Catalytic oxidation of p-xylene with molecular oxygen in the presence of N-hydroxyphthalimide

Article abstract of DOI:10.1134/S1070427214070222

Relationships of p-xylene oxidation in the presence of N-hydroxyphthalimide and Co(II) and Mn(II) salts were studied. The activity of the catalytic system strongly depends on the volume of the ligand incorporated in the salt. The synergism in combined use of Co(II) and Mn(II) salts is observed only in the step of p-toluic acid oxidation, whereas replacement of a half of the Co(II) salt by the Mn(II) salt in p-xylene oxidation leads to additive increase in the reaction rate.

Full text of DOI:10.1134/S1070427214070222

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2014, Vol. 87, No. 7, pp. 982−985. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © A.L. Plekhov, O.V. Kushch, I.O. Opeida, M.A. Kompanets, 2014, published in Zhurnal Prikladnoi Khimii, 2014, Vol. 87, No. 7, pp. 986−989.
BRIEF
COMMUNICATIONS
Catalytic Oxidation of p-Xylene with Molecular Oxygen
in the Presence of N-Hydroxyphthalimide
A. L. Plekhov, O. V. Kushch, I. O. Opeida, and M. A. Kompanets
Litvinenko Institute of Physical Organic Chemistry and Coal Chemistry,
National Academy of Sciences of Ukraine, ul. Rozy Luksemburg 70, Donetsk, 830114 Ukraine
e-mail: pliekhov@gmail.com
Received July 14, 2014
Abstract—Relationships of p-xylene oxidation in the presence of N-hydroxyphthalimide and Co(II) and Mn(II)
salts were studied. The activity of the catalytic system strongly depends on the volume of the ligand incorporated
in the salt. The synergism in combined use of Co(II) and Mn(II) salts is observed only in the step of p-toluic
acid oxidation, whereas replacement of a half of the Co(II) salt by the Mn(II) salt in p-xylene oxidation leads to
additive increase in the reaction rate.
DOI: 10.1134/S1070427214070222
Recently there has been a great deal of interest in
functionalization of organic compounds by oxidation with
molecular oxygen, catalyzed by N-hydroxyphthalimide
Metal catalysts also actively participate in decompo-
sition of hydroperoxides into radicals, followed by the
formation of carbonyl compounds. However, published
data on the nature and mechanism of catalysis of p-xylene
oxidation with molecular oxygen in the presence of the
(
NHPI) [1, 2]. NHPI in combination with cobalt salts
forms an effective catalytic system for autooxidation
of a number of organic substrates such as alkanes and
alkylbenzenes [3]. Ishii et al. [4] developed a process
for preparing terephthalic acid without using halogen-
containing catalysts. In this process, p-xylene is oxidized
with molecular oxygen in the presence of the catalytic
NHPI–Со(ОАс)2
–Мn(ОАс) system are incomplete.
2
As we showed previously [7], the synergistic effect of
the catalytic system NHPI–Co(II) is due to complexation
between the system components, and the magnitude of
the synergistic effect [8] depends on the structure of the
NHPI molecule. The catalysis efficiency also depends on
the nature of the cocatalyst.
system NHPI–Со(ОАс) . To oxidize xylenes to the
2
corresponding dicarboxylic acids, it is necessary to use
high temperatures (423 K) and a combination of Со(II)
and Mn(II) salts [5]. Ishii and Sakaguchi [6] suggested a
mechanism of the catalytic action of the NHPI–Со(ОАс)2
system, involving participation of the cobalt salt in
the radical generation step. In the process, the cobalt–
In this paper we analyze how the catalytic activity
of the NHPI–metal(II) salt system in separate steps
of p-xylene oxidation depends on the nature of the
cocatalyst.
oxygen complex formed by Со with О reacts with
2
EXPERIMENTAL
NHPI to form phthalimide N-oxyl radical (PINO), which
subsequently participates in the catalytic oxidation cycle.
PINO abstracts a hydrogen atom from the RH molecule
to form alkyl radicals with the regeneration of NHPI.
The alkyl radicals react with oxygen to form peroxy
p-Xylene was purified by the standard procedure [9].
N-Hydroxyphthalimide (Fluka) was used without pre-
liminary purification.Acetic acid was distilled from Р2О5
(118–120°С at 1 atm). Со(ОАс) ·4Н О was of analyti-
·
radicals (ROO ), which subsequently transform into alkyl
2
2
hydroperoxide. The catalysis is cyclic and involves return
to the initial oxidation state of the metal, and the PINO
radical transforms into the initial NHPI.
cally pure grade; anhydrous cobalt acetate was prepared
according to [10]. Cobalt(II) stearate (analytically pure
grade) was used without preliminary purification. Cobalt
9
82

CATALYTIC OXIDATION OF p-XYLENE WITH MOLECULAR OXYGEN
983
salts of valeric and caprylic acids were prepared by the
reactions of the corresponding carboxylic acids with
cobalt chloride, according to [11].
[
O ], M
2
The oxidation kinetics was monitored by gas volum-
etry, by measuring the amount of oxygen taken up at a
constant pressure. The reactor rocking frequency ensur-
ing the kinetic control of the reactions was determined in
preliminary experiments. The conversion was determined
by gas–liquid chromatography with chlorobenzene as
internal reference. Analysis was performed with a flame
ionization detector using a column of size 2.5 mm × 2 mm
(
Superphase–Inerton N-AW).
RESULTS AND DISCUSSION
The commercially important process of p-xylene oxi-
τ, s
Fig. 1. Kinetic curves of p-xylene oxidation (3.6 M) in acetic
acid at 338 K with various cobalt salts. ([O ]) Oxygen concen-
tration and (τ) time; the same for Fig. 2. [NHPI] = 0.04 and
[Co(II)] = 0.002 M. Catalytic system: (1) cobalt stearate–NHPI,
2
dation with oxygen was used as model reaction. Acetic
acid was used as solvent, as it ensures high solubility of
the reaction mixture components.
(
(
2) cobalt caprylate–NHPI, (3) cobalt valerate–NHPI, and
4) cobalt acetate–NHPI.
Figure 1 shows the kinetic curves of the oxygen uptake
in p-xylene oxidation catalyzed by NHPI and cobalt(II)
organic salts.
tion of the p-xylene oxidation, and the reaction products
An increase in the length of the alkyl chain of the
carboxylic acid leads to a decrease in the oxidation rate,
which can be attributed to a change in the redox potential
of the metal cation under the influence of the ligand. Ac-
cording to [7, 8], the activity of the NHPI–Co catalytic
system is associated with the formation of a complex com-
pound from the system components. Increased volume of
the cocatalyst molecule gives rise to steric hindrance to
incorporation of the NHPI molecule into the structure of
the complex and, as a consequence, leads to a decrease
in the activity of the catalytic system.
contained only the above-indicated intermediates.
The carboxy group of p-toluic acid exerts an electron-
withdrawing effect on the methyl group in the p-position,
complicating the abstraction of the hydrogen atom from
the latter. p-Toluic acid was isolated and subjected to
further oxidation at a higher temperature.
As seen from Fig. 2, the initial rate of p-toluic acid
oxidation considerably increases on adding manganese
acetate to the NHPI–Co(OAc) catalytic system. This ef-
2
fect can be attributed to the formation of multicomponent
catalytic complexes containing cobalt and manganese
ions simultaneously (Table 2).
Analysis of the products of p-xylene oxidation in the
presence of the NHPI–Co catalytic system and of the
classical cobalt manganese bromide catalyst of p-xylene
oxidation shows that, when the reaction is performed at
The presence of manganese salts facilitates the oxi-
dation of Co(II) to Со(III). Peroxy radicals react with
bivalent manganese salts very readily. The reaction yields
a carbonyl product or hydroperoxide. The hydroperoxide
formation prevails in an acetic acid solution owing to
proton-donor properties of acetic acid and occurs via
formation of an intermediate complex with partial charge
transfer [14]:
3
38 K for 3 h, it yields only the intermediate products:
p-tolualdehyde and p-toluic acid. However, with the
NHPI–Co system, the initial reaction rate and the sub-
strate conversion considerably exceed the values obtained
when the p-xylene oxidation is performed in the presence
of the cobalt manganese bromide catalyst (Table 1).
·
→
2
+
–
3+
Addition of manganese salts to the cobalt bromide
catalyst enhances the catalyst activity [13], i.e., the syn-
ergistic effect is observed. However, under the conditions
of our experiments, addition of manganese salts to the
NHPI–Co(II) catalytic system caused only slight accelera-
RО + Mn ← RО Mn ,
(1)
(2)
2
2
RО –Mn3+ + Н+
→
ROOH + Mn3+.
2
←
Bivalent manganese is more reactive than Co(II)
toward peroxy radicals, which is due to its lower
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 7 2014

984
PLEKHOV et al.
[
O ], M
2
the hydrogen atom from the substrate by peroxy radicals,
occurs by the donor–acceptor mechanism. Electron-donor
substituents such as methyl group decrease the electron-
withdrawing power of the peroxy group (the electron
density on oxygen atoms increases) and the reactivity
of the peroxy radical [15]. Thus, the peroxy radical
·
СН –С Н –СН ОО formed in the first step of p-xylene
3
6
4
2
oxidation is less active in reaction (1) than the peroxy
·
radical СООН–С Н –СН ОО formed in the second step
6
4
2
of the process.
CONCLUSIONS
1) The oxidation rate in acetic acid solution decreases
with an increase in the volume of the ligand incorporated
in the cobalt salt in the order acetate > valerate > capry-
late > stearate.
τ, s
(
Fig. 2. Kinetic curves of p-toluic acid oxidation (0.1 M) in ace-
tic acid at 363 K, Р = 1 atm. (1) [NHPI] = 0.01 and [Со(II)] =
.005 M; (2) [NHPI] = 0.01 and [Co(II)] = [Mn] = 0.0025 M.
0
(
2) The positive effect from adding a manganese
redox potential. Therefore, the equilibrium constant of
reaction (1) should be considerably higher than that
of the corresponding reaction with Со(II). This fact is
responsible for a dramatic increase in the oxidation rate on
adding Mn(II). Reaction (1), as well as the abstraction of
salt in p-xylene oxidation with molecular oxygen in the
presence of the N-hydroxyphthalimide–cobalt acetate
catalytic system is manifested only in the step of p-toluic
acid oxidation.
Table 1. Initial reaction rates, p-xylene conversion (3.6 M), p-toluic acid yield, and selectivity of p-xylene oxidation in acetic
acid at Р = 1 atm, Т = 338 K, τ = 3 h
4
Woxidation × 10 ,
p-Xylene
conversion, %
p-Toluic acid
yield, %
Composition of catalytic system
Selectivity, %
20
mol L–1
s
–1
NaBr–Co(OAc) –Мn(ОАс) , [NaBr] = 0.025,
0.6
12
35
40
<1
48
52
2
2
[
Co(II)] = [Mn(II)] = 0.0125 M
NHPI–Co(OAc) , [NHPI] = 0.04,
4.1
4.6
85
89
2
[
Со(II)] = 0.002 M
NHPI–Co(OAc) –Mn(OAc) , [NHPI] = 0.04,
2
2
[Co(II)] = [Mn(II)] = 0.001 M
Table 2. Initial reaction rates, p-toluic acid conversion (0.1 M), terephthalic acid yield, and selectivity of p-toluic acid oxidation
in acetic acid at Р = 1 atm, Т = 363 K, τ = 3 h
4
Woxidation × 10 , p-Toluic acid con- Terephthalic acid
Composition of catalytic system
Selectivity, %
93
mol L–1
s
–1
version, %
yield, %
NHPI–Co(OAc) , [NHPI] = 0.01,
0.2
12
10
2
[Со(Н)] = 0.005 M
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 7 2014

CATALYTIC OXIDATION OF p-XYLENE WITH MOLECULAR OXYGEN
985
REFERENCES
pp. 366–368.
9
. Gordon,A.J. and Ford, R.A., The Chemist’s Companion. A
Handbook of Practical Data, Techniques, and References,
New York: Wiley, 1972.
1
2
3
4
5
6
7
. Recupero, F. and Punta, С., Chem. Rev., 2007, vol. 107,
pp. 3800–3842.
. Bordado, J.С.M. and Gomes, J.F.P., Chem. Rev., 2013,
vol. 113, no. 10, pp. 7421–7469.
10. Armarego, W.L.F., and Li Lin Chai, С., Purification of
Laboratory Chemicals, New York: Elsevier, 2003.
. Ishii, Y., Iwahama, Т., Sakaguchi, S., et al., J. Org. Chem.,
1
1. Becker, H., Berger, W., Domschke, G., et al., Organikum.
1
996, vol. 61, p. 4520.
. Ishii, Y., Tashiro, Y., and Iwahama, T., Adv. Synth. Catal.,
001, vol. 343, no. 2, pp. 220–225.
Organisch-chemisches Grundpraktikum, Berlin: Wissen-
schaften, 1976.
2
1
2. Ovchinnikov, V.I., Nazimok, V.F., and Smirnova, T.A.,
Proizvodstvo tereftalevoi kisloty i ee dimetilovogo efira
(Production of Terephthalic Acid and Its Dimethyl Ester),
Moscow: Khimiya, 1982.
. Falcona, H., Campos-Martina, J.M.,Al-Zahrani, S.M., and
Fierroa, J.L.G., Catal. Commun., 2010, vol. 12, pp. 5–8.
. Ishii, Y. and Sakaguchi, S., Catal. Surv. Jpn., 1999, vol. 3,
pp. 27–35.
13. Partenheimer, W., Catal. Today, 1995, vol. 23, no. 2,
pp. 69–158.
. Opeida, I.A., Plekhov, A.L., Kushch, O.V., and Matvi-
enko, A.G., Russ. J. Phys. Chem. A, 2011, vol. 85, no. 7,
pp. 1119–1123.
14. Zakharov, K.V., Kinet. Catal., 1998, vol. 39, no. 4,
pp. 485–492.
8
. Opeida, I.A., Plekhov, A.L., Kushch, O.V., and Kompa-
15. Kucher, R.V., Opeida, I.A., and Dmitruk, A.F., Fiz. Mol.,
nets, M.A., Russ. J. Phys. Chem. A, 2012, vol. 86, no. 3,
1977, no. 4, pp. 47–57.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 7 2014