GB2102000A - 2-(Cyclohexyl)ethyl-cyclo- hexylnitriles and their use in liquid crystal compositions - Google Patents

Abstract

Compounds of the formula <IMAGE> wherein R<1> signifies a straight-chain alkyl group containing 1 to 12 carbon atoms, are especially valuable as components of nematic and cholestric liquid crystal mixtures with positive anisotropy of the dielectric constants and are used for electro- optical purposes.

Description

SPECIFICATION Nitriles The present invention is concerned with novel trans-4-[2-(trans-4-alkylcyclohexyl)ethyl]cyclohexa- necarbonitriles of the general formula

wherein R1 signifies a straight-chain alkyl group containing 1 to 1 2 carbon atoms.

The invention is also concerned with the manufacture of the compounds of formula I hereinbefore, liquid crystalline mixtures containing these compounds as well as their use in electro-dptical devices.

The representation of the cyclohexane ring used in formula I signifies in the scope of the present invention trans, 4-disubstituted cyclohexane.

The compounds in accordance with the invention are especially valuable as components of nematic and cholestric liquid crystal mixtures with positive an isotropy of the dielectric constants (e" > ey, e11 signifying the dielectric constant along the longitudinal molecular axis and E, signifying the dielectric constant perpendicular thereto).

Liquid crystals with positive dielectric an isotropy orientate themselves in an electric field with the direction of the largest dielectric constants (i.e. with the longitudinal molecular axes) parallel to the field direction. This effect is used, inter alia, in the interaction between embedded molecules and the liquid crystalline molecules (guest-host interaction) described by J.H.

Heilmeier and L.A. Zanoni [Appl. Phys. Lett. 13(1968) 91] or D.L. White and G.N. Taylor [J.

Appl. Phys. 45 (1 974) 4718]. A further interesting application of the dielectric field device lies in the rotation cell discovered by M. Schadt and W. Helfrich [Appl. Phys. Lett. 18(1971) 127].

These electro-optical rotation cells comprise essentially a condenser with transparent electrodes, the dielectric of which is formed from a nematic crystal with " > ỳ. The longitudinal molecular axes of the liquid crystals are arranged in twisted form in the fieldless state, the twisting structure being determined by the given wall orientation of the molecules. After the application of an electric potential to the condenser plates, the molecules adjust themselves with their longitudinal axes in the field direction (i.e. perpendicular to the surface of the plates), whereby linear polarized liquid is no longer rotated in the dielectric (the liquid crystal is uniaxially perpendicular to the surface of the plates). This effect is reversible and can be used to electrically control the optical transmissivity of the condenser.

Further, it is known that the addition of cholestric substances (or generally soluble, optically active substances as long as the total mixture remains liquid crystalline) to a matrix of nematic liquid crystals with positive anisotropy of the dielectric constants leads to a cholestric mixture which undergoes a cholesteric-nematic phase transition upon application of an electric field (phase-change effect). By suitable choice of the cholesteric additives such mixtures can also be used to improve the electro-optical properties of rotation cell indicators.

It has now surprisingly been found that the compounds in accordance with the invention are low-viscous liquid crystals with positive anisotropy of the dielectric constants and very small optical anisotropy. Further, the compounds in accordance with the invention have an excellent chemical and photochemical stability and small electrical conductivity. Furthermore, they are miscible with all known classes of liquid crystals and can be used in mixtures in high concentrations.

The following compounds can be named in the scope of the present invention: Trans-4-[2-(trans-4-methylcyclohexyl)ethyl]cyclohexanecarbonitrile, trans-4-[2-trans-4-ethylcyclohexyl)ethyl]cyclohexanecarbonitrile, trans-4-[2-trans-4-propylcyclohexyl)ethyl]cyclohexanecarbonitrile, trans-4-[2-trans-4-butylcyclohexyl)ethyl]cyclohexanecarbonitrile, trans-4-[2-trans-4-pentylcyclohexyl)ethyl]cyclohexanecarbonitrile, trans-4-[2-trans-4-hexylcyclohexyl)ethyl]cyclohexanecarbonitrile, trans-4-[2-trans-4-heptylcyclohexyl)ethyl]cyclohexanecarbonitrile, trans-4-[2-trans-4-octylcyclohexyl)ethyl]cyclohexanecarbonitrile, trans-4-[2-trans-4-nonylcyclohexyl)ethyl]cyclohexanecarbonitrile, trans-4-[2-trans-4-decylcyclohexyl)ethyl]cyclohexanecarbonitrile, trans-4-[2-trans-4-u ndecyclohexyl)ethyl]cyclohexa necarbon itrile, trans-4-[2-trans-4-dodecylcyclohexyl)ethyl]cyclohexanecarbonitrile.

Preferred compounds of formula I are those in which the straight-chain alkyl group R' contains 2 to 9, especially 3 to 7, carbon atoms. The compounds of formula I in which R' signifies propyl or pentyl are especially preferred.

The compounds of formula I can be manufactured in accordance with the invention by (a) reacting a compound of the general formula

wherein Y represents chlorine, bromine, or iodine and R' has the significance given earlier, and a compound of the general formula

wherein z signifies bromine, iodine, an alkylsulphonyloxy group or an arylsulphonyloxy group, in the presence of dilithium tetrachlorocuprate or dilithium tetrabromocuprate, or (b) catalytically hydrogenating a compound of the general formula

wherein R' has the significance given earlier.

The reaction of a compound of formula II with a compound of formula III can be carried out in a manner known per se. As the catalyst there is conveniently used dilithium tetrachlorocuprate or dilithium tetrabromocuprate, preferably dilithium tetrachlorocuprate. As alkylsulphonyloxy and arylsulphonyloxy groups Z there come into consideration all sulphonyloxy groups which are usually used as leaving groups in such reactions such as, for example, methanesulphonyloxy, benzenesulphonyloxy, tosyloxy, naphthalenesulphonyloxy and the like. Y in formula II preferably stands for bromine and Z in formula Ill preferably stands for bromine or tosyloxy. The reaction is conveniently carried out in an ether such as dimethoxyethane, diethylene glycol dimethyl ether, tetrahydrofuran, dioxan, diethyl ether and the like.The preferred solvent is tetrahydrofuran or a mixture of tetrahydrofuran and diethyl ether. Temperature and pressure can be held in wide limits. However, the reaction is generally carried out at atmospheric pressure and a temperature between about -80 C and room temperature. A reaction temperature of below about 0 C and especially about -1 5'C is preferred.

The catalytic hydrogenation of the compounds of formula IV can be carried out in a manner known per se using any usual hydrogenation catalyst such as palladium, platinum, Raney-nickel and the like (optionally on an inert carrier material such as carbon). Palladium and platinum are the preferred catalysts. As solvents there can be used any inert organic solvent such as saturated alcohols, ethers, esters, carboxylic acids, aromatic hydrocarbons and the like; for example, ethanol, dioxan, ethyl acetate, glacial acetic acid and toluene. Temperature and pressure are not critical aspects in this catalytic hydrogenation. The catalytic hydrogenation is, however, conveniently carried out at a temperature between room temperature and the boiling point of the mixture and under a pressure of about 1 to about 5 atmospheres.

The starting materials of formulae II to IV and especially the liquid crystalline trans-1,2dicyclohexylethenes of the general formula

wherein R' has the significance given earlier, which fall under formula IV, are novel and also form objects of the present invention.

The compounds of formulae II to IV can be prepared as illustrated in the following Schemes A-C in which R', Y and Z have the significance given earlier and Ts denotes a tosyl group.

Scheme A

Rosenmund R1 CHO RIM COGH reduction VII VIZ 1) LiAlH4 e pyridinium 2) H3o thlorochromate R v TsCI R1 o CH20Ts CH OH R1 R1 2 pyridine Ix VIII CC14 or CBr4, "- NaI P zP(C6H5)3 / EceTtone R1 X CH2Y > R > refulux R1 X refulux (C6H5)Y Mg XI tetrahydrofuran or diethyl ether RL CH2HgV II Scheme B

5 PCH3 ss + C N X C N 10 (CH3)3Si0 XII XIII XIV a H21 Pd-C 5 5oCH,p(C,Hs), H ) -'rN CH3 CH30 - (613) 3cocii31 (CS3) N XVI: XV Oxv H30 Q I tetrahydrofl C 1) NaBH4 < OH N 2) H30 e #OGH;yqH OCH N xvII Suiphonyl chloride,pvridine or Cur4, P(C6H5)3 2) PlaI, acetone,T 1) TsCl; pyridine | 2) Nel, acetone, T 4 n ChMgr2ph. n ZCH Z troreir MN separation III XIX Scheme C

HqOC--'0PN TsOCHMN XX III XaI 1'1 acetone + / p-çridine HOCH N e N CCi4 or Y CH o N P(C)3 2NErII a XXI PyIidinium chlorochrote e(CgHg)3.

xy lene, reflux O HC t N < N (CsL5)3 ZVII a XXII Trg) (Wittig / c3yO vII 0cZiF=rH-0cCN lv The compounds of formulae XVII-XIX in Scheme B are generally obtained as cis/trans mixtures which can subsequently be separated by chromatography. Starting from trans-4cyanocyclohexanecarboxylic acid of formula XX (known from Chem. Abstr. 85: 123431 d) there can, however, as shown in Scheme C for some examples, also be obtained directly the corresponding trans compounds.

The Wittig reactions for the preparation of the compounds of formula IV can be carried out in a manner known per se in the presence of a base, for example butyl lithium, phenyl lithium, sodium hydride, potassium hydride, sodium amide, potassium t-butylate, sodium ethylate, sodium hexamethyldisilazide, lithium diisopropylamide and the like, in an inert organic solvent such as an alkane, a chlorinated or aromatic hydrocarbon, an ether, an alcohol, an aprotic polar solvent and the like. Hexane, methylene chloride, benzene, toluene, diethyl ether, t-butyl methyl ether, ethanol, t-butanol, dimethyl sulphoxide and hexamethyl-phosphoric acid triamide are examples of preferred solvents. If sodium amide is used as the base, liquid ammonia can also be used as the solvent. Temperature and pressure are not critical.The reaction is conveniently carried out at atmospheric pressure and a temperature between -40 C and about + 65"C. The reaction in t-butyl methyl ether in the presence of potassium t-butylate at about 0 C is especially preferred. Y in the compounds of formulae Xl, XXI and XXII preferably signifies bromine.

The compounds of formula IV are generally obtained as mixtures of the corresponding cis-and trans-1 2-dicyclohexylethenes which can subsequently be converted directly into compounds of formula I by catalytic hydrogenation. However, if desired, the compounds of formula V can also be obtained in pure form from these mixtures, for example by chromatographic separation and recrystallization.

The compounds of formula I can be used in the form of mixtures consisting only of compounds of formula I or in the form of mixtures with other liquid crystalline or non-liquid crystalline substances such as, for example, with substances from the classes of Schiff's bases, azobenzenes, azoxybenzenes, phenyl benzoates, cyclohexanecarboxylic acid phenyl esters, cyclohexanecarboxylic acid cyclohexyl esters, biphenyls, terphenyls, phenylcyclohexanes, cinnamic acid derivatives, phenylpyrimidines, diphenylpyrimidines, cyclohexylphenylpyrimidines, phenyldioxanes and the like. Such substances are known to the person skilled in the art and many of them are, moreover commercially available.

The mixtures in accordance with the invention can contain, in addition, equatorially substituted trans-decalins of the general formula

wherein ring A is aromatic or represents a trans-1 ,4-disubstituted cyclohexane ring; R2 denotes methyl or one of the groups -CH2R', -OR', -CO-R', -CN, -COOH, -CO-OR', -CO-SR', or -O-CO-R'; R5 signifies hydrogen, methyl or one of the groups -CH2R, -OR, -CH2OR or, when R2 denotes methyl or one of the groups -CH2R', -OR' -CO-R', R5 also signifies -CN, -COOH, -CO-OR, -CO-SR or -O-CO-R; R and R' stand for straight-chain or branched-chain alkyl groups;R2 and R5 have the same significance or different significances; and R2 and R5 individually contain up to 1 2 carbon atoms and together contain at most 1 4 carbon atoms, and/or (trans-4-alkylcyclohexyl)ethanes of the general formula

wherein R7 represents one of the groups -R8, -OR8, -CO-R8, -CO-OR8 or -O-CO-R8, R6 and R8 signify straight-chain alkyl groups containing 1 to 1 2 carbon atoms and n stands for one of the numbers 1 or 2.

The compounds of formulae XXIII and XXIV are novel and to a large extent themselves have liquid crystalline properties.

The preparation of the compounds of formula XXIII is shown in the following Schemes 1 to 7 in which A, R and R' have the significance given above. Further, R" signifies a readily cleavable alcohol protecting group, R3 signifies hydrogen, methyl or one of the groups -CH2R, -OR, -OR", -CH2OR or -CH2OR", R4 signifies hydrogen or alkyl, R" signifies hydrogen, methyl or one of the groups -CH2R, -OR, -OR", -CH2OR, -CH2OR", -CO-OR or -O-CO-R, R12 has any of the values accorded to R" or signifies the carboxyl group, X signifies oxygen or sulphur, X' signifies bromine or iodine, Ts signifies the p-tosyl group and the symbol - indicates that the bond denoted thereby can lie below or above the plane of the drawing, i.e. the cyano group (in Schemes 1 and 3) can be in the a- or ss-position or the cyclohexane ring (in Scheme 4) can be trans- or cis-disubstituted. Furthermore, the representation of the decalin structure used in formula XXIII as well as hereinafter signifies trans-decalins with equatorial arrangement of the substituents unless indicated otherwise.

Scheme 1

1) S 2) CE 3) Cw3COOE/Cw3COONa 1) LLX NBj/(B3) 3COH 2) Naqc1 u l) Na2N82 N I(OHIT MIVTfI b 322' XXYII 3 (Cg3)3COX Li A14 / ri kl34 NCTo Rco xxvZII j 1) e u::8 chioro per- enzoic acid INI N Dc XXXI XYX XXXI Introduction oÇ the protecting > R 2) RI R"O R"O R XXVZ s XXVIII e Scheme 2

HYYV3II R"OCB2 H3 XXVII 2 XXVIII XXVIIT h 1) t (C6H5)3 C1 03 e Introduction of ( l)3 / the protecting the group R" (CH3) 3COCM+3 2) H30 XXVIII g 0 S XXVIII g 1) nab4,3 / / 12) g Dcx= 2) | E20 / Jones' oxidation or or -pyridinium dichro XXXIII mate, dimethyl fonnamide TsC, pyridine < LiAlB4 cM' YXXIV z=VIII C Rugs, Li2CuC14 (cat.) ra3 1) NE2NE2 C -2) 'oH,T XXVIII d xxx Scheme 3

N cqoc-03 N XXX a 2 S ystallization .- 1) OH.o Chromat. 2)Pract csta11ization 1) NaOBr separation \ 2)r F E30 (X II NI N woo N XXXV XXIX a ' 1) tccJapH 2) CsHg pyrldllle \ Rose==d N reduction cHC xxam DQZ BF, TCcB s CS SZ 1 g-03" RX03" xxxvn xwIIr i cM=c' XXVIII C Scheme 4

on' N1 03 N Rl1 z 3 R1 < XXIII f XXVIII (optional for C. 0R) .H2ML2o3 |R (3 OH e OH E30 (3 on.

NI 2 n:2 XXXVIII XXIII g 1) Pyridinium dichr'rn,te or pyridinium chlorochrozate 2) ROE/Ca30E, OOC 3) optional esterifiration of a group COOH ar obtained from Eel2 r -WB or -O-CO-R f31 Hod oR RlW / 1) ClC CC2ES'{C2 5 3 z ClCOOc2H5,N(C253 mIII 2) XXIII h 2) ~~~ a::nle / zole 3} c6H5S02c1, pyridine nf OR' 4, > OR' XXIII j XXIII k Scheme 5

a3 OtH1 a3 R XXIII 1 1) N O 2) 1 H3 ( C30H 1) ScC12 AjOXR 3 2) RxH l N (C285 R == n $2J N83 g > CONs z CX C6eiSo2cl wJ R - pyridine R3+/J o b X== o 1J N82o8 2) (CH3co)20 Sca3) zi ~ H2 2 3H 2 26 'iP296 purist nium chloro A teIcH C A 2 12 ~ I R3 ;J XLI I21))TSCL/r,1ff 2) LLLTC HH3 R33 xXz= p Scheme 6

33 /03- sr2/Fe or -"fI1 - N. XLIT N a3 2J 3J 3 4 R3 ZvTI k Co t BCl, 1CuCS, cu2 ci 2-C13 dimethylformamide (Gax: =.;Cod) B3 r 3 2 2 gP cur N a 3 a xXI= a ~ < z 1) ESC2}2C 25a/gFZ 0" L3,I a3 X:XlIIr 2) Rane 3 for a3 - -ca R - 20a") 1) Cleavage of tie Protect;; Sl) Cleavage of the protect: 2) acoct rug group a group a" 2) zones' oxidation or pyri RA minium dichromate, dineth; A ^ C 42 ornarnide XXIII a XXIII çv- > ooss XXIV t 1IC1CDCCZH,N(C29j) 3 Il)tSagMZC1. $;COoc;2B51N(C2H5)3 0"" 50 Cl -0~'" nt 2- N XXIII u J -~ v Scheme 7

ACOR' < rOCOR' R3 z 3-Chloroperbenzoic acid A 3 w XITS' a I w t | or OH RCOv lSo - -Qa"} XLIII XMIT z 1) Cleavage of the protecting 2) ROC1, \ group R 1) Base \ ; 2) R'I C (for R3 A (for a3 -) A 1) 1 J R3 zl)Cleavåge o < protecting group R" I1" 3 HOOC 2) Jones' oxidpt;nn R X=II a or pyridinium di romate/di=athylforrna:mide XXIIt y 1) ClcooC2H5,N(C2H5)3 1) soClz 2) NH3 2) RXE 3) C6H5502C1, pyridine fOR NC MiMA' Mn xXIII ss XXIII Y The diastereomeric mixture of the compound of formula XXIX can be separated by chromatography.However, conversion into the acid of formula XXXV, separation by fractional crystallization and conversion into the nitrile of formula XXIXa is more suitable. On the other hand, if the nitrile of formula XXIX is to be converted into a compound of formula XXX, then the separation is advantageously carried out only after the Grignard reaction and the subsequent equilibrating hydrolysis by crystallization of the compounds of formula XXX.

The acid of formula XXXV can, for example, also be obtained from the aldehyde of formula XXXII by oxidation with potassium permanganate.

The racemate of the acid of formula XXXV can, if desired, be resolved into the optical antipodes. In so doing, the acid of formula XXXV is conveniently reacted with an optically active base such as optically active phenylethylamine, ephedrine, cinchonidine, naphthylethylamine, methylbenzylamine and the like, the mixture of diastereomeric salts obtained is separated by crystallization and the optically active salt obtained is hydrolyzed. Thus, all optically active compounds of formula XXIII can be obtained starting from an optically active acid of formula XXXV.

The term "readily cleavable alcohol protecting group" used for the groups R" embraces those alcohol protecting groups which can be cleaved off under conditions which do not affect an alkoxy group. Preferred examples of such groups denoted by R" are the benzyl group and the tetrahydropyranyl group [Adv. Org. Chem. 3 (1963) 216], groups of the formulae -CH2OCH3 [J. Amer. Chem. Soc. 99 (1977)1275] and and -CH2OCH2CH2OCH3 (Tetrahedron Letters 1976, 809), the t-butyl-dimethyl-silyl group (J. Amer. Chem Soc. 94(1972) 6190) and the like. The benzyl group can be cleaved off, for example, by catalytic hydrogenation; palladium/carbon being the preferred catalyst.The group -CH2OCH3, the tetrahydropyranyl group and the t-butyldimethyl-silyl group can be removed by reaction with a strong acid such as sulphuric acid, hydrochloric acid, p-toluenesulphonic acid and the like. The removal of the group -CH2O- CH2CH2OCH3 can be carried out, for example, by reaction with zinc (II) bromide or titanium (IV) chloride in methylene chloride at room temperature. The t-butyl-dimethyl-silyl group can also be cleaved off by reaction with a fluoride, preferably an alkali metal fluoride or tetraalkylammonium fluoride such as potassium fluoride, tetrabutylammonium fluoride and the like.The introduction of the aforementioned protecting groups can be carried out, for example, by reacting the alcohol to be protected with benzyl chloride, dihydropyran, chloromethyl methyl ether, ss-methoxye- thoxy-methyl chloride, t-butyl-dimethyl-silyl chloride and the like, if desired in the presence of a base. A detailed description relating to the introduction and cleavage of alcohol protecting groups is found in the literature mentioned earlier.

The compounds of formula XXIV can be prepared by reducing a compound of the general formula

wherein R9 represents hydrogen, hydroxy, halogen or one of the groups -R8 or -OR8 and R6, R8 and n have the significances given earlier, and acylating the resulting compound of the general formula

wherein R6, R9 and n have the significances given earlier, when R9 signifies hydrogen, or, when R9 signifies hydroxy, esterifying the resulting compound of formula VL with a carboxylic acid of the formula R8COOH or a reactive derivative thereof or, when R9 signifies halogen, reacting the resulting compound of formula VL with magnesium and subsequently with carbon dioxide, hydrolyzing the carboxylate obtained and esterifying the resulting acid or a reactive derivative thereof with an alcohol of the formula R80H.

The compounds of formula XXXXIV used as the starting materials can be prepared by acylating a compound of the general formula

wherein R9 and n have the significances given earlier, with the acid chloride derived from a compound of the general formula

wherein R6 has the significances given earlier.

This reaction can be carried out according to methods known per se for the Friedel-Crafts acylation. The acid chlorides can be prepared, for example, by heating the corresponding acids of formula VLII with thionyl chloride.

The liquid crystal mixtures in accordance with the invention contain, in addition to one or more compounds of formula I, preferably one or more of the following compounds: 4-Cyanobiphenyls of the general formula

wherein R'3 signifies a straight-chain alkyl or alkoxy group containing 2 to 7 carbon atoms, p-(trans-4-alkylcyclohexyl)benzonitriles of the general formula

wherein R'4 signifies a straight-chain alkyl group containing 2 to 7 carbon atoms, p(5-alkyl-2-pyrimidinyl)benzonitriles of the general formula

wherein R'4 has the significance given earlier, p-[5-(trans-4-alkylcyclohexyl)-2-pyrimidinyl]benzonitriles of the general formula

wherein R'4 has the significance given earlier, Schiff's bases of the general formula

wherein R'5 denotes the cyano group or a straight-chain alkyl or alkoxy group containing 1 to 5 carbon atoms and R'4 has the significance given earlier, p-alkylbenzoic acid phenyl esters of the general formula

wherein R16 denotes the cyano group or a straight-chain alkoxy group containing 1 to 6 carbon atoms and R'4 has the significance given earlier, trans-4-alkylcyclohexanecarboxylic acid phenyl esters of the general formula

wherein R'4 and R16 have the significance given earlier, trans-4-alkycyclohexanecarboxylic acid cyclohexyl esters of the general formula

wherein R'7 denotes the cyano group or a straight-chain alkyl group containing 1 to 6 carbon atoms and R'4 has the significance given earlier, p.[2-(trans-4.alkylcyclohexyl)ethyl]benzonitriles of the general formula

wherein R'4 has the significance given earlier, equatorially substituted trans-decalins of formula XXIII hereinbefore in which R and R' signify straight-chain alkyl groups and, preferably, R5 denotes methyl or one of the groups -CH2R or -OR and R2 denotes methyl or one of the groups -CH2R', -OR', -CO-R', -CN, -CO-OR' or -O-CO-R', and (trans-4-alkylcyclohexyl)ethanes of formula XXIV hereinbefore in which n stands for the number 1 and R7 preferably represents one of the groups -R8 or -OR8.

The amount of the compounds of formula I present in the mixtures in accordance with the invention can generally be chosen at will; for example, mixtures which consist of two or more compounds of formula I can also be used. However, there are preferred mixtures which contain about 1 wt.% to about 80 wt.% of compounds of formula I and there are especially preferred those mixtures which contain about 10 wt.% to about 60 wt.% of compounds of formula I.

Further, the mixtures in accordance with the invention can contain suitable optically active compounds, for example optically active biphenyls, and/or dichroic colouring substances, for example azo, azoxy and anthraquinone colouring substances. The amount of such compounds is determined by the solubility, the desired pitch, colour, extinction and the like. The amount of opticaily active compounds preferably amounts to at most about 4 weight percent and the amount of dichroic colouring substance preferably amounts to at most about 10 weight percent.

The manufacture of the liquid crystalline mixtures in accordance with the invention can be carried out in a manner known per se; for example, by heating a mixture of the components to a temperature barely above the clearing point and subsequently cooling down.

The manufacture of an electro-optical device containing one or more compounds of formula I can also be carried out in a manner known per se; for example, by evacuating a suitable cell and introducing the desired compound or mixture into the evacuated cell.

The invention is also concerned with all novel compounds, mixtures, processes, uses and devices as herein described.

The following mixtures are examples of preferred mixtures in accordance with the invention. 17 denotes the viscosity (bulk viscosity).

Mixture Example 1 40.4 wt.% of 4'-pentyl-4-cyanobiphenyl, 59.6 wt.% of trans-4-[2-(trans-4-pentylcyclohexyl)ethyl]-cyclohexanecarbonitrile, m.p. -10 C, cl.p. 56.5"C, nematic.

Mixture Example 2 34.35 wt.% of 4'-pentyl-4-cyanobiphenyl, 10.6 wt.% of p-[(5-(trans-4-ethylcyclohexyl)-2-pyrimidinyl]-benzonitrile, 54.9 wt. % of trans-4-[2-(trans-4-pentylcyclohexyl)ethyl]-cyclohexanecarbonitrile, m.p. -10 C, cl.p. 70"C, nematic.

Mixture Example 3 1 6.8 wt.% of 4'-pentyl-4-cyanobiphenyl, 62. wt.% of p-[5-(trans-4-ethylcyclohexyl)-2-pyrimidinyl]-benzonitrile, 1 6.6 wt.% of 2-(trans-4-propylcyclohexyl)- 1 -(p-ethoxyphenyl)-ethane, 1 9.3 wt. % of 2-(trans-4-pentylcyclohexyi)- 1 -(p-ethoxyphenyl)-ethane, 41. 1 wt.% of trans-4-[2-(trans-4-pentylcyclohexyl)ethyl]-cyclohexanecarbonitrile, m.p. < -10 C, cl.p. 58"C, nematic; 71=27.2 cp.

The manufacture of the compounds of formula I in accordance with the invention is illustrated on the basis of the following Examples: Example 1 121 mg of magnesium shavings were covered with 3 ml of absolute tetrahydrofuran while gassing with argon, treated with a crystal of iodine and then treated at reflux temperature with a solution of 989 mg of trans-1-(bromomethyl)-4-pentylcyclohexane in 7 ml of absolute tetrahydrofuran. After completion of the addition, the mixture was added to reflux of a further 45 minutes.

Subsequently, the mixture, cooled to -78 C, was treated with 0.7 ml of a 0.1 N solution of dilithium tetrachlorocuprate (prepared in accordance with M. Tamura et al, Synthesis 1971, 303) in tetrahydrofuran and treated with a solution of 587 mg of trans-4-(tosyloxymethyl)cyclohexanecarbonitrile in 9 ml of absolute tetrahydrofuran. The mixture, warmed to -15 C, was stirred for a further 21 hours, then treated with about 10 ml of saturated ammonium chloride solution and extracted three times with 50 ml of diethyl ether each time. The organic phases were washed with 50 ml of saturated sodium chloride solution, dried over magnesium sulphate and concentrated.Low-pressure chromatography (0.5 bar) of the residue on silica gel with 3% ethyl acetate/petroleum ether gave, besides a large amount of coupling product of trans-1 (bromomethyl)-4-pentylcyclohexane, 1 64 mg (28.5%) of trans-4-[2-(trans-4-pentylcyclohexyl) ethyl]cyclohexanecarbonitrile [353 mg of trans4.(tosyloxymethyl)cyclohexanecarbonitrile could be recovered with 30% ethyl acetate/petroleum ether]. A single recrystallization from 5 ml of methanol yielded 96 mg of trans-4-[2-(trans-4-pentylcyciohexyl)ethyl]cyclohexanecarbonitrile as colourless crystals (purity 99.98%); solid-solid transition 39.3"C, m.p. 56.5"C, cl.p. 72.7"C (nematic).

The trans.1.(bromomethyl).4.pentylcyclohexane used as the starting material was prepared as follows: (n) 3.79 g of lithium aluminium hydride were placed in 100 ml of absolute tetrahydrofuran while gassing with argon and treated within 30 minutes with a solution of 19.83 9 of trans-4pentycyclohexanecarboxylic acid in 100 ml of absolute tetrahydrofuran. After completion of the addition, the mixture was heated to reflux for 1 hour, then cautiously added to 200 ml of 2N hydrochloric acid and extracted three times with 100 ml of diethyl ether each time. The organic phases were washed with 100 ml of saturated sodium carbonate solution, dried over potassium carbonate and concentrated.Distillation of the residue (19.2 g) gave in the main run 17.7 g (96%) of (trans-4-pentylcyclohexyl)methanol as a colourless oil (purity 99.9%); b.p. 89"C/0.2 mmHg.

(b) A solution of 3.69 g of (trans-4-pentylcyclohexyl)-methanol and 5.51 g of triphenylphosphine in 70 ml of methylene chloride at -30 C was placed under argon gasification and treated portionwise within 1 5 minutes with 7.30 g of solid tetrabromomethane in such a manner that the internal temperature did not exceed -20C. After completion of the addition, the cooling bath was removed and the mixture was stirred for a further 1 8 hours with gradual warming to room temperature. The mixture was then concentrated on a rotary evaporator and the semicrystalline residue obtained with triturated with 200 ml of warm hexane, filtered and the concentrated filtrate was chromatographed with hexane on a column of silica gel.There were obtained 4.79 g (97%) of trans-1-(bromomethyl)-4.pentylcyclohexane as a colourless liquid which was purified further by distillation; b.p. 82"C/0.08 mmHg.

The trans.4.(tosyloxymethyl)cyclohexanecarbonitrile also used as the starting material was prepared as follows: (c) A mixture of 18.9 g of 1.methoxy.3.(trimethylsilyloxy).1,3.butadiene [S. Danishefsky et al, J.

Amer. Chem. Soc. 96, (1974) 7807], 6.4 g of acrylonitrile, 100 mg of dibenzoyl peroxide and 50 ml of benzene was heated to reflux for 23 hours while gassing with argon. After cooling, the volatile constituents (benzene and excess acrylonitrile) were removed on a rotary evaporator and the residue was heated to reflux for 2 hours in 100 ml of tetrahydrofuran/ 1 N hydrochloric acid (4:1). The cooled mixture was subsequently extracted three times with 100 ml of methylene chloride each time. The organic phases were washed twice with 100 ml of water each time and once with 100 ml of saturated sodium chloride solution, dried over magnesium sulphate and concentrated.There were obtained 10.3 g of yellow oil which consisted of 87.9% of 4-cyano-3cyclohexen-1-one, of 4.1% of 4-cyano-2-cyclohexen-1-one and of 2.7% of trans-4-cyano-3methoxycyclohexanone (an intermediately occuring hydrolysis product). Bulb-tube distillation (130-140"C/O. 27-0.1 5 mmHg) of the oil obtained gave 7.64 9 of a mixture of 4-cyano-3cyclohexen-1-one and 4.cyano-2.cyclohexen-1-one as an orange, crystallizing oil. This was dissolved in 70 ml of ethanol and hydrogenated at normal pressure in the presence of 764 mg of 10% palladium/carbon (hydrogen uptake 1 425 ml).After filtration of the catalyst, washing with methylene chloride, concentration of the filtrate and bulb-tube distillation (130-150 C/0.11 mmHg), there were obtained 5.45 g (70%) of 4-cyanocyclohexanone as a colourless oil; Rf/value (toluene/ethyl acetate 3:1):0.25.

(d) 9.6 g of triphenyl(methoxymethyl)phosphonium chloride were suspended in 50 ml of t-butyl methyl ether while gassing with argon and treated portionwise at -10 C with 3.39 g of solid potassium t-butylate. After completion of the addition, the mixture was stirred at O to 5"C for a further 30 minutes and then the deep orange, partialiy heterogeneous mixture was treated dropwise within 10 minutes with a solution of 2.30 g of 4-cyanocyclohexanone in 20 ml of tbutyl methyl ether.In so doing the internal temperature should not exceed 5"C. After completion of the addition, the now yellow-orange mixture was warmed to 25"C and stirred for a further 2 hours. 50 ml of a 2% sodium hydrogen carbonate solution were subsequently added and the separated, aqueous phase was extracted twice with 50 ml of diethyl ether each time.

The organic phases were washed with 50 ml of saturated sodium chloride solution, dried over potassium carbonate and concentrated. The residual, semi-crystalline, orange oil was triturated with 400 ml of hexane, cooled to -20 C and freed from precipitated triphenylsphosphine oxide by filtration (rinsing with cold hexane). Low-pressure chromatography (0.4 bar) of the concen trated residue on silica gel using 10% ethyl acetate/petroleum ether as the elution agent gave 1.60 g (56%) of 4-(methoxymethylene)cyclohexanecarbonitrile as a colourless oil (purity 97%).

(e) The 4-(methoxymethylene)cyclohexanecarbonitrile obtained was heated to reflux for 1.5 hours in 100 ml of tetrahydrofuran/0.2N hydrochloric acid (4:1). The cooled mixture was then poured into 50 ml of water and extracted three times with 50 ml of diethyl ether each time. The organic phases were washed with 50 ml of water and 50 ml of saturated sodium hydrogen carbonate solution, dried over magnesium sulphate and concentrated. There were obtained 1.35 g (94%) of a colourless oil which, in accordance with gas chromatographical analysis, contained 92% of a mixture of the cis- and trans-4-cyanocyclohexanecarboxaldehydes (in the ratio of about 1:1). This material was used in the following reduction without additional purification. Rf-values (toluene-ethyl acetate 3:1): cis-4-cyanocyclohexanecarboxaldehyde 0.36, trans-4-cyanocyelohexanecarboxaldehyde 0.32.

(f) A solution of 1.34 g of 4-cyanocyclohexanecarboxyaldehyde (cis/trans mixture) in 40 ml of 0.1 N methanoiic potassium hydroxide solution was treated portionwise at 0 C while gassing with argon with 378 mg of solid sodium borohydride. After completion of the addition, the mixture was stirred at 0 C for a further 20 minutes. then 50 ml of water were added and the mixture was extracted three times with 50 ml of methylene chloride each time. The organic phases were washed twice with 50 ml of water each time, dried over magnesium sulphate and concentrated. Low-pressure chromatography (0.4 bar) of the residual oil on silica gel with chloroform/ethyl acetate (1:1) gave 1.22 g (90%) of 4-(hydroxymethyl)cyclohexanecarbonitrile (likewise as an about 1:1 mixture of the two epimers) as a colourless, viscous oil.This material was used in the following tosylation without further purification. Rf-value of 4-(hydroxymethyl)cyclohexanecarbonitrile [chloroform/ethyl acetate (1:1 ):0. 29 (longish spot).

(g) A solution of 1.20 g of the 4-(hydroxymethyl)cyclohexanecarbonitrile obtained in 5 ml of pyridine was treated portionwise at room temperature and while gassing with argon with 2.46 g of tosyl chloride. After stirring at room temperature for 3.5 hours (formation of a white precipitate), the mixture, cooled to 0 C was treated with about 2 ml of water, cautiously made acid with about 7 ml of concentrated hydrochloric acid and extracted three times with 30 ml of diethyl ether each time. The organic phases were washed with 50 ml of water and 50 ml of saturated sodium chloride solution, dried over magnesium sulphate and concentrated, 2.31 g of semi-crystalline oil remaining behind.Low-pressure chromatography (0.5 bar) on 480 g of silica gel using 30% ethyl acetate/petroleum ether as the elution agent gave 1.06 g (42%) of trans4-(tosyloxymethyl)-cyclohexanecarbonitrile as a colourless, crystallizing oil (m.p. 84-85"C) and 1.03 g (41%) of cis-4-(tosyloxymethyl)-cyclohexanecarbonitrile as a colourless viscous oil. Rfvalue (30% ethyl acetate/petroleum ether): trans product 0.25, cis product 0.20.

The following compounds can be manufactured in an analogous manner: Trans-4-[2-(trans-4-ethylcyclohexyi)ethyl]cyclohexanecarbonitrile; m.p. 33.8"C, cl.p. 39.1to (nematic); trans-4-[2-trans-4-propylcyclohexyl)ethyl]cyclohexanecarbonitrile; m.p. 47.5 C, cl.p. 64.3"C (nematic); and trans-4-[2-trans-4-butylcyclohexyl)ethyl]cyclohexanecarbonitrile; m.p. 60.1"C, cl.p. 64.5"C (nematic).

Claims (8)

1. Compounds of the general formula

wherein R1 signifies a straight-chain alkyl group containing 1 to 1 2 carbon atoms.

2. Compounds according to claim 1, wherein R' signifies a straight-chain alkyl group containing 2 to 9 carbon atoms.

3. Compounds according to claim 1 or claim 2, wherein R' signifies a straight-chain alkyl group containing 3 to 7 carbon atoms.

4. Trans-4-[2-(trans-4-pentylcyclohexyl)ethyl]cyclohexanecarbonitrile.

5. Trans-4-[2-(trans-4-propylcyclohexyl)ethyl]cyclohexanecarbon itrile.

6. A liquid crystalline mixture containing at least two components, wherein at least one component is a compound of formula I defined in claim 1.

7. A process for the manufacture of compounds of the general formula

wherein R' signifies a straight-chain alkyl group containing 1 to 1 2 carbon atoms, which process comprises (a) reacting a compound of the general formula

wherein Y represents chlorine, bromine or iodine and R' has the significance given earlier in this claim, and a compound of the general formula

wherein Z signifies bromine, iodine, an alkylsulphonyloxy group or an arylsulphonyloxy group, in the presence of dilithium tetrachlorocuprate or dilithium tetrabromocuprate, or (b) catalytically hydrogenating a compound of the general formula

wherein R' has the significance given earlier in this claim.

8. The use of the compounds of formula I defined in claim 1 for electro-optical purposes.