One-pot synthesis of 1-butylpyrrolidine and its derivatives from aqueous ammonia and 1,4-butandiol over CuNiPd/ZSM-5 catalysts

Article abstract of DOI:10.1039/d0nj02224a

The synthesis of 1-butylpyrrolidine and its derivatives (1-butylpyrrolidine with a little of 1-butenylpyrrolidines) was developed via a one-pot method from ammonia and 1,4-butandiol. Here, the product of 1-butylpyrrolidine was emphatically investigated, and the yield was 76% under the optimized conditions. Such a route was realized through successive N-alkylation using aqueous ammonia as the nitrogen source over the CuNiPd/ZSM-5 catalyst, which was prepared by a simple incipient wetness method. In this route, 1,4-butandiol not only participated in the formation of the N-heterocycle, but also acted as an alkylating reagent. This work offers a straightforward, economical route for 1-butylpyrrolidine and its derivatives. This journal is

Full text of DOI:10.1039/d0nj02224a

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DOI: 10.1039/D0NJ02224A
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One-pot synthesis of 1-butylpyrrolidine and its derivatives from
aqueous ammonia and 1,4-butandiol over CuNiPd/ZSM-5
catalyst†
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Received 00th January 20xx,
Accepted 00th January 20xx
Yan Longa,b , Shimin Liu a,* , Xiangyuan Ma a, Liujin Lu a, Yude He a, Youquan Deng a,*
DOI: 10.1039/x0xx00000x
employed raw materials are readily available and easy to
handle13-15
In our recent work, the synthesis of 1-
The synthesis of 1-butylpyrrolidine and its derivatives (1-
butylpyrrolidine with a little of 1-butenylpyrrolidines) was
developed via one-pot method from ammonia and 1,4-butandiol.
Here, the product of 1-butylpyrrolidine was emphatically
investigated, and the yield was 76% under optimization
conditions. Such route was realized through successive N-
alkylation using aqueous ammonia as the nitrogen source over
CuNiPd/ZSM-5 catalyst, which was prepared by simple
incipient wetness method. In this route, 1,4-butandiol not only
participated in the formation of N-heterocycle, but also acted as
alkylating reagent. This work offers a straightforward,
economical route for 1-butylpyrrolidine and its derivatives.
.
methylpyrrolidine with >90% yield from BDO and
methylamine via a one-pot method was realized successfully16.
As well known, aqueous ammonia is a more attractive nitrogen
source due to its advantages in safety and handling17, 18. In the
previous report19, 1-BP was obtained from the reaction
between BDO and NH3 over iron catalyst under hydrogen
atmosphere (Scheme 1), and the highest yield of 1-BP was only
38%. It should be noted that 1-BP was not the object of study
in the mentioned reference, which just was one of the products.
The design of catalyst is central to promote 1-BP yields in this
route. As is well known, Cu and Ni based catalysts were very
efficient for the N-alkylation of amines or ammonia with
alcohols 20. However, it was found that some 1-BePs were
generated using our recently developed Cu and Ni modified
ZSM-5 16, which derived from the dehydration of BDO moity
21. 1-BePs are also value-added products, which would be our
next work for synthesis of 1-BePs and this work focuses on 1-
BP. It is an alternative strategy to prompt the yield of 1-BP via
hydrogenation of 1-BePs over a hydrogenation catalyst. It was
reported that Pd based catalysts could facilitate both N-
alkylation and hydrogenation22, 23. Based on the above, a
ternary catalyst (including Pd, Cu and Ni species) supported on
ZSM-5 was further developed, and the catalyst was prepared
by impregnation method (See in SI), which displayed fine
catalytic performance with just low content of Pd (0.2%) for
synthesis of 1-BP.
The optimization of reaction conditions was carried out
carefully, and 76% yield of 1-BP was obtained. There is still 5%
selectivity of 1-BePs in the products, whereas 1-BePs could
convert to 1-BP via further hydrogenation from the view of
practical application. Meanwhile, the relationship between
structure and performance of the prepared catalyst was
preliminarily explored by various characterizations. Therefore,
a simple method for synthesis of 1-BP with good yield was
realized from BDO and NH3 over developed ZSM-5 catalyst in
this work, in which the employed raw materials were much
cheaper than the routes involving pyrrolidine, and the un-green
reagents or by-products were also avoided. Considering the
simple and economical features in this protocol, it has a
promising perspective for industrial application. Besides, it
may provide an alternative method for synthesis of N-
heterocycle derivatives using NH3 as the nitrogen source.
The development of new reaction route for chemicals synthesis,
with more simple, green, and atomic economy features, is
always a central theme in chemistry, and catalysis would play
an important role in this respect. 1-Butylpyrrolidine (1-BP) and
its derivatives (mainly be 1-butenylpyrrolidines, 1-BePs),
could be used as organic intermediates1,2, which also are
important raw materials for the preparation of pyrrolidinium
ionic liquids 3-5. Currently, the traditional synthetic methods for
1-BP and its derivatives mainly include the following
processes: 1) the butylation of pyrrolidine with
halohydrocarbons, butyraldehyde or 1-butanol 1,6-8, 2) the
cyclization of 1,4-dichlorobutane or 1,4-butandiol (BDO) with
6, 9,
1-butylamine
10. However, the above-mentioned routes
often suffer from the high cost of raw materials or
environmental pollution (the previous reported routes for the
synthesis of 1-BP were listed in Table S1). Firstly, both
pyrrolidine and 1-butylamine are relatively expensive raw
materials; secondly, using toxic butyraldehyde as the
butylation reagent is a hazardous threat to the environment and
human health; besides, as butyl halides are involved in the
process, it needs a large amount of NaOH to neutralize the
inorganic acid by-product (HCl or HBr), which would produce
a great deal of waste salts. Herein, we try to develop a simple
and economical route for the synthesis of 1-BP and its
derivatives through a forthright reaction between NH3 and
BDO, and the product 1-BP was emphatically studied.
Ammoniation and cyclization of BDO with amines to
pyrrolidine derivatives with only water by-product could be
considered as an atom-efficient and green route11, 12, and the
Scheme 1 Synthesis of 1-BP from BDO and NH3
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Initially, the catalytic performance of different catalysts
was investigated for the synthesis of 1-BP from BDO and
NH3, and the results were listed in Table 1. It could be seen
that only 8% BDO conversion was obtained in the absence of
catalyst (Entry 1, Table 1), and the support HZSM-5 zeolite
also showed poor catalytic performance with 32% BDO
conversion and 2% 1-BP selectivity (Entry 2, Table 1). As
Cu/ZSM-5 and Ni/ZSM-5 were used, although the conversion
of BDO increased by a large margin, the selectivity of 1-BP
was moderate (22% and 43%, respectively; Entry 3 and 4,
Table 1), and 1-BePs including 1-(3-buten-1-yl)-pyrrolidine
(1-3-BeP) and 1-(2-buten-1-yl)-pyrrolidine (1-2-BeP) were
also formed. While, it was found that full conversion of BDO
was achieved and the selectivity of 1-BP increased to 55%
with the decline of 1-BePs, when both Cu and Ni were
modified on ZSM-5 (Entry 5, Table 1), which implied that the
synergistic effect between Cu and Ni species on ZSM-5
improved the N-alkylation of ammonia with BDO and
enhanced the hydrogenation of 1-BePs to some extent.
Further, the 1-BP selectivity could be up to 76% maintaining
the full conversion of BDO as 0.2wt% Pd was added (Entry 6,
Table 1). It could be seen that 1-BePs declined distinctly, and
the selectivity of 1-3-BeP and 1-2-BeP was 4% and 1%,
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respectively, which meant that PDdOI:s1p0e.1c0i3e9s/D0pNrJo0m22o2t4eAd
hydrogenation. Meanwhile, the total amounts N-substituted
pyrrolidine compounds (including 1-BP and 1-BePs) also
increased, which might imply that the introduction of Pd was
also benefit to the N-alkylation. Next, the effect of Pd loading
was studied. With the increase of the loading of Pd, although
the content of 1-BePs reduced, the selectivity of 1-BP
declined slightly; while 1-propylpyrrolidine (1-PP) and 1-
butanol were raised as the by-products (Entry 7-8, Table 1).
The reason might be due to the catalytic action of excessive
Pd species for the hydrodealkylation of BDO to 1-propanol
(which would react with pyrrolidine to 1-PP) and partial
hydrogenation of BDO to 1-butanol 24, 25. Other zeolites as
carriers were also screened, such as Y or Beta zeolite (Entry
9-10, Table 1), but the catalytic performance was inferior to
ZSM-5 zeolite. Besides, ZSM-5 zeolites with different ratios
of Si/Al were tested (entries 11-12, Table 1). It could be seen
that, as the ratio of Si/Al was 25 and 300, the yield of 1-BP
was 69% and 71 %, respectively, which may mean that ZSM-
5 with an 80 Si/Al ratio provided suitable acidity for this
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process 14
.
Table 1 Catalytic performance of different catalysts a
Selectivity/%
Entry
Catalyst b
Conv./%
1-BP
1-PP
THF
1-Butanol 1-3-BePc 1-2-BePc Othersd
1
2
none
H-ZSM-5
7
32
1
2
99
98
15
7
4
4
2
1
7
2
26
15
13
4
2
2
20
15
4
3
4
5
6
7
8
9
10
11e
12e
3Cu/ZSM-5
3Ni/ZSM-5
3Cu-3Ni/ZSM-5
69
97
22
43
55
76
68
72
50
62
69
71
9
8
4
1
28
27
24
8
10
1
100
100
100
100
100
100
100
100
3Cu-3Ni-0.2Pd/ZSM-5
3Cu-3Ni-0.5Pd/ZSM-5
3Cu-3Ni-1Pd/ZSM-5
3Cu-3Ni-0.2Pd/USY
3Cu-3Ni-0.2Pd/Beta
3Cu-3Ni-0.2Pd/ZSM-5
3Cu-3Ni-0.2Pd/ZSM-5
3
11
10
1
4
7
14
10
2
6
4
2
3
6
4
7
4
11
14
9
3
5
1
8
a Reaction conditions: 0.2mol BDO, 0.1mol NH3 (25wt% aqueous solution), 1.8g catalyst, 300 °C, 4Mpa H2, 4h.
b The catalysts were labeled as xCu-yNi-zPd/ZSM-5 (x, y, z denoted the wt.% of Cu, Ni, Pd to support, respectively.
c 1-BePs including: 1-(3-buten-1-yl)-pyrrolidine (1-3-BeP) and 1-(2-buten-1-yl)-pyrrolidine (1-2-BeP)
d Other by-products including pyrrolidine, 1-propanol, etc.
e Ratio Si/Al of ZSM-5 for Entry 11 and 12 was 25 and 300, respectively.
In order to optimize the reaction conditions for 1-BP, the synthesis of 1-BP under different hydrogen pressure was
effects of different parameters were studied in detail using carried out. When the pressure of H2 varied from 1 MPa to 4
3Cu-3Ni-0.2Pd/ZSM-5 as catalyst, including the ratio of BDO MPa (Entry 3, 7-8, Table 2), the selectivity of 1-BP was
to NH3, reaction atmosphere, pressure and temperature, etc. As elevated from 56% to 76% with the complete conversion of
shown in Table 2, the selectivity of 1-BP increased with the BDO; but the selectivity slightly declined to 65% as the
increase the ratio of BDO to NH3 (Entry1-3, Table 2), and the pressure of H2 increased to 6 Mpa (Entry 9, Table 2), because
highest selectivity could be up to 76% as the BDO: NH3 was the by-products from the hydrodealkylation and hydrogenation
2:1; whereas, the 1-BP content in the products decreased increased under higher hydrogen pressure. Additionally, the
obviously when the ratio of BDO to NH3 was further added to reaction temperature was also optimized for this process (Entry
3:1 (Entry 4, Table 2). The reason was that excessive BDO 2, 10-12, Table 2). When the reaction temperature was 230 °C,
converted to THF smoothly based on the obtained results. Next, only 35% conversion of BDO with 45% selectivity of 1-BP
the influence of reaction atmosphere on performance was was gained. Clearly, both the conversion of BDO and
explored. Using N2 as the reaction atmosphere, only 56% selectivity of 1-BP increased with the temperature rising from
selectivity of 1-BP was obtained (Entry 5, Table 2), while as 250 to 300 °C. The selectivity of 1-BP reached 76% at 300 °C.
the reaction atmosphere was changed to H2, the 1-BP As the temperature continued to be elevated to 330 °C, the
selectivity could be improved significantly (Entry 6, Table 2). content of 1-BP decreased to 61% with more 1-butanol by-
It was found that H2 played a vital role in the reaction, which product. Thus, 1-BP could be yielded via a simple and efficient
was expected to not only maintain the catalyst activity 26, 27, but route from BDO and NH3 over 3Cu-3Ni-0.2Pd/ZSM-5 catalyst
also take part in the hydrogenation of 1-BePs. Also, the at 300 °C for 4 h under a 4 MPa pressure of H2. The reuse
2 | J. Name., 2012, 00, 1‐3
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performance of the 3Cu-3Ni-0.2Pd catalyst was tested in 0002). Besides, the characteristic peak located at V3ie7w°Ar(tJicClePODnliSne:
second run (Entry 13, Table 2), the selectivity of 1-BP dropped 34-1354) and 43° (JCPDS: 47-1049) was assigned to Cu O
DOI: 10.1039/D0NJ02224A
2
dramatically, which might be due to the catalyst structure was (111) and NiO (200) facets, respectively, and the results were
destroyed during the reaction process. But the result was still consistent with XPS analyses. Moreover, there was no evident
better than that of the previous report (38% yield).17
diffraction pattern for Pd species, which might suggest that Pd
species were amorphous or highly dispersed in the catalyst. For
the used catalyst, it was found that the intensity of peak for
ZSM-5 support became weaker, while the intensity of peak for
NiO (200) facets strengthened, which might mean that the
structure of the zeolites was destroyed partly during the
reaction and the NiO particles agglomerated on the surface of
the molecular sieve. The change of the catalyst was one of the
reasons for deactivation of the catalyst in the reuse process.
High-resolution transmission electron microscopy (HRTEM)
gave the information about morphology and distributions of the
active species on the surface of catalyst. From the HRTEM
image of 3Cu-3Ni-0.2Pd/ZSM-5 (Fig. 2a), the lattice fringes
spacing of 0.24 and 0.21 nm matched well with the Cu2O (111)
and NiO (200) facets, respectively, which was in accordance
with the XRD results according to the corresponding PDF cards
(JCPDS: 34-1354, JCPDS: 47-1049). And no detectable lattice
fringe for Pd species in the HRTEM image. EDX mapping (Fig.
2b) was conducted to identify the distribution of the elements.
The visual inspection of map revealed that Cu, Ni and Pd
species clearly overlapped, which indicated that the metal
species were uniformly distributed in the catalyst.
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Table 2 Optimization of the reaction conditions for 1-BP
Reaction Conv. Sel.
Entry
T/°C
BDO : NH3
atmosphere
4 Mpa H2
4 Mpa H2
4 Mpa H2
4 Mpa H2
4 Mpa N2
4 Mpa H2
1 Mpa H2
2 Mpa H2
6 Mpa H2
4 Mpa H2
4 Mpa H2
4 Mpa H2
4 Mpa H2
/%
35
/%
45
15
26
38
56
76
59
69
65
61
58
52
63
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
2
3
4
5
6
7
8
9
10
11
12
13*
300
300
300
300
300
300
300
300
300
330
270
250
300
1
1
2
3
2
2
2
2
2
2
2
2
2
：
：
：
：
：
：
：
：
：
：
：
：
：
2
1
1
1
1
1
1
1
1
1
1
1
1
100
100
100
100
100
100
100
100
100
81
50
100
Reaction conditions: 1.8g catalyst, 0.2mol BDO, 4h, * 2nd run.
To understand the relationship between catalytic
performance and the catalyst properties, the prepared catalysts
were characterized by several analytical techniques. Firstly, the
contents of Cu, Ni and Pd in the catalysts were determined by
atomic absorption spectroscopy (AAS, Table S2). It could be
seen that the contents of Cu, Ni and Pd were very close to their
theoretical values in all samples. For the 3Cu-3Ni-0.2Pd/ZSM-
5, the loading of Cu, Ni and Pd was 2.91%, 2.88% and 0.19%
respectively. The loss of Cu and Ni could be detected after use
(especially for Cu), but the loss of Pd was not obvious. The Cu
loss was likely due to its stronger coordination ability with NH3.
Thus, the loss of metal species may be one of the reasons for
the decrease of catalyst activity after use. The X-ray
photoelectron spectroscopy (XPS) studies on the catalyst (3Cu-
3Ni-0.2Pd/ZSM-5) were performed to examine the chemical
state of active species (Cu, Ni and Pd). As shown in Table S3,
the presence of Cu2O and NiO could be revealed by XPS
analyses, the corresponding binding energy of Cu 2p3/2 and Ni
2p3/2 was 932.8 and 855.8 eV, respectively. In addition, the
peak appearing at 336.2 eV for Pd 3d5/2 was detected by XPS
technique, revealing that PdO formed on the surface of the
developed catalyst.
(a)
(b)
Fig.1. XRD patterns of fresh and used catalysts
The XRD of fresh and used 3Cu-3Ni-0.2Pd/ZSM-5 catalysts
were illustrated in Fig. 1. The diffraction peaks at 8, 8.9, 14.8
and 23° could be attributable to ZSM-5 support (JCPDS: 44-
Fig.2. (a) HRTEM image and (b) EDX mapping of 3Cu-3Ni-
0.2Pd/ZSM-5
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Scheme 2 (a) Synthesis of 1-BP from pyrrolidine and BDO, (b)
possible route for 1-BP from NH3 and BDO
It has been proved that Ni and Cu species displayed excellent
catalytic activation in the N-alkylation reaction12. Meanwhile,
Pd species were effective for both hydrogenation and N-
alkylation of amines and alcohols 13, which was also embodied
in this work. And ZSM-5 support might provide appropriate
acid-based environment and pore structure 7, 14. In this work,
the reducing ambient, introduction of Pd and high dispersion of
metals might be conducive to the fine catalytic performance.
Besides, a reference reaction of pyrrolidine with BDO was
tested under the optimized conditions, and a similar yield (74%)
of 1-BP was achieved (Scheme 2a). According to the obtained
results, a possible reaction process was speculated (Scheme 2b),
namely, pyrrolidine formed firstly through twice N-alkylation
between BDO and NH3 in the presence of ternary catalyst; then
BDO as an alkylating agent reacted with the resulted
pyrrolidine via another N-alkylation and followed by
dehydration to generate 1-BePs21; finally, the product 1-BP was
obtained after a hydrogenation from 1-BePs. The study on
catalytic mechanism of the composite catalyst for this route
should be our next work.
In conclusion, the catalytic synthesis of 1-BP and its
derivatives was realized using BDO and aqueous ammonia as
the raw materials, and the product of 1-BP was emphatically
studied. BDO acted as a part of the ring skeleton and the
alkylating reagent. The Cu, Ni, and Pd modified ZSM-5
catalyst showed the best catalytic performance, and 76% yield
of 1-BP with 5% yield of 1-BePs was obtained under
optimization conditions. The preparation of the ternary metals
modified catalyst could be carried out by simple impregnation
method. It was found that the H2 atmosphere, introduction of Pd
and high dispersion of metals were contributed to the fine
catalytic performance. This work provides a promising method
with simple and economical characteristics for catalytic
synthesis of 1-BP and its derivatives.
This work was financially supported by National Key
Research and Development Program of China (No.
2017YFA0403101) and the National Natural Science 25. F. Liguori and P. Barbaro, J. Catal., 2014, 311, 212‐220.
Foundation of China (No. 21761132014).
26. A. Baiker and J. Kijenski, Cataly Rev, 2006, 27, 653‐697.
27. M. H. S. A. Hamid, P. A. Slatford and J. M. J. Williams, Adv.
Synth. Catal., 2007, 349, 1555‐1575.
Conflicts of interest
There are no conflicts to declare.
Notes and references
4 | J. Name., 2012, 00, 1‐3
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