COMMUNICATIONS
Bartholomew, Tetrahedron Lett. 1984, 25, 2035 2038; J. I. Concep-
A New Catalyst for the Selective Oxidation of
Butane and Propane**
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cion, C. G. Francisco, R. Hernandez, J. A. Salazar, E. Suarez,
Tetrahedron Lett. 1984, 25, 1953 1956; A. MartÌn, J. A. Salazar, E.
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Suarez, J. Org. Chem. 1996, 61, 3999 4006; R. L. Dorta, A. MartÌn,
Mark E. Davis,* Christopher J. Dillon,
Joseph H. Holles, and Jay Labinger
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J. A. Salazar, E. Suarez, T. Prange, J. Org. Chem. 1998, 63, 2251 2261.
[7] K. Orito, S. Satoh, H. Suginome, J. Chem. Soc. Chem. Commun. 1989,
1829 1831.
[8] A. E. Dorigo, K. N. Houk, J. Org. Chem. 1988, 53, 1650 1664.
[9] V. S. R. Rao, P. K. Qasba, P. V. Balaji, R. Chandrasekaran, Confor-
mation of Carbohydrates, Harwood Academic Publishers, Singapore,
1998, pp. 91 122.
[10] Molecular mechanics calculations were performed using the AM-
BER* all-atom force field and the GB/SA solvation model for CHCl3
as implemented in version 7.0 of the MacroModel and BatchMin
packages.
The abundance and low cost of light alkanes has motivated
the search for new catalytic materials that can accomplish
selective oxidation processes. The conversion of n-butane to
maleic anhydride over V-P-O catalysts with molecular oxygen
is commercially well established.[1] Other reactions of current
interest are the production of acetic acid from ethane and
acrylic acid from propane. Polyoxometalates are among the
numerous catalytic materials that have been extensively
investigated for each of the aforementioned reactions. Typ-
ically different polyoxometalate compositions have been used
for each alkane. These compounds (and other mixed-metal
oxides) have not been found to perform as well as V-P-O
catalysts for the conversion of n-butane to maleic anhydride,[2]
or as well as mixed-metal oxides containing Mo-V-Nb-Te[3a,b]
or Mo-V-Nb-Sb[4] for conversion of propane to acrylic acid.
We have discovered a new catalyst system that achieves
selective oxidation of both n-butane and propane. Li et al.
reported that a solid obtained by treating molybdophosphoric
acid, H3PMo12O40 (henceforth denoted as PMo12) with
pyridine followed by activation in nitrogen at 4208C exhibits
catalytic activity for oxidation of propane to acrylic acid.[5]
Ueda and Suzuki also showed that molybdovanadophosphor-
ic acid (denoted as PMo11V) similarly treated gives a less
active and selective catalyst.[6] Our catalysts are obtained from
PMo12 and PMo11V (prepared by known methods[7]), ex-
changed sequentially with niobium oxalate (giving NbPMo12
and NbPMo11V) and pyridine (giving NbPMo12pyr and
NbPMo11Vpyr) in aqueous media, followed by heating to
4208C in flowing helium. The elemental compositions of the
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[11] F. Brisse, R. H. Marchessault, S. Perez, P. Zugenmaier, J. Am. Chem.
Soc. 1982, 104, 7470 7476.
[12] H. Senderowitz, W. C. Still, J. Org. Chem. 1997, 62, 1427 1438.
[13] Molecular mechanics calculations of the transition state were
performed using the MM2 force field as implemented in Chem3D,
release 3.2 (CambridgeSoft Corp., Cambridge, MA), parametrized
according to ref. [8].
[14] K. Bock, H. Pedersen, Acta Chem. Scand. Ser. B 1988, 42, 75 85; S.
Cottaz, C. Apparau, H. Driguez, J. Chem. Soc. Perkin Trans. 1 1991,
2235 2241.
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[15] J. L. Courtneidge, J. Lusztyk, D. Page, Tetrahedron Lett. 1994, 35,
1003 1006.
[16] CCDC 174444 (2) contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge via
Crystallographic Data Centre, 12, Union Road, Cambridge CB21EZ,
UK; fax: (44)1223-336-033; or deposit@ccdc.cam.ac.uk).
[17] F. A. L. Anet in Conformational Analysis of Medium-Sized Hetero-
cycles (Ed.: R. S. Glass), VCH, New York, 1988, pp. 35 95; R. R.
McGuire, J. L. Pflug, M. H. Rakowsky, S. A. Shackelford, A. A.
Shaffer, Heterocycles 1994, 38, 1979 2004; U. Burkert, Z. Natur-
forsch. B 1980, 35, 1479 1481.
[18] G. O. Aspinall, T. N. Krishnamurthy, W. Mitura, M. Funabashi, Can. J.
Chem. 1975, 53, 2182 2188; G. O. Aspinall, O. Igarashi, T. N.
Krishnamurthy, W. Mitura, M. Funabashi, Can. J. Chem. 1976, 54,
1708 1713.
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[19] C. G. Francisco, E. I. Leon, A. MartÌn, P. Moreno, M. S. RodrÌguez, E.
¬
Suarez, J. Org. Chem. 2001, 66, 6967 6976.
solids thus obtained are typically Nb0.1 0.25PMo12(pyr)3 or
4
[20] S. Kim, T. A. Lee, Y. Song, Synlett 1998, 471 472; D. Crich, X. Huang,
M. Newcomb, J. Org. Chem. 2000, 65, 523 529.
Nb0.1 0.25PMo11V(pyr)3 4 within experimental error.
Table 1 reports the catalytic performance of various mate-
rials for n-butane oxidation under hydrocarbon-rich condi-
tions (C4/O2 2/1). All the solids prepared from precursors
containing both pyridine and niobium are very active and
selective. Note particularly the high space time yield (STY)
for NbPMo12pyr and NbPMo11Vpyr achieved by increasing
the total flow rate by a factor of eight (15 mLminÀ1 to
120 mLminÀ1; see entries 6 and 7, and 13 and 14, respectively,
in Table 1). In contrast, the polyoxometalates that have not
been exposed to pyridine do not exhibit significant activity
(entries 1, 2, 8, and 9, Table 1), while samples treated with
pyridine but without niobium do not give the highest activities
[21] P. Luger, H. Paulsen, Carbohydr. Res. 1976, 51, 169 178; J. R. Snyder,
A. S. Serianni, J. Org. Chem. 1986, 51, 2694 2702.
[22] S. Berger in Encyclopedia of Nuclear Magnetic Resonance, Vol. 2
(Eds.: D. M. Grant, R. K. Harris), Wiley, Chichester, 1996, pp. 1168
1172.
[23] D. Crich in Radicals in Organic Synthesis, Vol. 2 (Eds.: P. Renaud,
M. P. Sibi), Wiley-VCH, Weinheim, 2001, pp. 188 205.
[24] For recent papers, see: H. G. Bazin, M. W. Wolff, R. J. Linhardt, J.
Org. Chem. 1999, 64, 144 152; A. Lubineau, O. Gavard, J. Alais, D.
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Bonnaffe, Tetrahedron Lett. 2000, 41, 307 311; R. Ojeda, J. L. Paz, M.
MartÌn-Lomas, J. M. Lasaletta, Synlett 2000, 1316 1318; H. Takaha-
shi, Y. Hitomi, Y. Iwai, S. Ikegami, J. Am. Chem. Soc. 2000, 122, 2995
3000; S.-C. Hung, S. R. Thopate, F.-C. Chi, S.-W. Chang, J.-C. Lee, C.-
C. Wang, Y.-S. Wen, J. Am. Chem. Soc. 2001, 123, 3153 3154; I.
Capila, R. J. Linhardt, Angew. Chem. 2002, 114, 428 451; Angew.
Chem. Int. Ed. 2002, 41, 390 412.
[*] Prof. M. E. Davis, C. J. Dillon, J. H. Holles
Chemical Engineering
California Institute of Technology
Pasadena, CA 91125 (USA)
Fax : (1)626-568-8743
Dr. J. Labinger
Beckman Institute
California Institute of Technology
Pasadena, CA 91125 (USA)
[**] This work was funded by BP.
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¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002
1433-7851/02/4105-0858 $ 17.50+.50/0
Angew. Chem. Int. Ed. 2002, 41, No. 5