WO1995013257A1

WO1995013257A1 - 2,6-difluorobenzenes and their use in liquid-crystal mixtures

Info

Publication number: WO1995013257A1
Application number: PCT/EP1994/003534
Authority: WO
Inventors: Hubert Schlosser; Dietmar Jungbauer
Original assignee: Merck Patent Gmbh
Priority date: 1993-11-11
Filing date: 1994-10-27
Publication date: 1995-05-18

Abstract

The invention concerns 2,6-difluorobenzenes of general formula (I) in which the symbols and indices are defined as follows: R1 is H, a straight-chain or branched-chain alkyl (with or without an asymmetric C-atom) with 1 to 15 C-atoms, whereby one or two non-adjacent CH¿2? groups may be replaced by -O-, -S-, -CO-, -CO-O-, -O-CO-, -CO-S-, -S-CO-, -O-CO-O-, -CH=CH-, -C C-, cyclopropane-1,2-diyl or -Si(CH3)2- and whereby one or more H-atoms in the alkyl group may be replaced by F, Cl or CN; A?1, A2 and A3¿, which may be the same or different are 1,4-phenylene, pyrazine-2,5-diyl, pyridine-2,5-diyl or pyrimidine-2,5-diyl in which one or two H-atoms may be replaced by F, trans-1,4-cyclohexylene, 1,4-cyclohexenylene, (1,3,4)-thiadiazole-2,5-diyl, 1,3-dioxane-2,5-diyl, naphthaline-2,6-diyl, bicyclo[2.2.2]octane-1,4-diyl or 1,3-dioxaborinane-2,5-diyl; M?1, M2 and M3¿, which may be the same or different, are -CH¿2?CH2-, -CH=CH-, -C C-, -CH2CH2CH2CH2-, -CH2CH2CH2-O-, -O-CH2CH2CH2-, -CH2CH2CO-O-, -O-CO-CH2CH2-, -CH2-O-, -O-CH2-, -CO-O- or -O-CO-; k, l, m, n, o and p are zero or one, under the condition that the sum k+m+o is greater than zero; with the following provisions: a) when M?3¿ is -O-CO-, R1(-A1)k(-M1)l(-A2)m(-M2)n(-A3)o is replaced by formulae (II) or (III); b) when M3 is -CO-O-, R1(-A1)k(-M1)l(-A2)m(-M2)n(-A3)o is replaced by formulae (IV) in which g is 0 or 1 and (V). The compounds of formula (I) are chemically and photochemically stable. They have low melting points and, in general, wide liquid-crystal phases, in particular wide nematic liquid-crystal phases.

Description

2,6-difluorobenzenes and their use in liquid crystal mixtures

The unusual combination of anisotropic and fluid behavior of the liquid crystals has for their use in electro-optical switching and

Display devices led. Their electrical, magnetic, elastic and / or their thermal properties can increase

Orientation changes can be used. Optical effects can be achieved, for example, with the help of birefringence, the incorporation of dichroic dye molecules (guest host mode) or light scattering.

Practical requirements are constantly increasing, not least because of the increasing number of light valve types (TN, STN, DSTN, TFT, ECB, DECB, DS, GH, PDLC, NCAP, SSFLC, DHF, SBF etc.). Next

thermodynamic and electro-optical variables, such as phase sequence and

Phase temperature range, refractive index, birefringence and dielectric anisotropy, switching time, threshold voltage, steepness of the electro-optical

Characteristic curve, elastic constants, electrical resistance, multiplexability or pitch and / or polarization in chiral phases, is the stability of the

Liquid crystals against moisture, gases, temperature and

electromagnetic radiation as well as to the materials with which they are associated during and after the manufacturing process (e.g.

Orientation layers), of great importance. The toxicological and ecological harmlessness as well as the price are coming more and more

Meaning too.

The following references and the references contained therein provide a broad overview of the field of liquid crystals:

H.Kelker, H.Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim,

1980;

W.E. De Jeu, Physical Properties of Liquid Crystal Materials, Gordon and

Breach, Philadelphia, 1980; H. Kresse, Dielectric Behavior of Liquid Crystals, Advances in Physics, Berlin 30, 10, 1982, 507-582;

B. Bahadur, Liquid Crystals: Applications and Uses, World Scientific, Singapore,

1990;

Landolt-Börnstein, New Series, Group IV, Volume 7 Liquid Crystals, 1992-1993 and

J. W. Goodby et al., Ferroelectric Liquid Crystals: Principals, Properties and

Applications, Gordon Breach, Philadelphia, 1991.

Special derivatives of 2,6-difluorobenzene for use in liquid crystal mixtures are known from the literature (see: JP-A 59/155338 and

JP-A 59/082346).

However, since individual compounds have so far not been able to meet the many different requirements simultaneously, there is an ongoing need for new, improved liquid crystal mixtures and thus for a large number of mesogenic and non-mesogenic compounds of different structures which enable the mixtures to be adapted to the most varied of applications. This applies both to the areas where nematic LC phases are used in

Find light valves, as well as for those with smectic phases.

It has now surprisingly been found that certain derivatives of 2,6-difluorobenzene are particularly suitable for use in liquid crystal mixtures.

The invention therefore relates to new 2,6-difluorobenzenes of the formula (I)

where the symbols and indices have the following meanings: R ¹ is H, a straight-chain or branched (with or without asymmetrical C atom) alkyl with 1 to 15 C atoms, one or two non-adjacent CH ₂ groups also being represented by -O-, -S-, -CO- , -CO-O-, -O-CO-, -CO-S-, -S-CO-, -O-CO-O-, -CH = CH-, -CH C-, cyclopropane-1,2- diyl or -Si (CH ₃ ) ₂ - can be replaced, and one or more H atoms of the alkyl radical can also be substituted by F, Cl or CN;

A ¹ , A ² , A ³ are identical or different 1, 4-phenylene, pyrazine-2,5-diyl, pyridine 2,5-diyl, pyrimidine-2,5-diyl, in which one or two H atoms are represented by F may be replaced, trans-1,4-cyclohexylene, 1,4-cyclohexenylene, (1,3,4) thiadiazole-2,5-diyl, 1,3-dioxane-2,5-diyl, naphthalene-2, 6-diyl, bicyclo [2.2.2] octane-1,4-diyl or 1,3-dioxaborinane-2,5-diyl;

M ¹ , M ² , M ³ are the same or different -CH ₂ CH ₂ -, -CH = CH-, -C≡C-,

-CH ₂ CH ₂ CH ₂ CH ₂ ^_ , -CH ₂ CH ₂ CH ₂ -O-, -0-CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CO-O-,

-O-CO-CH ₂ CH ₂ -, -CH ₂ -O-, -O-CH ₂ -, -CO-O- or -O-CO-; k, I, m, n, o, p are zero or one, provided that the sum k + m + o is greater than zero; with the following requirements:

1. for M ³ equal to -O-CO- R ¹ (-A ¹ ) _k (-M ¹ ) _l (-A ² ) _m (-M ² ) _n (-A ³ ) _o does not apply

and

;

2. and for M ³ equal to -CO-O- R ¹ (-A ¹ ) _k (-M ¹ ), (- A ² ) _m (-M ² ) _n (-A ³ ) _{0 is} omitted

equal with g = 0.1

In a preferred embodiment of the invention, the symbols and indices in the formula (I) while maintaining the above-described requirements have the following meanings:

R ¹ is a straight-chain alkyl having 1 to 15 carbon atoms;

A ¹ , A ² , A ³ are identical or different 1, 4-phenylene, in which one or two H atoms can be replaced by F, trans-1, 4-cyclohexylene or 1, 4cyclohexenylene;

M ¹ , M ² , M ³ are identical or different -CH ₂ CH ₂ -, -C≡ C-, -CH ₂ CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -O-, -O- CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CO-O-, -O-CO-CH ₂ CH ₂ -, -CH ₂ -O-, -O-CH ₂ -, -CO-O- or - O-CO-; k, I, m, n, o, p are zero or one, provided that the sum k + m + o is greater than zero.

Particularly preferred compounds of the formula (I) are the 2,6-difluorobenzenes of the formulas (I1) to (228) listed below:

in which

R ^{1 is} methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl. The compounds according to the invention can generally be prepared without problems by methods known per se from literature and to the person skilled in the art.

Excellent starting compounds for the synthesis of the 2,6-difluorobenzenes (I) illustrated in Scheme 1 are the commercially available compounds 2,6-difluorophenol (II), 2,6-difluorobenzoic acid (III), 2,6-difluorobromobenzene (IV ), 2,6-difluorobenzaldehyde (V) and 2,6-difluorobenzyl alcohol (VI).

2,6-difluorophenol (II) can by esterification with carboxylic acids or carboxylic acid halides of Z ² or by etherification with hydroxymethyl or. Convert halomethyl derivatives of Z ² to 2,6-difluorobenzene derivatives (I) (see: Tetrahedron 1980, 36, 2409; Organic Synthesis, Coll. Vol. 5, 1973, 258; Journal of the American Chemical Society 1947, 69, 245;

Synthesis 1981, 1).

2,6-difluorobenzoic acid (III) gives compounds (I) according to the invention by esterification with alcohols of Z ² (see: Tetrahedron 1980, 36, 2409).

By cross-coupling bromo-2,6-difluorobenzene (IV) with organometallic derivatives of Z ² , for example Grignard, lithium and zinc derivatives, and boronic acids of Z ² using transition metal catalysts, for example dichloro [1, 3-bis (diphenylphosphino) propane] nickel (II), tetrakis (triphenylphosphine) palladium and [1, 1 'bis (diphenylphosphino) ferrocene] palladium (II) chloride

2,6-difluorobenzenes of the formula (I) according to the invention are obtained (see: P. W. Jolly in Comprehensive Organometallic Chemistry, Vol. 8, 1982, p. 721;

Miyaura, M. et al., Synthetic Communications 1981, 1 1, 513; T. Hayashi et al., Journal of the American Chemical Society 1984, 106, 158; Paul L. Castle et al., Tetrahedron Letters 1986, 27, 6013). 2,6-difluorobenzaldehyde (V) is included in Wittig olefins

Methylphosphonium salts of Z ² and subsequent hydrogenation of the olefinic intermediate to species (I) according to the invention (see: I. Gosney, AG Rowley in Organophosphorous Reagents in Organic Synthesis, Academic Press, New York, 1979, Chpt. 2).

Compounds of the formula (I) can also be obtained from 2,6-difluorobenzyl alcohol (VI) by etherification of the same with alcohols and halides of Z ² (see: HO House in Modern Synthetic Reactions, Benjamin, New York, 1972, p. 49; Journal of the American Chemical Society 1947, 69, 2451; Synthesis 1981, 1).

The synthesis of the radical R ¹ (-A ¹ ) _k (-M ¹ ) ₁ (-A ² ) _m (-M ² ) _n (-A ³ ) _o or a suitable precursor is carried out in accordance with known and familiar to the person skilled in the art Methods.

The preparation takes place 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.

For example, reference is made to DE-A 23 44 732, 24 50 088, 24 29 093, 25 02 94, 26 36 684, 27 01 591 and 27 52 975 for connections with

1,4-cyclohexylene and 1,4-phenylene groups; DE-A 26 41 724 for

Compounds with pyrimidine-2,5-diyl groups; DE-A 40 26 223 and

EP-A 03 91 203 for compounds with pyridine-2,5-diyl groups;

WO-A 92/16500 for naphthalene-2,6-diyl groups.

The production of disubstituted pyridines and disubstituted pyrimidines can also be found, for example, in the corresponding volumes of the series "The

Chemistry of Heterocyclic Compounds "by A. Weissberger and E.C. Taylor (editors).

Dioxane derivatives are useful by reacting an appropriate aldehyde (or one of its reactive derivatives) with one

corresponding 1,3-diol (or one of its reactive derivatives)

prepared, preferably in the presence of an inert solvent such as benzene or toluene and / or a catalyst e.g. a strong acid like

Sulfuric acid, benzene or p-toluenesulfonic acid, at temperatures between about 20 ° C and about 150 ° C, preferably between 80 ° C and 120 ° C. Acetals are primarily suitable as reactive derivatives of the starting materials.

Some of the aldehydes and 1,3-diols mentioned and their reactive derivatives are known, and some of them can be copied without difficulty

Standard methods of organic chemistry from literature

Connections are made. For example, the aldehydes are through Oxidation of corresponding alcohols or by reduction of nitriles or corresponding carboxylic acids or their derivatives, the diols obtainable by reduction of corresponding diesters.

Compounds in which an aromatic ring has at least one F atom as

Can also be substituted from the corresponding diazonium salts by exchanging the diazonium group for a fluorine atom, e.g. according to the methods of Balz and Schiemann.

Regarding the connection of the ring systems with each other, reference is made to:

N. Miyaura, T. Yanagai and A. Suzuki, Synth. Comm. 1981, 1 1, 513-519; DE-C-39 30 663; M.J. Sharp, W. Cheng, V. Snieckus, Tetrahedron Letters 1987, 28, 5093; G.W. Gray, J. Chem. Soc. Perkin Trans II 1989, 2041 and Mol. Cryst. Liq. Cryst. 1989, 172, 165; 1991, 204, 43 and 91; EP-A 0 449 015; WO-A 89/12039; WO-A 89/03821 and EP-A 0 354 434 for direct

Linking aromatics and heteroaromatics; DE-A 32 01 721 for

Connections with -CH ₂ CH ₂ bridge members and Koji Seto et al., Liquid Crystals 1990, 8, 861 -870 for connections with -C≡C bridge members.

Esters of the formula (I) can also be correspondingly esterified

Carboxylic acids (or their reactive derivatives) with alcohols or

Phenols (or their reactive derivatives) or by the DCC method (DCC = dicyclohexylcarbodiimide) can be obtained.

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

Suitable reactive derivatives of the carboxylic acids mentioned are

in particular the acid halides, especially the chlorides and bromides, furthermore the anhydrides, for example also mixed anhydrides, azides or esters, in particular alkyl esters with 1-4 C atoms in the alkyl group. Reactive derivatives of the alcohols or phenols mentioned include, in particular, the corresponding metal alcoholates or phenolates,

preferably an alkali metal such as sodium or potassium.

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 carbon tetrachloride, dichloromethane or tetrachlorethylene and sulfoxides such as dimethyl sulfoxide or sulfolane.

Ethers of the formula (I) are more appropriate by etherification

Hydroxy compounds, preferably corresponding phenols, are available, the hydroxyl compound expediently first in a corresponding

Metal derivative, for example by treatment with NaH, NaNH ₂ , NaOH, KOH, Na ₂ CO ₃ or K ₂ CO _{3 is converted} into the corresponding alkali metal alcoholate or alkali metal phenolate. This can then be reacted with the corresponding alkyl halide, sulfonate or dialkyl sulfate, advantageously in an inert solvent such as acetone, 1, 2-dimethoxyethane, DMF or dimethyl sulfoxide, or with an excess of aqueous or aqueous-alcoholic NaOH or KOH at temperatures between about 20 and 100 ° C.

With regard to the synthesis of special R ¹ radicals, reference is also made, for example, to EP-A 0 355 008 for compounds with silicon-containing compounds

Side chains and EP-A 0 292 954 and EP-A 0 398 155 for compounds with cyclopropyl groups in the side chain.

The compounds of the general formula (I) according to the invention are chemically and photochemically stable. They have low melting points and generally broad liquid-crystalline phases, in particular broad nematic ones. Compounds of the formula (I) can be used, for example, for the preparation of nematic or chiral nematic liquid-crystal mixtures

use that are for use in electro-optical or fully optical elements, e.g. Display elements, switching elements,

Light modulators, elements for image processing, signal processing or generally in the field of nonlinear optics are suitable. This also applies to compounds that have no liquid-crystalline phases as the pure substance. In general, the compounds of formula (I) are for introduction or

Suitable for widening a nematic phase in LC mixtures.

The invention therefore also relates to the use of compounds of the formula (I) in liquid-crystal mixtures.

The invention further relates to liquid crystal mixtures which contain one or more compounds of the formula (I).

The liquid crystal mixtures according to the invention generally consist of 2 to 20, preferably 2 to 15 components, including at least one, preferably 1 to 5, particularly preferably 1 to 3, compounds of the formula (I). The LC mixtures according to the invention can be nematic or chiral nematic, for example. The liquid crystal mixtures generally contain 0.1 to 70 mol%, preferably 0.5 to 50 mol%, in particular 1 to 25 mol%, of the compound (s) of the formula (I) according to the invention.

Further constituents of the mixtures according to the invention are preferably selected from the known compounds with nematic or

cholesteric phases; these include, for example, biphenyls, terphenyls, phenylcyclohexanes, bicyclohexanes, cyclohexylbiphenyls, mono-, di- and

Trifluorophenyls. Generally, there are those available commercially

Liquid crystal mixtures before the addition of the invention

Compound (s) as mixtures of various components, at least one of which is mesogenic. Suitable further constituents of nematic or chiral nematic liquid crystal mixtures according to the invention are, for example, 4-fluorobenzenes, as for example in EP-A 494 368, WO 92/06 148, EP-A 460 436, DE-A 4 1 1 1 766, DE-A 4 1 12 024, DE-A 4 1 12 001, DE-A 4 100 288, DE-A 4 101 468, EP-A 423 520, DE-A 392 3064, EP-A 406 468, EP-A 393 577 , EP-A 393 490, - 3,4-difluorobenzenes, as described for example in DE-A 4 108 448, EP-A 507 094 and EP-A 502 407, - 3,4,5-trifluorobenzenes, as for example in DE-A 4 108 448, EP-A

387 032, 4-benzotrifluoride, as described for example in DE-A 4 108 448, phenylcyclohexane, as described for example in DE-A 4 108 448.

Liquid-crystalline mixtures which contain compounds of the general formula (I) are particularly suitable for use in electro-optical switching and display devices (displays). Such switching and

Display devices (LC displays) generally have, inter alia, the following

Components on: a liquid-crystalline medium, carrier plates (e.g. made of glass or plastic), coated with transparent electrodes, at least one orientation layer, spacers, adhesive frames, polarizers and thin color filter layers for color displays. Other possible components are antireflection, passivation, compensation and barrier layers as well as electrically non-linear elements, such as thin-film transistors (TFT) and metal-insulator-metal (MIM) elements. The structure of liquid crystal displays has already been described in detail in relevant monographs (eg E. Kaneko, "Liquid Crystal TV Displays: Principles and Applications of Liquid Crystal Displays", KTK Scientific Publishers, 1987, pages 12-30 and 63-172). Examples

Various measurement methods are used to physically characterize the compounds according to the invention.

The phase transition temperatures are determined with the help of a polarizing microscope on the basis of the texture changes. The

The melting point, however, is determined with a DSC device

carried out. The indication of the phase transition temperatures between the phases

Isotropic (I)

Nematic (N or N ^* )

Smectic-C (S _C or S _C ^* )

Smectic-A (S _A or S _A ^* )

Crystalline (X)

Glass transition (Tg) takes place in ° C and the values are between the phase names in the phase sequence.

With different values for heating and cooling, the latter are in

Parentheses are set, or the phase sequence is given ascending and descending in temperature.

Electro-optical investigations are carried out using methods known from the literature (e.g. B. Bahadur: Liquid Crystals Application and Uses, Vol. I, World Scientific, Singapore, 1990).

For nematic liquid crystals (pure or in a mixture), the values for the optical and dielectric anisotropy and the electro-optical characteristic are recorded at a temperature of 20 ° C. Liquid crystals which do not have a nematic phase at 20 ° C. are mixed to 10% by weight in ZLI-1565 and / or to 20% by weight in ZLI-4792 (commercial nematic liquid crystal mixtures from E. Merck, Darmstadt) the values are extrapolated from the results of the mixture.

Electro-optical characteristics are determined on the basis of the transmission of a measuring cell. For this purpose, the cell is positioned between crossed polarizers in front of a light source. There is a light detector behind the cell, the sensitivity of which is optimized by filters for the visible area of the light. Analogous to the gradual increase in the voltage applied to the cell, the change in transmission is recorded. Values such as threshold voltage and slope are determined from this.

The optical anisotropy is determined using an Abbό refractometer (from Zeiss). To orient the liquid crystal, a

Orientation layer, obtained from a 1% by weight lecithin-methanol solution.

To determine the dielectric anisotropy, a measuring cell with homeotropic and planar orientation is produced and its capacities and dielectric losses are determined with a multi-frequency LCR meter (Hewlett Packard 4274 A). The dielectric constants are calculated as described in the literature (W. Maier, G. Meier, Z. Naturforsch. 1961, 16a, 262 and W.H. de Jeu, F. Leenhonts, J. Physique 1978, 39, 869).

The electrical variable HR (holding ratio) is in accordance with the

References determined (M. Schadt, Linear and nonlinear liquid crystal materials, Liquid Crystals 1993, 14, 73-104).

To determine switching speed (r) and contrast (K), the

Measuring cell attached to the turntable of a polarizing microscope between crossed analyzer and polarizer. To determine the contrast, the measuring cell is positioned by turning so that a photodiode is minimal Indicates light passage (dark state). The microscope illumination is controlled so that the photodiode shows the same light intensity for all cells. After a switching operation, the light intensity (bright state) changes, and the contrast is calculated from the ratio of the light intensity of these states.

Example 1 :

1- [Trans-4- (trans-4-pentylcyclohexyl) cyclohexyl-2,6-difluorobenzene

5.77 g (18.30 mmol) of trans-4- (trans-4-pentylcyclohexyl) bromocyclohexane are dissolved in 50 ml of toluene / tetrahydrofuran (4: 1) with 2.06 g (9.15 mmol) of zinc bromide and 0.25 g (36.60 mmol) of thinly hammered lithium disks in one

Ultrasonic bath exposed to ultrasound until lithium is no longer recognizable. Then 0.21 g of tetrakis (triphenylphosphine) palladium (0) and 3.53 g (18.30 mmol) of bromo-2,6-difluorobenzene are added and the mixture is stirred at room temperature for 18 h. The mixture is then extracted with water and dichloromethane, the organic phase is dried over sodium sulfate and evaporated. To

Chromatography with hexane: ethyl acetate = 9: 1 on silica gel gives 3.85 g of product.

The following are prepared as in Example 1:

Example 2:

1- (trans-4-pentylcyclohexyl) -2,6-difluorobenzene

Example 3:

1- (trans-4-pentylcyclohexylmethoxy) -2,6-difluorobenzene

4.38 g (16.70 mmol) triphenylphosphine are at 0 ° C in 40 ml

Tetrahydrofuran with 2.62 ml (16.70 mmol) diethyl azodicarboxylate and stirred for 0.5 h at room temperature. Then 3.08 g (16.70 mmol) of trans-4-pentylcyclohexylmethanol and 1.44 g (11, 10 mmol) of 2,6-difluorophenol are added and the mixture is stirred at room temperature for 18 h. To

Evaporation of the solvent and chromatography on silica gel with hexane give 3.18 g of product.

The following are prepared as in Example 3:

Example 4:

1- [Trans-4- (trans-4-pentylcyclohexyl) cyclohexylmethoxy] -2,6-difluorobenzene

Example 5:

1- [4- (Trans-4-pentylcyclohexyl) phenylmethoxy] -2,6-difluorobenzene

Example 6:

1 - [3-Fluoro-4- (trans-4-butylcyclohexyl) phenylmethoxy] -2,6-difluorobenzene

Example 7:

1 - [3,5-difluoro-4- (trans-4-pentylcyclohexyl) phenylmethoxy] -2,6-difluorobenzene

Example 8:

4- (Trans-4-propylcyclohexyl) phenyl-2,6-difluorophenyl methyl ether

Phase sequence: X 70 (31) I Example 9:

3-fluoro-4- (trans-4-butylcyclohexyl) phenyl-2,6-difluorophenyl methyl ether

Example 10:

3,5-difluoro-4- (trans-4-pentylcyclohexyl) phenyl-2,6-difluorophenyl methyl ether

Example 11:

4- (Trans-4-pentylcyclohexyl) benzoic acid 2,6-difluorophenyl ester

2.29 g (11.10 mmol) of dicyclohexylcarbodiimide, 3.05 g (11.10 mmol) of 4- (trans-4-pentylcyclohexyl) benzoic acid and 1.44 g (11.10 mmol) of 2,6-difluorophenol stirred with 10 mg of 4-N, N-dimethylaminopyridine in 50 ml of dichloromethane at room temperature for 18 h. After filtration, evaporation of the solvent and chromatographic purification (silica gel; hexane: dichloromethane = 9: 1), 3.17 g of product are obtained.

The following are prepared as in Example 1 1: Example 12:

3-Fluoro-4- (trans-4-propylcyclohexyl) benzoic acid 2,6-difluorophenyl ester

Example 13:

3,5-difluoro-4- (trans-4-butylcyclohexyl) benzoic acid 2,6-difluorophenyl ester

Example 14:

3-fluoro-4- (trans-4-butylcyclohexyl) phenyl 2,6-difluorobenzoate

Example 15:

2,6-difluorobenzoic acid-3,5-difluoro-4- (trans-4-propylcyclohexyl) phenyl ester

Example 16:

1- [2,6-difluorophenyl] -2- (trans-4-pentylcyclohexyl) ethane

1.85 g (3.64 mmol) of trans-4-pentylcyclohexylmethyltriphenylphosphonium bromide are mixed in 20 ml of tetrahydrofuran with 0.44 g (4.00 mmol) of potassium tert-butylate and stirred for 1 hour. Then 0.52 g (3.64 mmol) of 2,6-difluorobenzaldehyde in 3 ml of tetrahydrofuran are added dropwise and the mixture is stirred for 18 hours

Room temperature stirred. After extraction with ether and dilute hydrochloric acid, the organic phase is dried over Na ₂ SO ₄ , concentrated and

purified by chromatography (silica gel, dichloromethane). 0.98 g of 1 - (trans-4-pentylcyclohexyl) -2- [2,6-difluorophenyl] ethene are obtained,

which is hydrogenated in 20 ml of tetrahydrofuran using 10 mg of 10% palladium on activated carbon until the calculated amount of hydrogen has been taken up, filtered off from the catalyst and concentrated. After chromatography on silica gel with hexane: ethyl acetate = 9: 1, 0.84 g of product are obtained.

Phase sequence: Tg -86 X -2 (-42) I Analogously to Example 16 are produced: Example 17: 1- [2,6-difluorophenyl] -2- [trans-4- (trans-4-pentylcyclohexyl) cyclohexyl] ethane

Phase sequence: X 43 S _B 105 (101) I

Example 18:

1- [2,6-difluorophenyl] -2- [4- (trans-4-pentylcyclohexyl) phenyl] ethane

Phase sequence: X 48.5 (0.5) N 3 I

Example 19:

1 - [2,6-difluorophenyl] -2- [3-fluoro-4- (trans-4-butylcyclohexyl) phenyl] ethane

Example 20:

1- [2,6-difluorophenyl) -2- [3,5-difluoro-4- (trans-4-propylcyclohexyl) phenyl] ethane

Example 21:

2 ', 6'-difluoro-4- (trans-4-ethylcyclohexyl) biphenyl

0.77 g (4.00 mmol) bromo-2,6-difluorobenzene 0.93 g (4.00 mmol) 4- (trans-4-ethylcyclohexyl) benzeneboronic acid, 1.02 g (9.60 mmol) sodium carbonate and 0.05 g (0.04 mmol) of tetrakis (triphenylphosphine) palladium (O) are heated in 30 ml of toluene, 15 ml of ethanol and 15 ml of water at 80 ° C. for 4 h. The organic phase is then separated off, evaporated and purified by chromatography on silica gel with heptane, after which 0.81 g of product is obtained.

Phase sequence: X 81 (35) I

The following are prepared as in Example 21:

Example 22:

2 ', 6'-difluoro-4- (trans-4-propylcyclohexyl) biphenyl

Phase sequence: X 74 (41) I

Example 23:

2 ', 6'-difluoro-4- (trans-4-butylcyclohexyl) biphenyl

Phase sequence: X 80 (55)

Example 24:

2 ', 6'-difluoro-4- (trans-4-pentylcyclohexyl) biphenyl

Phase sequence: X ₁ 72 X ₂ 77 (52) I

Example 25:

2 ', 3, 6'-trifluoro-4- (trans-4-pentylcyclohexyl) biphenyl

Example 26:

2 ', 3, 5, 6'-tetrafluoro-4- (trans-4-butylcyclohexyl) biphenyl

Example 27:

2 ', 2 ", 3, 5, 6', 6" -hexafluoro-4-pentylterphenyl

Example 28:

1- [4- (2,6-difluorophenyl) -2,6-difluorophenyl] -2- [4- (trans-4-pentylcyclohexyl) phenyl] ethane

The production takes place analogously to example 16.

Phase sequence: X ₁ 84 X ₂ 111 (98) N 98.5 I

Example 29:

1- [4- (2,6-difluorophenyl) -2,6-difluorophenyl] -2- [trans-4- (trans-4-pentylcyclohexyl) cyclohexyl] ethane The production takes place analogously to example 16.

Phase sequence: X 103 (53) S _x 108 N 165 I

Example 30:

1- [4- (2,6-difluorophenyl) -2,6-difluorophenyl] -2- (trans-4-pentylcyclohexyl) ethane

The production takes place analogously to example 16.

Phase sequence: X 72 (15) I

Example 31:

4- (4-propyl-1-cyclohexenyl) -2 ', 3,5,6'-tetrafluorobiphenyl

3.03 g (29.99 mmol) diisopropylamine and 18.6 ml (29.99 mmol) 1.6 molar n-BuLi solution in hexane are stirred for 0.5 h at 0 ° C. in 125 ml tetrahydrofuran, to -70 ° C cooled and a solution of 5.60 g (24.78 mmol) of 2 ', 3,5,6'-tetrafluorobiphenyl in 750 ml of tetrahydrofuran was added dropwise. After stirring for four hours at -70 ° C., 4.20 g (30.00 mmol) of 4-propylcyclohexanone in 50 ml of tetrahydrofuran are added dropwise. You leave that

Warm the reaction mixture to room temperature overnight, distribute it between aqueous ammonium chloride solution and ether, wash the organic phase with water, dry over sodium sulfate, concentrate and purify the residue by chromatography (silica; dichloromethane), after which 4.60 g of 4- (1- Hydroxy-4-propylcyclohexyl) -2 ', 3,5,6'-tetrafluorobiphenyl can be obtained,

which with 0.25 g of p-toluenesulfonic acid in 250 ml of toluene for 1.5 hours

Water separator is boiled. After partitioning the reaction mixture between aqueous sodium bicarbonate solution and ether, drying the organic phase over sodium sulfate, concentrating and purifying the residue by means of chromatography (silica gel; n-heptane) and recrystallization

Acetonitrile gives 2.53 g of product.

Phase sequence: X 88 (52) I

Example 32:

4- (4-pentyl-1-cyclohexenyl) -2 ', 3,5,6'-tetrafluorobiphenyl

The production takes place analogously to example 31.

Phase sequence: X 94 (85) I Examples of use:

The table shows examples of mixtures with substances according to the invention in comparison with the commercial mixture

ZLI-4792 (E. Merck, Darmstadt).

The two trinuclear substances according to the invention (Ex. 31 and 30) suppress the recrystallization and melting of crystals in the basic mixture, which is very advantageous. A higher order smectic phase transition is also not observed, which leads to a clear broadening of the nematic phase range.

The electro-optical examinations show a reduction in the threshold voltage, which is also an advantage.

The 4-core substances according to the invention (Examples 29 and 28) also significantly reduce the smectic phase transition in the mixture and in some cases also suppress recrystallization very well. They also advantageously increase the nematic-isotropic phase transition; especially the substance from Ex. 28 far more than expected after the pure substance phases.

Claims

Claims:

1 . 2,6-difluorobenzenes of the general formula (I),

where the symbols and indices have the following meanings:

R ¹ is H, a straight-chain or branched (with or without asymmetrical C atom) alkyl with 1 to 15 C atoms, one or two non-adjacent CH ₂ groups also being represented by -O-, -S-, -CO- , -CO-O-, -O-CO-, -CO-S-, -S-CO-, -O-CO-O-, -CH = CH-, -C≡C-, cyclopropane-1,2 -diyl or -Si (CH ₃ ) ₂ - can be replaced, and where one or more H atoms of the alkyl radical can be substituted by F, Cl or CN;

A ¹ , A ² , A ³ are identical or different 1, 4-phenylene, pyrazine-2,5-diyl, pyridine-2,5-diyl, pyrimidine-2,5-diyl, in which one or two H atoms can be replaced by F, trans-1,4-cyclohexylene, 1,4-cyclohexenylene, (1,3,4) thiadiazole-2,5-diyl, 1,3-dioxane-2,5-diyl, naphthalene 2,6-diyl, bicycio [2.2.2] octane-1,4-diyl or 1,3-dioxaborinane-2,5-diyl;

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

-O-CO-CH ₂ CH ₂ -, -CH ₂ -O-, -O-CH ₂ -, -CO-O- or -O-CO-; k, I, m, n, o, p are zero or one, provided that the sum k + m + o is greater than zero; with the following requirements: a. for M ³ equal to -O-CO- R ¹ (-A ¹ ) _k (-M ¹ ) _l (-A ² ) _m (-M ² ) _n (-A ³ ) _o does not apply

b. and for M ³ equal to -CO-O- R ¹ (-A ¹ ) _k (-M ¹ ) _l (-A ² ) _m (-M ² ) _n (-A ³ ) _{o is} omitted

right away

2. 2,6-difluorobenzenes according to claim 1, characterized in that the

Symbols and indices in the general formula (I) have the following meanings while maintaining the stipulations:

R ¹ is a straight-chain alkyl having 1 to 15 carbon atoms;

M ¹ , M ² , M ³ are identical or different -CH ₂ CH ₂ -, -C≡C-, -CH ₂ CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -O-, -O- CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CO-O-, -O-CO-CH ₂ CH ₂ -, -CH ₂ -O-, -O-CH ₂ -, -CO-O- or - O-CO-; k, I, m, n, o, p are zero or one, provided that the sum k + m + o is greater than zero.

3. 2,6-difluorobenzenes of the formula (I) according to claim 1 and / or 2, characterized by the formulas (I1) to (I28):

in which

R ^{1 is} methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl.

4. Use of 2,6-difluorobenzenes according to one or more of claims 1 to 3 in liquid crystal mixtures.

5. A liquid crystal mixture comprising at least one compound of the formula (I) according to one or more of claims 1 to 3.

6. Liquid crystal mixture according to claim 5, characterized in that the liquid crystal mixture is nematic.

7. Liquid crystal mixture according to claim 5 or 6, characterized in that it contains 1 to 8 compounds of formula (I).

8. Liquid crystal mixture according to one or more of claims 5 to 7, characterized in that it contains 0.1 to 70 mol% of at least one

Contains compound of formula (I).

9. switching and / or display device, comprising carrier plates,

Electrodes, at least one polarizer, at least one orientation layer and a liquid-crystalline medium, characterized in that the

liquid-crystalline medium is a liquid-crystal mixture according to one or more of claims 5 to 8.