New technology of ultra-pure TFT negative monomer liquid crystal for large-size panel

Abstract

The invention relates to the technical field of photoelectric materials, in particular to a novel process of ultra-pure TFT (thin film transistor) negative monomer liquid crystal for a large-size panel, which comprises the following steps: S1.1, preparing 4-chlorophenyl cyclohexane formaldehyde from 4-(4-chlorophenyl) cyclohexanecarboxylic acid; S1.2, performing protection treatment on the 4-chlorophenyl cyclohexane formaldehyde, and preparing 4-alkyl biphenyl cyclohexane formaldehyde from the 4-chlorophenyl cyclohexane formaldehyde; s1.3, preparing a negative monomer liquid crystal; according to the preparation method, 4-(4-chlorphenyl) cyclohexanecarboxylic acid is directly reduced into 4-chlorphenyl cyclohexane formaldehyde by using a loaded reducing agent, and oxidation after excessive reduction is not needed, so that two-step reaction in a traditional process is reduced into one step, and the preparation process is simpler and more convenient.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic materials, and more specifically, to a new process for ultra-pure 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 liquid crystal materials. Liquid crystal materials for TFT-LCDs 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 requiring at least greater than 1012 Ω·cm. When liquid crystal molecules are affected by voltage, their arrangement state changes, and the incident light can be deflected. When the negative monomer liquid crystal displays a pure black picture on the screen, the liquid crystal molecules in the horizontal direction can better block most of the light emitted by the backlight source, making the screen display black more purely and deeply; during the power-on process, the liquid crystal molecules deflect to the vertical direction, which is conducive to more light passing through, thereby achieving the effect of enhancing the screen brightness. The combination of the two will ultimately bring an overall improvement in the screen display in terms of brightness, clarity, and contrast. Currently, the negative liquid crystal technology has become the preferred LCD screen solution for mainstream manufacturers. However, due to the problems commonly faced by negative liquid crystal materials, such as high viscosity, slow response time, low resistivity, and low reliability in terms of VHR and Ion, these defects limit the application of negative liquid crystals in displays. In particular, applying them to large-size FFS TVs is still a major technical problem. Therefore, it is of great significance to develop TFT-LCD negative liquid crystal materials with low viscosity, fast response, and high reliability suitable for large-size panels. However, the domestic and foreign research on the preparation of such monomer liquid crystals is quite scarce, 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 purpose of the present invention is to provide a new process for ultra-pure TFT negative monomer liquid crystals for large-size panels to solve the problems raised in the above background art.

[0004] To achieve the above purpose, the present invention provides a new process for ultra-pure TFT negative monomer liquid crystals for large-size panels. S1.1: Under argon protection, 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 device to a dry ice / acetone bath, quickly cool it to -75 to -78 °C, then add a supported reducing agent while maintaining continuous stirring. The reaction time is 2-4 h, and 4-chlorophenylcyclohexanecarbaldehyde is obtained after treatment. S1.2. Pretreat 4-chlorophenylcyclohexanecarbaldehyde to form an acetal solution. Under anhydrous and anaerobic conditions, add the acetal solution and 4-alkylbenzeneboronic acid to N,N-dimethylformamide, and add palladium acetate and potassium carbonate. Heat the reaction mixture to 110 - 120 °C and maintain for 8 - 10 h. After the reaction is completed, let it cool to room temperature, quench with water, filter, extract, and concentrate to obtain Substance A. Then, perform acetal deprotection to obtain 4-alkylbiphenylcyclohexanecarbaldehyde; S1.3. Under argon protection, mix ethyl bromide triphenylphosphonium salt with potassium tert-butoxide and cool to 0 - 5 °C in an ice bath. Then, dropwise add pre-cooled anhydrous tetrahydrofuran to form an orange-red solution. Drop the orange-red solution into 4-alkylbiphenylcyclohexanecarbaldehyde through a dropping funnel. The reaction temperature is 0 - 5 °C and the time is 1 - 2 h, and keep stirring continuously. After the reaction is completed, perform treatment to obtain a negative monomer liquid crystal.

[0005] Preferably, in S1.1, the mass ratio of 4-(4-chlorophenyl)cyclohexanecarboxylic acid to the supported reducing agent is 1:0.64 - 0.82.

[0006] Preferably, in S1.2, the specific steps for pretreating 4-chlorophenylcyclohexanecarbaldehyde to form an acetal solution are as follows: Under the protection of inert gas argon, dissolve 4-chlorophenylcyclohexanecarbaldehyde in ethanol to form a solution with a concentration of 41.7 - 43.5 mg / mL, and add dihydropyran and stir at room temperature for 1 - 3 h. Among them, the molar ratio of 4-chlorophenylcyclohexanecarbaldehyde to dihydropyran is 1:1.1 - 1.5. After treatment, an acetal solution is obtained.

[0007] Preferably, in S1.2, the mass ratio of the acetal solution to 4-alkylbenzeneboronic 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 4-alkylbenzeneboronic acid.

[0008] Preferably, in S1.2, the molar ratio of palladium acetate, potassium carbonate to the acetal solution is 0.01 - 0.05:2 - 3:1.

[0009] Preferably, in S1.2, the specific steps for acetal deprotection are as follows: Add p-toluenesulfonic acid to Substance A. Among them, the mass ratio of Substance A to p-toluenesulfonic acid is 5:0.3 - 0.6. Stir at room temperature for 2 - 4 h, then dropwise add saturated sodium bicarbonate aqueous solution to neutralize the pH, and finally extract, concentrate, and purify.

[0010] Preferably, in S1.3, the mass ratio of ethyl bromide triphenylphosphonium salt, potassium tert-butoxide and 4-alkylbiphenylcyclohexanecarbaldehyde is 3.5 - 3.7:1:2.7 - 2.9; the addition amount of anhydrous tetrahydrofuran is 1 - 3 times the total volume of ethyl bromide triphenylphosphonium salt and potassium tert-butoxide.

[0011] Preferably, the steps for preparing the supported reducing agent are specifically as follows: The silica gel is dried, and under the protection of an inert gas, diisobutylaluminum hydride is added dropwise to the silica gel, allowed to stand for 2 - 4 h, and then dried to obtain the supported reducing agent.

[0012] Preferably, the particle size range of the silica gel is 60 - 120 mesh, and the pore size range of the silica gel is 200 - 300 Å.

[0013] Preferably, the loading amount of the supported reducing agent is 5% - 10%.

[0014] Compared with conventional strong reducing agents such as lithium aluminum tetrahydride and sodium borohydride, diisobutylaluminum hydride has a milder and more stable 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 a 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 steric hindrance and dispersion effects. On the other hand, since silica gel is a solid support, the loaded diisobutylaluminum hydride can be separated from the reaction system by simple filtration operation, which is convenient for recycling and reuse.

[0015] Compared with the prior art, the beneficial effects of the present invention are: In the new process of the ultra-pure TFT negative monomer liquid crystal for large-size panels, a supported reducing agent is used. By utilizing the porous structure of silica gel, diisobutylaluminum hydride is adsorbed on the surface and inside the micropores of silica gel. Through steric hindrance and dispersion effects, the reducing ability of diisobutylaluminum hydride is reduced, enabling it to selectively reduce the carboxyl group to an aldehyde group and avoiding direct reduction to a hydroxyl group at one time. Compared with the traditional preparation process, the synthesis route is reduced. Specific Embodiments

[0016] 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.

[0017] The new process of the ultra-pure TFT negative monomer liquid crystal for large-size panels of the present invention: S1.1. Under argon protection, 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 device to a dry ice / acetone bath, quickly cool it to -75 - 78 °C, then add the supported reducing agent while maintaining continuous stirring. React for 2 - 4 h, and after treatment, obtain 4-chlorophenylcyclohexanecarbaldehyde; S1.2. Pretreat 4-chlorophenylcyclohexanecarbaldehyde as an acetal solution. Under anhydrous and anaerobic conditions, add the acetal solution and 4-alkylphenylboronic acid to N,N-dimethylformamide, and add palladium acetate and potassium carbonate. Heat the reaction mixture to 110 - 120 °C and maintain for 8 - 10 h. After the reaction ends, let it cool to room temperature, quench with water, filter, extract, and concentrate to obtain substance A, and then deprotect the acetal to obtain 4-alkylbiphenylcyclohexanecarbaldehyde; S1.3. Under argon protection, mix ethyl bromide triphenylphosphonium salt with potassium tert-butoxide and cool it to 0 - 5 °C in an ice bath. Then, dropwise add pre-cooled anhydrous tetrahydrofuran to form an orange-red solution. Drop the orange-red solution into 4-alkylbiphenylcyclohexanecarbaldehyde through a dropping funnel. The reaction temperature is 0 - 5 °C, the time is 1 - 2 h, and continuous stirring is maintained. After the reaction ends, obtain the negative monomer liquid crystal after treatment.

[0018] Example 1: A new process for ultra-pure TFT negative monomer liquid crystal for large-size panels, including the following steps: S1.1. Under argon protection, add tetrahydrofuran to 4-(4-chlorophenyl)cyclohexanecarboxylic acid to form a clear solution with a concentration of 0.5 M. Transfer the reaction device to a dry ice / acetone bath, quickly cool it to -78 °C, then add the supported reducing agent while maintaining continuous stirring. React for 4 h, and after treatment, obtain 4-chlorophenylcyclohexanecarbaldehyde; Among them, the mass ratio of 4-(4-chlorophenyl)cyclohexanecarboxylic acid to the supported reducing agent is 1:0.64; the mass ratio of the acetal solution to 4-alkylphenylboronic acid is 1.5:1.1, and 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 to the acetal solution is 0.05:3:1; the mass ratio of ethyl bromide triphenylphosphonium salt, potassium tert-butoxide and 4-alkylbiphenylcyclohexanecarbaldehyde is 3.7:1:2.9; the addition amount of anhydrous tetrahydrofuran is 3 times the total volume of ethyl bromide triphenylphosphonium salt and potassium tert-butoxide; S1.2. Under the protection of inert gas argon, dissolve 4-chlorophenylcyclohexanecarbaldehyde in ethanol to form a solution with a concentration of 43.5 mg / mL, add dihydropyran, and stir at room temperature for 3 h. Among them, the molar ratio of 4-chlorophenylcyclohexanecarbaldehyde to dihydropyran is 1:1.2. After treatment, an acetal solution is obtained. Under anhydrous and anaerobic conditions, add the acetal solution and 4-alkylphenylboronic acid to N,N-dimethylformamide, add palladium acetate and potassium carbonate, heat the reaction mixture to 120 °C, and maintain for 10 h. After the reaction is completed, let it cool to room temperature, quench with water, filter, extract and concentrate to obtain substance A. Add p-toluenesulfonic acid to substance A. Among them, the mass ratio of substance A to p-toluenesulfonic acid is 5:0.6. After stirring at room temperature for 4 h, dropwise add saturated sodium bicarbonate aqueous solution to neutralize the pH, and finally extract, concentrate and purify, and then deprotect the acetal to obtain 4-alkylbiphenylcyclohexanecarbaldehyde; Dry and treat silica gel with a particle size of 100 mesh and a pore size of 200 Å. Under the protection of inert gas, drop diisobutylaluminum hydride onto the silica gel drop by drop, let it stand for 2 h, and dry to obtain a supported reducing agent with a loading of 7%; S1.3. Under the protection of argon, mix bromoethane triphenylphosphonium salt with potassium tert-butoxide, cool to 5 °C in an ice bath, then dropwise add pre-cooled anhydrous tetrahydrofuran to form an orange-red solution. Drop the orange-red solution into 4-alkylbiphenylcyclohexanecarbaldehyde through a dropping funnel. The reaction temperature is 3 °C and the time is 2 h, and keep stirring continuously. After the reaction is completed, through treatment, a negative monomer liquid crystal is obtained.

[0019] Example 2: A new process for ultra-pure TFT negative monomer liquid crystal for large-size panels, including the following steps: S1.1. Under the protection of argon, add tetrahydrofuran to 4-(4-chlorophenyl)cyclohexanecarboxylic acid to form a clear solution with a concentration of 0.5 M. Transfer the reaction device to a dry ice / acetone bath, quickly cool to -78 °C, then add the supported reducing agent, while keeping continuous stirring. The reaction time is 4 h. After treatment, 4-chlorophenylcyclohexanecarbaldehyde is obtained; Among them, the mass ratio of 4-(4-chlorophenyl)cyclohexanecarboxylic acid to the supported reducing agent is 1:0.73; the mass ratio of the acetal solution to 4-alkylphenylboronic acid is 1.5:1.1, and 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 to the acetal solution is 0.05:3:1; the mass ratio of bromoethane triphenylphosphonium salt, potassium tert-butoxide and 4-alkylbiphenylcyclohexanecarbaldehyde is 3.7:1:2.9; the addition amount of anhydrous tetrahydrofuran is 3 times the total volume of bromoethane triphenylphosphonium salt and potassium tert-butoxide; S1.2. Under the protection of inert gas argon, dissolve 4-chlorophenylcyclohexanecarbaldehyde in ethanol to form a solution with a concentration of 43.5 mg / mL, add dihydropyran, and stir at room temperature for 3 h. Among them, the molar ratio of 4-chlorophenylcyclohexanecarbaldehyde to dihydropyran is 1:1.2. After treatment, an acetal solution is obtained. Under anhydrous and anaerobic conditions, add the acetal solution and 4-alkylbenzeneboronic acid to N,N-dimethylformamide, add palladium acetate and potassium carbonate, heat the reaction mixture to 120 °C, and maintain for 10 h. After the reaction is completed, let it cool to room temperature, quench with water, filter, extract and concentrate to obtain substance A. Add p-toluenesulfonic acid to substance A. Among them, the mass ratio of substance A to p-toluenesulfonic acid is 5:0.6. Stir at room temperature for 4 h, then dropwise add saturated sodium bicarbonate aqueous solution to neutralize the pH. Finally, extract, concentrate and purify, and then remove the acetal protection to obtain 4-alkylbiphenylcyclohexanecarbaldehyde; Dry and treat silica gel with a particle size of 100 mesh and a pore size of 200 Å. Under the protection of inert gas, dropwise add diisobutylaluminum hydride to the silica gel, let it stand for 2 h, and dry to obtain a supported reducing agent with a loading amount of 7%; S1.3. Under the protection of argon, mix bromoethanetriphenylphosphonium salt with potassium tert-butoxide, cool to 5 °C in an ice bath, then dropwise add precooled anhydrous tetrahydrofuran to form an orange-red solution. Drop the orange-red solution into 4-alkylbiphenylcyclohexanecarbaldehyde through a dropping funnel. The reaction temperature is 3 °C and the time is 2 h, and keep stirring continuously. After the reaction is completed, through treatment, a negative monomer liquid crystal is obtained.

[0020] Example 3: A new process for ultra-pure TFT negative monomer liquid crystal for large-size panels, including the following steps: S1.1. Under the protection of argon, add tetrahydrofuran to 4-(4-chlorophenyl)cyclohexanecarboxylic acid to form a clear solution with a concentration of 0.5 M. Transfer the reaction device to a dry ice / acetone bath, quickly cool to -78 °C, then add the supported reducing agent while keeping continuous stirring. The reaction time is 4 h. After treatment, 4-chlorophenylcyclohexanecarbaldehyde is obtained; Among them, the mass ratio of 4-(4-chlorophenyl)cyclohexanecarboxylic acid to the supported reducing agent is 1:0.82; the mass ratio of the acetal solution to 4-alkylbenzeneboronic acid is 1.5:1.1, and the mass of N,N-dimethylformamide is 5 times the total mass of the acetal solution and 4-alkylbenzeneboronic acid; the molar ratio of palladium acetate, potassium carbonate to the acetal solution is 0.05:3:1; the mass ratio of bromoethanetriphenylphosphonium salt, potassium tert-butoxide and 4-alkylbiphenylcyclohexanecarbaldehyde is 3.7:1:2.9; the addition amount of anhydrous tetrahydrofuran is 3 times the total volume of bromoethanetriphenylphosphonium salt and potassium tert-butoxide; S1.2. Under the protection of inert gas argon, dissolve 4-chlorophenylcyclohexanecarbaldehyde in ethanol to form a solution with a concentration of 43.5 mg / mL, add dihydropyran, and stir at room temperature for 3 h. Among them, the molar ratio of 4-chlorophenylcyclohexanecarbaldehyde to dihydropyran is 1:1.2. After treatment, an acetal solution is obtained. Under anhydrous and anaerobic conditions, add the acetal solution and 4-alkylbenzeneboronic acid to N,N-dimethylformamide, add palladium acetate and potassium carbonate, heat the reaction mixture to 120 °C, and maintain for 10 h. After the reaction is completed, let it cool to room temperature, quench with water, filter, extract and concentrate to obtain substance A. Add p-toluenesulfonic acid to substance A. Among them, the mass ratio of substance A to p-toluenesulfonic acid is 5:0.6. Stir at room temperature for 4 h, then add saturated aqueous sodium bicarbonate solution dropwise to neutralize the pH, and finally extract, concentrate and purify, and then deprotect the acetal to obtain 4-alkylbiphenylcyclohexanecarbaldehyde; Dry the silica gel with a particle size of 100 mesh and a pore size of 200 Å. Under the protection of inert gas, dropwise add diisobutylaluminum hydride to the silica gel, let it stand for 2 h, and dry to obtain a supported reducing agent with a loading amount of 7%; S1.3. Under the protection of argon, mix bromoethanetriphenylphosphonium salt with potassium tert-butoxide, cool to 5 °C in an ice bath, then dropwise add precooled anhydrous tetrahydrofuran to form an orange-red solution. Drop the orange-red solution into 4-alkylbiphenylcyclohexanecarbaldehyde through a dropping funnel. The reaction temperature is 3 °C and the time is 2 h, and keep stirring continuously. After the reaction is completed, through treatment, a negative monomer liquid crystal is obtained.

[0021] Example 4: A new process for ultra-pure TFT negative monomer liquid crystal for large-size panels, including the following steps: S1.1. Under the protection of argon, add tetrahydrofuran to 4-(4-chlorophenyl)cyclohexanecarboxylic acid to form a clear solution with a concentration of 0.5 M. Transfer the reaction device to a dry ice / acetone bath, quickly cool to -78 °C, then add the supported reducing agent, while keeping continuous stirring, and the reaction time is 4 h. After treatment, 4-chlorophenylcyclohexanecarbaldehyde is obtained; Among them, the mass ratio of 4-(4-chlorophenyl)cyclohexanecarboxylic acid to the supported reducing agent is 1:0.82; the mass ratio of the acetal solution to 4-alkylbenzeneboronic acid is 1.5:0.8, and the mass of N,N-dimethylformamide is 3 times the total mass of the acetal solution and 4-alkylbenzeneboronic acid; the molar ratio of palladium acetate, potassium carbonate to the acetal solution is 0.01:2:1; the mass ratio of bromoethanetriphenylphosphonium salt, potassium tert-butoxide and 4-alkylbiphenylcyclohexanecarbaldehyde is 3.5:1:2.7; the addition amount of anhydrous tetrahydrofuran is 1 times the total volume of bromoethanetriphenylphosphonium salt and potassium tert-butoxide; S1.2. Under the protection of inert gas argon, dissolve 4-chlorophenylcyclohexanecarbaldehyde in ethanol to form a solution with a concentration of 43.5 mg / mL, add dihydropyran, and stir at room temperature for 3 h. Among them, the molar ratio of 4-chlorophenylcyclohexanecarbaldehyde to dihydropyran is 1:1.2. After treatment, an acetal solution is obtained. Under anhydrous and anaerobic conditions, add the acetal solution and 4-alkylbenzeneboronic acid to N,N-dimethylformamide, add palladium acetate and potassium carbonate, heat the reaction mixture to 120 °C, and maintain it for 10 h. After the reaction is completed, let it cool to room temperature, quench with water, filter, extract and concentrate to obtain substance A. Add p-toluenesulfonic acid to substance A. Among them, the mass ratio of substance A to p-toluenesulfonic acid is 5:0.6. Stir at room temperature for 4 h, then dropwise add saturated sodium bicarbonate aqueous solution to neutralize the pH. Finally, extract, concentrate and purify, and then deprotect the acetal to obtain 4-alkylbiphenylcyclohexanecarbaldehyde; Dry silica gel with a particle size of 100 mesh and a pore size of 200 Å. Under the protection of inert gas, dropwise add diisobutylaluminum hydride to the silica gel, let it stand for 2 h, and dry to obtain a supported reducing agent with a loading amount of 7%; S1.3. Under the protection of argon, mix bromoethanetriphenylphosphonium salt with potassium tert-butoxide, cool it to 5 °C in an ice bath, then dropwise add precooled anhydrous tetrahydrofuran to form an orange-red solution. Drop the orange-red solution into 4-alkylbiphenylcyclohexanecarbaldehyde through a dropping funnel. The reaction temperature is 3 °C and the time is 2 h, and keep stirring. After the reaction is completed, through treatment, a negative monomer liquid crystal is obtained.

[0022] Comparative Example 1: Using the method of Example 3, directly use diisobutylaluminum hydride without modifying diisobutylaluminum hydride through silica gel.

[0023] The present invention adopts a supported reducing agent to prepare an ultra-pure TFT negative monomer liquid crystal for large-size panels. Among them, the performance index inspection items and inspection standards of the ultra-pure TFT negative monomer liquid crystal for large-size panels are as follows: The yield refers to the molar percentage of the target product relative to the starting materials. Specifically, it measures the ratio between the quantity of the actually produced target product and the theoretically maximum possible quantity in a chemical reaction. The yield is usually expressed as a percentage. Weigh the purified 4-chlorophenylcyclohexanecarbaldehyde and calculate the yield (%) = (the mass of the actually produced target product) / (the mass of the theoretically produced target product) × 100%. A high yield indicates that the reaction conditions are well optimized, the choice of catalyst or reagent is appropriate, 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 part of the substrate not being converted into the target product.

[0024] Through the above criteria, the ultra-pure TFT negative monomer liquid crystals for large-size panels prepared in the above Examples 1-4 and Comparative Example 1 were tested, and the obtained data are shown in Table 1: Table 1 Performance data of Examples 1-4 and Comparative Example 1

[0025] The above data fully show that compared with Comparative Example 1, in Examples 1-4, it can be fully seen that the loaded reducing agent has an effect on the selective reduction of the ultra-pure TFT negative monomer liquid crystal for large-size panels.

[0026] Since the present invention uses a loaded reducing agent to prepare an ultra-pure TFT negative monomer liquid crystal for large-size panels, the selective reduction of the ultra-pure TFT negative monomer liquid crystal for large-size panels is effectively improved by the loaded reducing agent, specifically as follows: It can be seen from Examples 1-3 that as the content of the loaded reducing agent increases continuously, 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 surface or inside the micropores of silica gel, due to space constraints, its active centers are partially shielded, thus reducing the overall reaction activity. This steric hindrance effect makes diisobutylaluminum hydride more inclined to undergo a selective reaction with specific substrates and will not be over-reduced to the hydroxyl stage. In addition, the silica gel carrier can help diisobutylaluminum hydride disperse better in the reaction system, reducing side reactions caused by too high local concentration. Therefore, the selective reduction of the negative monomer liquid crystal material is significantly improved.

[0027] It can be seen from Example 3 and Example 4 that as the content of other components increases continuously, the selective reduction of the negative monomer liquid crystal material does not change significantly, which shows that small changes within a certain range of other components are not sufficient to significantly affect the yield of the negative monomer liquid crystal material.

[0028] According to the above test experiments, it can be known that the ultra-pure TFT negative monomer liquid crystal for large-size panels prepared according to Example 3 has the optimal performance, so Example 3 is taken as the optimal example; It can be seen from the comparison between Example 3 and Comparative Example 1: In Comparative Example 1, diisobutylaluminum hydride was directly used without modifying diisobutylaluminum hydride through silica gel, and the selective reduction of the negative monomer liquid crystal material was poor. This is because the unloaded diisobutylaluminum hydride is not restricted by steric hindrance and dispersion effects, is more likely to undergo over-reduction, and there are local high-concentration regions of the unloaded diisobutylaluminum hydride in the solution, increasing the probability of side reactions and resulting in low selectivity.

[0029] In summary, through the silica-supported diisobutylaluminum hydride, a higher selective reduction effect is achieved, mainly due to the steric hindrance, dispersion effect, stability, and easy recyclability provided by silica. In contrast, the unloaded diisobutylaluminum hydride is prone to side reactions and has a lower selectivity due to its reactivity and dispersion distribution problems. Therefore, the use of the supported reducing agent has the advantages of simplifying the production process, improving efficiency, reducing by-product formation, and lowering production costs.

[0030] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed.

Claims

1. A new process for ultra-pure TFT negative monomer liquid crystal for large-size panels, characterized in that: S1.

1. Under argon protection, 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 device to a dry ice / acetone bath, quickly cool it to -75 to -78 °C, then add the supported reducing agent while maintaining continuous stirring. React for 2 - 4 h, and after treatment, obtain 4-chlorophenylcyclohexanecarbaldehyde; S1.

2. Pretreat 4-chlorophenylcyclohexanecarbaldehyde as an acetal solution. Under anhydrous and anaerobic conditions, add the acetal solution and 4-alkylphenylboronic acid to N,N-dimethylformamide, and add palladium acetate and potassium carbonate. Heat the reaction mixture to 110 - 120 °C and maintain for 8 - 10 h. After the reaction ends, let it cool to room temperature, quench with water, filter, extract, and concentrate to obtain substance A, and then deprotect the acetal to obtain 4-alkylbiphenylcyclohexanecarbaldehyde; S1.

3. Under argon protection, mix ethyl bromide triphenylphosphonium salt with potassium tert-butoxide and cool it to 0 - 5 °C in an ice bath. Then, add pre-cooled anhydrous tetrahydrofuran dropwise to form an orange-red solution. Drop the orange-red solution into 4-alkylbiphenylcyclohexanecarbaldehyde through a dropping funnel. The reaction temperature is 0 - 5 °C, the time is 1 - 2 h, and continuous stirring is maintained. After the reaction ends, obtain the negative monomer liquid crystal through treatment.

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

82.

3. The new process for the ultra-pure TFT negative monomer liquid crystal for large-size panels according to claim 1, characterized in that: In S1.2, the specific steps for pretreating 4-chlorophenylcyclohexanecarbaldehyde as an acetal solution are as follows: Under the protection of inert gas argon, dissolve 4-chlorophenylcyclohexanecarbaldehyde in ethanol to form a solution with a concentration of 41.7 - 43.5 mg / mL, and add dihydropyran and stir at room temperature for 1 - 3 h. Among them, the molar ratio of 4-chlorophenylcyclohexanecarbaldehyde to dihydropyran is 1:1.1 - 1.5, and after treatment, obtain the acetal solution.

4. The new process for the ultra-pure 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 4-alkylphenylboronic 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 4-alkylphenylboronic acid.

5. The new process for ultra-pure 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 to the acetal solution is 0.01 - 0.05:2 - 3:

1.

6. The new process for the ultra-pure TFT negative monomer liquid crystal for large-size panels according to claim 1, characterized in that: In S1.2, the specific steps for acetal deprotection are as follows: Add p-toluenesulfonic acid to substance A. Among them, the mass ratio of substance A to p-toluenesulfonic acid is 5:0.3 - 0.

6. Stir at room temperature for 2 - 4 h, then dropwise add saturated sodium bicarbonate aqueous solution to neutralize the pH, and finally extract, concentrate, and purify.

7. The new process for the ultra-pure TFT negative monomer liquid crystal for large-size panels according to claim 1, characterized in that: In S1.3, the mass ratio of ethyl bromide triphenylphosphonium salt, potassium tert-butoxide and 4-alkylbiphenylcyclohexanecarbaldehyde is 3.5 - 3.7:1:2.7 - 2.9; the addition amount of anhydrous tetrahydrofuran is 1 - 3 times the total volume of ethyl bromide triphenylphosphonium salt and potassium tert-butoxide.

8. The new process for the ultra-pure TFT negative monomer liquid crystal for large-size panels according to claim 1, characterized in that: The specific steps for preparing the supported reducing agent are as follows: The silica gel is dried, and diisobutylaluminum hydride is added dropwise to the silica gel under the protection of an inert gas, and left standing for 2 - 4 h, and then dried to obtain a supported reducing agent.

9. The new process for the ultra-pure TFT negative monomer liquid crystal for large-size panels according to claim 8, characterized in that: The particle size range of the silica gel is 60 - 120 mesh, and the pore size range of the silica gel is 200 - 300 Å.

10. The new process for the ultra-pure TFT negative monomer liquid crystal for large-size panels according to claim 8, characterized in that: The loading amount of the supported reducing agent is 5% - 10%.

Images