‡ The ca. 20% loss of the catalyst is attributed to losses incurred during
sampling and mechanical losses associated with the small scale of the
reactions (200 mg of catalyst).
§ A standard catalytic experiment was interrupted by cooling to 0 °C at 70%
conversion. The catalyst was removed by filtration. The filtrate was again
heated under reflux. The reaction proceeded but with a rate about 30 times
lower; comparable to the blank reaction.
oxide and a-pinene oxide. These epoxides can be obtained in
moderate yields by buffering the reaction mixture with a small
amount of base (Na2HPO4).
Simple cooling of the reaction mixture in an ice-bath (0 °C)
gave crystallisation of the catalyst. Filtration and washing with
a small amount of cold solvent gave the pure catalyst in about
80% yield. Quantitative GC measurements showed that the
catalyst was not decomposed under the reaction conditions and
was completely removed from the reaction mixture after
filtration.‡ An interrupted catalytic experiment§ showed that no
catalytically active material was present in the filtrate. A
catalytic experiment on a larger scale (1 g of catalyst) gave a
recovery of the catalyst of 92% after cooling to 0 °C and
filtration. The recovered catalyst was still active in epoxidation
with the same rates and yield.
1 I. T. Horva´th and J. Ra´bai, Science, 1994, 266, 72; I. T. Horva´th, Acc.
Chem. Res., 1998, 31, 641; see also D. W. Zhu, Synthesis, 1993, 953.
2 I. T. Horva´th and J. Ra´bai, US Pat. 5463082 (1995), to Exxon Research
and Engineering Company; I. T. Horva´th, G. Kiss, R. A. Cook, J. E.
Bond, P. A. Stevens, J. Ra´bai and E. J. Mozeleski, J. Am. Chem. Soc.,
1998, 120, 3133.
The reaction could also be performed with 60% aqueous
hydrogen peroxide in boiling trifluoroethanol. This solvent is
known to be an excellent solvent in combination with aqueous
hydrogen peroxide.7 Table 3 shows the results for the
epoxidation of several alkenes catalysed by perfluoroheptade-
can-9-one in boiling trifluoroethanol. The yields are moderate
to high, but the formation of acid-sensitive epoxides is only
possible when the reaction medium is buffered by a phosphate
buffer (e.g. 5 mol% of Na2HPO4). In this solvent simple cooling
of the reaction mixture also resulted in crystallisation of the
catalyst, but the recovery was generally lower than in
dichloroethane. GC measurements indicated that a part of the
catalyst remained dissolved in the reaction mixture after
filtration.
3 G. Pozzi, S. Banfi, A. Manfredi, F. Montanari and S. Quici, Tetrahedron,
1996, 52, 11879; G. Pozzi, I. Colombani, M. Miglioli, F. Montanari and
S. Quici, Tetrahedron, 1997, 53, 6145; G. Pozzi, M. Cavazzini, S. Quici
and S. Fontana, Tetrahedron Lett., 1997, 38, 7605–8; J.-M. Vincent, A.
Rabion, V. K. Yachandra and R. H. Fish, Angew. Chem., Int. Ed. Engl.,
1997, 36, 2346; G. Pozzi, F. Montanari and S. Quici, Chem. Commun.,
1997, 69; G. Pozzi, F. Cinato, F. Montanari and S. Quici, Chem.
Commun., 1998, 877.
4 L. Kim, Br. Pat., 1399639 (1972) to Shell Internationale Research
Maatschappij N.V.; R. P. Heggs and B. Ganem, J. Am. Chem. Soc., 1979,
101, 2484; A. J. Biloski, R. P. Heggs and B. Ganem, Synthesis, 1980, 810;
P. A. Ganeshpure and W. Adam, Synthesis, 1996, 179.
5 L. S. Chen, G. J. Chen and C. Tamborski, J. Fluorine Chem., 1984, 26,
341.
6 G. Legemaat, W. Drenth, M. Schmidt, G. Prescher and G. Goor, J. Mol.
Catal., 1990, 62, 119.
7 T. M. Shryne and L. Kim, US Pat. 4024165 (1977) to Shell Oil
Company.
We are currently investigating the scope of perfluoro ketones
as catalysts for oxidations with hydrogen peroxide.
Notes and references
† Hexafluoroacetone is a gas. Perfluoroheptadecan-9-one is a solid with a
melting point of 110 °C and an atmospheric boiling point of about
170 °C.
Communication 8/09204D
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Chem. Commun., 1999, 263–264