Highly efficient vanadium-catalyzed transformation of CH4 and CO to acetic acid

Article abstract of DOI:10.1021/ol990073r

(Matrix presented) The VO(acac)₂ (acac = 2,4-pentanedionato) catalyst in the presence of K₂S₂O₈ and CF₃COOH has been found to efficiently transform methane and CO to acetic acid selectively. The reaction of methane (5 atm) with CO (20 atm) at 80°C for 20 h gives acetic acid in 93% yield based on methane. Other vanadium compounds such as V₂O₃, V₂O₅, and NaVO₃ and various vanadium-containing heteropolyacids such as H₅PV₂-MO₁₀O₄₀, H₄PVW₁₁O₄₀, and H₅SiVW₁₁O₄₀ also work as catalysts.

Full text of DOI:10.1021/ol990073r

ORGANIC
LETTERS
1999
Vol. 1, No. 4
557-559
Highly Efficient Vanadium-Catalyzed
Transformation of CH and CO to Acetic
4
Acid
Yuki Taniguchi, Taizo Hayashida, Hiroyasu Shibasaki, Dongguo Piao,
Tsugio Kitamura, Teizo Yamaji, and Yuzo Fujiwara*
Department of Chemistry and Biochemistry, Graduate School of Engineering,
Kyushu UniVersity, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan
yfujitcf@mbox.nc.kyushu-u.ac.jp
Received May 4, 1999
ABSTRACT
The VO(acac)2 (acac ) 2,4-pentanedionato) catalyst in the presence of K2S O and CF3COOH has been found to efficiently transform methane
2
8
and CO to acetic acid selectively. The reaction of methane (5 atm) with CO (20 atm) at 80 °C for 20 h gives acetic acid in 93% yield based on
methane. Other vanadium compounds such as V O , V O , and NaVO and various vanadium-containing heteropolyacids such as H PV -
2
3
2
5
3
5
2
Mo10O , H PVW O , and H SiVW O40 also work as catalysts.
40
4
11 40
5
11
Herein we report the highly efficient transformation of
methane and CO to acetic acid by a vanadium catalyst in
the presence of K2S2O8 and CF3COOH.
acid based on methane in these metal-catalyzed reactions
are low. Therefore, there is a need to investigate new catalyst
systems to increase the methane-based yield from the
practical point of view.
In continuing studies on C-H bond activations,2f,9 we have
found that the VO(acac)2 catalyst in the presence of K2S2O8
and CF3COOH affords acetic acid almost quantitatively from
methane and CO.10 We report this novel reaction of methane
with CO in the presence of a catalytic amount of VO(acac)2
to afford acetic acid almost quantitatively (eq 1).
Activation and functionalization of C-H bonds of alkanes
have attracted great attention recently in connection with
resources for energy and chemicals production. Particularly,
methane, a major component of natural gas, is the most
abundant organic molecule, so its selective and high-yield
conversion into useful chemicals is strongly desired in
industry.1 In 1992, we reported the first direct catalytic
conversion of methane and CO to acetic acid by the Pd-
(OAc)2/Cu(OAc)2/K2S2O8/CF3COOH and Cu(OAc)2/K2S2O8/
CF3COOH catalyst systems.2 Most recently, we found that
the Yb(OAc)3/Mn(Ac)2/NaClO/H2O catalyst system causes
methane carboxylation, giving acetic acid.3 Acetic acid
synthesis from methane and CO by Hogeveen et al.4 and
Olah et al.5 has been reported using magic acids. Further-
more, K2S2O8-assisted,6 RhCl3-catalyzed,7 and V-catalyzed8
carboxylations of methane with CO were reported by Sen
and Lin and Shul’pin et al. However, the yields of acetic
To improve the acetic acid yield, we first examined the
catalytic activities of various vanadium compounds and
(2) (a) Nishiguchi, T.; Nakata, K.; Takaki, K.; Fujiwara; Y. Chem. Lett.
1992, 1141-1142. (b) Miyata, T.; Nakata, K.; Yamaoka, Y.; Taniguchi,
Y.; Takaki, K.; Fujiwara, Y. Chem. Lett. 1993, 1005-1008. (c) Nakata,
K.; Miyata, T.; Jintoku, T.; Kitani, A.; Taniguchi, Y.; Takaki, K.; Fujiwara,
Y. Bull. Chem. Soc. Jpn. 1993, 66, 3755-3759. (d) Nakata, K.; Yamaoka,
Y.; Miyata, T.; Taniguchi, Y.; Takaki, K.; Fujiwara, Y. J. Organomet. Chem.
1994, 473, 329-334. (e) Nakata, K.; Miyata, T.; Taniguchi, Y.; Takaki,
K.; Fujiwara, Y. J. Organomet. Chem. 1995, 489, 71-75. (f) Fujiwara, Y.;
Takaki, K.; Taniguchi, Y. Synlett 1996, 591-599. (g) Kurioka, M.; Nakata,
K.; Jintoku, T.; Taniguchi, Y.; Takaki, K.; Fujiwara, Y. Chem. Lett. 1995,
244.
* Corresponding author. Tel and Fax: 81-92-642-3548.
(1) (a) Shilov, A. E. ActiVation of Saturated Hydrocarbons by Transition
Metal Complexes; Reidel Publishing Co.: Dordrecht, 1984. (b) Hill, C. L.
ActiVation and Functionalization of Alkanes; Wiley-Interscience: New York,
1989. (c) Crabtree, R. H. Chem. ReV. 1995, 95, 987-1007. (d) Shilov, A.
E.; Shul’pin, G. B. Chem. ReV. 1997, 97, 2879-2932.
(3) Asadullah, M.; Taniguchi, Y.; Kitamura, T.; Fujiwara, Y. Appl.
Organomet. Chem. 1998, 12, 277-284.
10.1021/ol990073r CCC: $18.00 © 1999 American Chemical Society
Published on Web 07/08/1999

heteropolyacids using K2S2O8 (5.0 mmol) as an oxidant in
CF3COOH (5.0 mL) for the reaction of methane (40 atm)
with CO (20 atm). The results are summarized in Table 1.
K2S2O8 was found to be the best oxidant (TON 27.5) for
the VO(acac)2 catalyst in CF3COOH. Other oxidants such
as tert-BuOOH and NaOCl also work, while the TONs are
low (TON: 6-9).11 The reaction depends on the solvent.
CF3COOH is the best solvent for the carboxylation of
methane. Water can also serve as a solvent, although the
turnover number is low (TON: 5.9). Figure 1 shows the plot
Table 1. Reaction of Methane and CO Leading to Acetic Acid
in the Presence of Various Metal Catalysts, K2S2O8 and
CF3COOHa
yield (%) based on
acetic acid
catalyst
(mmol)
TONb CH4 CO K2S2O8
none
0
0
0
0
H3PMo12O40‚30H2O
H4PVMo11O40‚30H2O
H5PV2Mo10O40‚30H2O
H6PV3Mo9O40‚30H2O
H7PV4Mo8O40‚30H2O
H8PV5Mo7O40‚30H2O
H3PW6Mo6O40‚30H2O
H3PW12O40‚30H2O
H4SiW12O40‚30H2O
H5SiVW11O40‚29H2O
H4SiW4Mo8O40‚29H2O
H4SiMo12O40‚28H2O
VO(acac)2
0.01
1.11
1.23
1.21
1.46
1.21
0.02
0.11
0.01
1.56
0.04
0.03
1.38
2.00
1.28
1.41
0.08
0.19
0.2 0.01 0.02
22.2 0.56 1.12
24.5 0.64 1.28
24.2 0.63 1.26
29.2 0.76 1.52
24.2 0.63 1.26
0.4 0.01 0.02
2.1 0.05 0.10
0.2
22.2
24.5
24.2
29.2
24.2
0.4
2.1
0.1
31.1
0.8
0.6
27.5
39.9
25.5
28.2
1.6
0.1
0
0
31.1 0.81 1.62
0.8 0.02 0.04
0.6 0.02 0.04
27.5 0.71 1.42
39.9 1.03 2.06
25.5 0.66 1.32
28.2 0.73 1.46
1.6 0.04 0.08
3.8 0.10 0.20
VOSO4‚3H2O
V2O5
NaVO3
Pr6O11
Gd2O3
3.8
Figure 1. Plot of CH4 pressure vs turnover number (TON) of the
VO(acac)2 catalyst (0.05 mmol). The reaction of CH4 and CO (20
atm) in the presence of K2S2O8 (5.0 mmol) and CF3COOH (5 mL)
was carried out under the conditions of 80 °C, 20 h in a 120 mL
autoclave.
a CH4 (40 atm, 193 mmol), CO (20 atm, 97 mmol), catalyst (0.05 mmol),
K2S2O8 (5.0 mmol), CF3COOH (5.0 mL), 80 °C, 20 h in a 120mL autoclave.
b Turnover numbers (moles of acetic acid per mole of catalyst) determined
by GLC based on the catalyst.
As can be seen from the table, no acetic acid was formed in
the absence of catalyst. Addition of a catalytic amount (0.05
mmol) of vanadium compound increases the yield of acetic
acid. Interestingly, the vanadium-containing heteropolyacids
work as the catalyst, although the compounds are insoluble
in CF3COOH. Of the heteropolyacids tested, H7PV4Mo8O40
and H5SiVW11O40 gave high turnover numbers (TON), 29.2
and 31.1, respectively. Furthermore, simple vanadium com-
pounds such as VO(acac)2, VOSO4‚3H2O, and NaVO3 were
found to have high catalytic activity (TON: 27.5, 39.9, and
28.2, respectively, giving 0.71, 1.03, and 0.73% yields of
acetic acid based on methane, respectively). We selected
VO(acac)2 as a catalyst for the reaction of methane and CO
to convert to acetic acid because of its stability, solubility
in CF3COOH, and simplicity of the catalyst.
of CH4 pressure vs TON of the catalyst of the reaction of
methane with CO to give acetic acid. From the figure, one
can see that the TON increases with increasing methane
pressure until 20 atm. The TON became constant (ca. 30) at
pressures of methane higher than 20 atm. On the basis of
these results, a VO(acac)2/K2S2O8/CF3COOH catalyst system
was found to be one of the best catalyst systems for efficient
conversion of methane and CO to acetic acid.
To increase the yield of acetic acid based on methane, we
examined the carboxylation of methane (5 atm) under various
CO pressures in the presence of K2S2O8 (10 mmol),
CF3COOH (20 mL), and a catalytic amount of VO(acac)2
using a 25 mL stainless steel autoclave. The reaction with 2
and 5 atm of CO gave acetic acid in 37 and 45% yields based
on methane (the yields correspond to 92 and 45% based on
CO), respectively.12 The yield increased with increasing
pressure of CO and reached 93% at 20 atm. In this case, the
yields based on CO and K2S2O8 are 23 and 8.7%, respec-
tively.13 This is the highest yield of acetic acid from methane
(4) Hogeveen, H.; Lukas, J.; Roobeek, C. F. J. Chem. Soc., Chem.
Commun. 1969, 920-921.
(5) Bagno, A.; Bukala, J.; Olah, G. A. J. Org. Chem. 1990, 55, 4284-
4289.
(6) Lin, M.; Sen, A. J. Chem. Soc., Chem. Commun. 1992, 892-893.
(7) Lin, M.; Sen, A. Nature 1994, 368, 613-615.
(8) Nizova, G. V.; Su¨ss-Fink, G.; Stanislas, S.; Shul’pin, G. B. J. Chem.
Soc., Chem. Commun. 1998, 1885-1886.
(11) From a practical point of view, expensive K2S2O8 would not be
appropriate. The investigation to substitute K2S2O8 with air (O2) is now
under way.
(12) In all cases, the oxidation of CO leading to CO2 did not occur under
these reaction conditions on the basis of gas analysis.
(9) Fujiwara, Y.; Jintoku, T.; Takaki, K. Chemtech 1990, 636-640.
(10) Presented at the Symposium on Oceanian-Japanese Organic Chem-
istry, Tokushima, Japan, December, 1996, and the International Forum on
Environmental Catalysis ’97, Tokyo, Japan, March, 1997.
558
Org. Lett., Vol. 1, No. 4, 1999

and CO so far reported.14 Reactions at CO pressures higher
than 20 atm resulted in lower yields of acetic acid.
at 19.4 ppm) of acetic acid and the absence of a carbonyl
group (disappearance of the singlet at 182.3 ppm) (Figure 3).
From the 13C NMR spectra of the control experiments
using C-13 labeled CH4 and CO and the comparison with
authentic samples, it is confirmed that the methyl group and
carboxyl group of the acetic acid formed come from CH4
and CO, respectively. Figure 2 shows the 13C NMR spectrum
Figure 3. Carbon-13 NMR spectrum of the reaction mixture after
the reaction of 13CH4 with CO, showing that the sole product is
13CH3COOH.
Although the mechanism of the reaction is not yet clear
at this stage, a high oxidation state oxo-vanadium species
V(V)dO could abstract H• from CH4 to form a methyl
radical (CH3•), which could react with CO to give an acetyl
radical (CH3CO•). The CH3CO• radical would give acetic
acid via oxidation by V(V)dO to CH3CO+. The details of
the mechanism are under investigation.15
Figure 2. Carbon-13 NMR spectrum of the reaction mixture after
the recation of CH4 with 13CO, showing that the sole product is
CH313COOH.
In conclusion, we have found a new catalytic system that
converts methane and CO to acetic acid almost quantitatively.
The present reaction has the advantage that it employs cheap
methane and thus would have a potential to be industrialized
in the near future.
of the reaction mixture after the reaction of CH4 and 13CO.
Except for two quartets due to CF3COOH used as solvent,
only a singlet at 182.3 ppm assigned to the carbonyl group
of acetic acid was seen. In contrast to this, the spectrum of
the reaction mixture of a similar reaction using 13CH4 and
CO showed the presence of only the methyl group (singlet
Acknowledgment. This work was supported in part by
the Grant-in Aid for Scientific Research on Priority Area
No. 283 “Innovative Synthetic Reactions” and Scientific
Research (A) No. 09355031 from Monbusho. We thank the
Frontier Technology Research Institute, Tokyo Gas Co., Ltd.,
for the gift of 13CH4. We are also grateful to the Sumitomo
Chemical Co. Ltd. and the Sanyo Kasei Co. Ltd. for financial
support.
(13) The volumetric productivity of the present reaction is 6.04 × 10-10
mol/(cm3 s) lower than required for a practical process. The challenges in
increasing volumetric productivity are also under way by optimizing the
reaction conditions and the apparatus.
(14) Typical procedure: In a 25 mL stainless steel autoclave were placed
VO(acac)2 (0.05 mmol), K2S2O8 (10 mmol), CF3COOH (20 mL), and a
Teflon-coated magnetic stirring bar. The autoclave was closed, flushed three
times with CO, and pressurized to 20 atm with CO (3.80 mmol) and then
5 atm with CH4 (0.94 mmol). The mixture was heated at 80 °C with stirring
for 20 h. After cooling and venting of residual gases, the autoclave was
opened and the mixture was analyzed directly by GLC (Unisole 10T +
H3PO4) without aqueous workup using butyric acid as an internal standard
to give acetic acid (0.87 mmol) in 93% yield based on CH4.
OL990073R
(15) It is reported that radical initiators decompose CF3COOH to give
CF3•, which abstracts H• from CH4. However, the absence of VO(acac)2
in our reaction gives a very low yield of acetic acid. (a) Sen, A. Chem.
Res. 1998, 31, 550-557. (b) Reference 2d.
Org. Lett., Vol. 1, No. 4, 1999
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