JPH03181471A - Pyrazine derivative - Google Patents

Abstract

NEW MATERIAL:A racemic modification composed of a compound expressed by formula I (R<1> is 4-18C alkyl; m is 2-8; n is 1-4). EXAMPLE:2-(4-hexylphenyl)-5-(6-methyloctyloxy)pyrazine. USE:Used as ferroelectric liquid crystalline indicating material having excellent responsibility and memory property, especially useful as an indicating opto- switching element. PREPARATION:2-(4-alkylphenyl)-5-chloropyrazine expressed by formula II is reacted with an alcohol expressed by formula III in a solvent such as DMF and in the presence of a strong base (e.g. t-butoxypotassium) to afford the compound expressed by formula I.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a racemic form of a novel birazodine derivative useful as a ferroelectric liquid crystal display material with particularly excellent responsiveness and memory properties.

[Prior art]

Liquid crystal display elements are currently widely used due to their excellent features (low voltage operation, low power consumption, thin display capability, and can be used in bright places without tiring the eyes). However, in the most common TN type display system, CRT
The response is extremely slow compared to luminescent display methods such as
In addition, it is not possible to memorize the display when the applied electric field is turned off (memory effect), so optical shutters that require high-speed response,
There are many limitations to its application to printer heads and video screens such as TVs that require time-division drive, and it could not be said to be a suitable display method.

However, recently reported display systems using ferroelectric liquid crystals have high response times and memory effects that are 100 to 1000 times faster than TN display systems, so they are expected to be used as next-generation liquid crystal display devices, and are currently , research and development is actively underway.

The liquid crystal phase of ferroelectric liquid crystal belongs to the tilted chiral smectic phase, but in practical terms, the chiral smectic C (hereinafter abbreviated as "SC") phase, which has the lowest viscosity, is the most desirable.

Many liquid crystal compounds exhibiting the "sc" phase (hereinafter referred to as "sc" compounds) have already been synthesized and studied, but the conditions for using them as ferroelectric display elements are (a)
exhibiting an “sc” phase in a wide temperature range including room temperature, (b)
In order to obtain good orientation, the high temperature side of the sc" phase should have an appropriate phase series and the helical pitch should be large; (c)
Although it is preferable to have an appropriate tilt angle, (d) have low viscosity, and (e) have a certain degree of spontaneous polarization, there is no known material that satisfies all of these requirements alone.

Therefore, it is currently used as a liquid crystal composition that exhibits the SC1 phase by mixing (hereinafter referred to as SC "liquid crystal composition"). Although there is a method of mixing only the smectic C (hereinafter referred to as SC) phase, it is also possible to use it as an SC''' liquid crystal composition by adding an optically active compound as a xyl dopant to a liquid crystal compound or m-parabolic exhibiting a smectic C (hereinafter referred to as SC) phase. In this case, it is possible to lower the viscosity, so
This method is commonly used because it enables faster response. The compound used as a xyl dopant does not necessarily have to exhibit an sc" phase when used alone;
When made into a liquid crystal composition, it is necessary to exhibit similar properties.

Many compounds exhibiting an SC phase (hereinafter referred to as SC compounds) are already known. However, although SC compounds generally have a lower viscosity than SC'' compounds, it is rarely sufficient. Also, their melting points are relatively high, and it is not easy to maintain the SC phase over a wide temperature range, even at low temperatures. There wasn't.

At present, the host liquid crystal composition exhibiting the SC phase (hereinafter referred to as S
S used as the main component of C matrix liquid crystal)
The C compound is mainly a phenylbenzoate compound represented by the following general formula (A) or a pyrimidine compound represented by the general formula (B), for example.

(In the formula, R1 and Rh each independently represent a linear alkyl group, alkoxyl group, alkoxycarbonyl group, alkanoyloxy group, or alkoxycarbonyloxy group, but do not represent an alkyl group at the same time.) (Formula Among these, in the compound represented by the general formula (A), R1 and R1' have the same meaning as in the above general formula (A).
Due to the presence of ester bonds in the molecule, its viscosity is relatively high.

On the other hand, in the case of a compound represented by general formula (B), in which one of R'' and Rh represents an alkyl group and the other represents an alkoxyl group, the viscosity is relatively low, but the viscosity is sufficiently satisfactory. Moreover, this compound did not have a low melting point, and it was not easy to obtain a base liquid crystal composition that exhibited an SC phase in a wide temperature range including low temperatures using only this compound.

As the SC compound, a pyrazine compound represented by the general formula (C) is also known.

(In the formula, RhI and Rb represent the same meanings as in the above general formula (A).) This pyrazine compound often has a lower viscosity than the corresponding pyrimidine compound of the general formula (B). Since their melting points are generally high and their compatibility with other liquid crystal compounds is not good, it has been even more difficult to obtain a parent liquid crystal composition that exhibits an SC phase over a wide temperature range down to low temperatures. .

[Problem to be solved by the invention]

As described above, the viscosity and temperature range of conventional SC compounds are insufficient to prepare SC matrix liquid crystals, and by adding a xyl dopant consisting of an optically active compound, it is possible to create SC" liquid crystals with high response speed. There are problems in providing such compositions, and improvements have been desired.

The problem to be solved by the present invention is to provide a compound with low viscosity and a low melting point to be used in a parent liquid crystal exhibiting an SC phase, thereby providing a parent liquid crystal with low viscosity and a wide temperature range of an SC phase. The object of the present invention is to provide a ferroelectric liquid crystal composition with high-speed response by adding a xyl dopant consisting of an optically active compound to the ferroelectric liquid crystal composition.

[Means to solve the problem]

In order to solve the above problems, the present invention provides the following general formula (1
) provides a racemic compound consisting of the compound represented by

<In formula A, R1 represents a linear alkyl group having 4 to 18 carbon atoms, and a linear alkyl group having 6 to 12 carbon atoms is particularly preferred. m represents an integer of 2 to 8, preferably an integer of 3 to 5, and n represents an integer of 1 to 4, preferably 2 or 2.

The compound represented by the general formula (1) of the present invention is, for example,
It can be manufactured as follows.

That is, general formula (n) (In the formula, R1 has the same meaning as general formula (I).

2-(4-alkylphenyl)-5-chloropyrazine represented by
) (where m and n have the same meanings as in general formula (I)) may be reacted with an alcohol represented by the following in the presence of a strong base.

Here, the compound represented by general formula (II) is a known compound.

The alcohol represented by the general formula (III) has m,
Depending on n, it can be easily produced using a commercially available compound as a raw material, for example, in the following manner.

In the case of n=1 and n=2, it can be obtained by performing a commercially available carbon chain extension reaction.

When n = 3, commercially available 2-bromohexane can be converted into a Grignard compound, reacted with formaldehyde, or reacted with carbon dioxide, and then reduced to obtain alcohol (2-methylhexanol). I can do it,
In the case where n=4, it can be manufactured in the same manner.

In addition, the compound represented by the -i formula (1) is represented by the general formula (■)
2-(4-alkyphenyl)-5-hydroxypyrazine represented by ' and general formula (■)' CH.

Br-(ct+z)-i CH(CHi
It can also be obtained by reacting a bromide represented by "'(m)'" in the presence of a base.

Here, the bromide represented by (■)' has the general formula ([[)
It can also be obtained by brominating the alcohol represented by by a conventional method.

The compound represented by the general formula (1) of the present invention is obtained as described above, and the melting point, phase transition temperature, infrared absorption spectrum (IR
), can be confirmed by means such as nuclear magnetic resonance spectroscopy (NMR).

Examples of representative compounds are shown in Table 1.

/ The pyrazine derivative of general formula (1) does not contain a highly viscous group such as an ester bond like the compound represented by general formula (A), so its viscosity is low.

In addition, although it does not exhibit an SC phase when used alone, the upper limit temperature of the SC phase of the liquid crystal composition does not decrease significantly when mixed. Furthermore, its melting point is relatively low, making it an excellent compound for SC matrix liquid crystals.

As comparative examples, examples of compounds represented by general formula (C) having similar structures are shown in Table 1. This compound is
Although it has a low viscosity and does not exhibit an SC phase, it has the characteristics that the upper limit temperature of the SC phase of the liquid crystal composition is hardly lowered by mixing. When made into a composition, it stably maintains S even at low temperatures.
Since it is difficult to exhibit the C phase and the compatibility with other compounds is not good, there is a risk that crystals will precipitate if left at low temperatures for a long time.

In the compound represented by the general formula (1), by introducing a racemic methyl branched side chain, the melting point can be significantly lowered without deteriorating the above-mentioned viscosity or temperature characteristics, and the liquid crystal phase temperature can be lowered. By expanding the range and mixing with other compounds exhibiting an SC phase, it has become possible to more easily obtain a composition exhibiting an SC phase stably up to low temperatures. Further, when the composition is prepared, the nematic (N) phase is not eliminated and the smectic A (SA) phase is not expanded.

In order to obtain good orientation, it is necessary to add S to the high temperature region of the sc” phase.
It is said that a phase series having an A phase and an N" phase is preferable. Generally, introducing a branching group into a side chain tends to suppress the nematic property of a liquid crystal compound and increase the smectic A property. In the compound represented by general formula (1),
There is no such tendency, and it is easy to prepare a liquid crystal composition having a preferable phase series suitable for alignment.

The liquid crystal composition using the compound represented by the general formula (1) of the present invention is composed of a racese fruit obtained from the compound represented by the general formula (I) and a liquid crystal composition other than this. In particular, when used as a constituent material of a ferroelectric liquid crystal display element, substances other than the compound represented by general formula (1) include a liquid crystal compound or liquid crystal composition exhibiting an SC phase as a main component and a minor component. A composition containing optically active compounds is desirable. Furthermore, by adding a small amount to nematic liquid crystal, it can be used for lowering the viscosity.

Examples of SC compounds that can be used as an SC matrix liquid crystal together with the compound represented by the general formula (1) of the present invention include:
For example, phenylbenzoate compounds represented by the general formula (A) above, pyrimidine compounds represented by the general formula (B), pyrazine compounds represented by the general formula (C), or the following general formula (D- 1) ~ (D-6)
Three prototype compounds such as the compound represented by can be mentioned.

(In the formula, RC and R' each independently represent a linear alkyl group or an alkoxyl group. Also, the benzene ring may be substituted with fluorine.) (R" and Rb are represented by the general formula (A) ) By adding a chiral dopant consisting of an optically active compound to the thus obtained Sc liquid crystal composition, a low-viscosity liquid crystal that easily exhibits the sc'' phase over a wide temperature range including room temperature can be obtained. &
[You can obtain 1 precept.]

〔Example〕

The present invention will be specifically explained below with reference to Examples.
Of course, the gist and scope of the present invention are not limited to these examples.

The structure of the compound is 5, and the nuclear magnetic resonance spectrum (NM
R), and by infrared absorption spectrum (IR) and mass spectrum (MS). The phase transition temperature was measured using a polarizing microscope equipped with a temperature control stage and a differential scanning calorimeter (DSC). In JR, (Br) indicates measurement by tablet molding, (neat) indicates measurement using a liquid film, and (Nujol) indicates measurement in a suspended state in liquid paraffin.

In NMR, (CDCI, ) represents a solvent, S represents a singlet, d represents a doublet, t represents a triplet, q represents a quartet, m represents a multiplet, broad represents a broad absorption, and J represents a Represents a coupling constant. Moreover, temperature represents °C.

All "%" in Mi Bomono means "% by weight".

Example a 1 (2-(4-hexylphenyl)-5(6
Synthesis of 2-(4-hexylphenyl)-5-hydroxypyrazine (162 mg of 2-(4-hexylphenyl)-5-hydroxypyrazine) in dimethylformamide (DMF) 10
Tar! dissolved in 122 mg of t-butoxypotassium was added to this solution, and the mixture was stirred at room temperature for 40 minutes. To this mixture was added racemic 6-bromide dissolved in 3 ml of DMF.
A solution of 181 mg of methyloctyl was added dropwise, and the mixture was further stirred at room temperature for 8 hours.

After adding water and ether and making it acidic with hydrochloric acid, the organic layer and
Separated into aqueous layer. The aqueous layer was simply extracted with ether and the ether layer was combined with the organic layer. The a-layer was washed with water and then with saturated brine, and dried over anhydrous sodium sulfate. The residue obtained by distilling off the solvent from the organic layer was subjected to silica gel column chromatography (solvent: hexane/ethyl acetate =
5) to obtain 112 mg of the title compound.

NMR (CDCl5): 0.81-0.93 (m
, 911), 1.07-1.70 (m, 178)
, 1.77-1.87 (m, 2H), 2.65 (
t, 7.5Hz.

2)1), 4.34(t, J=6.5Hz, 2H
), 7.28 (d, J=8.5Hz.

2H), 7.80(d, J=8.511z, 2fl
), 8.25 (S, IH), 8.45 (S,
il+) IR (Nujol): 2950, 2875, 154
5,1465,1350゜1295.1180,106
0,1015,850 (cm-') Example 2 (S
(Preparation of C'' liquid crystal Mi paraboloid and creation of display element) An SC matrix liquid crystal having the following composition was prepared.

Formula (B-i) Formula (B-gut) formula () Compound No. 1 in Table 1 20% Next, this SC mother liquid crystal 80%, From the following composition SCh liquid crystal group admonishing from 20% chiral dopant A paraboloid was prepared.

CH3 -OCOCH-0-n-Czll.

73% of compounds CH.

10COCH-0-n-CJt 27% of compounds This sc” The liquid crystal composition is SC” below 57.5°C. phase death, SA phase at 61.5℃ or less, N” below 67.5℃ phase Each is shown.

Further, the melting point of this sc'' liquid crystal composition was as low as 4.5°C.

Next, this "sc" liquid crystal composition was heated to I phase, and filled into a cell with a thickness of approximately 2 μm consisting of two glass transparent electrodes that had been subjected to an orientation treatment by polyimide coating and rubbing. Slowly cooled to room temperature. As a result, uniformly oriented SC* phase monodomains were obtained.

When a rectangular wave with an electrolytic strength of 10 Vp- was applied to this cell at 25 DEG C. and the electro-optic response speed was measured, it was found to be extremely fast at 29 microseconds.

Reference Example 1 In Example 2, the compound of formula (B-i) was used in the SC matrix liquid crystal without using the compound of No. 1 in Table 1.
%, 28% each of the compounds of formula (B-1) and formula (B-c)
An "sc" liquid crystal composition was prepared in the same manner as in Example 2 except that % was used.

This sc''' liquid crystal composition exhibited an sc'' phase at temperatures below 67.5°C, an SA phase at temperatures below 70.5°C, and an N0 phase at temperatures below 76°C.

Using this SC liquid crystal composition, the electro-optical response speed measured in the same manner as in Example 2 was as slow as 35 μs. Reference Example 2 In Example 2, in place of the compound No. 1 in Table 1, , sc'' liquid crystal compositions were prepared in the same manner as in Example 2, except that the same amounts of the compounds of Comparative Examples in Table 1 were used. This SC
Although the liquid crystal composition 1 exhibited an sc''' phase at temperatures below 58°C, its melting point was as high as -1.5°C.

〔Effect of the invention〕

Compound (racemate) represented by general formula (I) of the present invention
has a low melting point and does not exhibit an SC phase, but when mixed, it does not significantly lower the upper limit temperature of the SC phase in the composition, has a low viscosity, and is compatible with other SC liquid crystal compounds, etc. By using it as an SC matrix liquid crystal, it is possible to obtain a U acid with a wide temperature range and low viscosity. As a result, especially in the SC8 liquid crystal composition, high-speed response can be achieved over a wide temperature range. Further, as shown in the Examples, the compound of the present invention can be easily manufactured industrially, is colorless, and has excellent chemical stability against water, light, heat, etc., and is therefore practical.

Furthermore, the chiral smectic liquid crystal material using the compound of the present invention can achieve a high-speed response of 30 μsec or less, and is extremely useful as an optical switching element for display.

Claims (1)

[Claims] 1. General formula▲ Numerical formula, chemical formula, table, etc.▼ (In the formula, R^1 represents a linear alkyl group having 4 to 18 carbon atoms, and m is an integer of 2 to 8. , and n represents an integer of 1 to 4.) A racemic body consisting of a compound represented by the following. 2. The racemate according to claim 1, wherein n is 1. 3. A liquid crystal composition containing the racemate according to claim 1. 4. The liquid crystal composition according to claim 3, which exhibits a chiral smectic phase. 5. A liquid crystal display element constructed using the liquid crystal composition according to claim 3 or 4.