One-pot synthesis of: N -substituted pyrroles from nitro compounds and 2,5-hexadione over a heterogeneous cobalt catalyst

Article abstract of DOI:10.1039/c7nj01898c

In this study, the one-pot heterocyclization of nitro compounds with 2,5-hexadione was studied for the synthesis of N-substituted pyrroles via a Paal-Knorr condensation process. The heterogeneous cobalt-nitrogen catalyst (Co-N_x/C-800-AT) was found to be active for this reaction with formic acid. Formic acid served as a hydrogen donor for the transfer hydrogenation, and also acted as an acid catalyst. More importantly, this method was tolerant of other functional groups, and hence various N-substituted pyrroles were produced with good to excellent yields. The Co-N_x/C-800-AT catalyst was highly stable, and could be reused several times without loss of its catalytic activity.

Full text of DOI:10.1039/c7nj01898c

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Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
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One-pot synthesis of N-substituted pyrroles from nitro
compounds and 2,5-hexadione over a heterogeneous cobalt
catalyst
Zheng Gong, Yu Lei, Peng Zhou, Zehui Zhang*,
Key Laboratory of Catalysis and Materials Sciences of the Ministry of Education,
South-Central University for Nationalities, Wuhan, 430074, P. R. China.
*Tel.: +86ꢀ27ꢀ67842572. Fax: +86ꢀ27ꢀ67842572. Eꢀmail: zehuizh@mail.ustc.edu.cn
Abstract: In this study, the oneꢀpot heterocyclization of nitro compounds with
2,5ꢀhexadione was studied for the synthesis of Nꢀsubstituted pyrroles via a Paal–
Knorr condensation process. The heterogeneous cobaltꢀnitrogen catalyst
(CoꢀNx/Cꢀ800ꢀAT) was found to be active for this reaction with formic acid. Formic
acid served as a hydrogen donor for the transfer hydrogenation, and also acted as an
acid catalyst. More importantly, this method was tolerant to other functional groups,
and hence various Nꢀsubstituted pyrroles were produced with good to excellent yields.
The CoꢀNx/Cꢀ800ꢀAT catalyst was highly stable, and could be reused for several times
without the loss of its catalytic activity.
Keywords: Nitro compounds; 2,5ꢀHexadione; Pyrroles; Paal–Knorr condensation;
Transfer hydrogenation
1

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Introduction
The pyrrole ring is one kind of the most important heterocycles, which have been
found to be useful in many fields [1ꢀ4]. Compounds with pyrrole rings are present in a
variety of natural and biologically important molecules such as porphyrins,
coꢀenzymes, bile pigments and alkaloids [5]. In addition, pyrroles have also been
found to be useful in other areas [6]. For example, polypyrroles can be used as
conducting materials in the preparation of electroluminescence devices [7], while
pyrrolic macrocycles have been used as anion receptors [8, 9]. Due to the significant
importance of the pyrrole ringꢀcontaining chemicals, the interest in the synthesis of
pyrrole compounds has increased in recent years [10ꢀ12].
Various methods have been developed to synthesize pyrroles, including Hantzsch
synthesis [13], tandem reaction [14], rearrangement of oꢀvinyl oximes [15], [3 + 2]
cycloaddition of 1,3ꢀdipolar reagents with alkynes [16], hydroamination of diynes
[17], and olefin crossꢀmetathesis [18]. Among them, the PaalꢀKnorr condensation of
primary amines with 1,4ꢀdicarbonyl precursors has been considered one of the most
attractive and effective methods for the synthesis of pyrroles [19ꢀ23]. The PaalꢀKnorr
reaction involves the condensation of a 1,4ꢀdicarbonyl compound with a primary
amine, which is promoted by the acid catalysts. Therefore, many kinds of acid
catalysts including Brønsted acids and Lewis acids have been used for the synthesis of
pyrroles via PaalꢀKnorr reactions.
In modern organic synthesis, the oneꢀpot reaction strategy has received particular
interest since they are more sustainable process by integrating several steps in the
same reaction vessel [24, 25]. Obviously, the oneꢀpot reaction strategy is much more
sustainable, which avoids the intermediate separation, purifications steps, and
minimizing energy cost. As primary amines can be produced from the hydrogenation
2

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of nitro compounds in the presences of acid catalyst, it is highly desirable to perform
oneꢀpot the synthesis of Nꢀsubstituted pyrroles directly from nitro compounds and
1,4ꢀdicarbonyl compounds, which involves the hydrogenation of nitro compounds
into primary amines and the subsequent PaalꢀKnorr condensation reaction.
However, the one tandem process for the synthesis of Nꢀsubstituted pyrroles
starting from nitro compounds and 1,4ꢀdicarbonyl compounds have rarely been
studied [21ꢀ23]. One of the possible reasons should be the side reactions. For example,
the possible hydrogenation of the carbonyl groups to the alcohol would impede the
formation of the intermediate hemiaminal [26]. In addition, there is also a risk that the
pyrrole ring can also be reduced. To date, there are fewer examples on the oneꢀpot
synthesis of pyrroles [21ꢀ23]. For example, the indiumꢀmediated reductive
[22ꢀ23]
heterocyclization was reported for the oneꢀpot synthesis of pyrrole compounds
.
In these catalytic systems, a large amount (5 equiv.) of indium was used as the
reducing agent to promote the transformation of nitroarenes to the primary amines. In
addition, 10 equiv. of acetic acid was used as the acid catalysts for the PaalꢀKnorr
condensation reaction. Obviously, these methods demonstrated several drawbacks
such as the high cost of the reducing agent, the difficulty in the purification of the
product, and the generation of large amounts of waste. Later, the oneꢀpot catalytic
synthesis of pyrrole compounds with H2 as the reducing agent has been reported over
the noble metal catalysts [21]. However, the use of noble metal catalysts also made
this method less competitive due to the high cost of these catalysts. Herein, it is still
highly desirable to develop new catalytic routes for the effective oneꢀpot synthesis of
pyrrole compounds in an environmentallyꢀfriendly way.
In recent years, great effort has been devoted to screen earth abundant transition
metals as alternatives to noble metal catalysts for organic transformations [27, 28]. In
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our recent work, nitrogenꢀdoped carbon based cobalt catalyst (CoꢀNx/Cꢀ800ꢀAT) was
observed to be highly active for the reduction of nitro compounds into primary amines
with formic acid as the hydrogen donor [29]. The CoꢀNx/Cꢀ800ꢀAT catalyst with high
activity was prepared by the pyrolysis of cobalt phthalocyanineꢀsilica colloids
composites and the subsequent removal of silica template and cobalt nanoparticles, in
which the active site was identified to be cobaltꢀnitrogen complex (CoꢀNx). Therefore,
it is anticipated that this catalyst should be active for the oneꢀpot transformation of
nitro compounds and 1,4ꢀdicarbonyl compounds into pyrrole compounds with formic
acid as the hydrogen donor and the acid catalyst.
Results and discussion
Optimal
reaction
conditions
for
the
one-pot
synthesis
of
2,5-dimethyl-1-phenylpyrrole
In our recent work, nitrogenꢀdoped carbon based cobalt catalyst
(CoꢀNx/Cꢀ800ꢀAT) was discovered to be highly active for the reduction of nitro
compounds into primary amines either with H2 or with formic acid as the
hydrogen donor [29]. The CoꢀNx/Cꢀ800ꢀAT catalyst with a high activity was
prepared by the pyrolysis of cobalt phthalocyanineꢀsilica colloids composites
and the subsequent removal of silica template and cobalt nanoparticles, in
which the active site was identified to be cobaltꢀnitrogen complex (CoꢀNx). In
continuous interest in the synthesis of nitrogenꢀcontaining chemicals, we
anticipated to perform the synthesis of nitrogenꢀsubstituted pyrroles via the
oneꢀpot heterocyclization of various nitro compounds with 2,5ꢀhexadione. Firstly, the
effect of the reaction solvents was studied by the use of oneꢀpot reaction of
nitrobenzene with 2,5ꢀhexadione as the model reaction, and the results are shown in
Table 1. Although nitrobenzene was fully consumed for all tested solvents, the
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selectivity of the aim product 2,5ꢀdimethylꢀ1ꢀphenylpyrrole was greatly affected by
the reaction solvents. For example, no desirable product of
2,5ꢀdimethylꢀ1ꢀphenylpyrrole was observed when the reaction was performed in
N,Nꢀdimethylformamide (DMF) with high polarity and high boiling point (Table 1,
Entry 1). Low selectivity of 2,5ꢀdimethylꢀ1ꢀphenylpyrrole was observed in the
solvents such as tetrahydrofuran (THF), acetone, ethyl acetate and water (Table 1,
Entries 2~5). Moderate selectivity of the 2,5ꢀdimethylꢀ1ꢀphenylpyrrole product was
observed in acetonitrile (Table 1, Entry 6). Ethanol and toluene were found to be the
best solvent for this reaction, which produced 2,5ꢀdimethylꢀ1ꢀphenylpyrrole with the
highest selectivity of 89.8% (Table 1, Entries 7 & 8). The huge difference in the
products distribution should be caused by the different properties of the solvents, as
different solvents bears different properties such as acidicꢀbasic properties, polarity
and boiling points. As far as the influence of the reaction solvents on this reaction, the
reasons seem to be complex. One possible reason should be that different solvents
have different abilities to stabilize aniline or 2,5ꢀhexadione either by the van der
Waals force or hydrogen bonding. Another possible reason should be that different
solvents might have different abilities to coordinate with the cobalt sites of the
catalysts, thus lowering the catalyst. For example, the lowest selectivty of
2,5ꢀdimethylꢀ1ꢀphenylpyrrole in DMF should be possibly caused by the above two
reasons. On the one hand, DMF with nitrogen atoms can coordinate with the active
sites of cobalt atoms in the CoꢀNx/Cꢀ800ꢀAT catalyst. On the other hand, DMF should
also have the ability to stablize the intermediate (aniline), thus preventing the
subsequent reaction.
Table 1. The oneꢀpot heterocyclization of nitrobenzene with 2,5ꢀhexadione in
different solvents.
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Yield (%)
Conversion
(%)
Entry
Solvent
DMF
1
2
1
2
3
4
5
6
7
8
100
100
100
100
0
THF
90.7
76.7
73.7
69.4
46.4
10.2
12.3
9.3
Acetone
23.3
26.3
30.6
53.6
89.8
87.7
Ethyl acetate
H2O
100
100
100
100
100
Acetonitrile
Ethanol
Toluene
a Reaction conditions: nitrobenzene (1 mmol), 2,5ꢀhexadione (1.2 mmol), solvent (10
mL), CoꢀNx/Cꢀ800ꢀAT catalyst (40 mg), formic acid (4.5 mmol), temperature (110 oC)
and 10 h.
Secondly, the effect of the reaction temperature on the oneꢀpot heterocyclization of
nitrobenzene with 2,5ꢀhexadione was studied. Interestingly, it was observed that the
reaction was sensitive to the reaction temperature. The conversion of nitrobenzene
was noted to increase with the increase of the reaction temperature. For example,
o
o
nitrobenzene conversion increased from 28.1% at 50 C to 100% at 70 C after 12 h.
The increase of nitrobenzene conversion with an elevated temperature should be
caused by the fact that a higher reaction temperature accelerates the contact of the
reaction molecules, and hence increases the reaction rate. It should be pointed out that
our catalytic system could be performed under very mild conditions at a low
o
temperature of 50 C. A low reaction temperature was preferable in sustainable and
industrial chemistry, as the low reaction temperature makes the reaction process much
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safer and more energyꢀsaving. As far as the yield of 2,5ꢀdimethylꢀ1ꢀphenylpyrrole, it
initially increased with the increase of the reaction temperature from 50 oC to 110 oC.
However, further increasing the reaction temperature resulted in a decrease in the
yield of 2,5ꢀdimethylꢀ1ꢀphenylpyrrole. The possible reason should be that the
formation of intermediates proposed in Figure 3 in the condensation of aniline with
2,5ꢀhexadione was reversible, and a higher reaction temperature (beyond 110 oC) was
not beneficial for their formation. Therefore, the best reaction temperature for the
oneꢀpot heterocyclization of nitrobenzene with 2,5ꢀhexadione was 110 oC.
Conversion
Yield of aniline
Yield of pyrrole
100
80
60
40
20
0
40
60
80
100
120
140
Temperature (oC)
Fig. 1 The effect of the reaction temperature on the oneꢀpot heterocyclization of
a
nitrobenzene with 2,5ꢀhexadione. Reaction conditions: nitrobenzene (1 mmol),
2,5ꢀhexadione (1.2 mmol), ethanol (10 mL), CoꢀNx/Cꢀ800ꢀAT catalyst (40 mg),
formic acid (4.5 mmol), and 10 h.
Reaction pathway for the one-pot heterocyclization of nitrobenzene with
2,5-hexadione
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Aniline
Nitrobenzene
2,5-dimethyl-1-phenylpyrrole
100
80
60
40
20
0
0
2
4
6
8
10
12
Time (h)
Fig. 2 Time course of the products distribution during the oneꢀpot synthesis of
a
2,5ꢀdimethylꢀ1ꢀphenylpyrrole.
Reaction conditions: nitrobenzene (1 mmol),
2,5ꢀhexadione (1.2 mmol), ethanol (10 mL), CoꢀNx/Cꢀ800ꢀAT catalyst (40 mg),
formic acid (4.5 mmol), and 12 h.
To elucidate the reaction pathway clearly, the time course of products distribution
was recorded during the reaction process of the oneꢀpot reaction of nitrobenzene and
2,5ꢀhexadione. As listed in Fig. 2, the transfer hydrogenation of nitrobenzene was a
very fast step. Nitrobenzene conversion reached 45.1% in the first hour, and then it
gradually increased. Full nitrobenzene conversion reached after 12 h. Then, the
formed aniline reacted with 2,5ꢀhexadione through Paal–Knorr condensation to
release the water with the assist of formic acid as the acid catalyst. It reached the
highest yield of 29.2% after 2 h. As shown in Fig. 2, it was observed that the Paal–
Knorr condensation was a slow step, and the yield of 2,5ꢀdimethylꢀ1ꢀphenylpyrrole
sharply increased to 40.5% after 2 h, which was due to the high concentration of
aniline and 2,5ꢀhexadione at the early reaction stage. From 2 h to 12 h, the yield of
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aniline slowly decreased, while the yield of 2,5ꢀdimethylꢀ1ꢀphenylpyrrole slowly
increased. After 12 h, 2,5ꢀdimethylꢀ1ꢀphenylpyrrole was produced in a high yield of
95.2%. However, aniline was still remained in reaction mixture with a little yield of
2.8%.
Although an actual mechanism of the oneꢀpot synthesis of
2,5ꢀdimethylꢀ1ꢀphenylpyrrole via heterocyclization of nitrobenzene with
2,5ꢀhexadione is unclear.
A possible mechanism for the formation of
2,5ꢀdimethylꢀ1ꢀphenylpyrrole was proposed and shown in Fig. 3. Firstly, nitrobenzene
was reduced to aniline via transfer hydrogenation of formic acid over the
CoꢀNx/Cꢀ800ꢀAT catalyst. Then, the carbonyl groups of the 2,5ꢀhexadione is activated
by protons to give the intermediate 1 in Fig. 3. Therefore, the protonated carbon atom
in 2,5ꢀhexanedione in the intermediate 1 became more positive charged and made it
easier to be attacked by the loneꢀpair electron of nitrogen atoms in primary amine,
affording intermediate 2. Following a similar process in which another carbon atom of
the carbonyl groups was attacked by loneꢀpair electron of nitrogen as described in the
intermediate 1, which was further converted into the product 5 by releasing two
molecular water and catalyst.
Fig. 3 Scheme illustration of the oneꢀpot synthesis of
2,5ꢀdimethylꢀ1ꢀphenylpyrrole from nitro compounds and with 2,5ꢀhexadione.
Substrate scope for the one-pot synthesis of N-substituted pyrroles
o
With the optimal reaction conditions (110 C) in hand, the general scope of the
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developed method for the heterocyclizations of variously substituted nitrobenzenes
with 2,5ꢀhexadione was examined. As shown in Table 2, the oneꢀpot
heterocyclizations of nitro compounds with 2,5ꢀhexadione occurred successfully,
affording the corresponding Nꢀsubstituted pyrroles with high to excellent yields.
Firstly, various kinds of nitro compounds were studied for this reaction (Table 2). It
was noted that the electronic nature of the substituted groups showed no significant
influence on the catalytic activity of nitro compounds for the synthesis of
Nꢀsubstituted pyrroles. Nitrobenzene substituted with electronꢀdonating or
ꢀwithdrawing groups produced the corresponding Nꢀsubstituted pyrroles with
excellent yields via the oneꢀpot heterocyclizations with 2,5ꢀhexadione after 12 h at
110 oC (Table 2). For halogen substituted nitrobenzene, there were no dehalogenation
byproducts (Table 2, Entries 6~8), which were reported to be observed over noble
metal catalysts [30]. The position of the substituted groups showed a slightly steric
hindrance on the catalyst activity. For example, the Nꢀsubstituted pyrrole yield from
the heterocyclizations of orthoꢀmethylꢀnitrobenzene with 2,5ꢀhexadione was slightly
lower than those using the paraꢀ and metaꢀisomers (Table 2, Entries 3~5). This was
due to the larger steric hindrance of the methyl group at the neighbor of the nitro
group. However, there was a huge difference of the steric hindrance when
pꢀnitrobenzaldehyde and oꢀnitrobenzaldehyde was used as the substrates (Table 2,
Entries 9 & 10). For example, the heterocyclization of pꢀnitrobenzaldehyde with
2,5ꢀhexadione produced the corresponding Nꢀsubstituted pyrrole with 74.2% at a full
conversion of pꢀnitrobenzaldehyde (Table 2, Entry 9). GCꢀMS analysis of the reaction
mixture indicated that the other products were the selfꢀcondensation products (imine
and secondary amine) from pꢀaminobenzaldehyde (the hydrogenation of nitro group
from pꢀnitrobenzaldehyde), which was formed via the aldehyde group in one
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pꢀaminobenzaldehyde molecule with the amino group in the other
pꢀaminobenzaldehyde molecule. However, only the transfer hydrogenation of the
nitro group when oꢀnitrobenzaldehyde was used as the substrate for the
heterocyclization with 2,5ꢀhexadione
(Table 2, Entry 10).
Unlike
pꢀaminobenzaldehyde, no intermolecular condensation products were observed from
two molecules of oꢀaminobenzaldehyde (the hydrogenation product from
oꢀnitrobenzaldehyde), which was due to the steric hindrance. On the other hand, there
were also no intramolecular condensation products of oꢀaminobenzaldehyde, which
was due to the fact that the fourꢀmember ring condensation products were not stable.
As listed in Table 2, Entry 5, oꢀmethylꢀnitrobenzene could produce the corresponding
Nꢀsubstituted pyrrole with a high yield. However, there was no heterocyclization of
oꢀnitrobenzaldehyde with 2,5ꢀhexadione. We presumed that the amino group in
oꢀaminobenzaldehyde was stabilized to give a six member ring by the aldehyde group
via the hydrogen bonding. Unlike the result using of pꢀnitrobenzaldehyde as the
substrate (Table 2, Entry 9), no selfꢀcondensation products of the
pꢀaminoacetophenone (the product of the hydrogenation of nitro group from
pꢀnitroacetophenone) were observed (Table 2, Entry 11). These results suggested that
aldehydes were much more active than ketons due to the steric effect. In addition, the
fusedꢀring aromatic and heteroaromatic nitro compound (6ꢀnitroquinoline) was also
successfully converted to the corresponding Nꢀsubstituted pyrrole with a high yield of
90.6% after 12 h and 110 °C (Table 2, Entry 15). It is more challenging to perform the
heterocyclization of inactive nonꢀaromatic nitro compounds with 2,5ꢀhexadione. For
example, 1ꢀnitropropane and nitrocyclohexane also successfully underwent the
heterocyclization with 2,5ꢀhexadione, giving the corresponding Nꢀsubstituted pyrroles
with high yields. As shown in Table 2, a distinct advantage of the developed catalytic
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system was that our method was highly tolerant to other functional groups such as
halogen, ether, ketone, nitrile and phenol. Hence, our method showed a great
promising in the practical synthesis of nitrogen substituted pyrroles via the oneꢀpot
heterocyclization of readily available nitro compounds with 2,5ꢀhexadione. However,
the selectivity of the corresponding Nꢀsubstituted pyrrole from 4ꢀnitrostyrene was
moderate, and the side reaction was the hydrogenation of the carbonꢀcarbon double
bond.
Table 2. The oneꢀpot heterocyclization of different nitro compounds with
2,5ꢀhexadione.a
Yield (%)
2
Conversion
(%)
Entry
Substrate
1
100
100
100
100
2.8
95.2
1
2
3
4
1.1
0
98.9
100
100
0
100
98.6
99.6
100
100
9.9
2.7
0
90.0
93.9
97.6
96.1
74.2
5
6
7
0
8
0
9
100
100
0
10
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84.1
100
100
100
0
0
84.1
96.2
85.8
60.3
11
12
13b
14
13.4
4.5
100
8.3
90.6
15
95.6
94.5
1.8
0
93.6
94.5
16
17
a
Reaction conditions: nitro compound (1 mmol), 2,5ꢀhexadione (1.2 mmol), ethanol
(10 mL), CoꢀNx/Cꢀ800ꢀAT catalyst (40 mg), formic acid (4.5 mmol), and 12 h.
b
The reaction was performed for 24 h under otherwise the same conditions as
described above.
Catalyst recycling experiments
As heterogeneous catalysts, one of the most advantages over the homogeneous
catalysts is that the heterogeneous could be recycled and reused without the loss of its
catalyst activity. Therefore, the stability of CoꢀNx/Cꢀ800ꢀAT was finally studied. The
synthesis of 2,5ꢀdimethylꢀ1ꢀphenylpyrrole from the oneꢀpot heterocyclization of
nitrobenzene and 2,5ꢀhexadione was used as the model reaction. After each run, the
CoꢀNx/Cꢀ800ꢀAT catalyst was separated from the reaction mixture via centrifugation.
Then the spent catalyst was washed with copious amounts of water and ethanol to
remove any physisorbed reagents, respectively. Then, it was dried at under vacuum at
o
60 C for 12 h, and then reused in the next run under identical conditions to those of
the first run. It was observed that the CoꢀNx/Cꢀ800ꢀAT catalyst could be recovered
and reused several times without the decrease of the catalytic activity. Indeed, a
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conversion of 92% was still achieved in the fifth run (Fig. 4). These results indicated
that the CoꢀNx/Cꢀ800ꢀAT catalyst was stable during the oneꢀpot synthesis of
2,5ꢀdimethylꢀ1ꢀphenylpyrrole from the oneꢀpot reaction of nitrobenzene and
2,5ꢀhexadione.
100
80
60
40
20
0
1
2
3
4
5
Recycling number
Fig. 4 Reusability of the CoꢀNx/Cꢀ800ꢀAT catalyst. Reaction conditions: nitrobenzene
(1 mmol), 2,5ꢀhexadione (1.2 mmol), ethanol (10 mL), CoꢀNx/Cꢀ800ꢀAT catalyst (40
mg), formic acid (4.5 mmol), and 12 h.
Conclusions
In summary, we have developed an effective method for the oneꢀpot synthesis of
Nꢀsubstituted pyrroles via the heterocyclizations of nitrobenzene derivatives with
2,5ꢀhexadione via a Paal–Knorr condensation process over the CoꢀNx/Cꢀ800ꢀAT
catalyst. The asꢀmade CoꢀNx/Cꢀ800ꢀAT catalyst exhibits high catalytic activity and
selectivity towards this reaction with formic acid, in which the formic acid acted as a
hydrogen donor and an acid catalyst. This method produced the corresponding
o
Nꢀsubstituted pyrroles with good to excellent yields at 110 C. In addition, the
CoꢀNx/Cꢀ800ꢀAT catalyst could be reused seven times without any loss in activity and
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selectivity. The high catalytic efficiency of the CoꢀNx/Cꢀ800ꢀAT catalyst holds
promising potential as a greener alternative to nobleꢀmetal catalysts for the synthesis
of Nꢀsubstituted pyrroles.
Experimental section
Materials
The solvents were provided by Sinopharm Chemical Reagent Co., Ltd. (Shanghai,
China), and used directly without purification. All of the chemicals were purchased
from Aladdin Chemicals Co. Ltd. (Beijing, China). The catalyst (abbreviated as
CoꢀNx/Cꢀ800ꢀAT) was prepared and characterized in our previous work [29].
General Procedure of the One-pot Synthesis of Pyrrole Compounds
The oneꢀpot synthesis of pyrrole compounds was performed in a 50 mL autoclave,
which was equipped with a magnetic stirrer and a temperature controller. Typically,
nitrobenzene (1.0 mmol), 2,5ꢀhexadione (1.2 mmol), tetrahydrofuran (THF, 10 mL),
and formic acid (6 mmol) were placed to the autoclave. Then the autoclave was sealed,
o
and the air was exchanged with N2. The reaction was performed at 120 C for 12 h
with a magnetic stirring at 1000 rmp. After reaction, the reactor was cooled down to
room temperature with iceꢀwater, the chemicals in the reaction mixture were
quantified by gas chromatography using toluene as the internal standard to quantify
the products, respectively. Products were identified by comparison of their retain
times with the authentic chemicals, and further confirmed by GCꢀMS (Agilent 7890A
GC/5973 MS, HPꢀ5 column).
Analytic Methods
Products analysis was conducted on an agilent 7890A gas chromatography (GC) with
a flame ionization detector and a crosslinked capillary HPꢀ5 column (30 m×0.32
mm×0.4 mm). Analytic conditions were described as follows: N2 carrier gas was
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o
flowed at a rate of 40 mL·minꢀ1, the injection port temperature was 300 C. The GC
oven temperature program was as follows: 50 °C ramp 10 °C/min to 280 oC and the
detector temperature was set to 300 oC.
Recycling Experiments
After reaction, the spent CoꢀNx/Cꢀ800ꢀAT catalyst was collected from the reaction
mixture via centrifugation. The spent catalyst was exhaustively washed with water
and ethanol, respectively. Then the spent catalyst was dried in a vacuum oven at 60 oC
for 12 h. The spent catalyst was used for the next run with the reaction conditions as
described in the first run. Other repeated cycles were the same as described above.
Acknowledgements
The Project was supported the Chenguang Youth Science and Technology Project of
Wuhan City (No. 2014070404010212).
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