Chemistry Reference
In-Depth Information
EFFECT OF CHAIN LENGTH ON CATALYST SELECTIVITY
AlCl3
EPA10
Modified EPA10
95
90
85
80
75
70
65
60
55
50
6
7
8
9 0 1 2 3 4 5 6
Chain length
Fig. 13.2
Effect of chain length on
catalyst selectivity.
ride to form diphenyl methane, di- and tri- alkylated
products also are produced. If these by-products are
isolated, dissolved in benzene and treated with AlCl
3
,
transalkylation or scrambling occurs to form more
diphenyl methane (see Scheme 13.30). Envirocat
EPA10 will not perform this reaction. Once the alkyl
group has been attached to the aromatic, the active
sites in the catalyst will not remove the alkyl group.
This demonstrates that EPA10 possesses some differ-
ent properties to homogeneous AlCl
3
and, along with
the leaching studies, shows that EPA10 is a true het-
erogeneous version of AlCl
3
.
Octyl
EPA10
+
Octene
20-25
°
C/2h
Scheme 13.2
8
In a study that compared EPA10 with homo-
geneous AlCl
3
, a determination of the effect of olefin
chain length on the selectivity was performed. In all
cases, EPA10 was approximately 10% more selective
than AlCl
3
with respect to monoalkylation. (Fig.
13.2). The graph in Fig. 13.2 also shows the selec-
tivity of a modified version of EPA10. This version
of the catalyst has been prepared from hexagonal
mesoporous silica [56-58] and exhibits a further 5%
selectivity for monoalkylation over EPA10.
Other aromatic substrates that have been olefin
alkylated using Envirocat EPA10 include diphenyl
ether. Alkylated diphenyl ether is a monomer.
Studies have shown that when using EPA10, higher
reaction temperatures are required, presumably to
break up the complex formed between the active site
and the ether linkage. Again, by using a 4 : 1 sub-
strate/olefin molar ratio, remarkable selectivity is
observed (see Scheme 13.29).
One other important feature of EPA10 that distin-
guishes it from its homogeneous counterpart is that
it will not perform scrambling reactions. For ex-
ample, in the alkylation of benzene with benzyl chlo-
9.2 Envirocat EPCS
The supported reagents described above make use of
the physical and chemical properties of inorganic
materials that are already available. However, the
emphasis has moved towards either modification
of the surface of existing materials or preparing a
support that will possess the desired properties,
e.g. hexagonal mesoporous silicas, the ultimate aim
being the engineering of a supported reagent that
can be fine-tuned to a particular application.
Envirocat EPCS is a cobalt-based catalyst that has
been prepared from modified mesoporous silica [59].
The metal centre is chemically bound to the support
via a ligand that is attached to the surface OH groups
found on the surface of the silica (see Scheme 13.31).
It has been designed to catalyse selectively the for-
mation of epoxides. Epoxide functionalities are
found in a wide variety of fine chemical, agrochem-
ical and pharmaceutical products [60]. The classical
