156
PALOMEQUE, LOPEZ, AND FIGUERAS
substrates of low reactivity, stronger bases are required. Let ported by Choudary et al. (19), which reaches a yield of
us recall here that in earlier work on the epoxidation of α- 90% in 5 min with 2-cyclohexen-1-one; however it shows
isophorone on solid bases (calcined HDT and KF/γ Al2O3) an interesting possibility of recycling after being obtained
the best yield in epoxide was reported to be 66% after 72 h, from activation at 923 K—the solid is thermally stable and
withaoxygenselectivitylimitedto41%. TheworkofHutter can therefore be regenerated by calcination.
et al. (17, 18) and Beck et al. (4) has been relative to the use
of TBHP, so the epoxidation by H2O2 was far less doc-
umented. The MgLa catalyst works approximately in the
same conditions as HDT but gives a significantly higher ac-
tivity, since the same yield is reached in 24 instead of 72 h,
with a high selectivity to H2O2, thus illustrating the impor-
tance of basic strength in this reaction.
Our results can be compared with those on titania–silica
aerogels reported by Hutter et al. (17) for the oxidation
by TBHP: in both cases a good selectivity to the epoxide
was noticed (>98%) in spite of the different solvents—
ethylbenzene for Ti catalysts and methanol for MgLa ox-
ides. The yield reported on Ti catalyst was about 70% af-
ter 16 h at 323 K compared with the 47% after 9 h and
67% after 24 h at room temperature observed here. It was
reported earlier (16) that a faster rate could be obtained
at 333 K with no loss of TBHP selectivity. It can there-
fore be supposed that the result of basic catalysis can be
improved.
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In conclusion, TBHP can indeed be activated by hydro-
talcites provided they are decarbonated, then rehydrated.
The main difference between basic catalysts and titanosili-
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This may have practical implications for the separation of
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