WO1995010495A1 - 2,3,4,5-tetrafluorobenzenes and their use in liquid crystal mixtures - Google Patents

Abstract

2,3,4,5-tetrafluorobenzenes of formula (I), in which: R1 is H, a straight-chained or branched alkyl (with or without an asymmetrical C atom) with 1 to 15 C atoms, in which one or two non-adjacent -CH¿2?- groups may also be substituted by -O-, -CH=CH-, -C≡C-, cyclopropane-1,2diyl or -Si(CH3)2- and in which one or more H atoms of the alkyl radical may be substituted by F; A?1, A2 and A3¿ are the same or different and stand for 1,4-phenylene, pyridine-2,5-diyl, pyrimidine-2,5-diyl, in which one or two H atoms may be substituted by F, trans-1,4-cyclohexylene, 1,3-dioxane-2,5-diyl or naphthaline-2,6-diyl; M?1 and M2¿ are the same or different and stand for -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-; X is -CH2-O-, -O-CH2, -CH2CH2- or -O-CO-; k, l, m, n, o and p are zero or one provided that the sum k+m+o is greater than zero; provided that, if X = -CH2CH2- or -O-CO-, the group R?1(-A1)¿k(-M1)l(-A2)m(-M2)n(-A3)o is (a). The substances of the invention are characterized by broad nematic phases in technically relevant temperature ranges. They are highly soluble and, even at high temperatures, exhibit very low conductivity, expressed in a very high holding ratio.

Description

description

2,3,4,5-tetrafluorobenzenes and their use in liquid crystal mixtures

The unusual combination of anisotropic and fluid behavior of the liquid crystals has led to their use in electro-optical switching and display devices. Their electrical, magnetic, elastic and / or their thermal properties can be used to change the orientation. Optical effects can be achieved, for example, with the help of birefringence, the incorporation of dichroic dye molecules (guest host mode) or light scattering.

The practical requirements for liquid crystals are constantly increasing, not least because of the increasing number of light valve types (TN, STN, DSTN, TFT, ECB, DS, GH, PDLC, NCAP, SSFLC, DHF, SBF etc.). In addition to 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, the stability of the liquid crystals is opposite Moisture, gases, temperature and electromagnetic radiation as well as the materials with which they are connected during and after the manufacturing process (eg orientation layers) are of great importance. The toxicological and ecological harmlessness as well as the price are becoming more and more important.

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; WE De Jeu, Physical Properties of Liquid Crystal Materials, Gordon and Breach, Philadelphia, 1 980; H. Kresse, Dielectric Behavior of Liquid Crystals, Progress in Physics, Berlin 1 982, 30, 507-582; HD Koswig, Liquid Crystals, Aulis Verlag Deubner, Cologne, 1 985; "Liquid Crystals, Measurement of the Physical Properties" by E. Merck, Darmstadt; B. Bahadur, Liquid Crystals: Applications and Uses, World Scientific, Singapore, 1,990; HJ Plach et al. _f Liquid Crystals for Active Matrix Displays, in: Solid State Technology, 1992, 6, 186-193; Landolt-Börnstein, New Series, Group IV, Volume 7 Liquid Crystals, 1992-1 993; JW Goodby et al., Ferroelectric Liquid Crystals: Principles, Properties and Applications, Gordon Breach, Philadelphia, 1,991.

The use of special derivatives of 2,3,4,5-tetrafluorobenzene in nematic liquid crystal mixtures is known (see: DE-A 420371 9, DE-A 41 1 1 765 and DE-A 4037519).

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 in which nematic LC phases are used in light valves and to those with smectic phases.

The present invention therefore relates to new 2,3,4,5-tetrafluorobenzene derivatives of the formula (I)

) _n ( _- A _A 3 )x ₀ _- X_v ( I )

1 / -_ A _Λ - _I M _J , / (_-A _A X

) _n (_- A _A 3) x ₀ _- X _v (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-, -CH = CH- , -C ≡ 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;

sind gleich oder verschieden 1 ,4-Phenylen, Pyridin-2,5-diyl, Pyrimidin- 2,5-diyl, in denen ein oder zwei H-Atome durch F ersetzt sein können, trans- 1 ,4-Cyclohexylen, 1 ,3-Dioxan-2,5-diyl oder Naphthalin-2,6-diyl;

are identical or different 1, 4-phenylene, 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, 3-dioxane-2,5-diyl or naphthalene-2,6-diyl;

M ¹ , M ² are identical or different -CH ₂ CH ₂ -, -CH = CH-, -C ≡ C-, -CH ₂ CH ₂ CH CH ₂ -, -CH ₂ CH CH ₂ -O-, -O -CH ₂ CH ₂ CH ₂ -, -CH ₂ CH CO-O-, -O-CO-CH ₂ CH ₂ -, -CH ₂ -O-, -O-CH ₂ -, -CO-O- or - O-CO-;

X is -CH ₂ -O-, -O-CH ₂ -, -CH ₂ CH ₂ - 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 proviso that when X is -CH ₂ CH ₂ - or -O-CO-, the group R ¹ (-A ¹ ) _k (-M ¹ ), (- A ² ) _m (-M ² ) _n ( -A ³ ) ₀

^R EK means.

In a preferred embodiment of the invention, the symbols and indices in the formula (I), while maintaining the above-described proviso, 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, or trans-1, 4-cyclohexylene;

M ¹ , M ² are identical or different -CH ₂ CH ₂ -, -C≡C-, -CH ₂ -O-, -O-CH ₂ -, -CO-O- or -O-CO-;

X is -CH ₂ -O-, -O-CH ₂ -, -CH ₂ CH ₂ - or -O-CO-;

k, I, m, n, o, p are zero or one, provided that the sum k + m + o is greater than zero.

In particular, the 2,3,4,5-tetrafluorobenzenes (11) to (16) listed below are preferred:

F F

R ¹ ^ -CH ₂ 0 → -F (II)

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

The substances according to the invention are distinguished by broad nematic phases in technically relevant temperature ranges. They are readily soluble and show a very low conductivity even at high temperatures, which is expressed in a very high value for the voltage holding capacity (holding ratio).

The compounds according to the invention can generally be prepared without problems by methods known from the literature and familiar to the skilled worker.

Excellent starting compounds for the synthesis of the 2,3,4,5-tetrafluorobenzene (illustrated in Scheme 1) according to the invention are 2,3,4,5-tetrafluorobenzoic acid (II) and bromo-2,3,4,5-tetrafluorobenzene (III) , both of which are commercially available. 2,3,4,5-Tetrafluorobenzoic acid (II) thus provides compounds (I) according to the invention by esterification with alcohols of Z ¹ (see: Tetrahedron 1980, 36, 2409).

Bromine-2,3,4,5-tetrafluorobenzene (III) is converted to 2,3,4,5-tetrafluorophenoKIV by conversion into the corresponding boronic acid using magnesium and trimethyl borate and their subsequent oxidation with hydrogen peroxide (see: Organic Synthesis 1969, 49, 90).

2,3,4,5-tetrafluorophenol (IV) can be converted into 2,3,4,5-tetrafluorobenzene derivatives O) by etherification with hydroxymethyl or halomethyl derivatives of Z ¹ (see: J. Am. Chem. Soc. 1947, 69, 2451; Synthesis 1981, 1).

The metalation of bromine-2,3,4,5-tetrafluorobenzene (III) with lithium or magnesium, followed by reaction with dialkylformamides gives 2,3,4,5-tetrafluorobenzaldehyde (V) (see: J. Org. Chem 1 941, 6, 437; 1986, 51, 3762 and 5106; Organic Synthesis 1985, 64, 1 14), which in Wittig olefins with methylphosphonium salts of Z ¹ and subsequent hydrogenation of the olefinic intermediate leads to species (I) according to the invention ( see: I. Gosney, AG Rowley in Organophosphorous Reagents in Organic Synthesis, Academic Press, New York, 1 979, Chpt. 2).

Compounds of the formula (I) can also be obtained by reducing the 2,3,4,5-tetrafluorobenzaldehyde (V) to the 2,3,4,5-tetrafluorobenzyl alcoholKVI) and then etherifying the same with alcohols and halides of Z ¹ (see here : HO House in Modern Synthetic Reactions, Benjamin, New York, 1 972, p. 49; J. Am. Chem. Soc. 1 947, 69, 2451; Synthesis 1981, 1). Scheme 1:

(I)

Z ¹ = R ¹ (-A ¹ ) _k (-M ¹ ), (- A ² ) _m (-M ² ) _n (-A ³ ) ₀ ; Y = Cl, Br

The synthesis of the radical R ¹ (-A ¹ ) _k (-M ¹ ) ₁ (-A ² ) _m (-M ² ) _n (-A ³ ) ₀ or suitable precursors is carried out according to methods known per se and familiar to the person skilled in the art.

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 compounds 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 (editor).

Dioxane derivatives are expediently prepared by reacting an appropriate aldehyde (or one of its reactive derivatives) with a corresponding 1,3-diol (or one of its reactive derivatives), preferably in the presence of an inert solvent, such as benzene or toluene, and / or a catalyst, e.g. a strong acid, such as 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 in some cases they can be prepared without difficulty from standard compounds of organic chemistry from compounds known from the literature. For example, the aldehydes are through Oxidation of corresponding alcohols or by reducing nitriles or corresponding carboxylic acids or their derivatives, the diols obtainable by reducing corresponding diesters.

Compounds in which an aromatic ring carries at least one F atom as a substituent can also be obtained 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; MJ Sharp, W. Cheng, V. Snieckus, Tetrahedron Letters 1987, 28, 5093; GW 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; EP-A 0 354 434 for the direct linking of 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 obtained by esterifying corresponding carboxylic acids (or their reactive derivatives) with alcohols or phenols (or their reactive derivatives) or by the DCC method (DCC = dicyclohexylcarbodiimide).

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, and also the anhydrides, for example also mixed anhydrides, azides or esters, in particular alkyl esters with 1 -4 C atoms in the alkyl group. Suitable reactive derivatives of the alcohols or phenols mentioned are 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. In particular, 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 are particularly suitable , Dichloromethane or tetrachlorethylene and sulfoxides such as dimethyl sulfoxide or sulfolane.

Ethers of the formula (I) can be obtained by etherification of corresponding hydroxyl compounds, preferably corresponding phenols, the hydroxyl compound advantageously first being converted into a corresponding metal derivative, for example by treatment with NaH, NaNH ₂ , NaOH, KOH, Na ₂ CO ₃ or K CO ₃ in the corresponding alkali metal alcoholate or alkali metal phenolate is converted. 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 radicals R ¹ , reference is also made, for example, to EP-A 0 355 008 for compounds with silicon-containing 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. The provision of compounds of the formula (I) broadly broadens the range of liquid-crystalline substances which are suitable for the preparation of liquid-crystalline mixtures from various application points of view.

In this connection, the compounds of formula (I) have a wide range of uses. Depending on the selection of the substituents, they can serve as base materials from which liquid-crystalline phases are predominantly composed; However, it is also possible to add compounds of the formula (I) to liquid-crystalline base materials from other classes of compounds in order, for example, to influence the dielectric and / or optical anisotropy of such a dielectric and / or to optimize its threshold voltage and / or its viscosity.

Liquid crystalline compounds of formula (I) can be used, for example, for the production of nematic or chiral nematic liquid crystal mixtures which are suitable for use in electro-optical or completely optical elements, e.g. Display elements, switching elements, light modulators, elements for image processing, signal processing or generally in the field of non-linear optics are suitable. In general, they are suitable for the introduction or broadening of a nematic phase in LC mixtures.

The invention therefore also relates to the use of compounds of the formula (I) in liquid crystal mixtures, preferably nematic and chiral nematic.

The invention furthermore relates to liquid crystal mixtures, preferably nematic and chiral nematic, comprising one or more compounds of the formula (I). The liquid crystal mixtures according to the invention generally contain 2 to 20, preferably 2 to 15, particularly preferably 2 to 12 components.

They generally contain 0.1 to 70 mol%, preferably 0.5 to 50 mol%, particularly preferably 1 to 25 mol%, of at least one, preferably 1 to 5, particularly preferably 1 to 3, compounds of the formula ( I).

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. In general, the commercially available liquid crystal mixtures already exist as mixtures of various components, at least one of which is mesogenic, before the addition of the compound (s) according to the invention.

Suitable further constituents of nematic or chiral nematic liquid crystal mixtures according to the invention are examples

4-fluorobenzenes, 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 described for example in DE-A 4 108 448, EP-A 387 032, 4-benzotrifluorides, as described for example in DE-A 4 108 448,

Phenylcyclohexanes, 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). Liquid crystal switching and display devices (LC displays) generally have, inter alia, contains the following components: a liquid-crystalline medium, carrier plates (e.g. made of glass or plastic) coated with electrodes, at least one of which is transparent, 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 nonlinear 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 (e.g. E. Kaneko, Liquid Crystal TV Displays: Principles and Applications of Liquid Crystal Displays, KTK Scientific Publishers, 1987, pp. 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 determination of the melting point, however, is carried out with a DSC device. 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.

If the values for heating and cooling differ, the latter are put in brackets, or the phase sequence is given in ascending and descending order 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 have no nematic phase at 20 ° C. are mixed to 10% by weight in ZLI-1 565 and / or to 20% by weight in ZLI-4792 (commercial nematic liquid crystal mixtures from E. Merck, Darmstadt) and extrapolated the values 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 Abbe refractometer (from Zeiss). To orient the liquid crystal, an orientation layer, obtained from a 1% by weight solution of lecithin in methanol, is applied to the prism.

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. Leehonts, J. Physysique 1978, 39, 869). The electrical variable HR (holding ratio) is determined according to the literature (M.Schadt, Linear and nonlinear liquid crystal materials, Liquid Crystals, 1993, 14, 73-104).

To determine the switching speed (r) and contrast (K), the measuring cell is attached to the turntable of a polarizing microscope between the crossed analyzer and polarizer. To determine the contrast, the measuring cell is positioned by turning it so that a photodiode indicates minimal light transmission (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.

The invention is further illustrated by the following examples, without wishing to restrict it thereby. example 1

2, 3,4, 5-tetrafluorophenyl (trans-4-pentylcyclohexyl) methyl ether

1.97 g (7.50 mmol) of triphenylphosphine are mixed at 0 ° C. in 30 ml of tetrahydrofuran with 1.31 g (7.5 mmol) of diethyl azodicarboxylate and stirred for 0.5 h at room temperature. Then 1.24 g (7.50 mmol) of 2,3,4,5-tetrafluorophenol and 0.92 g (5.00 mmol) of trans-4-pentylcyclohexylmethanol are added and the mixture is stirred at room temperature for 18 hours. After evaporation of the solvent and chromatography on silica gel with hexane, 1.03 g of product are obtained.

The following are prepared as in Example 1:

Example 2 2,3,4,5-Tetrafluorophenyl (trans-4-ethylcyclohexyl) methyl ether

F

Example 3

2,3,4,5-tetrafluorophenyl (trans-4-propylcyclohexyl) methyl ether

Example 4 2,3,4,5-Tetrafluorophenyl (trans-4-butylcyclohexyl) methyl ether

Example 5

2,3,4,5-tetrafluorophenyl- [trans-4- (trans-4-ethylcyclohexyl) cyclohexyl] methyl ether

Example 6

2,3,4,5-tetrafluorophenyl- [trans-4- (trans-4-propylcyclohexyl) cyclohexyl] methyl ether

Beispiel 7

Example 7

2,3,4,5-tetrafluorophenyl- [trans-4- (trans-4-butylcyclohexyl) cyclohexyl] methyl ether

Example 8

2,3,4,5-tetrafluorophenyl- [trans-4- (trans-4-pentylcyclohexyl) cyclohexyl] methyl ether

Example 9 2,3,4,5-Tetrafluorophenyl- [4- (trans-4-ethylcyclohexyl) phenyl] methyl ether

F F

Example 10

2,3,4,5-tetrafluorophenyl- [4- (trans-4-propylcyclohexyl) phenyl] methyl ether

Example 1 1 2,3,4,5-Tetrafluorophenyl- [4- (trans-4-butylcyclohexyl) phenyl] methyl ether

Example 12

2,3,4,5-tetrafluorophenyl- [4- (trans-4-pentylcyclohexyl) phenyl] methyl ether

Example 13

2,3,4,5-tetrafluorophenylmethyl [4- (trans-4-ethylcyclohexyl) phenyl] ether

F F

Beispiel 14 2,3,4,5-Tetrafluorphenylmethyl-[4-(trans-4-propylcyclohexyl)phenyl]ether

Example 14 2,3,4,5-Tetrafluorophenylmethyl [4- (trans-4-propylcyclohexyl) phenyl] ether

Example 15

2,3,4,5-tetrafluorophenylmethyl [4- (trans-4-butylcyclohexyl) phenyl] ether

F F

H _{9 4} - ^ - 0CH ₂ - ^ -F

Example 16

2,3,4,5-tetrafluorophenylmethyl [4- (trans-4-pentylcyclohexyl) phenyl] ether

Example 17 1- (2,3,4,5-Tetrafluorophenyl) -2- [4- (trans-4-pentylcyclohexyl) phenyl] ethane

4.10 g (7.00 mmol) of [4- (trans-4-pentylcyclohexyl) phenyl] methyltriphenylphosphonium bromide are mixed with 0.90 g (7.70 mmol) of potassium tert-butoxide in 41 ml of tetrahydrofuran and stirred for 1 hour . Then 1.25 g (7.00 mmol) of 2,3,4,5-tetrafluorobenzaldehyde in 5 ml of tetrahydrofuran are added dropwise and the mixture is stirred at room temperature for 18 h. 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: hexane = 1: 1). 2.14 g of 1 - (2,3,4,5-tetrafluorophenyl) -2- [4- (trans-4- pentylcyclohexyUphenyljethen are obtained,

which is hydrogenated in 50 ml of tetrahydrofuran using 0.15 g of palladium (10% on activated carbon) until the calculated amount of hydrogen is taken up, filtered off from the catalyst and concentrated. After chromatography on silica gel with hexane, 1.72 g of product are obtained.

The following are prepared as in Example 1 7:

Example 1 8

1 - (2,3,4,5-Tetrafluorophenyl) -2- [4- (trans-4-ethylcyclohexyl) phenyl) ethane

Example 19

1 - (2,3,4,5-Tetrafluorophenyl) -2- [4- (trans-4-propylcyclohexyl) phenyl] ethane

F F

Example 20 1 - (2,3,4,5-Tetrafluorophenyl) -2- [4- (trans-4-butylcyclohexyl) phenyl] ethane

Example 21 2,3,4,5-Tetrafluorobenzoic acid [4- (trans-4-pentylcyclohexyl) phenyl] ester

1.00 g (5.20 mmol) 2,3,4, 5-tetrafluorobenzoic acid, 1.30 g (5.20 mmol) 4- (trans-4-pentylcyclohexyl) phenol, 1.10 g (5.20 mmol ) Dicyclohexylcarbodiimide and 10 mg N, N-dimethylaminopyridine are stirred at room temperature for 18 h. After filtration and evaporation of the solvent purified by column chromatography (silica gel; dichloromethane) and by recrystallization from acetonitrile.

1.05 g of product are obtained.

Phase sequence: X 98 N 126 I 126 N 80 S _A 76 X

The following are prepared as in Example 21:

Example 22

2,3,4,5-Tetrafluorobenzoic acid [4- (trans-4-ethylcyclohexyl) phenyl] ester

Example 23 [4- (trans-4-propylcyclohexyl) phenyl] 2,3,4,5-tetrafluorobenzoate

Beispiel 24 2,3,4,5-Tetrafluorbenzoesäure-[4-(trans-4-butylcyclohexyl)phenyl]ester

Example 24 [4- (trans-4-butylcyclohexyl) phenyl] 2,3,4,5-tetrafluorobenzoate

Examples of use

Table 1 compares the phase ranges and holding ratio of the substance according to the invention from Example 21 with those of reference substances from DE-A 42 03 719, DE-A 41 1 1 765 and JP-A 57/187 380.

Table 1

One recognizes the far better nematic phase positions and phase widths of the compound according to the invention compared to the reference substances R ¹ and R ² . In comparison to R ^3, there is no highly ordered smectic phase (favorable for mixture development) and in particular a significantly better value for the holding ratio.

Table 2 compares the phase ranges of the substance according to the invention from Example 21 with those of a commercially available nematic liquid crystal mixture (ZLI-4792, E. Merck, Darmstadt).

Table 2

The influence of the compound according to the invention on the mixture ZLI-4792 is also very favorable. The nematic-isotropic phase transition is significantly increased and the transition to the smectic phase is shifted by 30 K to lower temperatures, which is very advantageous.

Claims

Claims: 1. 2,3,4,5-tetrafluorobenzene derivatives of the formula (I), F F R ^, (-A ^, ) _k (- ¹ ), (-A ² ) _n (-M ² ) „(- A ³ ) .- X - ^ -F (') 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-, -CH = CH-, -C≡C-, cyclopropane-1,2-diyl or -Si (CH ₃ ) ₂ - can be replaced, and wherein one or more H atoms of the alkyl radical can also be substituted by F; A ¹ , A ² , A ³ are identical or different 1,4-phenylene, pyridine-2,5-diyl, pyrimidine-2,5-diyl, in which one or two H atoms can be replaced by F, trans- 1,4-cyclohexylene, 1,3-dioxane-2,5-diyl or naphthalene-2,6-diyl; M ¹ , M ² are identical or different -CH ₂ CH ₂ -, -CH = CH-, -C≡C-, -CH ₂ CH ₂ CH 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-; X is -CH ₂ -O-, -O-CH ₂ -, -CH ₂ CH ₂ - 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 proviso that when X is -CH ₂ CH ₂ - or -O-CO-, the group R ¹ (-A ¹ ) _k (-M ¹ ), (- A ² ) _m (-M ² ) _n (- A ³ ) ₀

means. 2. 2,3,4,5-tetrafluorobenzenes according to claim 1, characterized in that the symbols and indices in the formula (I) 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, or trans-1, 4-cyclohexylene; M ¹ , M ² are identical or different -CH ₂ CH ₂ -, -C ≡ C-, -CH ₂ -O-, -O-CH ₂ -, -CO-O- or -O-CO-; X is -CH ₂ -O-, -O-CH ₂ -, -CH ₂ CH ₂ - 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 proviso stated in claim 1. 3. 2,3,4,5-tetrafluorobenzenes of the formula (I) according to claim 1 and / or 2, characterized by the formulas (11) to (16): F F

F

in which R ^{1 is} methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl. 4. Use of compounds of formula (I) 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 and / or 6, characterized in that it contains 0.1 to 70 mol% of at least one compound of the formula (I). 8. Liquid crystal mixture according to one or more of claims 5 to 7, characterized in that it contains 1 to 5 compounds of formula (I). 9. Switching and / or display device containing 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 4 and 5.