N. Al-Haq et al. / Tetrahedron Letters 44 (2003) 769–771
771
A typical procedure17 involves the gentle reflux of a
References
mixture containing the catalyst at concentrations of
2.7–3.3 mol% Ce(IV)18 and sodium bromate as the
re-oxidant in an acetonitrile-water solvent system.
1. Miyazawa, T.; Endo, T.; Shihashi, S.; Okawara, M. J.
Org. Chem. 1985, 50, 1332–1334.
2. Adam, W.; Curci, R.; Edwards, J. O. Acc. Chem. Res.
1989, 22, 205–211.
3. Arterburn, J. B. Tetrahedron 2001, 57, 9765–9788.
4. Dess, D. B.; Martin, J. C. J. Am. Chem. Soc. 1991, 113,
7277–7287.
5. Trost, B. M.; Masuyama, Y. Tetrahedron Lett. 1984, 25,
4417–4420.
Although neither the procedure nor the catalyst systems
have been optimised, yields are very good and the
catalyst can be effectively recycled, as the examples
with 1-phenyl-1-propanol and benzyl alcohol demon-
strate. It has been reported11 that sodium bromate
alone does not oxidise alcohols. However, in order to
confirm this finding we investigated its reaction with
benzyl alcohol, 2-octanol and 2-dodecanol, respectively.
Only starting alcohols were obtained even after pro-
longed reaction times. To check for leaching, the cata-
lyst was filtered, at the reaction temperature, from the
oxidation of 1-phenyl-1-propanol after two hours and
the filtrate was allowed to react further. No further
oxidation was observed. This suggests that oxidation is
occurring at the immobilised cerium(IV) site.
6. Murahashi, S.; Naota, T.; Kuwabara, T. Tetrahedron
Lett. 1985, 26, 925–929.
7. Besson, M.; Gallezot, P. In Fine Chemicals through Het-
erogeneous Catalysis; Sheldon, R. A.; van Bekkum, H.,
Eds.; Wiley-VCH: Weinheim, 2001; pp. 491–518.
8. Trahanovsky, W. S.; Brown, G. L.; Young, B. L. J. Org.
Chem. 1967, 32, 3865–3868.
9. Trahanovsky, W. S.; Young, B. L. J. Org. Chem. 1967,
32, 2349–2350.
10. Ho, T.-L. Synthesis 1973, 347–355.
11. Ho, T.-L. Synthesis 1978, 936.
12. Tomioka, H.; Oshima, K.; Nizaki, H. Tetrahedron Lett.
1982, 23, 539–542.
13. Aliev, A.; Li Ou, D.; Ormsby, B.; Sullivan, A. C. J.
Mater. Chem. 2000, 10, 2758–2764.
Fragmentation and dehydration were observed side
reactions10 when stoichiometric quantities of ceriu-
m(IV) ammonium nitrate or sulphate were used with
alcohols containing aryl, heteroaryl or a range of other
functionalities. Reaction using the CeEPS catalysts with
benzoin, mandelic acid and 1-phenyl-1-propanol gave
the corresponding ketones in very high yield. No frag-
mentation or dehydration products were observed in
these cases. Oxidation of a number of benzylic alcohols
utilising the CeEPS catalysts afforded the correspond-
ing carboxylic acids. The presence of the respective
aldehydes19 was observed during the reaction. Interest-
ingly it has been reported8 that reaction of benzyl
alcohol with stoichiometric quantities of the homoge-
neous reagent CAN gives only benzaldehyde. The
CeEPS catalysts can also oxidise primary alcohols
although at a slower rate.
14. Jurado-Gonzalez, M.; Li Ou, D.; Ormsby, B.; Sullivan,
A. C.; Wilson, J. R. H. Chem. Commun. 2001, 67–68.
15. Idealised structure assuming 100% condensation.
16. Jurado-Gonzalez, M.; Sullivan, A. C.; Wilson, J. R. H. J.
Mater. Chem. 2002, 12, 3605–3609.
17. Typical procedure. The alcohol dissolved in acetonitrile
(4 ml) was added to the CeEPS catalyst. The mixture was
stirred and then sodium bromate (0.3 g, 2 mmol) and
water (0.5 ml) was added and the mixture was gently
refluxed under an atmosphere of nitrogen. On completion
the catalyst was filtered and washed well with ether and
water. The filtrate was separated, dried and concentrated
under reduced pressure.
18. Ce+4 concentration was determined by titration after the
metal ion was liberated by treatment of the CeEPS with
concentrated nitric acid.
19. The cerium(IV) immobilised silica phosphonate catalysts
oxidises benzaldehyde to benzoic acid.
In conclusion we have demonstrated that a new cata-
lytic system based on immobilised cerium(IV) phospho-
nates can effectively oxidise a range of alcohols to
either ketones or carboxylic acids in very high yield.