Table 3 Alcoholysis carried out over CuO/SiO2 on different
substratesa
Conv. Sel.
Epoxide
Product
Alcohol t (h) (%)
(%)
2-PrOH 1
EtOH
98
98
92b
93b
4
2-PrOH 3
EtOH
98
96
96
98
8
2-PrOH 0.75 100
100
Fig. 3 TPR analysis.
unambiguously show that catalytic activity has to be ascribed to
the presence of dispersed copper oxide on the catalyst surface.
Some other important points about the catalyst activity rise
from the comparison with related materials. Silica used as the
support does not show any activity in this reaction under the
same conditions, showing that the presence of copper oxide is
essential to generate acidity (Table 2, entry 1).
On the other hand, bulk copper oxide does not lead to any
reaction (Table 2, entry 2) and poor activity was also observed
with a catalyst prepared by Incipient Wetness (IW) technique
with a comparable copper content (Table 2, entry 3). These
data strongly support the hypothesis of a direct correlation
between copper oxide dispersion and acidic activity and once
again put in light the peculiar features of catalysts prepared
with this technique. Thus, the preparation method used, that is
the so-called chemisorption hydrolysis one, grants the formation
of highly dispersed CuO, in turn generating dispersed metallic
phase upon reduction, as shown by comparison with catalysts
prepared by IW technique.17
2-PrOH 18 91
2-PrOH 18 39
100
66
a T = 60 ◦C, P = 1 atm N2, magnetic stirring = 1400 rpm. b 6% of the
other regioisomer was formed.
Moreover, the presence of a metallic phase obtained through
reduction of CuO would give the chance to spread the synthetic
scope of the material to polyfunctional transformations and to
make a step forward with respect to common heterogeneous
acidic systems.
Thus, this catalyst in its reduced form already showed
outstanding properties for synthetic purposes, particularly in
alcohol dehydrogenation and both C O and C C double bond
reduction.18
Tests carried out with a much lower amount of catalyst show
that the catalyst still performs like his homogeneous counterpart
(Table 2 entry 5 vs. 7) but rising the TOF up to 18 (Table 2, entry
5).
As far as substrate scope is concerned, the reaction protocol
can be successfully applied also to other epoxides (Table 3),
even if poorly activated, showing to be competitive with respect
to the other heterogeneous systems reported, especially when
using bulky alcohols.
Work is in progress in order to further investigate the features
of the material and to widen its application as an acidic catalyst.
Acknowledgements
The authors thank the Italian Ministry of Education, University
and Research for financial support through the Project ‘‘Ital-
NanoNet’’ (Rete Nazionale di Ricerca sulle Nanoscienze; prot.
no. RBPR05JH2P).
Opening of 1,2-epoxyoctane, for example, is reported to be
promoted by [Fe(BTC)] with 1-propanol with 50% yield after
24 h.10b The difference in activity is more evident by comparing
the turnover numbers; namely TON = 1.67 in the case of
[Fe(BTC)] in the n-propanolysis of epoxyoctane and TON =
3.84 in the case of the alcoholysis of the same substrate with the
more hindered 2-propanol by using CuO/SiO2. This particular
behaviour puts CuO/SiO2 in a favorable position, as it reveals
its highest activity right when the other systems slow down.
From these results it is evident that the catalyst preparation
method used represents a convenient tool in order to have a
robust and reliable catalyst starting from homely materials.
Activity observed under air further demonstrates the high
versatility of this material. CuO/SiO2 is in addition an economic,
safe and non toxic catalyst, allowing one to carry out a no-
waste reaction due to both its heterogeneous nature and high
selectivity.
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This journal is
The Royal Society of Chemistry 2011
Green Chem., 2011, 13, 545–548 | 547
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