A process for the preparation of sodium N,N-dimethylglycinate

Abstract

The application provides a method for preparing sodium N,N-dimethylglycinate. The method comprises the following steps: (1) adding a sodium chloroacetate solution into a dimethylamine solution and reacting to obtain a reaction solution; wherein the pH of the reaction is controlled to be greater than 10.5 by adding alkali before or during the reaction; (2) mixing the reaction solution with hydrochloric acid after deamination treatment to obtain a solution containing N,N-dimethylglycinate; (3) reacting the solution containing N,N-dimethylglycinate with sodium hydroxide after impurity removal, solvent crystallization and drying to obtain a sodium N,N-dimethylglycinate product. The method can obtain sodium N,N-dimethylglycinate with high purity, high yield and good stability, and by controlling the drying temperature of the wet product of sodium N,N-dimethylglycinate, the sodium N,N-dimethylglycinate hydrate with good stability can be obtained.

Description

Technical Field

[0001] This invention belongs to the field of chemical synthesis technology, specifically relating to a method for preparing sodium N,N-dimethylglycinate. Background Technology

[0002] N,N-Dimethylglycine sodium salt, CAS No.: 18319-88-5, molecular weight: 127.11, molecular formula: C4H8NNaO2, is a white flaky crystal or powder.

[0003] Sodium dimethylglycine (DMG-Na) is a sodium salt form of dimethylglycine, which makes its molecular structure and properties more stable. In animal production, DMG-Na has been studied for its ability to improve broiler production performance and reduce economic costs. Studies have shown that adding appropriate amounts of DMG-Na to feed can improve the apparent digestibility of crude protein in broilers, increase protease activity in pancreatic tissue, and reduce the feed conversion ratio, thereby improving broiler production performance. Adding 0.1% DMG-Na to the diet also has a positive effect on improving liver antioxidant capacity and immune function. On September 4, 2023, the European Commission issued Regulation (EU) 2023 / 1682, updating the approval of dimethylglycine sodium salt as a feed additive for fattening chickens.

[0004] Traditional methods for producing sodium N,N-dimethylglycinate involve first preparing dimethylglycine, which is then reacted with sodium hydroxide. One method for preparing N,N-dimethylglycine involves reacting chloroacetic acid with sodium carbonate or sodium hydroxide to pH 7-8, then cooling the temperature below 30°C, adding an aqueous solution of dimethylamine dropwise to the sodium chloroacetate solution, followed by desalting via electrodialysis and crystallization from ethanol to obtain N,N-dimethylglycine, with a yield of only about 60%. Alternatively, patent document CN103524363B uses chloroacetic acid and n-butanol reacting under p-toluenesulfonic acid conditions to produce butyl chloroacetate. The butyl chloroacetate is then reacted with dimethylamine under specific conditions to produce butyl N,N-dimethylglycinate. Finally, liquid alkali is added to the butyl N,N-dimethylglycinate to adjust the pH, while the reaction system is strictly controlled within a specific temperature range to ultimately produce sodium N,N-dimethylglycinate. However, this method uses a large amount of organic solvents, requiring specialized solvent recovery and cumbersome post-processing. The use of sodium benzyl sulfonate as a catalyst is relatively expensive and difficult to process, increasing production costs. Furthermore, the high-temperature debutylation of N,N-dimethylglycine butyl ester under alkaline conditions is incomplete, resulting in residual impurities in the product, requiring multiple purification processes. For example, patent document CN103467324B discloses a method for preparing dimethylglycine suitable for industrial production. This method first prepares an aqueous solution of chloroacetic acid, then adds the chloroacetic acid solution to an aqueous solution of dimethylamine for reaction. After the reaction is complete, excess dimethylamine is removed, and the product is concentrated, crystallized, centrifuged, and dried to obtain dimethylglycine. This method uses the direct reaction of chloroacetic acid and dimethylamine to generate dimethylglycine; the released hydrogen chloride is absorbed by free dimethylamine to form dimethylamine hydrochloride impurities. The chloroacetic acid concentration must reach 50%, and the acid-base neutralization of chloroacetic acid and dimethylamine to form carboxylic amines is difficult to separate. Summary of the Invention

[0005] To address one of the aforementioned technical problems in the prior art, this invention provides a method for preparing high-purity and high-yield sodium N,N-dimethylglycinate, which is simple in process and easy for industrial production.

[0006] The technical solution of the present invention is as follows:

[0007] On one hand, the present invention provides a method for preparing sodium N,N-dimethylglycinate, the method comprising the following steps:

[0008] (1) Add sodium chloroacetate solution to dimethylamine solution and react to obtain reaction solution; wherein, the pH of the reaction is controlled to be greater than 10.5 by adding alkali before or during the reaction;

[0009] (2) The reaction solution is treated with deamine and then mixed with hydrochloric acid to obtain a solution containing N,N-dimethylglycine;

[0010] (3) The N,N-dimethylglycine-containing liquid is purified and then reacted with sodium hydroxide. The solvent is crystallized and dried to obtain sodium N,N-dimethylglycine product.

[0011] According to some embodiments of the present invention, in step (1), the pH of the reaction is controlled to be greater than 10.5 by adding alkali before or during the reaction. For example, it can be 10.6, 10.8, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5 or any value between them.

[0012] According to some embodiments of the present invention, in step (1), the pH of the reaction is controlled to be 11.0-13.5 by adding alkali before or during the reaction, for example, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5 or any value between them.

[0013] In some embodiments, in step (1), the pH of the reaction is controlled to be 11.5-13.5 by adding alkali before or during the reaction. In some embodiments, in step (1), the pH of the reaction is controlled to be 12.0-13.5 by adding alkali before or during the reaction. In some embodiments, in step (1), the pH of the reaction is controlled to be 12.5-13.5 by adding alkali before or during the reaction.

[0014] The present invention controls the pH of the reaction within a specific range by adding alkali before or during the reaction in step (1), which can effectively reduce the content of quaternary ammonium salt impurities in the reaction solution. In some embodiments, the quaternary ammonium salt content in the reaction solution in step (1) is not higher than 20 wt%. In some embodiments, the quaternary ammonium salt content in the reaction solution in step (1) is not higher than 15 wt%. In some embodiments, the quaternary ammonium salt content in the reaction solution in step (1) is not higher than 10 wt%, for example, 10 wt%, 9 wt%, 8 wt%, 7 wt%, 6 wt%, 5 wt%, 4 wt%, 3 wt%, 2 wt%, 1 wt%, or any value between them.

[0015] According to some embodiments of the present invention, in step (1), the alkali includes, but is not limited to, alkali metal hydroxides, and examples of the alkali include, but are not limited to, sodium hydroxide, potassium hydroxide, etc., with sodium hydroxide being preferred.

[0016] In this invention, in step (1), the sodium chloroacetate solution is preferably added to the dimethylamine solution by dripping.

[0017] According to some embodiments of the present invention, in step (1), the mass concentration of dimethylamine in the dimethylamine solution is 30-50%, preferably 35-45%.

[0018] According to some embodiments of the present invention, in step (1), the pH of the sodium chloroacetate solution is 7.0-9.0.

[0019] According to some embodiments of the present invention, in step (1), the sodium chloroacetate solution is prepared by reacting a chloroacetic acid solution with sodium hydroxide. In some embodiments, the sodium chloroacetate solution is prepared by a method comprising the following steps: adding sodium hydroxide to the chloroacetic acid solution until the pH is greater than 7.0 (e.g., 7.0-9.0, preferably 7.0-8.0), and reacting to obtain the sodium chloroacetate solution. In some embodiments, the mass concentration of the chloroacetic acid solution is 30-50%; for example, 30%, 35%, 40%, 45%, 50%, or any value between therewith.

[0020] According to some embodiments of the present invention, when preparing a sodium chloroacetate solution, the reaction temperature between the chloroacetate solution and sodium hydroxide is 30-40°C. In this invention, the reaction temperature between the chloroacetate solution and sodium hydroxide can be controlled at 30-40°C by controlling the dropping rate of sodium hydroxide.

[0021] According to some embodiments of the present invention, in step (1), the molar ratio of sodium chloroacetate in the sodium chloroacetate solution to dimethylamine in the dimethylamine solution is 1:(1-5), for example, 1:1, 1:1.2, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5 or any value between them, preferably 1:(1.2-3).

[0022] According to some embodiments of the present invention, in step (1), the temperature of the reaction is 20-70°C, for example 20°C, 30°C, 40°C, 50°C, 60°C, 70°C or any value between them, preferably 30-60°C.

[0023] According to some embodiments of the present invention, in step (2), the deamine treatment includes vacuum concentration to remove amine impurities. Preferably, the vacuum concentration temperature is 55-65°C. Preferably, the vacuum concentration is carried out until salts precipitate.

[0024] According to some embodiments of the present invention, in step (2), the amount of hydrochloric acid used satisfies the following condition: the pH of the reaction solution after deamination treatment is 4.0-8.0, preferably 5.0-6.0.

[0025] According to some embodiments of the present invention, in step (3), the impurity removal includes removing impurities such as chloride ions and pigments from the liquid.

[0026] According to some embodiments of the present invention, in step (3), the impurity removal includes:

[0027] The solution containing N,N-dimethylglycine was subjected to electrodialysis, decolorization, and concentration.

[0028] Preferably, the feed solution is treated by electrodialysis until the chloride ion concentration is ≤1000ppm.

[0029] Preferably, activated carbon is used for decolorization.

[0030] Preferably, the concentration process is vacuum concentration, and more preferably, the concentration is carried out until the liquid is viscous and oily.

[0031] According to some embodiments of the present invention, in step (3), the amount of sodium hydroxide added satisfies the following condition: the pH of the purified solution is 10.0-13.0, for example, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0 or any value between them.

[0032] According to some embodiments of the present invention, in step (3), the solvent used for solvent crystallization includes, but is not limited to, alcohol solvents, preferably ethanol.

[0033] According to some embodiments of the present invention, in step (3), the solvent crystallization includes: using ethanol as a solvent to perform cooling crystallization, preferably cooling to below 10°C.

[0034] According to some embodiments of the present invention, the drying temperature in step (3) is 30°C-60°C, for example, 30°C, 40°C, 50°C, 60°C, or any value between them. The method of the present invention, by controlling the drying temperature of the wet N,N-dimethylglycinate sodium product, can obtain N,N-dimethylglycinate sodium hydrate, which is a N,N-dimethylglycinate sodium crystal with a specific water content and high stability.

[0035] According to some embodiments of the present invention, the method includes the following steps:

[0036] (S1) Add sodium hydroxide to an aqueous solution of chloroacetic acid until the pH is 7.0-9.0, and react (preferably at 30-40℃) to obtain a sodium chloroacetate solution;

[0037] (S2) Add the sodium chloroacetate solution to the dimethylamine solution and react to obtain a reaction solution, wherein the pH of the reaction is controlled to be 11.0-13.5 by adding sodium hydroxide before or during the reaction;

[0038] (S3) The reaction solution is concentrated under reduced pressure to remove amine impurities, and then hydrochloric acid is added to adjust the pH to 5.0-6.0; to obtain a solution containing N,N-dimethylglycine.

[0039] (S4) The feed solution containing N,N-dimethylglycine is subjected to electrodialysis until the chloride ion concentration in the feed solution is ≤1000ppm. Then, it is decolorized with activated carbon and concentrated under reduced pressure to obtain a concentrated solution. Sodium hydroxide is added to the concentrated solution to adjust the pH to 10.0-13.0, and ethanol is added to cool it to below 10°C to precipitate crystals. After drying at 30°C-60°C, the sodium N,N-dimethylglycine product is obtained.

[0040] On the other hand, the present invention provides a sodium N,N-dimethylglycinate crystal, wherein the sodium N,N-dimethylglycinate crystal is a hydrate of sodium N,N-dimethylglycinate.

[0041] In some embodiments, the water content of the crystals is 20 wt%-25 wt%, for example, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, or any value between therewith. In some embodiments, the water content in the N,N-dimethylglycinate sodium crystals is 21 wt%-23 wt%.

[0042] In some embodiments, Cu-Kα radiation is used, and the X-ray powder diffraction pattern of the crystal, expressed in 2θ angles, has a diffraction peak at 7.16 ± 0.2°.

[0043] In some embodiments, Cu-Kα radiation is used, and the X-ray powder diffraction pattern of the crystal, expressed in 2θ angles, has diffraction peaks at 7.16±0.2° and at one or more of the following 2θ angles: 14.26±0.2°, 28.66±0.2°, 36.01±0.2°.

[0044] In some embodiments, Cu-Kα radiation is used, and the X-ray powder diffraction pattern of the crystal, expressed in 2θ angles, has diffraction peaks at 7.16±0.2°, 14.26±0.2°, and 28.66±0.2°.

[0045] In some embodiments, Cu-Kα radiation is used, and the X-ray powder diffraction pattern of the crystal, expressed in 2θ angles, has diffraction peaks at 7.16±0.2°, 14.26±0.2°, 28.66±0.2°, and 36.01±0.2°.

[0046] In some embodiments, the X-ray powder diffraction pattern of the crystal, expressed in 2θ angles, is compared with... Figure 1 Basically the same.

[0047] In some embodiments, the N,N-dimethylglycine sodium crystals are prepared by the method described above in this invention, provided that the drying temperature in step (3) is 30°C-60°C, for example, 30°C, 40°C, 50°C, 60°C, or any value between them. If the drying temperature is too high, for example above 80°C, the moisture content of the N,N-dimethylglycine sodium crystals will decrease, increasing their hygroscopicity and thus reducing their stability.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1. The method of the present invention reduces the generation of impurities such as quaternary ammonium salts and carboxylic acid amines by controlling the material dropwise addition method and pH during the reaction of dimethylamine with sodium chloroacetate, thereby reducing the difficulty of post-processing and impurity treatment, reducing the use of dimethylamine, and improving product yield and purity.

[0050] 2. The method of the present invention uses a dimethylglycine solution treated by electrodialysis desalination to directly generate sodium dimethylglycine by liquid alkali, reducing one crystallization step, simplifying the process steps, and at the same time avoiding the dimethylglycine in the product preparation from absorbing moisture and clumping, which would affect the product quality.

[0051] 3. This invention improves the stability of N,N-dimethylglycine sodium by drying the wet product at a suitable temperature to obtain N,N-dimethylglycine sodium hydrate and control the water content in the product.

[0052] 4. The present invention produces no byproducts in the preparation of N,N-dimethylglycine, does not require complicated post-processing steps, and the resulting crystallization mother liquor can be recycled, saving costs and being environmentally friendly. Attached Figure Description

[0053] Figure 1 The image shows the XRD pattern of sodium dimethylglycinate crystals obtained in Example 1 of this invention. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way.

[0055] This application reveals that in existing processes for preparing N,N-dimethylglycine, the addition of dimethylamine to sodium chloroacetate leads to an excess of sodium chloroacetate reacting with the generated dimethylglycine to form a large amount of quaternary ammonium salt impurities. This increases the difficulty of subsequent impurity treatment, and the resulting N,N-dimethylglycine significantly reduces the yield and quality of sodium N,N-dimethylglycinate during preparation. This application creatively discovers that by adding sodium chloroacetate solution dropwise to the dimethylamine solution during the preparation of N,N-dimethylglycine and adjusting the pH within a suitable range, this problem can be effectively solved.

[0056] Based on this, the present invention provides a method for preparing high-purity and high-yield sodium N,N-dimethylglycinate that is convenient for industrial production, the method comprising the following steps:

[0057] (1) Add sodium chloroacetate solution to dimethylamine solution and react to obtain reaction solution; wherein, the pH of the reaction is controlled to be greater than 10.5 by adding alkali before or during the reaction;

[0058] (2) The reaction solution is treated with deamine and then mixed with hydrochloric acid to obtain a solution containing N,N-dimethylglycine;

[0059] (3) The N,N-dimethylglycine-containing liquid is purified and then reacted with sodium hydroxide. The solvent is crystallized and dried to obtain sodium N,N-dimethylglycine product.

[0060] This invention employs a method of adding sodium chloroacetate (preferably slowly dropwise) to an aqueous solution of dimethylamine (counter-dropwise addition), while simultaneously adding sodium hydroxide to control the pH within a specific range. This prevents the generated dimethylglycine from reacting with excess sodium chloroacetate to form impurity quaternary ammonium salts, thus reducing the amount of dimethylamine used and increasing the yield. The purified dimethylglycine solution is then directly used to prepare sodium dimethylglycinate dihydrate, reducing the need for a single crystallization step and preventing the dimethylglycine in the product from absorbing moisture and clumping, which would negatively impact product quality.

[0061] Furthermore, this invention has found that by controlling the drying temperature in step (3) to not exceed 80°C (e.g., 30-60°C), N,N-dimethylglycine sodium hydrate can be obtained, and by controlling the water content in the N,N-dimethylglycine sodium product to be within a suitable range, the product stability can be improved.

[0062] As one specific embodiment, the method for preparing sodium N,N-dimethylglycine according to the present invention includes the following steps:

[0063] A. Prepare an aqueous solution of sodium chloroacetate by adding sodium hydroxide to a 30%-50% chloroacetic acid solution to adjust the pH to 7.0-9.0;

[0064] B. Add sodium chloroacetate aqueous solution dropwise to dimethylamine aqueous solution, while simultaneously adding sodium hydroxide solution to control the pH of the reaction at 11.0-13.5, to obtain the reaction solution;

[0065] C. The reaction solution is concentrated under reduced pressure to remove the amine, and the pH is adjusted to 4.0-8.0 with hydrochloric acid;

[0066] D. After removing sodium chloride by electrodialysis, the product is concentrated, the pH is adjusted to 10.0-13.0 with sodium hydroxide, ethanol is added to induce crystallization, and the product is obtained by filtration and drying at 30-60℃.

[0067] Unless otherwise specified, all reagents used in the following experiments of this invention are commercially available products or reagents prepared according to conventional methods. Unless otherwise specified, all methods used in the experiments are conventional experimental methods. Unless otherwise specified, all instruments used in the experiments are commercially available.

[0068] In the following experiments of this invention, the quaternary ammonium salt content in the reaction solution was tested by HPLC, and then calculated by the area normalization method. The chromatographic conditions were as follows:

[0069] The chromatographic column was an amino column, model Welch Ultimate XB-NH2, with a particle size of 5 μm and a diameter × length of 4.6 × 250 mm. The mobile phase was 20 mM ammonium dihydrogen phosphate solution (pH = 3-4): acetonitrile = 40:60 (V / V). The column temperature was 30℃ and the detection wavelength was 205 nm.

[0070] The moisture content of the product was determined by the loss on drying method, which involves drying the product at 105°C until constant weight before testing.

[0071] The powder X-ray diffraction measurement conditions in the following experiments of this invention are as follows:

[0072] Equipment used: SmartLab 3KW X-ray Diffractoment; Conditions: CuKα (40kV, 40mA); Scan rate: 20.00deg / min; Scan range: 3°~40°.

[0073] Example 1

[0074] Step 1: Dissolve 180g of chloroacetic acid in 180g of water (50%). After stirring and dissolving, start adding sodium hydroxide solution dropwise. Stop adding the solution when the pH reaches 7.0-9.0. Control the dropping rate of sodium hydroxide solution during the process and keep the solution temperature at 30℃ to obtain sodium chloroacetate solution.

[0075] Step 2: Slowly add the sodium chloroacetate solution prepared in Step 1 to 257g of a 40% dimethylamine aqueous solution, controlling the sodium chloroacetate addition time to 3 hours; simultaneously add sodium hydroxide solution to control the reaction pH to 13.5, and maintain the reaction temperature at 30℃. After the addition is complete, begin concentrating under reduced pressure at 55℃ to remove the amine. Concentrate until a significant amount of salt precipitates, then stop concentration. Add hydrochloric acid to the concentrated solution to adjust the pH to 5.0, and then cool to room temperature.

[0076] After the reaction was completed, a sample was taken and the quaternary ammonium salt content of the reaction solution was measured to be 8.6%.

[0077] Step 3: The feed solution is desalted by electrodialysis. Electrodialysis is stopped when chloride ions are ≤1000ppm. The final feed solution is collected, activated carbon is added, and the solution is heated and stirred for decolorization. After filtration, the decolorized solution is concentrated under reduced pressure to a viscous oily state. Sodium hydroxide solution is added to the concentrate to adjust the pH to 10.5, and ethanol is added to cool the solution to below 10°C to induce crystallization. The solution is centrifuged to obtain wet sodium dimethylglycinate.

[0078] Step 4: Transfer the wet sodium dimethylglycinate to a vacuum drying oven and dry it under reduced pressure at 30°C.

[0079] The final product yielded 128.3 grams, with a yield of 71.3%, a purity of 99.83%, and a moisture content of 22.9 wt%. It consisted of white crystalline granules. XRD characterization results are as follows: Figure 1 As shown in Table 1.

[0080] Table 1

[0081]

[0082] Example 2

[0083] Step 1: Dissolve 180g of chloroacetic acid in 180g of water (50%). After stirring and dissolving, start adding sodium hydroxide solution dropwise. Stop adding the solution when the pH reaches 7.0-9.0. Control the dropping rate of sodium hydroxide solution during the process to keep the solution temperature at 35℃, and obtain sodium chloroacetate solution.

[0084] Step 2: Slowly add the sodium chloroacetate solution prepared in Step 1 to 644.1g of a 40% dimethylamine aqueous solution, controlling the sodium chloroacetate addition time to 4 hours; simultaneously add sodium hydroxide solution to control the reaction pH to 13.5, and maintain the reaction temperature at 40℃. After the addition is complete, begin concentrating under reduced pressure at 65℃ to remove the amine. Concentrate until a significant amount of salt precipitates, then stop concentration. Add hydrochloric acid to the concentrated solution to adjust the pH to 5.5, and then cool to room temperature.

[0085] After the reaction was completed, a sample was taken and the quaternary ammonium salt content of the reaction solution was measured to be 7.9%.

[0086] Step 3: The feed solution is desalted by electrodialysis. Electrodialysis is stopped when chloride ions are ≤1000ppm. The final feed solution is collected, activated carbon is added, and the solution is heated and stirred for decolorization. After filtration, the decolorized solution is concentrated under reduced pressure to a viscous oily state. Sodium hydroxide solution is added to the concentrate to adjust the pH to 12.5, and ethanol is added to cool the solution to below 10°C to induce crystallization. The solution is centrifuged to obtain wet sodium dimethylglycinate.

[0087] Step 4: Transfer the wet sodium dimethylglycinate to a vacuum drying oven and dry it under reduced pressure at 40°C.

[0088] The final product yielded 132.3 grams, with a yield of 73.5%, a purity of 99.91%, and a moisture content of 22.1 wt%. It was a white crystalline granule.

[0089] Example 3

[0090] Step 1: Dissolve 180g of chloroacetic acid in 420g of water (30%). After stirring and dissolving, start adding sodium hydroxide solution dropwise. Stop adding the solution when the pH reaches 7.0-9.0. Control the dropping rate of sodium hydroxide solution during the process to keep the solution temperature at 40℃, and obtain sodium chloroacetate solution.

[0091] Step 2: Slowly add the sodium chloroacetate solution prepared in Step 1 to 644.1g of a 40% dimethylamine aqueous solution, controlling the sodium chloroacetate addition time to 3 hours; simultaneously, add sodium hydroxide solution to control the reaction pH to 12.5, and maintain the reaction temperature at 40℃. After the addition is complete, begin concentrating under reduced pressure at 60℃ to remove the amine. Concentrate until a significant amount of salt precipitates, then stop concentration. Add hydrochloric acid to the concentrated solution to adjust the pH to 5.0, and then cool to room temperature.

[0092] After the reaction was completed, a sample was taken and the quaternary ammonium salt content of the reaction solution was measured to be 8.4%.

[0093] Step 3: The feed solution is desalted by electrodialysis. Electrodialysis is stopped when chloride ions are ≤1000ppm. The final feed solution is collected, activated carbon is added, and the solution is heated and stirred for decolorization. After filtration, the decolorized solution is concentrated under reduced pressure to a viscous oily state. Sodium hydroxide solution is added to the concentrate to adjust the pH to 12.0, and ethanol is added to cool the solution to below 10°C to induce crystallization. The solution is centrifuged to obtain wet sodium dimethylglycinate.

[0094] Step 4: Transfer the wet sodium dimethylglycinate to a vacuum drying oven and dry it under reduced pressure at 50°C.

[0095] The final product yielded 131.04 grams, with a yield of 72.8%, a purity of 99.79%, and a moisture content of 21.7 wt%. It was a white crystalline granule.

[0096] Example 4

[0097] Step 1: Dissolve 180g of chloroacetic acid in 270g of water (40%). After stirring and dissolving, start adding sodium hydroxide solution dropwise. Stop adding the solution when the pH reaches 7.0-9.0. Control the dropping rate of sodium hydroxide solution during the process to keep the solution temperature at 40℃, and obtain sodium chloroacetate solution.

[0098] Step 2: Slowly add the sodium chloroacetate solution prepared in Step 1 to 644.1g of a 40% dimethylamine aqueous solution. The sodium chloroacetate addition time is controlled at 3h (pH measured at 10.5), and the reaction temperature is 40℃. After the addition is complete, the temperature is raised to 60℃ and the solution is concentrated under reduced pressure to remove the amine. Concentration is stopped when a significant amount of salt precipitates. Then, hydrochloric acid is added to the concentrated solution to adjust the pH to 5.0, and the solution is cooled to room temperature.

[0099] After the reaction was completed, a sample was taken and the quaternary ammonium salt content of the reaction solution was measured to be 34.8%.

[0100] Step 3: The feed solution is desalted by electrodialysis. Electrodialysis is stopped when chloride ions are ≤1000ppm. The final feed solution is collected, activated carbon is added, and the solution is heated and stirred for decolorization. After filtration, the decolorized solution is concentrated under reduced pressure to a viscous oily state. Sodium hydroxide solution is added to the concentrate to adjust the pH to 12.0, and ethanol is added to cool the solution to below 10°C to induce crystallization. The solution is centrifuged to obtain wet sodium dimethylglycinate.

[0101] Step 4: Transfer the wet sodium dimethylglycinate to a vacuum drying oven and dry it under reduced pressure at 90°C.

[0102] The final product yielded 118.8 grams, with a yield of 66.0%, a purity of 98.5%, and a moisture content of 12.1 wt%. It was a white crystalline powder.

[0103] Example 5

[0104] Step 1: Dissolve 180g of chloroacetic acid in 420g of water (30%). After stirring and dissolving, start adding sodium hydroxide solution dropwise. Stop adding the solution when the pH reaches 7.0-9.0. Control the dropping rate of sodium hydroxide solution during the process to keep the solution temperature at 40℃, and obtain sodium chloroacetate solution.

[0105] Step 2: Slowly add the sodium chloroacetate solution prepared in Step 1 to 644.1g of a 40% dimethylamine aqueous solution, controlling the sodium chloroacetate addition time to 3 hours; simultaneously add sodium hydroxide solution to control the reaction pH to 11.0, and maintain the reaction temperature at 40℃. After the addition is complete, begin heating to 60℃ and concentrating under reduced pressure to remove the amine. Concentrate until a significant amount of salt precipitates, then stop concentration. Add hydrochloric acid to the concentrated solution to adjust the pH to 5.0, and then cool to room temperature.

[0106] After the reaction was completed, a sample was taken and the quaternary ammonium salt content of the reaction solution was measured to be 15.6%.

[0107] Step 3: The feed solution is desalted by electrodialysis. Electrodialysis is stopped when chloride ions are ≤1000ppm. The final feed solution is collected, activated carbon is added, and the solution is heated and stirred for decolorization. After filtration, the decolorized solution is concentrated under reduced pressure to a viscous oily state. Sodium hydroxide solution is added to the concentrate to adjust the pH to 12.0, and ethanol is added to cool the solution to below 10°C to induce crystallization. The solution is centrifuged to obtain wet sodium dimethylglycinate.

[0108] Step 4: Transfer the wet sodium dimethylglycinate to a vacuum drying oven and dry it under reduced pressure at 60°C.

[0109] The final product yielded 122.76 grams, with a yield of 68.2%, a purity of 99.23%, and a moisture content of 21.2 wt%. It was a white crystalline granule.

[0110] Comparative Example 1

[0111] Step 1: Dissolve 143g of chloroacetic acid in 150g of water. After stirring and dissolving, start adding sodium hydroxide solution dropwise. Stop adding the solution when the pH reaches 7.0-9.0. Control the dropping rate of sodium hydroxide solution during the process to keep the solution temperature at 40℃, and obtain sodium chloroacetate solution.

[0112] Step 2: Add a 40% dimethylamine aqueous solution dropwise to the sodium chloroacetate solution prepared in Step 1. The molar ratio of sodium chloroacetate to dimethylamine is 1:1.2. The addition time is controlled at about 1.5 hours. After the dimethylamine addition is completed, keep the reaction at the temperature for 1.5 hours (the pH value is measured to be 9.5). After the temperature is maintained, adjust the pH value to 5-6 with hydrochloric acid and cool down to room temperature.

[0113] After the reaction was completed, a sample was taken and the quaternary ammonium salt content of the reaction solution was measured to be 36.7%.

[0114] Step 3: The solution is desalted by electrodialysis. Electrodialysis is stopped when chloride ion concentration is ≤1000ppm. The power is turned off and the solution is collected. The solution is concentrated under reduced pressure until it becomes a viscous oil. Sodium hydroxide solution is added to the concentrate to adjust the pH to 12.0, and ethanol is added to cool the solution to below 10°C to induce crystallization. The solution is centrifuged to obtain wet sodium dimethylglycinate.

[0115] Step 4: Transfer the wet sodium dimethylglycinate to a vacuum drying oven and dry it under reduced pressure at 80°C.

[0116] The final product yielded 88.66 grams, with a yield of 62%, a purity of approximately 98%, and a moisture content of 17.7 wt%, and was a white crystalline powder.

[0117] Comparative Example 2

[0118] Step 1: Dissolve 180g of chloroacetic acid in 420g of water (30%), stir to dissolve, and then add dropwise to 644.1g of a 40% dimethylamine aqueous solution. The chloroacetic acid addition time is controlled at 3 hours, and the reaction temperature is 40℃. After the addition is complete, the temperature is raised to 60℃ and the solution is concentrated under reduced pressure to remove the amine, until a large amount of white crystals appear.

[0119] Step 2: Add sodium hydroxide solution to the concentrated solution to adjust the pH to 12.0, and simultaneously add ethanol to cool the solution to below 10°C to allow crystals to form. Centrifuge to obtain wet sodium dimethylglycinate.

[0120] Step 3: Transfer the wet sodium dimethylglycinate to a vacuum drying oven and dry it under reduced pressure at 50°C.

[0121] The final product yielded 95.76 grams, with a yield of 53.2%, a purity of approximately 96.4%, and a moisture content of 21.8 wt%. It was a white crystalline granule.

[0122] The synthesis conditions (addition method of dimethylamine aqueous solution and sodium chloroacetate, pH of sodium chloroacetate reaction with dimethylamine, quaternary ammonium salt content of impurities in the reaction solution, drying temperature of wet dimethylglycinate sodium, etc.) of the above embodiments and comparative examples, as well as the comparison results of N,N-dimethylglycinate sodium yield, purity, water content, etc., are shown in Table 2.

[0123] Table 2

[0124]

[0125]

[0126] Note: In Table 2, dimethylamine is added dropwise to sodium chloroacetate – forward addition; sodium chloroacetate is added dropwise to dimethylamine – reverse addition; chloroacetic acid is added dropwise to dimethylamine – reverse addition. ※ .

[0127] As can be seen from the data in Table 2, the schemes of Examples 1-5 of the present invention significantly improved the yield and purity of sodium N,N-dimethylglycine by adding sodium chloroacetate solution dropwise to dimethylamine solution and adjusting the pH of the reaction within a suitable range by adding alkali during the preparation of N,N-dimethylglycine.

[0128] High humidity stability test

[0129] Take the sample from the example and spread it evenly in a dry, clean petri dish to form a thin layer of about 3 mm. Place it in an environment with a temperature of 25°C and a relative humidity of 75% ± 5% (for constant humidity conditions, a saturated salt solution can be placed in the bottom of a sealed container such as a desiccator, and a relative humidity of 75% ± 1%). Take it out on the 5th and 10th days respectively, and measure the average weight gain of the sample. The results are shown in Table 3.

[0130] Table 3

[0131] sample Average weight gain (%) on day 5 Average weight gain (%) on day 10 Example 1 2.13±0.04 2.71±0.24 Example 2 2.41±0.23 2.97±0.33 Example 3 2.52±0.16 3.03±0.18 Example 4 20.07±0.43 28.51±0.37 Example 5 3.01±0.17 3.61±0.07 Comparative Example 1 26.51±1.02 30.42±1.13 Comparative Example 2 2.16±0.20 2.54±0.02

[0132] As shown in Table 3, the products obtained by drying wet sodium dimethylglycinate in Examples 1-3, Example 5, and Comparative Example 2 within a suitable temperature range (30-60℃) have a high water content of crystallization (21-23%). After being placed under constant temperature and humidity conditions of 25℃ and 75% ± 5% for 10 days, their moisture absorption and weight gain are less than 4%, indicating relatively high stability. In contrast, the products obtained by drying wet sodium dimethylglycinate at a higher temperature (80-90℃) exhibit moisture absorption and weight gain exceeding 20%, indicating low stability.

[0133] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing sodium N,N-dimethylglycine, comprising the following steps: (1) Add sodium chloroacetate solution to dimethylamine solution and react to obtain a reaction solution; wherein, The pH of the reaction is controlled to be greater than 10.5 by adding alkali before or during the reaction; (2) The reaction solution is treated with deamine and then mixed with hydrochloric acid to obtain a solution containing N,N-dimethylglycine; (3) The N,N-dimethylglycine-containing liquid is purified and then reacted with sodium hydroxide. The solvent is crystallized and dried to obtain sodium N,N-dimethylglycine product.

2. The method according to claim 1, characterized in that, In step (1), the pH of the reaction is controlled to be 11.0-13.5, preferably 12.0-13.5, and more preferably 12.5-13.5, by adding alkali before or during the reaction; and / or, The alkali comprises an alkali metal hydroxide, preferably sodium hydroxide and / or potassium hydroxide, more preferably sodium hydroxide; and / or, In step (1), the sodium chloroacetate solution is added dropwise.

3. The method according to claim 1 or 2, characterized in that, In step (1), the dimethylamine solution has a dimethylamine mass concentration of 30-50%, preferably 35-45%; and / or, The sodium chloroacetate solution has a pH of 7.0-9.0, preferably 7.0-8.0; and / or, In step (1), the quaternary ammonium salt content in the reaction solution is no more than 20 wt%, preferably no more than 15 wt%, and more preferably no more than 10 wt%.

4. The method according to any one of claims 1-3, characterized in that, The sodium chloroacetate solution is prepared by reacting chloroacetic acid solution with sodium hydroxide. Preferably, sodium hydroxide is added to the chloroacetic acid solution to adjust the pH to 7.0-9.0, more preferably 7.0-8.0, and the sodium chloroacetate solution is obtained after the reaction; Preferably, the chloroacetic acid solution has a mass concentration of 30-50%; Preferably, the reaction temperature of the chloroacetic acid solution with sodium hydroxide is 30-40°C.

5. The method according to any one of claims 1-4, characterized in that, The molar ratio of sodium chloroacetate in the sodium chloroacetate solution to dimethylamine in the dimethylamine solution is 1:(1-5), preferably 1:(1.2-3); and / or, In step (1), the reaction temperature is 20-70℃, preferably 30-60℃.

6. The method according to any one of claims 1-5, characterized in that, In step (2), the deamine treatment includes vacuum concentration to remove amine impurities; preferably, the vacuum concentration temperature is 55-65°C; preferably, vacuum concentration is carried out until salt precipitation occurs; and / or, The amount of hydrochloric acid used is such that the pH of the reaction solution after deamination is 4.0-8.0, preferably 5.0-6.

0.

7. The method according to any one of claims 1-6, characterized in that, In step (3), the impurity removal includes removing chloride ions and pigments from the feed solution; preferably, the impurity removal includes: The solution containing N,N-dimethylglycine was subjected to electrodialysis, decolorization, and concentration. Preferably, the feed solution is treated by electrodialysis until the chloride ion concentration is ≤1000ppm; Preferably, activated carbon is used for decolorization; Preferably, the concentration is vacuum concentration, and more preferably, the concentration is carried out until the liquid is viscous and oily.

8. The method according to any one of claims 1-7, characterized in that, In step (3), the amount of sodium hydroxide added satisfies the following conditions: the pH of the purified solution is 10-13; and / or, The solvent used for solvent crystallization includes lower alcohols, preferably ethanol; preferably, the solvent crystallization includes: using ethanol as a solvent for cooling crystallization; and / or, The drying temperature in step (3) is 30℃-60℃.

9. The method according to any one of claims 1-8, characterized in that, The method includes the following steps: (S1) Sodium hydroxide is added to an aqueous chloroacetic acid solution until the pH is 7.0-9.0, and a sodium chloroacetic acid solution is obtained after the reaction; preferably, the reaction temperature of the aqueous chloroacetic acid solution with sodium hydroxide is 30-40℃; (S2) Add the sodium chloroacetate solution to the dimethylamine solution and react to obtain a reaction solution, wherein the pH of the reaction is controlled to be 11.0-13.5, preferably 12.5-13.5, by adding sodium hydroxide before or during the reaction; (S3) The reaction solution is concentrated under reduced pressure to remove amine impurities, and then hydrochloric acid is added to adjust the pH to 5.0-6.0 to obtain a solution containing N,N-dimethylglycine; (S4) The feed solution containing N,N-dimethylglycine is subjected to electrodialysis until the chloride ion concentration in the feed solution is ≤1000ppm. Then, it is decolorized with activated carbon and concentrated under reduced pressure to obtain a concentrated solution. Sodium hydroxide is added to the concentrated solution to adjust the pH to 10.0-13.0, and ethanol is added to cool it to below 10°C to precipitate crystals. After drying at 30°C-60°C, the sodium N,N-dimethylglycine product is obtained.

10. A sodium N,N-dimethylglycinate crystal, which is a hydrate of sodium N,N-dimethylglycinate; Preferably, the water content in the crystal is 20wt% to 25wt%, more preferably 21wt% to 23wt%; Preferably, using Cu-Kα radiation, the X-ray powder diffraction pattern of the crystal, expressed in 2θ angles, has a diffraction peak at 7.16±0.2°; Preferably, using Cu-Kα radiation, the X-ray powder diffraction pattern of the crystal, expressed in 2θ angles, also has diffraction peaks at one or more of the following 2θ angles: 14.26±0.2°, 28.66±0.2°, 36.01±0.2°; Preferably, using Cu-Kα radiation, the X-ray powder diffraction pattern of the crystal, expressed in 2θ angles, has diffraction peaks at 7.16±0.2°, 14.26±0.2°, and 28.66±0.2°; Preferably, the X-ray powder diffraction pattern of the crystal, expressed at a 2θ angle, is substantially the same as that in Figure 1; Preferably, the crystal is prepared by the method of claim 8 or 9.

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