Synthetic method of fluoromethane

Abstract

The invention discloses a synthetic method of fluoromethane, which comprises the following steps: (1) taking trifluoromethanesulfonic anhydride and methanol as raw materials, and synthesizing methyl trifluoromethanesulfonate through esterification reaction; and (2) taking methyl trifluoromethanesulfonate as a methyl donor, and carrying out nucleophilic substitution reaction on potassium fluoride under the assistance of phase transfer agents such as crown ether / PEG (Polyethylene Glycol) to generate fluoromethane. The reaction condition is mild, esterification is completed at normal temperature and normal pressure, and the high toxicity risk of a traditional dimethyl sulfate method is avoided. The conversion rate is high, the activity of trifluoromethanesulfonic anhydride is high, excessive methanol ensures complete reaction, and the esterification efficiency is not less than 95%. The invention provides a novel process for synthesizing fluoromethane by taking methyl trifluoromethanesulfonate as a methyl donor and potassium fluoride as a fluorine source, and the novel process has the technical significance of low cost, low energy consumption and controllable equipment, and is suitable for commercial amplification.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fluorinated chemical synthesis, and particularly relates to a synthesis method of methyl fluoride. BACKGROUND

[0002] Methyl fluoride (CH3F) is an important organic fluorine compound, which is a colorless gas at room temperature, has the characteristics of non-toxicity, non-corrosiveness and flammability, and has a wide application in the fields of electronic special gas, refrigerant, anesthetic and synthesis of fluorine-containing intermediates. In particular, electronic-grade methyl fluoride, as a key etching gas in semiconductor manufacturing, has excellent selectivity etching performance on silicide thin film in 3D NAND flash memory chips and 14 nm and below advanced processes, and is an indispensable core material in the semiconductor industry chain.

[0003] The existing preparation technology and limitations, the current industrialized preparation method of methyl fluoride mainly includes: 1. Gas phase fluorination method: direct reaction of methane with fluorine gas, but fluorine gas is highly toxic and the reaction is violent, which can easily cause explosion risk, and the safety requirements for equipment and operation are extremely high. 2. Hydrogen fluoride method: using hydrogen fluoride (HF) as fluorine source and halogenated hydrocarbon such as chloromethane for fluorine exchange reaction, but HF has strong corrosiveness and high toxicity, which requires strict safety protection measures, and the by-product treatment is complex. 3. Fluorination agent method: using nitrogen trifluoride (NF3) or hydrofluoric acid (HF) as fluorination agent, although it can improve the controllability of the reaction, but the process has high energy consumption and high cost, and the fluorination agent itself has environmental risk. The current methods generally have the following problems: 1. Poor safety: involving highly toxic gases (such as F2, HF) or high pressure and high temperature conditions, with high operation risk. 2. Insufficient environmental protection: the by-product fluorine-containing waste is difficult to handle, which can easily cause environmental pollution. 3. Purity and cost contradiction: electronic-grade methyl fluoride has very high purity requirements (≥99.999%), and the existing process depends on fractional distillation or low-temperature condensation method, which has high energy consumption and low yield, and is difficult to meet the large-scale demand of the semiconductor industry.

[0004] In summary, the existing fluoromethane preparation technology generally has the following defects:

[0005] 1) High safety risk: the traditional method relies on highly dangerous fluorinating agents such as fluorine gas (F2) and hydrogen fluoride (HF), which has the risk of leakage, explosion and strong corrosion. For example, the gas phase fluorination method requires direct reaction of methane with fluorine gas, which has high process risk, and the hydrogen fluoride method needs to handle toxic by-products.

[0006] 2) Complex process and high energy consumption: most methods require high temperature and high pressure conditions (such as 300-600℃ catalytic hydrogenation defluorination) or complex catalyst systems (such as noble metal catalysts), which have high equipment investment and energy consumption costs.

[0007] 3) Purity and environmental protection conflict: by-product waste containing chlorine and fluorine (such as HCl and HF) is difficult to handle, and purification relies on multi-stage rectification or cryogenic separation, which is difficult to meet the large-scale production needs of electronic-grade fluoromethane (≥99.999%).

[0008] The present application proposes a new process for synthesizing fluoromethane using methyl triflate as a methyl donor and potassium fluoride as a fluorine source, which has the technical significance of low cost, low energy consumption and controllable equipment, and is suitable for commercial scale-up. SUMMARY

[0009] In view of the above technical problems existing in the prior art, the purpose of the present application is to provide a safe, efficient and environmentally friendly method for preparing fluoromethane, which has mild reaction conditions and can be completed at room temperature and pressure to avoid the high toxicity risk of traditional dimethyl sulfate method. Moreover, the conversion rate is high, the activity of triflic anhydride is high, and the excess of methanol ensures the completion of the reaction, and the esterification efficiency is ≥95%.

[0010] The technical solution adopted by the present application is as follows:

[0011] A method for synthesizing fluoromethane, comprising the following steps:

[0012] S1 esterification reaction: using triflic anhydride and methanol as raw materials, reacting in an inert solvent under inert gas protection and at a temperature of 0-25℃ to generate methyl triflate;

[0013] S2 fluorination reaction: performing a nucleophilic substitution reaction between the methyl triflate obtained in step S1 and potassium fluoride in the presence of a phase transfer catalyst to generate fluoromethane.

[0014] Further, an inert solvent is also added in step S1.

[0015] Further, the methanol in step S1 needs to be pre-treated by dehydration. The dehydration process can be: treating the methanol (CH3OH) by 3A molecular sieve adsorption to control the water content to be ≤50ppm to avoid the hydrolysis of triflic anhydride ((CF3SO2)2O). The inert gas protection in step S1 is to replace the air in the system with nitrogen or argon to make the oxygen content ≤0.1%.

[0016] Further, in step S1, the molar ratio of triflic anhydride to methanol is 1:1-1.8, and the preferred molar ratio is 1:1.1-1:1.3; the inert solvent is selected from at least one of tetrahydrofuran, dichloromethane and toluene, and the preferred solvent is dichloromethane.

[0017] Further, in step S1, the esterification reaction is monitored to the end by monitoring the reaction progress through online infrared spectroscopy (IR) to track the 1720cm -1The characteristic peak of trifluoromethanesulfonic anhydride disappears (reaction time 2-4 hours). The termination condition: when the conversion rate of trifluoromethanesulfonic anhydride is ≥95%, the reaction is stopped, and the acidic by-product CF3SO3H is generated.

[0018] Further, the step S1 can also add an organic base for neutralizing the by-product acid, which is triethylamine, pyridine or N,N-diisopropyl ethylamine, and the amount is 1.0-1.5 times, preferably 1.2-1.5 times of the molar amount of trifluoromethanesulfonic anhydride; after the reaction of step S1 is completed, the following post-processing steps are included: pour the reaction liquid into ice water, stir to quench the reaction, add acid to adjust the pH to 3-4, convert the triethylamine salt to water-soluble hydrochloride, extract with dichloromethane, wash the organic phase with water and saturated brine in turn, dry with anhydrous Na2SO4 or anhydrous magnesium sulfate, remove the solvent by reduced pressure distillation, and continue to distill to obtain the fraction of methyl trifluoromethanesulfonate, i.e. the post-processing is completed.

[0019] Further, in step S1, the operation process of esterification reaction is: first mix methanol with inert solvent and organic base, cool to 0-5℃, slowly add trifluoromethanesulfonic anhydride, so that the temperature of the mixed solution during the dropwise addition process is ≤5℃, after the dropwise addition is completed, continue to stir for 0.5-2h until the reaction is complete.

[0020] Further, in step S2, the molar ratio of potassium fluoride to methyl trifluoromethanesulfonate is 1.05-1.5:1; the phase transfer catalyst is crown ether or polyethylene glycol (PEG), and the mass amount is 30-50%, preferably 40-45% of the mass of methyl trifluoromethanesulfonate; the reaction is carried out in a polar aprotic solvent selected from at least one of acetonitrile, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), DEGME and TEDM.

[0021] Further, the potassium fluoride raw material of step S2 is pre-dried (water content ≤100ppm) to enhance the solubility and reactivity of potassium fluoride (KF).

[0022] Further, the crown ether is 18-crown-6, 15-crown-5 or 12-crown-4; the molecular weight of the polyethylene glycol (PEG) is 400-800.

[0023] Further, the reaction conditions of step S2 are: reaction temperature 40-80℃, reaction pressure normal pressure-0.5MPa, reaction time 1-6 hours, and the preferred reaction conditions are: temperature 60℃, reaction pressure normal pressure, and reaction time 2-6 hours; during the reaction process, the gaseous product fluoromethane is collected by low-temperature condensation.

[0024] Further, the particle size of the potassium fluoride raw material of step S2 is ≤100μm.

[0025] Further, the reaction pressure in step S2 is normal pressure to micro-positive pressure, avoiding the premature escape of fluoromethane gas.

[0026] Further, the fluoromethane is condensed and collected, the gaseous fluoromethane is liquefied and collected, and the unreacted KF and by-product CF3SO3K remain in the reaction solution.

[0027] Further, the by-product is recycled, and the potassium trifluoromethanesulfonate is recovered: the reaction solution is filtered under reduced pressure to separate the residual solid potassium trifluoromethanesulfonate, the filtrate is acidified (concentrated sulfuric acid is added to pH = 1), and trifluoromethanesulfonic acid (CF3SO3H) is precipitated. Regeneration of trifluoromethanesulfonic anhydride: CF3SO3H and P2O5 are dehydrated and condensed at 80-100℃ to regenerate (CF3SO2)2O, realizing the closed loop of raw materials.

[0028] By using the above-mentioned technology, compared with the prior art, the beneficial effects of the present application are as follows:

[0029] 1) The present application uses trifluoromethanesulfonic anhydride as raw material to prepare methyl trifluoromethanesulfonate as a methyl donor to prepare fluoromethane through esterification reaction. The recycling rate of the by-product is high, the potassium trifluoromethanesulfonate is regenerated into trifluoromethanesulfonic anhydride through acidification, realizing the closed loop utilization of raw materials, the atomic economy is > 90%, no toxic gas is involved in the whole process, the corrosion of equipment is low, and it meets the green chemistry standard.

[0030] 2) The fluoromethane preparation method of the present application has mild reaction conditions (normal temperature / low pressure), avoids high temperature cracking or complex purification steps, has low energy consumption and investment cost, and is relatively simple to operate, and is very suitable for industrialization.

[0031] 3) The fluoromethane prepared by the present application is collected in gas phase after reaction through condensation, and then a small amount of impurities is removed through molecular sieve adsorption and low-temperature rectification, and finally the purity of fluoromethane ≥ 99.99% (5N grade) is directly synthesized, the proportion of fluoromethane in synthesis gas > 99%, and after rectification, it reaches the electronic grade standard (5N), meeting the demand of semiconductor etching process.

[0032] 4) The preparation method of the present application is fine control: online monitoring to ensure efficient and stable reaction. Closed loop production design: by-product regeneration rate > 85%, raw material cost reduced by 35%, meeting the "zero emission" industrial standard. Equipment compatibility: conventional chemical equipment (glass lined reactor, rectification column) can realize production without special fluorine-resistant materials. DETAILED DESCRIPTION

[0033] The present application will be further described below in conjunction with specific examples, but the scope of protection of the present application is not limited thereto.

[0034] Example 1

[0035] A method for synthesizing fluoromethane, comprising the following steps:

[0036] S1 esterification reaction:

[0037] S1.1) Install a mechanical stirrer, a thermometer and a constant pressure funnel on a three-necked flask, and fill the constant pressure funnel with 282.1 g of triflic anhydride. In a dry three-necked flask, add 32.04 g of methanol, 100 mL of dichloromethane and 101.2 g of triethylamine, and perform a nitrogen purging process on the device, empty the air in the flask, and place it in an ice water bath and cool it to 0-5°C. Then, drop the triflic anhydride into the methanol-triethylamine mixture in the three-necked flask through the constant pressure funnel, control the dropping speed to keep the reaction temperature ≤5°C (about 1-2 hours to complete the dropping), and the molar ratio of methanol / triethylamine / triflic anhydride is 1:1:1. After the dropping is completed, continue to stir the reaction at 0-5°C for 1 hour to ensure the completion of the reaction. The obtained crude product is methyl triflate (CH3OTf) and triethylamine salt (Et3NH + CF3SO3-), and the reaction formula of the esterification reaction is as follows:

[0038]

[0039] S1.2) After the reaction of step S1.1) is completed, slowly pour the reaction solution into 500 mL of ice water and stir for 10 minutes to quench the unreacted anhydride. Adjust the pH to 3-4 with dilute hydrochloric acid (5% HC1) to convert the triethylamine salt to water-soluble hydrochloride (Et3NH + Cl-). Extract the mixture with dichloromethane (3 x 100 mL) and combine the organic phases. Wash the organic phase with 100 mL of water and 100 mL of saturated brine successively to remove residual triethylamine hydrochloride. Add 20 g of anhydrous magnesium sulfate, stir for 30 minutes, and filter to remove the drying agent. Evaporate the dichloromethane under reduced pressure (20 mmHg) at 40°C using a rotary evaporator. Purify the remaining crude product by reduced pressure distillation: collect the fraction at 60-65°C / 20 mmHg (CH3OTf is a colorless liquid with a boiling point of 96.5°C at normal pressure), weigh the obtained methyl triflate product and sample it into a gas chromatograph for analysis. The yield of methyl triflate is calculated to be 90.4% and the purity is 98.9%.

[0040] S2 fluorination reaction:

[0041] S2.1) Weigh a certain amount of potassium fluoride and place it in a muffle furnace at 280°C for 1 h, take it out while hot after the calcination is completed, and grind it, then place it in the muffle furnace again for 0.5 h at 280°C, repeat the operation twice to ensure that the particle size of the prepared potassium fluoride is <100 μm.

[0042] S2.2) Put 74 g (1.275 mol) of dried potassium fluoride, 750 mL of acetonitrile reagent and 60 g (0.227 mol) of phase transfer catalyst 18-crown-6 into a high-pressure reaction kettle, and heat to 60°C under stirring. After the temperature is raised, 140.47 g (0.85 mol) of methyl triflate prepared in step S1 is titrated dropwise at a rate of 6 mL / min. The titration takes about 20 min. The temperature is kept at 60°C, and the reaction continues for 6 h after the titration is completed. The molar ratio of potassium fluoride to methyl triflate is controlled to be 1.5:1. The reaction gas is collected by condensation at -80°C, and the crude product is adsorbed by 4A molecular sieve and then distilled at low temperature. 20.38 L (standard condition) of fluoromethane gas is obtained, with a yield of 90% and a purity of 99.93% (HPLC detection). The reaction equation of the fluorination reaction is as follows:

[0043]

[0044] Experimental Example 2

[0045] The esterification reaction step of Experimental Example 2 is repeated in Example 1, with the following differences:

[0046] ① The inert solvent is replaced by 120 mL of toluene instead of 100 mL of dichloromethane;

[0047] ② The amount of 32.04 g of methanol is not changed, and the amounts of trifluoromethanesulfonic anhydride and triethylamine are increased, so that the molar ratio of methanol: trifluoromethanesulfonic anhydride: triethylamine = 1:1.2:1.2;

[0048] The post-treatment and purification steps after the esterification reaction of Example 2 are the same as those of Example 1. The final experimental results of the esterification reaction of Example 2 are as follows: the yield of methyl triflate is 87.1%, and the purity is 98.3%.

[0049] The fluorination reaction step of Experimental Example 2 is repeated in Example 1, with the following difference: the solvent is replaced by 750 mL of dimethyl sulfoxide instead of 750 mL of acetonitrile, and the other conditions are the same as those of Example 1. The final experimental results of the fluorination reaction of Example 2 are as follows: the yield of fluoromethane is 93.12%, and the purity is 99.99%.

[0050] Experimental Example 3

[0051] The esterification reaction step of Experimental Example 3 is repeated in Example 1, with the following difference: the inert solvent is replaced by 120 mL of tetrahydrofuran instead of 100 mL of dichloromethane, and the other conditions are not changed.

[0052] The post-treatment purification step after the esterification reaction of Example 3 is the same as that of Example 1. The final experimental results of the esterification reaction of Example 3 are as follows: the yield of methyl triflate is 90.9%, and the purity is 98.3%.

[0053] The fluorination reaction step of Experimental Example 3 is repeated Example 1, with the exception that the solvent is replaced by 750 mL of N,N-dimethylformamide instead of 750 mL of acetonitrile, and the remaining conditions are the same as those of Example 1. The final experimental results of the fluorination reaction of Example 3 are as follows: the yield of fluoromethane is 93.12%, and the purity is 99.99% (it is proved that different polar solvents have little effect on the yield and purity of the fluorination reaction).

[0054] Experimental Example 4

[0055] Experimental Example 4 repeats the operations and steps of Experimental Example 1, and the proportion of potassium fluoride is reduced.

[0056] The experimental steps and chemical inputs of the esterification reaction of Example 4 are the same as those of Experimental Example 1, and the post-treatment process is the same as that of Experimental Example 1. The experimental results of the esterification reaction of Example 4 are as follows: the yield of methyl triflate is 90.7%, and the purity is 98.4%.

[0057] The fluorination reaction step of Experimental Example 4 is repeated Example 1, with the exception that the amount of potassium fluoride is reduced, so that the molar ratio of potassium fluoride to methyl triflate is 1:1.05, and the remaining conditions are unchanged. The experimental results of the fluorination reaction of Experimental Example 3 are as follows: the yield of fluoromethane is 82.32%, and the purity is 99.99%. Compared with Experimental Examples 1 to 3, the yield is decreased, and the analysis shows that the insufficient potassium fluoride leads to the residual ester, which makes the reaction incomplete.

[0058] Experimental Example 5

[0059] Experimental Example 5 repeats the operations and steps of Experimental Example 1, and the reaction rate is accelerated by changing the temperature and pressure.

[0060] The experimental steps and chemical inputs of the esterification reaction of Example 5 are the same as those of Experimental Example 1, and the post-treatment process is the same as that of Experimental Example 1. The experimental results of the esterification reaction of Example 5 are as follows: the yield of methyl triflate is 90.1%, and the purity is 98.8%.

[0061] The fluorination reaction step of Experimental Example 5 is repeated Example 1, with the exception that after the titration of methyl triflate is completed, the reaction temperature, pressure, and time conditions are changed to "80°C, 0.5 MPa pressure for 1 hour in a closed reaction kettle", and the remaining conditions are unchanged. The experimental results of the fluorination reaction of Experimental Example 5 are as follows: the yield of fluoromethane is 90.10%, and the purity is 99.99%.

[0062] Experimental Example 6

[0063] The esterification reaction step of Experimental Example 6 was repeated with Example 1, except that the reaction temperature was lowered to -10°C after the completion of the dropwise addition of trifluoromethanesulfonic anhydride, and the reaction was stirred for an additional 1 hour at -10°C, and the remaining conditions were the same as in Example 1. The experimental results of the esterification reaction of Example 6 were that the yield of methyl trifluoromethanesulfonate was 89.1%, and the purity was 99.2% (the side reaction was inhibited at low temperature, but the reaction rate was reduced).

[0064] The fluorination reaction step of Experimental Example 6 was repeated with Example 1, except that the phase transfer catalyst was replaced from 60 g of 18-crown-6 to 60 g of 12-crown-4, and the remaining conditions were the same as in Example 1. The final experimental results of the fluorination reaction of Example 6 were that the yield of fluoromethane was 85.75%, and the purity was 99.99%. It was analyzed that the crown ether cavity size of 12-crown-4 was smaller, and the KF activation efficiency was lower than that of 18-crown-6.

[0065] Experimental Example 7

[0066] Experimental Example 7 repeated the operations and steps of Experimental Example 1, except that crown ethers were not used, and tetrabutylammonium bromide (TBAB) was used as a phase transfer catalyst.

[0067] The fluorination reaction step of Experimental Example 7 was repeated with Example 1, except that the phase transfer catalyst was replaced from 60 g of 18-crown-6 to 60 g of TBAB, and the remaining conditions were the same as in Experimental Example 1. The experimental results of Example 7 were that the yield of fluoromethane was 88.11%, and the purity was 99.99%. Example 7 proved that TBAB was well adapted to the non-polar solvent system.

[0068] Experimental Example 8

[0069] The fluorination reaction step of Experimental Example 8 was repeated with Example 1, except that the phase transfer catalyst was replaced from 60 g of 18-crown-6 to 60 g of PEG-800, and the remaining conditions were the same as in Example 1. The final experimental results of the fluorination reaction of Example 8 were that the yield of fluoromethane was 87.12%, and the purity was 99.99%.

[0070] Experimental Example 9

[0071] Experimental Example 9 further dried the raw materials, and optimized the temperature and time conditions required for the reaction. The required methanol and dichloromethane reagents were added to calcium hydride, and the distillate was collected to obtain dehydrated and dried methanol and inert solvent dichloromethane.

[0072] The experimental procedure and chemical input of the esterification reaction of Example 9 are the same as those of Experimental Example 1, and the post-treatment process is the same as that of Experimental Example 1. The only difference from Example 1 is that "both methanol and the inert solvent dichloromethane are pre-processed by dehydration and drying treatment". The experimental results of the esterification reaction of Example 9 are that the yield of methyl triflate is 90.1%, and the purity is 99.3%.

[0073] Experimental Example 10

[0074] Experimental Example 10 is optimized for high molar ratio of methanol. The ratio of triflic anhydride and methanol is adjusted based on Experimental Example 1. After adjustment, the ratio of triflic anhydride: methanol = 1:1.2.

[0075] The experimental procedure and chemical input of the esterification reaction of Example 10 are the same as those of Experimental Example 1, and the post-treatment process is the same as that of Experimental Example 1. The only difference from Example 1 is that "the amount of methanol is increased, and the amounts of 281.2 g of triflic anhydride and 101.2 g of triethylamine remain unchanged, so that the molar ratio of methanol: triflic anhydride: triethylamine = 1.2:1:1", and other conditions remain unchanged. The experimental results of the esterification reaction of Example 10 are that the yield of methyl triflate is 93.1%. GC analysis shows that the purity is 98.8%.

[0076] Experimental Example 11

[0077] Experimental Example 11 basically repeats the steps of Experimental Example 1, wherein the conditions of the esterification step are changed to not add inert solvents and acid binders, and triflic anhydride and methanol are directly mixed.

[0078] The experimental procedure of the esterification reaction of Experimental Example 11 is the same as that of Experimental Example 1, except that triethylamine and dichloromethane are no longer added, and triflic anhydride is directly titrated with methanol. The experimental results of the esterification reaction of Example 11 are that the yield of methyl triflate is 80.1%, and the purity is 93.1%.

[0079] Compared with Experimental Examples 1 to 10, the yield and purity of methyl triflate of Example 11 have decreased significantly. The analysis shows that the reaction is not diluted by adding solvents, and the local heat release of the esterification reaction causes partial hydrolysis of the ester.

[0080] Experimental Example 12

[0081] Experimental Example 12 The operation and steps of Experimental Example 1 were repeated to verify the by-product recycling and scale-up production. First, esterification regeneration verification was performed using the by-product Et3N-CF3SO3H of Example 1, which was acidified with H2SO4 to recover CF3SO3H, then dehydrated and condensed with P2O5 at 85°C to generate acid anhydride again. The product was weighed to calculate the molar mass, and the recovery rate reached 84%. Second, fluorination and ring closure experiments were performed, and the acid anhydride generated again was used for esterification (the experimental conditions were the same as those of Experimental Example 1). The experimental results were as follows: the yield of methyl trifluoromethanesulfonate was 90.1%, the purity was 93.1%, the yield of fluoromethane was 91.13%, and the purity was 99.99%. Experimental Example 12 confirmed the stability of the cycle.

Claims

1. A method for the synthesis of fluoromethane, characterized in that, The method comprises the following steps: S1 esterification reaction: triflic anhydride and methanol are used as raw materials, and the reaction is carried out in an inert gas protection and an inert solvent at a temperature of 0-25℃ to generate methyl triflate; S2 fluorination reaction: the methyl triflate obtained in step S1 is subjected to a nucleophilic substitution reaction with potassium fluoride in the presence of a phase transfer catalyst to generate fluoromethane.

2. The method of claim 1, wherein, In step S1, the molar ratio of triflic anhydride to methanol is 1:1-1.8, and preferably the molar ratio is 1:1.1-1:1.3; the inert solvent in step S1 is selected from at least one of tetrahydrofuran, dichloromethane and toluene, and preferably the solvent is dichloromethane.

3. The method according to claim 1 or 2, characterized in that, Step S1 also includes adding an organic base for neutralizing the by-product acid, and the organic base is triethylamine, pyridine or N,N-diisopropyl ethylamine, and the amount of the organic base is 1.0-1.5 times the molar amount of triflic anhydride, and preferably the amount is 1.2-1.5 times the molar amount of triflic anhydride.

4. The method of claim 3, wherein, In step S1, the operation process of the esterification reaction is as follows: first, the methanol is mixed with the inert solvent and the organic base, and then the mixture is cooled to 0-5℃, and the triflic anhydride is slowly added dropwise, so that the temperature of the mixture during the dropwise addition process is ≤5℃, after the dropwise addition is completed, the stirring is continued for 0.5-2h until the reaction is completed. After the reaction in step S1 is completed, the following post-processing steps are further included: the reaction liquid is poured into ice water, and the reaction is quenched by stirring, and then acid is added to adjust the pH to 3-4, so that the triethylamine salt is converted into water-soluble hydrochloride salt, dichloromethane is used for extraction, the organic phases are combined, and then the organic phases are washed with water and saturated brine in sequence, and then the organic phases are dried by anhydrous Na2SO4 or anhydrous magnesium sulfate, and then the solvent is removed by distillation under reduced pressure, and then the distillation is continued to obtain the fraction of methyl triflate, and the post-processing is completed.

5. The method of claim 1, wherein, In step S2, the molar ratio of potassium fluoride to methyl triflate is 1.05-1.5:1; the phase transfer catalyst is a crown ether or polyethylene glycol PEG, and the mass amount of the phase transfer catalyst is 30-50% of the mass of methyl triflate, and preferably the mass amount is 40-45% of the mass of methyl triflate; the reaction is carried out in a polar aprotic solvent, and the solvent is selected from at least one of acetonitrile, N,N-dimethylformamide DMF, dimethyl sulfoxide DMSO, DEGME and TEDM.

6. The method of claim 5, wherein, The crown ether is 18-crown-6, 15-crown-5 or 12-crown-4; and the molecular weight of the polyethylene glycol PEG is 400-800.

7. The method of claim 1, wherein, The reaction conditions of step S2 are as follows: the reaction temperature is 40-80℃, the reaction pressure is normal pressure-0.5 MPa, and the reaction time is 1-6 hours, and preferably the reaction conditions are as follows: the reaction temperature is 60℃, the reaction pressure is normal pressure, and the reaction time is 2-6 hours; during the reaction process, the gaseous product fluoromethane is collected by low-temperature condensation.

8. The method of claim 1, wherein, The particle size of the potassium fluoride raw material is ≤100 μm.

9. The method of claim 1, wherein, The by-product of the nucleophilic substitution reaction in step S2 is potassium triflate, and the potassium triflate is regenerated into triflic anhydride by acidification, and the regeneration process specifically includes the following steps: the reaction liquid is filtered to obtain potassium triflate solid; concentrated sulfuric acid is added to the filtrate to acidify the pH to ≤1 to generate triflic acid; dehydrating agent P2O5 is added to the triflic acid to regenerate triflic anhydride by dehydration condensation at 80-100℃.

10. The method of claim 9, wherein, The regenerated trifluoromethanesulfonic anhydride is reused in the esterification reaction of step S1 to realize closed-loop utilization of raw materials.

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