Synthesis of acetamides using CO2, methanol, H2 and amines

Article abstract of DOI:10.1039/c8gc03476a

Herein, we report the synthesis of acetamides from CO₂, methanol, H₂ and corresponding amines, which is a new route used to synthesize acetamides. It was found that the Rh catalyst with LiI/LiCl as promoters could effectively catalyze this reaction. Interestingly, no ligand was required and amine substrates played a role in accelerating the reaction.

Full text of DOI:10.1039/c8gc03476a

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Synthesis of acetamides using CO , methanol, H
2
2
and amines†
a,b
Cite this: DOI: 10.1039/c8gc03476a
a
a,b
Jingjing Zhang, Qingli Qian, * Ying Wang,
Received 7th November 2018,
Accepted 13th December 2018
a,b
a,b
a
Bernard Baffour Asare Bediako, Meng Cui, Guanying Yang and
a,b
Buxing Han
*
DOI: 10.1039/c8gc03476a
rsc.li/greenchem
Herein, we report the synthesis of acetamides from CO
2
, methanol, Acetanilide can also be applied to inhibit hydrogen peroxide
H and corresponding amines, which is a new route used to syn- decomposition, and was the first aniline derivative possessing
2
1
4
thesize acetamides. It was found that the Rh catalyst with LiI/LiCl antipyretic as well as analgesic properties. Currently, the pro-
as promoters could effectively catalyze this reaction. Interestingly, duction of acetamides is usually based on acetic acid, acetic
no ligand was required and amine substrates played a role in accel- anhydride, and acetyl chloride or acetate as a feedstock. CO is
2
erating the reaction.
a renewable, safe and easily available carbon resource. Clearly,
the synthesis of acetamides using CO
highly desirable.
2
as a C1 synthon is
Recently, we reported the synthesis of acetic acid via metha-
nol hydrocarboxylation with CO and H , where an imidazole
or its derivative was a necessary ligand for the catalyst.
Introduction
2
2
1
5,16
As an abundant, non-toxic and renewable C1 resource, CO
2
has been widely used to synthesize value-added chemicals, Herein, we report a method to produce acetamides from CO
such as alcohols, urea, carboxylic acids, esters, hydrocarbons, methanol, H , and amines (Scheme 1). In this method, CO
Amides are important chemicals was converted to an acetic acid intermediate via methanol
that are widely used in human life. Over the past decades, the hydrocarboxylation to provide the acetyl source in the acet-
synthesis of formamides using CO
has been extensively inves- amide products. The reaction could be effectively accelerated
tigated and significant progress has been made.
2
,
2
2
1
–6
amides, and carbonates.
2
7
–9
However, by a Rh catalyst with LiI/LiCl as promoters in the cyclic amide
the synthesis of acetamides using CO as a C1 synthon has not solvent. Interestingly, no ligand was needed to trigger the cata-
2
been reported till date. In many cases, acetamides are more lysis. To the best of our knowledge, this is the first report of
useful than formamides. For example, N,N-dimethylacetamide, acetamide synthesis using CO
as a C1 synthon.
2
abbreviated as DMA, is usually utilized as a solvent in the
1
0
chemical synthesis and analysis of cellulose. DMA is also a
promising substitute for the well-known solvent DMF
because of its better stability and solubility, particularly for
Results and discussion
1
1
the synthesis of adhesives, resins and pesticides.
N,N-Dimethylacetamide is an important and the simplest acet-
N-Acetylmorpholine is an important intermediate for the syn-
thesis of fungicides, such as dimethomorph and flumorph. It
also plays a key role in aromatic extraction and natural gas
amide. We adopted DMA synthesis from methanol, CO /H ,
2
2
and dimethylamine as a model reaction to screen the basic
catalytic system and reaction conditions. Dimethyl ammonium
dimethylcarbamate (DIMCARB), which dissociates to dimethyl-
1
2
desulphurization. Acetanilide is a precursor for manufactur-
ing penicillin and other pharmaceuticals, and an important
2
amine and CO above 60 °C, was widely used as a safe source
1
3
intermediate for the synthesis of camphor and sulfa drugs.
a
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Colloid,
Interface and Chemical Thermodynamics, CAS Research/Education Center for
Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of
Sciences, Beijing 100190, China. E-mail: qianql@iccas.ac.cn, hanbx@iccas.ac.cn
b
University of Chinese Academy of Sciences, Beijing 100049, China
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
2 2
Scheme 1 Synthesis of acetamides using CO , methanol, H , and
c8gc03476a
amines.
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7
for dimethylamine. In this study, we utilized DIMCARB to When other Rh complexes, i.e., Rh
2 2 2
(1,5-cod) Cl ,
release dimethylamine in the reaction. We conducted the reac- Rh (CO) Cl , Rh(acac) , RhCl(CO)(PPh ) , RhI , RhCl , were
2
4
2
3
3 2
3
3
tions in different catalytic systems, and the results are shown used as catalysts, the yield of DMA was much lower or no
in Table 1. The reaction proceeded efficiently with Rh(acac) DMA was observed in the reaction (entries 6–11). When
(
CO)2 as the catalyst and LiI/LiCl as the promoters in heterogeneous Rh (Rh/C, Rh/Al O ) was used as the catalyst,
2 3
1
,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone
(DMPU) the reaction did not occur (entries 12 and 13). Apart from the
solvent at 190 °C (entry 1). DMA was the major product and Rh complexes, we tested other metal complexes, namely,
the yield of DMA based on dimethylamine was 65.3%. Ru (CO) , Ir (CO) , Ni(PPH ) Br , Co (CO) , Re (CO) . The
3
12
4
12
3 2
2
2
8
2
10
Trimethylamine, acetic acid, and trace dimethylformamide results revealed that these metal complexes could not acceler-
(DMF) were the by-products.
ate the reaction at all (entries 14–18). We also combined
The effective cooperation of different catalytic components Rh(acac)(CO)2 with other metal complexes (Ru (CO) ,
3
12
is crucial for improving the reaction rate. Without one or two Ir
of the components, the reaction activity was much lower or remarkably lower than that of a single Rh(acac)(CO)
4
(CO)12, Co
2
(CO)
8
), but the catalytic performances were
catalyst
2
the reaction did not take place at all (entries 2–5). The Rh pre- (entries 1 and 19–21). In short, Rh(acac)(CO) was the appro-
2
cursor was important for the good catalytic performance. priate catalyst for the model reaction.
a
2 2
Table 1 Different catalytic systems of DMA synthesis from methanol, CO , H , and DIMCARB
b
Entry
Catalyst
Promoter I
Promoter II
Solvent
Yield (%)
1
2
3
4
5
6
7
8
9
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
—
2
2
2
2
LiI
—
LiI
—
LiCl
LiCl
—
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMPU
DMI
65.3
0
17
0
—
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
NaI
KI
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiBr
LiBF
LiF
KF
NaCl
KCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
LiCl
0
Rh
Rh
2
(1,5-cod)
(CO) Cl
2
Cl
2
0.5
40.9
3.6
0.2
0.3
0
0
0
0
0
2
4
2
Rh(acac)
RhI
RhCl
3
3
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
3
RhCl(CO)(PPh
3 2
)
Rh/C
Rh/Al
Ru (CO)12
Ir (CO)12
Ni(PPH
Co (CO)
Re (CO)10
2
O
3
3
4
3
)
2
Br
2
0
0
0
2
8
2
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
Rh(acac)(CO)
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
, Ir
, Ru
, Co
4
(CO)12
(CO)12
(CO)
0.1
1.3
33.4
10.2
0
0
0.8
0
31.5
21.8
32.3
22.2
50.1
43.8
45.1
39.3
36.9
35.4
0
3
2
8
LiCl
LiBr
I
2
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
4
NMP
NEP
NOP
Tetramethylurea
3-Methyl-2-oxazolidinone
Squalane
Water
Cyclohexane
THF
0
0
0
0
0
a
Reaction conditions: 40 μmol Rh catalyst (based on the metal), 3 mmol promoter I, 1 mmol promoter II, 5 mmol MeOH, 2 mL solvent, 0.15 g
b
2 2
DIMCARB (i.e. 2 mmol dimethylamine), 5 MPa CO , and 3 MPa H (at room temperature), 190 °C, 14 h. The yield of DMA was based on di-
methylamine in DIMCARB (100 × moles of DMA product per mole of dimethylamine feedstock). All the yields were calculated based on gas
chromatography using toluene as the internal standard.
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The promoters were indispensable in the reaction. Without
LiI, no DMA could be observed (entries 2 and 4). Without LiCl,
the yield of DMA was markedly lower (entry 3). When other
alkali metal halides (NaI, KI, LiCl, and LiBr) were used instead
of LiI, the catalytic performance was either much worse or the
target reaction did not proceed (entries 1 and 22–25). As can
be seen from the abovementioned results, the promoting
+
effect of the alkali metal cations followed the sequence: Li >
+
+
Na > K , while the promoting effect of the halide anions fol-
lowed the order: Cl− < Br < I . No DMA was generated when
−
−
−
iodine (I ) was used instead of LiI, indicating that I was indis-
2
pensable in this reaction (entry 26). Hence, LiI was a suitable
promoter for the reaction. The eminent promoting effect of LiI
may lie in two aspects: the stronger Lewis acidity and smaller
+
− 18
size of Li and the better nucleophilicity of I . In addition,
the very good solubility of LiI in the reaction solution was also
Fig. 1 Effect of reaction conditions (a–d) over 5 mmol MeOH, 0.15 g
2
DIMCARB (i.e. 2 mmol dimethylamine), 2 mL DMPU, 5 MPa CO , and 3
beneficial for the reaction. We also replaced another promoter MPa H2 (at room temperature) and 14 h. (a) Effect of reaction tempera-
ture, 40 μmol Rh(acac)(CO) catalyst, 3 mmol LiI, and 1 mmol LiCl; (b)
effect of Rh catalyst dosage, 190 °C, 3 mmol LiI, and 1 mmol LiCl; (c)
effect of LiI dosage, 190 °C, 40 μmol Rh(acac)(CO) catalyst, and 1 mmol
4
LiCl with LiBr, LiBF , LiF, KF, NaCl, or KCl, but the yields of
2
DMA decreased (entries 1 and 27–32). This indicated that
synergistic effects existed between the Rh catalyst and promo-
ters in stabilizing the catalytic system and accelerating the
reaction.
2
2
LiCl; (d) effect of LiCl dosage, 190 °C, 40 μmol Rh(acac)(CO) catalyst,
and 3 mmol LiI.
The solvent also significantly affected the catalytic perform-
ance. On the basis of Rh(acac)(CO) and LiI/LiCl, we conducted
2
the reaction using 1,3-dimethyl-2-imidazolidinone (DMI) as the emerged at 130 °C and the yield increased remarkably with the
solvent. DMI was used as the optimal solvent in the acetic acid elevation of reaction temperature. At 190 °C, the yield of DMA
synthesis via methanol hydrocarboxylation with CO
2
and H
2
.
reached 65.3%, and then gradually increased with the increase
However, in the model reaction of this study, the solvent effect in temperature. Hence, 190 °C was a suitable reaction tempera-
was significantly lower than that of DMPU (entries 1 and 33). ture. At 190 °C, we investigated the impact of dosages of Rh
DMPU has a similar structure to DMI, but DMPU has one more catalyst, LiI and LiCl. The yield of DMA increased with an
carbon in the ring skeleton of the cyclic amide compared to increase in Rh dosage and it reached 65.3% at 40 μmol Rh
DMI. The different solvent effects may be ascribed to their catalyst; however, the yield decreased when the Rh dosage was
different ring strains, which may affect the state of the lone pair further enhanced (Fig. 1b). The impact of LiI and LiCl dosages
electrons. We also tested other cyclic amides with five-mem- followed a similar trend and their suitable dosages were
bered rings as the reaction solvent, namely, 1-methyl-2-pyrrol- 3 mmol and 1 mmol, respectively (Fig. 1c and d). It can be
idone (NMP), 1-ethyl-2-pyrrolidone (NEP), and 1-n-octyl-2-pyrrol- deduced that excess I− and/or Cl− may occupy the active sites
idone (NOP). The results demonstrated that yields of DMA were of the Rh catalyst and thus inhibit the reaction.
less than that obtained using DMI (entries 34–36). In addition,
The pressure of CO and H also remarkably influenced the
2 2
the larger the alkyl substituent on the N atom, the lower was catalytic performance (Table 2). No product was detected when
the yield of DMA in the corresponding reaction. We also tried a the total pressure was 2 MPa (entry 1). With the enhancement
solvent with similar structure to DMPU and DMI, but without of the pressure, the yield of DMA increased markedly and
the ring skeleton, i.e., tetramethylurea. However, no DMA was 65.3% of DMA could be obtained when the CO /H pressure
2 2
detected after the reaction (entry 37). Thus, the ring structure reached 5/3 MPa (entries 2–4). The effect of pressure became
was necessary for triggering the catalysis. The cyclic structure minor when the pressure was further increased (entry 5). The
affected the p–π conjugation between the lone pair electrons of ratio of CO
N atom and π-electrons of CvO group, which may account for ance. We fixed the total pressure at 8 MPa and altered the ratio
this phenomenon. Based on the cyclic amide structure, we sub- of CO /H . It was found that 5 MPa CO and 3 MPa H gave the
stituted one N atom on the ring skeleton with an O atom, but best result (entries 4 and 6–9). The presence of CO and H
no DMA was observed (entry 38). We also used squalane, water, was necessary for the reaction. Without CO and/or H , no
2 2
/H was also important for the catalytic perform-
2
2
2
2
2
2
2
2
cyclohexane, and THF as the solvents, but the target reaction DMA was observed after reaction (entries 10–12). The sub-
did not take place (entries 39–42). Thus, the cyclic amide struc- strates were also indispensable in the target reaction because
ture was necessary for the solvent and DMPU was a suitable the reaction did not proceed without methanol or DIMCARB
choice. In brief, the catalytic system consisting of Rh(acac) (entries 13 and 14).
(
CO)
Based on the above catalytic system, we studied the impact amine substrates could also be used as a substrate to produce
of the reaction temperature, as shown in Fig. 1a. DMA the corresponding acetamides (Table 3). The amine with
2
, LiI/LiCl and DMPU was fit for the model reaction.
Based on the Rh-LiI/LiCl catalytic system, more complex
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a
Table 2 Impact of gas pressure on the yield of DMA after the reaction
pyrrole, imidazole or purine were used as a substrate, no acet-
amide was observed in the products. A further study revealed
that no N-acetylation took place even when acetic acid was
directly used in the reaction with these heteroaromatic com-
pounds under similar conditions. This may be due to the weak
basicity of the N atoms in these compounds. Thus, hetero-
aromatic compounds were unfit substrates for this reaction.
As a byproduct, trace acetic acid was detected after the reac-
tion. Amines are well-known bases and acetic acid is a
common organic acid. The experiment indicated that acet-
amide can be formed easily via the neutralization of an amine
with acetic acid at reaction conditions. Thus, the reaction
should be considered a cascade reaction consisting of metha-
nol hydrocarboxylation and subsequent N-acetylation of the
amines. To verify this deduction, we conducted several control
Entry
2
CO /MPa
2
H /MPa
Yield (%)
1
2
3
4
5
6
7
8
9
1.25
2.5
3.75
5
6.25
2
3
4
6
0
0
5
5
5
0.75
1.5
2.25
3
3.75
6
5
4
2
3
0
0
3
3
0
1.7
22.6
65.3
66.2
0
6.2
24.9
45.5
0
0
0
0
0
10
11
12
13
14
15
b
c
d
5
3
49.0
a
Reaction conditions: 40 μmol Rh(acac)(CO) (based on the metal), experiments. The GC-MS spectra of a tracer experiment using
mmol LiI, 1 mmol LiCl, 5 mmol MeOH, 0.15 g DIMCARB (i.e.,
mmol dimethylamine), 2 mL DMPU, 190 °C, and 14 h. No MeOH
was added before the reaction. No DIMCARB was added before the
2
3
2
13
CH OH demonstrated that the CH group of the methanol
b
3
3
c
substrate was transferred to acetamide (Fig. S1†). We further
1
8
reaction and trace acetic acid was observed after the reaction. conducted a tracer test with CH
OH. Results indicated that
3
d
0.5 mmol 4-methylimidazole was added before the reaction.
the bond to the OH group in the methanol substrate cleaved
during the reaction and the O atom in the acetamide product
2
was from CO (Fig. S2†). These facts support the above deduc-
tion. In our previous report, an imidazole-like ligand was
Table 3 Rh-Catalyzed N-acetylation of various amines via reductive
a
CO
2
hydrogenation with methanol
essential to the acetic acid synthesis via an Rh-catalyzed
1
6
methanol hydrocarboxylation. Interestingly, no such ligand
was needed in the DMA synthesis and an additional 4-methyl-
imidazole ligand evidently inhibited the reaction (entry 15 of
Table 2). Although remarkable amounts of DMA could be pro-
duced in the target reaction, only trace acetic acid was observed
when the reaction was conducted without the amine substrate
b
Entry
1
Substrate
Product
Yield (%)
54.2
2
41.7
(
entry 14 of Table 2). A further experiment revealed that DMA
3
4
37.2
40.4
had no promoting effect on the methanol hydrocarboxylation.
These phenomena suggest that the consumption of the acetic
acid intermediate by the neutralization reaction with the
amine could accelerate the methanol hydrocarboxylation. In
our previous reports, we had suggested that acetic acid syn-
5
6
60.5
48.8
thesis via methanol hydrocarboxylation with CO
2
and H
To clarify the reaction path of this study, we
performed experiments using CO at different pressures (0.5
MPa, 1 MPa, 3 MPa) instead of CO . However, no DMA was
2
was
1
5,16
not via CO.
a
Reaction conditions: 40 μmol Rh
(CO) Cl
2 4 2
catalyst (based on the
2
metal), 3 mmol LiI, 1 mmol LiCl, 5 mmol MeOH, 2 mL DMI, 1.5 mmol detected after these reactions. Therefore, the target reaction
amines, 5 MPa CO
2
, and 3 MPa H
4 h. The yield of acetamides was based on the corresponding
amines.
2
(at room temperature), 190 °C and
also did not occur via the CO route. The reaction contained
four reactants and three catalytic components and proceeded
at a relatively high temperature. Thus, acquiring a very high
yield of the corresponding acetamide in such a complex reac-
tion system is still a challenge at the present stage.
b
1
benzene or cyclohexane as the substituent was successfully
converted to the corresponding acetamide (entries 1 and 2).
The cyclic amines of various structures were also suitable for
the reaction. For example, cyclic amines with different ring
Conclusions
sizes (five-, six- and seven-membered rings) could be used as In summary, we developed a route for producing acetamides
substrates to obtain the corresponding acetamides (entries from CO , methanol, H and corresponding amine substrates.
2
2
3
–5). Notably, the cyclic amines with a heteroatom (O) or com- The reaction can be effectively accelerated using Rh-LiI/LiCl as
bined with a benzene group could also be converted to the a catalyst at 190 °C. Evident synergy exists between the Rh cata-
corresponding acetamides and even with higher yields (entries lyst and the promoters in catalyzing the reaction. The yield of
5
and 6). When heteroaromatic compounds such as indole, DMA can reach 65.3% using DIMCARB as the feedstock. This
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method also applies for various amine substrates, such as
cyclic amines and amines with benzene or cycloalkane substi-
tuents. We believe that this report will trigger more investi-
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2
as the
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and W. Leitner, Angew. Chem., Int. Ed., 2013, 52, 12119–
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The authors thank the National Natural Science Foundation of
China (21875262, 21733011), National Key Research and
Development Program of China (2017YFA0403102), Beijing
Municipal
(
(
Science
Z181100004218004), and the Chinese Academy of Sciences
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