EP0258430A1

EP0258430A1 - Nematic liquid crystal phases

Info

Publication number: EP0258430A1
Application number: EP19870902459
Authority: EP
Inventors: Eike Poetsch; Claus Escher
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 1986-02-27
Filing date: 1987-02-13
Publication date: 1988-03-09
Also published as: WO1987005316A1; DE3606312A1; JPS63502756A

Abstract

Phases de cristaux liquides nématiques comportant au moins deux constituants de cristaux liquides, dont au moins un est un composé chiral, caractérisées en ce que le composé chiral ne contient pas plus d'un seul centre chiral, le centre chiral étant un élément constituant d'un pont avec un nombre égal d'éléments de pont entre deux résidus mésogènes cycliques.Nematic liquid crystal phases comprising at least two constituents of liquid crystals, at least one of which is a chiral compound, characterized in that the chiral compound does not contain more than a single chiral center, the chiral center being a constituent element of a bridge with an equal number of bridge elements between two cyclic mesogenic residues.

Description

Nematic liquid crystal phase

The invention relates to a new nematic (the generic term “nematic” is intended to include the term “cholesteric” in the following) liquid crystal phase (LC phase) which contains at least one chiral (optically active) compound.

For liquid crystal displays, LC phases are increasingly required, which form a helical structure with a given direction of rotation. Such materials are required, for example, for the Schadt-Helfrich effect, for the cholesteric-nematic phase transition effect, for bistability effects, for the SBE effect (Mol. Cryst. Liq. Cryst. 123 ,, 303-319 (1985); DE- A-34 23 993) and for the White Taylor cell.

An important problem is the generation of a suitable temperature function of the helical pitch, which depends on the respective electro-optical effect and its specific design.

For liquid crystal display elements based on the twisted nematic cell, for example, a temperature-independent pitch to avoid the "reverse twist" comes into question. Furthermore, it could be shown that compensation of the temperature drift of the threshold voltage of a twisted nematic cell can be achieved if the helical pitch decreases with increasing temperature (PR Gerber, Physics Letters 78A, 285 (1980). The same applies to the phase change effect that, as the temperature decreases, the threshold voltage drift is compensated for with increasing temperature (A. Göbl-Wunsch, G. Heppke and F. Oestreicher, Journal de Physique 40, 773 (1979)).

In general, the LC phases used for this purpose consist of mixtures of non-chiral liquid-crystalline compounds, to which chiral compounds are added to produce the helical structure. Practically all known chiral dopants induce helical structures, the pitch of which increases over a wide range with temperature to a greater or lesser extent. The often desired negative slope of the temperature function could be achieved by using two suitable dopants with different directions of rotation and different relative temperature dependencies (DE-A-28 27 471). Disadvantages of this multiple doping method include a. compliance with the exact concentration ratio of the two chiral compounds and the restriction to a limited temperature interval as well as the necessary high total concentration of the dopants (A. Göbl-Wunsch, G. Heppke and F. Oestreicher, I.c.). Outdoor applications are therefore not possible.

The invention was therefore based on the object of finding an LC phase which has temperature-independent electro-optical parameters, in particular a temperature-independent threshold voltage, in which a negative increase in the temperature function of the pitch for inside and outside is also achieved by adding the dopant is induced over a wide temperature range with a high twisting capacity.

According to the invention, these objects are achieved with the aid of the nematic LC phase described below.

The invention relates to a nematic liquid crystal phase with at least two liquid crystalline components, including at least one chiral compound, characterized in that the chiral compound contains no more than one chiral center, the chiral center being part of a bridge with an even number of bridge members between two cyclic is mesogenic residues.

The invention furthermore relates to such a nematic phase, characterized in that the chiral compound corresponds to the formula I:

R ¹ -X ¹ -CHR °- (CH ₂ ) _p -X ² -R ² I

wherein

X ¹ and X ² each independently of one another -CO-O-, -O-CO-,

-CH ₂ -CO-O-, -CO-O-CH ₂ -, -CH ₂ O-, -OCH ₂ -, -CH ₂ CH ₂ -, -O- or a single bond,

R ¹ and R ² each independently represent a group

- (A ¹ -Z) _m - (A ² ) _n -Y,

A ¹ and A ² each independently of one another 1,4-phenylene, in which one or more CH groups can also be replaced by N, 1,4-cyclohexylene, in which also one or two non-adjacent ones CH ₂ groups can be replaced by -O- and / or -S- or 1,4-bicyclo- (2,2,2) -octylene, where these groups can also be substituted one or more times by F, Cl, Br, CN and / or alkyl groups with up to 12 C atoms, it being possible for 1 or 2 non-adjacent CH ₂ groups in the alkyl groups to be replaced by O atoms,

Z -CO-O-, -O-CO-, -CH ₂ CH ₂ -, -OCH ₂ -, -CH ₂ O-, -CH = N-, -N = CH-, -N = N-, - N (O) = N- or one

Single bond,

m 0, 1 or 2,

n 1 or 2,

Y is a straight-chain or branched alkyl group with up to 12 carbon atoms, where 1 or

2 non-adjacent CH ₂ groups can be replaced by O atoms, F, Cl, Br or CN,

p 0 or 1 and

R ° is an alkyl group with up to 5 carbon atoms,

Halogen, CN, a phenyl group or a cyclohexyl group

mean, with the proviso that the number of members of the bridge -X ¹ -CHR ° - (CH ₂ ) _p -X ² - is even, and with the further proviso that at least one of the groups

X ¹ and X ² mean a single bond. Temperature-compensated LC phases or LC display elements should be understood to mean LC phases or LC display elements with largely temperature-independent electro-optical parameters, in particular with a largely temperature-independent threshold voltage.

This temperature independence is generally guaranteed for normal areas of application. H. from -40 to + 100 °, in particular from -20 to + 80 °. Electro-optical parameters are, as is generally customary, referred to as largely temperature-independent if they do not exceed approximately ± 0.15% per degree Celsius, preferably not more than approximately ± 0.1% per degree, in the temperature range from -20 to + 80 ° Celsius, fluctuate. It is obvious to the person skilled in the art that the degree of the required temperature independence depends on the intended application in each case.

In particular, the new nematic LC phases are characterized in that the chiral dopant produces a relatively high and, above all, largely temperature-independent twist. These properties are e.g. B. for an application in TN cells or in SBE cells of great advantage. The twisting force of the new phases is less temperature-dependent than the previously known phases. In some temperature ranges, a decrease in the induced pitch with temperature can even be observed.

Above and below, X ¹ , X ² , R ¹ , R ² , A ¹ , A ² , Z, m, n, Y, p and R ° have the meaning given for formula I, unless expressly stated otherwise. In the compounds of the formula I, the "bridge" -X -CHRº- (CH ₂ ) pX -preferably for grouping -CO-O-CHRº-CH ₂ -, further preferably for the following grouping:

-CH ₂ -CO-O-CHRº- -CHR ° -CO-O-CH ₂ - -O-CO-CHR ° -CH ₂ - -CHR ° -CH ₂ -CO-O-

-CH ₂ -OCHR ° -CH ₂ - -CHR ° -CH ₂ -O-CO-

-OCH ₂ -CHR ° -CH ₂ - -CHR ° -CH ₂ -O-CH ₂ -

-CH ₂ CH ₂ -CHR ° -CH ₂ - -CHR ° -CH ₂ -CH ₂ -O-

-O-CHRº- -CHR ° -CH ₂ -CH ₂ -CH ₂ - -CHR ° -CH ₂ - -CHR ° -O-.

The radical R ° is preferably methyl, more preferably ethyl, propyl, isopropyl, butyl, F, Cl, Br, CN, phenyl or cyclohexyl.

In general, compounds of the formula I are preferred which contain an ester group in the bridge (X 1 or X2 =

-CO-O-, -O-CO-, -CH ₂ -CO-O- or -CO-O-CH ₂ -).

The radical R ¹ is preferably Y-Pyr-Phe-, the radical R ^{2 is} preferably -Phe-Y.

Furthermore, R ¹ and R ^{2 are} preferably:

Y-Phe- (also R ¹ !) Y-Phe-COO-Phe-

Y-Cy- Y-Cy-COO-Phe- γ-Py- Y-Phe-COO-Cy- γ-Pyr- Y-Cy-COO-Cy-

Y-Dio- Y-Phe-OCO-Phe- Y-Phe-Phe- Y-Cy-OCO-Phe-

Y-Phe-Cy- Y-Phe-OCO-Cy-

Y-Cy-Phe- Y-Cy-OCO-Cy-

Y-Cy-Cy- Y-Phe-CH ₂ O-Phe-

Y-Phe-Dio- Y-Cy-CH ₂ O-Phe- Y-Dio-Phe- Y-Phe-CH ₂ O-Cy-

Y-Cy-Dio- Y-Phe-CH ₂ O-Py-

Y-Dio-Cy- Y-Phe-CH ₂ O-Pyr-

Y-Phe-Py- Y-Phe-CH ₂ CH ₂ -Phe- Y-Py-Phe- Y-Cy-CH ₂ CH ₂ -Phe-

Y-Cy-Py- Y-Phe-CH ₂ CH ₂ -Cy-

Y-Py-Cy- Y-Cy-CH ₂ CH ₂ -Cy-

Y-Phe-Pyr- Y-Phe-CH ₂ CH ₂ -Py-

Y-Pyr-Phe- (also R ² !) Y-Py-CH ₂ CH ₂ -Phe- Y-Cy-Pyr- Y-Phe-CH ₂ CH ₂ -Pyr-

Y-Pyr-Cy- Y-Pyr-CH ₂ CH ₂ -Phe-

Y-Tri-Phe- Y-Tri-CH ₂ CH ₂ -Phe-

Y-Phe-Tri- Y-Phe-CH ₂ CH ₂ -Tri-

where (above and below) Phe unsubstituted or substituted by a fluorine atom, 1,4-phenylene, Cy 1,4-cyclohexylene, py pyridine-2, 5-diyl, pyr pyrimidine-2, 5-diyl, dio 1,3- Dioxane-2, 5-diyl and tri 1,2,4-triazine-3,6-diyl mean and the substituents in Cy and Dio are preferably in the trans position to one another.

Those compounds of the formula I which contain one or more of the groups dio, py, pyr or tri include all possible positional isomers. So z. B. a formula Y-Dio-Bridge-R ² (I, R ¹ = Y-Dio) both the 2-Y-5- (R ² bridge) -1,3-dioxanes and the 2- (R ² Bridge) -5-Y-1,3-dioxanes, the preferred sub-formula

Y-Pyr-Phe-CO-O-CHR ° -CH ₂ -Phe-Y (Ice, see below) both the

5-Y-2 - (- Phe-CO-O-CHR ° -CH ₂ -Phe-Y) -pyrimidines as well as the isomeric 2-Y-5 - (- Phe-CO-O-CHR ° -CH ₂ - Phe-Y) pyrimidines. In particular, the compounds of the formula I preferably comprise compounds of the sub-formulas Ia to Im with 2-4 rings in the molecule:

YA ² bridge-A ² -Y la YA ² -ZA ¹ bridge-A ² -Y Ib

YA ² -A ² bridge-A ² -Y Ic

YA ² -Bridge-A ¹ -ZA ² -Y Id

YA ² bridge-A ² -A ² -Y Ie

YA ² -ZA ¹ bridge-A ¹ -ZA ² -Y If YA ² -ZA ¹ bridge-A ² -A ² -Y Ig

YA ² -A ² -bridge-A ¹ -ZA ² -Y Ih

YA ² -A ² bridge-A ² -A ² -Y Ii

YA ² -Bridge-A ¹ -ZA ¹ -ZA ² -Y Ij

YA ² -bridge-A ¹ -ZA ² -A ² -Y Ik YA ² -ZA ¹ -ZA ¹ -bridge-A ² -Y II

YA ² -A ² -ZA ¹ -bridge-A ² -Y Im

If two residues Y, A ¹ , A ² , Z are present in the molecule, they can be the same or different.

The sub-formulas la and Ic are preferred, in particular the sub-formulas Iaa to lad and Ica to Icn:

Y-Phe-CHR ° -CO-O-CH ₂ -Cy-Y Iaa

Y-Cy-CHR ° -CO-O-CH ₂ -Cy-Y lab

Y-Phe-CHR ° -CO-O-CH ₂ -Phe-Y Iac

Y-Cy-CHR ° -CO-O-CH ₂ -Phe-Y lad Y-Phe-Phe-CO-O-CHR ° -CH ₂ -Phe-Y Ica

Y-Phe-Phe-CO-O-CHR ° -CH ₂ -Cy-Y lcb

Y-Phe-Cy-CO-O-CHR ° -CH ₂ -Phe-Y Icc

Y-Phe-Cy-CO-O-CHR ° -CH ₂ -Cy-Y Icd

Y-Pyr-Phe-CO-O-CHR ° -CH ₂ -Phe-Y Ice

Y-Pyr-Phe-CO-O-CHR ° -CH ₂ -Cy-Y Icf

Y-Pyr-Phe-CHR ° -CH ₂ -CO-O-Phe-Y lcg Y-Pyr-Phe-CHR ° -CH ₂ -CO-O-Cy-Y i

Y-Pyr-Phe-CH ₂ -CHR ° -CO-O-Phe-Y Ici

Y-Pyr-Phe-CH ₂ -CHR ° -CO-O-Cy-Y Icj

Y-Cy-Cy-CH ₂ -CO-O-CHR ° -Phe-Y Ick Y-Cy-Cy-CH- ₂ -CO-O-CHR ° -Cy-Y Icl

Y-Cy-Phe-CH ₂ -CHR ° -Phe-Y lcm

Y-Cy-Phe-CH ₂ -CHR ° -Cy-Y Icn.

Among these, the compounds of the formula Ice are particularly preferred.

In the compounds of the formulas above and below, Y preferably denotes alkyl, furthermore alkoxy, another oxaalkyl group, CN or F. The alkyl radicals, in which also one ("alkoxy" or "oxaalkyl") or two non-adjacent CH ₂ groups ("Alkoxyalkoxy" or "Dioxaalkyl") can be replaced by O atoms, can be straight-chain or branched. They are preferably straight-chain, have 2, 3, 4, 5, 6 or 7 carbon atoms and are therefore preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy, 2- Oxapropyl (= methoxymethyl), 2-oxabutyl (= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxyheptyl, furthermore methyl, octyl, nonyl, decyl, methoxy, octoxy, nonoxy, decoxy, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2 -, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl; 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl, 1,3-dioxabutyl (= methoxymethoxy), 1,3-, 1,4- or 2,4-dioxapentyl , 1,3-, 1,4-, 1,5-, 2,4-, 2,5- or 3,5-dioxahexyl, 1,3-, 1,4-, 1,5-, 1,6 -, 2,4-, 2,5-, 2,6-, 3,5-, 3,6- or 4,6-dioxaheptyl.

Compounds of formulas I and Ia to Im with branched wing groups Y can also be important. Branched groups of this type usually do not contain more than a chain branch. Preferred branched radicals Y are isopropyl, 2-butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, isopentyl (= 3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl , 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy, 1-methylheptoxy, 2-oxa-3-methylbutyl, 3 -Oxa-4-methylpentyl.

A ¹ and A ² are each, independently of one another, preferably Cy, Phe, Pyr or Dio; the compound of the formula I preferably contains no more than one of the radicals Dio, Py or

Pyr.

Z is preferably a single bond, -CO-O- or -O-CO-, further preferably a -CH ₂ CH ₂ group.

The compounds of the formula I are prepared by methods known per se, as described in the literature (for example in the standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart), namely under Reaction conditions which are known and suitable for the reactions mentioned. Use can also be made of variants which are known per se and are not mentioned here in detail.

If desired, the starting materials can also be formed in situ in such a way that they are not isolated from the reaction mixture, but instead are immediately converted further into the compounds of the formula I.

As a rule, one of the starting materials for the preparation of the compounds of the formula I is a chiral compound. For example, the compounds of the formula I can be prepared by reducing a compound which otherwise corresponds to the formula I but contains one or more reducible groups and / or CC bonds instead of H atoms.

As reducible groups are preferably carbonyl groups, in particular keto groups, z. B. free or esterified hydroxyl groups or aromatic halogen atoms. Preferred starting materials for the reduction correspond to the formula I, but can instead of a cyciohexane ring a cyclohexene ring or cyclohexanone ring and / or instead of a -CH ₂ CH ₂ group a -CH = CH group and / or instead of a -CH ₂ - Group contain a -CO group and / or instead of an H atom, a free or a functional (e.g. in the form of its p-toluenesulfonate) modified OH group.

The reduction can e.g. B. done by catalytic hydrogenation at temperatures between about 0 ° and about 200 ° and pressures between about 1 and 200 bar in an inert solvent, for. B. an alcohol such as methanol, ethanol or isopropanol, an ether such as tetrahydrofuran (THF) or dioxane, an ester such as ethyl acetate, a carboxylic acid such as acetic acid or a hydrocarbon such as cyclohexane. Suitable catalysts are suitably noble metals such as Pt or Pd, which can be used in the form of oxides (e.g. PtO ₂ , PdO), on a support (e.g. Pd on carbon, calcium carbonate or strontium carbonate) or in finely divided form .

Ketones can also by Clemmensen's methods (with zinc, amalgamated zinc or tin and hydrochloric acid, suitably in aqueous alcoholic solution or in a heterogeneous phase with water / toluene at temperatures between about 80 and 120 °) or Wolff-Kishner (with hydrazine, advantageously in the presence of alkali such as KOH or NaOH in a high-boiling solvent such as diethylene glycol or triethylene glycol at temperatures between about 100 and 200 °) to the corresponding compounds of formula I, the alkyl groups and / or contain -CH ₂ CH ₂ groups can be reduced.

Reductions with complex hydrides are also possible. For example, arylsulfonyloxy groups can be removed reductively with LiAlH ₄ , in particular p-toluenesulfonyloxymethyl groups can be reduced to methyl groups, expediently in an inert solvent such as diethyl ether or THF at temperatures between about 0 and 100 °. Double bonds can be hydrogenated (even in the presence of CN groups!) With NaBH ₄ or tributyltin hydride in methanol; so arise z. B. from 1-cyanocyclohexene derivatives, the corresponding cyclohexane derivatives.

Esters of the formula I (X ¹ , X ² and / or Z = -CO-O- or

-O-CO-) can also by esterification of appropriate carboxylic acids z. B. the formulas R ¹ -COOH, R ¹ -CHR ° -CH ₂ -COOH,

R ¹ -CHR ° -COOH, R ² -COOH, R ² -CH ₂ -CHR ° -COOH, YA ² -COOH or

R ¹ -X ¹ -CHR ° - (CH2 ₂ ) _p -X ² -A ¹ -COOH (or its reactive

Derivatives) with alcohols or phenols of the formulas R ¹ -OH, R ¹ -CHR ° -CH ₂ -OH, R ² -OH, R ² -CH ₂ -CHR ° -OH, R ² -CH ₂ OH, R ¹ -X ¹ -CHR ° - (CH ₂ ) -X ² -A ¹ -OH or YA ² -OH.

Suitable reactive derivatives of the carboxylic acids mentioned are, in particular, the acid halides, especially the chlorides and bromides, furthermore the anhydrides, also mixed anhydrides, for. B. the formula R -CO-O-COCH ₃ , azides or esters, in particular alkyl esters with 1-4 C atoms in the alkyl group, furthermore the salts, for. B. the Na, K, Cs or Ag salts. Suitable reactive derivatives of the alcohols or phenols mentioned are, in particular, the corresponding metal alcoholates or phenolates, for. B. the formula R ¹ -OM or R ² -CH ₂ -CHR ° -OM into consideration, in which M is an equivalent of a metal, preferably an alkali metal such as Na or K, furthermore the corresponding halides, for. B. the formulas R ¹ Br, R ¹ -CH ₂ -CHR ° -Br or R ² -CHR ° -Br.

The esterification is advantageously carried out in the presence of an inert solvent. Particularly suitable are ethers such as diethyl ether, di-n-butyl ether, THF, dioxane or anisole, ketones such as acetone, butanone or cyclohexanone, amides such as DMF or phosphoric acid hexamethyltriamide, hydrocarbons such as benzene, toluene or xylene, halogenated hydrocarbons such as dichloromethane or tetrachlorethylene and sulfoxides such as Dimethyl sulfoxide or sulfolane. Water-immiscible solvents can at the same time advantageously be used for azeotropically distilling off the water formed during the esterification. Occasionally, an excess of an organic base, e.g. B. pyridine,

Quinoline or triethylamine can be used as a solvent for the esterification. The esterification can also be carried out in the absence of a solvent, e.g. B. by simply heating the components in the presence of sodium acetate. The reaction temperature is usually between -50 ° and + 250 °, preferably between -20 °. and + 80 °. At these temperatures, the esterification reactions are usually complete after 15 minutes to 48 hours.

In particular, the reaction conditions for the esterification largely depend on the nature of the starting materials used. So a free carboxylic acid is usually countered with a free alcohol or phenol were reacted with a strong acid, for example a mineral acid such as hydrochloric acid or sulfuric acid, or in the presence of a water-releasing agent such as dicyclohexylcarbodiimide. A preferred reaction mode is the reaction of an acid anhydride or in particular an acid chloride with an alcohol, preferably in a basic medium, the bases being in particular alkali metal hydroxides such as sodium or potassium hydroxide, alkali metal carbonates or hydrogen carbonates such as sodium carbonate, sodium hydrogen carbonate, potassium carbonate or potassium hydrogen carbonate, alkali metal acetates such as sodium or Potassium acetate, alkaline earth metal hydroxides such as calcium hydroxide or organic bases such as triethylamine, pyridine, lutidine, collidine or quinoline are important. Another preferred embodiment of the esterification consists in first converting the alcohol or the phenol into the sodium or potassium alcoholate or phenolate, e.g. B. by treatment with ethanol or sodium hydroxide solution, isolate this and suspend it together with sodium bicarbonate or potassium carbonate with stirring in acetone or diethyl ether and add a solution of the acid chloride or anhydride in diethyl ether, acetone or DMF to this suspension, advantageously at temperatures between about - 25 ° and + 20 °. Furthermore, z. B., a salt, e.g. B. an alkali metal salt

Carboxylic acid with a halide, e.g. B. a bromide, which corresponds to the alcohol to be esterified.

It is also possible to prepare compounds of the formula I by organometallic synthesis. So you can z. B. an organometallic compound of the formula R ² -MgBr or R ² Li with a halide, e.g. B. a bromide of the formula R ¹ -X ¹ -CHR ° - (CH ₂ ) -Br, advantageously with the addition of a catalyst such as Li ₂ CuCl ₄ in an inert solvent such as THF at about 10-30 °. The LC phases according to the invention consist of 2 to 18, preferably 3 to 15 components, including at least one chiral compound of the type specified, preferably a compound of the formula I. The other constituents are preferably selected from the nematic or nematogenic substances, in particular the known substances , from the classes of azoxybenzenes, benzylidene anilines, biphenyls, terphenyls, phenyl- or cyclohexylbenzoates, cyclohexane-carboxylic acid phenyl- or cyclohexyl esters, phenylcyclohexanes, -cyclohexylbiphenyls, cyclohexylcyclohexanes, cyclohexylnaphthalenes, 1,4-bis-cyclones, 1,4-bis-cyclones cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexyldioxanes, optionally halogenated stilbenes, benzylphenyl ether, tolanes and substituted cinnamic acids.

The most important compounds which can be considered as constituents of such LC phases can be characterized by the formula II,

R ³ -LGER ⁴ II

where L and E are each a carbo- or heterocyclic ring system consisting of the system consisting of 1,4-disubstituted benzene and cyclohexane rings, 4,4'-disubstituted biphenyl, phenylcyclohexane and cyclohexylcyclohexane systems, 2,5-disubstituted pyrimidine and 1,3- Dioxane rings, 2,6-disubstituted naphthalene, di- and tetrahydronaphthalene, quinazoline and tetrahydroquinazoline,

G -CH = CH- -N (O) = N-

-CH = CQ- -CH = N (O) - -CΞC- -CH ₂ -CH ₂ -

-CO-O- -CH ₂ -O-

-CO-S- -CH ₂ -S-

-CH = N- -COO-Phe-COO- or a CC single bond, Q halogen, preferably chlorine, or -CN, and R ³ and R ^{4 are} each alkyl, alkoxy,

Alkanoyloxy or alkoxycarbonyloxy having up to 18, preferably up to 8 carbon atoms, or one of these radicals is also CN, NC, NO, CF, NCS, F, Cl or Br. In most of these compounds, R ³ and R ⁴ are different from one another, one of these radicals usually being an alkyl or alkoxy group. Other variants of the proposed substituents are also common. Many such substances or mixtures thereof are commercially available. All of these substances can be produced by methods known from the literature.

The LC phases according to the invention preferably contain 0.05 to 35%, in particular 0.1 to 10%, of one or more of the chiral compounds of the type indicated, preferably the compounds of the formula I.

Most preferred LC phases according to the invention for liquid-crystalline dielectrics contain 0.1 to 3% of one or more compounds of the formula I. Particularly preferred are dielectrics which contain only one compound of the formula I.

The LC phases according to the invention are produced in a conventional manner. As a rule, the components are dissolved in one another, advantageously at elevated temperature. By means of suitable additives, the LC phases can be modified according to the invention in such a way that they can be used in all types of LC display elements which have become known to date.

Such additives are known to the person skilled in the art and are described in detail in the literature. For example, conductive salts, preferably ethyl-dimethyl-dodecyl-ammonium-4- Hexoxybenzoate, tetrabutylammonium tetraphenylboranate or complex salts of crown ethers to improve the conductivity, dichroic dyes for the production of colored guest-host systems or substances for changing the dielectric anisotropy, the viscosity and / or the orientation of the nematic phases are added. Such substances are described for example in DE-OS 22 09 172, 22 40 864, 23 21 632, 23 38 281, 24 50 088, 25 37 430, 28 53 728 and 29 02 177.

Compounds of the formula I can also be used, if appropriate without the addition of further components, as liquid-crystal phases for temperature indicators. Compounds which are preferred for this purpose contain at least one of the groups R ¹ or R ² two ring structures.

The following examples are intended to illustrate the invention without limiting it. Before and after are all

Temperatures given in ° C. It means: F. = melting point; Klp. = Clearing point; [α] = [α] - 20 with c = 1 in CH ₂ Cl ₂ . The percentages relate to percentages by weight.

"Conventional work-up" means: water and a water-immiscible solvent such as CH ₂ Cl ₂ , diethyl ether or toluene are added, shaken, the phases are separated, the organic phase is washed, dried over Na ₂ SO ₄ , evaporated and purified Residue by chromatography on silica gel and / or crystallization.

Examples of the preparation of compounds of the formula I:

example 1

A mixture of 2.98 g of p- (5-heptylpyrimidin-2-yl) benzoic acid, 2.5 g of (-) - 1-p-heptoxyphenyl-2-propanol ([α] -3.15 °; available from R-propylene oxide and C ₇ H ₁₅ MgBr), 2.3 g of dicyclohexylcarbodiimide, 0.2 g of 4-dimethylaminopyridine and 25 ml of dichloromethane are stirred at 20 ° for 48 hours. It is cooled in an ice bath, the dicyclohexylurea formed is filtered off, the filtrate is evaporated and, after chromatography on silica gel with toluene / ethyl acetate (98: 2) (-) - p- (5-heptylpyrimidin-2-yl) -benzoic acid (1 -p-heptoxyphenyl-2-propyl ester), mp 80 ° (from ethanol); [α] -80.6 °.

Analogously, one obtains by esterification:

(+) - P- (5-Heptylpyrimidin-2-yl) -benzoic acid- (1-heptoxyphenyl-2-propyl ester) as well as the (+) - and (-) - forms of

1-p-methoxyphenyl-2-propyl ester

1-p-ethoxyphenyl-2-propyl ester 1-p-propoxyphenyl-2-propyl ester

1-p-butoxyphenyl-2-propyl ester

1-p-pentoxyphenyl-2-propyl ester

1-p-hexoxyphenyl-2-propyl ester

1-P-heptoxyphenyl-2-propyl ester 1-p-octoxyphenyl-2-propyl ester

1-p-Nonoxypnenyl-2-propyl ester

1-p-decoxyphenyl-2-propyl ester of

p- (5-Propylpyrimidin-2-yl) -benzoic acid p- (5-Butylpyrimidin-2-yl) -benzoic acid p- (5-Pentylpyrimidin-2-yl) -benzoic acid p- (5-Hexylpyrimidin-2-yl) -benzoic acid p- (5-heptylpyrimidin-2-yl) -benzoic acid p- (5-octylpyrimidin-2-yl) -benzoic acid p- (5-nonylpyrimidin-2-yl) -benzoic acid

5-propylpicolinic acid

5-butylpicolinic acid

5-pentylpicolic acid

5-hexylpicolinic acid

5-heptylpicolinic acid

5-octylpicolinic acid

5-nonylpicolinic acid

5-methoxypicolinic acid

5-ethoxypicolinic acid

5-propoxypicolinic acid

5-butoxypicolinic acid

5-pentoxypicolinic acid

5-hexoxypicolinic acid

5-heptoxypicolinic acid

6-propylnicotinic acid

6-butylnicotinic acid

6-pentylnicotinic acid

6-hexylnicotinic acid

6-heptylnicotinic acid

6-octylnicotinic acid

6-nonylnicotinic acid

6-methoxynicotinic acid

6-ethoxynicotinic acid

6-propoxynicotinic acid

6-butoxynicotinic acid

6-pentoxynicotinic acid 6-hexoxynicotinic acid 6-heptoxynicotinic acid 5- (p-propylphenyl) -picolinic acid5- (p-butylphenyl) -piColinic acid5- (p-pentylphenyl) -picolinic acid5- (p-hexylphenyl) -picolinic acid5- (p-heptylphenyl) -picolinic acid5- -Octylphenyl) -picolinic acid5- (p-nonylphenyl) -picolinic acid5- (p-methoxyphenyl) -picαlinic acid5- (p-ethoxyphenyl) -picolinic acid5- (p-propoxyphenyl) -picolinic acid5- (p-butoxyphenyl) -picolinic acid5- (p-pentoxyphenyl ) -picolinic acid5- (p-hexoxyphenyl) -picolinic acid 5- (p-heptoxyphenyl) -picolinic acid6- (p-propylphenyl) -nicotinic acid6- (p-butylphenyl) -nicotinic acid6- (p-pentylphenyl} -nicotinic acid 6- (p-hexylphenyl ) -nicotinic acid6- (p-heptylphenyl) -nicotinic acid 6- (p-octylphenyl) -nicotinic acid6- (p-nonylphenyl) -nicotinic acid 6- (p-methoxyphenyl) -nicotinic acid 6- (p-ethoxyphenyl) -nicotinic acid6- (p- Propoxyphenyl) nicotinic acid 6- (p-butoxyphenyl) nicotinic acid 6- (p-pentoxyphenyl) nicotinic acid 6- (p-hexoxyphenyl) nicotinic acid 6- (p-heptoxyphenyl) nicotinic acid p- (5-propyl-2-pyridyl) - benzoic acid p- (5-butyl-2-p yridyl) -benzoic acid p- (5-pentyl-2-pyridyl) -benzoic acid p- (5-hexyl-2-pyridyl) -benzoic acid p- (5-heptyl-2-pyridyl) -benzoic acid p- (5-octyl-2 -pyridyl) -benzoic acid p- (5-nonyl-2-pyridyl) benzoic acid p- (5-methoxy-2-pyridyl) benzoic acid p- (5-ethoxy-2-pyridyl) benzoic acid p- (5-propoxy-2-pyridyl) -benzoic acid p- (5-butoxy-2-pyridyl) -benzoic acid p- (5-pentoxy-2-pyridyl) -benzoic acid p- (5-hexoxy-2-pyridyl) -benzoic acid p- (5-heptoxy-2- pyridyl) -benzoic acid p- (2-propyl-5-pyridyl) -benzoic acid p- (2-butyl-5-pyridyl) -benzoic acid p- (2-pentyl-5-pyridyl) -benzoic acid p- (2-hexyl-5 -pyridyl) -benzoic acid p- (2-hepty1-5-pyridyl) -benzoic acid p- (2-octyl-5-pyridyl) -benzoic acid p- (2-nonyl-5-pyridyl) -benzoic acid p- (2-methoxy -5-pyridyl) -benzoic acid p- (2-ethoxy-5-pyridyl) -benzoic acid p- (2-propoxy-5-pyridyl) -benzoic acid p- (2-butoxy-5-pyridyl) -benzoic acid p- (2nd -Pentoxy-5-pyridyl) -benzoic acid p- (2-hexoxy-5-pyridyl) -benzoic acid p- (2-Heptoxy-5-pyridyl) -benzoic acid p- (trans-4-propylcyclohexyl) -benzoic acid p- (trans -4-butylcyclohexyl) -benzoic acid p- (trans-4-pentylcyclohexyl) -benzoic acid p- (trans-4-hexylcyclohexyl) -benzoic acid p- (trans-4-heptylcyclohexyl) -benzoic acid re p- (trans-4-octylcyclohexyl) benzoic acid p- (trans-4-nonylcyclohexyl) benzoic acid p- (trans-4-methoxycyclohexyl) benzoic acid p- (trans-4-ethoxycyclohexyl) benzoic acid p- (trans- 4-propoxycyclohexyl) benzoic acid p- (trans-4-butoxycyclohexyl) benzoic acid p- (trans-4-pentoxycyclohexyl) benzoic acid p- (trans-4-hexoxycyclohexyl) benzoic acid p- (trans-4-heptoxycyclohexyl) benzoic acid trans-4- (trans-4-propylcyclohexyl) cyclohexane carboxylic acid trans-4- (trans-4-butylcyclohexyl) cyclohexane carboxylic acid trans-4- (trans-4-pentylcyclohexyl) cyclohexane carboxylic acid trans-4- (trans-4- Hexylcyclohexyl) cyclohexane carboxylic acid trans-4- (trans-4-heptylcyclohexyl) cyclohexane carboxylic acid trans-4- (trans-4-octylcyclohexyl) cyclohexane carboxylic acid trans-4- (trans-4-nonylcyclohexyl) cyclohexane carboxylic acid trans-4- (trans- 4-methoxycyclohexyl) cyclohexane carboxylic acid trans-4- (trans-4-ethoxycyclohexyl) cyclohexane carboxylic acid trans-4- (trans-4-propoxycyclohexyl) cyclohexane carboxylic acid trans-4- (trans-4-butoxycyclohexyl) cyclohexane carboxylic acid trans-4- ( trans-4-pentoxycyclohexyl) cyclohexane carboxylic acid trans-4- (trans-4-hexoxycyclohexyl) cyclohexane carboxylic acid trans-4- (trans-4-heptoxycyclohexyl) cyclohexane carboxylic acid

2- (trans-4-propylcyclohexyl) -1, 3-dioxane-5-carboxylic acid 2- (trans-4-butylcyclohexyl) -1,3-dioxane-5-carboxylic acid

2- (trans-4-pentylcyclohexyl) -1,3-dioxane-5-carboxylic acid

2- (trans-4-hexylcyclohexyl) -1,3-dioxane-5-carboxylic acid

2- (trans-4-heptylcyclohexyl) -1, 3-dioxane-5-carboxylic acid

2- (trans-4-octylcyclohexyl) -1,3-dioxane-5-carboxylic acid 2- (trans-4-nonylcyclohexyl) -1,3-dioxane-5-carboxylic acid 2- (trans-4-methoxycyclohexyl) -1,3-dioxane-5-carboxylic acid 2- (trans-4-ethoxycyclohexyl) -1,3-dioxane-5-carboxylic acid 2- (trans-4-propoxycyclohexyl) -1, 3-dioxane-5-carboxylic acid 2- (trans-4-butoxycyclohexyl) -1,3-dioxane-5-carboxylic acid 2- (trans-4-pentoxycyclohexyl) -1,3-dioxane-5-carboxylic acid 2- (trans- 4-Hexoxycyclohexyl) -1,3-dioxane-5-carboxylic acid 2- (trans-4-heptoxycyclohexyl) -1,3-dioxane-5-carboxylic acid

2-fluoro-4- (trans-4-propylcyclohexyl) benzoic acid 2-fluoro-4- (trans-4-butylcyclohexyl) benzoic acid 2-fluoro-4- (trans-4-pentylcyclohexyl) benzoic acid 2-fluoro-4 - (trans-4-hexylcyclohexyl) benzoic acid 2-fluoro-4- (trans-4-heptylcyclohexyl) benzoic acid 2-fluoro-4- (trans-4-octylcyclohexyl) benzoic acid 2-fluoro-4- (trans-4 -nonylcyclohexyl) -benzoic acid 2-fluoro-4- (trans-4-methoxycyclohexyl) -benzoic acid 2-fluoro-4- (trans-4-ethoxycyclohexyl) -benzoic acid 2-fluoro-4- (trans-4-propoxycyclohexyl) -benzoic acid 2-fluoro-4- (trans-4-butoxycyclohexyl) benzoic acid 2-fluoro-4- (trans-4-pentoxycyclohexyl) benzoic acid 2-fluoro-4- (trans-4-hexoxycyclohexyl) benzoic acid 2-fluoro-4 - (trans-4-heptoxycyclohexyl) benzoic acid trans-4-propyl-cyclohexanecarboxylic acid trans-4-butyl-cyclohexanecarboxylic acid trans-4-pentyl-cyclohexanecarboxylic acid trans-4-hexyl-cyclohexanecarboxylic acid trans-4-heptyl-cyclohexanecarboxylic acid trans-4-octyl -cyclohexane carboxylic acid trans-4-nonyl-cyclohexane carboxylic acid trans-4-methoxy-cyclohexane carboxylic acid trans-4-ethoxy-cyclohexanecarboxylic acid trans-4-propoxy-cyclohexanecarboxylic acid trans-4-butoxyτcyclohexanecarboxylic acid trans-4-pentoxy-cyclohexanecarboxylic acid trans-4-hexoxy-cyclohexanecarboxylic acid trans-4-heptoxy-cyclohexanecarboxylic acid 5- (p-propylbenzoxy) -picolinic acid 5- (p-butylbenzoxy) -picolinic acid 5- (p-pentylbenzoxy) -picolinic acid 5- (p-hexylbenzoxy) -picolinic acid 5- (p-heptylbenzoxy) -picolinic acid 5- (p- Octylbenzoxy) -picolinic acid 5- (p-nonylbenzoxy) -picolinic acid 5- (p-methoxybenzoxy) -picolinic acid 5- (p-ethoxybenzoxy) -picolinic acid 5- (p-propoxybenzoxy) -picolinic acid 5- (p-butoxybenzoxy) -picolinic acid 5 - (p-Pentoxybenzoxy) -picolinic acid 5- (p-hexoxybenzoxy) -picolinic acid 5- (p-heptoxybenzoxy) -picolinic acid 6- (p-propylbenzoxy) -nicotinic acid 6- (p-butylbenzoxy) -nicotinic acid 6- (p-pentylbenzoxy ) -nicotinic acid 6- (p-hexylbenzoxy) -nicotinic acid 6- (p-heptylbenzoxy) -nicotinic acid 6- (p-octylbenzoxy) -nicotinic acid 6- (p-nonylbenzoxy) -nicotinic acid 6- (p-methoxybenzoxy) -nicotinic acid 6- (p-Ethoxybenzoxy) -nicotinic acid 6- (p-propoxybenzoxy) -nicotinic acid 6- (p-butoxybenzoxy) -nicotinic acid 6- (p-pentoxybenzoxy) -nicotinic acid 6- (p-hexoxybenzoxy) -nicotinic acid6- (p-heptoxybenzoxy) - nicotinic acid 5- (p-propylphenethyl) -picolinic acid 5- (p-butylphe 5- (p-Pentylphenethyl) -picolinic acid 5- (p-hexylphenethyl) -picolinic acid 5- (p-heptylphenethyl) -picolinic acid 5- (p-octylphenethyl) -picolinic acid 5- (p-nonylphenethyl) -picolinic acid 5- (p-methoxyphenethyl) -picolinic acid 5- (p-ethoxyphenethyl) -picolinic acid 5- (p-propoxyphenethyl) -picolinic acid 5- (p-butoxyphenethyl) -picolinic acid 5- (p-pentoxyphenethyl) -picolinic acid 5- (p- Hexoxyphenethyl) -picolinic acid 5- (p-heptoxyphenethyl) -picolinic acid p- [2- (trans-4-propylcyclohexyl) -ethyl] -benzoic acid p- [2- (trans-4-butylcyclohexyl) -ethyl] -benzoic acid p- [ 2- (trans-4-pentylcyclohexyl) ethyl] benzoic acid p- [2- (trans-4-hexylcyclohexyl) ethyl] benzoic acid p- [2- (trans-4-heptylcyclohexyl) ethyl] benzoic acid p- [2- (trans-4-octylcyclohexyl) ethyl] benzoic acid p- [2- (trans-4-nonylcyclohexyl) ethyl] benzoic acid p- [2- (trans-4-methoxycyclohexyl) ethyl] benzoic acid p - [2- (trans-4-ethoxycyclohexyl) ethyl] benzoic acid p- [2- (trans-4-propoxycyclohexyl) ethyl] benzoic acid p- [2- (trans-4-butoxycyclohexyl) ethyl] benzoic acid p- [2- (trans-4-pentoxycyclohexyl) ethyl] benzoic acid p- [2- (trans-4-hexoxycyclohexyl) ethyl] benzoic acid p- [2- (trans-4-heptoxycyclohexyl) ethyl] - benzoic acid 2-fluoro-4- [2- (tr ans-4-propylcyclohexyl) ethyl] benzoic acid 2-fluoro-4- [2- (trans-4-butylcyclohexyl) ethyl] benzoic acid 2-fluoro-4- [2- (trans-4-pentylcyclohexyl) ethyl ] -benzoic acid 2-fluoro-4- [2- (trans-4-hexylcyclohexyl) -ethyl] -benzoic acid 2-fluoro-4- [2- (trans-4-heptylcyclohexyl) -ethyl] -benzoic acid 2-fluoro-4 - [2- (trans-4-octylcyclohexyl) ethyl] benzoic acid 2-fluoro-4- [2- (trans-4-nonylcyclohexyl) ethyl] benzoic acid 2-fluoro-4- [2- (trans-4-methoxycyclohexyl) ethyl] benzoic acid

2-fluoro-4- [2- (trans-4-ethoxycyclohexyl) ethyl] benzoic acid

2-fluoro-4- [2- (trans-4-propoxycyclohexyl) ethyl] benzoic acid

2-fluoro-4- [2- (trans-4-butoxycyclohexyl) ethyl] benzoic acid

2-fluoro-4- [2- (trans-4-pentoxycyclohexyl) ethyl] benzoic acid

2-fluoro-4- [2- (trans-4-hexoxycyclohexyl) ethyl] benzoic acid

2-fluoro-4- [2- (trans-4-heptoxycyclohexyl) ethyl] benzoic acid p- (trans-4-propylcyclohexylcarbonyloxy) benzoic acid p- (trans-4-butylcyclohexylcarbonyloxy) benzoic acid p- (trans-4- Pentylcyclohexylcarbonyloxy) benzoic acid p- (trans-4-hexylcyclohexylcarbonyloxy) benzoic acid p- (trans-4-heptylcyclohexylcarbonyloxy) benzoic acid p- (trans-4-octylcyclohexylcarbonyloxy) benzoic acid p- (trans-4-nonylcycloxyhexylcarbonyl acid (trans-4-methoxycyclohexylcarbonyloxy) benzoic acid p- (trans-4-ethoxycyclohexylcarbonyloxy) benzoic acid p- (trans-4-propoxycyclohexylcarbonyloxy) benzoic acid p- (trans-4-butoxycyclohexylcarbonyloxy) benzoic acid p- (trans-4-pentoxycyclohexyl ) -benzoic acid p- (trans-4-hexoxycyclohexylcarbonyloxy) -benzoic acid p- (trans-4-heptoxycyclohexylcarbonyloxy) -benzoic acid p- (trans-4-propylcyclohexylmethoxy) -benzoic acid p- (trans-4-butylcyclohexylmethoxy) -benzoic acid p- ( trans-4-pentylcyclohexylmethoxy) benzoic acid p- (trans-4-hexylcyclohexylmethoxy.) benzoic acid p - (trans-4-Heptylcyclohexylmethoxy) -benzoic acid p- (trans-4-Octylcyclohexylmethoxy) -benzoic acid p- (trans-4-nonylcyclohexylmethoxy) -benzoic acid p- (trans-4-Methoxycyclohexylmethoxy) -benzoic acid p- (trans-4-Ethoxycyclohexylmethoxy) -benzoic acid p- (trans-4-Propoxycyclohexylmethoxy) -benzoic acid p- (trans-4-Butoxycyclohexylmethoxy) -benzoic acid p- (trans-4 -Pentoxycyclohexylmethoxy) -benzoic acid p- (trans-4-hexoxycyclohexylmethoxy) -benzoic acid p- (trans-4-heptoxycyclohexylmethoxy) -benzoic acid trans-4- [2- (trans-4-propylcyclohexyl) -ethyl] -cyclohexane carboxylic acid trans-4- [2- (trans-4-butylcyclohexyl) ethyl] cyclohexane carboxylic acid trans-4- [2- (trans-4-pentylcyclohexyl) ethyl] cyclohexane carboxylic acid trans-4- [2- (trans-4-hexylcyclohexyl) ethyl ] -cyclohexanecarboxylic acid trans-4- [2- (trans-4-heptylcyclohexyl) -ethyl] -cyclohexanecarboxylic acid trans-4- [2- (trans-4-octylcyclohexyl) -ethyl] -cyclohexanecarboxylic acid trans-4- [2- (trans -4-nonylcyclohexyl) ethyl] cyclohexane carboxylic acid trans-4- [2- (trans-4-methoxycyclohexyl) ethyl] cyclohexane carboxylic acid trans-4- [2- (trans-4-ethoxycyclohexyl) ethyl] cyclohexane carboxylic acid trans- 4- [2- (trans-4-propoxycyclohexyl) ethyl ] -cyclohexanecarboxylic acid trans-4- [2- (trans-4-butoxycyclohexyl) -ethyl] -cyclohexanecarboxylic acid trans-4- [2- (trans-4-pentoxycyclohexyl) -ethyl] -cyclohexanecarboxylic acid trans-4- [2- (trans -4-Hexoxycyclohexyl) ethyl] cyclohexane carboxylic acid trans-4- [2- (trans-4-heptoxycyclohexyl) ethyl] cyclohexane carboxylic acid p- [2- (2-Propyl-pyrimidin-5-yl) ethyl] benzoic acid p- [2- (2-butyl-pyrimidin-5-yl) ethyl] benzoic acid p- [2- (2- Pentyl-pyrimidin-5-yl) -ethyl] -benzoic acid p- [2- (2-hexyl-pyrimidin-5-yl) -ethyl] -benzoic acid p- [2- (2-heptyl-pyrimidin-5-yl) -ethyl] -benzoic acid p- [2- (2-octyl-pyrimidin-5-yl) -ethylJ-benzoic acid p- [2- (2-nonyl-pyrimidin-5-yl) -ethyl] -benzoic acid p- [2 - (2-methoxypyrimidin-5-yl) ethyl] benzoic acid p- [2- (2-ethoxypyrimidin-5-yl) ethyl] benzoic acid p- [2- (2-propoxypyrimidin- 5-yl) ethyl] benzoic acid p- [2- (2-butoxypyrimidin-5-yl) ethyl] benzoic acid p- [2- (2-pentoxypyrimidin-5-yl) ethyl] - benzoic acid p- [2- (2-hexoxypyrimidin-5-yl) ethyl] benzoic acid p- [2- (2-heptoxypyrimidin-5-yl) ethyl] benzoic acid.

Example 2

3.16 g of p- (5-heptylpyrimidin-2-yl) benzoyl chloride are added to a solution of 2.5 g (+) - 1-p-heptoxyphenyl-2-propanol ([α] +3.15 °, available from S-propylene oxide and C ₇ H ₁₅ MgBr) in 15 ml pyridine at 0 ° with stirring, allowed to warm to 20 ° and stirred for 16 hours at 20 °. The mixture is worked up as usual with water / toluene to give (+) - p- (5-heptylpyrimidin-2-yl) benzoic acid (1-p-heptoxyphenyl-2-propyl ester); [α] +79.3 °.

Example 3

Analogously to Example 1, from (+) - 3- [p- (5-heptylpyrimidin-2-yl) phenyl] butyric acid [obtainable by hydrogenation of 3- [p- (5-heptylpyrimidin-2-yl) phenyl -2-butenoic acid at 5%. Pd-C in THF and resolution with (+) - ephedrine; [α] +3.3 °] and trans-4-propylcyclohexanol the corresponding 3- [p- (5-heptylpyrimidin-2-yl) phenyl] butyric acid (trans-4-propylcyclohexyl ester) .. The (+) and (-) forms of 3- [p- (5-heptylpyrimidin-2-yl) phenyl] butyric acid are obtained analogously.

- [trans-4- (trans-4-pentylcyclohexyl) cyclohexyl ester]

- [trans-4- (trans-4-butylcyclohexyl) cyclohexyl ester]

- (trans-4-pentylcyclohexyl ester)

- (p-pentylphenyl ester) - (p-pentoxyphenyl ester)

- (4'-heptyl-4-biphenylyl ester)

- (2-pentyl-5-pyridyl ester).

Example 4

1.7 g of (-) - 3- [p- (5-heptylpyrimidin-2-yl) phenyl] butyric acid are converted into the acid chloride using SOCl ₂ , the mixture is dissolved in 10 ml of diethyl ether and the solution is added dropwise to that of 1 , 64 g p-pentylphenol and 3 ml pyridine in 15 ml diethyl ether at 0 ° with stirring. The mixture is stirred for a further 1 hour at 0 °, then for 16 hours at 20 °, and the corresponding 3- [p- (5-heptylpyrimidin-2-yl) phenyl] butyric acid (p-pentylphenyl ester) is obtained after customary working up.

The (+) and (-) forms of 3- [p- (5-heptylpyrimidin-2-yl) phenyl] butyric acid - (p-propylphenyl ester) - (p-heptoxyphenyl ester) - (4 '-heptyl-4-biphenylyl ester) - (trans-4-pentylcyclohexyl methyl ester) - [trans-4- (trans-4-propylcyclohexyl) cyclohexyl ester] - (2-propyl-5-pyridyl ester) - (5-butyl- 2-pyridyl ester). Example 5

A mixture of 3.97 g of the cesium salt of all-trans-4- (4-propylcyclohexyl) cyclohexane acetic acid, 2.55 g (+) - 1-bromo-1-p-pentylphenyl-ethane and 30 ml of DMF is 16 hours stirred at 60 ° and worked up as usual (water / hexane). The corresponding trans-4- (trans-4-propylcyclohexyl) cyclohexane acetic acid (1-p-pentylphenyl ethyl ester) is obtained.

The (+) - and (-) - forms of 2- (trans-4-pentylcyclohexyl) propionic acid - trans-4-pentylcyclohexane carboxylic acid - trans-4-pentylcyclohexane acetic acid - trans-4- (trans-4-pentylcyclohexyl) are obtained analogously -cyclohexanacetic acid- p- (trans-4-pentylcyclohexyl) -phenylacetic acid- (1-p-pentylphenyl-ethyl ester).

Example 6

Analogously to Example 1, (-) - 3- (p-5-heptylpyrimidin-2-yl-phenyl) -2-methylpropionic acid [[α] -2.3 °; obtainable by hydrogenation of 3- (p-5-heptylpyrimidin-2-yl-phenyl) -2-methylacrylic acid in 5%. Pd-C in THF and racemate resolution with (+) - ephedrine] and p-nonylphenol the corresponding 3- (p-5-heptylpyrimidin-2-yl-phenyl) -2-methylpropionic acid (p-nonylphenyl ester).

Analogously, the (+) - and (-) - forms of the following 2-methylpropionic acid p-nonylphenyl esters are obtained by esterification

3- [p- (tranε-4-propylcyclohexyl) phenyl] - 3- (trans-4-pentylcyclohexyl) - 3- [p- (2-heptyl-5-pyridyl) phenyl) - 3- (2-heptyl-5-pyridyl) -

3- [p- (3-Octyl-1,2,4-triazin-6-yl) phenyl] - 3- [p- (6-Octyl-1,2,4-triazin-3-yl) phenyl ] -.

Example 7

A Grignard solution prepared from 2.69 g of p- (trans-4-propylcyclohexyl) bromobenzene, 0.24 g of Mg and 10 ml of THF is added dropwise with stirring to a mixture of 2.7 g of (+) - 1-bromo-2-p-pentylphenyl propane, 66 mg Li ₉ CuCl ₄ and 30 ml THF. After 16 hours of stirring at 20 °, the mixture is decomposed with hydrochloric acid, evaporated, worked up as usual and the corresponding l- (p-trans-4-propylcyclohexylphenyl) -2-p-pentylphenyl-propane is obtained.

The (+) - and (-) - forms of the following 2-p-pentylphenyl-propanes are obtained analogously with the corresponding Grignard compounds:

1- (p-trans-4-butylcyclohexylphenyl) -

1- (p-trans-4-pentylcyclohexylphenyl) -

1- (p-trans-5-propyl-1,3-dioxan-2-yl-phenyl) -.

Example 8

Analogously to Example 4, the corresponding 2- (trans-4-pentylcyclohexyl) propionic acid (trans-4-pentylcylohexyl) is obtained from (-) - 2- (trans-4-pentylcyclohexyl) propionic acid via its chloride with trans-4-pentylcyclohexylmethanol methyl ester). The (+) - and (-) - forms of 2- (trans- 4-pentylcyclohexyl) propionic acid are obtained analogously.

- (p-propylbenzyl ester) - (p-heptoxybenzyl ester) - [p- (5-heptyl-pyrimidin-2-yl) -benzyl ester] - (trans-4-pentylcyclohexylmethyl ester) - [trans-4- (trans-4-propylcyclohexyl ) cyclohexyl methyl ester]

- (2-propyl-5-pyridylmethyl ester) - (5-butyl-2-pyridylmethyl ester).

Example 9

Analogously to Example 1, p-hexylbenzoic acid and 1- (4'-octoxybiphenyl-4-yl) propan-2-ol [obtained from S - (-) - propylene oxide] give the (+) - p-hexylbenzoic acid [1 - (4'-octoxybiphenyl-4-yl) -2-proppy l -e st er], F. 67 °; [α] _D ²⁰ + 66.0 ° (c = 5% in dichloromethane).

Examples of nematic liquid crystal phases:

Example A

A mixture of

15.8% p-trans-4-propylcyclohexyl-benzonitrile 9.8% p-trans-4-butylcyclohexyl-benzonitrile

10.9% trans-1-p-ethoxyphenyl-4-propylcyclohexane

8.8% trans, trans-4-propylcyclohexyl-4'-propoxycyclohexane

7.8% trans, trans-4-pentylcyclohexyl-4'-methoxycyclohexane

7.8% trans, trans-4-pentylcyclohexyl-4'-ethoxycyclohexane 3.9% trans, trans-4-propylcyclohexyl-cyclohexane-4'-carboxylic acid (trans-4-propylcyclohexyl ester)

3.9% trans, trans-4-propylcyclohexyl-cyclohexane-4'-carboxylic acid (trans-4-pentylcyclohexyl ester) 3.9% trans, trans-4-butylcyclohexyl-cyclohexane-4'-carboxylic acid (trans-4- propylcyclohexyl ester)

2.9% trans, trans-4-butylcyclohexyl-cyclohexane-4'-carboxylic acid (trans-4-pentylcyclohexyl ester) 3.9% 2-fluoro-4,4 '- (trans-4-propylcyclohexyl) biphenyl 5, 9% 2-fluoro-4- (trans-4-pentylcyclohexyl) -4 '- (trans-4-propylcyclohexyl) biphenyl

2.9% 2-fluoro-4,4 '- (trans-4-pentylcyclohexyl) biphenyl 3.9% 4,4'-bis (trans-4-propylcyclohexyl) biphenyl 5.9% 4- (trans -4-pentylcyclohexyl) -4 '- (trans-4-propylcyclohexyl) biphenyl 2.0% (-) - p- (5-heptylpyrimidin-2-yl) benzoic acid (1-pheptoxyphenyl-2-propyl ester) )

shows F. <-40 °; Klp. 105.4 °; HTP 11.17 [μm ^-1 ] at 0 °,

11.24 at 20 °, 11.17 at 40 °. Example B

A mixture of

22.8% p-trans-4-propylcyclohexyl benzonitrile

34.2% p-trans-4-pentylcyclohexyl-benzonitrile 23.8% p-trans-4-heptylcyclohexyl-benzonitrile

14.2% 4-cyan-4 '- (trans-4-pentylcyclohexyl) biphenyl 5.0% (-) - p- (5-heptylpyrimidin-2-yl) benzoic acid (1-pheptoxyphenyl-2-propyl ester) )

shows F. -5 °, Klp. 69.7 °.

Example C

A mixture of

13% p-trans-4-ethylcyclohexyl-benzonitrile 16% p-trans-4-propylcyclohexyl-benzonitrile 12% p-trans-4-butylcyclohexyl-benzonitrile 9% 4-ethyl-4'-cyanbiphenyl 8% 4-propyl-4 '-cyanbiphenyl

14% trans-l-p-methoxyphenyl-4-propylcyclohexane i2% 4-ethyl-4 '- (trans-4-propylcyclohexyl) biphenyl

8% 4-ethyl-4 '- (trans-4-pentylcyclohexyl) biphenyl 7% 4- (trans-4-pentylcyclohexyl) -4' - (trans-4-propylcyclohexyl) biphenyl

1% (-) - p- (5-Heptylpyrimidin-2-yl) -benzoic acid- (l-p-heptoxyphenyl-2-propyl ester)

shows F. -16 °, Klp.- 65 °.

Claims

1. Nematic liquid crystal phase with at least two liquid crystalline components, including at least one chiral compound, characterized in that the chiral compound contains no more than one chiral center, the chiral center being part of a bridge with an even number of bridge members between two cyclic mesogenic residues .

2. Nematic phase according to claim 1, characterized in that the chiral compound corresponds to formula I:

R ¹ -X ¹ -CHR ° - (CH ₂ ) _p -X ² -R ² I

wherein

X ¹ and X ² each independently of the other -CO-O-,

-O-CO-, -CH ₂ -CO-O-, -CO-O-CH ₂ , -CH ₂ O-,

--OOCH ₂ -, -CH ₂ CH ₂ -, -O- or a single bond,

R ¹ and R ² each independently represent a group - (A ¹ -Z) _m - (A ² ) _n -Y, A ¹ and A ² each independently of one another 1,4-phenylene, in which one or more CH groups are also

N can be replaced, 1,4-cyclohexylene, in which one or two non-adjacent CH ₂ groups can also be replaced by -O- and / or -S- or 1,4-bicyclo- (2,2,2) - octylene, where these groups can also be substituted one or more times by F, Cl, Br,

CN and / or alkyl groups with up to 12 C atoms, it being possible for 1 or 2 non-adjacent CH ₂ groups in the alkyl groups to be replaced by O atoms,

Z -CO-O-, -O-CO-, -CH ₂ CH ₂ -, -OCH ₂ -, -CH ₂ O-, -CH = N-, -N = CH-, -N = N-, - N (O) = N or a single bond,

m 0, 1 or 2,

n 1 or 2,

Y is a straight-chain or branched alkyl group with up to 12 C atoms, it being possible for 1 or 2 non-adjacent CH ₂ groups to be replaced by O atoms, F, Cl, Br or CN,

p 0 or 1 and

R ° is an alkyl group with up to 5 carbon atoms, halogen, CN, a phenyl group or one

Cyclohexyl group

mean, with the proviso that the number of members of the bridge -X ¹ -CHR ° - (CH ₂ ) _p -X ² - is even, and with the further proviso that at least one of the groups X ¹ and X ^{2 is} a single bond means.