Chemistry Reference
In-Depth Information
F
F
CH
2
Cl
25ºC / 4h
+
EPZ10
10
°
C / 5h
Br
2
+
EPZ10
Scheme 13.6
Br
O
Scheme 13.
8
C
12
- C
14
ALKENE
+
results in low yields and large volumes of dibromi-
nated aromatic waste.
4-Bromofluorobenzene is an intermediate to agro-
chemical and some pharmaceutical products [33]
and currently is prepared using AlCl
3
. The selectiv-
ity for the
para
isomer is typically 90%. However, the
assay of the final product must be >98%
para
with
little contamination of dibrominated products, there-
fore a significant amount of over-bromination is
required to increase the concentration of the
para
isomer to the required specification. Replacing AlCl
3
with EPZ10 resulted in some remarkable selectivity
for this bromination (see Scheme 13.8). The reaction
was performed neat using a slight excess of Br
2
. Gas
chromatography analysis of the reaction mixture
showed that 98% conversion had occurred, with a
selectivity of ca.99% for the
para
isomer and no
dibrominated products detected. On work-up, an
isolated yield of 90% was achieved for 4-bromoflu-
orobenzene.
EPZ10
Cyclohexane
140ºC / 8h
O
C
12
- C
14
ALKYL
Scheme 13.7
The use of AlCl
3
, however, also catalyses the
oligomerisation of the olefin. Envirocat EPZ10 was
found to be superior to AlCl
3
in the alkylation of
diphenyl ether (see Scheme 13.7). Using a sub-
strate/olefin molar ratio of 5 : 1, >98% conversion
was achieved over 8 h, with a selectivity of >85%
monoalkylates and no oligomers detected by GC. On
filtration of the catalyst and distillation of unreacted
substrate an isolated yield of 93% was obtained from
this process.
7.6 Sulfonylation
Diphenylsulfones are usually intermediates to agro-
chemicals and their formation using AlCl
3
results in
the production of about 3 tonnes of effluent per
tonne of product. Envirocat EPZE was used success-
fully as a replacement for AlCl
3
in the production of
3,4-dimethyldiphenylsulfone—an intermediate to a
polyimide—by SNPE, France (see Scheme 13.9).
SNPE observed an 80% conversion and obtained a
60% yield of the 3,4-dimethyl isomer. SNPE were
very impressed, not only with the efficiency of the
sulfonylation but also with the selectivity for the
required isomer. By using Envirocat technology, they
reduced their effluent production compared to the
AlCl
3
process by >80%.
7.5 Aromatic bromination
Aromatic bromine compounds are used as interme-
diates to pharmaceutical and agrochemical products.
The desired product is usually the
para
isomer.
Although AlCl
3
is used in catalytic quantities, it pro-
duces significant amounts of the
ortho
isomer.
However, the rate of bromination of the
ortho
isomer
is greater than that of the
para
isomer. Therefore, by
using an excess of bromine, the
ortho
isomer can be
removed from the reaction mixture. Unfortunately,
some of the
para
isomer is also consumed and this
