Preparation method of high-purity 2-fluorobiphenyl

Abstract

The invention discloses a preparation method of high-purity 2-fluorobiphenyl, which comprises the following steps: by taking 2-fluorophenylboronic acid and bromobenzene as raw materials, carrying out coupling reaction in a methanol aqueous solution under the action of a plant fiber-based palladium complex and sodium carbonate, cooling to room temperature after the reaction is finished, extracting with ethyl acetate, and concentrating to obtain a crude product; and recrystallizing, washing and drying to obtain the product 2-fluorobiphenyl. The reaction synthesis route is simple, the used plant fiber-based palladium type catalyst is high in activity, good in selectivity and very stable, and the high catalytic efficiency can still be kept after multiple times of recovery. In addition, the plant fibers have rich functional groups such as hydroxyl groups, reaction substrates can be adsorbed and concentrated to catalytic active sites through the acting force of chemical bonds, and the reaction rate and the conversion efficiency can be further improved; high-toxicity and high-harm organic solvents are not involved in the reaction process, so that the difficulty in the aspects of environmental protection and safety management is reduced; the product prepared by the method is high in purity, low in impurity content, few in variety and low in moisture content.

Description

Technical Field

[0001] The present invention relates to the technical field of battery electrolyte additives, and relates to a preparation method of halogenated biphenyls, specifically a preparation method of high-purity 2-fluorobiphenyl. Background Art

[0002] 2-Fluorobiphenyl is a relatively common compound. It can not only be used as an intermediate in the fields of medicine and pesticides, but also be directly added as an additive to lithium-ion battery electrolytes. When used as an electrolyte additive, 2-fluorobiphenyl can effectively prevent the overcharging of batteries and improve the safety performance of batteries.

[0003] 2-Fluorobiphenyl belongs to halogenated biphenyl compounds. One of the synthetic routes is to select suitable halogenated aniline raw materials, diazotize them and then carry out a coupling reaction with benzene to obtain halogenated biphenyl products. For example, the Chinese invention patent "Synthesis Method of 2-Fluorobiphenyl" with the document number 201710202098.2 discloses that o-fluoroaniline is first diazotized and then reacted with benzene to obtain 2-fluorobiphenyl. In the disclosed preparation process, trifluoroacetic acid, anhydrous magnesium sulfate, and a composite metal catalyst need to be added. This reaction process does not require high temperature and the reaction conditions are milder. However, during the preparation process, the temperature needs to be continuously adjusted. For example, during the feeding process, it needs to be cooled to 4°C - 15°C, after adding isoamyl nitrite, the temperature needs to be controlled at 20°C - 30°C, during the dropping of o-fluoroaniline, the temperature needs to be controlled at 30°C - 45°C, and after the feeding is completed, the reaction temperature needs to be controlled at 25°C - 32°C. The whole temperature control reaction process is complex. When applying this method to industrial production, the heating and cooling processes take time, reducing the production efficiency. Moreover, the reaction yield of this method is 88% and the purity is 99.4%. Both the yield and the purity need to be further improved. Another synthetic route is to use suitable fluorobenzene boronic acid and aryl bromide as raw materials, and carry out Suzuki coupling reaction in an organic solvent in the presence of a base and a catalyst. Generally, a palladium-type catalyst with high catalytic activity and strong selectivity is selected as the catalyst. However, the above reaction system is an organic solvent system. In industrial production, a large amount of organic solvents need to be used, generating a large amount of waste solvents, bringing pressure to environmental protection. At the same time, the recovery process of the palladium-type catalyst is relatively complex.

[0004] Therefore, there is a need to provide a preparation method of 2-fluorobiphenyl that can not only improve the reaction yield and product purity, but also reduce the types and usage amounts of organic solvents involved in the reaction process, reduce the environmental protection pressure, and save production costs. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of high-purity 2-fluorobiphenyl, which can not only improve the product purity and production yield, but also reduce the usage amount of organic solvents used in the reaction, and the recovery of the catalyst used is also simpler.

[0006] To achieve the above object, the present invention provides the following technical solution. A preparation method of high-purity 2-fluorobiphenyl, which is characterized in that 2-fluorobenzeneboronic acid and bromobenzene are used as raw materials, and in an aqueous methanol solution at 40°C to 45°C, a coupling reaction occurs under the action of a plant fiber-based palladium complex and sodium carbonate. The reaction time is controlled for 1 h to 2 h. After the reaction is completed, the temperature is lowered to room temperature, and after extraction with ethyl acetate and concentration, a crude product is obtained. Then, after recrystallization, washing, and drying, the product 2-fluorobiphenyl is obtained. The preparation method of the above plant fiber-based palladium complex is as follows:

[0007] The plant fiber is pretreated and added to water. Under the action of sodium periodate, the reaction is carried out at 50°C to 60°C for 2 h to 4 h. After filtration and washing, aldehyde-functionalized plant fiber is obtained; the aldehyde-functionalized plant fiber is placed in water, chlorous acid and hydrogen peroxide are added, and an oxidation reaction is carried out at 50°C to 60°C for 6 h to 10 h. After filtration and washing, carboxylated plant fiber is obtained; the carboxylated plant fiber is added to absolute ethanol, glycine is added, and the mixture is stirred and reacted to obtain plant fiber grafted with glycine. Then, acetic anhydride and palladium chloride are added to the system, and the reflux reaction is carried out for 4 h to 6 h. After filtration, the precipitate is washed and dried to obtain the plant fiber-based palladium complex.

[0008] Specifically, the pretreatment of the above plant fiber is carried out as follows: the plant fiber raw material is ground and sheared.

[0009] Preferably, the mass ratio of the above 2-fluorobenzeneboronic acid to bromobenzene is 139:172 to 188.

[0010] Preferably, the mass ratio of the above plant fiber-based palladium complex to 2-fluorobenzeneboronic acid is 0.5 to 2:139.

[0011] Furthermore, the mass ratio of the above palladium chloride to glycine is 177:166 to 222, and the mass of the above plant fiber is 1.5 to 2 times the total mass of palladium chloride and glycine.

[0012] Even further, the above process further includes recovering the plant fiber-based palladium complex after the reaction is completed, washing it alternately with absolute ethanol and water, drying it, and storing it at room temperature.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] The reaction synthesis route of the present invention is simple. 2-fluorobiphenyl can be synthesized only through one-step coupling reaction. The used palladium-based catalyst has high activity and good selectivity. In particular, it has been proved by experiments that it can still maintain a high catalytic efficiency after being recycled 6 times, fully ensuring the high purity of the product. It can be seen that the present invention uses plant fiber as the substrate, which not only improves the stability of the palladium-based catalyst, but also is conducive to the recovery and reuse of the catalyst.

[0015] The present invention can be successfully completed in a methanol and water system. Although plant fibers are insoluble in water, the porous structure of plant fibers can provide sufficient space for the action of palladium catalysts, and the reaction efficiency will not be affected by the incompatibility between the catalyst and the reactants. In addition, plant fibers have abundant functional groups such as hydroxyl groups, which can adsorb and concentrate reaction substrates to catalytic active sites under the action of chemical bond forces, increasing the contact frequency between reaction substrates and between them and the catalyst, and further improving the reaction rate and conversion efficiency. The organic solvents involved in the whole reaction process are only common solvents with low toxicity and low safety management level such as methanol, ethanol, ethyl acetate and acetic acid. These solvents are not only relatively simple to recycle and process, but also can reduce the difficulty in environmental protection and safety management.

[0016] The purity of the prepared crude product has reached more than 97.9%, the yield of the product can reach more than 93.6%, the purity of the product can reach 99.6%, the content of the largest single impurity is less than 0.28%, the water content in the product is at least 80 ppm at the lowest, and the types of impurities detectable by GC in this product are few. It can be seen that the 2-fluorobiphenyl prepared by the present invention has high purity, few impurities and low water content. Using the present invention as an electrolyte additive can effectively enhance the battery environmental safety performance of lithium batteries, improve the thermal stability of the batteries, and improve the high temperature resistance performance of the batteries in the environment. Description of the Drawings

[0017] Figure 1 is the gas chromatogram of 2-fluorobiphenyl prepared by the present invention.

[0018] In the appendix Figure 1 1 is the standard product peak and 2 is the 2-fluorobiphenyl product peak. Detailed Embodiments

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] For convenience of description, the dosages of the test materials in the embodiments and comparative examples are all the amounts after being converted to pure substances.

[0021] Example 1

[0022] Preparation process of plant fiber-based palladium complex:

[0023] Step 1: Grind and shear the plant fiber raw material to improve the reaction accessibility of the plant fiber. Add 1 g of plant fiber to 10 g of water, and then add 0.1 g of sodium periodate. React at 50 °C, 55 °C, and 60 °C for 4 h, 3 h, and 2 h respectively. After the reaction, filter and wash to obtain aldehyde-functionalized plant fiber samples 1, 2, and 3 respectively;

[0024] Step 2: Redisperse aldehyde-functionalized plant fiber samples 1, 2, and 3 in 10 g of water respectively. Add 2 g of chlorous acid and 2 g of hydrogen peroxide with a mass concentration of 30%. Conduct oxidation reactions at 55 °C, 60 °C, and 50 °C for 8 h, 10 h, and 6 h respectively. After filtration and washing, obtain carboxylated plant fiber samples 1, 2, and 3 respectively;

[0025] Step 3: Add carboxylated plant fiber samples 1, 2, and 3 to anhydrous ethanol respectively. Add glycine and stir to react to obtain plant fibers grafted with glycine. Then add acetic anhydride and palladium chloride to the system and reflux for 4 h - 6 h. Filter, wash the precipitate, and dry to obtain plant fiber-based palladium complexes. Obtain plant fiber-based palladium complex samples 1, 2, and 3; The mass of palladium chloride used in the above preparation process is 0.18 g, the masses of glycine are 0.17 g, 0.20 g, and 0.22 g respectively, and the masses of the carboxylated plant fibers used are 0.70 g, 0.65 g, and 0.60 g respectively (corresponding to 2 times, 1.8 times, and 1.5 times the total mass of palladium chloride and glycine). After calculation, the yields of plant fiber-based palladium complex samples 1, 2, and 3 are 95.6%, 96.1%, and 94.9% respectively.

[0026] Example 2

[0027] Add 2.8 g of 2-fluorophenylboronic acid and 3.6 g of bromobenzene to a reaction flask. Then add 40 mL of a methanol aqueous solution with a methanol mass concentration of 40%. Add 0.02 g of plant fiber-based palladium complex sample 1 and 7.0 g of sodium carbonate. Heat to 40 °C, stir slowly for 1.5 h. After the reaction, cool the reaction flask to room temperature. Filter the plant fiber-based palladium complex, wash it alternately with anhydrous ethanol and water twice, and dry to remove the solvent and store it at room temperature; The obtained filtrate is extracted with ethyl acetate, concentrated by rotary evaporation, and dried to obtain crude 2-fluorobiphenyl sample 1. Then recrystallize, wash, and dry crude 2-fluorobiphenyl sample 1 to obtain product 2-fluorobiphenyl sample 1.

[0028] Example 3

[0029] Add 2.8 g of 2-fluorophenylboronic acid and 3.5 g of bromobenzene to a reaction flask, then add 35 mL of an aqueous methanol solution with a methanol mass concentration of 35%. Add 0.01 g of the plant fiber-based palladium complex sample 2 and 5.6 g of sodium carbonate, heat to 42 °C, stir slowly for 2 h. After the reaction is completed, cool the reaction flask to room temperature, filter the plant fiber-based palladium complex, wash it 4 times alternately with absolute ethanol and water, dry to remove the solvent and store it at room temperature. The obtained filtrate is extracted with ethyl acetate, concentrated by rotary evaporation and dried to obtain the crude 2-fluorobiphenyl sample 2. Then, recrystallize, wash and dry the crude 2-fluorobiphenyl sample 2 to obtain the product 2-fluorobiphenyl sample 2.

[0030] Example 4

[0031] Add 2.8 g of 2-fluorophenylboronic acid and 3.8 g of bromobenzene to a reaction flask, then add 45 mL of an aqueous methanol solution with a methanol mass concentration of 30%. Add 0.04 g of the plant fiber-based palladium complex sample 3 and 8.4 g of sodium carbonate, heat to 45 °C, stir slowly for 1 h. After the reaction is completed, cool the reaction flask to room temperature, filter the plant fiber-based palladium complex, wash it 2 times alternately with absolute ethanol and water, dry to remove the solvent and store it at room temperature. The obtained filtrate is extracted with ethyl acetate, concentrated by rotary evaporation and dried to obtain the crude 2-fluorobiphenyl sample 3. Then, recrystallize, wash and dry the crude 2-fluorobiphenyl sample 3 to obtain the product 2-fluorobiphenyl sample 3.

[0032] Comparative Example

[0033] Comparative Example 1

[0034] The implementation process is the same as that of Example 2, except that instead of using the plant fiber-based palladium complex as a catalyst, 0.01 g of palladium glycinate complex is used. The preparation method is to add 1 g of glycine and 0.8 g of palladium chloride to a reaction flask, add absolute ethanol and glacial acetic acid, stir and react at room temperature for 24 h, filter to obtain the precipitate, filter the precipitate and wash it with absolute ethanol, and dry to obtain the palladium glycinate complex. The obtained palladium glycinate complex is soluble in water. Use the above palladium glycinate complex for catalysis, and the specific implementation process is the same as that of Example 2 to obtain the crude 2-fluorobiphenyl reference 1 and the product 2-fluorobiphenyl reference 1.

[0035] Comparative Example 2

[0036] The implementation process is the same as that of Example 2, except that the reaction system used is n-butanol, and the other implementation processes are the same as those of Example 2 to obtain the crude 2-fluorobiphenyl reference 2 and the product 2-fluorobiphenyl reference 2.

[0037] Comparative Example 3

[0038] The implementation process is the same as that of Example 2, except that the plant fiber-based palladium complex used is the catalyst recycled 3 times, 6 times, and 10 times, and the crude product 2-fluorobiphenyl reference standards 3-1, 3-2, 3-3 and the product 2-fluorobiphenyl reference standards 3-1, 3-2, 3-3 are obtained respectively.

[0039] Analysis and testing

[0040] The samples of the examples and the reference standards were respectively detected by a high-performance gas chromatograph (internal standard method) to determine the purity of the samples to be measured. The results are shown in Tables 1, 2 and 3; a moisture analyzer was used to determine the moisture in the samples to be measured, and the results are shown in Table 3.

[0041] The yields in each example and control example were calculated according to Formula 1, and the results are shown in Tables 2 and 3.

[0042] Formula 1: Yield (%) = actual weight of the obtained sample (g) / theoretical obtained amount calculated based on the usage amount of 2-fluorobenzeneboronic acid (g) × 100%.

[0043] Among them, the relevant inspection chromatograms of the product 2-fluorobiphenyl sample 1 are shown in the appendix Figure 1 .

[0044] Table 1: Peak table of gas chromatogram of product 2-fluorobiphenyl sample 1

[0045] Retention time Peak height Peak area Peak area % 3.045 3417 4975 0.0104 15.567 56651 70898 0.1488 15.646 133483 168589 0.3538 15.773 31572269 47313323 99.2854 15.922 76141 90799 0.1905 16.691 1782 2514 0.0053 17.213 1844 2741 0.0058 Total 31845587 47653839 100.0

[0046] Table 2: Summary table of yield, purity and moisture detection results of crude product samples and crude product reference standards

[0047] Sample Yield (%) Purity (%) Crude sample 1 96.5 98.5 Crude sample 2 97.1 97.9 Crude sample 3 96.9 98.2 Crude reference standard 1 93.7 96.9 Crude reference standard 2 85.1 92.1 Crude reference standard 3-1 96.4 98.0 Crude reference standard 3-2 95.2 96.9 Crude reference standard 3-3 88.6 93.1

[0048] Table 3: Summary table of yield, purity and moisture detection results of product samples and reference standards

[0049]

[0050]

[0051] As can be seen from the results in Tables 2 and 3, the purity of the crude products in each example of the present invention is above 97.9%, the yield of the product can reach above 93.6%, the product purity can reach 99.6%, the maximum single impurity content is lower than 0.28%, the moisture content in the product is at least 80 ppm at the lowest, and the types of impurities that can be detected by GC in this product are few. It can be seen that the 2-fluorobiphenyl prepared by the present invention has high purity, few impurities and low moisture.

[0052] In Comparative Example 1, the water-soluble palladium glycine complex was used as the catalyst. The purity and yield of the prepared product were slightly lower than those of the present invention, indicating that although the palladium glycine complex can also catalyze this reaction to proceed smoothly, it is inferior to the plant fiber-based palladium complex used in the present invention in terms of selectivity and catalytic efficiency. In addition, the catalyst obtained in Comparative Example 1 needs to go through steps such as extraction and separation before it can be recycled, which brings inconvenience to practical applications. In Comparative Example 2, the reaction system was changed. Although it was confirmed that this reaction can also proceed smoothly in a pure organic system, the yield was low. In Comparative Example 3, plant fiber-based palladium complexes with different recycling times were used, proving that the catalyst used in the present invention can still maintain a high catalytic efficacy within 6 recycles.

[0053] Application test

[0054] The test articles prepared according to the methods of Example 2, Comparative Example 1, and Comparative Example 3 were successively added to the lithium battery electrolyte as electrolyte additives. The electrolyte without 2-fluorobiphenyl was used as the blank example. The addition amount of the electrolyte additive was 2% of the total mass of the electrolyte. At the same time, lithium batteries with a capacitance of 1000 mAh were made using these electrolytes for battery electrical safety testing and battery environmental safety testing.

[0055] Battery electrical safety test

[0056] 1. External short circuit at room temperature

[0057] After the battery is fully charged, it is placed in an environment of 20°C ± 5°C. After the surface temperature of the battery reaches 20°C ± 5°C, it is placed for another 30 min, and then the positive and negative terminals of the battery are connected with a wire, and it is ensured that the total external resistance is 80 mΩ ± 20 mΩ. During the test process, the temperature change of the battery is monitored. The battery should not catch fire or explode, and the maximum temperature should not exceed 150°C.

[0058] 2. External short circuit at high temperature

[0059] After the battery is fully charged, it is placed in an environment of 55°C ± 5°C. After the surface temperature of the battery reaches 55°C ± 5°C, it is placed for another 30 min, and then the positive and negative terminals of the battery are connected with a wire, and it is ensured that the total external resistance is 80 mΩ ± 20 mΩ. During the test process, the temperature change of the battery is monitored. The battery should not catch fire or explode, and the maximum temperature should not exceed 150°C.

[0060] 3. Overcharge

[0061] After the battery is discharged, it is first charged at a constant current of 3 C to a test voltage of 4.6 V, and then charged at a constant voltage with this test voltage. The battery should not catch fire or explode.

[0062] After discharging the battery completely, first charge it at a constant current of 3CA until the test voltage of 4.8V is reached, and then charge it at a constant voltage with this test voltage. The battery should not catch fire or explode.

[0063] 4. Forced Discharge

[0064] After discharging the battery completely, charge it reversely at a current of 1CA for 90 minutes. The battery should not catch fire or explode.

[0065] The test results of the battery electrical safety test are shown in Table 4:

[0066] Table 4: Test Results of Battery Electrical Safety Test

[0067] Sample Normal temperature external short circuit High temperature external short circuit Overcharge (4.6V) Overcharge (4.8V) Forced discharge Sample 1 Normal Normal Normal Normal Normal Reference standard 1 Normal Normal Normal Fire Normal Reference standard 3-1 Normal Normal Normal Fire Normal Blank example Fire Temperature exceeds 150°C Fire Fire ——

[0068] As can be seen from the results in Table 4, adding 2-fluorobiphenyl prepared by this product to the lithium battery electrolyte effectively enhances the electrical safety performance of the lithium battery. However, when the purity of the added 2-fluorobiphenyl is too low or the moisture content is too high, the overcharge safety performance of the battery under high voltage cannot be improved well.

[0069] Battery Environmental Safety Test

[0070] 1. Low Air Pressure

[0071] After charging the battery fully, place the battery in a vacuum chamber at 20°C, evacuate the chamber to reduce the pressure inside to 11.6 kPa, and maintain it for 6 hours. The battery should not catch fire, explode, or leak liquid.

[0072] 2. Temperature Cycling

[0073] After charging the battery fully, place the battery in a temperature-controlled chamber at 20°C ± 5°C and perform the following steps:

[0074] a) Place the sample in an experimental chamber at 75°C ± 2°C and maintain it for 6 hours;

[0075] b) Then lower the temperature of the experimental chamber to -40°C ± 2°C and maintain it for 6 hours. The temperature conversion time should not be greater than 30 minutes;

[0076] c) Raise the temperature of the experimental chamber to 75°C ± 2°C again. The temperature conversion time should not be greater than 30 minutes;

[0077] d) Repeat steps a) to c) for a total of 10 cycles. The battery should not catch fire, explode, or leak liquid.

[0078] 3. Acceleration Shock

[0079] After charging the battery fully, fix it on the impact table and perform a half-sine pulse shock experiment. In the initial 3 ms, the minimum average acceleration is 75g n, the peak acceleration is 150g n ±25g n , the pulse duration is 6ms ± 1ms, and the battery is subjected to three acceleration shocks in each direction. The battery should not catch fire, explode, or leak liquid.

[0080] 4. Drop

[0081] After fully charging the battery, it is freely dropped from a height of 1m onto a concrete slab. A total of four drop tests are carried out, and the battery should not catch fire or explode.

[0082] 5. Extrusion

[0083] After fully charging the battery, the battery is placed between two planes and extruded perpendicular to the plate direction. An extrusion force of 13.0kN ± 0.78kN is applied between the two flat plates. Once the pressure reaches the maximum value, the extrusion test can be stopped. During the test, the battery should not have an external short circuit.

[0084] 6. Thermal abuse

[0085] After fully charging the battery, it is placed in a test chamber. The test chamber is heated at a temperature rise rate of (5 ± 2) °C / min. When the temperature in the chamber reaches 130°C ± 2°C, it is kept constant for 30 min. The battery should not catch fire or explode.

[0086] 7. Combustion jet

[0087] After fully charging the battery, it is placed on the wire mesh of the test fixture.

[0088] If the battery slips during the test, the battery sample can be fixed on the wire mesh with a single metal wire; if such a situation does not occur, the battery cannot be tied up.

[0089] The battery is heated with a flame, and the heating is stopped when any of the following three situations occurs: a) the battery explodes; b) the battery burns completely; c) heating continues for 30 min, but the battery does not catch fire or explode.

[0090] After the test, the components of the battery (except for dust-like products) or the whole battery shall not penetrate the aluminum mesh.

[0091] The test results of the battery environmental safety test are shown in Table 5:

[0092] Table 5: Test results of battery environmental safety test

[0093] Sample Low air pressure Temperature cycle Acceleration shock Drop Extrusion Thermal abuse Combustion jet Sample 1 Normal Normal Normal Normal Normal No change Fire Sample 2 Normal Normal Normal Normal Normal No change Fire Reference standard 1 Normal Normal Normal Normal Normal Fire Fire Reference standard 3-1 Normal Normal Normal Normal Normal Fire Fire Blank example Normal Leakage Leakage Normal Short circuit Explosion Explosion

[0094] As can be seen from the results in Table 5, 2-fluorobiphenyl prepared by the present invention can effectively enhance the battery environmental safety performance of lithium batteries, improve the thermal stability of the batteries, and improve the high-temperature resistance performance of the batteries in the lithium battery electrolyte.

Claims

1. A preparation method of high-purity 2-fluorobiphenyl, characterized in that, using 2-fluorophenylboronic acid and bromobenzene as raw materials, in an aqueous methanol solution at 40°C to 45°C, under the action of a plant fiber-based palladium complex and sodium carbonate, a coupling reaction occurs, controlling the reaction time for 1 h to 2 h. After the reaction ends, it is cooled to room temperature, and the crude product is obtained after extraction with ethyl acetate and concentration, and then the product 2-fluorobiphenyl is obtained after recrystallization, washing, and drying. The preparation method of the plant fiber-based palladium complex is as follows: The plant fiber is pretreated, added to water, and reacted at 50°C to 60°C for 2 h to 4 h under the action of sodium periodate, and the aldehyde-grouped plant fiber is obtained after filtration and washing; the aldehyde-grouped plant fiber is placed in water, chlorous acid and hydrogen peroxide are added, and an oxidation reaction is carried out at 50°C to 60°C for 6 h to 10 h, and the carboxylated plant fiber is obtained after filtration and washing; the carboxylated plant fiber is added to absolute ethanol, glycine is added, and stirring reaction is carried out to obtain the plant fiber grafted with glycine. Then, absolute acetic acid and palladium chloride are added to the system, and reflux reaction is carried out for 4 h to 6 h, and after filtration, the precipitate is washed and dried to obtain the plant fiber-based palladium complex.

2. The preparation method of high-purity 2-fluorobiphenyl according to claim 1, characterized in that, the specific operation of the pretreatment of the plant fiber is: grinding and shearing the plant fiber raw material.

3. The preparation method of high-purity 2-fluorobiphenyl according to claim 1, characterized in that, the mass ratio of the 2-fluorophenylboronic acid to the bromobenzene is 139:172 to 188.

4. The preparation method of high-purity 2-fluorobiphenyl according to claim 1, characterized in that, the mass ratio of the plant fiber-based palladium complex to the 2-fluorophenylboronic acid is 0.5 to 2:

139.

5. The preparation method of high-purity 2-fluorobiphenyl according to claim 1, characterized in that, the mass ratio of the palladium chloride to the glycine is 177:166 to 222, and the mass of the plant fiber is 1.5 to 2 times the total mass of the palladium chloride and the glycine.

6. The preparation method of high-purity 2-fluorobiphenyl according to claim 1, characterized in that, it further includes, after the reaction ends, recovering the plant fiber-based palladium complex, washing it alternately with absolute ethanol and water, drying it, and storing it at room temperature.

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