Liquid-phase hydroamination of cyclohexanone

Article abstract of DOI:10.1007/s11172-010-0330-x

Activity and selectivity of supported Ni, Pt, and Pd catalysts were studied in the liquidphase reductive amination of cyclohexanone at temperatures ranging from 100 to 150 °C. The catalyst 20% Ni/SiO₂ is most active and selective providing a maximum yield of cyclohexylamine. The influence of the reaction conditions on the parameters of the catalytic process was studied. A detailed analysis of the reaction products was carried out using ¹³C NMR spectroscopy and gas chromatography coupled with mass spectrometry (GC-MS). This made it possible to refine the reaction mechanism and to identify a new by-product earlier unknown in the literature.

Full text of DOI:10.1007/s11172-010-0330-x

Russian Chemical Bulletin, International Edition, Vol. 59, No. 10, pp. 1896—1901, October, 2010
1896
Liquidꢀphase hydroamination of cyclohexanone
D. P. Ivanov, K. A. Dubkov, D. E. Babushkin, L. V. Pirutko, and S. V. Semikolenov
G. K. Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences,
5 prosp. Akad. Lavrent´eva, 630090 Novosibirsk, Russian Federation.
Fax: +7 (383) 330 8056. Eꢀmail: dubkov@catalysis.ru
Activity and selectivity of supported Ni, Pt, and Pd catalysts were studied in the liquidꢀ
phase reductive amination of cyclohexanone at temperatures ranging from 100 to 150 °C. The
catalyst 20% Ni/SiO2 is most active and selective providing a maximum yield of cyclohexylꢀ
amine. The influence of the reaction conditions on the parameters of the catalytic process was
studied. A detailed analysis of the reaction products was carried out using 13C NMR spectroscoꢀ
py and gas chromatography coupled with mass spectrometry (GCꢀMS). This made it possible
to refine the reaction mechanism and to identify a new byꢀproduct earlier unknown in the
literature.
Key words: amination, reductive amination, cyclohexanone, cyclohexylamine.
The annual worldwide demand for cyclohexylamine
ate primary imine, which is further hydrogenated on the
catalyst to form primary amine. In turn, the primary amine
can react with ketone to form secondary imine, whose
hydrogenation gives secondary amine. Such side reactions
as the hydrogenation of ketone and its aldol condensation
can also occur during hydroamination.7,8
stands at several thousands tonnes1 and, hence, it is an
important product of modern largeꢀscale chemistry. The
main methods for its production are the hydrogenation of
aniline and reductive amination (hydroamination) of
cyclohexanone.1—4
Carbonyl compounds are hydroaminated by ammonia
and hydrogen in the presence of hydrogenation catalysts,
among which the catalysts based on nickel and platinum
group metals are used most frequently.4 This reaction was
first carried out in the liquid phase at room temperature
and atmospheric pressure on the nickel and copper cataꢀ
lysts.5 Higher yields of amines were obtained by using
Raney nickel at elevated hydrogen pressure (20—150 atm)
and 40—150 °С (see Ref. 6). Further investigations showed
that this reaction can be carried out in the liquid or gas
phase in the presence of massive metal and supported hetꢀ
erogeneous hydrogenation catalysts based on transition
metals Ni, Co, and Fe or platinum group metals.3,4,7—9
The synthesis of primary amines is complicated by the
formation of secondary and tertiary amines. The product
distribution can depend on the catalyst nature, the ratio of
a carbonyl compound and ammonia, and other reaction
conditions. For instance, the liquidꢀphase hydroaminaꢀ
tion of cyclohexanone by ammonia in the presence of the
nickel catalysts leads to predominant formation of cycloꢀ
hexylamine, whereas secondary amine is the major prodꢀ
uct in the case of the platinum catalysts.4,7,10,11 The nickꢀ
el catalysts are considered to be most available and effiꢀ
cient for cyclohexylamine production.4,7
It is of certain interest to use in this reaction supported
catalysts having a more developed surface (compared to
bulky catalysts) but containing a smaller amount of metal.
The purpose of this work is to study the activity and selecꢀ
tivity of a series of supported catalysts based on Ni, Pt,
and Pd in the liquidꢀphase hydroamination of cycloꢀ
hexanone and to reveal specific features of the reaction
mechanism.
Experimental
The study was carried out in the presence of the following
supported catalysts: 3% Pt/SiO2, 3% Ni/SiO2, 4% Pd/Al2O3, and
20% Ni/SiO2.
Catalyst 3% Pt/SiO2 was prepared by the adsorption impregꢀ
nation of SiO2 (Ssp = 300 m2 g–1, Vpore = 1.1 cm3 g–1) with
an aqueousꢀammonia solution of H2PtCl6 for 20 h. Catalyst
4% Pd/Al2O3 was prepared by the impregnation to incipient wetꢀ
ness of γꢀAl2O3 (Ssp = 250 m2 g–1, Vpore = 0.4 cm3 g–1) with
a solution of Pd(NO3)2. After preparation the catalysts were
dried for 12 h at room temperature and then for 12 h at 110 °С,
after which they were calcined in an air flow for 4 h at 300 °С.
Catalysts 3% Ni/SiO2 and 20% Ni/SiO2 were prepared using the
coprecipitation method by the consecutive impregnation of SiO2
with solutions of nickel nitrate and ammonium carbonate, storꢀ
ing the suspension formed for 1 h at 80 °С. After drying, the
catalysts were calcined in an air flow for 2 h at 200 °С. Then the
Ni and Pd catalysts were reduced for 2 h in an Н2 flow at 450 and
300 °С, respectively.
According to the commonly accepted mechanism of
ketone hydroamination,2,4,7,8,12,13 at the first nonꢀcataꢀ
lytic step ammonia reacts with ketone to form intermediꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1846—1851, October, 2010.
1066ꢀ5285/10/5910ꢀ1896 © 2010 Springer Science+Business Media, Inc.

Liquidꢀphase hydroamination of cyclohexanone
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 10, October, 2010
1897
Cyclohexanone (1) was hydroaminated in a 25ꢀcm3 highꢀ
pressure steel reactor (Parr) according to the following proceꢀ
dure. A catalyst (0.01—0.2 g) was loaded into the reactor. Prior
to the reaction, the Ni and Pd catalysts were subjected to an
additional reductive treatment in the reactor at 250 °C and 50 atm
for 2 h. After the end of reduction, the reactor was evacuated
with a fore pump and a solution containing cyclohexanone (1)
(0.02 mol) and a solvent (10 mL) was pumped into the reactor.
This procedure excludes contact of the reduced catalyst and air
oxygen. Catalyst 2% Pt/SiO2 was used without the additional
treatment in the reactor. After solutions were loaded, the reactor
was evacuated for 30 s and ammonia (0.06 mol) was fed with
stirring (300 rpm). Then the reactor was fed with hydrogen
(0.04 mol) to the pressure about 50 atm. The reactor was heated
with a rate of 6 °C min–1 to 100—150 °C and stored for a speciꢀ
fied time. After the end of experiment, the reactor was cooled to
room temperature and the pressure was slowly dropped. The
resultant solution was separated from the catalyst and analyzed
by gas chromatography (GC) on a Kristall 2000 chromatograph
using a capillary column (diameter 0.2 mm, length 50 m, phase
SЕꢀ50) and a flameꢀionization detector. An analysis was carried
out in the temperatureꢀprogrammed regime from 50 to 250 °С
with a rate of 3 °С min–1. The temperature of the injection port
was 270 °С. Calibration solutions of the corresponding comꢀ
pounds were used for the identification of the major products
and determination of their concentration. The data obtained
were used to calculate the conversion of cyclohexanone (1) and
selectivity of formation of the reaction products.
a
b
4
4
4
2
3
1
3
2
1
2
58 56 54 52 50
42 40 38 36
δ
Fig. 1. a. Chemical shifts of carbon atoms in the 13C NMR
spectra for compounds 1—4. b. The 13C NMR spectra of
the reaction mixtures after cyclohexanone conversion in the
presence of 3% Pt/SiO2 (1) and after the addition of cycloꢀ
hexanone (2).
The structures of products were additionally refined by
13С NMR spectroscopy (Bruker AVANCEꢀ400, working freꢀ
quency 100.61 MHz) and GCꢀMS (Varian Saturn 2000). 13C NMR
spectra were recorded at room temperature. The procedure of
recording inverseꢀgated decoupling (IGATED) spectra with long
delays between pulses (30—60 s) for complete 13C nuclei relaxꢀ
ation was used for quantitative measurements. The concentraꢀ
tions of the products calculated from the GC and NMR data
showed good correspondence within 5 rel.%.
The GC and GCꢀMS analyses of the liquid phase after
the reaction show three major products (Table 1): primary
amine, cyclohexylamine (2, m/z = 99); secondary amine,
dicyclohexylamine (3, m/z = 181); and secondary imine,
Nꢀcyclohexylidenecyclohexylamine (4, m/z = 179). The
13С NMR spectrum of the reaction mixture exhibits sigꢀ
nals indicating the presence of compounds 1—4 (Fig. 1
and Table 1, entry 1).
Results and Discussion
Identification of products and the reaction mechanism.
Several experiments at 150 °С in the presence of catalyst
3% Pt/SiO2 were carried out for the reliable identification
of products of reductive amination of cyclohexanone.
To reveal whether secondary imine 4 is the final reacꢀ
tion product or not, a small amount of cyclohexanone
(0.005 mol) was added to the reaction mixture at room
temperature. As can be seen from the 13С NMR spectra
a
Table 1. Hydroamination of cyclohexanone (1) in the presence of 3% Pt/SiO2
Entry
Catalyst
amount/g
t/h
Conversion of 1
X (%)
Composition of productsb
(mol.%)
Selectivity
(mol.%)
2
3
4
5c
2
3
6
1
2
3
4
0.05
0.05
0.05
0.20
1
3
6
4
23.4
58.3
73.0
24.5
22.1
20.6
63.5
5.6
15.7
26.5
36.2
66.1
58.8
51.7
0.0
3.8
3.5
1.2
0.3
90.6
80.9
72.3
63.5
5.6
15.7
26.5
36.2
3.8
3.4
1.2
0.3
100.0
a Reaction conditions: 1 (0.03 mol), NH3 (0.06 mol), H2 (0.04 mol), decane (10 mL) as solvent, 150 °C.
b According to the gas chromatography data.
c Three products with M = 177.

1898
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 10, October, 2010
Ivanov et al.
(see Fig. 1, b), after the addition of 1 the intensity of
signals of cyclohexylamine 2 decreases and that of secꢀ
ondary imine 4 increased, while the intensity of signals of
dicyclohexylamine 3 remained unchanged. This indicates
that 4 is formed by the nonꢀcatalytic reaction of cycloꢀ
hexanone (1) with cyclohexylamine (2) even at room temꢀ
perature (Scheme 1).
amplified by the value of concentration of 4 according to
the reaction stoichiometry (see Scheme 1).
According to chromatographic analysis data, the final
reaction mixture contains additional three products in
a minor concentration. The GCꢀMS data show that they
have the same molecular weight (M = 177) and, obviously,
are isomers of the same compound (compound 5, see
Table 1 and Scheme 2). However, the 13C NMR analysis
of the solutions at room temperature does not detect these
products. In this case, only one byꢀproduct, which we
named the adduct (compound 6) is observed along with
major products 2—4. It is most likely that products 5 are
formed due to the decomposition and subsequent isomerꢀ
ization of adduct 6 in the injection port of the chromatoꢀ
graph at 270 °C.
Scheme 1
To reveal the mechanism of formation of adduct 6, we
carried out the reaction without a catalyst at 100 °С for 1 h
at the same reactant load as in the catalytic reaction
(0.03 mole of cyclohexanone (1), 0.06 mole of NH3,
0.04 mole of H2). In this case, the conversion of 1 was 4%
and adduct 6 was the single reaction product. The strucꢀ
ture of earlier unknown compound 6 was elucidated by
13C NMR spectroscopy of the reaction mixture obtained.
An additional experiment with pure reactants 1 and 2
confirmed that the reaction occurs under normal condiꢀ
tions and its equilibrium shifts to the right as the temperaꢀ
ture decreases.
It is evident that secondary imine 4 is not the final
reaction product but is formed on cooling of the reaction
mixture (see Scheme 1). Indeed, imine 4 is observed by
analysis only in products of incomplete ketone conversion
(see Table 1, entries 1—3) when cyclohexanone (1) and
cyclohexylamine (2) are simultaneously present in the
solution. Only primary and secondary amines are the
products of complete ketone conversion (see Table 1,
entry 4).
According to the common hydroamination mechaꢀ
nism,2,4,7,8,12 the catalytic hydrogenation of secondary
imine affords secondary amine. Thus, under the reaction
conditions, secondary imine 4 is but an intermediate.
Therefore, for the calculation of the conversion of ketone
and selectivity for final products (see Table 1), the conꢀ
centrations of 1 and 2 determined by GC analysis were
δ (CH2)
δ (CH2)
C
C
21.70
29.22
29.47
35.81
38.95
26.61
36.69
40.81
42.84
22.03
22.87
23.00
26.79
26.84
The obtained results suggest that adduct 6 is formed
via the nonꢀcatalytic route from cyclohexanone 1 and
Scheme 2
5 (3 isomers, M = 177)

Liquidꢀphase hydroamination of cyclohexanone
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 10, October, 2010
1899
ammonia. The probable mechanism of its formation inꢀ
cludes the following consecutive steps (Scheme 2): formaꢀ
tion of primary imine, cyclohexylideneamine (7), through
the interaction of cyclohexanone (1) with ammonia
(step (1)); condensation of two molecules 7 with proton
elimination (steps (2) and (3)); rearrangement of the prodꢀ
uct and proton addition (steps (4) and (5)); and condenꢀ
sation of the product with cyclohexanone to form adduct
6 (step (6)). The adduct undergoes thermal destruction
(step (7)) during chromatographic analysis of the reaction
mixture to give three isomers of compound 5.
The data in Table 1 show that the content of 6 in the
products decreases with the conversion of cyclohexanone
1. This indicates that adduct 6 is consumed in the reacꢀ
tion, i.e., the steps of its formation should be reversible
(see Scheme 2).
Based on the common mechanism and the study perꢀ
formed, the main chemical transformations occurring
upon hydroamination of cyclohexanone 1 can be presentꢀ
ed in the simplified form by Scheme 3. This scheme inꢀ
cludes the addition of ammonia to cyclohexanone (1) to
form primary imine 7 (reaction (1.1)), catalytic hydrogeꢀ
nation of 7 to cyclohexylamine (2) (reaction (1.2)), interꢀ
action of cyclohexanone (1) with 2 to form secondary
imine 4 (reaction (2.1)), catalytic hydrogenation of 4 to
dicyclohexylamine 3 (reaction (2.2)), and condensation
of cyclohexanone (1) and NH3 to form 6 (reaction (3)).
Effect of the catalyst nature. The data on the effect of
the catalyst nature on the selectivity of the reaction at the
complete cyclohexanone conversion are presented in
Table 2. The reaction was carried out for a fairy long time
(3 h) using a larger amount of the catalyst (0.2 g). Note that
in the case of the catalyst 3% Ni/SiO2, which exhibited
the lowest activity, the reaction time was elongated to 6 h
(see Table 2, entry 1) to achieve the complete conversion.
In the presence of the both nickel catalysts, the major
reaction product is cyclohexylamine 2, whose selectivity
of formation exceeds 99%. In the case of 4% Pd/Al2O3
and 3% Pt/SiO2, the selectivity for 2 is lower (80.8 and
64.5%, respectively) due to the additional formation of
a considerable amount of secondary amine 3. This result
agrees with the previous studies, which showed that priꢀ
mary amines were the major products of hydroamination
of carbonyl compounds in the presence of the nickelꢀconꢀ
taining catalysts.4,7
The data on the catalyst activity at a moderate converꢀ
sion of cyclohexanone are listed in Table 3. The moderate
cyclohexanone conversion is achieved due to a decrease
in the amount of the catalyst used (0.01 g) and the reacꢀ
tion time (1 h). Under these conditions, the catalysts
20% Ni/SiO2, 4% Pd/Al2O3, and 3% Pt/SiO2 showed simꢀ
ilar levels of conversion (X) and, correspondingly, activity.
The selectivity for primary amine in the presence of
20% Ni/SiO2 (98.4%, see Table 3) is close to that obꢀ
served at the full conversion (see Table 2). A considerable
amount of secondary amine is formed on the catalysts
4% Pd/Al2O3 and 3% Pt/SiO2 under the conditions of both
moderate and full conversion.
Scheme 3
In the case of 3% Ni/SiO2 and loading a fivefold larger
amount of the catalyst (0.05 g), the conversion of cycloꢀ
hexanone (1) is only 15.8%. Thus, this catalyst is apꢀ
proximately an order of magnitude less active than
20% Ni/SiO2 (X = 29.1%), which is evidently due to the
lower content of active metal.
The results show that on all catalysts the reaction proꢀ
ceeds via the common mechanism (see Scheme 3) to form
Table 2. Effect of the catalyst nature on the selectivity of
hydroamination at the complete conversion of cycloꢀ
hexanone (1)a
Cat is catalyst
Entry
Catalyst
Selectivity (mol.%)
Primary imine 7 was not observed by analysis of the
reaction mixtures, which indicates its instability. Accordꢀ
ing to the literature data,4,7,8 secondary imine can be
formed not only by the interaction of ketone with primary
amine but also by the addition of primary amine to primaꢀ
ry imine followed by the elimination of an NH3 molecule.
In an ammonia excess, the probability of this route is low.
Secondary amine can interact with ketone to yield tertiary
amine; however, this product is not formed under the conꢀ
ditions used.
2
3
6
b
1
2
3
4
3% Ni/SiO2
99.2
99.7
80.8
64.5
0.2
0.2
19.0
35.2
0.6
0.1
0.2
0.3
20% Ni/SiO2
4% Pd/Al2O3
3% Pt/SiO2
a Reaction conditions: 1 (0.02 mol), NH3 (0.06 mol),
H2 (0.04 mol), THF (10 mL) as solvent, catalyst amount
0.2 g, 150 °С, 3 h.
b The reaction time was 6 h.

1900
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 10, October, 2010
Ivanov et al.
Table 3. Activity of the catalysts in the hydroamination of cycloꢀ
hexanone (1)a
tivity for primary amine is also higher (98.4—98.8%). Preꢀ
sumably, this is due to a higher solubility of ammonia in
polar solvents compared to nonpolar solvents. As the NH3
concentration in the liquid phase increases, the rate of
reaction (1.2) (see Scheme 3) should increase because the
shift of equilibrium of stage (1.1) toward the formation of
imine 7. An increase in the NH3 concentration should
also suppress the formation of dicyclohexylamine (3), since
it favors the predominant interaction of cyclohexanone (1)
with ammonia (reaction (1.1)) rather than with cycloꢀ
hexylamine (2) (reaction (2.1)).
The highest values of conversion of 1 and selectivity of
formation of 2 are achieved in 1,4ꢀdioxane. A molecule of
1,4ꢀdioxane contains one oxygen atom more than a THF
molecule, which probably facilitates more efficient coꢀ
ordination interaction of NH3 molecules with solvent
molecules.
Entry
Catalyst
Conversion
Selectivity (mol.%)
of 1, X (%)
2
3
6
b
1
2
3
4
3% Ni/SiO2
15.8
29.1
18.6
27.0
95.7
98.4
70.9
85.1
0.3
0.4
26.9
13.3
4.0
1.2
2.2
1.6
20% Ni/SiO2
4% Pd/Al2O3
3% Pt/SiO2
a Reaction conditions: 1 (0.02 mol), NH3 (0.06 mol), H2
(0.04 mol), THF (10 mL) as solvent, catalyst weight 0.01 g,
150 °С, 1 h.
b The catalyst amount was 0.05 g.
the same products, whose ratio depends on the catalyst
nature and reaction conditions.
Effect of the temperature and the ammonia : cycloꢀ
hexanone ratio. The data on the temperature effect on the
reaction parameters in THF in the presence of catalyst
20% Ni/SiO2 are given in Table 5. As the temperature
increases from 100 to 150 °С, the conversion of cycloꢀ
hexanone 1 increases from 20.4 to 71.7%. In all cases, the
selectivity for primary amine exceeds 99%.
The data on the effect of the ratio NH3 : 1 on the reacꢀ
tion parameters at 125 °С (Table 6) indicate that with
a decrease in an ammonia excess from 10 : 1 to 3 : 1 the
cyclohexanone conversion increases from 31.7 to 46.3%,
the selectivity for primary amine 2 remains at a level of
99.2—99.5%, and the fraction of dicyclohexylamine 4 in
the products increases slightly. The fraction of adduct 6
decreases from 0.8 to 0.3%, which agrees with the mechaꢀ
nism of its formation (see Scheme 2), because an increase
in the amount of NH3 should shift the equilibrium to the
formation of adduct 6.
Catalyst 20% Ni/SiO2 is one of the most active in the
series studied. In addition, regardless of conversion, in the
presence of this catalyst cyclohexanone (1) almost excluꢀ
sively transforms into cyclohexylamine (2), whereas diꢀ
cyclohexylamine (3) and adduct 6 are formed in trace
amounts. Therefore, the influence of the reaction condiꢀ
tions on the parameters of the process was studied on this
catalyst.
Solvent effect. The results of cyclohexanone hydroamꢀ
ination in various solvents at 150 °С in the presence of the
catalyst 20% Ni/SiO2, which were obtained at moderate
ketone conversion, are presented in Table 4. It is seen that
the solvent nature affects the reaction parameters. In nonꢀ
polar solvents (benzene, cyclohexane, and decane) the seꢀ
lectivity for primary amine is 95.2—97.5% at the cycloꢀ
hexanone conversion 23.8—25.6%. The lower selectivity
in decane is due to the formation of a comparatively large
amount of adduct 6 (4.5%). The reason for such an effect
of decane is unclear, because all these solvents are similar
in nature (see Table 4).
As the ratio NH3 : 1 further decreases to the stoichioꢀ
metric value (1 : 1), the conversion remains nearly unꢀ
changed but the selectivity for primary amine decreases to
97.5% due to an increase in the fraction of dicyclohexylꢀ
amine 3 to 2.2%. According to the reaction mechanism
(see Scheme 3), a decrease in the amount of NH3 should
In polar solvents, in THF, and especially in 1,4ꢀdioxꢀ
ane, the conversion is higher (29.1 and 40.8%, respectively)
than that in nonpolar solvents. In these solvents the selecꢀ
Table 4. Solvent effect on the hydroamination of cyclohexanone
(1) in the presence of 20% Ni/SiO2*
Table 5. Temperature effect on the hydroamination of cycloꢀ
hexanone (1) in the presence of 20% Ni/SiO2*
Entry
Solvent
Conversion
Selectivity (mol.%)
of 1, X (%)
Entry Temperaꢀ Conversion
Selectivity (mol.%)
2
3
6
ture/°C
of 1, X (%)
2
3
6
1
2
3
4
5
Benzene
Cyclohexane
Decane
THF
1,4ꢀDioxane
23.8
24.0
25.6
29.1
40.8
97.5
97.4
95.2
98.4
98.8
0.6
0.5
0.3
0.4
0.5
1.9
2.1
4.5
1.2
0.7
1
2
3
100
125
150
20.4
38.6
71.7
99.1
99.5
99.7
0.0
0.1
0.1
0.9
0.4
0.2
* Reaction conditions: 1 (0.01 mol), NH3 (0.06 mol), H2
(0.04 mol), THF (10 mL) as solvent, catalyst amount 0.01 g;
the reaction time was 1 h.
* Reaction conditions: 1 (0.02 mol), NH3 (0.06 mol), H2
(0.04 mol), solvent (10 mL), catalyst amount 0.01 g, 150 °С, 1 h.

Liquidꢀphase hydroamination of cyclohexanone
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 10, October, 2010
1901
Table 6. Effect of the ammonia amount on the hydroamination of cyclohexanone (1) in the presence
of 20% Ni/SiO2*
Entry
Amount of NH3 NH3 : 1
Conversion of 1,
X (%)
Selectivity (mol.%)
/mol
2
3
6
1
2
3
4
0.10
0.06
0.03
0.01
10 : 1
6 : 1
3 : 1
1 : 1
31.7
38.6
46.3
46.6
99.2
99.5
99.5
97.5
0.0
0.1
0.2
2.2
0.8
0.4
0.3
0.3
* Reaction conditions: 1 (0.01 mol), H2 (0.04 mol), THF (10 mL) as solvent, catalyst amount 0.01 g,
125 °С, 1 h.
5. Pat. FR 529159, 24.11.1921.
6. E. D. Schwoegler, H. Adkins, J. Am. Chem. Soc., 1939,
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7. M. B. Klyuev, M. L. Khidekel´, Usp. Khim., 1980, 49, 28
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increase, in fact, the contribution of step (2.1) leading to
the formation of imine 4, whose hydrogenation gives
dicyclohexylamine (3). The decrease in the conversion
with an increase in the ammonia amount can be due to
a decrease in the rate of hydrogenation step (2.2) because
of the competitive adsorption of NH3 and primary amine
on the catalyst surface.
Thus, the results obtained in this work show that a twoꢀ
to threefold excess of ammonia is sufficient to provide the
maximum yield of primary amine in a wide range of
hydroamination conditions.
10. A. Skita, F. Keil, Ber. Dtsch. Chem. Ges., 1928, 61, 1682.
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Received December 11, 2009;
in revised form August 2, 2010