1778
GALSTYAN et al.
Then we studied the effect of the crystallization
time at 14 C. Below are given the crystallization time
(min) and acid yields (%): 0, 52; 3, 60; 6, 70; 10, 78;
15, 78; and 20, 78. Thus, it is appropriate to perform
crystallization for 10 min.
After keeping for 10 min, 4-nitrobenzoic acid was
washed with concentrated HCl to remove the absorbed
cobalt(II) acetate. After fivefold use in the washing
stage, hydrochloric acid was distilled off, and cobalt
chloride was used in the oxidation stage without addi-
tional treatment.
When we used the filtrate from crystallization of
the target product as the solvent, we noticed a pro-
gressing decrease in the accumulation rate and yield
of the aromatic acid with increasing number of re-
cycles (Fig. 1). This might be due to partial loss of
the catalyst. However, even addition of a full portion
of the catalyst in experiments with the filtrate had no
noticeable effect on the oxidation results (Fig. 1, sec-
ond and third runs of the cycle).
Fig. 2. Effect of water on (1) accumulation rate and
(2) yield of 4-nitrobenzoic acid. (v) Accumulation rate,
( ) yield, and (C) water concentration.
waters containing cobalt(II) chloride were evaporated,
and the cobalt(II) salt was used as the reaction catalyst.
To optimize the crystallization conditions, we pre-
pared standard mixtures consisting of 4-nitrobenzoic
acid, cobalt(II) acetate, potassium bromide, and acetic
acid taken in the same amounts as in the experiment
on 4-nitrotoluene oxidation. The reaction solution
obtained at 95 C was cooled with slow stirring.
We found that the optimal conditions of quantitative
isolation of 4-nitrobenzoic acid are cooling from 95
The oxidation deceleration may also be due to for-
mation of oxidation inhibitors: phenols, nitrobenzene,
and water. The effect of inhibitors on the oxidation
was studied after compensating for the partial loss of
the catalyst in the previous run. We found that the rate
of 4-nitrotoluene oxidation in the presence of phenol
and nitrobenzene does not change noticeably, whereas
addition of water appreciably decreases the oxidation
rate and the process selectivity (Fig. 2). Therefore,
under conditions of multiple use of the filtrate, when
the content of water formed by the reaction increases
from run to run, the oxidation selectivity will de-
crease.
1
to 35 C at a rate of 1 deg min and from 30 to 14 C
1
at a rate of 0.5 deg min . With this schedule, 30
60- m crystals of the acid are formed.
Oxidation of 4-nitrotoluene by an ozone oxygen mixture
in a closed process cycle (95 C)*
Degree
of ozone
utilization, % yield, %
4-Nitrobenzoic acid
Run
no.
To bind the water formed by the reaction, we per-
formed experiments with addition of acetic anhydride.
We found that at a concentration of acetic anhydride
in the primary filtrate of 0.495 M (provided that the
catalyst loss is compensated for, see table), the oxida-
tion rate becomes equal to the rate of 4-nitrotoluene
oxidation in glacial acetic acid, and the yield of the
aromatic acid reaches 93%. Further increase in the
concentration of acetic anhydride decreases the oxida-
tion rate and selectivity, because, when the water
formed by the reaction is completely bound, excess
acetic anhydride starts to react with intermediate 4-ni-
trobenzaldehyde to form 4-nitrobenzylidene diacetate,
which is more resistant to ozone [7].
mp,
C
content, %
1
2
3
4
5
6
7
8
9
90.2
89.6
89.3
91.0
90.1
89.9
89.0
89.3
90.4
90.1
78.0
92.9
93.0
93.1
92.9
93.1
92.9
93.0
93.2
93.1
242.0
99.2
99.4
99.1
99.3
99.2
99.3
99.3
99.1
99.4
99.3
241.5
241.0
241.5
242.5
242.0
241.5
242.5
242.0
241.5
10
*
Charged, M: 4-nitrotoluene 1.01, KBr 0.095 (in run no. 1,
0.126), Co(II) acetate or chloride 0.014 (in run no. 1, 0.023),
The amount of the catalyst lost in the cycle was
determined in the presence of acetic anhydride
(0.495 M). We found that, on adding potassium bro-
mide (0.063 M, 75%) and cobalt diacetate (0.012 M,
61.5%) to the recycling filtrate, the selectivity of 4-ni-
acetic anhydride 3.7 (in run no. 1, 0); in run no. 1, CH COOH
3
(40 ml); in run nos. 2 10, filtrate after filtering off 4-nitro-
benzoic acid (36.3 ml) containing cobalt(II) and bromine com-
pounds.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 10 2001