NOVEL OPTICALLY ACTIVE TOLAN DERIVATIVE

Abstract: A novel optically active compound of the formula is capable of forming a chiral nematic liquid crystal composi­ tion having short spiral pitch by adding a small amount of it to a generally nematic liquid crystal composition. The com­ pound of this invention is useful in the manufacture of SBE display device which is excellent especially in high level multi­ plexing driving system.

Description: FIELD OF THE INVENTION This invention relates to a novel optically active tolan derivative which is useful as an electro-optical display material. BACKGROUND OF THE INVENTION At present, as the means of preventing the generation of reverse domain in the TN type (Twisted Nematic) liquid crystal display device, it is usually preferred to use a process wherein about 0.1% of cholesteric liquid crystal or about 0.1 to 1% of optically active compound is added to a nematic liquid crystal composition. The SBE (Supertwisted Birefringence Effect) display device which was recently proposed by T. J. Scheffer et al. [Applied Physics Letters, 45 , 1021 - 1023 (1984)] is excellent especially in high level multiplexing driving system and adapted for a flat panel. The nematic liquid crystals in the SBE display device are those which have been twisted in an angle of 180 to 270° by the addition of an optically active compound. For this purpose an optically active dextro or laevo compound is required which can afford short spiral pitch by its addition in an amount as small as possible. Chemical Abstracts, Volume 82 (1975) p. 413, Abstract 79031 k discloses p, p¹ - disubstituted tolans which are not optically active compounds. SUMMARY OF THE INVENTION It is the object of this invention to provide a novel optically active compound which can form a chiral nematic liquid crystal composition having short spiral pitch by adding a small amount thereof to a nematic liquid crystal composition. Said object is achieved by a compound represented by the following general formula: (I) wherein R represents a straight chain alkyl group having 1 to 20 carbon atoms, an alkoxyl group, or R' represents a straight chain alkyl group having 2 to 8 carbon atoms or phenyl group; and R'' represents a straight chain alkyl group having 1 to 5 carbon atoms, provided that R' and R'' are different groups; n represents 0 or 1; m represents an integer of 1 to 4; and represents an assymmetric carbon atom. BRIEF DESCRIPTION OF THE DRAWING Figures 1 and 2 indicate the relationship between the amount added of the compounds of this invention (wt% based on the total weight) and the reciprocal (1/p) of the spiral pitch p of the liquid crystals obtained when the compounds of this invention Nos. 1 to 5 and Nos. 6 to 7 are added respectively in varying proportions to the host liquid crystal (A) which is now widely used as a nematic liquid crystal material. DETAILED DESCRIPTION OF THE INVENTION One example of the process for the preparation of a compound represented by the general formula (I) will be explained below. In the reaction scheme, R, R' and R'' are as defined above, and R''' represents an alkyl group. First Step : 4-Alkylphenylacetylene or 4-alkoxyphenylacetylene is reacted with 4-iodobenzoic acid ester in a solvent such as diethylamine in the presence of a catalyst such as bis(triphenylphosphine) palladium (II) chloride to produce a compound of formula (II). Second Step : The compound of formula (II) produced in the first step is reacted with a base such as sodium hydroxide in a solvent such as ethanol to produce a compound of formula (III). Third Step : The compound of formula (III) produced in the second step is reacted with a halogenating agent to produce a compound of formula (III)': X in the compound of formula (III)' is preferably a chlorine atom, wherein thionyl chloride may be preferably used as the halogenating agent. The reaction is carried out under ordinary pressure at the reflux temperature of the reaction mixture. It is not necessary to isolate the compound of formula (III)' from the mixture formed in the reaction, while it is required to simply remove an excess of the halogenating agent. Fourth Step : The crude compound of formula (III)' produced in the third step is reacted with an optically active alcohol of formula (IV) in a basic solvent such as pyridine. By subjecting the reaction product to purification treatments such as solvent extraction, water washing, drying or recrystallization, the final product of formula (I) can be isolated. The transition temperature and the optical rotation of typical compounds of formula (I) thus produced are shown in Table 1. (In the above Table 1, C represents the crystalline phase, Ch represents the cholesteric phase, and I represent the isotropic liquid phase. The same shall be applied hereinafter.) The compound of formula (I) can be used in admixture with an ordinary nematic liquid crystal mixture. Preferable examples which can be used in admixture with the compound of formula (I) include 4-substituted phenyl 4'-substituted benzoates, 4-substituted phenyl 4'-substituted cyclohexanecarboxylates, 4-substituted biphenyl 4'-substituted cyclohexanecarboxylates, 4-substituted phenyl 4'-(4''-substituted cyclohexanecarbonyloxy)benzoates, 4-substituted phenyl 4'-(4''-substituted cyclohexyl)benzoates, 4-substituted cyclohexyl 4'-(4''-substituted cyclohexyl)benzoates, 4-substituted 4'-substituted biphenyls, 4-substituted phenyl 4'-substituted cyclohexanes, 4-substituted 4'-substituted terphenyls, 4-substituted biphenyl 4'-substituted cyclohexanes, and 2-(4'-substituted phenyl)-5-substituted pyrimidines, etc. In addition, the host liquid crystal (A) comprises From Figures 1 and 2 it is found that the compound of formula (I) can form nematic liquid crystal compositions, whose 1/p values have rapidly increased, that is, chiral nematic liquid crystal compositions which have short spiral pitch may be prepared, by adding a small amount thereof to the host nematic liquid crystal. Also, the compound of formula (I) can produce a ferroelectric liquid crystal composition by adding it to or mixing it with a liquid crystal compound having a chiral smectic crystalline phase (Sc*). EXAMPLE 1 26 g (0.1 mol) of 4-iodobenzoic acid methyl ester was dissolved in 30 ml of diethylamine, and after addition of 0.21 g (0.0003 mol) of bis(triphenylphosphine)palladium (II) chloride and 0.19 g (0.001 mol) of cuprous iodide, 17.2 g (0.1 mol) of 4-n-pentylphenylacetylene was dropwise added to the resulting solution at room temperature. After the dropping was complete, stirring was continued for 7 h at room temperature. After the reaction was completed, the reaction liquid was added to an excess of ice-cooled hydrochloric acid. The crystals deposited were recovered by filtration, washed with water until neutral, and then purified by recrystallization from ethanol, whereby 25 g (0.08 mol) of the following compound was obtained. The compound was added to a mixture of 300 ml of ethanol and 100 ml of water, and after addition of 13 g (0.3 mol) of sodium hydroxide thereto, the resulting solution was heat refluxed for 3 h. After the reaction was completed the reaction liquid was added to an excess of ice-cooled hydrochloric acid. The crystals deposited were recovered by filtration, washed with water until neutral, and purified by recrystallization from chloroform, whereby 20 g (0.07 mol) of the following compound was obtained 2.9 g (0.01 mol) of this compound was added to an excess of thionyl chloride, and after 3 h of heat refluxing the excess thionyl chloride was distilled off under reduced pressure. The compound thus obtained was dissolved in 15 ml of pyridine, and after addition of 0.8 g (0.01 mol) of (S)-(+)-2-butanol, reaction was effected for 1 h at 50°C. After the reaction was completed, the reaction product was extracted with toluene in an acid state containing hydrochloric acid, washed with water, dried, and recrystallized from ethanol, which gave 2.7 g (0.008 mol) of the following compound. Yield: 80%, [α] 25 / D= +20.0° Transition temperature: -2°C (C→I) EXAMPLE 2 The following compound was obtained in the same manner as in Example 1 except that (R)-(-)-2-butanol was used as the raw material alcohol. Yield: 74%, [α] 25 / D= -22.8° Transition temperature: 15°C (C→I), -2°C(I⇄Ch) EXAMPLE 3 The following compound was obtained in the same manner as in Example 1 except that (R)-(-)-2-ocatanol was used as the raw material alcohol. Yield: 77%, [α] 25 / D= - 39.7° Transition temperature: 35°C (C→I) EXAMPLE 4 The following compound was obtained in the same manner as in Example 1 except that (S)-(+)-2-methylbutanol was used as the raw material alcohol. Yield: 78%, [α] 25 / D= +4.5° Transition temperature: liquid at -60°C. EXAMPLE 5 The following compound was obtained in the same manner as in Example 1 except that 4-{(S)-(+)-3'-methylamyl}phenylacetylene was used as the raw material 4-alkylphenylacetylene, and (S)-(+)-2-butanol was used as alcohol. Yield: 63%, [α] 25 / D= -22.8° Transition temperature: liquid at -60°C EXAMPLE 6 15 ml of thionyl chloride was added to 0.94 g (0.0032 mol) of a compound of the formula: and after the resulting mixture was allowed to react for 30 min under reflux, the excess thionyl chloride was distilled off under reduced pressure. To the reaction product thus obtained there were added 0.4 g (0.0032 mol) of compound of formula: 30 ml of toluene, and 1 g of pyridine, and the resulting mixture was allowed to react for 30 min under reflux. The reaction liquid was washed with 9% hydrochloric acid and then with water until neutral, after which toluene was distilled off from the reaction liquid under reduced pressure. By recrystallizing the reaction product from ethanol, 0.95 g (0.0024 mol) of the following compound was obtained. Yield: 76%, [α] 25 / D= -101.7° Transition temperature: 73°C (C→I) EXAMPLE 7 The following compound was obtained in a similar manner as in Example 6. Yield: 72%, [α] 25 / D= +44.5° Transition temperature: 36°C (C→I); 30°C(I⇄Ch) The compound of the present invention is capable of preparing a chiral nematic liquid crystal composition having short spiral pitch by adding a small amount thereof to a nematic liquid crystal composition. Thus, the compound is effective for forming an SBE display devise having excellent property in high level multiplexing driving system.

Claims: An optically active tolan derivative represented by the general formula (I) wherein R represents a straight chain alkyl group having 1 to 20 carbon atoms, an alkoxyl group, or represents a straight chain alkyl group having 2 to 8 carbon atoms or phenyl group, and R'' represents a straight chain alkyl group having 1 to 5 carbon atoms, provided that R' and R'' are different groups; n represents 0 or 1, m represents an integer of 1 to 4; and represents an asymmetric carbon atom. The compound as defined in Claim 1, wherein R is n-C₅H₁₁-, R' is n-C₆H₁₃- and R'' is CH₃-. The compound as defined in Claim 1, wherein R is n-C₅H₁₁-, R' is C₂H₅- and R'' is CH₃-. The compound as defined in Claim 1, wherein R is R' is C₂H₅-, and R'' is CH₃-. The compound as defined in Claim 1, wherein R is n-C₅H₁₁-, R' is and R'' is CH₃-. A process for preparing a compound of the formula wherein R represents a straight chain alkyl group having 1 to 20 carbon atoms, an alkoxyl group, or R' represents a straight chain alkyl group having 2 to 8 carbon atoms or phenyl group, and R'' represents a straight chain alkyl group having 1 to 5 carbon atoms; n represents 0 or 1, m represents an integer of 1 to 4; and represents an asymmetric carbon atom, which comprises reacting 4-alkyl- or 4-alkoxyphenyl acetylene of the formula: with 4-iodobenzoic acid ester of the formula wherein R''' represents alkyl group in the presence of a catalyst to obtain a compound of the formula reacting the compound of formula (II) with a base in a solvent to form a compound of the formula reacting the compound of the formula (III) with a halogenating agent, followed by reacting with an optically active alcohol of formula in a basic solvent to produce and isolate.

Inventors: SASAKI, MAKOTO, TAKATSU, HARUYOSHI, TAKEUCHI, KIYOHUMI
Applicants: DAINIPPON INK AND CHEMICALS, INC.
Application year: 1986
Main classification: C07C69
IPC codes: C09K19