DD227706A1 - PROCESS FOR PREPARING CRYSTALLINE-LIQUID TRANS-4-TRANS-5-SUBST.-1,3-DIOXAN-2-YL / - CYCLOHEXANCARBOXIC ACID ESTERS - Google Patents

Abstract

The invention relates to a process for the preparation of novel crystalline liquid trans-4- (trans-5-Subst.-1,3-dioxan-2-yl) cyclohexanecarboxylic acid esters of the general formula I. The invention relates to a process for the preparation of crystalline -fluid subst. 4- (1,3-dioxan-2-yl) -cyclohexanecarboxylic esters I and the intermediates required for their preparation.

Description

A process for the preparation of crystalline liquid trans-4- / trans-5-Subst »-1,3-diosan-2-yl / -cyclohexanecarboxylic acid esters

Field of application of the invention

The invention relates to a process for the preparation of novel crystalline liquid trans-4- / 1: rans-5-Subst, -1,3-diosan-2-yl7-oyclohexancarbonsäureester,

- ° ^H 2n + 1

CH

R ² = R ¹ , ITG- (HV,

= CS, S ¹ , Ct, Br, -CH = CC

, -CH = CH-ClT, r5_ _CO O-, <

= CU, F, oil, Br,

COO

and with

χ = 0 or S with η = 0-10

which can be used as a dielectric in optoelectronic components (displays) for displaying numbers and characters.

Characteristic of the known technical solutions

Very many derivatives of trans-4-substituted cyclohexanecarboxylic acid are known (D. Demus, H. Demus, H. Zasehke: Liquid Crystals in Tables, Leipzig 1974, Volume II, Leipzig 1984). However, among these compounds are no intermediates of the trans-4- (trans-5-Subst.-1,3- <3ioxan-2-yl ^ cyclohexane ar bonsäur en or their esters and no derivatives of trans-4 ~ formyl-cyclohexanecarboxylic or, the free acids themselves.

Derivatives of cyclohexanearbonic acid having crystalline-liquid properties are obtained by catalytic hydrogenation from the corresponding aromatic compounds. This naturally produces a mixture of ice-trans isomers, which is difficult to separate. Only the pure trans compounds form crystalline-liquid phases.

Object of the invention ....

The object of the invention is to prepare crystalline trans-4 / trans-5-substituted-1,3-dioxan-2-yl-7-carboxylic acid esters and the starting materials required therefor.

Explanation of the essence of the invention

The object of the invention is a process for the preparation of liquid crystals, wherein the trans-4- (trans-5-Subst "-1,3-dioxan-2-yl) cyclohexanecarboxylic acid esters are formed in the desired trans conformation on the cyclohexane ring.

It has been found that crystalline liquid (1,3-dioxan-2-yl) cyclohexanecarboxylic acid esters of the general formula I can be prepared by reaction of trans-4- (trans-5-alkyl-1,3-dioxane 2-yl) -cyclohexaaicarbonsäuren with alcohols, phenols and their thio analogues in the presence of dehydrating reagents such as Thionyl chloride or garbodiimides in the presence of tertiary amines or pyridine in anhydrous aprotic solvents

It has furthermore been found that alkyl 4-formylcyclohexanecarboxylates V are accessible starting from hexahydroterephthalic acid monoalkyl esters II. For this purpose, compound II is converted with alkyl chloroformates into the mixed anhydride III, which is reduced to 4-hydroxymethyl-cyclohexanecarboxylic ester IV. The selective oxidation of IV to V can e.g. with pyridinium chlorochromate or CrOo / pyridine. During the individual reaction steps, the trans configuration of the cyclohexane ring is retained.

The compounds of the invention can be used as a dielectric in electro-optical displays.

The reaction sequence of the invention: targeted activation of the carboxyl group in Terephthalsäuremonoalkylester II, selective reduction of III and subsequent oxidation of carbinol IV to the aldehyde V, allows for the first time access to trans ^ -formyl-cyclohexancarbonsäureestern V. It was surprising that during the following reaction steps: acetalization with a 2-substituted propane-1,3-diol, release of the acid VIII from the ester VII and reesterification no isomerization of the cyclohexane ring takes place. The reaction of V with VI leads to the formation of gis-trans isomers on the 1,3-dioxane ring, only

the trans-isoser compounds exhibit crystalline-liquid behavior. By recrystallization from a suitable solvent such as 3 B ₉ methanol or η-hexane, it is possible to separate off the trans isomer. The mother liquor with enriched cis isomers can be equilibrated by heating in the presence of acidic catalysts to the original ice-to-trans ratio, so that almost all of the material used can be isolated as a crystalline liquid trans-trans compound by repeated recrystallization and subsequent equilibration , In the synthesis of previously described structurally analogous crystalline liquid Vn-alkyl-bicyclohexane icärbonsäureester (R. Eidenschink, J. Krause, L. Pohl, J. Eichler: Liquid Crystals Proc. Int Conf · (edited by S. Ghandrasekhar), Heyden , London 19BQ , p. 515), it is naturally also the formation of cis-isomeric products, which, however, show no mesomorphic behavior and must be separated from the reaction mixture. However, a subsequent equilibration in the manner described is not possible here, whereby part of the starting materials used is lost.

Synthesis A for the preparation of 1-dioxane-cy-cyclohexane carboxylic acid esters I:

R ⁶ 00g / h \ g00H

II

0 Gl-C-OR ⁵ 0 0

r ⁶ oog- / h \ goc-os ⁶

III

IV

T + R-CH (CH ₂ OH) ₂

TI 0

R '- <VhVgooh

Till

Λ 0 / - \ s 1. OH

- <Η H VCOOR ⁰ T

V 0 \ - / 2. H ⁺

, 0H ~ / H ₂ 0

TII

Till + R-X

2 _v a) DGC / Base

b) SOCl ₂ / base E '- (HH O'

R ⁶ =

embodiments Example ^ i ^

Synthesis of Trans ^ -hydroxymethyl-cyclohexanecarboxylic acid ethyl ester IV (R ⁶ _s C ₂ H ₅ )

To 19> 0 g (0.1 mol) of hexahydro-terephthalic acid monoethyl ester II (R ⁶ = G ₂ H ₅ ) dissolved in 75 ml of abs. THF are 10.8 g (0.1 mol) of ethyl chloroformate in 50 ml of abs. THF at -J? ⁰ C added. When the addition is complete, the mixture is stirred for a further 30 min. The precipitated solid is then filtered off and the filtrate is subjected to reduction with WaBH ₂ .

For this purpose, a solution of 7.4 g of aEH ₂ , (0.2 mol) in 50 ml of water under cooling at 10 ⁰ C to 15 ⁰ G is added dropwise to the filtrate. The mixture is left for 4 h at room temperature retrofit this hr s and acidified with 3 η HCl. After exhaustive extraction with ethyl acetate, washing of the combined extracts with 5% K ₂ CQO solution, drying over JTa ₂ SO ₂ , and distillation in vacuo, 14.5 g (78.% of theory) of pure trans- 4-hydroxymethyl-cyclohexanecarboxylic acid ethyl ester IV (Kp ^ ₂ : I50 ⁰ G).

BeispJ.el_2 £

Synthesis of trans -formylcyclohexanecarboxylic acid ethyl ester V (R ⁶ = C ₂ H ₅ )

In 200 ml abs. Methylene chloride 32.2 g (0.15 mol) of pyridiniumchloroehromat are suspended. For this purpose, 18.6 g (0.1 mol) of IV in 30 ml of methylene chloride are added at once with stirring. After stirring for 1.5 h, it is decanted from the precipitated black residue, washed with methylene chloride, and the combined methylene chloride solutions are concentrated. The residue is taken up in petroleum ether, whereby at the same time precipitate oily impurities, which are separated by decantation or filtration · Hach removal of the petroleum ether on a rotary

Damper the purification by vacuum distillation yield: 15.5% ^d · SW 128-131 ⁰ C.

Synthesis of ethyl trans -benzyl-n-hexyl-1,3-dioxan-2-yl / cyclohecanecarboxylate VII (R = CgH 2; R = 1.6 g (10 mmol) of 2-n-hexyl-propane 1,3-diol VI (R ¹ = 1.84 g (10 mmol) of trans-4-formyl-cyclohe 3: ethylcarboxylate V (R = CpHt-) are dissolved in 100 ml of benzene in the presence of 100 mg of p-toluenesulfonic acid for 1 h The cooled reaction mixture is washed with 2% KoCO.sub.2 solution and water and then dried with BapSO.sub.4 ETach evaporation of the solvent on a rotary evaporator and repeated recrystallization from .eta.-hexane gives 1.5 S of pure trans-4- / ^: brans-5-n-hexyl-1,3- <3-oxan-2-yl-7-cyanohexylcarboxylic acid ethyl ester

 Yield: (45% of theory)

The compound melts at 42 ⁰ C, forms the smectic B phase from ⁰ to 70 and G is isotropic above this temperature.

Synthesis of trans-4- / brans-5 ~ ⁿ ~ ^x He yl-'1> ^ -üi osmL--2-yl7-cyclohezancarbonsäure VIII R = CGH ^ o)

3.26 g (10 mmol) of VII are refluxed in 50 ml of alcohol in the presence of 1 ml of water and 1.12 g (20 mmol) of KOH for 1 h. After distilling off the solvent, the residue is dissolved in 20 ml of water and neutralized at ⁰ ° C. with hydrochloric acid. The free acid VIII is taken up in ether and the ethereal phase washed twice with water. After drying the ether phase with SfaoSO.sub.4, filtration and distilling off the ether on a rotary evaporator, the residue is recrystallized three times from .eta. -Hexane. 2.4 g (80 % of theory ) are obtained.

on pure compound YIII, which has a smectic phase until 161 ⁰ G and is nematic in the range of 161-183 ⁰ G.

Synthesis of trans-4 - / "trans-5-n-He: £ yl-1,3-diosan-2-yl / cyclohexanecarboxylic acid 4-cyanophenyl ester I R- // ~ Α_ £ κ | R- CH.-,

308 mg (1 mmol) of YIII and 120 mg (1 mmol) of 4-cyanophenol and 22? mg (1.1 mmol) of dicyclohexylcarbodiimide (DGC) are dissolved in 10 ml of absolute ether and 79 mg (1 mmol) of absolute pyridine are added, followed by stirring for 3-4 minutes at room temperature, with exclusion of! Moisture The precipitated dicyclohexylurea is filtered off and the filtrate is concentrated, the residue is purified by repeated recrystallization from methanol and η-hexane to constant clearing temperature.

Yield: 220 mg (55 % of theory ) K 95-96 N 191 I

Synthesis of trans-4- / ^: E; rans-5-n-hesyl-1 _} 3-diosan-2-yl7-cyclohexanecarboxylic acid - / - pentyloxyphenyl ester? (R ¹ = C ₆ H ₁₃ ; R ² = G ₅ H ₁₁ O ^ g) -

3O8 mg (1 mmol) of YIII are dissolved in 10 ml of dry ether and treated with 129 nig (1 mmol) of thionyl chloride. The mixture is allowed to stand for 12 h at room temperature, cooled to 0 ⁰ G and gives a solution of 180 mg (1 mmol) of hydroquinone monopentyl ether and 303 mg (3 mmol) of TEA in 5 ml abs. Ether added and allowed to stand for a further 12 h at room temperature. The mixture is then washed with 5 ml of HoO, 2% KOH and again with HgO, dried with Ua ₂ SOn and distilled off the ether on a rotary evaporator. The residue is recrystallized several times from n-hexane

 Yield: 229 mg (48% of theory)

K 20 S 128 Ή 146 I

As additional representatives are cited:

Claims (2)

Invention claim. 1. A process for the preparation of novel crystalline liquid trans .4 / ^: urans-5-Subst.-1,3-dioxan-2-yl / -cyclohexancarbon acid esters of the general formula I. and R ² = R ¹ , ^ / Λ 4 = CS, P, Cl, Br, -CH = C, -CH = CH-CN, - <OV ^R » R 1 is -OOC-, R ^{5 is} -COO-, G _n with R ⁴ = CU, P, Cl, Br, OC _n H _{2n + 1} and with = ° n ^H 2n ₊ 1 = ° n ^H such as X = O or S with η = 0-10, characterized in that hexahydro-terephthalic acid monoalkyl esters are reacted with Cnlorameisensäurealky! Ester, selectively reduced to carbinol and selectively oxidized to trans - ^ - porrnyl-cyclotLexancarbonsäurealkylester, with 2-substituted propane-1, Reacted 3-diols to the trans-4- / cis-trans-5-substituted-1,3-dioxan-2-yl7-cyclohezancarbonsäurealkylester and after esterification with appropriate hydroxy compounds is reesterified, after which the dioxane ring trans-configured compound separated becomes. 2. A process for the preparation of novel crystalline liquid trans-4-Zorans-5-Subst. 1 ^ -Dioxan ^ -yiy-cyclohesancarbonsäureestern according to item 1, characterized in that after recrystallization, for. from methanol or n-hezane and separation of the trans isomer in the mother liquor enriched cis isomer is equilibrated by heating with acidic catalysts such as p-toluenesulfonic acid, mineral acids or Levis acids, the resulting trans isomers is separated again and repeated these processes until almost all of the amount is isolated as the trans isomer.