Liquid-phase oxidation of isopropyl-meta-xylene to tertiary hydroperoxide

Article abstract of DOI:10.1134/S1070427214070088

Fundamental aspects and the mechanism of the reaction of liquid-phase oxidation of isopropyl-meta-xylene to a tertiary hydroperoxide by atmospheric oxygen, initiated by isopropylbenzene hydroperoxide or catalyzed by N-hydroxyphthalimide were studied. It was found that using N-hydroxyphthalimide in the course of oxidation of isopropyl-meta-xylene makes it possible to raise, compared with the initiator (isopropylbenzene hydroperoxide), the oxidation rate and the conversion of the hydrocarbon by a factor of 2-2.5 at a 90-95% formation selectivity of a tertiary hydroperoxide of isopropyl-meta-xylene up to a conversion of 20-25%.

Full text of DOI:10.1134/S1070427214070088

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2014, Vol. 87, No. 7, pp. 895−898. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © A.S. Frolov, E.A. Kurganova, G.N. Koshel’, 2014, published in Zhurnal Prikladnoi Khimii, 2014, Vol. 87, No. 7, pp. 902−906.
ORGANIC SYNTHESIS AND INDUSTRIAL
ORGANIC CHEMISTRY
Liquid-Phase Oxidation of Isopropyl-meta-Xylene
to Tertiary Hydroperoxide
A. S. Frolov, E. A. Kurganova, and G. N. Koshel’
Yaroslavl State Technical University, Moskovskii pr. 86, Yaroslavl, 150023 Russia
e-mail: koshelgn@ystu.ru
Received July 22, 2014
Abstract—Fundamental aspects and the mechanism of the reaction of liquid-phase oxidation of isopropyl-meta-
xylene to a tertiary hydroperoxide by atmospheric oxygen, initiated by isopropylbenzene hydroperoxide or catalyzed
by N-hydroxyphthalimide were studied. It was found that using N-hydroxyphthalimide in the course of oxidation
of isopropyl-meta-xylene makes it possible to raise, compared with the initiator (isopropylbenzene hydroperoxide),
the oxidation rate and the conversion of the hydrocarbon by a factor of 2–2.5 at a 90–95% formation selectivity
of a tertiary hydroperoxide of isopropyl-meta-xylene up to a conversion of 20–25%.
DOI: 10.1134/S1070427214070088
The liquid-phase oxidation of alkyl aromatic hydro-
carbons underlies promising methods for production of
various oxygen-containing compounds (alkyl)phenols
and aliphatic ketones widely used in syntheses of poly-
meric materials possessing a set of valuable properties [1].
The present study is concerned with the reaction of
liquid-phase selective oxidation of isopropyl-meta-xylene
(IP-m-X) to a tertiary HP, which underlies the synthesis
of 1,3,5-xylenol, a large-tonnage product of petrochemi-
cal synthesis, widely used in manufacture of plasticizers,
paint-and-varnish materials, and disinfectants. The oxida-
tion process is shown in Scheme 1.
The “cumene” method for obtaining phenol and ac-
etone and the joint synthesis of styrene and propylene
oxide (“chalcone-process”) have been studied in detail
and are widely used in the industry. The key stage in these
methods is the liquid-phase initiated oxidation of isopro-
pylbenzene (IPB) and ethylbenzene to the corresponding
hydroperoxides (HP).
The choice of meta-xylene to obtain an isopropyl
derivative of benzene is not accidental. The point is that,
among the three isomers of xylenes, only para- and
ortho-xylenes are the most widely used in large-tonnage
manufacture of therephthalic acid and phthalic anhydride.
At the same time, meta-xylene does not find efficient use
and expanding its application field is a topical task.
This important way to obtain valuable organic syn-
thesis products can be enhanced by using other alkyl
aromatic hydrocarbons and their HPs.
The oxidation of IP-m-X is, in fact, rather close to
the process of UPB oxidation to an HP. However, the
Scheme 1.
895

896
FROLOV et al.
Table 1. Effect of the IPB HP concentration and temperature on the formation selectivity of tertiary IP-m-X HP and on the con-
version of IP-m-X HP in liquid-phase oxidation. Reaction duration 90 min
Content, wt %
Conversion
Formation selectivity of tertiary
Temperature, °C
of IP-m-X,
tertiary
IP-m-X HP
IP-m-X HP, %
IPB HP initiator
organic acid,a %
%
120
130
2.0
1.0
2.0
4.0
2.0
5.3
6.9
0.2
0.2
89.3
88.6
88.8
86.8
85.7
5.6
7.3
7.4
0.23
0.2
7.8
10.5
11.5
11.4
12.6
140
0.7
a In terms of xylylic acid.
fundamental aspects of the cumene method cannot be
transferred to the process of IP-m-X oxidation for a num-
ber of reasons. The liquid-phase oxidation of isopropyl
derivatives of xylene occurs at a lower rate than that for
IPB, with primary and tertiary IPB HPformed simultane-
ously. As a rule, the formation selectivity of the tertiary
HPdoes not exceed 60–65%. Until recently, these difficul-
ties have not been surmounted, which strongly hinders the
practical implementation of the “oxidative” method for
obtaining quite a number of valuable organic-synthesis
products on the basis of IPX and its HP. Thus, carrying
out a set of studies aimed to intensify the selective oxida-
tion of IP-m-X to tert-HPand performing syntheses based
on these materials are of scientific and practical interest.
82–84%, which does not contradict the results of ear-
lier studies [2]. As by-products of IP-m-X oxidation are
formed dimethylacetophenone (DMAP) and dimethyl
phenyl carbinol, the presence of which compounds was
confirmed by the GLC method. Further oxidation of
DMAP presumably yields xylylic acid, which favors
decomposition of tertiary IP-m-X HP to give products
of phenolic nature, which hinder (inhibit) the process of
IP-m-X oxidation.
Analysis of the main and by-products of IP-m-X oxi-
dation shows that only the isopropyl group is oxidized in
IP-m-X, with no products of oxidation of methyl groups
observed. At the same time, it can be seen in the figure
that the presence of methyl groups strongly affects the
oxidation rate of the isopropyl derivative of the aromatic
hydrocarbon.
Originally, we examined the liquid-phase oxidation of
IP-m-X in the presence of an initiator, IPB HP. IP-m-X
was oxidized by atmospheric oxygen at a temperature of
120–140°C under atmospheric pressure under permanent
oxidation in a kinetic installation of the flow-through–
closed-loop type. The reaction course was monitored by
measuring the absorption of oxygen. IP-m-X was oxidized
in the kinetic mode. The resulting oxide was analyzed for
the content of IP-m-X HPby iodometry, and the content of
organic acids was determined by potentiometric titration.
The conversion of IP-m-X and the formation se-
lectivity of tertiary IP-m-X HP were raised with N-hy-
droxyphthalimide (N-HPI), which has been successfully
used previously to intensify the liquid-phase oxidation
of alkyl and cyclohexyl aromatic hydrocarbons [3, 4].
It can be seen in Table 2 that, if IP-m-X is oxidized
in the temperature range 120–140°C in the presence of
N-HPI, the oxidation rate of IP-m-X becomes 2–2.5 times
faster. In this case, the accumulation rate of IP-m-X HP
increases from 5 to 14% per hour, and the selectivity of its
formation grows from 85 to 94–95%, compared with IPB
HPused as initiator. The oxidation rate of IP-m-X depends
on the N-HPI concentration, and its reuse does not lead
to a decrease in the rate and selectivity of HP formation,
which indicates that N-HPI catalyzes the process.
RESULTS AND DISCUSSION
It can be seen in the data in Table 1 that, as the reac-
tion temperature is raised from 120 to 140°C, the oxida-
tion rate of the hydrocarbon becomes approximately
2–2.5 times higher. Under these conditions, it is possible
to accumulate in 1.5 h approximately 11% tertiary IP-m-
X HP, with the selectivity of its formation not exceeding
The catalytic role of N-hydroxypthalimide in
the selective liquid-phase oxidation of IP-m-X to a
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 7 2014

LIQUID-PHASE OXIDATION OF ISOPROPYL-meta-XYLENE
Scheme 2.
897
VO2, cm3
τ, min
from the C–H bond of alkyl arenes to give the correspond-
ing alkyl arene radicals. The given C-centered alkyl arene
radical is converted to a peroxide radical in the presence
of oxygen, which, in turn, interacts with N-HPI to form
N-OPIR and a hydroperoxide [5]. The process occurs
with high conversion and selectivity by the radical-ion
mechanism, with N-HPI regenerated in each cycle. The
termination occurs as a result of recombination of the
peroxy radical. B-HPI shows activity in chain-initiation
reactions, is not involved in the termination, and does not
catalyze the decomposition of HP being formed, either,
which is highly important in development of a technique
for synthesis of hydroperoxides by liquid-phase oxidation
of alkylbenzenes.
Comparative data on the liquid-phase oxidation of IPB and its
methyl derivatives. Substrate: (1) IPB, (2) para-isopropyltol-
uene, and (3) IP-m-X. Temperature 120°C, initiator (IPB HP)
content 2.5 wt % relative to the hydrocarbon charge, reaction
duration 90 min.
hydroperoxide can be described as a catalytic cycle shown
in Scheme 2.
It is assumed that, in the given oxidation processes, an
N-oxyphthalimide radical (N-OPIR) is formed from an
N-HPI molecule in its interaction with the radical of the
initiator or with a peroxide radical of the substance being
oxidized. N-OPIR can selectively detach a hydrogen atom
Table 2. Effect of the N-HPI concentration and temperature on the formation selectivity of tertiary IP-m-X HP and on the conver-
sion of IP-m-X HP in liquid-phase oxidation. Reaction duration 90 min
Content, wt %
Formation selectivity
Conversion
of IP-m-X, %
Temperature, °C
of tertiary
IP-m-X HP, %
N-HPI catalyst
tertiary IP-m-X HP
110
120
2.0
2.0
1.0
1.5
2.0
2.0a
3.0
4.0
2.0
3.3
8.0
98.3
96.4
96.2
97.1
94.1
93.8
94.5
95.7
90.6
3.4
8.3
9.7
10.1
14.4
22.3
21.6
17.6
14.5
25.4
14.0
21.0
20.7
16.6
13.9
23.1
130
140
a Repeated use of the catalyst.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 7 2014

898
FROLOV et al.
The tertiary hydroperoxide we synthesized was sub-
tion course was monitored by measuring the absorption
of oxygen. The oxidation was performed in the kinetic
mode in which the reaction rate was independent of the
agitation intensity.
jected to acid decomposition in the presence of concentra-
tion sulfuric acid as a catalyst. We found 3,4-xylenol and
acetone in the reaction products. The yields of xylenol
and acetone were 90–95 and 80–85%, respectively, which
indirectly confirms the structure of the HP obtained.
Balance experiments on IP-m-X oxidation were car-
ried out in a three-necked vessel with a rabble equipped
with a glycerol seal. The oxidized product was washed
with water to extract acids. IP-m-X HPwas isolated from
the product by rectification in a vacuum. The resulting
substance contained 97% HP (bp 92°C at 0.3 mmHg,
nD20 1.5211, d420 1.017).
EXPERIMENTAL
IP-m-X was produced by alkylation of meta-xylene
with isopropanol in the presence of concentrated sulfuric
acid (temperature 20°C, meta-xylene : isopropanol :
sulfuric acid molar ratio 3 : 1 : 3, reaction duration 2 h).
After the reaction was complete, the hydrocarbon layer
was separated from the aqueous solution of sulfuric
acid, washed with water to neutral reaction, dried over
calcium chloride, and then heated to 65°C for 30 min in
the presence of 5–7% aluminum chloride. The resulting
product was again washed with water to neutralize the
catalyst and subjected to rectification in a vacuum.
The thus isolated IP-m-X had the following constants:
bp 194–195°C, d420 0.865, nD20 1.4955. According to
IR spectroscopic data, isopropyl-meta-xylene is a
mixture of two isomers: 1,3,5-isomer (850 cm–1) 92%
and 1,2,4-isomer (810 cm–1) 8%. The IR spectroscopic
analysis was made with a RX-1 IR Fourier spectrometer.
The spectra were processed using Spektrum software
provided by Perkin Elmer company. The spectra were
recorded in the range 4000–400 cm–1 for a microlayer
between potassium bromide glasses and in a 0.0011-cm-
thick KBr cuvette.
The acid decomposition of IP-m-X HPwas performed
with concentrated sulfuric acid in acetone (0.5% H2SO4
relative to the HP content) at a temperature of 65°C.
After the decomposition of IP-m-X HP was complete,
the reaction mixture was analyzed by the GLC method.
CONCLUSIONS
(1) It was found that the liquid-phase oxidation
of isopropyl-meta-xylene in the presence of N-hy-
droxyphthalimide yields tertiary isopropyl-meta-xylene
hydroperoxide with a selectivity of 90–95% and conver-
sion of up to 20–25%.
(2) It was demonstrated that only the isopropyl group
is oxidized in the course of a liquid-phase oxidation of
isopropyl-meta-xylene, with presence of methyl groups in
the isopropyl derivative of benzene substantially reducing
their oxidation rate.
(3) The mechanism of the liquid-phase oxidation
of isopropyl-meta-xylene in the presence of N-hy-
droxyphthalimide was discussed.
Additionally, the composition of IP-m-X was con-
firmed by the GLC and 1H NMR techniques. The chro-
matographic analysis was made on a Khromatek-kristall
5000.2 chromatograph with a flame-ionization detector.
The SK-5 capillary column (length 30 m, diameter
0.32 mm) was packed with 5% phenylpolysiloxane and
95% dimethylpolysiloxane. As the carrier gas served
nitrogen delivered at a flow rate of 2 cm3 min–1. The
temperature was raised in the programmed mode from
80 to 200°C at a rate of 8 deg min–1. A 1H NMR spec-
trum was recorded with a Bruker DRX 400 spectrometer
(400.4 MHz) [6].
REFERENCES
1. Kharlampovich, G.D., Kalechits, I.V., and Churkin, Yu.V.,
Khim. Prom-st’, 1968, no. 1, pp. 16–20.
2. Bondarenko, A.V., Farberov, M.I., Zasova, V.A., and Vede-
neeva, N.V., Zh. Prikl. Khim., 1966, no. 2, pp. 404–409.
3. Koshel’, G.N., Smirnova, E.V., Kurganova, E.A., et al.,
Kataliz Prom–sti, 2010, no. 3, pp. 26–29.
4. RF Patent 2378253 (publ. 2010).
5. Sapunov, V.N., Koshel’, G.N., Rumyantseva, Yu.B., et al.,
IP-m-X was oxidized in the presence of IPB HP
initiator or N-HPI catalyst with atmospheric oxygen in
a 10-cm3 glass reactor on a flow-through–closed-loop
installation under permanent vigorous agitation. The reac-
Petrol. Chem., 2013, vol. 53, no. 3, pp. 171–176.
6. Ewing, G.W., Instrumental Methods of Chemical Analysis,
McGraw-Hill, Inc., 1981, 4th ed.
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