B. Orlińska, I. Romanowska
2 can be obtained with yield of 73 mol% when 1 is
oxidised for 3 h at 60ºC in acetonitrile as a solvent in the
presence of NHPI (10 mol%). Higher yield and reaction
time reduction were achieved in comparison to a process
described in literature [4,25].The oxidation process of 1
to hydroperoxide can have an application as a step in
4-methoxyphenol synthesis by a method analogous to
phenol synthesis from cumene.
3.2.3. Effect of amount of NHPI and Cu(acac)2
The conversion of 1 was decreased when the amount of
Cu(acac)2 was increased to 10 mol% (Table 4).
This phenomenon most likely resulted from the
reaction of copper ions with peroxyl radicals that could
lead to chain termination (Eq. 5) [2].
CuI
(5)
+
ROOCuII
ROO
It has been established that the highest selectivity of
ketone 3 amounted to about 65-75 mol% was obtained
by oxidation of 1-methoxy-4-(1-methylethyl)benzene in
the presence of a catalyst composed of NHPI and Cu(II).
However direct synthesis of ketone 3 by 1-methoxy-4-(1-
methylethyl)benzene oxidation catalysed by the NHPI/
Cu(II) system can be limited by the low conversion of 1.
On the other hand both unreacted hydrocarbon 1 as well
as by-product 4-isopropenylanisole (product of alcohol 4
dehydration) can be recycled in the oxidation step after
hydrogenation.
The influence of the amount of NHPI was determined for
NHPI/Cu(acac)2 and NHPI/CuCl2 at temperatures of 70
and 120°C (Table 5).
It was found that at 70°C, an increase in NHPI led to
an increase in conversion with a simultaneous decrease
in ketone selectivity. It is probably an effect of the
increase of alcohol formation in the reaction of NHPI with
alkoxyl radicals [14]. At 120°C, the increase of the NHPI
concentration enhanced the ketone 3 yield. It suggests
that the participation of a mentioned reaction of NHPI
with alkoxyl radicals is lower at higher temperature
probably as a result of NHPI decomposition.
Acknowledgements
Financial help from the Ministry of Science and Higher
Education of Poland (Grant No. N N209 153836) is
gratefully acknowledged.
4. Conclusions
It has been demonstrated that NHPI was an effective
catalyst in the oxidation process of 1-methoxy-4-(1-
methylethyl)benzene to hydroperoxide. Hydroperoxide
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