A process for the preparation of a monofluorophosphate

Abstract

The application discloses a preparation method of monofluorophosphate, and the preparation method comprises the following steps: adding a stabilizer into obtained monofluorophosphate reaction solution, wherein the stabilizer is at least one selected from metal oxides, anhydrous carbonates and anhydrous bicarbonates, and the monofluorophosphate has the following structure shown in formula (I): wherein R is selected from C1-C6 alkyl, C1-C6 fluoroalkyl, C2-C6 alkenyl and C2-C6 fluoroalkenyl. The monofluorophosphate product prepared by the method has high yield, high purity, low acidity and low impurity content.

Description

TECHNICAL FIELD

[0001] The present application relates to the synthesis of lithium ion battery electrolyte additives, in particular to a method for preparing high-purity monofluorophosphate. BACKGROUND

[0002] Fluorophosphate compounds are often used as additives in lithium ion battery electrolytes, which have the effect of inhibiting gas production and help to improve normal temperature cycle, high temperature storage and high temperature cycle performance. Monofluorophosphate is a kind of fluorophosphate compound, and its preparation route mainly includes the following two kinds:

[0003] 1) Monochlorophosphate route

[0004] Monochlorophosphate and fluorinating reagent as raw materials, in the presence of solvent, the reaction formula is as follows:

[0005]

[0006] Patent JP2017119690A discloses a method for obtaining diethyl fluorophosphate by reacting diethyl chlorophosphate and potassium fluoride in acetonitrile solvent. In this method, the reaction solution is filtered to remove excess potassium fluoride and precipitate potassium chloride, and then the solvent is evaporated to obtain the product, with a yield of 92%, but the purity of the product is not mentioned.

[0007] Herath, Mahesha B, et al. (ChemPhysChem 2010, 11, 2871-2878) discloses a method for obtaining diethyl fluorophosphate by injecting diethyl chlorophosphate into a mixed solution of potassium fluoride and acetonitrile at room temperature. In this method, the reaction solution is filtered, distilled under reduced pressure, and vacuum distilled to obtain the product, with a yield of 76%, but the purity is not mentioned.

[0008] Sierakowski, Timothy, et al. (Tetrahedron Letters, 46(13), 2215-2217; 2005) discloses a method for synthesizing diethyl fluorophosphate by using ion exchange resin as fluorine source and diethyl chlorophosphate in the presence of tetrahydrofuran. In this method, the reaction solution is filtered and distilled to obtain the product, with a yield of 81%, but the purity of the product and the actual reaction raw material ratio are not mentioned, and the recycling of ion exchange resin is not described.

[0009] 2) Phosphite route

[0010] Phosphite and fluorinating reagent as raw materials, in the presence of chlorinating reagent and solvent, the reaction formula is as follows:

[0011]

[0012] Purohit, Ajay Kumar et al. (Tetrahedron Letters 56(31), 4593-4595; 2015) disclosed a method of reacting diethyl phosphite, copper chloride, cesium fluoride in a 1:2:2 feed ratio in acetonitrile solvent to obtain diethyl fluorophosphite, and the reaction solution was filtered and concentrated to obtain the product with a yield of 92%, but the actual purity of the product was not mentioned, and the separation and purification method was not mentioned.

[0013] Acharya, J et al. (Synthetic Communications 38(21), 3760-3765; 2008) disclosed a method of reacting diethyl phosphite, trichloroisocyanuric acid, potassium fluoride in a 1:0.34:1.1 feed ratio in acetonitrile solvent to obtain diethyl fluorophosphite, and the reaction solution was filtered and concentrated to obtain the product with a yield of 89%, but the purity of the product was not mentioned.

[0014] It can be seen that the prior art does not mention the purity of the product, and the post-treatment of the reaction solution is limited to filtration, distillation and other methods. The inventors synthesized monofluorophosphates by the method of the above patent JP2017119690A, and purified the product by conventional vacuum distillation method. Under different temperature and vacuum degree conditions, the purity of the separated product is generally 89-95%, and even if the distillation product with a content of 94% is subjected to secondary distillation purification, the final product purity content is only about 96%. Similarly, when monofluorophosphates are synthesized by the methods disclosed in other documents, the fluorine ions, chlorine ions and acidity of the purified monofluorophosphates are high.

[0015] As is known, as a lithium ion battery electrolyte additive, the low purity of the additive, high acidity and high impurity content will greatly reduce the capacity and cycle performance of the battery, which is extremely detrimental to lithium ion batteries. Therefore, it is necessary to prepare high-purity monofluorophosphates as electrolyte additives. SUMMARY

[0016] To solve the above technical problems, the present application provides a method for preparing monofluorophosphates with high product purity, low acidity and low impurity content, which is suitable for industrial production.

[0017] The inventors found in actual research that monofluorophosphates have poor thermal stability and are easily disulfurized into phosphoric acid triesters under heat, which results in low purity of monofluorophosphates and cannot meet the demand of lithium battery electrolyte additives.

[0018] The purpose of the present application is achieved by the following technical solutions:

[0019] A method for preparing a monofluorophosphate ester, the method comprising: adding a stabilizer to a monofluorophosphate ester reaction solution obtained, the stabilizer being selected from at least one of a metal oxide, anhydrous carbonate, and anhydrous bicarbonate, the monofluorophosphate ester having a structure as shown in the following formula (I):

[0020]

[0021] wherein R is selected from C1-C6 alkyl, C1-C6 fluoroalkyl, C2-C6 alkenyl, and C2-C6 fluoroalkenyl.

[0022] Preferably, R is selected from C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, and C2-C4 fluoroalkenyl. More preferably, R is selected from methyl, trifluoromethyl, difluoromethyl, ethyl, trifluoroethyl, propyl, isopropyl, allyl, butyl, isobutyl, and tert-butyl.

[0023] The present application adds a stabilizer to a monofluorophosphate ester reaction solution, which not only effectively reduces the decomposition of the monofluorophosphate ester during distillation, but also captures impurity ions such as fluoride ions and chloride ions in the reaction solution, reduces the impurity content in the product, reduces the acidity of the reaction solution, controls the moisture content in the product, and inhibits the hydrolysis of the product, so that the battery performance is not affected when the product is applied to an electrolyte.

[0024] Therefore, the metal oxide is selected from at least one of calcium oxide, magnesium oxide, and barium oxide; the anhydrous carbonate is selected from at least one of anhydrous sodium carbonate, anhydrous potassium carbonate, anhydrous calcium carbonate, and anhydrous magnesium carbonate; and the anhydrous bicarbonate is selected from at least one of anhydrous sodium bicarbonate, anhydrous potassium bicarbonate, anhydrous calcium bicarbonate, and anhydrous magnesium bicarbonate.

[0025] Preferably, the stabilizer is selected from at least one of calcium oxide, anhydrous sodium carbonate, and anhydrous potassium carbonate.

[0026] The method for preparing the monofluorophosphate ester of the present application specifically comprises:

[0027] A1. filtering the monofluorophosphate ester reaction solution, adding the stabilizer to the filtrate, and stirring;

[0028] A2. obtaining a monofluorophosphate ester with a purity of ≥99.5% through distillation or rectification.

[0029] In the A1 step, the amount of the stabilizer added is 0.01-0.1 of the theoretical yield of the monofluorophosphate ester. Preferably, the amount of the stabilizer added is 0.01-0.03 of the theoretical yield of the monofluorophosphate ester.

[0030] In the A1 step, the stirring time is 15-120 minutes, and preferably the stirring time is 30-60 minutes.

[0031] To further improve the product yield, in the step A1, the filter cake is washed with a low boiling point solvent, and the filtrate is combined and distilled or rectified. The low boiling point solvent is selected from at least one of dichloromethane, dichloroethane, n-hexane, methyl tert-butyl ether, and the amount is 0.1-1 times the theoretical yield of monofluorophosphates, and preferably the amount is 0.2-0.5 times the theoretical yield of monofluorophosphates. Further, in the step A2, the low boiling point solvent is removed by atmospheric distillation, and then the monofluorophosphates are obtained by vacuum rectification.

[0032] The monofluorophosphates reaction solution of the present application can be obtained by reacting monochlorophosphates and potassium fluoride, and the reaction formula is as follows:

[0033]

[0034] The monochlorophosphates can be obtained by reacting phosphorus oxychloride and corresponding alcohol.

[0035] The above reaction is a solvent-free reaction, the reaction temperature is 20-80℃, and the reaction time is 2-12 hours. Preferably, the reaction temperature is 30-50℃, and the reaction time is 4-5 hours.

[0036] The molar ratio of potassium fluoride to monochlorophosphates is 1.0-2.0:1, and preferably the molar ratio is 1.05-1.2:1.

[0037] In a specific embodiment, the monofluorophosphates of the present application are obtained by the following steps:

[0038] 1) Solvent-free reaction of monochlorophosphates and potassium fluoride, after monitoring that the raw material monochlorophosphates are completely converted, the monofluorophosphates reaction solution is cooled, and the potassium chloride precipitate and excess potassium fluoride generated by the reaction are removed by filtration; the filter cake is washed with a low boiling point solvent, and the filtrate is combined;

[0039] 2) A stabilizer is added to the filtrate, and stirred thoroughly, the low boiling point solvent is removed by atmospheric distillation, and then the monofluorophosphates are obtained by vacuum rectification, and the product purity is ≥99.5%.

[0040] Compared with the prior art, the present application has the beneficial effects including:

[0041] 1) The present application uses solvent-free reaction to prepare monofluorophosphates, which avoids the product yield reduction caused by thermal decomposition of reactants in the solvent recovery process, and greatly improves the product yield and purity.

[0042] 2、The application adds stabilizer in the reaction solution, removes inorganic acid, fluoride ion, chloride ion and trace moisture in the reaction solution, so that the purity of the monofluorophosphate product after rectification is greater than or equal to 99.5%, the yield is greater than or equal to 90%, the impurity ion content is less than or equal to 10ppm, and the acidity is less than or equal to 50ppm. DETAILED DESCRIPTION

[0043] The application will be further described in conjunction with specific embodiments, but the application will not be limited to these specific embodiments. Those skilled in the art should realize that the application covers all alternatives, improvements and equivalents included in the scope of the claims.

[0044] Example 1

[0045] 63.9g (1.1mol) of potassium fluoride and 172.5g (1mol) of diethyl chlorophosphate are added into a 500mL three-necked flask at room temperature, heated to 50℃ under nitrogen protection, and stirred for 4 hours. GC detection shows that the content of diethyl chlorophosphate is less than 0.2%, and the content of the product monofluorophosphate is 94.2%.

[0046] The potassium chloride and excess potassium fluoride are removed by filtration, the filter cake is washed with 30g of dichloromethane, the filtrate is combined, 3.1g of calcium oxide is added into the filtrate, stirred for 60 minutes, dichloromethane is recovered by normal pressure distillation, the distillation is stopped after the recovery is completed, the rectification device is changed, and 87℃ distillate 142.5g is collected under vacuum at 150 hundred pascals.

[0047] Calculation shows that the product yield is 91.3%, the GC product purity is 99.8%, and no impurities with a content greater than 0.1% are found.

[0048] Example 2

[0049] 63.9g (1.1mol) of potassium fluoride and 172.5g (1mol) of diethyl chlorophosphate are added into a 500mL three-necked flask at room temperature, heated to 50℃ under nitrogen protection, and stirred for 4 hours. GC detection shows that the content of diethyl chlorophosphate is less than 0.2%, and the content of the product monofluorophosphate is 94.2%.

[0050] The potassium chloride and excess potassium fluoride are removed by filtration, the filter cake is washed with 30g of dichloromethane, the filtrate is combined, 3.1g of calcium oxide is added into the filtrate, stirred for 60 minutes, dichloromethane is recovered by normal pressure distillation, the distillation is stopped after the recovery is completed, the rectification device is changed, and 87℃ distillate 142.5g is collected under vacuum at 150 hundred pascals.

[0051] Calculation shows that the product yield is 91.3%, the GC product purity is 99.8%, and no impurities with a content greater than 0.1% are found.

[0052] Example 3

[0053] Into a 500ml flask, add 63.9g (1.1mol) potassium fluoride and 144.5g (1mol) dimethyl chlorophosphate, under nitrogen protection, heat to 50°C, stir for 4 hours, GC detection of raw material dimethyl chlorophosphate content is less than 0.2%, product dimethyl monofluorophosphate content is 94.6%.

[0054] Filter to remove potassium chloride and excess potassium fluoride, wash the filter cake with 30g dichloromethane, combine the filtrate, add 3.1g calcium oxide, stir for 60 minutes, recover dichloromethane by normal pressure distillation, stop distillation when recovery is complete, change the distillation device, collect 116.1g of 79°C fraction under vacuum at 150 hundred pascals.

[0055] The product yield is calculated to be 90.7%, the GC product purity is 99.6%, and no impurities with a content greater than 0.1% are observed.

[0056] Example 4

[0057] Into a 500ml flask, add 63.9g (1.1mol) potassium fluoride and 280g (1mol) bis(trifluoroethyl) chlorophosphate, under nitrogen protection, heat to 50°C, stir for 4 hours, GC detection of raw material bis(trifluoroethyl) chlorophosphate content is less than 0.2%, product bis(trifluoroethyl) monofluorophosphate content is 94%.

[0058] Filter to remove potassium chloride and excess potassium fluoride, wash the filter cake with 30g dichloromethane, combine the filtrate, add 3.1g calcium oxide, stir for 60 minutes, recover dichloromethane by normal pressure distillation, stop distillation when recovery is complete, change the distillation device, collect 234g of 85°C fraction under vacuum at 150 hundred pascals.

[0059] The product yield is calculated to be 88.7%, the GC product purity is 99.7%, and no impurities with a content greater than 0.1% are observed.

[0060] Example 5

[0061] Into a 500ml flask, add 63.9g (1.1mol) potassium fluoride and 172.5g (1mol) diethyl chlorophosphate, under nitrogen protection, heat to 80°C, stir for 2 hours, GC detection of raw material diethyl chlorophosphate content is less than 0.2%, product diethyl monofluorophosphate content is 91.1%.

[0062] Filter to remove potassium chloride and excess potassium fluoride, wash the filter cake with 30g dichloromethane, combine the filtrate, add 3.1g calcium oxide, stir for 60 minutes, recover dichloromethane by normal pressure distillation, stop distillation when recovery is complete, change the distillation device, collect 134.7g of 87°C fraction under vacuum at 150 hundred pascals.

[0063] The product yield is 85.8% and the GC product purity is 99.5% with no impurities greater than 0.1%.

[0064] Example 6

[0065] Into a 500 mL three-necked flask, 116.2 g (2 mol) of potassium fluoride and 172.5 g (1 mol) of diethyl chlorophosphate were added at room temperature. The reaction was heated to 50°C under nitrogen protection and stirred for 2.5 hours. GC detection showed that the content of diethyl chlorophosphate was less than 0.2% and the content of diethyl monofluorophosphate was 95.3%.

[0066] The potassium chloride and excess potassium fluoride were removed by filtration, and the filter cake was washed with 30 g of dichloromethane. The filtrate was combined, 3.1 g of calcium oxide was added, and stirred for 60 minutes. The dichloromethane was recovered by atmospheric distillation, and the distillation was stopped after recovery. The distillation apparatus was changed, and 144 g of 87°C fraction was collected under vacuum at 150 hundred Pa.

[0067] The product yield is 92% and the GC product purity is 99.6% with no impurities greater than 0.1%.

[0068] Comparative Example 1

[0069] The operation of this example is the same as that of Example 1, except that no stabilizer calcium oxide is added to the filtrate.

[0070] The 87°C fraction was collected, and 132.9 g was obtained. The product yield is 81.1% and the GC product purity is 95.9% with 3.7% triethyl phosphate impurities.

[0071] Comparative Example 2

[0072] The operation of this example is the same as that of Example 1, except that the reaction is carried out in acetonitrile solvent and no stabilizer calcium oxide is added to the filtrate.

[0073] The solvent acetonitrile needs to be distilled and collected before the product is collected. The 87°C fraction was collected, and 124.9 g was obtained. The product yield is 76.3% and the GC product purity is 96.1% with 3.2% triethyl phosphate impurities.

Claims

1. A process for the preparation of a monofluorophosphate ester characterized by: The preparation method comprises: adding a stabilizer into the obtained monofluorophosphonate reaction solution, wherein the stabilizer is calcium oxide or sodium carbonate, and the monofluorophosphonate has the following structure (I): R is selected from C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl and C2-C4 fluoroalkenyl.

2. The process for the preparation of monofluorophosphates according to claim 1, characterized in that: R is selected from methyl, trifluoromethyl, difluoromethyl, ethyl, trifluoroethyl, propyl, isopropyl, allyl, butyl, isobutyl and tert-butyl.

3. Process for the preparation of monofluorophosphates according to any one of claims 1-2, characterized in that: The preparation method comprises: A1. filtering the monofluorophosphonate reaction solution, adding the stabilizer into the filtrate and stirring; A2. obtaining the monofluorophosphonate with a purity of ≥99.5% through distillation or rectification.

4. The process for the preparation of monofluorophosphates according to claim 3, characterized in that: In the step A1, the amount of the stabilizer added is 0.01-0.1 of the theoretical yield of the monofluorophosphonate.

5. The process for the preparation of monofluorophosphates according to claim 3, characterized in that: In the step A1, the stirring time is 15-120 minutes.

6. The process for the preparation of monofluorophosphates according to claim 3, characterized in that: The monofluorophosphonate reaction solution is obtained by reacting monochlorophosphonate and potassium fluoride.

7. The process for the preparation of monofluorophosphates according to claim 6, characterized in that: The reaction temperature is 20-80℃, and the reaction time is 2-12 hours.

8. The process for the preparation of monofluorophosphates according to claim 6, characterized in that: The molar ratio of the potassium fluoride to the monochlorophosphonate is 1.0-2.0:1.

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