DE2836086A1 - DIESTER TYPE LIQUID CRYSTALS AND ELECTRO-OPTICAL DEVICE CONTAINING SUCH - Google Patents

Description

THOMSON - CSF August 17, 1978

173t vol. Haussmann
75008 Paris / France

Our reference: T 3145

Diester type liquid crystals and electro-optical devices containing the same

The invention relates to a group of liquid crystals of the "Dlester" type, which are composed of organic compounds with three benzene nuclei connected by - C 0 0 - groups. The pure compounds, the mixtures of these compounds with each other or with other liquid crystals as well as the synthesis of these organic compounds, as well the electro-optical devices operated using such liquid crystals form the invention.

Most of the organic compounds in this group have at least one nematic mesomorphic phase. Also own certain compounds have one or more smectic mesomorphic phases in addition to a nematic mesomorphic phase. In their mesomorphic phase, certain compounds have a high negative dielectric anisotropy.

Dr Ha / Ma

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2836036

The organic compounds according to the invention correspond to the general chemical formula:

X > - C O - O - Y 0 C. - O - (ö) - R ₁ - <9> & - wherein: ? n + 1 or ^C n ^{H :} 2n + 1 , whereby R ₁ - C _n H, from 0 until 10 R ₁ = number 1 is.

(1)

^R 2 ^ ^C m ^H 2m + 1 ' ^{where m is an} integer from 1 to 10.

The pair (X, Y) can be?

(H, B * O> H = a hydrogen atom and Br = a bromine atom; (H, CN), H = a hydrogen atom and CN = the cyanide group; (Br, Cl), Br = a bromine atom and Cl = a chlorine atom; (CN, Cl), CN = the cyanide group and Cl = a chlorine atom; (Br, CN), Br = a bromine atom and CN = the cyanide group.

The so defined members of this group are as follows designated:

- (n-Alkoxy-4-benzoyloxy) -4-bromo = 3-benzoate of n-alkyl-4-benzene when R _{1 is} the alkoxy group C _n H _{2n + 1} 0, X is hydrogen and Y is bromine.

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(n-Alklyl-4-benzoyloxy) -4-bromo-3-benzoate of n-alkyl-4-benzene when R _{1 is} the alkyl group C ^H 2n + 1 ' ^{X is} hydrogen and Y is bromine.

(n-Alkoxy-4-benzoyloxy) -4-cyano ~ 3-benzoate of n-alkyl-4-benzene when R _{1 is} the alkoxy group C _n H _{2n + 1} 0, X is hydrogen and Y is the cyanide group.

(n-alkyl-4-benzoyloxy) -4-cyano-3-benzoate of n-alkyl-4-benzene when R _{1 is} the alkyl group
and Y is the cyanide group.

benzene, when R _{1 is} the alkyl group C _n Hp _{n + 1} , X is hydrogen

(Bromo-3-n-alkoxy-4-benzoyloxy) -4-chloro-3-benzoate of n-alkyl-4-benzene when R _{1 is} the alkoxy group C Hp _{n + 1} 0, X is bromine and Y is chlorine.

(Bromo-3-n-alkyl-4-ben2oyloxy) -4-chloro-3-benzoate of n-alkyl-4-benzene when R _{1 is} the alkyl group C _n H _{2n + 1} , X is bromine and Y is chlorine.

(Cyano-3-n-alkoxy-4-benzoyloxy) -4-chloro-3-benzoate of n-alkyl-4-benzene when R _{1 is} an alkoxy group, X is the cyanide group and Y is chlorine.

(Cyano-3-n-alkyl-4-benzoyloxy) -4-chloro-3-benzoate of n-alkyl-4-benzene when R _{1 is} an alkyl group, X is the cyanide group and Y is chlorine.

(Bromo-3-n-alkoxy-4-benzoyloxy) -4-cyano-3-benzoate of n-alkyl-4-benzene when R _{1 is} an alkoxy group, X is bromine and Y is the cyanide group.

909809/0969

- (Bromo-3-n-alkyl-4-benzoyloxy) -4-cyano-3-benzoate of n-alkyl-4-benzene when R _{1 is} an alkyl group, X is bromine and Y is the cyanide group.

The following describes the general procedure for preparing the compounds of the group, followed by some characteristic process steps are explained in more detail:

General manufacturing process:

First case: X = H. The formula (1) is then:

OY O ^R l * (I} - ^C - O - (Ö) - Q ^{/ r} - O - (θ} - R ₂ (2)

The process then comprises the following stages: Stage (a):

Bromine is allowed to act on p-hydroxybenzoic acid in an aqueous medium:

⁰ n "Br °

HO - (θ) - C - OH ? -> HO - (θ) - C

Water - \

OH

Hydroxy-4-bromo-3-benzoic acid is obtained.

909809/0969

Stage (b) t

One leads between an alkylphenol and hydroxy-4-bromo-3-benzoic acid of stage (a) an esterification reaction by:

// ._ toluene

'- C ₊ HO- (O) - R ₂ ^H0 - <°> - ^C ' - ° - <°> - ^R 'OH ^ H j))

The hydroxy 4-bromo-3-benzoate of p-alkylbenzene is obtained in this way.

Stage (c);

Cuprocyanide is left on the hydroxy-4-bromo-3-benzoate in dimethylformamide act of p-Alky! benzene:

W / ^ CN ^C / HO - ^ O) -C -0- ^ O) -R ₂ * HO- (O) -C - 0 - (θ) -

This gives the hydroxy-4-cyano-3-benzoate of p-alkyl benzene.

Output stage:

1) If Y = Br

The product obtained in step (b) is left with p-alkoxybenzoyl chloride or p-alkylbenzoyl chloride react:

9098D9 / 0969

Br

O i

+ HO- {o> - <i-O- <o) -R

'- C-O- (O) - C-O - <0> - R,

This gives (η-alkoxy- or n-alkyl-4-benzoyloxy) -4-bromo-3-benzoate of n-alkyl-4-benzene.

2) If Y = CN

The product obtained in step (c) is left with p-alkoxybenzoyl chloride or p-alkylbenzoyl chloride react.

"Λ

H0- <5> -c-0-®-

B ₁ -

This gives (η-alkoxy- or n-alkyl-4-benzoyloxy) -4-cyano-3-benzoate of n-alkyl-4-benzene.

Second case; X = Br and Y = Cl;

the process then comprises the following stages:

Stage (d):

Bromine is allowed to react with the p-alkoxy or p-alkylbenzoic acid act

£> Br

.0

R ₁ - (O) -C> R ₁ - <0>"

OH

OH

909809/0969

1) When R _{1 is} an alkoxy group, the reaction is carried out in an aqueous medium;

2) when R _{1 is} an alkyl group, the reaction is carried out in the presence of silver nitrate in a nitric acid medium;

Stage (s);

The product from stage (d) is allowed to act with SO Cl ₂ !

Bi

O SO Cl

Br .0

OH

Cl

Stage (f):

Hydroxy-4-chloro-3-benzoic acid is left with p-alkylphenol react:

Cl
HO-ZbV-C '+ HO

Cl

-0-

toluene

HO- <0} - C-0- <0

Stage (g):

The product of step (e) is left in pyridine with the React product of stage (f):

Cl

Br O Cl O

909809/0969

Third case; X = CN and Y = Cl

The steps (d) to (g) described above for the second case are carried out.

Following these steps, the product obtained is allowed to react with cuprocyanide in dimethylformamide:

B.

- C-O-iO> -C-O- (O> -

Fourth case; X = Br and Y = CN

The reactions (a) to (c) described above for the first case are carried out once and for on the other hand, steps (d) and (e), as described for the second case, are carried out »

The product obtained in step (e) is then left with the product obtained in step (c) react:

0
//

CN

+ HO- <O) -CO- <O> -R _r

Pyridine

0 CN 0> -C-0- / 0

- R.-

Cl

909809/0969

Procedure

First example; X = H

Stage (a) t

Synthesis of the hydroxy - ^ - bromo - ^ - benzoic acid.

41.4 g are suspended in 300 ecm of softened water (0.3 mole) p-hydroxybenzoic acid. The solution is heated to a temperature between 50 and 55 ° C and is within Add 52.8 g (0.33 mol) of bromine over 3 hours. Then the solution is allowed to cool, whereupon the suspended solid filtered off. It is recrystallized from 2/3 ethanol 1/3 softened water.

The product obtained sublimes from 150 ^° C.

Second example: X = H, R ₂ = pentyl

Stage (b) t

Synthesis of the hydroxy 4-bromo-3-benzoate from p-pentylbenzene.

21.7 g (0.1 mol) of hydroxy-4-bromo-3-benzoic acid are added to 500 ecm of toluene, 18 g (0.11 mole) p-pentylphenol, 0.3 g boric acid and 0.5 g concentrated sulfuric acid. One brings the solution to reflux with removal of the water formed. The reaction is then allowed to proceed for 120 hours go, whereupon the toluene is distilled off. A brown solid is obtained, which is washed out with petroleum ether. The crude product is chromatographed on a

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Purified silica column eluting with benzene and then recrystallized from benzene.

19 »7 g of pure product with a melting point of 153 ^° C. are obtained

Third example; X = H, R ₂ = pentyl

Stage (c);

Synthesis of the hydroxy-4-cyano-3-benzoate from p-pentylbenzene.

To 30 ecm of dimethylformamide are added 7.26 g (0.02 mol) Hydroxy 4-bromo-3-benzoate of p-pentylbenzene and 2.5 g (0.028 mole) cuprocyanide. It is refluxed for 6 hours, what to cool down on. The solution is poured into a mixture of 4 ecm ethylenediamine in 200 ecm softened water. The mixture is stirred for half an hour, whereupon 5 normal hydrochloric acid is added dropwise and always with stirring until the Solution has reached a pH of 6. The product precipitates and is extracted with ether. The crude product obtained is recrystallized twice from benzene.

This gives 3 g of pure product with a melting point of 168 ^° C.

Fourth example: X = H, R ₂ = pentyl final stage with X = CN:

Synthesis of the (n-octyloxy-4-benzoyloxy) -4-cyano-3-benzoate of p-pentylbenzene.

909809/0969

0.62 g (2.10% mol) of hydroxy-4-cyano-3-benzoate of p-pentylbenzene are dissolved in 5 ecm of pyridine. Then 0.54 g (2.1O ^- - ⁵ mol) of p-octyloxybenzoyl chloride are added. The mixture is stirred for 4 hours at ambient temperature, after which the solution is poured into a mixture of 20 g of ice and 2 ml of concentrated sulfuric acid. The mixture is stirred for a further 3 hours, after which the solution is extracted with benzene. The crude product obtained in this way is purified by chromatography on a silica column and then recrystallized from ethanol. This gives 0.85 g of pure product.

Fifth example: X = Br, R ₁ = octyloxy

Stage (d):

Synthesis of octyloxy-4-bromo-3-benzoic acid.

37.5 g (0.15 mol) of p-octyloxybenzoic acid are suspended in 180 ml of softened water. Heating the reaction mixture to a temperature between 50 and 55 ⁰ C and treated at this temperature with 8.7 cc (0.17 mol) of bromine within 7 hours and 30 minutes. The product is then filtered off, washed with softened water and recrystallized from ethanol. This gives 37 »9 g of pure substance.

Sixth example; X = Br, R> | = Octyl

Stage (d):

Synthesis of octyl-4-bromo-3-benzoic acid.

909809/0969

7 g (0.03 mol) of p-octylbenzoic acid and 6.4 g (0.04 mol) of bromine are added to a mixture of 15 ecm of softened water, 20 ecm of nitric acid and 90 ecm of acetic acid, the temperature of which is 25 ° C. A solution of 5 »1 g (0.03 mol) of silver nitrate in 15 ecm of softened water is then added over the course of half an hour. The solution is stirred for 3 hours and 30 minutes, after which the suspended solid is filtered off and washed with softened water until the wash water is neutral. The acid is dissolved in ethanol and the solution is decolorized in the heat with biochar. The crude product obtained after distilling off the ethanol is recrystallized from a mixture of 75% ethanol and 25 % water.

This gives 5.1 g of pure substance »

Seventh example; Y = Cl, R ₂ = pentyl

Stage (f):

Synthesis of the hydroxy ~ 4-chloro-3-benzoate from p-pentylbenzene.

17.25 g (0.1 mol) of hydroxy-4-chloro-3-benzoic acid, 18 g (0.11 mol) of p-pentylphenol, 0.5 g of concentrated sulfuric acid and 0.3 g of boric acid are added to 600 ecm of toluene . The mixture is refluxed for 100 hours, the water formed during the reaction being drawn off. The toluene is then distilled off and a brown solid is obtained which is dissolved in 700 ecm of a mixture of 79 % hexane - 20 % benzene - 1 % ethanol. The solution is decolorized in the warm with biochar and then filtered while hot »The product crystallizes out.

909809/0989

This gives 16 g of pure substance with a melting point of 136 ^° C.

Eighth example; X = CN, Y = Cl, R ₁ = octyloxy, R ₂ = pentyl

Synthesis of (cyano-3-n-octyloxy-4-benzoyloxy) -4-chloro-3-benzoate from p-Penty! benzene.

Add 2.1 g (3.10 mol) of dimethylformamide to 7 ecm (Bromo 3-n-octyloxy-4-benzoyloxy) -4-chloro-3-benzoate of p-pentylbenzene and 0.31 g (3.4.10 moles) cuprocyanide. Man reflux for 1 hour and 15 minutes, followed by cooling and the product is poured into a mixture of 40 ecm softened water and 3.3 ecm ethylenediamine. the Solution is extracted with ether. The crude product obtained is purified by chromatography on a silica column and recrystallized from ethanol.

This gives 0.3 g of pure substance with a melting point of 130 ° C.

Results of measurements carried out on compounds according to the invention.

In the table below, the temperature ranges of some of the compounds of the present invention are as follows indicated phases:

K = solid crystalline phase;

N = nematic phase;

I = isotropic phase;

S _c = smectic phase of type C.

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Reference
sign ^C 8 H 17 ⁽ links Br - \ "/ -
Oy- CO- (O ₇ C ₅ IL H L. H 11 Temperature range
in ⁰ C 70 N 133 I. ^C 8 H 17th 0 Br 6 ■ ο - (<Γ) - 0
K-C-O- (O) -C Ll 51 N 102, , 5 I. Λ ^C 8 H 17 ⁽ Br
■ o - (T) -
Br ^ ^C 5 11 K 99 N 136 I. B. ^C 8 H 17- 0 Br
CO- (Oj -0 - ^> H K 97 N 113 I. C. 0 C2
) - c-o- ( ^ ^C 5 ^{μ C} 5 K D. ^C 8 H 17 ⁽ 0 C ^ N
CO- ^ O) 5 "l- H 11 K 93 N 106 I. 0 cl
It \ N 0
(T) - c-0-ζο ^ - c ^KC 5 E. ^C 8 H 17 ⁽ y CO-? - c-o- <fdy H 11 K K 130 I. 0 cl O ^C 5 ^H il F. ^C 8 H 17 ^C } - CO- ^ —Ν / ->
0 V- CO- (O ^C 5 ^H n 11 89 S _c 93.5 N 113 I. 0 CN O
If C ₅ Ii ₁₁ G C, H
D. 13th > - £ >> C-0- < ' - "V J A
P> co - <@ K 50 N 108.5 I. C ₇ H 15th 0 0 55 N 109 I. H C ₇ H 3 -CpI - © - L O) - C-O- (O] K 39.5 5 N 136 I. I. - <ö> - -Cc 0 K K 3 - (cT O - < J-o- © - K ί - (öy ~ 0
Λ ^{f /}
0 0
// / -.
co - (T) -
0 ■ Br
* ®- c ^ ^,
CO - (O) - CN > -
3 - (O Br

These substances all show the very interesting phenomenon of dielectric isotropy at a very low frequency.

909809/0969

For example the substance labeled "A": Its dielectric anisotropy e _a was measured at different frequencies and different temperatures. The orientation magnetic field was 10,000 Oe.

The table below gives the values of the dielectric constants parallel, t, ,, and perpendicular, ε. , as well as the anisotropy that results from it, e _a = zii - £ _l »at two extreme measuring frequencies N = 1 kHz and N = 1 MHz and for four temperatures.

A frequency N _{Q is} specified for each temperature, the so-called “dielectric isotropy”, which _{corresponds to an anisotropy e a} of zero ( ^ε // = ^e ι).

temperature
in ⁰ C N 4.9
3.1 LL ^e a N ₀ (WIz) 50
- 1 kHz
1 MHz 4.55
3.0 4.1
4.1 + 0.8
- i, o 12.5 61 1 kHz
1 MHz 4.3
2.9 3.85
3.85 + 0.7
- 0.85 27 69 1 kHz
1 MHz 4.1
2.85 3.75
3.75 + 0.55
- 0.85 65 76 1 kHz
1 MHz 3.6
3.6 + 0.5
- 0.75 125

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The substance is therefore positive at low frequency and negative at high frequency.

The eutectic mixture of the three compounds "A", ^M H "and" I "is nematic from 35 to 105 ° C. Its composition is:

Fabric "A": Fabric "H": Fabric "I":

28 MoI-Ji 36 MoI-Ji 36 MoI-Ji.

The table above is completed below with respect to this eutectic mixture (A, H, I);

Temperature in ⁰ C N ^ε // lL ^e a N _Q (kHz) 38 1 kHz
1 MHz 3.1 4.2 + 0.7
- i, i N ₀ = 3.7

The minimum value for ε reached.

(namely 3.1) becomes for N = 20 kHz

The dielectric constants of the compounds "C" and "G", each mixed with a liquid crystal "J" with a nematic phase between 29 and 43 ° C, were measured; "J" is p-methoxybenzoate of p-pentylphenol. The composition of the mixture was 90 % of the compound "N" to 10% of the compound of the invention.

909809/0969

The table below contains the result of at 22 ° C on the supercooled liquid crystal "J" and on mixtures of the same as defined above with the compounds "C" and "G", respectively. Man worked in a magnetic orientation field of 10 000 Oersted, being a periodic electric field (F = 10 kHz) was applied to the liquid crystal.

Liquid crystal ε parallel ε perpendicular Δ ε J
Mixture "C + J"
Mixture "G + J" 5.7
5.2
4.5 5.6
5.8
5.2 + 0.1
- 0.6
- 0.7

The last two results of the fourth column show that the negative dielectric anisotropy of the pure substances C and G must be very high, since the influence of these substances on the anisotropy of the mixture is also strong, although they only have a very small proportion in the thus formed liquid crystal. The results would be analogous if the compound according to the invention were present in a proportion of 5 to 15 % of the mixture.

If the frequency of the electric field is changed, an even more negative anisotropy is observed; in particular between 100 kHz and 1 MHz it is for the liquid crystal "G + N" - 1.8; the relative dielectric constants, parallel and perpendicular, are then 3.5 and 5.3 respectively.

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For example, the compounds according to the invention can be used in electro-optical display devices with dynamic Light scattering and in electro-optical field effect devices with memory effect as well as in display devices use with double frequency effect.

In the display devices with double frequency action, for example, the molecules remain parallel to the applied one High-frequency field aligned (positive dielectric anisotropy) and tilt under vertical orientation to the electric field at lower frequencies (negative dielectric anisotropy).

An example of such a device is shown in the drawing. This shows a liquid crystal cell 10 and a generator with variable frequency 11. The cell has two glass plates 1 and 2, which with translucent electrodes 3 and 4 are clad, one of these electrodes being cut, for example is that they have a character (number or letter) when the cell is illuminated under the conditions described below lets appear. A liquid crystal droplet 5 is out between the two on two shim plates 6 and 7 Insulating material pressed plates included. Two terminals 8 and 9 connect electrodes 3 and 4, respectively with an output 112 of the generator 11.

_{The generator 11 can generate two frequencies F 1} and Fp under the control of signals received at its input terminals 111. The frequencies F. and Fp lie on either side of a frequency N of the dielectric isotropy of the liquid crystal 5.

909809/0969

When the generator 11 emits the (highest) frequency F ₁ , the molecules are aligned parallel to the electric field so that they _{do not interrupt the light beams L 1} penetrating into the interelectrode spaces, which leads to a uniform illumination Lp at the exit of the cell.

When the generator 11 emits the (lowest) frequency F ₂ , the molecules tilt, and the result is a partial extinction of the illumination L ^ depending on the design of the electrode 3, so that the one described by the electrode 3 for an appropriately placed observer Character becomes visible.

A eutectic mixture of the substances according to the invention B (18 mol%), H (24 mol-tf), I (25 mol-56) and K (33 mol-90 made.

The temperature range of this mixture is as follows; where the same explanations as above apply:

K 20 ⁰ CN 116 ° C I.

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Claims (15)

Patent Attorneys Oipl.-Incj. Dipl-Chem Dipl.-Ing. E. Prince - Dr. G. Hauser - G. Leiser Ernsber9erstrasset9 2836086 8 Munich 60 THOMSON - CSF August 17, 1978 173, Bd. Haussmann 75008 Paris / France Our reference; T 3145 claims 1. Diester-type liquid crystals, labeled by the general formula: XOYO
R. - <JÖ ~> - CO - &F> - CO - (cT> - R _n in which R .. an alkyl or alkoxy group C Hpn + 1 or C ** 2n + 1 ^, where η is an integer of Is 1 to 10; R _{2 represents} an alkyl group C _m H _{2m + 1} , in which m is an integer from 1 to 10; X is hydrogen, bromine, or the cyanide group; Y when X is hydrogen is bromine or the cyanide group, when X is bromine or the cyanide group is chlorine means and when X is bromine means the cyanide group. Dr Ha / Ma 909809/0969 -Z- 2. Liquid crystals according to claim 1, characterized in that: R ₁ = C ₈ H ₁₇ O or C ₇ H ₁₅ O R ₂ = C ₅ H ₁₁ X = HY = Br. 3. Liquid crystals according to claim 1, characterized in that: R ₁ = C ₈ H ₁₇ or CgH ₁ , or R ₂ = C ₅ H ₁₁ X = HY = Br. 4. Liquid crystals according to claim 1, characterized in that that: R ₁ = C ₈ H ₁₇ R ₂ = C ₅ H ₁₁ X = HY = CN. 5. Liquid crystals according to claim 1, characterized in that: R ₁ = C ₈ H ₁₇ R ₂ = C ₅ H ₁₁ X = HY = CN. 909809/0969 6. Liquid crystals according to claim 1, characterized in that that: R ₁ = C ₈ H ₁₇ O R ₂ - C ₅ H ₁₁ X - Br Y = Cl. 7. Liquid crystals according to claim 1, characterized in that: ^R 1 - ^C 8 H ₁₇ O R ₂ = c ₅ H ₁₁ X = C N Y = Cl • 8. Liquid crystals according to claim 1, characterized in that that: ^R 1 = ^C 8 H ₁₇ O R ₂ = c ₅ H ₁₁ X = Br Y = C N. 9. Liquid crystal according to claim 3 »characterized in that it consists of a mixture of three Verbin each of the following formula: Ο am j) ^C 8 ^H 17 "0 - C - O - 0 - C - O - 0 - C ₅ H ₁₁ O Bn Ο r ~ \ U r ~ \ ⁿ / ~ \ ^C 6 ^H 13 -0 - ^C - ° -0 - ^C - ° "(l> - ^C 5 ^H 11 O Br _x Ο 0 1 ' ^ll
-CO 909809/0969 10. Liquid crystal according to claim 9, characterized in that it contains about 28 mol% of the first compound and contains about 36 mole percent each of the other two compounds. 11. Electro-optical device, characterized in that it comprises a liquid crystal according to one of the Claims 1 to 10 contains. 12. Electro-optical device according to claim 11, characterized in that it has means for changing the frequency of the electric field applied to the liquid crystal. 13. The method for producing a liquid crystal according to claim 1, when: X = H
Y = Br, characterized by the following procedural stages: Step (a): reaction of bromine in an aqueous medium with p-hydroxybenzoic acid to form hydroxy-A-bromo-3-benzoic acid; Step (b): esterification of an alkylphenol with the acid obtained in step (a) to form the hydroxy-4-bromo-3-benzoate of p-alkylbenzene; Final stage: reaction of the product obtained above with p-alkylbenzoyl chloride to form the n-alkylbenzoyloxy-4-bromo-3-benzoate of n-alkyl-4-benzene. 909809/0969 14. Method of making a liquid crystal according to claim 1, wherein: X = H Y = CN, characterized by the following process stages: Step (a): reaction of bromine in an aqueous medium with p-hydroxybenzoic acid to form hydroxy-4-bromo-3-benzoic acid; Step (b): esterification of an alkylphenol with the acid obtained in step (a) to form the hydroxy-4-bromo-3-benzoate of p-alkylbenzene; Step (c): action of cuprocyanide in formamide on the product obtained in step (b) with formation of the hydroxy ~ 4-cyano-3-benzoate of p-alkylbenzene; Final stage: reaction of the product obtained in stage (c) with p-alkoxy- or p-alkylbenzoyl chloride to form the (n-alkoxy- or n-alkyl-4-benzoyloxy) -4-cyano-3-benzoate of n-alkyl 4-benzene. 15. Process for the preparation of a group of liquid Crystals according to claim 1 if: X = Br and Y = Cl, characterized by the following process stages: 909809/0969 Stage (d); Reaction of bromine with p-alkoxy or p-alky! Benzoic acid; Stage (s); Reaction of SOCl «with the product obtained in step (d); Step (f): reaction of the hydroxy-4-chloro-3-benzoic acid with p-alkylphenol; Step (g): reaction of the products obtained in steps (e) and (f) in pyridine. 909809/0969