Liquid Crystalline Substituted 1,3-Dioxanes and Mixtures Containing These

The invention relates to liquid crystalline substituted 1,3 dioxanes and substances containing the same, for electro-optical arrays for the modulation of transmitted or incident light as well as for the reproduction of figures, symbols and images.

It is known that different electro-optical effects will occur in nematic liquid crystals due to the optical and dielectric anisotropy of the latter, which can be utilized for the production of electro-optical components (G. Meier, E. Sackmann, J. G. Grabmaier, Applications of Liquid Crystals, Springer Verlag, Heidelberg-Berlin -New York 1975; M. Tobias, International Handbook of Liquid Crystal Displays 1975-76, Ovum Ltd., London 1976).

Components on the basis of twisted nematic strata are of particular interest herein, where their twist may be cancelled under the influence of the electric field as a consequence of which effects of which effects of brightness-darkness will occur. A precondition for such components is the use of nematic substances with positive dielectric anisotropy found in compounds with a strong longitudinal component of the dipole moment. The dynamic scattering effect will occur in substances with negative dielectric anisotropy and is also suitable for electro-optical components.

The substances hitherto used for optoelectronic components all have certain disadvantages, consisting of too high a melting point or too low a clarification point, or of a limited stability toward thermal stress, the effect of light and chemicals as well as of electric fields or a deleterious self-coloration.

The objects of the invention are nematic liquid crystal substances with favorable properties relative to melting and clear points; stability towards thermal stress, effects of light and chemicals as well as electric fields; as well as processes for their production.

According to the invention, this object is accomplished by the creation of new nematic liquid crystal substances and processes for their synthesis, not previously known.

It has been found that liquid crystal 2,5 disubstituted derivatives of 1,3 dioxanes of the general formula: ##STR3## wherein ##STR4## and wherein n=1 to 10, can be produced by the reaction of alkanals, substituted benzaldehydes or their acetals with glycerine or 2-substituted (1,3)-propanediols, in organic solvents and in the presence of an acidic catalyst, according to the general scheme: ##STR5## with, in given instances, subsequent esterification or etherification.

According to the invention, the new compounds are used in mixtures having as a constituent at least one of these substances of the invention. The substances of the invention are of particular advantage in mixtures consisting of themselves or in mixtures with other liquid crystal or non-liquid-crystal substances.

The advantages of the substances of the invention reside in the low melting points and with adequately high clear points, in their stability toward the effects of heat, light, chemicals and electric fields.

The substances with three rings possess the most favorable properties for a considerable rise of the clear point of mixtures.

The invention is to be explained below in more detail and with the aid of seven embodiments.

21 g (0.5 mol) LiAlH.sub.4 in 1 l abs. ether is first prepared in a 2 l three-neck flask. Under cooling with ice and strong agitation, 1 mol n-alkylmalonester or 1 mol 4-subst.-phenylmalonester which is mixed with the identical volume of abs. ether, is slowly added and agitation at room temperature is continued for another 2 hours. The mixture is subsequently carefully diluted with 100 ml ice water. The resulting precipitate (Al(OH).sub.3, LiOH) is dissolved by the addition of 700 ml of 10% strength H.sub.2 SO.sub.4. The organic phase is separated, the aqueous phase de-ethered twice and the combined organic phases eluted with a 2% solution of NaHCO.sub.3 and water. After drying with Na.sub.2 SO.sub.4, the solvent is distilled off under vacuum and the residue is subjected to fractional distillation. Embodiments are found in Tab. 1 and 2.

0.1 mol alkanol, or 0.1 mol substituted benzaldehyde or their acetals and 0.11 mol 2-alkyl-(1,3)-propanediol or 0.12 mol glycerin or 0.11 mol 2-[4-subst.-phenyl]-(1,3)-propanediol are heated with agitation with the separation of water until the conclusion of the reaction, in 150 ml abs. benzene, chloroform, methylene chloride, carbon tetrachloride or toluene, in the presence of 100 mg p-toluene sulfonic acid of AlCl.sub.3, SbCl.sub.5, TiCl.sub.4 or 2 ml of a mineral acid (HCl, H.sub.2 SO.sub.4, H.sub.3 PO.sub.4). After the constituents of the reaction have cooled down they are eluted with a 2% solution of NaHCO.sub.3 and water, and dried over Na.sub.2 SO.sub.4. The solvent is distilled off at the rotating evaporator and the residue recrystallized from methanol. The yield is approx. 80-100% of the theoretical value. In the table, identification is made as follows: K=crystalline solid, S.sub.A, S.sub.B,=smectic A or B respectively, N=nematic, I= isotropic liquid.

1. 0.1 mol 2-[4-hydroxy-phenyl]-5-alkyl-1,3-dioxane is dissolved in 50 ml abs. tetrahydrofuran and diluted with 0.12 mol sodiumhydride. After agitation for two hours, 0.12 mol of the requisite alkyl bromide is added and the mixture of the reaction is heated under reflux for 4 hours. The solvent is then distilled off at the rotary evaporator, the product of the reaction absorbed in 100 ml ether and the etheric phase eluted twice with 100 ml water. Drying over Na.sub.2 SO.sub.4 is subsequently accomplished, the solvent distilled off and the residue recrystallized from methanol. (Tab. 6).

2. 0.1 mol 2-[4-hydroxy-phenyl]-5-alkyl-1,3-dioxane is dissolved in a small quantity of benzene and added to a suspension of 0.23 g (0.1 g-atom) sodium in 100 ml abs. toluene. After heating to 80.degree. C. for three hours, cooling is accomplished to room temperature and 0.11 mol alkyl bromide is added. Heating is effected to 80.degree. C. for three hours, followed by cooling down to room temperature thereafter, and 0.11 mol alkyl bromide is added. Subsequently, heating to 80.degree. C. is effected for four hours and the constituents of the reaction are eluted with water thereafter. Drying is accomplished over Na.sub.2 SO.sub.4, the solvent is distilled off and the product of the reaction is crystallized (Tab. 6).

3. 0.1 mol 2-[4-hydroxy-phenyl]-5-alkyl-1,3-dioxane is introduced under stirring into the solution of 0.23 g (0.1 g atom) sodium in 100 ml abs. of ethanol. 0.1 mol alkyl bromide is then added and the composition heated for four hours at reflux. After the solvent has been distilled off, the residue is absorbed in ether, eluted, and dried over Na.sub.2 SO.sub.4. The ether distilled off and the product of the reaction is recrystallized from methanol (Tab. 6).

1. The sodium salt of 0.1 mol 2-[4-hydroxy-phenyl]-5-subst.-1,3-dioxanes (produced according to Example 3), is reacted under stirring, in 50 ml abs. tetrahydrofuran, ether, benzene, or toluene, with 0.15 mol of the requisite acid chloride. These constituents are left standing overnight, the solvent distilled off, the residue absorbed in ether, eluted, dried with Na.sub.2 SO.sub.4 and recrystallized from methanol. The yield amounts to 90-95% of the theoretical value.

2. 0.1 mol 2-[4-hydroxy-phenyl]5-subst.-1,3-dioxane or, respectively, 0.1 mol 2-[4-subst.-phenyl]5-hydroxy-1,3-dioxane are dissolved in 15 ml abs. pyridine and 0.11 mol of a requisite acid chloride is slowly added under cooling and agitation. The mixture of the reaction is left standing overnight and the residue is worked up as described under 1.

The yield is 90% of theoretical.

The yield amounts to 90% of the theoretical amount.

To a solution of 0.1 mol 5-alkyl-2-[4-hydroxyphenyl]-1,3-dioxane, or respectively 0.1 mol 2-[4-subst.-phenyl]-5-hydroxy-1,3-dioxane, 300 mg sodium methylate and 0.12 mol acrylonitrile are added at 35.degree. to 40.degree. C. The contituents of the reaction are stirred for 6 hours at room temperature and subsequent extraction is accomplished with ether.

The etheric phase is eluted, dried with potash and the solvent distilled off. The residue is crystallized from methanol. The yield is 54-80% of the theoretical quantity.

5-n-hexyl-2-[4-cyano-phenyl]-1,3-dioxane (Compound No. 1.30) is suitable for electro-optical components based on twisted nematic strata and has the following indicators:

measuring temperature: 35.degree. C.

threshold voltage: 0.65 V/50 Hz

onset time t.sub.E (50%)=376 ms at U=1.3 V/50 Hz

decay time t.sub.A (50%)=190 ms, stratum thickness .mu.m.

The substance No. 1.33 (Tab. 3) has a strong DK anisotropy of .DELTA..epsilon.=+11, at 10.degree. C. below the clear point.