New process for ultra-pure TFT negative monomer liquid crystal for large-size panels

Abstract

The present invention relates to the technical field of optoelectronic materials, and in particular to a new process for ultrapure TFT negative monomer liquid crystals for large-size panels. The process comprises the following steps: S1.1, preparing 4-chlorophenylcyclohexanecarboxaldehyde from 4-(4-chlorophenyl)cyclohexanecarboxylic acid; S1.2, performing protective treatment on the 4-chlorophenylcyclohexanecarboxaldehyde, and preparing 4-alkylbiphenylcyclohexanecarboxaldehyde from the 4-chlorophenylcyclohexanecarboxaldehyde; S1.3, preparing a negative monomer liquid crystal; and using a loaded reducing agent to directly reduce the 4-(4-chlorophenyl)cyclohexanecarboxylic acid to 4-chlorophenylcyclohexanecarboxaldehyde without the need for over-reduction and subsequent back-oxidation, thereby reducing the two-step reaction required in the traditional process to one step, making the preparation process simpler and more convenient.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic materials, and in particular to a new process for producing ultrapure TFT negative monomer liquid crystals for large-size panels. Background Art

[0002] The larger the panel size, the higher the requirements for the quality stability and technological maturity of the liquid crystal material. The liquid crystal materials used in TFT-LCD are different from traditional liquid crystal materials. In addition to requiring good physical and chemical stability and a wide operating temperature range, they must also have a high resistivity, generally required to be at least greater than 1012Ω·cm. The liquid crystal molecules will change their arrangement state under the influence of voltage and can cause the incident light to deflect. When the negative monomer liquid crystal displays a pure black image on the screen, the horizontal liquid crystal molecules can better block most of the light emitted by the backlight, making the screen display black purer and deeper. During the power-on process, the liquid crystal molecules deflect to the vertical direction, which allows more light to pass through, thereby achieving the effect of improving the screen brightness. The combination of these two will ultimately lead to an overall improvement in screen brightness, clarity, and contrast. Currently, negative liquid crystal technology has become the preferred LCD screen solution for mainstream manufacturers. However, the common problems faced by negative liquid crystal materials are high viscosity, slow response time, low resistivity, and low reliability in terms of VHR and Ion. It is these defects that limit the application of negative liquid crystal in displays, especially in large-size FFS. TV remains a major technical challenge, so the development of TFT-LCD negative liquid crystal materials with low viscosity, fast response and high reliability suitable for large-size panels is of great significance. However, research on the preparation of such monomer liquid crystals is quite scarce at home and abroad, and there are few literature reports. In view of this, we propose a new process for ultra-pure TFT negative monomer liquid crystals for large-size panels. Summary of the Invention

[0003] The object of the present invention is to provide a new process for producing ultrapure TFT negative monomer liquid crystals for large-size panels, so as to solve the problems raised in the above-mentioned background technology.

[0004] To achieve the above objectives, the present invention provides a new process for producing ultrapure TFT negative monomer liquid crystals for large-size panels. S1.1: Under argon protection, tetrahydrofuran is added to 4-(4-chlorophenyl)cyclohexanecarboxylic acid to form a clear solution with a concentration of 0.1-0.5 M. The reaction apparatus is transferred to a dry ice / acetone bath and rapidly cooled to -75-78°C. A loaded reducing agent is then added while maintaining continuous stirring. The reaction is continued for 2-4 hours, and 4-chlorophenylcyclohexanecarboxaldehyde is obtained after treatment.

[0005] S1.2. 4-chlorophenylcyclohexanecarboxaldehyde is pretreated to an acetal solution. Under anhydrous and oxygen-free conditions, the acetal solution and 4-alkylphenylboronic acid are added to N,N-dimethylformamide, and palladium acetate and potassium carbonate are added. The reaction mixture is heated to 110-120°C and maintained for 8-10 hours. After the reaction is completed, it is allowed to cool to room temperature, quenched with water, filtered, extracted, and concentrated to obtain substance A. The acetal is then deprotected to obtain 4-alkylbiphenylcyclohexanecarboxaldehyde.

[0006] S1.3. Under argon protection, bromoethane triphenylphosphine salt is mixed with potassium tert-butoxide and cooled to 0-5°C in an ice bath. Then, pre-cooled anhydrous tetrahydrofuran is added dropwise to form an orange-red solution. The orange-red solution is dropped into 4-alkylbiphenylcyclohexanecarboxaldehyde through a dropping funnel. The reaction temperature is 0-5°C, the time is 1-2h, and stirring is continued. After the reaction is completed, a negative monomer liquid crystal is obtained after treatment.

[0007] Preferably, in S1.1, the mass ratio of 4-(4-chlorophenyl)cyclohexanecarboxylic acid to the supported reducing agent is 1:0.64-0.82.

[0008] Preferably, in S1.2, the specific steps of pre-treating 4-chlorophenylcyclohexanecarboxaldehyde to form an acetal solution are:

[0009] Under the protection of inert gas argon, 4-chlorophenylcyclohexanecarboxaldehyde is dissolved in ethanol to form a solution with a concentration of 41.7-43.5 mg / mL, and dihydropyran is added and stirred at room temperature for 1-3 hours, wherein the molar ratio of 4-chlorophenylcyclohexanecarboxaldehyde to dihydropyran is 1:1.1-1.5, and an acetal solution is obtained after treatment.

[0010] Preferably, in S1.2, the mass ratio of the acetal solution to the 4-alkylphenylboric acid is 1.5:0.8-1.1, and the mass of N,N-dimethylformamide is 3-5 times the total mass of the acetal solution and the 4-alkylphenylboric acid.

[0011] Preferably, in S1.2, the molar ratio of palladium acetate, potassium carbonate and acetal solution is 0.01-0.05:2-3:1.

[0012] Preferably, in S1.2, the specific steps of acetal deprotection are:

[0013] p-Toluenesulfonic acid is added to substance A, wherein the mass ratio of substance A to p-toluenesulfonic acid is 5:0.3-0.6. After stirring at room temperature for 2-4 hours, a saturated sodium bicarbonate aqueous solution is added dropwise to neutralize the pH, and finally extraction, concentration and purification are performed.

[0014] Preferably, in S1.3, the mass ratio of bromoethane triphenylphosphine, potassium tert-butoxide and 4-alkylbiphenylcyclohexanecarboxaldehyde is 3.5-3.7:1:2.7-2.9; and the amount of anhydrous tetrahydrofuran added is 1-3 times the total volume of bromoethane triphenylphosphine and potassium tert-butoxide.

[0015] Preferably, the steps of preparing the loaded reducing agent are specifically as follows:

[0016] The silica gel was dried, and under the protection of inert gas, diisobutylaluminum hydride was added dropwise onto the silica gel, allowed to stand for 2-4 hours, and dried to obtain the supported reducing agent.

[0017] Preferably, the silica gel particle size ranges from 60 to 120 mesh, and the silica gel pore size ranges from 200 to 300Å.

[0018] Preferably, the loading amount of the loaded reducing agent is 5%-10%.

[0019] Compared with conventional strong reducing agents such as lithium aluminum tetrahydride and sodium borohydride, diisobutylaluminum hydride has a more stable and mild reducing property. In order to achieve the selective reduction of carboxylic acid to aldehyde group, diisobutylaluminum hydride is loaded on silica gel. Since silica gel is a porous material with a large specific surface area and uniformly distributed microporous structure, diisobutylaluminum hydride can be adsorbed on its surface or inside the micropores. On the one hand, its overall activity is reduced through spatial restriction and dispersion. On the other hand, since silica gel is a solid carrier, the loaded diisobutylaluminum hydride can be separated from the reaction system by simple filtration operation, which is convenient for recycling and reuse.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] In the new process for ultra-pure TFT negative monomer liquid crystal for large-size panels, a loaded reducing agent is used. The porous structure of silica gel is utilized to adsorb diisobutylaluminum hydride on the surface of silica gel and inside the micropores. The reducing ability of diisobutylaluminum hydride is reduced through steric hindrance and dispersion, so that the carboxyl group is selectively reduced to an aldehyde group, avoiding a one-time reduction to a hydroxyl group. Compared with the traditional preparation process, the synthesis route is shortened. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0023] The new process of the present invention for ultra-pure TFT negative monomer liquid crystal for large-size panels:

[0024] S1.1. Under argon, add tetrahydrofuran to 4-(4-chlorophenyl)cyclohexanecarboxylic acid to form a clear solution with a concentration of 0.1-0.5 M. Transfer the reaction apparatus to a dry ice / acetone bath and rapidly cool to -75-78°C. Then, add the loaded reducing agent while maintaining continuous stirring. The reaction is continued for 2-4 hours to obtain 4-chlorophenylcyclohexanecarboxaldehyde.

[0025] S1.2. 4-chlorophenylcyclohexanecarboxaldehyde is pretreated to an acetal solution. Under anhydrous and oxygen-free conditions, the acetal solution and 4-alkylphenylboronic acid are added to N,N-dimethylformamide, and palladium acetate and potassium carbonate are added. The reaction mixture is heated to 110-120°C and maintained for 8-10 hours. After the reaction is completed, it is allowed to cool to room temperature, quenched with water, filtered, extracted, and concentrated to obtain substance A. The acetal is then deprotected to obtain 4-alkylbiphenylcyclohexanecarboxaldehyde.

[0026] S1.3. Under argon protection, bromoethane triphenylphosphine salt is mixed with potassium tert-butoxide and cooled to 0-5°C in an ice bath. Then, pre-cooled anhydrous tetrahydrofuran is added dropwise to form an orange-red solution. The orange-red solution is dropped into 4-alkylbiphenylcyclohexanecarboxaldehyde through a dropping funnel. The reaction temperature is 0-5°C, the time is 1-2h, and stirring is continued. After the reaction is completed, a negative monomer liquid crystal is obtained after treatment.

[0027] Example 1: A new process for producing ultra-pure TFT negative monomer liquid crystal for large-size panels, comprising the following steps:

[0028] S1.1. Under argon, tetrahydrofuran was added to 4-(4-chlorophenyl)cyclohexanecarboxylic acid to form a clear solution with a concentration of 0.5 M. The reaction apparatus was transferred to a dry ice / acetone bath and rapidly cooled to -78°C. The loaded reducing agent was then added while maintaining continuous stirring. The reaction was continued for 4 h to obtain 4-chlorophenylcyclohexanecarboxaldehyde.

[0029] The mass ratio of 4-(4-chlorophenyl)cyclohexanecarboxylic acid to the loaded reducing agent is 1:0.64; the mass ratio of the acetal solution to 4-alkylphenylboronic acid is 1.5:1.1, the mass of N,N-dimethylformamide is 5 times the total mass of the acetal solution and 4-alkylphenylboronic acid; the molar ratio of palladium acetate, potassium carbonate, and acetal solution is 0.05:3:1; the mass ratio of bromoethane triphenylphosphine salt, potassium tert-butoxide, and 4-alkylbiphenylcyclohexanecarboxaldehyde is 3.7:1:2.9; and the amount of anhydrous tetrahydrofuran added is 3 times the total volume of bromoethane triphenylphosphine salt and potassium tert-butoxide.

[0030] S1.2. Under the protection of inert gas argon, 4-chlorophenylcyclohexanecarboxaldehyde was dissolved in ethanol to form a solution with a concentration of 43.5 mg / mL, and dihydropyran was added and stirred at room temperature for 3 hours, wherein the molar ratio of 4-chlorophenylcyclohexanecarboxaldehyde to dihydropyran was 1:1.2. After treatment, an acetal solution was obtained. Under anhydrous and oxygen-free conditions, the acetal solution and 4-alkylphenylboronic acid were added to N,N-dimethylformamide, and palladium acetate and potassium carbonate were added. The reaction mixture was heated to 120°C and maintained for 10 hours. After the reaction was completed, it was allowed to cool to room temperature, quenched with water, filtered, extracted and concentrated to obtain substance A. p-Toluenesulfonic acid was added to substance A, wherein the mass ratio of substance A to p-toluenesulfonic acid was 5:0.6. After stirring at room temperature for 4 hours, a saturated sodium bicarbonate aqueous solution was added dropwise to neutralize the pH. Finally, extraction, concentration and purification were performed, and then the acetal was deprotected to obtain 4-alkylbiphenylcyclohexanecarboxaldehyde.

[0031] Silica gel with a particle size of 100 mesh and a pore size of 200Å was dried. Under the protection of inert gas, diisobutylaluminum hydride was added dropwise onto the silica gel, allowed to stand for 2 hours, and dried to obtain a loaded reducing agent with a loading amount of 7%;

[0032] S1.3. Under argon protection, bromoethane triphenylphosphine salt is mixed with potassium tert-butoxide and cooled to 5°C in an ice bath. Then, pre-cooled anhydrous tetrahydrofuran is added dropwise to form an orange-red solution. The orange-red solution is dropped into 4-alkylbiphenylcyclohexanecarboxaldehyde through a dropping funnel. The reaction temperature is 3°C, the time is 2h, and stirring is continued. After the reaction is completed, a negative monomer liquid crystal is obtained after treatment.

[0033] Example 2: A new process for producing ultrapure TFT negative monomer liquid crystal for large-size panels, comprising the following steps:

[0034] S1.1. Under argon, tetrahydrofuran was added to 4-(4-chlorophenyl)cyclohexanecarboxylic acid to form a clear solution with a concentration of 0.5 M. The reaction apparatus was transferred to a dry ice / acetone bath and rapidly cooled to -78°C. The loaded reducing agent was then added while maintaining continuous stirring. The reaction was continued for 4 h to obtain 4-chlorophenylcyclohexanecarboxaldehyde.

[0035] The mass ratio of 4-(4-chlorophenyl)cyclohexanecarboxylic acid to the loaded reducing agent is 1:0.73; the mass ratio of the acetal solution to 4-alkylphenylboronic acid is 1.5:1.1, the mass of N,N-dimethylformamide is 5 times the total mass of the acetal solution and 4-alkylphenylboronic acid; the molar ratio of palladium acetate, potassium carbonate, and acetal solution is 0.05:3:1; the mass ratio of bromoethane triphenylphosphine salt, potassium tert-butoxide, and 4-alkylbiphenylcyclohexanecarboxaldehyde is 3.7:1:2.9; and the amount of anhydrous tetrahydrofuran added is 3 times the total volume of bromoethane triphenylphosphine salt and potassium tert-butoxide.

[0036] S1.2. Under the protection of inert gas argon, 4-chlorophenylcyclohexanecarboxaldehyde was dissolved in ethanol to form a solution with a concentration of 43.5 mg / mL, and dihydropyran was added and stirred at room temperature for 3 hours, wherein the molar ratio of 4-chlorophenylcyclohexanecarboxaldehyde to dihydropyran was 1:1.2. After treatment, an acetal solution was obtained. Under anhydrous and oxygen-free conditions, the acetal solution and 4-alkylphenylboronic acid were added to N,N-dimethylformamide, and palladium acetate and potassium carbonate were added. The reaction mixture was heated to 120°C and maintained for 10 hours. After the reaction was completed, it was allowed to cool to room temperature, quenched with water, filtered, extracted and concentrated to obtain substance A. p-Toluenesulfonic acid was added to substance A, wherein the mass ratio of substance A to p-toluenesulfonic acid was 5:0.6. After stirring at room temperature for 4 hours, a saturated sodium bicarbonate aqueous solution was added dropwise to neutralize the pH. Finally, extraction, concentration and purification were performed, and then the acetal was deprotected to obtain 4-alkylbiphenylcyclohexanecarboxaldehyde.

[0037] Silica gel with a particle size of 100 mesh and a pore size of 200Å was dried. Under the protection of inert gas, diisobutylaluminum hydride was added dropwise onto the silica gel, allowed to stand for 2 hours, and dried to obtain a loaded reducing agent with a loading amount of 7%;

[0038] S1.3. Under argon protection, bromoethane triphenylphosphine salt is mixed with potassium tert-butoxide and cooled to 5°C in an ice bath. Then, pre-cooled anhydrous tetrahydrofuran is added dropwise to form an orange-red solution. The orange-red solution is dropped into 4-alkylbiphenylcyclohexanecarboxaldehyde through a dropping funnel. The reaction temperature is 3°C, the time is 2h, and stirring is continued. After the reaction is completed, a negative monomer liquid crystal is obtained after treatment.

[0039] Example 3: A new process for producing ultrapure TFT negative monomer liquid crystal for large-size panels, comprising the following steps:

[0040] S1.1. Under argon, tetrahydrofuran was added to 4-(4-chlorophenyl)cyclohexanecarboxylic acid to form a clear solution with a concentration of 0.5 M. The reaction apparatus was transferred to a dry ice / acetone bath and rapidly cooled to -78°C. The loaded reducing agent was then added while maintaining continuous stirring. The reaction was continued for 4 h to obtain 4-chlorophenylcyclohexanecarboxaldehyde.

[0041] The mass ratio of 4-(4-chlorophenyl)cyclohexanecarboxylic acid to the loaded reducing agent is 1:0.82; the mass ratio of the acetal solution to 4-alkylphenylboronic acid is 1.5:1.1, the mass of N,N-dimethylformamide is 5 times the total mass of the acetal solution and 4-alkylphenylboronic acid; the molar ratio of palladium acetate, potassium carbonate, and acetal solution is 0.05:3:1; the mass ratio of bromoethane triphenylphosphine salt, potassium tert-butoxide, and 4-alkylbiphenylcyclohexanecarboxaldehyde is 3.7:1:2.9; and the amount of anhydrous tetrahydrofuran added is 3 times the total volume of bromoethane triphenylphosphine salt and potassium tert-butoxide.

[0042] S1.2. Under the protection of inert gas argon, 4-chlorophenylcyclohexanecarboxaldehyde was dissolved in ethanol to form a solution with a concentration of 43.5 mg / mL, and dihydropyran was added and stirred at room temperature for 3 hours, wherein the molar ratio of 4-chlorophenylcyclohexanecarboxaldehyde to dihydropyran was 1:1.2. After treatment, an acetal solution was obtained. Under anhydrous and oxygen-free conditions, the acetal solution and 4-alkylphenylboronic acid were added to N,N-dimethylformamide, and palladium acetate and potassium carbonate were added. The reaction mixture was heated to 120°C and maintained for 10 hours. After the reaction was completed, it was allowed to cool to room temperature, quenched with water, filtered, extracted and concentrated to obtain substance A. p-Toluenesulfonic acid was added to substance A, wherein the mass ratio of substance A to p-toluenesulfonic acid was 5:0.6. After stirring at room temperature for 4 hours, a saturated sodium bicarbonate aqueous solution was added dropwise to neutralize the pH. Finally, extraction, concentration and purification were performed, and then the acetal was deprotected to obtain 4-alkylbiphenylcyclohexanecarboxaldehyde.

[0043] Silica gel with a particle size of 100 mesh and a pore size of 200Å was dried. Under the protection of inert gas, diisobutylaluminum hydride was added dropwise onto the silica gel, allowed to stand for 2 hours, and dried to obtain a loaded reducing agent with a loading amount of 7%;

[0044] S1.3. Under argon protection, bromoethane triphenylphosphine salt is mixed with potassium tert-butoxide and cooled to 5°C in an ice bath. Then, pre-cooled anhydrous tetrahydrofuran is added dropwise to form an orange-red solution. The orange-red solution is dropped into 4-alkylbiphenylcyclohexanecarboxaldehyde through a dropping funnel. The reaction temperature is 3°C, the time is 2h, and stirring is continued. After the reaction is completed, a negative monomer liquid crystal is obtained after treatment.

[0045] Example 4: A new process for producing ultrapure TFT negative monomer liquid crystal for large-size panels, comprising the following steps:

[0046] S1.1. Under argon, tetrahydrofuran was added to 4-(4-chlorophenyl)cyclohexanecarboxylic acid to form a clear solution with a concentration of 0.5 M. The reaction apparatus was transferred to a dry ice / acetone bath and rapidly cooled to -78°C. The loaded reducing agent was then added while maintaining continuous stirring. The reaction was continued for 4 h to obtain 4-chlorophenylcyclohexanecarboxaldehyde.

[0047] The mass ratio of 4-(4-chlorophenyl)cyclohexanecarboxylic acid to the loaded reducing agent is 1:0.82; the mass ratio of the acetal solution to 4-alkylphenylboronic acid is 1.5:0.8, the mass of N,N-dimethylformamide is 3 times the total mass of the acetal solution and 4-alkylphenylboronic acid; the molar ratio of palladium acetate, potassium carbonate, and acetal solution is 0.01:2:1; the mass ratio of bromoethane triphenylphosphine salt, potassium tert-butoxide, and 4-alkylbiphenylcyclohexanecarboxaldehyde is 3.5:1:2.7; and the amount of anhydrous tetrahydrofuran added is 1 times the total volume of bromoethane triphenylphosphine salt and potassium tert-butoxide.

[0048] S1.2. Under the protection of inert gas argon, 4-chlorophenylcyclohexanecarboxaldehyde was dissolved in ethanol to form a solution with a concentration of 43.5 mg / mL, and dihydropyran was added and stirred at room temperature for 3 hours, wherein the molar ratio of 4-chlorophenylcyclohexanecarboxaldehyde to dihydropyran was 1:1.2. After treatment, an acetal solution was obtained. Under anhydrous and oxygen-free conditions, the acetal solution and 4-alkylphenylboronic acid were added to N,N-dimethylformamide, and palladium acetate and potassium carbonate were added. The reaction mixture was heated to 120°C and maintained for 10 hours. After the reaction was completed, it was allowed to cool to room temperature, quenched with water, filtered, extracted and concentrated to obtain substance A. p-Toluenesulfonic acid was added to substance A, wherein the mass ratio of substance A to p-toluenesulfonic acid was 5:0.6. After stirring at room temperature for 4 hours, a saturated sodium bicarbonate aqueous solution was added dropwise to neutralize the pH. Finally, extraction, concentration and purification were performed, and then the acetal was deprotected to obtain 4-alkylbiphenylcyclohexanecarboxaldehyde.

[0049] Silica gel with a particle size of 100 mesh and a pore size of 200Å was dried. Under the protection of inert gas, diisobutylaluminum hydride was added dropwise onto the silica gel, allowed to stand for 2 hours, and dried to obtain a loaded reducing agent with a loading amount of 7%;

[0050] S1.3. Under argon protection, bromoethane triphenylphosphine salt is mixed with potassium tert-butoxide and cooled to 5°C in an ice bath. Then, pre-cooled anhydrous tetrahydrofuran is added dropwise to form an orange-red solution. The orange-red solution is dropped into 4-alkylbiphenylcyclohexanecarboxaldehyde through a dropping funnel. The reaction temperature is 3°C, the time is 2h, and stirring is continued. After the reaction is completed, a negative monomer liquid crystal is obtained after treatment.

[0051] Comparative Example 1: The method of Example 3 was adopted, and diisobutylaluminum hydride was directly used without modifying the diisobutylaluminum hydride by silica gel.

[0052] The present invention uses a loaded reducing agent to prepare ultrapure TFT negative monomer liquid crystal for large-size panels. The performance index inspection items and inspection standards of the ultrapure TFT negative monomer liquid crystal for large-size panels are as follows:

[0053] Yield refers to the molar percentage of the target product relative to the starting material. Specifically, it measures the ratio between the actual amount of target product produced in a chemical reaction and the theoretical maximum possible amount produced. Yield is usually expressed as a percentage. The purified 4-chlorophenylcyclohexanecarboxaldehyde is weighed and the yield (%) is calculated as (the actual mass of the target product produced) / (theoretical mass of the target product produced) × 100%. A high yield indicates that the reaction conditions are well optimized, the catalyst or reagent is appropriately selected, and there are fewer side reactions. A low yield may mean that the reaction conditions are not ideal, or there are many side reactions, resulting in some substrates not being converted into the target product.

[0054] The ultrapure TFT negative monomer liquid crystals for large-size panels prepared in Examples 1-4 and Comparative Example 1 were tested using the above standards. The obtained data are shown in Table 1:

[0055] Table 1 Performance data of Examples 1-4 and Comparative Example 1

[0056]

[0057] The above data fully demonstrate that Examples 1-4, compared with Comparative Example 1, can fully demonstrate the effect of the loaded reducing agent on the selective reduction of ultra-pure TFT negative monomer liquid crystal for large-size panels.

[0058] Since the present invention adopts a loaded reducing agent to prepare ultrapure TFT negative monomer liquid crystal for large-size panels, the loading reducing agent effectively improves the selective reduction of ultrapure TFT negative monomer liquid crystal for large-size panels, as follows:

[0059] It can be seen from Examples 1-3 that with the continuous increase in the content of the loaded reducing agent, the selective reduction of the negative monomer liquid crystal material is significantly improved. Since silica gel is a porous material with a large specific surface area and a uniformly distributed microporous structure, when diisobutylaluminum hydride is adsorbed on the silica gel surface or inside the micropores, due to spatial limitations, its active center is partially shielded, thereby reducing the overall reaction activity. This steric hindrance effect makes diisobutylaluminum hydride more inclined to react selectively with specific substrates without excessive reduction to the hydroxyl stage. In addition, the silica gel carrier can help diisobutylaluminum hydride to be better dispersed in the reaction system, reducing side reactions caused by excessive local concentration. Therefore, the selective reduction of the negative monomer liquid crystal material is significantly improved.

[0060] It can be seen from Examples 3 and 4 that with the continuous increase in the content of other components, the selective reduction of the negative monomer liquid crystal material does not change significantly, which shows that a small change in other components within a certain range is not sufficient to significantly affect the yield of the negative monomer liquid crystal material.

[0061] According to the above test experiments, the ultrapure TFT negative monomer liquid crystal for large-size panels prepared according to Example 3 has the best performance, so Example 3 is regarded as the best example;

[0062] By comparing Example 3 with Comparative Example 1, it can be seen that:

[0063] In Comparative Example 1, diisobutylaluminum hydride was directly used without modification by silica gel, and the selective reduction of the negative monomer liquid crystal material was poor. This was because the unloaded diisobutylaluminum hydride was not restricted by steric hindrance and dispersion effects and was more prone to over-reduction. In addition, the unloaded diisobutylaluminum hydride had a local high concentration area in the solution, which increased the probability of side reactions and resulted in lower selectivity.

[0064] In summary, a higher selective reduction effect is achieved by silica gel-supported diisobutylaluminum hydride, which is mainly due to the steric hindrance, dispersion effect, stability and easy recycling provided by silica gel. In contrast, unsupported diisobutylaluminum hydride is prone to induce side reactions due to its reactivity and dispersion distribution problems, resulting in lower selectivity. Therefore, the use of supported reducing agents has the advantages of simplifying the production process, improving efficiency, reducing by-product generation, and reducing production costs.

[0065] The basic principles, main features, and advantages of the present invention are shown and described above. It should be understood by those skilled in the art that the present invention is not limited to the above-described embodiments. The above-described embodiments and descriptions are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention claimed.

Claims

1. A process for preparing ultrapure TFT negative monomer liquid crystal for large-size panels, characterized by: S1.

1. Under argon, add tetrahydrofuran to 4-(4-chlorophenyl)cyclohexanecarboxylic acid to form a clear solution with a concentration of 0.1-0.5 M. Transfer the reaction apparatus to a dry ice / acetone bath and rapidly cool to -75-78°C. Then, add the loaded reducing agent while maintaining continuous stirring. The reaction is continued for 2-4 hours to obtain 4-chlorophenylcyclohexanecarboxaldehyde. S1.

2. 4-chlorophenylcyclohexanecarboxaldehyde is pretreated to an acetal solution. Under anhydrous and oxygen-free conditions, the acetal solution and 4-alkylphenylboronic acid are added to N,N-dimethylformamide, and palladium acetate and potassium carbonate are added. The reaction mixture is heated to 110-120°C and maintained for 8-10 hours. After the reaction is completed, it is allowed to cool to room temperature, quenched with water, filtered, extracted, and concentrated to obtain substance A. The acetal is then deprotected to obtain 4-alkylbiphenylcyclohexanecarboxaldehyde. S1.

3. Under argon protection, bromoethane triphenylphosphine salt and potassium tert-butoxide are mixed and cooled to 0-5°C in an ice bath. Pre-cooled anhydrous tetrahydrofuran is then added dropwise to form an orange-red solution. The orange-red solution is added dropwise to 4-alkylbiphenylcyclohexanecarboxaldehyde through a dropping funnel. The reaction temperature is 0-5°C for 1-2 hours with continuous stirring. After the reaction is complete, the negative monomer liquid crystal is obtained by treatment. The steps of preparing the loaded reducing agent are specifically as follows: The silica gel was dried, and under the protection of inert gas, diisobutylaluminum hydride was added dropwise onto the silica gel, allowed to stand for 2-4 hours, and dried to obtain the supported reducing agent.

2. The process for preparing ultrapure TFT negative monomer liquid crystal for large-size panels according to claim 1, characterized in that: In the above S1.1, the mass ratio of 4-(4-chlorophenyl)cyclohexanecarboxylic acid to the supported reducing agent is 1:0.64-0.

82.

3. The process for preparing ultrapure TFT negative monomer liquid crystal for large-size panels according to claim 1, characterized in that: In S1.2, the specific steps of pre-treating 4-chlorophenylcyclohexanecarboxaldehyde to form an acetal solution are: Under the protection of inert gas argon, 4-chlorophenylcyclohexanecarboxaldehyde is dissolved in ethanol to form a solution with a concentration of 41.7-43.5 mg / mL, and dihydropyran is added and stirred at room temperature for 1-3 hours, wherein the molar ratio of 4-chlorophenylcyclohexanecarboxaldehyde to dihydropyran is 1:1.1-1.5, and an acetal solution is obtained after treatment.

4. The process for preparing ultrapure TFT negative monomer liquid crystal for large-size panels according to claim 1, characterized in that: In S1.2, the mass ratio of the acetal solution to the 4-alkylphenylboric acid is 1.5:0.8-1.1, and the mass of N,N-dimethylformamide is 3-5 times the total mass of the acetal solution and the 4-alkylphenylboric acid.

5. The process for preparing ultrapure TFT negative monomer liquid crystal for large-size panels according to claim 1, characterized in that: In S1.2, the molar ratio of palladium acetate, potassium carbonate and acetal solution is 0.01-0.05:2-3:

1.

6. The process for preparing ultrapure TFT negative monomer liquid crystal for large-size panels according to claim 1, characterized in that: In S1.2, the specific steps of acetal deprotection are: p-Toluenesulfonic acid is added to substance A, wherein the mass ratio of substance A to p-toluenesulfonic acid is 5:0.3-0.

6. After stirring at room temperature for 2-4 hours, a saturated sodium bicarbonate aqueous solution is added dropwise to neutralize the pH, and finally extraction, concentration and purification are performed.

7. The process for preparing ultrapure TFT negative monomer liquid crystal for large-size panels according to claim 1, characterized in that: In S1.3, the mass ratio of bromoethane triphenylphosphine, potassium tert-butoxide and 4-alkylbiphenylcyclohexanecarboxaldehyde is 3.5-3.7:1:2.7-2.9; the amount of anhydrous tetrahydrofuran added is 1-3 times the total volume of bromoethane triphenylphosphine and potassium tert-butoxide.

8. The process for preparing ultrapure TFT negative monomer liquid crystal for large-size panels according to claim 1, characterized in that: The silica gel particle size ranges from 60 to 120 meshes, and the silica gel pore size ranges from 200 to 300 Å.

9. The process for preparing ultrapure TFT negative monomer liquid crystal for large-size panels according to claim 1, characterized in that: The loading amount of the loaded reducing agent is 5%-10%.

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