Liquid crystal compounds having fluoroalkyl radical

Abstract: The invention lies in novel ferroelectric liquid crystal compounts particularly represented by the general formulae, having a good responsibility in relation to the applied electric field and a wide range of phase transition points inclusive of the room temperature so as to be useful alone as the liquid crystal material but also to be mixed with other liquid crystal compounds for expanding the phase transition points to a desired range and making the response speed of the liquid crystal composition faster. In the formulae, m and n are same or different with each other and represent an integral of 1 - 20.

Description: The invention relates to novel liquid crystal compounds, and more particularly to novel smectic and ferroelectric liquid crystal compounds having a fluoroalkyl group. The ferroelectric liquid crystal compounds are characterized by the molecular structure comprising at least one asymmetric carbon atom in the molecule, having a large dipole moment in the direction vertical to the molecular apsis line and showing a smectic phase in which the molecular apsis line is tilted to the phase normal by a some degree. Such are generally optically active compounds having an optically active radical at the side chain. Recently it has been made clear that the molecular structure of the optically active radical as well as the interaction between the asymmetrical carbon part and the dipole moment carrying part may considerably affect on the liquid crystallization e.g. by J.W. Gooddy, E. Chin et al., J. Am Chem. Soc. 108 4729-4735 (1986), ibid. 108 4736-4742 (1986). It has been tried, thus, to derive a liquid crystal compound from an optically active compound. The optically active compounds used until now for that purpose are for instance derivatives of lactic acid, butyric acid, amino acid and an optically active 2-alkanol such as 2-octanol and amyl alcohol. Perfluoro compounds having an optically active perfluoroalkyl radical, substituted with a perfluoroalkyl, perfluoroalkoxy or perfluoroalkenyloxy group are chemically, thermally or optically stable so as to be useful compounds for that purpose. Despite of that these compounds have not yet been used for the asymmetric carbon part of the liquid crystal compounds, possibly due to the fact that synthesis thereof has been thought to be difficult. SUMMARY OF THE INVENTION It is an object of the invention, thus, to provide novel ferroelectric liquid crystal compounds having an optically active fluoroalkyl radical. According to the present invention there are provided liquid crystal compounds having fluoroalkyl radical represented by the formula (I) wherein R means an alkoxy group having 1-20 carbon atoms; R' means a normal or branched perfluoroalkyl group having 1-20 carbon atoms; (A) represents or (B) represents and X means or -CH₂O-. DESCRIPTION OF THE DRAWINGS Fig. 1 shows infrared absorption spectrum of 4-[1,1,1,2-tetrafluoro-2-(perfluoro-n-propoxy) propionyloxyphenyl-4-n-octyloxybenzoate, one of the objective compounds according the invention, Fig. 2 shows infrared absorption spectrum of 4-[1,1,1,2-tetrafluoro-2-(perfluoro-n-propoxy) propionyloxy]phenyl-4-n-nonyloxybenzoate according to the invention, and Fig. 3 shows infrared absorption spectrum of 4-[1,1,1,2-tetrafluoro-2-(perfluoro-isopropoxy) propionyloxy]phenyl-4-n-nonyloxybenzoate according to the invention. DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Among the novel liquid crystal compounds according to the invention those having the following optically active radicals connected to the skeleton R-(A)-X-(B) are particularly useful as ferroelectric liquid crystals. 1) Perfluoro-2-propoxy-propionyloxy radical (II) 2) Perfluoro-2-isopropoxy-propionyloxy radical (III) 3) Perfluoro-2-alkoxy-fatty acid radical (IV) In the formula, Rf1, Rf2, and Rf3 may be same or different to one another and means a perfluoroalkyl or perfluoroalkenyl group of 6 carbon atoms or less. In the liquid crystal compounds of the formula (I), R more preferably means hexyloxy, octyloxy and isobutoxy. In the compounds of the formula (I), particularly suitable -(A)-X-(B) are; In the optically active radical (IV) Rf1, Rf2 and Rf3 more preferably means a perfluoroalkyl such as perfluoromethyl, perfluoroethyl, perfluoropropyl, perfluoroisopropyl, perfluorobutyl and perfluoroisobutyl, or a perfluoroalkenyl corresponding to any of the above having carbon-carbon double bonds. In the-novel compounds (I), the radical are preferably derived from optically active perfluorofatty acids as follows:- Perfluoro-2-methoxypropionic acid, Perfluoro-2-ethoxypropionic acid, Perfluoro-2-propoxypropionic acid, Perfluoro-2-isopropoxypropionic acid, Perfluoro-2-butyloxypropionic acid, Perfluoro-2-isobutyloxypropionic acid, Perfluoro-2-pentyloxypropionic acid, and Perfluoro-2-hexyloxypropionic acid. The perfluorocarboxylic acids exemplified above are synthesized by the per se known processes e.g. disclosed in J. Fluorine Chemistry 20 475-485 (1981) and Chemistry Letters 745-748 (1982). The liquid crystal compounds (I) of the invention may be synthesized for instance as follows; Benzylbromide and hydroquinone are reacted to obtain 4-benzyloxyphenol (i), which is reacted with optically active perfluoro-2-(perfluoroalkoxy) propionic chloride in pyridine as a solvent to obtain 4-benzyloxyphenyl-perfluoro-2-(Perfluoroalkoxy) propionate (ii), which is then subjected to the hydrogenation in the presence of a palladium/carbon catalyst to obtain 4-hydroxyphenyl-perfluoro-2-(perfluoropropoxy) propionate (iii), which is reacted to 4-alkyloxybenzoic acid chloride in pyridine as a solvent to obtain an objective optically active compound, 4-[perfluoro-2-(perfluoropropoxy)propionyloxy]phenyl 4'-alkyloxybenzoate. The above synthesis is shown by reaction formulae; In the formulae, m and n may be same or different with each other and represent an integer of 1 - 20. The other objective compound is manufactured as follows; The compound (iii) as referred to above is treated with a base such as potassium hydroxide and sodium hydroxide or an alkali metal hydride such as sodium hydride in a solvent such as dimethyl ether, tetrahydrofuran, dimethylformamide and dimethyl sulfoxide to form a corresponding phenoxide, which is reacted with 4-alkoxy-4'-monobromo-methylbiphenyl to obtain an objective optically active compound, 4-(4'-alkyloxy-4''-biphenylcarbinyloxy)phenyl perfluoro-2-alkoxy-propionate. In the reaction formulae, m and n respectively represent the above. The invention will be explained in more detail in reference to the following Examples. It is noted that the invention is of course not limited thereto. Example 1 (1) (+)-4-Benzyloxyphenyl-1,1,1,2-tetrafluoro-2-(perfluoro-n-propoxy)propionate In 40 ml of pyridine, 3.6g of 4-benzyloxyphenol was dissolved to prepare a solution, to which under ice-cooling 7g of optically active 1,1,1,2-tetrafluoro-2-(perfluoro-n-propoxy) propionic chloride (as a precursor perfluoro-2-propoxypropionic acid, [α] 20 / D =+28° was used) was droppingly added. The liquid mixture was held at the room temperature for reaction for a whole day and night, then taken in ice-water and extracted with ether. The organic phase was washed successively with water, diluted hydrochloric acid and water, dried over anhydrous magnesium sulfate, distilled for removing the solvent and treated with the silica gel chromatography (n-hexane/ethyl acetate, volume ratio of 10:1) to obtain the compound captioned above in the amount of 3.5 g. (2) (+)-4-Hydroxyphenyl-1,1,1,2-tetrafluoro-2-(perfluoro-n-propoxy)propionate The compound obtained in the above (1) in the amount of 3.5 g and 0.4 g of 10% palladium/carbon were added in methanol as a solvent to be reacted in an atmosphere of hydrogen at the room temperature for 5 - 6 hours to obtain the above compound in the amount of 2.9 g. (3) (+)-4-[1,1,1,2-tetrafluoro-2-(perfluoro-n-propoxy)propionyloxy]phenyl-4′-n-octyloxybenzoate (Objective Compound) 4-n-Octyloxybenzoic acid in the amount of 2.0 g was reacted with 1 g of thionyl chloride in 10 ml of benzene at a tempreature of 100 - 110°C for 6 hours to obtain 4-n-octyloxybenzoic acid chloride in the amount of 2.2 g. This 2.2 g of 4-n-octyloxybenzoic acid chloride and 2.9 g of the compound obtained in the above (2) were dissolved in 50 ml of pyridine to be held at the room temperature for reaction for a whole day and night. The reaction liquid was taken in ice-water and extracted with ether. The organic phase was washed successively with water, diluted hydrochloric acid and water to be neutral and then dried over anhydrous magnesium sulfate. The dried product was treated with silica gel chromatography (n-hexane/ethyl acetate, volume ratio of 10:1) to obtain the optically active objective compound as captioned above in the amount of 1.6 g. The objective liquid crystal compound of the invention showed a smectic phase and the phase transition points thereof according to observation by means of a polarizing microscope with hot stage and DSC are as follows; The infrared absorption spectrum (KBr) of this compound is shown in Fig. 1 of the accompanying drawing. Example 2 (-)-4-[1,1,1,2-tetrafluoro-2-(perfluoro-n-propoxy)propionyloxy]phenyl-4-n-nonyloxybenzoate Treatments described in Example 1 were repeated except that instead of 4-n-octyloxybenzoic acid chloride in Example (3) 4-n-nonyloxybenzoic acid chloride was used to obtain the objective compound as captioned above. The phase transition points of this liquid crystal compound is as follows; The infrared absorption spectrum (KBr) of this compound is shown in Fig. 2. Example 3 (+)-4-[1,1,1,2-tetrafluoro-2-(perfluoro-isopropoxy)propionyloxy]phenyl-4-n-nonyloxybenzoate The treatments in Example 1 were repeated except that instead of optically active 1,1,1,2-tetrafluoro-2-(perfluoro-n-propoxy)propionic acid in Example (1), (+)-1,1,1,2-tetrafluoro-2-(perfluoro-isopropoxy)propionic acid ([α] 20 / D = +31°) was used and instead of 4-n-octyloxybenzoic acid chloride in Example 1 (3), 4-n-nonyloxybenzoic acid chloride was used to obtain the above optically active objective compound. The phase transition points thereof are as follows; The infrared absoption spectrum (KBr) is shown in Fig. 3. The objective compounds (I) of the invention have a good responsibility in relation to the applied electric field as the ferroelectric liquid crystal so as to be used as non-linear display elements and liquid crystal optical shutters. Furthermore, the ferroelectric liquid crystal compounds (I) of the invention have a wide range of phase transition points inclusive of the room temperature so as not only to be used alone as the liquid crystal material but also to be mixed with other liquid crystal compounds for expanding the phase transition points to a desired range and making the response speed of the liquid crystal composition faster.

Claims: Liquid crystal compounds having fluoroalkyl radical represented by the formula (I) wherein R means an alkoxy group having 1-20 carbon atoms; R' means a normal or branched perfluoroalkyl group having 1-20 carbon atoms; (A) represents or (B) represents and X means or -CH₂O-. Liquid crystal compounds as set forth in Claim 1, wherein R' means normal- or iso-C₃F₇; (A) represents and X means A liquid crystal compound as set forth in Claim 1, which is (+)-4-[perfluoro-2-(perfluoropropoxy) propionyloxy]phenyl 4'-n-octyloxybenzoate. A liquid crystal compound as set forth in Claim which is 4-(4'-alxyloxy-4''-biphenylyl-carbonyloxy) phenyl perfluoro-2-alkoxy-propionate. A liquid crystal compound as set forth in Claim 1, which is (+)-4-[1,1,1,2-tetrafluoro-2-(perfluoro-n-propoxy) propionyloxy]phenyl 4'-n-octyloxybenzoate; A liquid crystal compound as set forth in Claim 1, which is (-)-4-[1,1,1,2-tetrafluoro-2-(perfluouro-n-propoxy)propionyloxy]phenyl 4-n-nonyloxybenzoate; A liquid crystal compound as set forth in Claim 1, which is (+)-4-[1,1,1,2-tetrafluoro-2-(perfluoroisopropoxy)propionyloxy]phenyl 4-n-nonyloxybenzoate;

Inventors: HAGIWARA TAKASHI C O SHOWA SHE, MOGAMIYA HIROYUKI C O SHOWA SH, SUZUKI YOSHIICHI C O SHOWA SHE, HAGIWARA, TAKASHI C/O SHOWA SHELL SEKIYU K.K., MOGAMIYA, HIROYUKI C/O SHOWA SHELL SEKIYU K.K., SUZUKI, YOSHIICHI C/O SHOWA SHELL SEKIYU K.K.
Applicants: SHOWA SHELL SEKIYU, SHOWA SHELL SEKIYU KABUSHIKI KAISHA
Application year: 1989
Main classification: C09K19
IPC codes: C09K19