DE19636214A1 - Multimetal catalyst and process for the preparation of substituted aromatic amines - Google Patents

Description

The present invention relates to a catalyst which iridium and at least one more Contains doping element on a carrier for the Production of substituted aromatic amines by Hydrogenation of the corresponding substituted nitro aromatics.

The hydrogenation of aromatic nitro compounds with Halogen substituents - especially chlorine - for the production the corresponding amines have long been known (Ullmann, Encyclopedia of Technical Chemistry, 5th Edition, Volume A2, Page 46 (1985)) and is in the presence of metal catalysts with hydrogen as a reducing agent carried out. A key problem in the response is that unwanted dechlorination of the aromatics, resulting in a Reduction in the yield of aromatic amine compound leads. For this reason, many are concerned Patents with processes involving halogen elimination try to keep it as low as possible.

So can by using platinum and ruthenium Carrier materials (U.S. Patent 4,760,187) as well Selectivity improvement can be achieved as through the Use of platinum, palladium, rhodium, iridium, ruthenium and osmium-containing catalysts with acid After-treatment of phosphorus compounds (DE-OS 30 06 748).

Activity and selectivity of the noble metal catalysts can by the presence of a cocatalyst in the Reaction mixture can be influenced. According to US 5,105,012  is next to palladium on a carbon support as Main catalyst iron powder or an iron salt as Cocatalyst added to the reaction mixture. The US 3,253,039 suggests in addition to a catalyst Platinum on carbon silver nitrate in the To give reaction mixture. Silver is in the distributed throughout the reaction mixture without using the platinum of the catalyst to be alloyed. As another heavy metal additives were lead, copper, nickel, bismuth, and Chromium nitrate examined.

By doping a precious metal catalyst with various main and sub-group elements also activity and selectivity of the hydrogenation to be influenced. For example, in the DE 42 36 203 A1 proposed one with nickel and / or Cobalt-doped platinum catalyst on activated carbon use. According to DE 42 18 866 C1, the selectivity hydrogenation by doping a platinum catalyst Activated carbon improved with copper. Platinum and copper deposited on the activated carbon carrier at the same time and then reduced.

The known hydrogenation catalysts are for example by introducing the carrier material into a Precious metal salt solution and evaporation of the solvent produced. If necessary, the catalyst then reduced. Alternatively, it can Backing material also with the catalytically active elements be impregnated by the carrier material with a Solution of these elements is brought into contact and the Hydroxides of these elements precipitated in an alkaline environment will. This can also be a reduction connect. Furthermore, it is known on the  Carrier material a solution of the precious metal salts spray on.

The previously known processes for hydrogenation substituted aromatic amines, however a few more in terms of activity and selectivity Problems on. So do metal doping in connection with nitrogenous additives in the hydrogenation halogenated azo and azoxybenzene derivatives (EP-OS 0 073 105). Because of the toxicity of such Compounds is their by-products in the Avoid hydrogenation of halonitroaromatics.

The object of the present invention is a Catalyst for the hydrogenation of substituted Specify nitro aromatics, which is compared to the known Catalysts in particular through an improved Selectivity distinguishes.

This task is performed by a multimetal Dissolved catalyst, which iridium and at least one contains further doping element on a carrier. Of the Catalyst is characterized in that iridium with at least one element from the group manganese, cobalt, Iron, nickel or ruthenium is doped.

Suitable support materials for the catalyst are Activated carbon or oxidic materials such as aluminum oxide, Titanium dioxide, silicon dioxide or mixed oxides thereof. Activated carbon is preferably used. It can be vegetable or be of animal origin, and by various Process (e.g. water vapor, phosphoric acid, etc.) activated have been. It can be made of porous and non-porous Activated carbon consist, preferably at least 80 wt .-% the activated carbon particles have a grain size of less than  100 µm. Such activated carbons are generally over different providers accessible.

The catalyst according to the invention contains iridium in one Amount between 0.3 and 12, preferably between 0.5 and 7 wt .-% based on the carrier material used, and at least one metal from the group manganese, iron, cobalt Nickel, copper and ruthenium, in an amount between 1 and 100, preferably between 5 and 50% by weight, based on Iridium.

The carrier is first used to produce the catalyst suspended in water and by adding salt solutions corresponding metals impregnated. Then the Metals with the help of a water-soluble reducing agent reduced at temperatures between 0 and 100 ° C. The Order of joining carrier material, water, Metal salt solutions and reducing agents can also be different to get voted.

With the catalyst of the invention can be substituted Nitroaromate to the corresponding aromatic amines with high selectivity are hydrogenated. For this, the Nitro aromatics dissolved in suitable solvents and at elevated temperature with the addition of hydrogen to the Catalyst hydrogenated to the amine compounds.

Chlorine-substituted aromatic are preferred Nitro compounds of formula (I) are hydrogenated.

In (I), R1 and R2 can be the same or different and Hydrogen, an alkyl, alkoxy, hydroxy, carboxy, Carbonyl, phenyl or amino residues as well as chlorine, fluorine, Alkylcarbonylamido, alkyloxycarbonylamido mean.

Examples of chlorinated aromatic nitro compounds according to formula (I) are 2-nitrochlorobenzene, 3-nitrochlor benzene, 4-nitrochlorobenzene, 2,4-dichloronitrobenzene, 3,4-dichloronitrobenzene, 2,5-dichloronitrobenzene, 2-chloro-4- nitrobenzene, 4-chloro-3-nitrobenzene, 2-chloro-4-nitroaniline, 2,3,5-trichloronitrobenzene, 2,4,6-trichloronitrobenzene, and Mixtures of isomers of the compounds mentioned.

Suitable solvents for these compounds are aliphatic alcohols such as B. methanol, ethanol, Isopropanol, butanol or hexanol, carboxylic acid esters such as Acetic acid and aromatic hydrocarbons such as benzene, Toluene and xylene.

The hydrogenation can be carried out at temperatures between 40 and 200 preferably between 60 and 120 ° C, and at pressures of 1 to 200, preferably from 4 to 150 bar will. It is advantageous to hydrogenate in the presence an organic or inorganic basic compound to carry out any halogens that are split off tie. Triethylamine in is preferably used for this purpose an amount of 0.05 to 5 wt .-% based on the aromatic, substituted nitro compound used.

The hydrogenation can be carried out batchwise as well operated continuously. With continuous Driving style must be the amount of aromatic converted Nitro compound (educt) replaced and, if necessary, the used portion of basic compound replenished will.  

The hydrogenation of substituted aromatic amines with the The catalyst according to the invention is particularly notable for a high selectivity with regard to possible Dehalogenation and other undesirable by-products (e.g. azoxy and azobenzene derivatives). especially the Cleavage of chlorine can occur when using the described multimetallic catalyst almost completely avoided will. In many cases, therefore, an additional After-cleaning of the desired chlorine-substituted aromatic amine compound of dechlorinated Secondary connections are omitted. This is especially true against the background of increased quality requirements significant improvement in the state of the art.

example 1

There were 94.8 g of activated carbon in deionized water suspended. A solution of 20.74 g hexachloroiridium (IV) acid (23%), 0.72 g Manganese (II) chloride tetrahydrate and 0.87 g sublimed Iron (III) chloride added, alkaline with sodium hydroxide solution (pH 10) placed at 80 ° C with a freshly prepared one Sodium borohydride solution (2 wt .-%) reduced and after Filtered to adjust pH 4.

The finished catalyst contained based on Total weight 5.0% by weight of iridium and 4.2 based on iridium % By weight of manganese and 6.2% by weight of iron.

Example 2

In the same manner as in Example 1, a catalyst using 20.74 g of hexachloroiridium (IV) acid (23%) and 1.45 g sublimed iron (III) chloride produced.  

The finished catalyst contained based on Total weight 5.0% by weight of iridium and based on iridium 10.5% by weight iron.

Example 3

To a suspension of 94.8 g activated carbon in deionized Water became 20.74 g hexachloroiridium (IV) acid, 0.404 g Cobalt (II) chloride-6 hydrate and 1.16 g sublimed Iron (III) chloride added. The suspension was with Sodium hydroxide solution made alkaline (pH 10) and with a fresh prepared sodium borohydride solution (2 wt .-%) reduced and filtered off after adjusting pH 4.

The finished catalyst contained based on Total weight 5.0% by weight of iridium and based on iridium 2.1% by weight of cobalt and 8.4% by weight of iron.

Example 4

In the same manner as in Example 3, a catalyst was using 20.74 g hexachloroiridium (IV), 1.48 g Nickel (II) nitrate hexahydrate and 0.72 g manganese (II) chloride tetrahydrate produced.

The finished catalyst contained based on Total weight 5.0% by weight of iridium and based on iridium 6.3% by weight of nickel and 4.2% by weight of manganese.  

Example 5

In the same manner as in Example 3, a catalyst was using 20.74 g of hexachloroiridium (IV) acid, and 3.54 g of ruthenium (III) chloride (14.1%).

The finished catalyst contained based on its total weight 5.0 wt .-% iridium and based on iridium 10.4 wt% ruthenium.

Example 6

In the same manner as in Example 3, a catalyst was using 20.74 g of hexachloroiridium (IV) acid, 0.438 g iron (III) chloride and 0.58 g copper (II) nitrate tetrahydrate produced.

The finished catalyst contained based on its total weight 5.0 wt .-% iridium and based on iridium 3.2 % Iron and 3.2% copper.

Comparative Example 1

A copper-doped platinum catalyst was used in accordance with the DE 42 18 866 C1 produced.

100 g of activated carbon were placed in 800 ml of deionized water suspended. A solution of 2.5 g was added to this suspension Hexachloroplatinic (IV) acid and 0.32 g copper acetate monohydrate added in 200 ml of water. The suspension was heated to 80 ° C, made alkaline with sodium hydroxide solution and reduced with 0.3 ml formaldehyde solution (37 wt .-%). The Suspension was stirred for 20 min and then the Filtered catalyst.  

The finished catalyst contained based on its total weight 1% by weight of platinum and based on platinum 10% by weight Copper.

Comparative Example 2

It was a pure platinum catalyst according to the DE 42 18 866 C1 manufactured. Except for the missing ones Addition of copper was made according to the Comparative Example 1 made.

Comparative Example 3

It was a pure iridium catalyst according to the DE 42 18 866 C1 manufactured. Except for the missing ones Addition of manganese and iron was used to manufacture Example 1 made.

Application example

Those made in the previous examples Catalysts were evaluated for their activity and Selectivity in high pressure hydrogenation of 2-Chloronitrobenzene tested.

The hydrogenations were carried out in a stirred autoclave with a volume of 0.5 l. The following reaction parameters were observed to determine the catalytic activity and selectivity of the catalysts:
Heating pressure: 5 bar
Reaction pressure: 10 bar
Temperature: 90 ° C
Stirring speed: 700 rpm.

There were 78 g of 2-chloronitrobenzene in the presence of 0.8 mol% of triethylamine converted quantitatively. The end of  Reaction is the result of a rapid decline Hydrogen absorption can be determined to zero. The catalyst weight was 0.385 g each. As possible Dehalogenation product can aniline in this reaction be formed. The proportion of aniline in the product was reduced therefore determined by gas chromatography.

The results of the investigations are as follows Table summarized. They show that Catalysts according to the invention are characterized by a high Mark selectivity.

table

Testing the activity and selectivity of the catalysts

Claims (3)

1. Multimetallic catalyst containing iridium and at least one further doping element on a support, characterized in that iridium is doped with at least one element from the group consisting of manganese, cobalt, iron, nickel, copper and ruthenium. 2. Catalyst according to claim 1, characterized, that he 0.3 to 12 wt .-% iridium based on the Weight of the carrier and based on iridium 1 to 100 % By weight of the doping elements. 3. Process for the preparation of substituted aromatic Amines by hydrogenating the corresponding substituted ones Nitroaromatics, characterized, that the hydrogenation on a catalyst according to the Claims 1 to 2 is made.