JPS6251259B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel liquid crystal compound having positive dielectric anisotropy. As is well known, nematic liquid crystal materials with positive dielectric anisotropy are used not only for twisted nematic mode display elements (TN displays), but also for color liquid crystal display elements that apply the guest-host effect by adding appropriate dyes. used. The liquid crystals used in these devices are stable against moisture, air, light, heat, etc., and it is desirable that they remain in a liquid crystal state not only at room temperature but also over a wide temperature range from low to high temperatures. . However, there is currently no single compound that satisfies all of these properties, and in practice, several types of liquid crystal compounds or non-liquid crystal compounds are mixed to achieve the desired purpose. An object of the present invention is to provide a compound useful as a component of such a liquid crystal composition that has excellent practical performance and good stability. The present invention provides a novel liquid crystal compound having positive dielectric anisotropy, a wide liquid crystal temperature range, and a highly stable clearing point (NI point). That is, the compound of the present invention has the general formula (In the above formula, R represents H or an alkyl group having 1 to 10 carbon atoms, and X represents F, Cl, Br or NO ₂ group) 4-(trans-4'-alkylcyclohexylmethoxy)benzoin It is an acid 4"-substituted phenyl ester. Although the compound of the present invention has a wide liquid crystal temperature range, it has a high melting point, so this compound alone is not practical for use in display devices. However, it has a high compatibility with other liquid crystal compounds. Because of its high clearing point, it is difficult to use other liquid crystal materials such as biphenyl, ester, azoxy, cyclohexanecarboxylic acid phenyl ester, phenylcyclohexane, phenylpyrimidine, and phenylmethadioxane. By mixing with one type or a mixture of several types, the clearing point can be raised, making it useful as a so-called high-temperature liquid crystal component.Cyanoterphenyl and cyanobiphenylcyclohexane systems are currently widely used as high-temperature liquid crystal components. The compound of the present invention has a relatively low viscosity compared to other liquid crystals, so it can be used to construct excellent liquid crystal compositions with good response characteristics and less temperature dependence. Although △ε is positive, it is quite small, and even though △ε is small, it is possible to lower the operating voltage, so it is useful as a component for dynamic drive liquid crystals. Especially when X is F, This effect is remarkable. Next, the method for producing compound (I) of the present invention will be described. First, the chemical formula will be shown briefly. First, trans-4-alkylcyclohexanecarboxylic acid () is used as a starting material, and this and ethyl alcohol are reacted under an acid catalyst to obtain an ester compound () (Step A). Next, () is reacted with lithium aluminum hydride LiAlH ₄ in a solvent at low temperature to obtain a carbinol compound () (Step B). This reduction reaction can also be carried out by hydrogen reduction using a catalyst. Next, () is reacted with a halogenating agent such as hydrogen bromide or phosphorus tribromide to obtain bromide (V) (Step C), and this (V) and p
- When reacted with hydroxybenzoic acid, 4-(trans-4'-cyclohexylmethyl)benzoic acid () is obtained (Step D). to this ()
A halogenating agent represented by SOCl ₂ is reacted to form an acid chloride (or acid halide) (Step E), and a p-halogenated phenol is reacted with the halogenated agent in an inert organic solvent to obtain the desired product ( I) A compound of formula is obtained (Step F). Hereinafter, the production method and properties of the compounds of the present invention will be explained in more detail with reference to Examples. Example 1 [Production of 4-(trans-4′-n-propylcyclohexylmethoxybenzoic acid-4″-fluorophenyl ester (compound with R=C ₃ H ₇ and X=F in the formula ())] [Steps A] Dissolve 170.24 g (1 mol) of trans-4-n-propylcyclohexanecarboxylic acid () in 350 ml of ethyl alcohol, add 40 ml of 95% concentrated sulfuric acid, react under reflux for 3 hours, and remove excess ethyl. The alcohol was distilled off. The reaction product was extracted with 100 ml of n-hexane, the extract was washed with water, dried over anhydrous magnesium sulfate, the n-hexane was distilled off, and the residual liquid was distilled under reduced pressure to give 167.2 g. Trance-4-
n-propylcyclohexanecarboxylic acid ester () was obtained. Boiling point 73℃/1mmHg, yield 84.3%. [Step B] Ethyl ester obtained in Step A ()
198g (1 mol) of dried tetrahydrofuran
24 g of lithium aluminum hydride dissolved in 100 ml, while 700 ml of dry tetrahydrofuran
(0.633 mol) is suspended, and the solution in () is added dropwise while stirring vigorously. After the addition is complete, the mixture is heated under reflux for 2 hours, and after cooling, ethyl acetate is carefully added to decompose the excess lithium aluminum hydride. Then 20% sulfuric acid was added until the inorganics were dissolved. The product was extracted with n-hexane, the extract was washed with water, dried over anhydrous magnesium sulfate, the n-hexane was distilled off, and the residual liquid was distilled under reduced pressure to obtain trans-4-n-propylcyclohexylcarbinol ( ) 148g (0.94mol)
I got it. Yield 94.0%, boiling point 76℃/1mmHg. [Step C] 156.3 g of carbinol obtained in Step B (1
307 g (1.784 mol) of 47% hydrogen bromide water (mol), 95%
93 g of sulfuric acid was added and heated under reflux for 3 hours. After the reaction was cooled, the reaction product was extracted with n-hexane, and the extract was washed with a 2% aqueous sodium sulfur solution and then with water, dried over anhydrous magnesium sulfate, and extracted with n-hexane.
-Hexane was distilled off, and the residual liquid was distilled under reduced pressure to obtain 162.2 g (0.74 mol) of trans-4-n-propylcyclohexylmethyl bromide (V). Yield 74.0
%, boiling point 64℃/1mmHg. [Step D] 13.81 g (0.1 mol) of 4-hydroxybenzoic acid was dissolved in 50 ml of ethylene glycol monomethyl ether, and then an aqueous alkaline solution prepared by dissolving 8 g (0.2 mol) of caustic soda in 15 ml of water was carefully added and stirred for 30 minutes. Next, 21.92 g (0.1 mol) of the compound (V) obtained in Step C was added over 30 minutes, and the mixture was further heated under reflux for 5 hours. After cooling, 50% hydrochloric acid was added and the precipitated reaction product was filtered out, washed with water and dried. Recrystallize it with 15.0ml of glacial acetic acid and get 20.72g.
(0.75 mol) of 4-(trans-4-n-propylcyclohexylmethoxy)benzoic acid () was obtained. Yield 75%, and this product is smectic (S)
and shows a nematic (N) liquid crystal phase, and the C-S point is
The temperature was 213°C, the SN point was 228°C, and the NI point was 235°C. [Steps E and F] Benzoic acid derivative obtained in Step D ()
Dissolve 27.63g (0.1 mol) in 50g of thionyl chloride,
After reacting under reflux for 1 hour, excess thionyl chloride is distilled off to obtain acid chloride (Step E). Separately, 11.21 g (0.1 mol) of 4-fluorophenol was dissolved in 15 ml of dry pyridine, and the above acid chloride was added thereto at room temperature, followed by further heating and stirring at 70° C. for 2 hours. After cooling, the reaction product was extracted with 100ml of benzene, and the extract was mixed with dilute hydrochloric acid, dilute alkali,
After washing with water, it was dried using anhydrous magnesium sulfate, and then benzene was distilled off. The obtained reaction product is recrystallized from a benzene-ethyl alcohol mixed solvent to obtain the desired 4-(trans-4-
n-propylcyclohexylmethoxy)benzoic acid
4″-fluorophenyl ester (I) 21.49g
(0.058 mol) was obtained (yield 58%). Its melting point (C
-N point) was 104°C, clearing point (N-I point) was 145°C, and heat of fusion △H was 12.1 Kcal/mol. Moreover, the elemental analysis values are in good agreement with the calculated values as shown below. Analytical value Calculated value (as C ₂₃ H ₂₇ O ₃ F) C 74.75% 74.57% H 7.61% 7.35% Examples 2 to 10 Other compounds of formula (I) synthesized in exactly the same manner as Example 1 The characteristic values for the compound of Example 1 are also shown in Table 1.

【table】

[Table] Examples 11 to 13, Comparative Example 1 (Application example) Liquid crystal compositions were prepared using the compound of the present invention and conventionally used compounds as high-temperature liquid crystal components, and their various properties were measured and compared. The results are shown in Table 2.

【table】

[Table] As can be seen from Table 2, by adding the compound of the present invention as a component, the NI point of the liquid crystal composition increases significantly, and the threshold voltage and saturation voltage are low.

Claims (1)

[Claims] 1. General formula (In the above formula, R represents H or an alkyl group having 1 to 10 carbon atoms, and X represents F, Cl, Br, or _NO2 group) 4-(trans-4'-alkylcyclohexylmethoxy) Benzoic acid 4″-substituted phenyl ester. 2 General formula (In the above formula, R represents H or an alkyl group having 1 to 10 carbon atoms.) The compound according to claim 1, represented by: 3 General formula (In the above formula, R represents H or an alkyl group having 1 to 10 carbon atoms, and X represents F, Cl, Br, or _NO2 group) 4-(trans-4'-alkylcyclohexylmethoxy) A liquid crystal composition comprising at least one 4″-substituted phenyl ester of benzoic acid.