WO1991015450A1

WO1991015450A1 - Phenyl cyclohexanes and liquid crystal medium

Info

Publication number: WO1991015450A1
Application number: PCT/EP1991/000603
Authority: WO
Inventors: Eike Poetsch; Volker Meyer; Ulrich Finkenzeller
Original assignee: MERCK Patent Gesellschaft mit beschränkter Haftung
Priority date: 1990-04-04
Filing date: 1991-03-28
Publication date: 1991-10-17
Also published as: EP0476103A1; JPH04506361A

Abstract

Novel phenyl cyclohexanes of formula (I) in which Q is -O- or -CO-O-; R is alkyl or alkenyl with up to 12 C atoms; E is -A-, -CH2-CH2-,-CH2CH2-A- or -A-CH2CH2-; A is trans-1,4-cyclohexylene, 1,4-phenylene, 3-fluoro-1,4-phenylene, 3,5-difluoro-1,4-phenylene or a simple bond; X is F, Cl, -CF3, -OCF3 or -OCHF2; and Y and Z are independently H or F; with the proviso that if E = trans-1,4-cyclohexylene and at the same time Q = -CO-O-, X is Cl, -CF3, -OCF3 or -OCHF2 and/or Y = Z = F; can be used as components of liquid crystal media.

Description

Phenylcyclohexanes

and liquid crystalline medium

The invention relates to new phenylcyclohexanes of the formula I

wherein

Q -O- or -CO-O-,

RR alkyl or alkenyl with up to 12 carbon atoms, E -A-, -CH ₂ CH ₂ -, -CH ₂ CH ₂ -A- or -A-CH ₂ CH ₂ -,

A trans-1,4-cyclohexylene, 1,4-phenylene,

3-fluoro-1,4-phenylene, 3,5-difluoro-1,4-phenylene or a single bond.

XF, Cl, -CF ₃ , -OCF ₃ or -OCHF ₂ , and Y and Z are each independently H or F mean, with the proviso that in the case of E = trans-1, 4-cyclohexylene and simultaneously Q = -CO-O-, X Cl, -CF ₃ , -OCF ₃ or

-OCHF ₂ and / or Y = Z = F means.

EP-OS 0 351 846 discloses similar compounds of the formula (X ¹ = H or F)

known. However, these compounds show relatively low values for the dielectric anisotropy. Liquid crystal mixtures containing these compounds

moreover, relatively small values for the electrical resistance and are less suitable for various applications.

The compounds of formula I can be prepared like similar e.g. Compounds known from DE-OS 29 07 332 are used as components of liquid-crystalline media, in particular for displays which are based on the principle of the twisted cell.

The substances hitherto used for this purpose all have certain disadvantages, for example melting points that are too high, clearing points that are too low, stability that is poor with respect to the action of heat, light or electrical fields, electrical resistance that is too low, temperature dependence of the threshold voltage that is too high. Especially with ads of the Supertwist type (STN) with

Twist angles of significantly more than 220 ° C or in displays with an active matrix have disadvantages in the materials used to date. The object of the invention was to find new liquid-crystalline compounds which are suitable as components of liquid-crystalline media, in particular for nematic media with positive dielectric anisotropy, and which do not show the disadvantages of the known compounds or only show them to a lesser extent. This object was achieved by the provision of the new compounds of the formula I.

It has been found that the compounds of the formula I are particularly suitable as components of liquid-crystalline media. In particular, liquid-crystalline media with wide nematic ranges, excellent nematogenicity to very low temperatures, excellent chemical stability, low viscosity with positive dielectric anisotropy, low temperature dependence of the threshold voltage and / or small optical anisotropy can be obtained with their help. The new compounds also show good solubility for other components of such media and relatively high positive dielectric anisotropy with a favorable viscosity.

The compounds of the formula I enable STN displays with a very high steepness of the electro-optical characteristic as well as displays with an active matrix with excellent long-term stability. The compounds of the formula I are colorless in the pure state and form liquid-crystalline mesophases in a temperature range which is favorable for electro-optical use. The invention thus relates to the compounds of

Formula I and the use of the compounds of formula I as components of liquid-crystalline media, liquid-crystalline media containing at least one compound of formula I and electro-optical displays containing such media.

R and Q, E, A, X, Y and Z have the meaning given above and below, unless expressly stated otherwise.

In the compounds of formula I the groups Q are preferably -O-.

The rest are preferred

X is preferably F, Cl, -OCHF ₂ or -OCF ₃ . The compounds of the formula I are prepared by methods known per se, as described in the literature (for example in the standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart), and under reaction conditions that are known and suitable for the implementations mentioned. Use can also be made of variants which are known per se and are not mentioned here in detail.

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

A cyclohexanol of the formula II is preferably

wherein X, Y and Z have the meaning given, by esterification or etherification according to routine methods (e.g.

Tetrahedron, Vol. 44, No. 21, pp. 6677-6680, 1988) converted into the compounds according to the invention.

Some of the starting materials and their reactive derivatives are known, and some of them can be prepared without difficulty from standard compounds of organic chemistry from compounds known from the literature. The precursors of formula II suitable for synthesis can be obtained, for example, according to the following synthesis scheme:

The compounds of formula I with E = trans-1, 4-cyclohexylene are obtained in a completely analogous manner by using

The compounds of formula I with E = 1,4-phenylene, 3-fluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene are also obtained in analogy to the above scheme by using

instead of the bromobenzene derivative. The bromobiphenyl compound can be produced in a manner known per se by coupling reactions catalyzed by noble metals (E. Poetsch, Contacts, Merck, Darmstadt 1988, 15).

The synthesis of the compounds of the formulas according to the invention

Ia and Ib

c

can be seen from the following diagrams:

In addition to one or more compounds according to the invention, the liquid-crystalline media according to the invention preferably contain 2 to 40, in particular 4 to 30, components as further constituents. These media very particularly preferably contain 7 to 25 components in addition to 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 biphenyls, ter phenyls, phenyl or cyclohexyl benzoates, cyclohexane-carboxylic acid phenyl- or cyclohexyl ester, phenyl or cyclohexyl esters of cyclohexylbenzoic acid, phenyl or cyclohexyl esters of cyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl of benzoic acid, of cyclohexanecarboxylic acid, or of cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, Cyclohexylcyclohexenes, cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl or cyclohexylpyridines, phenyl- or cyclohexyldioxanes, phenyl- or cyclohexyl-1,3-diphenyls , 1,2-dicyclohexylethane, 1-phenyl-2-cyclohexylethane, 1-cyclohexyl-2- (4-phenyl-cyclohexyl) -ethane, 1-cyclohexyl-2-biphenylylethane, 1-phenyl-2-cyclohexylphenylethane and tolane. The 1,4-phenylene groups in these compounds can also be fluorinated.

The most important compounds which are suitable as further constituents of media according to the invention can be characterized by the formulas 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-CH ₂ CH ₂ -ER "4

R '-LC≡CER "5 In formulas 1, 2, 3, 4 and 5, L and E, which may be the same or different, each independently represent a bivalent radical from the group consisting of -Phe-, -Cyc-, -Phe-Phe-, -Phe- Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc- as well as their mirror images formed group, whereby Phe unsubstituted or substituted by fluorine-substituted 1,4-phenylene, Cyc- 1,4-cyclohexylene or 1,4-cyclohexenylene, pyr pyrimidine-2,5-diyl or pyridine-2,5-diyl, dio 1,3-dioxane-2,5-diyl and G 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 contain one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, in which L and E are selected from the group Cyc, Phe and Pyr and at the same time one or more components selected from the compounds of Formulas 1, 2, 3, 4 and 5, in which one of the radicals L and E is selected from the group Cyc, Phe and Pyr and the other radical is selected from the group -Phe-Phe-, -Phe-Cyc-, - Cyc-Cyc-, -G-Phe- and -G-Cyc-, and optionally one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, in which the radicals L and E are selected from the group -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-. In the compounds of partial formulas 1a, 2a, 3a, 4a and 5a, R 'and R "each independently represent alkyl, alkenyl, alkoxy, alkenyloxy or alkanoyloxy having up to 8 carbon atoms. In most of these compounds, R' and R" are different from one another different, one of these radicals is usually alkyl or alkenyl. In the connections of the

Sub-formulas Ib, 2b, 3b, 4b and 5b mean R "-CN, -CF ₃ , -OCF ₃ , F, Cl or -NCS; R has the meaning given for the compounds of sub-formulas Ia to 5a and is preferably alkyl or Alkenyl. Particularly preferred is R ", selected from the group consisting of F, Cl, -CF ₃ and

-OCF ₃ . However, other variants of the proposed substituents in the compounds of the formulas 1, 2, 3, 4 and 5 are also common. Many such substances or mixtures thereof are commercially available. All of these substances can be obtained by methods known from the literature or by analogy.

In addition to components from the group of compounds 1a, 2a, 3a, 4a and 5a (group 1), the media according to the invention preferably also contain components from the group of

Compounds 1b, 2b, 3b, 4b and 5b (Group 2), the proportions of which are preferably as follows:

Group 1: 20 to 90%, in particular 30 to 90%,

Group 2: 10 to 80%, in particular 10 to 50%, the sum of the proportions of the compounds according to the invention and of the compounds from groups 1 and 2 giving up to 100%.

The media according to the invention preferably contain 1 to 40%, particularly preferably 5 to 30%, of compounds according to the invention. Also preferred are media containing more than 40%, in particular 45 to 90%, of compounds according to the invention. The media preferably contain three, four or five compounds according to the invention.

The media according to the invention are produced in a conventional manner. As a rule, the components are dissolved in one another, advantageously at elevated temperature. By means of suitable additives, the liquid-crystalline phases according to the invention can be modified so that they can be used in all types of liquid-crystal display elements which have hitherto become known. Such additives are known to the person 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 for producing colored guest-host systems or substances for changing the dielectric anisotropy, the viscosity and / or the orientation of the nematic phases can be added. The media according to the invention are particularly suitable for use in MLC displays. The following examples are intended to illustrate the invention without limiting it, mp. = Melting point, cp. - Clarification point. Foreland below percentages mean percentages by weight; all temperatures are given in degrees Celsius. "Conventional work-up" means: water is added, the mixture is extracted with methylene chloride, the mixture is separated off, the organic phase is dried, evaporated and the product is purified by crystallization and / or chromatography.

They also mean: K: crystalline-solid state, S: smectic phase (the index denotes the phase type), N: nematic state, Ch: cholesteric phase, I: isotropic phase. The number between two symbols indicates the transition temperature in degrees Celsius. DAST Diethylaminosulfur trifluoride

DCC dicyclohexylcarbodiimide

DDQ dichlorodicyanobenzoquinone

DIBALH diisobutyl aluminum hydride

DMSO dimethyl sulfoxide

KOT potassium tertiary butanolate

THF tetrahydrofuran

pTSOH p-toluenesulfonic acid Example 1 a) 7.3 g of trans-4- (p-trifluoromethylphenyl) cyclohexanol (prepared according to scheme 1) in 45 ml of toluene and 3 are added to a mixture of 6.5 g of KOH in 27 ml of tetraethylene glycol dimethyl ether and 45 ml of toluene, 1 g of 1-bromopropen-3 added and stirred for 2 hours at 30 ° in an ultrasonic bath. After the usual work-up and purification, p- (trans-4-allyloxycyclohexyl) trifluoromethylbenzene is obtained as a colorless oil (bp ₁ ~ 180 °). b) This compound according to the invention gives

by hydrogenation on Pd / C or Pt0 ₂ in tetrahydrofuran p- (trans-4-propoxycyclohexyl) trifluoromethylbenzene as a further compound according to the invention.

Analogously to Example 1, the following compounds of the formula I are obtained from the corresponding cyclohexanols

Example 2

0.55 mol benzaldehyde and 0.55 mol Wittigsalz (prepared as described in Scheme 2) are placed at 0 ° C in 820 ml THF. In portions within 15 minutes 0.55 mol of potassium tert-butoxide was added. After stirring for 24 h, the mixture is poured into water, the pH is adjusted to 7 and the organic phase is worked up as usual. The product is dissolved in THF and hydrogenated with 4% palladium-activated carbon at room temperature. The mixture is then filtered off and the filtrate is concentrated in vacuo to the residue. This is chromatographed on a silica gel column.

The following compounds of the formula according to the invention become analogous from the corresponding starting compounds

manufactured:

The following are examples of media containing at least one compound of formula I:

Example A

A mixture of

7% p- (trans-4-propylcyclohexyl) benzonitrile,

5% trans-1- (3,4-difluorophenyl) -4-butyloxycyclohexane,

24% p- (trans-4-pentylcyclohexyl) fluorobenzene,

14% p- (trans-4-heptylcyclohexyl) fluorobenzene,

15% 2-trans-4- (3,4-difluorophenyl) cyclohexyl-5-butyl-1,3-dioxane,

18% 2-trans-4- (p-fluorophenyl) cyclohexyl-5ethyl-1,3-dioxane and

17% 2-trans-4- (p-fluorophenyl) cyclohexyl-5-propyl-1,3-dioxane shows a high electrical resistance.

Claims

1. phenylcyclohexanes of the formula I,

wherein

Q -O- or -CO-O-,

R alkyl or alkenyl with up to 12 carbon atoms,

E -A-, -CH ₂ -CH ₂ -, - CH ₂ CH ₂ -A- or -A-CH ₂ CH ₂ -,

A trans-1,4-cyclohexylene, 1,4-phenylene,

3-fluoro-1,4-phenylene, 3,5-difluoro-1,4-phenylene or a single bond,

XF, Cl, -CF ₃ , -0CF ₃ or -OCHF ₂ , and

Y and Z each independently represent H or F, with the proviso that in the case of E = trans-1,4-cyclohexylene and at the same time Q = -CO-O-, X Cl, -CF ₃ , -OCF ₃ or -OCHF ₂ and / or Y = Z = F.

2. phenylcyclohexane according to claim 1, characterized in that XF, Cl, -OCHF ₂ or -OCF ₃ .

3. phenylcyclohexanes according to claim 1 or 2, characterized

characterized in that Y = Z = H.

4. phenylcyclohexanes according to claim 1 or 2, characterized

characterized in that Y = F and Z = H.

5. Use of the phenylcyclohexanes of the formula I according to

Claim 1 as components of liquid crystalline media for electro-optical displays.

6. Liquid-crystalline medium for electro-optical displays with at least two liquid-crystalline components, characterized in that at least one component is a phenylcyclohexane of the formula I according to claim 1.

7. Electro-optical display based on a liquid crystal cell, characterized in that the liquid crystal cell contains a medium according to claim 6.