Beta-keto perfluorophosphonate vinyl ether and preparation method thereof

Abstract

The invention discloses beta-keto perfluorophosphonate vinyl ether and a preparation method thereof, and belongs to the field of fluorine chemical synthesis. The beta-keto perfluorophosphonate vinyl ether has the following structural formula: # imgabs0 #, wherein Et is ethyl. The beta-keto perfluorophosphonate vinyl ether prepared by the method disclosed by the invention not only contains unsaturated double bonds and phosphonate functional groups, but also further activates phosphonate groups by beta-keto with electron-withdrawing activity, so that a new method is provided for preparing perfluorophosphonate resin and fuel cell membrane materials thereof. The invention also provides a method for preparing the beta-keto perfluorophosphonate vinyl ether from the perfluorovinyl ether carboxylate in one step, the reaction conditions are relatively mild, the yield of the beta-keto perfluorophosphonate vinyl ether is high, and the method is easy to industrialize.

Description

Technical Field

[0001] The invention belongs to the technical field of fluorine chemical synthesis, and particularly relates to beta-keto perfluorophosphonate vinyl ether and a preparation method thereof. Background Art

[0002] Proton exchange membranes are the core of fuel cells. Currently, commonly used proton exchange membranes can be divided into perfluorosulfonic acid proton exchange membranes and hydrocarbon proton exchange membranes based on the type of polymer material they use. The backbone of hydrocarbon proton exchange membranes, such as polybenzimidazole, sulfonated polyetheretherketone, sulfonated polyaryletherketonesulfone, and sulfonated polyarylethersulfone, is primarily composed of C-H bonds and some polar bonds (branched and aromatic structures). Because the backbone and side chains of these proton exchange membranes are all composed of C-H bonds, phase separation between the backbone and side chains is difficult, and the C-H bonds are unstable, resulting in poor thermal and chemical stability. Consequently, their overall performance cannot match that of perfluoroproton exchange membranes.

[0003] Perfluorosulfonic acid proton exchange membrane (PFSA) is one of the most widely used key core materials in proton exchange membrane fuel cells (PEMFCs) and largely determines the performance of PEMFCs. However, high temperature and low humidity environments can greatly reduce the proton conductivity of the PFSA membrane, shortening the life of the fuel cell and hindering the high-temperature application of PEMFCs. Introducing phosphoric acid structures is currently a common strategy to improve the high-temperature mass transfer performance of PEM. Existing methods for introducing phosphoric acid structures include introducing phosphoric acid structures such as tungsten phosphate, tungstosilicophosphate, and zirconium phosphate into polymer membranes through organic-inorganic composite methods; and preparing composite membranes using organic-organic composite methods. For example, Unal et al. used a casting method to prepare Nafion / polyvinylphosphonic acid composite membranes.

[0004] However, existing methods for introducing phosphate structures suffer from poor compatibility between the heterogeneous phosphate components and PFSA, which can affect the physical and mechanical properties of the membrane. Furthermore, the cost of introducing phosphate structures is high, and the implementation of composite processes is difficult. Compared to preparing composite membranes, using monomers with phosphate structures in the resin synthesis to prepare proton exchange membranes with phosphate groups is more likely to address compatibility issues.

[0005] Therefore, there is an urgent need to provide a monomer that is easy to prepare, has a phosphoric acid structure and is easily polymerized. Summary of the Invention

[0006] In order to solve the above problems, the present invention provides β-keto perfluorophosphonate vinyl ether and a preparation method thereof.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] β-Keto perfluorophosphonate vinyl ether having the following structural formula:

[0009] Wherein, Et is ethyl.

[0010] The present invention also provides a method for preparing the above-mentioned β-keto perfluorophosphonate vinyl ether, characterized in that the preparation method is selected from one of routes (I), (II), (III), and (IV), wherein:

[0011] Route (I) comprises the following steps: in the presence of a Grignard reagent, perfluorovinyl ether carboxylate and diethyl bromofluoromethylphosphonate are reacted in a one-step process to obtain β-keto perfluorophosphonate vinyl ether;

[0012] Route (II) comprises the following steps: dissolving perfluorovinyl ether carboxylate, diethyl bromofluoromethylphosphonate, and magnesium powder in an organic solvent, followed by adding an initiating amount of 1,2-dibromoethane to synthesize β-keto perfluorophosphonate vinyl ether in one step;

[0013] Route (III) comprises the following steps: dissolving perfluorovinyl ether carboxylate and diethyl difluoromethyl phosphate in an organic solvent, and then slowly adding a strong base to synthesize β-keto perfluorophosphonate vinyl ether in one step;

[0014] Route (IV) comprises the following steps: diethyl difluoromethyl phosphate and lithium diisopropylamide (LDA) are mixed in an organic solvent and reacted for a certain period of time, and then perfluorovinyl ether carboxylate is slowly added to synthesize β-keto perfluorophosphonate vinyl ether.

[0015] Specifically, the synthetic route for preparing β-keto perfluorophosphonate vinyl ether from perfluorovinyl ether carboxylate is as follows: Figure 1 shown.

[0016] Wherein, compound 1 is a perfluorovinyl ether carboxylate, and compound 2 is a β-keto perfluorophosphonate vinyl ether. Compound 1 is specifically 2,2,3,3,5,6,6,8,9,9-decafluoro-5-trifluoromethyl-4,7-dioxa-8-nonenecarboxylic acid methyl ester. Compound 2 is specifically 1,1,3,3,4,4,6,7,7,9,10,10-dodecafluoro-6-trifluoromethyl-5,8-dioxa-2-carbonyl-9-decenephosphonic acid diethyl ester.

[0017] Preferably, the reactions in routes (I), (II), (III), and (IV) are all carried out under a nitrogen atmosphere. In the above synthetic routes, the organic solvent is selected from diethyl ether, methyl tert-butyl ether, tetrahydrofuran, 1,4-dioxane, and anisole; the reaction temperature is -78 to 0°C, and the reaction time is 1 to 24 hours.

[0018] The molar ratio of the perfluorovinyl ether carboxylate, the phosphonate group and the Grignard reagent, or the strong base, or the magnesium powder or the lithium diisopropylamide (LDA) is 1:(0.5-3):(0.5-3).

[0019] The synthetic route (I) provided by the present invention comprises the following steps: under a nitrogen atmosphere, dissolving perfluorovinyl ether carboxylate and diethyl bromofluoromethylphosphonate in an organic solvent to obtain a mixed reaction liquid; slowly adding a Grignard reagent to the mixed reaction liquid to react and obtain β-keto perfluorophosphonate vinyl ether.

[0020] Preferably, the Grignard reagent is R 1 MgX,R 1 is selected from isopropyl, 4-methoxyphenyl, phenyl, and cyclohexyl, and X is selected from Cl, Br, and Cl·LiCl; further preferably, the Grignard reagent is one of isopropylmagnesium chloride (i-PrMgCl), i-PrMgCl·LiCl, 4-methoxyphenylmagnesium bromide (4-CH3OC6H4MgBr), phenylmagnesium bromide (PhMgBr), and cyclohexylmagnesium bromide. More preferably, it is i-PrMgCl·LiCl.

[0021] Preferably, the organic solvent is one of diethyl ether, methyl tert-butyl ether, tetrahydrofuran (THF), 1,4-dioxane, and anisole; diethyl ether is further preferred.

[0022] Preferably, the molar ratio of the perfluorovinyl ether carboxylate, the phosphonate group and the Grignard reagent is 1:(0.5-3):(0.5-3).

[0023] More preferably, the molar ratio of perfluorovinyl ether carboxylate, diethyl bromofluoromethylphosphonate, and Grignard reagent is 1:(0.5-1.5):(0.5-2), preferably 1:0.65-0.7:0.9-1.1, and most preferably 1:0.67:1. The reaction temperature is -10 to -78°C, preferably -10 to -20°C, and most preferably -15°C. The reaction time is 1 to 24 hours, preferably 4 to 6 hours, and most preferably 4 hours. The maximum isolated yield is 46%.

[0024] After the reaction was completed, saturated ammonium chloride was added to quench the reaction.

[0025] The above-mentioned synthetic route (II) provided by the present invention is as follows: under a nitrogen atmosphere, perfluorovinyl ether carboxylate, diethyl bromofluoromethylphosphonate and magnesium powder are dissolved in an organic solvent to obtain a mixed reaction liquid, and then an initiating amount of 1,2-dibromoethane is added to react to obtain β-keto perfluorophosphonate vinyl ether.

[0026] Preferably, the magnesium powder is freshly activated magnesium powder, that is, newly prepared magnesium powder that has not been oxidized.

[0027] The molar ratio of the perfluorovinyl ether carboxylate, the phosphonate group and the magnesium powder is 1:(0.5-3):(0.5-3).

[0028] Preferably, the organic solvent is one of diethyl ether, methyl tert-butyl ether, tetrahydrofuran (THF), 1,4-dioxane, and anisole, preferably THF.

[0029] Preferably, the molar amount of 1,2-dibromoethane accounts for 0.1 to 1.5% of the molar amount of the perfluorovinyl ether carboxylate, more preferably 0.9 to 1.1%, and even more preferably 1%.

[0030] More preferably, the molar ratio of perfluorovinyl ether carboxylate to diethyl bromofluoromethylphosphonate and magnesium powder is 1:(1.5-2.5):(1.2-2.5), preferably 1:1.9-2.1:2.1-2.3, and most preferably 1:2.0:2.2. The reaction temperature is 0-30°C, preferably -10-5°C, and most preferably -15°C. The reaction time is 1-24 hours, preferably 4-6 hours, and most preferably 4 hours. The maximum isolated yield is 23%.

[0031] After the reaction was completed, saturated ammonium chloride was added to quench the reaction.

[0032] The synthetic route (III) provided by the present invention comprises the following steps: under a nitrogen atmosphere, dissolving perfluorovinyl ether carboxylate and diethyl difluoromethyl phosphate in an organic solvent to obtain a mixed reaction liquid, slowly adding a strong base to the mixed reaction liquid, and reacting to obtain β-keto perfluorophosphonate vinyl ether.

[0033] Preferably, the strong base is one or more of lithium bis(trimethylsilyl)amide (LiHMDS), sodium bis(trimethylsilyl)amide (NaHMDS) or potassium bis(trimethylsilyl)amide (KHMDS).

[0034] Preferably, the molar ratio of the perfluorovinyl ether carboxylate, the phosphonate group and the strong base is 1:(0.5-3):(0.5-3).

[0035] Preferably, the organic solvent is one of diethyl ether, methyl tert-butyl ether, tetrahydrofuran (THF), 1,4-dioxane, and anisole, and THF is more preferred.

[0036] Further preferably, the molar ratio of perfluorovinyl ether carboxylate to diethyl difluoromethyl phosphate and strong base is 1:(1.5-2.5):(1.5-2.5), preferably 1:(1.9-2.1):(1.9-2.1), most preferably 1:2:2, the reaction temperature is -20-78°C, preferably -25-35°C, most preferably -30°C, the reaction time is 1-24h, preferably 4-6h, most preferably 4h, and the maximum isolation yield is 35%.

[0037] After the reaction was completed, saturated ammonium chloride was added to quench the reaction.

[0038] The synthetic route (IV) provided by the present invention is as follows: under a nitrogen atmosphere, diethyl difluoromethyl phosphate and lithium diisopropylamide (LDA) are mixed in an organic solvent and reacted for a certain period of time, and then perfluorovinyl ether carboxylate is slowly added to react to obtain β-keto perfluorophosphonate vinyl ether.

[0039] The lithium diisopropylamide (LDA) is a freshly prepared LDA solution. The molar ratio of the perfluorovinyl ether carboxylate, the phosphonate group and the lithium diisopropylamide is 1:(0.5-3):(0.5-3).

[0040] Preferably, the organic solvent is one of diethyl ether, methyl tert-butyl ether, tetrahydrofuran (THF), 1,4-dioxane, and anisole, preferably THF.

[0041] More preferably, the molar ratio of perfluorovinyl ether carboxylate to diethyl difluoromethyl phosphate and lithium diisopropylamide (LDA) is 1:(0.9-1.5):(0.9-1.5), more preferably 1.05-1.15:1:1, and most preferably 1.1:1:1. The reaction temperature is -80°C to -70°C, preferably -78°C, and the reaction time is 1 to 24 hours, preferably 4 to 6 hours, and most preferably 4 hours. The maximum isolated yield is 20%.

[0042] After the reaction was completed, saturated ammonium chloride was added to quench the reaction.

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] (1) The β-keto perfluorophosphonate vinyl ether prepared by the method of the present invention not only contains an unsaturated double bond and a phosphonate functional group, but also the electron-withdrawing active β-keto group further activates the phosphonate group, providing a new method for preparing perfluorophosphonic acid resin and its fuel cell membrane material.

[0045] (2) The present invention prepares the target product β-keto perfluorophosphonate vinyl ether through a one-step reaction. The reaction conditions are relatively mild, the yield of β-keto perfluorophosphonate vinyl ether is high, and it is easy to industrialize.

[0046] (3) The present invention avoids the use of highly toxic chlorine gas and liquid bromine to protect unsaturated double bonds, and greatly simplifies the reaction steps and synthesis process.

[0047] (4) The β-keto perfluorophosphonate vinyl ether prepared by the method of the present invention contains a double bond and an ether bond, and can also be used to prepare other fluorine-containing polymers, fluorine-containing phosphate polymers, etc., thereby expanding the source of fluorine-containing polymer monomers and increasing the types of fluorine-containing polymers. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 The synthetic route for the preparation of β-ketoperfluorophosphonate vinyl ether from perfluorovinyl ether carboxylate is given in FIG. DETAILED DESCRIPTION

[0048] The present invention is described in detail below with reference to specific embodiments.

[0049] Example 1 (Route I)

[0050] An eggplant-shaped reaction flask was thoroughly oven-dried at 120°C and the atmosphere was replaced with nitrogen three times. Methyl 2,2,3,3,5,6,6,8,9,9-decafluoro-5-trifluoromethyl-4,7-dioxa-8-nonenecarboxylate (Compound 1, 500 mg, 1.18 mmol, 1.5 equiv) and diethyl bromofluoromethylphosphonate (210 mg, 0.79 mmol, 1.0 equiv) were dissolved in 3 mL of anhydrous ether and added to the flask. 910 μL of i-PrMgCl·LiCl (dissolved in THF at a molar concentration of 1.3 M, 1.5 equiv) was added dropwise to the reaction system at -15°C and stirred for 4 h. After the reaction, 2 mL of saturated ammonium chloride was added to quench the reaction, the ether was removed by rotary evaporation, and dichloromethane (3 mL) was added for extraction three times. The organic phase was collected, dried over anhydrous sodium sulfate, concentrated, and separated by column chromatography (particle size 200-300 mesh, volume ratio of petroleum ether / ethyl acetate of 5 / 1) to obtain 1,1,3,3,4,4,6,7,7,9,10,10-dodecafluoro-6-trifluoromethyl-5,8-dioxa-2-carbonyl-9-decenephosphonic acid diethyl ester (compound 2, 210 mg, yield 46%).

[0051] The spectral data of compound 2 are:

[0052] 1 H NMR (400MHz, CDCl3), δ: 4.19 (m, 4H), 1.29 (t, J = 8Hz, 6H); 19 F NMR (376MHz, CDCl3), δ: -145.1 (t, J = 24Hz, 1F), -136.2 (ddt, J = 120, 68Hz, 1F), 123.3 (t, J = 16Hz, 2F), -121.1 (ddt, J = 120, 88Hz, cis F),-120.9(m,2F),-113.3(dd,J=88,72Hz,transF),-84.6(m,2F),-79.7(s,3F),-79.3(m,2F); 31P NMR (162MHz, DMSO-d6), δ: 5.39 (t, J = 236Hz); HRMS m / z (ESI): [M+Na] + Calcd for C 13 H 10 F 15 NaO6P 600.9868, found 600.9868.

[0053] Example 2 (Route II)

[0054] The eggplant-shaped reaction flask was thoroughly dried in an oven at 120°C, fresh activated magnesium powder (63 mg, 2.61 mmol, 2.2 equiv) was added, and the atmosphere was replaced with nitrogen three times. Methyl 2,2,3,3,5,6,6,8,9,9-decafluoro-5-trifluoromethyl-4,7-dioxa-8-nonenecarboxylate (1,500 mg, 1.18 mmol, 1.0 equiv) and diethyl bromofluoromethylphosphonate (632 mg, 2.37 mmol, 2.0 equiv) were dissolved in 3 mL of anhydrous THF and added to the flask. 1,2-Dibromoethane (100 μL dissolved in 200 μL of anhydrous ether, 1.16×10 -3 mmol, 0.01 equiv) and stirred for 4 h. After completion, 2 mL of saturated ammonium chloride was added to quench the reaction. THF was removed by rotary evaporation, and the mixture was extracted three times with dichloromethane (3 mL). The organic phase was collected, dried over anhydrous sodium sulfate, concentrated, and isolated by column chromatography (200-300 mesh particle size, petroleum ether / ethyl acetate volume ratio of 5 / 1) to obtain compound 2 (158 mg, 23% yield).

[0055] Example 3 (Route III)

[0056] An eggplant-shaped reaction flask was thoroughly oven-dried at 120°C and the atmosphere was replaced with nitrogen three times. Methyl 2,2,3,3,5,6,6,8,9,9-decafluoro-5-trifluoromethyl-4,7-dioxa-8-nonenecarboxylate (1,500 mg, 1.18 mmol, 1.0 equiv) and diethyl difluoromethylphosphonate (446 mg, 2.37 mmol, 2.0 equiv) were dissolved in 3 mL of anhydrous THF and added to the flask. 2.37 mL of LiHMDS (1.0 M, 2.0 equiv, dissolved in THF) was added dropwise at -30°C and stirred for 4 h. After the reaction, 2 mL of saturated ammonium chloride was added to quench the reaction, and THF was removed by rotary evaporation. The product was extracted with dichloromethane (3 mL) three times. The organic phase was collected, dried over anhydrous sodium sulfate, concentrated, and separated by column chromatography (particle size 200-300 mesh, petroleum ether / ethyl acetate volume ratio of 5 / 1) to obtain 2 (240 mg, yield 35%).

[0057] Example 4 (Route IV)

[0058] The eggplant-shaped reaction flask was thoroughly dried in an oven at 120°C and replaced with nitrogen three times. Freshly diisopropylamine (109 mg, 1.08 mmol, 1.0 equiv) was dissolved in 1 mL of anhydrous THF and added to the reaction flask. 430 μL of n-butyl lithium (the n-butyl lithium was dissolved in hexane with a molar concentration of 2.5 M, 1.0 equiv) was slowly added dropwise to the reaction solution at -78°C. The temperature was raised to 0°C and stirred for 10 min to obtain a freshly prepared light yellow lithium diisopropylamide (LDA) solution (1.0 eq).

[0059] The reaction system was cooled again to -78°C. Diethyl difluoromethylphosphate (203 mg, 1.08 mmol, 1.0 equiv) was dissolved in 2 mL of anhydrous THF and added to the reaction flask. After stirring for 1 hour, methyl 2,2,3,3,5,6,6,8,9,9-decafluoro-5-trifluoromethyl-4,7-dioxa-8-nonenecarboxylate (1,500 mg, 1.18 mmol, 1.1 equiv) was dissolved in 3 mL of anhydrous THF and slowly added dropwise to the reaction solution. The reaction was stirred for 4 hours. After the reaction, 2 mL of saturated ammonium chloride was added to quench the reaction. The THF was removed by rotary evaporation, and the mixture was extracted three times with dichloromethane (3 mL). The organic phase was collected, dried over anhydrous sodium sulfate, concentrated, and purified by column chromatography (200-300 mesh particle size, 5 / 1 petroleum ether / ethyl acetate volume ratio) to afford 2 (125 mg, 20% yield).

Claims

1. β-keto perfluorophosphonate vinyl ether, characterized in that It contains the following structural formula: Wherein, Et is ethyl.

2. The method for preparing the β-keto perfluorophosphonate vinyl ether according to claim 1, wherein The preparation method is selected from one of routes (I), (II), (III), and (IV), wherein: Route (I) comprises the following steps: in the presence of a Grignard reagent, perfluorovinyl ether carboxylate and diethyl bromofluoromethylphosphonate are reacted in a one-step process to obtain β-keto perfluorophosphonate vinyl ether; Route (II) comprises the following steps: dissolving perfluorovinyl ether carboxylate, diethyl bromofluoromethylphosphonate, and magnesium powder in an organic solvent, followed by adding an initiating amount of 1,2-dibromoethane to synthesize β-keto perfluorophosphonate vinyl ether in one step; Route (III) comprises the following steps: dissolving perfluorovinyl ether carboxylate and diethyl difluoromethyl phosphate in an organic solvent, and then slowly adding a strong base to synthesize β-keto perfluorophosphonate vinyl ether in one step; Route (IV) comprises the following steps: diethyl difluoromethyl phosphate and lithium diisopropylamide are mixed in an organic solvent and reacted for a certain period of time, and then perfluorovinyl ether carboxylate is slowly added to synthesize β-keto perfluorophosphonate vinyl ether.

3. The preparation method according to claim 2, characterized in that In routes (I), (II), (III), and (IV), the organic solvent is selected from one of diethyl ether, methyl tert-butyl ether, tetrahydrofuran, 1,4-dioxane, and anisole; the reaction temperature is -78 to 0°C, and the reaction time is 1 to 24 hours. Preferably, the molar ratio of the perfluorovinyl ether carboxylate, the phosphonate group and the Grignard reagent, or the strong base, or the magnesium powder or the lithium diisopropylamide is 1:(0.5-3):(0.5-3).

4. The preparation method according to claim 2, characterized in that Route (I): The Grignard reagent is R 1 MgX,R 1 is selected from isopropyl, 4-methoxyphenyl, phenyl, cyclohexyl, and X is selected from Cl11, Br, and Cl·LiCl; preferably, the Grignard reagent is one of i-PrMgCl, i-PrMgCl·LiCl, 4-CH3OC6H4MgBr, PhMgBr, and cyclohexylmagnesium bromide. Preferably, the organic solvent is one of diethyl ether, methyl tert-butyl ether, tetrahydrofuran, 1,4-dioxane, and anisole.

5. The preparation method according to claim 2, characterized in that Route (I): The molar ratio of perfluorovinyl ether carboxylate, diethyl bromofluoromethylphosphonate, and Grignard reagent is 1:(0.5-1.5):(0.5-2), preferably 1:0.65-0.7:0.9-1.

1. Preferably, the reaction temperature is -10 to -78°C, preferably -10 to -20°C, most preferably -15°C, and the reaction time is 1 to 24 hours, preferably 4 to 6 hours.

6. The preparation method according to claim 2, characterized in that Route (II): The organic solvent is one of diethyl ether, methyl tert-butyl ether, tetrahydrofuran, 1,4-dioxane, and anisole, preferably THF. Preferably, the molar amount of 1,2-dibromoethane accounts for 0.1 to 1.5% of the molar amount of the perfluorovinyl ether carboxylate, and more preferably 0.9 to 1.1%.

7. The preparation method according to claim 2, characterized in that Route (II): The molar ratio of perfluorovinyl ether carboxylate to diethyl bromofluoromethylphosphonate and magnesium powder is 1:(1.5-2.5):(1.2-2.5), preferably 1:1.9-2.1:2.1-2.

3. Preferably, the reaction temperature is 0 to -30°C, preferably -10 to -5°C, most preferably -15°C, and the reaction time is 1 to 24 hours, preferably 4 to 6 hours.

8. The preparation method according to claim 2, characterized in that Route (III): The strong base is one or more of lithium bis(trimethylsilyl)amide, sodium bis(trimethylsilyl)amide or potassium bis(trimethylsilyl)amide. Preferably, the organic solvent is one of diethyl ether, methyl tert-butyl ether, tetrahydrofuran (THF), 1,4-dioxane, and anisole.

9. The preparation method according to claim 2, characterized in that Route (III): The molar ratio of perfluorovinyl ether carboxylate, diethyl difluoromethyl phosphate and strong base is 1:(1.5-2.5):(1.5-2.5), preferably 1:(1.9-2.1):(1.9-2.1). Preferably, the reaction temperature is -20 to -78°C, preferably -25 to -35°C, most preferably -30°C, and the reaction time is 1 to 24 hours, preferably 4 to 6 hours.

10. The preparation method according to claim 2, characterized in that Route (IV): The organic solvent is one of diethyl ether, methyl tert-butyl ether, tetrahydrofuran, 1,4-dioxane, and anisole. Preferably, the molar ratio of perfluorovinyl ether carboxylate to diethyl difluoromethyl phosphate and lithium diisopropylamide is 1:(0.9-1.5):(0.9-1.5), more preferably 1.05-1.15:1:

1. Preferably, the reaction temperature is -80°C to -70°C, preferably -78°C, and the reaction time is 1 to 24 hours, preferably 4 to 6 hours.

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