Synthesis of ethanol from paraformaldehyde, CO2 and H2

Article abstract of DOI:10.1039/c7gc01887h

Ethanol is an important bulk chemical and alternative fuel that is currently synthesized by catalytic hydration of ethylene or fermentation of foods. CO₂ is a cheap and renewable carbon resource. Transformation of CO₂ into useful chemicals is an interesting topic in green chemistry. Production of ethanol using CO₂ and H₂ is a promising route, but the efficiency of the reaction is not satisfactory. In this paper, we propose a protocol to synthesize ethanol from paraformaldehyde, CO₂ and H₂. The reaction could be efficiently accelerated by a Ru-Co bimetallic catalyst using LiI as the promoter in 1,3-dimethyl-2-imidazolidinone (DMI) under mild conditions. The selectivity of ethanol in total products reached 50.9 C-mol%, which was obviously higher than that of the reported routes. Furthermore, the TOF of ethanol based on Ru metal was as high as 17.9 h^-1. To our knowledge, this is the first report on ethanol synthesis from paraformaldehyde, CO₂ and H₂. A detailed study indicated that the outstanding results of the reaction originated from the synergy of paraformaldehyde hydrogenation, reverse water gas shift reaction and methanol homologation.

Full text of DOI:10.1039/c7gc01887h

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PAPER
Synthesis of ethanol from paraformaldehyde,
CO and H †
2
2
Cite this: DOI: 10.1039/c7gc01887h
a,b
a
a,b
a,b
a,b
Jingjing Zhang, Qingli Qian, * Meng Cui, Chunjun Chen, Shuaishuai Liu
a,b
and Buxing Han
*
Ethanol is an important bulk chemical and alternative fuel that is currently synthesized by catalytic
hydration of ethylene or fermentation of foods. CO is a cheap and renewable carbon resource.
Transformation of CO into useful chemicals is an interesting topic in green chemistry. Production of
ethanol using CO and H is a promising route, but the efficiency of the reaction is not satisfactory. In this
paper, we propose a protocol to synthesize ethanol from paraformaldehyde, CO and H . The reaction
could be efficiently accelerated by a Ru–Co bimetallic catalyst using LiI as the promoter in 1,3-dimethyl-
2
2
2
2
2
2
2-imidazolidinone (DMI) under mild conditions. The selectivity of ethanol in total products reached
5
0.9 C-mol%, which was obviously higher than that of the reported routes. Furthermore, the TOF of
ethanol based on Ru metal was as high as 17.9 h− . To our knowledge, this is the first report on ethanol
1
Received 23rd June 2017,
Accepted 7th August 2017
2 2
synthesis from paraformaldehyde, CO and H . A detailed study indicated that the outstanding results of
DOI: 10.1039/c7gc01887h
the reaction originated from the synergy of paraformaldehyde hydrogenation, reverse water gas shift reac-
tion and methanol homologation.
rsc.li/greenchem
The reports of ethanol synthesis using CO2 were mostly
Introduction
6
–12
limited to CO
2
hydrogenation at high temperatures.
In
As an important bulk chemical, ethanol is widely used as a such routes, CO usually reacted with H to generate reactive
2
2
solvent, food, medicine, pesticide, organic feedstock, etc. C intermediates, including CO, CH * and/or CH OH, and the
1
3
3
Moreover, ethanol has played an ever-increasing role in the intermediates underwent the C–C bond formation step to
1
6,7
current energy infrastructure. Nowadays, ethanol is mainly produce C2+ products, such as ethanol and higher alcohols.
manufactured by catalytic hydration of ethylene from Because the in situ generation of C intermediates from CO
1
2
petroleum or fermentation of foods such as corn and sugar- hydrogenation and the carbon chain growth took place simul-
cane. CO is the major greenhouse gas. It is also an economi- taneously, the product distribution was usually broad and the
2
2
cal, safe, renewable and readily available carbon resource.
Transforming CO
attention from the scientific community. So far, CO has been genation the best result was obtained at 340 °C. The mixed
selectivity of ethanol in the alcohols and/or total products was
hydro-
2
into useful chemicals has received much generally low. For example, in the CoMoS catalyzed CO
2
1
0
2
utilized to synthesize a variety of products, such as carboxylic alcohols were produced and methanol was the predominant
acids, esters, carbonates, urea, formamides, hydrocarbons and alcohol (20.0 C-mol%), while ethanol selectivity was only 5.5
3
alcohols. As for alcohols, significant progress has been made C-mol% in the total products. When CO hydrogenation was
2
in methanol synthesis via CO hydrogenation in the past few catalyzed by K/Cu–Zn at 300 °C, C –C alcohols were formed
2
1
5
4
decades. Synthesis of ethanol using CO
is obviously of great importance. But it is still a great challenge 19.5 wt%. In the Pt/Co O catalyzed synthesis of higher alco-
2 2
and H as feedstock and the ethanol selectivity in the total products was merely
1
1
3
4
because it involves CO hydrogenation with simultaneous C–C hols from CO hydrogenation, C –C alcohols were produced
2
2
1
4
5
bond formation.
and the ethanol selectivity in the total products was also low
1
2
(
18.9 C-mol%). To improve the ethanol selectivity, introdu-
cing certain substrates to react with CO2 and H2 is a viable
way. When methanol, CO and H were used as the starting
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
2
2
materials, ethanol was the only alcohol product and
the ethanol selectivity in the total products reached
13
3
4.2 C-mol%. In addition, the yield of ethanol based on
b
University of Chinese Academy of Sciences, Beijing 100049, China
methanol was 32% and the highest TOF of ethanol based on
Ru metal was only 1.1 h− . At the present stage, methanol was
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
1
c7gc01887h
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Table 1 Different catalytic systems of ethanol synthesis from para-
a
2 2
formaldehyde, CO and H
TOF (h−1)
b
Entry Catalyst
Promoter Solvent
2 2
Scheme 1 Synthesis of ethanol from paraformaldehyde, CO and H .
c
1
2
3
4
5
6
7
8
9
1
Ru(acac)
3
, CoBr
, CoBr
2
2
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
LiI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
DMI
NMP
THF
DMF
Water
Cyclohexane
17.9
0.3
0.2
0
0.2
0
0
0
1.2
0
13.4
13.6
9.0
11.6
14.7
0
7.5
7.7
0
d
d
d
Fe(acac)
3
Mn(acac)
3
, CoBr
2
the only substrate reported to react with CO and H for the
2
2
Ni(acac)
2
, CoBr
2
synthesis of ethanol. Exploration of the route for ethanol
synthesis by reaction of other substrates with CO and H is
interesting from both scientific and practical perspectives.
Formaldehyde is a bulk chemical that can be produced by
various routes, such as CO hydrogenation, methane and/or
Paraformaldehyde, which can be
easily derived from formaldehyde, is a facile source of formal- 13
Ru(acac) , CuBr
3
2
Ru(acac)
Rh (CO)16, Fe
Ir(OAc) , NiBr
Ru(acac)3
CoBr
Ru(acac)
Ru (CO)12, CoBr
RuBr , CoI
3
, NiBr
2
2
2
d
d
6
2
(CO)
9
n
2
d
0
2
2
14–16
11
3
, CoI
2
methanol oxidation.
12
3
2
d
d
3
2
14
RuCl
Ru(PPh
Ru(acac)
Ru(acac) , CoBr
3
, CoCl
Cl
, CoBr
2
LiI
dehyde that is preferred especially when anhydrous conditions
1
7
15
3
)
3
3
2
, Co(PPh)
3
Cl LiI
—
are required. Herein we report the synthesis of ethanol from
paraformaldehyde, CO and H
16
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
(Scheme 1). The reaction could 17
3
LiCl
LiBr
LiBF
18
19
20
Ru(acac)
Ru(acac)
Ru(acac)
3
3
3
, CoBr
, CoBr
, CoBr
proceed very efficiently by homogeneous catalysis under mild
conditions. To the best of our knowledge, this is the first
d
d
4
I
2
0
report on the synthesis of ethanol from aldehyde, CO
2
and H
2
.
21
Ru(acac) , CoBr
NaI
KI
ZnI
13.4
9.6
0.1
0
0
0
11.3
0
0
0
0
3
22
23
24
25
26
27
28
Ru(acac)
Ru(acac)
Ru(acac)
Ru(acac)
Ru(acac)
Ru(acac)
Ru(acac)
Ru(acac)
Ru(acac)
Ru(acac)
3
3
3
3
3
3
3
3
3
3
, CoBr
, CoBr
, CoBr
, CoBr
, CoBr
, CoBr
, CoBr
, CoBr
, CoBr
, CoBr
d
d
d
d
2
MgI
2
CaI
CuI
LiI
LiI
LiI
LiI
LiI
2
Results and discussion
d
d
The reaction was effectively catalyzed by the Ru–Co bimetallic
catalyst using LiI as the promoter in 1,3-dimethyl-2-imidazo- 29
3
3
0
1
lidinone (DMI) solvent under milder conditions, as shown in
Table 1. Ethanol was the predominant product in the reaction
solution (Fig. S1 and S2†). The yield of ethanol based on the
a
Reaction conditions: 7.5 μmol Ru catalyst and 45 μmol Co catalyst
O)
(at room
(
(
based on the metal), 3 mmol promoter, 2 mL solvent, 0.1 g (CH
2
n
2
“CH O” monomer in paraformaldehyde was 37.8%. Only small
i.e., 3.2 mmol “CH O” monomer), 3 MPa CO and 5 MPa H
2 2 2
b
amounts of CO and methane were generated, and the ethanol temperature), 180 °C, 9 h. TOF denotes moles of ethanol produced
c
per mole of Ru catalyst per hour. The yield of ethanol based on the
CH O” monomer in paraformaldehyde was 37.8% and ethanol selecti-
2
selectivity in the total products reached 50.9 C-mol%, which is
“
superior to that of reported methanol homologation using CO
2
vity in the total products reached 50.3 C-mol% (the product distri-
1
3
and H
2
.
Interestingly, the TOF of ethanol based on Ru metal bution: ethanol 1.21 mmol, methanol 0.12 mmol, propanol
d
−
1
0
.05 mmol, CO 1.11 mmol, and methane 0.95 mmol). Precipitate was
was as high as 17.9 h (entry 1), which is much higher than
9
,13
observed after the reaction.
that of the reported routes.
The Ru–Co bimetallic catalyst is crucial for the target reac-
tion. When the Ru(acac) catalyst was replaced with other com-
monly used transition metal complexes, i.e., Fe, Mn, and Ni, LiI was replaced with other halogen anions (Cl , Br ), the reac-
3
−
−
the reaction rates were very low or the reaction did not take tion proceeded at much lower rates (entries 17 and 18). We also
place (entries 2–4). When Ru(acac) was fixed and CoBr was tried LiBF
, but no ethanol was generated (entry 19). When we
4
3
2
replaced with other metal complexes (Cu, Ni), the results were used I
2
as the promoter the reaction did not take place (entry
also poor (entries 5 and 6). When we tried other combinations 20). Thus, the ionic state of the halogen was needed as a promo-
of metal complexes (Rh/Fe, Ir/Ni), no ethanol was produced ter and I− was the best choice. The I− helped to maintain the
after the reaction (entries 7 and 8). Thus Ru–Co was the suit- catalyst stability (entries 1 and 19). In addition, the larger size
able combination of catalysts for the reaction. When we used of iodide compared with other halides has a stronger steric
Ru(acac) or CoBr separately, the results revealed that the Ru effect, leading to better catalytic selectivity (entries 1, 17 and
3
2
1
8
complex was the major catalyst and the Co complex was the 18). The metal cation of the iodide promoter also greatly
cocatalyst (entries 9 and 10). The activity of the Ru catalyst was affected the catalytic performance. The alkali metal (Li, Na, K)
greatly enhanced by the Co cocatalyst, indicating a synergic iodides were effective promoters, and the LiI displayed the best
effect between the Ru and Co complexes (entries 1 and 9). catalytic performance (entries 1, 21 and 22), due to its stronger
7,13
After screening the combinations of Ru and Co complexes, it Lewis acidity and better solubility in the reaction solution.
was found that Ru(acac) /CoBr exhibited better performance However, the ethanol formation rate was very low or the reaction
3
2
in accelerating the reaction (entries 1 and 11–15).
2 2 2
did not proceed when other metal iodides (ZnI , MgI , CaI ,
The promoter was also important for the reaction. Without CuI) were utilized (entries 23–26). The reason may result from
the promoter, no ethanol was observed (entry 16). If the I− of their poor solubility in the reaction solvent. We also screened
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a
the reaction solvent, such as NMP, THF, DMF, water and cyclo- Table 2 Effect of reaction parameters on the reaction
hexane, and the results indicated that DMI was the suitable
1
Entry Ru (μmol) Co (μmol) LiI (mmol) CO
2
/H
2
(MPa) TOF (h−
)
solvent for the reaction (entries 27–31). In brief, the catalytic
system consisting of Ru(acac) , CoBr , LiI and DMI was appro-
priate for the target reaction.
3
2
1
2
3
4
5
6
7
8
9
1
1
1
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5
7.5
5
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
30
60
47.5
37.5
30
7.5
3
3
3
3
3
3
3
3
3
3
3
3
3
3
2
4
3
3
3
3
3
3
0.75/1.25
1.5/2.5
2.25/3.75
3/5
3.75/6.25
1/7
2/6
4/4
5/3
0/0
5.0
10.6
14.1
17.9
18.7
13.6
15.5
12.8
8.9
0
0
1.2
0.2
15.6
14.8
8.4
16.4
13.7
15.2
7.8
Fig. 1 showed the impact of temperature on the catalytic
activity. The reaction did not take place at 120 °C, and obvious
ethanol was observed at 140 °C. The reaction rate increased
remarkably with the increase of temperature until 180 °C. At
this temperature the TOF of ethanol reached 17.9 h− . After
1
0
1
2
1
80 °C, the catalytic activity had little elevation with the temp-
3/0
0/5
3/5
erature rise. So, 180 °C is suitable for this reaction.
b
c
Based on the optimization of the reaction temperature as 13
above, we further studied the influence of other reaction para-
meters, such as pressure and dosage of the catalyst com-
1
1
1
4
5
6
3/5
3/5
3/5
3/5
ponents, as revealed in Table 2. At a fixed ratio of CO
3/5), the ethanol formation rate increased evidently with the
increasing total pressure (entries 1–4). However, the effect of
2
and H
2
17
1
1
2
8
9
0
10
5
15
22.5
45
3/5
3/5
3/5
3/5
(
total pressure was not obvious at >8 MPa (entry 5). When the 21
5.8
0.4
2
2
3/5
total pressure of CO and H was fixed at 8 MPa, the best cata-
2
2
lytic performance was also obtained at 3 MPa CO
(entries 4 and 6–9). Both CO and H
reaction, because no or little ethanol was produced without
CO and/or H (entries 10–12). Interestingly, a small amount
2
and 5 MPa
a
Reaction conditions: Ru(acac)
3
and CoBr
2
were used as catalyst pre-
H
2
2
2
were necessary for the cursors; 2 mL DMI, 3.2 mmol “CH
2
O” monomer (0.1 g), 180 °C, 9 h.
b
c
No (CH
O)
2 n
was added before the reaction. 1,3,5-Trioxane (3.2 mmol
O)
“
CH O” monomer, 0.1 g) was used instead of (CH
2
2
n
.
2
2
of ethanol could be observed when paraformaldehyde reacted
with H2 under reaction conditions (entry 12), which may be
due to the small amount of CO generated in situ via partial (entries 4 and 14). These results indicate that the synthesis
1
9
decomposition of paraformaldehyde. Paraformaldehyde was route in this work can be applied to paraformaldehydes from
also necessary for the target reaction. Without this substrate, different sources.
only trace ethanol was detected after the reaction (TOF =
The dosage of LiI may affect the catalytic properties and
.2 h ) (entry 13). The ethanol synthesis via Ru–Co catalyzed 3 mmol LiI in the catalytic system resulted in high efficiency
CO hydrogenation has been reported in the literature, where (entries 4, 15 and 16). Iodide anions are not only good nucleo-
−
1
0
2
−
1
the catalytic rates were also low (TOF < 0.8 h based on Ru philes but also good ligands for transition metals. Hence,
metal, at 200 °C). Thus the introduction of the paraformalde- suitable amounts of LiI were necessary for the reaction, while
9
hyde not only markedly improved the ethanol selectivity, but too much of it would occupy the active sites of the catalyst,
1
8
also greatly enhanced the reaction rate. When the substrates of inhibiting the reaction. The dosages of the Ru and Co
different polymerization degrees were used to react with CO
catalysts also evidently influenced the reaction. At the fixed
and H , respectively, ethanol was produced at similar rates proportion of Ru and Co metals (1/6), the combination of
2
2
7.5 μmol Ru and 45 μmol Co gave the highest catalytic activity
(
entries 4, 17 and 18). When the total amount of Ru and Co
catalysts was kept at 52.5 μmol, the best ratio of Ru and Co cat-
alysts was also 1/6 (entries 4 and 19–22).
Under the optimized conditions, we tested the reusability
of the catalytic system (Ru(acac) /CoBr -LiI-DMI). After the
3
2
reaction, the alcohols produced in the reaction were removed
under vacuum at 85 °C for 5 h, which was proved by GC ana-
lysis. Then the catalytic system was used directly for the next
run. The results demonstrated that the catalytic system could
be recycled at least five times without obvious loss of activity
and the TON of ethanol reached 805 in the five cycles (Fig. 2).
Fig. 3 depicts the time course of the alcohol formation. The
paraformaldehyde was quickly transformed into methanol at
the initial period of the reaction. After 1 h ethanol began to
emerge and it grew steadily until 9 h. Accordingly, methanol
generated at the beginning decreased continuously with the
increase of the ethanol amount, suggesting that ethanol was
Fig. 1 The TOF of ethanol at different temperatures. Reaction con-
ditions: 7.5 μmol Ru(acac) and 45 μmol CoBr , 3 mmol LiI, 2 mL DMI,
.2 mmol “CH O” monomer (0.1 g), 3 MPa CO and 5 MPa H (at room
temperature), 9 h.
3
2
3
2
2
2
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Scheme 2 The synergy of the reactions for ethanol synthesis from par-
Fig. 2 The results of the recycling tests. Reaction conditions: 7.5 μmol
2 2
aformaldehyde, CO and H . Ru* and Co* represent the active species of
Ru(acac)
monomer (0.1 g), 3 MPa CO
80 °C, 9 h. TON denotes moles of ethanol produced per mole of Ru
3
and 45 μmol CoBr
2
, 3 mmol LiI, 2 mL DMI, 3.2 mmol “CH
2
O”
Ru and Co, respectively.
2
and 5 MPa H (at room temperature),
2
1
catalyst.
by the homologation of ethanol. The results obtained using
(
CD
2
O)
n
indicated that H/D exchange took place in the reaction
O) entered the metha-
(
Fig. S5†). Most of the D atoms on (CD
2
n
nol molecules (CD H O), and H/D exchange was observed
2
2
3
because a small amount of CD HO was observed after the reac-
tion. Then the major D atoms on methanol were further
replaced by the H atoms of H2 during the formation of
ethanol, because only a small amount of C
detected. The results using D also demonstrated a similar
exchange process (Fig. S6†). The H–D exchange was also
2 2 4
D H O was
2
2
0
studied for other reactions.
The hydrogenation of paraformaldehyde to methanol could
be promoted by the Ru or Co catalyst, respectively (Fig. S7 and
S8†). The hydrogenation of paraformaldehyde to methanol is a
2
1
well-known reaction. The RWGS reaction could be catalyzed
Fig. 3 Time course of the reaction. Reaction conditions: 7.5 μmol
by the Ru catalyst (Fig. S9†). The Ru promoted RWGS reaction
Ru(acac)
DMI, 3.2 mmol “CH
at room temperature), and 180 °C.
3
and 45 μmol CoBr
2
(based on the metal), 3 mmol LiI, 2 mL
2
2
has been studied by other researchers. Methanol homologa-
tion into ethanol could be accelerated by a Ru–Co bimetallic
catalyst (Fig. S10†). The Ru–Co catalyzed methanol homologa-
2
O” monomer (0.1 g), 3 MPa CO
2
and 5 MPa H
2
(
2
3
tion has also been investigated in the literature. The high
formed via the methanol homologation pathway. After 9 h, the catalytic rate and selectivity of this work lie in not only the
reaction rate became much lower because methanol was nearly synergy of the cascade reactions but also the synergy of
used up. Moreover, trace propanol could be detected at 6 h different catalytic components. The presence of a small
and it grew slowly with time. As for the gaseous products, CO amount of the propanol product revealed that the catalytic
was produced at the start of the reaction and its content was system has strong capability for promoting alcohol homologa-
nearly kept constant in the reaction process, indicating the tion, while no higher alcohol was observed in ethanol syn-
1
3
2 2
fast consumption of CO in the subsequent steps. However, in thesis from methanol, CO and H reported in the literature.
the literature the CO content increased evidently at the initial The very high rate of paraformaldehyde hydrogenation and
period of the reaction and dropped continuously with methanol homologation caused the quick consumption of CO
13,9b
time.
it increased gradually during the reaction.
From the above results, we can deduce that synthesis of RWGS process was also crucial to the reaction (Fig. S11†). If
ethanol from paraformaldehyde, CO and H is the synergy of the CO formation rate was too low the ethanol generation
Methane was observed when the reaction began and generated by the RWGS reaction, resulting in a high ethanol
formation rate with less CO byproduct. The catalytic rate of the
2
2
three basic reactions (Scheme 2), i.e., hydrogenation of parafor- would certainly be depressed, whereas the ethanol formation
maldehyde to methanol (1), reverse water gas shift reaction was also inhibited when the CO content was high enough
(
RWGS) (2), and methanol homologation (3). The GC-MS and during the reaction. This could be attributed to the poisoning
1
3
3e
NMR spectra of tracer experiments using ( CH
2
O)
n
indicated of the catalyst by excess CO. Furthermore, only a small
/CO hydrogenation
OH, supporting the above argument promoted by the catalytic system (Fig. S12–S14†), which helps
Fig. S3 and S4†). A small amount of propanol was generated to explain the low methane content in the final products.
1
3
that the
C atoms were transformed into alcohols, i.e., amount of methane was detected in CO
2
1
3
13
3 3 2
CH OH and CH CH
(
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a typical experiment, certain amounts of the Ru and/or Co
catalyst, LiI or another promoter, paraformaldehyde or tracer
Conclusions
In summary, we have developed a strategy for ethanol syn- (if used) and 2 mL solvent were added into the reactor. At
thesis from paraformaldehyde, CO and H . The reaction can room temperature, CO and H were charged sequentially into
be effectively accelerated by a Ru–Co bimetallic catalyst. the reactor to the desired pressure after the reactor was purged
Ethanol can be generated at above 140 °C. The TOF of ethanol with 1 MPa CO for three times. The reactor was placed in an
2
2
2
2
2
−
1
based on Ru metal can be as high as 17.9 h at 180 °C, and air bath at constant temperature, and the magnetic stirrer was
the selectivity of ethanol in the total products reaches 50.9 set at 800 rpm. After the reaction was complete, the reactor
C-mol%. In addition, the catalytic system can be easily reused was cooled in an ice-water bath. Then the residual gas was
and the TON of ethanol exceeds 805 after 5 cycles. This route released slowly and collected in a gas bag. Using toluene as
can be applied for paraformaldehydes of different molecular the internal standard, the reaction solution was analyzed by
weights. The high efficiency of this process can be ascribed to GC (Agilent 7890B) equipped with a flame ionization detector
the good synergy of the cascade reactions. The Ru and Co cata- and a HP-5 capillary column (0.32 mm in diameter and 30 m
lysts also work cooperatively to promote the reaction. This pro- in length). The liquid products were identified using GC-MS
tocol offers a new way for ethanol production and CO
utilization.
2
(Agilent-7890B-5977A) as well as by comparing the retention
times with the standards in the GC traces. The yields of the
products were calculated from the GC data. NMR data were
obtained on a Bruker Avance III HD 400 MHz NMR spectro-
meter ( H NMR, 400 MHz; C NMR, 100 MHz). The gaseous
samples were detected by a GC (Agilent 4890D) equipped with
a TCD detector and a packed column (carbon molecular sieve
TDX-01, 3 mm in diameter and 1 m in length) using argon as
the carrier gas.
1
13
Experimental
Chemicals
Ruthenium(III) acetylacetonate (Ru(acac) , 98%), dodecacarbo-
3
nyl triruthenium (Ru
chloride (RuCl , 99%), dichlorotris(triphenylphosphine) ruthe-
nium(II) ((PPh ) RuCl , 97%), nickel(II) acetylacetonate (Ni Recycling test
3
(CO)12, purity >98%), ruthenium(III)
3
3
3
2
(
2 3
acac) , 98%), manganese(III) acetylacetonate (Mn(acac) , 98%)
After the reaction, the reactor was cooled in an ice-water bath
for 2 h and the residual gas was released slowly. The amount
of the product was determined by the above method. The pro-
ducts generated in the reaction were removed under vacuum at
and lithium bromide (LiBr, 99.5%) were purchased from
Adamas Reagent. Paraformaldehyde (97%), cobalt(II) bromide
(
phenyl phosphine) cobalt(I) ((PPh )
(
CoBr
2
, 99.5%), cobalt(II) iodide (CoI
CoCl, 97%), lithium iodide
LiI, 99.95%), sodium iodide (NaI, 99.95%), ruthenium(III)
2
, 99.5%), chlorotris(tri-
3 3
85 °C for 5 h, which was affirmed by GC analysis. Then the
catalytic system was used directly for the next cycle.
bromide hydrate (RuBr
3
, Ru 25% min), potassium iodide
, Ir 48–54%), iron nona-
carbonyl (Fe (CO) , 99%), hexarhodium hexadecacarbonyl
(
KI, 99.9%), iridium acetate (Ir(OAc)
n
2
9
Conflicts of interest
(
Rh (CO)16, 98%) and 1-methyl-2-pyrrolidinone (NMP, 99%)
6
were provided by Alfa Aesar China Co., Ltd. Iron(III) acetyl-
acetonate (Ir(acac) , 99+%), copper(II) bromide (CuBr , 99%)
There are no conflicts of interest to declare.
3
2
and nickel(II) bromide (NiBr
2
, 99%) were purchased from Acros
Organics Company. Lithium chloride (LiCl, 98%) and 1,3-
dimethyl-2-imidazolidinone (DMI, 98%) were obtained from TCI
Acknowledgements
Shanghai Co., Ltd. Cobalt(II) chloride (CoCl
acetylacetonate (Co(acac) 99%), N,N-dimethylformamide
DMF, 99.5%), 1,3,5-trioxane (99%), tetrahydrofuran (THF,
2
, 99%), cobalt(II)
The authors thank the National Natural Science Foundation of
China (21373234 and 21533011), the National Key Research
and Development Program of China (2017YFA0403102), and
the Chinese Academy of Sciences (QYZDY-SSW-SLH013).
2
,
(
9
9.5%) and cyclohexane (99%) were purchased from J&K
Scientific Ltd. Toluene (99.8%) was obtained from Xilong
1
3
13
Chemical Co., Ltd. C paraformaldehyde (99 atom% C) was
supplied by Cambridge Isotope Laboratories, Inc. CO
99.99%), H (99.99%) and CO (99.99%) were purchased from
2
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