A kind of preparation method of boric acid

Abstract

The invention relates to a method for preparing boric acid, and belongs to the field of synthesis of boron-containing compounds. The preparation method comprises the following steps: boron trifluoride and a nitrogen-containing organic base are subjected to a complex reaction in an organic solvent to form a complex; the complex is subjected to an esterification reaction with an alkyl alcohol to generate a boric ester; and the boric ester is hydrolyzed to obtain boric acid. The invention generates a boric ester by reacting a boron trifluoride nitrogen-containing organic base complex with an alkyl alcohol. The side reaction of the reaction is small, impurities are not easily introduced, and the obtained boric ester has a high purity. Then, the boric acid is obtained by hydrolyzing the boric ester to improve the purity of the boric acid.

Description

Technical Field

[0001] The invention relates to a method for preparing boric acid, and belongs to the field of synthesis of boron-containing compounds. Background Art

[0002] Boric acid is a white powdery crystal or a shiny crystal with triclinic flaky surface, which is soluble in water, ethanol and glycerin. Industrial boric acid is widely used in various industries such as light industry, building materials industry, electromechanical industry, chemical industry, electronics industry, metallurgical industry, pharmaceutical industry and nuclear power industry due to its unique properties such as light weight, flame retardancy, heat resistance, high hardness, high strength and catalytic properties.

[0003] In order to meet the needs of higher standards, the synthesis and purification methods of high-purity boric acid are widely studied by industry personnel. In the prior art, the Chinese invention patent with the authorization announcement number CN114275794B discloses a method for preparing high-purity boric acid, using boron halide as raw material, generating boric acid and hydrogen halide through hydrolysis reaction, and the boric acid is concentrated, crystallized, filtered and dried to obtain high-purity boric acid, and the halogen in the boron halide is chlorine or bromine. Since the hydrogen halide by-product generated in the preparation method is soluble in water, and the reaction is carried out under hydrolysis conditions, it is very easy to introduce by-product impurities in the production process, and the impurities are not easy to be separated from boric acid and completely removed, affecting the purity of boric acid, in addition, hydrogen halide can further generate by-products such as fluoroborate with boron halide, reducing yield, separation difficulties, and corrosive equipment. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing boric acid, so as to solve the problem that impurities are easily introduced and difficult to remove during the preparation of boric acid in the prior art.

[0005] In order to achieve the above purpose, the technical solution of the present invention is:

[0006] A method for preparing boric acid comprises the following steps: boron trifluoride and a nitrogen-containing organic base are subjected to complexation reaction in an organic solvent to form a complex; the complex is subjected to esterification reaction with an alkyl alcohol to generate a boric acid ester; and the boric acid ester is hydrolyzed to obtain boric acid.

[0007] The present invention generates boric acid ester and byproduct hydrogen fluoride by reacting a boron trifluoride nitrogen-containing organic base complex with an alkyl alcohol, and the byproduct hydrogen fluoride can be captured in situ by the nitrogen-containing organic base, so as to avoid further reaction of hydrogen fluoride with the raw material boron trifluoride to generate HBF4, so that the obtained boric acid ester has a higher purity, and then the boric acid ester is hydrolyzed to obtain boric acid, thereby improving the purity of the boric acid. Therefore, the reaction has fewer side reactions and is not easy to introduce impurities.

[0008] In order to further improve the purity of boric acid, preferably, after the esterification reaction, filtration and distillation are performed, and fractions are collected to obtain the boric ester. The boric ester is an organic phase, which is convenient for separation and impurity removal from by-products in the reaction, thereby improving the purity of the boric ester, and further improving the purity of the boric acid after the boric ester is hydrolyzed.

[0009] In order to improve the reaction efficiency of boron trifluoride and the nitrogen-containing organic base, preferably, the molar ratio of boron trifluoride to the nitrogen-containing organic base is 1:(1-1.2).

[0010] Preferably, the nitrogen-containing organic base is one or more of pyridine, triethylamine, 4-dimethylaminopyridine, 2,6-lutidine, pyrrole, and aniline. When the nitrogen-containing organic base is selected from these substances, it is favorable to form a complex with boron trifluoride at room temperature, and the reaction conditions are mild.

[0011] In order to improve the reaction efficiency of the complex and the alkyl alcohol, preferably, the molar ratio of the alkyl alcohol to boron trifluoride is (5-30):1.

[0012] In order to facilitate the esterification reaction, preferably, the alkyl alcohol is a low molecular alcohol having 1 to 3 carbon atoms.

[0013] Preferably, the low molecular alcohol is one or more of methanol, ethanol and isopropanol. It has good solubility, low system viscosity, good reaction activity, and is easy to carry out esterification reaction.

[0014] Preferably, the temperature for reacting the complex with the alkyl alcohol is 40-70° C. and the time is 24-60 hours. Reaction at this temperature can improve the reaction efficiency, while the reaction time can ensure the complete reaction.

[0015] Preferably, the organic solvent is one or more of n-hexane, n-pentane, n-heptane, toluene, mesitylene, and trifluoromethylbenzene. The organic solvent can better dissolve the nitrogen-containing organic base and promote the reaction of boron trifluoride and the nitrogen-containing organic base.

[0016] In order to improve the reaction efficiency, preferably, the amount of organic solvent used per 1 mol of boron trifluoride is 1 to 1.2 L.

[0017] In order to promote the efficiency of hydrolysis, preferably, the molar ratio of water to boron trifluoride in the hydrolysis is (40-50):1.

[0018] Further preferably, the boron trifluoride is natural abundance BF3, enriched 10 BF3, enriched 11 One or more of BF3. The method according to the present invention can obtain high purity natural abundance B(OH)3, enriched 10 B(OH)3 and enriched 11B(OH)3. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described below in conjunction with specific implementation methods.

[0020] The present invention forms a complex by reacting boron trifluoride with a nitrogen-containing organic base, then reacts the complex with an alkyl alcohol to form a boric acid ester, removes impurities from the boric acid ester, and hydrolyzes the boric acid ester after the impurities removal to obtain boric acid. The reaction route is as follows:

[0021]

[0022] The method for preparing boric acid of the present invention comprises the following steps:

[0023] (1) Under a protective atmosphere, boron trifluoride and a nitrogen-containing organic base are reacted in an organic solvent to obtain a complex; the reaction can be completed by stirring at room temperature, the reaction conditions are mild, and the operation is convenient;

[0024] (2) Under a protective atmosphere, reacting the complex obtained in step (1) with an alkyl alcohol at 40-70° C. for 24-60 hours to obtain a boric acid ester; cooling the boric acid ester to room temperature, filtering out solid precipitates, and distilling; the boric acid ester is an organic phase, which is convenient for separation and impurity removal from the by-products of the reaction, thereby improving the purity of the boric acid ester; the solid precipitate is a composite salt generated by in-situ capture of the HF produced in step (2) by the nitrogen-containing organic base;

[0025] (3) adding the boric acid ester obtained by distillation in step (2) into water for hydrolysis and purification to obtain boric acid. When the boric acid ester is hydrolyzed at a high purity, the purity of the obtained boric acid is also high; the purification comprises distillation, cooling, and crystallization.

[0026] 1. The specific embodiment of the preparation method of boric acid of the present invention is as follows:

[0027] Example 1

[0028] The preparation method of boric acid in this embodiment adopts the following steps:

[0029] Under nitrogen atmosphere, pyridine (79 g, 1 mol) and n-hexane (1 L) were added into a reaction flask, and then naturally abundant BF3 gas (68 g, 1 mol) was introduced into the reaction flask system, stirred at room temperature for 12 hours, and then the complex precipitate was filtered out; the obtained complex was added into a reaction flask containing methanol (480 g, 15 mol) under nitrogen atmosphere, and then reacted at 50°C for 48 hours; after the reaction, the temperature was cooled to room temperature, the solid precipitate was filtered out, and distillation was performed at 80°C. The 70°C fraction was dripped into high-purity water (900 g, 50 mol) for hydrolysis, and finally distilled at 100°C, cooled to room temperature (room temperature refers to 25±5°C), cooled to 10°C for crystallization to obtain 56 g of naturally abundant boric acid with a yield of 91% and a purity of 99.999%.

[0030] Example 2

[0031] The preparation method of boric acid in this embodiment adopts the following steps:

[0032] Under nitrogen atmosphere, pyridine (79 g, 1 mol) and n-hexane (1 L) were added into a reaction flask, and then naturally abundant BF3 gas (68 g, 1 mol) was introduced into the reaction flask system, and stirred at room temperature for 12 hours. Then methanol (160 g, 5 mol) was added to the system, and then reacted at 50°C for 48 hours. After the reaction was completed, the temperature was lowered to room temperature, the solid precipitate was filtered out, and distillation was performed at 80°C. The 70°C fraction was dropped into high-purity water (900 g, 50 mol) for hydrolysis, and finally distilled at 100°C, lowered to room temperature (room temperature refers to 25±5°C), and cooled to 10°C for crystallization to obtain 55 g of naturally abundant boric acid with a yield of 89% and a purity of 99.998%.

[0033] Example 3

[0034] The preparation method of boric acid in this embodiment adopts the following steps:

[0035] Under nitrogen atmosphere, triethylamine (101 g, 1 mol) and n-hexane (1 L) were added into a reaction flask, and then naturally abundant BF3 gas (68 g, 1 mol) was introduced into the reaction flask system, and stirred at room temperature for 12 hours. Then methanol (160 g, 5 mol) was added to the system, and then reacted at 40°C for 24 hours. After the reaction was completed, the temperature was lowered to room temperature, the solid precipitate was filtered out, and distillation was performed at 80°C. The 70°C fraction was dropped into high-purity water (900 g, 50 mol) for hydrolysis, and finally distilled at 100°C, lowered to room temperature (room temperature refers to 25±5°C), and cooled to 10°C for crystallization to obtain 50 g of naturally abundant boric acid with a yield of 81% and a purity of 99.995%.

[0036] Example 4

[0037] The preparation method of boric acid in this embodiment adopts the following steps:

[0038] Under nitrogen atmosphere, pyridine (79 g, 1 mol) and n-hexane (1 L) were added to the reaction flask, and then the system was introduced into 11 B abundance is 99.7% enrichment 11 BF3 gas (68g, 1mol), stirred at room temperature for 12 hours, and then filtered out the complex precipitate; the obtained complex was added to a reaction bottle filled with methanol (480g, 15mol) under a nitrogen atmosphere, and then reacted at 50°C for 48h; after the reaction, it was cooled to room temperature, the solid precipitate was filtered out, and distilled at 80°C, and the 70°C fraction was dripped into high-purity water (900g, 50mol) for hydrolysis, and finally distilled at 100°C, cooled to room temperature (room temperature refers to 25±5°C), and cooled to 10°C for crystallization to obtain 11 57 g of enriched boric acid with B abundance of 99.7%, a yield of 92% and a purity of 99.999%.

[0039] Example 5

[0040] The preparation method of boric acid in this embodiment adopts the following steps:

[0041] Under nitrogen atmosphere, pyridine (79 g, 1 mol) and n-hexane (1 L) were added to the reaction flask, and then the system was introduced into 10 B abundance is 99% enrichment 10 BF3 gas (68g, 1mol) was added, stirred at room temperature for 12 hours, and then the complex precipitate was filtered out; the obtained complex was added to a reaction bottle containing methanol (480g, 15mol) under a nitrogen atmosphere, and then reacted at 50°C for 48h; after the reaction, it was cooled to room temperature, the solid precipitate was filtered out, and distilled at 80°C, and the 70°C fraction was dripped into high-purity water (900g, 50mol) for hydrolysis, and finally distilled at 100°C, cooled to room temperature (room temperature refers to 25±5°C), and cooled to 10°C for crystallization to obtain 10 56 g of enriched boric acid with B abundance of 99%, a yield of 91% and a purity of 99.999%.

[0042] Example 6

[0043] The preparation method of boric acid in this embodiment adopts the following steps:

[0044] Under nitrogen atmosphere, pyrrole (74 g, 1.1 mol) and toluene (1 L) were added to the reaction flask, and then the system was introduced into 11 B abundance is 99.9% enrichment 11BF3 gas (68g, 1mol) was added, stirred at room temperature for 12 hours, and then the complex precipitate was filtered out; the obtained complex was added to a reaction bottle containing ethanol (690g, 15mol) under a nitrogen atmosphere, and then reacted at 70°C for 60h; after the reaction, it was cooled to room temperature, the solid precipitate was filtered out, and distilled at 80°C. The 70°C fraction was dripped into high-purity water (900g, 50mol) for hydrolysis, and finally distilled at 100°C, cooled to room temperature (room temperature refers to 25±5°C), and cooled to 10°C for crystallization to obtain 11 49 g of enriched boric acid with B abundance of 99.9%, a yield of 79% and a purity of 99.992%.

[0045] In other embodiments, ethanol is replaced with isopropanol, and the obtained boric acid performance effect is equivalent to that of this embodiment.

[0046] Example 7

[0047] The preparation method of boric acid in this embodiment adopts the following steps:

[0048] Under nitrogen atmosphere, aniline (112 g, 1.2 mol) and mesitylene (1.2 L) were added to the reaction flask, and then the system was introduced into 10 B abundance is 95% enrichment 10 BF3 gas (68g, 1mol) was added and stirred at room temperature for 12 hours, and then the complex precipitate was filtered out; the obtained complex was added to a reaction bottle containing ethanol (460g, 10mol) under a nitrogen atmosphere, and then reacted at 65°C for 30h; after the reaction, it was cooled to room temperature, the solid precipitate was filtered out, and distilled at 80°C. The 70°C fraction was dripped into high-purity water (720g, 40mol) for hydrolysis, and finally distilled at 100°C, cooled to room temperature (room temperature refers to 25±5°C), and cooled to 10°C for crystallization to obtain 10 53 g of enriched boric acid with B abundance of 95%, a yield of 86% and a purity of 99.98%.

[0049] Example 8

[0050] The preparation method of boric acid in this embodiment adopts the following steps:

[0051] Under nitrogen atmosphere, 4-dimethylaminopyridine (122 g, 1 mol) and trifluoromethylbenzene (1 L) were added to the reaction bottle, and then naturally abundant BF3 gas (68 g, 1 mol) was introduced into the system, and stirred at room temperature for 12 hours. Then methanol (960 g, 30 mol) was added to the system, and then reacted at 55°C for 40 hours. After the reaction, the temperature was lowered to room temperature, the solid precipitate was filtered out, and distillation was performed at 80°C. The 70°C fraction was dropped into high-purity water (900 g, 50 mol) for hydrolysis, and finally distilled at 100°C, lowered to room temperature (room temperature refers to 25±5°C), and cooled to 10°C for crystallization to obtain 55 g of naturally abundant boric acid with a yield of 89% and a purity of 99.995%.

[0052] Example 9

[0053] The preparation method of boric acid in this embodiment adopts the following steps:

[0054] Under nitrogen atmosphere, 2,6-dimethylpyridine (107 g, 1 mol) and n-heptane (1 L) were added to the reaction flask, and then the system was introduced into 10 B abundance is 98% enrichment 10 BF3 gas (68g, 1mol) was stirred at room temperature for 12 hours, and then methanol (192g, 6mol) was added to the system, and then reacted at 55°C for 40h; after the reaction, the temperature was lowered to room temperature, the solid precipitate was filtered out, and distillation was performed at 80°C. The 70°C fraction was dropped into high-purity water (900g, 50mol) for hydrolysis, and finally distilled at 100°C, lowered to room temperature (room temperature refers to 25±5°C), and cooled to 10°C for crystallization to obtain 57g of natural abundance boric acid with a yield of 92% and a purity of 99.993%.

[0055] Example 10

[0056] The preparation method of boric acid in this embodiment adopts the following steps:

[0057] Under nitrogen atmosphere, 2,6-dimethylpyridine (107 g, 1 mol) and n-heptane (1 L) were added to the reaction flask, and then the system was introduced into 10 B abundance is 98% enrichment 10BF3 gas (68g, 1mol) was added, stirred at room temperature for 12 hours, and then the complex precipitate was filtered out, and the complex was added to a reaction bottle containing ethanol (460g, 10mol) under a nitrogen atmosphere, and then reacted at 55°C for 40 hours. After the reaction was completed, the temperature was lowered to room temperature, the solid precipitate was filtered out, and distillation was performed at 80°C. The 70°C fraction was dripped into high-purity water (900g, 50mol) for hydrolysis, and finally distilled at 100°C, lowered to room temperature (room temperature refers to 25±5°C), cooled to 10°C for crystallization, and 58g of natural abundant boric acid was obtained, with a yield of 95% and a purity of 99.994%.

Claims

1. A method for preparing boric acid, characterized in that: The following steps are involved: Boron trifluoride and a nitrogen-containing organic base undergo a complex reaction in an organic solvent to form a complex; the complex undergoes an esterification reaction with an alkyl alcohol to generate a boric ester; the boric ester is hydrolyzed to obtain boric acid; the nitrogen-containing organic base is one or more of pyridine, triethylamine, 4-dimethylaminopyridine, 2,6-lutidine, pyrrole, and aniline.

2. The method for preparing boric acid according to claim 1, characterized in that: The molar ratio of boron trifluoride to nitrogen-containing organic base is 1:(1-1.2).

3. The method for preparing boric acid according to claim 1, characterized in that: The molar ratio of the alkyl alcohol to boron trifluoride is (5-30):

1.

4. The method for preparing boric acid according to claim 1 or 3, characterized in that: The alkyl alcohol is a low molecular alcohol having 1 to 3 carbon atoms.

5. The method for preparing boric acid according to claim 4, characterized in that: The low molecular alcohol is selected from one or more of methanol, ethanol and isopropanol.

6. The method for preparing boric acid according to claim 1 or 3, characterized in that: The temperature for the reaction of the complex with the alkyl alcohol is 40-70° C. and the time is 24-60 h.

7. The method for preparing boric acid according to claim 1, characterized in that: The organic solvent is one or more of n-hexane, n-pentane, n-heptane, toluene, mesitylene, and trifluoromethylbenzene.

8. The method for preparing boric acid according to claim 7, characterized in that: The amount of organic solvent used for every 1 mol of boron trifluoride is 1~1.2 L.

9. The method for preparing boric acid according to claim 1, characterized in that: The molar ratio of water to boron trifluoride in the hydrolysis is (40-50):1.

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