Kinetics and products of the catalytic oxidation of acetamidotoluenes with ozone in acetic acid

Article abstract of DOI:10.1134/S0023158410040099

The kinetics of acetamidotoluene oxidation in glacial acetic acid in the presence of cobalt acetate is reported. At 95°C and atmospheric pressure, acetamidotoluenes are oxidized by molecular oxygen very slowly: oxidation is complete in 10-12 h, and the major reaction products are acetamidobenzoic acids (27-36% yield). The introduction of ozone into the reactive gas increases the reaction rate by one order of magnitude. The main role of ozone is to generate the active form of the catalyst.

Full text of DOI:10.1134/S0023158410040099

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2010, Vol. 51, No. 4, pp. 516–520. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.G. Galstyan, A.S. Bushuev, A.Yu. Sementsov, 2010, published in Kinetika i Kataliz, 2010, Vol. 51, No. 4, pp. 542–546.
Kinetics and Products of the Catalytic Oxidation
of Acetamidotoluenes with Ozone in Acetic Acid
A. G. Galstyan, A. S. Bushuev, and A. Yu. Sementsov
Institute of Chemical Technologies, East Ukrainian National University, Rubezhnoe, Lugansk oblast, Ukraine
eꢀmail: ozon@megabit.com.ua
Received March 25, 2009
Abstract—The kinetics of acetamidotoluene oxidation in glacial acetic acid in the presence of cobalt acetate
is reported. At 95°C and atmospheric pressure, acetamidotoluenes are oxidized by molecular oxygen very
slowly: oxidation is complete in 10–12 h, and the major reaction products are acetamidobenzoic acids (27–
36% yield). The introduction of ozone into the reactive gas increases the reaction rate by one order of magꢀ
nitude. The main role of ozone is to generate the active form of the catalyst.
DOI: 10.1134/S0023158410040099
INTRODUCTION
scheme presented below (route I) [2], mainly at the
amino group, to form resinous compounds of
unknown structure and small amounts of 4ꢀnitrotoluꢀ
We demonstrated in an earlier study [1] that the
oxidation of 4ꢀaminotoluene by an ozone–air mixture
in glacial acetic acid proceeded according to the ene and toluquinone:
+
H2N O−
NO2
O3
–O2
II
I
..
+
NHAc
NH2
H2N OOO−
CH3
CH3
O3
AcOH
.
+
NH2
+
NH2
CH3
CH3
CH3
–O•3–
O3
.
CH3
CH3
Ozonolysis
products
–O•3–
NHAc
COOH
Resinous
compounds
O
NH
O
O
CH3
CH3
Scheme.
The reaction route changes after Nꢀacylation. the methyl group to form 4ꢀacetamidobenzoic acid
However, in this case, the oxidation again occurs (14%) (scheme, route II). Our study showed that 4ꢀ
mainly at the aromatic ring to yield the ozonolysis acetamidotoluene (4ꢀAAT) is oxidized via a nonchain
product (84%) and, to a considerably lesser extent, at radical mechanism and ozone is consumed in two
516

KINETICS AND PRODUCTS OF THE CATALYTIC OXIDATION
517
routes: at 20°С ozone reacts with the initial substrate
Concentration, mol/l
0.4
via the nonchain mechanism, whereas at higher temꢀ
peratures the chain reaction of ozone with the aroꢀ
matic ring destruction products begins to play a
noticeable role along with the nonchain route.
1
2
0.3
Here, we report the kinetics of the oxidation of isoꢀ
meric acetamidotoluenes (AATs) by ozone in acetic
acid in the presence of cobalt acetate, which is a conꢀ
ventional catalyst for the oxidation of methylbenzenes
[4], and to establish the main factors determining the
efficiency of oxidation at the methyl group.
3
0.2
3'
2
'
0.1
EXPERIMENTAL
2
4
6
8
10
12
Experiments were carried out under kinetic control
using a 20ꢀml temperatureꢀcontrolled glass column
with a porous membrane for gas dispersion. Glacial
acetic acid (10 ml), AAT (0.4 mol/l), and cobalt aceꢀ
tate tetrahydrate were placed in the airꢀpurged colꢀ
umn, and a reactive gas (air, oxygen, or an ozone–air
mixture) was fed at a rate of 30 l/h. The ozone concenꢀ
Reaction time, h
Fig. 1. Oxidation of 4ꢀAAT by oxygen in acetic acid at
95°С and initial concentrations of [ААТ] = 0.4 mol/l and
0
[Со(ОАс) ] = 0.14 mol/l, a feed rate of 30 l/h, and a soluꢀ
2 0
tion volume 0.01 l: (
1
–3
) 4ꢀAAT consumption in oxidaꢀ
) dioxygen in the presence of Co(II)
) dioxygen in the presence of Co(III); ( ',
4ꢀAABA buildup in experiments and , respectively.
tion with (
1) air and (2
3
and with (
2 3')
tration in the gas phase was (1.5–6.0) ×
10–4 mol/l.
2
3
Oxidation in the Presence of Co(III) and Co(II)
18 l/h, respectively. 4ꢀNitrochlorobenzene was used as
the internal standard. The current concentration of 4ꢀ
The solution of cobalt(II) acetate in acetic acid was
ozonated for 40 min. After the complete oxidation of AABA was determined by alkaline titration: a sample
Co(II) to Co(III), the gas flow was shut off, the soluꢀ
tion was purged with nitrogen for 3 min, an appropriꢀ
ate amount of AAT was added, and feeding of the
ozoneꢀcontaining gas or dioxygen was resumed. After
the completion of oxidation, the reaction mixture was
poured into a glass beaker twoꢀthirds full of finely
crushed ice and was diluted with cold water to a total
volume of 50 ml. The acetamidobenzoic acid (AABA)
precipitate was filtered off, washed with cold water,
and diluted with a mixture consisting of concentrated
HCl (10 ml), water (20 ml), and alcohol (4 ml). The
solution was held under stirring for 1 h at 60°С in a
flask with a reflux condenser. The reaction mixture was
then cooled, and the resulting aminobenzoic acid was
filtered and dried.
(0.5 ml) was taken from the reaction mixture, the solꢀ
vent was distilled out from the sample, the dry residue
was dissolved in 50% ethanol (30 ml) brought to neuꢀ
trality to phenolphthalein, and the solution was
titrated with 0.05 N NaOH.
Determination of Rate Constants
The apparent rate constants of the reaction of
ozone with AAT and the ozone uptake during the
reaction were calculated using standard procedures
[2]. The rate constants of the reaction of Co(III) with
AAT were determined graphically under the assumpꢀ
tion that this process is a secondꢀorder irreversible
reaction [3].
Oxidation in the presence of Co(II) was carried out
similarly, but without Co(II) preconversion into
Co(III).
RESULTS AND DISCUSSION
Analysis of the Reaction Products and Reactants
Acetamidotoluenes were oxidized at 95°С and
atmospheric pressure in glacial acetic acid. The initial
concentrations of the reaction components were as
The ozone concentration in the gas phase at the
inlet and outlet of the reactor was determined by specꢀ
trophotometry [2].
Acetamidotoluenes and the corresponding alcoꢀ
hols and aldehydes were analyzed chromatographiꢀ
cally (flame ionization detector, column 3 m in length
and 4 mm in diameter, Inerton AWꢀDMCS support,
SEꢀ30 (5%) stationary phase). The chromatographic
conditions were as follows: evaporator temperature of
250°С; oven temperature of 190°С; carrier gas (nitroꢀ
follows: [AAT]0
0.14 mol/l, and [O3]0 = (1.5–6.0)
=
0.4 mol/l, [Со(ОАс)2]0
=
×
10–4 mol/l. The
oxidation of 4ꢀAAT by atmospheric oxygen in the
presence of cobalt(II) acetate occurs very slowly
(Fig. 1, curve 1): in 12 h, the substrate conversion does
not exceed 10% and 4ꢀAABA is observed in the reactꢀ
ing solution, whose yield is 31% in terms of the reacted
gen), hydrogen, and air flow rates of 1.8, 1.8, and 4ꢀAAT.
KINETICS AND CATALYSIS Vol. 51
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2010

518
GALSTYAN et al.
A different situation is observed when trivalent
cobalt is introduced into the system (Fig. 1, curve ).
Oxidation develops without an induction period and is
complete within 10 h. Throughout the reaction time,
cobalt is predominantly in the trivalent state, 4ꢀAABA
forms in 36% yield, and traces of 4ꢀacetamidobenzalꢀ
dehyde are observed.
Concentration, mol/l
3
0.4
1
0.3
0.2
0.1
O3
Similar results were obtained for the catalytic oxiꢀ
dation, with oxygen, of 3ꢀAAT (oxidation time of
~10 h, 3ꢀAABA yield of 35%) and 2ꢀAAT (oxidation
time of ~11 h, 2ꢀAABA yield of 27%).
2
3
The experimental data obtained in the presence of
Co(II) acetate are quite consistent with the view that radꢀ
icals form at the early stages of the reaction via the interꢀ
action of divalent cobalt with oxygen and AAT [4]:
10
20
30
Reaction time, min
Со2+ + О2
Со2+…О2,
(I)
Fig. 2. Oxidation of 3ꢀAAT with the ozone–air mixture in
acetic acid at 95°С in the presence of cobalt(II) acetate at
initial concentrations of [Со(OAc) ] = 0.14, [3ꢀААТ]
=
2 0
0
Со2+…О2 + AcНNArCH3
Со3+ + AcHNArCH2O• + НO–.
4
0.4, and [O ] = 4.5
×
10⎯ mol/l (reacting gas flow rate of
30 l/h, solution volume of 0.01 l): ( ) 3ꢀAAT, ( ) [Co(III)],
and ( ) 3ꢀAABA. The dashed lines show how curves
change after the ozone feed is shut off.
3 0
(II)
1
2
3
1–3
The induction period due to the slow formation of
Co(III) and radicals via reaction (II) is observed in
kinetic curve 2 (Fig. 1).
The 4ꢀAAT oxidation rate increases with an
increasing concentration of dioxygen in the system.
Oxidation with pure oxygen in the presence of
cobalt(II) acetate is complete within 12 h (Fig. 1,
The induction period ends once a certain amount
of trivalent cobalt is accumulated in the system (for the
oxidation of 4ꢀAAT, [Со3+] 10–2 mol/l) and the
≈ 1.7 ×
curve 2). In this case, the Co(III)/Co(II) = 0.14 ratio
radicals begin to form via reaction (III). The absence
of an induction period in the case of trivalent cobalt
confirms this assumption and proves that the oxidaꢀ
tion of AAT occurs at the methyl group:
is established in the system within the first 2 h and
remains unchanged to the end of the experiment. At
the early stages of oxidation (2 h), the kinetic curve
indicates an induction period, whose end point coinꢀ
cides in time with the appearance of Co(III) in the sysꢀ
tem. The reaction products include 4ꢀAABA (30.6%
yield), and traces of 4ꢀacetamidobenzaldehyde were
detected in the time interval from 2 to 4 h.
Со3+ + AcНNArCH3
(III)
Со2+ + AcHNArCH•2 + Н+.
Thus, to accelerate the process, a sufficiently high
Co(III) formation rate should be ensured in the initial
period, which would be favorable for the acceleration
of reaction (III) and for the rapid oxidation of AAT at
the methyl group. This problem can be successfully
solved by using ozone as the oxidizer, passing it
together with air or dioxygen through an acetic acid
solution of AAT and cobalt(III) acetate. Cobalt(III)
acetate is obtained by the complete ozonation of
cobalt(II) acetate in an acetic acid solution.
Table 1. Effect of the ozone concentration in the ozone–air
mixture on the rate and selectivity of AAT oxidation
[O3]0
×
104,
w
×
104,
mol l–1 s–1 of AABA, %
Yield
Compound
mol/l
2ꢀAAT
1.5
3.0
4.5
1.5
3.0
4.5
1.5
3.0
4.5
1.1
1.8
2.1
1.2
1.8
2.2
1.3
3.7
7.4
20.0
23.0
25.0
25.0
27.0
34.0
28.1
32.5
35.5
Figure 2 shows that, as an ozone–air mixture is
passed through the 3ꢀААТ–Со(ОАс)3–АсОН sysꢀ
tem, oxidation occurs at a high rate and the oxidation
time shortens from 10 to 0.3 h (compare Figs. 1 and 2).
Ozone should be fed continuously, otherwise the proꢀ
3ꢀAAT
4ꢀAAT
cess is terminated (Fig. 2). The AAT oxidation rate (w)
increases with an increasing ozone concentration,
whereas the yield of the corresponding AABA changes
insignificantly, ranging from 20.0 to 35.5% (Table 1).
The AAT consumption rate depends linearly on the
initial ozone concentration in the ozone–air mixture.
The order of the 4ꢀAAT oxidation reaction with
Note: For the reaction conditions, see the caption to Fig. 2.
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KINETICS AND PRODUCTS OF THE CATALYTIC OXIDATION
519
respect to ozone is 1.5, whereas the order of the reacꢀ
The low selectivity of oxidation at the methyl group
tion with respect to the substrate and cobalt acetate is is a consequence of the high rate of the noncatalytic
unity (Fig. 3). From one to two moles of ozone is conꢀ reaction between ozone and AAT, which results
sumed in the oxidation of 1 mol of AAT (Table 2).
mainly in the opening of the aromatic ring [1, 2]:
NHAc
kIV.1
NHAc
kIV
HOOC
+ O3
(IV)
NHAc
NHAc
CHO
H3C
H
O
AcOH
kIV.2
O
CH OOH
OAc
O
H
H3C
H3C
For instance, for 4ꢀAAT oxidation (Fig. 2) at 95°С to the total AAT oxidation rate in reactions (III) and
III = 0.074 and kIV = 70.8 l mol–1 s–1. The data on the (IV), the selectivity can be calculated as
k
selectivity of 4ꢀAAT oxidation by ozone at the methyl
group and aromatic ring (14.2 and 85.8%, respectively
[1]) were used to estimate kIV.1 and kIV.2 since it can be
assumed in the first approximation that the kIV.1 and
kIV.2 values and the selectivity in this direction are
k
IV.1[O3]0 + kIII[Co(OAc) ]
2 0 ×100.
S =
kIV [O3]0 + kIII[Co(OAc)2]0
mutually proportional. Therefore, kIV.1 = 70.8
×
=
The calculated selectivity checks well with the
experimental data (Table 3). It can be seen from the
0.142 = 10.1 l mol–1 s–1 and kIV.2 = 70.8
×
0.858
60.7 l mol–1 s–1. Under the assumption that the selecꢀ data in Table 3 that, in the presence of cobalt acetate,
tivity of oxidation at the methyl group (in percent) is the oxidation of AAT without aromatic ring breaking is
determined by the ratio of the sum of the oxidation possible only at moderate catalyst concentrations
rates at the methyl group in reactions (III) and (IV.1) (0.14 mol/l). It is impossible to increase the selectivity
log[O3] [mol/l
]
−
4.0
−
3.7
−
3.4
−
3.1
−1.1
−1.4
−1.7
−2.0
2
3
1
−
1.9
−
1.6
−
1.3
−
1.0
0.1
log[Co(OAc)2] [mol/l
]
−1.0 −0.7 −0.4
−
log[ArCH3] [mol/l
]
Fig. 3. 4ꢀAAT oxidation rate versus the concentration of (
KINETICS AND CATALYSIS Vol. 51 No. 4 2010
1) cobalt acetate, (2) ozone, and (3) substrate.

520
GALSTYAN et al.
Table 2. Ozone uptake per mole of AAT at 95°C
Amount of ozone
Ozone uptake,
Ozone uptake
per mole of AAT
Compound
Oxidation time, min
passed, mol × 10–3
mol × 10–3
2ꢀААТ
3ꢀААТ
4ꢀААТ
40
30
20
11.0
8.3
8.0
6.3
4.2
2.0
1.6
1.1
5.5
–4
Note: [AAT] = 0.4, [Co(OAc)
] = 0.14, [O ] = 5.5 × 10 mol/l, gas flow rate of 30 l/h, solution volume of 0.01 l.
2 0 3 0
0
Table 3. Effect of the cobalt(II) acetate concentration on the AAT oxidation rate and selectivity
Yield of acetamidobenzoic acids, %
[Co(ОАс)2]0,
mol/l
w ×
104,
Compound
mol l–1 s–1
calculated
observed
2ꢀААТ
0.05
0.10
0.14
0.20
0.05
0.10
0.14
0.20
0.05
0.10
0.14
0.20
1.2
1.5
2.1
3.7
1.3
1.6
2.2
3.9
1.8
3.7
7.4
10.2
13.4
20.3
24.7
30.8
21.1
29.0
33.1
40.6
23.2
29.9
35.1
41.3
19.0
22.5
25.0
27.5
21.8
28.1
34.0
34.4
22.6
31.2
35.5
35.5
3ꢀААТ
4ꢀААТ
Note: For the reaction conditions, see the caption to Fig. 2.
by further raising the catalyst concentration, because
of the increasing viscosity of the solution, which
decreases the rate of ozone dissolution in the liquid
phase.
REFERENCES
1. Galstyan, A.G., Bushuev, A.S., and Solomyannii, R.M.,
Ukr. Khim. Zh., 2008, vol. 74, no. 7, p. 57.
2. Razumovskii, S.D. and Zaikov, G.E., Ozon i ego reaktsii
s organicheskimi soedineniyami (Ozone and Its Reacꢀ
tions with Organic Compounds), Moscow: Nauka,
1974.
3. Emanuel, N.M. and Knorre, D.G., Kurs khimicheskoi
kinetiki (Chemical Kinetics), Moscow: Vysshaya
Shkola, 1969, p. 166.
4. Emanuel, N.M., Denisov, E.T., and Maizus, Z.K.,
Tsepnye reaktsii okisleniya uglevodorodov v zhidkoi faze
(Chain Oxidation Reactions of Hydrocarbons in the
Liquid Phase), Moscow: Nauka, 1965.
Thus, in the present work we studied, for the first
time, the oxidation of isomeric acetamidotoluenes by
an ozoneꢀcontaining gas in glacial acetic acid in the
presence of cobalt(II) acetate as the catalyst. Under
the catalytic conditions, the selectivity achieved for
the oxidation at the methyl group is not higher than
27–36%, which is a consequence of the high ozonolyꢀ
sis rate (
k
kIII).
IV.1 ӷ
KINETICS AND CATALYSIS Vol. 51
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2010