DE2715519C2 - Phenol carboxylic acid esters and their use as liquid crystals with strongly negative dielectric anisotropy - Google Patents

Description

where R is the nitro group NO2, bromine or the 2nd liquid crystal mixture, characterized by a

Nitrile group -C = N, R ₁ denotes an alkyl group η content of at least one compound according to

C _n H2n + 1 or an alkoxy group C "H2n + iO denotes, claim 1 in addition to a compound of the general

wherein η is an integer from 1 to 10 and R _{2 is} a formula alkyl group having 1 to 10 carbon atoms.

R ₃ O -

where R ₃ 'and R _{4 are} alkyl groups C _; , H ₂ "-n denote and /; can mean a value between 1 and 10. 3. Liquid crystal mixture according to claim 2, characterized by a content of 10% of the compound:

C ₅ H ₁₁ .

4. Liquid crystal mixture according to claim 2, characterized by a content of 10% of the compound: Br

C ₅ H ₁₁ .

5. Liquid crystal mixture according to claim 2, characterized by a content of 10% of the compound:

CN

-O ^ - XCO- / VC ₅ H ₁₁ .

The invention relates to organic compounds, and

although a group of diesters with alkyl or, alkoxy groups, which are mutually only through one

- '' differentiate between NO2 group, Br or CsN group and alone or in a mixture a liquid crystal, with large represent negative dielectric anisotropy, so that they give a large dynamic light scattering. the Mixtures of such liquid crystals with other nematic liquid crystals also form part of the Invention.

It is known that certain liquid crystals have the effect in the temperature range in which they are present in the nematic, mesomorphic phase; To scatter light dynamically when exposed to a direct or alternating electric field. This effect is used in the field of electro-optics and for display purposes.
The services essentially concern:

- the temperature range in which the effect occurs;

- the contrast

- the response times to a given signal;

- the service life (under voltage).

It is well known that dynamic light scattering occurs only with nematic substances with a negative dielectric Anisotropy on, d. H. for compounds in which the measured perpendicular to the major axis of the molecules Dielectric constant is greater than that measured parallel to this axis. To achieve such substances For example, one adds a group with a strong dipole moment to an elongated organic molecule at such a point that the resulting dipole moment is approximately perpendicular to the main axis of the molecule.

The present invention enables the above conditions to be satisfied in addition, achievements in terms of dynamic light scattering that are higher than they have been achieved so far observed with the known liquid crystals.

The liquid crystal according to the invention consists of a phenol carboxylic acid ester of the general formula:

where R denotes the nitro group NO2, bromine or the nitrile group -CsN, Rj denotes an alkyl group C _n H _{2n +} I or an alkoxy group CH2 + 1O, where π is an integer from 1 to 10 and R _{2 is} an alkyl group with 1 to 10 carbon atoms means. The members of this group so defined are called ^:;

° - 4-alkyl (alkoxy) -3-nitrobenzoate of 4'-hydroxybenzoate of para-alkylphenol in the case of the nitro · group;

4-alkyl (alkoxy) -3-bromobenzoate of 4'-hydroxybenzoate of para-alkylphenol in the case of bromine;

· - 4-Alkyl (a! Koxy) -3-nitrile benzoate of 4, ', - hydroxybenzoate of para-alkylphenol in the case of the nitrile group,

To demonstrate the technical superiority of the compounds according to the invention, the following compounds 1 to 4 according to the invention were compared with the known compounds 5 and 6 compared, in admixture with a liquid crystal of the following Formula:

CH ₃ O-

R ₁ R

c-o / Vc-o / Vr,

Liquid crystals according to the invention

No. 1 CH ₃ O Br

No. 2 CH ₃ O NO ₂

No. 3 CH ₃ O CN

No. 4 C ₃ H ₇ CN

Well-known liquid crystals

No. 5 C ₅ H _n O Cl

No. 6 CH ₃ OH

The known liquid crystal No. 6 still contained Cl in the meta position to R instead of H.

R ₂ consisted of C5H11 both in the liquid crystals according to the invention and in the known liquid crystals.

The mixture tested consisted of 10 mol% in each case of the mixture according to the invention or the known Compound and 90 mol% of the compound of formula II.

65 The dielectric anisotropy of the mixture was determined and is given in the table below with ej ^u , while the electrical anisotropy calculated therefrom for the pure compounds in the table above is given with e ,, ¹ . The table below also shows the temperature range for the nematic phase.

m **

Liquid crystal crystals according to the invention c CII ₁ O Br No. I. CH ₁ O NO No. 2 CII ₁ O CN No. 3 GH; CN No. 4 Well-known liquid crystals GII || 0 Cl No. 5 CH, 0 Il No. 6

-0.6 -1.35 - 1.45 -1.0

-Ü.6 -0.1

ΙΚΊΊ1ίΙΙΙΜ.ΙΚ ' l'liiisi; -7 38 C - 14.5 17.5 C - 15.5 35 C- - | · Ί 30 C -0.7 49 c- -2.0 59.5 C-

It can be seen from the table above that the liquid crystals according to the invention overall have properties which make them extremely suitable for use in electro-optical devices. For example, they have (in the pure state) > pronounced dielectric anisotropies and relatively large temperature ranges for the mesomorphic phases. The known liquid crystals, on the other hand, in particular No. 6, have either only weakly negative dielectric anisotropies or a very small temperature range of the nematic phase.

The following is the general mechanism of the manufacturing process of the compounds of the present invention described, whereupon the procedure within the individual stages is explained.

The first stage is common to all connections in the group.

35 to obtain 4-hydn> xy-beny <:> al from p-alkylphenol:

c-o-

Synthesis of the compound with Nilro group '

An esterification is between 4-alkyl (alkbxy) - _ιμ 3-nitfobenzoyIchlorid:

NO

General manufacturing process

First stage
This concerns the esterification between alkylphenol:

C-Cl

and 4-hydroxybenzoate of p-alkylphenol:

to obtain 4-alkyl- (alkox:) /) - 3-nitrobenzoate of 4'-hydroxybenzoate of p-alkyl pfteriol:

and p-hydroxybenzoic acid:

-OH

carried out.

Synthesis of the bromine compound First, p-alkyl- (alkoxy) -benzoic acid is brominated:

Br ^Bh > R ₁ -VV

Depending on whether R | is an alkyl or alkoxy group, the reaction medium is either an aqueous silver nitrate solution or simply pure water (see the later embodiments).
Then the acid chloride is synthesized:

-OH

SOCI ₂

R ₁ O

, Finally, an esterification reaction between this acid chloride and 4-hydroxybenzoate of p-alkylphenol is:

- ^ r Vc-o-f

to obtain 4-alkyl (alkoxy) -3-bromobenzoate from 4'-hydroxybenzoate from p-alkylphenol: Br

Synthesis of the compound with nitrile group

M.in uses the bromine compound obtained above as the starting product, which is debrominated in dimethylformiimide in the presence of copper cyanide.
νΐ, ιπ thus gives the 4-alkyl- (alkoxy) -3-nitrile benzoate from 4'-hydroxybenzoate from p-alkylphenol:

C = N

Implementation of the main procedural stages
in the case of an alkoxy compound

First stage
example

Production of 4-hydroxybenzoate
of p-pentylphenol

In 1 Litjr Toluo! add 49.2 g (03 mol) p-pentylphenol, 27.6 g (0.2 mol) p-hydroxybenzoic acid, ί g concentrated sulfuric acid and 0.62 g boric acid. The mixture is refluxed for 21 hours, where to decant the water formed during the reaction- The toluene is then evaporated and the obtained solid is kn'stallisiert from acetonitrile.

This gives 4-hydroxybenzoate from p-pentylphenol.

Brömterungsreaktiori

example
Production of 4-OctyIoxy'3-bromobenzoic acid

in (20 cm * with ion exchanger purified water one brings 25 g (0.1 mol) of p-octyioxybenzoic acid in Suspension. It is heated to a temperature between 50 and 55 ° C. and at this temperature 17.6 g (0.11 Mol) of bromine over 7 hours. The suspended solid is then filtered off and extracted from ethanol recrystallized.

This gives 4-OctyIoxy-3-brombeπzoic acid.

Debromination reaction
example

4-methoxy-3-nitrile benzoate of 4'-hydroxybenzoate
From p-pentylphenol

In 10 cm ³ of dimethylformamide is added 2.5 g (5 x 10- ³ mol) of 4-methoxy-3-bromobenzoate of 4'-hydroxybenzoate p-Pentylphenof and 0.55 g (6 x 1Ό- ³ moles) fCupfercyanid, It is kept under reflux for 6 hours, before the solution is poured into a mixture of 5 g of ethylenediamine in 60 cm ^{3 of} water treated with permutitol. The mixture is stirred and the solution is then extracted with ether. The solid obtained after distilling off the ether is purified by chromatography on a silica column.

The 4-methoxy-3-nitrile benzoate is thus obtained from 4'-Hydroxyberrzoai of p-pentyiphenol.

230 226/289

Procedure in the case of an alkyl compound

Prepress

example

Preparation of the 4-hydroxybenzoate of p-pentylphenol

49.2 g (0.3 mol) of p-pentylphenol, 27.6 g (0.2 mol) of p-hydroxybenzoic acid are added to 1 Liier toluene, 1 g concentrated sulfuric acid and 0.62 g boric acid. The mixture is refluxed for 21 hours, the water formed during the reaction is decanted off. 'The toluene is then evaporated and the obtained Solid is crystallized from acetonitrile.

The 4-hydroxybenzoate of p-pentylphenol is obtained.

Bromination reaction

example
Synthesis of 4-propyl-3-bromobenzoic acid

8.2 g (0.05 mol) of p-propylbenzoic acid and 8.8 g (0.055 mol) of bromine are added to a mixture of 150 cm ^{3 of} glacial acetic acid, 33 cm ^{3 of} concentrated nitric acid and 25 cm ^{3 of water which has been purified with an ion exchanger.} You then give a solution of at 25 ° C for half an hour

Examples: (R, = alkoxy)

20 8.5 g (0.05 mol) of silver nitrate in 25 cm ^{3 of} ion-exchanged water. The solution is then kept agitated for 3 hours and 30 minutes, whereupon the suspended solid is filtered off, washed until neutral, whereupon the acid is dissolved in ethanol.

Recrystallization from hexane gives 4-propyl-3-bromobenzoic acid.

Debromination reaction
example

Synthesis of 4-propyl-3-nitrile benzoate
of 4'-hydroxybenzoate of p-pentylphenol

:. In 10 cm ³ of dimethylformamide is one 2.55 g (5 · ΙΟ- ³ moles) of 4-propyl-3-bromobenzoate of 4'-hydroxybenzoate, p-pentylphenol and 0.55 g (6 - ΙΟ- ³ mol) of copper cyanide . The mixture is refluxed for 7 hours 30 minutes, whereupon the solution is poured into a mixture of 5 g of ethylenediamine in 60 cm ^{3 of} ion-exchanged water . The solution is stirred and then extracted with ether. The solid obtained after the ether has been distilled off is chromatographed purified on a silica column.

This gives 4-propyl-3-nitrile benzoate from 4'-hydroxybenzoate from p-pentylphenol.

a) Pure connections: R

CH ₃ O

C5H11

(4-methoxybenzoate of p-pentyl-phenol substituted in the 3-position)

No, the substitute

Example group

Transition temperatures

from K to N (note A)

from K. to I.

-C

Br
-NO ₂

123 C 125 C 134 ° C

158 ° C 163 ° C 151, S ° C

45

50

Note A:

K = solid crystalline phase, ^

K = nematic phase.

Γ = isotropic phase.

b) mixtures

For example, the nematic compound is used with a pure compound according to the invention Liquid crystal of the formula:

CH ₃ O

COO-

-C ₅ H ₁₁ (4)

1. Eutectic mixture »Mi« (in mol): 10% of the compound of Example 1; 90% of the compound (4).

65 The characteristics of the mixture are as follows:
Transition temperatures: 25 ° C and 53 ° C
dielectric anisotropy at 25 ° C and 5 kHz: -0.8 (Note that compound 4 shows weak positive dielectric anisotropy under the same conditions; it is seen that the negative anisotropy is introduced by the compound of Example { .)
Response times to a signal obtained by chopping a DC voltage of 30 volts:
Response time on rise: less than 10 ms;
Response time when falling: approx. 100 ms.
{Contrast: excellent.

«Lifespan: satisfactory, the liquid crystal was kept in operation for a long time with direct or alternating voltage. This property is explained by the good chemical stability of the compounds according to the invention.
Other mixtures:

40% of the compound of Example 2 (Br) with 90% of the compound (4):

dielectric anisotropy at 25 ° C: -035.
In general, when the compounds according to the invention are mixed with the compound (4), the response time, the contrast and the service life are increased by increasing the proportion of

compound according to the invention in the mixture improved. In more general terms, the connection (4) can be connected by a connection

replace where R _{3 is} an alkyl group C “H ₂ n + i , where π is an integer from 1 to 10 and where R.4 is a similar group.

Examples: (R) = alkyl)

a) Pure compounds; example

C ₃ H ₇ -

O ,,, Ö

(4-Propyl-3-nitrile benzoate of 4'-Hydroxyjenzoate of p-penlylphenol).

This product is nematic from 80 to HO ^{0 C.} ', - Its dielectric anisotropy was at 84.5 ° C jo

sen at a frequency of 15 kHz using a ■> h orientation magnetic field of 8,000 Gauss gemes -.'_. It is -2.9.
b) · -, mixtures; example

''. Mixture of the above compound with the following liquid crystal:

CH ₃ O-

-COO

'(p-methoxybenzoal of p-pentylphenol).

'A 90% of this latter compound containing .Gemisch is nematic from 20 to 50 ⁰ C; it has a dielectric anisotropy at ambient temperature of -0.6. At a potential difference of .20 volts (for a 12 micron thick liquid crystal cell) it shows the phenomenon of dynamic light scattering with good contrast and short response times. Its threshold voltage is 7 volts under the same conditions of use.

{Mixtures of compounds with Ri = alkoxy with! A compound with Ri = alkyl.
(Such mixtures have a wide mesomorphism range, a negative dielectric anisotropy and excellent properties with regard to dynamic light scattering.

Claims (1)

Π 15519 Patent claims: Phenol carboxylic acid esters of the general formula: R Il ο y_c-of / Ii
ο (I)