GB2153345A

GB2153345A - Liquid crystal cyanophenyl-pyridines

Info

Publication number: GB2153345A
Application number: GB8401698A
Authority: GB
Inventors: Assya Iosifovna Pavljuchenko; Natalya Ivanovna Smirnova; Evgeny Ivanovich Kovshev; Viktor Vasilievich Titov; Mikhail Fedorovich Grebenkin; Alexandr Vasilievic Ivaschenko; Vadim Mikhailovich Shoshin; Boris Georgievich Gribov; Vladimir Ivanovich Grigos; Galina Ivanovna Karpushkina; Jury Petrovich Bobylev; Alexandr Ivanovich Vasiliev; Vladimir Alexeevich Kozunov; Valentin Alexeevich Tsvetkov; Gennady Alexeevich Beresnev; Mikhail Ivanovich Barnik
Original assignee: VASILIEV ALEXDR IVANOVICH
Current assignee: VASILIEV ALEXDR IVANOVICH
Priority date: 1984-01-23
Filing date: 1984-01-23
Publication date: 1985-08-21
Also published as: CH660362A5; DE3404055C2; NL8400195A; DE3404055A1; FR2558831B1; FR2558831A1; GB8401698D0; GB2153345B

Abstract

Novel 2,5-disubstituted pyridines of the formula: <IMAGE> in which R is C4-C8 alkyl or alkoxy, find utility in liquid crystal compositions comprising one or more of the said compounds optionally with one or more 2,5-disubstituted pyridines of the formula: <IMAGE> in which R' is C1-C9 alkyl, for use in electro-optical devices. Mesomorphic liquid crystal materials comprising the 2,5-disubstituted pyridines of Formula II, in the absence of those of Formula I, are also disclosed.

Description

SPECIFICATION 2,5-disubstituted pyridines, their preparation, and mesomorphic materials and electrooptical devices incorporating same The present invention is concerned with certain novel 2,5-disubstituted pyridines, with a method of preparing same, with mesomorphic liquid crystal materials incorporating same, and with electro-optical devices incorporating such liquid crystal materials.

The 2,5-disubstituted pyridines with which the invention is concerned are useful as intermediate in organic syntheses, as constituents of liquid crystal materials, for the preparation of pharmaceutical compositions, and in a number of other applications.

The most important application of liquid crystals is their use as the working elements of electro-optical devices for information presentation and processing. A whole set of requirements is imposed on liquid crystal materials used for this purpose, among which requirements the most important are the range of working temperatures and the dielectric constants.

The best known liquid crystal electro-optical device is a twist indicator in which use is made of nematic mesomorphic materials with a positive dielectric anisotropy (he > 0). This property is due to the presence in the active compound of a component containing a nitrile group with its constant dipole moment oriented along the long axis of the molecule. Such compounds may be exemplified by cyanodiphenyls of formula I (see British Patent Specification 1,452,826) and cyanophenylcyclohexanes of formula II (see USSR Patent 738516):

in which R is a C3-C8 alkyl group.

Another class of known liquid crystal compounds are 4,4-dialkyl-2,5-diphenylpyridines of formula Ill:

in which R' and R3 are C1-C6 alkyl groups (see D. Demus et al., Fliissige Kristale in Tabellen, 1 974, ''VEB Deutscher Verlag fur Grundstoffindustrie' ' Publishing House, Leipzig, p. 254). The use of these compounds for the provision of mesomorphic materials with a positive dielectic anisotropy is limited by their very high (from 100 to 21 3 'C) melting points and low dielectric constants.

Various 2,5-disubstituted pyridines containing a nitrile group (formulae IV-VII) are also known as mesomorphic materials:

The phase transition temperatures of compounds of formulae IV to VI do not fully satisfy the requirements imposed on the components of mesomorphic materials. Thus, the compound of formula IV (R = C6 alkyl) has a relatively high melting point (52"C) and a low clearing point (26"C) (see A.l. Pavljuchenko, E.l. Kovshev, V.V. Titov, "Khimqa geterocyklicheskikh soedineny" (Chemistry of Heterocyclic Compounds Journal, in Russian), Zinatne Publishing House, Riga, 1981, No. 1, pp. 85-88).Compounds of formulae V and VI also have high melting points (58 to 97"C); among compounds of formula V no enantiotropic liquid crystals have been found, while clearing temperatures of compounds VI are within the range of 80-90"C (see A.

Pavljuchenko, V.V. Titov, N.l. Smirnova, V.T. Grachev, Chemistry of Heterocyclic Compounds Journal, Zinatne Publishing House, Riga, 1980, No. 7 pp. 888-891).

Compounds of formulae IV-VI have dielectric constants which are not too high.

Compounds of formula VII have only been mentioned as mesomorphic, but their properties and a method of preparing them have not hitherto been described in the literature (see V.T.

Grachev, B.E. Zaitsev, E.M. Itskovich, A.l. Pavljuchenko, V.V. Titov, K.M. Djumaev, Molecular Crystals and Liquid Crystals, 1981, vol. 65, No. 1/2, pp. 133-142).

Cyanodiphenyl derivatives of formula I and cyanophenylcyclohexane derivatives of formula II are used in nematic mesomorphic materials. For example, a mesomorphic material having a molar composition of 50% 4-pentyl-4'-cyanobiphenyl, 25% 4-heptyl-4'-cyanobiphenyl, 1 6% 4octyloxy-4'-cycanobiphenyl, and 9% 4-penyl-4'-cyanoterphenyl is known; it has the following characteristics: Lone= 14, the temperature range of the meso-phase is from - 9, to + 60"C. the threshold voltage of the twist effect (Uth,) is 1.5 V, and the saturation voltage (U,,,,) is 1.96 V.

This mixture is extensively used in the manufacture of indicators and is known under the trade mark E7 (availabie from BDH Co., Great Britain). Mixtures based on cyanophenylcyclohexanes of formula II have still lower values of Ae and, accordingly, higher values of threshold and control voltages.

We have now found that 2,5-disubstituted pyridines of formula VI II:

in which R is an alkyl or alkoxy group having from 4 to 8 carbon atoms. have a positive dielectric anisotropy and are suitable for use as components of mesomorphic liquid crystal materials. These compounds are novel and constitute one aspect of the present invention The compounds of formula VIII are, under normal conditions, colourless crystals; they are stable on storage and under the conditions of operation of electro-optical devices. The melting points, clearing temperatures and dielectric constants of these compounds are very favourable to their use as components of mesomorphic liquid crystal materials.

According to another aspect of the invention, there is provided a method of preparing a compound of formula VIII, which comprises reacting a pyrilium salt of formula IX:

in which R has the meaning specified in relation to formula VIII, with ammonium acetate in an organic medium.

Pyrilium salts of formula IX can be prepared from substituted phenylacetic acid and 4cyanoacetophenone according to the following scheme:

As will be seen from this reaction scheme, the preparation of compounds of formula VIII is based on relatively inexpensive and readily available starting materials; the process consists of a small number of stages which do not necessitate any sophisicated process equipment and can be readily implemented on a commercial scale. According to a further aspect of the invention, there is provided a mesomorphic liquid crystal material comprising at least one 2,5-disubstituted pyridine of formula VIII and/or of formula VII.

This liquid crystal material may additionally comprise an organic dielectric and/or a dichroic dyestuff (for the purpose of providing a coloured display).

A mesomorphic material containing 2,5-disubstituted pyridines of formula VII has been described by V.T. Grachev, B.E. Zaitsev, E.M. Itskovich, A.I. Pavljuchenko, V.V. Titov, K.M.

Djumaev, in Molecular Crystals and Liquid Crystals, 1981, vol. 65, No. 1/2, pp. 133-142).

However, neither the properties of the material nor a method of preparing the compounds VII have hitherto been described. These compounds can be prepared from the corresponding pyrilium salts according to the scheme:

The main stage of the synthesis in both cases (ie. the preparation of compounds VIII and compounds VII) is the conversion of a pyrilium salt into a 2,5-disubstituted pyridine derivative.

The bromo-derivative of formula X is converted into the desired product of formula VII by a conventional method, for example treatment with copper cyanide.

The phase transition temperature and dielectric constants of the compounds VII are favourable for their use as components of liquid crystals materials.

The mesomorphic materials according to the invention have a wide range of working temperatures, a high value of positive dielectric an isotropy, and can be used in electro-optical devices which are operated under both static and dynamic control conditions.

According to a still further aspect of the invention, there is provided an electro-optical device containing a mesomorphic liquid crystal material according to the invention.

A preferred embodiment of electro-optical device will now be described, by way of example, with reference to the single Figure of the accompanying drawing, which is a cross-section of the device.

The device comprises a body of mesomorphic liquid crystal material 1 interposed between two spaced, parallel, glass or other transparent electrically non-conducting plates 2. The inner surfaces of the plates 2 are provided with transparent electrodes 3 which are, in turn, provided with conductors 4 for connection to a power supply (not shown).

When a mesomorphic material containing a dichroic dyestuff is used, the device can be used without polarizing layers or with a single polarizing layer 5 positioned on the outer surface of one of the plates 2. When the device is operated under twist indicator conditions, it should be provided with two polarizing layers 5 which are positioned on outer surfaces of both plates 2.

In the device according to the present invention, the molecules of the liquid crystal material in the initial state (before application of an electric field) are oriented parallel to the transparent plates so that in the twist indicator, the direction of orientation in one plate is at the angle of 90 relative to the orientation direction in the other plate. Upon application of an electric field, the liquid crystal molecules are reoriented so that their longitudinal axes become perpendicular to the plates. Visually this is manifested as a colour change (when a mesomorphic material containing a dichroic dyestuff is used) or darkening (under twist conditions) of the cell.

In order that the invention may be more fully understood, the following examples are given by way of illustration. Examples 1 to 9 describe methods of preparing compounds of formula VIII and the properties thereof; Examples 10 to 1 6 describe methods of preparing compounds of formula VII and the properties thereof; Examples 1 7 to 43 describe mesomorphic liquid crystal materials and the properties thereof for use in twist indicators (Examples 1 7 to 40) and materials containing dichroic dystuffs (Examples 41 to 43).

Example 1 Preparation of 5-(4-butylphenyl)-2-(4-cyanophenyl)-pyridine 0.3 Mol of phosphorus oxychloride was added dropwise to 0.5 Mol of anhydrous dimethylformamide at 0 C and 0.1 mol of 4-butylphenylacetic acid was then added at a temperature of - 0 C. The mixture was stirred for 1 hour at 20'C, 2 hours at 60"C and 5 hours at 80"C.

Dimethylformamide was distilled off in vacuo, the residue was cooled and mixed with 20 ml of water and 0.1 mol of magnesium perchlorate in the form of a saturated aqueous solution at the temperature of - 1 0'C. The precipated salt was filtered off and washed with ether to give 21.5 g of a salt melting at 102"C.

0.0182 Mol of 4-cyanoacetophenone was added to a solution of 6.5 g of thus thus-prepared salt in 10 ml of anhydrous pyridine and 0.0182 mol of a 2.5M solution of sodium methylate was slowly added dropwise at a temperature of 20"C. The mixture was stirred for 24 hours at 20'C, pyridine was distilled off, the residue was treated with water and then extracted with benzene. Benzene was distilled off from the extract, the residue was recrystallized from methanol and dissolved in 30 ml of methanol. 5 ml of a 2N hydrochloric acid was added to the resulting solution, the mixture was stirred for 30 minutes, the residue was filtered off, washed with methanol, dissolved in 10 ml of acetic acid and 5 ml of a 70% perchloric acid was slowly added dropwise to the resulting solution.The mixture was diluted with diethyl ether, the residue was filtered off and dissolved in a mixture of 30 ml of acetic acid and 8 g of ammonium acetate. The resulting mixture was stirred for 2 hours, cooled, poured into water, the residue was filtered off and recrystallized from methanol to give 5-(4-butylphenyl)-2-(4-cyanophenyl)pyridine, m.p. 95'C, clearing point 233'C. Dielectric constants (measured at 95'C): E,, = 23.6; E, =6.3; lSe= + +17.3.

Example 2 to 9 Further compounds of formula VIII having the different values of R indicated, were prepared in a manner similar to that described in Example 1. The compounds, and their properties, are shown in Table 1.

Table 1 Example R Temperature, OC, of: No. Melting Clearing 2 C5H11 76 232 3 C6H13 72 221 4 C7H15 69 217 5 C8H17 67 210 6 C4H90 117 165 7 C6H 130 8 251 8 C7H15 0 83 243 9 8 17 89 235 Example 10 Preparation of 5-butyl-2-(4-cyanophenyl)-pyridine A solution of 14.7 g of p-bromophenyl-,P-chlorovinylketone in 20 ml of diethyl ether was added dropwise with stirring to a solution of 10.2 g of N-(hexenyl-1 )-piperidine and 8.34 ml of triethylamine in 10 ml of diethyl ether and the mixture was allowed to stand at room temperature for 1 2 hours.The reaction mixture was diluted with water, ether was distilled off, the residue was filterd off, washed twice with water and mixed with a solution of 25 ml of a 54% perchloric acid in 20 ml of water. The mixture was heated at reflux for 1 5 minutes. The precipitate formed was filtered off after cooling, washed with ether and mixed with a solution of 40 g of ammonium acetate in 150 ml of acetic acid. This mixture was refluxed for 4 hours, poured into 300 ml of water and extracted with benzene. The benzene extract was washed with water, dried over a sodium sulphate, and benzene was distilled off. The residue was recrystallized from hexane to give 5-butyl-(4-bromophenyl)-pyridine, m.p. 76"C.

A mixture of 6 g of 5-butyl-2-(4-bromophenyl)-pyridine, 5.5 g of copper cyanide and 20 ml of N-methyl-pyrrolidone was heated at reflux for 2 hours, cooled, poured into a mixture of 25 ml of a 25% aqueous ammonia and 100 ml of water, and extracted with benzene. The benzene extract was washed to neutral reaction with water, dried over sodium sulphate, and chromatographed by being passed through a bed of alumina having an activity degree of II, elution being effected with benzene. Benzene was distilled from the eluate and, the residue was recrystallized from hexane to give 5-butyl-2-(4-cyanophenyl)-pyridine having m.p. 31"C and clearing temperature, 27.5"C; e,, = 29, e, = 15.5, Ae = + 13.5.

Example 11 to 16 Further compounds of formula VII, having the different values of R indicated, were prepared in a similar manner to that of Example 10. The compounds, and their properties, are shown in Table 2.

Table 2 Exam- Temperature, OC, of Dielectric constants,250C ple R No. Melting Clearing ;,, at L 11 C2H5 68.0 35.5 37 14 +23 12 C3H7 42.3 43.7 36 9.5 +26.5 13 C5H11 32.2 43.5 29 11 +18 14 C6H13 27.2 32.6 25.5 12 +13.5 15 C7H15 28.5 47 24 9.5 +15.5 16 C8H17 39.5 43 - Example 17 Preparation of a mesomorphic material 39.0 mol % of 5-butyl-2-(4-cyanophenyl)pyridine, 40.5 mol% of 5-hexyl-2-(4-cyanophenyl)pyridine and 20.5 mol % of 5-(4-amylphenyl)-2-(4-cyanophenyl)pyridine were introduced into glass breaker, heated with stirring to 90 C and then cooled to room temperature. In this manner a ready-to-use mesomorphic material was obtained which had the following characteristics : range of existence of the meso-phase - from - 7 to + 78 C ; ## = + 18.5 ; Uthr = 1.1 V, Usat = 1.5V ; viscosity at 25 C, 27 cPs.

Examples 18 to 28 In the same manner as in Example 17, other mesomorphic materials were obtained by mixing compounds of the formulae VII and VIII. The resulting mesomorphic materials had the compositions and properties shown in Table 3.

Table 3 Example Composition of mesomorphic No. material Compound R molar % 18 VIII C5H11 22.8 VII C3H7 33.0 VII C4H9 44.2 19 VIII C5H11 25.5 VII C2H5 26.0 VII C4H9 15.8 VII C6H13 32.7 20 VIII C6H13 27.2 VII C 4H9 41.7 VII C6H13 31.1 21 VIII C4H9 18.2 VII C4H9 39.2 VII C5H11 28.9 VII C8H17 13.7 22 VIII C7H15 16.8 VII C4H9 30.4 VII C5H11 21.5 VII C6H13 31.3 Table 3 (continued) 23 VIII C5H11 14.2 VII C3H7 19.2 VII C4H9 24.7 VII C5H1l 16.9 VII C6H13 25.0 24 VIII C8H17O 18.3 VII CH3 25.7 VII C5H11 24.4 CH VII 7 15 20.ö VII C9H19 10.8 25 VIII C6H13 21.5 VII C5H11 21.2 VII C6H13 30.7 VII C7H15 17.6 VII C8H17 9.0 26 VIII C5H1l 15.6 VII C2H5 13.5 VII C5H1l 19.2 VII C6H13 28.1 VII C7H15 15.7 VII C8H17 7.9 Table 3 (continued) 27 VIII C7H15 1.0 VII C2H5 10.0 VII C3H7 16.6 VII C4H9 21.1 VII C51111 14.1 VII C6H13 21.3 VII C7H15 10.8 VII C8H17 5.1 28 VIII C5H11 0.5 VII C2H5 16.5 VII C3H7 26.1 VII C5H11 24.7 VII C7H15 21.1 VII C8H17 11.1 Properties of mesomorphic material Exam- Temperature, Voltage, Anisotropy ple C of V of dielectric No. @@@@ @ constant, Melting Clearing Threshold Saturation 18 -4 +79 0.9 1.3 +20.0 19 -13 +67 1.0 1.4 +19.2 Table 3 (continued) 20 -5 +84 1.1 1.5 +18.6 21 -7 +70.6 1.15 1.6 +18.0 22 -15 +67 1.2 1.6 +18.0 23 -22 +63 1.1 1.5 +18.2 24 -12 +7 1.15 1.65 +18.0 25 -16 +78.6 1.2 1.65 +18.0 26 -25 +62 1.3 1.7 +17.2 27 -16 +40 1.05 1.5 +19.0 28 -12 +45 1.05 1.45 +19 Example 29 to 35 Mesomorphic liquid crystal materials containing compounds of formulae VII and Vlil and, additionally, cyanodiphenyl derivatives of formula I and cyanophenylcyclohexane derivatives of formula II were prepared as described in Example 18. The compositions, and the properties, of these materials are shown in Table 4.

Table 4 Example Mesomorphic material composition No. Compound R Percent by weight 29 II C H 36.1 3 7 II C5H11 30.8 II C7H15 21.1 VIII C5H11 12.0 30 I C5H11 34.5 I C7H15 39.3 VIII C6H13 12.0 VII C5H11 6.0 31 II C3H7 33.6 II C5H11 28.7 II C7H15 19.7 VIII C7H15 8.9 VII C5H11 9.1

32 1 C5H11 55.0 I C7H15 21.0 I C8H17-0 14.0 I 11 + 9.0 VII C5H11 1.0 5 1 33 I C5Hll 10.0 VIII C4H90 17.9 VII C4H9 25.3 VII C5H11 17.5 VII C6H13 29.3 34 II CH 31.5 3 7 II C5H11 20.5 CH VIII 7 15 12.1 VII C5H1l 14.4 VII C6H13 21.7 35 I C3H70 11.8 3 7 I C41igO 7.0 49 I C5H110 10.3 I C6H130 7.3 I C H 0 9.4 1 5 9-4 I CBH170 13.6 I C8H17 5.8 VIII C5H11 5.1 VII C5H11 19.6 Table 4 (continued) Example Mesomorphic material properties No. Temperature, C Voltage, V Melt. Clear Thresh. Satur.

29 -6 +74 1.6 2.35 30 -3 +60 1.4 1.8 31 -12 78 1.6 2.2 32 -10 +60 1.4 1.8 33 -18 +72 1.1 1.5 34 -22 +66 1.4 1.9 35 -7 +70 1.2 1.7 Example 36 In the same manner as in Example 18, a mesomorphic material was prepared which consisted, by weight, of 9.0% of 4-butylbenzoic acid 4-cyanophenyl ester, 21.6% of 4hexylbenzoic acid 4-cyanophenyl ester, 16.5% of 4-heptylbeflzoic acid 4-cyanophenyl ester, 5.0% of 5-methyl-2-(4-cyanophenyl)pyridine, 7.2% of 5-ethyl-2-(4-cyanophenyl)pyridine, 8.4% of 5-propyl-2-(4-cyanophenyl)-pyridine, 13.6% of 5-heptyl-2-(4-cyanophenyl)-pyridine, 6.1% of 5-octyl-2-(4-cyanophenyl)-pyridine, 3.8% of 5-nonyl-2-(4-cuanophenyl)-pyridine and 8.8% of 5 (4-hexylphenyl)-2-(4-cyanophenyl)-pyridine. M.p. - 1 2'C, clearing point + 72 C ; Uthr. 1.OV; Usat. 1.5V.

Example 37 In the same manner as in Example 18, a mesomorphic material was prepared which consisted, by weight, of 25.0% of 5-propyl-2-(4-cyanophenyl)-pyridine, 35.0% of 5-amyl-2-(4cyanophenyl)-pyridine, 18.0% of 4-transbutylcyclohexane carboxylic acid 4-ethyloxyphenyl ester, 12.0% of 4-trans-hexylcyclohexane carboxylic acid 4-ethyloxyphenyl ester, and 11.0% of 4-(4-transbutylcylohexanecarbonyloxy)-4-cyanodiphenyl. M.p. - 80 C, clearing point + 68 C ; Uth,. 1. V; Utat. 1.81 V.

Example 38 In the same manner as in Example 18, a mesomorphic material was prepared which is particularly suitable for use under multiplex control conditions; the material consisted, by weight, of 30.0% of trans-4-n-butylcyclohexane carboxylic acid, 30% of trans-4-n-hexylcyclohexane carboxylic acid, 10% of 2-chloro-4-(4-n-heptylbenzoyloxy)benzoic acid 4-cyanophenyl ester, 10.0% of 5-propyl-2-(4-cyanophenyl]-pyridine, and 10.0% of 5-hexyl-2-(4-cyanophenyl)pyridine; m.p. - 9"C, clearing point + 64 C ; Uthr 1.6 V, multiplex ratio 1:6.

Example 39 In the same manner as in Example 18, a mesomorphic material was prepared which is particularly suitable for use under multiplex control conditions; the material consisted, by weight, of 25.0% of trans-4-butylcyclohexane carboxyic acid, 25.0% of trans-4-hexylcyclohexane carboxylic acid, 15.8% of 4'-octyl-4-cyanodiphenyl, 9.7% of 5-ethyl-2-(4-cyanophenyl) pyrid ine, 15.0% of 5-propyl-2-(4-cyanophenyl)-pyridine, 9.5% of 5-hexyl-2-(4-cyanophenyl)pyridine; m.p. - 5"C, clearing point + 70 C ; Utah. 1.7 V; multiplex ratio 1:5.

Example 40 In the same manner as in Example 18, a mesomorphic material was prepared which consisted, by weight, of 24.7% of 5-butyl-2-(4-cyanophenyl)-pyridine, 1 7.1 % of 5-amyl-2-(4cyanophenyl)-pyridine, 28.6% of 5-hexyl-2-(4-cyanophenyl)-pyridine, 17.4% of 5-(4-butylphenyl)-2-(4-cyanophenyl)-pyridine, 10% of 4-amyl-4'-cyanodiphenyl), and 2.2% of a red dichroic dyestuff with a positive dichroic ratio of 10. This material had m.p. - 1 7'C, clearing temperature + 72.5 C, Uthr 1.1 V ; Usat 1.5 V ; it gave colourless symbols against a red background in a twist indicator.

Example 41 In the same manner as in Example 18, a mesomorphic material was prepared which consisted, by weight, of 25.0% of 5-butyl-2-(4-cyanophenyl)-pyridine, 17.3% of 5-amyl-2-(4cyanophenyl)-pyridine, 29.1% of 5-hexyl-2-(4-cyanophenyl)-pyridine, 17.4% of 5-(4-butylphenyl)-2-(4-cyanophenyl)-pyridine, 10.2% of 4-amyl-4'-cyanodiphenyl, and 1.0% of a goldenyellow dyestuff. The material had m.p. - 1 8'C, clearing point 72 C, Unit, 1.1 V, U 1.5 V and gave black symbols against a golden-yellow background in a twist indicator.

Example 42 In the same manner as in Example 1 8, a mesomorphic material was prepared which consisted, by weight, of 26.8% of trans-4-propyl-(4-cyanophenyl)-cyclohexane, 18.0% of trans4-amyl-(4-cyanophenyl)cylohexane, 12.7% of 5-amyl-2-(4-cyanophenyl)-pyridine, 19.1% of 5hexyl-2-(4-cyanophenyl)-pyridine, 11.4% of 5-(4-heptylphenyl)-2-(4-cyanophenyl)-pyridine, and 12.0% of a red dyestuff with a negative dichroism. This material had m.p. - 1 8'C, clearing point + 63 C, Uthr 1.5V, Usat. 2.0 V and gave pink-red symbols against a colourless background.

Example 43 In the same manner as in Example 1 8, a mesomorphic material was prepared which consisted, by weight, of 30.0% of trans-4-propyl-(4-cyanophenyl)-cyclohexane, 20.2% of 4amyl-(4-cyanophenyl)-cyclohexane, 14.2% of 5-amyl-2-(4-cyanophenyl)-pyridine, 21.4% of 5hexyl-2-(4-cyanophenyl)-pyridine, 12.7% of 5-(4-octylphenyl)-2-(4-cyanophenyl)-pyridine, and 1.5% of a dyestuff having a positive dichroism at the absorption band of 430 nrn and a negative dichrorism at the absorption band of 540 nm. This material had m.p. - 20"C, clearing point + 66.5 C; Utah, 1.4 V, U 1.9 V and gave violet symbols against a yellow background.

Claims

CLAIMS 1. 2-5-Disubstituted pyridines of the formula: in which R is an alkyl or alkoxy group having from 4 to 8 carbon atoms. 2. A method of preparing a 2,5-disubstituted pyridine of the formula set forth in claim 1, which comprises reacting a pyrilium salt of the formula: in which R has the meaning specified in claim 1, with ammonium acetate in an organic medium. 3. A mesomorphic liquid crystal material, which comprises at least one 2,5-disubstituted pyridine of the formula in which R is an alkyl or alkoxy group having from 4 to 8 carbon atoms, and R' is an alkyl group having up to 9 carbon atoms. 4. A mesomorphic liquid crystal material according to claim 3, which additionally comprises up to 99% by weight of one or more organic dielectrics. CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 3 and 4 above have been deleted or textually amended. New or textually amended claims have been filed as follows:-

1. 2,5-Disubstituted pyridines of the formula:

in which R is an alkyl or alkoxy group having from 4 to 8 carbon atoms.

2. A method of preparing a 2,5-disubstituted pyridine of the formula set forth in claim 1, which comprises reacting a pyrilium salt of the formula:

in which R has the meaning specified in claim 1, with ammonium acetate in an organic medium.

3. A mesomorphic liquid crystal material, which comprises at least one 2,5-disubstituted pyridine of the formula specified in claim 1.

4. A mesomorphic liquid crystal material according to claim 3, which additionally comprises up to 99% by weight of one or more organic dielectrics.

5. A mesomorphic liquid crystal material according to claim 3 or 4, which additionally comprises at least one 2,5-disubstituted pyridine of the formula:

in which R' is an alkyl group having up to 9 carbon atoms.

5. A mesomorphic liquid crystal material according to claim 3 or 4, which additionally comprises from 1.0 to 12.0% by weight of a dichroic dyestuff.

6. An electro-optical device containing a mesomorphic liquid crystal material as claimed any of claims 3 to 5.

7. The 2,5-disubstituted pyridine of the formula set forth in claim 1, described in any of Examples 1 to 9.

8. A mesomorphic liquid crystal material substantially as herein described in any of Examples 1 8 to 44.