DE1266765B - Process for the preparation of aromatic amines - Google Patents

Description

Process for Making Aromatic Amines The invention relates to a process for the preparation of aromatic amines by catalytic hydrogenation of aromatic nitro compounds in the liquid phase.

It is known that aromatic amines as intermediates for Manufacture of dyes, media and rubber additives are important It is also known that 2,4-tolylened or 2,6-tolylenediamine can be used as the starting material use for the production of a polymeric polyurethane via tolylene diisocyanate can. These aromatic amines were previously made by reacting one acid and one Metal produced in the presence of aromatic nitro compounds. In more recent times were they obtained by catalytic reduction in the gas or liquid phase, with various catalysts, e.g. B. nickel, palladium and platinum are used became.

Aluminum oxide, Titanium oxide, activated carbon, diatomaceous earth, pumice stone, acid clay, active earth, kaolin and Known graphite. Although these catalysts have good catalytic effectiveness, but usually no satisfactory mechanical properties. For example is the most widely used nickel-diatomaceous earth catalyst cheap, shows good catalytic Effectiveness and does not have major drawbacks when working in batches is used; however, this catalyst is not suitable for continuous Way of working. For continuous operation, the substance to be reduced, the catalyst and a solvent suitably into a reaction system be introduced.

Here, one made of diatomaceous earth with a Mohs hardness of 4.5 to 6.5 and harder nickel composite catalyst the reaction vessels can be damaged, and constant feeding cannot be carried out.

A process for the preparation of aromatic amines has now been carried out catalytic hydrogenation of aromatic nitro compounds found in the liquid phase. The process is characterized in that the hydrogenation in the presence of 5 to 20 percent by weight nickel on talc as a catalyst at 70 to 120 "C and 10 up to 100 at.

Talc is a sliding substance, which has a low hardness and high smoothness having. It is sometimes used as a lubricant and has a Mohs hardness of 1 and occurs as metamorphic rock consisting of about 650/0 silica and about 350 / o magnesium oxide. Talk is widespread and cheap Disposal. The one used in the present invention Catalyst has good mechanical properties and a superior constant catalytic efficiency, which the activity of Catalysts with diatomaceous earth as a carrier even surpasses.

In general, nickel is used in a weight ratio of 1: 1 the carrier material, d. H. used at a concentration of 500 / ,,.

However, it was found that the catalyst activity per unit weight Nickel in the nickel catalyst used according to the invention with a reduction in this Nickel concentration increases and activity, especially at one concentration below 20 0 / ,, rises rapidly, so that the new catalyst has a better effectiveness shows than the commonly used Raney nickel.

It has now been found that the activity per unit weight Nickel almost unchanged at a nickel concentration of 30 to 50 0in; at a concentration of below 200! o, the catalytic activity is decreasing Nickel concentration unexpectedly increased. So showed a catalyst with a Nickel concentration from 2001, about three times the activity per unit weight of nickel, compared with a catalyst with a nickel concentration from 30 to 50 ° / 0. Also showed a catalyst with a nickel concentration of 10 01o actually two to three times the activity compared to Raney nickel on the same condition. The same catalyst showed about 1.5 times the activity compared to a catalyst prepared in the same way with diatomaceous earth. In the case of great effectiveness, mild reaction conditions or small amounts of catalyst can be used can be applied.

However, if the nickel concentration is further decreased, so will the required amount of carrier so large that the benefit of the improved activity is canceled again by the required larger amount of carrier.

In view of the above-mentioned factors, the present invention Catalyst used 5 to 200 / o nickel applied. To achieve full activity it is necessary to put the catalyst in a stream of hydrogen 1 bis before use 3 hours at 350 to 500 "C to activate.

When performing a whirled-up reduction in liquid phase are to be reduced using a suitable pump A material, a catalyst and a solvent are continuously fed into a reaction system introduced. The wall of the pump or the reaction vessel can be used here a Raney nickel or nickel diatomaceous earth catalyst are damaged and due to the hardness of the nickel or the diatomaceous earth, a reduction in the service life enter from the pump and reaction vessel. Furthermore, such catalysts can Load the pump heavily, causing fluctuations in the feed rate and controlling the response becomes difficult. On the other hand, talc is used as a carrier is used, there is no damage to the walls, and a reaction liquid is fed smoothly and with little fluctuation in quantity. When using Talc is the nickel hardness due to the low concentration of nickel (5 to 200in).

Another advantage is that talc is too fine powder with a particle diameter of less than 0.074mm can be crushed and a has a lower specific weight than a metal such as Raney nickel. Therefore it is easy to achieve a uniform suspension with the new catalyst, that does not collapse or coagulate.

Even if the reaction is interrupted, the new one solidifies Catalyst not at the bottom, but can be removed by stirring or introducing gas easily redisperse in the reaction system.

For the production of the catalyst used according to the invention The main substances required are talc, a nickel source and alkali for precipitation. Nickel nitrate, nickel sulfate or nickel chloride can be used as the source of nickel will.

Up to now, nickel nitrate has been used for the production of catalysts, but in recent times nickel sulfate is available in high purity, and the Catalyst made from nickel sulfate differs in activity not from a catalyst made from nickel nitrate. As an alkali for felling of nickel, calcined soda is mainly used. Implementation for Production of the catalyst according to the invention proceeds almost quantitatively.

The catalysts used in the present invention were prepared as follows been: In an aqueous solution of nickel sulfate is talc until it is reached entered desired nickel concentration. The amount of water is measured so that an easily stirrable slurry is obtained. This is then heated to 50 to 60 ° C and an aqueous solution of soda ash in an amount of 1 to 2 moles per mole Nickel sulfate added dropwise. After that, the slurry will remain for some time heated to 60 to 90 "C. After filtering, washing and drying the suspension the ready-to-use catalyst is obtained. There is no reduction in the catalytic Effectiveness when the catalyst is produced in the opposite direction, i.e. by Adding an aqueous solution of a nickel salt to a talc suspension in a Alkali solution takes place. Talc can be used without cleaning; one achieves however with purified talc carrier, better and more consistent results. The cleaning can be done in the usual way with nitric acid or hydrochloric acid or by burning the Talks are done at a few 1000 C.

You can also first precipitate the nickel from the nickel salt and Then simply mix the precipitate mechanically with talc; thereby receives a catalyst of the same activity.

Below is the inventive method using the new catalyst explained.

The reduction of nitro compounds with the catalyst can be both can be carried out batchwise as well as continuously. With continuous Process must supply the starting materials and the catalyst at a constant rate Speed take place and the catalyst in the reaction system as evenly as possible to be dispersed.

With the new catalytic converter, this can be done easily, and through a stirring device, the catalyst is easily mixed and forms one satisfactorily dispersed state. In the case of the reduction of nitro compounds, use is generally made a reaction pressure between 10 and 150 at and a temperature between 50 and 150 "C. With regard to the activity and life of the catalyst as well For controlling the reaction and its mechanism, preference is given to a reaction temperature from 70 to 120 "C and a reaction pressure of 10 to 100 at. After completion of the Reaction under the above-mentioned conditions, the catalyst is filtered off, Removed water and solvent from the filtrate and then the obtained aromatic Amine separated by distillation or recrystallization.

The yield depends on the compound used, in almost all of them However, in some cases it exceeds 9001, and in some cases it is almost quantitative Exploit. The filtration of the new catalyst is very easy.

The amount of the catalyst supported on talc depends on the reaction conditions and the type of nitro compounds used. Among those commonly used Conditions of 50 at and 100 "C are those for the reduction of nitrobenzene and Nitrotoluene required amount of catalyst less than 0.5 percent by weight nickel, based on the amount of nitro compounds.

When a reaction is carried out continuously, part of the exhausted catalyst removed and the same amount of new Catalyst fed so that the catalyst consumption on average only about 0.1 0/0.

The following nitro compounds, for example, can be used according to the invention reduce: nitrobenzene, dinitrobenzene, p-nitrotoluene, o-nitrotoluene, 2,4-dinitrotoluene, 2,6-dinitrotoluene, fl-nitronaphthalene, 1,5-nitronaphthalene and nitrophenol resp. their mixtures. A gas chromatographic examination showed that there was only a small Amount of tarry by-products forms and that by the choice of reaction conditions only the nitro group is reduced and side reactions, for example the hydrogenation of the benzene nucleus, can be suppressed.

Suitable solvents in the process according to the invention are Alcohols such as methanol, ethanol and isopropanol, and ethers such as dioxane, tetrahydrofuran and alkylene glycol dialkyl ethers. Depending on the reaction conditions, they are also aromatic Compounds such as benzene, toluene, xylene, monochlorobenzene and dichlorobenzene are useful. The most common solvent used is methanol; however, it can also be Use chlorobenzenes as a solvent in the process according to the invention, with the hydrogen absorption occurs more rapidly than when using methanol.

Other mixed solvents such as alcohol-water or alcohol-halogenated Benzene can also be used with success.

The following examples explain the process according to the invention.

Example 1 49.2 parts of nitrobenzene, 150 parts of methanol and 3.5 parts Catalyst (7010 nickel on talc support) are placed in an autoclave. the Reaction takes place at a hydrogen pressure of 50 kg / cm2 and a temperature of 1000 C and finished after 16 minutes. After filtering off the catalyst the reaction product appears as an almost colorless, transparent liquid.

The liquid is distilled off and the amount of residue is less than 0.1 part. The yield is almost quantitative, as is the gas chromatographic Analysis shows no by-product formation.

If instead of a catalyst on talc, a catalyst on diatomaceous earth is used, there is 25 minutes for hydrogen absorption to cease required in the nitrobenzene reduction under the same conditions as above.

When using Raney nickel, the reaction time is longer under the same conditions as above for 38 minutes.

Example 2 In a methanol solution containing about 140% dinitrotoluene a catalyst is dispersed which contains 20 / o nickel, based on the amount of dinitrotoluene, contains. Then the solution is pumped into a reaction system in which a temperature of 100 "C and a hydrogen pressure of 10 kg / cm2 is maintained. By controlling of the residence time, a tolylenediamine solution is obtained which is less than 0.01 ° / o contains unreacted nitro groups. The yield is 96010.

If the catalyst is partially replaced with the used catalyst through new catalyst is reused, the catalyst consumption is average 0.1% calculated on the weight of the nickel.

The fluctuation of the supply amount per unit of time is in the above example small amount. However, when diatomaceous earth is used as the carrier, the fluctuation reaches 6 times the fluctuation when using talc. Hence the control difficult to react when a carrier made of diatomaceous earth is used will.

Example 3 54.8 parts of p-nitrotoluene and 3.9 parts of catalyst become implemented under the same conditions as in Example 1. The reaction is after Completed 25 minutes. Distillation under reduced pressure gives p-toluidine, the residue being 0.1 part. A gas chromatographic analysis shows none Formation of by-products. The yield is almost quantitative.

Example 4 Example 3 was repeated, with instead of p-nitrotoluene o-nitrotoluene was used. The reaction proceeds in the same way. It no by-product is obtained. The yield is almost quantitative.

Example 5 33.6 parts of dinitrobenzene, 7.2 parts of a catalyst and 150 parts of methanol are placed in an autoclave. The response will be at 1000 C and 50 kg / cm2. The reaction goes smoothly, and phenylenediamine is obtained in a yield of 96%.

Example 6 72.8 parts of 2,4-dinitrotoluene, 5.2 parts of catalyst (nickel concentration 70 / o) and 150 parts of methanol are placed in an autoclave. Then it becomes hydrogen introduced until a pressure of 50 kg / cm2 is established. Then the autoclave heated. When the internal temperature has reached 100 "C, the internal pressure has increased less than 30 kg / cm2. Hydrogen is then immediately introduced until the pressure is reached Shows 50 kg / cm2, and then the reaction is carried out at 100 "C and 50 kg / cm2.

The reaction is over after 50 minutes. The reaction product will distilled under reduced pressure, leaving 2,4-tolylenediamine, which is less than 0.01 Contains 0 / o unreacted nitro groups, is obtained in 990 /, iger purity. The yield is 96%. If the reaction is carried out under otherwise identical conditions, however, running using Raney nickel are 100 to 150 minutes required until implementation is complete.

Example 7 In a mixture of 80% 2,4-dinitrotoluene and 20%, 2,6-Dinitrotoluene (hereinafter the mixture will be referred to as DNT-80) becomes a Catalyst (nickel concentration 100 / o) added in an amount that the nickel content 0.50 /, of the DNT-80.

Then the reaction is carried out. The hydrogen absorption is finished after 60 minutes.

Example 8 The reaction described in Example 6 is carried out under the the same conditions, but with the exception that dichlorobenzene is carried out Instead of methanol is used as a solvent. The rate of hydrogen absorption achieves the 1, thing of that of Example 6. Also the formation of tarry Mass is less. The yield is 96 ° lo

Claims (1)

Claim: Process for the production of aromatic amines by catalytic hydrogenation of aromatic nitro compounds in the liquid phase, d a d u r c h gekennzeichne t that the hydrogenation is carried out in the presence of 5 to 20 percent by weight Performs nickel on talc as a catalyst at 70 to 120 "C and 10 to 100 at.