Preparation method of 3, 5-difluoroethyl benzene for display material

Abstract

The invention discloses a preparation method of 3, 5-difluoroethyl benzene for a display material, and the preparation method comprises the following steps: S1, preparing a 3, 5-difluoroethyl benzene crude product; s2, magnesium chips are added into methanol for water vapor heating; s3, adding a 3, 5-difluoroethyl benzene crude product into the mixture obtained in the step S2 to initiate Grignard reaction, and after successful initiation, adding magnesium chips to continue stirring and heat preservation reaction to obtain feed liquid; s4, cooling the feed liquid, hydrolyzing, washing, separating liquid and drying to obtain an organic phase; and S5, carrying out normal-pressure rectification on the organic phase, and collecting a main fraction, namely a refined product of 3, 5-difluoroethyl benzene. The crude product is purified by adopting water vapor distillation, Grignard debromination, four-stage water washing, alkali washing and low-temperature rectification to form a closed-loop purified chain, the product purity is relatively high, the brominated substance residual quantity is low, the metal ion content is low, the acid value is reduced, and the chromaticity is not changed (delta APHAlt; and 5) the strict requirements of high-end applications (such as liquid crystal display) on purity, stability and safety are met in all directions.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of organic synthesis, in particular to a preparation method of 3,5-difluoroethylbenzene for display material. BACKGROUND

[0002] 1-ethyl-3,5-difluorobenzene (3,5-difluoroethylbenzene) is an important fluorine-containing organic compound, the 3,5 positions of the benzene ring are substituted by fluorine atoms, the 1 position is connected with an ethyl group (-CH2CH3), the molecular formula is C8H8F2, it is a colorless transparent liquid, the density is 1.065-1.1 g / cm 3 (25 DEG C), the boiling point is 127.5+ / -20.0 DEG C (760 mmHg), and it has wide application prospects in the fields of liquid crystal materials, medicine and pesticide synthesis, and functional polymer materials due to unique structure and performance. As a key synthesis raw material of fluorine-containing liquid crystal monomers, 1-ethyl-3,5-difluorobenzene is widely used in high-performance liquid crystal displays (LCDs), and the introduction of fluorine atoms enhances the molecular polarity and improves the thermal stability, response speed and optical performance of the liquid crystal material.

[0003] Chinese patent CN118108571A discloses a synthesis method of 3,5-difluoroethylbenzene, which comprises the following steps: taking 3,5-difluorobromobenzene as a starting raw material, generating Grignard reagent 3,5-difluorophenyl magnesium bromide through a Grignard reaction; dropping the Grignard reagent 3,5-difluorophenyl magnesium bromide into bromoethane to generate crude 3,5-difluoroethylbenzene; and distilling the crude product to obtain high-purity product 3,5-difluoroethylbenzene. Although the above synthesis method has certain advantages in shortening the production cycle and improving the production efficiency, the synthesized product still has the following defects:

[0004] (1) bromide azeotrope residue: in the distillation process, bromoethane (boiling point: 38.4 DEG C) and tetrahydrofuran (THF) form an azeotrope, so that about 0.5% (GC detection) of bromide is contained in the recovered solvent, the THF recovered contains a certain amount of bromide, which not only affects the quality of the solvent but also may interfere with or contaminate the subsequent batches of reactions. Meanwhile, the product also contains >=0.3% of bromide residue, and the bromide residue in the product may become a cause for accelerated decomposition, thereby reducing the stability of the product, especially during storage, which may cause the performance of the product to decrease.

[0005] (2) High temperature thermal decomposition: When collecting the distillate at the temperature range of 128-135℃, high temperature distillation will cause a certain degree of thermal decomposition of the product, a large amount of target product is converted into by-products, which significantly reduces the yield of the final product, so that the yield is ≤60%, and the decomposition by-products account for 8-10% of the total amount. In addition, the colority of the product will also be affected, which will rise from the initial >30 APHA to 100+ after 30 days of storage, indicating that the chemical properties of the product have changed, which may be due to the influence of decomposition by-products, thereby affecting the application value and market acceptance of the product.

[0006] (3) Uncontrolled metal impurities: The catalysts such as Cu 2+ and Mg 2+ metal ions used in the synthesis process have a residual amount of more than 500ppm in the final product, which exceeds the standard requirement of liquid crystal materials (≤50ppm). The high content of metal impurities will seriously affect the performance of liquid crystal display products, and even cause equipment failure or poor display effect.

[0007] In summary, the existing synthesis method can obtain a product with high purity by directly distilling the 3,5-difluoroethylbenzene crude product, but there are obvious deficiencies in the residual bromide, thermal decomposition caused by high temperature and metal impurity control. These problems limit the application efficiency and product quality of the method in large-scale production, especially in fields with extremely high purity requirements such as liquid crystal material manufacturing. Therefore, it is urgent to develop a more efficient synthesis method for 3,5-difluoroethylbenzene to overcome the above-mentioned shortcomings. SUMMARY

[0008] The purpose of the present application is to provide a preparation method of 3,5-difluoroethylbenzene for display materials, which solves the problem that the existing synthesis method can obtain a product with high purity by directly distilling the 3,5-difluoroethylbenzene crude product, but there are obvious deficiencies in the residual bromide, thermal decomposition caused by high temperature and metal impurity control.

[0009] To achieve the above-mentioned purpose, the present application provides a preparation method of 3,5-difluoroethylbenzene for display materials, comprising the following steps:

[0010] S1: preparing 3,5-difluoroethylbenzene crude product;

[0011] S2: adding magnesium chips to methanol and performing steam heating;

[0012] S3: adding 3,5-difluoroethylbenzene crude product to step S2 to initiate Grignard reaction, and after successful initiation, adding magnesium chips to continue stirring and heat preservation reaction to obtain a liquid;

[0013] S4: After the feed liquid is cooled, hydrolyzed, washed, separated and dried, an organic phase is obtained;

[0014] S5: The organic phase is subjected to normal pressure rectification, and a main fraction is collected, which is 3,5-difluoroethylbenzene product.

[0015] Preferably, in step S1, the specific steps for preparing 3,5-difluoroethylbenzene crude product are as follows:

[0016] S11: Steam heating is performed on the reaction kettle by adding magnesium chips and tetrahydrofuran, and after being heated to 55-75°C, slow reflux is performed;

[0017] S12: After stopping heating, a portion of 3,5-difluorobromobenzene is added to the reaction kettle to initiate Grignard reaction, and after successful initiation, the reflux is slowed down, and tetrahydrofuran is continuously added;

[0018] S13: The remaining 3,5-difluorobromobenzene is continuously added to the reaction kettle, and after the addition is completed, the reaction is carried out by keeping the temperature and stirring;

[0019] S14: A portion of bromoethane is added to the reaction kettle, and after stirring, the remaining bromoethane, lithium chloride and cuprous chloride are added to continue the reaction, and after the reaction is completed, a reaction liquid is obtained;

[0020] S15: After the reaction liquid is hydrolyzed, separated, washed and separated multiple times, an intermediate product is obtained;

[0021] S16: After steam distillation and normal pressure rectification of the intermediate product, a main fraction is collected, and after alkali washing and drying of the main fraction, 3,5-difluoroethylbenzene crude product is obtained.

[0022] Preferably, in step S1, the mass ratio of magnesium chips to 3,5-difluorobromobenzene is 1:(6-9).

[0023] Preferably, in step S1, the mass ratio of 3,5-difluorobromobenzene to bromoethane is (1-1.5):1, the mass ratio of bromoethane to lithium chloride is (48-50):1, and the mass ratio of bromoethane to cuprous chloride is (25-28):1.

[0024] Preferably, in step S1, the in-bottle temperature of the normal pressure distillation is controlled to be not more than 100°C, the main fraction is collected, the top temperature is not more than 80°C, and when the temperature exceeds 72°C, the distillation is stopped.

[0025] Preferably, in step S1, the GC purity of 3,5-difluoroethylbenzene crude product is 80%, and the bromide residue is ≥0.3%.

[0026] Preferably, in step S2, the amount of magnesium chips added is 1-3% of the 3,5-difluoroethylbenzene crude product, and in step S3, the amount of magnesium chips added is 0.1-0.3% of the 3,5-difluoroethylbenzene crude product.

[0027] In step S2, the temperature of the steam heating is 55-75℃.

[0028] Preferably, in step S4, the feed liquid is cooled to 40℃ by cooling water, then water and hydrochloric acid are added to the feed liquid, and the hydrolysis is stirred, then water and sodium bicarbonate are added for washing, after the washing is completed, the lower organic phase is obtained by standing and separating, and anhydrous sodium sulfate is added to the organic phase for drying, to obtain the dried organic phase.

[0029] Preferably, in step S5, the in-bottle temperature is controlled to be not more than 170℃, the top temperature is controlled to be not more than 150℃, the front fraction is collected, and the main fraction is collected until the top temperature is stable at 130-140℃.

[0030] Preferably, in step S5, after detection, the 3,5-difluoroethylbenzene product is a colorless transparent liquid, the GC is >99.5%, the solvent is <0.2%, the raw material is less than 0.02%, the maximum impurity is less than 0.1%, the moisture is less than 0.1%, the metal ion is <50ppm, the acid value is <0.05mg KOH / g, the bromide residue is <0.01%, and there is no color change at 60℃ for 30 days.

[0031] Therefore, the application has the following beneficial effects by using the above-mentioned structure of a preparation method of 3,5-difluoroethylbenzene for display material:

[0032] (1) The application converts the residual bromoethane into soluble magnesium bromide salt through the format bromine removal step, the bromide residue is reduced from the initial 0.3% to <0.02%, the separation problem caused by the azeotrope is completely solved, the product chemical stability is significantly improved (no color change for 30 days), and the quality deterioration caused by the decomposition of bromide is avoided.

[0033] (2) The application deeply removes metal ions, removes Mg 2+ , Cu 2+ , Li + and other metal ions by using a four-stage countercurrent water washing gradient, supplemented by alkali washing and neutralization and anhydrous sodium sulfate drying, and the metal ion residue is reduced from >500ppm to <50ppm, which meets the electronic grade standard of liquid crystal materials (≤50ppm), and avoids the catalytic decomposition of metal impurities.

[0034] (3) The application accurately controls the thermal decomposition risk, and the distillation temperature is strictly controlled at 130-140℃, avoiding the thermal decomposition window of >135℃, the product yield is increased from 60% of the comparative process to 82%, the decomposition byproduct is reduced by 8-10%, the molecular rupture caused by high temperature is reduced, and the product purity and yield are ensured.

[0035] (4) The present application adopts water vapor distillation→ Grignard debromination→ four-stage water washing→ alkali washing→ low-temperature rectification for purification of the crude product, forming a closed-loop purification chain, and the product has high purity, low bromide residue, low metal ion content, and reduced acid value, and the color does not change (ΔAPHA<5) after 30 days of accelerated aging at 60℃, which fully meets the stringent requirements of high-end applications (such as liquid crystal display) on purity, stability and safety.

[0036] The technical solutions of the present application will be further described below with the aid of drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 NMR spectrum of 3,5-difluoroethylbenzene prepared for the display material of Example 2. DETAILED DESCRIPTION

[0038] The present application will be further described below, and it should be noted that the present embodiment is based on the technical solutions, and detailed implementation methods and specific operation processes are given, but the present application is not limited to the present embodiment.

[0039] Example 1

[0040] The present embodiment provides a preparation method of 3,5-difluoroethylbenzene crude product, and the specific steps are shown in Table 1.

[0041] Table 1 Preparation steps of 3,5-difluoroethylbenzene crude product

[0042]

[0043]

[0044]

[0045] Example 2

[0046] The present embodiment provides a process for purifying the 3,5-difluoroethylbenzene crude product of Example 1 to prepare 3,5-difluoroethylbenzene for display material, and the specific steps are shown in Table 2.

[0047] Table 2 Preparation steps of 3,5-difluoroethylbenzene for display material

[0048]

[0049]

[0050]

[0051] The prepared 3,5-difluoroethylbenzene for display material was tested by NMR spectrum, and the test results are shown in Figure 1 ,Figure 1 As can be seen, the product has been successfully synthesized.

[0052] A novel purification process for the crude 3,5-difluoroethylbenzene product is proposed in the present application, which replaces the distillation method in the prior art. The core of the present application is a multi-step synergistic purification mechanism, specifically including water vapor distillation, Grignard bromine removal, four-stage countercurrent water washing, alkali washing, and low-temperature rectification. Each step has its specific role. The water vapor distillation is azeotropic breaking below 100℃, which separates tetrahydrofuran and bromoethane. The Grignard bromine removal utilizes the reaction of bromoethane and magnesium chips to generate ethylmagnesium bromide, and the removal rate of bromide in the product is >98%, specifically from 0.1% to below 0.02%. The four-stage countercurrent water washing is used to remove metal ions such as MgBr2 / CuCl2 / LiCl by gradient, and the metal ion content in the product is reduced by 90%, specifically from 500ppm to below 50ppm. The alkali washing mainly utilizes the reaction of hydrochloric acid and sodium hydroxide to reduce the acid value, and the acid value in the product is reduced by 90%, from 0.5mg KOH / g to 0.05mg KOH / g. The low-temperature rectification is mainly carried out at 130-140℃ to avoid the thermal decomposition window (>135℃), and the product yield is increased by 33%, from 60% to 80%.

[0053] Comparative Example 1

[0054] Using the synthesis method in Chinese patent CN118108571A, 3,5-difluoroethylbenzene was prepared, and the specific process was as follows:

[0055] Device: nitrogen-protected three-necked flask (with condenser, thermometer, dropping funnel).

[0056] (1) Preparation of Grignard reagent (3,5-difluorophenylmagnesium bromide)

[0057] Initiation of reaction: add magnesium strip (particle size ≤4×3×2mm, metallic luster) and anhydrous tetrahydrofuran (THF), with mass ratio of magnesium strip: THF = 1:15, warm up to 60℃, and add 4.5% of the total amount of 3,5-difluorobromobenzene to initiate the reaction (sign: liquid surface bubbles increase, reflux accelerates).

[0058] Main reaction: slowly add the remaining 95.5% of 3,5-difluorobromobenzene (molar ratio of magnesium: raw material = 1:1.3), control the temperature at 55℃. After dropping, warm up to 65℃, react for 6 hours, naturally cool to room temperature, and transfer the Grignard reagent under nitrogen protection.

[0059] (2) Alkylation reaction (preparation of crude product)

[0060] Reaction system: Another nitrogen-protected flask was added with bromoethane, lithium halide (LiCl / LiBr), cuprous halide (CuCl / CuBr). According to the molar ratio, Grignard reagent: bromoethane = 1:1.4; the amount of lithium halide / cuprous halide was 1 / 10 of the Grignard reagent.

[0061] Dropwise addition control: The Grignard reagent was slowly added through a dropping funnel, and the flow rate was adjusted to prevent violent reflux. The temperature was kept at 60°C, and the reaction was continued for 6 hours.

[0062] Post-treatment: After cooling, concentrated hydrochloric acid was added dropwise to quench (according to the weight ratio, concentrated hydrochloric acid: Grignard reagent = 1:12), and weak reflux was maintained. The upper organic phase was washed with 1.0 mol / L NaOH / KOH solution (according to the volume ratio, organic phase: lye = 2.5:1), and anhydrous sodium sulfate was used for drying overnight.

[0063] (3) Distillation purification

[0064] Initial distillation: The crude product was heated and distilled, and the fraction collected at 55-74°C was recovered (THF was recycled).

[0065] Product collection: The temperature was raised to 128-135°C, and the distillate was the target product 3,5-difluoroethylbenzene (boiling point 127.5°C, 760 mmHg).

[0066] Comparative Example 2

[0067] The difference between this comparative example and Example 2 is that the format bromination step is omitted, and the specific process is as follows:

[0068] (1) Grignard reaction control

[0069] Feeding: 26.6 kg of magnesium chips was added to the kettle, steam heating was started, 160 kg of tetrahydrofuran was added, heating was started to raise the temperature to about 60°C, and slow reflux was started.

[0070] Initiation: 6 kg of 3,5-difluorobromobenzene was added to initiate, after successful initiation, the reflux was slowed down, and 160 kg of THF was added.

[0071] (2) Alkylation reaction

[0072] Feeding: 194 kg of 3,5-difluorobromobenzene was added through a high tank, which took about 3 hours to complete, and about 40 kg of THF was used to flush the high tank twice after feeding was completed. After feeding, the temperature was kept constant for 4 hours. Sampling, hydrolysis, and detection were qualified (raw material 3,5-difluorobromobenzene <0.15%), and the next step was carried out.

[0073] Feeding: 13 kg of bromoethane was added through a diaphragm pump, and after stirring for 30 minutes, 150 kg of bromoethane was added, 3.3 kg of anhydrous lithium chloride and 6.2 kg of cuprous chloride were added through the tank opening, and after feeding was completed, the tank opening was covered.

[0074] Cooling: first slowly pass water to cool to 40℃, then use frozen liquid to cool to 15℃.

[0075] Hydrolysis: add 206 kg of water from the high tank, then add 45 kg of hydrochloric acid.

[0076] Separation: separate the lower water into a 3# 1500L porcelain kettle, neutralize with a small amount of sodium hydroxide, and then treat.

[0077] (3) Impurity removal, four times of water washing: completely remove inorganic salts and water-soluble impurities.

[0078] (4) Distillation:

[0079] Steam distillation: transfer the organic phase of the previous step into a 1# porcelain kettle, heat with steam in the jacket, add 300 kg of water in the kettle, start steam distillation, and transfer the oil-water mixture into a 2# 1000L stainless steel kettle.

[0080] Rectification: divide the feed liquid into about 9 bottles, add to a 20L three-neck distillation flask for atmospheric rectification, add about 17 kg of feed liquid per bottle, collect the main fraction until the top temperature stabilizes in the range of 130-140℃, and the collected main fraction is the product.

[0081] Test example

[0082] The products obtained from Example 2 and Comparative Examples 1-2 were subjected to performance testing, and the test results are shown in Table 3.

[0083] Table 3 Product performance test results

[0084]

[0085] As can be seen from Table 3, the specific purification method of the crude product in the present application can significantly reduce the bromide residue, metal ion content and other impurities in the final product, and also can improve the product yield to a certain extent. In addition, more importantly, the product can maintain its color almost without yellowing at a relatively high temperature, which enables the product 3,5-difluoroethylbenzene to be applied to high-end products such as display materials, thereby expanding the application range of the product.

[0086] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit them. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can still be modified or equivalently replaced, and these modifications or equivalent replacements should not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for producing 3,5-difluoroethylbenzene for a display material, characterized by: The method comprises the following steps: S1: preparing 3,5-difluoroethylbenzene crude product; S2: adding magnesium chips into methanol for water vapor heating; S3: adding 3,5-difluoroethylbenzene crude product into step S2 to initiate Grignard reaction, after successful initiation, adding magnesium chips to continue stirring and heat preservation reaction to obtain a liquid; S4: after cooling, hydrolysis, washing, separation and drying of the liquid, an organic phase is obtained; S5: performing normal pressure rectification on the organic phase to collect main fraction, which is 3,5-difluoroethylbenzene refined product.

2. The method for preparing 3,5-difluoroethylbenzene for display materials according to claim 1, characterized in that: In step S1, the specific steps for preparing 3,5-difluoroethylbenzene crude product are as follows: S11: adding magnesium chips and tetrahydrofuran into a reaction kettle for water vapor heating, and after heating to 55-75℃, slowly refluxing; S12: stopping heating, adding part of 3,5-difluorobromobenzene into the reaction kettle to initiate Grignard reaction, after successful initiation, slowing down refluxing, and continuously adding tetrahydrofuran; S13: continuously adding the remaining 3,5-difluorobromobenzene into the reaction kettle, and after adding, heat preservation and stirring for reaction; S14: adding part of bromoethane into the reaction kettle, stirring, then adding the remaining bromoethane, lithium chloride and cuprous chloride for continuous reaction, and after reaction completion, obtaining a reaction liquid; S15: after hydrolysis, separation, multiple washing and separation of the reaction liquid, an intermediate product is obtained; S16: after water vapor distillation and normal pressure rectification of the intermediate product, main fraction is collected, and after alkali washing and drying of the main fraction, 3,5-difluoroethylbenzene crude product is obtained.

3. The method for preparing 3,5-difluoroethylbenzene for display materials according to claim 2, characterized in that: In step S1, the mass ratio of magnesium chips and 3,5-difluorobromobenzene is 1:(6-9).

4. The method for preparing 3,5-difluoroethylbenzene for display materials according to claim 2, characterized in that: In step S1, the mass ratio of 3,5-difluorobromobenzene and bromoethane is (1-1.5):1, the mass ratio of bromoethane and lithium chloride is (48-50):1, and the mass ratio of bromoethane and cuprous chloride is (25-28):

1.

5. The method for preparing 3,5-difluoroethylbenzene for display materials according to claim 2, characterized in that: In step S1, the temperature in the bottle is controlled to be not more than 100℃ during normal pressure distillation, main fraction is collected, the top temperature is not more than 80℃, and when the temperature exceeds 72℃, the distillation is stopped.

6. The method for preparing 3,5-difluoroethylbenzene for display materials according to claim 2, characterized in that: In step S1, the GC purity of 3,5-difluoroethylbenzene crude product is 80%, and the bromide residue is ≥0.3%.

7. The method for preparing 3,5-difluoroethylbenzene for display materials according to claim 1, characterized in that: In step S2, the amount of magnesium chips added is 1-3% of 3,5-difluoroethylbenzene crude product, and in step S3, the amount of magnesium chips added is 0.1-0.3% of 3,5-difluoroethylbenzene crude product; In step S2, the water vapor heating temperature is 55-75℃.

8. The method for preparing 3,5-difluoroethylbenzene for display materials according to claim 1, characterized in that: In step S4, the liquid is cooled to 40℃ by cooling water, then water and hydrochloric acid are added to the liquid for stirring hydrolysis, then water and sodium bicarbonate are added for washing, after washing, the lower organic phase is obtained by standing and separation, and anhydrous sodium sulfate is added to the organic phase for drying to obtain dried organic phase.

9. The method for preparing 3,5-difluoroethylbenzene for display materials according to claim 1, characterized in that: In step S5, the temperature in the bottle is controlled to be not more than 170℃ during normal pressure rectification, the top temperature is not more than 150℃, the front fraction is collected, and the main fraction is collected until the top temperature is stable at 130-140℃.

10. The method for preparing 3,5-difluoroethylbenzene for display materials according to claim 9, characterized in that: In step S5, the 3,5-difluoroethylbenzene product is a colorless transparent liquid, GC > 99.5%, solvent < 0.2%, raw material < 0.02%, maximum impurities < 0.1%, moisture < 0.1%, metal ions < 50 ppm, acid value < 0.05 mg KOH / g, bromide residue < 0.01%, and no color change after storage for 30 days at 60°C.

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