WO1995010496A1

WO1995010496A1 - 2,3,4-trifluorobenzenes and their use in liquid crystal mixtures

Info

Publication number: WO1995010496A1
Application number: PCT/EP1994/003209
Authority: WO
Inventors: Hubert Schlosser; Dietmar Jungbauer
Original assignee: Merck Patent Gmbh
Priority date: 1993-10-08
Filing date: 1994-09-26
Publication date: 1995-04-20

Abstract

2,3,4-trifluorobenzenes of formula (I), in which R<1> is methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl and M is (a), (b), (c), (d), (e) or (f) in which X is -CH2-O- or -O-CH2, are suitable as components of nematic liquid crystal mixtures.

Description

description

2,3,4-trifluorobenzenes 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 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, WE De Jeu, Physical Properties of Liquid Crystal Materials, Gordon and

Breach, 1980; H. Kresse, Dielectric Behavior of Liquid Crystals, Progress in Physics, Berlin, 1982, 30, 10, 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.

Derivatives of 2,3,4-trifluorobenzene and their use in nematic liquid crystal mixtures are known from DE-A 39 06 052 and DE-A 39 06 058.

However, since individual compounds have so far not been able to meet all of the requirements mentioned at the same time, there is an ongoing need for new, improved liquid-crystal mixtures and therefore 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.

It has now surprisingly been found that special derivatives of

2,3,4-trifluorobenzene in a special way for use in

Liquid crystal mixtures are suitable.

The invention therefore relates to new 2,3,4-trifluorobenzene derivatives of the formula (I).

where the symbols have the following meanings:

R ¹ : methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl;

where X is -CH ₂ -O- or -O-CH ₂ -.

In addition to high positive values for the dielectric anisotropy, the substances according to the invention are distinguished by low melting points and broad nematic phases.

Preferred subclasses of the compounds of the formula (I) according to the invention are those of the formulas (Ia) to (Ig):

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

The compounds according to the invention are chemically and photochemically stable. They are characterized by low melting points, broad nematic phases and surprisingly high positive values for dielectric anisotropy.

The compounds according to the invention can be prepared by methods known per se from the literature (see, for example, Houben-Weyl, methods of

Organic chemistry, Georg Thieme Verlag, Stuttgart).

Excellent starting compounds for the synthesis of 2,3,4-trifluorobenzenes according to the invention illustrated in Scheme 1 are the commercially available species bromo-2,3,4-trifluorobenzene (II) and 2,3,4-trifluorobenzaldehyde (III): Scheme 1:

By cross-coupling bromine-2,3,4-trifluorobenzene (II) with organometallic derivatives of R ¹ -M, for example Grignard, lithium and zinc derivatives, or

Boronic acids of R ¹ -M using transition metal catalysts, for example dichloro [1, 3-bis (diphenylphosphino) propane] nickel (II),

Tetrakis (triphenylphosphine) palladium (O) and [1, 1 'bis (diphenylphosphino) ferrocene] palladium (II) dichloride, 2,3,4-trifluorobenzenes 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. Castie et al., Tetrahedron Letters 1986, 27, 6013).

Furthermore, 2,3,4-trifluorobenzaldehyde (III) leads in Wittig olefinations with methylphosphonium salts of Z ¹ 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). Excellent starting compounds for the synthesis of 2,3,4-trifluorobenzenes with ether bridge according to the invention illustrated in Scheme 2 are 2,3,4-trifluorophenol (IV) and 2,3,4-trifluorobenzyl alcohol (V).

Starting from 2,3,4-trifluorophenol (IV), species of the formula (I) are obtained by etherification with hydroxymethyl or halomethyl derivatives of 4- (trans-4-alkylcyclohexyl) benzene.

The etherification of 2,3,4-trifluorobenzyl alcohol (V) with 4- (trans-4-alkylcyclohexyl) phenols also gives compounds of the formula (I).

For the synthesis, see u. a .:

Journal of the American Chemical Society 1947, 69, 2451;

Synthesis 1981, 1st

Scheme 2:

Y = OH, Cl, Br 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. Of the compounds of formula (I) according to the invention, the liquid crystal mixtures generally contain 0.1 to 70 mol%, preferably 0.5 to 50 mol%, in particular 1 to 25 mol%.

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 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). 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 in 10% by weight in ZLI-1565 and / or in 10% by weight in ZLI-4792 (commercial nematic liquid crystal mixtures from E. Merck, Darmstadt) and 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 Abbέ 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 (T) 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-ethylcyclohexyl) cyclohexyl] -2,3,4-trifluorobenzene

5.00 g (18.30 mmol) of 4- (trans-4-ethylcyclohexyl) 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) thin hammered lithium discs in one

Ultrasonic bath exposed to ultrasound until lithium is no longer recognizable. Then 0.21 g of tetrakis (triphenylphosphine) palladium and 3.86 g (18.30 mmol) of bromo-2,3,4-trifluorobenzene are added and the mixture is stirred for 18 hours

Room temperature stirred. Then it is mixed with water and dichloromethane

extracted, the organic phase dried over sodium sulfate and evaporated. After chromatography with hexane: ethyl acetate = 9: 1 on silica gel, 3.42 g of product are obtained.

The following are prepared as in Example 1:

Example 2:

1 - [Trans-4- (trans-4-propylcyclohexyl) cyclohexyl] -2,3,4-trifluorobenzene

Example 3:

1- [Trans-4- (trans-4-butylcyclohexyl) cyclohexyl] -2,3,4-trifluorobenzene

Example 4:

1- [Trans-4- (trans-4-pentylcyclohexyl) cyclohexyl] -2,3,4-trifluorobenzene

Example 5:

1 - [4- (Trans-4-pentylcyclohexyl) phenyl] -2,3,4-trifluorobenzene

1.00 g (4.74 mmol) bromo-2,3,4-trifluorobenzene, 1.60 g (5.70 mmol) 4- (trans-4-pentylcyclohexyl) benzeneboronic acid, 1.21 g (11.40 mmol) sodium carbonate and 0.06 g (0.05 mmol) tetrakis (triphenylphosphine) palladium (0) are heated in 30 ml toluene, 15 ml ethanol and 15 ml 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 1.10 g of 1 - [4- (trans-4-pentylcyclohexyl) phenyl] -2,3,4-trifluorobenzene are obtained.

Phase sequence: X 52 (23) N 102 I

The following are prepared as in Example 5: Example 6:

1- [4- (Trans-4-ethylcyclohexyl) phenyl] -2,3,4-trifluorobenzene

Phase sequence: X 58 (30) N (56) I

Example 7:

1 - [4- (Trans-4-propylcyclohexyl) phenyl] -2,3,4-trifluorobenzene

Phase sequence: X 50 (21, 5) N 95 I

Example 8:

1- [4- (Trans-4-butylcyclohexyl) phenyl] -2,3,4-trifluorobenzene

Phase sequence: X 51 (9) N 92 I

Example 9:

1 - [4- (Trans-4-hexylcyclohexyl) phenyl] -2,3,4-trifluorobenzene

Example 10:

1 - [4- (Trans-4-heptylcyclohexyl) phenyl] -2,3,4-trifluorobenzene

Example 1 1:

1- [4- (Trans-4-octylcyclohexyl) phenyl] -2,3,4-trifluorobenzene

Example 12:

1 - (Trans-4-pentylcyclohexyl) -2- (2,3,4-trifluorophenyl) ethane

1.85 g (3.64 mmol) of trans-4-pentylcyclohexylmethyl triphenylphosphonium bromide are mixed with 0.44 g (4.00 mmol) of potassium tert-butylate in 20 ml of tetrahydrofuran and the mixture is stirred for 1 hour. Then 0.58 g (3.64 mmol) of 2,3,4-trifluorobenzaldehyde in 3 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). There are 0.93 g of 1 - (trans-4-pentylcyclohexyl) -2- (2,3,4-trifluorophenyl) ethane obtained, which in 20 ml of tetrahydrofuran using 10 mg of palladium 10% on activated carbon until the calculated

Amount of hydrogen is hydrogenated, filtered off from the catalyst and concentrated. After chromatography on silica gel with hexane: ethyl acetate = 9: 1, 0.85 g of product is obtained.

Phase sequence: Tg -92 X -5 (-45) N (-34) I

The following are prepared as in Example 12:

Example 13:

1- (Trans-4-ethylcyclohexyl) -2- (2,3,4-trifluorophenyl) ethane

Example 14:

1- (Trans-4-propylcyclohexyl) -2- (2,3,4-trifluorophenyl) ethane

Example 15:

1- (Trans-4-butylcyclohexyl) -2- (2,3,4-trifluorophenyl) ethane

Example 16:

1- [Trans-4- (trans-4-propylcyclohexyl) cyclohexyl] -2- (2,3,4-trifluorophenyl) ethane

Example 17:

1- [Trans-4- (trans-4-pentylcyclohexyl) cyclohexyl] -2- (2,3,4-trifluorophenyl) ethane

Phase sequence: X 33 (-41) S _B 91 N 121 I

Example 18:

1 - [4- (Trans-4-ethylcyclohexyl) phenyl] -2- (2,3,4-trifluorophenyl) ethane

Example 19:

1 - [4- (Trans-4-propylcyclohexyl) phenyl] -2- (2,3,4-trifluorophenyl) ethane

Example 20:

1 - [4- (Trans-4-butylcyclohexyl) phenyl] -2- (2,3,4-trifluorophenyl) ethane

Example 21:

1 - [4- (Trans-4-pentylcyclohexyl) phenyl] -2- (2,3,4-trifluorophenyl) ethane

Phase sequence: X 52 N (50) I

Example 22

2,3,4-trifluorophenyl- [4- (trans-4-ethylcyclohexyl) phenyl] methyl ether

1.97 g (7.50 mmol) triphenylphosphine are at 0 ° C in 30 ml

Tetrahydrofuran was mixed with 1.31 g (7.5 mmol) of diethyl azodicarboxylate and stirred at room temperature for 0.5 h. Thereafter, 1.1 g (7.50 mmol) of 2,3,4-trifluorophenol and 1.64 g (7.50 mmol) of 4- (trans-4-ethylcyclohexyl) benzyl alcohol are added and the mixture is stirred at room temperature for 18 h. After evaporation of the solvent and chromatography on silica gel with hexane, 1.86 g of product are obtained.

The following are prepared as in Example 22:

Example 23

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

Example 24

2,3,4-trifluorophenyl- [4- (trans-4-butylcyclohexyl) phenyl] methyl ether

Example 25

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

Phase sequence: X 39.5 (20) N 40 I

Example 26

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

Phase sequence: X 77 (49) I Example 27

2,3,4-trifluorophenylmethyl [4- (trans-4-propylcyclohexyl) phenyl] ether

Phase sequence: X 77 (56) I

Example 28

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

Phase sequence: X 72.5 (57.5) I

Example 29

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

Phase sequence: X 70 (60) N (61) I

Example of use:

10% by weight are added to a commercial nematic liquid crystal mixture (ZLI-4792, E. Merck, Darmstadt, Germany).

the substance from Example 5 mixed.

The phase sequence results:

S _x - 54 N 94 I

In contrast, the mixture has the phase sequence without addition of the substance according to the invention

S _x - 44 N 94 I

on.

It can be seen how the substance according to the invention significantly broadens the nematic phase and is able to suppress the highly ordered smectic phase.

The extrapolated values for the dielectric and the optical anisotropy are:

Δ∈ = + 1.8 (25 ° C) and Δn _D = 0.139 (25 ° C)

They are in good agreement with the results obtained from the pure substance.

Δ∈ = + 2.2 (60 ° C) and Δn _D = 0.139 (25 ° C).

Comparative Example:

The substance according to the invention from Example 5 is compared with a 2,3,4-trifluorobenzene derivative from DE-A 39 06 052:

Phase sequence Ex. 5: X 52 (23) N 102 I

Phase sequence comparative example: X 81 (42) S _B (65) N 1 1 1 The substance according to the invention is distinguished by a broader nematic phase, a lower melting point and the absence of a higher-order smectic phase.

Furthermore, the extrapolated values for the dielectric anisotropy, Δ∈, were compared:

A € Example 5: 1, 8 (25 ° C)

A € comparative example: -3 (25 ° C).

The substance according to the invention shows a significantly stronger positive

dielectric anisotropy, which is more favorable, for example, for use in TN, STN and TFT-TN cells.

Claims

Claims:

1. 2,3,4-trifluorobenzene derivatives of the formula (I),

where the symbols have the following meanings:

M:

where X is -CH ₂ -O- or -O-CH ₂ -.

2. 2,3,4-trifluorobenzene derivatives of the formula (I) according to claim 1,

characterized by the formulas (la) to (Ig),

3. Use of 2,3,4-trifluorobenzenes according to claim 1 and / or 2 in liquid crystal mixtures.

4. Liquid crystal mixture containing at least one compound of the formula (I) according to claim 1 and / or 2.

5. Liquid crystal mixture according to claim 4, characterized in that the liquid crystal mixture is nematic.

6. Liquid crystal mixture according to claim 4 or 5, characterized in that it contains 1 to 8 compounds of formula (I).

7. Liquid crystal mixture according to one or more of claims 4 to 6, characterized in that it contains 0.1 to 70 mol% of at least one

Contains compound of formula (I).

8. 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 4 to 7.