Preparation method of dimethylamino borane

Abstract

The invention relates to the technical field of chemical preparation, in particular to a preparation method of a reducing agent material dimethylamino borane for pretreatment of horizontal chemical copper deposition in a PCB (printed circuit board) process. The preparation method comprises the following steps: firstly adding an organic solvent I in an inert gas atmosphere, cooling to 0 DEG C or below, sequentially adding dimethylamine hydrochloride and sodium borohydride for reaction, and adding a mixed solvent for continuous reaction after the reaction is performed for a period of time; and separating and purifying the reaction product to obtain the product dimethylamino borane. The dimethylamino borane is prepared under the reaction condition of minus 10 DEG C to 0 DEG C, dimethylamine hydrochloride is firstly added into an organic solvent (such as tetrahydrofuran), then sodium borohydride is controlled to be added in batches, and nitrogen protection is carried out in a drying stage, so that by-products can be avoided, and the yield of the dimethylamino borane is effectively increased.

Description

Technical Field

[0001] This invention relates to the field of chemical preparation technology, and in particular to a method for preparing dimethylaminoborane, a reducing agent material for pretreatment of chemical copper plating in PCB manufacturing processes. Background Technology

[0002] The reduction treatment of horizontal copper plating lines in PCB (Printed Circuit Board) manufacturing is a necessary process before copper plating. This step ensures that the palladium ion layer adsorbed in the holes and on the non-conductive substrate of the PCB material is reduced to a metallic palladium layer, ensuring effective catalysis of the uniform and efficient deposition of copper ions in the chemical copper plating bath on the non-conductive substrate. Dimethylaminoborane (DMAB), as a reducing agent material for the pretreatment of horizontal chemical copper plating in PCB manufacturing, directly affects the quality and uniformity of the copper plating layer, and thus the reliability and performance of the entire PCB board. Therefore, in-depth research on the preparation method of DMAB is of great significance for improving the technical level of PCB manufacturing.

[0003] The synthesis of DMAB typically involves the reduction reaction of borohydrides (such as NaBH4) with dimethylamine hydrochloride at low temperatures, accompanied by the release of a large amount of hydrogen gas. Existing methods for preparing dimethylaminoborane require stringent reaction conditions and still present numerous problems in practice, such as: 1) High safety risks and difficulty in controlling hydrogen release; insufficient protection under an inert atmosphere (such as N2 or Ar) or inadequate heat dissipation can easily lead to explosions; 2) High temperature sensitivity: Strict temperature control is required during the reaction; excessively high temperatures can lead to increased side reactions (such as excessive hydrolysis of borane), reducing product purity and yield; 3) High toxicity of raw materials: Some routes require the use of dimethylamine gas, which is highly corrosive and toxic, increasing operational complexity and safety protection costs; 4) Difficult product separation and purification: The reaction generates large amounts of by-product inorganic salts (such as NaCl or KCl), requiring multiple purification steps such as solvent extraction and vacuum distillation (e.g., repeated extraction of the aqueous phase followed by vacuum concentration to obtain solid DMAB), resulting in a lengthy process and potential product loss.

[0004] Chinese invention patent application CN108586266A discloses a synthesis process for dimethylamine borane. The process mainly involves mixing and reacting borohydride MBH4 and dimethylamine hydrochloride in a solvent under an inert gas atmosphere at a controlled temperature of 5-15°C to generate dimethylamine borane. Then, post-processing steps (such as filtration and vacuum distillation) remove the organic solvent and salt, yielding solid dimethylamine borane or its aqueous solution. This synthesis process, conducted under inert gas protection, effectively reduces safety risks by promptly removing the hydrogen generated during the reaction. However, borohydrides have limited solubility in organic solvents. Adding large amounts of organic solvent during the process significantly reduces economic efficiency. Furthermore, while borohydrides and water can react directly, adding water would cause significant raw material degradation. Additionally, the saturation of byproducts such as salts in the solvent further inhibits the dissolution of the reactants, greatly hindering the reaction. Extending the reaction time to ensure completeness can easily lead to the generation of byproducts.

[0005] Japanese patent application JPH0597866A discloses a method for preparing dimethylamine borane. The method involves dissolving dimethylamine hydrochloride in a tetrahydrofuran solution with a water content of 7-40 wt%, cooling to 5°C, adding 1.2-1.4 equivalents of sodium borohydride in portions, reacting at below 10°C for 1.5-2 hours, then reacting at room temperature for 1 hour. The mixture is filtered, and the residue is washed with anhydrous tetrahydrofuran. The filtrate and washings are mixed and concentrated under reduced pressure to obtain crude dimethylamine borane. The yield of this method is 84-87%, and the purity is 93.4-99.0%. This method uses excessive sodium borohydride, which is commercially available at more than five times the price of dimethylamine hydrochloride, resulting in waste and poor economic efficiency. Furthermore, using a tetrahydrofuran solution with a water content of 7-40% as the direct reaction solvent allows water in the solvent to react directly with the sodium borohydride, further increasing its consumption.

[0006] US Patent Application US6060623 discloses a method for preparing dimethylamine borane. The method involves stirring dimethylamine hydrochloride in ethylene glycol dimethyl ether solvent, adding a sodium borohydride suspension in ethylene glycol dimethyl ether dropwise at a temperature not exceeding 20°C, reacting for 24 hours, removing the ethylene glycol dimethyl ether solvent by distillation, washing with sodium hydroxide solution to remove impurities, and cooling to crystallize, yielding the dimethylamine borane product. This method has a yield of 85% and a purity of 99%. This approach relies primarily on the solubility of the pure organic solvent ethylene glycol dimethyl ether in the reaction of dimethylamine hydrochloride and sodium borohydride. The sodium chloride salts generated in the system gradually dissolve in the solvent as the reaction proceeds, inhibiting the dissolution of the solid raw materials. Therefore, the reaction becomes slower and even incomplete over time, affecting the yield, and the reaction process is too long, resulting in low production efficiency.

[0007] Chinese invention patent application CN112940022A discloses a method for preparing dimethylamine borane. The method involves dissolving dimethylamine hydrochloride in a water / water and organic solvent mixture, cooling the solution to -20 to -10°C, and then adding sodium borohydride. Potassium dihydrogen phosphate is dissolved in a water and tetrahydrofuran mixture, cooled to -5°C, and then added dropwise to the dimethylamine hydrochloride and sodium borohydride mixture over 10 hours at a controlled temperature of -5 to -5°C. The reaction is maintained at this temperature for 5 hours after the addition is complete. After the reaction, insoluble matter is removed by filtration, the aqueous phase is extracted twice with tetrahydrofuran, and the organic phase is distilled to obtain a concentrated solution. The solution is then cooled, crystallized, and centrifuged to obtain the final product. The yield of this method is 70%, and the purity is 97%. However, this method suffers from the drawback that sodium borohydride reacts directly with water in aqueous solution, resulting in a relatively low yield.

[0008] Against this backdrop, providing a simple, safe, and economical method for preparing high-yield dimethylaminoborane has become an urgent technical problem to be solved in the field of PCB electronic chemical material preparation technology. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention provides a simple, safe, and economical method for preparing dimethylaminoborane using dimethylamine hydrochloride, sodium borohydride, and sodium hydroxide as reactants, and tetrahydrofuran and water as solvents. The resulting dimethylaminoborane has high yield and purity, meeting both production requirements and product quality.

[0010] The first aspect of this invention provides a method for preparing dimethylaminomethylborane, the preparation steps of which include: adding an organic solvent under an inert gas atmosphere, cooling to below 0°C, and then adding dimethylamine hydrochloride and sodium borohydride sequentially to react, with a mixed solvent added during the reaction; separating and purifying the reaction product to obtain the product dimethylaminomethylborane.

[0011] Optionally, the molar ratio of dimethylamine hydrochloride to sodium borohydride is 1:(0.8-1.2); more preferably, it is 1:1.

[0012] In the preparation method of this invention, the ratio of sodium borohydride and dimethylamine hydrochloride is close to 1:1, which can achieve the effect of full reaction without controlling the excess of sodium borohydride; and the optimization of preparation conditions effectively reduces the reaction between sodium borohydride and water, improves the yield and avoids the waste of raw materials, thus achieving good economic benefits.

[0013] In some embodiments, the preparation steps specifically include: S1: Replace the air in the reaction apparatus with an inert gas, then add organic solvent one, and cool down to -10~0℃; S2: Add dimethylamine hydrochloride to the reaction apparatus and stir at high speed; S3: Add sodium borohydride to the reaction apparatus in batches, and control the temperature rise to not exceed 3°C during the batch addition process; continue the reaction for 1-6 hours after adding sodium borohydride in batches. S4: Add the mixed solvent to the reaction apparatus in batches, and control the temperature rise to not exceed 3°C during the batch addition process; continue the reaction for 0.5-2 hours after adding the mixed solvent in batches. S5: Add the alkaline solution into the reaction apparatus all at once and stir for 1-10 minutes; S6: Filter the reaction product and collect filtrate one and solid filter residue separately; separate filtrate one to obtain an upper organic liquid and a lower aqueous solution; wash the solid filter residue with organic solvent two, extract the lower aqueous solution with the washed solution, and combine the extracted solution with the upper organic liquid to obtain an organic phase solution; S7: Dry the organic phase solution, and filter the dried organic phase solution to obtain filtrate two; S8: The filtrate 2 is subjected to vacuum distillation, and the liquid phase is collected by filtration to obtain a crude product; the crude product is then vacuum dried to obtain product 1.

[0014] Optionally, step S8 further includes recrystallizing product one using organic solvent three to obtain product two (pure dimethylaminoborane).

[0015] Based on the preparation of 100g of dimethylaminoborane (theoretical), the amount of dimethylamine hydrochloride used is 1.5-2 mol; more preferably 1.7 mol; the amount of sodium borohydride used is 1.5-2 mol; more preferably 1.7 mol.

[0016] In some embodiments, organic solvent one, organic solvent two, and organic solvent three may each include at least one of tetrahydrofuran, diethyl ether, dioxane, toluene, n-hexane, and ethylene glycol dimethyl ether.

[0017] In some embodiments, the reaction apparatus may be a flask, and more specifically, a four-necked flask; further still, a four-necked flask with a volume of 2L may be selected.

[0018] In some embodiments, the reaction apparatus may be a large-volume reactor (e.g., 200L).

[0019] The preparation method of the present invention can be used for both small-scale fine synthesis and large-scale batch synthesis, and can ultimately yield high-quality pure dimethylaminoborane.

[0020] Optionally, the inert gas is nitrogen or argon; more specifically, it may be nitrogen.

[0021] Optionally, when using nitrogen to replace the air in the reaction apparatus, the nitrogen input is kept slow throughout the process; further optionally, the nitrogen input flow rate is 0.1-5 L / 15 min; even more preferably, it is 1 L / 15 min.

[0022] Optionally, the organic solvent is tetrahydrofuran.

[0023] In some embodiments, based on an addition amount of 1.7 mol of dimethylamine hydrochloride, the addition amount of organic solvent one can be set to 500-1000 mL; for example, 500 mL, 550 mL, 600 mL, 650 mL, 700 mL, 750 mL, 800 mL, 850 mL, 900 mL, 950 mL, 1000 mL; further optionally, it can be 600-800 mL.

[0024] Optionally, the sodium borohydride is added in 15-30 batches; more preferably, the sodium borohydride is added in 20 batches.

[0025] Optionally, when adding sodium borohydride in batches, one batch is added to the reaction apparatus every 10-60 minutes.

[0026] Optionally, the mixed solvent is a mixture of water and tetrahydrofuran; the volume ratio of water to tetrahydrofuran is (1-3.5):(4-10); more preferably, it is 3:7.

[0027] Optionally, the mixed solvent is added in 5-20 batches; more preferably, the mixed solvent is added in 10 batches.

[0028] Optionally, when adding the mixed solvent in batches, one batch is added to the reaction apparatus every 10-60 minutes.

[0029] Optionally, when the mixed solvent is added in batches, each batch can be added at once or drop by drop; it can be further selected to be drop by drop; for example, a dropping funnel can be used for drop addition in order to control the temperature and time of the reaction.

[0030] In some embodiments, the present invention adds sodium borohydride or mixed solvent in batches, precisely controlling the temperature rise during the feeding process to not exceed 3°C.

[0031] This invention prepares dimethylaminoborane under reaction conditions of -10 to 0°C. By first adding dimethylamine hydrochloride to an organic solvent (such as tetrahydrofuran), and then controlling the batch addition of sodium borohydride, the occurrence of by-products can be avoided, effectively improving the yield of dimethylaminoborane. Furthermore, after adding sodium borohydride, adding a mixed solution of water and tetrahydrofuran to the system can enhance the degree of reaction of the raw materials, further improving the yield. In addition, by using the batch addition of the mixed solvent, the reaction temperature can be effectively controlled, avoiding the exothermic reaction that accelerates the formation of by-products, thus increasing the yield of dimethylaminoborane to over 80%.

[0032] Optionally, the alkaline solution is an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide; more preferably, it is an aqueous solution of sodium hydroxide.

[0033] Optionally, the concentration of the sodium hydroxide aqueous solution is 5-20 wt%; more preferably 10-15 wt%.

[0034] Optionally, the second organic solvent is tetrahydrofuran.

[0035] The present invention does not impose a particular limitation on the amount of organic solvent II added, as long as it can achieve the cleaning purpose; based on the amount of dimethylamine hydrochloride added as 1.7 mol, the amount of organic solvent II added can be set to 100-200 mL.

[0036] The drying step specifically includes: placing the organic phase solution collected in step S6 into a flask, adding a desiccant, and stirring and drying for 1-4 hours; continuously blowing nitrogen gas during the drying process. This invention uses nitrogen gas for protection during the drying stage, which can further suppress the formation of byproducts and increase the yield of dimethylaminoborane to over 86%.

[0037] In some implementations, step S7 uses a three-necked or four-necked flask; taking a four-necked flask as an example, one flask neck is a nitrogen inlet, one flask neck is a gas outlet, one flask neck is a stirring inlet, and one flask neck is sealed.

[0038] Optionally, the ratio of the desiccant to the organic phase solution is 50-150g:500-2000mL; further, it is 70-200g:1000mL; even further, it is 80-200g:1000mL; and still further, it is 90g:850mL. The present invention uses 8-20wt% of the organic phase solution as the desiccant, achieving both improved yield and economic efficiency. When the desiccant content is below 8wt%, the drying time is longer (extending the drying time can also achieve good drying results); when the desiccant content exceeds 20wt%, the desiccant will absorb a small amount of dimethylaminoborane, leading to a decrease in the final yield.

[0039] Optionally, the desiccant includes one or more combinations of anhydrous magnesium sulfate, anhydrous sodium sulfate, and calcium chloride; further, it may be anhydrous magnesium sulfate.

[0040] Optionally, the organic solvent tri is tetrahydrofuran.

[0041] In some embodiments, organic solvent three is mixed with crude product two to form a solution with a concentration of 60-80 wt%.

[0042] Optionally, the vacuum drying temperature is 30-45°C; further preferably 32-38°C; and even more preferably 35°C.

[0043] Optionally, the recrystallization temperature is 0-15℃; examples include 0℃, 1℃, 2℃, 3℃, 4℃, 5℃, 6℃, 7℃, 8℃, 9℃, 10℃, 11℃, 12℃, 13℃, 14℃, and 15℃.

[0044] In some embodiments, the residual solution after recrystallization of product one can be used as an organic solvent (solution) for the next recrystallization, thus achieving recycling.

[0045] Optionally, the yield of dimethylaminoborane in product one is 93-98%.

[0046] Optionally, the yield of dimethylaminoborane in product two is 86-92%.

[0047] Beneficial effects: This invention provides a method for preparing dimethylaminoborane, which has the following advantages: (1) The present invention prepares dimethylaminoborane under reaction conditions of -10~0℃. By first adding dimethylamine hydrochloride to an organic solvent (such as tetrahydrofuran) and then controlling the addition of sodium borohydride in batches, the occurrence of by-products can be avoided and the yield of dimethylaminoborane can be effectively improved. (2) In addition to sodium borohydride, the present invention further adds a mixed solution of water and tetrahydrofuran to the system, which can improve the degree of reaction of the raw materials and further improve the yield; further, by adding the mixed solvent in batches, the reaction temperature is effectively controlled, avoiding the exothermic acceleration of the generation of by-products, and the yield of dimethylaminoborane is increased to more than 80%. (3) The ratio of sodium borohydride and dimethylamine hydrochloride added in the preparation scheme of the present invention is close to 1:1, so there is no need to control the excess of sodium borohydride to achieve the effect of full reaction; and the optimization of preparation conditions effectively reduces the reaction between sodium borohydride and water, improves the yield and avoids the waste of raw materials, and is economical. (4) The present invention uses nitrogen gas for protection during the drying stage, which can further suppress the generation of by-products and increase the yield of dimethylaminoborane to over 86%. (5) The preparation method of the present invention solves the problems of incomplete reaction, long reaction time and low production efficiency caused by the solubility of solid raw materials in organic solvents, effectively shortens the reaction process and improves the reaction efficiency; (6) The preparation method of the present invention can be applied to both laboratory scenarios and large-scale reactor synthesis scenarios. The implementation method can be flexibly selected according to the needs, and the application prospects are broad. Attached Figure Description

[0048] Figure 1 UV absorption spectrum of the control sample; Figure 2 UV absorption spectrum of sample from Example 1; Figure 3 Example 2: Ultraviolet absorption spectrum of the sample; Figure 4 UV absorption spectrum of sample in Example 3; Figure 5 Example 4: Ultraviolet absorption spectrum of the sample; Figure 6 UV absorption spectrum of sample in Example 5; Figure 7 .Ultraviolet absorption spectrum of sample 1 (Comparative Example 1) Figure 8 .Ultraviolet absorption spectrum of sample 2 (Comparative Example 2) Figure 9 .Ultraviolet absorption spectrum of sample 3 (Comparative Example 3) Figure 10 .Ultraviolet absorption spectrum of sample 4 (Comparative Example 4) Figure 11 .Ultraviolet absorption spectrum of sample 5 (Comparative Example 5); Figure 12 .Ultraviolet absorption spectrum of sample 6 (Comparative Example 6) Figure 13 .Ultraviolet absorption spectrum of sample 7 (Comparative Example 7) Figure 14 .H NMR spectrum of the sample in Example 1. Detailed Implementation

[0049] Note: Unless otherwise specified, all raw materials and consumables used in this invention are commercially available.

[0050] Example 1 This embodiment provides a method for preparing dimethylaminoborane, the specific preparation steps of which include: S1: Slowly introduce nitrogen gas (flow rate controlled at 1L / 15min) into a 2L straight four-necked flask to replace the air in the flask, then add 650mL of organic solvent 1 (tetrahydrofuran) and cool to -5℃ to prepare 100.16g (1.7mol) of dimethylaminoborane. S2: Add 140g of dimethylamine hydrochloride (1.7mol) to a straight four-necked flask and stir at high speed (150rpm) to make the solid particles evenly distributed in the solvent system; S3: Divide 65.5g of sodium borohydride (1.7mol) into 20 equal batches and add them to a straight four-necked flask. The time interval between each batch is 15min, and the temperature rise should not exceed 3℃. After adding sodium borohydride in batches, continue the reaction for 4h. S4: Divide the mixed solution (30 mL water and 70 mL tetrahydrofuran) into 10 equal batches and add them to a straight four-necked flask. The time interval between each batch is 15 min, and the temperature rise should not exceed 3 °C. After adding the mixed solvent in batches, continue the reaction for 2 h. S5: Add the sodium hydroxide aqueous solution (15.2g solid sodium hydroxide dissolved in 122g water) into the straight four-necked flask all at once, and stir for 2 minutes; S6: Filter the reaction product and collect filtrate one and solid filter residue separately; separate filtrate one to obtain an upper organic liquid and a lower aqueous solution; wash the solid filter residue with 150 mL of organic solvent two (tetrahydrofuran), extract the lower aqueous solution with the washed solution, and combine the extracted solution with the upper organic liquid to obtain 850 mL of organic phase solution. S7: Place the organic phase solution collected in step S6 into a 2L straight four-necked flask, add 90g of desiccant (anhydrous magnesium sulfate) and stir to dry for 1 hour; during the drying process, keep blowing nitrogen gas continuously (one flask mouth is the nitrogen inlet, one flask mouth is the gas outlet, one flask mouth is the stirring port, and one flask mouth is closed); filter the dried organic phase solution to obtain filtrate two; S8: Place the filtrate 2 in a three-necked flask, connect a vacuum distillation device and a heating device, and filter and collect the liquid phase to obtain the crude product (and collect 800 mL of solvent); place the crude product in a vacuum drying oven and dry it under vacuum at 35°C to obtain product 1; dissolve product 1 in organic solvent 3 (tetrahydrofuran) at a concentration of 70 wt%, and recrystallize it at 5°C to obtain product 2 (pure dimethylaminoborane); the residual solution after recrystallization of product 1 can be used as the organic solvent (solution) for the next recrystallization, realizing recycling.

[0051] In Example 1, 97.2 g of dimethylaminoborane was prepared in Product 1, with a yield of 97.2%; and 88.1 g of dimethylaminoborane was prepared in Product 2, with a yield of 88.1%.

[0052] Example 2 This embodiment provides a method for preparing dimethylaminoborane, and the specific implementation method is the same as in Example 1; the difference is: In step S3, the time interval between each batch of sodium borohydride is 30 minutes, and the reaction continues for 2 hours after the sodium borohydride is added in batches. In step S4, the time interval between each batch of mixed solution is 30 minutes, and the reaction continues for 0.5 hours after the mixed solvent is added in batches. Stir for 5 minutes during step S5; Stir and dry for 2 hours in step S7.

[0053] In Example 2, 94.6 g of dimethylaminoborane was prepared in Product 1, with a yield of 94.62%; and 86.8 g of dimethylaminoborane was prepared in Product 2, with a yield of 86.82%.

[0054] Example 3 This embodiment provides a method for preparing dimethylaminoborane, and the specific implementation method is the same as in Example 1; the difference is: In step S3, the time interval between each batch of sodium borohydride is 20 minutes, and the reaction continues for 1 hour after the sodium borohydride is added in batches. In step S4, the time interval between each batch of mixed solution is 30 minutes, and the reaction continues for 1 hour after the mixed solvent is added in batches. Stir for 5 minutes during step S5; Stir and dry for 2 hours in step S7.

[0055] In Example 3, 95.3 g of dimethylaminoborane was prepared in Product 1, with a yield of 95.32%; and 90.1 g of dimethylaminoborane was prepared in Product 2, with a yield of 90.1%.

[0056] Example 4 This embodiment provides a method for preparing dimethylaminoborane (large-scale reactor synthesis method), the specific preparation steps of which include: S1: Slowly introduce nitrogen gas (flow rate controlled at 100L / 15min) into a 200L straight four-necked flask to replace the air in the flask, then add 65L of organic solvent 1 (tetrahydrofuran) and cool to -5℃ to prepare 10kg (170mol) of dimethylaminoborane. S2: Add 14 kg of dimethylamine hydrochloride (170 mol) to a straight four-necked flask and stir at high speed (150 rpm) to make the solid particles evenly distributed in the solvent system; S3: Divide 6.55 kg of sodium borohydride (170 mol) into 20 batches and add them to a straight four-necked flask. The time interval between each batch is 20 min, and the temperature rise should not exceed 3 °C. After adding sodium borohydride in batches, continue the reaction for 2 h. S4: Divide the mixed solution (3L water and 7L tetrahydrofuran) into 10 equal batches and add them to a straight four-necked flask. The time interval between each batch is 30 min, and the temperature rise should not exceed 3℃. After adding the mixed solvent in batches, continue the reaction for 1 h. S5: Add the sodium hydroxide aqueous solution (1.52 kg of solid sodium hydroxide dissolved in 12.2 kg of water) to the straight four-necked flask all at once, and stir for 5 min; S6: Filter the reaction product and collect filtrate one and solid filter residue separately; separate filtrate one to obtain an upper organic liquid and a lower aqueous solution; wash the solid filter residue with 15L organic solvent two (tetrahydrofuran), extract the lower aqueous solution with the washed solution, and combine the extracted solution with the upper organic liquid to obtain 85L organic phase solution. S7: Place the organic phase solution collected in step S6 into a 200L straight four-necked flask, add 9kg of desiccant (anhydrous magnesium sulfate) and stir to dry for 2 hours; during the drying process, keep blowing nitrogen gas continuously (one flask mouth of the four-necked flask is the nitrogen blowing inlet, one flask mouth is the gas outlet, one flask mouth is the stirring port, and one flask mouth is closed); filter the dried organic phase solution to obtain filtrate two; S8: Place the filtrate 2 in a three-necked flask, connect a vacuum distillation device and a heating device, and filter and collect the liquid phase to obtain a crude product (and collect 80L of solvent); place the crude product in a vacuum drying oven and dry it under vacuum at 35°C to obtain product 1; dissolve product 1 in organic solvent 3 (tetrahydrofuran) at a concentration of 70wt%, and recrystallize it at 5°C to obtain product 2 (pure dimethylaminoborane); the residual solution after recrystallization of product 1 can be used as the organic solvent (solution) for the next recrystallization, realizing recycling.

[0057] In Example 4, 9.53 kg of dimethylaminoborane was prepared in Product 1, with a yield of 95.3%; and 8.75 kg of dimethylaminoborane was prepared in Product 2, with a yield of 87.5%.

[0058] Example 5 This embodiment provides a method for preparing dimethylaminoborane (large-scale reactor synthesis method), and the specific implementation method is the same as that in Example 4; the difference is: In step S1, the temperature is lowered to -8°C; In step S3, the time interval between each batch of sodium borohydride is 15 minutes, and the reaction continues for 4 hours after the sodium borohydride is added in batches. In step S8, crude product 2 is dissolved in organic solvent 3 (tetrahydrofuran) at a concentration of 80 wt%.

[0059] In Example 5, 9.73 kg of dimethylaminoborane was prepared in Product 1, with a yield of 97.3%; and 9.02 kg of dimethylaminoborane was prepared in Product 2, with a yield of 90.2%.

[0060] Comparative Example 1 This comparative example provides a method for preparing dimethylaminoborane, the specific preparation steps of which include: S1: Slowly introduce nitrogen gas (flow rate controlled at 1L / 15min) into a 2L straight four-necked flask to replace the air in the flask, then add 650mL of organic solvent 1 (tetrahydrofuran) and cool to -5℃ to prepare 100.16g of dimethylaminoborane. S2: Add 140g of dimethylamine hydrochloride (1.7mol) to a straight four-necked flask and stir at high speed (150rpm) to make the solid particles evenly distributed in the solvent system; S3: Add 65.5g of sodium borohydride (1.7mol) directly to a straight four-necked flask and continue the reaction for 4 hours after adding sodium borohydride; S4: Add the sodium hydroxide aqueous solution (15.2g solid sodium hydroxide dissolved in 122g water) to the straight four-necked flask all at once and stir for 5 minutes; S5: Filter the reaction product and collect filtrate one and solid filter residue separately; separate filtrate one to obtain an upper organic liquid and a lower aqueous solution; wash the solid filter residue with 150 mL of organic solvent two (tetrahydrofuran), extract the lower aqueous solution with the washed solution, and combine the extracted solution with the upper organic liquid to obtain 780 mL of organic phase solution. S6: Place the organic phase solution collected in step S5 into a 2L straight four-necked flask, add 90g of desiccant (anhydrous magnesium sulfate) and stir to dry for 2 hours; during the drying process, keep blowing nitrogen gas continuously (one flask mouth is the nitrogen inlet, one flask mouth is the gas outlet, one flask mouth is the stirring port, and one flask mouth is closed); filter the dried organic phase solution to obtain filtrate two; S7: Place the filtrate 2 in a three-necked flask, connect a vacuum distillation device and a heating device, and filter and collect the liquid phase to obtain the crude product (and collect 720 mL of solvent); place the crude product in a vacuum drying oven and dry it under vacuum at 35°C to obtain product 1; dissolve product 1 in organic solvent 3 (tetrahydrofuran) at a concentration of 70 wt%, and recrystallize it at 5°C to obtain product 2 (pure dimethylaminoborane); the residual solution after recrystallization of product 1 can be used as the organic solvent (solution) for the next recrystallization, realizing recycling.

[0061] In Comparative Example 1, 65.3 g of dimethylaminoborane was prepared in Product 1, with a yield of 65.3%; and 52.2 g of dimethylaminoborane was prepared in Product 2, with a yield of 52.2%.

[0062] Comparative Example 2 This comparative example provides a method for preparing dimethylaminoborane (large-scale reactor synthesis method), and the specific implementation method is the same as that of Comparative Example 1; the difference is: In step S3, sodium borohydride is added and the reaction continues for 10 hours.

[0063] In Comparative Example 2, product one contained 66.2 g of dimethylaminoborane, with a yield of 66.2%; product two contained 53.6 g of dimethylaminoborane, with a yield of 53.6%.

[0064] Comparative Example 3 This comparative example provides a method for preparing dimethylaminoborane, with the specific implementation method being the same as that of Comparative Example 1; the difference is that: after adding sodium borohydride in step S3 and continuing the reaction for 4 hours, the mixed solution (30 mL of water and 70 mL of tetrahydrofuran) is added to a straight four-necked flask at once, and the reaction continues for 3 hours after adding the mixed solvent; then step S4 is carried out.

[0065] In Comparative Example 3, product one contained 81.3 g of dimethylaminoborane, with a yield of 81.3%; product two contained 68.2 g of dimethylaminoborane, with a yield of 68.2%.

[0066] Comparative Example 4 This comparative example provides a method for preparing dimethylaminoborane, and the specific implementation method is the same as in Example 3; the difference is: In step S4, the mixed solution (30 mL water and 70 mL tetrahydrofuran) is added to the straight four-necked flask at once, and the reaction continues for 3 hours after the mixed solvent is added. In Comparative Example 4, product one contained 83.4 g of dimethylaminoborane, with a yield of 83.4%; product two contained 72.5 g of dimethylaminoborane, with a yield of 72.5%.

[0067] Comparative Example 5 This comparative example provides a method for preparing dimethylaminoborane, and the specific implementation method is the same as in Example 3; the difference is: Nitrogen gas was not used for protection during the drying process in step S7.

[0068] In Comparative Example 5, 94 g of dimethylaminoborane was prepared in Product 1, with a yield of 94%; and 85 g of dimethylaminoborane was prepared in Product 2, with a yield of 85%.

[0069] Comparative Example 6 This comparative example provides a method for preparing dimethylaminoborane, and the specific implementation method is the same as in Example 3; the difference is: In step S1, the temperature is lowered to 5°C.

[0070] In Comparative Example 6, product one contained 87.3 g of dimethylaminoborane, with a yield of 87.3%; product two contained 74.6 g of dimethylaminoborane, with a yield of 74.6%.

[0071] Comparative Example 7 This comparative example provides a method for preparing dimethylaminoborane, and the specific implementation method is the same as in Example 3; the difference is: In step S1, the temperature is lowered to -15°C.

[0072] In Comparative Example 7, product one contained 82.6% g of dimethylaminoborane, with a yield of 82.6%; product two contained 71.4% g of dimethylaminoborane, with a yield of 71.4%.

[0073] Comparison Example Commercially available analytical grade dimethylaminoborane.

[0074] Performance testing The UV absorption spectra of the control example, Examples 1-5, and Comparative Examples 1-7 were measured, and the results are shown in the figure. Figure 1-13 The 1H NMR spectrum of the sample from Example 1 was determined, and the results are shown in [the table below]. Figure 14 .

[0075] The UV absorption spectrum test results show that the spectra of Examples 1-5 are completely consistent with those of commercially available dimethylaminoborane, indicating high sample purity.

[0076] Comparative Examples 1 and 2 used a single-addition method of sodium borohydride, and after the reaction, a single-addition of sodium hydroxide aqueous solution was added without the addition of a mixed solvent. The yield of dimethylaminoborane was significantly reduced, and the yield difference between reaction times of 4 h and 10 h was not significant, far lower than that of Examples 1-3. This demonstrates that there is a limit to the solubility of the raw materials in organic solvents. The salts produced after continuous reaction dissolve in the organic solvent, limiting the solubility of the raw materials, causing reaction difficulties, and reducing the yield. The UV absorption spectra of Comparative Examples 1 and 2 are shown below. Figure 7 , Figure 8 Compared with Examples 1-5 and the control example, the presence of higher UV absorption peaks of by-products confirms that the presence of a large amount of unreacted raw materials after the one-time addition of sodium borohydride makes it difficult to control the temperature, resulting in side reactions and a decrease in product purity.

[0077] The results of Comparative Examples 3 and 4 show that adding sodium borohydride in batches or adding a mixture of tetrahydrofuran and water after the reaction with sodium borohydride can improve the product yield. The addition of tetrahydrofuran and water enhances the reaction of the raw materials, thus improving the yield to some extent; however, a single addition causes intense exothermic reactions, making temperature control difficult, and the resulting byproducts are difficult to remove even after crystallization. Figure 9 The results showed that byproduct UV absorption peaks were still present. Adding sodium borohydride in batches could further suppress the formation of byproducts. Figure 10 This shows the ratio of the ultraviolet absorption peaks of its byproducts. Figure 9 Lower.

[0078] The results of Comparative Example 5 show that nitrogen protection in the post-processing stage is particularly critical for the generation of by-products. If nitrogen protection is not performed in the drying stage, although the yield of crude product 2 is higher, the amount of by-products after crystallization is still higher than in the example. However, nitrogen protection in the drying stage can ensure that the product yield after recrystallization reaches more than 86%.

[0079] Comparative Examples 6 and 7 compared the effect of reaction temperature on the reaction system. In Comparative Example 6, the reaction temperature was increased to 5°C. Due to the high reactivity of water with sodium borohydride, even with batch addition, the tendency for side reactions was greater, resulting in a lower final product yield. Figure 12 A high UV absorption peak for byproducts was observed. In Comparative Example 7, the reaction temperature was lowered to -15℃. Although fewer byproducts were produced under the lower temperature conditions, Figure 13 No obvious UV absorption peaks of byproducts were observed, but the reactants had low reactivity, the reaction was slow, and the final yield was still lower than that of Examples 1-5. Therefore, the preferred reaction temperature of this invention is -10~0℃, which can improve the yield and purity of the product while maintaining synthesis efficiency.

Claims

1. A method for preparing dimethylaminoborane, characterized in that, The preparation steps include: adding organic solvent one under an inert gas atmosphere, cooling to below 0°C, and then adding dimethylamine hydrochloride and sodium borohydride in sequence to react, with a mixed solvent added during the reaction; separating and purifying the reaction product to obtain the product dimethylaminoborane.

2. The method for preparing dimethylaminoborane according to claim 1, characterized in that, The preparation steps specifically include: S1: Replace the air in the reaction apparatus with an inert gas, then add organic solvent one, and cool down to -10~0℃; S2: Add dimethylamine hydrochloride to the reaction apparatus and stir at high speed; S3: Add sodium borohydride to the reaction apparatus in batches, and control the temperature rise to not exceed 3°C during the batch addition process; continue the reaction for 1-6 hours after adding sodium borohydride in batches. S4: Add the mixed solvent to the reaction apparatus in batches, and control the temperature rise to not exceed 3°C during the batch addition process; continue the reaction for 0.5-2 hours after adding the mixed solvent in batches. S5: Add the alkaline solution into the reaction apparatus all at once and stir for 1-10 minutes; S6: Filter the reaction product and collect filtrate one and solid filter residue separately; separate filtrate one to obtain an upper organic liquid and a lower aqueous solution; wash the solid filter residue with organic solvent two, extract the lower aqueous solution with the washed solution, and combine the extracted solution with the upper organic liquid to obtain an organic phase solution; S7: Dry the organic phase solution, and filter the dried organic phase solution to obtain filtrate two; S8: The filtrate 2 is subjected to vacuum distillation, and the liquid phase is collected by filtration to obtain a crude product; the crude product is then vacuum dried to obtain product 1.

3. The method for preparing dimethylaminoborane according to claim 2, characterized in that, Step S8 further includes recrystallizing product one using organic solvent three to obtain product two.

4. The method for preparing dimethylaminoborane according to claim 2, characterized in that, Based on a total sodium borohydride addition of 1.7 mol, the sodium borohydride was added in 15-30 batches; When adding sodium borohydride in batches, one batch is added to the reaction apparatus every 10-60 minutes.

5. The method for preparing dimethylaminoborane according to claim 2, characterized in that, The mixed solvent is a mixture of water and tetrahydrofuran; the volume ratio of water to tetrahydrofuran is (1-3.5):(4-10).

6. The method for preparing dimethylaminoborane according to claim 5, characterized in that, The mixed solvent is added in 5-20 batches; When adding the mixed solvent in batches, one batch is added to the reaction apparatus every 10-60 minutes.

7. The method for preparing dimethylaminoborane according to claim 2, characterized in that, The drying step in step S7 specifically includes: placing the organic phase solution collected in step S6 into a flask, adding a desiccant and stirring to dry for 1-4 hours; and continuously blowing nitrogen gas during the drying process.

8. The method for preparing dimethylaminoborane according to claim 3, characterized in that, Organic solvent one, organic solvent two, and organic solvent three can each include at least one of tetrahydrofuran, diethyl ether, dioxane, toluene, n-hexane, and ethylene glycol dimethyl ether.

9. The method for preparing dimethylaminoborane according to claim 8, characterized in that, Organic solvent one, organic solvent two, and organic solvent three are all tetrahydrofuran.

10. The method for preparing dimethylaminoborane according to claim 2, characterized in that, The ratio of the desiccant to the organic phase solution is 50-150g: 500-2000mL.

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