NO133195B - - Google Patents

Description

The invention relates to new connections with the general

formula

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

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

which compounds are applicable in liquid crystalline to-

state as a dielectric in electro-optical devices.

The compounds according to the invention have in liquid crystalline form

state a positive anisotropy for the dielectric constants (67/ > £ , 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 (then 6^ £^) se(3 so that the direction of their largest dielectric constants, i.e. their length-

axes, lie parallel to the field direction. This effect exploit-

is tested, among other things, in the according to J.H. Heilmeier and L.A. Zanoni [Applied Physics Letters 13, 91 (1968)] described interactions

between embedded molecules and liquid crystalline molecules

coolers (guest-host interaction). A further interesting application of the dielectric field orientation is that of M. Schadt and W. Helfrich [Applied Physics Letters 18,

129 (1971)] Dppfound rotary cell.

As far as this electro-optical rotary cell is concerned, it is essentially a capacitor with light-permeable electrodes, whose dielectric is formed by a nematic substance with £//f ^ The molecular longitudinal axes of the liquid crystals are in the field-free state helically arranged between the capacitor the planes, whereby the screw structure is determined by the given side face 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 compounds which have a low melting point and a low viscosity. The compounds 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 compounds 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.

In DOS No. 1 928 003 describes alkoxy-benzylideneaminobenzonitriles - either alone or in mixtures. These compounds do indeed have the positive anisotropy for the dielectric constants required for the rotary cell, but nevertheless exhibit a higher melting point than the compounds of formula I according to the present invention. In addition, they have known mixtures, especially those listed in table 2 in DOS No. 1 928 003, in the best case a melting point of approximately 30°C, while the mixtures described in the present invention have a melting point of 0-10°C. Furthermore, the mixtures containing compounds of formula I have in a rotary cell a threshold value of 1.1 volts. (see Proceeding of the I.E.E.E., volume 60, p. 1002, No. 8, Aug. 1972). In opposition to this, it has in Appl. Phys. Easy. 18, 127-128 (1971) investigated mixture of alkoxy-benzylideneaminobenzonitriles a threshold value of 3 volts. A lower threshold value is, however, necessary for applications requiring a small volume and leads to a lower energy consumption.

It was now surprisingly found that the compounds according to the present invention with the general formula I not only exhibit the necessary large positive anisotropy for the dielectric constants, but that they individually or in the form of mixtures with each other or with other nematic or non-nematic substances are liquid crystalline at relatively low temperatures, and that they exhibit a low viscosity. It is therefore possible to carry out the process at lower voltages, and the response time is shorter. A further advantage of the substances 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 application.

The compounds according to the invention with the general formula I can be prepared by

a) reacts with a compound of formula II

where R has the above meaning,

with p-aminobenzonitrile or

b)' dehydrogenates a compound of formula III

where R has the above meaning.

In embodiment a) of the method, a p-alkylbenzaldehyde of formula II is condensed with p-aminobenzonitrile. This reaction is suitably 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. methanesulfonic acid, p-toluenesulfonic acid, benzenesulfonic acid etc. 1 embodiment b) of the method, the compounds of formula I are produced by dehydrogenation of corresponding compounds of formula III. For the dehydrogenation, all means known in the literature for analogous dehydrogenations 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 nematic substances

according to the invention is visualized with the help of the tables below:

x) monotropic xx) smectic up to 54.4°

The compounds according to the invention are preferably used

in the form of their mixtures with each other, whereby mixtures corresponding to a eutectic are particularly preferred.

Some exemplary compositions are summarized in the following tables:

All values are in mol%

EXAMPLE 1

A mixture of 5.9 g (0.05 mol) p-aminobenzonitrile and 6.7 g

(0.05 mol) of p-ethylbenzaldehyde gas in lOO ml of benzene after adding 150 mg of p-toluenesulfonic acid with nitrogen and heating for 1 hour under reflux (bath temperature 120°C). The water formed is separated with a water separator. After a further hour, the benzene condensed 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 in a vacuum at 50° bath temperature. 11.5 g of yellow oil remains, which crystallizes on cooling. For purification, crystallize several times in i-propanol until constant m.p. and until the by-products have disappeared in the gas chromatogram. The pure p-[(p-ethylbenzylidene)aminojbenzonitrile melts at 76.2 - 77.0° and is liquid-crystalline on cooling from 63.0 - 59.7°.

UV (EtOH): ^ 2 77 = 25800 (shoulder 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 of benzene with the addition of 150 mg of p-toluenesulfonic acid is reacted as described in example 1. After evaporation, 12.5 g of yellowish oil remains which crystallizes on cooling. For cleaning, recrystallize as described in example 1 several times in 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): 5_280 = 24300 (shoulder 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) p-n-butylbenzaldehyde in 200 ml of benzene while adding

300 mg of p-toluenesulfonic acid is reacted as described in example 1. After adding 3 g of solid potassium carbonate, it is filtered and evaporated. 27.0 g of yellow oil is obtained, which crystallizes on cooling. For purification, it is recrystallized, as indicated in example 1, several times in i-propanol. The clean

p-[ (p-n-butylbenzylidene)aminojbenzonitrile has a m.p. of 38.1 - 38.7° and a kip. of 62.6°.

UV (EtOH): €_280 = 24900 (shoulder 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 indicated in example 1. After the evaporation leaves 13.9 g of a yellow oil, which crystallizes on cooling. For purification, it is recrystallized, as stated in example 1, several times in i-propanol. The pure p-[(p-n-pentylbenzylidene)aminojbenzonitrile has a m.p. on

45.6 - 46.4° and a kip. of 75.0°.

UV (EtOH): S. 27g = 24400 (shoulder 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 of benzene with the addition of 150 mg of p-toluenesulfonic acid is reacted as described in example 1. After evaporation leaves 14.4 g of a brownish oil which crystallizes on cooling. For purification, as described in example 1, it is recrystallized several times in i-propanol. The pure p[(p-n-hexylbenzylidene)aminoj-benzonitrile has a mp 32.2 - 33.0° and bp 64.5° UV (EtOH) : <r>c_ 281 = 23500 (shoulder at 310 nm).

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

The starting product is produced as follows:

p-n-hexylbenzaldehyde is prepared according to the instructions of A. Rieche et al., Chem. Pray. 93, 88 (1960): To a cooled mixture of 42.5 g of n-hexylbenzene (0.274 mol), 146 ml of methylene chloride and 48 ml of titanium (IV) chloride (0.437 mol) is added dropwise under nitrogen gassing and stirring in the course of 20 minutes at 0-5° 25.1 g of dichloromethyl ether (0.218 mol), stirring

15 minutes at 0-5°, then 15 minutes at 20°, pour the dark brown reaction solution into 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 vacuum. 48.7 g of brownish oil is thus obtained which, according to the gas chromatogram, consists of 41% of n-hexylbenzene, 12% of o-hexylbenzaldehyde and 47% of 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 mol) p-isohexylbenzaldehyde in 100 ml benzene with the addition of 150 mg p-toluenesulfonic acid is reacted in the same way as in example 1 After evaporation, 14.2 g of a yellow oil remain, which crystallizes on cooling. For purification, one crystallizes, as described in example 1, several times in i-propanol. The pure p-[(p-isohexylbenzylidene)amino]benzonitrile has a m.p. of 37.7 - 38.5° and a kip. of 45.3°.

UV (EtOH): £_ 2Q0 = 23900 (shoulder 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 nm of methylene chloride and 124.5 ni of titanium (IV) chloride (1.13 mol) is added dropwise under nitrogen gassing over the course of 20 minutes at 0- 5° 65.0 g of dichloromethyl ether (0.565 mol), stir 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 a brownish oil remain, which is further purified by normal distillation in vacuum. The fraction distilling at 143° at 13 mm (25.7 g) consists of isohexylbenzene, the fraction that distills from 143 - 146° at 13.. mm (65.0 g) consists, according to the gas chromatogram, of 20% isohexyl-benzaldefc»' d„- This mixture is separated by distillation i

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 evaporation leaves 15.4 g of a yellow oil, which crystallizes on cooling. For purification, recrystallize, as described in example 1, several times in i-propanol. The pure p-[(p-n-heptylbenzylidene)amino]-benzonitrile has a m.p. of 32.7 - 33.0° and a kip. of 72.3°.

UV (EtOH): £-281 = 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) are 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 a brown oil remains, which is purified by normal distillation in a vacuum. The up to 165° at 17 mm distilling fraction (23.2 g) consists of n-heptylbenzene, the

fraction which distills" from 166 - 168° at 17 mm (55.7 g) according to the gas chromatogram consists of 20% o-heptylbenzaldehyde and 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 in example 1. After evaporation 16.5 g of a yellow oil remains which crystallizes on cooling. For purification, recrystallize as indicated in example 1 several times in i-propanol. The pure p-[(p-n-octylbenzylidene)amino]benzonitrile has a m.p. of 32.5 -

32.8 and a kip. of 68.8°. Up to 54.4°, the compound is smectic.

UV (EtOH): & 280 = 24200 (shoulder at 312 nm).

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

The starting material can be produced 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 a brown oil remains which is further purified by normal distillation in vacuum. The fraction that distills at 160° at 14 mm (22.9 g) consists of n-octylbenzene and the fraction that distills at 161 - 180° at 14 mm (52.8 g) consists, according to the gas chromatogram, to 18% of o-n-octylbenzaldehyde and 76% of 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)) are boiled together with 500 ml of benzene for 5 hours under reflux and the water formed is separated with a water separator. Then 11.80 g of p-[(p-ethylbenzyl)amino]-benzonitrile (0.05 mol) are added (prepared, for example, by reaction of 4-fluorobenzonitrile with p-ethylbenzylamine according to J.Org.Chem. 31 ,' 2319 (1966), boil for a further 10 hours under reflux and separate the water as indicated above. After cooling, filter through celite, wash with benzene and remove the solvent in vacuo (50° bath temperature). 10.5 is obtained. g of a yellow oil which crystallizes on cooling. For purification, crystallize as indicated in example 1 several times in i-propanol. Pure p-[(p-ethylbenzylidene)amino]benzonitrile is thus obtained, which is identical in all respects with the product produced according to example 1.

EXAMPLE 10

3.1 g (26 mmol) of p-hydroxybenzonitrile are dissolved in 40 ml of abs. pyridine. Then 6 g (28.5 mmol) of p-n-pentyl-benzoic acid chloride in 20 ml of benzene are added dropwise at room temperature and then stirred overnight. After brief heating, the work-up is carried out as described in example 1 and 7.5 g of crude ester is obtained. This is chromatographed with toluene/acetone 19:1 on silica gel. From a uniform fraction, after recrystallization in hexane, 2.6 g of p-n-pentyl-benzoic acid p<1->cyanophenyl ester with a melting point of 60.5°C and a monotropic clearing point of 56.5°C are obtained.

The starting product can be produced as follows:

Dissolve 15 g of p-n-pentylbenzoic acid in 100 ml of thionyl chloride and boil under reflux for 1 hour. The excess thionyl chloride is then removed by distillation and the acid chloride is distilled in high vacuum. Kp. 104°/2mm.

Claims (3)

1. Liquid crystalline Schiff bases for use as dielectrics in electro-optical devices, characterized in that they have the general formula where R means ethyl, n-propyl, n-butyl, n-pentyl, iso-hexyl, n-hexyl, n-heptyl or n-octyl. 2. Schiff's base according to claim 1, characterized in that the base is p-[(p-n-hexylbenzylidene)amino]-benzonitrile. 3. Schiff's base according to claim 1, characterized in that the base is p-[(p-n-heptylbenzylidene)amino]-benzonitrile.