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Organic Process Research & Development
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three atmospheres.9,10 Generally, during the oxidation reaction, EB conversion is maintained
at about 12 wt.%. Nevertheless, for commercial applications, PEHP selectivity should be
more than 95%. The main by-products are acetophenone (ACP) and 1-phenylethanol (1-
PE). The ACP is converted to 1-PE by the hydrogenation process and 1-PE is converted
into the styrene by the dehydration process.11 Particular amounts of carboxylic acids and
water are produced during the reaction, which is traditionally removed by alkali treatments.
The oxidation reaction mixture is concentrated by vacuum distillation up to 20 wt.% with
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respect to PEHP, which is utilized as a feed (oxygen carrier) for the catalytic reaction of
propene epoxidation.8
The oxidation reaction of EB in the presence of homogeneous or heterogeneous metal
catalysts using oxidants such as H O , tert-butyl hydroperoxide (TBHP), and O has been
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studied by others.12–15 However, when metal-containing compounds are used in the alky-
laromatics oxidation processes, the ROOHs selectivity is low, and the products are mainly
ketones and alcohols.16,17 Therefore, in order to achieve high selectivity of ROOHs, it is
necessary to use metal-free systems. In addition, since the epoxidation process is strongly
hindered by the presence of metallic catalysts and it is very difficult to remove them by
distillation,17 it was decided that the oxidation reaction of EB was carried out without any
catalyst, that provided the very best performance in PEHP production.
The oxidation of EB in the presence of metal-free organic catalysts such as
N-Hydroxyphthalimids (NHPI) has also been studied by others.18–22 In these processes, NHPI
in combination with some metal salts or aldehydes acts as a precursor to phthalimide-N-Oxyl
(
PINO) radicals. The PINO radicals are able to abstract hydrogen atoms from organic sub-
strates. The use of NHPI in the oxidation processes of alkylaromatics has many advantages,
including higher conversion, greater hydroperoxide selectivity, and milder reaction condi-
tions, compared to non-catalytic processes. However, there are serious drawbacks with the
use of NHPI, for example, product separation is difficult, and the NHPI catalyst is not easily
recovered and reused, leads to low synthetic efficiency.
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