DE2019261B2 - Process for the preparation of alkanone or cycloalkanone oximes by partial reduction of nitroalkanes or nitrocycloalkanes - Google Patents

Description

The invention relates to the partial reduction of nitro (cyclo) alkanes to the corresponding oximes under conditions in which the oximes are obtained essentially free of amines and in good yield will.

The invention particularly relates to the use of copper salts for implementation this reduction reaction, which takes place essentially quantitatively and under mild conditions.

Oximes are valuable products and intermediate products. For example, they react with hydrogen cyanide to form hydroxyaminonitriles, can be subjected to the Beckmann rearrangement and acylated to form valuable products.
'(CycloJ-alkanone oximes are usually prepared by reacting ketones with hydroxyamine hydrochloride (or sulfate) in the presence of an inorganic base. However, this reaction is reversible, and although it yields the desired products, undesirable accompanying substances are formed at the same time, which are separated off Furthermore, the ketone starting materials are not always available or are relatively expensive to produce. It is therefore desirable to produce the (cyclo) alkanone oximes from nitro (cyclo) alkanes, which are readily available in large quantities.

There are therefore already various processes for the preparation of oximes from nitro (cyclo) alkanes have been described, but for various reasons they are not entirely satisfactory. So is z. B. the direct reduction of nitroalkanes with acetic acid and zinc is known, but it delivers as a result of the simultaneous production of fully reduced amine low yields.

It is also known the reduction of nitrocyclohexane in the presence of copper.

which is bound by chelating side chains of a polymer. With this catalyst must a very large molar amount of copper, based on the nitro compound to be reduced, can be used. The desired oxime is obtained in poor yields; in addition to the oxime will be significant Amounts of ketone formed. Finally, there is a method for making cyclohexanone oxime too call, in which one of the alkali salt of nitrocyclo-

hexane runs out and reduced with carbon monoxide. The disadvantage is that the reduction is relatively high temperature and high pressure must be carried out, and even in this process let the Yields of cyclohexanone oxime leave something to be desired.

There are other indirect methods known to them

however usually require several stages to prepare

Difficulties in isolating the products or

require special equipment.

It is therefore particularly necessary to create a direct reduction process that is based on the relatively cheap and easily accessible nitro (cyclo) alkanes and in good finals too leads to an oxime which is essentially free of amines. This procedure should be carried out under mild temperature and pressure conditions must be feasible and equally applicable to nitroalkanes in pure form or in the form of their crude nitration mixtures.

Another advantage would be the use of long-lived and relatively inexpensive hydrogenation catalysts be in the facilities currently in place. A selective reduction process that Satisfying most of these requirements would therefore be a significant advance for the synthetic represent organic chemistry.

It has now surprisingly been found that a catalyst system which consists of copper salts, a complex-forming aliphatic amine with a pK _a value of at least 9.5, and water and is known per se for the complete reduction of aromatic nitro compounds to their amines, is known in this way can be modified so that it can quantitatively, selectively and partially reduce certain nitro (cyclo) alkanes to the oximes, with little or no aminoalkane being formed. This behavior of the catalyst system known per se was all the less to be expected since the published working conditions not only permit the use of the catalyst for the partial reduction of acrylonitro compounds

not suggest their oximes. but the desired ones (Cyclo) alkanone oximes also do not deliver. By carefully regulating the concentration and the mutual ratio of copper salt, nitrogen base and water content of the catalyst system

the applicant, however, create a process with which the desired oxime can be obtained in the best possible yield and can generally be obtained free of amine accompanying substances within a short reaction time.

The invention therefore provides a process for the preparation of alkanone or cycloalkanone oximes by partial reduction of nitroalkanes or nitrocycloalkanes, which is characterized in that a nitroalkane or nitrocycloalkane containing at least 3 carbon atoms is added in a carbon monoxide atmosphere at 60 to 150 ⁿ C and 0 to 17.6 atmospheres in the presence of an aqueous, 0.5 to 20 percent by weight of a dissolved copper salt containing, at least 60 percent by weight solution of a

aliphatic amine a pK _a value of at least speed immeasurably low, while above 105 to

9.5 converts

All non-aromatic compounds which contain at least 3 carbon atoms and at least one or more nitro groups per molecule are suitable as nitro-icyclo-alkanes for the process according to the invention. The most useful substrates are the singly nitrated straight-chain and ring-shaped alkanes, such as nitrohexanes, nitrocyclohexanes, nitro-110 ^: C the volatility of water and the aliphatic amine requires a pressure-resistant system to reduce evaporation losses. The method may in principle be carried out between about 60 and about 150 "C or more. Since the best balance of yield and reaction time at about 80-1 \ 5 ^C C at atmospheric pressure sets in, then this the preferred range of working

heptane, nitrooctane, nitrononane, nitrodecane, Ni-i ₀ temperature.

troundecane, nitrododecane and their higher homo- The process according to the invention can be carried out in one

lied. The preferred nitro-paraffins are nitro-reactor at atmospheric pressure or over-

cyclohexane and the 10 to 20 carbon atoms pressure can be carried out. From previously unexplained

containing nitroparaffins, either in the form of reasons retard pressures of about 17 to 70atü

pure individual compounds or their mixtures or the rate of conversion and should therefore

• Shape of your raw nitration mixtures. This ..— ~: —1— . "^ A ~~ 'jxk. ™ nriirl · ,. prfm-rtern hesnn-

20th

Group of nitroparaffins is preferred because they are under relatively mild reduction conditions within short reaction times essentially completely converted into the alkanone or cycloalkanone oximes. Also are these nitroalkanes are readily available in large quantities and at low cost.

The process of the invention runs fastest in the absence of an inert diluent away. However, it is often desirable to use the crude or partially purified nitration mixtures, which are obtained by vapor-liquid-phase nitration of n-alkanes as starting materials without separation the unreacted n-alkanes obtained. It also facilitates the presence of one with water immiscible diluents or solvents isolate the oxime product by enrichment of the product in the organic phase. For these reasons, one can use inert diluents or Use solvents without affecting the degree of conversion to oxime. Let general all liquids in which the nitro- (cyclo-) alkane substrate is soluble and which are against reduction behaves inertly under the working conditions according to the invention, use as diluent. These include the alkyl ethers such as diethyl ether, dibutyl ether, aromatics such as benzene, toluene and xylene as well the liquid alkanes mentioned above. Will the nitroalkanes in the absence of such diluents reduced, one or more of them can be used to extract the oxime product from the reaction mixture to extract and facilitate cleaning. Are especially useful for this purpose the dialkyl ethers.

Based on the findings so far, carbon oxide seems to be the best protective gas that has a high level Degree of conversion into the oxime within a short reaction time and without substantial amine formation gesti'f'et nitrogen or hydrogen alone are unsatisfactory, and reductions made in mixtures of CO with hydrogen or nitrogen either ran undesirably slow or gave rise to noticeable amounts of amine.

Usually carbon oxide is fed into the reactor after all liquid components of the Reaction mixture are added until the air is displaced from the system. Then the heating continued in the CO atmosphere until the desired reduction takes place.

The reaction temperature is critical for the process according to the invention in two respects. Below 40 ¹¹ C the reduction rate should be avoided. Higher pressures require particularly pressure-resistant reactors and increase the operational risk without any corresponding benefit. For these reasons, a pressure between atmospheric pressure and about 18 atm is used.

The reaction time required to produce the oximes depends mainly on the amount of batch, the concentration of the copper catalyst, the concentration of the complexing amine in the Approach and the number of reducible nitro groups in the molecule. When the concentration of the amine at least 60 percent by weight and the molar ratio of copper salt to mononitro (cyclo) alkane at least 1: 4, the reduction is complete within 12, usually within 6 hours. Di- and higher nitrated (cyclo) alkanes may require longer reaction times.

The catalyst system consists of the copper salt, the amine used to form the complex and the water. The parameters of the catalyst, based on the reduction of a mononitro (cyclo) alkane, are specified in more detail below. Di- and higher nitrated (cyclo) alkanes can be a little different Make ratio of the individual components of the catalyst system necessary.

As already mentioned, copper salts which are soluble in the aqueous solutions of aliphatic amines having a pK _a value of at least 9.5 can be used as the copper salt component. These include the copper salts of acids such as mono-, di- and polycarboxylic acids, e.g. B. copper acetate, formate, tartrate, citrate, and the copper salts of strong acids, e.g. B. copper (II) - and copper (I) chloride and copper (II) sulfate. Although both types of copper salts give approximately the same yield, the reaction times are generally shorter when the copper salts of weak acids are used, so that these are the preferred copper salts. The concentration of the copper salts in the aqueous aliphatic amine is usually about 0.5 to 20 percent by weight or more. The preferred range is 5 to 15 weight percent.

Generally, the aliphatic amines are suitable which have _a pK in aqueous solution -Basenstärken of at least 9.5 (measured at 25 to 30 ⁰ C), such as ethylenediamine, 1,2-propanediamine, 1,3-propanediamine, 3,3'-diaminodipropylamine, 1 , 6-hexanediamine, triethylenetetramine and the like, which are easily accessible and therefore preferred. Ammonia, pyridine, tetramethylethylenediamine, morpholine and diethanolamine are unsuitable. The role of the base in the reduction process has not been clarified. However, there is no significant reduction until at least about 60

60

weight percent of the aliphatic amine is present in the reaction mixture. Preferably even should at least 75 percent by weight of the base must be present in the reaction mixture for optimum yields of the oxime can be obtained in the shortest possible reaction time.

The concentration of water in the reaction mixture is necessary as it is likely the source represents the hydroxyl ion required for reduction. On the other hand, if too much water is present it becomes the diluent for the amine and the reduction to the oxime either does not take place or its speed is significantly reduced. Therefore the presence of water is necessary for the successful implementation of the procedure, and before the water-base ratio, the required concentration of 60 percent by weight of the amine, the reduction is extremely slow.

The reduction process according to the invention is usually carried out as follows:

A pressure-tight reaction vessel that is provided with a gas inlet, condenser and stirrer is pro Equivalent of the nitro (cyclo) alkane filled with 0.05 to 100 equivalents of copper salt, 0.1 to 500 equivalents of the aliphatic amine and 0.1 to 500 equivalents of water, the water content no longer than 25 percent by weight of the base solution. Then carbon oxide is introduced and the catalyst solution is saturated and creates a CO atmosphere. The resulting reaction mixture caused by the copper-amine complex is dark blue, is to about 80 to 115 ° C heated for up to 12 hours, with pressures varying between approximately atmospheric up to about 17.6 atm until the desired oxime is formed. If an inert diluent is present, if the oxime collects in the organic phase, if not, the reaction mixture is mixed with dialkyl ether or an aromatic solvent to separate the oxime in each case the crude product washed several times with water in the organic solvent and then in vacuo distilled. Elemental analysis, infrared and NMR spectra can be used to ensure that the desired Oxime has been obtained.

As the above description and the numerous examples show, the sequence is according to the invention Reduction process both beneficial and unexpected. Such are the oxime yields, for example not only well, but the reduction is rapid, and the oxime is in contrast to the previously known processes essentially free of completely reduced aminoalkanes. Furthermore are the reaction conditions are mild, the catalyst is stable and relatively inexpensive, and the Usual equipment can be used.

The results of the reduction process according to the invention are unexpected in view of the already mentioned publication in the Journal American Chemical Society, Vol. 32 (1967), pp. 2021 and 2022. This work describes the use of a copper salt amine catalyst complex for the complete reduction of aryl nitro compounds to their corresponding amines in a CO atmosphere. However, as can be seen from Example 15, the experiments were as given in Table 1 of the said reference Reworking the method using nitroalkanes, unsuccessful. It is considered supreme It is considered surprising that the known process does not apply to the substrates according to the invention before not using a critical amine to water ratio.

While the ratio of aliphatic amine to water is critical to the process of the invention, the new method is relatively flexible in other respects, i. i.e., substrates, solvents, reaction temperatures and prints can be modified, ίο The following examples are intended to illustrate the process further explain the invention:

example 1

Production of n-dodecane oxime from one

Nitrododecane / n-Dodecane mixture

In a reactor which is provided with overpressure heating, cooling, stirring and distillation devices, 1 part by weight of a nitrided starting material containing 25.9 percent by weight nitrododecane (0.25 mol) and 64.1 percent by weight of n-dodecane, and 2 parts by weight of an aqueous, 87 percent by weight Solution containing ethylenediamine,

the 5% (parts by weight / volume) copper acetate (0.25 mol) contains, given. The molar ratio of copper salt to nitrododecane is 1: 1. To create a gas atmosphere CO is introduced into the reactor and the reaction mixture in the CO atmosphere

90 ⁰ C heated. After 4 hours the reduction is complete and the reaction mixture is allowed to cool to room temperature. On cooling, two phases form, a lower aqueous blue phase and an upper, yellowish, organic phase. the

organic phase containing the oxime is separated off and washed with excess water. The organic phase gives the oxime in quantitative yield in the vacuum distillation. Means Gas chromatography, infrared and NMR spectra

became the identity of the oxime and the absence of amines or other substances accompanying the reduction proven.

Examples 2 to 4

Reduction of the same nitrododecane-n-dodecane mixture with different ones
Reaction conditions

Using the same starting material

same reaction and work-up procedures as

in example 1 the oxime was modified

the ratio of copper salt to nitroalkane and the reaction temperature prepared:

example

No.

reaction time

(Hours)

20th

Molar ratio of copper salt to
Nitroalkane

1: 2
1: 4
1:10

temperature

Conversion
degree of efficiency

82 ° C
83-88 ° C
80-95 ° C

100
100
100

Again, by IR-NMR spectra, gas chromatography and comparing the oxime with otherwise prepared standards the desired oxime proven.

7 «Ί 8

Examples 5-15

Influence of changes in the catalyst concentration and the composition of the Solvent on the oxime obtained

The procedure of Example 1 was repeated with the difference that the concentration of copper salt, Ethylenediamine and water was changed. Table 1 shows the results obtained:

Table 1

example Copper acetal Molar ratio 4th Ethylene temperature CO pressure Time Conversion No. concentration I copper acetate 2 diamine degree (%) of ! U nitro concentration Nitrododecane lodecan in oxime (Weight (Volume C-C) (atm) (Hours.) percent)·) percent) 5 1 : 10 90 85 1 6th 35 6th 2.5 90 85 1 6th 52 7th 5 1 90 85 ■ 1 5.5 100 8th 10 1 90 85 1 5.5 95 9 20: I. 90 85 1 6th 66 10 10 100 85 1 2.5 100 11th 10 95 85 1 2.5 100 12th 10 80 85 1 6th 48 13th 10 : 70 85 1 6th 38 14th 10 : 60 85 1 6th 15th 15th 10 : 50 85 1 6th no reaction *) (Weight / volume).

As can be seen in Table I, concentrations of ethylenediamine between 60 and 70% lower degrees of conversion, while concentrations of 50% give no measurable reduction.

Examples 16 to 29

Preparation of the oxime of Example 1
using various amines

The procedure of Example 1 is repeated with the difference that instead of ethylenediamine

Table II

the same volume of the following amines shown in Table II is used. All listed aliphatic amines are miscible with water and dissolve copper salts. As Table II shows, only those amines listed are suitable solvents for the reduction of nitroalkanes to oximes which have pK _a values of 9.5 and above. Aliphatic amines with base strengths significantly below 9.5 do not produce an oxime product.

example solvent PKa *) Mole Amine too temperature Time Oxime No. relationship Water- obtain copper Volume- acetate too relationship Substrate CC) (Hours.) 16 Pyridine 5.17 1: 2 9: 1 85 5 no 17th Ν, Ν, Ν ', Ν'-tetramethyl- 5.85 1: 2 9: 1 85 6th no ethylenediamine 18th Morpholine 8.36 1: 2 9: 1 80 6th no 19th ammonia 9.21 1: 1 3: 7 60-80 5 no 20th Diethanolamine 9.35 1: 1 9: 1 85 6th no 21 1,2-diaminopropane 9.78 1: 1 9: 85 8th Yes 22nd Triethylenetetramine 9.92 1: 2 9: 85 6th Yes 23 Ethylenediamine 9.98 1: 2 9: 90 2.5 Yes 24 n-hexylamine 10.40 1: 1 9: 85 3.5 Yes 25th 1,3-dietino propane 10.54 1: 1 9: 85 8th Yes 26th n-butylamine 10.59 1: 1 9: 75 2.5 Yes 27 3,3'-iminobispropylamine 10.70 1: 2 9: 85 6th Yes 28 1,6-diaminohexane 11.11 1: 1 85 8th Yes 29 Piperidine 11.22 1: 1 70 6th Yes 9: 1 9: 1

• I First acid dissociation constant at 25'C in aqueous solution.

509 542

(ο

ίο

Examples 30 to 40 Influence of different temperatures and gas atmospheres

In these examples, the procedure of Example 1 is repeated, but the gas atmosphere and reaction temperature are changed. Table III shows the results obtained. It should be noted that is obtained in the range of 70 to 14O ⁰ C, good yields.

The fastest conversions are obtained between 8 (1 and 115 ° C. The use of hydrogen or mixtures of hydrogen and CO or nitrogen does not seem to have any advantages over CO alone to offer.

Table III Copper acetate molar ratio Nitro (Weight 1 Ethylene temperature concentration (C) percent) For example 140 pressure Time % Conversion example Concentration of copper acetate dodecane percent)*) diamine 90 Influence> 115 Nitrododecane No. to 10 1 (Volume 90 105 10 1 90 95 10 1 90 85 (Hours.) 10 1 90 70 10 1 90 40 1 atm CO 6th 100 30th 10 1 90 1 atm CO 2 100 31 10 1 105 1 atm CO i '/ ₄ 100 32 95 85 1 atm CO l ^3/4 100 33 10 1 90 1 atm CO 5 94 34 10 1 85 1 atm CO 6th 51 35 90 85 1 atm CO 6th no 36 10 1 90 reaction 10 1 ele 41 to 46 1 atm CO % 100 37 'Volume). / on overpressure 1 atm 33 / CO 6th 51 38 67 / H, 1 atm H ₁ 6th 37 39 1 atm N ₂ 6th 18th 40 *) (Weight

Following the procedure of Example 1, reduction tests were carried out on a feedstock that from 12 to 15 percent by weight nitroalkane with 10 to 14 carbon atoms and 88 to 85 percent by weight of an n-alkane with 10 to 14 carbon atoms consisted, with a concentration of ethylenediamine in water of 90 percent by volume and the copper catalyst of Example 1 in a molar ratio of 1: 4

were applied to the nitroalkane. The reductions were carried out at 85 to 90 ^° C. under CO pressures of 0 to 70 atmospheres. After 4 hours, the reaction mixtures were cooled and the degree of conversion to the desired oxime was analyzed by gas chromatography. As the following tables show, pressures above 17.6 atmospheres reduce the rate of conversion.

Table IV Reactor type Catalysis Concentrated Ethylene Tempe pressure Reak Nitro example sator diamine solution rature ions alkane-um No. Concentration Time wandlunü tration (Ge
weight (Volume percentage) (C) (Hours.) (%) percent)*) Glass 10 90% in water 85 1 atm CO 4th 49.6 41 Stirred autoclave IG 90% in water 90 17.6 atmospheres CO 4th 51.5 42 Stirred autoclave 10 90% in water 90 35.2 atmospheres CO 4th 33.8 43 Shaking autoclave 10 90% in water 85 14.1 atmospheres CO 4th 46.9 44 Shaking autoclave 10 90% in water 85 35.2 atmospheres CO 4th "8.1 45 Shaking autoclave 10 90% in water 85 70.3 atmospheres CO 4th 37.0 46 *)! Weight volume).

Example 47

Modification of the composition of the copper salt

In these experiments, the nitrided n-dodecane substrate of Example 1 was used under the same reaction conditions and reduced using equal amounts of amine, water and copper salts. The only difference in all three experiments was the replacement of the copper acetate with the equal amount by weight of copper (I) chloride, copper (II) sulfate and copper (II) chloride. Fraud in all cases the degree of conversion to oxime 50% within 2 hours and 90% after 10 hours.

15th

Example 48

Reduction of nitrocyclohexane too

Cyclohexanone oxime

Following the procedure described in Example 1, 1 part by weight of nitrocyclohexane was added to a reactor mixed with 1 part by weight of copper acetate, 1 part by weight of water and 9 parts by weight of ethylenediamine. CO was passed into the reaction mixture at atmospheric pressure and the reaction mixture heated with stirring to 100 ° C. for 3 hours, during which time a 90% conversion to cyclohexanone oxime occurred. After cooling, the oxime was removed from the reaction mixture twice with 5 parts by weight of benzene extracted and gave a deep red extract. Upon vacuum distillation, the oxime was in shape white crystals obtained. Through elemental analysis, IR, NMR spectra and gas chromatography the structure of the desired product was ensured.

This product could be converted quantitatively into caprolactam, an intermediate product, by acid hydrolysis for the technical production of nylon-6.

Example 49

Reduction of C ₁₀ -C ₁₄ -nitro-n-alkanes in
C ₁₀ -C _M n -alkanone oximes

One part by weight of a mixture consisting of 15 _{parts by weight of C 10} -C ₁₄ nitroalkanes, 3 parts by weight of oxidation products and 82 _{parts by weight of C 10} -C ^ paraffins and by vapor-liquid phase nitration of C ₁₀ -C ^ n-alkanes with NO ₂ obtained was placed in a reactor. which was provided with heating, cooling, distilling and stirring devices, together with 0.15 parts by weight of copper acetate, 0.1 parts by weight of water and 1.2 parts by weight of ethylenediamine, then the resulting reaction mixture was flushed with CO until a CO atmosphere had set. The reaction mixture was kept with stirring for 2 hours at 105 ^° C. and then cooled, whereupon it separated into a lighter organic phase and a blue aqueous phase. The organic phase was separated off, washed with excess water and distilled in vacuo, the alkanone oximes being obtained in 90% yield. As confirmed by IR, NMR spectra, elemental analysis and gas chromatography.

Example 50

Reduction of C ₁₆ -C ₂₀ nitroalkanone to
C ₁₆ -Cjo-alkanone oximes

According to the method described in Example 49, a batch of 0.3 _{parts by weight of nitrated C 16} -C ₂ one-alkanes containing 25% by weight of C ₁₆ -C ₂₀ -nitroalkanes in 75% by weight of C ₁₆ -C ₂₀ -n-alkanes was used . The reduction was carried out at atmospheric pressure with heating to 90 ^° C. and stirring for 48 hours; a conversion of 70% was obtained. In the vacuum distillation (0.4 to 1.5 mm pressure) a purified oxime product was obtained, whose elemental analysis, gas chromatography, IR and NMR values confirmed that it was the desired product.

Example 51

Reduction of C ₁₄

C ₁₄ -C ₁₅ n-alkanone oximes

C ₁₅ -n-nitroalkanes to

According to the method described in Example 1, a batch of 10 _{parts by weight of nitrated C 14} -C ₁₅ -n-alkanes containing 25 percent by weight of C ₁₄ -C ₁₅ -nitroalkanes was introduced into the reactor described in Example 49. The crude, acidic nitriding mixture was obtained by vapor-liquid-phase nitration of C ₁₄ -C ₁₅ -n-alkanes with NO ₂ .

The catalyst consisted of 0.6 parts by weight of copper acetate, 10 parts by weight of ethylenediamine and 1 part by weight of water. The reduction was carried out in a CO atmosphere. It was heated for 2 hours at 100 ^° C. and atmospheric pressure. As confirmed by the IR, gas chromatography and NMR analyzes, C ₁₄ -C ₁₅ alkanone oxime was obtained in a yield of 97%.

40 Example 52
Reduction of nitrodecane to its oxime

Following the procedure of Example 1, a batch of 5 parts by weight of copper acetate was made. 90 parts by weight Ethylenediamine and 10 parts by weight of water stirred vigorously and saturated with CO. To the The deep blue solution obtained was added with vigorous stirring 10.5 parts by weight of nitrodecane. The reaction mixture was heated to 85 ° C. for 5 hours, cooled and extracted with diethyl ether. The ether extract was distilled under a vacuum of 5 mm and left a reddish color Residue, the IR and NMR values of which confirmed the expected oxime structure.

55 Example 53
Reduction of other nitroalkanes

Using the same amounts of copper acetate, ethylenediamine and water were after dei Procedure of Example 1 10 parts by weight of Nitrc propane and nitrobutane selective to the corresponding Oximes reduced after the stirred reaction:

mixture was saturated with CO. In both companies Temperatures of 85 ° C. were used and the reduction lasted 8 hours. The identity di Oxime product was again detected by IR and NMR spectra.

Claims (4)

Patent claims: 1. A process for the preparation of alkanone or cycloalkanone oximes by partial reduction of nitroalkanes or nitrocycloalkane [s] with carbon monoxide, characterized in that one, at least 3 carbon atoms containing nitroalkane or nitrocydoalkanfen] in a carbon monoxide atmosphere at 60 to 150 ° C and 0 to 17.6 atmospheres in the presence of an aqueous, 0.5 to 20 percent by weight of a dissolved copper salt containing at least 60 percent by weight solution of an aliphatic amine having a pK _a value of at least 9.5. 2. The method according to claim 1, characterized in that the nitroalkane or nitrocycloalkane [s] reacted dissolved in an inert diluent. 3. The method according to claim 1 or 2, characterized in that the salt is used as the copper salt a weak acid and ethylenediamine as an aliphatic amine. 4. The method according to any one of claims 1 to 3, characterized in that there is a mixture of nitroalkanes with 10 to 20 carbon atoms is used.