DE1233878B - Process for the preparation of aromatic amines - Google Patents

Description

Process for the preparation of aromatic amines The hydrogenation of aromatic Nitro compounds to the corresponding amines under the influence of metal catalysts is known per se, but prepares certain in its practical implementation Difficulties because the known methods are cumbersome and disproportionate require a high expenditure of catalysts as well as energy and time. This is based inter alia that the rate of conversion of nitro groups to amino groups low or very high dilution of the nitro compounds in a solvent is required. When using noble metal catalysts, as they are, for. B. in U.S. Patent 2,619,503 is a very close observation the reaction basic condition, and the reaction mixture must be during the whole time The response will be overseen as it is never more than a relatively low one Percentage of the nitro compound to be reduced may contain.

But that means that the nitro compound only works at one speed can be added, which corresponds to the hydrogen uptake. Other known methods z. B. that described in British Patent 832 153, require a rigorous Purification of the nitro compound used as the starting material to make it complete of phenolic impurities and are therefore uneconomical.

To reduce the nitro group in m-halonitrobenzenes has metallic rhodium has proven its worth as a catalyst, which is otherwise (see e.g. German patent 1118777) acts in the sense of a hydrogenation of the ring carbons. Presumably weakens in this case the halogen substituent present determines the activity of the rhodium catalyst such that no hydrogenation occurs on the aromatic ring.

Surprisingly, it has now been found that you can also be absent inactivating substituents nitro groups in aromatic compounds with rhodium catalysts can hydrogenate without ring hydrogenation taking place if one is used for ring hydrogenation already exhausted catalyst used. It was by no means foreseeable that an already exhausted catalyst for the reduction of nitro groups for ring hydrogenation is still completely usable even after repeated use. With this one for ring hydrogenations already exhausted catalyst can be used according to the invention at moderate temperatures, without the use of high pressure devices and in a relatively short time, in very pure hydrogenation products obtained in almost quantitative yield. Since the used catalyst has already been exhausted for ring hydrogenation, it is available practically free of charge.

The process according to the invention for the preparation of aromatic amines of the general formula where R is a stable to catalytic hydrogenation substituent, m is an integer from 1 to 3 and n is an integer from 0 to 5, by the action of gaseous hydrogen in the presence of a catalyst at temperatures from room temperature to 1500 C and hydrogen pressures between atmospheric pressure and 10.5 at on nitro compounds of the general formula is characterized in that the hydrogenation is carried out in the presence of a smaller amount of a rhodium catalyst, the effect of which as a catalyst for ring hydrogenation is largely exhausted.

The term "largely exhausted" denotes a catalyst which had previously been used for hydrogenations involving an aromatic compound was converted into a saturated alicyclic compound. According to the invention Rhodium catalyst to be used may already have been used several times, with Regenerations have been turned on between uses. He can practically all or only a major part of its ring hydrogenation activity have lost. In any case, they are catalysts for the original Intended use have become practically worthless. Is the catalyst for ring hydrogenation Not yet completely exhausted, the aromatic bonds only become after reduction attacked by the nitro groups, d. H. after absorbing 3 moles of hydrogen per nitro group became. In this case, however, the reduction can easily be interrupted before the much slower ring hydrogenation reaction due to the residual activity of the Catalyst uses.

The preferred amount of catalyst is 0.01 to 2 percent by weight, based on the nitro compound.

The activity of the rhodium catalysts according to the invention is based on the metallic rhodium, which is in the form of granules or in the form of a sponge, of scales or lumps present and on a support, e.g. B. kieselguhr, aluminum oxide, Carbon, zirconium oxide or bentonite can be applied. It is not a regeneration of the largely exhausted catalyst required before it for the invention Method is used and it can even be used for a whole number of consecutive times Reductions of the nitro groups can be used.

When carrying out the process according to the invention, the theoretical Amount of hydrogen from the reaction mixture without the use of excessive temperatures or pressures recorded in a few hours. The implementation of the invention Procedure at pressures less than 7 at was found to be particularly advantageous.

The method according to the invention is illustrated by the following examples explained in more detail.

Example 1 p-phenylenediamine A mixture of 13.9 g of p-nitroaniline, 35 ml water, 20 ml concentrated hydrochloric acid, 0.1 g Nuchar C-190 (a Activated carbon, sold by West Virginia Pulp & Paper Company), 0.1 g of diatomaceous earth as a filtration aid and 0.5 g of a catalyst containing 50 / o rhodium on aluminum oxide (catalyst ratio 0.18 O / o) was placed in a Parr shaker brought in.

The catalyst was previously all a catalyst for ring hydrogenations, namely for the reduction of p-nitroaniline to p-cyclohexanediamine, used and been exhausted.

After purging the Parr shaker with nitrogen as a precaution and then with hydrogen in the usual way the reduction was made by increasing the hydrogen pressure to 4 atmospheres and shaking initiated. The temperature was left Rise to 1000 C in the course of the reaction, partly through application external heating and partly through the exothermic reaction itself. After 3 hours and 25 minutes were 96010 of the theoretical the amount of hydrogen absorbed. To After 5 hours 97.5% of the theoretical amount of hydrogen had been absorbed, whereupon the Hydrogenation was interrupted. The catalyst was filtered off and the filtrate was cooled and neutralized with ammonium hydroxide.

It crystallized p-phenylenediamine of extremely high purity in a yield of 95% of theory from the mixture.

Example 2 Aniline A mixture of 200 ml nitrobenzene, 2 ml Arquad 18-50'3 (a quaternary ammonium compound used as a dispersant and sold by Armor & Company), 3.6 g of diatomaceous earth as a filtration aid and 7.2 g of a catalyst which contained 2.50 / o rhodium on aluminum oxide (catalyst ratio 0.08%) was in a hydrogenation vessel of 500 ml content at a maximum temperature hydrogenated at 600 C and a maximum hydrogen pressure of 4.6 atm. After 10 hours and 40 minutes the theoretical amount of hydrogen had been absorbed. The reaction mixture was filtered and the filtrate analyzed, with a concentration of 98.1 ovo Aniline, on an anhydrous basis, was found.

The catalyst used in this example was previously used as a catalyst for ring reductions in the hydrogenation of aniline to cyclhexylamine.

Example 3 2,4-diaminotoluene A mixture of 132 g of 2,4-dinitrotoluene, 2.64 g of a catalyst containing 2.50 / 0 rhodium on aluminum oxide (catalyst ratio 0.05%) and had previously been exhausted as a catalyst for ring hydrogenations and 1 ml Ethoquad 0/1263 '(a polyethoxylated amine used as a dispersant and sold by Armor & Company) was placed in a hydrogenation vessel of 500 ml and following the usual precautionary measures under one maximum hydrogen pressure of 2.8 atmospheres and at a maximum temperature of 1050 C hydrogenated. After 6 hours 97% of the theoretical amount of hydrogen had been absorbed been. The mixture was filtered warm and the filtrate cooled, followed by 2,4-diaminotoluene crystallized out almost quantitatively. The crystalline product was used for purification dissolved in alcohol and fractionally distilled the solution. The 2,4-diaminotoluene content the crude fraction had a purity of 99 O / o, and by recrystallization of the 2,4-diaminotoluene of 1000% purity was obtained from crude distillate from water.

Example 4 Aniline (reuse of the catalyst) A mixture of 200 ml of nitrobenzene, 2 ml of Ethoquad 0/12 and 9.6 g of a catalyst, the 2.50 / o Rhodium on aluminum oxide (catalyst ratio; 0.100 / o) contained and before had been used in 33 consecutive ring hydrogenation reactions placed in a Parr shaker and at a maximum temperature from Hydrogenated at 600 C and a maximum pressure of 4.2 atmospheres. The hydrogen uptake ended in 4 hours and 15 minutes. The mixture was filtered and removed from the Filtrate recovered an almost theoretical amount of aniline. The catalyst was on sucked dry the filter and again with another 200 ml of nitrobenzene and 2 ml of des Add the above dispersant to the Parr shaker. Among the same Under hydrogenation conditions, the uptake of hydrogen was complete in less than 5 hours; almost the theoretical amount of aniline was recovered again.

Example 5 Aniline This example shows that the type of Dispersant has no influence on the process according to the invention (if a such dispersant is used).

A mixture of 200 ml of nitrobenzene, 9.6 g of a 2.5% rhodium catalyst on aluminum oxide (catalyst ratio 0.10%), previously used as a catalyst for Ring hydrogenations had been exhausted, 4.8 g of kieselguhr was used as a filtration aid and 2 ml of a dispersant are mixed and placed in a 500 ml hydrogenation vessel introduced and under a maximum pressure of 4.2 atü at a reaction temperature hydrogenated from 50 to 600 C. The following types of dispersants have been used: A diamine salt, e.g. B. Duomeen TDO, a polyethoxylated amine, e.g. B. Ethomeen S / 12e, a quaternary ammonium methyl sulfate, e.g. B.

PropoquadHT / 12 @, a quaternary ammonium chloride, e.g. B. Arquad 2 C-75s, (these products are sold as dispersants by Armor & Company).

In all of these examples the theoretical amount is hydrogen added in less than 4 hours and removed from the reaction mixture after filtering off of the catalyst, aniline obtained in almost quantitative yield by distillation.

From the above examples it can be seen that according to the invention Process one or more nitro groups attached to an aromatic ring in the corresponding amino groups are converted, in the presence or absence a dispersant, the double bonds in the aromatic nucleus not being attacked will.

The use of a dispersant is indicated when that passes the water formed in the reaction is not soluble in the reaction mixture. Will the reaction carried out in the presence of water and / or if the starting material is water-soluble, a dispersant can optionally be used, wherein any type of dispersant can be used.

The advantages of using the new catalyst in the inventive Procedures are under Others include: Aromatic nitro groups become aromatic Amino groups hydrogenated without attacking the aromatic double bonds; the in that The method used catalyst is almost free for the user because of its activity has already been used to the full in other proceedings; the catalyst used can be metallic rhodium, rhodium on a carrier and / or with a filter aid be mixed up; a very small amount of catalyst gives a satisfactory one Rate of hydrogenation, e.g. B. provides a catalyst ratio of 0.01 to 0.5 Weight percent of the new rhodium catalyst gave excellent results. Although you can higher catalyst ratios can be used, yet an amount greater than 2 g rhodium per 100 ml nitro compound does not have any more favorable effects. Another advantage of the process according to the invention is that very mild process conditions bring about the desired hydrogenation, d. i.e., they are not high temperatures necessary, the process is particularly suitable for the application of low pressures and allows the use of so-called low-pressure hydrogenation devices. That is in contrast to other known processes for the reduction of aromatic substances Nitro compounds that require high temperatures and / or high pressures and / or high catalyst ratios require.

Claims (3)

Claims: 1. Process for the preparation of aromatic amines of the general formula where R is a stable to catalytic hydrogenation substituent, m is an integer from 1 to 3 and n is an integer from 0 to 5, by the action of gaseous hydrogen in the presence of a catalyst at temperatures from room temperature to 1500 C and hydrogen pressures between atmospheric pressure and 10.5 at on nitro compounds of the general formula characterized in that the hydrogenation is carried out in the presence of a smaller amount of a rhodium catalyst, the effect of which as a catalyst for ring hydrogenations is largely exhausted. 2. The method according to claim 1, characterized in that the Rhodium catalyst in an amount of 0.01 to 2.0 0 / o, based on the nitro compound, used. 3. The method according to claim 1, characterized in that the Carries out hydrogenation at a hydrogen pressure of less than 7 atmospheres.