DE2335937A1 - Purificn of crude N-paraffinone oximes - by reaction with ahydrous base to decompose impurities, inters for lubricants and caprolactam - Google Patents

Abstract

Impure oxime (paraffinone oxime from photolytic nitrosation of 5-30C n-paraffins) contg. large amts. of carbonyl and chlorinated impurities is purified by (1) treating it at 25-200 degrees C with 1-20 wt.% of anhydrous basic reagents to decompose impurities and (2) distilling the oxime under moderate vacuum in a thin film evaporator. The base is an alkaline earth metal oxide or alkali(ne earth) metal carbonate.

Description

Patent assessor Hamburg, July 6, 1973

Dr. Gerhard Schupfner Deutsche Texaco AG

2000 Hamburg 76 T 73066 (D "71,393-F)

.Sexlingsport 2 547 / HH

TEXACO DEVELOPMENT CORPORATION

135-East 42nd Street New York, N.Y. 10017

UNITED STATES.

Process for purifying crude oximes

The invention relates to a process for the purification of crude oximes by substantial amounts of carbonyl and / or Chlorine compounds are contaminated. A special embodiment the invention is due to the exemption of one photolytic nitrosation obtained crude oxime of essential Amounts of carbonyl compounds and organic chlorine compounds directed.

Oximes are used as organic intermediates · and for numerous other compounds useful for utilities. So let them

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i,

rearrange, for example, according to Beckmann, can be alkoxylated and hydrogenated, are used as additives to lubricants and Suitable for anti-freeze agents and some oximes can be converted into synthetic fibers (e.g. cyclohexanone oxime can hydrolyzed to caprolactam, which is an intermediate in the manufacture of polyamide 6).

Paraffin oximes have been produced by the catalytic Conversion of ketones with hydroxylamine salts, and more recently by the photolytic nitrosation of normal paraffins. In both syntheses, a crude product is obtained which has substantial amounts of impurities, which boil near the boiling point of the oxime or the boiling points of the impurities overlap with that of the oxime Oxims. Most of the impurities encountered in these processes are aldehydes or ketones (which are used herein generally referred to as carbony compounds), while in the photolytic process crystalline (like) nitroso-chlorides and hydrochloride condensation products as well

Can cause separation difficulties. In any case, the usual distillation with preceding or following extraction has failed in the production of high purity products (ie degree of purity of 98 % or above).

The invention is based on the object of providing a process for the purification of crude oximes that contain substantial amounts of carbonyl and contain organic chlorine compounds as impurities. In particular, a simple

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drive to the purification of crude oximes, which have been obtained by photolytic nitrosation of η-paraffins - for example according to the process described in the applicant's German patent application ρ 21 15 049 - which contain substantial amounts of carbonyl and / or organic chlorine compounds as impurities contain, be created. The method should be applicable to products with an oxime content of 95 % and below and lead to products with an oxime content of 98 % and above. It should work as economically as possible, no special skilled workers should be required to carry it out, and it should be possible to carry out it with a commercially available device.

The object is, generally speaking, by a method of purifying crude oximes containing substantial amounts of carbonyl compounds and inorganic chlorine compounds are contaminated, dissolved, which is characterized by

the
that / crude oxime is treated in a step (a) with 1-20% by weight, based on the oxime content, of a largely anhydrous basic reagent until the impurities are decomposed, and in a step (b) the treated oximes are below be separated under a weak vacuum.

The process according to the invention thus produces crude oximes, which contain substantial amounts of carbonyl and organic chlorine compounds as impurities contained, purified «More precisely, those containing these impurities are purified raw oxime treated so that the impurities largely

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be decomposed. According to a particular embodiment of the invention, a crude oxime product with an oxime content of 95 % or below and the remainder carbonyl compounds and organic chlorine compounds is converted into a highly purified oxime product with an oxime content of 98 % and above, which is largely free of carbonyl and chlorine compounds. Connections is.

The practice of the invention will now be described in more detail.

In practicing the invention, an oxime, however prepared, will be which with essential Amounts of carbonyl and / or organic chlorine compounds is contaminated with an alkaline reagent treated until the impurities are decomposed. Thereafter the purified oxime is separated from the decomposed impurities.

In a preferred embodiment of the invention, a paraffinic oxime, which is made from a mixture of paraffins having 5 to 30 or more carbon atoms, has an oxime content of 95 % or less and contains a substantial amount of carbonyl compounds and organic chlorine compounds as impurities treated with anhydrous basic reagents at room temperature or elevated temperature until the impurities are decomposed; thereafter, the oxime is separated from the decomposed impurities by molecular distillation to largely remove one of the impurities

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to get free oxine.

According to a "particularly" preferred embodiment of the invention, a crude oxime which has been obtained by photolytic nitrosation of η-paraffins having 10 to 15 carbon atoms has an oxime content of 95 % or below and up to 5 % or more carbonyl and organic chlorine compounds as impurities, first with 1 to 20 wt -. (based on the Oximgehalt)% of what serfreien basic reagent selected from the group consisting of alkali metal and alkaline earth metal carbonates and oxides, wherein etv Treated / a atmospheric pressure and a temperature of about 85 to 125 ⁰ C for 2 to 6 hours until the impurities are largely decomposed. An inert solvent is then added with the base-treated oxime in order to facilitate the separation of the oxime (by filtration or the like); then the oxime is separated from the solids

the

and under the conditions for molecular distillation / sufficient, an increase in the concentration of carbonyl and chlorine compounds to prevent distilled off.

A. The Paraffinone Oximes Any Suitable For The Practice Of The Invention Oxime, especially paraffinic oxime, at least Containing 5 to 50 or more carbon atoms can be used as feedstock can be used as long as they contain substantial amounts of carbonyl and / or organic chlorine compounds contained as impurities. Cheap oximes are the linear and cyclic crude oximes, such as: the hexanone oximes, the cyclohexanone oximes, the heptanone oximes ^

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the octanone oximes, the nonanonoximes, the decanonoximes, the Undecanonoxime, the dodecanonoxime, their higher homologues and / or mixtures thereof.

The preferred oximes are crude cyclohexanone oximes and the paraffinone oximes having 10 to 15 carbon atoms and an oxime content of 95 % or less. They can be in the form of the relatively dry, crude, individual oxime, free of inert solvents, or as a mixture of oximes with 10 to 15 carbon atoms, either largely free of solvents or containing up to 25% by weight of inert solvents. The group of oximes with 10 to 15 carbon atoms, whether solvent-free or not, is preferred because they can be obtained in large quantities from the nitrosation of the corresponding paraffins according to the German patent application P 21 15 049 mentioned at the beginning,

B. Appropriate Bases - The basic substances used in the New treatment used in accordance with this invention are the anhydrous oxides, hydroxides, and carbonates Alcoholates, preferably of the elements of groups 1A and 2A of the periodic table. Examples of such bases are:

Calcium oxide, magnesium oxide, sodium carbonate, potassium carbonate, lithium carbonate, sodium hydroxide, potassium hydroxide, Sodium methoxide, sodium ethoxide, potassium methoxide, potassium ethoxide and the same.

The preferred basic reagents are the anhydrous oxides and carbonates of the alkaline earth metals and the water-

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free carbonates of the alkali metals. These basic reagents are used in amounts of 1 to 20% by weight, preferably up to 10% by weight, based on the oxime content, is used.

C. Reaction conditions:

1. Temperature - The reaction temperatures required for the process according to the invention are relatively flexible and are in the range from about 25 to 200 ^° C. Since the best results are obtained in the temperature range from about 85 to 125 ^° C., this represents the preferred temperature range,

2. Pressure - Atmospheric or near atmospheric pressure is commonly used. There are no visible ones Benefits result from the application of positive or negative pressure, and the maintenance of such Printing is costly, atmospheric pressure is preferred.

3. Response time - The response time varies with the Reaction temperature and the concentration of the base used, as well as the size of the batch that is treated will. For these reasons, the response time cannot be precisely defined. However, under most conditions the reaction is within 0.1 to Completed 12 hours of treatment, longer periods being not harmful. Under the more common reaction conditions the reaction is complete within 2 to 6 hours. '

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4. Separation of the solids - The separation of the solid materials can be carried out by adding one or more inert solvent to be facilitated to the reaction mixture. Usually the inert solvent is im Following the treatment of the oximes with basic material added to the removal of the pesticides (by filtration, centrifugation, etc.) to facilitate. If inert solvent is added at this point any alkane, cycloalkane, arylalkane, aromatic hydrocarbon, alcohol or ketone can be used, which is the basic Material does not dissolve significantly. The preferred solvents are alkanes, cycloalkanes, alcohols with 5 to 10 C atoms and ketones with 3 to 8 C atoms. Acetone is the preferred inert solvent when used immediately is added after treatment with a base. If desired, the inert solvent before To add treatment to the base, only hydrocarbons, such as alkanes, cycloalkanes, arylalkanes or aromatic hydrocarbons are used. In each pail the inert solvent should be used before the Distillation can be removed under high vacuum.

D. Process Conditions - As described above, based this invention based on the discovery that the oxime content of the crude oximes by a corresponding reduction in Carbonyl compounds and the organic chlorine compounds by treating the crude oxime with certain water

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free or largely anhydrous basic substances can be increased significantly. This is particularly true for crude oximes with an oxime content of 95 % or below, which originate from the photolytic nitrosation of the corresponding η-paraffins. The treatment according to the invention leads to an increase in the oxime content to 98 % or above with a content of impurities from carbonyl and organic chlorine compounds of less than 2 % _t together and this is completely surprising this increase in the degree of purity and this decrease in the Impurities cannot be maintained if the separation of the oxime from the impurities is carried out using conventional vacuum distillation, even at pressures as low as 0.4 to 2 mm Hg. However, when the purified, treated, and filtered oxime product is distilled using molecular distillation techniques such as continuous film vacuum distillation (CPD), the purity and amount of impurities remain largely unchanged. For this reason, the method according to the invention is preferably carried out as follows:

1. Bringing the neutralized crude oxime into contact with an oxime content of 95 % or below with 5 to 10 % by weight of anhydrous basic reagent (based on the oxime

content), selected from the group consisting of earth metal oxides alkali metal and alkali metal carbonates and alkaline earth /

2 to 6 hours at 8.5 to 125 Qy ⁰ "to the above-

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largely decompose the described impurities,

2. Adding inert solvents and separating the solid material by filtration, centrifugation and the like., removal of the inert solvent,

3. Subject the clarified mixture of Oxira and decompose Contaminants of thin film vacuum distillation under conditions sufficient that the Content of the contaminating carbonyl and organic chlorine compounds remains unchanged.

E. Sufficiently weak vacuum - As described above, is followed by the alkaline treatment of the neutralized crude oxime, preferably a distillation connected under vacuum to maintain the high purity of the treated oxime. Under sufficient Low vacuum means that the distillations are carried out at less than 1 mm Hg. Although not special type of vacuum distillation is required particularly good results have been obtained using molecular distillation methods and are therefore these methods are preferred. Molecular distillations like them Applied here are those in which the vapor path of the molecules being distilled is not obstructed and wherein the cooler of the device is separated from the evaporation and at a distance therefrom which is smaller than the mean free path of the evaporating, emerging molecules. Although molecular distillation methods are used gladly applied as it is often

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the pall eats where a broad class is employed, but for one reason or another becomes a more specific one Method preferred within this broad class. In the present case, a distillation in a pot-like Molecular still preferred because of the low content of ter-impurities in the treated Oxime remains essentially unchanged. These types of distillation can be carried out in a variety of devices in the Vacuum range from 0.001 to 0.0001 mm Hg can be performed. With two types of commercially available molecular stills One of the widespread uses is centrifugal or thin film (or falling film) method of application. Other publications include exemplary stills in the each in the Chemical Engineering Handbook by Perry, Chilton, and Kirkpatrick, 4th Edition, published by McGraw Hill Inc., New York, N.Y., Chapter 17, pages 29 to 32, - described.

After the inventive method in general has been described, the following examples and embodiments are provided to illustrate the invention in greater detail and its practical implementation.

Embodiment A - Preparation of a crude mixed Cj ₀ to Cj 3 - Paraffin oxime j which contains substantial amounts of carbonyl compounds as impurities.

One serving of 22.981 kg of mixed G _4n to C _1x n-paraffins

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was placed in a photoreactor equipped with heating and cooling devices and means for controlling a light source excluding wavelengths below 200 µm (millimicrons). The paraffin mixture was reacted with excess gaseous nitrosyl chloride at 15.6 ^° C. in the presence of gaseous hydrogen chloride at flow rates of 1.64 grams per minute and 0.95 grams per minute, respectively. After the crude oxiric acid salt had been separated off, the acid was neutralized with aqueous ammonia and the crude C ₁₀ -C 1 -oxime mixture was separated off. The molar selectivity of the crude oxime was 87.4 % with an overall recovery of 90.7% by weight oxime. The crude oxime contained about 2% by weight Cj ₀ to C ^ ketones.

Example 1 - Attempt to purify neutralized crude Cj ₀ to C ^ n paraffinone oxime, using the usual vacuum distillation.

An 800 gram sample of crude Cj ₀ to C .., n-paraffinone oxime, which was prepared according to embodiment A and contained 4.3 wt .-% ketones and 0.41 wt .-% chlorine, was vacuum at 0 , 4 to 0.6 mm Hg fractionated on a 45 »72 cm Hempel column, which was filled with 6.35 mm packing made of stainless steel, in the presence of 100.0 grams of hydrocarbon with a boiling point of 371 ^° C. The results obtained are summarized in the following table:

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Group No. 1 2 3 4 5 6 7

Boiling point, ° C 100 110 108 108 112 120 130

Pressure, mm Hg 0.5 0.6 0.4 0.4 0.4 0.5 0.6

Weight, g 6.0 74.0 164.1 204.3 101.2 37.0 58.2

Wt% ketones

in the group> 50> 19> 13 > 9> 13? 19.5

Like the increase in ketones (increase to over 175 wt%) shows, the degree of purity of the oxime is determined by the usual vacuum distillation without treatment with basic reagents worsened. The distillation product looks cloudy.

Example 2 - Attempt to purify a crude Cj ₀ to C ~ n-paraffinone oxime mixture using thin film distillation without prior treatment with a base.

A 90 gram serving of raw Cj ₀ to C ..., paraffinone oxime, prepared according to embodiment A, containing 3.6% by weight of 6 ketones and 1.15 % by weight of chlorine, was placed in a 5 , 08 mm Rodney Hunt Yaca-Pilm Processor from Rodney Hunt Machine Co. and heated to 100 to 105 ° C at 0.3 mm Hg. 67.0 grams of a pale oxime distillate were obtained which contained 2.6% by weight of ketones and 0.93% by weight of chlorine. The product had an undesirable hazy appearance.

This example shows that thin-film distillation can be carried out without the previous alkaline treatment according to the invention

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is not an effective means, carbonyls and the organic chlorine compounds largely from the neutralized crude Remove oxime.

Example 3 Significant reduction in the carbonyl and organic chlorine compounds which _{contain crude mixtures of C 10 to} Ο ... paraffin oximes as impurities, using a preferred embodiment of the process according to the invention with anhydrous calcium oxide as the basic reagent.

A 500-gram mixture of C ^ C ^ ₀ ~ to -Paraffinonoximen prepared according to embodiment A, containing 2.0 wt -.% Containing ketones and 0.51 wt .-% of chlorine, was thoroughly mixed with 100 grams of anhydrous calcium oxide and heated ^{to 100 °} C. in a reaction vessel for 2 hours. After vacuum filtration, the 435 grams of oximes contained less than 0.5 weight percent 6 ketones and 0.42 weight percent organic chlorine compounds. This substantial reduction in impurities is exemplary of the effectiveness of the treatment according to the invention with basic reagents.

The calcium oxide-treated Oximgemisch was subjected to thin film distillation at 98 to 10O ⁰ C and 0.4 mm Hg in said distillation apparatus in Example 2. A pale colored oxime mixture (69 grams) containing less than 0.5 wt% ketone and 0.23 wt% chlorine was recovered.

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This example shows the effectiveness of this preferred ' Execution form of the process according to the invention and the Use of alkaline earth metal oxides as a basic reagent with regard to a substantial reduction in the level of impurities. '

The same results were obtained using molecular distillation obtained according to the centrifugal principle.

Example 4 - Substantial Reduction in Carbonyl and Organic Chlorine Impurities Using the Inventive Procedure in which anhydrous sodium carbonate is used as the basic reagent:

A 500 gram serving of crude C ^ ₀ to Cj, n-paraffinone oxime prepared according to embodiment A and containing 2.3% by weight of ketones and 0.93% by weight of chlorine was carefully mixed with 100% Mixed grams of anhydrous sodium carbonate and ^{heated to 100 °} C. for 2 hours. The purified oxime (406.5 grams), which was obtained by vacuum filtration, containing less than 1 wt .-% ketones and 0.78 wt -.% Organic chlorine.

After thin-film distillation in the still mentioned in Examples 2 and 3 at 100 to 105 ⁰ C and 0.15 to 0.35 mm Hg, a light colored oxime (307.6 grams) was obtained,

Wt. # That had less than 1 wt. # Of ketone and 0.41 / chlorine.

This example shows the anhydrous alkali metal carbonate

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are effective basic treatment reagents.

Example 5 - Substantial Reduction in Carbonyl and organic chlorine compounds when using a preferred embodiment of the process according to the invention which an inert solvent is used.

A 500 gram portion of a neutralized crude C ₁₀ to Ο .._ oxime mixture, prepared according to embodiment A, which contained 2.3% by weight of ketone and 0.93% by weight of chlorine, was mixed with 25 grams of anhydrous calcium oxide and heated to 100 ^° C. for 2 hours. After cooling, the reaction mixture was diluted with 1300 grams of mixed heptanes and washed three times with equal volumes of water. The solution was filtered and the heptanes stripped in vacuo. An oxime product (376 grams) was obtained that was substantially free of ketones.

A 6.8 gramin-7 serving of the treated oxime was in a Thin film still distilled at 100 to 125 ° C and 0.25 mm Hg, producing a pale colored oxime, the was largely free of ketones was obtained.

This example shows the application of the preferred embodiment of the process according to the invention in the presence of large amounts of inert solvent.

Example 6 - Example 5 was repeated, except that the reaction mixture with inert solvent before filtration

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has been diluted.

The procedure of Example 5 was repeated, except that 25 grams of sodium carbonate was _{mixed with 500 grams of the same crude Cj 0} to C «oxime and 1 liter of the heptanes was added prior to filtration. The initial ketone concentration of 2.3% by weight was reduced to less than 1% by weight and the initial chlorine concentration was reduced from 0.93% by weight to 0.55% by weight. In the thin film distillation of 341.9 grams at 100 to 105 ⁰ C and 0.2 to 0.3 mm Hg in the still used in the preceding examples, a pale oxime (298.4 grams) which was less than 1 wt % Ketones and 0.42% by weight chlorine was obtained. .

Example 7 - Example 6 was repeated, but below. Use of cyclohexane as an inert solvent before Filtration:

In this example, 500 grams of the neutralized C ^ ₀ to Cj, Oximgemisches were the example with 25 grams of anhydrous sodium carbonate for 3 hours at 100 ⁰ C heated. 5 After cooling, as in Example 5, the reaction mixture was diluted with one liter of cyclohexane and filtered. The solvent was stripped under vacuum leaving an oxime product (417 grams) containing less than 1 wt.% Ketone (original ketone content 2-3 wt.%) And 0.51 wt.% Chlorine (original chlorine concentration 0.93 % By weight). The stripped oxime was used in the above-mentioned thin-layer film

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Distillation apparatus at 100 to 105 ° C and 0.2 to 0.33 mm Eg distilled, 220.9 grams of distillate were obtained which contained less than 1 wt .-% ketone.

Example 8 - Example 7 was repeated using of acetone as an inert diluent.

In this example, 500 grams of a crude neutralized mixture of C ₁₀ to C ₁₅ n-paraffinone oximes containing 2.6 wt. % Ketone and 1.05 wt ⁰ C heated. The mixture was diluted with one liter of acetone, filtered, stripped, the acetone under vacuum and 428 grams of a treated product was obtained containing less than 1 wt -.% Ketones and 0.91 wt -.% Contained organic chlorine.

A 158.8 gram portion of the treated Oximgemisches was using the thin film distillation apparatus described above at 95 and 115 ⁰ C and 0.05 to 0.1 mm Hg distilled to give a slightly colored oxime obtained (139.3 grams) which contained less than 1.0 wt% ketones and 0.80 wt% chlorine.

Example 9 - Fractional distillation in vacuo of the alkali-treated oxime mixture of Example 8 _ψ

A 210 gram serving of the filtered, alkaline treated

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1 2 3 105 118 137 1.35 1.65 1.55 9.0 144.5 32.5 20th 1.0 8.4

Oxiragemisch.es, prepared according to Example 8, was in the in The device described in Example 1 was fractionated, the following results being obtained:

Fraction No. Boiling point, ⁰ C pressure, mm Hg weight, g.

Ketones in the fraction, wt .- #

The above data show that with conventional vacuum distillation an alkaline, treated oxime batch with reduced ketone and chlorine content not only the previously obtained

does not reduce the impurities / remains, but actually compared the impurities to over $ 184 wt with the alkaline treated oxime, increase. This shows that both the alkaline treatment and one are necessary Heat-sensitive separation stage.

Embodiment B - Preparation of a particular oxime that Contains substantial amounts of carbonyl compounds as impurities.

Using the general method described in Sedgwick, Organic Chemistry of Nitrogen, pp. 169-175, 1937 Edition, 1.2 moles of diethyl ketone were mixed with an aqueous solution of one mole of hydroxylamine at room temperature

NOH reacted to 0.8 mol of diethyl ketoxime _{CH CH} g _{CH CH f} the with

3.5% diethyl ketone is contaminated.

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Example 10 - Purification of a particular paraffin oxide containing substantial amounts of carbonyl compounds as an impurity contains.

0.8 mol of diethyl ketoxime, prepared according to embodiment B, was. carefully mixed with 10 grams of anhydrous calcium oxide and heated to 105 ° C for 4 hours. The reaction mixture was filtered and it was found that less than 1 wt .-? 6 ketone enthielt.'Nach thin film distillation at 90 to 110 ⁰ C and 0.5 to 0.6 mm Hg was the concentration of ketone to 1 wt. -%. This example shows:

1. that the process according to the invention works even more favorably if, instead of raw oxime mixtures, raw specific oximes are used is applied, and

2. that the inventive method can also be applied to oximes that are not obtained by photolytic nitrosation have been.

As can be seen from the many examples, the method according to the invention has several advantages over the prior art. For example, the purification process according to the invention provides a way of purifying and working up crude oximes and their mixtures which contain substantial amounts of carbonyl and organic chlorine compounds as impurities . In addition, the process is simple and economical, and it is customary to carry it out xciie reagents are required. Furthermore fl ~ ° provides methods for the first time a practical, ej ~ --ohes mixture of C ^ to C ₅₀ oximes of

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To convert an initial oxime content of less than 95 % into a mixture, an oxime content of 98 % or above with a corresponding decrease in impurities.

The inventive method is not only the Significantly reduces the amount of carbonyl and chlorine impurities in the oxime; Surprisingly, too, is the order of the Critical level. That is, when a thin film distillation of the alkaline treatment is used in the method of the present invention precedes, a relatively small reduction in impurities is achieved. In contrast, thin film distillation is used (or an adequate separation process) after the alkaline treatment carried out, a permanent and substantial reduction in impurities is achieved. Another unexpected aspect of the invention is that if, following the alkaline treatment of the oxime, a normal vacuum distillation is carried out, even at a very low vacuum, i.e. a vacuum of 0.2 to 0.4 nm Hg, a substantial increase in contamination over that before Treatment amount is observed.

As shown above, the method according to the invention allows - except for the order of the levels - numerous modifications, substitutions and changes in the Reaction conditions, the type of base, etc., without departing from the scope of the invention.

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Claims (9)

^τ 73066 claims j 1, A method of purifying crude oximes with essential Amounts of carbonyl and organic chlorine compounds are contaminated, characterized that the crude oxime in a step (a) with 1 to 20 wt .-%, based on the oxime content, one largely anhydrous basic reagent is treated until the impurities are decomposed, and in a step (b) the oximes treated in this way are separated off under a weak vacuum. 2.) Process according to claim 1, characterized in that a paraffinone oxime is used as the crude oxime is used. 3.) The method according to claim 1 and 2, characterized in that one by photonitrosation from η-paraffins with 5-30 C-atoms obtained product is used as crude oxime. 4.) The method according to any one of the preceding claims, d a du χ ch characterized in that the after Step (a) treated oxime is freed from solid impurities by filtration in a step (c) and then the separation in step (b) is carried out at a pressure below 100 mm Hg. 409885 / U55 '- «τη 5.) Method according to claim 1, characterized in that a crude oxime obtained by photonitrosation of η-paraffins having 10 to 15 carbon atoms. is used, the treatment in step (a) with an anhydrous oxide of an alkaline earth metal or carbonate of an alkali or alkaline earth metal is carried out at a temperature between 25 and 200 ⁰ C and the oxime is separated in step (b) by thin film evaporation. 6.) Method according to claim 5 »characterized in that that between stages (a) and (b) stage (c), - separation of the solid impurities by filtration - made and the reaction mixture before step (c) inert solvent is added. 7.) The method according to claim 5 or 6, characterized in that step (a) at made at a temperature between 85 and 125 ° C will. 8.) Method according to one of the preceding claims, characterized in that calcium oxide or sodium carbonate is used as the anhydrous basic reagent. 9.) Method according to one of the preceding claims, characterized in that as crude oxime one is used which has an oxime content of 95 wt .-% or below. 409885/1455