Colloid and Nanosized Catalysts in Organic Synthesis: XVIII.1 Disproportionation and Cross-Coupling of Amines During Catalysis with Immobilized Nickel Nanoparticles

Article abstract of DOI:10.1134/S1070363217120015

It has been stated that immobilized nickel nanoparticles catalyze disproportionation and cross-coupling of amines. The influence of the support on the catalysis of these properties in the in plug-flow reactor has been studied. The use of active carbon as the support has been found advantageous for the cross-coupling of amines, whereas alumina was a better support for the disproportionation reaction.

Full text of DOI:10.1134/S1070363217120015

ISSN 1070-3632, Russian Journal of General Chemistry, 2017, Vol. 87, No. 12, pp. 2757–2761. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © Yu.V. Popov, V.M. Mokhov, S.E. Latyshova, D.N. Nebykov, A.O. Panov, T.M. Davydova, 2017, published in Zhurnal Obshchei
Khimii, 2017, Vol. 87, No. 12, pp. 1937–1941.
Colloid and Nanosized Catalysts in Organic Synthesis:
XVIII.1 Disproportionation and Cross-Coupling of Amines
During Catalysis with Immobilized Nickel Nanoparticles
Yu. V. Popov*, V. M. Mokhov, S. E. Latyshova, D. N. Nebykov,
A. O. Panov, and T. M. Davydova
Volgograd State Technical University, pr. Lenina 28, Volgograd, 400131 Russia
*e-mail: tons@vstu.ru
Received June 15, 2017
Abstract―It has been stated that immobilized nickel nanoparticles catalyze disproportionation and cross-
coupling of amines. The influence of the support on the catalysis of these properties in the in plug-flow reactor
has been studied. The use of active carbon as the support has been found advantageous for the cross-coupling
of amines, whereas alumina was a better support for the disproportionation reaction.
Keywords: catalysis, nanoparticles, nickel, immobilized catalysts, amines, cross-coupling, disproportionation
DOI: 10.1134/S1070363217120015
Disproportionation and cross-coupling reactions are
among the most promising approaches to prepare
symmetrical secondary and non-symmetrical tertiary
amines. Disproportionation of primary amines affords
symmetrical N,N-dialkylamines, and cross-coupling of
different amines gives di- and trialkylamines with
different hydrocarbon groups at the nitrogen atom.
However, the use of such reactions for the formation of
new С–N bond has been scarcely discussed in the
literature. For example, cross-coupling of amines using
metal complex iridium catalyst has been studied [2].
The interaction of various amines with 4-methoxy-
aniline at 155°С during 10 h has been considered; the
highest product yield (of 90%) has been found in the
reaction with a secondary amine (diisopropylamine).
Metal nanoparticles immobilized on a support can
accelerate the processes of substituted amines prepara-
tion via cross-coupling as well. For example, platinum
nanoparticles applied onto γ-alumina (particles size
0.8 nm) have been used; the yield of the product in the
reaction of aniline with diisopropylamine has reached
93% [7].
This study aimed to elaborate the catalysts of
disproportionation and cross-coupling of amines.
Nickel nanoparticles immobilized on different supports
were used as the catalyst. The effect of the support
nature on the conversion of the amines and the
reactions selectivity was studied using γ-Al2O3, active
carbon (BAU-A), and aluminosilicate cracking catalyst
(Ceokar-2).
The use of nanosized catalysts allows the synthesis
of amines (for example, via the Leuckart–Wallach
reaction [3] catalyzed by copper nanoparticles or
alkylation of amines with alcohols in the presence of
cobalt and nickel nanoparticles [4–6]) under milder
conditions. However, the longer duration and the
complex procedure of the catalyst regeneration make
the colloidal catalysts less efficient as compared with
the heterogeneous ones.
The catalysts were prepared via impregnation of the
solid supports (1–1.5 mm fraction) with a solution of
nickel(II) chloride, filtration, and washing with
distilled water, followed by the treatment with aqueous
solution of sodium borohydride. A humid catalyst was
loaded into the reactor and dried in a hydrogen stream
immediately prior to the reaction [8].
The catalysts surface was studied by means of
scanning electron microscopy. We have earlier shown
[1, 9] that the supports surface contains the large
(about 1 µm) nickel aggregates as well as smaller (30–
1
For communication XVII, see [1].
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POPOV et al.
Scheme 1.
R1
R2
NH2
NH2
R1
R2
R1
R2
R1
R2
R1
R2
H
NH2
1a_1c
NH
N
_H2
R1
R1
R2
R1
R2
R1
R2
H2
H
N
N
_NH3
R2
3a_3c
R1,R2 = (CH2)5 (a); R1 = H (b, c), R2 = C6H5 (b), CH3(CH2)4 (c).
Scheme 2.
H2, Nio/Cact
NH3
+
+
H3C
NH2
H3C
NH2
H3C
N
CH3
1 atm, 190οС
H
3d
1d
2а
100 nm) particles. The catalyst surface contains about
5–7 wt% of nickel.
To elaborate the method of synthesis of non-
symmetrical di- and trialkylamines, we investigated
the reaction of cross-coupling of amines. The reactions
were performed at 160–200°С, the feeding rate of the
Disproportionation of amines was performed
according to Scheme 1.
–1
starting amines 0.9–3.6 L kgcat h–1 using alumina,
The process was performed at 200–230°С, the
feeding rate of the starting amines was of 0.9 L kgcat–1 h–1
when using alumina or Ceokar-2 as the supports or
3.6 L kgcat–1 h–1 in the case of active carbon. Hydrogen
(0.5 L/h) was used as the diluent.
Ceokar-2, or active carbon as the catalyst support.
Hydrogen feeding rate was of 0.5 L/h.
We studied the reaction of cross-coupling of
n-octylamine 1d and n-butylamine 2a (Scheme 2) over
temperature range 160–200°С using the Ni0/Сact catalyst.
Cyclohexylamine 1a and benzylamine 1b were
used as the primary amines in the investigation of
disproportionation catalyzed by nickel nanoparticles
immobilized on active carbon. The target products
(dialkylamines 3a–3c) yield did not exceed 32%. For
example, conversion of amine 1a 96%, but further
transformation of the product in phenylcyclohexyl-
amine due to aromatization of the cyclohexane ring
reduced the reaction selectivity.
We found that amine 2a was less reactive than
amine 1d. On top of the target product (n-octyl-n-
butylamine 3d, yield 28%), the side reaction gave di-1-
octylamine (40%), whereas tri-n-butylamine was
formed in the yield as low as 14.5%, despite the use of
fivefold excess of the starting amine 2a. Di-n-
butylamine was not detected in the reaction mixture.
Since cyclic secondary amines did not undergo
disproportionation under the process conditions, the
reactions could be performed in their excess to
suppress the disproportionation of the starting primary
amines. That reaction could be used for the preparation
of widely used non-symmetrical tertiary amines. It was
found that the optimal ratio between the primary and
the secondary amines was of 1 : (10–15).
Disproportionation of n-hexylamine 1c into di-n-
hexylamine 3c was chosen for comprehensive
investigation of the effect of the nickel nanoparticles
support nature. The conversion of the starting amine
equaled 10 and 64% when using the Ni0/Сact and
Ni0/Ceokar-2 catalysts, respectively, the selectivity of
the main reaction being 55 and 69%. The best results
were obtained when the reaction was performed in the
presence of the Ni0/Al2O3 catalyst: conversion of
amine 1c 95% and selectivity of the target reaction
90%. The yield of dialkylamine 3c was 88%.
The first stage of the suggested cross-coupling
transformations could be dehydrogenation of the
primary amine into aldimine (Scheme 3), followed by
the condensation of the imine with the secondary
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COLLOID AND NANOSIZED CATALYSTS IN ORGANIC SYNTHESIS: XVIII.
2759
Scheme 3.
R3
NH2
R3
R1
R2
R1
R2
R1
R2
HN
NH2
1a_1d
NH
R3
N
_H2
2b_2d
R3
R1
R2
R1
R2
H2
N
N
_NH3
3e_m
R1,R2 = (CH2)5 (1a, 3e, 3g), R1 = H (1b, 1d, 3f–3l), R2 = CH3(CH2)6 (1d, 3f, 3h, 3m), C6H5 (1b, 3i, 3j), CH3(CH2)4 (1c, 3k,
3m), R3 = –CH2CH2– (2b, 3e, 3f, 3i), –CH2O– (2c, 3g, 3h, 3k), –CH2– (2d, 3l, 3m).
amine to form the aminal further eliminating the
ammonia molecule. The formed enamine was
hydrogenated by hydrogen adsorbed on the catalyst
surface to afford the non-symmetrical tertiary amine.
In summary, we found that nickel nanoparticles
immobilized on active carbon, alumina, or
aluminosilicate support were catalytically active in the
reactions of disproportionation and cross-coupling of
amines. The experimental data revealed that the
Ni0/Сact catalyst was more efficient in the cross-
coupling that in the disproportionation of primary
amines, whereas the Ni0/Al2O3 catalyst was more
efficient in the disproportionation reaction.
Cross-coupling in the presence of nickel
nanoparticles on active carbon (Ni0/Cact) was studied
using primary amines 1a, 1b, and 1d as well as
piperidine 2b and morpholine 2c as the substrates. The
reactions were performed at 160–180°С under
atmospheric pressure. The yield of the target products
was 62–86%. In the synthesis of N-cyclohexylpiperidine
3e, the conversion of the primary amine was 85%,
whereas in other cases, the conversion reached 98–
99% with the selectivity of the main reaction 74–92%.
EXPERIMENTAL
Chromato–mass spectral analysis was performed
using a Saturn 2100 T/GC3900 instrument (EI, 70 eV).
Quantitative GLC analysis of the reaction mixtures
was performed using
a
Kristallyuks-4000M
Cross-coupling in the presence of nickel nano-
particles on alumina (Ni0/Al2O3) was studied using
amines 1c, 1d, 2c, and pyrrolidine 2d as the substrates.
The yield of the target products 3j–3l was 15, 5, and
28%, respectively, with the low conversion of the
substrates.
chromatograph (tstart = 100–210°С, tevaporator = 250°С,
polar column HP-5, l = 50 m, d = 0.32 mm, nitrogen as
support gas, flame ionization detector, tdetector = 250°C,
acetonitrile as solvent). Scanning electron microscopy
studies were performed using an FEI Versa 3D
DualBeam instrument (working distance 10 mm, ETD
secondary electrons detector, CBS backscattered
electrons detector, EDS for elemental analysis).
Cross-coupling of primary amine 1d and secondary
amine 2d in the presence of the catalyst supported by
Ceokar-2 gave N-octylpyrrolidine 3m in 61% yield,
the conversion of the primary amine being almost
complete, and the selectivity of the main reaction
being 56%. Di-n-octylamine and tri-n-octylamine were
formed in 22 and 16% yield, respectively, were formed
via the side disproportionation reactions.
Catalyst preparation. The support portion (2 g of
γ-Al2O3 or Ceokar-2 or 0.5 g of active carbon BAU-A)
was kept during 1 day in an aqueous solution of nickel
chloride prepared by dissolving 0.5 g of NiCl2·6H2O in
4 mL of water. The impregnated support was filter off
and washed with water. Reduction with NaBH4 was
performed by adding the reductant portionwise (3×0.1 g
with 2 min waiting) at room temperature.
The study of cross-coupling between primary and
secondary amines in the presence of immobilized
nickel nanoparticles revealed the effect of the support
nature on the substrates conversion and the products
yield. The side products were symmetrical dialkyl-
amines formed via the disproportionation of the
starting primary amines.
Cross-coupling and disproportionation. The
reactions were performed in a flow-through reactor at
atmospheric pressure and temperature 160–230°С. The
reduced humid catalyst was loaded in the reactor
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POPOV et al.
between the glass layers of the nozzle and dried in a
hydrogen stream at 120°С prior to the reaction. The
laboratory-grade reaction was a 12Kh18N10T steel
tube (inner diameter 9 mm) put in an electric oven
(heating zone height 50 mm). Temperature in the
reactor was measured using a thermocouple. Hydrogen
feed was adjusted using a GV-7 hydrogen generator.
The feeding rate of the starting amines was 0.9 and
octylamine. Mass spectrum, m/e (Irel, %): 242.2 (10)
[M + 1], 199 (14), 198.1 (100), 156.2 (12), 142.1 (60),
100.0 (71), 58.0 (51). Tri-1-butylamine. Mass
spectrum, m/e (Irel, %): 143.0 (10), 142.0 (100), 100.0
(82), 58.1 (52), 44.1 (9).
Cross-coupling of cyclohexylamine 1a and pi-
peridine 2b was performed in the presence of 0.5 g of
Ni0/Сact at 160°С and molar ratio 1a : 2b = 1 : 10.
Conversion of amine 1a 85%, selectivity with respect
to N-cyclohexylpiperidine 3e 74%. 62% of N-cyclo-
hexylpiperidine 3e and 26.3% of dicyclohexylamine
were obtained. N-Cyclohexylpiperidine (3e). Mass
spectrum, m/e (Irel, %): 167.0 (12) [M], 125.0 (9),
124.0 (100), 96.0 (8). Dicyclohexylamine. Mass
spectrum, m/e (Irel, %): 182.0 (13) [M + 1], 181.0 (12)
[M], 138.0 (100), 56.0 (28), 55.0 (9).
–1
3.6 L kgcat–1 h–1 and that of hydrogen was 0.5 L h–1 gcat
at atmospheric pressure.
Disproportionation of cyclohexylamine 1a was
performed in the presence of 0.5 g of Ni0/Сact at 230°С.
Conversion of amine 1a 96%, selectivity with respect
to dicyclohexylamine 3a 35%, yield 32%. Mass
spectrum, m/e (Irel, %): 182.9 (8) [M + 2], 182.0 (73)
[M + 1], 181.0 (14) [M], 138.9 (10), 138.0 (100), 56.0
(31), 55 (10). Selectivity with respect to phenyl-
cyclohexylamine 54%, yield 50%.
Cross-coupling of octylamine 1d and piperidine
2b was performed in the presence of 0.5 g of Ni0/Сact
at 180°С and molar ratio 1d : 2b = 1 : 10. Conversion
of amine 1d 99%, selectivity with respect to N-octyl-
piperidine 3f 81%, yield 75%. Mass spectrum, m/e (Irel,
%): 198.0 (10) [M + 1], 99.0 (7), 98.1 (100).
Disproportionation of benzylamine 1b was
performed in the presence of 0.5 g of Ni0/Сact at 200°С.
Conversion of amine 1c 70%, selectivity with respect
to dibenzylamine 3b 64%, yield 25%. Mass spectrum,
m/e (Irel, %): 197.9 (18) [M + 1], 197.0 (8) [M], 196.0
(25) [M – 1], 105.9 (72), 91.9 (14), 91.0 (100), 77.0
(10), 65.0 (21).
Cross-coupling of cyclohexylamine 1a and mor-
pholine 2c was performed in the presence of 0.5 g of
Ni0/Сact at 180°С and molar ratio 1a : 2c = 1 : 10.
Conversion of amine 1a 99%, selectivity with respect
to N-cyclohexylmorpholine 3g 88%. 86% of N-cyclo-
hexylmorpholine 3g and 18% of dicyclohexylamine
were obtained. Mass spectrum, m/e (Irel, %): 182.0 (26)
[M + 1], 181.0 (14) [M], 139.0 (10), 138.0 (100), 56.1
(29), 55.0 (9).
Disproportionation of 1-hexylamine 1c. a. The
process was performed in the presence of 0.5 g of
Ni0/Сact at 200°С. Conversion of amine 1c 10%,
selectivity with respect to dihexylamine 3c 55%, yield
6%. Mass spectrum, m/e (Irel, %): 186.0 (10) [M + 1],
113.8 (59), 44.0 (100), 43.0 (10), 41.0 (11).
b. The process was performed in the presence of 0.5 g
of Ni0/Ceokar-2 at 200°С. Conversion of amine 1c
64%, selectivity with respect to dihexylamine 3c 69%,
yield 19%.
Cross-coupling of octylamine 1d and morpholine
2c. a. The process was performed in the presence of
0.5 g of Ni0/Сact at 180°С and molar ratio 1d : 2c =
1 : 10. Conversion of amine 1d 99%, selectivity with
respect to N-1-octylmorpholine 3h 82%. 81% of N-1-
octylmorpholine 3h and 18% of di-1-octylamine were
obtained. Mass spectrum, m/e (Irel, %): 200.1 (16) [M +
1], 101.0 (6), 100.0 (100), 70.2 (6).
c. The process was performed in the presence of
0.5 g of Ni0/Al2O3 at 200°С. Conversion of amine 1c
95%, selectivity with respect to dihexylamine 3c 90%,
yield 88%.
b. The process was performed in the presence of
0.5 g of Ni0/Al2O3 and 200°С molar ratio 1d : 2c =
1 : 10. Conversion of amine 1d 6%, selectivity with
respect to N-1-octylmorpholine 3h 71%, yield 5%.
Cross-coupling of 1-octylamine 1d and 1-butyl-
amine 2a was performed in the presence of 0.5 g of
Ni0/Сact at 190°С and molar ratio 1d : 2a = 1 : 10.
Conversion of octylamine 99%, сselectivity with
respect to 1-octyl-1-butylamine 3d 29%. 28% of
1-octyl-1-butylamine 3d, 40.3% of di-1-octylamine,
and 14.5% of tri-1-butylamine were obtained. 1-Octyl-
1-butylamine (3d). Mass spectrum, m/e (Irel, %): 187.1
(13) [M + 2], 186.2 (100) [M + 1], 44.1 (46). Di-1-
Cross-coupling of benzylamine 1b and piperidine
2b was performed in the presence of 0.5 g of Ni0/Сact
at 190°С and molar ratio 1b : 2b = 1 : 10. Conversion
of amine 1b 98.5%, selectivity with respect to
N-benzylpiperidine 3i 80%. 79% of N-benzylpiperidine
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COLLOID AND NANOSIZED CATALYSTS IN ORGANIC SYNTHESIS: XVIII.
2761
3i and 21% of dibenzylamine 3b were obtained. Mass
spectrum, m/e (Irel, %): 175.9 (12) [M + 1], 175.0 (52)
[M], 174.0 (100) [M – 1], 98.1 (45), 92.0 (9), 91.1
(100), 84.1 (33), 65.0 (20), 42.0 (12).
of tri-n-octylamine were obtained. N-n-Octyl-
pyrrolidine (3m). Mass spectrum, m/e (Irel, %): 185.1
(1) [M + 2], 184.2 (8) [M + 1], 182.0 (3) [M – 1], 84.0
(100), 42.0 (8). Tri-n-octylamine. Mass spectrum, m/e
(Irel, %): 354.4 (2) [M + 1], 353.3 (2) [M], 352.5 (5)
[M – 1], 255.3 (21), 254.5 (100), 156.3 (14), 58.1 (16).
Cross-coupling of benzylamine 1b and mor-
pholine 2c was performed in the presence of 0.5 g of
Ni0/Сact at 185°С and molar ratio 1b : 2c = 1 : 10.
Conversion of amine 1b 99%, selectivity with respect
to N-benzylmorpholine 3j 75%. 74% of N-benzyl-
morpholine 3j and 6.7% of dibenzylamine 3b were
obtained. Mass spectrum, m/e (Irel, %): 178.0 (8) [M +
1], 176.9 (42) [M], 176.0 (16) [M – 1], 146.0 (35), 91.9
(10), 91.0 (100), 86.0 (35), 65.1 (18).
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Cross-coupling of hexylamine 1c and pyrrolidine
2d was performed in the presence of 0.5 g of
Ni0/Al2O3 at 180°С and molar ratio 1c : 2d = 1 : 10.
Conversion of amine 1c 86%, selectivity with respect
to N-n-hexylpyrrolidine 3l 74%. 14% of N-n-hexyl-
pyrrolidine 3l and 5% of di-1-hexylamine were ob-
tained. Mass spectrum, m/e (Irel, %): 155.1 (3) [M],
154.0 (25) [M – 1], 152.8 (15) [M – 2], 152.1 (10)
[M – 3], 110.0 (100), 96.2 (5).
Cross-coupling of octylamine 1d and pyrrolidine
2d was performed in the presence of 0.5 g of
Ni0/Ceokar-2 at 180°С and molar ratio 1d : 2d =
1 : 10. Conversion of amine 1d 99%, selectivity with
respect to N-n-octylpyrrolidine 3m 56%. 61% of N-n-
octylpyrrolidine 3m, 22% of di-n-octylamine, and 16%
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 12 2017