BIPHENYLS AND THEIR USE IN THE PRODUCTION OF LIQUID CRYSTAL COMPOUNDS

Abstract: A novel fluorobiphenyl suitable for use in the prepara­ tion of chiral nematogenic compounds, including compunds which selectively reflect light at certain temperatures, eg room temperature, has a formula: wherein represents a 4-biphenylyl radical carrying a fluorine substi­ tuent in at least one lateral position and R₁ is an optically active alkyl group.

Description: BIPHENYLS AND THEIR USE IN THE PRODUCTION OF LIQUID CRYSTAL MATERIALS Liquid crystal materials which are of the type known in the art as chiral nematic materials generally consist of one or more chiral nematogenic compounds which are optically active compounds exhibiting the property or tendency of forming liquid crystal phases. These materials may be used for example in various kinds of electro-optical device employing appropriate effects, eg the so-called phase change" effect. They may also be used in various temperature sensing applications involving the selective reflection of radiation of different wavel,engths dependent on temperature. For such temperature sensing applications the selective reflection preferably. occurs in the visible spectral region. According to the present invention in a first aspect a novel fluorobiphenyl suitable for use in the preparation of chiral nematogenic compounds has a formula: EMI1.1 Formula I wherein EMI1.2 represents a 4-biphenylyl radical carrying a fluorine substituent in at least one lateral position; R1 is an optically active alkyl group (+)-cH3.C112.CH(CH3)(CH2) n - where n is an integer in the range 0 to 6. Preferably, the compound is a separate optically active isomer. Preferably n is the range 1 to 6, desirably n = 1. The symbol (+)- indicates an optically active group showing a positive optical rotation angle. Preferably, fluorine is present in the 2 or 2' position (the group R1 being in the 4-position). Although laterally fluorinated 4-alkylbiphenyls are known such compounds have not hitherto been suggested in a form in which the terminal alkyl group is a chiral group, ie contains an optically active centre. According to the present invention in a second aspect there is provided the use of a compound of Formula I in the preparation of chiral nematogenic compounds suitable for use in chiral nematic liquid crystal materials. Examples of chiral nematogenic compounds which may be prepared from the biphenyls of Formula I are the compounds of Formula II as follows: EMI2.1 Formula II wherein R2 is n-alkyl, and X and Y are selected from H and F, at least one being F. Liquid crystalline compounds synthesised from compounds of Formula I unexpectedly can have advantageous properties, eg can show selective reflection of light at room temperature as exemplified below. Compounds of Formula I may be produced by the route: EMI3.1 Examples of the preparation and properties of compounds of Formulae I and II given above will now be described by way of example. In the following Examples the meanings of the various symbols used are as follows: glc = gas liquid chromatography bp = boiling point mp = melting point Ch-I = chiral nematic to isotropic liquid-trAnsition temperature S-Ch = Smectic to chiral nematic transition temperature K-Ch = Crystalline solid to chiral nematic transition temperature Example : The preparation of (+) trans-4-n-butylcyclohexyl) -2-t2'-fluoro-4'(2-methylbutyl)-4-biphenylyll-ethane Step P: The preliminary preparation of (+)-2 Fluoro- 4- (2-methylbutyl) -biphenyl 10 ml of a solution of a 4-bromo-2-fluorobiphenyl (90 gram) in tetrahydrofuran (90 ml) was added to magnesium turnings (9.6 gram) and tetrahydrofuran (20 ml) under nitrogen. A single crystal of iodine was added and the reaction was initiated bv warming. The remainder of the solution of was then added dropwise over 1/2 hour. After heating under reflux for 1 hour, the solution of the Grignard reagent was cooled to 250C. 10 ml of a solution of 2methylbutylphenyl- sulphonate (150 gram) in tetrahydrofuran t140 ml) was then added to the reaction mixture followed by cuprous chloride (3 gram). The remainder of the phenylsulphonate solution was added over a 40 minute period. The temperature of the resulting grey/green reaction mixture rose to 450C which was then elevated by heating to boiling for 1 hour. The reaction was allowed to cool to room temperature, then added to, a 20% (by volume) hydrochloric acid solution (2.5 litres). and the product extracted with dichloromethane (2 x 500 ml). The organic layer was washed with water (2 x 500 ml) dried over anhydrous sodium sulphate (15 gram) and the solvent evaporated to give an orange liquid residue. On cooling some white solid crystallised out from the residue. After filtration the residue (88.6 gram) was fractionally distilled under vacuum (0,5 torr) to give a colourless liquid (65 gram). This was found to be 98.8Z Dure by glc. The bp was 1200C at 0.5 torr. The optical rotation was + 14.620 (solvent). Step 1a2: .The preparation of (+)-4-(trans-4-n-Butylcyclohexyl- acetyl)-2'-fluoro-4 '-(2-methylbutyl)biphenyl A mixture of (+)-2-Fluoro-4(2-methylbutyl)biphenyl (10 gram) and trans-4-n-butylcyclohexylacetyl chloride (9.4 gram) in dichloromethane (20 ml) was added over 20 minutes to a cooled (5-100C), stirred suspension of anhydrous aluminium chloride 6.1 gram) in dichloromethane (20 ml). After the addition the reaction mixture was allowed to warm to 230C and left stirring for 17 hours. The resulting solution was added to water (200 ml), extracted successively with petroleum spirit (bp. 60-80 :180 ml +100 ml). The organic extract was then washed with water (200 ml), dried over anhydrous sodium sulphate (5 gram) and evaporated. The yellow crystalline residue (17.9 gram) was recrystallised from ethanol (35 ml) at 25"C to give the product (14.8 gram; 85Z yield). The product had mp = 71.4-72.1 C; Virtual Ch-I, (68.5-68.8 C). It was found to be 99.5Z pure by glc. Step 1b2: The preparation of (+)-1-trans-4-n-Butylcyclohexyl)2- [2'-fluoro-4' (2methylbutyl)-4- biphenylyll-ethane The ketone prepared above (14.4 gram), 99: hydrazine hydrate (14.4 ml) potassium hydroxide (7.2 gram) and digol (120 ml) were heated with stirring under a reflux condenser at 125 C for 4 hours, after which time temperature was raised to 1750C by distillation of the excess hydrazine hydrate. The mixture was then heated under reflux for 17 hours, cooled to 600C and poured onto ice water (500 gram). The organic product was extracted with petroleum spirit (bp. 60-80C:2 x 200 ml), the extract washed with water (2 x 200 ml) and dried over anhydrous sodium sulphate. Evaporation of the solvent yielded a yellow oil This gram). This was dissolved in petroleum spirit (bp. 60-80:100 ml) and adsorbed onto a column of basic alumina (50 gram) over silica gel (20 gram). Elution with petroleum spirit- (320 ml). gave on evaporation of the solvent a colourless oil (11.7 gram). Crystallisation from propan-1-ol (70 ml) at -50 C gave a chiral nematic material 9.4 gram; 68% yield). This was found to be 99.8% pure by glc. The product had the properties: S-Ch, = 60C; Ch-I, 720C Helical molecular pitch = 0.23 microns Example2 : The preparation of 1-(trans-4-ethylcyclohexyl)-2-[ 2t-fluoro-4'-(2-methylbutyl)-4-b iphenylyl] ethane z Step 1a3: The preparation of 4-(trans-4-ethylcyclohexylacetyl)- Z'-fluoro-4'(2-methylbutyl)biphenyl This was carried out in a manner analogous to Step 1a2 using 4-ethylcyclohexyl acetyl chloride as starting material. The product had the properties: Mp = 40-420C;virtual Ch-I = (27.5"C) Step 1b3: The preparation of 1-(trans-4-ethylcytlohexyl))-2- [2'-fluoro-4'-(2-methylbutyl)-4-biphenyiyl1ethane This was carried out in a manner analogous to Step 1b2 above. This product had the properties: S-Ch = -110C Ch-I = 45 C Example3: The preparation of 1-(trans-4-n-heptylcyclohexyl)-2- [2'-fluoroG '-(2¯methylbutyl)4 -biphenylyl]ethane: Step 1a4: The preparation of 4-( trans-4a-heptylcyclohexylacetyl)- 2 2'-fluoro-4'(2-methylbutyl)biphenyl This was carried out in a manner analogous to Step 1a2 above. The product had the properties: K-Ch t 69.8-70.3 C; Ch-I = 74.1-74.3 C Step 1b4: The preparation of 1-(trans-4-n-heptylcyciohexyl)-2- [2'-fluoro-4'-(2-methylbuty) -4-biphenylyl ) ethane This was carried out in a manner analogous to Step 1b2 above. The product had the properties: S-Ch ='52CC Ch-I = 790C

Claims: CLAIMS 1. A fluorobiphenyl suitable for use in the preparation of chiral nematogenic compounds and having a formula-: EMI8.1 wherein EMI8.2 represents a 4-biphenylyl rÅadical carrying a fluorine substitutent in at least one lateral position, ie in at least one of the 2, 3, 2' or 3' positions, and R1 is an optically active alkyl group (+)-CH3. CH2CH(CH3)n(CH2)n where n is an integer in the range 0 to 6. 2. A fluorobiphenyl as claimed in claim I and wherein EMI8.3 is selected from EMI8.4 3. A fluorobiphenyl as claimed in claim 1 and wherein R1 Is (+)2-methylbutyl. 4. A fluorobiphenyl as claimed in claim z and wherein R1 is (+)2-methylbutyl. 5. A fluorobiphenyl as claimed in claim 1 and which is separate optically active isomer. 6. The use of a fluorbiphenyl as claimed in claim 1 in the production 9f chiral nematic 4, 4'-disubstituted biphenyls carrying a lateral fluorine substitutent. 7. The use of a fluorobiphenyl as claimed in claim l in the production of chiral nematic ethane compounds of formula: EMI8.5 where R2 is n-alkyl and X and Y are selected from H and F, at least one being F.

Inventors: BISHOP, DAVID IAN, MCDONNELL, DAMIEN GERARD, SAGE, IAN CHARLES
Applicants: MERCK PATENT GESELLSCHAFT MIT BESCHRANKTER HAFTUNG, THE SECRETARY OF STATE FOR DEFENCE IN HER BRITANNIC MAJESTY'S GOVERNMENT OF THE UNITED KINGDOM OF GREAT BRITAIN AND
Application year: 1984
Main classification: C07C25
IPC codes: C07C17, C07C25, C07C49, C09K19