DE2052167C3 - Process for the production of the purified ammonium salt of 11-cyanundecanoic acid or the pure free 11-cyanundecanoic acid - Google Patents

Description

The invention relates to a process for the preparation of the purified ammonium salt of 11-cyanundecanoic acid or the pure free 11-cyanundecanoic acid.

11 -Cyanundecanoic acid is a valuable compound which can be used in the preparation of polymers, e.g. B. by hydrogenation of 11 cyanundecanoic acid to 12-aminododecanoic acid, from which the C ₁ , polyamide can be prepared.

It is very desirable that compounds used in the manufacture of polymers are in as pure a condition as possible. Any treatment that leads to greater purity, is valuable. Belgian patent specification 702603 a process for the production of 11-cyntindecanoic acid by pyrolysis of 1,1 'peroxydicyck)! ic \) lamin. the production of which is described in the domestic patent specification 701327. The pyrolysis is preferably carried out at a temperature of 300 to 1000 ° C. in the vapor phase.

The content of the 11-cyanundecanoic acid in the pyrolysis product can vary depending on the temperature and residence time used in the pyrolysis reaction. The pyrolysis product can also contain caprolactam and cyclohexanone and these are mostly removed before the 11-cyanundecanoic acid is recovered from the resulting product or before the pyrolysis product is sent to a further reaction. Even if the cyclohexanone is removed, however, the product obtained may only contain 50% (50%) and 80% 11-cyanundecanoic acid, e.g. only 70% by weight. The remainder of the reaction product consists of a large number of compounds, among which the larger proportions of C ₍₁ -saturated and unsaturated acids and nitriles, residual caprolactam, isomers of 11-cyanundecanoic acid and cyclic imides.

Other methods for the preparation of 1 1-Cyanundccansäurc can also lead to products with contents of I 1-cyanundecanoic acid together with bc-

lead to significant amounts of impurities.

DE-AS 1 261 845 describes a two-stage process for the separation of aliphatic ω-cyanocarboxylic acids described by the corresponding dicarboxylic acids. Here, the as possible anhydrous Mixture of the crude acids with ammonia first to precipitate the ammonium salts of the dicarboxylic acid at 35 to 110 ° C in an anhydrous organic Treated solvent, this ammonium salt is then filtered off while hot and the anhydrous mother liquor obtained cooled with precipitation of the ammonium salt of the ω-cyanocarboxylic acid. Compared to this previously known, two-stage process, the process according to the invention works with only one stage and

i ^r > requires the presence of water in the solvent, if this does not even consist entirely of water. The nature of the impurities present in the raw starting product in both cases is also different. The crude 11-cyanocarboxylic acid used in the process according to the invention contains branched-chain isomers together with caproic acid, but no dicarboxylic acids. As shown in the following comparative example, this previously known procedure provides below

2> Use of one in the method according to the invention used, no dicarboxylic acids containing starting material when using chloroform only a yield of 40% of the 11-cyanundecanoic acid initially used in the form of ammonium

JO salts, which, however, still contain 1.5% impurities contains, while in the process according to the invention a Ciewinnung of 83% of the original 11-cyanundecanoic acid used in the form of the ammonium salt with a purity of 99% is possible wherein the impurity consists of a small amount of the free 11-cyanundecanoic acid and the other impurities could not be detected.

The inventive method for production

■ in the purified ammonium salt of 11-cyanundecanoic acid or pure free 11-cyanundecanoic acid is characterized in that crude 11-cyanundecanoic acid dissolved in an aqueous ammonia-containing solvent, the ammonium salt of 11-Cy-

r> anundecanoic acid crystallized out by cooling the solution and separated, if desired recrystallized from aqueous ammonia, and optionally is converted into the free acid with acid in a manner known per se.

so the crystals can have some free 11-cyanundecanoic acid additionally contain / u the ammonium salt; however, they will always have a higher stake in that 11 -Cyanundccanoic acid component either as free acid or as ammonium salt contained as the crude

Vi acid. The extent of purification effected will depend on the conditions of the recrystallization. However, if the ammonium salt / is found to be insufficiently pure, it can be extracted from a suitable solvent, /. B. aqueous ammonia to

ho can be crystallized, or it can be with a non-polar Solvent washed. However, there can be increases in purity of 75% 11 -cyanundecanoic acid (based on the weight of 1 1-cyanundecanoic acid in the total weight of the crude in aqueous

i, ¹ ) ammonia dissolved product) to 98% by weight ammonium salt of 11-cyanundecanoic acid can be achieved by the process according to the invention.

The crude 11-cyanogen fed to the process

Decanoic acid can contain 60 to 80% by weight of 11-cyanundecanoic acid, and the crude 11-cyanundecanoic acid can also contain 5 to 15% C ₃ and C ₁₂ acids with imides and other impurities. The process according to the invention is particularly suitable for treating the product obtained by the above-mentioned pyrolysis of Ι, Γ-peroxydicyclohexylamine. Preferably a reaction product substantially free of cyclohexanone is used and this compound can be obtained from the product of the pyrolysis reaction by any conventional method, e.g. B. by distillation can be removed. The solvent in which the crude acid is dissolved can conveniently be aqueous ammonia. Chloroform saturated with water can also be used.

The ammonia can be introduced into the solvent before or after the crude 11 -cyanundecanoic acid is resolved. So the crude acid can be found in aqueous ammonia or in hydrous chloroform, in which ammonia is then introduced, can be dissolved.

When aqueous ammonia is used as the solvent for the crystallization, it is desirable to use the crude 11-cyanundecanoic acid with a water-immiscible, non-polar organic solvent, z. B. chloroform, before the crystallization is carried out to remove certain impurities, z. B. Caprolactam, which can be found in the crude 11-cyanundecanoic acid and which are not easily removed by the crystallization stage. This can be done by touching an aqueous ammonia-containing solution of 11-cyanundecanoic acid with the organic Solvent and then separating off the aqueous containing 11-cyanundecanoic acid Dissolution of the phase containing organic impurities take place. Washing with the organic Solvent can be carried out in any suitable apparatus. Suitable apparatus are well known to those skilled in the art of liquid-liquid extra ion.

The molar ratio of ammonia to total acids can be over a fairly wide range, e.g. B. 1: 1 to 40: 1, but preferably in the range 1: 1 to 10: 1.

The crude 11-cyanundecanoic acid is preferably dissolved in the aqueous ammonia at a temperature of K) dissolved up to 60 ° C. The use of room temperature or neighboring temperatures, e.g. B. 15 to 30.degree. C., in particular 20.degree. To 30.degree. C., is particularly expedient.

The concentration of the crude acid in the solvent can vary over a fairly wide range and will depend on the solvent used and the temperature at which the crude acid is dissolved. Examples of useful concentrations are those in the range from 5 to 50 % by weight. based on the weight of the solvent, in particular 10 to 20% by weight.

The crystallization of the ammonium salt of 11-cyanundecanoic acid is caused by cooling the solution. The required cooling is provided by the Depend on the amount of the crude product dissolved in a given amount of solvent. It was found a satisfactory amount of the ammonium salt in the Cooling down by no more than 10 ° C can be obtained. The solution can for example to 0 to 15 ° C, especially 3 to 10 ° C, are cooled, especially when the crude acid is at about the room temperature, d. i. 20 to 30 ° C.

The crystallized ammonium salt can from the

Mother liquor can be obtained by filtration or centrifugation.

The liquid from which the ammonium salt has crystallized can be recycled and used to get more amounts of crude 11-cyanundecanoic acid dissolve. It is therefore not necessary

ίο all of the ammonium salt from the aqueous ammonia solution to be obtained in a single crystallization. It may be desirable to use a portion of the filtrate discard if necessary to avoid the build-up of impurities in the solvent

after preventing a number of return lines. It may be desirable to use the crystals obtained to wash with a non-polar solvent to remove all neutral impurities, which might be present to remove. That

2 »ammonium salt obtained from the aqueous ammonia solution can in the usual way in 11-cyanundecanoic acid by treatment with sufficient acid, to replace all of the ammonium groups, transferred. However, if the next

2 ^r ) the stage is a hydrogenation to 12-aminododecanoic acid, it is not necessary to convert the ammonium salt into the free acid. Rather, the ammonium salt can be passed into the hydrogenation reaction without further treatment.

iii The invention is further illustrated by the following examples explained.

example 1

Crude 11 -cyanundecanoic acid (50 g) with a

Jj contains 84% by weight of 11-cyanundecanoic acid, 5 % By weight of isomeric compounds and 1.1% by weight of C ,, acids, was found at room temperature (approx. 23 ° C) in an aqueous ammonia solution (200 ml), prepared by adding water to ammonia (a aqueous solution of ammonia with a relative density of 0.880) (43.6 g), dissolved. The solution to the crude acid was cooled to 8 ° C, the crystals formed on cooling were filtered off, diluted with 22 ml aqueous ammonia washed and

4 ¹ J dries. The resulting product contained 89% by weight of the 11-cyanundecanoic acid originally present in the crude acid in the form of the ammonium salt along with a small amount of free acid and was free of others

j »acids.

Example 2

Crude 11-cyanundecanoic acid (50 g) was added to Room temperature dissolved in the filtrate, which in

> ■> Example 1 was obtained after the crystals were filtered off had been. When cooling to 8 ° C, filtering off, washing and drying as in Example 1, 42% by weight of the 11-cyanoundecanoic acid was obtained from the amount of crude acid added in the form

bo of the ammonium salt and a little free acid obtained.

Example 3

Crude 11-cyanundecanoic acid (250 g) with a hi content of 67 wt .-% 11-cyanundecanoic acid, TYc isomeric compounds, 1.6% C ₆ acids and 12% caprolactam was at room temperature in a mixture of ammonia (aqueous solution of Ammo

nial. with a relative density of 0.880} (233 g) and Water MISOl ') dissolved. The solution was at 4 ° C chilled. The crystals formed were filtered off Washed and dried with aqueous ammonia (50 g). 148 g of ammonium-11-cyanundecanoate were obtained of 99% purity. The filtrate including the washing liquid was brought to room temperature warmed up and used to make another 213g dissolve crude 11-cyanundecanoic acid. The solution was cooled to 4 ° C and the crystals formed were filtered off, washed with aqueous ammonia (40 g) and dried. There were 154 grams of aramonium-11 canundecanoate obtained of 97% purity.

Example 4

Crude 11-cyanundecanoic acid (375 g), of the same Composition like that used in Example 3 was made at room temperature in a mixture of Ammonia (aqueous solution of ammonia with a relative density of 0.880) (350 g) and water (1771 g) solved. The solution was a like Weight of chloroform using a rotating disc contactor (5 cm diameter and 36 plates), which removed 80% of the caprolactam from the aqueous phase. The washed one Solution was cooled to 4 ° C and the crystals formed were filtered off with aqueous Ammonia (70 g) washed and dried. They yielded 231g of ammonium 11-cyanundecanoate of 99% purity. The filtrate including the washing liquid was warmed to room temperature and used to dissolve another 320 g of crude 11-cyanundecanoic acid. The solution was a like Weight of chloroform washed using a rotating disc contactor which is 90% of the caprolactam removed from the aqueous phase and cooled to 4 ° C. The obtained crystals were filtered off, washed with aqueous ammonia (70 g) and dried to give 189 g of ammonium 11-cyanundecanoate of 99% purity. The procedure was repeated twice with additional batches of raw material and yielded additional quantities of ammonium salt of 99% purity.

Comparative example
Operation according to DE-AS 1261845

Crude 11-cyanundecanoic acid (20.1g), the 71st W / w% 11-cyanundecanoic acid, 5.6% isomeric cyanic acids, 10% caprolactam, 1.1% hexane and Hexenecarboxylic acids containing 5% dibutyl succinimide and approximately 7% water was dissolved in 700 ml of chloroform solved. The water was removed in the form of its azeotrope with chloroform and the solution cooled to ambient temperature and saturated with ammonia. The saturated solution was on Cooled 10 ° C, and the obtained crystals became filtered off and dried. Of the 11-cyanundecanoic acid originally used, only 40% obtained in the form of crystals of the ammonium salt, but still 1.2% hexanecarboxylic acid and containing hexene carboxylic acid, 0.2% caprolactam and 0.1% dibutyl succinimide.

In contrast, the purity of the ammonium salt of 11-cyanundecanoic acid, which corresponds to

accordingly the procedure of Example 3 was purified, 99%, with about 83% of the originally used 11-cyanundecanoic acid was recovered. The purified ammonium salt obtained according to Example 3 Contains a small amount of free 11-cyanundecanoic acid as an impurity.

Claims (3)

Patent claims: 1. Process for the preparation of the purified ammonium salt of 11-cyanundecanoic acid or pure free 11-cyanundecanoic acid, characterized in that crude 11-cyanundecanoic acid Dissolved in an aqueous ammonia-containing solvent, the ammonium salt of 11-cyanundecanoic acid by cooling the Solution crystallized out and separated, if desired recrystallized from aqueous ammonia and optionally converted into the free acid with acid in a manner known per se will. 2. The method according to claim I _1, characterized in that a mixture of water and chloroform is used as the solvent for the crude 11-cyanundecanoic acid. 3. The method according to any one of claims I or 2, characterized in that the molar ratio of ammonia to the total acids in the solvent is in the range from 1: 1 to 10: 1.