Note: Descriptions are shown in the official language in which they were submitted.
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PCT-9893
PROCESS FOR THE PRODUCTION OF DINITROTOLUENE :
OR MONONITROBENZENE `-`~
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This invention relates generally to aromatic ~-s
nitration reactions and, more specifically, to a process
for nitrating toluene to dinitrotoluene or benzene to ,,"'.'`,'~"~!,~,`,'~
mononitrobenzene. `
Nitration reactions of aromatic hydrocarbons
are generally conducted in mi~ed acid systems, such as ``` `~
10 mixed nitric and sulfuric acids. However, these mixed `~`
acid systems usually involve reconcentration of the spent ~ ~ ^
sulfuric acid after the nitration reaction. This `~
reconcentration step is time consuming, energy intensive `~
and requires the use of expensive materials of ~
15 construction. In addition, the use of sulfuric acid~`` ``
tends to result in significant nitrocreosol and cyanide
by-product formation which re~uires e~pensive waste-water `
treatment to remove.
In view of these disadvantages associated with
mixed nitric/sulfuric acid systems, there have been
recent attempts to perform gas phase or liquid phase
nitrations in concentrated nitric acid in the absence of
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sulfuric acid. By way of illustration, U.S. Patent No.
4,064,147 discloses the preparation of aromatic mononitro
compounds (such as mononitrobenzene) by a liquid phase
reaction with nitric acid havin~ an acid concentration of
between 70 percent and 100 percent by weight using a
reaction temperature of between 0C and 80C. When
employing a relatively reactive compound such as benzene ~ ~-
or toluene as a starting material, this patent teaches -
that a nitric acid concentration of between 70 and 90 - -
percent by weight is preferred. The disclosure of this
patent requires a ratio of nitric acid plus water to
organic components of not below 3 when using 70 percent
nitric acid, and not below 8 when using 100 percent
nitric acid. However, it has now been found that such a
high acid ratio using 100 percent nitric acid tends to
favor dinitro-compound production, not desired by the
patentee in the '147 patent.
Since mononitrobenzene is useful in producing
MDI and since dinitrotoluene is useful as an intermediate
in producing TDI, new processes for the selective
manufacture o these intermediates would be highly
desirable to the polyisocyanate manufacturing community. `~
The present invention relates to a process for -
nitrating benzene or toluene by a liquid phase nitration
25 reaction of anhydrous nitric acid with benzene or toluene -~
in a reactor at a reaction temperature not exceeding
80C in the absence of sulfuric acid to produce
mononitrobenzene or dinitrotoluene in a product mixture,
followed by vacuum distillation of the product mixture to
30 remove unreacted nitric acid. ~;
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This and other aspects of the present ~ ;
invention will become apparent upon reading the following
detailed description of the invention.
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In accordance with the process of the present ~a
5 invention, the nitration reaction is conducted using ~-~
anhydrous nitric acid in the absence of sulfuric acid. -
As used herein, the term "anhydrous nitric acid~ is
intended to designate nitric acid having an acid `~
concentration of between 95 and 100 weight percent, ` -`
10 preferably at least 98 weight percent, the remainder ~`
being water. It is desirable to minimize the amount of
water in the reaction mixture since water (a) causes the
nitration reaction to stop at the mononitration stage in
toluene reaction and (b) prevents the nitration of
benzene to mononitrobenzene.
' The process of the present invention utilizes
a one-step reaction in a single phase liquid medium and
does not involve the formation of the two phase emulsions
observed in conventional, mi~ed sulfuric/nitric acid ~`~
20 nitration processes. Another surprising aspect of this ~
invention is that the reaction can be conducted under ;
moderate reaction conditions to provide an excellent
yield of the desired mononitrobenzene or dinitrotoluene
product. Thus, the reaction is suitably conducted at a :- -
reaction temperature not e~ceeding 80C, preferably
between 0C and 60C, more preferably between 10C
and 60C, most preferably between 20C and 30C.
The reaction is suitably conducted at atmospheric -
pressure, although superatmospheric pressure can be
employed if desired. The reaction time is typically less
than one-half hour, preferably less than lS minutes, and
more preferably less than 5 minutes.
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For the reaction of toluene to dinitrotoluene, ~ ;
the molar ratio of nitric acid plus water to toluene
employed is generally between 10:1 and 15:1, preerably -
between 11:1 and 12:1. :`~
For the reaction of benzene to mononitro~
benzene, the molar ratio of nitric acid plus water to ~ -
benzene employed is generally between 2:1 and about 4:1,
preferably between 2.5:1 and 3.
Operating within the above-recited broad
ranges of molar ratios (and particularly within the
preferred ranges) maximizes the production of the desired ``
product and minimizes by-product formation. ~
After reaction and product formation, it is ~-`
desired that excess ~unreacted) nitric acid be removed
from the reactor, preferably by vacuum distillation, thus
providing a low temperature, low pressure distillation.
Suitable distillation temperatures range from 30C to
60C. Suitable distillation pressures range from 50 mm
of Hg to 300 mm of Hg. `~
Following removal of the excess anhydrous
nitric acid, DNT separation rom the distillation still `~
bottoms can be effected by phase separation, brought
about by the addition of a small quantity of water or ~: ~
dilute nitric acid. Washing with water and a basic ` .
solution produces a purified DNT product. These wash
waters are free of the nitrocresol impurities observed in ,~
the wastewater produced in a conventional, mixed
sulfuric/nitric acid DNT process. The aqueous nitric
acid from the phase separation step can be purified by
toluene extraction, the toluene phase being recycled to
the reaction step and the 60-70~ aqueous nitric acid
phase reconcentrated, sold or used in other product -~.-
manufacture. Analogous phase separation procedures can
be employed for nitrobenzene separation and recovery.
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The following examples are intended to
illustrate, but in no way limit the scope of, the present
invention. i;~,
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EXAMPLE 1
Synthesis ~f Dinit~Q~olu~Q
A four milliliter glass vial, equipped with a
magnetic stir bar and a silicone septum, was immersed in
a water bath. The reaction vial was flushed with
nitrogen at a rate of 20 cc/min, purging to a 100 ml
glass receiving flask immersed in an ice water bath. To
the reaction vial was fed 50 ml of 98 percent HNO3, -
75.0 g, 1.13 mole of HNO3 and 10 ml, 8.67 g, 0.094 mole
of toluene. Feed rates were 0.60 ml HNO3/min and 0.12
ml toluene~min, controlled by Sage Instrument Syringe
pumps, Models 351 and 355. Reactor content was adjusted
to 2 ml, by height adjustment of the reactor exit line in
the reaction vial, for a mean reaction residence time of .
2.8 minutes. The reactor water bath was maintained at 15
5C by the periodic addition of ice during reactant .
addition. Upon completion of the reactant addition, the
reactor contents were stirred for 3 minutes, then purged ~-
to the receiYer. A total of 83.31 9 of pale yellow -
product solution was obtained. Distillation of this
solution ~53C, 75-160 mm Hg) gave 38.75 g of pale ~ -~
yellow acid which analyzed, by titration with ` ~ `~
standardized NaOH, as 100 percent HNO3. The pot `
contained 44.21 g of pale yellow solution; 0.42 9 of
HNO3 was lost to the walls of the glassware, leaving an
estimated 0.43 g of product lost to NO2 vapors during
the distillation. The pot solution was diluted with `~
21.72 g of water and extracted with 33.30 g of toluene. `
Separation of the layers furnished 48.74 g of weak, `-~
aqueous acid and 48.11 g of toluene/DNT solution. The
organic layer was washed once with 20 ml of water, then
dried over MgSO4 and filtered. DNT recovery was
calculated at 86 percent, with a normalized GC analysis ~
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of 0.02 weight percent 4-nitrotoluene, 17.36 percent
2,6-DNT, 0.48 percent 2,5-DNT, 78.97 percent 2,4-DNT,
1.65 percent 2,3-DNT, 1.92 percent 3,4-DNT and 0.09
percent TNT. HNO3 accountability, as recovered weak
S acid and DNT equivalent, was 99 percent.
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XAMPLE 2 ;
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Additional ~yntheses of Dinitrotoluene ;
In the manner described in EXAMPLE 1, 100 ml
o~ 98 percent HNO3, 150.0 g, 2.38 mole HNO3 and 21
10ml, 18.2 9, 0.20 mole of toluene were fed at 0.80 ml/min
and 0.17 ml/min, respectively, to the reaction vial. A
total of 166.26 g of pale yellow product solution was
obtained. The product was heated for two hours at 55
to 60C, then cooled and diluted with 46.5 g of ice
15 water. The resulting suspension was extracted once with ~ -~
41.5 9 of toluene and then a second time with 46.3 g of
toluene. The combined toluene extract was extracted with ;~
3 x 15 ml of 5 percent sodium hydr~ide solution. The ~-
combined, yellow caustic extract was cooled, acidified ~ ;
with dilute sulfuric acid, and extracted with 3 x 10 ml
of methylene chloride. After evaporation of the bulk of
the methylene chloride, the methylene chloride extract,
containing the acidic organic species from the original
DNT product, was characterized by gas chromatography/mass
spectrometry analysis. No mononitro- or dinitro-cresol
species were detected (minimum detectability calculated `
at 2 ppm, based on original weight of DNT produced).
Additional experiments were performed to
define the reactant ratio suitable for selective DNT -
synthesis. These products are characterized in TABLE I
below for various molar rat~os of HNO3 to toluene.
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TABLE I
Toluene Nitration ~
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HNO3/Toluene Product i~ Wt. %
Mole Wt.
5 Sample Ratio Ratio o-NT m-NT -NT D~
1 3.4 2.3 53.17 4.0439.29 3.49 1~
2 5.6 3.8 28.~0 2.7029.57 38.93 ~;
3 7.8 5.3 8.21 1.7214.66 75.40
4 11.6 7.9 0.94 ---- 0.22 98.84
10 Reaction at 54 to 57C `
NT - mononitrotoluene, ortho, meta and para isomers
EXAMPLE 3 ~
Synthesis of Nitrobenzene , i
In the manner described in EXAMPLE 1, 7.0 ml of
98 percent HNO3, 10.5 9, 0.163 mole of HNO3 and 5.0 j~
ml, 4.39 9, 0.056 mole of benzene were fed at 0.22 ml/min l`
and 0.135 ml/min, respectively, to the reaction vial. i~
The 14.65 g of pale yellow product solution was diluted
with 42.49 g of ice water and e~tracted with 2 x 15 ml of `
methylene chloride. Dilute acid recovery was 51.39 9,
for an organic recovery of 5.75 9, by difference. Gas ` -~
chromatographic analysis of the organic product showed i
only nitrobenzene, exclusive of the methylene chloride
solvent peak, for a recovery of 0.047 mole (83 percent) -~
of nitrobenzene. HNO3 accountability, as recovered
weak acid and nitrobenzene equivalent, was 96 percent.
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