JPH02196782A - 1,3-dioxan derivative - Google Patents

Abstract

NEW MATERIAL:The compound of formula I (R is 1-8C straight-chain alkyl). EXAMPLE:5-Pentyl-2-(3',4'-difluorophenyl)-1,3-dioxan. USE:A component constituting a nematic liquid crystal composition to be used in a liquid crystal display device. PREPARATION:The objective substance can be produced by (1) reacting a bromoalkane of formula R-Br with diethyl malonate of formula II in ethanol in the presence of sodium ethoxide to obtain diethyl alkylmalonate of formula III, (2) reducing the compound with lithium aluminum hydride in THF to form 2-alkylpropane-1,3-diol of formula IV, (3) dissolving the obtained 2- alkylpropane-1,3-diol and 3,4-difluorobenzaldehyde in a solvent forming an azeotropic mixture with water and (4) reacting the components in the presence of a catalyst such as p-toluenesulfonic acid, sulfuric acid or H-type cation exchange resin while removing the produced water with a water-separator.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a 1,3 dioxane derivative useful as a component constituting a nematic liquid crystal composition used in a liquid crystal display device.

[Summary of the invention]

(In the above formula, R represents a straight-chain alkyl group having 1 to 8 carbon atoms.) A 1,3-dioxane derivative represented by the following.

2) A 1,3-dioxane derivative characterized in that the formula (1) according to claim 1 contains 60% or more of the 1,3-dioxane ring in the trans configuration.

3) A 1,3-dioxane derivative according to claim 1, characterized in that the 1,3-dioxane ring in formula (1) has a trans configuration.

(In the above formula, R represents a straight-chain alkyl group having 1 to 8 carbon atoms.)
) is large and positive, and the anisotropy of the refractive index (80) is small. Therefore, by using the compound (1) of the present invention as a component of a nematic liquid crystal composition, it is possible to provide a liquid crystal display device that has a low driving voltage and is capable of high time division driving with a wide viewing angle range.

[Conventional technology]

Liquid crystal phases used in liquid crystal display devices include a cholesteric phase, a smectic phase, and a nematic phase, and there are various display systems that utilize the electro-optical effects of these liquid crystal phases. In addition, liquid crystal display devices using a nematic phase are the most popular, and their display methods include dynamic scattering type, guest-host type, twisted nematic type (TN type), super twisted nematic type (STN type), There are super twisted birefringent type (SBE type), etc. The driving methods for operating these devices include a static driving method, a time division driving method (simple matrix driving method), an active matrix driving method, a two-frequency driving method, and the like. Conventionally, liquid crystal display devices, especially TN type and STN type, can be made smaller and thinner, have a lower driving voltage, have extremely low power consumption, and are light-receiving elements, so they do not cause eye strain even when used for long periods of time. It has advantages such as: Therefore, by taking advantage of these features, we have been manufacturing watches, calculators, audio equipment,
It is widely used in automobile dashboards, telephones, and various measuring instruments, and recently it is being applied to display devices with a large number of pixels such as word processors, personal computer displays, and LCD televisions, and is attracting attention as a display device that can replace CRTs. has been done. Liquid crystal materials used in liquid crystal display devices, which are widely used in this way,
In particular, nematic liquid crystal materials used in TN-type or STN-type display systems are required to have various characteristics depending on the application, and the characteristics can be summarized as follows.

1. Must be non-colored and stable in terms of light, heat, electricity, and chemistry.

2. The nematic temperature range should be as wide as possible.

3. The threshold voltage (Vlh) of the voltage-luminance characteristic should be as low as possible, and its temperature dependence should be small.

4. Wide viewing angle range.

5. Fast electro-optical response speed.

Among these characteristics, a large number of compounds are known that satisfy characteristic 1, but there is currently no single-component liquid crystal compound that satisfies characteristics 2 to 5. Therefore, in practice, the current goal is to be achieved by using a liquid crystal composition that is an appropriate mixture of a plurality of types of liquid crystal compounds or similar compounds thereof. Here, the liquid crystal analog compound refers to a compound whose molecular shape is similar to that of a liquid crystal compound, but which does not exhibit a liquid crystal phase, and is often used when producing a liquid crystal composition.

[Problem to be solved by the invention]

In a liquid crystal display device, in the case of power supply or high time division driving, there are restrictions on the withstand voltage of the driving IC, so it is desirable that the driving voltage be as low as possible. Since this drive voltage is represented by Vl, it is sufficient to make Vlh as low as possible. In order to lower Vlh, compounds with positive Δε as large as possible are mixed, but compounds conventionally used for this purpose, such as (here, R represents a linear alkyl group or an alkoxy group), have a liquid crystal composition. Although it is effective in lowering the Vlh of objects, △
n is large. By the way, the viewing angle range of 4 is due to the pretilt of the liquid crystal molecules, and it is known that the smaller 80, the wider the viewing angle range.

Therefore, since the above-mentioned compound has a large Δn, it has the drawback of narrowing the viewing angle range.

Therefore, an object of the present invention is to provide a compound useful for obtaining a nematic liquid crystal composition having a low Vlh and a small Δn.

[Means to solve the problem]

The 1,3-dioxane derivative of the present invention is characterized by being represented by the general formula (in the above formula, R represents a straight chain alkyl group having 1 to 8 carbon atoms).

In addition, in formula (1), 60% or more of the 1,3-dioxane ring is in the trans configuration. Features.

(In the above formula, R represents a straight-chain alkyl group having 1 to 8 carbon atoms.) It is a 1,3-dioxane derivative represented by the following formula and can be synthesized by the following manufacturing method.

R-Br (2) CH2(COOE
t) 2 (3) R-CI(COOEt) 2
(4) R-CI (CH2011) 2
(5) (In the above formula, R represents a straight-chain alkyl group having 1 to 8 carbon atoms.) Step 1, bromoalkane (2) and diethyl malonate (3
) is reacted with sodium ethoxide in ethanol to obtain diethyl alkylmalonate (4).

Step 2, reduction of diethyl alkylmalonate (4) with lithium aluminum halide in THF to obtain 2-alkylpropane-1,3-diol (5).

Step 3. 2-alkylpropane-1,3-diol and 3
, 4-difluorobenzaldehyde is dissolved in a solvent that is azeotropic with water, such as methylene chloride, chloroform, benzene, toluene, etc., and p-toluenesulfonic acid, sulfuric acid, H
Using a type cation exchange resin or the like as a catalyst, the 1,3-dioxane derivative (1) of the present invention is obtained while removing water generated in a water separator.

The 1,3-dioxane derivative obtained here is a mixture of those in which the 1゜3-dioxane ring is in the trans form and in the cis form, and the production ratio is determined by the reaction temperature, reaction time,
Although it varies depending on factors such as the type of solvent, the production ratio of the trans isomer is generally higher. Additionally, although it would be ideal to use only the trans isomer, it is difficult to separate the cis isomer, so in practice a mixture of the trans and cis isomers is used, but the cis isomer is acceptable. The ratio etc. will be described in Examples.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Method for producing 5-pentyl-2-(3',4'-difluorophenyl)-1,3-dioxane (mixture of trans and cis forms).

Step 1 Dissolve 23 g (1.0 mol) of metallic sodium in 500 cm' of absolute ethanol, and add 1 mol of diethyl malonate.
60 g (1,0 mol) and 151 g of 1-bromopentane
(1.0 mol) was added and refluxed for 7 hours with stirring. The reaction was cooled to room temperature, the formed NaBr was filtered off,
Ethanol in the filtrate was removed by distillation. The residual solution was dissolved in 500 cm3 of 60% filtrate, washed in this order with water, 5% hydrochloric acid, and water, and chloroform was removed by distillation. The remaining oily substance was distilled under reduced pressure (b, p, 103°C/3 Torr).

193 g (0.84 mol) of diethyl pentylmalonate was obtained.

Step 2 Anhydrous tetrahydrofuran (THF) 420c
35g of lithium aluminum halide (0,9
2 mol) was dispersed therein, and 193 g (0.84 mol) of diethyl pentylmalonate was added dropwise to the solution while stirring at such a rate that the THF was gently refluxed, and the mixture was refluxed for 3 hours while stirring. The reaction mixture was cooled with water, THF containing 10% water was added until no more foaming occurred, and 500 cm' of concentrated hydrochloric acid was added. Separate the oil layer, extract the aqueous layer three times with 200 cm of ether,
The ether layer combined with the oil layer was washed with saturated brine.

The ether layer was dried over anhydrous sodium sulfate, and the ether was distilled off. The residual liquid was distilled under reduced pressure (b, p.

120°C/2 Torr) and 2-pentylpropane-1
, 3-diol (83 g (0.57 mol)) was obtained.

Step 3 83g of 2-pentylpropane-1,3-diol
(0.57 mol), 3,4-difluorobenzaldehyde (manufactured by Aldrich), 81 g (57 mol), and p
4.9 g (0.02 mol) of -1 luenesulfonic acid was dissolved in 285 cm3 of benzene and refluxed for 5 hours while a water separator was attached to remove the generated water. Add the reaction solution to water,
It was washed with a 5% aqueous NaHCO3 solution and then with water, and benzene was removed by distillation. Vacuum distillation of the remaining oily substance (b.

5-pentyl-2-(3',4'-difluorophenyl)-1,3
-Mixture of trans and cis dioxane (mixing ratio trans:cis -80:20) 121g (0,
45 mol) was obtained. This mixture was isotropic at room temperature.

Similarly, 5-ethyl-2-(3',4'-difluorophenyl)-1,3-dioxane (trans:cis-70:3
0) b, p, 110°C/3 m m Hg5-propyl-2-(3',4'-difluorophenyl)-1
, 3-dioxane (trans:cis-75:25)b,
p, 120°C/3 mm Hg5-butyl-2-(
3',4'-difluorophenyl)-1,3-dioxane (trans:cis=77:23)b, p, 128
°C/3mmHg5-hexyl-2-(3',4'-
difluorophenyl)-1,3-dioxane (trans:cis-81:19) b, p, 150°C/4 m
m Hg5-hebutyl-2-(3',4'-difluorophenyl)-1,3-dioxane (trans:cis-81:19) b, p, 164 °C/4 mm Hg
5-octyl-2-(3',4'-difluorophenyl)-1,3-dioxane (trans:cis-80
:20) b, p, 173°C/3 mm Hg was produced. These mixtures were isotropic liquids at room temperature.

Example 2 Effect of solvent in 5-pentyl-2-(3',4'-difluorophenyl)-1,3-dioxane production.

2-pentylpropane-1,3-diol obtained in step 1.2 of Example 1 11. 8 g (0,10 mol) and 14.2 g (0
, 10 mol) and p-) luenesulfonic acid 0.9 g (0
,005 mol) of methylene chloride (b, p,
°C), chloroform (b, p, ``C), toluene (b, p, ``C), and dissolved in step 3 of Example 1.
A mixture of 5-pentyl-2-(3',4'-difluorophenyl)-1,3-dioxane was produced in the same manner as above. Table 1 shows the yield and the ratio of trans isomer to cis isomer in each solvent. Therefore, in Table 1, it is practically possible to obtain a mixture of the present invention containing 60% or more of the trans isomer.

Example 3 An attempt was made to separate only the trans isomer from the mixture obtained in Example 1. First, an attempt was made to separate by recrystallization, but no crystals were precipitated, and separation by recrystallization was not possible.

Therefore, we decided to use a preparative liquid chromatograph (Hitachi 655 model) and C.
Separation was carried out using a reverse phase column (manufactured by Merck & Co., Ltd.) with a particle size of 7 μm, a diameter of 5 cm and a length of 25 cm, using methanol:water (85:15) as a solvent. However, even by this method, the R-C2H9 compound could not be separated.

Table 2 shows trans-5-alkyl-2-(3', 4'
Melting point of -difluorophenyl)-1,3-dioxane (
m, p, ) were shown.

Even considering that in Example 1, the formation ratio of the cis isomer increases as the alkyl group becomes shorter, the nematic phase-isotropic liquid transition point (N-1 point) of the composition in Table 2
The results of the measurements are shown in Table 3. In Example 3,
Table 3 Example 4 5-benzene 2- (3'4'-
Trans-form and cis-form of difluorophenyl)-1,3-dioxane are respectively 20:80.40:60.6
They were mixed at a ratio of 0:40.80:20. Liquid crystal compositions A-0 and A-20SA-4 were obtained by mixing 10% by weight of these and six types of samples of cis-form and trans-form in commercially available liquid crystal composition ZLI-1565 (manufactured by Merck & Co., Ltd.).
0, A-60, A-80, and A-100 were made. Although these cis isomers have been separated, it is practically difficult to separate them using preparative liquid chromatography in terms of cost and production volume. Therefore, in order to produce a practically usable liquid crystal composition, it is necessary to use the mixture of cis and trans isomers as they are when produced.

However, as shown in Table 3, if too much cis isomer is included, the N-1 point will drop. Practically N-1
Since a temperature of at least 50° C. is required, the content ratio of the cis isomer is preferably 40% or less, that is, the content of the trans isomer is preferably 60% or more.

Application Example Liquid crystal compositions [1] and [2] were prepared by mixing 10% by weight of a mixture of cis, trans, and cis forms (trans:cis-80:20). Comparative liquid crystal compositions [1] Liquid crystal compositions [2] Next, AC state liquid crystal compositions [Comparison 1] ZLI-156590% by weight C5H+++ 3N 10'' liquid crystal compositions were sealed in a TN type cell with a thickness of 8 μm. Comparison 2] ZLI-156590% by weight Voltage-luminance characteristics were measured at 25° C. with quick driving, and the threshold voltage V, (voltage when the luminance becomes 10%) was determined.These results are shown in Table 4. summarized in.

Table 4 (trans:cis-80+20) Crystal compositions [Comparison 1] and [Comparison 2] were prepared. The refractive index anisotropy (80) of these compositions was measured.

〔Effect of the invention〕

As described above, it has been found that by mixing the compound of the present invention with a conventional liquid crystal composition, a liquid crystal composition with small refractive index anisotropy and low driving voltage can be obtained.

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Claims (1)

[Claims] 1) Represented by the general formula ▲ Numerical formulas, chemical formulas, tables, etc. ▼ (1) (In the above formula, R represents a straight-chain alkyl group having 1 to 8 carbon atoms.) A 1,3-dioxane derivative characterized by: 2) A 1,3-dioxane derivative characterized in that the formula (1) according to claim 1 contains 60% or more of the 1,3-dioxane ring having a trans configuration. 3) A 1,3-dioxane derivative according to claim 1, characterized in that the 1,3-dioxane ring in formula (1) has a trans configuration.