DE2000502A1 - Platinum metal hydrogenation catalyst cont - aining group 5 or 6 elements for alkylhydrox - Google Patents

Abstract

Preparation of N- 1-6C alkyl hydroxylamines by hydrogenation of nitroalkanes in aqs. H2SO4 takes place in presence of a Pt metal-containing catalyst containing at least one Main Group V or VI element with atomatic weight > 31. Reduction can be carried out at normal pressure with high selectivity and good space-time yields. In example, good results are obtained by using 0.5% PtS/0.2 on graphite for nitromethane hydrogenation at 35 degrees C namely 53 1 H2/hr hydrogenation velocity at 92 mol% selectively when using 0.12% Pt per nitromethane charged.

Description

Process for the preparation of N-alkylhydroxylamines It is known that you can reduce nitroalkanes with hydrogen to N-alkylhydroxylamines. at this reaction occurs depending on the chosen catalysts and the reaction conditions, such as pressure and temperature, in addition to varying amounts of hydroxylamine compounds corresponding oximes or

Amines and resin-like products (see Grundmann, Ang. Chem.

62, (1950), pages 558 ff). The catalysts used here are zinc and chromium and copper-containing catalysts or silver-containing catalysts are used been.

Numerous proposals have already become known, this catalytic one To carry out the reduction in such a way that the alkylhydroxylamines are essentially formed will. According to Swiss patent specification 325 080, the reduction in Made in the presence of finely divided palladium, the nitroalkane with a organic solvents or water can be diluted. Here, too, it does not succeed to selectively form alkylhydroxylamines in the hydrogenation, but are still formed significant amounts of other reduction products, especially amines.

The same disadvantages occur with a British patent 800 529 described method in which the reduction ei a temperature below of 9000 and a pressure above 50 at in the presence of silver, in connection itt chromium and / or manganese carried out as a catalyst.

In the Fra asischen patent office 1 185 623 the Hydrioru of M Mitroalkanen su alkylhydroxylamines in the presence of platinum metals or their Oxides described as catalysts with the hydrogenation in the presence is carried out by at least one equivalent of sulfuric acid per mole of nitroalkane.

However, this process has the disadvantage that good hydrogenation rates can only be achieved with the application of a hydrogen overpressure, the best Results can be achieved with a palladium containing catalyst.

The present invention was based on the object of the catalytic To design the hydrogenation of nitroalkanes with up to 6 carbon atoms in the molecule, that the reduction even at normal pressure with high selectivity and good space-time yields leads to the corresponding alkyl hydroxylamines.

It has been found that this object can be achieved in that the hydrogenation in the presence of a platinum metal-containing catalyst, which is at least an element of the V. and / or VI. Main group of the periodic table with a Contains atomic weight greater than 31.

The mentioned elements of the V. and VI. Main group can already be at the production of the platinum metal catalyst are introduced into this, one can but they also - z.3. in the form of their oxides - the aqueous, sulfuric acid reaction add medium during the reduction of the nitroalkane. So you can, for example produce the platinum metal-containing catalysts according to German Patent 1,088,037, by making platinum (lr) compounds in two stages over platinum (II) compounds su metalliechem reduced platinum and sulfur-containing for the reduction in the first stage Reducing agents, such as dithionite or sulfides, wäblt. Simultaneously with the reduction becomes part of the sulfur. gobound as platinum sulfide.

The platinum catalyst is expediently applied to a support. In principle, the known carrier materials are suitable for this, but in particular carbonaceous carrier materials. Has been particularly suitable finely ground graphite with a grain size of 5 to 35 / u has been found. Based the catalyst has a platinum content of 0.1 to 2 percent by weight on the support, preferably from 0.5 to 1 percent by weight. The cheapest amount to be added Connection of the element of V. or VI. Main group of the periodic table depends on the nature of the element used and can be between 3 to 20 atomic percent of the element or elements concerned, based on the amount contained in the Ka catalyst Platinum metal. When added to the reaction medium during the hydrogenation In general, smaller amounts are sufficient, e.g. a one-time addition of about 3 to 7 atomic percent of the element or elements in question, based on that used Platinum metal. If, on the other hand, it is incorporated during the production of the catalyst, so the amount to be added is generally somewhat higher and is about 7 to 20 atomic percent, based on the amount of platinum metal contained in the catalyst. The trivalent compounds of the elements have proven to be particularly suitable additives the V main group or the two- to tetravalent compounds of the elements of the VI. Main group proved. They are produced under the reducing conditions of catalyst production or the hydrogenation reaction itself to the corresponding elements or their anions reduced and as such bound by platinum The catalyst becomes the reaction medium added in such an amount that, based on the nitro compound to be reduced, about 0.01 to 0.2, preferably 0.05 to 0.15, weight percent platinum metal.

As mentioned, di. Hydrogenation in dilute aqueous sulfuric acid performed. With regard to the activity of the catalyst and the selectivity of the reaction Eating a low starting concentration of acid is beneficial, however it expedient to a sensible. To obtain final concentration of alkylhydroxylamine, to use at least 10 Gewlchtoprosentlge 8sulfurodure. Usually one will on the other hand, do not exceed concentrations of 30 percent by weight.

Aliphatic or cycloaliphatic nitroalkanes can be used as nitroalkanes use with 1 to 6 carbon atoms, in particular nitromethane, nitroethane, 1- and 2-nitropropane and nitrocyclohexane.

The liquid nitroalkane, e.g. 3. Nitromethane, is the reaction medium Conveniently added in small portions to envelop the finely divided Catalyst by the generally poorly water-soluble organic liquid to avoid if possible. The total amount of nitro compound is set in each case one, which is necessary for a consumption of the submitted acid up to a residual content of approx. 0.3 equivalents of acid per liter is required. This should be low acidity to stabilize the solution and avoid unwanted further hydration of the alkylhydroxylamine formed are left.

The hydrogenation is depressurized by introducing gaseous hydrogen made in the vigorously stirred reaction mixture. Applying pressure can Although the reaction rate can be increased, there must be a loss of selectivity be accepted. The economic optimum is 0 to 1 atm. the The reaction is ended after uptake of 2 moles of hydrogen per mole of nitroalkane.

The gas uptake then usually drops considerably, since the alkylhydroxylammonium ion is stable to further hydrogenation under these conditions.

The reaction temperature is between 20 and 500, preferably by cooling 30 and 400C. In turn, higher temperatures impair the selectivity of hydrogenation.

EXAMPLE 1 5 l of 3.5 normal sulfuric acid and the amount of the corresponding catalyst indicated in the table are placed in a 10 l stainless steel stirred vessel Hydrogen pretreated. With vigorous stirring, 975 g of nitromethane are then added in several portions, and at the same time enough hydrogen is passed into the reaction mixture that there is always a small excess. A reaction temperature of 35 ° C. is maintained, if necessary by cooling. The reaction is over as soon as the gas uptake drops sharply and the acid concentration of the reaction solution is 0.3 to 0.4 n-H2S04. The results are summarized in Table 1 below. catalyst precious metal medium selectivity amount per hydrogenation used speed Nitromethane resistance % l H2 / h mol.% 1. 0.5% PtS / 0.2 on graphite 0.04 18 93 0.08 42 92 0.12 53 92 2. 0.5 P Pd on graphite 0.04 15 84 0.08 21 90 0.12 29 92 1 P Pd on graphite 0.32 25 92 4.5 P Pd on activated carbon 0.16 21 84 The catalyst according to the invention listed under 1 corresponds to the procedure of the example. 1 of German Patent 1,088,037 and contains, based on platinum, about 20 atomic percent sulfur.

The table shows that the platinum catalyst according to the invention compared to the known palladium catalysts at Blneatt in comparable amounts o brings about a higher average hydrogenation rate with approximately the same selectivity.

Example 2 Effect of the addition of compounds of arsenic and antimony and Selenium for the suspension of the catalyst in the acid: In a 2 l stirred glass vessel 200 g nitrometban are added in 4 successively carried out humidifications Hydrogen under atmospheric pressure and using 50 g of a 0.5 percent Platinum catalyst on graphite, which is produced by reducing an aqueous platinum chloride solution was obtained with formic acid in the presence of graphite powder in 1.5 1 3.5 n-H2S04 0 brought to reaction at 40 C. While there was no further addition in experiment I, before the start of the reaction in experiment II, 6 atomic percent arsenic is added in the form of arsenic Acid, in experiment III 4 atomic percent antimony as potassium antimonyl tartrate and in experiment IV Add 4 atomic percent selenium as selenious acid. After each 2 hours of reaction time the attempts are evaluated. The results are shown in Table 2.

Table 2 Hydrogenation rate selectivity l / h H2 Trial I 52 72.5 II 52 89.5 III 46.5 86 IV 49.5 92 So while the hydrogenation rate by the addition of the elements of V. and VI. Main group of the periodic system remains unchanged or is only inevitably reduced, a noticeable increase in selectivity compared to experiment I is achieved in all cases.

Claims (1)

Claim Process for the preparation of alkyl hydroxylamines with up to 6 carbon atoms by catalytic hydrogenation of the corresponding nitroalkanes in aqueous sulfuric acid, characterized in that the hydrogenation is carried out in the presence of a platinum-metal containing Catalyst containing at least one element of V. and / or VI. Main group of the periodic System with an atomic weight greater than 31 contains.