GB2044767A - 5-Alkyl-2-(4-cyanophenyl)- 1,3-dioxanes - Google Patents

Abstract

Compounds of the formula <IMAGE> wherein R is an alkyl, alkoxy, aryl, aryloxy, carboxy or ester derived from carboxy are used as liquid crystal materials or mixtures in electro- optical displays.

Description

SPECIFICATION 5-Alkyl-2-(4-cyanophenyl)-l ,3-dioxanes BACKGROUND OF THE INVENTION It is known to use nematic liquid crystal compounds in electro-optic displays. Such displays are utilized in constantly increasing numbers in watches and other instruments. Such devices are well known to those skilled in the art.

One of the problems encountered in the utilization of nematic liquid crystal materials in such displays is the availability of stable low viscosity nematic compounds which are liquid at near room temperatures and have relatively low transition temperatures to make them practical for use in electro-optic display devices. Further, it is desirable that the nematic liquid crystal material require the appliction of the minimal amount of potential to obtain the desired effect in order to minimize the power requirements in the display device. Only an extremely limited number of nematic liquid crystal compounds thus far known possesses these desired characteristics.

SUMMARY OF THE INVENTION According to the present invention there is provided a new group of compounds which are stable liquid crystal materials having low viscosity, relatively and low transition temperatures.

They also have low threshhoid voltages as determined on rubbed indium oxide surfaces. Such compounds are useful alone or in mixtures in optical liquid crystal display devices which use nematic liquid crystal materials.

The compounds of the present invention are of the formula

wherein R is an alkyl, alkoxy, aryl, aryloxy, carboxy or ester derived from carboxy.

Preferably R is a straight chain, and more particularly a straight chain of 1 to 8 carbon atoms.

The compounds of the present invention may be prepared as follows:

Dimethyl malonate may also be employed in place of diethyl malonate.

In the foregoing synthesis R has the same meaning as previously indicated.

The reduction of the malonic acid ester is preferably carried out using a Vitride reducing agent from Eastman Chemicals or with borane-methyl sulfide. Other reducing reagents and methods well known to those skilled in the art may be employed if desired.

The dioxanes of the present invention are obtained as two isomers. Since the trans configuration is elongated it presumably is the one which accounts for nematic characteristics of the compounds.

The nature of the invention may be better understood by the following representative embodiments which are included to illustrate the nature of the invention without limiting its scope which is defined in the claims.

SPECIFIC EMBODIMENTS EXAMPLE I 5-Butyl-2-(4-cyanophenyl)- 1, 3-dioxane To a five liter, 3-neck round bottom flask fitted with condenser and mechanical stirrer the following are added: (1) 232 g of sodium methoxide in methanol.

(2) 264.24 g of dimethyl malonate in methanol and stirred for a short period.

(3) 274.06 g of 1-brombutane and 1 500 cc of methanol is then added.

The reaction mixture is heated for 65 hours and the resulting dimethyl butylmaionate ester isolated and identified by gas chromatography.

The dimethyl butylmalonate thus obtained is then reduced. To a 500 ml-3-neck round bottom flask the following are added: (1) Vitride Solution 1 22 ml (.44 m) (2) Benzene Solution 100 cc with dimethyl butylmalonate 37.6 g (.2 m) The addition to the Vitride is carried on over a 20 minute period and then the solution is refluxed for 1/2 hour, cooled, poured into a separating funnel, and then slowly added to a beaker containing 250 ml of 20% hydrochloric acid standing in ice water. The mixture is maintained below 35"C and stirred until set up.

The mixture is washed with 500 ml methanol and 1000 ml acetone filtered and a gelatinous precipitate obtained which is dried by azeotroping with benzene. The benzene is stripped and the organic phases combined and vacuum distilled. Pdt. b.p. 100-104"/0.75-1.1 mm.

A solution of 6.60 g (0.05 mole) 2-butyl-1,3-propanediol thus obtained and 6.55 g (0.05 g mole) p-cyanobenzaldehyde in 60 ml benzene plus a few crystals of p-toluene sulfonic acid is refluxed. Water is removed azeotropically and refluxing continued until no more water forms.

The benzene is removed. The residue is vacuum distilled and two fractions are obtained. Their infra-red spectra are identical. Gas chromatography of the fractions gives the following results: b.p. Gas chrom. Retention Times FRACT. I 155"-157"/0.85 mm 2.99 (28%) 3.45 (61.9%) 7.87 (5.1%) 9.92 (5.0%) FRACT. Il 165-167"/0.5-0.55 m 2.97 (24.2%) 3.47 (75.8%) Each fraction is therefore composed of 2 main components, approximately in the ratio of 1 :3.

The trans form of the product is predominate since its formation is less sterically hindered than the cis form.

The two compounds that elute from the gas chromatography at 2.99 min and 3.45 min were collected in capillary tubes and transferred to microscope slides using chloroform as the solvent.

Evaporation of solvent from peak 1 (2.99 min.) left an isotropic liquid. Evaporation of solvent from peak 2 (3.45 min) left a nematic liquid crystal.

CN = 30.7-31.0"C NL = 31 .4-32.7'C On rubbed indium oxide surfaces spaced 1/4 mil apart, Vth = 0.6 V Vsat = 1.3 V Similar values for threshhold voltage and saturated voltage were obtained on indium oxide surfaces having a MgF2 alignment layer slope evaporated therein (deposition angle of 30 ).

EXAMPLE II 5-Pentyl-2-(4-Cyanophenyl)- 1, 3-Dioxane 30.5 g Dimethyl malonate is dissolved in 200 ml of methanol. To this is added 500 ml 0.5 M sodium methoxide in methanol, and then a solution of 37.7 9 bromopentane in 100 ml of methanol. The solution is stirred and refluxed for 65 hours. A sample analyzed by gas chromatograph shows: 10% bromopentane 22% dimethyl malonate 65% dimethyl pentylamalonate The methanol is removed on a Roto-vac. The pasty solid remaining is treated with chloroform and separated by filtration. The removal of chloroform leaves a yellow liquid which is then vacuum distilled. A 7 ml forecut is obtained (75-110 C/12-14 mm Hg.). 12.2 9 of product is collected at 113-118 /14 mm. Gas chromatography shows it to be 98.7% pure.

12.2 g of the dimethyl pentylmalonate are then dissolved in 50 ml benzene. To this is added 25 ml 70% Vitride reducing agent in benzene, in 5 ml increments. The reduction of the ester is followed on gas chromatography. Twenty ml of water is added cautiously, and the mixture stirred overnight. 40 ml Concentrated hydrochloric acid is added and the benzene layer separated. The aqueous layer is extracted twice with chloroform, the benzene layer dried, and the chloroform layer dried. The aqueous layer is stripped on Roto-vac and the salt boiled with the chloroform second layer.

To a 50 milliliter round bottom flask fitted with magnetic stirrer and condenser, the following components were added: (1) benzene about 25 cc (2) cyanobenzaldehyde 1.1 5 (3) 2-pentyl-1,3-propanediol 1.146 g (4) p-toluene sulfonic acid few crystals (5) calcium sulphate 2.0 g and refluxed over a weekend. The mixture is cooled. 6% Product is shown by gas chromatography. More paratoluene sulfonic acid is added to the reaction mixture and heating is continued. A precipitate forms when the paratoluene sulfonic acid is added. The C5-diol is stirred overnight in 2% hydrochloric acid and the mixture is then placed in a separating funnel and extracted twice with chloroform and subsequently, dried over sodium sulfate with stirring. The chloroform is removed after filtering off the sodium sulfate.Gas chromatography confirms the identification of the end product.

EXAMPLE 3 5-Heptyl-2-(4-Cyanophenyl)- 1, 3-Dioxane Using the procedure of the previous example, the following are reacted together: (1)114.48 g of sodium methoxide (2) 70.02 g dimethyl malonate are first mixed together and stirred for a short period.

Then there is added 500 cc of methyl alcohol and 95.0 9 of n-bromoheptane.

The reaction mixture is heated over the weekend refluxing at 68"C, then cooled and the methyl alcohol stripped on the Roto-Vac. The product dimethyl heptyl malonate is taken up in chloroform, the salt filtered off, and chloroform stripped off on the Roto-Vac and the product vacuum distilled and identified by gas chromatography.

1 84 ml Vitride reducing agent are added to a one liter round bottom flask together with 250 ml benzene and the solution brought to reflux. Then the following solution was added: 60.0 g of the above dimethyl heptylmalonate ester in 100 cc benzene.

After addition of the ester solution, the reaction mixture is heated for 1 hour at reflux.

An additional amount (1 /2) more of Vitride was added and the reaction mixture heated for 40 more minutes.

Finally, after the addition of 20% then 50% hydrochloric acid solution, the pH was brought to 5. The product is pasty and difficult to filter. The organics were removed in a separating funnel.

Each half of the water layer was extracted with chloroform, combined and stripped on the Roto Vac. Organics were separated from the extracted water layers and combined, and then stripped on the Roto-Vac.

The heptyl diol obtained is then reacted as follows: In a 50 ml round bottom flask the following components are combined: (1) benzene 25 ml (2) cyanobenzaldehyde (.01 m) 1.2 9 (3) C7 diol from above 1.74 (4) Paratoluene sulfonic acid few crystals (5) Calcium sulphate CaSO4 2.0 g and refluxed overnight to obtain the desired end product, 5-Heptyl-2-(4-Cyanophenyl)-1 .3- Dioxane.

EXAMPLE 4 5-Octyl-2-(4-Cyanophenyl) 1,3 Dioxane The following are reacted together in a 3-neck round bottom flask fitted with a mechanical stirrer.

1 liter of Methanol 216.0 9 of Sodium Methoxide 160.17 g of Diethyl malonate The foregoing are stirred together for a short time and then 193.13 g of 1 -bromo-octane added.

The mixture is heated overnight at reflux, cooled, and the methanol stripped. The product is taken up in chloroform and the sodium bromide salt filtered off. The chloroform is evaporated and the sample distilled.

To a 3 neck, 1 liter round bottom flask the following components are added: (1) 500 cc fresh toluene.

(2) 136 9 of diethyl octyl malonate ester obtained as described and (3) 110 ml borane-methyl sulfide which is added dropwise over a one hour period.

The mixture is heated slowly to reflux, and refluxing continued for 12-15 hours. The reaction mixture is then cooled to room temperature and added from a separating funnel to a beaker containing 400 cc of methyl alcohol. After the mixture stands overnight the alcohol is stripped on the Roto-Vac.

10% Hydrochloric acid in 100 cc of water is added to the diol with stirring. After all of the acid solution has been added over about 15-20 minutes, a gelatinous mass is obtained which filtered and the diol product isolated as in the foregoing examples: A single neck 50 cc round bottom flask is charged with: 1.88 9 of the octyl diol obtained above; 1.1 5 9 of cyanobenzaldehyde 25 cc of benzene Few crystals of paratoluene sulfonic acid 2.0 9 of calcium sulfate powder The mixture is heated for 1 6 hours at reflux, the product isolated, and identified by gas chromatography.

In the instances of the compounds of Examples 2, 3, and 4, the following melting points and transition temperatures were obtained: M.P. CN (CL) NL (LN) Example 2 53.0 C 46.0 C 47.5"C Example 3 50.0'C (54.1"C) (49.8"C) Example 4 47.2"C (59.0 C) 47.3"C) While the invention has been explained by a detailed description of certain specific embodiments, it is understood that various modifications and substitutions can be made in any of them within the scope of the appended claims which are intended also to include equivalents of such embodiments.

Claims (4)

1. A compound of the formula:

wherein R is an alkyl, alkoxy, aryl, aryloxy, carboxy, or ester derived from carboxy.

2. A compound as claimed in claim 1 wherein R is a straight chain alkyl.

3. A compound as claimed in claim 2 wherein R is a straight chain alkyl of 1 to 8 carbon atoms.

4. An electro-optical display including the compound of claim 1 as a liquid crystal material.