Nitration of chlorobenzene with nitric acid in a continuous installation

Article abstract of DOI:10.1023/A:1014840627266

The procedures of production of mononitrochlorobenzene by nitration with 75-97% nitric acid with the yield of the target product of 97.5% were developed. A procedure of precipitation of crystalline p-nitrochlorobenzene from the reaction mixture without ad

Full text of DOI:10.1023/A:1014840627266

Russian Journal of Applied Chemistry, Vol. 74, No. 11, 2001, pp. 1872 1876. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 11,
2001, pp. 1815 1819.
Original Russian Text Copyright
2001 by Veretennikov, Lebedev, Tselinskii.
PROCESSES AND EQUIPMENT
OF CHEMICAL INDUSTRY
Nitration of Chlorobenzene with Nitric Acid
in a Continuous Installation
E. A. Veretennikov, B. A. Lebedev, and I. V. Tselinskii
St. Petersburg State Technological Institute, St. Petersburg, Russia
Received June 28, 2000
Abstract The procedures of production of mononitrochlorobenzene by nitration with 75 97% nitric acid
with the yield of the target product of 97.5% were developed. A procedure of precipitation of crystalline
p-nitrochlorobenzene from the reaction mixture without additional purification was proposed.
Nitration of chlorobenzene with sulfuric acid nitric
acid mixtures is the main procedure of mononitro-
chlorobenzene (MNCB) production [1]. The drawback
of this procedure is large amount of dilute spent sul-
furic acid as waste. The present-day procedures of
recovery of spent sulfuric acid do not eliminate its
environmental impact. The growing importance of
environmentally safe processes requires a search
for new nitration procedures without using sulfuric
acid.
by-product, dinitrochlorobenzene (DNCB), during
nitration.
Based on these data, we examined the possibility
of using nitric acid alone for production of MNCB.
Nitration of chlorobenzene was carried out in a
continuous installation (Fig. 1) including (1) main and
(2) surge reactors and (3) dilution vessel, equipped
with reflux condensers, blade stirrers, coil pipes, and
jackets. The volume of the apparatus made from
1Cr18Ni10Ti steel was 60 ml. The components were
dosed by piston pumps. Before start-up, the installa-
tion was filled with nitric acid with a composition
close to that of spent acid. The steady state of the
system was reached after passing a 5 6-fold volume
of the reaction mixture through the apparatus. The
temperature was maintaned with an accuracy of
0.5 C using thermostats. After nitration completion,
the reaction mixture was a solution of MNCB in spent
acid. To recover the nitro product, the reaction mixture
One of such procedures can be nitration of chloro-
benzene with nitric acid alone, which can be re-
covered on the industrial scale by environmentally
safer procedures, compared to sulfuric acid [2]. As
seen from published data, the major attention was
focused on the use of 67 68% nitric acid for nitration.
For example, it was proposed to carry out nitration of
chlorobenzene with a 20 30-fold molar excess of
nitric aicd in a tubular reactor or cascade of reactors at
90 C [3] or by adding chlorobenzene to an excess of
boiling nitric acid with simultaneous removal of the
reaction water [4]. Apparently, long reaction time,
large amounts of acids to be recovered, and difficul-
ties in temperature control of the process hinder in-
dustrial implementation of these procedures.
CB
Kinetic studies of mononitration of chlorobenzene
with aqueous nitric acid showed [5, 6] that, contrary
to nitration in sulfuric acid medium, the reaction pro-
ceeds in a homogeneous medium with the rates of
nitration close to or exceeding the rates of nitration of
chlorobenzene with sulfuric nitric acid mixtures; the
significant (three orders of magnitude) difference in
the rate constants of mono- and dinitration suggests
that the use of nitric acid alone as a nitrating agent
allows reduction or elimination of formation of the
p-NCB
To
separation
Fig. 1. Continious installation for nitration of chloroben-
zene with nitric acid: (1) main reactor, (2) surge reactor,
(3) dilution vessel, (4) vacuum funnel, and (5) reflux con-
densers.
1070-4272/01/7411-1872$25.00 2001 MAIK Nauka/Interperiodica

NITRATION OF CHLOROBENZENE WITH NITRIC ACID
Table 1. Nitration of chlorobenzene (CB) with 97% HNO3
1873
Yield of MNCB
Unreacted CB Yield of DNCB
HNO3 : CB
molar ratio
Run no.
T,
C
, min
%
1
2
3
1.5
1.5
1.5
75
85
75/85*
120
120
120
84.3
90.2
89
15.0
7.5
8.0
0.7
0.8
4
5
6
7
2
2
2
2
65
75
75
180
60
120
120
87.0
87.0
90.0
90.0
10.0
10.0
7.0
2.5
2.0
3.0
4.0
75/65*
6.0
8
9
10
11
12
2.5
2.5
2.5
2.5
2.5
65
65
75
75
75
45
60
45
60
120
97.5
93.0
94.0
94.0
91.3
2.5
1.5
1.0
1.5
1.0
2.0
6.0
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
55
55
65
65
65
65
65
65
65
65
75
75
75
75
75
75
75
75
7.5
15
5
98.0
98.2
93.5
98.6
99.0
99.0
95.3
93.8
93.6
92.4
94.9
97.9
98.7
96.0
94.5
97.5
90.0
89.7
1.7
0.2
2.1
0.7
0.3
0.1
7.5
10
15
30
45
60
75
5
7.5
10
15
30
45
60
75
0.1
0.2
0.2
3.0
1.5
0.3
0.6
0.6
0.7
0.8
* Temperature in the surge reactor.
was diluted in apparatus 3 at 20 C with a calculated
amount of water to the nitric acid concentration of
50.0%. The resulting nitro product, suspension of
p-NCB crystals in the liquid mixture of isomers, was
separated, washed with hot water, and dried. Dilute
spent acid was extracted with chlorobenzene. The
composition of the organic product was determined by
gas liquid chromatography. The concentration of
nitric acid was determined by alkalimetric titration.
the factors providing mass exchange in the reaction
system, dispersity of phases, and, hence, the required
residence time of components in the reaction zone [7].
Studying the effect of the strirring rate on nitration of
chlorobenzene with nitric acid alone showed that in
this reaction system variation in the stirring rate from
200 to 3000 rpm does not affect the reaction rate in
the entire range of nitric acid concentrations studied.
This fact suggests that the nitration occurs in the bulk
of the acid phase and the rate-determining stage of the
process is the reaction of chlorobenzene with nitric
acid. Therefore, in the subsequent experiments the
mixture was stirred at a rate of 400 rpm. The experi-
mental results are listed in Table 1.
After reaching the steady state, the reaction mixture
in the main reactor is heterogeneous and in the surge
reactor, homogeneous. It is well known that in hetero-
geneous nitration of chlorobenzene with sulfuric acid
nitric acid mixtures the diffusion of the components
into the reaction area affects substantially the nitration
process, and stirring of the reaction mixture is one of
As seen from Table 1, the use of a 1.5 2-fold
molar excess of nitric acid does not ensure complete
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 11 2001

1874
VERETENNIKOV et al.
Table 2. Nitration of chlorobenzene with 90 68% HNO3
Yield of MNCB
Unchanged CB
HNO3 : CB
molar ratio
Run no.
HNO3, %
T,
C
, min
%
31
32
90
90
3
3
75
75
45
60
98.2
98.2
33
34
35
85
85
85
3
3
3
65
75
75
45
45
60
74.0
86.2
94.1
25.4
13.0
5.1
36
37
38
80
80
80
5
5
5
75
75
85
120
180
120
94.2
97.0
95.4
4.9
1.0
3.0
39
40
80
80
4
4
75
85
180
180
91.0
95.0
8.0
3.5
41
42
43
75
75
75
4
4
5
85
95
75
180
180
120
93.2
97.5
89.8
5.0
1.5
10.0
44
45
46
68
68
68
5
7
8
95
95
95
180
180
200
88.0
90.0
92
10.0
7.0
6
conversion of chlorobenzene to MNCB, and an at-
tempt to increase the yield of the target product by
increasing reaction temperature or time is accom-
panied by formation of 2 4% DNCB (run nos. 1 7).
An increase in the amount of nitric acid to 2.5
3.0-fold molar excess results in practically complete
conversion of chlorobenzene; in this case, the result-
ing nitration product contains no DNCB (run nos. 8,
13, 14, 16 18, and 24 26). It should be noted that at
55 75 C the reaction was complete in 7.5 10 min.
Thus, it was established that in a wide concentra-
tion range nitric acid can be used for producing
MNCB in a nearly quantitative yield; the resulting
product contains no DNCB impurity.
Based on this study, we developed two procedures
for nitration of chlorobenzene with both concentrated
and dilute nitric acid. With 90 97% nitric acid, the
total amount of the nitrating agent required for at-
tainment of the maximum conversion is lower, but the
spent acid cannot be used for preparing nitrating mix-
ture. On the contrary, with 75 85% nitric acid a part
of spent acid can be used in production of MNCB.
To elucidate the effect of the acid concentration
on the yield of MNCB, we studied nitration of chloro-
benzene with 90 68% nitric acid. The results are
listed in Table 2.
We found that for nitration with 95% HNO the
3
optimum conditions are as follows: molar ratio
The experiments showed that a decrease in the acid
concentration below 85% is accompanied by notice-
able increase in its molar excess, reaction temperature,
and reaction time required to reach the maximum
yield of MNCB. However, despite higher temperature
and longer process time, DNCB was formed in none
of the runs. For example, in nitration of chloroben-
zene with 75% nitric acid at 95 C, fourfold molar
excess of nitric acid, and the reaction time of 180 min,
the yield of MNCB was 97.5% (run no. 39). A de-
crease in the nitric acid concentration to the composi-
HNO : chlorobenzene 2.5, reaction temperature 65 C,
and residence time in the main and surge reactors
45 min. The yield of MNCB was 97.5%.
3
The nitration process with partial acid circulation
was tested with 75% HNO as an example. The
3
optimum conditions are as follows: molar ratio
HNO : chlorobenzene 4, reaction temperature 95 C,
3
and residence time in the main and surge reactors
180 min. The acid mixture was prepared in the main
reactor by dosing of 98% HNO and spent 50%
3
HNO . The yield of MNCB was 97.5%.
3
tion of aqueous azeotrope (68% HNO ) results in
3
significant increase in the excess of nitric acid (more
than eightfold by moles) and inhibition of the nitration
process.
The MNCB formed by nitration has the following
isomeric composition (%): p-NCB 68.0 70.0, o-NCB
29.5 31.9, and m-NCB 0.1 0.5. In nitration of chloro-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 11 2001

NITRATION OF CHLOROBENZENE WITH NITRIC ACID
1875
Table 3. Isolation of MNCB from the reaction mixture at various degrees of its dilution
Product yield based on the total amount of MNCB,* %
Concentra- Temperature
Run
tion of spent of dilution,
no.
liquid phase (mixture residue extracted from spent
acid, %
C
crystalline phase ( p-NCB)
of o- and p-NCB)
acid
1
2
3
47
47
47
5
25
50
61.3
54.4
50.6
37.7
45.3
40.4d
1.0a
0.4b
9.0c
4
5
6
56
56
56
5
25
50
60.1
52.9
27.1
38.9
45.9
60.9
1.0
1.2
12.0
7
8
9
66
66
66
5
25
50
48.4
27.9
50.5
58.5
1.1
13.6
Crystalline phase is not precipitated
a
b
c
* Isomeric composition, %: p-NCB 46.4; o-NCB 14.6, m-NCB 39.0; p-NCB 16.5, o-NCB 41.7, m-NCB 41.8; p-NCB 18.9,
d
o-NCB 35.5, m-NCB 45.6;
p-NCB 44.3, o-NCB 55.6, m-NCB 0.1.
benzene with sulfuric acid nitric acid mixtures the
amount of m-NCB reaches 2.0 2.5% [1].
the spent acid noticeably increases, and the amount of
the para isomer precipitated from the reaction mixture
decreases (Table 3).
We found that during dilution a significant part of
p-NCB (up to 60% of the total amount in the mixture
of isomers) precipitates from the reaction mixture in
the crystalline form and can be separated by filtration.
A high degree of purity of p-NCB isolated by this
procedure (98.5 99.0%) allows this product to be used
without additional purification, which undoubtedly
facilitates the labor-consuming stage of isomer separa-
tion. The residual liquid mixture of isomers, contain-
ing on the average 20% p-NCB and 80% o-NCB, is
separated from the spent acid and washed with water.
To substantiate the choice of the conditions for
isolation of the nitro product, we studied the solubility
of MNCB isomers in nitric acid of various concentra-
tion. As seen from Figs. 2a 2c, the solubilities of the
isomers in 47 63% nitric acid in the range 0 80 C
somewhat increase with increasing temperature and
are comparable, but with increasing acid concentration
to 74% the solubility of p- and especially m-NCB ab-
ruptly increases. Contrary to para and meta isomers,
the solubility of o-NCB in 74% nitric acid decreases
Taking into account high solubility of MNCB in nitric with increasing temperature.
acid, we studied the dependence of the yield of the
The study of the interrelated effect of isomers on
their solubility in nitric acid showed that in 47%
nitro product on the temperature and degree of dilu-
tion of the reaction mixture with water.
HNO the minimum solubility of all three isomers of
3
We found that with increasing concentration of MNCB is observed at 20 C; in this case, the concen-
spent acid and temperature the solubility of MNCB in tration of both ortho and meta isomers in the solution
so, g/100 g HNO3
sp, g/100 g HNO3
(c)
(b)
(a)
sm, g/100 g HNO3
T, C
Fig. 2. Solubility of (a) p-NCB s , (b) o-NCB s , and (c) m-NCB s in nitric acid as a function of temperature T. Concentration
T, C
T, C
p
o
m
of HNO (wt %): (1) 47, (2) 63, and (3) 74.
3
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 11 2001

1876
VERETENNIKOV et al.
CONCLUSIONS
s, g/100 g HNO3
(1) Two methods were developed for production
of mononitrochlorobenzene by nitration of chloro-
benzene with 75 79% nitric acid, ensuring practically
quantitative yield of the target product and the ab-
sence of dinitrochlorobenzene in the reaction products.
(2) Based on the study of the solubility of mono-
nitrobenzene isomers in nitric acid, a procedure for
isolation of p-mononitrobenzene from the reaction
mixture in the crystalline form was proposed, which
simplifies isomer separation.
T, C
Fig. 3. Solubility s of MNCB isomers in 47% nitric acid
as a function of temperature T. Isomers: (1) para, (2) ortho,
and (3) meta.
is approximately two times greater than that of
p-MNCB (Fig. 3). The mixture of isomers precipitated
from nitric acid solution contains o- (40.5), m- (42.0),
and p-NCB (17.5%), and its composition is close
to that of the product isolated from the spent acid
(Table 3, run no. 2). These data provide an explana-
tion for the effect of temperature on the dilution proc-
ess: an increase in the solubility of nitro compounds
in spent acid with decreasing temperature (Table 3,
run no. 1) and increase in the content of ortho and
meta isomers of MNCB in spent acid with increasing
temperature (Table 3, run no. 3).
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1996, pp. 214 223.
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1569.
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in nitric acid showed that, to increase the recovery of
p-NCB from the mixture of isomers and to prevent
the loss of the nitro product with the spent acid, the
reaction mixture should be diluted at 18 22 C to a
nitric acid concentration below 60%.
5. Veretennikov, E.A., Lebedev, B.A., and Tselinskii, I.V.,
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