Chemistry Reference
In-Depth Information
ability to exploit a phenomenon where organic sub-
strates are soluble in supercritical water or carbon
dioxide, and reactions performed under these condi-
tions have shown remarkable yields and selectivities
and effluent can be virtually eliminated [4-6].
Another area of chemistry that currently is being
considered seriously by chemical companies is ionic
liquids [7]. These materials are ionic compounds that
are liquids over a wide range of temperature (from
-20 to 300°C). They possess no vapour pressure and
are highly stable. Like supercritical fluids, they have
the ability to solubilise a wide range of organic com-
pounds and inorganic reagents, and in some cases
act as the catalyst for the reaction, e.g. Friedel-Crafts
reactions [8,9].
However, the majority of investment centres on
the area of catalysis, with increasing emphasis on
heterogeneous catalysis. There are many types of
heterogeneous catalysts but the intention here is
to focus on supported reagents and their use and
application in the fine chemical, agrochemical and
pharmaceutical industries.
3 Envirocats
TM
Envirocats are a range of commercially available sup-
ported reagent catalysts, manufactured by Contract
Chemicals Ltd (CCL), that catalyse Friedel-Crafts,
Brønsted acid and oxidation reactions [17]. There
are five commercially available catalysts in the range:
EPZG, EPZ10, EPZE, EPIC and EPAD. Although each
has been designed for a particular reaction type,
various customers and researchers have found that
they are equally effective in a variety of other appli-
cations (see later).
All of these catalysts are 'simple' supported
reagents, i.e. they are produced by the deposition of
a metal salt onto a high-surface-area inorganic
support. Although they may be termed 'simple', it is
not known for certain how the reagent interacts with
the support and it is very likely that these interac-
tions are, in reality, quite complex. However, various
methods of surface analysis has given us very valu-
able information about the nature of the active
sites that reside within these supported reagents.
3.1 Envirocat EPZ10
2 Supported Reagents
This was the first of the Envirocats to be developed
as a result of the collaboration between the Univer-
sity of York and CCL. Its more familiar name is
'CLAYZIC' and there are many reports in the litera-
ture describing a range of applications [1,11,18-23].
As the name suggests, this catalyst is prepared by
supporting ZnCl
2
on an acid-treated Montmoril-
lonite, e.g. Süd Chemie's K10. Envirocat EPZ10 was
designed to catalyse Friedel-Crafts alkylation of
aromatics. Fourier transform infrared spectroscopy
(FTIR) studies have shown this catalyst to contain
predominantly strong Lewis acid sites as well as
weak Brønsted acid sites [20]. In fact, the Lewis acid
sites are considerably stronger than those found
in homogeneous ZnCl
2
. This means that both alkyl
halide and olefins can be used to alkylate an
aromatic.
Although the first supported reagent was discovered
over 100 years ago [10], in-depth investigations into
their preparation, physical properties and applica-
tions have occurred only over the last 30 years. The
concept of a supported reagent is very simple: take
an active reagent that is normally used under homo-
geneous conditions and 'fix it' to an inactive solid
support.
The support can be organic (e.g. ion-exchange
resins) or inorganic (e.g. silica, alumina, alumino-
silicates, activated carbon). Ideally it should possess
a high surface area (>100 m
2
g
-1
) and the loading of
the reagent should be sufficient to form no more
than a monolayer on the surface of the support.
Some of the best results in this area of heterogeneous
catalysis have been obtained when a mesoporous
solid has been used as the support, where the size of
the pore can vary between 20 and 150 Å [11,12].
There are a wide variety of active reagents that can
be supported successfully: from finely divided pre-
cious metals for hydrogenation [13] and simple
metal salts [14] to transition metal complexes [15]
and organometallics [16] that are chemically bonded
to the surface of the support.
3.2 Envirocat EPZG
This is an iron, clay-based reagent. Here, FTIR studies
have shown that this catalyst contains a mixture of
strong Brønsted and Lewis acid sites. This supported
reagent was designed as a Friedel-Crafts benzoyla-
tion catalyst [24]. It will also catalyse some acylation
