GB2367057A

GB2367057A - Benzonitriles with both chloro and fluoro lateral substituents for use as components of liquid crystalline media

Info

Publication number: GB2367057A
Application number: GB0115691A
Authority: GB
Inventors: Mark John Goulding; David Coates; Diona Ionescu
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2000-06-28
Filing date: 2001-06-27
Publication date: 2002-03-27
Also published as: GB0115691D0

Abstract

Halogenated benzonitriles of the formula I <EMI ID=1.1 HE=34 WI=129 LX=386 LY=610 TI=CF> <PC>[in which <DL TSIZE=7> <DT>R<SP>1</SP><DD>is H, an alkyl radical having 1-12 carbon atoms which is unsubstituted or at least monosubstituted by halogen or CN and in which, in addition, one or more CH<SB>2</SB> groups may each, independently of one another, be replaced by -O-, -C I C- or -CH=CH- in such a way that heteroatoms are not connected directly, <DT>A<DD>is <EMI ID=1.2 HE=21 WI=99 LX=657 LY=1527 TI=CF> <DT>Z, Z<SP>1</SP><DD>independently of one another are -CO-O-, -O-CO-, -CH<SB>2</SB>CH<SB>2</SB>-, -C I C- or a single bond, <DT>L<SP>1</SP>, L<SP>2</SP><DD>independently of one another are H or F, <DT>Q<SP>1</SP>, Q<SP>2</SP><DD>independently of one another are H or CI and <DT>m<DD>is 0, 1 or 2] </DL> have highly positive values of the dielectric anisotropy with moderate to high values of the optical anisotropy W n and relatively low viscosity and can be used as components of liquid-crystalline media, in particular for displays based on the principle of the twisted cell (eg TN, TFT and STN displays), the guest-host effect, the effect of aligned phases (DAP) or electrically controlled birefringence (ECB) or the effect of dynamic scattering. These compounds are distinguished, in particular, by high thermal stability (which is advantageous for a high "holding ration") and exhibit favourable clearing point values.

Description

Benzonitriles and liquid-crystalline medium

The invention relates to novel halogenated benzonitriles of the formula I

in which R1 is H, an alkyl radical having 1-12 carbon atoms which is unsubstituted or at least monosubstituted by halogen or CN and in which, in addition, one or more CH2 groups may each, independently of one another, be replaced by-0-,-C=C-or CH=CH-in such a way that heteroatoms are not connected directly,

Z, Z1 independently of one another are-CO-O-,-O-CO-,-CH2CH2-,- C=C-or a single bond, L', L2 independently of one another are H or F, Q1, Q2 independently of one another are H or Cl and m is 0,1 or 2.

The invention also relates to the use of the compounds of the formula I as components of liquid-crystalline media, and to liquid-crystal and electrooptical display elements which contain the liquid-crystalline media according to the invention.

The compounds of the formula I frequently have highly positive values of the dielectric anisotropy with moderate to high values of the optical anisotropy An and relatively low viscosity and can be used as components of liquid-crystalline media, in particular for displays based on the principle of the twisted cell, the guest-host effect, the effect of deformation of aligned phases (DAP) or electrically controlled birefringence (ECB) or the effect of dynamic scattering.

The substances employed hitherto for this purpose all have certain disadvantages, for example inadequate stability to the action of heat, light or electric fields, or unfavourable elastic and/or dielectric properties.

The invention had the object of finding novel, stable, liquid-crystalline or mesogenic compounds of particularly high positive dielectric anisotropy and moderate to high optical anisotropy at the same time as low viscosity which are suitable as components of liquid-crystalline media, in particular for TN, TFT and STN displays.

It has now been found that the compounds of the formula I are eminently suitable as components of liquid-crystalline media. They can be used to obtain stable liquid-crystalline media, in particular suitable for TFT or STN displays. The novel compounds are distinguished, in particular, by high thermal stability, which is advantageous for a high"holding ratio", and exhibit favourable clearing point values.

The provision of compounds of the formula I very generally considerably broadens the range of liquid-crystalline substances which are suitable, from various applicational points of view, for the preparation of liquidcrystalline mixtures.

The compounds of the formula I have a broad range of applications.

Depending on the choice of substituents, these compounds can serve as base materials of which liquid-crystalline media are predominantly composed; however, it is also possible to add compounds of the formula I

to liquid-crystalline base materials from other classes of compound in order, for example, to modify the dielectric and/or optical anisotropy of a dielectric of this type and/or to optimize its threshold voltage and/or its viscosity. Addition of compounds of the formula I to liquid-crystalline dielectrics allows the An values and As values of such media to be significantly affected.

The meaning of the formula I covers all isotopes of the chemical elements bound in the compounds of the formula 1. In enantiomerically pure or enriched form, the compounds of the formula I are also suitable as chiral dopants and in general for producing chiral mesophases.

In the pure state, the compounds of the formula I are colourless and form liquid-crystalline mesophases in a temperature range which is favourably located for electro-optical use. They are stable chemically, thermally and to light.

The invention thus relates to the compounds of the formula I and to the use of these compounds as components of liquid-crystalline media. The invention furthermore relates to liquid-crystalline media comprising at least one compound of the formula 1, and to liquid-crystal display elements, in particular electro-optical display elements, which contain media of this type.

Above and below, R, A, Z, Zl, L1, L2, Q\ Q2 and m are defined above, unless expressly stated otherwise.

The following group of compounds of the sub-formulae IA to IJ represents preferred embodiments of the invention:

in which R', Z and Z1 are as defined above.

If RI in the formulae above and below is an alkyl radical, this can be straight-chain or branched.

It is preferably straight-chain, has 2,3, 4,5, 6, or 7 carbon atoms and accordingly is preferably ethyl, propyl, butyl, pentyl, hexyl or heptyl, furthermore methyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl or pentadecyl.

If R1 is an alkyl radical in which one CH2 group has been replaced by-0-, this can be straight-chain or branched. It is preferably straight-chain and has 1 to 10 carbon atoms. Preferably, the first CH2 group of this alkyl radical has been replaced by-0-, so that the radical R'becomes alkoxy and is preferably methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy or nonyloxy.

Furthermore, one CH2 group elsewhere can also be replaced by-0-, so that the radical R1 is preferably straight-chain 2-oxapropyl (= methoxymethyl), 2- (= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3-or 4-oxapentyl, 2-, 3-, 4-or 5-oxahexyl, 2-, 3-, 4-, 5-or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6-or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7-or 8-oxanonyl, or 2-, 3-, 4-, 5-, 6-, 7-, 8-or 9-oxadecyl.

If R1 is an alkenyl radical, this can be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. Accordingly, it is in

particular vinyl, prop-1-or-2-enyl, but-1-,-2-or-3-enyl, pent-1-,-2-,-3-or -4-enyl, hex-1-,-2-,-3-,-4-or-5-enyl, hept-1-,-2-,-3-,-4-,-5-or-6-enyl, oct-1-,-2-,-3-,-4-,-5-,-6-or-7-enyl, non-1-,-2-,-3-,-4-,-5-,-6-,-7-or -8-enyl, or dec-1-,-2-,-3-,-4-,-5-,-6-,-7-,-8-or-9-enyl.

R1 is particularly preferably an alkenyl radical from the following group :

If R1 is an alkenyloxy radical, this can be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. It is particularly preferably a radical from the following group :

If R'is an alkyl radical which is at least monosubstituted by halogen, this radical is preferably straight-chain. Halogen is preferably F or CL In the case of polysubstitution, halogen is preferably F. The resultant radicals also include perfluorinated radicals. In the case of monosubstitution, the fluorine or chlorine substituent can be in any desired position, but is preferably in the o-position.

If R1 is an alkynyl radical, this can be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. Accordingly, it is in

particular ethynyl, prop-1-or-2-ynyl, but-1-,-2-or-3-ynyl, pent-1-,-2-,-3or-4-ynyl, hex-1-,-2-,-3-,-4-or-5-ynyl, hept-1-,-2-,-3-,-4-,-5-or-6-ynyl, oct-1-,-2-,-3-,-4-,-5-,-6-or-7-ynyl, non-1-,-2-,-3-,-4-,-5-,-6-,-7-or-8 ynyl, or dec-1-,-2-,-3-,-4-,-5-,-6-,-7-,-8-or-9-ynyl.

If RI is an oxaalkyl or alkoxy radical in which a CH2 group has been replaced by-C-C-, this can be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms.

Compounds of the formula I containing a branched wing group R'may occasionally be of importance owing to better solubility in the customary liquid-crystalline base materials, but in particular as chiral dopants if they are optically active. Smectic compounds of this type are suitable as components of ferroelectric materials.

Branched groups of this type generally contain not more than one chain branch. Preferred branched radicals R1 are isopropyl, 2-butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, isopentyl (= 3-methyl

butyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methyl pentoxy, 3-methylpentoxy, 2-ethylhexyloxy, 1-methylhexyloxy or 1-methylheptyloxy.

Formula I covers the racemates of these compounds and the optical antipodes, and mixtures thereof.

Of these compounds of the formula I and the sub-formulae, preference is given to those in which at least one of the radicals present therein has one of the preferred meanings indicated.

Further preferred compounds of the formula I are indicated below : Compounds of formula I whose R1 group is a linear alkyl radical having 1 to 10 C-atoms.

Compounds of the formula I whose R1 group is an alkyl, oxaalkyl or alkoxy radical having 1 to 10 carbon atoms in which one or more CH2 groups have been replaced by-C=C-or-CH=CH-.

Compounds of the formula I in which L 1 is F.

Compounds of the formula I in which 01 and 02 are simultaneously H.

Compounds of the formula I in which m is 0.

Compounds of the formula I in which the ring A is-0-.

Compounds of the formula I in which Z'is-CO-O-,-0-CO-or a single bond, preferably-CO-O-. Compounds of the formula I in which Z is-CH2CH2-or a single bond, preferably a single bond. Some very particularly preferred smaller groups of compounds of the formula I are those of the sub-formulae 11 to 19 :

Wherein R2 is alkyl having 1 to 10 carbon atoms, preferably n-alkyl having 1 to 7 carbon atoms, or alkenyl having 2 to 7 carbon atoms.

Very particularly preferred compounds from this group are those of the formulae 12, 13, 16 and 18.

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, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), to be precise, under reaction conditions which are known and suitable for said reactions.

Use can be made here of variants which are known per se, but are not mentioned here in greater detail.

The starting materials can, if desired, also be formed in situ by not isolating them from the reaction mixture, but instead immediately converting them further into the compounds of the formula 1.

The compounds according to the invention can be prepared, for example, as shown in the following reaction schemes:

Scheme 1

Ra = alkyl Esters of the formula I are preferably obtained by esterification of corresponding carboxylic acids (or reactive derivatives thereof) using alcohols or phenols (or reactive derivatives thereof) or by the DCC method (DCC = dicyclohexylcarbodiimide).

The corresponding carboxylic acids and alcohols or phenols are known or can be prepared analogously to known processes.

Suitable reactive derivatives of said carboxylic acids are in particular the acid halides, especially the chlorides and bromides, furthermore the anhydrides, azides or esters, in particular alkyl esters having 1-4 carbon atoms in the alkyl group.

Suitable reactive derivatives of said alcohols and phenols are in particular the corresponding metal alkoxide and phenoxides respectively, preferably of an alkali metal, such as Na or K.

The esterification is advantageously carried out in the presence of an inert solvent. Particularly suitable solvents are ethers, such as diethyl ether, di-n-butyl ether, THF, dioxane or anisol, ketones, such as acetone, butanone or cyclohexanon, amides, such as DMF or hexamethylphosphoric triamide, hydrocarbons, such as benzene, toluene or xylene, halogenated hydrocarbons, such as tetrachloromethane or tetrachlorethylene, and sulfoxides, such as dimethyl sulfoxide or sulfolan. Water immiscible solvents can at the same time advantageously be used for removal by azeotropic distillation of the water formed during the esterification. It may occasionally also be possible to use an excess of an organic base, for example pyridine, quinoline or triethylamine, as solvent for the esterification. The esterification can also be carried out in the absence of a solvent, for example by simply heating the components in the presence of sodium acetate. The reaction temperature is usually between-500 and +250 , preferably between-200 and +800. At these temperatures, the esterification reactions are generally complete after from 15 minutes to 48 hours.

In detail, the reaction conditions for the esterification depend substantially on the nature of the starting materials used. Thus, the reaction of a free carboxylic acid with a free alcohol or phenol is generally carried out in the presence of a strong acid, for example a mineral acid, such as hydrochloric acid or sulfuric acid. A preferred reaction procedure is to react an acid anhydride or, in particular, an acid chloride with an alcohol, preferably in a basic medium, important bases being, in particular, alkali metal hydroxides, such as sodium hydroxide or potassium hydroxide, alkali metal carbonates or hydrogencarbonates, such as sodium carbonate, sodium hydrogencarbonate, potassium carbonate or potassium hydrogencarbonate, alkali metal acetates, such as sodium acetate or potassium acetate, alkaline-earth metal hydroxides, such as calcium hydroxide, or organic bases, such as triethylamine, pyridine, lutidine, collidine or quinoline. A further preferred embodiment of the esterification comprises first converting the alcohol or phenol into the sodium or potassium alkoxide or phenoxide, for example by treatment with ethanolic sodium hydroxide or potassium hydroxide solution, and isolating the product and reacting it with an acid anhydride or, in particular, acid chloride.

Nitriles can be obtained by replacement of halogens using copper cyanide or alkali metal cyanide.

In a further process for the preparation of compounds of the formula I in which R1 is alkenyl, an aryl halide is reacted with an olefin in the presence of a tertiary amine and in the presence of a palladium catalyst (R. F. Heck, Acc.

Chem. Res. 12 (1979) 146). Examples of suitable aryl halides are chlorides, bromides and iodides, in particular bromides and iodides. The tertiary amines necessary for the success of the coupling reaction, such as, for example, triethylamine, are also suitable as solvent. Examples of suitable palladium catalysts are its salts, in particular Pd (II) acetate, with organophosphorus (ill) compounds, such as, for example, triarylphosphines. This process can be carried out in the presence or absence of an inert solvent at temperatures between about 0 C and 150 C, preferably between 20 C and 100C ; suitable solvents are, for example, nitriles, such as acetonitrile, or hydrocarbons, such as benzene or toluene. The aryl halides and olefins employed as starting materials are frequently commercially available and can be prepared by processes known from the literature, for example by halogenation of corresponding parent compounds or by elimination reactions on corresponding alcohols or halides.

Ethers of the formula I are obtainable by etherification of corresponding hydroxyl compounds, preferably corresponding phenols, the hydroxyl compound advantageously first being converted into a corresponding metal derivative, for example into the corresponding alkali metal alkoxide or alkali metal phenoxide, by treatment with NaH, NaNH2, NaOH, KOH, Na2CO3 or K2CO3. This metal derivative can then be reacted with the appropriate alkyl halide, alkyl sulfonate or dialkyl sulfate, advantageously in an inert solvent, such as, for example, acetone, 1,2-dimethoxyethane, DMF or dimethyl sulfoxide, or alternatively with an excess of aqueous or aqueous-alcoholic NaOH or KOH, at temperatures between about 20 C and 100 C.

In order to prepare the laterally substituted fluorine or chlorine compounds of the formula 1, corresponding aniline derivatives can be reacted with sodium nitrite and either with tetrafluoroboric acid (in order to introduce an F atom) or with copper (l) chloride (in order to introduce a chlorine atom), to give the diazonium salts, which are then decomposed thermally at temperatures of 100-140 .

The organometallic compounds are prepared, for example, by metalhalogen exchange (for example in accordance with Org. React. 6, 339-366 (1951) ) between the corresponding halogen compound and an organolithium compound, such as, preferably, tert-butyllithium or lithium naphthalenide, or by reaction with magnesium turnings.

The linking of an aliphatic group R1 to an aromatic ring is preferably carried out by Friedel-Crafts alkylation or acylation by reacting the corresponding aromatic compounds with Lewis acid catalysis. Examples of suitable Lewis

acids are Suc'4, ZnCI2 and in particular A) C ! s and Tical.

In addition, the compounds of the formula I can be prepared by reducing a compound which contains one or more reducible groups and/or C-C bonds in place of H atoms, but otherwise conforms to the formula 1.

Suitable reducible groups are preferably carbonyl groups, in particular keto groups, furthermore, for example, free or esterified hydroxyl groups or aromatically bonded halogen atoms. Preferred starting materials for the reduction are compounds which conform to the formula 1, but contain a CH=CH-group in place of a-CH2CH2-group and/or contain a-CO-group in place of a-CH2-group and/or contain a free or functionally derived (for example in the form of its p-toluenesulfonate) OH group in place of an H atom.

The reduction can be carried out, for example, by catalytic hydrogenation at temperatures between about 00 and about 2000 and at pressures between about 1 and 200 bar in an inert solvent, for example 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 advantageously noble metals, such as Pt or Pd, which may be employed in the form of oxides (for exampte PtO or PdO), on a support (for example Pd on carbon, calcium carbonate or strontium carbonate) or in finely divided form.

Ketones can also be reduced by the methods of Clemmensen (using zinc, zinc amalgam or tin and hydrochloric acid, advantageously in aqueousalcoholic solution or in the heterogeneous phase with water/toluene at temperatures between about 80 and 120 C) or Wolff-Kishner (using 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 2000C) to give the corresponding compounds of the formula I which contain alkyl groups and/or-CH2CH2bridges.

Furthermore, reductions using complex hydrides are possible. For example, arylsulfonyloxy groups can be removed reductively using LiAIH4, in particular p-toluenesulfonyloxymethyl groups can be reduced to methyl groups, advantageously in an inert solvent, such as diethyl ether or THF, at temperatures between about 0 and 100 C. Double bonds can be hydrogenated using NaBH4 or tributyltin hydride in methanol.

The starting materials are either known or can be prepared analogously to known compounds.

The liquid-crystalline media according to the invention preferably comprise from 2 to 40 components, in particular from 4 to 30 components, as further constituents besides one or more compounds according to the invention.

These media very particularly preferably comprise from 7 to 25 components besides one or more compounds according to the invention.

These further constituents are preferably selected from nematic or

nematogenic (monotropic or isotropic) substances, in particular substances from the classes of the azoxybenzenes, benzylideneanilines, biphenyls, ter phenyl, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl esters of cyclohexanecarboxylic acid, phenyl or cyclohexyl esters of cyclohexylbenzoic acid, phenyl or cyclohexyl esters of cyclohexylcyclohexane- carboxylic acid, cyclohexylphenyl esters of benzoic acid, of cyclohexanecarboxylic acid or of cyclohexylcyclohexanecarboxylic acid, phenylcyclohex

anes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, cyctohexyicydohexyicydohexenes, 1, 4-bis-cyclohexylbenzenes, 4, 4'-bis-cyclohexylbiphenyls, phenyl-or cyclohexylpyrimidines, phenyl-or cyclohexylpyridines, phenyl-or cyclohexyldioxanes, phenyl-or cyclohexyl1, 3-dithianes, 1, 2-diphenylethanes, 1, 2-dicyclohexylethanes, 1-phenyl-2cyclohexylethanes, 1-cyclohexyl-2- (4-phenylcyclohexyl) ethanes, 1-cyclo hexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexylphenylethanes optionally halogenated stilbenes, benzyl phenyl ethers, tolans and substituted cinnamic acids. The 1, 4-phenylen groups in these compounds may also be fluorinated.

The most important compounds suitable as further constituents of media according to the invention can be characterized by the formulae 1,2, 3,4 and 5: R'-L-E-R"1 R'-L-COO-E-R"2 R'-L-OOC-E-R"3 R'-L-CH2CH2-E-R"4 R'-L-C=C-E-R"5 In the formulae 1,2, 3,4 and 5, L and E, which may be identical or different, are in each case, independently of one another, a bivalent radical from the

group formed by-Phe-,-Cyc-,-Phe-Phe-,-Phe-Cyc-,-Cyc-Cyc-,-Pyr-,-Dio-, - G-Phe-and-G-Cyc-and their mirror images, where Phe is unsubstituted or fluorine-substituted 1, 4-phenylen, Cyc is trans-1, 4-cyclohexylen or 1, 4-cyclohexylene, Pyr is pyrimidine-2, 5-diyl or pyridine-2, 5-diyl, Dio is 1,3dioxane-2, 5-diyl and G is 2- (trans-1, 4-cyclohexyl) ethyl, pyrimidine-2, 5-diyl, pyridine-2, 5-diyl or 1,3-dioxane-2, 5-diyl.

One of the radicals L and E is preferably Cyc, Phe or Pyr. E is preferably Cyc, Phe or Phe-Cyc. The media according to the invention preferably comprise one or more components selected from the compounds of the formulae 1,2, 3,4 and 5 in which L and E are selected from the group consisting of Cyc, Phe and Pyr and simultaneously one or more components selected from the compounds of the formulae 1,2, 3,4 and 5 in which one of the radicals L and E is selected from the group consisting of Cyc, Phe and Pyr and the other radical is selected from the group consisting of-Phe-Phe-, - Phe-Cyc-,-Cyc-Cyc-,-G-Phe-and-G-Cyc-, and optionally one or more components selected from the compounds of the formulae 1,2, 3,4 and 5 in which the radicals L and E are selected from the group consisting of-Phe Cyc-,-Cyc-Cyc-,-G-Phe-and-G-Cyc-.

In a smaller sub-group of the compounds of the formulae 1,2, 3,4 and 5, R' and R"are each, independently of one another, alkyl, alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8 carbon atoms. This smaller sub-group is called group A below, and the compounds are denoted by the sub-formulae 1a, 2a, 3a, 4a and 5a. In most of these compounds, R' and R"are different from one another, one of these radicals usually being alkyl, alkenyl, alkoxy or alkoxyalkyl.

In another smaller sub-group of the compounds of the formulae 1,2, 3,4 and 5, which is called group B, R"is-F,-Cl,-NCS or- (OCHF, where i is 0 or 1, and k and I are 1,2 or 3; the compounds in which R"has this meaning are denoted by the sub-formulae 1b, 2b, 3b, 4b and 5b. Particular preference is given to those compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b in which R"is-F,-Cl,-NCS,-CF3,-OCHF2or-OCF3.

In the compounds of the sub-formulae 1 b, 2b, 3b, 4b and 5b, R'is as defined for the compounds of the sub-formulae 1a-5a and is preferably alkyl, alkenyl, alkoxy or alkoxyalkyl.

In a further smaller sub-group of the compounds of the formulae 1,2, 3,4 and 5, R"is-CN; this sub-group is called group C below, and the compounds of this sub-group are correspondingly described by sub-formulae 1 c,

2c, 3c, 4c and 5c. In the compounds of the sub-formulae 1 c, 2c, 3c, 4c and 5c, R'is as defined for the compounds of the sub-formulae 1 a-5a and is preferably alkyl, alkoxy or alkenyl.

In addition to the preferred compounds of groups A, B and C, other compounds of the formulae 1,2, 3,4 and 5 having other variants of the proposed substituents are also customary. All these substances can be obtained by methods which are known from the literature or analogously thereto.

Besides compounds of the formula I according to the invention, the media according to the invention preferably comprise one or more compounds selected from group A and/or group B and/or group C. The proportions by weight of the compounds from these groups in the media according to the invention are preferably: Group A: 0 to 90%, preferably 20 to 90%, in particular 30 to 90% Group B: 0 to 80%, preferably 10 to 80%, in particular 10 to 65% Group C: 0 to 80%, preferably 5 to 80%, in particular 5 to 50%, the sum of the proportions by weight of the group A and/or B and/or C compounds present in the particular media according to the invention preferably being 5%-90% and in particular from 10% to 90%.

The media according to the invention preferably comprise from 1 to 40%, particularly preferably from 5 to 30%, of the compounds according to the invention. Further preferred media are those which comprise more than 40%, in particular from 45 to 90%, of compounds according to the invention.

The media preferably comprise three, four or five compounds according to the invention.

The media according to the invention are prepared in a manner which is customary per se. In general, the components are dissolved in one another, advantageously at elevated temperature. By means of suitable additives, the liquid-crystalline phases can be modified in accordance with the invention in such a manner that they can be used in all types of liquid-crystal display elements which have been disclosed hitherto. Additives of this type are known to those skilled in the art and are described in detail in the literature (H. Kelker/R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). For example, pleochroic dyes can be added for the production of coloured guest-host systems, or substances can be added to modify the dielectric anisotropy, the viscosity and/or the alignment of the nematic phases.

The examples below are intended to illustrate the invention without representing a limitation. Above and below, percentages are percent by weight. All temperatures are given in degrees Celsius. m. p. denotes melting point, clip. = clearing point, Tg = glass transition temperature. Furthermore, C = crystalline state, N = nematic phase, Sm = smectic phase and I = isotropic phase. The numbers between these symbols indicate the conversion temperatures. An denotes the optical anisotropy (589 nm, 20 C) and As the dielectric anisotropy (1 kHz, 200C). The An and As values of the compounds according to the invention were obtained by extrapolation from liquid-crystalline mixtures consisting of 10% of the particular compound according to the invention and 90% of the commercially available liquid crystal Zou 4792 (Merck, Darmstadt).

The viscosity (mm2/sec) was determined at 20oC.

"Conventional work-up"means that water is added if necessary, the mixture is extracted with methylene chloride, diethyl ether or toluene, the phases are separated, the organic phase is dried and evaporated, and the product is purified by distillation under reduced pressure or crystallization and/or chromatography.

The following abbreviations are used : THF tetrahydrofuran KOtBu potassium tert-butoxide RT room temperature MTB ether methyl tert-butyl ether DCC N, N-dicyclohexylcarbodiimide DMAP 4-dimethylaminopyridine Example 1

10.00 g of2-Bromo-1-chloro-4-iodo-benzene (1) (obtainable by diazotization of 3-bromo-4-chloro-phenylamine and reaction with potassium iodide), 2.384 g of propyne, 0.200 g of Bis (triphenyl) phosphine, 0.054 g of coppersiodide and 25.0 ml Diisopropylamine were combinded at 0 C and stirred over night under nitrogen. Subsequently, the reaction mixture was subjected to conventional work-up, giving 2.

Example 2

7.50 g of 2 were hydrogenated in 225 ml of tetrahydrofurane in the presence of 1.500 g of PUG (10 %), and subjected to conventional work-up, giving 3.

Example 3

7. 00 g of 3 was dissolved in 30. 0 mi of tetrahydrofurane and cooled to -70 OC. At this temperature 17.297 ml of a 15 % solution of butyllithium in hexane were added dropwise and the mixture was stirred of 10 minutes.

Subsequently, CO2 was passed via an inductor tube into the reaction mixture so that the temperature was maintained below-50 oC. At the end of the reaction, the cold bath was removed and the reaction mixture was allowed to warm up to RT. The mixture was subjected to conventional work-up, giving 4.

Example 4

A mixture of 1.50 g of 4, 2.00 g of 5, 2.476 g of DCC and 1.222 g of DMAP in 20 ml of dichloromethan was stirred at RT for 24 h under nitrogen. The reaction mixture was subjected to conventional work-up, giving 6 (K 68.9 I, As = 42, An = 0.03).

The following examples can be prepared analogously : Examples 5-15

FTZ'Q'U (5) ethyl-CO-O-H H (6) n-propyl-CO-O-H F (7) n-pentyl-CO-O-Ct F (8) n-propyl-CO-O-H H (9) n-pentyl-CO-O-H F (10) n-propyloxy-CH2-CH2-H H (11) n-heptyl-CH2-CH2-H F (12) n-propynyl-CH2-CH2-H F (13) n-butyl-C=C-H H (14) n-pentyl-C=C-H F (15) n-pentyloxy-C=C-H F

Examples 16-26

Rr z1 Q (16) ethyl-co-o-H H (17) n-propyl-CQ-O-H F (18) n-pentyl-CO-O-C) F (19) n-propyl-CQ-O-H H (20) n-pentyl-CQ-O-H F (21) n-propyloxy-CH2-CH2-H H (22) n-heptyl-CH2-CH2-H F (23) n-propynyl-CH2-CH2-H F (24) n-butyl-C=C-H H (25) n-pentyl-C=C-H F (26) n-pentyloxy-C=C-H F

Claims

1. A benzonitrile of the formula I

in which R1 is H, an alkyl radical having 1-12 carbon atoms which is unsubstituted or at least monosubstituted by halogen or CN and in which, in addition, one or more CH2 groups may each, independently of one another, be replaced by -O-, -C#C- or

- CH=CH-in such a way that heteroatoms are not connected directly,

Z, Z1 independently of one another are -CO-O-, -O-CO-, CH2CH2-, -C--C-or a single bond, L1,L2 independently of one another are H or F, Q, Q2 independently of one another are H or Cl and

m is 1or2.

2. A benzonitrile as claimed in claim 1, wherein R1 is an alkyl, oxaalkyl or alkoxy radical having 1 to 10 carbon atoms in which one or more CH2 groups have been replaced by-C=C-or-CH=CH-.

3. A benzonitrile as claimed in claim 1 or 2, in which the radical L'is F.

4. A benzonitrile as claimed in claim 1, 2 or 3, in which both radicals Ql and Q2 are simultaneously H.

5. A benzonitrile as claimed in claim 1, 2 or 3, in which the ring A is

6. A benzonitrile as claimed in any of the preceding claims, in which m is 0.

7. A benzonitrile of the formulae 11 to 19 :

in which R2 is alkyl having 1 to 10 carbon atoms, atoms or alkenyl having 2 to 7 carbon atoms.

8. A benzonitrile substantially as hereinbefore described in the foregoing examples.

9. Use of a compound of the formula I as claimed in any of claims 1 to 8 as components of liquid-crystalline media.

10. A liquid-crystalline medium having at least two liquid-crystalline components, wherein it comprises at least one compound of the formula I as claimed in any of claims 1 to 8.

11. A liquid-crystal display element, wherein it contains a liquid crystalline medium as claimed in claim 10.

12. An electro-optical display element, wherein it contains, as dielectric, a liquid-crystalline medium as claimed in claim 10.