CN110551076A - benzoxazole liquid crystal compound containing acetylene bonds and preparation method thereof - Google Patents

Abstract

The invention discloses an acetylene bond-containing benzoxazole liquid crystal compound and a preparation method thereof, belonging to the technical field of materials. The structural formula of this compound is In the formula, R represents a C ₅ -C ₁₂ straight-chain alkyl group, and X represents hydrogen, methyl or nitro. The compound uses p-bromobenzaldehyde, 2-methyl-3-butyne-2-alcohol, 1-iodo-4-(alkoxy)benzene and aminophenol as raw materials, and is subjected to Sonogashira coupling, nucleophilic addition, Ring closure and other reactions. The liquid crystal compound of the present invention has large birefringence and wide liquid crystal phase region, and can be used in liquid crystal optoelectronic devices to improve its response speed.

Description

Alkyne bond-containing benzoxazole liquid crystal compound and preparation method thereof

technical field

The invention belongs to the technical field of materials, and particularly relates to an acetylene bond-containing benzoxazole liquid crystal compound and a preparation method thereof.

Background technique

Liquid crystal materials are widely used in display fields such as tablet computers, mobile phones, notebook computers and high-definition TVs, as well as non-display fields such as light modulators, laser beam deflection, and adaptive optics. Liquid crystal optoelectronic devices have the advantages of low driving voltage, large amount of phase modulation, light weight, and low power consumption.

Liquid crystal materials are the key core materials of liquid crystal optoelectronic devices, and the performance optimization of liquid crystal optoelectronic devices is mainly achieved by adjusting the structure and composition of liquid crystal materials. In recent years, fast response has been an important development direction of liquid crystal optoelectronic devices. In order to improve the response speed of liquid crystal optoelectronic devices, on the one hand, low-viscosity liquid crystal compounds can be used. The viscosity of liquid crystal compounds is directly related to the response time of liquid crystal devices. The faster the speed; on the other hand, the cell thickness of the liquid crystal device can be reduced. The lower the cell thickness of the liquid crystal device, the faster the response speed, and the use of large optical anisotropy (Δn) liquid crystal material can effectively reduce the cell thickness of the liquid crystal device in practical applications. . Therefore, large Δn liquid crystal is the key material for realizing fast response of liquid crystal optoelectronic devices.

The structure of liquid crystal compounds is generally constructed of benzene ring, cyclohexyl, aromatic heterocycle, etc. as a rigid skeleton. It can increase the conjugation length of liquid crystal molecules by introducing alkyne bonds, adding benzene rings, introducing cyano groups or isothiocyanato groups, etc., and then improving the liquid crystal compounds. Δn. Although there are many optically anisotropic liquid crystal materials at present, their Δn is not large enough and there are not enough types, which limits their application in liquid crystal optoelectronic devices. In particular, there are very few kinds of large Δn aromatic heterocyclic liquid crystal compounds that can be used as liquid crystal optoelectronic devices.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a benzoxazole liquid crystal compound containing an acetylene bond with a large birefringence, and to provide a preparation method for the compound with simple process steps and high yield.

For the above purpose, the structural formula of the acetylenic bond-containing benzoxazole liquid crystal compound used in the present invention is as follows:

In the formula, R represents a C ₅ -C ₁₂ straight-chain alkyl group, and X represents any one of H, CH ₃ and NO ₂ .

The preparation method of the above-mentioned acetylenic bond-containing benzoxazole liquid crystal compound consists of the following steps:

1. Preparation of 4-(4-(1,3-dioxolan-2-yl)phenyl)-2-methylbut-3-yn-2-ol

Add p-bromobenzaldehyde, p-toluenesulfonic acid and ethylene glycol to chloroform, react at 50-70°C for 6-8 hours, evaporate the solvent under reduced pressure, and then add 2-methyl-3- Butyn-2-ol, cuprous iodide, triphenylphosphine, tetrakis (triphenylphosphine) palladium, triethylamine, react at 80～90℃ for 8～10h, separate and purify to obtain 4-(4- (1,3-dioxolane-2-yl)phenyl)-2-methylbut-3-yn-2-ol, the reaction equation is as follows:

2. Preparation of 2-(4-((4-(alkoxy)phenyl)ethynyl)phenyl)-1,3-dioxolane

4-(4-(1,3-dioxolan-2-yl)phenyl)-2-methylbut-3-yn-2-ol, 1-iodo-4-(alkane shown in formula I Oxy)benzene, ethylene glycol ether, sodium hydroxide, and tetrakis(triphenylphosphine)palladium were added to toluene, and reacted at 60-80 °C for 8-10 h under nitrogen protection. After the reaction was completed, separation and purification were performed to obtain 2-( 4-((4-(alkoxy)phenyl)ethynyl)phenyl)-1,3-dioxolane, the reaction equation is as follows:

In formula I, R represents a C ₅ -C ₁₂ straight-chain alkyl group.

3. Preparation of 4-((4-(alkoxy)phenyl)ethynyl)benzaldehyde

Add 4-((4-(alkoxy)phenyl)ethynyl)phenyl)-1,3-dioxolane and formic acid to tetrahydrofuran, and react at 50～70℃ for 5～6h, after the reaction is over , separation and purification to obtain 4-((4-(alkoxy) phenyl) ethynyl) benzaldehyde, the reaction equation is as follows:

4. Preparation of 2-((4-((4-(alkoxy)phenyl)ethynyl)benzylidene)amino)phenol

Add 4-((4-(alkoxy)phenyl)ethynyl)benzaldehyde and aminophenol shown in formula II to ethanol, stir and reflux for 4-6h, remove the solvent by vacuum distillation, and recrystallize to obtain 2-(( 4-((4-(alkoxy) phenyl) ethynyl) benzylidene) amino) phenol, reaction equation is as follows:

In formula II, X represents any one of H, CH ₃ and NO ₂ .

5. Preparation of acetylene bond-containing benzoxazole liquid crystal compounds

Add 2-((4-((4-(alkoxy)phenyl)ethynyl)benzylidene)amino)phenol and dichlorodicyanobenzoquinone (DDQ) to chloroform, reflux reaction 4 After ~6h, stop the reaction, separate and purify, and obtain the target compound - a benzoxazole liquid crystal compound containing an alkyne bond. The reaction equation is as follows:

In the above step 1, the molar ratio of p-bromobenzaldehyde to p-toluenesulfonic acid and ethylene glycol is preferably 4:0.9～1.2:80～90, p-bromobenzaldehyde to 2-methyl-3-butyn-2-ol , the molar ratio of cuprous iodide, triphenylphosphine and tetrakis(triphenylphosphine) palladium is 1:0.4-1:0.01-0.03:0.04-0.08:0.007-0.01.

In the above step 2, preferably 4-(4-(1,3-dioxolane-2-yl)phenyl)-2-methylbut-3-yn-2-ol and 1-iodo-4-( The molar ratio of alkoxy)benzene, ethylene glycol ether, sodium hydroxide, and tetrakis(triphenylphosphine)palladium is 1:1-1.2:10-15:5-8:0.02-0.05.

In the above step 3, the molar ratio of 2-(4-((4-(hexyloxy)phenyl)ethynyl)phenyl)-1,3-dioxolane to formic acid is preferably 1:180-185.

In the above step 4, the molar ratio of 4-((4-(alkoxy)phenyl)ethynyl)benzaldehyde to aminophenol is preferably 1:1.1-1.5.

In the above-mentioned steps 5, the preferred mol ratio of 2-((4-((4-(alkoxy)phenyl)ethynyl)benzylidene)amino)phenol to dichlorodicyanoquinone is 1:1.1 ~1.5.

The beneficial effects of the present invention are as follows:

The liquid crystal compound of the present invention uses p-bromobenzaldehyde, 2-methyl-3-butyn-2-ol, 1-iodo-4-(alkoxy)benzene and aminophenol as raw materials, and is coupled through Sonogashira and nucleophilic. It is prepared by reactions such as addition and ring closure. It not only has the heterocyclic liquid crystal mesogenic phase type, but also has a large birefringence and a wide nematic phase interval, and the preparation method has simple steps and high yield. , which can be used in liquid crystal optoelectronic devices to improve their response speed.

Description of drawings

1 is a DSC curve of the liquid crystal compound obtained in Example 1 (temperature rise and fall rate of 5° C./min).

2 is a POM photograph (200×) of the liquid crystal compound obtained in Example 1 when the temperature was raised to 179.2°C.

3 is a POM photograph (200×) of the liquid crystal compound obtained in Example 1 when the temperature was lowered to 201.8°C.

Detailed ways

The present invention is further described in detail below with reference to the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

Example 1

1. Preparation of 4-(4-(1,3-dioxolan-2-yl)phenyl)-2-methylbut-3-yn-2-ol

In a 250mL three-necked flask equipped with a condenser tube and a stirrer, add p-bromobenzaldehyde 10g (54mmol), p-toluenesulfonic acid 2.3g (13.4mmol), ethylene glycol 75g (1203.6mmol), and add it to it after drying with molecular sieves 100 mL of chloroform was stirred in a constant temperature oil bath at 60 ° C for 6 h to stop the reaction, the solvent was evaporated under reduced pressure, and 2.01 g (23.8 mmol) of 2-methyl-3-butyn-2-ol, 2.01 g (23.8 mmol), 0.2 g (1.0 mmol) of cuprous iodide, 0.6 g (2.2 mmol) of triphenylphosphine, and 80 mL of triethylamine were added as the reaction solvent, heated in a constant temperature oil bath at 80 °C and protected by nitrogen, and reacted for 1 h after , 0.5 g (0.43 mmol) of tetrakis (triphenylphosphine) palladium was rapidly added under nitrogen protection, and the reaction was stopped after continuing the reaction for 8 h. After the reaction, the reaction system was diluted with water, extracted with dichloromethane, the organic phase was separated, and the aqueous phase was repeatedly extracted with dichloromethane. Magnesium was dried, the solvent was evaporated under reduced pressure, and 7g of silica gel was added to it for sample preparation, and column chromatography was performed (the eluent was a mixture of petroleum ether and ethyl acetate with a volume ratio of 30:1) to obtain a yellow oily liquid 4-( 4-(1,3-dioxolan-2-yl)phenyl)-2-methylbut-3-yn-2-ol, yield 44%, the reaction equation is as follows:

2. Preparation of 2-(4-((4-(hexyloxy)phenyl)ethynyl)phenyl)-1,3-dioxolane

4-(4-(1,3-dioxolan-2-yl)phenyl)-2-methylbut-3-yn-2- Alcohol 2.8g (12mmol), 1-iodo-4-(hexyloxy)benzene 3.8 (12.6mmol), ethylene glycol ether 10.8g (120.5mmol), sodium hydroxide 2.9g (72.2mmol), toluene 80mL, in It was heated in a constant temperature oil bath at 70°C and protected with nitrogen. After 1 h of reaction, 0.28 g (0.24 mmol) of tetrakis(triphenylphosphine) palladium was rapidly added under nitrogen protection, and the reaction was stopped after continuing the reaction for 8 h. After the reaction, the reaction system was diluted with water, extracted with dichloromethane, the organic phase was separated, and the aqueous phase was repeatedly extracted with dichloromethane, the organic phases were combined, and the obtained organic phase was washed three times with saturated ammonium chloride solution, and anhydrous sulfuric acid Magnesium was dried, the solvent was evaporated under reduced pressure, and 7g of silica gel was added to it for sample preparation, and column chromatography was performed (the eluent was a mixture of petroleum ether and ethyl acetate in a volume ratio of 30:1) to obtain a pale yellow solid 2-( 4-((4-(hexyloxy)phenyl)ethynyl)phenyl)-1,3-dioxolane, yield 59%, the reaction equation is as follows:

3. Preparation of 4-((4-(hexyloxy)phenyl)ethynyl)benzaldehyde

2-(4-((4-(hexyloxy)phenyl)ethynyl)phenyl)-1,3-dioxolane 2.5g ( 7.4 mmol), 62 g (1339 mmol) of formic acid, and 80 mL of tetrahydrofuran, heated and reacted in a constant temperature oil bath at 60° C. for 6 h. After the reaction, the reaction solution was extracted with dichloromethane and water, concentrated by rotary evaporation to obtain a white solid, which was recrystallized by adding absolute ethanol to obtain a white solid 4-((4-(hexyloxy)phenyl)ethynyl)benzene Formaldehyde, yield 83%, reaction equation is as follows:

4. Preparation of 2-((4-((4-(hexyloxy)phenyl)ethynyl)benzylidene)amino)-4-methylphenol

In a 100mL single-necked flask equipped with a stirring bar and a condenser tube, add 0.4g (1.4mmol) of 4-((4-(hexyloxy)phenyl)ethynyl)benzaldehyde, 0.20 g (1.4 mmol) of 2-amino-4-methylphenol, g (1.6 mmol), 40 mL of anhydrous ethanol, stirred and refluxed at 80° C. for 6 h until the reaction was complete. After cooling to room temperature, yellow needle crystals were precipitated, which was filtered with a Buchner funnel to obtain a yellow solid 2-((4-((4-(hexyloxy)phenyl)ethynyl)benzylidene)amino)- 4-methylphenol, yield 83%, reaction equation is as follows:

5. Preparation of 2-(4-((4-(hexyloxy)phenyl)ethynyl)phenyl)-5-methylbenzoxazole liquid crystal

0.2g of 2-((4-((4-(hexyloxy)phenyl)ethynyl)benzylidene)amino)-4-methylphenol was added to a 100mL single-necked flask equipped with a stirring bar and a condenser tube (0.50 mmol), 0.14 g (0.62 mmol) of DDQ, 80 mL of chloroform, heated to reflux with a constant temperature oil bath, and reacted for 5 h until the reaction was complete. When the reaction solution was cooled to room temperature, the reaction solution was extracted with dichloromethane and water, the organic phases were combined, the solvent was removed by rotation, 4 g of silica gel was added for sample preparation, and column chromatography was performed (the eluent was petroleum ether and the volume ratio of ethyl acetate was 30%). : 1 mixture) to obtain a white solid 2-(4-((4-(hexyloxy)phenyl)ethynyl)phenyl)-5-methylbenzoxazole liquid crystal compound with a yield of 89%, The reaction equation is as follows:

The spectral data of the product are as follows:

IR(KBr)v(cm ^-1 ): 2923, 2852, 2208, 1598, 1510, 1469, 1406, 1242, 1045, 833, 794.

¹ H-NMR (400MHz, CDCl ₃ , TMS) δ (ppm)=8.23-8.16 (m, 2H), 7.66-7.60 (m 2H), 7.57-7.52 (m, 1H), 7.51-7.45 (m, 2H) ), 7.45-7.40 (d, ³ J _HH = 8.45Hz, 1H), 7.19-7.12 (dd, ³ J _HH = 8.24Hz, ⁴ J _HH = 1.59Hz 1H), 6.93-6.83 (m, 2H), 4.00 -3.88(q, ³ J _HH = 6.55Hz, 2H), 2.48(s, 3H), 1.89-1.72(m, 2H), 1.51-1.32(m, 6H), 1.01-0.88(t, ³ J _HH = 6.68Hz, 3H).

MS(MALDI-TOF) m/z: theoretical value 409.53, measured value 409.22.

Example 2

In step 4 of the present embodiment, the 2-amino-4-methylphenol in step 4 of embodiment 1 is replaced with equimolar o-aminophenol, and other steps are the same as those of embodiment 1 to obtain the following 2-(4-( (4-(hexyloxy)phenyl)ethynyl)phenyl)benzoxazole, 89% yield.

The spectral data of the product are as follows:

IR(KBr)v(cm ^-1 ): 2927, 2852, 2208, 1598, 1510, 1458, 1280, 1240, 1174, 1049, 838. ¹ H-NMR (400 MHz, CDCl ₃ , TMS) δ (ppm)= 7.99-7.93(m, 1H), 7.86-7.83(m 1H), 7.64-7.60(m, 1H), 7.53-7.48(m, 2H), 7.43-7.35(m, 3H), 6.97-6.83(m, 2H), 4.07-3.91(q, ³ J _HH =6.57Hz, 2H), 1.86-1.72(m, 2H), 1.51-1.31(m, 6H), 0.99-0.84(t, ³ J _HH =6.88Hz, 3H).

MS(MALDI-TOF) m/z: theoretical value 395.5, measured value 395.21.

Example 3

In step 4 of this embodiment, 2-amino-4-methylphenol in step 4 of embodiment 1 is replaced with equimolar 2-amino-4-nitrophenol, and other steps are the same as those of embodiment 1, and the following structural formula is obtained 2-(4-((4-(hexyloxy)phenyl)ethynyl)phenyl)-5-nitrobenzoxazole, yield 67%.

The spectral data of the product are as follows:

IR(KBr)v(cm ^-1 ): 2933, 2862, 2204, 1596, 1512, 1344, 1249, 1016, 823, 738, 6.

¹ H-NMR (400MHz, CDCl ₃ , TMS) δ (ppm)=8.65-8.62 (d, J ⁴ _HH =2.44Hz, 1H), 8.35-8.29 (dd, J ³ _HH =8.9Hz, J ⁴ _HH = 2.26Hz, 1H), 8.25-8.20(m, 2H), 7.73-7.63(m, 3H), 7.50-7.44(m, 2H), 6.94-6.84(m, 2H), 4.07-3.94(q, ³ J _HH = 6.83Hz, 2H), 1.86-1.73 (m, 2H), 1.51-1.32 (m, 6H), 0.99-0.84 (t, ³ J _HH = 6.88Hz, 3H).

MS (MALDI-TOF) m/z: theoretical value 440.5, measured value 440.23.

The optical anisotropy and thermal properties of the liquid crystal compounds prepared in the above examples 1 to 3 were tested to obtain their birefringence, phase transition temperature and phase transition enthalpy. The theoretical value of birefringence is obtained by Gaussian09 software; the experimental value can also be obtained by Abbe refractometer test; the phase transition temperature and phase transition enthalpy are obtained by differential scanning calorimeter test. The results are shown in Tables 1 and 2.

Table 1 Birefringence

Table 2 Phase transition temperature and phase transition enthalpy

Note: Cr in the table represents crystalline phase; N represents nematic phase; I represents isotropic phase.

It can be seen from Table 1 and Table 2 that the liquid crystal compound of the present invention (experimental value Δn≥0.623) and the large birefringence liquid crystal compound in the literature (Liquid Crystals, 2017, 44: 14-15, 2184-2191) (test value Δn=0.305), Δn is significantly improved, which further proves that the liquid crystal compound of the present invention has excellent optical anisotropy.

It can be seen from Table 2 that the liquid crystal compounds of the present invention all have a wide nematic phase interval.

It can be seen from the DSC curve of Fig. 1 (temperature rise and fall rate of 5°C/min) and the POM photographs (200×) of Figs.

Claims (7)

1. a benzoxazole liquid crystal compound containing an alkyne bond, is characterized in that the structural formula of this compound is as follows: In the formula, R represents a C ₅ -C ₁₂ straight-chain alkyl group, and X represents any one of H, CH ₃ and NO ₂ . 2. the preparation method of the benzoxazole liquid crystal compound containing an acetylenic bond according to claim 1, is characterized in that it is made up of the following steps: (1) Preparation of 4-(4-(1,3-dioxolan-2-yl)phenyl)-2-methylbut-3-yn-2-ol Add p-bromobenzaldehyde, p-toluenesulfonic acid and ethylene glycol to chloroform, react at 50-70°C for 6-8 hours, evaporate the solvent under reduced pressure, and then add 2-methyl-3- Butyn-2-ol, cuprous iodide, triphenylphosphine, tetrakis (triphenylphosphine) palladium, triethylamine, react at 80～90℃ for 8～10h, separate and purify to obtain 4-(4- (1,3-dioxolane-2-yl)phenyl)-2-methylbut-3-yn-2-ol, the reaction equation is as follows: (2) Preparation of 2-(4-((4-(alkoxy)phenyl)ethynyl)phenyl)-1,3-dioxolane 4-(4-(1,3-dioxolan-2-yl)phenyl)-2-methylbut-3-yn-2-ol, 1-iodo-4-(alkane shown in formula I Oxy)benzene, ethylene glycol ether, sodium hydroxide, and tetrakis(triphenylphosphine)palladium were added to toluene, and reacted at 60-80 °C for 8-10 h under nitrogen protection. After the reaction was completed, separation and purification were performed to obtain 2-( 4-((4-(alkoxy)phenyl)ethynyl)phenyl)-1,3-dioxolane, the reaction equation is as follows: In formula I, R represents a C ₅ -C ₁₂ straight-chain alkyl group; (3) Preparation of 4-((4-(alkoxy)phenyl)ethynyl)benzaldehyde Add 2-(4-((4-(alkoxy)phenyl)ethynyl)phenyl)-1,3-dioxolane and formic acid to tetrahydrofuran, and react at 50～70℃ for 5～6h, After the reaction is finished, separation and purification are performed to obtain 4-((4-(alkoxy)phenyl)ethynyl)benzaldehyde, and the reaction equation is as follows: (4) Preparation of 2-((4-((4-(alkoxy)phenyl)ethynyl)benzylidene)amino)phenol Add 4-((4-(alkoxy)phenyl)ethynyl)benzaldehyde and aminophenol shown in formula II to ethanol, stir and reflux for 4-6h, remove the solvent by vacuum distillation, and recrystallize to obtain 2-(( 4-((4-(alkoxy) phenyl) ethynyl) benzylidene) amino) phenol, reaction equation is as follows: In formula II, X represents any one of H, CH ₃ , and NO ₂ ; (5) Preparation of acetylene bond-containing benzoxazole liquid crystal compounds Add 2-((4-((4-(alkoxy)phenyl)ethynyl)benzylidene)amino)phenol and dichlorodicyanobenzoquinone into chloroform, and react under reflux for 4 to 6 hours. , stop the reaction, separate and purify, and obtain the benzoxazole liquid crystal compound containing alkyne bond. 3. the preparation method of the acetylenic bond-containing benzoxazole liquid crystal compound according to claim 2, is characterized in that: in step (1), the mole of described p-bromobenzaldehyde and p-toluenesulfonic acid, ethylene glycol Ratio 4:0.9～1.2:80～90, moles of p-bromobenzaldehyde to 2-methyl-3-butyn-2-ol, cuprous iodide, triphenylphosphine, tetrakis(triphenylphosphine)palladium The ratio is 1:0.4～1:0.01～0.03:0.04～0.08:0.007～0.01. 4. The preparation method of the acetylenic bond-containing benzoxazole liquid crystal compound according to claim 2, characterized in that: in step (2), the 4-(4-(1,3-dioxolane- 2-yl)phenyl)-2-methylbut-3-yn-2-ol with 1-iodo-4-(alkoxy)benzene, ethylene glycol ether, sodium hydroxide, tetrakis(triphenylphosphine) ) The molar ratio of palladium is 1:1 to 1.2:10 to 15:5 to 8:0.02 to 0.05. 5. The preparation method of the acetylenic bond-containing benzoxazole liquid crystal compound according to claim 2, characterized in that: in step (3), the 2-(4-((4-(alkoxy)benzene The molar ratio of yl)ethynyl)phenyl)-1,3-dioxolane to formic acid is 1:180-185. 6 . The method for preparing an acetylenic bond-containing benzoxazole liquid crystal compound according to claim 2 , wherein: in step (4), the 4-((4-(alkoxy)phenyl)acetylene The molar ratio of benzaldehyde to aminophenol is 1:1.1～1.5. 7. The preparation method of the acetylenic bond-containing benzoxazole liquid crystal compound according to claim 2, wherein in step (5), the 2-((4-((4-(alkoxy) The molar ratio of phenyl)ethynyl)benzylidene)amino)phenol to dichlorodicyanobenzoquinone is 1:1.1-1.5.