Preparation method of alkene liquid crystal monomer

Abstract

The invention discloses a preparation method of an alkene liquid crystal monomer. The preparation method comprises the following steps: (1) carrying out esterification reaction on trans-2-butenol and a chlorophosphate compound to obtain a phosphate compound intermediate A; and (2) carrying out a metal insertion reaction on dicyclohexyl-substituted alkyl halide B and magnesium to generate a Grignard reagent, and coupling the generated Grignard reagent with the phosphate compound intermediate A obtained in the step (1) to prepare the alkene liquid crystal monomer C containing dicyclohexyl and trans-substituted alkenyl. According to the invention, a phosphate compound intermediate A with a trans-ene structure is prepared from an existing easily available material, namely trans-2-butenol, and then the phosphate compound intermediate A and a Grignard reagent prepared from dicyclohexyl-substituted alkyl halide B are subjected to a coupling reaction to directly form a target product with a high-content trans-ene structure. The problems of high product purification difficulty, low yield and the like caused by multi-step recarburization and cis-alkene structure isomerization in the prior art are effectively avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and in particular relates to a method for preparing an olefinic liquid crystal monomer. Background Art

[0002] At present, olefinic liquid crystal monomers are widely used in liquid crystal display materials, optical devices and high-performance polymer materials. In particular, trans-1-[(3E)-pent-3-enyl]-4-(4-alkylcyclohexyl)cyclohexane olefinic liquid crystal monomers have received extensive attention and application in the field of liquid crystal display due to their excellent liquid crystal phase behavior and stability. However, the existing preparation methods of such olefinic liquid crystal monomers have certain limitations. In the prior art, the common preparation routes are mainly the following:

[0003] 1. The traditional route (US2008 / 63814A1) reaction formula is as follows:

[0004]

[0005] This method has a long route and involves multiple Wittig reactions. In order to prepare a cis-trans mixture, sodium benzenesulfinate is also required for isomerization treatment, which makes the final target product difficult to purify, has a low yield, and has a high overall preparation cost.

[0006] 2. The conventional route has been improved in the prior art, and the reaction formula is as follows:

[0007]

[0008] By improving the traditional route, including using alkyl dicyclohexyl formaldehyde and bromoacetaldehyde glycol phosphonium acetal to prepare Wittig reagent, hydrogenating and deprotecting to obtain alkyl dicyclohexyl propionaldehyde, although this method has been optimized in some aspects, it still involves a multi-step carbon addition process and requires isomerization treatment. The problems of difficult purification and low yield still exist.

[0009] 3. The reaction formulas for other coupling and addition reaction routes are as follows:

[0010] Patent CN113024375A discloses the preparation of 4-alkylbiscyclohexylcarboxylic acid to 4-alkylbiscyclohexylmethanol to prepare the corresponding p-toluenesulfonate, which is then coupled with trans-2-butenyl chloride Grignard reagent to prepare the target product; the reaction formula is as follows:

[0011]

[0012] Patent CN113024335A discloses that 4-alkylbiscyclohexylcarbonyl chloride is first coupled with trans-2-butenyl chloride Grignard reagent, and then reduced to remove the hydroxyl group to obtain the target product; the reaction formula is as follows:

[0013]

[0014] Although these methods can produce trans-pentene products in principle, the trans-2-butenyl chloride required for the reaction is relatively expensive, and isomeric by-products are easily generated during the reaction, which increases the difficulty of purification. In addition, the use of trans-2-butenyl chloride in the preparation of Grignard reagents leads to a large feed ratio, further reducing economic efficiency.

[0015] In addition, patent CN202311268829 discloses coupling of 4-alkyldicyclohexylmethyl bromide with a Grignard reagent prepared by 1,3-dichloropropylene, and then coupling again with a methylmagnesium chloride Grignard reagent to prepare a target product; the reaction formula is as follows:

[0016]

[0017] According to the above route, by-product alkyl biscyclohexyl butene and residual intermediate alkyl biscyclohexyl butene chloride may be produced. The impurities with similar structures make it difficult to purify the product.

[0018] In general, various methods in the prior art have the problems of long preparation routes, complicated steps, difficult isomerization treatment, difficult product purification and high cost. These problems seriously limit the wide application and industrial promotion of trans-1-[(3E)-pent-3-enyl]-4-(4-alkylcyclohexyl)cyclohexane liquid crystal monomers.

[0019] In view of this, the present invention is proposed. Summary of the invention

[0020] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing an olefinic liquid crystal monomer, so as to achieve the purpose of providing an efficient, economical and easy-to-purify method for preparing an olefinic liquid crystal monomer, thereby solving the problems of the prior art such as long preparation route, difficult isomerization treatment, great difficulty in product purification and high cost.

[0021] In order to solve the above technical problems, the basic concept of the technical solution adopted by the present invention is:

[0022] A method for preparing an olefinic liquid crystal monomer, comprising:

[0023] (1) taking trans-2-butenol and a chlorophosphate compound for esterification reaction to obtain a phosphate compound intermediate A;

[0024] (2) The bicyclohexyl-substituted alkyl halide B undergoes a metal insertion reaction with magnesium to generate a Grignard reagent, and the generated Grignard reagent is coupled with the phosphate compound intermediate A obtained in step (1) to prepare an olefinic liquid crystal monomer C containing a bicyclohexyl group and a trans-substituted olefin group.

[0025] The dicyclohexyl-substituted alkyl halide B is reacted with magnesium to generate a Grignard reagent, which is then coupled with a phosphate compound intermediate A to directly construct an olefinic liquid crystal monomer C containing a dicyclohexyl group and a trans-substituted olefin group. The phosphate compound intermediate A with a trans-olefin structure is prepared using the existing readily available material trans-2-butenol, which is then coupled with a Grignard reagent prepared with the dicyclohexyl-substituted alkyl halide B to directly construct a target product with a high content of trans-olefin structure, thereby effectively avoiding the problems of difficulty in product purification and low yield caused by multi-step carbon addition and isomerization of cis-olefin structure in the prior art.

[0026] Furthermore, in the step (1), the chlorophosphate ester compound is diethyl chlorophosphate, and the reaction formula of step (1) is:

[0027]

[0028] In the step (2),

[0029] The dicyclohexyl-substituted alkyl halide B is:

[0030]

[0031] Wherein, R represents a C2-C5 alkyl straight chain hydrocarbon group, and X represents bromine or chlorine;

[0032] The reaction equation in step (2) is:

[0033]

[0034] Furthermore, in the step (2), the molar ratio of dicyclohexyl-substituted alkyl halide B: magnesium: phosphate compound intermediate A is 1.0: 1.0-1.1: 0.9-1.2.

[0035] Furthermore, in the step (2), the phosphate compound intermediate A and the tetrahydrofuran solution are mixed and cooled under nitrogen protection, and after cooling, a Grignard reagent is added to react to prepare an olefinic liquid crystal monomer C containing a bicyclohexyl group and a trans-substituted olefin group.

[0036] Furthermore, in step (2), the Grignard reagent is added when the temperature drops to -40 to -20°C; preferably, -40 to -30°C.

[0037] Furthermore, in the step (2), the Grignard reagent is added dropwise.

[0038] Furthermore, in the step (2), the Grignard reagent is added, stirred, and kept warm for reaction to prepare an olefinic liquid crystal monomer C containing a bicyclohexyl group and a trans-substituted olefin group.

[0039] Furthermore, after the insulation reaction in step (2) is completed, the feed liquid is poured into dilute hydrochloric acid cold water for hydrolysis, and after hydrolysis, the reaction product is extracted with toluene, the toluene layer is washed and neutralized with water, evaporated to dryness, dissolved in n-heptane and chromatographically separated by a silica gel column to remove impurities, the solvent is evaporated to dryness after separation, and dissolved in a mixed solvent of n-heptane and ethanol for crystallization to obtain trans, trans-1-[(3E)-pent-3-enyl]-4-(4-propylcyclohexyl)cyclohexane.

[0040] Furthermore, in the step (2), the dicyclohexyl-substituted alkyl halide B, magnesium and iodine are mixed into anhydrous tetrahydrofuran, and the reaction is initiated by heating under the protection of an inert gas, and then the dicyclohexyl-substituted alkyl halide B and anhydrous tetrahydrofuran solution are added dropwise at 60-70° C. and kept warm for 2-3 hours to prepare the Grignard reagent.

[0041] Furthermore, in the step (1), the trans-2-butenol compound and pyridine are added to a dichloromethane solvent, and the temperature is lowered to 0-10° C. under the protection of an inert gas, and a chlorophosphate compound is added dropwise. After the addition is complete, the temperature is slowly raised to 20-30° C., and the reaction is stirred and kept warm to obtain a reaction liquid;

[0042] After the reaction is completed, the reaction liquid is poured into sodium hydroxide ice water and stirred for hydrolysis, and the liquids are separated. After separation, the liquids are washed with saturated sodium bicarbonate water, dried, filtered, and the solvent is evaporated to remove low-boiling impurities, thereby obtaining the phosphate compound intermediate A.

[0043] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0044] First, a phosphate compound intermediate A containing a trans-olefin structure is directly obtained by esterifying a trans-2-butenol compound with a chlorophosphate compound. This step has mild reaction conditions, is easy to control, and is easy to scale up for industrial production.

[0045] Secondly, a dicyclohexyl-substituted alkyl halide B is reacted with magnesium to generate a Grignard reagent, which is then coupled with a phosphate compound intermediate A to directly construct an olefinic liquid crystal monomer C containing a dicyclohexyl group and a trans-substituted olefin group. The phosphate compound intermediate A having a trans-olefin structure is prepared by using an existing readily available material, trans-2-butenol, and then coupled with a Grignard reagent prepared with the dicyclohexyl-substituted alkyl halide B to directly construct a target product having a high content of trans-olefin structure, thereby effectively avoiding the problems of difficulty in product purification and low yield caused by multi-step carbon addition and isomerization of cis-olefin structure in the prior art.

[0046] The preparation method provided by the present invention makes the target product C have a high trans-olefin content and a low cis-isomer impurity content, is easy to purify, has a yield of more than 63.1%, a purity of more than 99.9%, and controllable impurities (all impurities are ≤ 0.005%), thereby ensuring the high quality of the product. This method not only optimizes the existing synthesis route, but also provides a feasible solution for industrial amplification, has broad application prospects, and meets the needs of modern production with high efficiency and low cost.

[0047] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation of the present invention. Obviously, the drawings described below are only some embodiments. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the accompanying drawings:

[0049] Figure 1 , is the mass spectrum of trans, trans-1-[(3E)-pent-3-enyl]-4-(4-propylcyclohexyl)cyclohexane prepared in Example 1 of the present invention.

[0050] Figure 2 , is the gas chromatogram of trans, trans-1-[(3E)-pent-3-enyl]-4-(4-propylcyclohexyl)cyclohexane prepared in Example 1 of the present invention.

[0051] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but are intended to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0053] Example 1

[0054] (1) Add 72 g of trans-2-butenol, 130 g of pyridine and 300 ml of dichloromethane to a 1000 ml four-necked bottle; under nitrogen protection, cool to -10°C and drop 258 g of diethyl chlorophosphate; after the dropwise addition is completed, slowly heat to room temperature 25°C and stir and keep warm for 8 hours; then pour the kept warm liquid into 500 ml of ice water (containing 20 g of sodium hydroxide) and stir and hydrolyze for 10 minutes. After separation, wash twice with 500 ml of saturated sodium bicarbonate, then dry with anhydrous sodium sulfate for 8 hours, filter after drying, evaporate the solvent, and then evaporate low-boiling impurities under high vacuum conditions to obtain 187.2 g of intermediate A (≈0.90 mol) of dark yellow liquid with a yield of 90%;

[0055] The reaction formula in the above process is:

[0056]

[0057] (2) Add 2.0 g of intermediate B (trans, trans-4-propyldicyclohexylmethyl bromide), 2.52 g of magnesium chips (0.105 mol), 2 grains of iodine, and 50 ml of anhydrous tetrahydrofuran into a 500 ml four-necked bottle, heat to 60-70° C. under nitrogen protection to initiate the reaction, then add dropwise a solution prepared by 28.1 g of intermediate B (a total of 0.1 mol of intermediate B) and 100 ml of anhydrous tetrahydrofuran at 60-70° C., stir and keep warm for 3 hours, and cool to room temperature for use;

[0058] Add 22.9g of intermediate A (0.11mol) and 100ml of tetrahydrofuran solution into a 500ml four-necked bottle, cool to -40~-30℃ under nitrogen protection, slowly drop the Grignard reagent prepared from intermediate B, keep warm and stir for 3 hours after the dropwise addition, that is, react for 3 hours in the temperature range of -40~-30℃. After sampling and testing, pour the feed liquid into 200ml of 5% dilute hydrochloric acid cold water and hydrolyze for 30 minutes;

[0059] Then the post-processing procedure is carried out: the reaction product is extracted with 200 ml of toluene, the toluene layer is washed and neutralized with water, and the toluene layer is evaporated to obtain a crude product; the crude product is dissolved in n-heptane and chromatographically separated by a silica gel column to remove impurities, and the separated solution is evaporated to obtain a purified white solid, which is dissolved in a n-heptane / ethanol mixed solvent (volume ratio 1:3) for crystallization. The crystallization process needs to be repeated 3 times to improve the purity. Finally, 21.69 grams of high-purity trans, trans-1-[(3E)-pent-3-enyl]-4-(4-propylcyclohexyl)cyclohexane is obtained; the reaction formula in the above process is:

[0060]

[0061] The prepared target product was tested by gas chromatography, and the test results were as follows: Figure 2 As shown in Table 1 below;

[0062] Table 1:

[0063] name RT(min) Peak area Peak area% FID2B 16.993 0.229 0.00135 FID2B 18.822 16889.466 99.98252 FID2B 18.900 2.251 0.01333 FID2B 19.008 0.120 0.00071 FID2B 20.564 0.233 0.00138 FID2B 22.593 0.120 0.00071

[0064] It can be seen that the purity of the target product is 99.982%, the content of cis isomer is 0.013% (the content of other single impurities except cis isomer is ≤ 0.005%), and the yield of the target product is 78.6%.

[0065] The prepared target product was tested by GC-MS, and the test results were as follows: Figure 1 As shown, it is consistent with the molecular weight (M / Z=276.2) and fragment peaks compared with the standard sample.

[0066] Example 2

[0067] On the basis of Example 1, only the mass of intermediate A was replaced with 24.9 grams (0.12 mol) to prepare 21.8 grams of the target product trans, trans-1-[(3E)-pent-3-enyl]-4-(4-propylcyclohexyl)cyclohexane; the prepared target product was subjected to gas chromatography detection, and the test results showed that the purity of the target product was 99.975%, the content of cis isomer was 0.016% (the content of other single impurities except cis isomer was ≤0.005%), and the yield of the target product was 79.3%.

[0068] Example 3

[0069] On the basis of Example 1, only the mass of intermediate A was replaced with 18.7 grams (0.09 mol) to prepare 17.4 grams of the target product trans, trans-1-[(3E)-pent-3-enyl]-4-(4-propylcyclohexyl)cyclohexane; the prepared target product was detected by gas chromatography, and the test results showed that the purity of the target product was 99.942%, the content of cis isomer was 0.015% (the content of other single impurities except cis isomer was ≤0.005%), and the yield of the target product was 63.1%.

[0070] Example 4

[0071] On the basis of Example 1, only "Intermediate B: trans, trans-4-propyldicyclohexylmethyl bromide" was replaced with "Intermediate B: trans, trans-4-ethyldicyclohexylmethyl bromide" to prepare trans, trans-1-[(3E)-pent-3-enyl]-4-(4-ethylcyclohexyl)cyclohexane, which had a purity of 99.963% and a cis-isomer content of 0.018% (the content of other single impurities except the cis-isomer was ≤0.005%); the reaction formula of this example is:

[0072]

[0073] Example 5

[0074] On the basis of Example 1, only "2.52 grams of magnesium turnings (0.105 mol)" is replaced by "2.4 grams of magnesium turnings (0.10 mol)".

[0075] Example 6

[0076] On the basis of Example 1, only "2.52 grams of magnesium turnings (0.105 mol)" is replaced by "2.64 grams of magnesium turnings (0.11 mol)".

[0077] Example 7

[0078] On the basis of Example 1, only "2.52 grams of magnesium turnings (0.105 mol)" is replaced by "2.64 grams of magnesium turnings (0.11 mol)".

[0079] Example 8

[0080] The difference between this comparative example and Example 1 is that in step (2), the temperature is lowered to -30 to -20°C under nitrogen protection, and the Grignard reagent prepared by intermediate B is slowly added dropwise.

[0081] Example 9

[0082] The difference between this comparative example and Example 1 is that in step (2), the temperature is lowered to -25 to -20°C under nitrogen protection, and the Grignard reagent prepared by intermediate B is slowly added dropwise.

[0083] Example 10

[0084] The difference between this comparative example and Example 1 is that in step (2), the temperature is lowered to -40 to -35°C under nitrogen protection, and the Grignard reagent prepared by intermediate B is slowly added dropwise.

[0085] Comparative Example 1

[0086] In this comparative example, p-toluenesulfonate and trans-2-butenyl chloride Grignard reagent were coupled to prepare the target product, trans-1-[(3E)-pent-3-enyl]-4-(4-propylcyclohexyl)cyclohexane; the details are as follows:

[0087] Put 50ml of anhydrous tetrahydrofuran and 7.2g of magnesium flakes into a 500ml four-necked bottle; under nitrogen protection, drop 3g of trans-2-butenyl chloride, heat to 50℃ to initiate the reaction; then cool to 10-20℃, drop 24.1g of trans-2-butenyl chloride and 100ml of tetrahydrofuran solution. After the dropwise addition is completed, keep warm for 2 hours, then cool to 10℃, drop 39.2g of propyl dicyclohexylmethanol-p-toluenesulfonate and 60ml of anhydrous tetrahydrofuran solution, warm to room temperature and stir for 4 hours.

[0088] After the reaction is completed, pour the feed liquid into 100 ml of 5% dilute hydrochloric acid cold water and hydrolyze for 30 minutes. Then carry out post-treatment: extract the reaction product with 150 ml of toluene, wash and neutralize the toluene layer with water, and then evaporate the toluene layer to obtain a crude product. The crude product is dissolved in n-heptane and chromatographically separated by a silica gel column to remove impurities. The separated solution is evaporated to dryness to obtain a purified white solid;

[0089] The reaction equation of the above process is as follows:

[0090]

[0091] The white solid was detected by gas chromatography (GC), and the detection results showed that the content of the target product trans, trans-1-[(3E)-pent-3-enyl]-4-(4-propylcyclohexyl)cyclohexane was 16%, and the content of by-products was 80%.

[0092] It can be seen that the purity of the final product in Comparative Example 1 is only 16%, and the by-product content is as high as 80%. Such low product purity and high by-product content indicate that the coupling method using p-toluenesulfonate and trans-2-butenyl chloride Grignard reagent has poor reaction selectivity, generates a large amount of by-products, and causes the product quality to be seriously substandard. Due to the poor reaction selectivity, a large amount of by-products are generated, resulting in the need for more complicated separation and purification steps in the post-processing process, and even after separation and purification, the purity of the final product is still low, which is difficult to meet the needs of practical applications.

[0093] Compared with Comparative Example 1, the present application uses trans-2-butenol and chlorophosphate compounds for esterification reaction, followed by coupling reaction through a Grignard reagent, and finally prepares high-purity trans, trans-1-[(3E)-pent-3-enyl]-4-(4-propylcyclohexyl)cyclohexane. The entire reaction is carried out at a relatively low temperature (-40°C to -30°C) and is completed under nitrogen protection. The purity of the final product is as high as 99.9% or more, and the yield is 78.6%. This high-purity, high-yield product shows that the process of the present invention can effectively avoid the formation of impurities and ensure the consistency and quality of the product.

[0094] Comparative Example 2

[0095] The only difference between this comparative example and Example 1 is that 16.64 g of intermediate A (0.08 mol) was added.

[0096] Comparative Example 3

[0097] The only difference between this comparative example and Example 1 is that 29.12 g of intermediate A (0.14 mol) was added.

[0098] Comparative Example 4

[0099] The difference between this comparative example and Example 1 is that in step (2), the temperature is lowered to -50 to -60°C under nitrogen protection, and the Grignard reagent prepared by intermediate B is slowly added dropwise.

[0100] Comparative Example 5

[0101] The difference between this comparative example and Example 1 is that in step (2), the temperature is lowered to 10-20° C. under nitrogen protection, and the Grignard reagent prepared by intermediate B is slowly added dropwise.

[0102] The products obtained from Examples 1 to 3 and Comparative Examples 2 to 5 were tested, and the results are shown in Table 2 below.

[0103] Table 2:

[0104]

[0105]

[0106] Comparing Comparative Example 2 and Comparative Example 3 with Examples 1 to 3, when the ratio of intermediate A to Grignard reagent is 1.1:1 or 1.2:1, the Grignard reagent reaction of intermediate B is relatively complete, and the purity of the target product C produced reaches 99.982% and 99.975%, respectively, and the yield is 78.6% and 79.3%, respectively. This shows that when there is more intermediate A, the reaction of the Grignard reagent can be more complete, the amount of by-products generated is extremely low (the content of other single impurities is <0.005%), the quality of the final crystalline product is high, and the yield is maximized.

[0107] In Comparative Example 3, the ratio of intermediate A to Grignard reagent is 1.4:1. Although the amount of intermediate A is relatively more, the yield is not significantly improved in the case of excess. The yield of the final target product C is 78.1%, which is slightly lower than 79.3% in Example 2. This is because the excess of intermediate A makes it difficult to fully remove impurities during the crystallization process. Although the purity remains high (99.979%), the yield is not further improved.

[0108] When the ratio of intermediate A to Grignard reagent was 0.9:1, the amount of intermediate A was reduced, and the relative excess of Grignard reagent in the reaction resulted in more impurities in the hydrolyzate after the reaction. The purity of the final crystalline product was 99.942%, and the content of other individual impurities increased to 0.013%. In addition, the yield also dropped significantly to 63.1%, indicating that the shortage of intermediate A led to incomplete reaction and a decrease in product quality.

[0109] In Comparative Example 2, the ratio of intermediate A to Grignard reagent is 0.8:1. Since the amount of intermediate A is less, the excess of Grignard reagent is more significant. The results show that the purity of the target product C is only 99.893%, the content of other single impurities rises to 0.027%, and the yield is only 58.3%. This further shows that when the amount of intermediate A is too small, the reaction is incomplete and there are more by-products, resulting in a significant reduction in product quality, purity and yield.

[0110] The cooling reaction temperature of Example 1 is controlled between -40°C and -30°C. This lower temperature helps to control the reaction speed so that the reaction will not be too fast, and the selectivity between the reactants can be fully exerted. The purity of the obtained target product C reaches more than 99.9%, the impurity content is extremely low, and the yield is also high. That is, within this temperature range, the reaction speed is moderate, the selectivity is high, and the formation of by-products is effectively suppressed, indicating that this temperature condition is very beneficial for obtaining high-purity and high-yield products.

[0111] The cooling reaction temperature of Comparative Example 4 was lowered to -50°C to -60°C. Too low a temperature would significantly slow down the reaction rate, and the reaction time would not be enough to completely consume the reactants, resulting in a large amount of raw material residues.

[0112] The reaction temperature of Comparative Example 5 is 10°C to 20°C. A higher temperature will significantly accelerate the reaction rate, but it will also reduce the selectivity of the reaction, resulting in the generation of more by-products. As can be seen from the above table, the purity of the target product C drops to 99.63%, and the content of other single impurities rises to 0.13%. Although the yield is 72.1%, it is slightly lower than that of Example 1 and the purity is also much lower than that of Example 1; that is, although the higher reaction temperature accelerates the reaction rate, it reduces the reaction selectivity, resulting in an increase in by-products and a decrease in product purity, which shows that too high a temperature is not conducive to the generation of high-purity products, but increases the difficulty of subsequent purification.

[0113] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment, it is not used to limit the present invention. Any technician familiar with this patent can make some changes or modify the technical contents suggested above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the solution of the present invention.

Claims

1. A method for preparing an olefinic liquid crystal monomer, characterized in that: include: (1) taking trans-2-butenol and a chlorophosphate compound for esterification reaction to obtain a phosphate compound intermediate A; (2) The bicyclohexyl-substituted alkyl halide B undergoes a metal insertion reaction with magnesium to generate a Grignard reagent, and the generated Grignard reagent is coupled with the phosphate compound intermediate A obtained in step (1) to prepare an olefinic liquid crystal monomer C containing a bicyclohexyl group and a trans-substituted olefin group.

2. The method for preparing an olefinic liquid crystal monomer according to claim 1, characterized in that: In the step (1), the chlorophosphate ester compound is diethyl chlorophosphate, and the reaction formula of step (1) is: In the step (2), The dicyclohexyl-substituted alkyl halide B is: Wherein, R represents a C2-C5 alkyl straight chain hydrocarbon group, and X represents bromine or chlorine; The reaction equation in step (2) is:

3. The method for preparing an olefinic liquid crystal monomer according to claim 2, characterized in that: In the step (2), the molar ratio of the dicyclohexyl-substituted alkyl halide B: magnesium: phosphate compound intermediate A is 1.0: 1.0-1.1: 0.9-1.

2.

4. A method for preparing an olefinic liquid crystal monomer according to any one of claims 1 to 3, characterized in that: In the step (2), the phosphate compound intermediate A and the tetrahydrofuran solution are mixed and cooled under nitrogen protection, and after cooling, a Grignard reagent is added to react to prepare an olefinic liquid crystal monomer C containing a bicyclohexyl group and a trans-substituted olefin group.

5. The method for preparing an olefinic liquid crystal monomer according to claim 4, characterized in that: In the step (2), the Grignard reagent is added when the temperature drops to -40 to -20°C; preferably, -40 to -30°C.

6. A method for preparing an olefinic liquid crystal monomer according to claim 4 or 5, characterized in that: In the step (2), the Grignard reagent is added dropwise.

7. A method for preparing an olefinic liquid crystal monomer according to any one of claims 1 to 6, characterized in that: In the step (2), the Grignard reagent is added, stirred, and kept warm to react to prepare an olefinic liquid crystal monomer C containing a bicyclohexyl group and a trans-substituted olefin group.

8. The method for preparing an olefinic liquid crystal monomer according to claim 7, characterized in that: After the heat preservation reaction in step (2) is completed, the feed liquid is poured into dilute hydrochloric acid cold water for hydrolysis, and the reaction product is extracted with toluene after hydrolysis. The toluene layer is washed and neutralized with water, evaporated to dryness, dissolved in n-heptane and chromatographically separated by silica gel column to remove impurities. After separation, the solvent is evaporated to dryness, and dissolved in a mixed solvent of n-heptane and ethanol for crystallization to obtain trans, trans-1-[(3E)-pent-3-enyl]-4-(4-propylcyclohexyl)cyclohexane.

9. A method for preparing an olefinic liquid crystal monomer according to any one of claims 1 to 8, characterized in that: In the step (2), a dicyclohexyl-substituted alkyl halide B, magnesium and iodine are mixed into anhydrous tetrahydrofuran, and the reaction is initiated by heating under the protection of an inert gas. Then, the dicyclohexyl-substituted alkyl halide B and anhydrous tetrahydrofuran solution are added dropwise at 60 to 70° C. and the mixture is kept warm for 2 to 3 hours to prepare a Grignard reagent.

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