Oxidation of 2,4-dinitrotoluene with ozone in the presence of a stop reagent

Article abstract of DOI:10.1134/S1070427214010042

Liquid-phase oxidation of 2,4-dinitrotoluene with ozone in the presence of acetic anhydride as stop reagent and manganese(II) acetate as catalyst was studied. The major products of oxidation with ozone in acetic anhydride are 2,4-dinitrobenzyl alcohol (65.8%) and 2,4-dinitrobenzaldehyde (18.8%) in the form of the corresponding acetates. A reaction scheme accounting for the results obtained is considered. Pleiades Publishing, Ltd., 2014.

Full text of DOI:10.1134/S1070427214010042

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2014, Vol. 87, No. 1, pp. 31−35.  Pleiades Publishing, Ltd., 2014.
Original Russian Text  A.G. Galstyan, V.V. Lysak, G.A. Galstyan, 2014, published in Zhurnal Prikladnoi Khimii, 2014, Vol. 87, No. 1, pp. 35−39.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Oxidation of 2,4-Dinitrotoluene with Ozone
in the Presence of a Stop Reagent
A. G. Galstyan, V. V. Lysak, and G. A. Galstyan
Institute of Chemical Technologies, Dal’East-Ukrainian National University, Gorodok Shorsa 17A,
Rubezhnoe, Lugansk oblast, 19011 Ukraine
e-mail: ozon@megabit.com.ua
Received December 5, 2013
Abstract—Liquid-phase oxidation of 2,4-dinitrotoluene with ozone in the presence of acetic anhydride as stop
reagent and manganese(II) acetate as catalyst was studied. The major products of oxidation with ozone in acetic
anhydride are 2,4-dinitrobenzyl alcohol (65.8%) and 2,4-dinitrobenzaldehyde (18.8%) in the form of the corre-
sponding acetates. A reaction scheme accounting for the results obtained is considered.
DOI: 10.1134/S1070427214010042
2,4-Dinitrobenzyl alcohol (2,4-DNBAl) and 2,4-dini-
trobenzaldehyde (2,4-DNB) are widely used as intermedi-
ates in fine organic synthesis [1, 2]. 2,4-DNBAl is mainly
prepared by hydrolysis of 2,4-dinitrobenzyl chloride [3].
The drawbacks of this method are low product yield and
formation of large amounts of toxic chlorine-containing
wastewaters.
in acetic anhydride in the presence of sulfuric acid
and catalytic amounts of manganese(II) acetate are
2,4-dinitrobenzyl acetate (2,4-DNBAt) (65.8%) and
2,4-dinitrobenzylidene diacetate (2,4-DNBDA) (18.8%)
(see figure). 2,4-DNBAc was detected in the solution
c, M
This study deals with oxidation of 2,4-dinitrotoluene
(2,4-DNT) with an ozone–air mixture and is aimed to
develop a low-waste procedure for preparing 2,4-DNBAl
in a high yield.
We showed previously [4] that 2,4-DNT is oxidized
with ozone in an acetic acid solution in the presence of
cobalt(II) acetate to 2,4-dinitrobenzoic acid (2,4-DNBAc)
in 87.6% yield. The process cannot be stopped at the steps
of formation of 2,4-DNBAl or 2,4-DNB because of their
high reactivity in reactions with ozone.
As a continuation of these studies, we examined
the possibility of stopping the oxidation at the step of
2,4-DNBAl formation by performing the reaction in the
presence of a stop reagent, acetic anhydride, which can
convert labile intermediates into acetates, more resistant
to ozone [5].
τ, min
Oxidation of 2,4-DNT with ozone in acetic anhydride in
the presence of manganese(II) acetate at 20°С. Reaction
conditions: [ArCH3]0 = 0.40, [Н2SO4]0 = 1.20, [O3] = 4 × 10–4,
[Mn(OAc)2]0 = 0.06 M; space velocity of the ozone–air mixture
0.83 s–1. (с) Concentration of oxidation products and (τ) time.
(1) 2,4-DNT, (2) 2,4-DNBAt, (3) 2,4-DNBDA, (4) 2,4-DNBAc,
and (5) manganese(III) acetate.
Our studies showed that the major products of
2,4-DNT ozonation at 20°C and atmospheric pressure
31

32
GALSTYAN et al.
Table 1. Rate constants of the catalytic cycle of 2,4-DNT oxidation with ozone in the presence of manganese(II) acetate in acetic
anhydride. Initial concentrations: [ArH]0 = 0.10–0.40, [Н2SO4]0 = 1.20, [Mn(OAc)2]0 = 0.06, [O3] = 4 × 10–5
k, L mol–2 s–1
M
Activation energy,
kJ mol–1
Reaction
5°С
20°С
2,4-DNT + О3
0.010
0.080
29.0 ± 3.0
2,4-DNBAl + О3
2,4-DNB + О3
0.540
0.420
0.004
0.002
1.660
1.340
0.023
0.015
23.5 ± 2.0
25.1 ± 2.0
32.5 ± 3.0
35.8 ± 3.0
2,4-DNBAt + О3
2,4-DNBDA + О3
Mn(II) + О3
10.200
0.010
47.600
0.020
22.8 ± 2.0
37.0 ± 4.0
2,4-DNT + Mn(III)
after exhaustive oxidation of 2,4-DNT. It should be noted
that cobalt(II) acetate exhibits no catalytic properties in
the presence of sulfuric acid.
more resistant to ozone (Table 1). The sequence of
the formation of 2,4-DNT oxidation products is shown
in the scheme.
Under the conditions of catalysis with manganese(II)
acetate in acetic anhydride and in the presence of sulfuric
acid, 7 min after starting the ozone feeding, the Mn(III)
concentration in the system reached 0.06 M and then did
The oxidation inhibition at the step of formation
of the alcohol and, to a lesser extent, aldehyde is due
to the conversion of nascent hydroxy and carbonyl
groups into acetate and acylal groups, which are
Scheme.
CH3
O2N
O
O
O
Products of benzene ring cleavage
NO2
CHO
CH(OAc)2
COOH
NO2
O2N
O2N
O2N
Ac2O, H+
O3, Mn
O3
(oz)
CH3
NO2
NO2
O2N
O3, Mn
O3 Mn
O3 Mn
CH2OH
CH2OAc
NO2
O2N
O2N
Ac2O, H+
NO2
NO2
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OXIDATION OF 2,4-DINITROTOLUENE WITH OZONE
33
not further change up to the end of the oxidation (see
figure). In the initial period of the reaction, 2,4-DNBAt
and 2,4-DNBDAare accumulated at a rate lower than the
maximal rate (see figure, curves 2, 3). The attainment of
the maximal rate of their formation coincides in time with
the conversion of Mn(II) to Mn(III). Ozone should be fed
continuously. If ozone feeding is stopped, the 2,4-DNT
oxidation and accumulation of the final products first
decelerate and then cease at all, and Mn(III) transforms
into Mn(II).
the methyl group [6, 7] and are capable to react with 2,4-
DNT with the formation of benzyl radicals [reaction (3)]:
ArCH3 + O3 → ozonolysis products,
Mn2+ + O3 + H+ → Mn3+ + HO· + O2,
ArCH3 + Mn3+ → ArСH2· + Mn2+ + H+.
(1)
(2)
(3)
High selectivity of 2,4-DNT oxidation to aromatic
alcohol is possible only at sufficiently high concentration
of the acylation catalyst, sulfuric acid (Table 2). With
an increase in the acid concentration, the selectivity of
the oxidation at the methyl group first increases, reaches
a maximum at the acid concentration of 1.2 M, and does
not increase further at higher acid concentrations. In
the examined interval of sulfuric acid concentrations,
the ratio of the products of the methyl group oxidation
remains virtually constant (Table 2).
The kinetic features of 2,4-DNT oxidation in the
presence of manganese(II) acetate and an increase in
the selectivity of methyl group oxidation under these
conditions suggest that ozone reacts primarily not with
2,4-DNT [reaction (1)], but with Mn(II) [reaction (2)]
{at 20°С, [ArCH3]0 = 0.4, [Mn(OAc)2]0 = 0.06, [O3]0 =
4 × 10–4 M; k1 = 0.08, k2 = 47.6 L mol–1 s–1; r2 : r1 = 10
(Table 1)}, generating active Mn(III) species that exhibit
high substrate selectivity in oxidation of methylarenes at
Our experimental data in combination with published
data [8–11] allowed us to suggest the reaction scheme
Table 2. Influence of sulfuric acid concentration on the yield of products and selectivity of 2,4-dinitrotoluene oxidation at the
methyl group. Reaction conditions: 20°С; initial concentrations: [ArСH3]0 = 0.10–0.40, [Mn(OAc)2]0 = 0.06, [O3] = 4 × 10–4 M;
liquid phase volume 0.01 L; reaction time 2.5 h
Content of reaction products, %
[H2SO4]0, M
Selectivity, %
2,4-DNBAt
2,4-DNBDA
DNBAc
0.6
0.8
1.0
1.2
1.4
37.1
48.2
55.3
65.8
59.2
12.5
16.3
19.1
18.8
20.0
22.0
30.8
22.3
12.5
18.0
71.6
95.3
96.7
97.1
97.2
Table 3. Influence of temperature on the selectivity of 2,4-DNT oxidation with ozone in an acetic anhydride solution. Reaction
conditions: initial concentrations: [Н2SO4] = 1.20, [ArСH3]0 = 0.10–0.40, [Mn(OAc)2]0 = 0.06, [O3] = 4 × 10–4 M; 20°С; liquid
phase volume 0.01 L; reaction time 2.5 h
Content of reaction products, %
T, °С
Selectivity, %
2,4-DNBAt
62.5
2,4-DNBDA
17.5
2,4-DNBAc
10.9
10
20
30
40
90.9
97.1
97.5
98.2
65.8
18.8
12.5
53.0
13.4
31.1
45.2
10.5
42.5
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 1 2014

34
GALSTYAN et al.
involving the radical ion nonchain mechanism of 2,4-
DNT oxidation:
was purified by repeated recrystallization from ethanol.
Analytically pure grade manganese(II) acetate was used
without additional purification.
ArСH2· + O2 → ArCH2O2·,
(4)
The reactor (a glass column with a porous partition
for dispersing the ozone–air mixture) was charged with
5 mL of acetic anhydride, 2,4-DNT to a concentration
of 0.4 M, and calculated amounts of the catalyst and
sulfuric acid. Then the setup was brought to the required
temperature, and, after the steady-state mode of the
ozonizer operation was reached, the ozone–air mixture
containing 4.0 × 10–4 M ozone was passed at a rate of
30 L h–1. The ozone concentration in the gas phase was
determined by spectrophotometry from the absorption
in the range 254–290 nm. Identification of oxidation
products and their quantitative determination in solution
were performed by GLC on a chromatograph equipped
with a flame ionization detector, using a column 3 m long
and 4 mm in diameter, under the following conditions:
stationary phase SE-30, 5 wt % on Inerton AW-DMCS;
vaporizer temperature 250, thermostat temperature
90–225°С; carrier gas nitrogen; flow rates: nitrogen 1.8,
hydrogen 1.8, and air 18 L h–1. 4-Nitrochlorobenzene
was used as internal reference. The effective rate
constants of the reactions of ozone with Mn2+, 2,4-
DNT, and its oxidation products were determined by
spectrophotometry using the procedure described in [12];
the rate constant of the reaction of 2,4-DNT with Mn3+
was calculated for the case of irreversible second-order
reactions [13].
ArСH2· + O3 → ArCH2O· + O2,
(5)
ArCH2O2· + ArCH3 → ArCH2O2H + ArCH2·,
ArCH2O2· + Mn2+ + H+ → ArCH2O2H + Mn3+,
ArCH2O2· + O3 → ArCH2O· + 2O2,
(6)
(7)
(8)
(9)
ArCH2O· + Mn2+ → ArCH2O– + Mn3+,
+
ArCH2O– + CH3–C=О → ArCH2OСОСН3.
(10)
The benzyl radicals generated in reactions (2) and (3)
under the conditions of our experiments ([O2] >> [O3]),
taking into account comparable rate constants of reac-
tions of reactions (4) and (5) (107–108 L mol–1 s–1 [8, 9]),
are presumably consumed in reaction (4) to form peroxy
radicals, which then rapidly react with ozone (for cyclo-
hexane, k8 = 1.2 × 104 L mol–1 s–1 [9]) to form alkoxyl
radical [reaction (8)]. Reactions (6) and (7) under the
conditions of our experiments do not occur to notice-
able extent; at [ArCH2O2·] = 3 × 10–6 M (calculated us-
ing the Bodenstein–Semenov method), 20°С, [Mn2+] =
6×10–3, [O3] = 4 × 10–4, [ArCH3]0 = 0.4 M, k6 ≈ 0.2 [9],
k7 ≈ 11.5 [10], and k8 ≈ 1.2 × 104 Lmol–1 s–1 [9], r6 ≈ 2.0 ×
10–7, r7 ≈ 1.9 × 10–7, and r8 ≈ 1.3 × 10–5 mol L–1 s–1.
Because alkoxyl radicals are strong oxidants [11], it
was natural to expect, by analogy with peroxy radicals,
their reaction in the bulk of the liquid phase with the
reduced Mn(II) species to form the anion [reaction (9)],
which subsequently reacts with acylium cation [reac-
tion (10)] to form 2,4-DNBAt. Apparently, the forma-
tion of 2,4-DNBDA and 2,4-DNBAc in the steady-state
mode follows the similar scheme.
CONCLUSIONS
The catalytic reaction of ozone with 2,4-dinitrotoluene
in the presence of a stop reagent was studied. In an acetic
anhydride solution in the presence of sulfuric acid and
manganese(II) acetate, it is possible to prevent ozonolysis
and direct the reaction of oxidation with ozone toward
methyl group oxidation with the predominant formation
of 2,4-dinitrobenzyl alcohol in the form of the correspond-
ing benzyl acetate in 65.8% yield.
The rate and selectivity of oxidation of 2,4-DNT
to 2,4-DNBAt depend on the reaction temperature.
The optimum reaction temperature is 20°С. At lower
temperatures, the total selectivity somewhat decreases
(Table 3), because an increase in temperature leads to
an increase in the extent of oxidation: 2,4-DNBAt and
2,4-DNBDA become intermediates, and 2,4-DNBAc is
formed (Table 3).
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OXIDATION OF 2,4-DINITROTOLUENE WITH OZONE
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