A method for synthesizing substituted naphthalene ring liquid crystal monomer

Abstract

The invention discloses a method for synthesizing a substituted naphthalene ring liquid crystal monomer, comprising: using 6-chloro-2-fluoronaphthalene and propylphenylboric acid as raw materials, adding a catalyst ligand DHPP and a catalyst under alkaline conditions, and performing a coupling reaction to obtain 2-fluoro-6-propylphenylnaphthalene, wherein the catalyst is a palladium catalyst or a nickel catalyst. The invention uses 4-(2'-nitro-1'2'-dibromo)ethylchlorobenzene as a raw material to prepare 2-fluoro-6-propylphenylnaphthalene, and the method is simple to operate, has mild process conditions, and has cheap and readily available raw materials, thereby overcoming the supply and purity problems of 2,6-substituted naphthalene raw materials in the existing method.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and in particular relates to a method for synthesizing a substituted naphthalene ring liquid crystal monomer. Background Art

[0002] Liquid crystal materials are widely used in modern display technology and many other fields. Liquid crystal monomers containing naphthalene rings are an important class of liquid crystal materials. Due to their unique structure and performance, they play an important role in liquid crystal displays, high-frequency technology components, etc. In the synthesis process of liquid crystal monomers containing naphthalene rings, halogen-substituted naphthalene is usually used as the key starting material for subsequent synthesis reactions.

[0003] At present, most of the synthesis of liquid crystal monomers containing naphthalene rings relies on 2,6-substituted naphthalene as raw materials. However, the supply of 2,6-substituted naphthalene in the market is very limited. This shortage of raw material supply has greatly restricted the large-scale production of liquid crystal monomers containing naphthalene rings. Even if a small amount of 2,6-substituted naphthalene can be obtained on the market, the purity of its raw materials will have a great impact on the subsequent synthesis capacity. Low-purity raw materials are prone to incomplete reactions or more side reactions during the synthesis process, thereby reducing the synthesis efficiency and restricting the production capacity. Especially for multiple substitutions and positional isomerization, impurities in the raw materials have a crucial impact on the purification of the products. In the 2,6-substituted naphthalene raw materials, there are often isomers and other impurities that are difficult to remove. These impurities will enter the intermediates and final products during the synthesis process, making product purification extremely difficult. Because the purity of the raw materials cannot be guaranteed and the impurities are difficult to remove, the quality of the finished liquid crystal monomer containing naphthalene rings will eventually be seriously affected. For example, the physical and chemical properties of the finished product may not meet the expected requirements, which in turn affects its performance in applications such as liquid crystal displays.

[0004] The method of synthesizing a liquid crystal monomer containing a naphthalene ring from 2,6-dihalide naphthalene through coupling or selective coupling, and then Grignard coupling with an alkyl halide has obvious defects. For example, the required 2,6-substituted naphthalene raw material is not only difficult to obtain from the market, but even if there is a small supply, there are problems of insufficient purity and difficulty in removing impurities, which seriously affects the subsequent purification and the quality of the final product. Summary of the invention

[0005] The purpose of the present invention is to provide a novel method for synthesizing a naphthalene ring-containing liquid crystal monomer containing a substituted group, which solves the problems of raw material supply and purity in the existing method, as well as a series of technical problems caused by the raw materials, so as to meet the market demand for the quality and output of the naphthalene ring-containing liquid crystal monomer.

[0006] In order to achieve the above object, the present invention provides a method for synthesizing a substituted naphthalene ring liquid crystal monomer, the synthetic route is:

[0007]

[0008] Among them, 6-chloro-2-fluoronaphthalene and propylphenylboric acid are used as raw materials, and under alkaline conditions, catalyst ligand DHPP and a catalyst are added to carry out a coupling reaction to obtain compound 1, and the catalyst is a palladium-based catalyst or a nickel-based catalyst.

[0009] Optionally, the molar ratio of propylphenylboric acid to 6-chloro-2-fluoronaphthalene is (1-1.3):1; the mass percentage of the catalyst and 6-chloro-2-fluoronaphthalene is 0.05%-0.1%.

[0010] Optionally, the alkaline condition refers to adding a base, the base is at least one of potassium carbonate, sodium carbonate, and sodium hydroxide, the molar ratio of the base to 6-chloro-2-fluoronaphthalene is (2 to 2.5):1, and the reaction temperature is 60°C to 90°C.

[0011] Alternatively, the synthetic route of 6-chloro-2-fluoronaphthalene is:

[0012]

[0013] Include:

[0014] Step 2.1, using 6-chloro-2-nitronaphthalene as a raw material, catalytic hydrogenation is performed under acidic conditions to prepare 6-chloro-2-aminonaphthalene;

[0015] Step 2.2, 6-chloro-2-aminonaphthalene is subjected to diazotization reaction with sodium nitrite and fluorine-containing acid to obtain 6-chloro

[0016] -2-Fluoronaphthalene

[0017] Optionally, in step 2.1, the acidic condition refers to adding an organic acid to the reaction solution, the organic acid comprises formic acid and / or acetic acid, and the molar ratio of the organic acid to 6-chloro-2-nitronaphthalene is (8-10):1; the catalyst is an aluminum-nickel alloy, and the mass ratio of the catalyst to 6-chloro-2-nitronaphthalene is (0.1-0.4):1; the reaction temperature is 50°C to 95°C.

[0018] Optionally, in step 2.2, the fluorine-containing acid is at least one of fluoroboric acid, hydrochloric acid / fluoroboric acid, and sulfuric acid / fluoroboric acid, and the molar ratio of the fluorine-containing acid to 6-chloro-2-aminonaphthalene is (2 to 4):1; and the reaction temperature is -5°C to 10°C.

[0019] Optionally, in step 2.2, the mass of the sodium nitrite solution is 1 to 3 times that of 6-chloro-2-aminonaphthalene, and the concentration of the sodium nitrite solution is 30wt%-50wt%.

[0020] Alternatively, the synthetic route of 6-chloro-2-nitronaphthalene is:

[0021]

[0022] The method comprises taking 4-chlorophenyl-3-nitro-3-ene-butyraldehyde as a raw material, and forming 6-chloro-2-nitronaphthalene through ring closure under the action of a condensing agent, wherein the condensing agent is at least one of hydrochloric acid, acetic acid, and trifluoromethanesulfonic acid, and the molar ratio of the condensing agent to 4-chlorophenyl-3-nitro-3-ene-butyraldehyde is (0.1-0.5):1, the reaction temperature is 60°C-90°C, and the reaction time is 8h-20h.

[0023] Alternatively, the synthetic route of 4-chlorophenyl-3-nitro-3-ene-butyraldehyde is:

[0024]

[0025] The steps include:

[0026] In the first stage, potassium carbonate is added to the dibromosubstrate (2) as a raw material, the molar ratio of potassium carbonate to the dibromosubstrate (2) is (1-1.5):1, and the reaction temperature is 10°C-40°C;

[0027] In the second stage, potassium carbonate and acetaldehyde trimer are added, wherein the molar ratio of potassium carbonate to dibrominated substrate (2) is (1-1.5):1, the molar ratio of acetaldehyde trimer to dibrominated substrate (2) is (1.1-2.5):1, and the reaction temperature is 30°C to 50°C;

[0028] In the third stage, potassium carbonate is added, wherein the molar ratio of potassium carbonate to dibromosubstrate (2) is (1-2):1, and the reaction temperature is 55°C to 70°C.

[0029] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0030] The present invention uses 4-(2'-nitro-1'2'-dibromo)ethylchlorobenzene as a raw material and adopts a one-pot method through three stages: in the first stage, one bromine is eliminated to prepare olefin; in the second stage, acetaldehyde is added; in the third stage, the second bromine is eliminated to obtain 4-chlorophenyl-3-nitro-3-olefin butyraldehyde. The present invention adopts a one-step method to complete the preparation of 4-chlorophenyl-3-nitro-3-olefin butyraldehyde without intermediate post-treatment and purification, which reduces the synthesis steps to a certain extent, ensures the reaction conversion rate and yield, and improves the reaction efficiency. The method is simple to operate, mild in conditions, and high in yield.

[0031] Furthermore, the present invention directly prepares 2,6-substituted naphthalene rings through the synthesis of naphthalene rings, and the substrate purity is higher, and there are no impurities such as isomers and multiple substitutions. Although the reaction route is slightly longer, the advantages of naphthalene ring synthesis are also obvious. Compared with the comprehensive later purification, this route is not restricted by raw materials, and the cost is relatively cheap compared to purchasing naphthalene ring substrates, and the overall cost is reduced. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The present invention provides a method for synthesizing a substituted naphthalene ring liquid crystal monomer, and the synthesis route is:

[0034]

[0035] Among them, 6-chloro-2-fluoronaphthalene and propylphenylboric acid are used as raw materials, and under alkaline conditions, catalyst ligand DHPP and a catalyst are added to carry out a coupling reaction to obtain compound 1, and the catalyst is a palladium-based catalyst or a nickel-based catalyst.

[0036] DHPP is 2-dicyclohexylphosphine-2',6'-dimethoxy-1,1'-biphenyl, CAS: 657408-07-6, and is used as a catalyst ligand in the present invention.

[0037] In some embodiments, the molar ratio of propylphenylboric acid to 6-chloro-2-fluoronaphthalene is (1-1.3):1; the mass percentage of the catalyst and 6-chloro-2-fluoronaphthalene is 0.05%-0.1%.

[0038] Optionally, the alkaline condition refers to adding a base, the base is at least one of potassium carbonate, sodium carbonate, sodium hydroxide, etc., the molar ratio of the base to 6-chloro-2-fluoronaphthalene is (2-2.5):1, and the reaction temperature is 60°C-90°C; the solvent can be toluene, petroleum ether, ethanol, etc., and the amount used is 3-8 times the weight of 6-chloro-2-fluoronaphthalene.

[0039] In some embodiments, the synthetic route of 6-chloro-2-fluoronaphthalene is:

[0040]

[0041] Include:

[0042] Step 2.1, using 6-chloro-2-nitronaphthalene as a raw material, catalytic hydrogenation is performed under acidic conditions to prepare 6-chloro-2-aminonaphthalene;

[0043] Step 2.2, 6-chloro-2-aminonaphthalene undergoes diazotization reaction with sodium nitrite and fluorine-containing acid to obtain 6-chloro-2-fluoronaphthalene.

[0044] Optionally, in the step 2.1, the acidic condition refers to adding an organic acid to the reaction solution, the organic acid comprises formic acid and / or acetic acid, and the molar ratio of the organic acid to 6-chloro-2-nitronaphthalene is (8-10):1; the catalyst is an aluminum-nickel alloy, and the mass ratio of the catalyst to 6-chloro-2-nitronaphthalene is (0.1-0.4):1; the reaction temperature is 50°C to 95°C; the solvent can be selected from toluene, chlorobenzene, petroleum ether, etc., and the amount used is 4-6 times the weight of the substrate (6-chloro-2-nitronaphthalene).

[0045] Optionally, in step 2.2, the fluorine-containing acid is at least one of fluoroboric acid, hydrochloric acid / fluoroboric acid, and sulfuric acid / fluoroboric acid, and the molar ratio of the fluorine-containing acid to 6-chloro-2-aminonaphthalene is (2 to 4):1; the reaction temperature is -5°C to 10°C, the reaction solvent is water, and the post-treatment temperature is 80°C to 120°C.

[0046] Optionally, in step 2.2, the mass of the sodium nitrite solution is 1 to 3 times that of 6-chloro-2-aminonaphthalene, and the concentration of the sodium nitrite solution is 30wt%-50wt%.

[0047] In some embodiments, the synthetic route of 6-chloro-2-nitronaphthalene is:

[0048]

[0049] The method comprises taking 4-chlorophenyl-3-nitro-3-ene-butyraldehyde as a raw material, and forming 6-chloro-2-nitronaphthalene through ring closure under the action of a condensing agent, wherein the condensing agent is at least one of hydrochloric acid, acetic acid and trifluoromethanesulfonic acid, and the molar ratio of the condensing agent to 4-chlorophenyl-3-nitro-3-ene-butyraldehyde is (0.1-0.5):1, the reaction temperature is 60-90°C, and the reaction time is 8-20 hours; the solvent can be selected from toluene, chlorobenzene, methyltetrahydrofuran and the like, and the amount used is 3-6 times the weight of the substrate (4-chlorophenyl-3-nitro-3-ene-butyraldehyde).

[0050] Alternatively, the synthetic route of 4-chlorophenyl-3-nitro-3-ene-butyraldehyde is:

[0051]

[0052] The steps include:

[0053] In the first stage, 4-(2'-nitro-1'2'-dibromo)ethylchlorobenzene (i.e., dibromo substrate 2) is used as a raw material, potassium carbonate is added, the amount of potassium carbonate and dibromo substrate (2) is used in a molar ratio of (1 to 1.5):1, and the reaction temperature is 10°C to 40°C;

[0054] In the second stage, potassium carbonate and acetaldehyde trimer are added, wherein the molar ratio of potassium carbonate to dibrominated substrate (2) is (1-1.5):1, the molar ratio of acetaldehyde trimer to dibrominated substrate (2) is (1.1-2.5):1, and the reaction temperature is 30°C to 50°C;

[0055] In the third stage, potassium carbonate is added, wherein the molar ratio of potassium carbonate to dibromosubstrate (2) is (1-2):1, and the reaction temperature is 55°C to 70°C.

[0056] Optionally, the reaction solvent is tetrahydrofuran, methyltetrahydrofuran, etc., and the amount used is 2 to 6 times the weight of the dibromosubstrate 2. The reaction time is 24 to 36 hours. The post-treatment solvent can be toluene, chlorobenzene, methyltetrahydrofuran, etc., and the amount used is 3 to 6 times the weight of the dibromosubstrate 2.

[0057] The following is a description of the specific examples. The raw materials, reagents, etc. used in the examples are commercially available unless otherwise specified.

[0058] Example

[0059]

[0060] Put 68.6g (0.2mol) of dibromosubstrate, 30.4g (0.22mol) of potassium carbonate and 200ml of tetrahydrofuran into a 500ml three-necked flask, stir at 20-30℃ for 6-8h under nitrogen protection until the raw material content is qualified, continue to add 34.5g (0.25mol) of potassium carbonate and 13.2g (0.3mol) of acetaldehyde trimer and 40ml of tetrahydrofuran to the system, heat to 40-45℃, continue to stir and react for 8-12h until the reaction is qualified, then add 30.4g (0.22mol) of potassium carbonate to the system, heat to reflux and continue to react for 10-12h. After the reaction is qualified, filter the salt in the system, add 250ml of toluene and 100ml of saturated brine to the filtrate, stir and wash the liquid, wash several times until neutral, and concentrate under reduced pressure to 150g solution, theoretical yield 45g, actual yield 34g, yield 75.56%.

[0061]

[0062] In a 500ml three-necked flask equipped with a condenser, mechanical stirring, and a thermometer, add 150g of a toluene solution of 34g (0.151mol) of 4-chlorophenyl-3-nitro-3-ene-butyraldehyde, add 1.8g (0.03mol) of glacial acetic acid, stir and heat to 80-85°C under nitrogen protection, and react for 12-16h until the raw material is qualified. Cool to room temperature, add 100ml of water to the reaction system, stir and separate, wash the organic layer with 100ml of water until neutral, concentrate toluene, and crystallize with 30ml of toluene and 60ml of petroleum ether to obtain 27.2g of the product 6-chloro-2-nitronaphthalene. Theoretical yield is 31.26g, and the yield is 87%.

[0063]

[0064] In a 500ml three-necked flask equipped with a condenser, mechanical stirring, and a thermometer, add 51.8g (0.25mol) of 6-chloro-2-nitronaphthalene, 92g (2mol) of 85% formic acid, 10g of aluminum-nickel alloy powder, and 250ml of toluene. Stir and heat to 80-85°C under nitrogen protection, and react for 8-10h until the raw material is qualified. Cool to room temperature, separate the liquids, wash the organic layer with 100ml of water until it is neutral, and concentrate the toluene to obtain 41.5g of the product 6-chloro-2-aminonaphthalene. The theoretical yield is 44.25g, and the yield is 93.79%.

[0065]

[0066] Put 41.5g (0.234mol) of 6-chloro-2-aminonaphthalene and 129g (0.588mol) of 40% fluoroboric acid into a 500ml three-necked flask, stir and cool to -5℃~0℃, add 60.5g (0.35mol) of 40% sodium nitrite aqueous solution, keep warm and stir until qualified, filter the reaction solution, wash the filter residue with ice water 5 times and vacuum dry. After drying, put the solid into another 500ml three-necked flask with reflux, add 200ml of xylene, stir and heat to 120-125℃ and react for 6-8h until qualified. Cool to room temperature, add water to the bottle to wash the liquid. Concentrate xylene, add 40ml toluene and 80ml petroleum ether to the system after concentration, crystallize, filter and dry to obtain 35g of 6-chloro-2-fluoronaphthalene product, with a theoretical yield of 42.2g and a yield of 82.9%.

[0067]

[0068] Put 45.3g (0.427mol) of sodium carbonate and 230g of pure water into a 1000ml three-necked flask, stir until completely dissolved, add 35g (0.194mol) of 6-chloro-2-fluoronaphthalene, 33.4g (0.204mol) of propylphenylboric acid, 0.022g (0.098mmol) of palladium acetate and 0.08g (0.195mmol) of ligand DHPP into the system, add 250ml of toluene, replace with nitrogen three times, stir and heat to 80-85℃ to react until qualified. Cool to room temperature, separate the liquid, wash the organic layer with water until neutral, concentrate and spin dry, add 50ml of toluene and 150ml of ethanol for crystallization, and obtain 49.2g of product 2-fluoro-6-propylphenylnaphthalene, with a theoretical yield of 51.2g and a yield of 96%.

[0069] In summary, the present invention uses 4-(2'-nitro-1'2'-dibromo)ethylchlorobenzene as a raw material, eliminates one bromine to prepare olefin, then adds acetaldehyde, eliminates the second bromine to obtain 4-chlorophenyl-3-nitro-3-olefin butyraldehyde, and then closes the ring to obtain 6-chloro-2-nitronaphthalene. 6-chloro-2-nitronaphthalene is then diazotized to prepare 6-chloro-2-fluoronaphthalene, and finally coupled with propylphenylboric acid to prepare the product 2-fluoro-6-propylphenylnaphthalene. The present invention synthesizes a 2,6-substituted naphthalene ring substrate for coupling to prepare a product, and the substrate (2,6-substituted naphthalene ring) has higher purity, is simple to operate, has mild process conditions, and has cheap and readily available raw materials, thereby overcoming the supply and purity problems of the 2,6-substituted naphthalene raw materials in the existing method.

[0070] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A method for synthesizing a substituted naphthalene ring-containing liquid crystal monomer, characterized in that: The synthetic route is: Among them, 6-chloro-2-fluoronaphthalene and propylphenylboric acid are used as raw materials, and under alkaline conditions, catalyst ligand DHPP and a catalyst are added to carry out a coupling reaction to obtain compound (1), wherein the catalyst is a palladium-based catalyst or a nickel-based catalyst.

2. The method for synthesizing a substituted naphthalene ring-containing liquid crystal monomer according to claim 1, characterized in that: The molar ratio of propylphenylboric acid to 6-chloro-2-fluoronaphthalene is (1-1.3):1; the mass percentage of the catalyst and 6-chloro-2-fluoronaphthalene is 0.05%-0.1%.

3. The method for synthesizing a substituted naphthalene ring-containing liquid crystal monomer according to claim 1, characterized in that: The alkaline condition refers to adding a base, the base is at least one of potassium carbonate, sodium carbonate, and sodium hydroxide, the molar ratio of the base to 6-chloro-2-fluoronaphthalene is (2-2.5):1, and the reaction temperature is 60°C-90°C.

4. The method for synthesizing a substituted naphthalene ring-containing liquid crystal monomer according to claim 1, wherein: The synthetic route of 6-chloro-2-fluoronaphthalene is: Include: Step 2.1, using 6-chloro-2-nitronaphthalene as a raw material, catalytic hydrogenation is performed under acidic conditions to prepare 6-chloro-2-aminonaphthalene; Step 2.2, 6-chloro-2-aminonaphthalene undergoes diazotization reaction with sodium nitrite and fluorine-containing acid to obtain 6-chloro-2-fluoronaphthalene.

5. The method for synthesizing a substituted naphthalene ring-containing liquid crystal monomer according to claim 4, characterized in that: In the step 2.1, the acidic condition refers to adding an organic acid to the reaction solution, wherein the organic acid comprises formic acid and / or acetic acid, and the molar ratio of the organic acid to 6-chloro-2-nitronaphthalene is (8-10):

1.

6. The method for synthesizing a substituted naphthalene ring-containing liquid crystal monomer according to claim 4, characterized in that: In the step 2.1, the catalyst is an aluminum-nickel alloy, and the mass ratio of the catalyst to 6-chloro-2-nitronaphthalene is (0.1-0.4):1; the reaction temperature is 50°C-95°C.

7. The method for synthesizing a substituted naphthalene ring-containing liquid crystal monomer according to claim 4, characterized in that: In the step 2.2, the fluorine-containing acid is at least one of fluoroboric acid, hydrochloric acid / fluoroboric acid, and sulfuric acid / fluoroboric acid, and the molar ratio of the fluorine-containing acid to 6-chloro-2-aminonaphthalene is (2-4):1; The reaction temperature is -5°C to 10°C.

8. The method for synthesizing a substituted naphthalene ring-containing liquid crystal monomer according to claim 4, characterized in that: In the step 2.2, the mass of the sodium nitrite solution is 1 to 3 times that of 6-chloro-2-aminonaphthalene, and the concentration of the sodium nitrite solution is 30 wt% to 50 wt%.

9. The method for synthesizing a substituted naphthalene ring-containing liquid crystal monomer according to claim 4, characterized in that: The synthetic route of 6-chloro-2-nitronaphthalene is: The method comprises taking 4-chlorophenyl-3-nitro-3-ene-butyraldehyde as a raw material, and forming 6-chloro-2-nitronaphthalene through ring closure under the action of a condensing agent, wherein the condensing agent is at least one of hydrochloric acid, acetic acid, and trifluoromethanesulfonic acid, and the molar ratio of the condensing agent to 4-chlorophenyl-3-nitro-3-ene-butyraldehyde is (0.1-0.5):1, the reaction temperature is 60°C-90°C, and the reaction time is 8h-20h.

10. The method for synthesizing a substituted naphthalene ring-containing liquid crystal monomer according to claim 8, characterized in that: The synthetic route of 4-chlorophenyl-3-nitro-3-ene-butyraldehyde is: The steps include: In the first stage, potassium carbonate is added to the dibromosubstrate (2) as a raw material, the molar ratio of potassium carbonate to the dibromosubstrate (2) is (1-1.5):1, and the reaction temperature is 10°C-40°C; In the second stage, potassium carbonate and acetaldehyde trimer are added, wherein the molar ratio of potassium carbonate to dibrominated substrate (2) is (1-1.5):1, the molar ratio of acetaldehyde trimer to dibrominated substrate (2) is (1.1-2.5):1, and the reaction temperature is 30°C to 50°C; In the third stage, potassium carbonate is added, wherein the molar ratio of potassium carbonate to dibromosubstrate (2) is (1-2):1, and the reaction temperature is 55°C to 70°C.

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