Single-pot conversion of methane into acetic acid in the absence of CO and with vanadium catalysts such as amavadine

Article abstract of DOI:10.1002/anie.200390219

Although its biological function is still unknown, the naturally occurring vanadium complex amavadine may be suitable for industrial applications: This compound (as well as other V^IV and V^V complexes with N,O and O,O ligands) are shown to act as catalysts for the direct conversion of methane into acetic acid, without requiring CO, under very mild conditions and in high yields (see scheme).

Full text of DOI:10.1002/anie.200390219

Angewandte
Chemie
The catalytic systems are based on a Viv or V complex
with poly- or bidentate N,O or O,O ligands in the presence of
the peroxodisulfate salt K S O as the oxidizing agent and in
v
Carboxylation of Methane
Single-Pot Conversion of Methane into Acetic
Acid in the Absence of CO and with Vanadium
Catalysts Such as Amavadine**
2
2
8
trifluoroacetic acid as the solvent. The V catalysts include:
oxovanadium(v) complexes 1 and 2 of the type [VO(N,O-L)];
Patrícia M. Reis, JosØ A. L. Silva, António F. Palavra,
Jo¼o J. R. Frafflsto da Silva,* Tsugio Kitamura,
Yuzo Fujiwara, and Armando J. L. Pombeiro*
2
CH3
CH
O
C
Despite current interest in the biological roles of vanadium,
its application in catalysis is still an underdeveloped field of
N
O
N
O
O
H3C CH
C
O
[
1]
O
research. We have already reported that amavadine, a
natural vanadium complex present in some Amanita fungi
and whose biological function is still unknown, can exhibit
haloperoxidase- and peroxidase-type activities and act as a
catalyst for the oxidation of some biological thiols,[ as well as
for the peroxidative halogenation, hydroxylation, and oxo-
V
O
C
CH CH3
O
O
C
O
2]
CH
CH3
[
3]
functionalization of alkanes and aromatic compounds.
3
Following this work, we have been searching for other
reactions that could be catalyzed by this and related V
complexes, in particular the conversion of methane—the
main component of natural gas and the most abundant and
least reactive alkane—into functionalized products with
added commercial value.[4] Recently attention has focused
2
+
synthetic amavadine 3 and its model 4, which are Ca salts of
V
IV
IV
complexes with N,O ligands; and V vanadyl complexes
5–9 of the type [VO(O,O-L) ]. Turnover numbers (TONs,
2
on the metal-catalyzed transformation of CH and CO into
moles of acetic acid per mol of metal catalyst) and yields
(based on methane) are given in Table 1, and typical
4
[
5–11]
acetic acid,
products without requiring the use of noxious CO, such as the
as well as the formation of carbonylated
conditions include conducting the reaction in CF COOH at
3
[
12]
conversion of CH into methyl esters and into acetic acid
808C with molar ratios of CH :V catalyst and K S O :V
4
9]
4
2
2
8
[
(
and methanol). The latter, the reaction of CH and CO2
catalyst of 46:1 (corresponding to CH pressure of 5 atm) and
4
4
catalyzed by NaVO /pyrazine-2-carboxylic acid (in the pres-
200:1, respectively. Usually the yields were determined after a
reaction time of 20 h, but often much shorter times were
sufficient to attain close values (see entries 1 and 11 for yields
obtained after 2h; the former is 92% of that in entry 2
obtained after 20 h).
3
ence of H O in aqueous solution), occurs in very low yield
2
2
based on CH (ca. 0.01%) and at a considerable pressure
4
[
9]
(
50 bar) of this gas, although at low temperature (408C).
The reaction also proceeds with CO, which apparently is the
carbonylating agent even when CO is used (CO is then
2
½
VOðNðCH CH OÞ ÞŠ 1
formed by reduction of CO by methyl and/or hydroxyl
2
2
3
2
[
9]
radicals). We now report the unprecedented (to our knowl-
edge) conversion of CH into CH COOH in the absence of
½VOðNðCH CH OÞ ðCH COOފ 2
2
2
2
2
4
3
either CO or CO , in a novel single-pot catalytic reaction
2
Ca½VðONðCHðCH ÞCOOÞ Þ Š 3
3
2 2
[Eq. (1)] under considerably mild conditions and in high yields.
Ca½VðONðCH
2
COOÞ
2
2
Þ Š 4
V cat:
CH ƒƒƒƒƒƒƒƒ ƒƒ !CH COOH
ð1Þ
4
3
K2S2O8; CF3COOH
½VOðmaltolateÞ
2
Š 5
ðmaltolate ¼ basic form of 3-hydroxy-2-methyl-4-pyroneÞ
[
*] Prof. J. J. R. Frafflsto da Silva, Prof. A. J. L. Pombeiro, P. M. Reis,
Dr. J. A. L. Silva, Prof. A. F. Palavra
Centro de Química Estrutural, Complexo I
Instituto Superior TØcnico
½
VOðHOCH CH NðCH CO Þ ÞŠ 6
2
2
2
2 2
½VOðCF COOÞ Š 7
3
2
Av. Rovisco Pais, 1049-001 Lisboa (Portugal)
Fax: (+351)21-846-4455
½
VOðCF SO Þ Š 8
3
3 2
E-mail: pcd1950@popsrv.ist.utl.pt
pombeiro@ist.utl.pt
VOSO4
9
Prof. T. Kitamura, Prof. Y. Fujiwara
Department of Chemistry and Biochemistry
Graduate School of Engineering
The most active catalysts, which can give yields over 50%
and TONs close to 30, are complex 1 within the type
[VO(N,O-L)], both amavadine (3) and its model 4 of the
Kyushu University, Fukuoka, 812-8581 (Japan)
[
V(N,O-L) salts, and complexes 5, 7, and 8 of the type
[**] This work was supported in part by the Fundaç¼o para a CiÞncia e a
Tecnologia (FCT) and the POCTI Programme, Portugal.
[VO(O,O-L) ]. In contrast 2, 6, and 9 exhibit much lower
2
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Communications
Table 1: Conversion of methane into acetic acid.[a]
iv
the þ5 oxidation state (the starting blue V complexes 3 and 4
v
Entry
Cat.
p(CH )
p(CO)
t [h]
TON[c]
Yield
[%]
are oxidized by K S O to the respective red V forms).
2
2
8
4
[
b]
[b]
[d]
[
atm]
[atm]
Interestingly, the carboxylation of CH does not require
4
CO. With amavadine (3) and its model 4, as well as with
complex 1, yields of acetic acid within the 20–30% range
1
2
3
4
5
6
7
1
1
1
1
1
1
1
1
1
2
3
3
3
3
3
4
4
4
4
5
5
6
7
7
7
8
8
8
9
9
5
5
5
5
3
8
12
5
5
5
5
5
5
5
5
5
5
12
5
5
5
5
5
5
5
5
5
5
5
5
–
–
5
15
15
15
15
15
5
–
–
–
5
15
15
–
15
15
15
–
15
–
–
5
20
–
5
20
–
2
9.2
19.7
21.4
23.5
22.2
18.5
33.7
25.6
35.3
42.7
4.8
15.3
29.4
21.2
17.3
54.3
20.9
20.6
25.4
24.5
14.9
17.6
4.5
20
20
20
20
20
20
20
20
20
2
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
10.0
10.9
10.4
5.1
24.7
28.2
10.4
3.9
2.2
7.0
13.4
9.7
8.1
12.0
9.6
9.6
27.9
5.4
6.8
8.2
2.0
1.8
10.5
8.8
(TON ca. 10–13) are commonly obtained under standard
conditions (entries 12, 16, and 2). CH is the carbon source for
4
the methyl group of acetic acid as we demonstrated by using
13
13
C-labeled CH . The product, CH COOH, was determined
4
3
by the C{ H} and 13C NMR spectra of the reaction solution.
13
1
[
e]
f]
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
The carbon source of the carboxylic acid group, in the absence
[
[
4d]
of CO, is CF COOH, which is known to undergo radical
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
reactions with K S O derivatives to form, for example, CO .
2
2
8
2
However, our reactions do not appear to proceed via a free
CO intermediate or free CH OH, since the former does not
2
3
promote the carboxylation and the latter is not converted into
the acid under our experimental conditions.
Although the mechanistic details are still unknown, the
carboxylation of methane may possibly involve the formation
of the methyl radical and the derived methyl cation (upon
[
[
g]
h]
hydrogen abstraction from CH followed by oxidation, for
4
v
v
example, by a V -oxo or V -peroxo species) which would
[12]
react with CF COOH. The role of the chelating N,O and
3
3.8
O,O ligands still remains unclear, but one can postulate their
involvement (upon decoordination of a single N or O atom of
the ligand) in proton-transfer steps, for example, among oxo-
or hydroxo-V species and CF COOH or K S O (which,
23.0
19.0
14.6
22.1
29.0
2.2
6.7
10.1
12.1
1.0
3
2
2
8
[
12]
ꢀ
acting as an oxidant, can give HSO4 and HSO C). A related
4
role in promoting proton transfer from coordinated H O to
2
2
20
2.3
5.0
[13]
oxo ligands has been suggested for some vanadium systems
[
(
a] Reaction conditions (unless stated otherwise): metal complex catalyst
such as nBu NVO /H O /O , whose activity towards alkane
4
3
2
2
2
0.0625 mmol), K S O (12.5 mmol, i.e. 200:1 molar ratio of K S O to
[9,13]
2
2
8
2
2
8
oxygenation requires
particular N,O additives as cocata-
metal catalyst), CF COOH (23 mL), 808C, in an autoclave (39-mL
capacity). Amounts of CH or CO gas correspond to 0.572 molatmꢀ1,
with pressure measured at 258C; for example, 2.86 and 8.58 mmol gas
for pressures of 5 and 15 atm, respectively. The catalyst complexes were
prepared according to the literature: 1, 3, 4, 5, 8. New
complexes 2, 6, and 7 were prepared by processes similar to those for 1,
of[18], and for 8, respectively, but with the appropriate ligand. VOSO4,
CF COOH, and K S O were purchased from Merck or Aldrich.
3
lysts (e.g. heteroaromatic aminocarboxylic acids like pyra-
4
zine-2-carboxylic acid). Moreover, in amavadine (3) and its
2
model 4, the hydroxyimino(1ꢀ) groups of the ligands, h -(O-
ꢀ
[
14]
[15]
[15]
[16]
[17]
N < ) , are isoelectronic with peroxo(2ꢀ), and their possible
behavior as peroxo-like ligands also deserves consideration.
The formation of CH COOH from CH can be enhanced
3
4
3
2
2
8
by the presence of CO at sufficiently low pressures, which
suggests that CO can behave as a carboxylating agent, as was
clearly observed for 7 (Table 1, entries 23–25) and 8 (en-
tries 26–28). For 1 this enhancing effect is very small
(Figure 1), whereas for 3 and 4 (entries 12–14 and 16, 17) it
was not detected at all. Moreover, higher CO pressures often
result in an inhibiting effect (Figure 1 for 1 and entries 23–25
for 7), conceivably because ligation of CO lowers the activity
of the catalyst; we are investigating this possibility.
[
b] Measured at 258C. [c] Turnover number (moles of acetic acid per mol
of metal catalyst) determined by GLC or GC-MS; the reaction mixture,
with an internal standard, was filtered to remove the ionic species and
the metal complex, diethyl ether was added (which leads to further
precipitation), and the reaction mixture was filtered again. [d] Molar yield
[
[
footnote [a] by using a higher volume of CF COOH (28 mL). [f] Five
times more metal catalyst (0.312 mmol) was used. [g] Less CH was
used (1.02 mmol) than in the conditions described in footnote [a] by
using a smaller reactor (23.5 mL): metal catalyst (0.046 mmol), K S O
8
%] based on CH , i.e. moles of acetic acid per 100 moles of methane.
4
e] Less CH was used (1.84 mmol) than in the conditions described in
4
3
4
2
2
(
9.2 mmol i.e. 200:1 molar ratio of K S O to metal catalyst), CF COOH
2 2 8 3
(
17 mL). [h] Less CH was used (1.02 mmol) than in the conditions
4
described in footnote [a] by using a higher volume of CF COOH (32 mL).
3
activities. Of the oxo-V complexes with aminoalcohol ligands
(
basic forms), 1 is the most active, whereas the activity
decreases on replacement of alcoholato by carboxylato
groups; that is, 2 and 6 are less active than 1 (Table 1,
entries 10, 22, 2). The active species, at least for the [VO(N,O-
Figure 1. Effect of CO pressure on the yield of acetic acid derived from
methane (at 5 atm) by using catalyst 1 and K S O in CF COOH (see
Table 1).
2
2
8
3
2
-
L)] and [V(N,O-L)] types, are believed to have the metal in
822
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Chemie
The increase of CH pressure (up to 12atm in our work)
[7] a) M. Asadullah, T. Kitamura, Y. Fujiwara, Angew. Chem. 2000,
12, 2609; Angew. Chem. Int. Ed. 2000, 39, 2 475; b) M.
Asadullah, T. Kitamura, Y. Fujiwara, Appl. Organomet. Chem.
999, 13, 539.
4
1
can have a notorious enhancing effect on the TONs (en-
tries 5–7 and 17, 18), whereas the yield tends to decrease after
reaching a maximum (entries 5–7). Higher yields can be
1
[
[
8] M. Asadullah, T. Kitamura, Y. Fujiwara, Chem. Lett. 1999, 449.
9] G. V. Nizova, G. Sꢀss-Fink, S. Stanislas, G. B. Shul'pin, Chem.
Commun. 1998, 1885.
obtained when less CH is used but at the same pressure (e.g.,
4
entry 8 vs. 4 and entry 15 vs. 14), or when more metal catalyst
is employed (entry 9 vs. 3).
[10] a) M. Lin, A. Sen, Nature 1994, 368, 613; b) M. Lin, A. Sen, J.
Chem. Soc. Chem. Commun. 1992, 892.
11] A. Bagno, J. Bukala, G. A. Olah, J. Org. Chem. 1990, 55, 4284.
12] a) D.-G. Piao, K. Inoue, H. Shibasaki, Y. Taniguchi, T. Kitamura,
Y. Fujiwara, J. Organomet. Chem. 1999, 574, 116; b) G. Yin, D.-
G. Piao, T. Kitamura, Y. Fujiwara, Appl. Organomet. Chem.
The reaction does not occur in the absence of K S O ,
2
2
8
[
[
CF COOH (which is replaced by ethanol or water as the
3
solvent), or the V catalyst. Related complexes with other
metals, even of the same periodic group, display little or no
catalytic activity. The carboxylation by CO is also strongly
2000, 14, 438.
hampered when acetonitrile is used instead of CF COOH.
[13] a) G. B. Shul'pin, J. Mol. Catal. A 2002, 189, 39; b) G. B. Shul'pin,
Y. N. Kozlov, G. V. Nizova, G. Sꢀss-Fink, S. Stanislas, A.
Kitaygorodskiy, V. S. Kulikova, J. Chem. Soc. Perkin Trans. 2
3
This direct one-pot synthesis of CH COOH from CH4
3
without required CO is a process whose simplicity and low
energy requirements contrast with the features of the
2001, 1351.
[
14] D. C. Crans, H. Chen, O. P. Anderson, M. M. Miller, J. Am.
Chem. Soc. 1993, 115, 6769.
15] R. E. Berry, E. M. Armstrong, R. L. Beddoes, D. Collison, S. N.
Ertok, M. Helliwell, C. D. Garner, Angew. Chem. 1999, 111, 871;
Angew. Chem. Int. Ed. 1999, 38, 795.
[
4e]
industrial route. The established synthesis involves three
separate stages: the metal-catalyzed high-temperature steam-
[
reforming of CH , conversion of the derived synthesis gas to
4
CH OH, and final carboxylation of CH OH with CO and
3
3
either an expensive Rh catalyst (Monsanto process) or an Ir
catalyst (BP–Amoco modified process). The route we now
report has also the advantage of requiring a cheap V catalyst,
but we are still searching for less expensive solvents,
carboxylating agents, and oxidants. The V catalysts used in
this work are also effective in the carboxylation of other
[16] P. Caravan, L. Gelmini, N. Glover, F. G. Herring, H. Li, J. H.
McNeill, S. J. Rettig, I. A. Setyawati, E. Shuter, Y. Sun, A. S.
Tracey, V. G. Yuen, C. Orvig, J. Am. Chem. Soc. 1995, 117, 12759.
[
17] C. T. Chen, J. H. Kuo, C. H. Li, N. B. Barhate, S. W. Hon, T. W.
Li, S. D. Chao, C. C. Liu, Y. C. Li, I. H. Chang, J. S. Lin, C. J. Liu,
Y. C. Chou, Org. Lett. 2001, 3, 3729.
[
18] B. J. Hamstra, A. L. P. Houseman, G. J. Colpas, J. W. Kampf, R.
LoBrutto, W. D. Frasch, V. L. Pecoraro, Inorg. Chem. 1997, 36,
4866.
alkanes apart from CH to give the corresponding carboxylic
4
acids, and the study of these catalytic reactions is underway.
Of particular interest is the behavior of amavadine, whose
catalytic activity is now extended to such interesting reactions.
Can they take place in natural conditions and also be of
biological significance?
Received: September 24, 2002 [Z50224]
[
1] a) J. J. R. Frafflsto da Silva, R. J. P. Williams, The Biological
Chemistry of the Elements, 2nd ed., Clarendon Press, Oxford,
2001; b) “Vanadium Compounds”: ACS Symp. Ser. 1998, 711;
c) D. Rehder, Coord. Chem. Rev. 1999, 182, 297.
2] a) C. M. M. Matoso, A. J. L. Pombeiro, J. J. R. Frafflsto da Silva,
M. F. C. G. da Silva, J. A. L. Silva, J. L. Baptista-Ferreira, F.
Pinho-Almeida, ACS Symp. Ser. 1998, 711, 241 – 247;
b) M. F. C. G. da Silva, J. A. L. Silva, J. J. R. Frafflsto da Silva,
A. J. L. Pombeiro, C. Amatore, J.-N. Verpeaux, J. Am. Chem.
Soc. 1996, 118, 7568.
[
[
3] P. M. Reis, J. A. L. Silva, J. J. R. Frµusto da Silva, A. J. L. Pom-
beiro, Chem. Commun. 2000, 1845.
[
4] a) C. Jia, T. Kitamura, Y. Fujiwara, Acc. Chem. Res. 2001, 34,
633; b) R. H. Crabtree, J. Chem. Soc. Dalton Trans. 2001, 2437;
c) A. E. Shilov, G. B. Shul'pin, Chem. Rev. 1997, 97, 2879; d) Y.
Fujiwara, K. Takaki, Y. Taniguchi, Synlett 1996, 591; e) Catalytic
Activation and Functionalisation of Light Alkanes (Eds.: E. G.
Derouane, J. Haber, F. Lemos, F. R. Ribeiro, M. Guisnet),
Kluwer, Dordrecht, 1998; e) R. H. Crabtree, The Organometal-
lic Chemistry of the Transition Metals, Wiley, New York, 2001,
chap. 12.
[
5] Y. Taniguchi, T. Hayashida, H. Shibasaki, D.-G. Piao, T.
Kitamura, T. Yamaji, Y. Fujiwara, Org. Lett. 1999, 1, 557.
6] a) T. Nishiguchi, K. Nakata, K. Takaki, Y. Fujiwara, Chem. Lett.
[
1992, 1141; b) M. Asadullah, Y. Taniguchi, T. Kitamura, Y.
Fujiwara, Appl. Catal. A 2000, 194–195, 443.
Angew. Chem. Int. Ed. 2003, 42, No. 7
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