JPH0825932B2 - Optically active-1- (2-halogen-substituted phenyl) ethanol - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel optically active alcohol which is an intermediate of an optically active substance useful as a component of a liquid crystal material used for a liquid crystal display device.

[Prior Art] Liquid crystal display devices have been rapidly expanded in their applications by improving circuits, driving methods and cell manufacturing techniques, and particularly by improving the characteristics of liquid crystal compositions encapsulated in the devices. However, there are many points to be improved in the liquid crystal display element.

Examples include narrow viewing angle, poor contrast, slow response speed, still small display capacity, and deterioration of display quality due to ambient temperature change. Among these, the deterioration of the display quality due to the temperature change of the surroundings is caused by the temperature change of the threshold voltage Vth.

As a commonly used means in recent years, a small amount of an optically active substance is added to a liquid crystal composition to suppress the reverse twist of the liquid crystal molecule and give the liquid crystal molecule a clockwise or counterclockwise spiral structure to maintain display quality. There is a way. For example,
This can have an advantageous effect in the case of a TN (twisted nematic) type display element and a recently proposed SBE (supertwisted birefrigence effect) type display element.

However, if the twisting ability of the optically active substance added as a doping agent is too low, it is necessary to add the doping agent at a relatively high concentration in order to obtain the required pitch, which is disadvantageous to other material parameters. It has obvious implications. Therefore, an optically active substance having a high twisting ability, that is, an ability to develop a shorter pitch with the same addition amount in a liquid crystal has been desired.

For example, CB-15 manufactured by BDH, JP 62-81354 A, JP
Each compound described in 62-81355 has the ability to develop a pitch of about 10 μm by adding 1% by weight to a nematic liquid crystal composition, and in a sense, it can be said that it is a practical optical substance.

However, generally known optically active substances, including the compounds mentioned above, increase the pitch of the liquid crystal substance due to the addition thereof as the temperature rises, often exerting an undesired effect. For example, in the SBE method, the characteristic pitch P of the liquid crystal composition changes due to the temperature change, and thereby the ratio P / d of the cell thickness d of the display element and the characteristic pitch P of the liquid crystal composition also changes. Normally, P / d is 2 or less, but if it becomes 2 or more due to temperature change, the 270 degree twist will change to 90 degree twist.

Further, in terms of improvement for increasing the display capacity, it is necessary to improve the steepness of change in transmittance when a voltage is applied to the display element. G. Bauer and W. Fehrenbach, 27th at the 15th Freiburg LCD Conference (1985)
Although we have reported the calculation result that the steepness is greatly improved when the twist of 0 degree is used, it is necessary to eliminate the change of the natural pitch due to the temperature here as well.

As a method for solving this problem, in recent years, an optically active compound having a negative temperature characteristic, that is, a substance in which an intrinsic pitch decreases with an increase in temperature, has been found, which is a conventional optically active substance having a positive temperature characteristic. A composition having no change in the characteristic pitch due to temperature has been obtained by mixing with an appropriate amount (Japanese Patent Application No. 61-179194, Emoto et al.).

However, any of the currently reported substances with negative temperature characteristics has a low twisting ability with respect to liquid crystal substances,
In order to obtain the required pitch, it is premised that the liquid crystal composition is added at a considerably high concentration, and it is presumed that the high concentration addition causes various adverse effects on the liquid crystal composition.

In order to solve these problems, a substance having a short pitch and a negative temperature characteristic is desired.

[Problems to be Solved by the Invention] An object of the present invention is to provide an optically active compound having properties required for realizing a liquid crystal composition having suitable properties, particularly negative temperature properties, and extremely high twisting ability. To provide an optically active alcohol useful as an intermediate raw material or precursor.

[Means for Solving Problems] The present invention provides (1) general formula (However, in the formula (I), X represents a halogen atom.)
It is an optically active alcohol represented by.

Next, a method for preparing the optically active alcohol of the present invention will be described.

The optically active alcohol of the present invention can be optically resolved by commercially available racemic alcohol or, for example, racemic alcohol synthesized according to the following reaction formula, through biochemical asymmetric transesterification or asymmetric ester synthesis.

In order to carry out the optical resolution by transesterification, it is suitable to carry out racemic alcohol together with triglyceride such as tributyrin in the absence of water, for example, by adding an enzyme such as lipase at 30 to 45 ° C in a liquid phase. is there. A commercially available product can be used as the enzyme.

The reaction time is 1 to several tens of days. After the reaction, the enzyme is separated by filtration, and the produced ester and unreacted alcohol are isolated from the filtrate by a separation means such as distillation and chromatography. The isolated alcohol is one of a pair of antipodes, and the other optically active alcohol is obtained by hydrolyzing the produced ester.

[Examples] Hereinafter, the present invention will be described in detail with reference to Examples. Further, the usefulness of the optically active alcohol of the present invention will be shown by application examples.

Example 1 Enzyme (Amano Pharmaceutical Co., Lipase "Amano" CES) 10 g,
(±) -1- (2-bromophenyl) ethanol 7.0g
(35m-mol) and tributyrin 15.9g (52.5m-mol)
Was placed in a three-necked flask and stirred at 35 ° C. for 15 days. After the reaction was stopped, the enzyme was removed by filtration, the filtrate was concentrated, and the desired product was isolated by silica gel chromatography. As a result, (S) -1- (2-bromophenyl)
Ethanol 2.6g, ▲ [α] ^{23.5 °} _D ▼ -26.3 ° (C3.72, C
HCl ₃ ) and (R) -1- (2-bromophenyl) -1'-
25 g of butanoyloxyethane was obtained. This was hydrolyzed to obtain (R) -1- (2-bromophenyl) utanol. (▲ [α] ^{23.5 °} _D ▼ + 33.5 ° (C3.52, CHC
l ₃ )).

Reference Example 1 (R) -1- (2-bromophenyl) ethanol produced in Example 1 (▲ [α] ^23.5 _D ▼ + 33.5 ° (C3.52, CHC
l ₃ )) 4g, 4-pentyloxybiphenyl-4'-carboxylic acid 6g, N, N-dicyclohexylcarbodiimide 7g, 4-N,
N-dimethylaminopyridine 0.4g, dichloromethane 100ml
The mixture was stirred at room temperature for 2 hours and the insoluble material was filtered off. The filtrate was washed with acid, washed with alkali and water, the solvent was distilled off, and the residue was recrystallized from a mixed solvent of ethanol and ethyl acetate to obtain 7.6 g of (R) -4-pentyloxybiphenyl-4'-carboxylic acid. 1- (2-Bromophenyl) ethyl ester was obtained. mp101.2-102.2 ° C. Moreover, this was in agreement with the title compound according to elemental analysis, NMR-spectra, and IR-spectra.

Reference Example 2 Nematic liquid crystal composition (commercially available from Merck, ZLI-113
2 was used) in the compound of Reference Example 1 Was added in an amount of 1% by weight to prepare a chiral nematic liquid crystal composition. When this chiral nematic liquid crystal composition was injected into a wedge-shaped cell which had been subjected to parallel treatment and observed under a polarizing microscope, the helical pitch was observed as shown in the following table.

However, ΔP _20-T in the above table is a parameter expressing the temperature characteristic and is defined by the following equation.

P (t); pitch length at t ° C. t; temperature The pitch developed as described above is extremely short, and further, the pitch length becomes shorter as the temperature rises. It was found that the compound (1) is an excellent pitch adjusting agent for liquid crystal compositions.

[Function and Effect of the Invention] The compound (Japanese Patent Application No. 62-255,326) filed by the applicant of the present invention, which uses the compound of the present invention as an intermediate, exhibits a number of extremely useful properties when added to a liquid crystal composition. Is disclosed.

These characteristics are not exhibited until the optically active alcohol which is the compound of the present invention is used as an intermediate, and the compound of the present invention is very useful as such an intermediate.

Claims (1)

[Claims] 1. A general formula (However, in the formula (I), X represents a halogen atom.) An optically active alcohol represented by the formula: