Liquidcrystalline cyclohexylbenzene derivatives their manufacturing and novel nematic admixtures containing same

Abstract: New compounds of the general formula I: wherein R¹ is a normal or branched alkyl chain H 2n+1 C n - or a normal or branched alkoxy group H 2n+1 C n O-, n being an integer number from 1 to 12; X is a bridging group from the set: -COO-, -OCO-, -CH₂O-, -OCH₂-, -COCH₂-, -CHOHCH₂-, -CH=CH-,-CH₂CH₂-, -CHClCH₂-, -CHCNCH₂-, -CHBrCH₂-, -CHFCH₂-, -CHOCH₃CH₂-; Y is a terminal group from the set: -NO₂, -NH₂, -NCS, -Cl, -Br, -F; the cyclohexane rings are trans-1,4-disubstituted ones and the benzene rings are 1,4-disubstituted ones, and besides one of them may contain sometimes additionally a fluorine atom in position 2 or 3, k and l are integer numbers from the set: 0, 1, 2 fulfilling the condition that k+1=2 or 3; besides, if X denotes the -COO- or -OCO- group, then k+1 also may assume the value of 1 , their manufacture and liquid crystalline admixture containing them and use for electro-optical devices as dielectrics are described.

Description: Field of the invention The present invention concerns naval cyclohexylbenzene derivatives and liquid crystals admixtures containing same applicable in electro-optical devices as dielectrics. The invention also concerns methods of manufacturing these liquid crystal coumpounds Description of the prior art Liquid crystals have gained in the recent years great importance as dielectrics in electro-optical displays thanks to that their optical properties may be easily influenced by an electric field. Many types of such devices are widely known and they can be based on various electro-optical effects such as for instance,dynamic scattering, twisted nematic effect, cholesteric-nematic phase transition. Liquid crystal displays are ever more widely used not only at practically constant indoor temperatures, but also at temperatures varying in a wide range. The latter application concern main outdoor use in such devices as parkometers, gasoline pump stations, car dashboards, portable measuring instruments etc. The quoted devices require liquid crystal admixtures of parameters higher as compared with these operating indoors at practically constant temperatures. These mixtures should reveal the nematic phase in the temperature range of -20 to +80°C or even wider, low viscosity also in the lower temperature region (since viscosity limit the switching on and off times). Under outdoor conditions the intensity of UV radiation and humidity also vary in a wide range, so the material used should be resistant to light and water. No such single liquid crystal compound exists that would. fulfil all the requirements laid before the liquid crystalline material, especially when the later is used outdoors. Attempts are therefore made to optimize the properties of such materials for given application by mixing many components. According to the present state of art a material with the required properties can be obtained by blending several or even a dozen or so different compounds. To the liquid crystal mixtures whose components reveal nematic or sometimes smectic properties also non-liquidcrystalline and or optically active compunds and dichroic dyes may be added. It is important, however, that these components enter no chemical reactions with each other and that they mutually readily dissolve. The mixture should also reveal a low solid-to-nematic transition point (T Cr→N ), high nematic-to-isotropic liquid transition point (T N→I ), and low viscosity. An admixture of suitably selected compounds meets better the requirements to be fulfilled by the liquid crystal material for a given application. To obtain liquid crystal admixtures with a wide range of the nematic phase, the components are chosen so that a base admixture of mesogenes with possibly low melting points and low melting enthalpies is prepared.To such admixtures 5 to 40% of tri-or tetranuclear compounds with high clearing points are added. For obtaining base mixtures with low viscosity most suitable are binuclear compounds - derivatives of cyclohexylbenzene - such as described in U.S. Patent 4.528.116 4-(trans-4-alkylcyclohexyl)-1-isothiocyanatobenzenes or in G.F.R. Patent 2.638.864 4-(trans-4-n-alkylcyclohexyl)-1-cyanobenzenes. A liquid crystal admixture composed of 4-(trans-4-n-alkyl cyclohexyl)-1-isothiocyanatobenzenes only has a viscosity of about 10 mPa s and clearing point below 45°C, besides, it reveals a low value of the elastic constant ratio k₃₃/k₁₁ close to unity.A liquid crystal mixture composed of 4-(trans-4-n-alkylcyclohexyl)-1-cyanobenzenes reveals viscosity of about 20 mPa s, clearing point of about 55°C, and high elastic constant ratio k₃₃/k₁₁ of about 2. The mixtures obtained of 4-(trans-4-n-alkylcyclohexyl)-1-cyanobenzenes or 4-(trans-4-n-alkylcyclohexyl)-1-isothiocyanatobenzenes only still have clearing points too low for their practical application. Cyano derivatives of terphenyl, cyclohexylbiphenyl or diphenylpyrimidine, or else esters of cyclohexylbenzoic or biphenyl acids are so far the most frequently used compounds for raising the clearing points. The above mentioned trinuclear compounds raise the clearing points of mixtures but at the same time also raise significantly their viscosities. For instance the mixture described in the USSR Patent 738.516 of the composition in wt %. 4-(trans-4-n-propylcyclohexyl)-1-cyanobenzene 36.1 4-(trans-4-n-pentylcyclohexyl)-1-cyanobenzene 30.8 4-(trans-4-n-heptylcyclohexyl)-1-cyanobenzene 21.1 2-(4-cyanophenyl)-5-(4-pentylphenyl)-pyrimidine 12.0 reveals a clearing point of 81°C, and viscosity of 35 mPa s. Besides, the trinuclear compounds often show low solubility in mixtures of binuclear liquid crystal compounds mostly due to the fairly high melting enthalpies and fairly high melting points. For this reason it happens quite often that these compounds precipitate as solid from liquid crystal admixtures after a certain time of storage of the latter at low temperatures. This is particularly often observed in case of admixtures of low viscosity containing trinuclear compounds in quantities exceeding the eutectic composition. Summary of the invention The present invention relates to the use of a new class of multi ring compounds of high chemical stability and excellent solubility which have the ability to extend the nematic range of the base mixture composed of binuclear compounds without significant increase of viscosity. The liquid crystal admixtures containing these new compounds reveal a small temperature dependence of viscosity and threshold voltage. Thanks to this, the performance of the liquid crystal display is improved and its control is simplified. In "Chemical Abstracts, Vol. 103, No. 17, 28th October 1985, page 691, abstract No. 141633r", trans-4'-(4'-substituted phenyl)cyclohexyl 4-substituted benzoates of the formula are described, wherein R, X = n-C₅H₁₁, Cl; Me, Cl; n-C₈H₁₇, Cl; MeO, Cl; n-C₆H₁₃O, Cl; cyano, Cl; n-C₅H₁₁, F, which were prepared and used as liquid crystals having a clearing point from high nematic phase to isotropic liquid phase. Thus, reaction of PhCl, AlCl₃, MeCOCl, and cyclohexene 3 h at max. -20° gave 12% trans-4-(p-chlorophenyl)-1-acetylcyclohexane (II). Oxidation of II with 4-ClC₆H₄C(O)OOH in CHCl₃ overnight gave 68% trans-4-(p-chlorophenyl)-1-acetyloxycyclohexane (III). Reduction of III with LiAlH₄ in Et₂O 2 h at 0° to room temperature gave 77% trans-4-(p-chlorophenyl)cyclohexanol (IV). Esterification of 4-n-C₅H₁₁C₆H₄COCl with IV in Et₂O containing pyridine 1 h at room temperature gave 69% I (R = n-C₅H₁₁, X = Cl). In "Chemical Abstracts, Vol. 101, No. 9, 27th August 1984, page 617, abstract No. 72557c" 4-substituted phenyl trans-4-(4-halophenyl)cyclohexanecarboxylates of the formula are described, wherein R = halo; R¹ = p-R²C₆H₄O where R² Cl, alkyl, alkoxy, cyano, useful as liquid crystals, which were prepared by esterification of acid chlorides I (R¹ = Cl) with p-R²C₆H⁴OH. Thus addition of 473 g AcCl and 555 g cyclohexene to a mixture of 1600 g PhCl and 1080 g AcCl₃ at -20° over 3 h followed by warming the resulting mixture to room temperature gave 12% I (R = Cl, R¹ = Me), treatment of which (165 g) in dioxane with aq. NaOBr (prepared from 385 g Br, 264 g NaOH, and H₂O) at room temperature for 2 h gave 160 g I (R = Cl, R¹ = OH), the acid chloride (prepared from 160 g of the acid and SO₂Cl) in Et₂O containing pyridine was tretaed with 1.64 g p-Me(CH₂)₄C₆H₄OH at room temperature for 1 h to give 77% I, wherein R = Cl, R¹ = Me(CH₂)₄. EP 0 144 648 refers to compunds of the formula wherein n stands for 1 and X for the group -COO-, -OOC- or -CH₂CH₂-, or n stands for 0 and X for the group -CH₂CH₂-; ring A denotes p-phenylene or trans-1,4-cyclohexylene; R² represents cyano, p-cyanophenyl or, when X stands for -COO- or -OOC-, also p-R³-phenyl or trans-4-R³-cyclohexyl; and R¹ and R³ are straight-chain C₁-C₁₀ alkyl, their preparation and use for electrooptical purposes and in gaschromatography. Detailed description of the invention The present invention concerns liquid crystalline compounds of the general formula I: and mixtures containing them. In formula I wherein R¹ is a normal or branched alkyl group H 2n+1 C n - or a normal or branched alkoxy group H 2n+1 C n O-, n being an integer number from 1 to 12; X is a bridging group from the set: -COO-, -OCO-, -CHOHCH₂-, -CH₂CH₂-, -CHOCH₃CH₂-; Y is a terminal group from the set: -NO₂, -NH₂, -NCS, the cyclohexane rings are trans-1,4-disubstituted ones and the benzene rings are 1,4-disubstituted ones, and besides one of them may contain sometimes additionally a fluorine atom in position 2 or 3; k and l are integer numbers from the set: 0, 1, 2 fulfilling the condition that k+l=2 or 3 ; besides, if X denotes the -COO- or group -OCO- then k+l also may assume the value of 1 ( k=1 and l=0 or k=0 l=1 ). By normal or branched alkyl groups C n H 2n+1 - we understand alkyl chains including 1 to 12 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, 2-methylbutyl, pentyl, 3-methylpentyl, 4-methylhexyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl ones. By unbranched or branched alkoxy group C n H 2n+1 O- we understand an alkyloxy chain in which alkyl portion has the above given meaning. For comparison the compounds of formula 1, wherein Y is a fluorine, chlorine or bromine atoms are described. To allow a better description of the compounds that can be derived from the general formula I, or are their intermediates and especially to make possible a short notation of the particularly preferred structures of compound I in a simplified form Arabic numbers and lower case as well as capital letters in addition to Roman numbers have been used additionally. Lower case letters are used to denote the meaning k and m in the formule of compounds with: a k=1 and l=0 e k=2 and l=0 , b k=o and l=1 f k=1 and l=2, c k=1 and l=1 g k=2 and l=1, d k=0 and l=2 Arabic numbers are assigned to the central groups as follows: 1 -COCH₂ 8 -CHF-CH₂- 2 -CHOHCH₂ 9 -CHOCH₃CH₂ 3 -CH=CH- 10 -CH₂O- 4 -CH₂CH₂-, 11 -OCH₂- 5 -CHClCH₂- 12 -COO- 6 -CHCN-CH₂-, 13 -OCO- 7 -CHBr-CH₂-, Capital letters are assigned to the terminal groups as follows: A -NO₂ D -F B -NH₂ E -Cl C -NCS F -Br According to the adopted notation the compound denoted as I.c4C has the following structural formula: If in the abbreviated notation any of the above given additional symbols is missing, this means that the relevant elements has the same meaning as in the general formula I. According to the abbreviated notation the length of an alkyl chain is defined by adding C n H 2n+1 as an prefix. The abbreviated notation will be then in the form C n H 2n+1 -I or C n H 2n+1 O-I e.g. C₃H₇-I. From the general formula I we can show groups of compounds with the preferred properties for the following values of the indicators k and l. For k=1 and l=0 the compunds are of the general formula Ia: wherein R¹ is a normal or branched alkyl chain with n varying from 1 to 12, preferably from 4 to 10, X is the bridging group -COO- or -OCO-; Y the terminal group -NCS or -NO₂ For k=0 and l=1 the compounds are of the general formula Ib: wherein R¹ is a normal or branched alkyl chain or a normal or branched alkoxy group C n H 2n+1 O- with n varying from 1 to 12, preferably from 4 to 10, X is the bridging group -COO- or -OCO-; Y is the terminal group -NO₂ or -NCS For k=1 and l=1 the compounds are of the general formula Ic: wherein R¹ is a normal or branched alkyl chain with n varying from 1 to 12, preferably from 4 to 10; X is the bridging group from the set: -CHOHCH₂-,-CH₂CH₂-, -CHOCH₃CH₂-; Y is the terminal group from the set: -NO₂, -NH₂, -NCS, preferably -NCS For k=0 and l=2 the compounds are of the general formula Id: wherein R¹ is a normal or branched alkyl chain with n varying from 1 to 12, preferably from 4 to 8; X is the bridging group from the set: -CHOHCH₂- , -CH₂CH₂-, -CHOCH₃CH₂; Y is the terminal group from the set: NO₂, -NCS, For k=2 and l=0 the compounds are of the general formula Ie: wherein R¹ is a normal alkyl chain with n varying from 1 to 12, preferably from 4 to 10, X is the bridging group from the set: -CHOHCH₂-, -CH₂CH₂-, -CHOCH₃CH₂-, preferably -CH₂CH₂- or, -CHOCH₃CH₂-; Y is a terminal group from the set: -NO₂, -NCS, -NH₂, preferably -NCS. For k=1 and l=2 the compounds are of the general formula If: wherein R¹ is a normal alkyl chain with n varying from 1 to 12, preferably from 6 to 10; X is a bridging group from the set: -CH₂CH₂-, Y is the terminal group -NCS. For k=2 and l=1 the compounds are of the general formula Ig: wherein R¹ is a normal or branched alkyl chain with n varying from 1 to 12; X is a bridging group from the set: -CH₂CH₂-, -CHOCH₃CH₂-, preferably -CH₂CH₂-; Y is the terminal group -NCS Manufacturing of compound I needs substrates which are not commercial attainabled and they should be previously prepared. The compounds of the general formula IIa are convinient substrates for synthesis of the compounds of our invention and also for synthesis of other compounds of a similar structure which are used for comparison. In IIa Z is a hydroxy group or halogen, preferably chlorine or bromine, r is zero or unity, and wherein the cyclohexane ring is a trans-1,4-disubstituted one, and the benzene ring is 1,4-disubstituted having sometimes additionally a fluorine atom in position 2 or 3. In schemes 1 and 2 some preferred methods of production of compounds II.A and use of them for obtaining other intermediates for preparation of liquid crystals are given. The crucial problem of the synthesis of compounds II.A shown in scheme 1 consists in the separation of the orto- and para-nitroesters of compound VII (in which R² is a fragment of the alcohol used for the esterification of acid V). They can he separated by crystallization. The initial trans-4-phenylcyclohexanecarboxylic (formula V, r=0) and trans-4-phenylcyclohexylacetic (formula V, r=1) acids are easily obtained from trans-4-acetylcyclohexylbenzene in the haloform and Willgerodt reaction, respectively. trans-4-Acetylcyclohexylbenzene is produced as described in Polish Patent 128609. The preferred method of producing new compounds of the general formula I is shown in scheme 3. The hydrocarbon of general formula III, wherein R¹ , k and l have the same meaning as in formula I, is acylated with the acid halide of the formula II.A where Z is a bromine atom or preferably a chlorine one, and the compound I.1A is obtained. The reaction of the hydrocarbon of formula III, which for example is trans-4-alkylcyclohexylbenzene or trans-4-n-alkylcyclohexylbiphenyl or trans-4-n-alkylbicyclohexlbenzene or 4-n-alkylbiphenyl or 4-n-alkoxybiphenyl or 4-(2-methylbutyl)biphenyl, and the acid halide of the formula II.A, which is 4-trans-(4-nitrophenyl)cyclohexylacetic chloride ( if 4-trans-(4-chlorophenyl)cyclohexylacetic chloride or 4-trans-(4-fluorophenyl)cyclohexylacetic chloride or 4-trans-(4-bromophenyl-)cyclohexylacetic chloride is used, then compounds analogous to compound I.1A are obtained) is conducted in an organic solvent, chosen from alkanes, chloroalkanes, nitroalkanes, in the presence of aluminum chloride, the temperature being kept in the range -20° to +10°C, preferably in the range -5° to +5°C. Among the enumerated solvents methylene chloride, ethylene chloride,chloroform or carbon tetrachloride are recommended in view of the convenience in carrying out further operations connected with the separation and purification of the product. The recommended procedure is as follows. Solid AlCl₃ is added to, e.g., methylene chloride and cooled to below 5°C upon which the solution of cycloalkaneacetic acid chloride of formula II.A in methylene chloride is added dropwise and next the compound of Formula III is added, also dropwise. The contents are stirred for several hours and poured onto a mixture of ice and hydrochloric acid in order to decompose the aluminum chloride complexes. Next generally known methods are applied to separate and purify the reaction product which is the keto compound of the general formula I.1A where the notation is the same as in formula I. The keto compound of formula I.1A is the basic substrate from which the remaining compounds of the general formula I differing as regards the bridging group X are obtained. Thus the keto compound of the formula I.1A is converted by reduction with sodium borohydride into the compound of the general Formula 1.2A, where the notation is the same as in the general Formula I. The use of sodium borohydride (NaBH₄) as reducing agent is justified by that it permits the reduction of the carbonyl group without affecting other substituents in the terminal position of the molecule liable to reduction; this relates especially to the nitro group. The compound of the general formula I.2A is after purification the final product or substrate for further reactions. If the compound of the general formula I.2A or I.2 is heated in the presence of an organic solvant preferably toluene, and an acid, preferably p-toluenesulfonic acid, than its dehydration takes place and it converts to the ethylene derivative of the general formula I.3A or I.3 (where the notation is the same as in the General formula I) which after purification is the final product or which is further converted by reduction with hydrogen in the presence of a palladium catalyst to the compound with the bridging group -CH₂CH₂- of formula I.4B. The terminal group -NO₂, reduces together with the double bond in the bridging group to yield compound I.4B, so in order to reproduce it, compound I.4B is oxidized with hydrogen peroxide in trifluoroacetic acid or is converted to the diazonium salt by the known method and next the diazonium group is substituted by the -NO₂ group in reaction with sodium nitrite in the presence of cuprous oxide and cuprous sulfate. It is advantageous to produce the compounds including ester group -COO- or -OCO- as the bridging groups X shown in schemes 4 and 5. The procedure consists in that the compound with alcohol or phenol properties of the general formula IV, where p is equal 1 or zero, and the remaining notation is the same as in the general formula I, is esterified with a compound being an acid or, acid chloride of the general formula II.3 or II.4, or else compound XV is esterified with an easily available acid or its chloride of the formula XIV; in the latter case it is advantageous to use pyridine as catalyst. The product thus obtained is next separated and purified according to the known methods, preferably by crystallization. The compound of general formula I with the terminal group -NO₂ and different central groups produced according to Scheme 3 can be easily converted to compounds with other kinds of terminal groups reserved for compound I. This is illustrated in Scheme 6. Such a way of proceeding is particularly recommended if we want to obtain compounds I.B or I.C, i.e. compounds with a -NH₂ or -NCS terminal groups. Via the compound with the nitro group one can easily obtain compounds with a -NH₂ or -NCS terminal group for any central group X by suitably selecting conditions of reduction of the nitro group so that the central group X remains unaffected. If the bridging group X is one from the set: -COO-, compound I is reduced with hydrogen over palladium; if X is -COCH₂- or -CHOHCH₂- compound I is reduced with iron in the presence of hydrochloric acid. If X is -CH=CH- the compound is reduced with iron in the presence of hydrochloric acid in order to preserve the bridging group -CH=CH- or, it is reduced with hydrogen over palladium to reduce the bridging group -CH=CH- to -CH₂CH₂-. The amine of the general Formula I.B obtained as a result of reduction is separated and purified by known methods upon which (a) it is dissolved in an organic solvent, preferably chloroform, and the obtained solution is added dropwise to the mixture containing tiophosgene, water, calcium carbonate and the organic solvent, or (b) it is dissolved in a hydrocarbon type solvent and triethylamine and carbon disulphide is added to the solution. The crystallizing dithiocarbamic acid salt is separated and subsequently dissolved in an chlorinated hydrocarbon solvent. Triethylamine and alkyl chloroformate are next added to the obtained solution. After the reaction is completed, the contents are washed with acid and water, dried and isothiocyanate of the general formula I.C is separated. The following procedure may also be applied. The amine of the general formula I.B is dissolved in a solvent of ether type, preferably in diethyl ether or tetrahydrofurane, upon which dicyclohexylcarbodiimide and carbon disulphide are added to the solution. The obtained isothiocyanate of the formula I.C is separated from dicyclohexylthiourea and purified by known methods. The compounds of the general formula I which are the object of the invention reveal unique liquid crystal properties.Particular attention should be drawn to their unusually strong nematogenic properties for different kinds of central groups. Nematic properties are revealed not only by the compounds with the -NCS or -F terminal group but also by those with the -NO₂ or -NH₂ group what is very seldom observed or with hydroxy group in the bridging group such as -CHOHCH₂. The nematic phases are observed for long alkyl chains. The above is illustrated in Table 1. In the table I the following notation is used: Cr denotes the crystalline phase, S-the smectic one, S-the smectic B one, N-the nematic one, I-the isotropic one; the temperature is given in centigrades. From the above mentioned compounds those are preferred which have general formula I in which k=1 and l=1, and Y=-NCS, and X=-CH₂CH₂-; they have low melting points, low viscosities, and low melting enthalpies what ensures their high solublity in other liquid crystal compounds; particulary advantageous properties are revealed by the compounds with 4 to 8 carbon atoms in the R³ alkyl chain (the range of the nematic phase is up to 180° and melthing enthalpy as low as 16 kJ/mole ). Table 2 gives the solubilities in wt.% of the compounds C₄H₉-I.c4C and C₆H₁₃-I.c4C in trans-4-(4-n-hexylcyclohexyl)benzeneisothiocyanate at various temperatures. Compound Temperature 30°C 20°C 10°C 0°C -10°C C₄H₉-I.c4C 40.2 32.1 25.1 19.2 14.1 C₆H₁₃-I.c4C 42.3 30.6 21.7 14.5 9.2 The liquid crystal composition according to the invention is a mixture of at least two liquid crystal components of which at least one is a compound of the general formula I: wherein R¹ is a normal or branched alkyl group H 2n+1 C n - or a normal or branched alkoxy group H 2n+1 C n O-, n being an integer number from 1 to 12; X is a bridging group from the set: -COO-, -OCO-, -CH₂CH₂-, -CHOCH₃CH₂-; Y is a terminal group from the set: -NCS, the cyclohexane rings are trans-1,4-disubstituted ones and the benzene rings are 1,4-disubstituted ones, and besides one of them may contain sometimes additionally a fluorine atom in position 2 or 3; k and l are integer numbers from the set: 0, 1, 2 fulfilling the condition that k+l=2 or 3 ; besides, if X denotes the -COO- or -OCO- group, then k+l also may assume the value of 1 ( k=1 and l=0 or k=0 and l-1 ). The liquid crystal admixtures according to the invention contains at least one component of the general formula I in a quantity exceeding 2 wt.% preferably 5 to 50 wt.% and if necessary also other non-liquid crystalline compounds such as dyes, solvents and optically active substances. It has been ascertained that the mixtures containing the compounds of the general formula I have the required, advantageous for application properties, discussed at the beginning of the description, such as low viscosity and particulary low viscosity at low temperatures. The threshold voltage of the liquid crystal display may easily be varied in a wide range, but the temperature dependence being small in a wide range of temperatures. This facilitates the control of the electro-optical devices. The compounds of the general formula I and their mixtures may be used, in principle, in any electrooptical device, it is preferred, however, that they be used outdoors where the temperature may vary in a wide range and high resistance to humidity and U.V. radiation is required. The devices utilizing these compounds may operate both in a direct control and multiplex control regime. The operation of the liquid crystal display filled with the liquid crystal mixture accordnig to the invention may be based on any electrooptical effect though particularly preferred are those taking advantage of the twisted nematic or guest-host effect. The dichroic dyes necessary in the case of the latter effect-such as anthraquinone ones-reveal excellent solubility in the mixtures according to the invention, and these mixtures give high contrast. The mixture according to the invention raises significantly the performance of the electrooptical devices in which it is used whose construction is generally known. The mixtures according to the invention may include alongside with one or several compounds of formula I additionally other liquid crystal compounds as, e.g. compounds selected from such classes of compounds as biphenyls, phenylcyclohexanes, phenylcyclohexylethanes, phenyldioxanes, phenylpyrimidines, phenyl esters of benzoic or cyclohexanecarboxylic acids, Schiff's bases, azoxy compounds, cyclohexylbiphenyls, diphenylpyrimidines, biphenylates. Among the enumerated classes of compounds the compounds of the following formulae are preferred: where R³ is an alkyl group including from 1 to 8 carbon atoms, and R⁴ is an alkyl group containing from 1 to 5 carbon atoms. Among the compounds with formulae from XVIII to XXXV the most preferred components of the mixtures are those of formualae XVIII, XIX, XXI, XXIII, XXIV, XXVI, XXVII, XXXV. Especially compound XVIII is suitable for producing base mixtures. As regards compounds XVIII, XXI, XXIII, XXVIII, XXXV, it is advantageous to combine them with compounds of the general formula I.cC which have alkyl groups with 2 to 8 carbon atoms. Especially recommended is the compound of formula C₄H₉-I.c4C which shows the phase transitions Cr87N260I, and C₆H₁₃-I.c4C which shows the phase transitions Cr74N247.5I. The compound or compounds of formula I and compounds of formulae from XIV to XXXI yield mixtures of advantageous properties if the former constitute 5 to 50 wt.%. Compounds of formulae XXI, XXVI, XXVIII have a smectic A or E phase, so it is not recommended that they be used alone with the compound or compounds of formula I but together with the compound of formula XVIII or XXIII, and their proportion in the mixture should not exceed 30 wt.%. The compounds of formula I reveal high clearing points, so non-liquidcrystalline compounds or a compound revealing mesogenic properties at low temperatures may also be added to the mixtures containing the former. Among the enumerated compounds those with formula XXXVI and XXXVII are advantageous compounds of the mixtures. Examples are given below characterizing the process of preparing the liquid crystal compounds and of the necessary substrates as well as the application of these compounds in liquid crystal mixtures. The examples are given to illustrate the invention rather than to limit its range. The temperatures are in all instances given in °C. Example 1 trans-4-(4-Nitrophenyl)cyclohexanecarboxylic acid (formula II.3A) (a) A mixture of 204 g trans-4-phenylcyclohexanecarboxylic acid, 300 cm³ CCl₄ , 96 g methanol and 5 cm³ conc. H₂SO₄ is prepared and refluxed for 12 hours with protection from humidity. Next the contents are diluted with water and the phases are separated. The aqueous phase is extracted with CCl₄, and the combined organic phases are washed with water, 5% NaHCO₃ and dried with MgSO₄. The drying agent is filtered off and the remainder after distilling off the solvent is distilled under vacuum and the 113-115°/0.1mmHg fraction being colleted. The yield of the methyl ester of trans-4-phenylcyclohexanecarboxylic acid is 198 g (91%), m.p. 34-35°. (b) A mixture of 172 g methyl ester of trans-4-phenylcyclohexanecarboxylic acid and 70cm³ nitrobenzene is cooled to 5° when a mixture of 150 cm³ of 96% H₂SO₄ and 88 cm³ of 65% HNO₃ is added dropwise with vigorous stirring, the temperature being kept in the range +5° - +10°. After adding the nitrating acids stirring is continued for 3 hours and the contents are poured onto ice. Then 400 cm³ of CCl₄ are added with vigorous agitation. From the obtained emulsion crystals precipitate. They are filtered, washed with water and dried. Next the organic layer of the filtrate is separated and it is washed with water, 5% NaHCO₃, dried with MgSO₄ and filtred. Carbon tetrachloride and nitrobenzene are distilled off under vacuum and the residue is crystallized from methanol. Both fraction of crystals, 162 g, are recrystallized from 2:1 mixture of hexane and benzene. The yield of the methyl ester of trans-4-(4-nitrophenyl)cyclohexanecarboxylic acid of m.p. 127-128.5° and purity 97% is 133 g (64%). (c) 40 g of the methyl ester of trans-4-(4-nitrophenyl)cyclohexanecarboxylic acid and a solution of 12 g of NaOH in 250 cm³ of water are refluxed until a clear solution is obtained. The solution is then cooled and acidified with hydrochloric acid. The precipitate is filtered, washed with water and dried. A yield of 37 g of trans-4-(4-nitrophenyl)cyclohexanecarboxylic acid (about 100%) is obtained with the phase transitions Cr182-165N240I with decomposition. Example 2 trans-4-(4-Nitrophenyl)cyclohexylacetic acid (formula II.1A) (a) A mixture of 152 g of trans-4-acetylcyclohexylbenzene, 37.5 g of sulphur and 105 cm³ of morpholine is refluxed for 10 hours. It is then poured into 750cm³ of rectified ethanol and cooled overnight at 0°. Next the crystals are filtered, a yield of 178 g of thiomorpholide of m.p. 135-140° being obtained. After drying thiomorpholide is hydrolyzed in a mixture of 320 cm³ of acetic acid, 47.5 cm³ conc. H₂SO₄ and 74 cm³ of water. Upon refluxing for 4 h the evolution of hydrogen sulphide practically ceases. A dark tarry residue remains at the bottom of the flask. The upper layer is separated by pouring it into 1500 cm³ of cold water. The precipitated trans-4-phenylcyclohexylacetic acid is filtered, washed with water and dissolved in a solution of 30g of NaOH in 1200cm³ of water. The undissolved substances are filtered off, the filtrate is acidified, upon which trans-4-phenylcyclohexylacetic acid precipitates. The precipitate is filtered and dried. Crude trans-4-phenylcyclohexylacetic acid, 152 g, 350 cm³ of CCl₄, 66 cm³ of methanol and 3 cm³ conc. H₂SO₄ are refluxed for 12 h., upon which the mixture is diluted with water and the phases separated. The organic phase is washed with water, 5% NaHCO₃ , water again, and after drying with MgSO₄ the solvent is distilled off. The residual oil is distilled under vacuum, the 132-138°/0.3 mmHg fraction being collected. A yield of 103g (55%) of the methyl ester of trans-4-phenylcyclohexylacetic acid is obtained. (b) 90g of methyl ester of trans-4-phenylcyclohexylacetic acid are cooled to 10° when the nitrating mixture of 41cm³ conc. HNO₃ and 51 cm³ conc. H₂SO₄ is added dropwise. After stirring for 4h the contents are poured onto ice and the product is extracted with CCl₄. The extracts are combined, washed with water and 5% NaHCO₃, and dried with MgSO₄. After distilling off CCl₄ 125 g of yellow oil are obtained which is three times crystallized from the 5:1 hexanebenzene mixture. A yield of 41g (38%) of methyl ester of trans-4-(4-nitrophenyl)cyclohexylacetic acid of m.p. 65-66° is obtained. (c) A 41g portion of the methyl ester of trans-4-(4-nitrophenyl)cyclohexylacetic acid is hydrolized analogously as in Example 1. The yield of the crude trans-4-(nitrophenyl)cyclohexylacetic acid is 38g (98%). After crystallization from 3:1 benzene-hexane mixture it has m.p. 135-137°. Example 3 trans-4-(4-Fluorophenyl)cyclohexylmethanol (II.5D) (a) 66 g of methyl ester of trans-4-(4-nitrophenyl)cyclohexanecarboxylic acid (obtained in Example 1) are dissolved in 600cm³ of ethyl acetate and 2 g of 5% Pd on active carbon are added. The contents are reduced with gaseous hydrogen under normal pressure with vigorous stirring, until the absorption of hydrogen ceases. Next the catalyst is filtred off and the filtrate is concentrated in a vacuum evaporator. A yield of 65 g of the aminoester of m.p. 54-64° are obtained.After crystalization from methanol, the methyl ester of trans-4-(4-aminophenyl)cyclohexanecarboxylic acid of m.p. 62-64° is obtained. (b) The methyl ester of trans-4-(4-aminophenyl)cyclohexanecarboxylic acid is dissolved in 200 cm³ of ethyl alcohol and the solution is added dropwise with vigorous mixing into 1500 cm³ of water. The obtained fine crystalline amine is filtered, washed with water and suspended in a mixture of 200 cm³ of water and 78.5 cm³ of conc. HCl. The obtained suspension is cooled to 0-5° and diazotized by adding dropwise 20 g NaNO₂ in 75 cm³ of water. The solution of the diazonium salt is filtered and then 38 g of NaBF₄ in 75 cm³ of water are added to the filtrate. Diazonium tetrafluoroborate is filtered, washed with cold water, methanol, and ether. A yield of 64 g the dry diazonium salt melting et 107-110° with decomposition is obtained. (c) The diazonium salt obtained in step (b) is suspended in 1200 cm³ of gasoline (70-110° fraction) and heated to distil slowly off the volatile components. The decomposition of diazonium tetrafluoroborate starts at about 80°. After the evolution of nitrogen and boron fluoride ceases, the mixture is filtered, the filtrate is washed with water and 5% NaHCO₃, again with water and dried with MgSO₄. Next the drying agent is filtered off and gasoline solution is concentrated. The remainder is distilled under vacuum (oil pump) the 120-125°/0.08 mmHg fraction being collected. A yield of 34.5 g (57.5%) of the methyl ester of trans-4-(4-fluorophenyl)-cyclohexanecarboxylic acid in the form of a colorless low-melting solid of m.p. 48-54° is obtained. (d) A solution of 76 g of the methyl ester of trans-4-(4-fluorophenyl)cyclohexanecarboxylic acid in 200 cm³ of ether is added dropwise to a mixture of 400 cm³ of diethyl ether and 10 g of LiBH₄ and the obtained mixture is heated for 3 h under reflux. After cooling the excess hydride is decomposed by adding dropwise 150cm³ of water acidified with H₂SO₄. The phases are then separated, and the water phase is extracted with ether. The combined other extracts are washed with brine and dried with MgSO₄. Ether is distilled off and the residue is crystallized from 250cm³ of hexane. A yield of 58g (87%) of trans-4-(4-fluorophenyl)cyclohexylmethanol of m.p. 75-77° is obtained. Example 4 Trans-4-(4-fluorophenyl)cyclohexylacetic acid (II.1D) (a) To 58g of trans-4-(4-fluorophenyl)cyclohexylmethanol (obtained in step (d) of Example 3) 27.3 cm³ of pyridine and 100cm³ of benzene are added. Then 95 g of thionyl chloride are slowly added dropwise without cooling and then the contents are heated under reflux for 4 h. The mixture is next cooled, poured onto water with ice and the phases are separated. The water phase is extracted with benzene. The combined organic phases are washed with water, 5% NaHCO³ and again with water, and dried with MgSO₄. The drying agent is then filtered off, and the filtrate is concentrated and distilled under vacuum, the 106-109°/0.08 mmHg fraction being coolected.A yield of 58 g (91%) of trans-4-(4-fluorophenyl)cyclohexylmethyl chloride is obtained of m.p. 68-70°. (b) A mixture of 58 g trans-4-(4-fluorophenyl)cyclohexylmethylchloride, 120 cm³ triethylene glycol, 16.7g NaCN is heated with stirring to 104° at which temperature it is kept for 2h. Next the contents are poured into 1000cm³ of water. The precipitate is filtered off and the filtrate is extracted with chloroform. The precipitate is then dissolved in chloroform and combined with the extract, washed with water, 50% H₂SO₄, again with water and dried with MgSO₄. After filtration and concentration a yield of 55 g (99%) of the crude trans-4-(4-fluorophenyl)cyclohexylmethyl cyanide is obtained, which after crystallization from hexane melts at 88°. (c) The cyanide obtained in step (b) is hydrolized to the acid by heating for 24 h in a mixture of 75cm³ of acetic acid, 60 cm³ of water end 48 cm³ of conc. H₂SO₄. The reaction mixture is poured into 1500 cm³ of water and filtered. The crude acid is dissolved in a solution of 40 g of NaOH in 500 cm³ of water. The solution is filtered through a layer of active carbon and acidified. The precipitated trans-4-(4-fluorophenyl)cyclohexylacetic acid is filtered, dried and crystallized from a 2:1 hexane-benzene mixture. A yield of 42g (70%) of trans-4-(4-fluorophenyl)-cyclohexyl-acetic acid of m.p. 128-130° is obtained. Example 5 trans-4-(4-Nitrophenyl)cyclohexylmethanol (II.5A) (a) 37.3 g of trans-4-(4-nitrophenyl)cyclohexanecarboxylic acid are heated with 47 g of oxalyl chloride.After the excess of oxalyl chloride is distilled off, the crude acid chloride is obtained. (b) The trans-4-(4-nitrophenyl)cyclohexanecarboxylic acid chloride (II.4A) obtained in step (a) is dissolved in 80 cm³ of anhydrous diglyme and the solution is added drowise to a flask with a supension of 9,5 g of NaBH₄ in 200 cm³ diglyme the temperature being kept at 35-40°, The contents of the flask are agitated for 3h and poured into 1000 cm³ of water acidified with 50 cm³ of conc. HCl. The precipitate is filtered off, and the filtrate is extracted with ether. The precipitate is dissolved in ether and combined with the extract, washed with brine, dried with MgSO₄ , filtered and concentrated. A yield of 34 g (95%) of the crude compound II.5A is obtained which after crystallization from a 1:2 hexane-benzene mixture has a m.p. of 115°. Example 6 trans-4-(4-Nitrophenyl)cyclohexylmethyl chloride (II.6A) The crude compound II.5A obtained in Example 5 is converted to the chloride by heating with thionyl chloride and pyridine analogously as in Example 4. After concentration the solid residue is crystallized from acetone.The yield is 25.7g(68%) of II.6A of m.p. 73-74°. Example 7 4-[trans-4-(4-Nitrophenyl)cyclohexylacetyl]-4'-n-butybiphenyl (C₄H₉-I.d1A) (a) A mixture of 5.26g trans-4-(4-nitrophenyl)-cyclohexylacetic acid and 5.2 cm³ of oxalyl chloride is prepared, and it is heated under reflux for 2 h.Then excess of oxalyl chloride is distilled off under vacuum, and the obtained crude trans-4-(4-nitrophenyl)cyclohexylacetyl chloride is used in the next step. (b) 3.06 g of anhydrous aluminum chloride are added to 150 cm³ of methylene chloride. The mixture is cooled to 5° when trans-4-(4-nitrophenyl)cyclohexylacetyl chloride obtained in step (a) and dissolved in 150 cm³ of methylene chloride is added dropwise with stirring. The mixture is vigorously stirred For 30 min upon which 5.25 g of 4-n-butylbiphenyl is slowly added dropwise keeping the temperature in the range of 0-5°. After continued mixing for a further 3h the reaction mixture is poured into 50 cm³ of 5% HCl with ice. The phases are separated, and the aqueous phase is extracted with 50 cm³ of methylene chloride. The organic phases are combined, washed with 5% HCl, water to a neutral reaction, and dried with MgSO₄. The solvent is distilled off and the residue is crystallized from a 2:1 ethanol-acetone mixture. The yield of the C₄H₉-I.d1A compound is 4.1 g (45%) and its phase transition points are: Cr152N219I. The compounds: C₅H₁₁-I.d1A, C₂H₅-I.c1A, C₃H₇-I.c1A, C₄H₉-I.c1A, C₅H₁₁-I.c1A, C₆H₁₃-I.c1A, C₇H₁₅-I.c1A, C₈H₁₇-I.c1A, C₉H₁₉-I.c1A are obtained in a similar manner; their phase transition points are listed in Table 1. Example 8 1-(4'-n-Butylbiphenylyl-4)-2-[trans-4-(4-nitrophenyl)cyclohexyl]ethanol (C₄H₉-I.d2A) 4.10 g of C₄H₉-I.d1A dissolved in mixture of 150 cm³ of anhydrous ethanol and 100 cm³ of dimethoxyethane. To the agitated solution 1g of NaBH₄ is added in two portions at 1h interval and the reaction mixture is left to stand for 24 h. Next the solvent is distilled off under vacuum, the residue is diluted with water, acidified with dilute hydrochloric acid and the precipitate is filtered. The crude product is crystallized from a 3:1 ethanol-acetone mixture, The yield of compound of C₄H₉-I.d2A is 3.55 g (86.3%) and its phase transition points are: Cr135N226I. The compounds: C₂H₅-I.d2A, C₃H₇-I.d2A, C₂H₅-I.c2A, C₃H₇-I.c2A, C₄H₉-I.c2A, C₅H₁₁-I.c2A, C₆H₁₃-I.c2A, C₇H₁₅-I.c2A, C₈H₁₇-I.c2A, C₉H₁₉-I.c2A C₁₀H₂₁-I.c2A are obtained in the similar manner. Example 9 1-(4'-n-Butylbiphenylyl-4)-2-[trans-4-(4-nitrophenyl)cyclohexyl]ethene (C₄H₉-I.d3A) 3.55 g of compound C₄H₉-I.d2A are dissolved in 130 cm³ of toluene, a catalytic quantity of p-toluenesulfonic acid is added and the reaction mixture is refluxed, the evolving water being removed by applying an azeotropic trap. Next the mixture is cooled, washed with a 5% NaHCO₃ solution, water and dried with MgSO₄. After Filtration toluene is distilled off and the solid residue is crystallized from a 3:1 acetone - THF mixture. The yield of compound C₄H₉-I.d3A is 2.A5 g (83.5%) and its phase transition points are: Cr158N310>I (above 310° decomposition of the compound is observed). The compounds: C₂H₅-I.c3A, C₃H₇-I.c3A, C₄H₉-I.c3A, C₆H₁₃-I.c3A, C₇H₁₅-I.c3A, C₈H₁₇-I.c3A, C₉H₁₉-I.c3A, C₁₀H₂₁-I.c3A are obtained in a similar manner. Example 10 1-(4-n-Butylbiphenylyl-4)-2-[trans-4-(4-isotiocyanatophenyl)-cyclohexyl]ethane (C₄H₉-I.d4C) To 2.85 g of C₄H₉-I.d3A 150 cm³ of ethyl acetate and 300 mg of 5% Pd on active carbon are added. The mixture in the flask is connected to a gasometer and saturated with hydrogen until the absorption of the latter ceases (about 2 h). Next the mixture is heated to the boil and at that temperature the catalyst is filtered off. The filtrate is concentrated to complete evaporation of the solvent, the yield of dry 1-(4'-n-butylbiphenylyl-4)-2-[trans-4-(4-aminophenyl)cyclohexyl]ethane (C₄H₉ I.d4B) being 2.60 g. The crude product is dissolved in 25 cm³ of chloroform and added dropwise with vigorous stirring at 5-10° to a mixture of 0.38 g of CaCO₃ and 0.62 cm³ of thiophosgene in 10 cm³ of chloroform and 10 cm³ of water. Stirring is continued for a further 1h at room temperature. Next 2.5 cm³ of 1N hydrochloric acid are added and the phases are separated. The organic phase is washed with water, dried with MgSO₄, filtered and the solvent distilled off. The dry residue is dissolved in benzene and filtered through a columm with silica gel in order to remove the color. The filtrate is concentrated by evaporation and the dry residue is crystallized from a 1:1:1 CHCl₃-ether-methanol mixture. The yield of the obtained C₄H₉-I.d4C is 1.76 g (63%) and its phase transition points are: Cr153N269I. The compounds: C₂H₅-I.c4C, C₃H₇-I.c4C, C₄H₉-I.c4C, C₆H₁₃-I.c4C, C₅H₁₁-I.c4C, C₇H₁₅-I.c4C, C₈H₁₇-I.c4C, C₉H₁₉-I.c4C, C₁₀H₂₁-I.c3C, C₁₂H₂₅-I.c4C are obtained in a similar manner. Example 11 4'-n-Butylphenyl ester of trans-4-(4-nitrophenyl)cyclohexane carboxylic acid (C₄H₉-I.b13A) (a) To 7.50 g of trans-4-(4-nitrophenyl)cyclohexanecarboxylic acid 7.5 cm³ of oxalyl chloride are added and the mixture is refluxed for 2 h. Excess of oxalyl chloride is distilled off under vacuum, and the obtained crude trans-4-(4-nitrophenyl)cyclohexanecarboxylic acid chloride is used in the next step. (b) To 50 cm³ of benzene 4.50 g of 4-n-butylphenol and 4.75 g of anhydrous pyridine are added. trans-4-(4-Nitrophenyl)cyclohexanecarboxylic acid chloride obtained in step (a) is dissolved in 20 cm³ of benzene and added dropwise to the stirred solution of phenol in benzene, the temperature being kept at 15-20°. The reaction mixture is then refluxed for 1 h, cooled, washed with a 5% HCl solution, and dried with MgSO₄. After filtering, the filtrate is concentrated, and the dry residue is crystallized twice from ethanol. The yield of compound C₄H₉-I.b13A is 6.80 g (59%) and its phase transition points are: Cr114N150I. The compounds: C₄H₉-I.a13A, C₃H₇-I.a13A, C₅H₁₁-I.a13A are obtained in a similar manner. Example 12 4-n-Butylphenyl ester of trans-4-(4-isothiocyanatophenyl)cyclohexanecarboxylic acid (C₄H₉-I.b13C) (a) 4.50g of compound C₄H₉-I.b13A are reduced with gaseous hydrogen in analogous manner as in Example 10 in the presence of 50 cm³ of ethyl acetate and 100 mg of 5% Pd on active carbon. The yield of the obtained ester C₄H₉-I.b13B is 4.0 g and its phase transition points are Cr107N124I. (b) The compound C₄H₉-I.b13B obtained in step (a) is dissolved in 30 cm³ of chloroform and added dropwise,with vigorous stirring, to a mixture prepared of 2.0 g CaCO₃, 1.13 cm³ of thiophosgene in 30 cm³ of chloroform and 10 cm³ water. The temperature being kept at 5-10°. After further stirring for 1h, 10cm³ of 1N hydrochloric acid are added and the phases are separated. The organic phase is washed with water and dried with MgSO₄. After filtration, chloroform is distilled off under vacuum and the residue is crystallized twice from a 3:1 methanol-ether mixture. The yield of compound C₄H₉-I.b13C is 2,55 g (55%) and its phase transition points are:Cr 107 N 189 I. The compounds: C₄H₉-I.a13C, C₃H₇-I.c13C, C₅H₁₁-I.a13C are obtained in a similar manner. Example 13 trans-4-(4-Fluorphenyl)cyclohexylacetyl-4-[trans-4-(ethyl cyclohexyl]benzene (C₂H₅-I.c1D) (a) From 9.4g of the trans-4-(4-fluorophenyl)cyclohexylacetic acid and 8 cm³ of oxalyl chloride, the acid chloride is prepared in an analogous manner as in example 7a (b) 8.0g of anhydrous aluminum chloride are added to 50 cm³ of methylene chloride and to this mixture, the trans-4-(4-fluorophenyl)cyclohexylacetyl chloride prepared in step (a) and dissolved in 20 cm³ methylene chloride, is added dropwise at 5°, with vigorus stirring. Stirring is continued for a further 20 min after which 7.55g of trans-(4-ethylcyclohexyl)benzene are added dropwise, the temperature being kept at 0-5°. Stirring is continued for 4h and then the mixture is poured into 100cm³ of 5% HCl with ice, the phases are separated, the aqueous phase being extracted with 50cm³ of methylene chloride. The combined organic phases are washed with 5% HCl,water to neutral reaction, and dried with MgSO₄. The solvent is distilled off and the residue is crystallized first from a 2:1 ethanol-acetone mixture, then from heptane and finally again from the ethanol-acetone mixture. The yield of compound C₅H₁₁-I.c1D is 7.7g (47.5%) and its phase transition points are: Cr158N164I. The compounds: C₄H₉-I.c1D, C₅H₁₁-I.c1D, C₆H₁₃-I.c1D are obtained in a similar manner. Example 14 1-[4-(trans-4-ethylcyclohexyl)phenyl]-2-[trans-4-(4-fluorophenyl)cyclohexy]ethanol (C₂H₅-I.c2D) 7.7g of C₂H₅-I.c1D are dissolved in a mixture of 100 cm³ of THF and 100 cm³ of anhydrous ethanol. To the mixture 2g of NaBH₄ are added in two portions in a several hour interval and the reaction mixture is heated to 40° and left to stand for 24h. Next the solvent is distilled off under vacuum, and the residue is diluted with water, acidified with dilute HCl and the precipitate filtered. After crystallized from hexane the yield of compound C₂H₅-I.c2D is 5.2g (67%), its m.p. is 128-130°. Compound C₄H₉-I.c2D is obtained in an analogous manner. Example 15 1-[4-(trans-4-ethylcyclohexyl)phenyl]-2-[trans-4-(4-fluorophenyl)cyclohexyl]ethene (C₂H₅-I.c3D) 5.2g of compound C₂H₅-I.c2D are dissolved in 150 cm³ of toluene, 100mg of p-toluanesulfonic acid are added and the mixture is heated under reflux, the evolving water being removed in an azeotropic trap. Next the mixture is diluted with toluene to dissolved the crystallizing product, washed with a 5% NaHCO₃ solution and water, then dried with MgSO₄. After filtration, the toluene is distilled off from the filtrate and the residue is crystallized from a 2:1 hexane-benzene mixture. The yield of compound C₂H₅-I.c3D is 4.8g, its phase transition points are: Cr164N310I. Compound C₄H₉-I.c3D is obtained in an analogous manner. Example 16 1-[4-(trans-4-ethylcyclohexyl)phenyl]-2-[trans-4-(4-fluorophenyl)cyclohexyl]ethane (C₂H₅-I.c4D) 4.8g of compound C₂H₅-I.c3D are added to 150 cm³ of ethyl acetate and in presence of 500 mg of Pd on active carbon the mixture is saturated with hydrogen until the absorption of the latter ceases. Then the catalyst is filtered from the hot solution, the filtrate is concentrated, and the solid residue is crystallized twice from hexane. The yield of compound C₂H₅-I.c4D is 3.04 g (63%) and its phase transition points are: Cr120N186I. The compound C₄H₉-I.c4D is obtained in a similar manner. Example 17 4-Butylphenyl ester of trans-4-(4-fluorophenyl)cyclohexanecarboxylic acid (C₄H₉-I.b13D) (a) The acid chloride is prepared from 3.85g of trans-4-(4-fluorophenyl)cyclohexanecarboxylic acid and 3.5 cm³ of oxalyl chloride analogously as in Example 11. (b) The solution chloride of trans-4-(4-fluorophenyl)cyclohexanecarboxylic acid, obtained in step (a) , in 15 cm³ of benzene is added dropwise at 15-20° to a mixture of 30 cm³ of benzene, 2.55g 4-n-butylphenyl and 2.7 cm³ anhydrous pyridine. Next the mixture is refluxed for 1h, cooled and washed with 5% HCl, water, dried with MgSO₄ and filtered. The filtrate is concentrated and the residue is crystallized from, ethanol and hexane. The yield of compound C₄H₉-I.b13D is 3.80g (61%) and its phase transition points are Cr94N116I. The compounds C₅H₁₁-I.a13D and C₃H₇-I.c13D are obtained in an analogous manner. Example 18 Mixture A is prepared of the following composition in wt.%: 4-(trans-4-n-propylcyclohexyl)-1-isothiocyanatobenzene 40 4-(trans-4-n-hexylcyclohexyl)-1-isothiocyanatobenzene 42 4-(trans-4-n-octylcyclohexyl)-1-isothiocyanatobenzene 18 The mixture has the following parameters: 1. Nematic phase range: from below -30° to 41.5° -20° 0° 20° 40° 2. Bulk viscosity [mPa.s] 50 21.5 11 7.2 3. Threshold voltage V₁₀, [V] -1.9 1.7 1.5 1.1 Mixture B is prepared of the following composition in wt.%: Mixture A 85 Compound C₆H₁₃-I.c4C 15 The mixture has the following parameters: 1. Nematic phase range: from below -35° to 73° -20° 0° 20° 40° 2. Bulk viscosity [mPa.s] 51 24 12.7 7.2 3. Threshold voltage V₁₀, [V] 2.0 1.9 1.75 1.65 If the mixture is composed of 75 wt.% of A and 25 wt.% of compound C₆H₁₃-I.c4C, than an increase of the clearing temperature to 93° is obtained, as well as very good mutual solubility of the mixture components at room temperature. If 10 wt.% of 2-(4-cyanophenyl)-5-(4-n-butylphenyl)pyrimidine or 10 wt.% of 4-n-pentyl-4'-cyanoterphenyl or 10 wt.% of 4-pentylphenyl 4-(trans-4-pentylcyclohexyl)benzoate are added to Mixture A, then dissolving of the components takes place only after heating; on cooling a solid phase precipitates from the mixture. Example 19 The mixture of the following composition in wt.%: 4-(trans-4-n-propylcyclohexyl)-1-isothiocyanatobenzene 20.35 4-(trans-4-n-hexylcyclohexyl)-1-isothiocyanatobenzene 18.46 4-n-pentyl-4'-isothiocyanatobiphenyl 12.92 4-n-heptyl-4'-isothiocyanatobiphenyl 13.53 1-(4'-n-hexylbiphenylyl-4)-2-(4-isothiocyanatophenyl)ethane 9.23 Compound C₆H₁₃-I.c4C 16.00 cholesteryl pelargonate 0.28 has the parameters: 1. Nematic phase range: from below -30° to 78° 2. Bulk viscosity at 20° [mPa.s] 19.5 3. Threshold voltage at 20° [V] 2.2 Example 20 The mixture of the following composition in wt.%: 4-(trans-4-n-propylcyclohexyl)-1-isothiocyanatobenzene 29.60 4-(trans-4-n-hexylcyclohexyl)-1-isothiocyanatobenzene 31.08 4-(trans-4-n-octylcyclohexyl)-1-isothiocyanatobenzene 18.32 Compound C₅H₁₁-I.a13C 12.00 Compound C₄H₉-I.b13C 8.00 Compound C₃H₇-I.c13C 6.00 has the clearing point at 86°, and its bulk viscosity at 20° is 20.0 mPa s Example 21 The mixture of the following composition in wt.%: 4-(trans-4-n-propylcyclohexy)-1-isothiocyanatobenzene 23.46 4-(trans-4-n-butylcyclohexyl)-1-isothiocyanatobenzene 12.95 4-(trans-4-n-hexylcyclohexyl)-1-isothiocyanatobenzene 21.50 4-(trans-4-n-octylcyclohexyl)-1-isothiocyanatobenzene 9.23 1-[4-(trans-4-n-butylcyclohexyl)phenyl]-2-(4-isothiocyanatophenyl)ethane 5.44 1-[4-(trans-4-n-hexylcyclohexyl)phenyl]-2-(4-isothiocyanatophenyl)ethane 5.44 Compound C₄H₉-I.c4C 10.90 Compound C₆H₁₃-I.c4C 10.90 Optically active 1-[4'-(2-methylbutyl)biphenylylyl-4]-2-(4-isothiocyanatophenyl)ethane 0.18 has the following parameters:

Claims: A cyclohexylbenzene derivative of the general formula wherein R¹ is a normal or branched alkyl group H 2n+1 C n -or normal or branched alkoxy group H 2n+1 C n O-, n being an integer from 1 to 12; X is a bridging group -CHOHCH₂-, -CH₂CH₂- or -CHOCH₃CH₂; -COO-, -OCO-; Y is a terminal group -NO₂, -NH₂ or -NCS; the cyclohexane rings are trans-1,4-disubstituted ones and the benzene rings are 1,4-disubstituted, in which the H-atom in 3- or 2-position can be replaced by F-atom; k and l are integers 0, 1 or 2, under the condition that k+1=2 or 3, besides if X denotes a -COO- or -OCO-group, k+1 also may be 1. The compound having the formula wherein R¹ is a normal or branched alkyl chain having 1 to 12 carbon atoms; X is a bridging group -COO- or -OCO-, Y is a terminal group -NO₂ or -NCS. The compound having the formula wherein R¹ is a normal or branched alkyl chain having 1 to 12 carbon atoms; X is a bridging group -COO- or -OCO, Y is a terminal group -NO₂ or -NCS. The compound having the formula wherein R¹ is a normal or branched alkyl chain having 1 to 12 carbon atoms; X is a bridging group -CHOHCH₂- or -CH₂CH₂-or -CHOCH₃CH₂-, Y is a terminal group -NO₂, -NH₂ or -NCS. The compound having the formula wherein R¹ is a normal or branched alkyl chain having 1 to 12 carbon atoms. The compound according to Claim 5 wherein R¹ is butyl, pentyl, hexyl or heptyl. The compound having the formula wherein R¹ is normal or branched alkyl chain or a normal or branched alkoxy group having 1 to 12 carbon atoms; X is a bridging group -CHOHCH₂-, -CH₂CH₂- or -CHOCH₃CH₂-, Y is a terminal group -NO₂, -NH₂ or -NCS. The compound having the formula wherein R¹ is a normal or branched alkyl chain having 1 to 12 carbon atoms; X is a bridging group -CHOHCH₂-, -CH₂CH₂ or -CHOCH₃CH₂-, Y is a terminal group -NO₂, -NH₂ or -NCS. A liquid crystalline mixture consisting of at least 2 components containing at least one component expressed by the formula wherein R¹ is a normal or branched alkyl group H 2n+1 C n -or a normal or branched alkoxy group H 2n+1 C n O-, n being an integer from 1 to 12, X is a bridging group -CHOHCH₂-, -CH₂CH₂-, -CHOCH₃CH₂-, -COO-, -OCO-, Y is the terminal group -NCS, the cyclohexane rings are trans-1,4-disubstituted and the benzene rings are 1,4-disubstituted, in which the H-atom in 3- or 2-position can be replaced by a F-atom, k and l are integers 0, 1 or 2, under the condition that k+1=2 or 3, besides if X denotes -COO- or -OCO-, then k+1 may also be 1. The liquid crystalline mixture according to Claim 9 wherein a component of formula I is used in a quantity of 5 to 50 wt.-%. In a liquid crystalline mixture comprising 4-(trans-4-n-alkylcyclohexyl)benzeneisothiocyanates the improvement which results from introducing a compound of the formula wherein R¹ is a normal or branched alkyl group H 2n+1 C n -or a normal or branched alkoxy group H 2n+1 C n O, n being an integer from 1 to 12, X is a bridging group -CHOHCH₂-, -CH₂CH₂-, -CHOCH₃CH₂-, -COO- or -OCO-, Y is the terminal group -NCS, the cyclohexane rings are trans-1,4-disubstituted and the benzene rings are 1,4-disubstituted, in which the H-atom in the 3- or 2-position can be replaced by a F-atom, k and l are integers 0, 1 or 2, under the condition that k+1=2 or 3, besides if X denotes a -COO- or -OCO-group, then k+1 may also be 1. In an electrooptical cell comprising a liquid crystal dielectric disposed between two electrode plates, at least one of them is transparent, the improvement specific in that the applied liquid crystal dielectric is the mixture according to Claim 9.

Inventors: DABROWSKI ROMAN, DZIADUSZEK JERZY, SZCZUCINSKI TOMASZ, DABROWSKI, ROMAN, DZIADUSZEK, JERZY, SZCZUCINSKI, TOMASZ
Applicants: WOJSKOWA AKAD TECH, WOJSKOWA AKADEMIA TECHNICZNA IM. JAROSLAWA DABROWSKIEGO
Application year: 1987
Main classification: C09K19
IPC codes: C07C33, C07C205, C07C45, C09K19, C07C253, C07C22, C07C17, C07C27, C07C255, C07C325, C07C67, C07C49, C07C41, C07C43, C07C215, G02F1, C07C29, C07C213, C07C25, C07C209, C07C211, C07C217, C07C331, C07C201