Process for the amination of bromoalkanoic acids

Abstract

The present invention mainly relates to a process for the production of omega-aminoalkanoic acids of formula NH2-(CH2)n-COOH n by reacting the corresponding omega-bromoalkanoic acids with ammonia, wherein n is an integer from 9 to 11, which process comprises the following steps: i) reacting said omega-bromoalkanoic acids with an excess of aqueous ammonia solution, and ii) isolating the omega-aminoalkanoic acids formed from the reaction mixture, characterized in that the aqueous ammonia solution has a concentration of 35 to 70 wt.-%, and in that phase i) is carried out at a pressure higher than atmospheric pressure, at a pressure of 0.11 to 2.0 MPa absolute.

Description

TECHNICAL FIELD

[0001] The present patent application relates to a process for the aminolysis of omega-brominated alkanecarboxylic acids in order to prepare the corresponding omega-aminocarboxylic acids used as monomers for polyamides. BACKGROUND

[0002] The process for the aminolysis of omega-brominated alkanecarboxylic acids of formula Br-(CH2) n -COOH (n = 9-11) using ammonia to obtain omega-aminocarboxylic acids NH2-(CH2) n -CO2H is known.

[0003] Thus, the document FR 988 699 describes the reaction of 10-bromodecanoic acid with a 25% aqueous ammonia solution at 15°C for 6 days to form 10-aminodecanoic acid with a yield of 77%. This process exhibits the drawback of a very long reaction time.

[0004] Raising the temperature makes it possible to accelerate the reaction, but promotes side reactions.

[0005] Thus, in the document FR 928 265, it is reported that the reaction of 11-bromoundecanoic acid with a 25% aqueous ammonia solution is carried out at 60°C for 10 hours in a closed vessel and thus under autogenous pressure. The yield of this reaction is 53%, thus very low.

[0006] This is because, when the aminolysis is carried out, the secondary amine of formula HO2C-(CH2) n -NH-(CH2) n -CO2H is produced in particular in more or less large amounts. This impurity is troublesome when the omega-aminocarboxylic acid is used to manufacture polyamides, since it causes branching of the chains. Since this secondary amine reduces the yield and is difficult to separate from the desired primary amine, it is desirable to minimize its formation.

[0007] The patent application CN 103804209 B describes in example 3 the aminolysis of 11-bromoundecanoic acid with anhydrous ammonia in the presence of a solvent and a phase transfer catalyst, at a pressure of 0.1 to 0.15 MPa. This process makes it possible to reduce the reaction time to less than 24 hours, but operates in a very dilute medium and thus requires large industrial installations, and exhibits a yield of 84.3%, still quite modest.

[0008] The patent application EP 2 358 662 B1 proposes to reduce the reaction time of the aminolysis of 11-bromoundecanoic acid and the secondary reactions by carrying out the reaction with an elevated temperature profile, the reaction medium being subjected to a temperature increase by passing through a regular stationary phase between an initial temperature of 15-25°C and a final temperature of 26-40°C.

[0009] There is still a need for a technical solution that makes it possible to minimize the production of secondary amines while at the same time controlling the size of the device. SUMMARY

[0010] It is an object of the present invention to provide a solution to one or more of the above-mentioned problems.

[0011] This is because the present invention is based on the unexpected observation that increasing the titer of the aqueous ammonia solution to more than 35% by weight, in combination with increasing the pressure to more than atmospheric pressure, makes it possible to accelerate the reaction while at the same time controlling the amount of secondary amines produced, and thereby increasing the yield.

[0012] Thus, according to a first aspect, the subject of the present invention is a process for the preparation of an omega-aminoalkanoic acid of formula NH2-(CH2) n -COOH by reacting the corresponding bromoalkanoic acid with ammonia, wherein n is an integer from 9 to 11, comprising the following stages:

[0013] i) reacting an omega-bromoalkanoic acid with an excess of aqueous ammonia solution,

[0014] ii) isolating the omega-aminoalkanoic acid formed from the reaction mixture,

[0015] characterized in that the aqueous ammonia solution exhibits a concentration of between 35% and 70% by weight and that stage i) is carried out at a pressure greater than atmospheric pressure, of between 0.11 and 2.0 MPa absolute.

[0016] Preferably, stage i) is carried out at a temperature of between 0 and 60°C. It can be carried out at a constant temperature or at an elevated temperature. When it is carried out at an elevated temperature, stage i) can advantageously be carried out with an initial temperature ranging from 0 to 25°C and a final temperature ranging from 26 to 60°C.

[0017] Preferably, the aqueous ammonia solution exhibits a concentration of between 36% and 60% by weight, preferably between 38% and 45% by weight.

[0018] Advantageously, the weight ratio of omega-bromoalkanoic acid to aqueous ammonia solution at the start of stage i) is between 1 :3 and 1 :20.

[0019] Stage i) of the process according to the invention can in particular be carried out at a pressure of between 0.125 and 0.5 MPa absolute, or at a pressure of between 0.13 and 0.3 MPa absolute.

[0020] The process of the invention can be carried out in continuous or batch mode.

[0021] Advantageously, the process according to the invention additionally comprises a stage iii) of washing and discharging the omega-aminoalkanoic acid obtained at the end of stage ii).

[0022] The process according to the application can additionally comprise a step iv) of purifying the crude omega-aminoalkanoic acid obtained at the end of step ii) or iii), preferably by recrystallization from boiling water.

[0023] Furthermore, the process according to the application can comprise a stage v) of recovering the residual omega-aminoalkanoic acid in the various filtrates and aqueous washing liquids obtained in stages ii), iii) and / or iv), in particular by degassing of the ammonia, liquid-liquid extraction, crystallization, filtration and washing.

[0024] Finally, the process of the application can additionally comprise a stage vi) of drying the obtained omega-aminoalkanoic acid. DETAILED DESCRIPTION

[0025] Throughout the present disclosure, percentages are understood as percentages by weight relative to the composition under consideration, unless otherwise stated.

[0026] Furthermore, the pressure values given in the present disclosure are understood as absolute pressure values, that is to say, with reference to absolute vacuum, unless otherwise stated.

[0027] The term "aqueous ammonia solution" is understood to mean a solution of NH3 in water. Its ammonia content is expressed as the weight of NH3 relative to the weight of the solution (NH3 and water).

[0028] Thus, according to the application, the process for preparing omega-aminoalkanoic acids of formula NH2-(CH2) n -COOH (in which n is an integer from 9 to 11) comprises the following stages:

[0029] i) reacting an omega-bromoalkanoic acid with an excess of aqueous ammonia solution,

[0030] ii) separating the omega-aminoalkanoic acid formed from the reaction mixture,

[0031] characterized in that the aqueous ammonia solution exhibits a concentration of between 35% and 70% by weight and that stage i) is carried out at a pressure greater than atmospheric pressure, of between 0.11 and 2.0 MPa absolute. The omega-bromoalkanoic acid can be 10-bromodecanoic acid, 11-bromoundecanoic acid or 12-bromododecanoic acid.

[0032] These omega-brominated alkanoic acids can be obtained in particular by a homobromination reaction of the corresponding unsaturated acid, i.e. 9-decenoic acid, 10-undecenoic acid or 11-dodecenoic acid. These compounds are commercially available. Furthermore, 9-decenoic acid can be obtained from oleic-based vegetable oils according to the process described in WO 2018 / 080869. 10-Undecenoic acid can be obtained from castor oil according to FR 928 265.

[0033] The name omega-brominated alkanoic acid is used to designate the compound in more or less purified form, thus including its possible impurities. Commercial omega-brominated alkanoic acids generally have a purity greater than 98%. However, according to one embodiment, the purity of the omega-brominated alkanoic acid used can also be between 90% and 98%, preferably between 93% and 96%. The omega-brominated alkanoic acid can in particular contain as impurities bromoalkanoic acids of formula CH3-CH2Br-(CH2) n -2-CO2H.

[0034] The process of the application first comprises a stage i) in which the omega-brominated alkanoic acid is mixed with an excess of aqueous ammonia solution, then allowed to react.

[0035] The omega-brominated alkanoic acid can be added in solid form or in liquid form, in particular in molten state. The solid form can be a powder, granules or flakes. Advantageously, the omega-brominated alkanoic acid is used in molten state, preferably at a temperature of 5 to 60°C, preferably 10 to 40°C, in particular 15 to 30°C above its melting point.

[0036] According to the application, the aqueous ammonia solution used contains 35 to 70% by weight of ammonia. Preferably, it contains 36 to 60% by weight of ammonia, more preferably 38 to 45% by weight. According to one embodiment, the ammonia content of the aqueous ammonia solution can be 35 to 40% by weight, or 40 to 45% by weight, or 45 to 50% by weight, or 50 to 55% by weight, or 55 to 60% by weight, or 60 to 65% by weight, or still can be 65 to 70% by weight.

[0037] Advantageously, part of this aqueous ammonia solution is derived from the excess ammonia and ammonium present in the reaction medium recovered at the outlet of the process.

[0038] Advantageously, the aqueous ammonia solution introduced into the reactor exhibits a temperature of not more than 25°C. Preferably, it is cooled to a temperature of -20 to 20°C, preferably -10 to 10°C.

[0039] The weight ratio of the omega-brominated alkane acid to the aqueous ammonia solution introduced in stage i) is such that ammonia is present in stoichiometric excess. This excess is not only to facilitate the reaction, but also to make it possible to disperse or dilute the omega-brominated alkane acid and the product formed. Generally, it is from 1 :20 to 1 :3, preferably from 1 :10 to 1 :4, preferably from 1 :8 to 1 :4. The term "weight ratio" means here the weight ratio of the reactants used in the case of a batch process and the weight ratio of the flow rates of the reactants in the case of a continuous process.

[0040] The process of the application further comprises a stage ii) in which the omega-brominated alkane acid formed is separated from the reaction mixture.

[0041] The reaction mixture is generally heterogeneous. It can in particular comprise a gas phase, one or more liquid phases and / or one or more solid phases.

[0042] The process of the application can be carried out continuously or batchwise.

[0043] When the process is carried out continuously, the mixing of the reactants can be carried out in a tank equipped with a stirrer. In an alternative form, it can also be carried out in an external mixing device, such as a static mixer, a venturi or a recirculation loop into which the omega-brominated alkane acid is injected.

[0044] Stage i) of the process can be carried out in the same device. According to one embodiment, stage i) can be carried out in one or more stirred tanks. According to a preferred embodiment, stage i) is carried out in a group of 2 to 25 reactors connected in series, the reaction mixture being transported from one reactor to another using a pump or by gravity flow. Each reactor can consist of a tank provided with stirring. This stirring can be generated by a stirring module inside the reactor or by external recirculation.

[0045] Preferably, stage i) is carried out at a temperature of between 0 and 60°C. According to one embodiment, this temperature can be between 0 and 5°C, or between 5 and 10°C, or between 10 and 15°C, or between 15 and 20°C, or between 20 and 25°C, or between 25 and 30°C, or between 30 and 35°C, or between 35 and 40°C, or between 40 and 45°C, or between 45 and 50°C, or between 50 and 55°C, or between 55 and 60°C.

[0046] The temperature of the reactor(s) can advantageously be controlled by circulation of a heat transfer fluid in the reactor jacket or in a heat exchanger outside or inside the reactor, or by injection of a hot fluid, in particular water or steam, into the reactor(s).

[0047] The temperature can also be controlled by evaporation of a portion of the ammonia in order to cool the reaction medium, as explained in more detail later.

[0048] When the process is carried out in a set of reactors, as explained above, the temperature in the first reactor is preferably between 0 and 25°C and the temperature in the final reactor is between 26 and 60°C, and the temperature increases from one reactor to the next. In this case, it is advantageous to provide individual control of the temperature in each reactor. Advantageously, the first reactor(s) can be cooled and the final reactor(s) can be heated.

[0049] The total residence time of stage i) (calculated as the ratio of the sum of the liquid phase volumes in the reactors to the sum of the reactant flow rates) is generally between 20 and 100 hours, and preferably between 40 and 80 hours.

[0050] According to a second alternative embodiment, stage i) of the process is carried out in batch in a reactor, which can be a tank equipped with stirring means. According to one embodiment, the reactants are mixed outside the reactor and then introduced into the reactor as a mixture. According to another embodiment, the ammonia solution is first introduced into the reactor and the omega-bromoalkanoic acid is then added.

[0051] The mixing of the omega-bromoalkanoic acid in the aqueous ammonia solution can be carried out in a tank provided with a stirrer. In an alternative form, the mixing can be carried out by mixing means outside the reactor, such as static mixers; or a Venturi device, which makes it possible to mix the two reactant streams on line before they are injected into the reactor; or a recirculation loop outside the reactor, to which the omega-bromoalkanoic acid is injected.

[0052] After mixing the reactants, stage i) consists in stirring the reaction medium for a sufficient period of time, generally between 20 and 100 hours, and preferably between 40 and 80 hours.

[0053] According to one embodiment, the reaction of stage i) is carried out in isothermal mode, in other words the temperature is regulated at the same value throughout the reaction.

[0054] In this case, stage i) is carried out at a temperature between 0 and 60°C. According to one embodiment, the temperature can be between 0 and 5°C, or between 5 and 10°C, or between 10 and 15°C, or between 15 and 20°C, or between 20 and 25°C, or between 25 and 30°C, or between 30 and 35°C, or between 35 and 40°C, or between 40 and 45°C, or between 45 and 50°C, or between 50 and 55°C, or between 55 and 60°C.

[0055] According to another embodiment, the reaction is carried out in increasing temperature mode. Among the different thermal profiles that can be envisaged, it has proved advantageous to provide a static phase at increasing temperature, in particular an initial temperature ranging from 0 to 25°C up to a final temperature ranging from 26 to 60°C.

[0056] According to an alternative embodiment, phase i) is carried out in a battery of reactors R1, R2,... Rn, independently maintained at variable temperatures, 2 < n < 25. Each reactor has a program available for raising the temperature over a given period of time, which depends on the temperature chosen. In each reactor, the initial temperature of the program is preferentially between 0 and 25°C, and the final temperature is between 26 and 60°C. In order to maintain the feed and the withdrawal constant, regular and continuous at the inlet and at the outlet of the battery of reactors, each reactor is operated according to a charge / reaction / emptying cycle, with an offset expressed in time equal to the reaction time divided by the number of reactors (n).

[0057] In all the alternatives, the pressure in the reactor, measured at the top point, generally in the gas headspace, is maintained higher than atmospheric pressure during phase i). This is because it makes it possible to maintain a high concentration of ammonia in the liquid reaction phase, which improves the high selectivity towards primary amines. Thus, the production of impurities, in particular secondary amines, and indeed even tertiary amines, can be limited. Nonetheless, in order to limit the cost of the reactor, it is preferable to limit the pressure.

[0058] Accordingly, the pressure in the reactor(s) is 0.11 to 2.0 MPa absolute pressure, and preferably 0.125 to 0.5 MPa absolute pressure, preferably 0.13 to 0.3 MPa absolute pressure. According to one embodiment, the pressure can be 0.11 to 0.15 MPa absolute pressure, or 0.15 to 0.2 MPa absolute pressure, or 0.2 to 0.25 MPa absolute pressure, or 0.25 to 0.3 MPa absolute pressure, or 0.3 to 0.35 MPa absolute pressure, or 0.35 to 0.4 MPa absolute pressure, or 0.4 to 0.45 MPa absolute pressure, or 0.45 to 0.5 MPa absolute pressure, or 0.5 to 0.55 MPa absolute pressure, or 0.55 to 0.6 MPa absolute pressure, or 0.6 to 0.65 MPa absolute pressure, or 0.65 to 0.7 MPa absolute pressure, or 0.7 to 0.75 MPa absolute pressure, or 0.75 to 0.8 MPa absolute pressure, or 0.8 to 0.85 MPa absolute pressure, or 0.85 to 0.9 MPa absolute pressure, or 0.9 to 0.95 MPa absolute pressure, or 0.95 to 1.0 MPa absolute pressure, or 1.0 to 1.05 MPa absolute pressure, or 1.05 to 1.1 MPa absolute pressure, or 1.10 to 1.15 MPa absolute pressure, or 1.15 to 1.2 MPa absolute pressure, or 1.2 to 1.25 MPa absolute pressure, or 1.25 to 1.3 MPa absolute pressure, or 1.3 to 1.35 MPa absolute pressure, or 1.35 to 1.4 MPa absolute pressure, or 1.4 to 1.45 MPa absolute pressure, or 1.45 to 1.5 MPa absolute pressure, or 1.5 to 1.55 MPa absolute pressure, or 1.55 to 1.6 MPa absolute pressure, or 1.6 to 1.65 MPa absolute pressure, or 1.65 to 1.7 MPa absolute pressure, or 1.7 to 1.75 MPa absolute pressure, or 1.75 to 1.8 MPa absolute pressure, or 1.8 to 1.85 MPa absolute pressure, or 1.85 to 1.9 MPa absolute pressure, or 1.9 to 1.95 MPa absolute pressure, or 1.95 to 2.0 MPa absolute pressure.

[0059] When stage i) is carried out in several reactors, the vents of the reactors can be connected such that they are operated at almost the same pressure. According to another embodiment, it can be advantageous to place the reactors under different pressures. Thus, when the temperature is carried out in a reactor- by-reactor increasing manner, as explained above, the pressure in the reactors can also be increased reactor-by-reactor. According to one embodiment, the prevailing pressure in the reactor is autogenous pressure, which is mainly exerted by the vapour pressure of ammonia in relation to the composition of the reaction mixture and its temperature.

[0060] According to one embodiment, a portion of the ammonia can be evaporated in order to maintain the temperature of the reaction medium. Thus, when operating continuously, the first reactor can be cooled in this way. When operating batchwise, the reactor can be cooled at the beginning of the reaction in this way. The flow rate of the ammonia evaporation can be adjusted, and in this case the pressure of the treatment, or a pressure slightly lower than the liquid-gas equilibrium is applied and the evaporation of the ammonia is treated. Advantageously, between 0.1 and 50%, preferably between 10 and 30% of the ammonia injected evaporates during stage i). The person skilled in the art knows how to adjust the amount of ammonia to be evaporated from the reaction medium in order to maintain the temperature profile during the reaction. This mode of operation makes it possible to limit or avoid expensive heat exchange devices, while at the same time providing a temperature profile that makes it possible to achieve optimal yields.

[0061] Thus, the process of the application makes it possible to greatly limit the amount of secondary amine formed and thus to improve the yield of the reaction.

[0062] According to the application, the process additionally comprises a stage ii) of separation of the ω-aminoalkanoic acid from the reaction mixture at the end of stage i).

[0063] The ω-aminoalkanoic acid formed at the end of stage i) can be separated from the reaction mixture in a conventional manner, for example by the following stages.

[0064] The reaction mixture resulting from stage i) can be diluted in water and heated to boiling. The ammonia released is washed in water to form an aqueous ammonia solution, which can be recycled to stage i) of the process. The ammonia-depleted reaction mixture can then be separated from a possible oil layer formed by settling under hot conditions, then cooled to separate the ω-aminoalkanoic acid by crystallization and solid-liquid separation.

[0065] Further, the filtrate enriched in ammonium bromide, recovered from the solid-liquid separation, can be treated, for example with sodium hydroxide, to reform the ammonia, which is evaporated, then washed in water to form an aqueous ammonia solution.

[0066] The ω-aminoalkanoic acid can also be separated from the reaction mixture obtained at the end of stage i) by a stripping stage, to remove the ammonia, which is washed out in water, then solid-liquid separation, for example filtration or draining on a filter (image processing). The mother liquor recovered can be subjected to liquid-liquid extraction, crystallization and / or filtration to form an aqueous solution enriched in ammonium bromide and depleted in ω-aminoalkanoic acid. This aqueous solution enriched in ammonium bromide can be treated with sodium hydroxide to reform the ammonia, which is evaporated, then washed in water to form an aqueous ammonia solution.

[0067] The process of the application can also comprise a further stage iii) in which the ω-aminoalkanoic acid obtained in stage ii) is subjected to washing and draining. The washing can in particular be carried out with water.

[0068] The process of the application can also additionally comprise a step iv) of purifying the crude omega-aminoalkanoic acid obtained at the end of step ii) or iii).

[0069] This purification stage can in particular comprise one or more of the following operations: recrystallization in a suitable solvent (for example water or an aqueous basic or acidic solution, for example a mixture of water and carboxylic acid), filtration, washing and draining. Preferably, the crude omega-aminoalkanoic acid obtained is purified by recrystallization from very hot water.

[0070] Thus, the process of the application can additionally comprise a stage v) of recovering the residual omega-aminoalkanoic acid in the various filtrates and aqueous washing liquids obtained in stages ii), iii) and / or iv), in particular by degassing of the ammonia, liquid-liquid extraction, crystallization, filtration and washing.

[0071] Finally, the process of the application can also comprise a stage vi) of drying the omega-aminoalkanoic acid obtained.

[0072] Advantageously, the process according to the application makes it possible to obtain an omega-aminoalkanoic acid in which the content of omega-aminodialkanoic acids is less than 1.8% by weight, preferably less than 1.5% by weight, relative to the content of omega-aminoalkanoic acid, at the end of stage i) and thus before purification.

[0073] Further, the process according to the application advantageously makes it possible for the omega-bromalkanoic acid to be completely converted in a reaction time of less than 75 hours, over the duration of the amination stage i).

[0074] The application will be explained in greater detail in the following examples.

[0075] [EXAMPLE]

[0076] Example 1

[0077] A 1 -liter autoclave, cooled to 0°C, was charged with 660 g of a 40% by weight ammonia solution, equipped with a mechanical stirrer with two turbines with five blades, a Rushton-type turbine rotating at 400 rpm, and a coil making it possible to circulate a heat transfer fluid, and a discharge valve set at 0.15 MPa absolute pressure, then the reactor was closed. 110 g of molten 11-bromoundecanoic acid (purity 98%) were rapidly added at 90°C, then the temperature of the reaction medium was adjusted to 22°C by means of the heat transfer fluid circulating in the coil. The pressure was adjusted very rapidly to 0.15 MPa absolute pressure and was maintained at this value throughout the reaction. After 12 hours 30 minutes, the temperature of the reaction medium was increased in order to carry out successive static phases at 24°C, 26°C, 28°C, 30°C and 32°C for 12 hours 30 minutes respectively. The exhaust of the reactor was then opened to bring the reactor to atmospheric pressure.

[0078] The reaction medium was then analyzed. The bromide ions were quantitatively determined by using silver nitrate with a silver electrode, all the 11-bromoundecanoic acid having reacted being found. The 11-aminoheneicosanoic acid was measured at 1.3% by weight relative to the 11-aminoundecanoic acid by HPLC quantification with external calibration.

[0079] Example 2 (comparative example)

[0080] Example 1 was repeated, but operating at atmospheric pressure throughout the experiment and simultaneously controlling the rate of addition of molten 11-bromoundecanoic acid so that the medium does not foam in an uncontrolled manner.

[0081] The analysis of the reaction medium showed that all the 11-bromoundecanoic acid had reacted. The 11-aminoheneicosanoic acid was measured at 1.9% by weight relative to the 11-aminoundecanoic acid.

[0082] Example 3 (comparative example)

[0083] Example 1 was repeated, but operating at atmospheric pressure throughout the experiment and using 660 g of a 32% by weight ammonia solution.

[0084] The analysis of the reaction medium showed that all the 11-bromoundecanoic acid had reacted. The 11-aminoheneicosanoic acid was measured at 2.0% by weight relative to the 11-aminoundecanoic acid.

[0085] [Bibliography list]

[0086] FR 988 699

[0087] WO 2018 / 080869 A1

[0088] FR 928 265

[0089] CN 103804209 B

[0090] EP 2 358 662 B1

Claims

1. Process for the production of ω-aminoalkanoic acids of formula NH2-(CH2)n-COOH by reacting the corresponding ω-bromoalkanoic acid with ammonia, wherein n is an integer from 9 to 11, which process comprises the following stages: a) reacting the ω-bromoalkanoic acid with ammonia in the presence of a catalyst, b) recovering the ω-aminoalkanoic acid. n 2. Process according to claim 1, wherein the catalyst is selected from the group consisting of: a) a mixture of sodium hydroxide and sodium bromide, b) a mixture of sodium hydroxide i) reacting the omega-brominated alkanoic acid with an excess of aqueous ammonia solution, and ii) separating the omega-aminoalkanoic acid formed from the reaction mixture, characterized in that said aqueous ammonia solution exhibiting a concentration of 35 to 70% by weight, and phase i) being carried out at a pressure greater than atmospheric pressure, of 0.11 to 2.0 MPa absolute pressure.

2. The manufacturing process according to claim 1, wherein phase i) is carried out at a temperature of between 0 and 60°C.

3. The manufacturing process according to claim 2, wherein phase i) is carried out at a constant temperature.

4. The manufacturing process according to claim 2, wherein phase i) is carried out at an elevated temperature.

5. The manufacturing process according to claim 4, wherein phase i) is carried out at an elevated temperature, the initial temperature ranging from 0 to 25°C and the final temperature ranging from 26 to 60°C.

6. The manufacturing process according to any one of claims 1 to 5, wherein the aqueous ammonia solution exhibits a concentration of 36 to 60% by weight.

7. The manufacturing process according to claim 6, wherein the aqueous ammonia solution exhibits a concentration of 38 to 45% by weight.

8. The manufacturing process according to any one of claims 1 to 5, wherein the weight ratio of omega-brominated alkanoic acid to aqueous ammonia solution at the start of phase i) is 1 :3 to 1 :

20.

9. The manufacturing process according to any one of claims 1 to 5, wherein the process is carried out at an absolute pressure of 0.125 to 0.5 MPa.

10. The manufacturing process according to claim 9, wherein the process is carried out at an absolute pressure of 0.13 to 0.3 MPa.

11. The manufacturing process according to any one of claims 1 to 5, which is carried out continuously.

12. The manufacturing process according to any one of claims 1 to 5, which is carried out batchwise.

13. The process according to any one of claims 1 to 5, further comprising a phase iii) of washing and discharging the omega-aminoalkanoic acid obtained at the end of phase ii).

14. The process according to claim 13, further comprising a phase iv) of purifying the crude omega-aminoalkanoic acid obtained at the end of step ii) or iii).

15. The process according to claim 14, further comprising a phase iv) of purifying the crude omega-aminoalkanoic acid obtained at the end of step ii) or iii) by recrystallization from boiling water.

16. The process according to claim 14, further comprising a phase v) of recovering the residual omega-aminoalkanoic acid in the various filtrates and aqueous washing liquids obtained in phases ii), iii) and / or iv), in particular by degassing of the ammonia, liquid-liquid extraction, crystallization, filtration and washing.

17. The process according to claim 16, further comprising a phase vi) of drying the omega-aminoalkanoic acid obtained.