DD297397A5 - PROCESS FOR THE PRODUCTION OF DINITROTOLUOLS - Google Patents

Abstract

The present invention relates to a process for the preparation of dinitrotoluene by the reaction of mononitrotoluene and nitric acid in the liquid phase. The process is characterized in that the reaction is carried out in the presence of a metal sulfate and optionally in the presence of a dismutating agent selected from the perfluorinated (poly) cycloalkanes having from 5 to 12 carbon atoms and perfluorotoluene. {Dinitrotoluene preparation; Reactants; Mononitro Aoluol; Nitric acid; Metal sulfate; Verduennungsmittel}

Description

Field of application of the invention

The present invention relates to a process for the preparation of Di iitrotoluolen. More particularly, the invention relates to a process for the preparation of dinitrotoluenes by reacting at least one mononitrotoluene and nitric acid in the liquid phase in the presence of a metal sulfate.

The dinitrotoluenes, especially the 2,4-dinitrotoluene, optionally in admixture with the 2,6-dinitrotoluene, are intermediates in the production of toluene diisocyanate (TDI), which serves to prepare various polyurethanes. The 2,4-dinitrotoluene is therefore industrially produced on a very large scale. In view of this, it is easy to understand what meaning z. An increase in the degree of conversion and / or selectivity by one percentage point, or an improvement at the level of any of the steps performed in the process.

Characteristic of the known state of the art

The 2,4-dinitrotoluene is conventionally prepared by double nitration of the toluene in the liquid phase with the aid of a mixture of nitric acid and concentrated sulfuric acid. The concentration of sulfuric acid used for the second nitration (nitration of mononitrotoluene to dinitrotoluene) is typically of the order of 96%. Apart from the problems of corrosion and the enormous cost of recycling large volumes of sulfuric acid, the process has significant other disadvantages, namely the problematic manner of removing the catalyst, which is generally solved by water washes, and the need to remove the sulfuric acid concentrate prior to their recycling, the reaction itself producing water.

In the introduction to the description of the American patent no. No. 3,957,889, various attempts have been made, in particular with regard to the selective nitration of the toluene in the para position, in which document it is proposed to nitrate certain aromatic compounds which are optionally substituted by a halogen atom, a haloalkyl group, a nitro or methoxy group substituted in the presence of anhydrous calcium sulfate, a product sometimes referred to as soluble anhydrite.

In this prior art document is further proposed, a diluent such. As chloroform, methylene chloride, nitrotoluene, to use, and the use of a diluent, in which the reactants are very soluble »vird than preferred r. in order to achieve a good outcome of the proceedings in question.

However, if it is the nitration of a substrate with low reactivity, such. As orthonitrotoluene, the proposed method does not seem fully satisfactory, namely, since on the one hand, the selectivity with respect to the 2,4-isomer is insufficient and on the other hand, the activity (or yield) remains negligible.

Object of the invention

The invention provides a process for the production of dinitrotoluene which eliminates the disadvantages of the known technical solutions.

Explanation of the essence of the invention The object of the present invention is to provide an effective process for the preparation of dinitrotoluene,

which makes it possible, at least in part, to overcome the aforementioned disadvantages.

He has now found that other metal sulfates have a higher activity over that of the anhydrous calcium sulfates

aul 'oisen.

On the one hand, the subject of the present invention is a process for the preparation of dinitrotoluene (s) by reaction

at least one mononitrotoluene and nitric acid in the liquid phase, which is characterized in that the reaction in

Presence of a metal sulfate is selected, selected from the group consisting of the sulfates one or more

mono-, di- or trivalent metals, with the exception of the simple sulphate of calcium.

It has also been found that certain diluents, in which the reactants are little or not soluble, are suitable

increase the effectiveness of the nitration and optionally the selectivity for a particularly desired isomer.

It is therefore in a second aspect a process for the preparation of Dinitrotoluen subject of the invention,

by reacting at least one mononitrotoluene and nitric acid in the liquid phase, characterized in that the reaction is carried out in the presence of a metal sulphate and a diluent selected from the group consisting of the perfluorinated (poly) cycloalkanes having from 5 to 12 carbon atoms and the perfluorotoluene.

By dinitrotoluene (s) is preferably understood in the context of the present process, the 2,4-dinitrotoluene, the

2,6-dinitrotoluene and mixtures thereof.

By mononitrotoluene (s) is meant the para-nitrotoluene, ortho-nitrotoluene and mixtures thereof. Of course, when the starting material is a mixture of ortho and para-nitrotoluene, a mixture of 2,4- and 3,4-is obtained

2,6 isomers of dinitrotoluene. When the starting material is para-dinitrotoluene, the only product observed is 2,4-dinitrotoluene.

The process of the invention requires the presence of nitric acid. One generally chooses concentrated forms

the nitric acid, the concentration being above 90% and preferably between 95 and 100%.

One of the essential features of the present process is the use of a metal sulfate. Metal sulphates are understood as meaning the salts of one or more metals which are suitable for forming cations which are 1 to 3 positive Charges carry with the sulfuric acid, in which at least one hydrogen atom has been replaced by a metal atom, wherein

these are either simple or mixed salts, which are in the form of more or less low-water hydrates, depending on whether the conditioning temperature is higher or lower.

In the present process, partially or completely dehydrated forms of these sulfates are used. The to Use in the context of the present process suitable metal salts are generally hydrates, at most the Amount of water that corresponds to the stable at ambient temperature hydrate. Examples of such hydrates are in the Column Il given in the following table. It is preferable to resort to hydrates of such salts which contain at most the amount of water that is the poorest in water Hydrate or the anhydrous salt, if the latter is available, thermally stabii and the Retaining rehydration properties. Examples of such sulfates are given in column III of the following table. When Examples of such sulfates can be named:

I Il III sulfate usable anhydrous salts or hydrates Hydrates, the preferred be used wisely MgSO ₄ x H ₂ O XS 7 O <χ <0.5 CaSO ₄ , y H ₂ O y S 2 O <y <0.5 CuSO ₄ , ζH ₂ O ζ <5 OSz s 1 NiSO ₄ , t H ₂ O t <6 Ost S1 La ₂ (SO ₄ J ₃ , η H ₂ O n <9 Os η s2 Al ₂ (SO ₄ J ₃ , ρ H ₂ O ρ S 18 0sps3

It is advantageous to use non-acidic sulfates or sulfates which are free of hydrogen atoms, and preferably

used are metal sulfates which are suitable for forming cations with 2 or 3 positive charges.

The sulphates of lanthanum, copper, magnesium and calcium are particularly suitable for the application of

present method.

The metal sulfates may be in solid or dispersed forms such as. As spheres, pastilles or powders, whose

average dimensions are generally between 0.1 microns and 10mm.

The optimum amount of metal sulfate to be used is chosen so that the molar ratio (theoretically determined by the Nitration-releasable water / metal sulfate is within a range that results in the least hydrated hydrate. examples for

such intervals can be found in the upper column (ill) of the table.

Of course, the scope of the present invention will not be abandoned, if one from this optimal amount after

deviates below or above. In particular, the Applicant proposes to deviate upwards or downwards from this optimum value by not more than 20% and preferably not more than 10%.

As set forth above in the first aspect, the invention does not involve the use of the simple one Calcium sulphates alone. However, this does not exclude recourse to a mixed sulphate containing calcium and one or more other metals. As set forth in the second aspect, the present invention comprises two essential features, namely

the presence of a metal sulfate and a particular diluent. Under metal sulfate is understood in this

The salts defined above including the simple calcium sulphates. The second west "'-th feature is

in that the nitration reaction is carried out in a diluent selected from the group consisting of the perfluorinated (poly) cycloalkanes having 5 to 12 carbon atoms and the perfluorotoluene.

Of the perfluorinated (poly) cycloalkanes can be mentioned in particular those compounds, each of the Cyclohexane or methylcyclohexane are derived by replacement of all hydrogen atoms by fluorine atoms (namely the Perfluorocyclohexane and perfluoromethylcyclohexane) and perfluorodecalin. The perfluorodecalin is preferably used. For a good procedure, the Applicant proposes 0.5 to 5 ml Use diluent per g of sulfate used, with different ratios in practice from economic Reasons and / or reasons associated with the design of the reactor chosen for a good contact liquid-solid

be related.

The reaction is generally carried out in an apparatus which ensures a good contact-liquid-solid,

such as S. a stirred reactor or a reactor with a loop for the circulation of the liquid.

The reaction between the (n) mononitrotoluene (s) and the nitric acid is carried out in the liquid phase, the molar Ratio of nitric acid to monomitrotoluene (s) can vary within wide ranges. For a good implementation

the molar ratio should be between 0.1 and 10.

In general, a temperature of at least 20 ° C proves necessary to be ak. Eptable To obtain conversion rate, wherein above 100 ⁰ C side reactions can be generated, such Process become less interesting. At the end of the reaction time (or residence time), the dinothromotoluene (s) is recovered Help of any suitable means, eg. B. by distillation, with optional previous decantation or filtration of the Metal sulfate. The following examples illustrate the invention. embodiments example 1 Comparative Experiments (a) and (b) In a glass reactor with 30ml capacity, which is equipped with a magnetic stirring, one gives

- 9.1 mmol of orthonitrotoluene, optionally 2.5 ml of diluent.

- 2.5g of anhydrous CaSO ₄ obtained by heating CaSO ₄ · 2 H ₂ O to 25O ⁰ C for 3 hours

- 9.4mMol 100% nitric acid.

The mixture is kept at 25 ^° C. with stirring for a period of 17 hours. Then the resulting mixture is filtered and the filtrate is washed with water. The organic phase is analyzed by gas phase chromatography. The specific conditions and the results obtained are given in the following Table I, in which

PFD perfluoridecalin means TT denotes the degree of conversion of ortho-nitrotoluene RT denotes the yield of dinitrotoluenes in relation to ortho-nitrotoluene Rep. Isom. represents the distribution of the isomers

+ indicates the presence of calcium sulfate.

Table I

attempt Diluent TT (%) RT (%) Rep. Isom% 2,4DNT 2,6DNT a b CHCl ₃ CHCl ₃ + 5 17.5 80 80 38 70 62 30

PFD + 58 95 68 32

Examples 2 to 9 Comparative experiment (c) In a 50 cc ^three- necked flask equipped with a central stirrer and condenser, if nothing is added

4g sulphate, the type of sulphate, the preparation on the market and optionally the conditions of a previous treatment are given in the following Table II, the stated volume of perfluorodecalin (PFD;

Cio Fts), unless otherwise stated, is 1.37 g (10 μmol) of para-nitrotoluene and 0.43 cm ³ (10.4 mmol) of 100% nitric acid. The Mixture is kept at 6O ⁰ C with stirring for the period of 1 hour (unless otherwise stated). The resulting mixture is filtered. The filtrate is washed with water. The organic phase is then analyzed by gas phase chromatography. The special conditions as well as the

The results obtained are shown in Table II below, in which TT represents the degree of conversion of p-nitrotoluene and RT indicates the yield of 2,4-dinitrotoluene (DNT).

Table II

Attempt PFD cm ³ Sulfate nature and origin treatment used TT (%) RT (%) c · 8th none - - 27 76 2 5 MgSO ₄ -7H ₂ O (PrOlBbO) 200 ° C-3h MgSO ₄ 0.2H ₂ O 57 94 3 · · 5 CaSO ₂ -2H ₂ O (Prolabo) 250 ^e C-3h CaSO ₄ 51 91 4 5 CaSO ₄ -2H ₂ O (prolabo) 250 ° C-3h CaSO ₄ 48 -100 5 » 5 CaSO ₄ -2H ₂ O (Proiabo) 250 ° C-3h CaSO ₄ 61 -100 6 3.5 CuS0 ₄ -5H ₂ 0 (Prolabo) 300 ° C-4h CuSO ₄ 71 98 7 5 La ₂ (SO ₄ I ₃ -8 H ₂ O (Ventron) 300 ° C-4h La ₂ (SO ₄ ); 54 95 8 (a) 5 CaSO ₄ -2H ₂ O (prolabo) 250 "C-3h CaSO ₄ 56 95 9 (b) 5 CaSO ₄ -2H ₂ O (prolabo) 250 ° C-3h CaSO ₄ 51 96

NB: * Duration: 3.5 hours - (a) Diluent Is perfluorinated methylcyclohexane

** 2 g sulfate used - (b) diluent the perfluorinated compound FC72 (trade name)

Example 10 In an apparatus described in the above Example 1 and according to the local procedure one leads one Try out with a batch consisting of

922 mg (6 mmol) of o-nitrotoluene 549 mg (4 mmol) of p-nitrotoluene

4cm ³ PFD

4 g anhydrous CaSO ₄ 0.43 cm ³ (10.6 mmol) 100% NHO ₃ .

After 1 hour and 30 minutes reaction at 6O ⁰ C is obtained the following results: Total degree of conversion of nitrotoluenes: 68.8% Total yield of dinitrotoluenes (2,4 and 2,6)

based on the nitrotoluenes: 92.9%

Degree of conversion of o-nitrotoluene: 77% Degree of conversion of p-nitrotoluene: 56% isomer

- 2,4-dinitrotoluene: 79%

- 2,6-dinitrotoluene: 21%.

Claims (10)

1. A process for the preparation of dinitrotoluene (s) by reacting at least one mononitrotoluene with nitric acid in the liquid phase, characterized in that the reaction in the presence of a metal sulfate selected from the group consisting of the sulfates one or more mono-, di- or trivalent metals, with the exception of simple calcium sulfates. 2. The method according to claim 1, characterized in that the reaction in the presence of a diluent selected from the group consisting of the perfluorinated (poly) cycloalkanes having 5 to 12 carbon atoms and the perfluorotoluene is performed. 3. The method according to claim 1 or 2, characterized in that the metal sulfate is selected from the partially or fully dehydrated salts of sulfuric acid with metals which are suitable to form cations which carry 1 to 3 positive charges. 4. The method according to claim 3, characterized in that the metal sulfate is selected from the partially or completely dehydrated salts of sulfuric acid with metals that are suitable to form cations tu carrying 2 or 3 positive charges. 5. The method according to any one of claims 2 to 4, characterized in that the diluent is perfluorodecalin, 6. The method according to any one of the preceding claims, characterized in that the amount of sulfate is selected so that the molar ratio (of the theoretically releasable by the nitration water) / metal sulfate within the interval of ± 20%, starting from the least hydrated hydrate defined , 7. The method according to claim 6, characterized in that the amount of sulfate is selected so that the molar ratio (theoretically released by the nitration water) / Metailsulfat within the interval of ± 10% starting from the lowest-hydrate hydrate defined. 8. The method according to any one of the preceding claims, characterized in that the molar ratio of HNO ₃ / mononitrotoluene (e) is between 0.1 and 10. 9. The method according to any one of claims, characterized in that the reaction temperature between 2O ⁰ C and 100 ⁰ C. 10. The method according to any one of claims 2 to 9, characterized in that the sulfate is selected from the sulphates of calcium, copper, lanthanum or magnesium.