Catalytic oxidation of alkylbenzenes with ozone in acetic acid in the presence of strong acids

Article abstract of DOI:10.1134/S0965544112020120

The oxidation of ethylbenzene with ozone in the acetic acid-sulfuric acid system in the presence of Mn(II) acetate and cumene in the acetic acid-trifluoroacetic acid system in the presence of Co(II) acetate has been studied. The main factors that affect the catalytic ozonation of alkylbenzenes are discussed. A redox catalysis mechanism is proposed. The kinetic characteristics of the main stages of the catalytic cycle have been determined. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S0965544112020120

ISSN 0965ꢀ5441, Petroleum Chemistry, 2012, Vol. 52, No. 2, pp. 113–118. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © E.V. Potapenko, P.Yu. Andreev, 2012, published in Neftekhimiya, 2012, Vol. 52, No. 2, pp. 132–137.
Catalytic Oxidation of Alkylbenzenes with Ozone in Acetic Acid
in the Presence of Strong Acids
E. V. Potapenko and P. Yu. Andreev
Institute of Chemical Technologies, Dal’ EastꢀUkrainian National University, Rubezhnoe, Ukraine
eꢀmail: potapenko@iht.lg.ua
Received March 25, 2011
Abstract—The oxidation of ethylbenzene with ozone in the acetic acid–sulfuric acid system in the presence
of Mn(II) acetate and cumene in the acetic acid–trifluoroacetic acid system in the presence of Co(II) acetate
has been studied. The main factors that affect the catalytic ozonation of alkylbenzenes are discussed. A redox
catalysis mechanism is proposed. The kinetic characteristics of the main stages of the catalytic cycle have
been determined.
DOI: 10.1134/S0965544112020120
The use of transition metal salts in the liquidꢀphase 30ꢀcoated Inerton AWꢀDMCS . The concentration of
oxidation of methylbenzenes with ozone in acetic acid the product benzoic acid was determined as described
has been analyzed using a number of examples [1–3]. in [7]. The procedures for determining the rate conꢀ
However, the ozonation of alkylbenzenes in the presꢀ stants of the ozone reaction with alkylbenzenes and
ence of transition metals is poorly understood [4]. In the transition metals are described in [8]; those for the
this study, we examined the oxidation of ethylbenzene oxidized metal form with alkylbenzenes are given in
and cumene with ozone in acetic acid in the presence [9].
of transition metals activated by strong acid additives
[
5, 6].
RESULTS AND DISCUSSION
Oxidation of Ethylbenzene in the Presence
of Manganese(II) Acetate
EXPERIMENTAL
The oxidation of alkylbenzenes was performed in a
It was previously shown that the ozonation of ethꢀ
ylbenzene in acetic acid is accompanied by the
destruction of the aromatic ring (formation of ozoꢀ
nides) and is characterized by an extremely low selecꢀ
tivity of formationl of the alkylꢀgroup oxidation prodꢀ
ucts, which include methylphenylcarbinol (MPC),
acetophenone (AP), traces of benzaldehyde, and, in
the case of deep oxidation, benzoic acid (BA). The
sideꢀchain oxidation selectivity depends on the severꢀ
ity of oxidation and does not exceed 18% [5].
sealed, thermostated glass reactor equipped with a
highꢀspeed turbine stirrer and a bubbler of 3 mm in
diameter. The reactor was charged with 0.05 L of glaꢀ
cial acetic acid and calculated amounts of alkylbenꢀ
zene, catalyst, and strong acid, and an ozone–air mixꢀ
–4
ture (
4 × 10 mol/L of ozone) was fed. At a stirrer
speed of 29.2 rps and a gas mixture flow rate of 6.0
×
–3
10
L/s, the oxidation occurred in the kinetic region.
The concentration of ozone in the gas phase was
determined spectrophotometrically according to
Taking into account that Mn(II) salts are ineffecꢀ
absorption in the range of 254–259 nm, the concenꢀ tive as catalysts for ozonation in acetic acid [2, 3], in
tration of Co(III) in the reaction mixture was found this work, we focused on studying the possibility of
photometrically by measuring the optical density with using Mn(II) acetate in the ozoneꢀenhanced oxidaꢀ
a KFKꢀ2 instrument ( = 315 nm, a 30ꢀmm cell), and tion of ethylbenzene in the СН СООН–H SO sysꢀ
λ
3 2 4
that of Mn(III) and product peroxides was determined tem. The results (Fig. 1) show that the use of Mn(II)
by iodimetric titration. Changes in the concentration acetate and sulfuric acid makes it possible to preclude
of ethylbenzene and its oxidation products were monꢀ to a significant extent the degradation of the aromatic
itored via gas–liquid chromatography using a flame ring and to direct the reaction toward oxidation of the
ionization detector on a 2 m
× 2 mm column packed side chain to form MPC, AP, and BA. In addition,
with Chromaton NꢀAWꢀDMCS as a support coated traces of the ester of MPC and acetic acid were found
with the polyethylene glycol adipate stationary phase in the reaction mass. The figure clearly shows theseꢀ
in an amount of 15% of the support weight; cumene quence of formation of the products: MPC, AP, and
and dimethylphenylcarbinol (DMPC) were deterꢀ BA. Within first 10 min of ozonation, a steadyꢀstate
mined on a 3 m
× 2 mm column packed with 5% SEꢀ concentration of Mn(III) is attained; after that, it
113

114
POTAPENKO, ANDREEV
An increase in temperature also contributes to an
increase in the selectivity of the reaction; however, in
this case, the content of BA in the oxidate increases
0.5
0.4
0.3
0.2
0.1
(
Table 1, runs 4–7).
Sulfuric acid is effective in a limited range of conꢀ
centrations (Table 2). As the concentration of H SO
2
4
1
increases to 1.0 mol/L, both the rate and selectivity of
oxidation increase. At a higher concentration of sulfuꢀ
ric acid, the rate of consumption of ethylbenzene
slows down and the selectivity continues increasing.
2
Oxidation of Cumene in the Presence
of Cobalt(II) Acetate
3
Preliminary experiments revealed that cumene
oxidation with ozone in acetic acid yields the followꢀ
ing main products: ozonides (47.6%), DMPC
4
5
(
38.4%), and AP (5.3%) (Fig. 2).
The use of Co(II) acetate leads to an increase in the
yield of aliphaticꢀchain oxidation products, and the
maximum selectivity (83.9%) is achieved at 80
Table 3, runs 3–7). The kinetic curves in Fig. 3a show
20
40
60 80 100 120 140
, min
°
С
τ
(
that under these conditions, the severity of cumene
oxidation increases, the concentration of DMPC and
AP pass through a maximum, and the reaction prodꢀ
ucts accumulate a significant amount of BA (43.0%).
It was previously shown [9] that admixtures of
haloacetic acids in the case of toluene ozonation in
acetic acid in the presence of Co(II) acetate enhance
the methylꢀgroup oxidation selectivity. The introducꢀ
Fig. 1. Ethylbenzene oxidation with ozone in acetic acid in
the presence of Mn(II) acetate and sulfuric acid at 20 С.
ArСH СН ] = 0.5 mol/L, [H SO4] = 1.0 mol/L, [O ] =
°
[
4
2
3
2
3
–
4
× 10 mol/L, [Mn(II)] = 0.1 mol/L, and the gas flow
–
3
rate is 6.0
×
10 L/s: (
1) ethylbenzene, (
2) AP, (3) benzoic
acid, ( ) MPC, and (
4
5) Mn(III).
remains almost unchanged (Fig. 1, curve 5). No slowꢀ
tion of СF COOH into the catalytic system made it
3
down of the reaction is observed until the complete
consumption of ethylbenzene. It should be noted that
cutoff of ozone supply to the developed process leads
to complete cessation of the process and rapid converꢀ
sion of Mn(III) to Mn(II).
possible to perform the reaction with an alkylꢀgroup
oxidation selectivity of 80.0% even at 20°С (Fig. 3b).
In this case, the main product is AP (44.7%), DMPC
is formed in lower amounts (23.6%), and BA appears
after accumulation of a sufficient amount of ketone in
The results of studying the effect of catalyst conꢀ the system and has a yield of 11.7%.
centration on the ethylbenzene oxidation selectivity
During oxidation, the catalyst varies its valence as
show that the maximum yield of the alkylꢀgroup oxiꢀ in the case of Mn(II) acetate; in addition, the time of
dation products is achieved at comparable catalyst and reaching a steadyꢀstate Co(III) concentration and the
substrate concentrations (Table 1, experiments 1–4). value of this concentration depend on the reaction
Table 1. Effect of the concentration of Mn(II) acetate and temperature on the selectivity (S) and composition of the alkylꢀ
group reaction products in the case of exhaustive oxidation of ethylbenzene in acetic acid. [ArCH CH ] = 0.5 mol/L,
2
3
–4
[
H SO ] = 1.0 mol/L, [O ] = 4 10 mol/L
×
2
4
3
Oxidation products, mol/L
AP
[
Mn(II)],
mol/L
Run no.
T
,
°
C
S, %
MPC
BA
1
2
3
4
5
6
7
0.034
0.049
0.07
0.1
20
20
20
20
30
40
50
0.005
0.006
0.008
0.019
0.011
0.004
traces
0.103
0.133
0.168
0.201
0.187
0.170
0.148
0.071
0.089
0.118
0.152
0.191
0.234
0.277
38.5
48.1
60.5
75.2
77.8
81.6
85.0
0.1
0.1
0.1
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CATALYTIC OXIDATION OF ALKYLBENZENES WITH OZONE IN ACETIC ACID
115
Table 2. Effect of the concentration of H SO on the initial ethylbenzene oxidation rate (W0), selectivity, and yield of alkylꢀ
2
4
–
4
group reaction products at 20
°
C. [ArCH CH ] = 0.5 mol/L, [Mn(II)] = 1.0 mol/L, [O ] = 4
×
10 mol/L,
τ
= 2.5 h
2
3
3
Oxidation products, mol/L
AP
[
H SO ], W0
×
104,
Degree
of conversion, %
2
4
S
, %
mol/L
mol/(L s)
MPC
BA
0.4
0.6
0.8
1.0
1.2
1.5
1.0
1.4
1.8
2.2
1.7
0.9
79
85
93
99
89
75
0.008
0.011
0.015
0.019
0.017
0.015
0.160
0.178
0.194
0.201
0.173
0.140
0.085
0.103
0.124
0.152
0.147
0.135
64.1
68.7
71.6
75.2
75.8
77.3
conditions. In the absence of a strong acid, within the that, with a rise in temperature, the rate of reaction (3)
first 15 min, almost the entire amount of Co(II) is increases faster than the rate of interaction of ozone
converted to Co(III); after that, its concentration with alkylbenzene and, as a consequence, in terms of
remains unchanged. In the case of trifluoroacetic acid, the proposed scheme, an increase in temperature must
9
0% of Co(II) converts into Co(III). The reaction did lead to an increase in the oxidation selectivity. Howꢀ
not slow down until the complete consumption of ever, in actual practice, this assumption holds true
cumene. The cutoff of ozone supply to the developed only for ethylbenzene (Table 1, runs 4–7; Fig. 4).
process also led to the cessation of cumene consumpꢀ
The subsequent transformations of the peroxide
tion and to the transition of Co(III) to Co(II). The
radical depend on the nature of the substrate. Thus,
the most likely route for ethylbenzene is as follows:
maximum oxidation selectivity is observed at the subꢀ
strate to catalyst ratio close to 2 : 1 and the trifluoroꢀ
acetic acid content of 2.0 mol/L (Table 3). Unlike the
case of ethylbenzene, an increase in the temperature
of cumene oxidation leads only to an increase in the
alkylbenzene consumption rate and hardly has an
effect on the process selectivity (Fig. 4).
•
•
ArСН(СН )ОО + O
3
ArСН(СН )О + 2O (5)
3 2
3
0.30
0.25
0.20
Based on the experimental data, we can propose
the following scheme of oxidation of alkylbenzenes:
•
•
Ar(R) C + HO + O (1а)
2
2
(1b)
Ar(R) CH + O
2
3
Ar(R)2CОH + O3
ozonolysis products
(1c)
1
H+
4
2
+
Ме 3+ + НО• + О
0.15
Ме + O
(2)
3
2
3
3
+
•
2+
+
Ar(R) CH + Ме
2
Ar(R) C + Ме + H (3)
2
0
.10
.05
•
Ar(R) CОО•
Ar(R) C + O
2
(4)
(5)
2
2
•
•
Ar(R) CОО + O
2
Ar(R) CО + 2O
2
3
2
0
In the absence of a catalyst, alkylbenzene is conꢀ
sumed according to reaction (1). In the presence of
transition metals, ozone primarily reacts with the catꢀ
alyst (reaction (2)) (Table 4) and the direct oxidation
of the alkyl group involves the metal in the higher oxiꢀ
dation state (reaction (3)). This assumption is proved
by the fact that a high selectivity is observed at compaꢀ
rable metal and alkylbenzene concentrations
2
2
0
40
60
80 100 120 140
, min
τ
Fig. 2. Oxidation of cumene with an ozone–air mixture in
acetic acid at 20 С. [Ar(СH ) CH] = 0.3 mol/l and [O ] =
°
3
2
3
–4
(
Tables 1, 3). An analysis of the kinetic characteristics
4
×
10 mol/l; (
1) cumene, (2) AP, (3) DMPC, and
of the main stages of the catalytic cycle (Table 4) shows
(
4) ozonides.
PETROLEUM CHEMISTRY Vol. 52
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116
POTAPENKO, ANDREEV
Table 3. Yield of alkylꢀgroup reaction products and process selectivity in the exhaustive oxidation of cumene with an
–
4
ozone–air mixture in acetic acid. [Ar(CH ) CH] = 0.3 mol/L and [O ] = 4
×
10 mol/L
3
2
3
Oxidation products, mol/L
[
Co(II)], [CF COOH],
3
Run no.
T
, °C
S, %
mol/L
mol/L
MPC
AP
BA
1
2
3
4
5
6
7
8
9
20
20
20
40
60
80
–
–
2.0
–
0.115
0.113
0.107
0.080
0.049
0.029
0.024
0.112
0.096
0.082
0.071
0.065
0.109
0.090
0.076
0.016
0.016
0.040
0.078
0.085
0.094
0.066
0.051
0.076
0.112
0.134
0.137
0.065
0.103
0.115
43.7
43.0
50.0
63.3
72.7
83.9
81.0
55.6
61.0
70.6
80.0
79.1
59.7
68.9
72.0
–
0.12
0.12
0.12
0.12
0.12
0.04
0.07
0.10
0.12
0.16
0.12
0.12
0.12
0.003
0.032
0.084
0.129
0.153
0.004
0.011
0.018
0.035
0.035
0.005
0.014
0.025
–
–
–
100
–
20
20
20
20
20
20
20
20
2.0
2.0
2.0
2.0
2.0
0.5
1.0
1.5
1
1
1
1
1
1
0
1
2
3
4
5
0
0
0
0
0
0
.30
(а)
0.30
0.25
0.20
0.15
0.10
0.05
(b)
.25
.20
.15
.10
.05
1
2
1
4
2
3
4
3
20
40
60
, min
80 100 120
20 40
60
, min
80 100 120
τ
τ
Fig. 3. Catalytic oxidation of cumene with an ozone–air mixture in acetic acid at (a) 80
°
С
and (b) 20
°С in the presence of
–4
[
СF COOH] = 2.0 mol/L. [Ar(СH ) CH] = 0.3 mol/L, [O ] = 4
×
10 mol/L, and [Co(II)] = 0.12 mol/L; (
1) cumene, (2) AP,
3
3 2
3
(3
) DMPC, and (4) benzoic acid.
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CATALYTIC OXIDATION OF ALKYLBENZENES WITH OZONE IN ACETIC ACID
117
Table 4. Kinetic parameters of elementary reactions in the ozoneꢀenhanced catalytic oxidation of alkylbenzenes in acetic
acid at 20
°
C
k
A
[
CF COOH],
3
Reaction
Mn2+ + O3
[H SO ], mol/L
E,
kJ/mol
2
4
mol/L
L/(mol s)
–
2.0
–
1.0
–
1.3
4.9
×
×
102
102
2.7
1.4
7.6
2.8
7.9
2.5
×
×
×
×
×
×
106
108
105
106
105
106
24.2
30.6
33.1
35.6
44.5
47.3
Co2+ + O3
ArCH2CH3 + O3
Ar(CH ) CH + O
1.0
–
0.95
2.0
–
1.25
3
2
3
3
+
10–3
10–3
ArCH CH + Mn
1.0
–
9.2
9.3
×
2
3
3+
Ar(CH ) CH + Co
2.0
×
3
2
H+
CONCLUSIONS
•
2+
3+
ArСН(СН )О +Ме
3
ArСН(СН )ОН+Ме (6)
3
During oxidation in acetic acid, ozone inters into
the reaction with both the aromatic ring and the side
chain of alkylbenzene. The yield of the alkylꢀgroup
ArСН(СH )ОО•
molecular products
.
(7)
3
The occurrence of reactions (5) and (6) can explain
the buildup of MPC as the primary oxidation product oxidation products depends on the nature of the subꢀ
[
10].
strate. The efficacy of Mn(II) acetate in the
СН СООН–H SO system has been shown using the
example of ethylbenzene oxidation with ozone. This
For the cumene peroxide radical, reactions (8)–
12) are possible [11–12]:
3
2
4
(
•
•
Ar(СH ) CОО + O
2
Ar(СH ) CО + 2O (8)
3 2 2
3
3
0.30
•
Ar(СH ) CО + Ar(СH ) CH
3
Ar(СH ) CОН
3 2
2
3 2
•
+
Ar(СH ) C
2
(9)
3
•
3
0.25
•
Ar(СH ) CО
3
ArCОСH + С
3
H
(10)
2
3
•
2
2Ar(СH ) CОО
3 2
0.20
1
Ar(СH ) CООС(СH ) Ar + O
3 2
(11)
(12)
3
2
2
•
•
2
Ar(СH ) CОО
3
2Ar(СH ) CО + O
3 2 2
2
The decrease in the [Ar(СH ) CОН]/ [ArCОСH3]
0.15
3
2
ratio from 7.2 in uncatalyzed ozonation to 0.55 in the
case of ozonation in the presence of Co(II) acetate
shows that the excess amount of alcohol in the absence
of the catalyst is most likely due to the primary reacꢀ
tion of ozone with cumene (reaction (1b)), and the
cumyloxy radical predominantly decomposes accordꢀ
ing to reaction (10).
0
.10
.05
0
The increase in the alkylbenzene ozonation selecꢀ
tivity with the increasing strong acid concentration
3'
2
'
1'
(
Tables 2, 3; runs 11–15) is attributed to an increase in
the activity of the metal in the higher oxidation state in
the reaction with the substrate (Fig. 5); this can be
20
40
60
80
100 120
explained
by
the
3
degradation
of
the
τ
, min
[
Ме O(OAc) (AcOH) ]OАc cluster complexes, the
3
6
formation of monomeric particles, and an increase in
electrophilicity of the metal atom [13]. However, at
Fig. 4. Rate curves for consumption of cumene (primed
high concentrations of acids, the activity of Me3+
numbers) and overall buildup of alkylꢀgroup oxidation
products at different temperatures. [Ar(СH ) CH] =
3
2
increases so that the oxidation of the solvent becomes
appreciable along with the oxidation of alkylbenzene
–4
0
.3 mol/L, [O ] = 4
×
10 mol/L, [Co(II)] = 0.12 mol/L,
3
and [СF COOH] = 2.0 mol/L; ( 1') 20°C, ( ') 40°C,
1,
2, 2
3
(
Fig. 5a, curve
6).
and (3, 3') 60°C.
PETROLEUM CHEMISTRY Vol. 52
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118
POTAPENKO, ANDREEV
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0
.10
(b)
6
1
(а)
0.08
0.06
0.04
2
3
0.02
4
5
0
.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
10
20
30
, min
40
50
τ
[
H SO ], mol/L
2
4
Fig. 5. Kinetics of consumption of the higher oxidized metal form in acetic acid at 20
°
С
at different concentrations of strong
acids in a nitrogen atmosphere: (a) dependence of the initial rate of Mn(III) consumption in reaction with ethylbenzene.
[
[
ArСH СН3] = 0.25 mol/L, [Mn(III)] = 0.08 mol/L and (b) kinetics of consumption of Co(III) in reaction with cumene.
2
Ar(СH ) CH] = 0.2 mol/L, [СF COOH], mol/L = (1) 0, (2) 1.0, (3) 1.5, (4) 2.0, (5) 2.5, and (6) 2.5 (in the absence of cumene).
3
2
3
catalyst system makes it possible to carry out ozonaꢀ
tion at 20 with an alkylꢀgroup oxidation selectivity
of 75.2%. The efficacy of Co(II) acetate in the
4. S. K. Rakovskii, D. R. Chernova, and D. M. Shopov,
Izv. Akad. Nauk SSSR, Ser. Khim., No. 9, 1991 (1979).
5. J. Hanotier, M. HanotierꢀBridoux, P. de Radzitzky,
J. Chem. Soc., Perkin Trans. 2, No. 4, 381 (1973).
°
С
СН СООН–СF СООН system has been shown
3
3
using the example of the oxidation of cumene with
ozone; the ozonation selectivity at 20 is 80%. The
6. E. V. Potapenko, P. Yu. Andreev, and I. P. Pogorelova,
Khim. Promꢀst’ Ukr., No. 1, 20 (2010).
°
С
redox catalysis mechanism has been considered;
according to it, the role of catalyst in the reaction with
ozone is reduced to the generation of the higher oxidaꢀ
tion state of the metal, which can subsequently proꢀ
vide the selective oxidation of the alkyl group.
7. G. A. Galstyan, E. V. Potapenko, I. M. Pluzhnik, et al.,
Proceedings of Regional Conference on Ozone Generation
and Application to Water and Waste Treatment (Moscow,
1998).
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Reactions with Organic Compounds (Nauka, Moscow,
1
974).
. E. V. Potapenko, P. Yu. Andreev, and I. P. Pogorelova,
Vopr. Khim. Khim. Tekhnol., No. 4, 31 (2010).
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PETROLEUM CHEMISTRY Vol. 52
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2012