L.S. Belaroui et al. / C. R. Chimie 13 (2010) 466–472
471
Table 4
Baeyer-Villiger oxidation of cyclohexanone on different catalysts.
À1
Catalyst
Oxidant
Temp-time
Yield (%)
TOF (h
)
Reference
Sn-BEA
H
H
H
2
2
2
0
0
0
2
2
2
90 8C-3 h
70 8C-24 h
70 8C-6 h
18 8C-3.5 h
50 8C-6 h
25 8C-8 h
20 8C-24 h
52
58
70
98
78
61
85
42
[43]
Sn-HDT
/CH
/C
3
CN
115
20
[23]
MgAlSn-HDT
Ni anchored on SiO
MnAlPO
6
H
5
2
2
2
CN
[24]
2
PhCHO/O
PhCHO/O
PhCHO/O
m-CPBA
49
[17,37]
[38]
257
400
–
Fe-Phtal/Silica
No catalyst
This work
[44]
3
.5. Heterogeneous catalysis in the presence of supported
favourably with the other catalysts, since a turnover
number of about 400 mol of cyclohexanone per mol of Fe
and per hour is observed, for a reaction at atmospheric
pressure. Experiments with solvents other than benzene
and with lower starting benzaldehyde concentrations have
been undertaken in order to complete this preliminary
study and to make the reaction process more economical
and environmental friendly.
iron-phthalocyanine
To avoid a leaching of iron into reaction solution, iron-
containing catalyst covalently grafted onto support would
be interesting. Fe-phthalocyanine based catalyst [39,41]
were thus applied. Pure Fe-tetrasulfophthalocyanine
3
showed a lower activity than Fe(acac) , probably because
of the lack of solubility. Nevertheless, the conversion
reached 60% after 9 h, with a selectivity to lactone of about
4. Conclusion
8
0% in the presence of 9.1 mg of complex (1.4 mmol FePcS).
Then, FePcS covalently anchored onto silica was used as
catalyst. The results are reported in Fig. 9. In the presence
Baeyer-Villiger oxidation on Fe containing oxide is most
likely catalysed not in the heterogenous phase but in the
liquid phase by the traces of Fe extracted from the solid.
Fe phtalocyanine is to the best of our knowledge the first
true iron based heterogeneous catalyst. This catalyst
reaches greater than 95% selectivity at 60% conversion.
2
of 50.9 mg FePcS-SiO , containing also 1.4 mmol of
complex, the induction period was suppressed. The
selectivity was close to 100% for the lactone, and the
conversion reached about 60% after 10 h. When the
catalyst amount was doubled the conversion increased
only slightly (Fig. 10) and the selectivity decreased below
2 2
The lower cost of H O compared to benzaldehyde is at
least in part compensated by that of the catalyst, and by the
higher yield observed here.
9
0%, suggesting possible mass transfer limitations.
In order to determine a possible leaching of the complex,
a decantation of the catalyst was done at the end of the
reaction. This decantation is very slow (over a week) due to
the small size of the silica particles, which prevent from any
separation of the catalyst by filtration. Consequently this
also prevent from any experiments on the filtrated solutions
and reusability of the catalyst. The isolated solution was
analyzed for Fe by inductively coupled plasma mass
spectrometry method. The residual iron content of the
solution was below the detection limit indicating the
expected absence of complex leaching into solution; as
expected because the phthalocyanine ligand strongly
retains iron cation in the macrocycle and the complex itself
is supported on the silica surface by covalent anchoring.
Since Baeyer-Villiger reaction is an important synthetic
tool, it is interesting to compare the selectivities and yields
obtained by different routes. The comparison of the results
obtained on different catalysts in their optimum reaction
conditions is reported in Table 4 in terms of catalytic cycles
per metal centre and per hour or turnover frequencies.
Selectivities for lactone above 95% are observed in all cases,
but the yields are different depending on the catalyst. The
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