CH651013A5 - Tetra- and pentacyclic esters and the use thereof as components of liquid-crystalline mixtures - Google Patents

Abstract

Compounds of the formula <IMAGE> in which X<2> is a single covalent bond or the ester group -COO-; X<1> is a single covalent bond, the ester group -COO-, the ethylene group -CH2CH2- or, if X<2> is the ester group -COO-, is alternatively p-phenylene; ring A is a benzene ring or trans-1,4-cyclohexylene; ring B is a benzene ring or, if X<2> is the ester group -COO- and X<1> is a single covalent bond, the ester group -COO- or the ethylene group -CH2-CH2-, is alternatively trans-1,4 cyclohexylene; the radicals Z<1>, Z<2> and Z<3> are hydrogen or, on a benzene ring which is not directly linked to a further ring via a single covalent bond, are alternatively halogen, cyano or methyl; Y<2> is cyano, nitro or 2,2-dicyanovinyl; Y<1> is halogen, cyano, C1-C3-alkyl or, if X<1> is p-phenylene and/or Y<2> is nitro, is alternatively hydrogen; and R<1> is C1-C12-alkyl or, on a benzene ring, is alternatively C1-C12-alkoxy, the preparation thereof, and the use thereof in liquid-crystalline mixtures are described.

Description

       

  
 

** WARNING ** beginning of DESC field could overlap end of CLMS **.

 
EMI2.1
 wherein R1, A, B, X1, X2, Z1, Z2 and Z3 have the meanings given in claim 1, or a reactive derivative thereof with a phenol of the general formula
EMI2.2
 wherein Y1 and Y2 have the meanings given in claim 1, esterified.



   17. A process for the preparation of the compounds of the formula I defined in claim 1, wherein Z ', Z2 or Z3 is cyano, characterized in that a compound of the formula I defined in claim 1, in which Z1, Z2 or Z3 is bromine, with Copper (I), sodium or potassium cyanide.



   18. Use of the compounds of formula I defined in claim 1 for electro-optical purposes.



   The present invention relates to new liquid-crystalline compounds, namely the tetra- and pentacyclic esters of the general formula
EMI2.3
 wherein X2 denotes a single covalent bond or the ester group-COO; X1 is a simple covalent bond, the ester group -COO-, the ethylene group -CH2CH2- or, if X2 denotes the ester group -COO-, also p-phenylene; Ring A represents a benzene ring or trans-1,4-cyclohexylene;

  Ring B is a benzene ring or, provided that X2 denotes the ester group -COO- and X1 denotes a simple covalent bond, the ester group -COO or the ethylene group -CH2CH2-, also represents trans1,4-cyclohexylene; the radicals Z1, Z2 and Z3 are hydrogen or on a benzene ring which is not linked directly to a further ring via a simple covalent bond, also halogen, cyano or methyl; Y2 represents cyano, nitro or 2,2-dicyanovinyl; Y1 denotes halogen, cyano, C1-C3-alkyl or, if X 'stands for p-phenylene and / or Y2 for nitro, also denotes hydrogen; and R 'is C1-C12-alkyl or on a benzene ring also Cl-Cl2-alkoxy.



   The invention further relates to the preparation of the compounds of the formula I above, their use for electro-optical purposes and liquid-crystalline mixtures which contain compounds of the formula I.



   In the above definition, the term benzene ring means p-phenylene, which optionally has a lateral halogen, cyano or methyl substituent.



   The term halogen stands for fluorine, chlorine and bromine and the term C1-C3-alkyl for methyl, ethyl, propyl and isopropyl.



   The term C1-C12-alkyl includes straight-chain and branched alkyl groups, in particular the n-alkyl groups methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undercyl and dodecyl and the isoalkyl groups isopropyl, isobutyl, isopentyl, Isoheptyl, isooctyl, isononyl, isoundecyl and isododecyl. The term Cl-12 alkoxy encompasses alkyloxy groups, in which the alkyl part has the above meaning.



   The lateral groups zl, Z2 and Z3 denote hydrogen or, if they are bound to an isolated benzene ring, i.e. to a p-phenylene ring, which is not directly linked to another ring via a simple covalent bond, also halogen, cyano or methyl.



   In recent years, liquid crystals have become particularly important as dielectrics in display devices, since the optical properties of such substances can be influenced by an applied voltage. Electro-optical devices based on liquid crystals are well known to the person skilled in the art and can be based on various effects, such as, for example, the dynamic scattering, the deformation of aligned phases (DAP type), the Schadt-Helfrich effect (rotary cell), the guest Host effect or a cholesteric-nematic phase transition.



   The conventional, static operation of liquid crystal display devices has been increasingly replaced in the past by the so-called multiplex control. This is usually an amplitude selective



  Multiplexing applied, however, generally only multiplexing ratios of about 1: 8 to 1:10 can be achieved by the commonly used methods. In order to achieve higher multiplex rates when driving liquid crystal displays, a two frequency matrix addressing method has therefore been proposed (e.g. German Offenlegungsschriften 2 856 134 and 2 907 940).



   This two-frequency method takes advantage of the fact that the dielectric anisotropy of liquid crystals, which, when a low-frequency voltage is applied, results in a positive anisotropy in the dielectric constant (± = EII-EI> 0, with all the dielectric constant along the longitudinal axis of the molecule and ± l die Dielectric constant mean perpendicular to it), becomes negative at high frequencies. This effect has been attributed to hindering the rotation of the long molecular axis about the short axis of the liquid crystal molecules (M. Schadt, Mol. Cryst. Liq. Cryst. 66 (1981) 319-336).

  In contrast to aj, due to the hardly impeded rotation of the molecules around their longitudinal axes, dispersion effects only appear in the microwave range. In the frequency range of interest here, ± l is constant, while all and therefore also Aa are frequency-dependent. The dielectric relaxation frequency, at which is ± ll- ± l, is referred to in technical terms as the cross-over frequency (fc). The most common nematic liquid crystals generally have cross-over frequencies of about 100 kHz and more at room temperature.



   Two AC sources are used to operate a display device using the two-frequency method, the frequency of one being above and the frequency of the other below the cross-over frequency of the liquid-crystalline dielectric. In addition, the voltage ratio of the signals for the on and off state must be above a certain value. The greater this tension ratio, the more lines can be written on. d. H. the greater the multiplex rate.



   The two-frequency method also offers the advantage that not only the switch-on process, but also the switch-off process can be directly influenced by applying an appropriate AC voltage, thereby accelerating the switch-off process. For example, in the case of a liquid crystal display element with a twisted nematic structure (rotary cell), the homogeneously oriented liquid crystal can be applied by applying a voltage of low frequency (f <fc) aligned in the field direction and converted back into the twisted, homogeneous orientation by applying a voltage of high frequency (f> f0).



   Furthermore, with liquid crystal cells which are based on guest host effects (Applied Physics Letters 13 (1968) 91; J. Appl. Phys. 45 (1974) 4718 and others), when using liquid crystals with positive dielectric anisotropy, only the display is generally more colorless Image elements possible on a colored background, since the dyes that can be used usually have positive dichroism. By means of homeotropic wall orientation and control according to the two-frequency method, colored image elements (homogeneously oriented by applying a voltage of high frequency) can now also be generated on such a colorless surface with such liquid crystals.



   However, the two-frequency method has the disadvantage that the energy consumption is high, since both the amplitude of the AC voltage applied and the frequency are high. In order to reduce energy consumption, it is therefore important that the operating voltage can be kept low. The cross-over frequency should be relatively low for the same reason (this reduces the capacitive losses).



   It has now been found that the compounds according to the invention have large mesophase ranges with high clearing points, the optically active compounds (with an asymmetric carbon atom in the side chain R1) generally having a cholesteric and the other compounds generally having a nematic mesophase. The compounds according to the invention also have a large positive anisotropy of the dielectric constant, good solubility in other liquid crystals and good chemical and photochemical stability. They are also characterized by very low cross-over frequencies.



   In principle, the compounds according to the invention can be used in any liquid-crystalline mixtures, and because of the above properties they are particularly suitable for increasing the dielectric anisotropy and the clearing points. However, the compounds according to the invention are particularly suitable as components of liquid-crystalline dielectrics which are controlled by the two-frequency method.



   In formula I above, ring B preferably represents a benzene ring. The residues z1, Z2 and Z3 preferably denote hydrogen or one of these residues on a benzene ring which is not directly linked to another ring via a simple covalent bond, also chlorine. The group X1 preferably denotes a simple covalent bond or p-phenylene, particularly preferably a single covalent bond. Preferred groups Y2 are cyano and nitro. Preferred groups yl are fluorine, chlorine, cyano and methyl, especially chlorine and cyano. Preference is furthermore given to those compounds of the formula I in which Y1 denotes hydrogen and Y2 denotes nitro, or Y1 denotes hydrogen, X1 p-phenylene and X2 denotes the ester group -COO-.

 

   R1 preferably denotes a straight-chain alkyl or alkoxy group or an isoalkyl or isoalkoxy group. Particularly preferred R 1 radicals are the straight-chain alkyl and alkoxy groups, in particular the straight-chain alkyl groups. The radical R1 preferably contains 3 to 10 and particularly preferably 5 to 9 carbon atoms. Very particularly preferred radicals R1 are hexyl and heptyl.



   A preferred group of compounds of the formula I are the compounds of the general formula
EMI3.1
  wherein Rl, X2 and Y2 have the above meanings; X1 is a simple covalent bond or, if X2 denotes the ester group -COF, also p-phenylene; Ring A represents p-phenylene or trans-1,4-cyclohexylene; Z3 represents hydrogen or, if X2 denotes the ester group -COO-, also chlorine; Y1 denotes fluorine, chlorine, cyano, methyl or, if X1 stands for p-phenylene and / or Y2 for nitro, also denotes hydrogen.



   Examples of preferred compounds according to the invention are the compounds of the above formula II, in which R1, ring A, X1, X2, Z3, yl and Y2 have the meanings given in table 1 (C6H4 denotes p-phenylene, C6H10 trans1,4-cyclohexylene and a dash - a simple convolution bond), as well as the other compounds of the formula I mentioned in the synthesis examples



   Table 1 RingA X1 X2 Z3 Y1 Y2 Pentyl C6H4 - COO H CN CN Hexyl C6H4 - COO H CN -CN Heptyl C6H4 - COO H CN CN Pentyl C6H10 - COO H CN CN Hexyl C6H10 - COO H CN CN Heptyl C6Hlo - COO H CN CN Heptyl C6H4 - - H CN CN Heptyl C6HIo - - H CN CN Pentyl C6H4 - COO Cl CN CN Hexyl C6H4 - COO Cl CN CN Heptyl C6H4 - COO C1 CN CN Pentyl C6H10 - COO Cl CN CN Hexyl C6HIo - COO Cl CN CN Heptyl C6Hlo - COO Cl CN CN Heptyl C6H4 C6H4 COO H CN CN Heptyl C6H10 C6H4 COO H CN CN Heptyl C6H4 C6H4 COO Cl CN CN Heptyl C6Hlo C6H4 COO Cl CN CN Pentyloxy C6H4 - COO H CN CN Pentyloxy C6H4 CH4 - COO Cl CN CN Pentyl C6H4 - COO H Cl CN Hexyl C6H4 - COO H Cl CN Heptyl C6H4

   - COO H Cl CN Pentyl C6H10 - COO H Cl CN Hexyl C6H10 - COO H Cl CN Heptyl C6H10 - COO H Cl CN Heptyl C6H4 - - H Cl CN Heptyl C6H10 - - H Cl CN Pentyl C6H4 - COO Cl Cl CN Hexyl C6H4 - COO Cl Cl CN Heptyl C6H4 - COO Cl Cl CN Pentyl C6H10 - COO Cl Cl CN Hexyl C6H10 - COO Cl Cl CN Heptyl C6HIo - COO Cl Cl CN Heptyl C6H4 C6H4 COO H Cl CN Heptyl C6H10 C6H4 COO H Cl CN Heptyl C6HO C6 Cl Cl CN Heptyl C6HIo C6H4 COO Cl Cl CN Pentyloxy C6H4 - COO H Cl CN Pentyloxy C6H4 - - H Cl CN Pentyloxy C6H4 - COO Cl Cl CN Pentyl C6H4 - COO HH NO2 Hexyl C6H4 - COO HH NO2 Heptyl C6H4 - COO HH NO C6H10 - COO HH NO2 Hexyl C6H10 - COO HH NO2 Heptyl C6H10 - COO HH NO2 Heptyl C6H4 - - HH NO2 Heptyl C6Hlo - - HH NO2 Heptyl C6H4 - COO Cl H

     NQ Heptyl C6H10 - COO Cl H NO2 Heptyl C6H4 - COO H Cl NO2 Heptyl C6H10 - COO H Cl NO2
Table 1 (continued)
R1 RingA X1 X2 Z3 Y1 Y2
Heptyl C6H4 - - H Cl NO2
Heptyl C6H10 - - H Cl NO2
Heptyl C6H4 - COO Cl Cl NO2
Heptyl C6H10 - COO Cl Cl NO2
Heptyl C6H4 C6H4 COO H H NO2
Heptyl C6H10 C6H4 COO H H NO2
Heptyl C6H4 C6H4 COO Cl H NO2
Heptyl C6H10 C6H4 COO Cl H NO2
Heptyl CH4 C6H4 COO H Cl NO2
Heptyl C6H10 CH4 COO H Cl NO2
Heptyl C6H4 C6H4 COO Cl Cl NO2
Heptyl C6H10 C6H4 COO Cl Cl NO2
Heptyl C6H4 C6H4 COO H H CN
Heptyl C6H10 C6H4 COO H H CN
Heptyl C6H4 C6H4 COO Cl H CN
Heptyl C6H10 CH4 COO Cl H CN
Heptyl C6H4 - COO H F CN
Heptyl C6H4 - COO C1 F CN
Heptyl C6H4 - COO C1 CH3 CN
Heptyl C6H4 - - H

   F CN
Heptyl C6H4 - - H CH3 CN
Heptyl C6H4 C6H4 COO H F CN
Heptyl C6H4 C6H4 COO Cl F CN
Heptyl C6H4 C6H4 COO Cl CH3 CN
Heptyl C6H4 - COO H Cl CH = C (CN) 2
Heptyl C6H4 - COO Cl Cl CH = C (CN) 2
Heptyl C6H4 - - H Cl CH = C (CN) 2
HeptylH4 C6H4 COO H Cl CH = C (CN) 2
Heptyl C6H4 C6H4 COO Cl Cl CH = C (CN) 2
According to the invention, the compounds of the formula I can be prepared by adding an acid of the general formula
EMI5.1
 wherein R1, A, B, X1, X2, Z1, Z2 and Z3 have the meanings given in formulas, or a reactive derivative thereof with a phenol of the general formula
EMI5.2
 wherein yl and Y2 have the meaning given in formula I, esterified.

  If desired, a compound of the formula I obtained, in which Z1, Z2 or Z3 is bromine, can be reacted with copper (I), sodium or potassium cyanide.



   The esterification of an acid of formula III or a reactive derivative thereof (e.g. acid chloride or -anydride) with a phenol of formula IV can be carried out according to methods known per se. A preferred method is the reaction of the acid chloride (which can be obtained from the acid of the formula III, for example by heating with thionyl chloride) with the phenol of the formula IV. This reaction is advantageously carried out in an inert organic solvent, such as, for example, diethyl ether, tetrahydrofuran, Dimethylformamide, benzene, toluoyl, cyclohexane, carbon tetrachloride and the like. In order to bind the hydrogen chloride liberated in the reaction, it is expedient to use an acid binder, for example tertiary amines, pyridines and the like.

  The acid binder is preferably used in large excess so that it can simultaneously serve as a solvent.



  Temperature and pressure are not critical and atmospheric pressure and a temperature between room temperature and the boiling temperature of the reaction mixture are generally used.



   In this way, it is also possible in principle to obtain the compounds of the formula I in which Z1, Z2 or Z3 is cyano. In this case, however, the corresponding bromine compound of the formula I is preferably first prepared (as described above) and then the bromine compound is reacted in a manner known per se with copper (I), sodium or potassium cyanide to give the cyano compound.



  This reaction is conveniently carried out in an inert organic solvent, for example in ethylene glycol, tetrahydrofuran, N-methylpyrrolidone, dimethylformamide, dimethyl sulfoxide, pyridine or acetonitrile. The reaction with copper (I) cyanide in dimethylformamide is preferred. Temperature and pressure are not critical issues in this reaction. Amospheric pressure and a temperature between room temperature and the boiling temperature of the reaction mixture are expediently used.



   The compounds of the formula IV, in which Y2 denotes 2,2-dicyanovinyl, can be prepared, for example, by reacting 3-yl anisole by Vilsmeier reaction with dimethylformamide in the presence of phosphorus oxychloride to give 4-methoxy-2-yl-benzaldehyde, then hydrolyzed the methoxy group (e.g. by refluxing with pyridinium chloride and then fractional distillation) and finally the 4-hydroxy-2-yl-benzaldehyde obtained by Knoevenagel condensation with malonitrile (e.g. in the presence of catalytic amounts of glacial acetic acid and sodium acetate in boiling toluene) in the compound of formula IV, wherein Y2 is 2,2-dicyanovinyl. The other compounds of formula IV are known or analogs of known compounds.



   The compounds of the formula III are likewise known or analogs of known compounds and can be prepared by known methods.



   The compounds of the formula III in which X2 denotes the ester group -COO- can be prepared, for example, by using a compound of the general formula
EMI6.1
 wherein X1 denotes a single covalent bond, the ester group -CO, the ethylene group -CH2CH2- or p-phenylene and R1, A, B, Z1 and Z2 have the meanings given in formula I, in methylene chloride in the presence of dicyclohexylcarbodiimide and 4- (dimethylamino ) esterified pyridine with 4-hydroxy-2-Z3benzaldehyde and converted the aldehyde obtained by Jones oxidation with chromic acid and sulfuric acid into the corresponding acid of formula III.



   In the preparation of the acids of the formula III, in which X is the ethylene group -CH2CH2- and X2 are a simple covalent bond, and the acids of the formula V, in which X1 is the ethylene group -CH2CH2-, the rings A and B are advantageously linked by fouquet Schlosser reaction or by Wittig reaction. For example, 4- (bromomethyl) -2-Z2-benzonitrile, 4 '- (bromomethyl) -4-biphenylcarbonitrile or trans-4- (tosyloxymethyl) cyclohexane carbonitrile in the presence of dilithium tetrachloromorphate with (4-R1 -2-Z1-phenyl) methylmagnesium - Bromide or (trans-4-R1-cyclohexyl) methylmagnesium bromide reacted and the nitrile obtained is hydrolyzed to the desired acid.

  Furthermore, for example, 4-R1 2-Zl-benzaldehyde or trans-4-R1 -cyclohexanecarboxaldehyde in the presence of a base (e.g. sodium methylate) with (4 methoxy-carbonyl-3-Z2-phenyl) methyl-triphenylphosphonium bromide (where Z1 and Z2 is hydrogen, fluorine, cyano or methyl) unset, then the double bond is catalytically hydrogenated and finally the ester group is saponified.



   The starting materials required for these reactions are known or can be prepared by methods known per se. For example, 4-alkoxy-2 Zl-acetophenone can be converted into 4-alkoxy-2-Zl-benzoic acid by haloform degradation and this can be converted into 4-alkoxy-l- (bromine) by reduction with lithium aluminum hydride and bromination (e.g. with tetrabromomethane and triphenylphosphine) methyl) -2-Z1 -benzene are transferred. From methyl 2,4-dimethylbenzoate, for example by reaction with N-bromo-succinimide and subsequent isomer separation, methyl 4- (bromomethyl) -2-methylbenzoate can be obtained, which is analogous to Org. Synth.



  Coll. V. 825 can be converted to 4-formyl-2-methylbenzoic acid methyl ester; the methyl 4-alkyl-2-methylbenzoic acid obtained after reaction with alkyltriphenylphosphonium bromide and base and subsequent catalytic hydrogenation of the double bond can then be saponified with sodium hydroxide solution to give the acid or reduced with lithium aluminum hydride to the alcohol, which is finally hydrogenated to 4-alkyl-1 - (Bromomethyl) -2-methylbenzene or with manganese dioxide can be further converted to 4-alkyl-2-methylbenzaldehyde. 1-Alkyl-3-fluorobenzene can be converted into 4-alkyl-2-fluorobenzoic acid, for example by reaction with butyllithium and carbon dioxide and subsequent hydrolysis, and l-alkyl-3-chlorobenzene or

   l-Alkyl-3-bromobenzene can be converted into 4-alkyl-2- (chloro or bromo) benzoic acid by Friedel Crafts acylation with acetyl chloride in the presence of aluminum trichloride and subsequent oxidation with sodium hypobromite; the acids obtained can then be further reacted with lithium aluminum hydride to form the alcohol and this with hydrogen bromide to form the bromide or with manganese dioxide to form the aldehyde. Furthermore, for example, 4-methyl-2-Z1-benzoic acid can be reacted in succession with thionyl chloride, ammonia and benzenesulfonyl chloride and the 4-methyl-2-Z1-benzonitrile obtained with N-bromosuccinimide to give 4- (bromomethyl) -2-Zl- benzonitrile to be implemented further.



   The compounds of formula I can be used in the form of mixtures with other liquid-crystalline or non-liquid-crystalline substances, such as. B. with substances from the classes of the Schiff bases, azoxybenzenes, or azo, phenyl benzoates, and Cyclohexancarbonsäurephenylester -cyclohexylbiester, cinnamic acid derivatives, Biund terphenyls, phenylcyclohexanes, Cyclohexylphenyle, phenyl and diphenylpyrimidines, Cyclohexylphenylpyrimidine, Phenyldioxane, 2-cyclohexyl-l-phenyläthane and the like . Such substances are known to the person skilled in the art and many of them are also commercially available.

 

   However, the compounds according to the invention are preferably used as components of liquid-crystalline dielectrics which are controlled by the two-frequency method. These liquid-crystalline mixtures are preferably characterized in that they consist of 3 components A, B and C, which each contain one or more compounds, and that component A has a viscosity of at most about 40 cp, a clearing point of at least about 40 ° C. and one has dielectric anisotropy between approximately -2 and approximately +1,

   Component B has a dielectric anisotropy below approximately -2, component C has a dielectric anisotropy above approximately +10, a clearing point of at least approximately 100 ° C. and a cross-over frequency in the total mixture of at most approximately 15 kHz at 20 ° C., and that Component C contains at least one compound of formula I.



   Mixtures of this type preferably consist of at least about 30% by weight of component A, about 3-50% by weight of component B and about 5-40% by weight of component C and particularly preferably of about 30-87% by weight of component A. , about 3-40% by weight of component B and about 10-30% by weight of component C. The proportion of compounds of the formula I in the total mixture is advantageously at least about 1% by weight and preferably at least about 5% by weight .



   Compounds and mixtures with the properties required above for components A, B and C are known in principle to the person skilled in the art. The overall mixture must have nematic or cholesteric properties. Component A can be nematic or cholesteric and component C nematic, cholesteric or - as long as the total mixture does not become smectic - also smectic. Components A and C must have at least monotropic liquid crystalline properties.



  However, preference is given to those mixtures in which at least component C is enantiotropically liquid-crystalline, and particular preference is given to those mixtures in which component A and C are enantiotropic liquid-crystalline.



  Individual compounds in the mixtures and component B according to the invention can, however, be liquid-crystalline or non-liquid-crystalline, although care should be taken in the latter case that the mesophase range of the overall mixture is not restricted too much.



   Compounds and mixtures which are suitable as component A are known in large numbers and in many cases are also commercially available. The following compounds or mixtures thereof are particularly suitable:
EMI7.1
  
EMI8.1
 wherein R3 and R4 represent straight-chain alkyl groups with 1 to 8 carbon atoms, R5 denotes a straight-chain alkyl or alkoxy group with 1 to 8 carbon atoms and n is 1 or 2;

  R6 trans-4-alkylcyclohexyl, 4'-alkyl
4-biphenylyl, p- (trans-4-alkylcyclohexyl) phenyl, 2- (trans-4-
Represent alkylcyclohexyl) ethyl or p- [2- (trans-4-alkylcyclohexyl) ethyl] phenyl and R7 trans-4-alkylcyclohexyl, or R6 trans-4-alkylcyclohexyl and R7 p- (trans4-alkylcyclohexyl) phenyl, p- [ Represent 2- (trans-4-alkylcyclohexyl) ethyl] phenyl or 4 '- (trans-4-alkylcyclohexyl) -4-biphenylyl, or R6 p-alkylphenyl and R7 p- [2- (trans-4-alkylcyclohexyl) ethyl ] represent phenyl, and the alkyl radicals in the
Substituents R6 and R7 straight-chain groups with 1 to 7
Denote carbon atoms; m represents the number 0 or 1;

   one of groups X3 or X4 is an ester group -COO- or -OOC- and the rest of groups X3,
X5 and X6 mean a simple covalent bond, or one of these groups also means the ethylene group -CH2CH2-; the rings A1 and A5 form a group of the formula
EMI8.2
 or designate trans-1,4-cyclohexylene; the rings A2, A3 and A4 are a group of the formula XIX or, if they are not linked to at least one of the other two of these rings by a simple covalent bond, also trans
Represent 2,4-cyclohexylene;

  Y3 is hydrogen or on one of the rings of the formula XIX, which is not linked to a further ring via a simple covalent bond, also means fluorine, chlorine or methyl; and R11 and R'2 straight-chain alkyl having 1 to 7 carbon atoms or on a ring of the formula XIX also straight-chain alkoxy
Denote 1 to 7 carbon atoms.



   The compounds of the formulas VII, IX and XV-XVIII and in particular the compounds of the formula VI are particularly preferably used.



   Compounds which are suitable for or as component B are, for example, pyridazine derivatives, such as, for. B. that in Z. Chemie 17, 333 (1977), J. Prakt. Chemie, 151, 221 (1938), Z. Chemie 6, 467 (1966) and Mol. Cryst. Liq. Cryst. 25, 299 (1974) mentioned phenyl- and diphenylpyridazines, and in particular the compounds described in German Offenlegungsschriften 2933 563 and T937 700, which have two lateral cyano groups on a benzene ring.

  Particularly preferred compounds are the dicyanophenyl esters of the general formula
EMI9.1
 wherein R3 and R4 represent straight-chain alkyl groups having 1 to 8 carbon atoms and ring C denotes p-phenylene or a trans-1,4-disubstituted cyclohexane ring, and the cyclohexylpyridazines of the general formula
EMI9.2
 wherein R8 represents a straight-chain alkyl group with 1 to 12 carbon atoms, R9 represents an alkyl, alkoxy, p-alkylphenyl, p-alkoxyphenyl or trans-4-alkylcyclohexyl group and the alkyl and alkoxy radicals in R9 straight-chain radicals with 1 are up to 10 carbon atoms.



   In the case of non-liquid-crystalline components, the above-mentioned dielectric anisotropy of component B means the extrapolated value (from liquid-crystalline mixtures which contain this component) of the dielectric anisotropy at a temperature which is 10 ° C. below the extrapolated (virtual) clearing point For example, the pyridazines mentioned have dielectric anisotropies of around -9.



   For or as component C, for example, compounds with 3 or 4 p-phenylene or trans-1,4 cyclohexylene groups, a polar end group and optionally a lateral halogen or cyano substituent are suitable.



  Such compounds are known in some cases and, for example, in Mol. Cryst. Liq. Cryst. 63, 129 (1981) and German Offenlegungsschriften 2 736 772, 2 752975 and 3 046 872.



   The compounds of formula I above and in particular the compounds of formula I mentioned as preferred have now proven to be particularly suitable compounds for component C. These compounds have large nematic or cholesteric mesophases with high clearing points, good solubility and cross-over frequencies which are generally well below 10 kHz. Furthermore, they have a large positive dielectric anisotropy at frequencies below the cross-over frequency and a large negative dielectric anisotropy at frequencies above the cross-over frequency. These properties enable, in particular, higher multiplex rates and lower energy consumption when operating display devices using the two-frequency method.



   In addition to the compounds of the formula I, compounds of the general formula are also particularly suitable for component C.
EMI9.3
 in which R2 denotes hydrogen, fluorine, chlorine, bromine or the cyano group, Y4 represents 2,2-dicyanovinyl, 2,2-dicyano-methylvinyl or cyano, R10 and E together p-R10-phenyl, trans-4-R10-cyclohexyl, 4'-R1 0-4-biphenylyl, p- (trans-4R1-cyclohexyl) phenyl, p - (- 5-R1 0-2-pyrimidinyl) phenyl, p- [2- (p'-R10 - Phenyl) ethyl] phenyl, p- [2- (trans-4 Rl -cyclohexyl) ethyl] phenyl, trans-4 [2- (p-R1-phenyl) - ethyl] cyclohexyl or trans-4- [2- ( means trans-4-R10-cyclohexyl) ethyl] -cyclohexyl,

   and R10 is a straight chain alkyl group of 1 to 12 carbon atoms or on one
Benzene ring also a straight chain alkoxy group with 1 to 12
Designated carbon atoms.



   These connections also have large nematic
Mesophase ranges, low cross-over frequencies and large absolute dielectric anisotropies.



   Mixtures according to the invention with cross-over
Frequencies of at most about 10 kHz at 20 C are preferred and those with cross-over frequencies of at most about 5 kHz are particularly preferred.



   The mixtures according to the invention can also contain optically active compounds, for example optically active biphenyls, and / or dichroic dyes, for example azo, azoxy or anthraquinone dyes (depending on the properties as components of components A, B and C). The proportion of such compounds is determined by the solubility, the desired pitch, color, extinction and the like. The proportion of optically active compounds is preferably at most about 4% by weight and the proportion of dichroic dyes is at most about 10% by weight in the total mixture.

 

   The liquid-crystalline mixtures according to the invention can be prepared in a manner known per se, e.g. B. by heating a mixture of the ingredients to a temperature just above the clearing point and then cooling.



   The manufacture of an electro-optical device containing a mixture according to the invention can also be carried out in a manner known per se, e.g. B. by evacuating a suitable cell and introducing the mixture into the evacuated cell.



   The compounds of formula XVII are new. They can be prepared using the following reaction schemes 1 and 2, in which R15 is trans-4-alkylcyclohexyl, 4'-alkyl-4-biphenylyl, p- (trans-4-alkylcyclohexyl) phenyl or 2trans-4-alkylcyclohexyl) ethyl and R16 represent trans-4-alkylcyclohexyl, or R15 trans-4-alkylcyclohexyl and R16 p- (trans-4-alkylcyclohexyl) phenyl, p- [2- (trans-4-alkylcyclohexyl) ethyl] phenyl or 4 '- (trans Represent -4-alkylcyclohexyl) -4biphenylyl, or R15 represent p-alkylphenyl and R '6 represents p- [2- (trans-4-alkylcyclohexyl) ethyl] phenyl, and R13 and R14 and the alkyl groups in the substituents R15 and R16 denote straight-chain alkyl radicals having 1 to 7 carbon atoms.



  Scheme 1
EMI10.1


 <tb> <SEP> R <SEP> 15 <SEP> < <SEP> C <SEP> N
 <tb> <SEP> CH (3I,] <SEP> A1H
 <tb> <SEP> 1
 <tb> <SEP> Rl5 <SEP> 4 <SEP> C <SEP> H <SEP> O
 <tb> <SEP> 4 / <SEP> XXVI <SEP> I
 <tb> <SEP> 4 <SEP> XXVII
 <tb> <SEP> R15t <SEP> CH20H
 <tb> <SEP> XXVIII <SEP> \ Br4, <SEP> P <SEP> (C6H5) <SEP> 3
 <tb> <SEP> R15 <SEP> CH26r
 <tb> <SEP> XXIX
 <tb> R15OH2- <SEP> CH2 <SEP> P <SEP> (C6H5) <SEP> 3
 <tb> <SEP> i5
 <tb> <SEP> XXX <SEP> \ 2 <SEP> ( <SEP> 3) <SEP> (CH), 02CH,

    <SEP> (CH3) <SEP> 3 (2OCH3
 <tb> <SEP> 16
 <tb> <SEP> R15 <SEP> O <SEP> H = C <SEP> C <SEP> H <SEP> - <SEP> C <SEP> H <SEP> - <SEP> R <SEP> 16
 <tb> <SEP> XXXI
 <tb> <SEP> H ,, Pd
 <tb> <SEP> toliol / ethanol
 <tb> <SEP> R'L5¯ \ - "" '""' <SEP> "" <SEP> I
 <tb> <SEP> XVII <SEP> A
 <tb> Scheme 2
EMI11.1
  
The compounds of formula R16 -CHO in Scheme 1 can be obtained in a simple manner from known compounds, e.g. the trans-4-alkylcyclohexane carboxaldehydes by Rosenmund reduction of the corresponding acid chlorides and the other compounds by reduction of the corresponding cyano compounds.



   By reacting the compound of the formula XXXIV with Grignard reagents according to Scheme 2, compounds of the formula XXXV or directly compounds of the formula XXIIIB, in which R13 and R14 have the same meaning, can be obtained. When using at least about 2 moles of Grignard reagent per mole of the compound of formula XXXIV, a compound of formula XXIIIB is generally predominantly formed directly.



   The esters of formula XVIII are also new. They can be obtained by esterification methods known per se (for example in an analogous manner to the preparation of the compounds of the formula I). The starting materials required here are known or analogs of known compounds and can be prepared by known methods.



   The compounds of formula XXI are also new.



  They can be prepared in a manner known per se by a) for preparing the compounds of the formula XXI, in which
R9 represents an alkyl, p-alkylphenyl, p-alkoxyphenyl or trans-4-alkylcyclohexyl group, a compound of the general formula
EMI12.1
 wherein R17 represents an alkyl, p-alkylphenyl, p-alkoxyphenyl or trans-4-alkylcyclohexyl group, the alkyl and alkoxy radicals in R'7 are straight-chain radicals having 1 to 10 carbon atoms and R8 has the meaning given above, or a tautomeric dihydropyridazine oxidized (e.g.

  B. with 2,3 dichloro-6,6-dicyano-p-benzoquinone in dioxane, with sodium nitrite in glacial acetic acid and ethanol, with isopentyl nitrite in glacial acetic acid or preferably by catalytic dehydrogenation with palladium, platinum and the like), or b) for the preparation of Compounds of formula XXI, wherein
R9 represents an alkoxy group, a compound of the general formula
EMI12.2
 where X7 denotes chlorine or bromine and R8 has the meaning given above, is reacted with an alkali metal alcoholate (e.g. sodium methylate).



   The compounds of the formula XXXVI can rearrange to tautomeric compounds by migration of the double bonds in the dihydropyridazine ring. Such rearrangements can e.g. can be triggered by the presence of a trace of acid or base. However, since the tautomeric dihydropyridazines can also be oxidized to compounds of the formula XXI under the above conditions, according to process variant a) both a compound of the formula XXXVI and a tautomeric dihydropyridazine or a mixture of such compounds can be reacted.



   The starting materials of formulas XXXVI and XXXVII are new. They can be prepared using the following Reaction Schemes 3-6, wherein R8, R17 and X7 have the above meanings and R18 represents a straight chain alkyl or alkoxy group with 1 to 10 carbon atoms.



   Scheme 3
EMI12.3
   Scheme 4
EMI13.1


 <tb> R8 <SEP> ¯ <SEP> X <SEP> - <SEP> COCH2CH2C1 <SEP> XXXIX
 <tb> <SEP> KCN
 <tb> R83 <SEP> COCH2CH2CN <SEP> XLIII
 <tb> <SEP> 1) <SEP> 1) <SEP> OH <SEP> e
 <tb> <SEP> 2) <SEP> H30
 <tb> <SEP> R8COCH2CH2COOH <SEP> XXXXIV
 <tb> <SEP> | <SEP> H2NNH2-H20
 <tb> <SEP> R8 <SEP> NCN <SEP> =
 <tb> <SEP> N
 <tb> <SEP> Br2 / glacial acetic acid
 <tb> RB <SEP> VLI
 <tb> <SEP> PO (X7) 3
 <tb> <SEP> 8 / \ X7 <SEP> XXXVII
 <tb> <SEP> N = N
 <tb> Scheme 5
EMI14.1
   Scheme 6
EMI15.1


 <tb> <SEP> 7 <SEP> 17
 <tb> <SEP> X <SEP> -;

   <SEP> O-R
 <tb> <SEP> \ <SEP> A1C13,
 <tb> <SEP> LII <SEP> A1C1.1
 <tb> <SEP> CHZ'CHZ
 <tb> <SEP> C <SEP> HIGH <SEP> CHOH <SEP> 2 <SEP> -CH2CH2-CO-R17
 <tb> <SEP> 2 <SEP>) <SEP> Mg <SEP> / <SEP> LIII
 <tb> <SEP> '2) <SEP> Mg
 <tb> <SEP> 7Mg-CH
 <tb> <SEP> 7
 <tb> X7Mg-CH2CH2 <SEP> R
 <tb> <SEP> LIV <SEP> RBICOCI <SEP> XXXVIII
 <tb> <SEP> THF, <SEP> -780C
 <tb> <SEP> O <SEP> O
 <tb> <SEP> 8
 <tb> <SEP> R8 <SEP> O0OH2OH <SEP> R <SEP> LV
 <tb> <SEP> R17 <SEP> LV
 <tb> <SEP> acetone / H20
 <tb> <SEP> R8 <SEP> 9 <SEP> COCH2CH2CO-R17 <SEP> XLII
 <tb> <SEP> H2NNH2'H20
 <tb> <SEP> 8 <SEP> I
 <tb> <SEP> R <SEP> MM <SEP> R17 <SEP> XXXVI
 <tb>
The starting substances of the formulas XXXVIII, XLI,
VLII, LI and LII are known or analogs of known compounds and can be prepared in a known manner.

  For example, the aldehydes of the formula LI can be prepared by Rosenmund reduction of the acid chlorides of the formula XXXVIII.



   The addition of an aldehyde to a compound of
Formula XL, VLIII or L can be carried out by the method of Stet ter (Chem. Ber. 114 (1981) 581) in the presence of a 1,3-thiazolium salt catalyst. A preferred catalyst for the addition of an aldehyde of the formula LI or an aldehyde of the formula XLI, in which R17 is alkyl or trans-4-alkylcyclohexyl, is 3-benzyl-5- (2-hydroxyethyl) -4-methyl-1,3 -thiazolium chloride and for the addition of an aldehyde of the formula XLI, in which R1 is 7 p-alkylphenyl or p-alkoxyphenyl, 3, 4-dimethyl-5- (2-hydroxyethyl) -1,3-thiazolium iodide.



   The coupling of a compound of the formula LIV with a compound of the formula XXXVIII can be carried out according to that of T.



  Sato et al. in Bull. Chem. Soc. japan 54 (1981) 505 described method.



   As already mentioned above, the compounds of the formula XXXVI can also be present in tautomeric form or as a mixture of tautomeric forms.



   Some of the compounds of the formula XXII are also new compounds. They can be prepared in an analogous manner to the compounds of formula I by esterification. The acids required here can be obtained using reaction scheme 7, in which R2, R10 and E have the meanings given in formula XXII above:

  : Scheme 7
EMI16.1


 <tb> <SEP> 2
 <tb> <SEP> 10 <SEP> -COO- <SEP> H <SEP> 0
 <tb> R <SEP> -E-OOOH <SEP> E <SEP> HO
 <tb> <SEP> XXIII <SEP> - <SEP> XXIV
 <tb> <SEP> 4- (dimethylamino) pyridine,
 <tb> <SEP> N, N'-dicyclohexylcarbodiimide
 <tb> <SEP> 2
 <tb> <SEP> 10 <SEP> E <SEP> - <SEP> COO <SEP> CHO <SEP> XXV
 <tb> <SEP> H2S04, <SEP> H2CrO4
 <tb> <SEP> Jones oxidation
 <tb> <SEP> R2
 <tb> <SEP> R10 <SEP> E <SEP> - <SEP> COO <SEP> OOOH <SEP> LVI
 <tb>
The compounds of the formulas XXIII and XXIV are known or can be prepared by methods known per se.



      In the following mixtures and synthesis examples, C means a crystalline phase, N a nematic, Ch a cholesteric and I the isotropic phase. fc denotes the crossover frequency, Ael the low-frequency (static) dielectric anisotropy (measured at frequencies that are significantly below the coss-over frequency), Ash the high-frequency dielectric anisotropy (measured at frequencies that significantly above the cross-over Frequency) and the viscosity (bulk viscosity).



   The following mixing examples are examples of preferred mixtures according to the invention which are suitable for control by the two-frequency method.



  The assignment of the individual components of the overall mixtures to components A, B and C results from the above information.



   Mixing example 1 11.4% by weight of trans-4-butylcyclohexane carboxylic acid p äthoxy-phenyl ester,
16.0% by weight of p-pentyloxy-phenyl trans-4-butylcyclohexane, 10.3% of p-methoxy-phenyl trans-4-pentylcyclohexane,
12.4% by weight of trans-4-pentylcyclohexane carboxylic acid propyloxyphenyl ester,
7.0% by weight of 2- (trans-4-pentylcyclohexyl) -1- (p-ethoxyphenyl) ether,
2.8 wt.

   % 3-propyl-6- (trans-4-ethylcyclohexyl) pyridazine,
6.9% by weight of 3-propyl-6- (trans-4-pentylcyclohexyl) pyriazine,
4.4% by weight of 3-propyl-6- (trans-4-heptylcyclohexyl) pyriazine,
8.8% by weight of 3-pentyl-6- (trans-4-pentylcyclohexyl) pyriazine,
10.0% by weight of 4'-hexyl-4-biphenylcarboxylic acid-3-chloro-4 [(3-chloro-4-cyanophenoxy) carbonyl] phenyl ester,
10.0% by weight of 4'-heptyl-4-biphenylcarboxylic acid-3-chloro-4 [(3-chloro-4-cyanophenoxy) carbonyl] phenyl ester;
M.p. (C-N) <0 C, clp. (N-I) 73 C; fc (22 C) =
3.4 kHz, ## 1 (22 C3 = 8.24, Ash (22 C) = -4.48; # (22 C) = 73 cP.



   Mixing example 2 10.0% by weight of trans-4-butylcyclohexanecarboxylic acid, p ethoxy-phenyl ester, 14.0% by weight of trans-4-butylcyclohexanecarboxylic acid, p pentyloxy-phenyl ester, 9.0% by weight, trans-4-pentylcyclohexanecarboxylic acid, p methoxy phenyl ester, 10.9% by weight trans-4-pentylcyclohexane carboxylic acid propyloxyphenyl ester,
6.1% by weight of 2- (trans-4-pentylcyclohexyl) -1- (p-ethoxyphenyl) -athan,
4.0% by weight of 3-propyl-6- (trans-4-ethylcyclohexyl) pyriazine,
9.6% by weight of 3-propyl-6- (trans-4-pentylcyclohexyl) pyriazine,
6.1% by weight of 3-propyl-6- (trans-4-heptylcyclohexyl) pyriazine,
12.3% by weight of 3-pentyl-6- (trans-4-pentylcyclohexyl) pyriazine,
6.0% by weight of 4'-heptyl-4-biphenylcarboxylic acid-3-chloro-4 [(3-chloro-4-cyanophenoxy) carbonyl] phenyl ester,
6.0% by weight of 4'-hexyl-4-biphenylcarboxylic acid-3-chloro-4

   [(3-chloro-4-nitrophenoxy) carbonyl] phenyl.



   ester,
6.0% by weight 4'-heptyl-4-biphenylcarboxylic acid 3-chloro [(3-chloro-4-nitrophenoxy) carbonyl] phenyl ester;
M.p. (C-N) <0 C, clp. (N-I) 63 C.



   Mixture example 3
10.2% by weight of trans-4-butylcyclohexane carboxylic acid p-pentyloxy-phenyl ester, 14.3% by weight of trans-4-butylcyclohexane-carboxylic acid p-pentyloxy-phenyl ester,
9.2% by weight of trans-4-pentylcyclohexanecarboxylic acid p-methoxy-phenyl ester, 11.1% by weight of trans-4-pentylcyclohexanecarboxylic acid-p-propyloxy-phenyl ester,
6.2% by weight of 2- (trans-4-pentylcyclohexyl) -1- (ethoxyphenyl) ether,
9.1% by weight - (trans-4-propylcyclohexyl) benzene,
2.6% by weight of 3-propyl-6- (trans-4-ethylcyclohexyl) pyrizine,
6.3% by weight of 3-propyl-6- (trans-4-pentylcyclohexyl) pyrizine,
4.0% by weight of 3-propyl-6- (trans-4-heptylcyclohexyl) pyrizine,
8.0% by weight of 3-pentyl-6- (trans-4-pentylcyclohexyl) pyridazin,
4.5% by weight of 4'-heptyl-4-biphenylcarboxylic acid 3-chloro [(p-cyanophenoxy) carbonyl] phenyl ester,

   
4.5% by weight of p- [2- (trans-4-heptylcyclohexyl) ethyl] benzoic acid 3-chloro-4 - [(p-cyanophenoxy) carbonyl] phenyl ester,
3.6% by weight of p- [2- (trans-4-heptylcyclohexyl) ethyl] benzoic acid-3-chloro-4 - [(p- (2,2-dicyano-1-methylvynyl) phenoxy) carbonyl phenyl ester,
6.4% by weight 4'-heptyl-4-biphenylcarboxylic acid 3-chloro [(3-chloro-4-cyanophenoxy) carbonyl] phenyester;
M.p. (C-N) <0 C, clp. (N-I) 70 C; fc (22 C) = 3 kHz, AEI (22 C) = 4.39, Ash (22 C) = -4.0.



   The following examples further illustrate the preparation of the compounds according to the invention.



   example 1
11.4 g of 2-chloro-4 - / [p- (p-hexylphenyl) benzoyl] oxy / benzoic acid were heated to boiling with 5.35 g of thionyl chloride in 100 ml of benzene for 2.5 hours. Solvent and excess thionyl chloride were distilled off in vacuo and the residue was taken up twice in 50 ml of toluene and concentrated.



   The crude 2-chloro-4 - / [p- (p-hexylphenyl) benzoyl] oxy / benzoic acid chloride obtained was dissolved in 125 ml of benzene and then to a solution of 4.0 g of 3-chloro-4-cyanophenol in 100 ml Dropped pyridine. The reaction mixture was stirred at a bath temperature of 65 ° C. overnight, then poured onto ice-cold, dilute hydrochloric acid and extracted with diethyl ether. The extract was washed several times with 3N hydrochloric acid, then washed neutral with water, dried and evaporated. The crude 4 'hexyl-4-biphenylcarboxylic acid-3-chloro-4 - [(3-chloro-4-cya phenoxy) -carbonyl] phenyl ester obtained was chromatographed 1: 1 on silica gel using toluene / dichloromethane. The fractions (8.2 g), which were practically pure after thin layer chromatography, were recrystallized once from ethyl acetate and once from ethyl acetate and a little hexane; M.p. (C-N) 95C, bp. (N-I) 235 C.

 

   The 2-chloro-4 - / [p- (p-hexylphenyl) benzoyl] oxy / benzoic acid used as starting material was prepared as follows: a) to a mixture of 42.5 g of 4'-hexyl-4-biphenylcarboxylic acid, 23.5 g of 2-chloro-4-hydroxybenzaldehyde and 1.5 g of 4 (dimethylamino) pyridine in 1500 ml of dichloromethane were added in portions over a period of 10 minutes to 37.2 g of N, N'-dicyclohexylcarbodiimide. The reaction mixture was stirred for 3 hours at room temperature and then the precipitated N, N'-dicyclohexylurea was filtered off with suction. The filtrate was washed twice with 200 ml of 2N sodium hydroxide solution and four times with 200 ml of water, dried over sodium sulfate, filtered and concentrated.



   b) The crude 2-chloro-4 - / [p- (p-hexylphenyl) benzoyl] oxy / benzaldehyde obtained (67.1 g) was dissolved in 2500 ml of acetone. 80 ml of Jones reagent were added dropwise to this solution in the course of 45 minutes, during which the mixture warmed slightly. The reaction mixture was stirred for a further 3 hours, then the precipitated inorganic material was filtered off with suction and the acetone was distilled off on a rotary evaporator. The residue was slurried in water and the suspension was sucked. The crude 2-chloro-4 - / [p (p-hexylphenyl) benzoyl] oxy / benzoic acid obtained was washed neutral on the suction filter with water, then boiled for cleaning with methanol, filtered off after cooling and dried. Yield 58.5 g; 163.8-165.5 "C.



   The following compounds were prepared in an analogous manner: 4'-heptyl-4-biphenylcarboxylic acid-3-chloro-4 - [(3-chloro-4-cyanophenoxy) carbonyl] phenyl ester; M.p. (C-N) 95C, bp. (N-I) 229 4'-heptyl-4-biphenylcarboxylic acid p - [(3-chloro-4 cyanophenoxy) carbonyl] phenyl ester; M.p. (C-N) 112C, bp. (N-I) 289 C.



     4 '- (Pentyloxy) -4-biphenylcarboxylic acid 3-chloro-4 - [(3-chloro-4-cyanophenoxy) carbonyl] phenyl ester; M.p. (C-N) 115.5C, bp. (N-I) 272 C.



  4'-Heptyl-4-biphenylcarboxylic acid 3-chloro-4 - [(3,4-dicyano phenoxy) carbonyl] phenyl ester; M.p. (C-N) 146 C, bp. (N-I) 211.5 C.



  4'-Heptyl-4-biphenylcarboxylic acid p - [(3,4-dicyanophenoxy) carbonyl] phenyl ester; M.p. (C-N) 162C, bp. (N-I) 266.5 C.



  4'-Pentyl-4-biphenylcarboxylic acid 3-chloro-4 - [(4-nitro-phen oxy) carbonyl] phenyl ester; M.p. (C-N) 124C, bp. (N-I)> 290 C.



  3'-Heptyl-4-biphenylcarboxylic acid 3-chloro-4 - [(4-nitro-phen oxy) carbonyl] phenyl ester; M.p. (C-N) 96.5C, bp. (N-I)> 280 C.



     4'-Hexyl-4-biphenylcarboxylic acid 3-chloro-4 - [(3-chloro-4-nitro-phenoxy) carbonyl] phenyl ester; M.p. (C-N) 94 0C, bp. (N-I) 203 C.



     4'-Heptyl-4-biphenylcarboxylic acid 3-chloro-4 - [(3-chloro-4-nitrophenoxy) carbonyl] phenyl ester; M.p. (C-N) 102.5C, bp. (N-I) 199.5 C.



     4'-Hexyl-4-biphenylcarboxylic acid 3-chloro-4 - [(3-methyl-4-cyanophenoxy) carbonyl] phenyl ester; M.p. (CkN) 110 C, bp. (N-I) 237 C.



     4'-Heptyl-4-biphenylcarboxylic acid 3-chloro-4 - [(3-methyl-4-cyanophenoxy) carbonyl] phenyl ester; M.p. (C-N) 101.5 0C, bp. (N-I) 232 C.



     4'-Hexyl-4-biphenylcarboxylic acid 3-chloro-4 [(3,4-dicyanophenoxy) carbonyl] phenyl ester; M.p. (C-N) 145C, bp. (N-I) 219 C.



   Example 2
A suspension of 2.6 g of 4 "-pentyl-4-terphenyl-4'carboxylic acid in 25 ml of thionyl chloride was heated to boiling for 2.5 hours. The thionyl chloride was then distilled off and the residue was taken up twice in 50 ml of toluene and concentrated.



   The crude 4 "-pentyl-4-terphenyl-4'-carbonyl chloride obtained was dissolved in 50 ml of benzene and then added to a solution of 1.15 g of 3-chloro-4-cyanophenol in 30 ml of pyridine. The reaction mixture was added heated overnight with an oil bath at 70 ° C., then poured onto ice water and extracted with dichloromethane. The extract was washed several times with 3N hydrochloric acid, then washed with 2N sodium carbonate solution and with water, dried and evaporated. The crude 4 "obtained Pentyl-4terphenyl-4'-carboxylic acid-3-chloro-4-cyanophenyl ester was chromatographed on silica gel with toluene / dichloromethane 4: 1. The fractions which were practically pure after thin layer chromatography were recrystallized twice from ethyl acetate: yield 2.3 g; M.p. (C-N) 161C, bp. (N-I) 299 C.



   Example 3
Analogously to Example 1, 2-chloro-4 - / [p (p-heptylphenyl) benzoyl] oxy / benzoic acid and 3-chloro-4 (2,2-dicyanovinylphenol 4'-heptyl-4-biphenylcarboxylic acid 3 - chloro-4 - [(3-chloro-4- (2,2-dicyanovinyl) phenoxy) carbonyl] phenyl ester; mp (CN) 120.5 C, clp (NI) 240.5 C.



   The 3-chloro-4- (2,2dicyanovinyl) phenol used as the starting material was prepared as follows:
A mixture of 3.2 g of 3-chloro-4-hydroxybenzaldehyde, 1.6 g of malonitrile, 0.31 g of ammonium acetate, 0.23 ml of glacial acetic acid and 100 ml of toluene was heated to boiling overnight in a water separator. The reaction mixture was allowed to cool, with some of the product precipitating. The precipitated product was brought back into solution by dilution with diethyl ether. The reaction mixture was then washed with saturated sodium chloride solution, dried over sodium sulfate, filtered and concentrated. The residue was dissolved in hot toluene and the solution filtered. 3.2 g of 3-chloro-4- (2,2-dicyanovinyl) phenol with mp. 161-162 "C. crystallized from the filtrate.



   Example 4
Those compounds of the formula I in which ring A is trans-1,4-cyclohexylene, X1 is the ethylene group -CH2CH2 and ring B is p-phenylene can be prepared analogously to example 1.



   The carboxylic acids used as starting materials can be prepared as illustrated below for p- [2- (trans-4-heptylcyclohexyl) ethyl] benzoic acid:
A solution of 21.3 g of p- [2- (trans-4-heptylcyclohexyl) ethylbenzonitrile and 14.0 g of potassium hydroxide (85%) in 500 ml of ethylene glycol was heated to boiling for 8 hours (bath temperature 210 ° C.). After cooling, the mixture was poured onto water and acidified with 3N hydrochloric acid. The precipitated p- [2- (trans-4-heptylcyclohexyl) ethyl] benzoic acid was filtered off with suction, washed on a suction filter with water and then taken up in diethyl ether. The solution was dried over sodium sulfate and evaporated. 22.9 g of pure product according to thin layer chromatography were obtained; M.p. 184-187 "C, m.p. 220-223" C.



   Example 5
Analogously to Example 1, those compounds of the formula I can be prepared in which ring A is p-phenylene, X1 is the ethylene group -CH2CH2-, ring B is trans-1,4-cyclohexylene and X2 is the ester group -COO.

 

   The trans-4- [2- (p R1-phenyl) ethyl] cyclohexanecarboxylic acids used as starting materials can be prepared as illustrated below using the pentyl compound.



   a) A mixture of 2.51 g (p-pentylphenyl) methyl-triphenylphosphonium bromide and 615 mg of 4-cyanocyclohexane carboxaldehyde (cis / trans mixture approx. 1: 1) in 30 ml of t-butyl methyl ether at 0 ° C. in a sulfonation flask while gassing with argon presented, mixed with 637 mg of solid potassium t-butoxide within 2 minutes and then stirred at 0 C for a further 1.5 hours. Then the red-brown, heterogeneous reaction mixture was poured onto 100 ml of water and extracted three times with 100 ml of diethyl ether. The organic phases were washed twice with 50 ml of water and once with 50 ml of saturated sodium chloride solution, dried over magnesium sulfate and concentrated. The residue was slurried in 150 ml of hexane, the precipitated triphenylphosphine oxide was removed by filtration (washing with hexane) and the filtrate was concentrated.

  Low pressure chromatography (0.4 bar) of the resulting oil (1.36 g) on silica gel with 3% ethyl acetate / petroleum ether as the eluent gave 1.02 g (81%) of 4- [2- (p-pentylphenyl) ethyl] cyclohexane carbonitrile as colorless Oil; Rf values of this isomer mixture (10% ethyl acetate / petroleum ether): 0.27 and 0.36.



   b) 956 mg of the 4- [2- (pentylphenyl) ethenyl] cyclohexanecarbonitrile obtained were dissolved in 50 ml of toluene in a sulfonation flask, 150 mg of palladium / carbon (10%) were added and the mixture was hydrogenated at atmospheric pressure and room temperature until the hydrogen uptake had ceased ( approx. 30 minutes). Filtration of the reaction mixture (washing with toluene), concentration of the filtrate and low pressure chromatography (0.4 bar) of the residue (890 mg) on silica gel with 5% ethyl acetate / petroleum ether gave 788 mg (82%) 4- [2- (p pentylphenyl) ethyl] cyclohexane carbonitrile as viscous, colorless oil. Although only a single spot appeared in the thin-layer chromatogram when using different solvent systems as solvent,

   According to gas chromatographic and NMR spectroscopic analysis, this material was a cis / trans isomer mixture (approx. 1: 3). Double crystallization of this material from pentane at - 20 "C finally gave trans-4- [2- (p pentylphenyl) ethyl] cyclohexane carbonitrile of sufficient purity (according to gas chromatographic analysis 98.8% trans and 1.2% cis-compound); Mp 22.4 "C, clp. (N-I) 14.1 C.



   c) In a round bottom flask with reflux condenser, a mixture of 567 mg of trans-4- [2- (p-pentylphenyl) ethyl] cyclohexane carbonitrile and 20 ml of a 10: 1 mixture of 2N potassium hydroxide solution and ethanol was added for 2 hours under argon gas Reflux heated. The cooled reaction mixture was diluted with 20 ml of water and extracted twice with 30 ml of diethyl ether. The separated aqueous phase was acidified with about 20 ml of 2N sulfuric acid and extracted three times with 50 ml of diethyl ether. The organic phases were washed twice with 50 ml of saturated sodium chloride solution, dried over magnesium sulfate and concentrated.

  490 mg (81%) of trans-4- [2 (p-pentylphenyl) ethyl] cyclohexane carboxylic acid resulted as colorless crystals, which were additionally purified by recrystallization from hexane.



   Example 6
Those compounds of the formula I in which the rings A and B are trans-1,4-cyclohexylene, X1 is the ethylene group -CH2CH2- and X2 is the ester group -COO can be prepared analogously to Example 1.



   The trans-4- [2 (trans-4-alkylcyclohexyl) ethyl] cyclohexanecarboxylic acids used as starting materials can be prepared as illustrated below with the aid of the pentyl compound: a) 3.79 g of lithium aluminum hydride in 100 ml of absolute tetrahydrofuran were initially introduced under gassing with argon and within 30 minutes with a solution of 19.83 g of trans-4 pentylcyclohexane carboxylic acid in 100 ml of absolute tetrahydrofuran. After the addition had ended, the reaction mixture was heated to reflux for 1 hour, then carefully added to 200 ml of 2N hydrochloric acid and extracted three times with 100 ml of diethyl ether each time. The organic phases were washed with 100 ml of saturated sodium carbonate solution, dried over potassium carbonate and concentrated.



  Distillation of the residue (19.2 g) gave 17.7 g (96%) (trans-4-pentylcyclohexyl) methanol as a colorless oil (purity 99.9%) in the main course; Bp 89 C / 0.2 mmHg.



   b) A solution of 3.69 g of (trans-4-pentylcyclohexyl) methanol and 5.51 g of triphenylphosphine in 70 ml of methylene chloride was introduced at - 30 ° C. while gassing with argon, and 7.30 g of solid tetrabromomethane were added in portions within 15 minutes that the internal temperature did not exceed -20 "C. After the addition had ended, the cooling bath was removed and the reaction mixture was stirred for a further 18 hours while gradually warming to room temperature. The mixture was then concentrated on a rotary evaporator and the semicrystalline residue obtained was triturated with 200 ml of warm hexane, filtered and the concentrated filtrate was chromatographed with hexane on a column with silica gel.

  4.79 g (97%) of trans-l- (bromomethyl) -4-pentylcyclohexane resulted as a colorless liquid which was further purified by distillation; Bp 82 "C / 0.08 mmHg.



   c) A mixture of 18.9 g of 1-methoxy-3- (trimethylsilyloxy) -l, 2-butadiene (S. Danishefsky et al., J. Amer. Chem.



  Soc. 96, (1974), 6.4 g of acrylonitrile, 100 mg of dibenzoyl peroxide and 50 ml of benzene was heated to reflux under argon gas for 23 hours. After cooling, the volatile components (benzene and excess acrylonitrile) were removed on a rotary evaporator and the residue is 100 ml of tetrahydrofuran / 1N hydrochloric acid 4: 1 for 2 hours under reflux. The cooled reaction mixture was then extracted three times with 100 ml of methylene chloride. The organic phases were washed twice with 100 ml of water and once with 100 ml of saturated sodium chloride solution, dried over magnesium sulfate and concentrated.

  10.3 g of yellow 01 resulted, which was 87.9% 4-cyano-3-cyclohexen-1-one, 4.1% 4 cyano-2-cyclohexen-1-one and 2.7% consisted of trans-4-cyano3-methoxycyclohexanone (an intermediate hydrolysis product). Kugelrohr distillation (130-140 "C / 0.27-0.15 mmHg) of the oil obtained gave 7.64 g of a mixture of 4-cyano-3-cyclohexen-1-one and 4-cyano-2-cyclohexene 1 - on as an orange, crystallizing 01. This was dissolved in 70 ml of ethanol and hydrogenated in the presence of 764 mg of 10% palladium / carbon at atmospheric pressure (hydrogen absorption 1425 ml).

  After filtering off the catalyst, washing with methylene chloride, concentrating the filtrate and bulb tube distillation (130-150 "C / 0.11 mmHg), 5.45 g (70%) of 4-cyanocyclohexanone was obtained as a colorless oil; Rf value (toluene / ethyl acetate 3: 1) 0.25.



   d) 9.6 g of triphenyl (methoxymethyl) phosphonium chloride were slurried in 50 ml of t-butyl methyl ether while gassing with argon, and 3.39 g of solid potassium t-butoxide were added in portions at -10 ° C. After the addition had ended, the mixture was stirred at 0 for a further 30 minutes stirred to 5 "C and then the deep orange, partially heterogeneous reaction mixture was added dropwise within 10 minutes with a solution of 2.30 g of 4-cyanocyclohexanone in 20 ml of t-butyl methyl ether. The internal temperature should not exceed 5 ° C. When the addition was complete, the now yellow-orange reaction mixture was heated to 25 ° C. and stirred for a further 2 hours.

  Then 50 ml of a 2% sodium hydrogen carbonate solution were added and the separated aqueous phase was extracted twice with 50 ml of diethyl ether.



  The organic phases were washed with 50 ml of saturated sodium chloride solution, dried over potassium carbonate and concentrated. The remaining, semi-crystalline, orange oil was triturated with 400 ml of hexane, cooled to −20 ° C. and freed from the precipitated triphenylphosphine oxide by filtration (rinsing with cold hexane). Low pressure chromatography (0.4 bar) of the concentrated residue on silica gel using 10 % Ethyl acetate / petroleum ether as eluent gave 1.60 g (56%) of 4- (methoxymethylene) cyclohexane carbonitrile as a colorless oil (purity 97%).



   e) The 4- (methoxymethylene) cyclohexane carbonitrile obtained was heated to reflux in 100 ml of tetrahydrofuran / 0.2N hydrochloric acid 4: 1 for 1.5 hours. The cooled reaction mixture was then poured onto 50 ml of water and extracted three times with 50 ml of diethyl ether each time. The organic phases were washed with 50 ml of water and 50 ml of saturated sodium bicarbonate solution, dried over magnesium sulfate and concentrated. It resulted
1.35 g (94%) of a colorless oil which, according to gas chromatographic analysis, contained 92% of a mixture of cis and trans-4-cyanocyclohexane carboxaldehyde (in a ratio of about 1: 1). This material was used in the following reduction without additional purification.

  Rf values (toluene / ethyl acetate 3: 1): cis-4-cyanocyclohexane carboxaldehyde 0.36, trans-4-cyanocyclohexane carboxaldehyde 0.32.



   f) A solution of 1.34 g of 4-cyanocyclohexane carboxaldehyde (cis / trans mixture) in 40 ml of 0.1N methanolic potassium hydroxide solution at 0 C was added in portions with 378 mg of solid sodium borohydride while gassing with argon. After the addition had ended, the mixture was stirred for a further 20 minutes at 0 ° C., then 50 ml of water were added and the mixture was extracted three times with 50 ml of methylene chloride each time. The organic phases were washed twice with 50 ml of water each time, dried over magnesium sulfate and concentrated. Low pressure chromatography (0.4 bar) of the remaining oil on silica gel with chloroform / ethyl acetate 1: 1 gave 1.22 g (90%) of 4 (hydroxymethyl) cyclohexane carbonitrile (also as an approx. 1: 1 mixture of the two epimers) as a colorless, viscous oil.



  This material was used in the following tosylation without further purification. Rf value of 4- (hydroxymethyl) cyclohexane carbonitrile (chloroform / ethyl acetate 1: 1) 0.29 (elongated spot).



   g) A solution of 1.20 g of the 4- (hydroxymethyl) cyclohexane carbonitrile obtained in 5 ml of pyridine was mixed in portions with 2.46 g of p-tosyl chloride at room temperature and with argon gas. After stirring for 3.5 hours at room temperature (formation of a white precipitate), the reaction mixture, cooled to 0 ° C., was mixed with about 2 ml of water, carefully acidified with about 7 ml of concentrated hydrochloric acid and extracted three times with 30 ml of diethyl ether. The organic phases were washed with 50 ml of water and 50 ml of saturated sodium chloride solution, dried over magnesium sulfate and concentrated, leaving 2.31 g of semicrystalline oil.

  Low pressure chromatography (0.5 bar) on 480 g of silica gel using 30% ethyl acetate / petroleum ether as the eluent gave 1.06 g (42%) of trans-4- (tosyloxymethyl) cyclohexane carbonitrile as a colorless, crystallizing oil (mp. 84-85 " C) and 1.03 g (41%) cis-4- (tosyloxymethyl) cyclohexane carbonitrile as a colorless, viscous 01. Rf values (30% ethyl acetate / petroleum ether): trans product 0.25, cis product 0.20.



   h) With argon gassing, 121 mg of magnesium shavings were covered with 3 ml of absolute tetrahydrofuran, a crystal of iodine was added and then at reflux temperature with a solution of 989 mg of trans-l- (bromomethyl) 4-pentyl-cyclohexane (from paragraph b) in 7 ml absolute tetrahydrofuran. After the addition had ended, the mixture was heated under reflux for 45 minutes.



   The reaction mixture, cooled to −78 ° C., was then treated with 0.7 ml of a 0.1N solution of dilithium tetrachlorocuprate (prepared according to M. Tamura et al., Synthesis 1971, 303) in tetrahydrofuran and with a solution of 587 mg trans-4- (Tosyloxymethyl) cyclohexane carbonitrile in 9 ml of absolute tetrahydrofuran was added. The reaction mixture, which had been heated to −15 ° C., was stirred for a further 21 hours, then mixed with about 10 ml of saturated ammonium chloride solution and extracted three times with 50 ml of diethyl ether each time. The organic phases were washed with 50 ml of saturated sodium chloride solution, dried over magnesium sulfate and concentrated.

  Low pressure chromatography (0.5 bar) of the residue on silica gel with 3% ethyl acetate / petroleum ether gave, along with a lot of coupling product of trans-l- (bromomethyl) -4-pentylcyclohexane, 164 mg (28%) trans-4- [2- (trans -4 pentylcyclohexyl) ethyl] cyclohexane carbonitrile (with 30% ethyl acetate / petroleum ether) 353 mg of trans-4- (tosyloxymethyl) cyclohexane carbonitrile could be recovered).

 

  Single recrystallization from 5 ml of methanol gave 96 mg of trans-4- [2- (trans-4-pentylcyclohexyl) ethyl] cyclohexaxarbonitrile as colorless crystals (purity 99.9%); Festfest conversion 39.3 "C, mp. 56.3" C. Klp. 72.3 "C (nematic).



   i) The nitrile obtained can be saponified in an analogous manner to Example 5c with 2N potassium hydroxide solution and ethanol under reflux to give trans 4 [2- (trans-4-pentylcyclohexyl) ethyl] cyclohexane carboxylic acid.


    

Claims (18)

 PATENT CLAIMS 1. Compounds of the general formula EMI1.1  wherein X2 denotes a single covalent bond or the ester group -COO-; X1 is a simple covalent bond, the ester group -CO (,, the ethylene group -CH2CH2- or, if X2 denotes the ester group -COO-, also p-phenylene; ring A stands for a benzene ring or for trans-1,4-cyclohexylene ; Ring B is a benzene ring or, provided that X2 denotes the ester group -COO- and X denotes a simple covalent bond, the ester group -COO or the ethylene group -CH2CH2-, also trans1,4-cyclohexylene; the radicals Z1, Z2 and Z3 are hydrogen or on a benzene ring which is not linked directly to a further ring via a simple covalent bond, also halogen, cyano or methyl; y2 represents cyano, nitro or 2,2-dicyanovinyl; Y1 is halogen, cyano, C1-C3-alkyl or, if X1 is p-phenylene and / or Y2 is nitro, also denotes hydrogen; and R 'is Cl-Cl2-alkyl or C1-C12-alkoxy on a benzene ring.  2. Compounds according to claim 1, characterized in that ring B represents a benzene ring.  3. Compounds according to claim 1 or 2, characterized in that the radicals Z1, Z2 and Z3 are hydrogen or one of these radicals on a benzene ring which is not linked directly to a further ring via a simple covalent bond, also chlorine.  4. Compounds according to any one of claims 1 to 3, characterized in that X1 is a simple covalent bond or p-phenylene.  5. Compounds according to any one of claims 1 to 4, characterized in that yl is fluorine, chlorine, cyano or methyl.  6. Compounds according to any one of claims 1 to 4, characterized in that they have the general formula EMI1.2  where R1, X2 and Y2 have the meanings given in claim 1; X1 is a simple covalent bond or, if X2 denotes the ester group -COO-, p is also phenylene; Ring A represents p-phenylene or trans-1,4 cyclohexylene; Z3 represents hydrogen or, if X2 denotes the ester group -COO-, also chlorine; and Y1 is fluorine, chlorine, cyano, methyl or, if X1 is p phenylene and / or Y2 is nitro. also called hydrogen.  7. Compounds according to any one of claims 1 to 6, characterized in that Y2 is cyano or nitro.  8. Compounds according to any one of claims 1 to 7, characterized in that Y 'denotes chlorine or cyano.  9. Compounds according to any one of claims 1 to 4 or 6, characterized in that Y 'denote hydrogen and Y2 nitro.  10. Compounds according to any one of claims 1 to 4 or 6, characterized in that yl hydrogen, X1 p phenylene and X2 denote the ester group -COO-.  11. Compounds according to any one of claims 1 to 10, characterized in that R1 represents a straight-chain alkyl group.  12. Compounds according to any one of claims 1 to 11, characterized in that the alkyl or alkoxy group R1 contains 3 to 10, preferably 5 to 9 carbon atoms.  13. Liquid-crystalline mixture with at least 2 components, characterized in that at least one component is a compound of the form defined in claim 1.  14. Liquid-crystalline mixture according to claim 13, characterized in that the mixture consists of 3 components A, B and C, each containing one or more compounds, and that component A has a viscosity of at most 40 cp, a clearing point of at least 40 "C. and has a dielectric anisotropy between 2 and +1, component B has a dielectric anisotropy below -2, component C has a dielectric anisotropy above + 10, a clearing point of at least 100 ° C. and a cross-over frequency in the total mixture of at most 15 kHz at 20 "C, and that component C contains at least one compound of formula I.  15. A liquid-crystalline mixture as claimed in claim 14, consisting of at least 30% by weight of component A, 3-50% by weight of component B and 5-40% by weight of component C.  16. A process for the preparation of the compounds of the formula I defined in claim 1, characterized in that an acid of the general formula EMI2.1  wherein R1, A, B, X1, X2, Z1, Z2 and Z3 have the meanings given in claim 1, or a reactive derivative thereof with a phenol of the general formula EMI2.2  wherein Y1 and Y2 have the meanings given in claim 1, esterified.  17. A process for the preparation of the compounds of the formula I defined in claim 1, wherein Z ', Z2 or Z3 is cyano, characterized in that a compound of the formula I defined in claim 1, in which Z1, Z2 or Z3 is bromine, with Copper (I), sodium or potassium cyanide.  18. Use of the compounds of formula I defined in claim 1 for electro-optical purposes.  The present invention relates to new liquid-crystalline compounds, namely the tetra- and pentacyclic esters of the general formula EMI2.3  wherein X2 denotes a single covalent bond or the ester group-COO; X1 is a simple covalent bond, the ester group -COO-, the ethylene group -CH2CH2- or, if X2 denotes the ester group -COO-, also p-phenylene; Ring A represents a benzene ring or trans-1,4-cyclohexylene; Ring B is a benzene ring or, provided that X2 denotes the ester group -COO- and X1 denotes a simple covalent bond, the ester group -COO or the ethylene group -CH2CH2-, also represents trans1,4-cyclohexylene; the radicals Z1, Z2 and Z3 are hydrogen or on a benzene ring which is not linked directly to a further ring via a simple covalent bond, also halogen, cyano or methyl; Y2 represents cyano, nitro or 2,2-dicyanovinyl; Y1 denotes halogen, cyano, C1-C3-alkyl or, if X 'stands for p-phenylene and / or Y2 for nitro, also denotes hydrogen; and R 'is C1-C12-alkyl or on a benzene ring also Cl-Cl2-alkoxy.  The invention further relates to the preparation of the compounds of the formula I above, their use for electro-optical purposes and liquid-crystalline mixtures which contain compounds of the formula I.  In the above definition, the term benzene ring means p-phenylene, which optionally has a lateral halogen, cyano or methyl substituent.  The term halogen stands for fluorine, chlorine and bromine and the term C1-C3-alkyl for methyl, ethyl, propyl and isopropyl.  The term C1-C12-alkyl includes straight-chain and branched alkyl groups, in particular the n-alkyl groups methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undercyl and dodecyl and the isoalkyl groups isopropyl, isobutyl, isopentyl, Isoheptyl, isooctyl, isononyl, isoundecyl and isododecyl. The term Cl-12 alkoxy encompasses alkyloxy groups, in which the alkyl part has the above meaning.  The lateral groups zl, Z2 and Z3 denote hydrogen or, if they are bound to an isolated benzene ring, i.e. to a p-phenylene ring, which is not directly linked to another ring via a simple covalent bond, also halogen, cyano or methyl.  In recent years, liquid crystals have become particularly important as dielectrics in display devices, since the optical properties of such substances can be influenced by an applied voltage. Electro-optical devices based on liquid crystals are well known to the person skilled in the art and can be based on various effects, such as, for example, the dynamic scattering, the deformation of aligned phases (DAP type), the Schadt-Helfrich effect (rotary cell), the guest Host effect or a cholesteric-nematic phase transition.    The conventional, static operation of liquid crystal display devices has been increasingly replaced in the past by the so-called multiplex control. This is usually an amplitude selective ** WARNING ** End of CLMS field could overlap beginning of DESC **.