Abstract:
Disclosed is an optically active substance represented by the formula: ##STR1## wherein m is an integer of 1 to 14, Y is ##STR2## R is --C n  H 2n+1 , --OC n  H 2n+1 , --OCOC n  H 2n+1  or --COOC n  H 2n+1  (in which n is an integer of 1 to 18), each of the asterisked carbon atoms is an asymmetric carbon atom, X a single bond, --CO 2  --, or --OCO--, and A 1  and A 2  is hydrogen, fluorine, chlorine, bromine, cyano or methoxy.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a novel optically active substance and a liquid crystal composition comprising this optically active substance. 
     The liquid crystals currently widely used in a liquid crystal display (LCD) are classified into the nematic phase, and since they are of the light-receiving type, the display system using these liquid crystals is characterized in that there is no eye fatigue therefrom and the power consumption is very low. Nevertheless, the display system using these liquid crystals has problems in that the response speed is low and the view angle of the display is narrow. 
     A display device or printer head using a ferroelectric liquid crystal having advantageous characteristics inherently possessed by nematic liquid crystals, such as no eye-fatigue property and very low power consumption, and having high response speed and high contrast comparable to those of display elements of the light-emitting type, has been investigated. 
     The ferroelectric liquid crystal was discovered for the first time by R. B. Meyer et al in 1975 [J. physique, 36, L-69 (1975)]. This ferroelectric liquid crystal is classified into the chiral smectic C phase (hereinafter referred to as &#34;Sm*C phase&#34;), and a typical compound of this ferroelectric liquid crystal is p-decyloxybenzylidene-p&#39;-amino-2-methylbutyl cinnamate (hereinafter referred to as &#34;DOBAMBC&#34;) represented by the following formula: ##STR3## 
     DOBAMBC and most of the ferroelectric liquid crystal materials proposed thereafter, have problems in that the temperature range showing the ferroelectricity (the temperature range in which the Sm*C phase is present) is narrow, and they cannot be used practically without an additive. Accordingly, attempts have been made to expand the temperature range showing the Sm*C phase of the lower and higher temperature sides, taking room temperature as the center, by mixing ferroelectric liquid crystals each other or with other liquid crystals. Under this circumstance, the development of a ferroelectric liquid crystal showing the Sm*C phase in the practical temperature range is desired. Furthermore, the development of a ferroelectric liquid crystal having a larger spontaneous polarization than those of the known ferroelectric liquid crystals is desired in the field of printer heads for which an ultra-high response speed is required. 
     When ferroelectric liquid crystals having the Sm*C phase are mixed, the kinds of applicable compounds (liquid crystals) are limited, and liquid crystal mixtures which give satisfactory various performances are difficult to obtain at present. Compounds having a Schiff base, such as DOBAMBC, have a poor light stability and a coloration thereof readily occurs. 
     SUMMARY OF THE INVENTION 
     Therefore, a primary object of the present invention is to provide an optically active substance which exhibits the Sm*C phase when incorporated in a composition having a smectic C phase (hereinafter referred to as &#34;SmC phase&#34;), which is chemically stable, is not colored, has an excellent light stability, and imparts large spontaneous polarization to a liquid crystal composition comprising this optically active substance. 
     Another object of the present invention is to provide a liquid crystal composition comprising this optically active substance as a part of the composition. 
     In accordance with the present invention, there is provided an optically active substance having a δ-valerolactone ring, which is represented by the following general formula (1): ##STR4## wherein m is an integer of from 1 to 14, Y represents ##STR5## or ##STR6## R represents --C n  H 2n+1 , --OC n  H 2n+1 , --OCOC n  H 2n+1  or --COOC n  H 2n+1  (in which n is an integer of from 1 to 18), each of the asterisked carbon atoms is an asymmetric carbon atom, X represents a single bond, --CO 2  --, or --OCO--, and A 1  and A 2  independently represent a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a cyano group, or a methoxy group. 
     In accordance with the present invention, there is further provided a liquid crystal composition comprising at least one optically active substance represented by the above formula (1). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates the NMR spectrum of (2S,5R)-2-(4-octyloxybenzoyloxy)-5-hexyl-δ-valerolactone. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     If the carbon number (n) of the alkyl group represented by R in formula (1) is 19 or larger, the purification of the starting materials used, such as ##STR7## becomes relatively difficult. If the carbon number (m) of the alkyl group bonded to the lactone ring is 15 or larger, the purification of the optically active lactone becomes relatively difficult. In each case, the productivity is reduced, and when the optically active substance is mixed with other liquid crystal, the intensity of the spontaneous polarization tends to decrease. 
     The process for the synthesis of the optical active substance will now be described. 
     The 3-hydroxy-6-alkyl-δ-valerolactone of the following formula: ##STR8## wherein m is an integer of from 1 to 14, which is used in the present invention, can be obtained by electrochemically synthesizing an optically active β-hydroxycarboxylic acid with a monoester of an optically active α-acetoxy-dibasic acid by Kolbe electrolysis and cyclizing the reaction product. 
     The optically active β-hydroxycarboxylic acid can be obtained, for example, by reacting a methyl alkyl ketone with diethyl carbonate in the presence of sodium hydride to form an ethyl ester of a β-ketocarboxylic acid and hydrolyzing the ethyl ester with potassium hydroxide, as indicated by the following reaction formula: ##STR9## and subjecting the carbonyl group at the β-position to the asymmetric reduction with baker&#39;s yeast to yield an optically active β-hydroxycarboxylic acid, as shown by the following reaction formula: ##STR10## 
     If the carbon number (m) of the alkyl group of the methyl alkyl ketone is 3 or smaller, the yield of the asymmetric reduction product in the above-mentioned process is not satisfactory, and therefore, preferably instead of the ethyl ester of the β-ketocarboxylic acid, and alkyl ester, having a larger carbon number (i.e., 6 or larger), of the β-ketocarboxylic acid is reduced. 
     Separately, S-(-)-malic acid is reacted with acetyl chloride and the obtained reaction product is reacted with anhydrous ethanol to yield an optically active monoethyl ester of α-acetoxydibasic acid, as represented by the following reaction formula [see Tetrahedron, 41, No. 13, 2751-2758 (1985)]: ##STR11## 
     The obtained optically active β-hydroxycarboxylic acid is electrolytically reacted with the optically active monoethyl ester of α-acetoxydibasic acid to Kolbe electrolysis, as indicated by the following reaction formula: ##STR12## and the obtained product is cyclized in the presence of p-toluene-sulfonic acid to obtain the above-mentioned valerolactone derivative as shown by the following reaction formula: ##STR13## 
     [Synthesis of Substance Represented by General Formula (1)] 
     The substance represented by General formula (1) can be synthesized through the following routes. 
     (a) Where Y is general formula (1) is --CO 2  --, the synthesis route is expressed as follows: ##STR14## 
     (b) Where Y in general formula (1) is --O--, the synthesis route is expressed as follows: ##STR15## 
     (c) Where Y in general formula (1) is --CH 2  O--, the synthesis route is expressed as follows: ##STR16## 
     Since the optically active substance of the present invention does not possess an azomethine bond inherently possessed by the conventional ferroelectric liquid crystal substances, the substance of the present invention has a greatly improved chemical stability such as the hydrolysis resistance and an improved light stability, compared to the conventional cinnamic acid type compounds. Therefore, the substance of the present invention has excellent characteristics required for a display material. 
     The optically active substance of the present invention does not always show the chiral smectic C phase (hereinafter referred to as &#34;Sm*C phase&#34;) alone, but the optically active substance of the present invention is characterized in that, when the substance is mixed with other liquid crystal substance having the Sm*C phase or other ferroelectric liquid crystal substance, the Sm*C phase is exhibited and the spontaneous polarization is increased, and therefore, the response time is shortened. 
     The liquid crystal composition of the present invention will now be described. 
     The liquid crystal composition of the present invention comprises at least one optically active substance of formula (1), but a composition comprising a plurality of ferroelectric liquid crystal substances, and optionally, an additive substance is advantageous over the liquid crystal composition comprising a single liquid crystal compound, because the applicable temperature rang can be broadened. As specific examples of other ferroelectric liquid crystal compound that can be mixed with at least one compound represented by general formula (1), the following compounds can be mentioned: ##STR17## 
     Other compounds can be mixed with the compounds of formula (1) and used in the form of liquid crystal compositions, if they are ferroelectric liquid crystal compounds. 
     If the compound of the present invention is mixed with a ferroelectric liquid crystal compound or composition showing the SmC phase, the mixture becomes a ferroelectric liquid crystal and as apparent from a high response speed, the mixture has a large spontaneous polarization. 
     Examples of the compound showing the SmC phase are described below, although other compounds and mixtures showing the SmC phase can be similarly used: ##STR18## 
     The present invention will now be described in detail with reference to the following examples. 
     REFERENTIAL EXAMPLE 1 
     Synthesis of β-hydroxynonanoic acid 
     To a solution comprising 210 ml of diethyl carbonate, 12.8 g of sodium hydride dispersed at a concentration of 60% by weight in an oil and 100 ml of dioxane was added dropwise a solution of 20.0 g of methyl ethyl ketone in 100 ml of dioxane in an argon atmosphere, the mixture was refluxed overnight, and the solvent was removed by distillation. The residue was subjected to distillation under a reduced pressure to obtain 20.0 g of ethyl hexylketoacetate (yield=62.5%, boiling point 83° C. at 0.65 mmHg). 
     In a solution comprising 75 ml of ethanol, 75 ml of distilled water and 5.02 g of potassium hydroxide was dissolved 15 g of the obtained ethyl hexylketoacetate, and the solution was stirred at room temperature for 7.5 hours. Then, 3 l of distilled water, 360 g of sucrose and 168 g of dry yeast were added to the solution and the mixture was shaken at 30° C. for 16 hours. The liquid was filtered through Celite. The obtained solid was air-dried and extracted with ethyl acetate, and the extract was concentrated. Hydrochloric acid was added to the filtrate to adjust the pH value to 1, and sodium chloride was added to form a saturated solution. The solution was extracted with chloroform, and the extract and the above-mentioned ethyl acetate extract concentrate were dissolved in diethyl ether and the solution was extracted two times with a 1N aqueous solution of sodium hydroxide. Then, hydrochloric acid and sodium chloride were added to the aqueous solution of sodium hydrochloride to form a saturated aqueous solution of sodium chloride having a pH value of 1. The solution was extracted with ether five times, and the ether solution was recovered, washed with a saturated aqueous solution of sodium chloride and dehydrated on magnesium sulfate. Ether was evaporated, and the residue was dissolved in n-hexane and recrystallized therefrom to obtain 7.81 g of β-hydroxynonanoic acid [melting point=49.3° to 50.0° C., [α] D   24 .5 =-20.1° (C=1.1, CHCL 3 )]. 
     REFERENTIAL EXAMPLE 2 
     Synthesis of β-hydroxybutanoic acid 
     In a liquid comprising 36 ml of absolute methanol and 36 ml of anhydrous 1,2-dichloroethane was suspended 5 g of optically active poly-β-hydroxybutyrate, and 1.1 ml of concentrated sulfuric acid was added to the suspension and the mixture was heated and refluxed for 57 hours. The mixture was cooled and a saturated aqueous solution of sodium chloride was added to the mixture. Then, the mixture was filtered through Celite. The filtrate was extracted with 70 ml of ethanol one time and with 20 ml of ethanol three times. The residue was washed with 100 ml of ether, and the ether used for this washing was combined with the above-mentioned extract. The mixture was washed with a saturated solution of sodium hydrogencarbonate and with a saturated aqueous solution of sodium chloride and was dried on magnesium sulfate. After the drying, ether was removed and the residue was subjected to distillation under a reduced pressure to obtain 4.0 g of ethyl (R)-β-hydroxybutanoate ([α] D   21 .5 =+43.9°). 
     In a liquid mixture comprising 15 ml of water, 15 ml of ethanol and sodium hydroxide was dissolved 4.0 g of ethyl (R)-β-hydroxybutanoate, and the solution was heated and refluxed for 3 hours and then cooled. Then, the solution was subjected to an ion exchange treatment with an ion exchange resin (Amberlite R120B supplied by Rohm &amp; Haas). The solvent was removed by distillation under a reduced pressure to obtain 3.6 g of (R)-β-hydroxybutanoic acid. 
     REFERENTIAL EXAMPLE 3 
     Synthesis of 1-ethyl S-(2)-acetoxybutanedioate of the following formula: ##STR19## 
     To 50 g of (S -(-)-malic acid was added 160 ml of acetyl chloride, the mixture was stirred and refluxed at 55° C. for 4 hours, and the solution was concentrated in vacuo. Then, 100 ml of benzene was added to the residue, and benzene and acetic acid were removed in vacuo by distillation. The residue was concentrated and cooled to room temperature, and 100 ml of absolute ethanol was added to the residue and the mixture was violently stirred while cooling now and then. The mixture was heated at 70° to 75° C. for 10 minutes and at 50° to 55° C. for 10 hours. Then, the solvent was removed from the mixture by distillation under reduced pressure, and the residue was separated and purified in a silica gel column by using methylene chloride/methanol (50/1) as the developing solvent to obtain 50.9 g of 1-ethyl S-(2)-acetoxybutanedioate [melting point=50° to 51° C., [α] D   23  =-31.6° (C=1.42, ethanol)]. 
     REFERENTIAL EXAMPLE 4 
     Synthesis of (2S,5R)-2-hydroxy-5-hexyl-δ-valerolactone of the following formula and the like: ##STR20## 
     In methanol were dissolved 2.30 g of (R)-β-hydroxynonanoic acid and 7.90 g of 1-ethyl S-(2)-acetoxybutanedioate, synthesized in Referential Examples 1 and 3, respectively, and 230 mg of sodium methylate was added to the solution and the Kolbe hydrolysis was carried out at 20° to 30° C., 40 V and 1.5 A for 5 hours by using a constant voltage electrolysis apparatus (Model VE-8 supplied by Yanaco). After completion of the electrolysis, 60 ml of a 3N aqueous solution of sodium hydroxide was added to the solution, and the mixture was stirred overnight and methanol was removed. The residue was washed with ether, the alkaline aqueous solution was recovered, hydrochloric acid was added thereto adjust the pH value to 1, and sodium chloride was added to the liquid to obtain a saturated aqueous solution of sodium chloride. The solution was extracted with chloroform, and the extract was dehydrated on magnesium sulfate. Chloroform was evaporated, and the residue was dissolved in 10 ml of benzene and a catalytic amount of p-toluenesulfonic acid was added to the solution. The mixture was stirred at room temperature for 2 hours and dissolved in ether, and the solution was washed with a saturated aqueous solution of sodium bicarbonate three times and with a saturated aqueous solution of sodium chloride one time and was then dehydrated on magnesium sulfate. Ether was removed by evaporation and the intended product was separated and purified in a silica gel column by using a mixed solvent of n-hexane and ethyl acetate as the developing solvent and was recrystallized from a mixed solvent of n-hexane and ethyl acetate to obtain 310 mg of (2S,5R)-2-hydroxy-5-hexyl-δ-valerolactone. The melting point of the obtained compound was 75.5° to 77.0° C., and the elementary analysis values were as follows. 
     Elementary Analysis Values 
     Found values: C=65.84%, H=10.29%, N=0.06% 
     Theoretical values: C=76.32%, H=10.07%, N=0% 
     The specific rotation [α] 25  of this compound was ±76.8° (in chloroform, C=1.1), and the results of the  1  H-NMR analysis were as follows. 
       1  H-NMR, δ ppm: 4.36 (2H), 3.21 (1H), 1.31 (14H), 0.89 (3H). 
     (2S,5R)-2-Hydroxy-5-methyl-δ-valerolactone was synthesized in the same manner as described above except that β-hydroxybutanoic acid synthesized in Referential Example 2 was used instead of (R)-β-hydroxynonanoic acid. 
     REFERENTIAL EXAMPLE 5 
     Synthesis of 3-chloro-4-octyloxybenzoic acid of the following formula: ##STR21## 
     In 40 ml of ethanol were dissolved 10 g of 3-chlorohydroxybenzoic acid and 8 g of octyl bromide, and 40 ml a 2N aqueous solution of potassium hydroxide was added to the solution and the mixture was refluxed for 6 hours. The solution was made acidic and the precipitated crystal was recovered and recrystallized from an ethanol/water mixed solvent to obtain 9.5 g of 3-chloro-4-octyloxybenzoic acid. 
     Other 3-substituted-4-alkoxybenzoic acids were similarly synthesized. 
     REFERENTIAL EXAMPLE 6 
     Synthesis of monodecyl terephthalate 
     In 10 ml of dry benzene was dissolved 1.71 g of terephthaloyl dichloride, and 2.5 g of benzyl alcohol and 5 ml of triethylamine were added to the solution and reaction was carried out at room temperature with stirring overnight. 
     The reacted solution was poured into dilute hydrochloric acid cooled with ice, and the reaction product was extracted with ethyl acetate. The extract was washed with water and dried on magnesium sulfate. Then, ethyl acetate was evaporated and removed from the solution, and the residue was recrystallized from ethanol to obtain 3.2 g of benzyl terephthalate. 
     In 20 ml of acetone was dissolved 1.7 g of the obtained benzyl terephthalate, and a solution of sodium hydroxide in an amount equimolar to the above ester in a 1/1 water/ethanol mixed liquid was added to the above solution and the mixture was stirred overnight. Acetone was evaporated and removed from the solution, and dilute hydrochloric acid was added to the residue, and the liquid was extracted with ethyl acetate. The extract was washed with water and dried on magnesium sulfate, and ethyl acetate was evaporated and the residue was recovered and recrystallized from an acetone/water mixed solution to obtain 1.0 g of monobenzyl terephthalate. Then, thionyl chloride was added to 0.5 g of the obtained monobenzyl terephthalate to form an acid chloride. Then, unreacted thionyl chloride was removed by distillation under a reduced pressure. Then, 5 ml of pyridine and 0.31 g of decyl alcohol were added to the residue, and the mixture was stirred at room temperature to effect reaction. The reacted solution was poured into dilute hydrochloric acid cooled with ice, and the precipitate was recovered by filtration, dried and purified by the silica gel column chromatography to obtain 0.68 g of benzyldecyl terephthalate. The obtained compound was dissolved in an ethyl acetate/ethanol mixed solvent, 0.06 g of platinum black was added to the solution, and catalytic reduction was carried out under a hydrogen pressure of 1.8 kg/cm 2 . The catalyst was removed by filtration and the solvent was removed from the reacted solution by distillation to obtain 0.48 g of monodecyl terephthalate. 
     REFERENTIAL EXAMPLE 7 
     Synthesis of 4-undecylcarboxybenzoic acid of the following formula: ##STR22## 
     From 2.3 g of benzyl 4-hydroxybenzoate and 2.5 g of lauroyl chloride, 3.5 g of benzyl 4-undecylcarboxybenzoate was obtained according to customary procedures. The obtained compound was subjected to catalytic reduction under a hydrogen pressure of 2 kg/cm 2  by using platinum black as the catalyst to obtain 2.8 g of 4-undecylcarboxybenzoic acid. 
     EXAMPLE 1 
     In dehydrated benzene were dispersed 200 mg of (2S,5R)-hydroxy-5-hexyl-δ-valerolactone synthesized in the same manner as described in Referential Example 4, 250 mg of p-octyloxybenzoic acid and 200 μl of azodicarboxylic acid, and 270 mg of triphenylphosphine was added to the dispersion and reaction was carried out with stirring overnight. The reacted solution was concentrated, and the concentrate was separated and purified by the silica gel column chromatography using n-hexane/benzene as the developing solvent. The obtained product was recrystallized from methanol to obtain 180 mg of (2S,5R)-2-(4-octyloxybenzoyloxy)-5-hexyl-δ-valerolactone. The NMR spectrum of the obtained compound is shown in FIG. 1. The results of the measurement of the phase transition behavior by a differential thermal scanning calorimeter and a polarization microscope are shown below: ##STR23## 
     Cryst. means the crystal, and Iso represents the isotropic phase. The numerical figure given in the vicinity of the arrow is the temperature (°C.) of the transition to the corresponding phase. 
     EXAMPLES 2 THROUGH 9 
     Compounds were prepared in the same manner as described in example 1 except that a predetermined amount of a compound shown in Table 1 was used instead of 250 mg of p-octyloxybenzoic acid, and 100 mg of (2S,5R)-2-hydroxy-5-hexyl-δ-valerolactone was used, and the phase transition temperatures were examined. The results are shown in Table 1. 
     
         TABLE 1 Phase transition Example No. Charged composition  Obtained substance  temperature (°C.)   2  ##STR24##  100 mg  ##STR25##  ##STR26## 80 mg  ##STR27##  120 mg  3 ##STR28##  100 mg  ##STR29##  ##STR30## 90 mg  ##STR31##  150 mg  4 ##STR32##  100 mg  ##STR33##  ##STR34##100 mg  ##STR35##  140 mg  5 ##STR36##  100 mg  ##STR37##  ##STR38## 60 mg  ##STR39##  140 mg  6 ##STR40##  100 mg  ##STR41##  ##STR42##130 mg  ##STR43##  150 mg  7 ##STR44##  100 mg  ##STR45##  ##STR46##120 mg  ##STR47##  160 mg  8 ##STR48##  100 mg  ##STR49##  ##STR50##100 mg  ##STR51##  120 mg  9 ##STR52##  100 mg  ##STR53##  ##STR54##140 mg  ##STR55##  120 mg 
    
     EXAMPLE 10 THROUGH 21 
     A liquid crystal composition A was formed by mixing the following components at mixing ratios shown below: 
     
         ______________________________________ ##STR56##                 4 mol % ##STR57##                 4 mol % ##STR58##                 4 mol % ##STR59##                 24 mol % ##STR60##                 24 mol % ##STR61##                 20 mol % ##STR62##                 20 mol %______________________________________ 
    
     This composition A showed the following phase transition, but since the composition A was comprised only of optically unactive compounds, the composition was not a ferroelectric liquid crystal and did not show a spontaneous polarization: ##STR63## 
     Note, SmC represents the smectic C phase, SmA represents the smectic A phase, and N represents the nematic phase. 
     This composition was mixed with a compound shown in Table 2 at a mixing ration shown in Table 2. 
     Some of the obtained compositions were independently cast in cells having a thickness of 2 μm, which were provided with transparent electrodes coated with a polyimide as the orientation treating agent, and subjected to a parallel orientation treatment by rubbing the surface. 
     Each element was arranged between two polarizers orthogonal to each other, and an electric field was applied. By application of a voltage of ±20 V, a change of the intensity of the transmitted light was observed. The response time was determined from this change, and the tilt angle was measured. The results are shown in Table 2. 
     As apparent from the results obtained in Examples 10 through 21, even if the substance of the present invention does not show a ferroelectric characteristic, when the substance is mixed with a compound showing the SmC phase, a ferroelectric composition having a good response characteristic is obtained. 
     
         TABLE 2  Compound incorporated in composition A Mixing ratio of  Response Example  Mixing ratio composition A  time Tilt angle No. Structural formula (mol %) (mol %) Phase transition temperature (μsec) (deg)     10  ##STR64##  5 95 ##STR65##  1000   9  11 ##STR66##  20 80  ##STR67##  380 15  12 ##STR68##  5 95 ##STR69##  490 22  13 ##STR70##  20 80  ##STR71##  240 19  14 ##STR72##  40 60  ##STR73##  190 26  15 ##STR74##  5 95 ##STR75##  240 20  16 ##STR76##  20 80  ##STR77##  17 ##STR78##  40 60  ##STR79##  18 ##STR80##  5 95 ##STR81##   small  19 ##STR82##  20 80  ##STR83##  3000   6  20 ##STR84##  40 60  ##STR85##  21 ##STR86##  5 95 ##STR87##  300 24 
    
     EXAMPLE 22 
     In 1 ml of dehydrated benzene were suspended 100 mg of (2S,5R)-2-hydroxy-5-hexyl-δ-valerolactone synthesized in the same manner as described in Referential Example 2 and 120 mg of 4-octyloxy-3-cyanobenzoic acid, and 0.1 ml of diethyl azodicarboxylate was added to the suspension with stirring at room temperature. Then, 150 mg of triphenylphosphine was added to the mixture and reaction was carried out overnight with stirring. The reaction mixture was concentrated under a reduced pressure and the residue was separated and purified by the silica gel column chromatography using an n-hexane/benzene (1/4) mixed solvent as the developing solvent. Recrystallization from ethanol gave 90 mg of (2R,5R)-(4&#39;-octyloxy-3&#39;-cyanobenzoyloxy)-5-hexyl-δ-valerolactone. When the phase transition behavior of the obtained compound was measured by a differential thermal scanning calorimeter and a polarization microscope, the following results were obtained: ##STR88## 
     Note, Cryst. indicates a crystal and Iso indicates an isotropic phase, and the numerical figure given in the vicinity of the arrow shows the transition temperature (°C.) to the corresponding phase. 
     EXAMPLE 23 
     A crude product was obtained in the same manner as described in Example 22 except that (2S,5R)-2-hydroxy-5-hexyl-δ-valerolactone was used in an amount of 125 mg and 125 mg of p-hydroxybenzoic acid was used instead of 120 mg of 4-octyloxy-3-cyanobenzoic acid. The crude product was purified by the silica gel column chromatography to obtain 20 mg of (2R,5R)-2-(4&#39;-pentyloxycarbonylphenoxy)-5-hexyl-δ-valerolactone. 
     EXAMPLE 24 
     The procedures of Example 23 were repeated in the same manner except that 180 mg of 4-(4&#39;-pentylcyclohexyl)phenol and 100 mg of (2S,5R)-2-hydroxy-5-hexyl-δ-valerolactone were used, whereby 50 mg of (2R,5R)-2-[4-(4&#39;-pentylcyclohexyl)-phenoxy]-5-hexyl-δ-valerolactone was obtained. 
     EXAMPLE 25 
     In 1.5 ml of dry dimethylformamide were dissolved 180 mg of octyl p-bromomethylbenzoate and 100 mg of (2S,5R)-2-hydroxy-5-hexyl-δ-valerolactone, and 300 mg of silver oxide was added to the solution and the mixture was stirred overnight at room temperature to effect reaction. After the reaction, diethyl ether was added to the reacted solution to extract the reaction product. The extract was washed with a saturated aqueous solution of sodium chloride and dried on anhydrous magnesium sulfate. Diethyl ether was removed by distillation under a reduced pressure. The obtained crude product was purified by the silica gel column chromatography to obtain 5 mg of (2S,5S)-2-(4&#39;-octyloxycarbonylbenzyloxy)-5-hexyl-δ-valerolactone. 
     EXAMPLE 26 THROUGH 29 
     A liquid crystal composition B was obtained by mixing the following compounds at weight ratios shown below. 
     
         ______________________________________ ##STR89##               18% by mole ##STR90##               28% by mole ##STR91##               20% by mole ##STR92##               14% by mole ##STR93##               10% by mole ##STR94##               10% by mole______________________________________ 
    
     The composition B showed the following transition but since the composition was not optically active, the composition did not show a spontaneous polarization: ##STR95## 
     Ferroelectric liquid crystal compositions were obtained by adding the compounds obtained in Examples 22 through 25 in amounts shown in Table 3 to the composition B. The phase transition temperatures, response times and tilt angles of these compositions are shown in Table 3. 
     
                                           TABLE 3__________________________________________________________________________Compound incorporated in composition B  Mixing ratio ofExample                          Mixing ratio                                   composition BNo.  Structural formula          (mol %)                                   (mol %)__________________________________________________________________________26 ##STR96##                  2      9827 ##STR97##                  2      9828 ##STR98##                  2      9829 ##STR99##                  2      98__________________________________________________________________________                             Response timeExample                           (0 to 50%)                                     Tilt angleNo.     Phase transition temperature (°C.)                             (μsec)                                     (deg)__________________________________________________________________________26    ##STR100##               224     1527    ##STR101##               176     2128    ##STR102##               252       17.529    ##STR103##               250     18__________________________________________________________________________ 
    
     As apparent from the foregoing description, the optically active substance of the present invention is chemically stable, is not colored and has an excellent light stability, and therefore, the substance of the present invention is valuable as a component of a ferroelectric liquid crystal showing a large spontaneous polarization. Moreover, the liquid crystal composition of the present invention shows a ferroelectric characteristic in a broad temperature range including a practical temperature range, and as apparent from a high response speed thereof, the spontaneous polarization of the composition is large.