Process for the preparation of omega-amino fatty acid methyl esters, long chain nylons

Abstract

The application relates to the technical field of organic synthesis, and particularly relates to a preparation method of omega-amino fatty acid methyl ester and long-chain nylon. The preparation method of the omega-amino fatty acid methyl ester specifically comprises the following steps: S1, ester exchange: long-chain dibasic acid dimethyl ester, methanol and a first organic solvent are mixed in the presence of a first catalyst, and the long-chain dibasic acid monomethyl ester is obtained through an ester exchange reaction; S2, ammonia addition: the long-chain dibasic acid monomethyl ester is used as a raw material, an amidation reaction is carried out, and then a reduction reaction is carried out to obtain the omega-amino fatty acid methyl ester, wherein n is greater than or equal to 8. The preparation method has the characteristics of a short process route and stable intermediates, can be suitable for batch production, and can also be suitable for continuous production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic synthesis, and particularly relates to a preparation method of omega-amino fatty acid methyl ester and long-chain nylon. BACKGROUND

[0002] Nylon 12 (PA12) is a long carbon chain nylon, which has excellent properties such as oil resistance, wear resistance, chemical corrosion resistance, low water absorption, good dimensional stability, low temperature resistance and the like, and thus is widely used in various fields of life.

[0003] According to starting materials, the production process of nylon 12 is mainly divided into three kinds: butadiene method, cyclohexanone method and castor oil method. Among them, (1) butadiene method: butadiene is used as raw material to prepare cyclododecatriene (CDT), which is prepared into lauryl lactam through different process methods, and the lauryl lactam is ring-opening polycondensed to obtain nylon 12. The process includes oxidation oximation method, photo-nitrosation method and snia method, wherein the oxidation oximation method is the mainstream process. Nylon 12 produced by the oxidation oximation method needs to go through seven steps of trimerization (CDT), catalytic hydrogenation, oxidation, ketonization, oximation, beckmann rearrangement and ring-opening polymerization, and toxic and corrosive raw materials such as benzene and fuming sulfuric acid are used in the whole process. The ring-opening polymerization temperature needs to be 270-300℃, and the production step operation is difficult. At present, most manufacturers represented by Yinkang Company use the mainstream process route of taking butadiene as raw material. The process schematic diagram of preparing nylon 12 from butadiene is as follows: Figure 1As shown. (2) Cyclohexanone method: A certain proportion of cyclohexanone, hydrogen peroxide and ammonia react under the catalysis of carboxylate or ammonium salt to obtain 1,1-dicyclohexyl peroxide, which is heated and decomposed into 11-cyanoundecanoic acid. Then, 11-cyanoundecanoic acid is reduced with hydrogen to obtain 12-aminododecanoic acid, which is polymerized to generate nylon 12. This method was implemented by Ube Industries of Japan after obtaining a technology license from British Petrochemical Company. The process route of PA12 using cyclohexanone as raw material has been industrialized. However, this method has problems such as low yield, high energy consumption, high cost and many by-products. (3) Castor oil method. Castor oil is thermally cracked to prepare 10-undecenoic acid. After addition and substitution, 11-cyanoundecanoic acid is prepared. After hydrogenation reduction, 12-aminododecanoic acid is obtained and polymerized to generate nylon 12. The typical representative manufacturer of this process is Arkema of France. For the typical domestic process, see patent CN107445850 B. However, this method requires the use of highly toxic cyano compounds. (4) Synthetic biology method. In recent years, with the development of biotechnology research, more and more enzyme-catalyzed reactions have been applied to the production research of ω-amino fatty acids. The biosynthetic pathways differ depending on the starting materials. For example, starting from free fatty acids, ω-hydroxy fatty acids (ω-HFAs) are formed by terminal hydroxylation using P450 hydroxylase; starting from fatty acid esters or lactones, ω-HFAs are generated by hydrolysis using esterases. Then, ω-aldehyde fatty acids are generated by oxidation using alcohol dehydrogenases, and finally, ω-amino fatty acids are generated by amination of the aldehyde acid using transaminases or amine dehydrogenases. Patent CN 110643555 B is based on this idea, constructing E. coli genetically engineered bacteria to prepare 12-aminododecanoic acid from lauric acid, which is then polymerized to prepare nylon 12. However, this method has high production costs, low yields, and complicated post-processing. Summary of the Invention

[0004] The main difficulties in preparing ω-amino fatty acid methyl esters using current technologies lie in monoesterification and amination, specifically:

[0005] In terms of monoesterification, the two carboxyl groups in long-chain diacid molecules are far apart, and theoretically, their mutual influence should be minimal, seemingly leading to stronger selective monoesterification. However, this is not actually the case. This invention reveals that because carbon-carbon single bonds are freely rotatable, the two carboxyl groups become very close during the actual reaction due to carbon chain torsion, thus influencing each other and making the synthesis of long-chain diacid monoesters more difficult. Therefore, the current synthesis of long-chain diacid monoesters generally suffers from problems such as uncontrollable reactions, numerous side reactions, low yields of target products, and high process costs. Furthermore, the use of enzymes and carriers presents challenges in post-processing.

[0006] Regarding amination, current routes for preparing ω-amino fatty acids suffer from problems such as demanding reaction conditions and significant safety risks. Specifically: One method involves the hydrolysis of lactams, requiring Beckmann rearrangement and hydrolysis steps. Representative manufacturers using this process include Yantai Wanhua and Evonik Industries, Germany. However, the Beckmann rearrangement route requires high-temperature and high-pressure reactions, using concentrated sulfuric acid as a catalyst to produce large amounts of ammonium sulfate as a byproduct. Furthermore, the Beckmann rearrangement requires stringent control conditions; if these conditions are not properly controlled, the ketoxime will hydrolyze into the corresponding cyclic ketones and hydroxylamines, preventing rearrangement. Another method involves the reduction of nitrile groups, requiring three steps: addition, substitution, and reduction. Representative manufacturers using this process include Wuxi Inda Nylon Co., Ltd., Arkema (France), and Yantai Wanhua. However, this process requires the use of the highly toxic chemical cyanide, posing significant safety risks. Moreover, the selective homogeneous catalytic hydrogenation of nitrile groups is difficult to control, requiring monitoring of ammonia gas flow and reaction pressure. The high reaction pressure and temperature further complicate controllability.

[0007] After extensive experimentation, this invention discovered that, regarding monoesterification, when long-chain diacids, dimethyl diacid esters, and methanol undergo transesterification in the presence of a first catalyst, the presence of methanol alters the transesterification process between the long-chain diacid and dimethyl diacid esters. At reflux temperature, the newly formed acid and ester are difficult to volatilize and distill, and side reactions increase with prolonged reaction time. To promote the reaction towards the product, methanol is added as an esterifying agent, effectively controlling the formation of side reactions and significantly improving the selectivity and yield of monomethyl diacid esters. Regarding amination, this invention found that using a route of first amidation followed by reduction of the monoamide effectively avoids high-temperature and high-pressure conditions, facilitating a more controllable ammonia addition method.

[0008] Based on this, the specific technical solution of the present invention includes:

[0009] This invention first provides a method for preparing ω-amino fatty acid methyl esters, which has the following reaction route:

[0010]

[0011] Specifically, it includes:

[0012] S1, transesterification:

[0013] Long-chain dicarboxylic acids long-chain dicarboxylic acid dimethyl ester Methanol and a first organic solvent are mixed in the presence of a first catalyst to obtain the long-chain dicarboxylic acid monomethyl ester via transesterification.

[0014] S2, Add ammonia:

[0015] As stated It is prepared from raw materials through an amidation reaction. then The preparation was obtained through a reduction reaction.

[0016] Where n≥8.

[0017] Preferably, the molar ratio of the long-chain dicarboxylic acid, the dimethyl long-chain dicarboxylic acid ester, and methanol is 1:(0.5-1):(1-2).

[0018] In this invention, by optimizing the amounts of long-chain dicarboxylic acid, dimethyl ester of long-chain dicarboxylic acid, and methanol, the yield and selectivity of the methyl esterification reaction can be further improved, while the reaction efficiency is also high.

[0019] Preferably, the first catalyst comprises one or more of concentrated hydrochloric acid, concentrated sulfuric acid, a strong acidic cation exchange resin, supported phosphotungstic acid, and a solid superacid; wherein the supported phosphotungstic acid includes silica-supported phosphotungstic acid and activated carbon-supported phosphotungstic acid, etc., and the solid superacid includes TiO2-ZrO2 / SO4. 2- wait.

[0020] More preferably, the first catalyst comprises one or more of concentrated sulfuric acid, p-toluenesulfonic acid, and a strong acid cation exchange resin.

[0021] More preferably, based on the total amount of solids in the transesterification reaction system, the amount of the first catalyst is 0.5 to 5 wt%.

[0022] Preferably, the first organic solvent includes one or more of cyclohexane, chloroform, benzene, toluene, and xylene.

[0023] More preferably, the first organic solvent is xylene.

[0024] In the transesterification process, in order to remove the water generated in the reaction from the reaction system in a timely manner, an organic solvent is used as a dehydrating agent. The dehydrating agent can form a binary or ternary azeotrope with water or one of the reactants, thereby removing the water from the reaction system in a timely manner, thus shifting the equilibrium towards the direction favorable to the formation of ester. In order to achieve a more effective removal of water in the reaction process, the above scheme optimizes the type of the first organic solvent in the transesterification, thereby further improving the purity and yield of the intermediate monomethyl ester.

[0025] More preferably, the weight-volume ratio of the total reactants in the transesterification reaction system to the first organic solvent is 1 g: (0.5-3) ml.

[0026] Preferably, the Depend on It is obtained through methyl esterification.

[0027] In a preferred embodiment of the present invention, the method for preparing the ω-amino fatty acid methyl ester has the following reaction route:

[0028]

[0029] More preferably, the methyl esterification reaction includes: taking the... Methanol and a third catalyst are mixed and reacted at reflux temperature;

[0030] The The mass-to-volume ratio of methanol to 1g is (1-50)ml;

[0031] The third catalyst comprises one or more of inorganic acids, organic acids, and strongly acidic ion exchange resins; the amount of the third catalyst used is... 0.1–20 wt% by mass.

[0032] Preferably, S2 includes:

[0033] S21, amidation reaction: the above The product is prepared by reacting urea at 80–200°C.

[0034] S22, Reduction reaction: (The following is a partial translation of the original text) Sodium borohydride, an organic acid, and a second organic solvent are mixed at low temperature and then refluxed to carry out the reaction.

[0035] Preferably, the low temperature is -4 to 80°C.

[0036] Preferably, the organic acid is one or more of formic acid, acetic acid and propionic acid;

[0037] Preferably, the second organic solvent includes one or more of tetrahydrofuran, methanol, and ethanol.

[0038] Preferably, the The molar ratio of urea to urea is 1:(0.5-5).

[0039] Preferably, in the reduction reaction, the The molar ratio of sodium borohydride to organic acid is 1:(1-6):(1-5).

[0040] This invention discovers that by using urea as a nitrogen source and preparing monoamides through thermodynamic control, and then reducing the monoamides in the aforementioned reduction system, the high-temperature and high-pressure reaction conditions can be effectively avoided, thereby improving the controllability of amination.

[0041] Preferably, the amidation reaction takes 5 to 24 hours, and the reduction reaction takes 0.5 to 24 hours.

[0042] Preferably, the mass / volume ratio of the total reactants in the reduction reaction system to the second organic solvent is 1 g: 1-15 ml.

[0043] Preferably, 10 ≤ n ≤ 14; more preferably, n = 10.

[0044] This invention also provides a method for preparing long-chain nylon, which is obtained by the above-described method for preparing ω-amino fatty acid methyl esters. Then the following reaction occurs:

[0045] Specifically, it includes:

[0046] The Deprotection was performed under alkaline solution conditions to obtain... Then the above Long-chain nylon is obtained by high-temperature polymerization under nitrogen protection.

[0047] Preferably, during the deprotection process, the Under alkaline solution stirring conditions, methanol protection was removed at 60–100°C, and the product was separated.

[0048] Preferably, the alkaline solution is one or a mixture of sodium hydroxide and potassium hydroxide, with a concentration of 1 to 10 M.

[0049] Preferably, the deprotection reaction time is 2–24 h.

[0050] Preferably, the polymerization includes:

[0051] The The mixture is combined with water, a second catalyst, an antioxidant, and a molecular weight regulator. Under a nitrogen atmosphere, the temperature is raised to 180–230°C to melt the material, followed by a first holding period. The temperature is then raised to 230–280°C for a second holding period. After the reaction is complete, the reactant is removed, which is long-chain nylon.

[0052] Preferably, the Drying is performed before the reaction.

[0053] As a preferred method, the first heat preservation time is 1.5 to 3 hours, and the second heat preservation time is 2.5 to 5 hours.

[0054] Preferably, the The mass ratio of water to water is 1:(0.5~4);

[0055] Preferably, based on the total mass of the polymerization reaction reactants, the mass fraction of the second catalyst is 0.01-1%, the mass fraction of the antioxidant is 0.05-1%, and the mass fraction of the molecular weight regulator is 0.001-5%.

[0056] In this invention, by processing the polymerization reaction raw materials... By rationally selecting the amount of water and other auxiliary materials, the efficiency of the polymerization reaction can be improved, thereby increasing the yield of long-chain nylon.

[0057] In a preferred embodiment of the present invention, the long-chain nylon has the following reaction pathway:

[0058]

[0059] In specific implementation, those skilled in the art can apply the scheme of this invention to the preparation of long-chain nylons using long-chain dicarboxylic acids as starting materials, such as nylon 11, nylon 12, nylon 13, nylon 14, nylon 15, nylon 16, etc.

[0060] As a preferred embodiment of the present invention, the method for preparing nylon 12 has the following reaction route:

[0061]

[0062] Compared to the existing butadiene method for preparing nylon 12, the above reaction route avoids the demanding Beckmann rearrangement reaction and does not produce large amounts of the industrial byproduct ammonium sulfate. Compared to the cyclohexanone method, the intermediates in the above reaction route are stable and controllable; the 1,1-dicyclohexyl peroxide produced by the cyclohexanone method is unstable and produces many byproducts. Compared to the castor oil method, this invention avoids the use of hydrogen bromide and the highly toxic substance cyanide. The above-described new process route for preparing nylon 12 has well-defined and stable intermediates, is suitable for both batch and continuous production, and provides new ideas for the production of other long-chain nylons.

[0063] Based on the above technical solution, the beneficial effects of the present invention are as follows:

[0064] This invention provides a method for preparing ω-amino fatty acid methyl esters and long-chain nylon, which can solve many problems in the existing production process, such as harsh reaction conditions, low yield, high energy consumption and high cost, and provides a new approach for preparing long-chain nylon using long-chain dicarboxylic acids as starting materials. Attached Figure Description

[0065] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0066] Figure 1 This is a reaction route diagram for the preparation of nylon 12 using the butadiene method in the existing technology;

[0067] Figure 2 This is the HPLC chromatogram of dimethyl dodecanoate, the intermediate obtained in Example 2 of the present invention;

[0068] Figure 3 This is the HPLC chromatogram of the intermediate dodecanoic acid monomethyl ester obtained in Example 2 of the present invention;

[0069] Figure 4 The intermediate dodecanoic acid monomethyl ester obtained in Example 2 of this invention 1 HNMR spectrum;

[0070] Figure 5 The intermediate dodecanoic acid monomethyl ester obtained in Example 2 of this invention 13 CNMR spectrum;

[0071] Figure 6 It is the intermediate methyl 12-amino-dodecanoate obtained in Example 2 of this invention. 1 HNMR spectrum;

[0072] Figure 7 It is the intermediate methyl 12-amino-dodecanoate obtained in Example 2 of this invention. 13 CNMR spectrum;

[0073] Figure 8 This is the infrared spectrum of 12-aminododecanoic acid, the product obtained in Example 2 of this invention;

[0074] Figure 9 This is the infrared spectrum of nylon 12, the product obtained in Example 2 of the present invention. Detailed Implementation

[0075] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0076] Example 1

[0077] This embodiment first provides a method for preparing ω-amino fatty acid methyl esters, which has the following reaction route:

[0078]

[0079] Its preparation method includes the following steps:

[0080] 1. Methylation:

[0081] 258g of tetradecanoic acid, 750ml of methanol, and 30ml of concentrated sulfuric acid were placed in a 2L three-necked reaction flask and refluxed at 66℃ for 6 hours. After the reaction, the mixture was neutralized to pH neutral with sodium hydroxide, and the methanol was removed by rotary evaporation to obtain a solid. The solid was washed with 500ml of water three times and then dried to obtain dimethyl tetradecanoic acid.

[0082] 2. Ester exchange:

[0083] 25 g of tetradecanoic acid, 25 g of dimethyl dodecanoic acid, 3.2 g of methanol, 0.5 g of p-toluenesulfonic acid, and 50 ml of xylene were placed in a three-necked flask, a water separator was added, and the mixture was refluxed at 150 °C for 7 hours. After the reaction was complete, the mixture was cooled to room temperature and washed twice with 100 ml of saturated sodium carbonate solution each time. Then, the organic phase was washed with 100 ml of deionized water. After washing, the aqueous phases were combined. The aqueous phase was neutralized with 3 M HCl to approximately pH 3.5, yielding a solid precipitate. The precipitate was collected by filtration and washed with water until neutral to obtain monomethyl tetradecanoic acid. The product yield was approximately 63%.

[0084] 3. Add ammonia:

[0085] 31. Amide reaction: 45g of tetradecanoic acid monomethyl ester was dissolved in 50ml of water and heated to 100℃. Then, 15g of urea was added and dissolved. The reaction temperature was increased to 160℃ and heated for 6 hours, then to 180℃ and heated for 2 hours, and finally to 200℃ and heated for 1 hour. The mixture was cooled to room temperature to obtain a solid. The solid powder was pulverized in a mortar and washed twice with water. The solid was collected and dried to obtain approximately 37.5g of the amide compound of tetradecanoic acid monomethyl ester. The product yield was approximately 82%, and the purity was approximately 95%.

[0086] 32. Reduction Reaction: 7.6 g of sodium borohydride was placed in 50 ml of anhydrous ethanol, and then 13 g of glacial acetic acid was slowly added at low temperature. The mixture was stirred at room temperature for 3 h. 40 g of the amide compound of tetradecanoic acid monomethyl ester was dissolved in 30 ml of anhydrous ethanol. After dissolution, the solution was slowly added to the sodium borohydride reaction system. The temperature was then raised to reflux temperature, and the reaction was timed for 12 h. After the reaction was completed, heating was stopped, and 50 ml of 3M hydrochloric acid solution was slowly added to the system. After no gas was released, the organic phase was removed by vacuum rotary evaporation to remove the solid solution. The product was then filtered to obtain methyl 12-amino-tetradecanoic acid. The product yield was approximately 65%, and the purity was approximately 98%.

[0087] This embodiment further provides a method for preparing long-chain nylon, which has the following reaction route:

[0088]

[0089] Its preparation method includes the following steps:

[0090] 4. Deprotection:

[0091] 15 g of the 14-amino-tetradecanoic acid monomethyl ester was placed in 100 ml of 2M sodium hydroxide solution and heated to 100°C for 12 h. After the reaction was completed, the pH was neutralized to approximately 6-7 with 3M hydrochloric acid to obtain a white suspension. The solid was collected by filtration and washed with water. The solid was then dried to obtain 14-aminotetradecanoic acid. The product yield was approximately 85%, and the purity was approximately 99%.

[0092] 5. Aggregation:

[0093] 10g of 14-amino-tetradecanoic acid, 10g of water, and 0.001g of lauric acid were placed in a nylon synthesis flask. Nitrogen gas was introduced, and a vacuum pump was used to evacuate the mixture to a vacuum level of 0.08 MPa. Nitrogen gas was then continuously introduced. After purging five times, the reaction was carried out under a nitrogen atmosphere. The temperature was increased from 100℃ to 220℃ over 3 hours to melt the materials, and maintained at 220℃ for 2 hours. Then, the temperature was increased to 250℃ at a rate of 10℃ / hour and maintained at 250℃ for 4 hours. After the reaction was complete, the reaction flask was broken, and the reactants were removed; this was Nylon 14.

[0094] Example 2

[0095] This embodiment first provides a method for preparing methyl 12-amino-dodecanoate, which has the following reaction route:

[0096]

[0097] Specifically, the steps include the following:

[0098] 1. Methylation:

[0099] 230 g of dodecanoic acid, 700 ml of methanol, and 30 ml of concentrated sulfuric acid were placed in a 2 L three-necked reaction flask and refluxed at 66 °C for 6 hours. After the reaction, the mixture was neutralized to pH neutral with sodium hydroxide, and the methanol was removed by rotary evaporation to obtain a solid. The solid was washed with 500 ml of water three times, and then dried to obtain dimethyl dodecanoic acid. The product yield was 95%. The product was analyzed by high-performance liquid chromatography (HPLC), and the chromatogram is shown below. Figure 2 As shown, the purity of the obtained dimethyl dodecanoate product is greater than 98%.

[0100] 2. Ester exchange:

[0101] 23 g of dodecanoic acid, 20 g of dimethyl dodecanoic acid, 3.2 g of methanol, 0.3 g of p-toluenesulfonic acid, and 50 ml of xylene were placed in a three-necked flask, a water separator was added, and the mixture was refluxed at 140 °C for 5 hours. After the reaction was complete, the mixture was cooled to room temperature and washed twice with 100 ml of saturated sodium carbonate solution each time. Then, the organic phase was washed with 100 ml of deionized water. After washing, the aqueous phases were combined. The aqueous phases were neutralized with 3 M HCl to approximately pH 3.5, yielding a solid precipitate. The precipitate was collected by filtration and washed with water until neutral to obtain monomethyl dodecanoic acid. The product yield was approximately 70%.

[0102] The product was analyzed by high performance liquid chromatography and nuclear magnetic resonance. The HPLC chromatogram is shown below. Figure 3 As shown, the chromatographic purity of the obtained dodecanoic acid monomethyl ester product is 95%. 1 H NMR spectrum as follows Figure 4 As shown, 13 C NMR spectra as follows Figure 5 As shown.

[0103] 3. Add ammonia:

[0104] 31. Amide reaction: Take 48g of monomethyl dodecanoic acid, add 50ml of water, and heat to 80℃ to dissolve. Then add 15g of urea, and after dissolving, raise the reaction temperature to 140℃ and heat for 1h, raise the temperature to 160℃ and heat for 5h, raise the temperature to 180℃ and heat for 1h, and raise the temperature to 200℃ and heat for 30min. Cool to room temperature to obtain a solid. Grind the solid in a mortar, wash the solid powder twice with water, collect the solid, and dry it to obtain the amide compound of monomethyl dodecanoic acid, about 41g, with a yield of about 85%.

[0105] 32. Reduction Reaction: 7.6 g of sodium borohydride was placed in 50 ml of anhydrous ethanol, and then 13 g of glacial acetic acid was slowly added. The mixture was stirred at room temperature for 3 h. 36 g of monomethyl dodecanoic acid was dissolved in 30 ml of anhydrous ethanol, and after dissolution, it was slowly added to the sodium borohydride reaction system. The temperature was then raised to reflux temperature, and the reaction was timed for 12 h. After the reaction was complete, heating was stopped, and 50 ml of 3M hydrochloric acid solution was slowly added to the system. After no gas was released, the organic phase was removed by vacuum rotary evaporation to remove the solid solution. The solution was then filtered to obtain methyl 12-amino-dodecanoic acid. The yield was approximately 65%.

[0106] The methyl 12-amino-dodecanoate 1 H NMR spectrum as follows Figure 6 As shown, 13 C NMR spectra as follows Figure 7 As shown.

[0107] This embodiment further provides a method for preparing nylon 12, the reaction route of which is as follows:

[0108]

[0109] 4. Deprotection:

[0110] 20 g of the 12-amino-dodecanoic acid monomethyl ester was placed in 100 ml of 2M sodium hydroxide solution and heated to 100°C for 8 h. After the reaction was completed, the pH was neutralized to approximately 6-7 with 3M hydrochloric acid to obtain a white suspension. The solid was collected by filtration and washed with water. The solid was then dried to obtain 12-amino-dodecanoic acid. The yield was approximately 85%.

[0111] The infrared spectrum of the 12-aminododecanoic acid is as follows: Figure 8 As shown.

[0112] 5. Aggregation:

[0113] 10g of 12-amino-dodecanoic acid, 10g of water, and 0.001g of lauric acid were placed in a nylon synthesis flask. Nitrogen gas was introduced, and a vacuum pump was used to evacuate the mixture to a vacuum level of 0.08 MPa. Nitrogen gas was then continuously introduced. This process was repeated five times, ensuring the reaction was carried out under a nitrogen atmosphere. The temperature was increased from 100℃ to 200℃ over three hours to melt the materials, and maintained at 200℃ for two hours. Then, the temperature was increased to 250℃ at a rate of 10℃ / hour and held at 250℃ for three hours. After the reaction was complete, the reaction flask was broken, and the reactants were removed; this was Nylon 12.

[0114] The infrared spectrum of the nylon 12 is as follows: Figure 9 As shown.

[0115] Example 3

[0116] This embodiment provides a method for preparing methyl 12-amino-dodecanoate, which is basically the same as the preparation method in Example 2, except that:

[0117] In the transesterification reaction, the molar ratios of dodecanoic acid, dimethyl dodecanoic acid, and methanol are different, as shown in Table 1 below. The chromatographic purity and yield of the obtained monomethyl dodecanoic acid are shown in Table 1 below.

[0118] Table 1

[0119]

[0120] Example 4

[0121] This embodiment provides a method for preparing methyl 12-amino-dodecanoate, which is basically the same as the preparation method in Example 2, except that the type of organic solvent used in the transesterification is different. The specific differences and the chromatographic purity and yield of the obtained dodecanoic acid monomethyl ester product are shown in Table 2 below.

[0122] Table 2

[0123] Organic solvent Product chromatographic purity Yield Benzene 50～65％ 15～30％ Toluene 70～80％ 40～65％

[0124] Example 5

[0125] This embodiment provides a method for preparing methyl 12-amino-dodecanoate, which is basically the same as the preparation method in Example 2, except that the p-toluenesulfonic acid is replaced with 0.5g of activated carbon-supported phosphotungstic acid.

[0126] The chromatographic purity of the product was 65.5%, and the yield was <40%.

[0127] Example 6

[0128] This embodiment provides a method for preparing methyl 12-amino-dodecanoate, which is basically the same as the preparation method in Example 2, except that the molar ratio of monomethyl dodecanoate monomethyl ester and urea is different in the amination step. The specific differences and the yield of the amide compound of monomethyl dodecanoate monomethyl ester are shown in Table 3 below.

[0129] Table 3

[0130] n(dodecanedioic acid monomethyl ester) : n(urea) Yield 1:0.5 55～60％ 1:5 88～92％ 1:2 85％

[0131] Example 7

[0132] This embodiment provides a method for preparing methyl 12-amino-dodecanoate, which is basically the same as the preparation method in Example 2, except that the molar ratio of the amide compound of the dodecanoic acid monomethyl ester, sodium borohydride and organic acid is different in the amination step. The specific differences and the yield of the obtained methyl 12-amino-dodecanoate are shown in Table 4 below.

[0133] Table 4

[0134]

[0135] Comparative Example 1

[0136] This comparative example provides a method for preparing methyl 12-amino-dodecanoate, which is basically the same as the preparation method in Example 2, except that the transesterification reaction system does not contain methanol.

[0137] The product has a chromatographic purity of 40% and a yield of less than 10%.

[0138] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing ω-amino fatty acid methyl esters, characterized in that, It has the following reaction pathway: ； Specifically, it includes: S1, transesterification: Long-chain dicarboxylic acids long-chain dicarboxylic acid dimethyl ester Methanol and a first organic solvent are mixed in the presence of a first catalyst to obtain the long-chain dicarboxylic acid monomethyl ester via transesterification. The first catalyst is p-toluenesulfonic acid, and the first organic solvent is xylene. S2, Add ammonia: S21, amidation reaction: the above The product is prepared by reacting urea at 80-200℃. ; S22, Reduction reaction: The above Sodium borohydride, an organic acid, and a second organic solvent are mixed at room temperature, and then the mixture is refluxed to prepare the desired product. ; Where n=10; The molar ratio of the long-chain dicarboxylic acid, the dimethyl ester of the long-chain dicarboxylic acid, and methanol is 1:(0.5~1):(1~2). The organic acid is acetic acid; The second organic solvent is one or more of tetrahydrofuran, methanol, and ethanol; The The molar ratio of urea to urea is 1:(2~5); The The molar ratio of sodium borohydride to organic acid is 1:(2~6):(2~5).

2. The method for preparing ω-amino fatty acid methyl ester according to claim 1, characterized in that, Based on the total amount of solids in the transesterification reaction system, the amount of the first catalyst is 0.5~5wt%.

3. The method for preparing ω-amino fatty acid methyl ester according to claim 1, characterized in that, The weight-to-volume ratio of the total reactants to the first organic solvent in the transesterification reaction system is 1 g : (0.5~3) ml.

4. A method for preparing long-chain nylon, characterized in that, The ω-amino fatty acid methyl ester was prepared by the method according to any one of claims 1 to 3. Then the following reaction occurs: ； Specifically, it includes: The Deprotection was performed under alkaline solution conditions to obtain... Then the above Long-chain nylon is obtained by high-temperature polymerization under nitrogen protection.

5. The method for preparing long-chain nylon according to claim 4, characterized in that, The aggregation includes: The The mixture is combined with water, a second catalyst, an antioxidant, and a molecular weight regulator. Under a nitrogen atmosphere, the temperature is raised to 180-230°C to melt the material, followed by a first holding at this temperature. The temperature is then raised to 230-280°C for a second holding. After the reaction is complete, the reactant is removed, which is the long-chain nylon.

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