent respectively. Typically, 0.39 M homogeneous aqueous 0.1 g of catalyst was loaded and pretreated in a helium gas flow
À1
salt solutions of magnesium and potassium were prepared using (99.9%, 50 ml min ) at 573 K for 1 h. After pretreatment the
2
deionised water. Both the solutions were mixed slowly under sample was saturated with 10% CO balanced helium at 373 K
vigorous stirring at a constant pH of 9 at room temperature. for 1 h and subsequently flushed with helium gas at the same
The precipitated gel was washed several times with hot water temperature for 1 h to flush off the physisorbed CO . The TPD
2
during separation through filtration under reduced pressure of the catalysts was carried out from 373 K to 1200 K in a
À1
and subsequently, the solid gel was dried at 393 K for 12 h and helium gas flow (99.9%, 30 ml min ) with a temperature ramp
À1
calcined at 723 K for 6 h in static air. The yield of MgO support of 10 K min . The desorbed CO
2
was monitored using GC
so obtained is approximately 91%.
equipped with a thermal conductivity detector (TCD).
Using this MgO as a support a series of four Cu–MgO catalysts
Vapour phase hydrogenation of benzonitrile was carried out
with Cu metal loading of 4, 8, 12 and 16% were prepared by a in a fixed bed glass reactor (11 mm id and 400 mm length) at
facile impregnation method, wherein the requisite amounts of atmospheric pressure in the temperature range of 473–553 K.
Cu (NO ) Á3H O (Sigma-Aldrich, USA, 99.9%) were deposited as In a typical experiment, about 1 g of the catalyst was diluted
3
2
2
an aqueous solution onto the MgO support. The excess water was with quartz grains and loaded into the reactor. Before starting
removed by evaporation followed by drying at 393 K for 12 h and the reaction the catalyst was reduced under H
calcination at 723 K for 6 h in static air. Finally, a portion of all with a flow rate of 30 ml h for 3 h. After reduction, the
2
flow at 553 K
À1
2
the Cu–MgO catalysts were reduced at 553 K under H flow with a reaction temperature was set and benzonitrile was fed at a flow
À1
À1
À1
2
flow rate of 30 ml h for 3 h. Based on the loading of metallic Cu rate of 1 ml h along with H flow of 30 ml min . The product
the catalysts are designated as 4Cu–MgO, 8Cu–MgO, 12Cu–MgO mixture was collected in an ice cold trap periodically every 1 h
and 16Cu–MgO, the prefixed numerical value represents the and analysed by GC 17A (M/s. Shimadzu instruments, Japan)
percentage of Cu loading (by weight) on the MgO support.
equipped with an FID detector using equity-5 capillary column
BET surface area measurements were made on a Quadrusorb-SI (30 ml  0.53 mm id  5 mm df). The analysis of the non-
V 5.06, adsorption unit (M/s. Quantachrome Instruments condensable exit gas mixture was analyzed using GC with TCD
Corporation, USA) by N
out-gassed at 573 K for 4 h before the measurement.
2
adsorption at 77 K. The samples were and it was confirmed that there were no organic species or oxides
of carbon in considerable range. The product components were
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identified by GCMS-QP5050A (M/s. Shimadzu Instruments, Japan)
using a ZB-5 capillary column (30 ml  0.32 mm id  1 mm df).
Results and discussion
The BET surface area of the MgO support and Cu–MgO catalysts
are displayed in Table 1, which reveals that the surface area of
the MgO support is higher compared to its supported Cu
catalysts. In general, the surface area decreases with increase
in metal loading when the catalysts are prepared by an impreg-
2
6
nation method, which is reflected in the present case.
The XRD patterns of Cu–MgO catalysts are depicted in Fig. 1,
wherein, three well resolved XRD reflections are observed at a
2y values of 42.83, 62.13 and 78.451, confirming the presence of
a MgO crystalline phase according to JCPDS card No. 04-829.
The rest of the peaks appeared in all the XRD patterns at
2y values of 43.2, 50.43 and 74.161, revealing the existence of
metallic Cu in accordance with JCPDS-04836. The peak intensity
of metallic Cu increased with increasing Cu loading. No other
copper phases are detected from the XRD analysis.
X-Ray photoelectron spectroscopy (XPS) is one of the impor-
tant techniques to explore the oxidation state of transition metal
compounds that have localized valance d-orbitals because of the
different energies of the photoelectrons. The Cu 2p spectra of
reduced Cu–MgO catalysts prepared with different Cu loading
are shown in Fig. 2 and the related binding energy values of Cu,
Mg and O are listed in Table 2. As is evident from the Cu 2p
Fig. 2 XPS spectra of the reduced Cu–MgO catalysts.
Table 2 Binding energy values of the reduced Cu–MgO catalysts
O 1s
Cu2p3/2
B.E/eV
Cu2p1/2
B.E/eV
Mg 2p
B.E/eV
Catalyst
B.E/eV
B.E/eV
4
8
1
Cu–MgO
Cu–MgO
2Cu–MgO
933.4
933.7
933.6
933.7
952.3
953.3
953.4
954.1
50.9
50.7
51.0
51.1
530.7
530.5
530.4
530.6
532.6
532.5
532.4
532.5
Table 1 BET surface area, average crystallite size and H
2
uptake of Cu–MgO
catalysts
a
c
16Cu–MgO
S
BET
Crystallite
size (nm)
H
2
uptake
2
À1
b
À1
Catalyst
MgO
(m g
)
(mmol g
)
54
48
41
36
25
32.5
11.5
21.3
27.2
33.4
—
spectra (Fig. 2), there are two distinct peaks corresponding to Cu
p3/2 and Cu2p1/2 at 933.4–933.7 eV and 952.3–954.1 eV respec-
4
8
1
1
Cu–MgO
Cu–MgO
2Cu–MgO
6Cu–MgO
45.1
81.7
163.2
301.3
2
tively. Apparently, no shake-up satellite peaks are present in the
Cu 2p range, confirming the absence of Cu and presence of
2+
0
+
a
b
BET surface area determined using N
2
gas as adsorbate. Determined either Cu or Cu species on the catalyst surface, as reported
c
27
0
+
from XRD line broadening. Determined from TPR analysis.
in the literature. However, Cu and Cu species cannot be
distinguished by the binding energy of Cu2p3/2 and Cu2p1/2
because they are almost identical.
,
It is observed that the peak intensities of Cu2p are signifi-
cantly increased with increasing Cu loading. The O1s spectra
showed two bands in the binding range of 530–533 eV for all
the catalysts. The Mg 2p binding energy value was around 51 eV
for all the samples. These XPS results suggest the presence of
0
Cu species on the MgO support in the reduced catalysts.
The reduction behaviour of the catalysts was studied by a well
established temperature programmed reduction (TPR) technique
with molecular hydrogen. The TPR profiles of calcined CuO–MgO
catalysts are shown in Fig. 3, where, a single symmetric reduction
peak is present in each profile, which demonstrate that CuO is
2 2 2
getting reduced by H in a single stage, i.e., CuO + H - Cu + H .
Apart from an increment in the hydrogen consumption with
loading, there is a slight shift in the reduction peak position
towards the higher temperature from 613 to 634 K. The defect
Fig. 1 XRD patterns of reduced Cu–MgO catalysts.
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Table 3 Total basicity of Cu–MgO catalysts from CO
2
-TPD
À1
S. No.
Catalyst
Total basicity (mmol g
)
1
2
3
4
5
MgO
351.2
338.3
329.5
318.2
306.2
4Cu–MgO
8Cu–MgO
12Cu–MgO
16Cu–MgO
Fig. 3 TPR patterns of calcined CuO–MgO catalysts.
sites known to be present in MgO probably contribute to the for-
mation of surface interacting species of copper in the CuO–MgO
catalysts that get reduced at lower temperatures compared to the
reduction of bulk CuO. The observation is in good agreement with
28
Scheme 1 Representation of reaction pathways over Cu–MgO catalysts.
the supported copper catalysts.
Temperature programmed desorption (TPD) of CO
2
is a
common technique to determine the basicity of solid catalysts.
The basicity of the MgO support and its Cu supported catalysts
products dibenzylimine and dibenzylamine are produced. The
reaction pathways are schematically represented in Scheme 1
based on the used reaction parameters.
are obtained by TPD of CO
Fig. 4.
2
and the profiles are displayed in
As shown in Scheme 1, due to the partial reduction of benzo-
nitrile, benzylimine initially produced, which is a key intermediate
According to the TPD profile, it is evident that the MgO
support has various kinds of basic sites such weak, moderate and
strong. As the loading of Cu increases the very weak basic sites
are newly developed and some weak basic sites are decreased and
moderate to strong basic sites are slightly increased.
Table 3, demonstrates that the total basicity of the MgO support
is higher compared all the supported copper catalysts. However,
the strength of the basic sites varied from support to catalysts.
In the gas-phase hydrogenation of benzonitrile over Cu–MgO
catalysts, benzylamine is produced as a main product, and as side
21,29
in the reaction network.
The initially produced benzylimine
readily transforms into benzylamine to some extent based on the
nature of the catalyst and the adapted reaction conditions. As is
noted by several authors, the formation of by-products is a major
30–32
obstacle.
In general, by-product formation occurs through
benzylimine, which undergoes nucleophilic attack on the electron
deficient imine carbon by benzylamine to produce a gem-diamine,
which undergoes either direct hydrogenolysis or elimination
3
of NH followed by hydrogenation to form dibenzylamine via
dibenzyimine. In the present study, considerable amount of
dibenzylamine formation occurred at high residence times. As
reported by several authors, toluene is one of the side products
3
3
in the hydrogenation of benzonitrile, which has been observed
in the product mixture, revealing the absence of hydrogenolysis
of either dibenzylamine or benzylamine over Cu–MgO catalysts
under the operated reaction conditions.
The influence of Cu loading in the gas-phase hydrogenation
of benzonitrile is carried out using different Cu–MgO catalysts
such as 4Cu–MgO, 8Cu–MgO, 12Cu–MgO and 16Cu–MgO with
molecular hydrogen at 473 K at atmospheric pressure. Fig. 5
shows that all the four Cu–MgO catalysts are effective in the
hydrogenation of benzonitrile. It has also been observed that
there is a gradual increase in the activity with increase in
Cu loading up to 12% Cu, i.e., 12Cu–MgO catalyst. Beyond
12% Cu loading, a decrease in activity is observed, which may be
Fig. 4 CO
2
-TPD patterns of Cu–MgO catalysts.
due to presence of larger Cu particles in the 16Cu–MgO catalyst.
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Fig. 5 Influence of Cu loading in Cu–MgO catalysts towards the hydrogenation
À1
of benzonitrile at 473 K with WHSV (weight hourly space velocity) of 1 h
.
Fig. 7 Influence of hydrogen to benzonitrile molar ratio on 12Cu–MgO catalyst
À1
at 513 K with a WHSV of 1 h
.
After realising 12Cu–MgO is the best catalyst in the present
system, further activity studies were made on this catalyst. With
all four catalysts only three products are formed, i.e., benzylamine, is 73% where the selectivities of benzylamine and dibenzyl-
dibenzylimine and dibenzylamine (Scheme 1, conventional amine are 44% and 56% respectively. With an increase in the
hydrogenation).
2
H /benzonitrile ratio, both the conversion of benzonitrile and
To establish the optimum reaction temperature, reactions selectivity of benzylamine are increased up to the ratio of 7.5.
have been carried out at various temperatures, viz., 473, 493, Beyond the ratio of 7.5, a continuous decrease in the conversion
5
13 and 533 K. The initial reaction temperature is 473 K, which of benzonitrile was observed, whereas the selectivity of desired
is just above the boiling point of benzonitrile (B. P. of benzo- primary amine product increased to approximately 100% (Fig. 7).
nitrile is 463 K). The product distribution and the conversion
To find out whether the high selectivity of benzylamine is
of benzonitrile are shown in Fig. 6, which reveals that the due to either the high partial pressure of H or low residence
2
optimum reaction temperature is 513 K, where the conversion time of the feed mixture, an experiment was conducted using
of benzonitrile is 98% with 70% selectivity of benzylamine and nitrogen as a carrier gas. Since the highest conversion is obtained
the selectivity of dibenzylamine is 30%.
at a hydrogen to benzonitrile molar ratio of 7.5, keeping this ratio
The effect of the hydrogen to benzonitrile ratio has been investi- as constant, different amounts of nitrogen were admixed with
gated over the 12Cu–MgO catalyst at 513 K. Stoichiometrically, one the feed (benzonitrile + hydrogen) and the data obtained is
mole of benzylamine is produced from one mole of benzonitrile shown in Fig. 8. Beyond the hydrogen to benzonitrile ratio
and two moles of hydrogen, i.e., C H –CN + 2H - C H –CH –NH . of 7.5, the influence of the hydrogen amount is not as significant.
6
5
2
6
5
2
2
The initial H /benzonitrile molar ratio is 2.5, where the conversion
2
Fig. 6 Influence of reaction temperature over 12%Cu–MgO catalyst in the
Fig. 8 Effect of H
2
dilution with N
2
over 12Cu–MgO catalyst at 513 K with a
À1
À1
hydrogenation of benzonitrile with a WHSV of 1 h
.
WHSV of 1 h
.
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1
6
It seems that the residence time is playing a key role in pressure of 50 bar. 10Pd–C is an important heterogeneous
achieving high selectivity. However, the results reveal that a catalyst from an activity (95% yield) point of view in NaH PO
balance could be struck between the hydrogen to benzonitrile base and DCM–water dual solvent at a hydrogen pressure of
2
4
3
3
ratio and the residence time.
6 bar. Pd–Al O is also a promising catalyst for the selective
2 3
Indeed, the high selectivity (B100%) towards benzylamine hydrogenation of benzonitrile to benzylamine in 2-propanol
through selective hydrogenation of benzonitrile over Cu–MgO solvent with 50% conversion and 95% selectivity of benzylamine
2
1
catalysts at 1 atmospheric pressure with a WHSV (weight hourly under 10 bar H
2
pressure. A Ni–Mo based catalyst exhibited
À1
space velocity) of 1 h is noteworthy example. The residence 100% conversion with a selectivity of 99% in methanol solvent at
3
5
s
time at 513 K (H
2 2
/BN = 7.5) is 4.44 s, where the selectivity of 41 bar H pressure. Similarly, the RANEY Ni catalyst also
benzylamine is about 70%, which is increased to 100% for the exhibited a conversion of 100% with 95% selectivity of primary
3
6
residence time of 2.29 s. From the experimental results pre- amine at a hydrogen pressure of 15 bar. In spite of the high
sented in Fig. 7 and 8, the selectivity of benzylamine is nearly activity, some of these catalysts are homogeneous, expensive,
100% with 50–60% conversion of benzonitrile at 513 K with a require additives and volatile organic solvents and high pressure
residence time of 2.29 s. In the present vapor phase catalytic operations and involve other harsh reaction conditions. Hence,
hydrogenation of benzonitrile, both reactant and products the present Cu–MgO catalyst is expected to be one of the best
reside together on the catalyst surface for a very short time alternatives from an industrial point of view.
(
o5 s), whereas in the liquid phase batch process they are
In order to study the stability of the catalyst, a time-on-stream
À1
together for hours. Due to the short contact time, the primary experiment was conducted at 513 K with a WHSV of 1 h for
amine desorbs from the catalyst surface before interacting with 20 h and found no significant loss in activity as shown in Fig. 9.
the initially formed imine. In other words, the rate of imine
hydrogenation to benzylamine is higher than the condensation
of imine and benzylamine. It is interesting to note that even in
Conclusions
the short residence time the active Cu sites are capable of
catalyzing the benzonitrile towards selective hydrogenation. The
MgO supported Cu catalysts are active not only at lower residence
times but also at lower reaction pressures (atmospheric pressure).
There are several reports regarding high primary amine selectivity
with good to excellent conversions of nitriles. For instance,
Pd–MCM-41, which exhibited superior activity with 90% con-
It can be concluded that the Cu–MgO catalysts are versatile,
inexpensive and efficient for the hydrogenation of benzonitrile
into benzylamine with nearly 100% selectivity even in the absence
of any additives in the gas-phase at 1 atmospheric pressure.
Acknowledgements
version and 91% selectivity of benzylamine at a partial pressure R. K. Marella, K. S. Koppadi and Y. Jyothi are thankful to
3
4
of H
2 2 2 3 3
and CO of 20 and 100 bar respectively. RuCl (PPh ) is Council of Scientific and Industrial Research (CSIR) New Delhi,
one of the highest yielding catalysts with 98% conversion and for awarding research fellowship.
9
8% selectivity of benzylamine in toluene in 24 h under a H
2
1
5
pressure of 50 bar. [Ru(cod)methylallyl
2
]–DPPF is also one of
Notes and references
the most prominent catalysts, showing 99% conversion and 99%
selectivity in t-BuOK base and toluene solvent at a hydrogen
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S. Gomez, J. A. Peters and T. Maschmeyer, Adv. Synth. Catal.,
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6
7
P. N. Rylander, Catalytic Hydrogenation over Platinum Metals,
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Fig. 9 Time-on-stream study over 12Cu–MgO catalyst for the hydrogenation of
À1
benzonitrile at 513 K with a WHSV of 1 h
.
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