OXIDATION OF 2,4-DINITROTOLUENE WITH AN OZONE OXYGEN MIXTURE
in the presence of catalysts based on salts of metal
593
with variable oxidation state. In this study, we exam-
ined the catalytic oxidation of DNT in the presence of
cobalt(II) acetate (Fig. 3). Previously, we found that
oxidation of DNT with molecular oxygen at 100 C in
the presence of cobalt(II) acetate is very slow: only
traces of DNBA were detected after 15-h oxidation.
Catalytic oxidation with an ozone oxygen mixture is
fast and yields mainly DNBA (Fig. 3). Oxidation at
100 C in the presence of 0.14 M cobalt(II) acetate is
complete in 3.5 h; the DNBA yield is 87%.
Selective oxidation of the methyl group with ozone
in the presence of cobalt(II) acetate is a two-step
process. Under the experimental conditions, ozone
oxidizes mainly Co2+ (k of Co2+ + O3 reaction is
930 [6], and k of the ArCH3 + O3 reaction is
Fig. 3. Kinetic curves of (1 1 ) DNT consumption,
3+
(2 2 ) DNBA accumulation, and (3) Co
accumula-
tion in oxidation of DNT with an ozone oxygen mix-
3
1
ture at 100 C. v
= 8.3 10 l s ; [ArCH ] = 0.5,
3 0
1
0.013 l mol 1 s at 30 C) to reactive Co3+ species
O2
4
[O ]
=
9.5 10
,
[Co(AcO) 4H O]
= 0.14 M.
3 0
2
2
0
which, in turn, rapidly and selectively oxidize the
methyl group of DNT:
(1 , 2 ) [KBr] = 0.1 M.
This complex is more reactive than Co3+ and oxi-
dizes DNT by the reaction
Co2+ + O3 + H+
Co3+ + HO + O2,
(1)
ArCH3 + Co3+ ArCH2 + Co2+ + O2 + H+. (2)
ArCH3 + Co2+ Br
ArCH2 + Co3+ Br + H+.
(5)
Since v1 >> v2 [v1 and v2 are the rates of reac-
tions (1) and (2), respectively], cobalt is in the oxi-
dized form throughout the process (Fig. 3). For reac-
tion (1) to occur, ozone should be continuously fed
to the system. If the ozone supply is interrupted, the
reaction will decelerate and then stop. For the forma-
tion of 1 mol of DNBA is spent 95% of the theoretical
amount of ozone. This indicates that DNT is mainly
oxidized with ozone under the experimental condi-
tions. The role of molecular oxygen is limited to
the reaction with benzyl radical
EXPERIMENTAL
Dinitrotoluene was oxidized in a glass column with
a fine-pore barrier for dispersion of the gas mixture.
The reactor was charged with 15 ml of glacial acetic
acid and a weighed portion of DNT of chemically
pure grade. Then it was heated to the required tem-
perature, and an ozone oxygen mixture was fed at
3
1
a rate of 8.3 10 l s . The concentrations of un-
changed DNT and of intermediate oxidation products
were determined by gas liquid chromatography on
an LKhM-80 chromatograph with a flame-ionization
detector, using a 2 m 3 mm column packed with
Chromaton N-AW with PNFS-6 stationary phase.
The DNBA concentration was determined by titration
with 0.01 N NaOH on an EV-74 ionometer.
ArCH2 + O2
ArCH2O2.
(3)
The amount of oxygen liberated in ozone reduction
by reaction (1) is sufficient for reaction (3) to occur.
The fact that the rate and selectivity of oxidation of
the methyl group are independent of the oxygen con-
centration in the ozone oxygen mixture confirms the
suggested scheme involving reactions (1) (3).
CONCLUSIONS
(1) The reaction of 2,4-dinitrotoluene with ozone
in acetic acid at 30 C occurs mainly via oxidation of
the aromatic ring. The yield of the products of oxida-
tion of the methyl groups does not exceed 34%. At
100 C, the selectivity of oxidation of the methyl
group reaches 48%.
Introduction of potassium bromide into the reac-
tion mixture substantially accelerates the DNT oxida-
tion with an ozone oxygen mixture but has no effect
on the selectivity of oxidation of the methyl group
(Fig. 3). We suggest that potassium bromide reacts
.
with cobalt(II) acetate to form Co2+Br
.
(2) The yield of 2,4-dinitrobenzoic acid in cat-
alytic ozonation of 2,4-dinitrotoluene in the pres-
Co3+ + Br
Co3+ Br
Co2+ Br .
(4)
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 77 No. 4 2004
Andreev
