A method for preparing thioxanthene liquid crystal compound

Abstract

The present invention provides a method for preparing a thioxanthene liquid crystal compound. The method uses compound A and compound B as raw materials, and synthesizes the thioxanthene liquid crystal compound of the present invention through a multi-step reaction by optimizing reaction conditions, organic solvents, etc. The preparation method has simple operating steps, low cost, environmental protection and high efficiency, can minimize or eliminate harmful reactions in industrial production processes and consumer applications, and avoids the problems of conventional organic solvents such as high toxicity, low safety, and high price, making the preparation method green and inexpensive. The prepared thioxanthene liquid crystal compound has high purity and high yield, can be used on a large scale in actual production, greatly improves raw material utilization and production efficiency, greatly saves production time, and reduces production costs. It is a resource-saving and environmentally friendly technical solution with good application prospects in the field of organic synthesis.

Description

Technical Field

[0001] The present invention relates to the field of organic synthesis, and in particular to a method for preparing a thioxanthene liquid crystal compound. Background Art

[0002] Liquid crystals are orientationally ordered fluids that lie between isotropic liquids and fully ordered crystals. They possess the fluidity of liquids and the anisotropic properties of crystals, such as birefringence. Liquid crystals were first discovered by Austrian botanist F. Reinitzer while observing the melting point of cholesterol benzoate. Following Reinitzer's lead, German physicist O. Lehmann observed the compound using a polarizing microscope and found that the turbid mesophase exhibited properties similar to crystals. He therefore named this anisotropic and fluid liquid crystal. Liquid crystals can be classified in many ways. Based on how they form, they can be divided into thermotropic and lyotropic types. The most common classification is based on the morphology of the liquid crystals they form. Generally, there are three types of liquid crystals: nematic, cholesteric, and smectic. The discovery of this new phase captivated numerous researchers, and theoretical research on liquid crystals gradually unfolded. It was not until the 1960s that liquid crystals began to find application in display applications.

[0003] Liquid crystal displays (LCDs) have experienced rapid development due to their small size, light weight, low power consumption, and excellent display quality, and have been widely used, in particular, in portable electronic information products. Liquid crystal display elements containing liquid crystal compositions with large absolute values ​​of dielectric anisotropy can reduce base voltage values, reduce driving voltages, and further reduce power consumption. Liquid crystal display elements containing liquid crystal compositions with relatively low threshold voltages can effectively reduce display power consumption, and in particular, will have longer battery life in consumables (such as mobile phones, tablet computers, and other portable electronic products). Thioxanthene liquid crystal compounds have been used in liquid crystal display elements with excellent results.

[0004] Chinese patent CN109652096B discloses a liquid crystal compound, a liquid crystal composition, and a liquid crystal display device. The liquid crystal compound exhibits a large negative dielectric constant due to the rigid structure within the molecule and the presence of lateral trifluoro. By introducing heteroatoms into the polyfluorodibenzocyclohexane liquid crystal molecules, it exhibits good mutual solubility and expands the application range of the liquid crystal composition. However, the synthesis method of the liquid crystal compound is difficult to operate and has high cost. The temperature must be controlled at -80°C, the yield is low, and a large amount of solvent is used, which will generate a large amount of industrial wastewater, is not conducive to environmental protection, and is difficult to use in large-scale production.

[0005] Therefore, how to provide a method for synthesizing trifluorothiol compounds with low cost, high purity, high yield and environmental friendliness has become an urgent problem to be solved. Summary of the Invention

[0006] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for synthesizing trifluorothiol compounds with simple operation, low cost, high purity, high yield and environmental friendliness, so as to meet the needs of practical applications and environmental protection requirements.

[0007] To achieve this object, the technical solution of the present invention is as follows:

[0008] The present invention provides a method for preparing a thioxanthene liquid crystal compound as shown in Formula G, characterized in that the preparation method comprises the following steps:

[0009] (1) dissolving compound A in an organic solvent,

[0010] Wherein, R1 represents an alkoxy group having 1 to 8 carbon atoms,

[0011] Add 3,4-dihydropyran and acid, stir, and react for 5-10 hours to obtain compound B

[0012]

[0013] (2) Under nitrogen protection, the organic solvent was cooled and isopropyl magnesium chloride was added and allowed to stand; Compound B and Compound b were added to the organic solvent and pre-dissolved respectively.

[0014] Wherein, R2 represents an alkoxy group having 1 to 8 carbon atoms,

[0015] The pre-dissolved compound B and compound b are mixed with an organic solvent containing an isopropyl magnesium chloride solution, and the mixture is naturally heated to room temperature for reaction to obtain compound C.

[0016]

[0017] (3) Dissolve compound C in an organic solvent, add trifluoroacetic acid and triethylsilane, and react at room temperature for 1-10 hours to obtain compound D.

[0018]

[0019] (4) Under nitrogen protection, compound D, dimethylaminothiocarbonyl chloride, and base are added to isododecane, heated to 170-280°C for reaction for 1-10 hours, and then cooled to 60-80°C to obtain compound E.

[0020]

[0021] (5) Compound E was dissolved in isododecane, heated to 170-280°C for reaction, and then cooled to 60-80°C to obtain compound F.

[0022]

[0023] (6) Add compound F to an organic solvent, then add a base, raise the temperature to 70-80°C and react for 1-10 hours to obtain compound G

[0024]

[0025] In some embodiments of the present invention, the organic solvent in step (1) is selected from one or more combinations of toluene, dichloromethane, and tetrahydrofuran; the acid is selected from one or more combinations of p-toluenesulfonic acid pyridinium salt, p-toluenesulfonic acid, hydrochloric acid, hydrobromic acid, and hydroiodic acid; the molar ratio of compound A, the 3,4-dihydropyran, and the acid is 2-3:3-5:1 (for example, it can be 2:3:1, 2:4:1, 2:5:1, 3:3:1, 3:4:1, 3:5:1, or any value therein); and the reaction temperature is 0-50°C (for example, it can be 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, or any value therein).

[0026] Preferably, the organic solvent in step (1) is tetrahydrofuran; and the acid is pyridinium p-toluenesulfonate.

[0027] In some embodiments of the present invention, the compound B in step (1) is obtained by concentration, column separation, re-concentration, and slurrying before purification.

[0028] In some embodiments of the present invention, the compound B in step (1) is obtained by concentrating the reaction solution, separating it through a column, and then concentrating it again, and then slurrying it with anhydrous ethanol and then purifying it.

[0029] In some embodiments of the present invention, the organic solvent in step (2) is selected from one or more combinations of tetrahydrofuran, diethyl ether, dichloromethane, and toluene; the molar ratio of compound B to compound b is 1:1-2 (for example, it can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2 or any value therein); the cooling treatment is performed at a temperature of -10 to 30°C (for example, it can be -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C or any value therein); and the reaction time is 2-6h (for example, it can be 2h, 3h, 4h, 5h, 6h or any value therein).

[0030] Preferably, the organic solvent is tetrahydrofuran.

[0031] In some embodiments of the present invention, the compound C in step (2) is obtained by extraction, drying, concentration, beating and then purification.

[0032] In some embodiments of the present invention, the compound C in step (2) is obtained by extraction, drying with anhydrous sodium sulfate, concentration, and then slurrying with petroleum ether and then purification.

[0033] In some embodiments of the present invention, the molar ratio of compound C, triethylsilane and trifluoroacetic acid in step (3) is 1:1-5:1-5 (for example, it can be 1:1:1, 1:2:2, 1:3:3, 1:4:4, 1:5:5 or any value therein).

[0034] In some embodiments of the present invention, the compound D in step (3) is obtained by concentration, column separation, re-concentration, and slurrying before purification.

[0035] In some embodiments of the present invention, the compound D in step (3) is obtained by concentrating the reaction solution, separating it through a column, concentrating it again, and then slurrying it with petroleum ether and then purifying it.

[0036] In some embodiments of the present invention, the molar amount of petroleum ether is 2-3 times that of compound D.

[0037] In some embodiments of the present invention, the base in step (4) is selected from one or more combinations of triethylamine, pyridine, potassium methoxide, and potassium tert-butoxide.

[0038] Preferably, the base in step (4) is triethylamine.

[0039] In some embodiments of the present invention, the molar amount of dimethylaminothiocarbonyl chloride in step (4) is 1-3 times that of compound D (for example, it can be 1 time, 1.2 times, 1.4 times, 1.6 times, 1.8 times, 2 times, 2.2 times, 2.4 times, 2.6 times, 12.8 times, 3 times or any multiple thereof).

[0040] In some embodiments of the present invention, the molar amount of the base in step (4) is 1-2 times that of the dimethylaminothiocarbonyl chloride (for example, it can be 1 time, 1.1 times, 1.2 times, 1.3 times, 1.4 times, 1.5 times, 1.6 times, 1.7 times, 1.8 times, 1.9 times, 2 times or any multiple thereof).

[0041] In some embodiments of the present invention, the reaction temperature of 170-280°C in step (4) can be 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C or 280°C.

[0042] In some embodiments of the present invention, the compound E in step (4) is purified after filtration, washing, beating, and refiltration.

[0043] In some embodiments of the present invention, the compound E in step (4) is obtained by filtration, washing, slurrying with ethanol, and purification after filtration.

[0044] In some embodiments of the present invention, the compound F in step (5) is purified after filtration and recrystallization.

[0045] In some embodiments of the present invention, the reaction temperature of 170-280°C in step (5) can be 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C or 280°C.

[0046] In some embodiments of the present invention, the organic solvent in step (6) is selected from one or more combinations of ethanol, dipropylene glycol dimethyl ether, and diphenyl ether; the base is selected from one or more combinations of potassium hydroxide, triethylamine, and pyridine, and the molar amount of the base is 1-2 times that of the compound F (for example, it can be 1 time, 1.1 times, 1.2 times, 1.3 times, 1.4 times, 1.5 times, 1.6 times, 1.7 times, 1.8 times, 1.9 times, 2 times, or any multiple thereof).

[0047] In some embodiments of the present invention, the compound G in step (6) is prepared by filtering after the reaction is completed, washing the filter residue with water until it is neutral, and then recrystallizing it with anhydrous ethanol.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The method for preparing thioxanthene liquid crystal compounds provided by the present invention ensures the purity and yield of thioxanthene liquid crystal compounds by using isododecane. Isododecane has a high degree of isomerization, extremely low impurity content, a narrow elution range, and almost no aromatic hydrocarbons and sulfur. It is harmless to the human body and easily biodegradable. In addition, the relative inertness of the saturated isoalkane structure can minimize or eliminate harmful reactions in industrial production processes and consumer applications, avoiding the problems of conventional organic solvents such as high toxicity, low safety, and high price, making the preparation method green and inexpensive, and greatly improving the yield. The purity can reach 99% and the yield can reach more than 90%.

[0050] (2) The method for preparing a thioxanthene liquid crystal compound provided by the present invention is to obtain a method for preparing a thioxanthene liquid crystal compound by selecting specific acids and bases and setting specific reaction temperature conditions, so that the prepared thioxanthene liquid crystal has high purity and high yield. In particular, in the final step of the synthesis, the reaction is carried out at a suitable temperature, which can greatly improve production efficiency and ensure a good yield. The preparation method provided by the present invention has simple operating steps, low cost, environmental protection and high efficiency. It can be prepared at room temperature and only needs to be heated in the final step. It can be applied on a large scale in actual production, greatly improving raw material utilization and production efficiency, greatly saving production time and reducing production costs. It is a resource-saving and environmentally friendly technical solution. DETAILED DESCRIPTION

[0051] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following examples are illustrative of the present invention and are intended only to illustrate the present invention and are not intended to limit the present invention. Other combinations and various modifications within the scope of the present invention may be made without departing from the spirit or scope of the present invention. In the following examples, the compounds and related reagents used can all be purchased from the market.

[0052] Example 1

[0053] A method for preparing a thioxanthene liquid crystal compound as shown in Formula G1 specifically comprises the following steps:

[0054] (1) 1 mol of compound A1 was added to a single-necked bottle, 5 mol of tetrahydrofuran was added to fully dissolve, 1.5 mol of 3,4-dihydropyran and 0.5 mol of pyridinium p-toluenesulfonate were added, and the mixture was fully dissolved with continuous stirring. The mixture was reacted at 25°C for 5 h. The reaction solution was concentrated and passed through a silica gel column. The mixture was eluted with a mixed solvent consisting of ethyl acetate and petroleum ether (the molar ratio of ethyl acetate to petroleum ether was 1:10). The mixture was concentrated and slurried with 5 mol of anhydrous ethanol to obtain compound B1.

[0055] (2) Under nitrogen protection, 5 mol of tetrahydrofuran was cooled to -10°C, and 1.1 mol of isopropylmagnesium chloride was added to fully dissolve the mixture at -10°C, and the mixture was allowed to stand for 20 minutes; 1 mol of compound B1 was added to 5 mol of tetrahydrofuran and fully dissolved, and 1.1 mol of compound b1 was added to 5 mol of tetrahydrofuran and fully dissolved, and the mixture was mixed with the tetrahydrofuran solution of isopropylmagnesium chloride prepared above, and reacted at room temperature for 2 hours; after the reaction was completed, the mixture was extracted twice with 3 mol of ethyl acetate, dried with 1 mol of anhydrous sodium sulfate, concentrated, and slurried with 5 mol of petroleum ether to obtain compound C1;

[0056] (3) 1 mol of compound C1 was dissolved in 8 mol of dichloromethane, 3 mol of trifluoroacetic acid and 5 mol of triethylsilane were added, and the mixture was fully dissolved. The mixture was stirred at room temperature for 6 h, concentrated, and passed through a silica gel column. The mixture was eluted with a mixed solvent consisting of ethyl acetate and petroleum ether (the molar ratio of ethyl acetate to petroleum ether was 1:1). The mixture was concentrated, and 3 mol of petroleum ether was added for slurrying to obtain the target product D1.

[0057] (4) Under nitrogen protection, 10 mol of isododecane, 1 mol of compound D1, and 2.5 mol of dimethylaminothiocarbonyl chloride were added to a three-necked flask, and 5 mol of triethylamine was added under stirring to fully dissolve. The mixture was heated to 170°C and refluxed for 6 h. The mixture was cooled to 70°C, and hydrochloric acid was added to adjust the pH to neutral. The mixture was filtered and the filter cake was washed with water three times. 5 mol of ethanol was added to slurry for 1 h, and the mixture was filtered to obtain compound E1.

[0058] (5) Dissolve 1 mol of compound E1 in 5 mol of isododecane, heat to 270°C, react for 2 h, cool to 70°C, filter, and recrystallize the filter cake twice with 5 mol of ethanol to obtain compound F1;

[0059] (6) 1 mol of compound F1 was mixed with 5 mol of anhydrous ethanol, and 1.5 mol of potassium hydroxide was added and fully dissolved. The mixture was heated to 80°C and reacted for 4 h. The mixture was filtered and the filter cake was washed with water until the aqueous layer was neutral. The filter cake was recrystallized twice with 5 mol of anhydrous ethanol to obtain compound G1 (purity: 99.5%, yield: 95%).

[0060]

[0061] Mass spectrometric data of thioxanthene liquid crystal compound G1: The obtained white solid was analyzed by LC-MS, and the m / z of the product was 368.1 (M+); elemental analysis: C, 61.94; H, 5.20; F, 15.47; O, 8.69; S, 8.70; H-NMR (300 MHz, CDCl3): 0.75-2.15 (m, 10H), 3.75-3.90 (s, 2H), 3.95-4.55 (m, 4H), 6.96-7.95 (m, 3H).

[0062] Example 2

[0063] A method for preparing a thioxanthene liquid crystal compound as shown in Formula G2 specifically comprises the following steps:

[0064] (1) 1 mol of compound A2 was added to a single-necked bottle, 5 mol of tetrahydrofuran was added to fully dissolve, 1.5 mol of 3,4-dihydropyran and 0.5 mol of pyridinium p-toluenesulfonate were added, and the mixture was fully dissolved with continuous stirring. The mixture was reacted at 5°C for 5 h. The reaction solution was concentrated and passed through a silica gel column. The mixture was eluted with a mixed solvent consisting of ethyl acetate and petroleum ether (the molar ratio of ethyl acetate to petroleum ether was 1:10). The mixture was concentrated and slurried with 5 mol of anhydrous ethanol to obtain compound B2.

[0065] (2) Under nitrogen protection, 5 mol of tetrahydrofuran was cooled to -10°C, and 1.1 mol of isopropylmagnesium chloride was added to fully dissolve the mixture at -10°C, and the mixture was allowed to stand for 20 minutes; 1 mol of compound B1 was added to 5 mol of tetrahydrofuran and fully dissolved, and 1.5 mol of compound b2 was added to 5 mol of tetrahydrofuran and fully dissolved, and the mixture was mixed with the tetrahydrofuran solution of isopropylmagnesium chloride prepared above, and reacted at room temperature for 2 hours; after the reaction was completed, the mixture was extracted twice with 3 mol of ethyl acetate, dried with 1 mol of anhydrous sodium sulfate, concentrated, and slurried with 5 mol of petroleum ether to obtain compound C2;

[0066] (3) 1 mol of compound C2 was dissolved in 8 mol of dichloromethane, 3 mol of trifluoroacetic acid and 5 mol of triethylsilane were added, and the mixture was fully dissolved. The mixture was stirred at room temperature for 6 h, concentrated, and passed through a silica gel column. The mixture was eluted with a mixed solvent consisting of ethyl acetate and petroleum ether (the molar ratio of ethyl acetate to petroleum ether was 1:1). The mixture was concentrated, and 3 mol of petroleum ether was added for slurrying to obtain the target product D2.

[0067] (4) Under nitrogen protection, 10 mol of isododecane, 1 mol of compound D2, and 2.5 mol of dimethylaminothiocarbonyl chloride were added to a three-necked flask, and 5 mol of triethylamine was added under stirring. The temperature was raised to 280°C and refluxed for 6 h. The temperature was lowered to 70°C, and hydrochloric acid was added to adjust the pH to neutral. The filter cake was filtered and washed with water three times. 5 mol of ethanol was added and the mixture was slurried for 1 h. The mixture was filtered to obtain compound E2.

[0068] (5) Dissolve 1 mol of compound E2 in 5 mol of isododecane, heat to 240°C, react for 2 h, cool to 70°C, filter, and recrystallize the filter cake twice with 5 mol of ethanol to obtain compound F2;

[0069] (6) 1 mol of compound F2 was mixed with 5 mol of anhydrous ethanol, and 1.5 mol of potassium hydroxide was added for elution. The temperature was raised to 80°C for reaction for 4 h, and the filter cake was washed with water until the water layer was neutral. The filter cake was recrystallized twice with 5 mol of anhydrous ethanol to obtain compound G2 (purity: 99.6%, yield: 94%).

[0070]

[0071] Mass spectrometric data of thioxanthene liquid crystal compound G2: The obtained white solid was analyzed by LC-MS, and the m / z of the product was 396.1 (M+); elemental analysis: C, 63.62; H, 5.85; F, 14.38; O, 8.07; S, 8.09; H-NMR (300 MHz, CDCl3): 0.75-2.15 (m, 14H), 3.75-3.90 (s, 2H), 3.95-4.55 (m, 4H), 6.96-7.95 (m, 3H).

[0072] Example 3

[0073] A method for preparing a thioxanthene liquid crystal compound as shown in Formula G3 comprises the following steps:

[0074] (1) 1 mol of compound A3 was added to a single-necked bottle, 5 mol of tetrahydrofuran was added to fully dissolve, 2 mol of 3,4-dihydropyran and 0.5 mol of pyridinium p-toluenesulfonate were added, and the mixture was fully dissolved with continuous stirring. The mixture was reacted at 5°C for 5 h. The reaction solution was concentrated and passed through a silica gel column. The mixture was eluted with a mixed solvent consisting of ethyl acetate and petroleum ether (the molar ratio of ethyl acetate to petroleum ether was 1:10). The mixture was concentrated and slurried with 5 mol of anhydrous ethanol to obtain compound B3.

[0075] (2) Under nitrogen protection, 5 mol of tetrahydrofuran was cooled to -10°C, and 1.1 mol of isopropylmagnesium chloride was added to fully dissolve the mixture at -10°C, and the mixture was allowed to stand for 20 minutes; 1 mol of compound B1 was added to 5 mol of tetrahydrofuran and fully dissolved, and 1.5 mol of compound b3 was added to 5 mol of tetrahydrofuran and fully dissolved, and the mixture was mixed with the tetrahydrofuran solution of isopropylmagnesium chloride prepared above, and reacted at room temperature for 2 hours; after the reaction was completed, the mixture was extracted twice with 3 mol of ethyl acetate, dried with 1 mol of anhydrous sodium sulfate, concentrated, and slurried with 5 mol of petroleum ether to obtain compound C3;

[0076] (3) 1 mol of compound C3 was dissolved in 8 mol of dichloromethane, and 2 mol of trifluoroacetic acid and 3 mol of triethylsilane were added to fully dissolve the mixture. The mixture was stirred at room temperature for 6 h, concentrated, and passed through a silica gel column. The mixture was eluted with a mixed solvent consisting of ethyl acetate and petroleum ether (the molar ratio of ethyl acetate to petroleum ether was 1:1). The mixture was concentrated and slurried with 3 mol of petroleum ether to obtain the target product D3.

[0077] (4) Under nitrogen protection, 10 mol of isododecane, 1 mol of compound D3, and 2.5 mol of dimethylaminothiocarbonyl chloride were added to a three-necked flask, and 5 mol of triethylamine was added under stirring to fully dissolve. The mixture was heated to 250°C and refluxed for 6 h. The mixture was cooled to 70°C, and hydrochloric acid was added to adjust the pH to neutral. The mixture was filtered and the filter cake was washed with water three times. 5 mol of ethanol was added to slurry for 1 h, and the mixture was filtered to obtain compound E3.

[0078] (5) Dissolve 1 mol of compound E3 in 5 mol of isododecane, heat to 280°C, react for 2 h, cool to 70°C, filter, and recrystallize the filter cake twice with 5 mol of ethanol to obtain compound F3;

[0079] (6) 1 mol of compound F3 was mixed with 5 mol of anhydrous ethanol, and 1.5 mol of potassium hydroxide was added and fully dissolved. The mixture was heated to 80°C and reacted for 4 h. The mixture was filtered and the filter cake was washed with water until the aqueous layer was neutral. The filter cake was recrystallized twice with 5 mol of anhydrous ethanol to obtain compound G3 (purity: 99.5%, yield 93%).

[0080]

[0081] Mass spectrometric data of thioxanthene liquid crystal compound G3: The obtained white solid was analyzed by LC-MS, and the m / z of the product was 424.1 (M+); elemental analysis: C, 65.07; H, 6.41; F, 13.43; O, 7.54; S, 7.55; H-NMR (300 MHz, CDCl3): 0.75-2.15 (m, 18H), 3.75-3.90 (s, 2H), 3.95-4.55 (m, 4H), 6.96-7.95 (m, 3H).

[0082] Comparative Example 1

[0083] This comparative example provides a method for preparing a thioxanthene liquid crystal compound. The isododecane in steps (4) and (5) was replaced with an equal amount of toluene, and the remaining steps remained the same as in Example 1. The resulting thioxanthene liquid crystal compound had a purity of 89.1% and a yield of 80%. LC-MS analysis of the resulting white solid revealed an m / z of 368.1 (M+); elemental analysis: C, 61.94; H, 5.20; F, 15.47; O, 8.69; S, 8.70; H-NMR (300 MHz, CDCl3): 0.75-2.15 (m, 10H), 3.75-3.90 (s, 2H), 3.95-4.55 (m, 4H), 6.96-7.95 (m, 3H).

[0084] Comparative Example 2

[0085] This comparative example provides a method for preparing a thioxanthene liquid crystal compound, wherein the isomeric dodecane in steps (4) and (5) is replaced with an equal amount of dimethylacetamide, and the rest is consistent with Example 1.

[0086] No product was formed as detected by GC-MS.

[0087] Comparative Example 3

[0088] This comparative example provides a method for preparing a thioxanthene liquid crystal compound. The operating steps are the same as those in Example 1, except that the temperature of the heating reaction in steps (4) and (5) is adjusted to 90°C, which is not within the range of 170-280°C.

[0089] No product was formed as detected by GC-MS.

[0090] Comparison of the test results of Comparative Examples 1, 2, and 3 with those of Example 1 shows that the preparation method of the thioxanthene liquid crystal compound provided in Example 1 uses isododecane, and the temperature is raised to 170-280°C in the later stage of preparation. The prepared thioxanthene liquid crystal compound not only has high purity, but also has high yield and yield.

[0091] Comprehensive comparison of the test results of each embodiment and the comparative example shows that the preparation method of the thioxanthene liquid crystal compound provided by the present invention, by using isomeric dodecane as a solvent, avoids the problems of conventional organic solvents such as high toxicity, low safety, and high price, making the preparation method green, cheap, and greatly improving the yield; by selecting specific acids and bases and setting specific reaction temperature conditions, a preparation method of a thioxanthene liquid crystal compound is obtained, so that the prepared thioxanthene liquid crystal has high purity and high yield, especially in the final step of the synthesis, it is increased to a suitable temperature for reaction, which can greatly improve production efficiency and ensure a good yield. The preparation method provided by the present invention has simple operating steps, low cost, environmental protection and high efficiency, can be prepared at room temperature, only needs to be heated in the final step, can be applied on a large scale in actual production, greatly improves raw material utilization and production efficiency, greatly saves production time, reduces production costs, is a resource-saving and environmentally friendly technical solution, and has good application prospects in the field of organic synthesis.

[0092] The above embodiments are only for illustrating the technical concept and features of the present invention. Its purpose is to enable people familiar with this technology to understand the content of the present invention and implement it. It cannot be used to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a thioxanthene liquid crystal compound as shown in formula G, characterized in that: The preparation method comprises the following steps: (1) dissolving compound A in an organic solvent, A, wherein R1 represents an alkoxy group having 1 to 8 carbon atoms, Add 3,4-dihydropyran and acid, stir, and react for 5-10 hours to obtain compound B (2) Under nitrogen protection, the organic solvent was cooled and isopropyl magnesium chloride was added and allowed to stand; Compound B and Compound b were added to the organic solvent and pre-dissolved respectively. Wherein, R2 represents an alkoxy group having 1 to 8 carbon atoms, The pre-dissolved compound B and compound b are mixed with an organic solvent containing an isopropyl magnesium chloride solution, and the mixture is naturally heated to room temperature for reaction to obtain compound C. (3) Dissolve compound C in an organic solvent, add trifluoroacetic acid and triethylsilane, and react at room temperature for 1-10 hours to obtain compound D. (4) Under nitrogen protection, compound D, dimethylaminothiocarbonyl chloride, and base are added to isododecane, heated to 170-280°C for reaction for 1-10 hours, and then cooled to 60-80°C to obtain compound E. (5) Compound E was dissolved in isododecane, heated to 170-280°C for reaction, and then cooled to 60-80°C to obtain compound F. (6) Add compound F to an organic solvent, then add a base, raise the temperature to 70-80°C and react for 1-10 hours to obtain compound G 2. The method for preparing the thioxanthene liquid crystal compound according to claim 1, characterized in that: The organic solvent in step (1) is selected from one or more combinations of toluene, dichloromethane and tetrahydrofuran.

3. The method for preparing the thioxanthene liquid crystal compound according to claim 1, characterized in that: The acid in step (1) is selected from one or more combinations of pyridinium p-toluenesulfonate, p-toluenesulfonic acid, hydrochloric acid, hydrobromic acid, and hydroiodic acid.

4. The method for preparing the thioxanthene liquid crystal compound according to claim 1, wherein: In step (1), the molar ratio of compound A, 3,4-dihydropyran and the acid is 2-3:3-5:1; the reaction temperature is 0-50° C.; the organic solvent is tetrahydrofuran, and the acid is pyridinium p-toluenesulfonate.

5. The method for preparing the thioxanthene liquid crystal compound according to claim 1, characterized in that: The organic solvent in step (2) is selected from one or more combinations of tetrahydrofuran, ether, dichloromethane and toluene.

6. The method for preparing a thioxanthene liquid crystal compound according to claim 1, wherein: The molar ratio of compound B to compound b in step (2) is 1:1-2; the cooling treatment temperature is -10 to 30°C; and the reaction time is 2 to 6 hours.

7. The method for preparing a thioxanthene liquid crystal compound according to claim 1, wherein: The molar ratio of the compound C, the triethylsilane and the trifluoroacetic acid in step (3) is 1:1-5:1-5.

8. The method for preparing a thioxanthene liquid crystal compound according to claim 1, wherein: The base in step (4) is selected from one or more combinations of triethylamine, pyridine, potassium methoxide, and potassium tert-butoxide.

9. The method for preparing a thioxanthene liquid crystal compound according to claim 1, wherein: In step (4), the molar amount of the dimethylaminothiocarbonyl chloride is 1-3 times that of the compound D; the molar amount of the base is 1-2 times that of the dimethylaminothiocarbonyl chloride; and the base is triethylamine.

10. The method for preparing a thioxanthene liquid crystal compound according to claim 1, wherein: The organic solvent in step (6) is selected from one or more combinations of ethanol, dipropylene glycol dimethyl ether, and diphenyl ether; the base is selected from one or more combinations of potassium hydroxide, triethylamine, and pyridine, and the molar amount of the base is 1-2 times that of the compound F.

11. The method for preparing a thioxanthene liquid crystal compound according to claim 5, characterized in that: The organic solvent in step (2) is tetrahydrofuran.

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