NO138631B - NEMATIC MIXTURES. - Google Patents

Description

The invention relates to nematic mixtures for electro-optics

purposes, which contain one or more compounds of the general formula

where R means ethyl, n-propyl, n-butyl, n-pentyl, iso-

hexyl, n-hexyl, n-heptyl or n-octyl,

and possibly one or more other nematic substances.

The mixtures according to the invention have in liquid crystalline

state a positive anisotropy for the dielectric constants (£yy • ^> S^, whereby means the dielectric constant along the molecular length axis and means the dielectric constant perpendicular to this).

In an electric field, the nematic liquid crystals orient

according to the invention (when £yy ^^ j} se<=* slilc that the direction of their largest dielectric constants, i.e. their length-

axes, lie parallel to the field direction. This effect is used, among other things, in the according to J.H. Heilmeier and L.A. Zanoni [Applied Physics letters 13, 91 (1968)] described interaction between

embedded molecules and liquid crystalline molecules (guest

host interaction). A further interesting application of the dielectric field orientation is found in that of M.

Schadt and W. Helfrich [Applied Physics Letters 18, 129 (1971)']

invented rotary cell.

When it comes to this electro-optical rotary cell, it is essentially a capacitor with light-transmitting . electrodes, the dielectric of which is formed by a nematic substance with c // The molecular longitudinal axes of the liquid crystals are in the field-free state helically arranged between the capacitor plates, whereby the helical structure is determined by the given lateral surface orientation of the molecules. After applying an electric voltage to the capacitor plates, the molecules align themselves in the field direction with their longitudinal axes (i.e. perpendicular to the plate surface), whereby linearly polarized light is no longer rotated in the dielectric. (The liquid crystal becomes vertically uniaxial in relation to the surface of the plate).

This effect is reversible and can be used to control the optical transparency of the electric capacitor.

In such a "light-turn cell" it is desirable to use substances which have a low melting point and a low viscosity.

The substances used for this purpose up to now have the disadvantage that they only show nematic properties at relatively high temperatures, so that the electro-optical devices, which contain liquid crystals, must be heated and possibly regulated by means of a thermostat. The known substances also exhibit a high viscosity, which e.g. in the case of electro-optical devices, this leads to the serious disadvantage that operation is conditioned by relatively high voltages and a long response time.

It was now surprisingly found that the mixtures according to the present invention not only exhibit the necessary large positive anisotropy for the dielectric constants, but are also liquid crystalline at relatively low temperatures, and exhibit a low viscosity. It is obviously possible to carry out the process at lower voltages, and the response time is shorter. A further advantage of the mixtures according to the present invention lies in the fact that they can form undercut nematic phases, which leads to a high stability in the nematic region which is very important for practical use.

The compounds of formula I can be used in the form of their mixtures with each other or with other nematic substances.

Particularly preferred are mixtures whose composition corresponds to a eutectic.

Particularly preferred are mixtures of

p-f(p-n-hexylbenzylidene)amino]benzonitrile and of p-[(p-n-butylbenzylidene)amino]benzonitrile in a molar ratio of 2:1 to 1:2, as well as

P-[(p-n-propylbenzylidene)aminojbenzonitrile and of P-[(p-n-hexylbenzylidene)amino]benzonitrile in a molar ratio of 1:2; of p-[(p-n-heptylbenzylidene)amino]benzonitrile and of p-[(p-n-butylbenzylidene)amino]benzonitrile in a molar ratio of 2:15 of p-[(p-n-octylbenzylidene)amino]benzonitrile and of p-[ (p-n-pentylbenzylidene)amino]benzonitrile in a molar ratio of 2:1 ■ •. ■ ...; p-[ (p-n-butoxybenzylidene)aminoJbénzonitrile, .and .av. " .v-P-[(p-n-hexylbenzylidene)amino]benzonitrile in a molar ratio, of 1:2. • ' i./'■ . '_■;

The compounds of the general formula I can be prepared by

that one -r- '':'. • •'.'.<'

a) reacts a compound of formula II -: .. /

wherein R has the above meaning,

with p-aminobenzonitrile or

b) dehydrates a compound of formula II

"wherein R has the meaning given above.

In embodiment a) of the method, a p-alkylbenzaldehyde of formula II is condensed with p-aminobenzonitrile. This reaction is conveniently carried out in an inert solvent, such as e.g. alcohol, such as methanol, ethanol, isopropanol, hydrocarbons, such as benzene, toluene, xylene, chlorinated hydrocarbons, such as chloroform, methylene chloride or ethylene chloride. The reaction temperature is between approx. 0 and 160°, preferably between 20 and 130°. The reaction is preferably carried out at normal pressure. By working in a water-immiscible solvent, the water formed is advantageously separated using a water separator. The reaction is accelerated by the addition of a catalytic amount (up to 5% of the aldehyde weight) of an inorganic, such as sulfuric acid, hydrochloric acid or an organic strong acid, such as e.g. ethanesulfonic acid, p-toluenesulfonic acid, benzenesulfonic acid etc.

In embodiment b) of the method, the compounds of formula I are prepared by dehydration of corresponding compounds of formula III. For the dehydration, all agents known in the literature for analogous dehydrations are suitable, such as e.g. potassium permanganate, selenium dioxide, hypochlorite, ferric chloride, chromic acid, solvoxide. Particularly preferred is manganese dioxide in chlorinated hydrocarbons, such as chloroform, methylene chloride or ethylene chloride or in hydrocarbons, such as benzene, toluene or xylene. According to a preferred embodiment, manganese dioxide (8 mol per mol amine) is first heated alone for 5 hours in benzene under reflux and the water obtained is separated using a water separator, then the amine is added and the mixture is heated for a further 10 hours under reflux and the water formed are separated from. The reaction is advantageously carried out at normal pressure.

The physical properties of the compounds of formula I are visualized with the help of the tables below:

Some exemplary compositions of the mixtures according to the invention are summarized in the following tables:

All indications are in mol%.

The compounds of formula I can also be used in the form of their mixtures with other known nematic substances, e.g. with compounds of formula IV

where means straight chain alkyl with 4-7 carbon atoms,

or with compounds of formula V

where R2 means straight-chain alkyl with 4-7 carbon atoms or straight-chain alkanoyl with 2-6 carbon atoms, or with compounds of the general formula VI

where R3 means straight-chain alkyl with 4-8 carbon atoms or straight-chain alkoxy with 5-8 carbon atoms.

The compounds with the general formula VI where R^ means straight-chain alkyl with 4-8 carbon atoms are described in Norwegian patent application 2390/73.

The preparation of the compounds of formula I is illustrated by means of the following examples. All temperatures are given in degrees Celsius.

EXAMPLE 1

A mixture of 5.9 g (0.05 mol) p-aminobenzonitrile and 6.7 g (0.05 mol) p-ethylbenzaldehyde is gassed in 100 ml of benzene after the addition of 150 mg of p-toluenesulfonic acid with nitrogen and heated for 1 hour under reflux (bath temperature 120°). The water formed is separated with a water separator. Over the course of a further hour, the benzene condensing in the reflux condenser is now led back through a layer of 50 g of aluminum oxide (Act. I) into the reaction vessel. After cooling, 2 g of solid potassium carbonate are added, the mixture is filtered and the filtrate is freed from the solvent at 50° bath temperature in vacuum. 11.5 g of yellow oil remains, which crystallizes on cooling. For purification, recrystallize several times from i-propanol until a constant melting point and until the by-products disappear in the gas chromatogram. The pure p-[(p-ethylbenzylidene)-amino]benzonitrile melts at 76.2 - 77.0° and is liquid crystalline on cooling at 63.0 - 59.7°.

UV (EtOH)<:> £-2 77 = 25800 (Schulter at 316 nm).

NMR, MS, IR and microanalysis correspond to the substance.

EXAMPLE 2

A mixture of 5.9 g (0.05 mol) p-aminobenzonitrile and 7.4 g (0.05 mol) p-n-propylbenzaldehyde in 100 ml benzene with the addition of 150 mg p-toluenesulfonic acid is reacted as described in example 1. After the evaporation leaves 12.5 g of yellowish oil, which crystallizes on cooling. For purification, recrystallize, as described in example 1, several times from i-propanol. The pure p-[(p-n-propylbenzylidene)amino]-benzonitrile has a melting point of 64.8 - 65.5° and a kip. of 77.6°.

UV (EtOH) <:><&>'280 <=> 24300 (Schulter at 310 nm).

NMR, MS, IR and microanalysis correspond to the substance.

EXAMPLE 3

A mixture of 11.8 g (0.1 mol) p-aminobenzonitrile and 16.2

g (0.1 mol) of p-n-butylbenzaldehyde in 200 ml of benzene with the addition of 300 mg of p-toluenesulfonic acid is reacted as described in example 1. After adding 3 g of solid potassium carbonate, filter and evaporate. 27.0 g of yellow oil is obtained,

which crystallizes on cooling. For purification, recrystallize, as described in example 1, several times from i-propanol. The pure p-[(p-n-butylbenzylidene)amino]benzonitrile has a melting point of 38.1 - 38.7° and a kip. of 62.6°.

UV (EtOH): a 280 = 24900 (Schulter at 314 nm).

NMR, MS, IR and microanalysis correspond to the substance.

EXAMPLE 4

A mixture of 5.9 g (0.05 mol) p-aminobenzonitrile and 8.8 g (0.05 mol) p-n-pentylbenzaldehyde in 100 ml benzene with the addition of 150 mg p-toluenesulfonic acid is reacted as described in example 1. After evaporation, 13.9 g of yellow oil remains, which crystallizes on cooling. For purification, recrystallize, as described in example 1, several times from i-propanol. The pure p-[(p-n-pentylbenzylidene)amino]benzonitrile has a melting point of 45.6 - 46.4° and a kip. of 75.0°.

UV (EtOH)<:><£.> 27g = 24400 (Schulter at 314 nm).

NMR, MS, IR and microanalysis correspond to the substance.

EXAMPLE 5

A mixture of 5.9 g (0.05 mol) p-aminobenzonitrile and 9.5 g (0.05 mol) p-n-hexylbenzaldehyde in 100 ml benzene with the addition of 150 mg p-toluenesulfonic acid is reacted, as described in example 1. After evaporation, 14.4 g of brownish oil remain, which crystallizes on cooling. For purification, recrystallize, as described in example 1, several times from i-propanol. The pure p-[(p-n-hexylbenzylidene)amino]-benzonitrile has a melting point of 32.2 - 33.0° and a kip. of 64.5°.

UV (EtOH): £- 00, = 23500 (Schulter at 310 nm).

NMR, MS, IR and microanalysis correspond to the substance.

The starting product can be prepared as follows: p_n-hexylbenzaldehyde is prepared according to the instructions of A, Rieche et al., Chem. Pray. 93, 88 (1960): Under nitrogen gassing and stirring in during

20 minutes at 0-5° 25.1 g of dichloromethyl ether (0.218 mol),

stir for 15 minutes at 0-5°, then 15 minutes at 20°, pour the dark brown reaction solution onto 600 g of ice, extract with ether, wash the organic layer with water, sodium bicarbonate solution and again with water, dry with sodium sulfate and remove the solvent in vacuo. 48.7 g of brownish oil is thus obtained, which according to the gas chromatogram consists of up to 41% n-hexylbenzene, up to 12% o-hexylbenzaldehyde and up to 47% p-n-hexylbenzaldehyde. The mixture is separated by distillation in an active column. The pure p-n-hexylbenzaldehyde boils at 2.7 mm at 113 - 115°.

EXAMPLE 6

A mixture of 5.9 g (0.05 mol) p-aminobenzonitrile and 9.5 g

(0.05 mole) of p-isohexylbenzaldehyde in 100 ml of benzene under

addition of 150 mg of p-toluenesulfonic acid is reacted as described in example 1. After evaporation, 14.2 g of a yellow oil remains, which crystallizes on cooling. For purification, recrystallize, as described in example 1, several times from i-propanol. The pure p-[(p-isohexylbenzylidene)-amino]benzonitrile has a melting point of 37.7 - 38.5° and a kip. of 45.3°.

UV (EtOH): £ 280 = 23900 (Schulter at 308 nm).

NMR, MS, IR and microanalysis correspond to the substance.

The starting material can be produced as follows:

To a cooled mixture of 110.3 g of isohexylbenzene (0.68 mol),

380 ml of methylene chloride and 124.5 ml of titanium (IV) chloride (1.13 mol) are added dropwise under nitrogen gassing over the course of 20 minutes at 0-5° to 65.0 g of dichloromethyl ether (0.565 mol), stirring 15

minutes at 0-5°, then 15 minutes at 20°, pour the dark brown reaction solution onto 1555 g of ice and extract with ether. After drying and evaporation of the solvent, 121.3 g of brownish oil remain, which is further purified by normal distillation in vacuum. The to 143° at 13 mm distilling fraction (25.7 g) consists of isohexylbenzene, that from 143 -

146° at 13 mm the distilling fraction (65.0 g) consists according to gas chromatogram of up to 20% o-isohexylbenzaldehyde and up to 78%

p-isohexylbenzaldehyde. This mixture is separated by distillation in an active column. The pure p-isohexylbenzaldehyde boils at 14 mm at 141 - 145°.

EXAMPLE 7

A mixture of 5.9 g (0.05 mol) p-aminobenzonitrile and 10.2 g (0.05 mol) p-n-heptylbenzaldehyde in 100 ml benzene with the addition of 150 mg p-toluenesulfonic acid is reacted as described in example 1. After the evaporation leaves 15.4 g of yellow oil, which crystallizes on cooling. For purification, recrystallize, as described in example 1, several times from propanol. The pure p-[(p-n-heptylbenzylidene)amino]benzonitrile has a melting point of 32.7 - 33.0° and a kip. of 72.3°.

UV (EtOH): £. 2Q1 = 24100 (shoulder at 310 nm).

NMR, MS, IR and microanalysis correspond to the substance.

The starting material can be produced as follows:

To a cooled mixture of 97.3 g of n-heptylbenzene (0.548 mol), 310 ml of methylene chloride and 102 ml of titanium(IV) chloride (0.924 mol) is added dropwise under nitrogen gassing over the course of 20 minutes at 0-5° 53, 3 g of dichloromethyl ether (0.463 mol), stir 15 minutes at 0 - .5°, then 15 minutes at 20°, pour the dark brown reaction solution onto 1270 g of ice and extract with ether. After drying and evaporation of the solvent, 106.1 g of brown oil remains, which is further purified by normal distillation in vacuum. The to 165° at 17 mm distilling fraction

(23.2 g) consists of n-heptylbenzene, the from 166 - 168° at 17 mm distilling fraction (55.7 g) consists according to gas chromatogram of up to 20% o-heptylbenzaldehyde and up to 77% p-n-heptylbenzaldehyde. This mixture is separated by distillation in an active column. The pure p-n-heptylbenzaldehyde boils at 12 mm at 166 - 168°.

EXAMPLE 8

A mixture of 5.9 g (0.05 mol) p-aminobenzonitrile and 10.9 g (0.05 mol) p-n-octylbenzaldehyde in 100 ml benzene with the addition of 150 mg p-toluenesulfonic acid is reacted as described in example 1. After the evaporation leaves 16.5 g of a yellow oil, which crystallizes on cooling. For purification, recrystallize, as described in example 1, several times from i-propanol. The pure p-[(p-n-octylbenzylidene)amino]-benzonitrile has a melting point of 32.5 - 32.8° and a kip.

of 68.8°. At 54.4° the compound is smectic. UV (EtOH): €, = 24200 (Schulter at 312 nm).

2oO

NMR, MS, IR and microanalysis correspond to the substance.-The starting material can be prepared as follows:

To a cooled mixture of 86.8 g of n-octylbenzene (0.456 mol),

255 ml of methylene chloride and 82.6 ml of titanium (iV) chloride (0.748 mol) are added dropwise under nitrogen gassing over the course of 20 minutes at 0-5° 43.2 g of dichloromethyl ether (0.375 mol), stirred for 15 minutes at 0 - 5 °, then 15 minutes at 20°, pour the dark brown reaction solution onto 1030 g of ice and extract with ether. After drying and evaporation of the solvent, 96.8 g of brown oil remains, which is further purified by normal distillation in vacuum. The to 160° at 14 mm distilling fraction

(22.9 g) consists of n-octylbenzene, the from 161 - 180° at 14

mm the distilling fraction (52.8 g) consists according to gas chromatogram of up to 18% o-n-octylbenzaldehyde and of up to

76% p-n-octylbenzaldehyde. This mixture is separated by distillation with an active column. The pure p-n-octylbenzaldehyde boils at 13 mm at 170 - 173°.

EXAMPLE 9

34.7 g of manganese dioxide (0.40 mol) (prepared according to J. Org. Chem. 29, 1540 (1964) is boiled in a stream of nitrogen together with

500 ml of benzene over the course of 5 hours under reflux and the water formed is separated with a water separator. 11.80 g of p-[(p-ethylbenzyl)amino]benzonitrile (0.05

mol) (prepared, for example, by reacting 4-fluorobenzonitrile with p-ethylbenzylamine according to J. Org. Chem. 31, 2319 (1966)), boil, continue for 10 hours under reflux and separate the water as indicated above. After cooling, filter through celite, wash with benzene and free from the solvent in vacuum (50° bath temperature). 10.5 g of yellow oil is obtained, which crystallizes on cooling. For cleansing

is recrystallized, as described in example 1, several times from i-propanol. One thus obtains pure p-[(p-

ethylbenzylidene)amino]benzonitrile, in which all the properties are identical to the product produced according to example 1.

Claims (6)

1. Nematic mixtures for electro-optical purposes characterized in that they contain one or more compounds with the general formula where R means ethyl, n-propyl, n-butyl, n-pentyl, iso-hexyl, n-hexyl, n-heptyl or n-octyl, and possibly one or more other nematic substances. 2. Mixture according to claim 1, characterized in that it consists of p-[(p-n-propylbenzylidene)amino]benzonitrile and p-[(p-n-hexylbenzylidene)amino]benzonitrile in a molar ratio of 1:2. 3. Mixture according to claim 1 characterized in that it consists of p-[(p-n-butylbenzylidene)amino]benzonitrile and p-[(p-n-hexylbenzylidene)amino]benzonitrile in a molar ratio from 2:1 to 1:2. 4. Mixture according to claim 1, characterized in that it consists of p-[(p-n-butylbenzylidene)amino]benzonitrile and p-[(p-n-heptylbenzylidene)amino]benzonitrile in a molar ratio of 1:2. 5. Mixture according to claim 1, characterized in that it consists of p-[(p-n-pentylbenzylidene)amino]benzonitrile and p-[p-n-octylbenzylidene)amino]benzonitrile in a molar ratio of 1:2. 6. Mixture according to claim 1 characterized in that it consists of p-[(p-n-hexylbenzylidene)amino]benzonitrile and p-[(p-n-butoxybenzylidene)amino]benzonitrile in a molar ratio of 2:1.