A high yield synthesis of high purity tris(trihydrocarbylsilyl)borate

Abstract

The application relates to the field of lithium ion battery electrolyte additives, in particular to a high-yield synthesis method of high-purity tris(trihydrocarbylsilyl)borate, and the synthesis steps are as follows: first, urea and hexahydrocarbyldisilazane are reacted to prepare hexahydrocarbyldisilourea; second, boric acid and the hexahydrocarbyldisilourea are reacted to obtain tris(trihydrocarbylsilyl)borate crude product; third, the crude product is purified to obtain high-purity tris(trihydrocarbylsilyl)borate. The synthesis method provided by the application has the advantages of high reaction conversion rate and yield, high product purity, recyclable filter residue and solvent after reaction, reduced waste emission and green and environment-friendly process.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery electrolyte additives, specifically to a high-yield synthesis method for high-purity tris(trialkylsilyl)boronic esters. Background Technology

[0002] Tris(trialkylsilyl)borate esters, as an additive material for lithium-ion battery electrolytes, are now widely used in the field of lithium-ion battery electrolytes. The addition of tris(trialkylsilyl)borate esters significantly improves the performance of lithium-ion batteries, not only greatly enhancing their high-temperature storage and high-temperature cycling performance, but also reducing internal resistance and improving performance at low temperatures.

[0003] In their article "Organosilicon derivatives of boric acid tris(trialkylsilyl)borates and polyboronorganosiloxanes" published in the journal *Zhurnal Organicheskoi Khimii*, 1957, 27(6), 1476–1483, MG Voronkov et al. synthesized tris(trimethylsilyl)borates from boric acid tris(trialkylsilyl)borates and polyboronorganosiloxanes using boron trioxide and hexamethyldisiloxane. The reaction was carried out at 350°C for 27 hours, with a yield of only 13.3%. Furthermore, the reaction was time-consuming, required high temperatures, and resulted in extremely low yields. In their article "Reactions of methylchlorosilanes with boric acid" published in the journal *Zhurnal Organicheskoi Khimii*, 1969, 39(3), 554–556, AS Shapatin et al. reacted trimethylchlorosilanes with boric acid using tetrahydrofuran as a catalyst. The reaction was heated for 24 hours, yielding a 22% yield, but also producing the harmful byproduct hydrogen chloride.

[0004] Chinese patent application number CN101870707 discloses a method for synthesizing and purifying tris(trimethylsilyl)boronic acid ester suitable for use as an electrolyte additive. The method involves reacting hexamethyldisilazane and boric acid at 60–150 °C for 5–10 h. The crude product is then washed with water, dried, and distilled to obtain tris(trimethylsilyl)boronic acid ester with a yield of 72%. The byproduct ammonia gas readily reacts with boric acid, thereby reducing the yield. Furthermore, at higher temperatures, boric acid is prone to dehydration, resulting in a large amount of solid waste residue after the reaction. Washing the crude product with water causes the tris(trimethylsilyl)boronic acid ester to decompose.

[0005] This invention provides a high-yield synthesis method for high-purity tris(trialkylsilyl)boronic esters, overcoming the shortcomings of the above-mentioned synthesis processes such as low reaction yield, high energy consumption, and easy generation of solid waste and harmful gases. It provides a synthesis method with high reaction conversion rate and yield, high product purity, and the ability to recycle and reuse the filter residue and solvent after the reaction, thereby reducing waste emissions and making the process green and environmentally friendly. Summary of the Invention

[0006] The purpose of this invention is to provide a method for synthesizing tris(trialkylsilyl)boronic acid esters with high product yield, high purity, high raw material utilization, and reusable by-products, which can overcome the shortcomings of existing methods for synthesizing tris(trialkylsilyl)boronic acid esters.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A high-yield synthesis method for high-purity tris(trialkylsilyl)boronic esters comprises the following three steps:

[0009] (1) First step: react urea and hexaalkyldisilazane to prepare hexaalkyldisilazane;

[0010] (2) In the second step, boric acid and hexaalkyldisilaurea are reacted to obtain crude tris(trialkylsilyl)boronic acid ester;

[0011] (3) In the third step, the crude product is purified to obtain high-purity tris(trialkylsilyl)boronic acid ester with a purity of over 99.95%. The general structural formula of the tris(trialkylsilyl)boronic acid ester is:

[0012]

[0013] Among them, R1, R2, and R3 are the same or different alkyl, unsaturated hydrocarbon or aromatic groups;

[0014] The general structural formula of the hexahydrodisilazane is:

[0015]

[0016] Among them, R1, R2, and R3 are the same or different alkyl, unsaturated hydrocarbon or aromatic groups;

[0017] The general structural formula of the hexahydrodisilylurea is:

[0018]

[0019] R1, R2, and R3 are the same or different alkyl, unsaturated hydrocarbon, or aromatic groups.

[0020] Preferably, the alkyl group is methyl, ethyl, n-propyl, isopropyl, trifluoromethyl, or trifluoroethyl; the unsaturated hydrocarbon group is vinyl, ethynyl, propynyl, propynyl, or cyanopropyl; and the aromatic group is phenyl or benzyl.

[0021] Preferably, the high-yield synthesis method of the high-purity tris(trialkylsilyl)boronic ester comprises the following three steps:

[0022] (1) In the first step, urea and hexaalkyldisilazane are heated and stirred under a catalyst and refluxed. The ammonia produced is absorbed by water to make ammonia water. After the reaction is completed, the reaction solution is cooled to room temperature and filtered. The filtrate is hexaalkyldisilazane, which is recycled. The filter cake is dried by vacuum rotary evaporation to obtain hexaalkyldisilazane.

[0023] (2) In the second step, boric acid and hexaalkyldisilure reacted in a solvent at a certain reaction temperature with stirring to obtain crude tri(trialkylsilyl)boronic acid ester;

[0024] (3) In the third step, the crude product is filtered to obtain a mixture of tris(trialkylsilyl)boronic acid ester and solvent, as well as filter residue. The mixture is then distilled, fractionated, or purified to collect the fraction and obtain high-purity tris(trialkylsilyl)boronic acid ester.

[0025] Preferably, the catalyst used for the reaction of urea and hexaalkyldisilazane is one or more of ammonium sulfate, ammonium chloride, ammonium nitrate, boron trifluoride, boron trifluoride diethyl ether complex, sulfur trioxide, titanium tetrachloride, ferric chloride, ferric bromide, aluminum chloride, phosphorus oxychloride, sulfuric acid, hydrochloric acid, and trifluoromethanesulfonic acid, and the amount added is 0.5% to 5% of the urea quality.

[0026] Preferably, the molar ratio of urea to hexaalkyldisilazane is 1:5 to 10; and the molar ratio of boric acid to hexaalkyldisilazane is 1:1 to 5.

[0027] Preferably, the urea and hexaalkyldisilazane react under normal pressure at a temperature of 70–180°C for 5–20 hours; the boric acid and hexaalkyldisilazane react under normal pressure at a temperature of -10–50°C for 1–20 hours.

[0028] Preferably, the solvent used in the reaction of boric acid and hexaalkyldisilaurea is one or more of the following: dichloromethane, dichloroethane, acetonitrile, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol dimethyl ether, tetrahydrofuran, ethyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, butanone, and N,N-dimethylformamide, and is recyclable.

[0029] The beneficial effects of this invention are:

[0030] This invention provides a high-yield synthesis method for high-purity tris(trialkylsilyl)boronic esters, which has high reaction conversion rate and yield, high product purity, and the filter residue and solvent after the reaction can be recycled and reused, reducing waste emissions and making the process green and environmentally friendly.

[0031] The most widely used synthesis process currently involves directly reacting boric acid and hexaalkyldisilazane at 60–150°C, with a product yield typically around 70–75%. At high temperatures, boric acid easily loses water to form metaboric acid or even pyroboric acid, resulting in a large amount of unreacted filter residue. This leads to low boric acid utilization, and the filter residue carries away a significant amount of product, further reducing the yield. Furthermore, the large amount of filter residue requires solid waste treatment, increasing production costs and being environmentally unfriendly. The dehydration of boric acid and the reaction of the byproduct ammonia with boric acid both produce water, which hydrolyzes hexaalkyldisilazane to form hexaalkyldisilaoxane, increasing the consumption of hexaalkyldisilazane and simultaneously increasing the load and difficulty of the distillation separation of hexaalkyldisilazane and hexaalkyldisilaoxane.

[0032] This invention provides a high-yield synthesis method for high-purity tris(trialkylsilyl)boronic esters. On one hand, the intermediate hexaalkyldisilazane is prepared by reacting urea and hexaalkyldisilazane. Ammonia is released during the first synthesis step, avoiding the problem of low yield caused by the hydrolysis of hexaalkyldisilazane and the final product tris(trialkylsilyl)boronic ester due to the reaction of ammonia with the raw material boric acid to generate water. Simultaneously, the reaction temperature between boric acid and hexaalkyldisilazane is mild, avoiding the loss of boric acid at high temperatures that would reduce yield, and the mild reaction temperature also reduces energy consumption. On the other hand, urea, as a reaction intermediate, can be recycled. After the reaction is complete, the filtered urea can be recycled without further treatment, and the boric acid is almost completely reacted, with no filter residue requiring solid waste treatment. The solvent is also recycled, reducing waste emissions, making the process route green and environmentally friendly. Detailed Implementation

[0033] The following section provides a more detailed description of a high-yield synthesis method for a high-purity tris(trialkylsilyl)boronic ester.

[0034] Unless otherwise specified, reaction temperature generally refers to the internal temperature of the reactants.

[0035] Product purity was tested using a Shimadzu GC-2014C gas chromatograph.

[0036] Yield is the percentage ratio of actual product quality to theoretical product quality, where theoretical product quality is calculated using raw materials in the reaction equation without excess.

[0037] The present application will be further described in detail below with reference to the embodiments. All raw materials involved in the present application can be obtained commercially.

[0038] Example 1

[0039] The synthesis process route of Example 1 is as follows:

[0040]

[0041] The specific operating steps are as follows:

[0042] (1) 150 g of urea was added to a 5-liter glass reactor equipped with an electric stirrer, a reflux condenser, and a tail gas absorption device. The amount of hexamethyldisilazane added was 7 times the molar amount of urea added, and the amount of ammonium chloride catalyst added was 5% of the mass of urea. The cooling water of the electric stirrer and the reflux condenser was turned on, and the reaction was carried out at atmospheric pressure and a temperature of 95-105°C for 15 hours. The ammonia gas produced was absorbed by water. After the reaction was completed, the reaction solution was cooled to room temperature and filtered. The filter cake was dried by vacuum rotary evaporation to obtain 490 g of hexamethyldisilazane, with a yield of 95.9%.

[0043] (2) Add 490 g of hexamethyldisilure obtained in the previous step to a 2-liter glass reactor equipped with an electric stirrer. The amount of boric acid added is 0.625 times the molar amount of hexamethyldisilure. Add ethylene glycol dimethyl ether as a solvent, turn on the electric stirrer, and stir and react for 3 hours at normal pressure and temperature of 5-10℃ to obtain crude product containing tris(trimethylsilyl)boronic acid ester.

[0044] (3) The crude product was filtered, and the resulting filter residue was urea, a byproduct, which was recycled. The purity of the filtrate was determined by gas chromatography. After deducting the solvent content, the product content in the filtrate was 94.54%, and the content of the hydrolysis product hexamethyldisiloxane was 1.69%. The filtrate was then subjected to vacuum distillation, and 401 grams of tris(trimethylsilyl)borate ester with a purity of 99.96% were collected. The yield of the second step reaction, calculated based on boric acid, was 95.6%, and the overall reaction yield was 91.7%.

[0045] Example 2

[0046] The synthesis process route of Example 2 is as follows:

[0047]

[0048] The specific operating steps are as follows:

[0049] (1) 150 g of urea was added to a 5-liter glass reactor equipped with an electric stirrer, a reflux condenser, and a tail gas absorption device. The amount of tetramethyldivinyldisilazane added was 5 times the molar amount of urea, and the amount of titanium tetrachloride catalyst added was 3% of the mass of urea. The cooling water of the electric stirrer and the reflux condenser was turned on, and the reaction was carried out at atmospheric pressure and a temperature of 160-170°C for 12 hours. The ammonia gas produced was absorbed by water. After the reaction was completed, the reaction solution was cooled to room temperature and filtered. The filter cake was dried by vacuum rotary evaporation to obtain 543 g of tetramethyldivinyldisilazane, with a yield of 95.1%.

[0050] (2) Add 543 g of tetramethyldivinyldisilamide obtained in the previous step to a 2-liter glass reactor equipped with an electric stirrer. The amount of boric acid added is 0.56 times the molar amount of tetramethyldivinyldisilamide. Add acetonitrile as a solvent, turn on the electric stirrer, and stir and react for 5 hours at normal pressure and temperature of 10-15℃ to obtain crude product containing tris(dimethylvinylsilyl)boronic acid ester.

[0051] The crude product was filtered, and the resulting filter residue, urea (a byproduct), was recycled. The purity of the filtrate was determined using gas chromatography. After deducting solvent content, the product content in the filtrate was 92.64%, and the content of the hydrolysis product, tetramethyldivinyldisiloxane, was 2.28%. The filtrate was then subjected to vacuum distillation, yielding 405 grams of tris(dimethylvinylsilyl)borate ester with a purity of 99.97%. The yield of the second reaction step, calculated based on boric acid, was 97.6%, and the overall reaction yield was 92.8%.

[0052] Example 3

[0053] Example 3 uses recycled urea for synthesis. The specific synthesis process is as follows:

[0054]

[0055] The specific operating steps are as follows:

[0056] (1) 150 g of recovered urea was added to a 5-liter glass reactor equipped with an electric stirrer, a reflux condenser, and a tail gas absorption device. The amount of tetravinyldimethyldisilazane added was 5 times the molar amount of urea added, and the amount of boron trifluoride diethyl ether complex catalyst added was 5% of the mass of urea. The cooling water of the electric stirrer and the reflux condenser was turned on, and the reaction was carried out at atmospheric pressure and a temperature of 145-155°C for 18 hours. The ammonia gas produced was absorbed by water. After the reaction was completed, the reaction solution was cooled to room temperature and filtered. The filter cake was dried by vacuum rotary evaporation to obtain 617 g of tetravinyldimethyldisilazane, with a yield of 97.9%.

[0057] (2) 617 g of tetravinyl dimethyl disilamide obtained in the previous step was added to a 3-liter glass reactor equipped with an electric stirrer. The amount of boric acid added was 0.59 times the molar amount of tetravinyl dimethyl disilamide. Ethylene glycol diethyl ether was added as a solvent. The electric stirrer was turned on and stirred and reacted for 6 hours at normal pressure and temperature of 10-15°C to obtain crude product containing tris(divinylmethyl silyl) borate.

[0058] (3) The crude product was filtered, and the resulting filter residue was urea, a byproduct, which was recycled. The purity of the filtrate was determined by gas chromatography. After deducting the solvent content, the product content in the filtrate was 93.97%, and the content of the hydrolysis product tetravinyldimethyldisiloxane was 3.76%. The filtrate was subjected to vacuum distillation, and 491 grams of tris(divinylmethylsilyl)borate ester with a purity of 99.96% were collected. The yield of the second step reaction, calculated based on boric acid, was 97.3%, and the overall reaction yield was 95.3%.

[0059] Comparative Example

[0060] The comparative synthesis process route is as follows:

[0061]

[0062] (1) 124 g of boric acid was added to a 2-liter glass reactor equipped with an electric stirrer, a reflux condenser and a tail gas absorption device. The amount of hexamethyldisilazane added was 1.6 times the molar amount of boric acid. The cooling water of the electric stirrer and the reflux condenser was turned on, and the mixture was stirred and reacted for 8 hours at atmospheric pressure and a temperature of 120-140°C to obtain a crude product containing tris(trimethylsilyl)boronic acid ester.

[0063] (2) The crude product was filtered to obtain 41 g of filter residue after dehydration of boric acid. The purity of the filtrate was determined by gas chromatography. The product content in the filtrate was 75.25%, the content of the hydrolysis product hexamethyldisiloxane was 20.52%, and the content of unreacted hexamethyldisilazane was 3.28%. The filtrate was subjected to vacuum distillation to collect 396 g of tris(trimethylsilyl)boronic acid ester product with a purity of 99.56%. The yield was 71.1% based on boric acid.

[0064] The existing synthesis process has low yield and conversion rate. The dehydration of boric acid produces a large amount of filter residue that cannot be used and must be treated as solid waste. At the same time, a large amount of hydrolysis products from the hydrolysis of raw materials remain in the crude product, making distillation separation more difficult and resulting in low product purity.

[0065] This invention provides a high-yield synthesis method for high-purity tris(trialkylsilyl)boronic esters. The synthesis process is simple, and by-products can be recycled, reducing waste emissions. The synthesis process of this invention features high yield and high conversion rate, and the obtained tris(trialkylsilyl)boronic ester product has high purity, meeting the requirements for use as an additive in lithium-ion battery electrolytes.

[0066] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for synthesizing tris(trialkylsilyl)boronic acid esters, characterized in that, It is carried out in the following three steps: (1) First step: react urea and hexaalkyldisilazane to prepare hexaalkyldisilazane; (2) In the second step, boric acid and hexaalkyldisilaurea are reacted to obtain crude tris(trialkylsilyl)boronic acid ester; (3) In the third step, the crude product is purified to obtain high-purity tris(trialkylsilyl)boronic acid ester with a purity of over 99.95%. The general structural formula of the tris(trialkylsilyl)boronic acid ester is: ； Among them, R1, R2, and R3 are the same or different alkyl, unsaturated hydrocarbon or aromatic groups; The general structural formula of the hexahydrodisilazane is: ； Among them, R1, R2, and R3 are the same or different alkyl, unsaturated hydrocarbon or aromatic groups; The general structural formula of the hexahydrodisilylurea is: ； Wherein, R1, R2, and R3 are the same or different alkyl, unsaturated hydrocarbon, or aromatic groups; the alkyl group is methyl, ethyl, n-propyl, isopropyl, trifluoromethyl, or trifluoroethyl; the unsaturated hydrocarbon group is vinyl, ethynyl, propynyl, or cyanopropyl; and the aromatic group is phenyl or benzyl.

2. The method for synthesizing a tris(trialkylsilyl)boronic ester according to claim 1, characterized in that, It is carried out in the following three steps: (1) In the first step, urea and hexaalkyldisilazane are heated and stirred under a catalyst and refluxed. The ammonia produced is absorbed by water to make ammonia water. After the reaction is completed, the reaction solution is cooled to room temperature and filtered. The filtrate is hexaalkyldisilazane, which is recycled. The filter cake is dried by vacuum rotary evaporation to obtain hexaalkyldisilazane. (2) In the second step, boric acid and hexaalkyldisilure reacted in a solvent at a certain reaction temperature with stirring to obtain a crude product containing tris(trialkylsilyl)boronic acid ester; (3) In the third step, the crude product is filtered to obtain a mixture of tris(trialkylsilyl)boronic acid ester and solvent, as well as filter residue. The mixture is then distilled, fractionated, or purified to collect the fraction and obtain high-purity tris(trialkylsilyl)boronic acid ester.

3. The method for synthesizing tris(trialkylsilyl)boronic acid esters according to claim 2, characterized in that, The catalyst used in the reaction of urea and hexaalkyldisilazane is a Lewis acid.

4. The method for synthesizing tris(trialkylsilyl)boronic acid esters according to claim 3, characterized in that, The catalyst is one or more of the following: ammonium sulfate, ammonium chloride, ammonium nitrate, boron trifluoride, boron trifluoride diethyl ether complex, sulfur trioxide, titanium tetrachloride, ferric chloride, ferric bromide, aluminum chloride, phosphorus oxychloride, sulfuric acid, hydrochloric acid, and trifluoromethanesulfonic acid, and the amount added is 0.5-5% of the urea quality.

5. The method for synthesizing tris(trialkylsilyl)boronic acid esters according to claim 2, characterized in that, The molar ratio of urea to hexaalkyldisilazane is 1:5~10; the molar ratio of boric acid to hexaalkyldisilazane is 1:1~5.

6. The method for synthesizing tris(trialkylsilyl)boronic acid esters according to claim 2, characterized in that, The urea and hexaalkyldisilazane react under normal pressure at a temperature of 70-180°C for 5-20 hours; the boric acid and hexaalkyldisilazane react under normal pressure at a temperature of -10-50°C for 1-20 hours.

7. The method for synthesizing tris(trialkylsilyl)boronic acid esters according to claim 2, characterized in that, The solvent used in the reaction of boric acid and hexaalkyldisilaurea is one or more of the following: dichloromethane, dichloroethane, acetonitrile, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol dimethyl ether, tetrahydrofuran, ethyl formate, methyl acetate, ethyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, butanone, and N,N-dimethylformamide.

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