CA2008342A1

CA2008342A1 - Process for the production of dinitrotoluene or mononitrobenzene

Info

Publication number: CA2008342A1
Application number: CA002008342A
Authority: CA
Inventors: Robert W. Mason
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-06-22
Filing date: 1990-01-23
Publication date: 1991-07-23
Also published as: CN1054247A; AU3863089A; WO1989012620A1; CA1340073C; CN1026583C

Abstract

PROCESS FOR THE PRODUCTION OF DINITROTOLUENE
OR MONONITROBENZENE

Abstract of the Disclosure Aromatic nitration reactions and, more specifically, a process for nitrating toluene to dinitrotoluene or benzene to mononitrobenzene.
Since mononitrobenzene is useful in producing MDI and since dinitrotoluene is useful as an intermediate in producing TDI, new processes for the selective manufacture of these intermediates would be highly desirable to the polyisocyanate manufacturing community.

Description

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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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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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- 7 - ~ -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 ~
: ,~ ",,, 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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Claims

1. A process for nitrating toluene to produce dinitrotoluene by a liquid phase nitration reaction of anhydrous nitric acid with toluene in a reactor at a reaction temperature of between 0°C and 60°C
for a reaction time of less than 15 minutes, said reaction employing a molar ratio of nitric acid plus any water to toluene of between 10:1 and 15:1, said reaction being conducted in the absence of sulfuric acid, to produce said dinitrotoluene in a product mixture, followed by vacuum distillation of the product mixture to remove unreacted nitric acid from said product mixture, thereby providing said dinitrotoluene.

2. The process of claim 1 characterized in that said molar ratio is between 11:1 and 12:1.

3. The process of claim 1 characterized in that said anhydrous nitric acid has an acid content of between 95 percent and 100 percent by weight based upon the acid plus water therein.

4. The process of claim 1 characterized in that said vacuum distillation is effected at a temperature of between about 30°C and about 60°C.

5. The process of claim 1 characterized in that said vacuum distillation is effected at a pressure of between about 50 mm of Hg and about 300 mm of Hg.

6. The process of claim 1 which additionally comprises, after said vacuum distillation, phase separation of dinitrotoluene from said product mixture.

7. The process of claim 9 characterized in that said phase separation is caused by the addition of water or dilute nitric acid to said product mixture.

8. The process of claim 1 characterized in that said reaction temperature is between 10°C and 60°C.

9. The process of claim 1 characterized in that said reaction temperature is between 20°C and 30°C.

10. The process of claim 1 characterized in that said nitration reaction is effected in less than 5 minutes.

11. The process of claim 1 characterized in that said anhydrous nitric acid has an acid concentration of between 95 and 100 weight percent.

12. The process of claim 1 characterized in that said anhydrous nitric acid has an acid concentration of at least 98 weight percent.

13. A process for nitrating toluene to produce dinitrotoluene by a liquid phase nitration reaction characterized in that it is effected in less than 5 minutes by reacting anhydrous nitric acid with toluene in the absence of sulfuric acid in a reactor at a reaction temperature of between 10°C and 60°C, said anhydrous nitric acid having an acid content of between 95 and 100 percent by weight based upon the weight of acid plus water therein, the molar ratio of nitic acid plus water to toluene being between 11:1 and 12:1.

14. The product mixture produced by the process of claim 1 which is free of mononitro- and dinitrocresol species.