GB2092576A - Anisotropic cyclohexylmethyl phenyl ethers for use in liquid crystal mixtures - Google Patents

Abstract

Anisotropic cyclohexylmethyl ether suitable for use as anisotropic, nitrile-free components of liquid crystal mixtures, have the formula: <IMAGE> in which X and Y are the same or are different and each is a hydrogen atom or a C1-C12 alkyl, alkoxy or monoalkylamino group or a group: <IMAGE> (in which R<1> and R<2> are each hydrogen or a C1-C12 alkyl, alkoxy or monoalkylamino group, and Z<1> and Z<2> are each a covalent bond or a methyleneoxy group).

Description

SPECIFICATION Anisotropic cyclohexyl methyl phenyl ethers This invention relates to new an isotropic cyclohexylmethylphenyl ethers and to liquid crystal (LC) mixtures containing them.

Anisotropic, nitrile-free cyclohexanecarboxylic acid esters of the formula:

(trans) (in which R' is an alkyl group and R" is an alkyl or alkoxy group) are known, for example from German Offenlegungsschrift No.2,429,093, and are a class of substance successfully used in LC mixtures. These esters, however, suffer from the disadvantage that they have a certain susceptibility to hydrolysis, a relatively low thermal stability and, due to the presence of the carboxyl group, a relatively high viscosity.

The present invention is concerned with new nitrile-free anisotropic cyclohexylphenyl compounds, in which the bridging group between the cyclohexyl ring and the phenyl ring imparts a higher resistance to hydrolysis and a higher thermal stability as well as a lower viscosity to the compounds.

According to the invention there are provided, as new compounds, cyclohexylmethylphenyl ethers of the formula:

in which: X and Y are the same or are different and each is a hydrogen atom, a C,-C,2 alkyl group, C,-C,2 alkoxy group or C,-C,2 monoalkylamino group or a group of the formula:

(in which: R1 and R2 are the same or are different and each is a hydrogen atom or a C,-C12 alkyl, C1-C12 alkoxy or C,-C,2 monoalkylamino group; and Z' and Z2 each represent a covalent bond or a methyleneoxy group).

Nitrile substituted cyclohexylmethylphenyl ethers are already known from G.W. Gray et al, Mol. Cryst. Liqu. Cryst., Vol.53(1979), pp. 147-166; namely (C3-C7)-alkyl-cyclohexylme- thoxy compounds, in which a pcyanophenyl, p'-cyanobiphenyl or 2-cyanonaphth-(6)-yl group is in each case attached to the methoxy oxygen atom.Although these nitrile compounds are described as being new an isotropic compounds (mesogenic compounds), express reference is made to their greatly reduced clear points (N-l transformation temperatures) and generally elevated melting points, as well as thier pronounced smectic character, compared with the corresponding ester compounds (containing a group -COO- in place of the group -CH2O- as the bridge between the cyclohexyl moiety and the aromatic moiety).

It has surprisingly been found that the nitrile-free cyclohexyl-methylphenyl ethers have comparatively lower melting points than the corresponding nitrile compounds, and in some cases do not exhibit smectic phases. For example, the melting point of the compound of formula (I) in which X is propyl and Y is rapentyl is almost 40"C below the melting point of the corresponding nitrile compound, and the compounds of formula (I) in which X is npentyl and Y is methyl or methoxy do not exhibit smectic phases.

Since nitrile-free anisotropic compounds are becoming increasingly important as components of LC mixtures, e.g. LC mixtures in multiplex operation or LC mixtures having overall negative DK anisotropy, the new nitrile-free cyclohexylmthylphenyl ethers of the invention provide a valuable addition to the range of anisotropic compounds that can be used for such LC mixtures.

A preferred group of compounds of formula (I) are those in which not more than one of the groups X and Y, preferably the group Y, is a cyclic radical (1 a) or (1 b).

Also, those compounds of formula (I), in which not more than one of the groups X, Y, R' and R2 is a hydrogen atom and X and Y are different, are generally preferred.

Preferred examples of the groups Y, R' and R2 are alkyl, alkoxy and monoalkyl amino groups containing not more than 12, preferably not more than 9 and particularly not more than 7 carbon atoms; particular examples of the alkyl residue in such alkyl, alkoxy and monoalkylamino groups are methyl, ethyl, propyl, butyl, npentyl, nhexyl, nheptyl, noctyl, nnonyl, ndecyl, nundecyl and dodecyl groups.

When, according to a preferred embodiment, one of Xand Y is a cyclic radical (la) or (Ib), the bridging group Z' or Z2 iS a metheneoxy group (-CH20-) or a covalent bond (-), the covalent bond generally being preferred to the methylene group.

The compounds of formula (I) can be obtained by known condensation methods according to the generalised reaction scheme (I).

wherein L1 and L2 are starting groups which can form a compound L1L2 during the condensation (I). Examples of the group L' are halogen atoms, e.g. chlorine or bromine, in which case the preferred starting group L2 is a hydrogen atom and the condensation is conveniently carried out in the presence of an acid-binding agent, namely an organic or inorganic base.

The starting materials for the condensation according to the reaction scheme (I) are known as such or can be prepared by analogy to known compounds.

As noted above, the new ethers of formula (I) may be used in LC mixtures. Such mixtures are provided as a further feature of the invention and consist, at least in part, e.g. from 5 to 95 mole %, of nitrile-free compounds which are at least in part those of formula (I). These mixtures may be prepared in a manner known per se, e.g. by mixing the components and heating, and then introducing into known indicator cells.

The ethers of formula (I) are particularly suitable for use in LC mixtures consisting of an an isotropic nitrile-free component and an anisotropic nitrile component. In this case, both the nitrile-free component and the nitrile component may consist of several different compounds and preferred mixtures contain a total of not more than 6 compounds; the nitrile-free component and the nitrile component in each containing from 1 to 5 compounds.

The nitrilefree component may make up 5 to 95 mole % of the mixture.

LC mixtures according to the invention contain at least one compound of formula (I), e.g. in optical proportions of 2 to 40 mole %; the nitrile-free component of the LC mixtures according to the invention may contain one or more compounds of formula (I) in admixture with other, known nitrile-free anisotropic compounds. Known compounds are suitable for use in the nitrile component.

LC mixtures according to the invention are generally suitable as nematic phases with a small optical-anisotropy and low viscosity, e.g. for LC indicators in the form of rotating cells in multiplex operation, for LC indicators operating on the basis of the so-called guest-host effect, and for LC indicators operating according to the inverse guest-host effect or as dynamic scattering cells (DS) or as so-called DDM cells. The LC mixtures of the invention may contain the additives appropriate to the relevant indicator effect, e.g. dyes and pigments for guest-host indicators, and/or optionally cholesterol additives of known type in conventional proportions.

In order that the invention may be well understood the following Examples are given by way of illustration only.

Example 1 Preparation of 4-(trans-4'-n-propylcyclohexylmethoxy)-n pentylbenzene 4-npentylphenol (0.04 M), potassium carbonate (0.2 M) and trans-4-n-proplycyclohexylme- thyl bromide (0.04 M) were mixed with 1 20 ml of 2-butanone. The mixture was heated under reflux and maintained at the reflux temperature for 48 hours with stirring. The mixture was then cooled to room temperature, poured into 400 ml of water, and extracted with diethyl ether. The ether extract was washed with water and dried over magnesium sulphate. The solvent was evaporated and the crude product was then recrystallised several times. The physical characteristics are summarised in Table 1 below.

Examples 2-6 The following compounds of formula (I) were prepared from appropriate starting phenol and cyclohexyl compounds according to the procedure described in Example 1: (2) 4-(trans-4'-*propylcyclohexylmethoxy)-rsbutoxybenzene (3) 4-(trans-4'- > propylcyclohexylmethoxy)-ethoxybenzene.

(4) 4-(trans-4'-n-propylcyclohexylmethoxy-4"-(trans-propylcyclohexyl)-benzene.

(5) 4-(trans-4'-npentylcyclohexylmethoxy)-toluene.

(6) 4-(trans-4'-npentylcyclohexylmethoxy)-anisole.

The properties of these compounds are also shown in Table 1.

TABLE 1 Ex- Formula (I) Phase transition ample temperature* ("C) X Y K S N 1 C3H7 C5H11 . 25.0 . (6.2) . (9.6) 2 C3H7 OC4Hg . 54.5 . (26.8) . (45.8) 3 C3H7 OC2H5 . 73.0 . (45.0) 4 C3H7 . 96.5 . (88.5) . 141.5 5 C5H11 CH3 . 46.5 . (18.1) .

6 C5H11 OCH3 . 46.1 . (38.4) .

* The phase transition temperatures refer to the phases K (crystalline), S (smectic), N (nematic) and (I) (isotropic). Values in brackets denote monotropic anisotropy.

Examples 6-25 The following Examples illustrate further anisotropic nitrile-free compounds of formula (I): (6) 4-(trans-4'-methylcyclohexylmethoxy)-nprnpylbenzene.

(7) 4-(trans-4'-methylcyclohexylmethoxy)- > heptylbenzene.

(8) 4-(trans-4'-n-pentylcyclohexylmethoxy)-n-propylbenzene.

(9) 4-(trans-4'-rFpentylcyclohexylmethoxy)-*pentylbenzene.

(10) 4-(trans-4'-nheptylcyclohexylmethoxy)-toluene.

(11) 4-(trans-4'-methylcyclohexyl methoxy)-nbutoxybenzene.

(12) 4-(trans-4'-methylcyclohexylmethoxy)- > hexyloxybenzene.

(13) 4-(trans-4'- nprnpylcyclohexylmethoxy)-nhexyloxybenzene.

(1 4) 4-(trans-4'- n-pentylcyclohexylmethoxy)-n-ethoxybenzene.

(15) 4(trans-4'-npenwlcyclohexylmethoxy)-nbutoxybenzene.

(16) 4-(trans-4'-methylcyclohexylmethoxy)-rFethylaminobenzene.

(17) 4-(trans-4'-methylcyclohexylmethoxy)-rFhexylaminobenzene.

(18) 4-(trans-4'-npentylcyclohexyl methoxy)-nethylaminobenzene.

(19) 4-(trans-4'-n-pentylcyclohexylmethoxy)-n-butylaminobenzene.

(20) 4-(trans-4'-n-pentylcyclohexylmethoxy)-4"-(trans-n-propylcyclohexyl)-benzene.

(21) 4-(trans-4'-n-propylcyclohexylmethoxy)-4"-(trans-n-pentylcyclohexyl)-benzene.

(22) 4-(trans-4'-tolylcyclohexylmethoxy)-npropylbenzene.

(23) 4-(trans-4'-tolylcyclohexylmethoxy)-rFheptylbenzene.

(24) 4-(trans-4'-methylcyclohexylmethoxy)-4"-rFpropylbiphenyl.

(25) 4-(trans-4'-methylcyclohexylmethoxy)-4"n-heptylbiphenyl.

Claims (11)

1. As new compounds, anisotropic cyclohexylmethylphenyl ethers of the formula:

in which: X and Y are the same or are different and each is a hydrogen atom, a C,-C,2 alkyl group, C1-C,2 alkoxy group or C,-C,2 monoalkylamino group or a group of the formula:

(in which R' and R2 are the same or are different and each is a hydrogen atom or C,-C,2 alkyl, C,-C,2 alkoxy or C,-Ct2 monoalkylamino group; and Z' and Z2 each represent a covalent bond or methyleneoxy group).

2. Compounds as claimed in claim 1 in which only one of X and Y is a group of the formula (la) or (lb).

3. Compounds as claimed in claim 1 in which X is an alkyl, alkoxy or monoalkylamino group containing not more than 9 carbon atoms.

4. Compounds as claimed in claim 3 in which X contains not more than 7 carbon atoms.

5. Compounds as claimed in claim 3 or claim 4 in which Y is an alkyl, alkoxy or monoalkylamino group containing not more than 9 carbon atoms or a group of the formula (la) or (lb).

6. Compounds as claimed in claim 5 in which Y is an alkyl, alkoxy or monoalkylamino group containing not more than 7 carbon atoms.

7. Compounds as claimed in claim 5 in which Y is a group of the formula (Ib).

8. Compounds as claimed in claim 7 in which R2 is an alkyl, alkoxy or alkylamino group containing not more than 9 carbon atoms and Z2 iS a covalent bond.

9. Compounds as claimed in claim 8 in which R2 contains not more than 7 carbon atoms.

10. Compounds as claimed in claim 1 as specifically disclosed herein.

11. A liquid crystal mixture comprising at least in part of nitrile-free anisotropic compounds in which the nitrile-free anisotropic compounds are, at least in part, compounds as claimed in claim 1.