Preparation method of fluorodinitrile

Abstract

The invention provides a preparation method of fluorodinitrile. The preparation method comprises the following steps: reacting trifluoromethanesulfonic anhydride with fluoroalkyl alcohol to obtain fluoroalkyl substituted trifluoromethanesulfonate; then, the fluoroalkyl substituted trifluoromethanesulfonate reacts with malononitrile, and fluorodinitrile is obtained; the reaction raw materials used in the method are easy to obtain and low in price, the target product conversion rate is high, byproducts are few, the purity of the prepared fluorodinitrile is as high as 99%, the yield is higher than 84%, the content of chloride and bromide ions is lower than 5 ppm, and the fluorodinitrile can meet the requirement of serving as an electrolyte additive.

Description

Technical Field

[0001] This invention relates to the field of nitrile compound preparation technology, and specifically to a method for preparing fluorodianitrons. Background Technology

[0002] Electrolytes, as a crucial component of lithium batteries, significantly influence various battery performance characteristics. Nitrile compounds possess advantages such as high dielectric constant, high oxidation decomposition potential, non-flammability, and high flash point, making them ideal choices for high-safety electrolytes in lithium secondary batteries. Recently, patent application CN202010389691.4 disclosed the application of fluorinated trinitrile compounds in electrolytes for high-voltage battery systems, while patent application CN202210255700.X disclosed fluorinated mononitrile and dinitrile compounds for use in high-voltage lithium battery electrolytes, with dinitrile and polynitrile compounds showing particularly superior performance.

[0003] However, existing technologies rarely involve the synthesis of fluorinated dinitrile and fluorinated polynitrile compounds, especially those used in lithium-ion battery electrolytes and additives. When fluorinated nitrile compounds are used in lithium-ion battery electrolytes and additives, a purity higher than 99% is typically required. This is because trace impurities in the electrolyte can cause side reactions during battery operation, affecting electrochemical stability, battery performance, and safety. In particular, the presence of chloride and bromide ions in the electrolyte can corrode aluminum current collectors, and a chloride and bromide ion content greater than 30 ppm can lead to battery failure. According to the requirements of the lithium-ion battery industry, the chloride and bromide ion content in solvents and additives used in lithium-ion battery electrolytes should be less than 5 ppm.

[0004] Patent CN100343233 C discloses a method for preparing 3,3,3-trifluoropropylmalononitrile, which uses 1-bromo-3,3,3-trifluoropropane and malononitrile to synthesize 3,3,3-trifluoropropylmalononitrile under potassium carbonate catalysis. However, the starting material 1-bromo-3,3,3-trifluoropropane is difficult to obtain and has a high cost. In addition, there are many reaction byproducts, and the purity and yield are low, with a yield of only 68%. The bromide ion content in the prepared fluoromalononitrile does not meet the requirements of the electrolyte field. Summary of the Invention

[0005] The technical problem this invention aims to solve is that existing methods for preparing fluorodianitrons suffer from insufficient chloride-bromine ion content, high reaction costs, and low purity and yield compared to electrolytes. This invention provides a method for preparing fluorodianitrons by reacting trifluoromethanesulfonic anhydride with a fluoroalkyl alcohol to obtain a fluoroalkyl-substituted trifluoromethanesulfonate ester; subsequently, the fluoroalkyl-substituted trifluoromethanesulfonate ester reacts with malononitrile to obtain a fluorodianitron. The reactants used in this invention—fluoroalkyl alcohol, trifluoromethanesulfonic anhydride, and malononitrile—are readily available and inexpensive. The resulting product exhibits high conversion rate and few byproducts. The fluorodianitron obtained achieves a purity of up to 99%, a yield exceeding 84%, and a chloride-bromine ion content below 5 ppm, meeting the requirements for use as an electrolyte additive.

[0006] The above-mentioned objective of the present invention is achieved through the following technical solution: This invention provides a method for preparing fluorodiacetonitrile, comprising the following steps: Step 1: React the fluoroalkyl alcohol R1R2FC-(CH2) n The -OH group undergoes esterification with trifluoromethanesulfonic anhydride in the presence of an acid-binding agent to generate a fluoroalkyl-substituted trifluoromethanesulfonate ester R1R2FC-(CH2). n -OTf; Step 2: The fluoroalkyl-substituted trifluoromethanesulfonate R1R2FC-(CH2) is then substituted. n -OTf reacts with malononitrile in the presence of an acid-binding agent to give fluorodianitrile R1R2FC-(CH2). n -C(CN)2; R1 and R2 are independently selected from any one of F atoms, H atoms, and C1~C3 alkyl groups, and n=1~5.

[0007] The reaction route of this invention is shown below: ; ; With the purity of the final target product E not less than 99%, the single-step reaction yield of the above reaction route is not less than 74.5%, and in particular, the yield of the second step reaction is higher than 84%.

[0008] Specifically, the preparation method includes the following steps: Step 1: Add fluorinated alkyl alcohol R1R2FC-(CH2) n Trifluoromethanesulfonic anhydride was added dropwise to a mixed solution of -OH and an acid-binding agent. After the addition was complete, the reaction was heated until complete to obtain a crude product. After purification, the fluoroalkyl-substituted trifluoromethanesulfonic acid ester R1R2FC-(CH2) was obtained. n -OTf; Step 2: Add the fluoroalkyl-substituted trifluoromethanesulfonate R1R2FC-(CH2) dropwise to the mixed solution of malononitrile and acid-binding agent. n After the -OTf solution was added dropwise, the reaction was heated until complete to obtain the crude product, which was then purified to obtain the fluorodiacetonide R1R2FC-(CH2). n -C(CN)2; R1 and R2 are independently selected from any one of F atoms, H atoms, and C1~C3 alkyl groups, and n=1~5.

[0009] Preferably, R1 and R2 are independently selected from either F or H atoms, and n = 1 to 2.

[0010] Specifically, in some embodiments of this application, the fluorodiacetonitrile is selected from any one of the following structures: ; Specifically, the solvent for the mixed solution in step one is selected from any one of dichloromethane, tetrahydrofuran, acetonitrile, dioxane, dichloroethane, or ethyl acetate, preferably dichloromethane. Using dichloromethane as the reaction solvent in step one can improve the yield.

[0011] Specifically, the acid-binding agent mentioned in step one is selected from at least one of triethylamine, pyridine, sodium hydroxide, potassium hydroxide, or piperidine, preferably triethylamine.

[0012] Specifically, the solvents for the mixed solution and the fluoroalkyl-substituted trifluoromethanesulfonate solution in step two are selected from any one of DMF, DMSO, THF, 1,4-dioxane, ethanol or NMP, preferably DMSO.

[0013] Specifically, the acid-binding agent mentioned in step two is selected from at least one of potassium carbonate, sodium carbonate, cesium carbonate, sodium hydroxide, potassium hydroxide, triethylamine, pyridine, or piperidine, preferably potassium carbonate.

[0014] Specifically, the molar ratio of trifluoromethanesulfonic anhydride to fluoroalkyl alcohol is 1:1 to 1.5, specifically 1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, and more preferably 1:1.

[0015] Specifically, the molar ratio of the fluoroalkyl-substituted trifluoromethanesulfonate to malononitrile is 1:2 to 3, preferably 1:2.

[0016] Specifically, in step two, the molar ratio of the acid-binding agent to malononitrile is 0.6 to 0.9:1, specifically 0.6:1, 0.7:1, 0.8:1, or 0.9:1, preferably 0.6:1.

[0017] Specifically, in step one, the heating reaction temperature is 40~60℃ and the heating reaction time is 3~6h; in step two, the dropping temperature is 0~5℃, preferably 0℃; in step two, the heating reaction temperature is 50~90℃ and the heating reaction time is 3~6h.

[0018] Specifically, the purification steps in step one are as follows: after removing the solvent and byproducts from the crude product, vacuum distillation is performed at a temperature of 60-70°C, and the fraction at 50-51°C is collected.

[0019] Specifically, the purification steps in step two are as follows: after removing the solvent and byproducts from the crude product, vacuum distillation is performed; the vacuum distillation temperature is 85~95℃, and the fraction at 70~72℃ is collected.

[0020] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a method for preparing fluorodianitrons, which involves an esterification reaction of a fluoroalkyl alcohol with trifluoromethanesulfonic anhydride to generate a fluoroalkyl-substituted trifluoromethanesulfonate; subsequently, the fluoroalkyl-substituted trifluoromethanesulfonate reacts with malononitrile to obtain the fluorodianitron. The reactants, fluoroalkyl alcohol, trifluoromethanesulfonic anhydride, and malononitrile, are readily available and inexpensive; the conversion rate of the target product is high and the byproducts are few; the prepared fluorodianitron has a purity higher than 99%, a yield higher than 84%, and a chloride-bromine ion content lower than 5 ppm, which meets the requirements for use as an electrolyte additive. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0022] Example 1 A method for preparing a fluorodiacetonitrile includes the following steps: Step 1: Preparation of 2,2-difluoroethyltrifluoromethanesulfonate: 2,2-Difluoroethanol (82.05 g, 1 mol) and triethylamine (111.31 g, 1.1 mol) were placed in a 2 L reaction flask. 500 mL of dichloromethane was added, and trifluoromethanesulfonic anhydride (282.13 g, 1 mol) was added dropwise at 0 °C. The mixture was then stirred at room temperature for 1 hour, and the temperature was raised to 60 °C for 3 hours. The reaction was monitored by gas chromatography until the difluoroethanol was completely converted, at which point the reaction was stopped. The reaction mixture was then poured into ice water and extracted with dichloromethane. The organic layer was washed successively with water and saturated sodium chloride aqueous solution, dried over anhydrous sodium sulfate, and then distilled under reduced pressure at 60–70 °C. The fraction collected at 50–51 °C yielded 2,2-difluoroethyltrifluoromethanesulfonate (185.4 g, yield 81.3%, purity 99.9%).

[0023] Step 2: Preparation of 2,2-difluoroethylmalononitrile: Malononitrile (66 g, 1.0 mol), potassium carbonate (82.9 g, 0.6 mol), and 200 mL of DMSO were added sequentially to a 2 L reaction flask, and the reaction mixture was stirred for 1 hour. Then, 2,2-difluoroethyltrifluoromethanesulfonate (107 g, 0.5 mol) dissolved in DMSO (200 mL) was added dropwise, and the mixture was reacted at 80 °C for 3 hours. The organic layer was washed sequentially with water, saturated sodium bicarbonate aqueous solution, and saturated sodium chloride aqueous solution, dried with anhydrous magnesium sulfate, and then distilled under reduced pressure at 85–95 °C. The fraction collected at 70–72 °C yielded 2,2-difluoroethylmalononitrile (56.6 g, yield 85.8%, purity 99.90%, chloride bromide ion content < 5 ppm).

[0024] Example 2 The only difference from Example 1 is: Step 1: 2-fluoroethanol (32.06 g, 0.5 mol) and triethylamine (55.65 g, 0.55 mol) were placed in a 1 L reaction flask, 300 mL of dichloromethane was added, and trifluoromethanesulfonic anhydride (141.14 g, 0.5 mol) was added dropwise at 0 °C. The mixture was then stirred at room temperature for 1 hour and heated to 50 °C for 3 hours to obtain 2-fluoroethyltrifluoromethanesulfonate (84.3 g, yield 80.3%).

[0025] Step 2: In a 2L reaction flask, malononitrile (131.8g, 2.0mol), potassium carbonate (165.8g, 1.2mol), and 400mL of DMSO were added sequentially, and the reaction mixture was stirred for 1 hour. Then, 2-fluoroethyltrifluoromethanesulfonate (196.2g, 1mol) dissolved in DMSO (400mL) was added dropwise, and the mixture was reacted at 80°C for 4 hours to obtain 2-fluoroethylmalononitrile (94.8g, yield 84.6%, purity 99.48%, chloride bromide ion content <5ppm).

[0026] The other steps are the same as in Example 1.

[0027] Example 3 The only difference from Example 1 is that: Step 1: the fluoroalkyl alcohol is 2,2,2-trifluoroethanol (100.04 g, 1 mol), to obtain 2,2,2-trifluoroethyltrifluoromethanesulfonate (206.4 g, yield 88.9%).

[0028] Step 2: In a 2L reaction flask, malononitrile (131.8g, 2.0mol), potassium carbonate (165.8g, 1.2mol), and 400mL of DMSO were added sequentially, and the reaction mixture was stirred for 1 hour. Then, 2-fluoroethyltrifluoromethanesulfonate (196.2g, 1mol) dissolved in DMSO (400mL) was added dropwise, and the mixture was reacted at 80°C for 4 hours to obtain 2,2,2-trifluoroethylmalononitrile (44.8g, yield 84.6%, purity 99.65%, chloride bromide ion content <5ppm).

[0029] The other steps are the same as in Example 1.

[0030] Example 4 The only difference from Example 1 is: Step 1: 3,3,3-trifluoropropanol (228.13 g, 2 mol) and triethylamine (222.62 g, 2.2 mol) were placed in a 2 L reaction flask, and 700 mL of dichloromethane was added. Trifluoromethanesulfonic anhydride (564.25 g, 2 mol) was added dropwise at 0 °C. The mixture was then stirred at room temperature for 1 hour and heated to 60 °C for 4 hours to obtain 3,3,3-trifluoropropyltrifluoromethanesulfonate (431.9 g, yield 83.7%).

[0031] Step 2: In a 2L reaction flask, malononitrile (218.05g, 3.30mol), potassium carbonate (310.96g, 2.25mol), and 500mL DMF were added sequentially, and the reaction mixture was stirred for 1 hour. Then, 3,3,3-trifluoropropyltrifluoromethanesulfonate (369.19g, 1.5mol) dissolved in DMF (300mL) was added dropwise, and the reaction was carried out at 80℃ for 4 hours to obtain 3,3,3-trifluoropropylmalononitrile (208.2g, yield 85.7%, purity 99.52%, chloride bromide ion content <5ppm).

[0032] The other steps are the same as in Example 1.

[0033] Example 5 The only difference from Example 1 is that the solvent added in step one is tetrahydrofuran, which yields 2,2-difluoroethyltrifluoromethanesulfonate (170.8 g, yield 74.9%), and step two yields 2,2-difluoroethylmalononitrile (yield > 84%, purity > 99%, chloride bromide ion content < 5 ppm).

[0034] The other steps are the same as in Example 1.

[0035] Example 6 The only difference from Example 1 is that the solvent added in step one is acetonitrile, which yields 2,2-difluoroethyltrifluoromethanesulfonate (175.4 g, yield 76.8%), and step two yields 2,2-difluoroethylmalonium (yield > 84%, purity > 99%, chloride bromide ion content < 5 ppm). The other steps are the same as in Example 1.

[0036] Comparative Example 1 A method for synthesizing a fluorodianitron includes the following steps: Malononitrile (27.6 g, 0.4 mol) was dissolved in N,N-dimethylformamide (50 mL), and potassium carbonate (27.6 g) was added. The reaction mixture was stirred for one hour, and then 1-bromo-3,3,3-trifluoropropane (17.7 g, 0.1 mol) dissolved in N,N-dimethylformamide (20 mL) was added dropwise, followed by stirring for another hour. Water was then added to the reaction mixture, and the mixture was extracted with diethyl ether. The organic layer was washed with water and saturated brine, dried thoroughly with anhydrous sodium sulfate, and concentrated under reduced pressure. The residue was passed through a silica gel column to give 11.3 g of 3,3,3-trifluoropropylmalononitrile in a yield of 68%, with a purity less than 99% and a bromide ion content exceeding 5 ppm.

[0037] The reactants used in this invention—fluoroalkyl alcohols, trifluoromethanesulfonic anhydride, and malononitriles—are readily available and inexpensive. The target product has a high conversion rate and few byproducts. The fluorodionitriles prepared in Examples 1-6 have a purity higher than 99%, a yield higher than 84%, and a chloride-bromine ion content lower than 5 ppm, making them suitable as battery electrolyte additives. In contrast, the reactant 1-bromo-3,3,3-trifluoropropane used in Comparative Example 1 is difficult to obtain, has high costs, and produces many byproducts. Its yield is only 68%, its purity is lower than 99%, and its chloride-bromine ion content is higher than 5 ppm, failing to meet the requirements for use as an electrolyte additive.

[0038] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A process for the preparation of a fluorodinitrile, characterized in that, The method comprises the following steps: Step one: esterification of a fluoroalkyl alcohol R1R2FC-(CH2) n -OH with triflic anhydride in the presence of an acid binding agent to form a fluoroalkyl substituted triflate R1R2FC-(CH2) n -OTf; Step two: reacting said fluorinated alkyl substituted triflate R1R2FC-(CH2) n -OTf with malononitrile in the presence of an acid binding agent to obtain a fluorinated dinitrile R1R2FC-(CH2) n -C(CN)2; R1 and R2 are independently selected from F atom, H atom, C1-C3 alkyl, and n=1-5.

2. The method of claim 1, wherein, The method comprises the following steps: Step one: To a mixture solution of fluoroalkyl alcohol R1R2FC-(CH2) n -OH and acid binding agent, triflic anhydride was added dropwise, after the addition was completed, the reaction was heated to completion to obtain the crude product, and after purification, the fluoroalkyl substituted triflate R1R2FC-(CH2) n -OTf; Step two: drop the solution of fluorinated alkyl substituted triflate R1R2FC-(CH2)3-C(CN)2; into the mixed solution of malononitrile and acid binding agent, after the drop is completed, heat the reaction to completion to obtain the crude product, and obtain the fluorinated dinitrile R1R2FC-(CH2)3-C(CN)2 after purification. n -OTf solution, after the drop is completed, heat the reaction to completion to obtain the crude product, and obtain the fluorinated dinitrile R1R2FC-(CH2)3-C(CN)2 after purification. n -C(CN)2; R1 and R2 are independently selected from F atom, H atom, C1-C3 alkyl, and n=1-5.

3. The preparation method according to claim 2, characterized in that, The molar ratio of the triflic anhydride to the fluoroalkyl alcohol is 1:1-1.

5.

4. The preparation method according to claim 2, characterized in that, The molar ratio of the fluoroalkyl substituted triflate to the malononitrile is 1:2-3.

5. The preparation method according to claim 2, characterized in that, The molar ratio of the acid binding agent to the malononitrile in step two is 0.6-0.9:

1.

6. The preparation method according to claim 2, characterized in that, The solvent of the mixed solution in step one is selected from dichloromethane, tetrahydrofuran, acetonitrile, dioxane, dichloroethane or ethyl acetate.

7. The preparation method according to claim 2, characterized in that, The temperature of the heating reaction in step one is 40-60℃, and the time of the heating reaction is 3-6h.

8. The preparation method according to claim 2, characterized in that, The temperature of the heating reaction in step two is 50-90℃, and the time of the heating reaction is 3-6h.

9. The preparation method according to claim 2, characterized in that, The specific purification step in step one is: after removing the solvent and by-products in the crude product, vacuum distillation is performed; the temperature of the vacuum distillation is 60-70℃.

10. The preparation method according to claim 2, characterized in that, The specific purification step in step two is: after removing the solvent and by-products in the crude product, vacuum distillation is performed; the temperature of the vacuum distillation is 85-95℃.