Chemistry Reference
In-Depth Information
Scheme 6.22
Scheme 6.23
Table 6.6
The
p
-cresol conversion, the
product selectivity over solid acid cata-
lysts after 1 h at 50°C and alkylation
rate
Selectivity (%)
Conversion
Alkylation rate
Catalyst
(%)
Ether
Alkylates
(mM g
-
1
catalyst h
-
1
)
13% Nafion
®
/SiO
2
8
2.6
0.6
99.4
5
8
1.0
Nafion
®
NR50
19.5
2
8
.2
71.
8
54.
8
Amberlyst
®
-15
62.4
14.5
8
5.5
171.0
resin/silica nanocomposite have values of 0.8 and
1030, respectively (mM (meqH
+
)
-1
h
-1
). A benzyla-
tion product yield of >97% is found.
Nafion
®
-resin-based catalysts are effective catalysts
for the transalkylation of alkylbenzenes (see Scheme
6.22). The transfer of a
t
-butyl group occurs very
easily over the Nafion
®
and Nafion
®
resin/silica
composites. 2-
t
-Butyl-
p
-cresol is converted with an
excess of toluene to give
p
-cresol and
n
-
t
-butyl-
toluene in about 99% yield.
Alkylated phenols and derivatives are widely used
commercially as antioxidants, herbicides, insecti-
cides, fragrances, polymerisation inhibitors, lubri-
cants [95], etc. Alkylated phenols are typically made
by cation-exchange-resin (e.g. Amberlyst
®
-15, -16)-
catalysed alkylation of phenol with the correspond-
ing olefins and the reaction proceeds preferentially
in the
para
position [96]. The use of a resin catalyst
in this reaction has almost entirely replaced H
2
SO
4
and BF
3
catalyst systems. Our results show that the
13 wt.% Nafion
®
resin/silica composite is a very
effective catalyst for catalysing the alkylation of
p
-
cresol with isobutene under mild conditions (see
Scheme 6.23 and Table 6.6). Under the conditions
employed, the Nafion
®
resin/silica composite seems
to be more active and more selective for catalysing
the C-alkylation versus O-alkylation.
Olefin isomerisation involving
cis
-/
trans
- transfor-
mation or double bond migration is a relatively easy
chemistry. However, various solid acid catalysts
frequently encounter quick deactivation [97]. The
13 wt.% Nafion
®
resin/silica composite was a very
active catalyst for the olefin isomerisation,
cis
-/
trans
-
transformations and the double bond migrations.
The olefin isomer products are useful in the formu-
lation of well fluids, especially in offshore drilling.
Clarembeau & Steylaerts used Amberlyst
®
, Nafion
®
resin pellets and Nafion
®
resin/silica composites to
catalyse the isomerization of 1-olefins with 14-20
carbon atoms [98]. Very high catalyst turnover
numbers were reported with the Nafion
®
resin/silica
composite catalysts. This composite also is active for
the isomerisation of 1-butene to the
cis
- and
trans
-2-
butene isomers [99]. Using the composite catalyst
