ELECTROPHILIC SUBSTITUTION OF TRIPHENYLENE-BASED DISCOTIC LIQUID CRYSTALS

Abstract: A triphenylene such as hexa- beta -substituted hexyloxytriphenylene is alpha -substituted by an electrophile in mixed polar cosolvents according to the reaction scheme (a).

Description: ELECTROPHILIC SUBSTITUTION OF TRIPHENYLENE-BASED DISCOTIC LIQUID CRYSTALS This invention relates to discotic liquid crystals and their synthesis by functionalising and structurally modifying triphenylenes through electrophilic substitution. The invention further relates to these substituted triphenylenes as intermediates or as products in their own right, and to devices incorporating these materials. The triphenylene discotic mesogens studied to date are predominantly featureless, and in their pure state are colourless, insulating materials. If discotic liquid crystals are to form the basis of molecular electronic or opto-electronic devices, materials must be prepared which combine suitable mesophase behaviour with the required molecular functionality, i.e. the molecular characteristics required to perform a specific function. Electrophilic substitution of triphenylene cores at α positions is a way, according to the invention, which allows new properties to be built into a discotic mesogen, e.g. a wider mesophase range, colouring of hitherto uncoloured compounds and insertion of a permanent dipole, the last-named opening up the possibilities of electro-optic switching with a low energy input. According to the present invention, a discotic liquid crystal with molecular functionality is synthesised by reacting a low molar mass or polymeric triphenylene derivative with an electrophile, with attack occurring at a positions. Thus the invention provides a triphenylene which is substituted by replacement of a hydrogen atom in an a position and a method of electrophilically substituting a triphenylene in an a position, comprising dissolving the triphenylene in a mixture of semipolar and polar solvents and adding an electrophile or a precursor that in said solvent yields an electrophile, either of which can replace a hydrogen atom at the α position. In general, in triphenylene-based discotic liquid crystals, the β positions are normally all occupied by alkoxy or acyloxy side chains. Conventional wisdom has it that, in the face of steric hindrance, substitution of hydrogen atoms at positions was not possible. However, we have discovered conditions under which these α-positions can be nitrated, chlorinated, brominated and alkylated (chloromethylated), and those substituents can then be further elaborated and modified. It is surprising and hitherto unreported that α hydrogens could be substituted where all the β positions were already occupied. Such substitution has led to an effect which was not predicted, viz. an enhanced mesophase range. In our International Application WO94/29243 we disclosed routes to the first triphenylene-based discotic liquid crystals in which some of the β positions were not occupied by alkoxy or acyloxy side chains but by hydrogen. We have now discovered conditions under which those materials can also be functionalised through electrophilic substitution at those β positions. This provides a route to a new class of discotic liquid crystals with enhanced properties. The invention extends to the substituted triphenylenes synthesised as set forth above, to those compounds per se, whether or not they are discotic liquid crystals in their own right, to their use as intermediates and to devices incorporating them and discotic liquid crystals derived from them by further reaction of the α substituent. The product may be a low molar mass or polymeric triphenylene based discotic liquid crystal bearing up to 12 substituents all of which may be the same or some of which may be different and which may be on the α and/or β positions of the aromatic nucleus The method according to the invention includes general reactions of the type: I π where I and or II are generalised formulae for triphenylene based discotic mesogens, E + is an electrophile such as N0 2 + (HNO 3 ), Br + (Br 2 ), R + (RC1), RCO + (RCOC1) or AiCO (ArCOCl) where R is alkyl and Ar is aiyl, X may be any one or more of a variety of substituents including halogen, alkyl, nitro, alkoxy and acyloxy and n = 0 to 1 1 , tyically 5, 6, or 7 with compound I being typically hexa-β-substituted. Such triphenylene derivatives (which may be highly coloured) can be incoφorated as solutes into other discotic mesogens (low molar mass or polymeric). Thus the invention includes both physical and chemical incoφoration of a chromophore into the system, whether as part of a polymer main chain, a side chain off a polymer main backbone, or a side chain off the core (or as the main core itself, as is the case with the monomer form of these materials substituted as set forth above). When considering the possible locations in the molecular structure for active functional groups, in principle any other functionality could also have one of these three locations: the main chain, a side chain or the polycyclic core. Such functionality could be, for example, susceptibility to externally applied electric or magnetic fields and inherent redox characteristics such as electron donor/acceptor characteristics which could permit construction of stacked column assemblies. Thus, such substitution allows new properties to be introduced into the system such as colour (for use in electrooptic displays), conductivity (the redox potentials can be modified to facilitate doping with oxidants and reductants), photoconductivity, a local molecular dipole peφendicular to the column axis (dipolar derivatives), non-linear optic properties, and chirality. Some of these induced properties are essential to certain applications of these materials. For example, a "handle" can be substituted into the mesogen for an electric field to switch the whole bulk medium from, for example, a coloured to an opaque state, and for more general bistable systems which consume current only while switching between states. The triphenylene which is used in the method according to the invention may be a hexaether or hexaester of 2,3,6,7,10,11-hexa-hydroxytriphenylene such as hexa-alkoxy or -acyloxy, e.g. hexahexyl (or pentyl or heptyl) oxytriphenylene, (HAT6), a known discotic mesogen whose structural formula is 1 in the reaction scheme below. The 2, 3, 6, 7, 10 and 11 positions are collectively the β positions, which are all occupied in HAT6, and the (unsubstituted) 1, 4, 5, 8, 9 and 12 positions are collectively the α positions. The mesophase range of 1 is from 70°C (crystal-mesophase transition) to 100°C ( esophase-isotropic liquid transition). The invention will now be described by way of example with reference to the following reaction scheme, according to which HAT6 can be converted to an α-nitro (and thence to an α-amino, and thence to an α-acylamino or α,α'-azo) derivative, each of which exhibits a discotic mesophase: (7) Nitration of HAT6 (1) under mild conditions, thus preferably conducted in ether and optionally a carboxylic acid, as will be described more fully, proceeds smoothly to form the mono-α-nitrated product (2). A further example of α-nitration is provided by Alternative reactions, some of which involve substitution at the β position include:- (17) (18) In the case of the polymer (17), the position of nitration is unclear and presumably the product is polydisperse although the elemental analysis indicates that on average ca. two nitro groups have been introduced into each triphenylene nucleus. Some doubt also exists over the exact site of nitration in the mononitro compounds (15) and (16) although the structures shown are those most probably, correct. It is important to note that, whereas compound (8) and the precursor to compound (I I) are not themselves liquid crystalline, compounds (9), (10) and (11) are all liquid crystals. Instead of nitration other electrophilic substitution reactions such as halogenation are possible. Hence, when HAT6 is reacted with iodine monochloride the monochloride (20) and a mixture of isomeric dichlorides (21) is obtained. OHx (21) The monochloro compound has an extended mesophase range of (37-98 °C) whereas the mixture of di chloro compounds is a room temperature discotic clearing at 36°C. Both give a single mesophase texture typical of a discotic hexagonal mesophase. The monochloro product can also be obtained using PIFA (phenyliodonium bistrifluoroacetate) followed by tetrabutylammonium chloride.. The chloro substituent can be elaborated into an alkyl group as shown. 0—C—CF 3 0 HAT6 (1) can also be brominated. Using an excess of molecular bromine gives a single product, the tribromide (24) (24) An example of alkylation is provided by the reaction of HAT6 with chloromethyl methyl ether. (25) 2.3.6.7.10.1 1-Hexahexyloxy-l-nitrotriphenylene (2) 2,3,6,7,10,11-Hexahexyloxytriphenylene (9.4 g, 11.3 mmol) was dissolved in ether (150 ml) and glacial acetic acid (30 ml). Concentrated nitric acid (3 ml) was added dropwise and the mixture stirred at room temperature for 15 minutes. This use of ether is meritorious and unusual. Normally, a nitration would employ concentrated aqueous H2SO4 to assist the HNO3, and HNO3 would be expected to decompose ether. Ether gives a milder reaction. The solution was washed with water and potassium carbonate solution and the solvent removed m vacuo. The residue was purified by column chromatography (silica, dichloromethane light petroleum 1:1) and reprecipitated from ethanol to give 2,3,6,7,10,11-hexahexyloxy-l- nitrotriphenylene (7.2 g, 73%). Anal. C, 74.15%; H, 9.75%; N, 1.65%; C5 4 H 83 NOg requires C, 74.19%; H, 9.57%; N, 1.60%. The mesophase range of 2 was from below room temperature to 136°C. The inventively synthesised product (2) can be further manipulated, for example as follows: l-Amino-2.3.6.7.10.1 1-hexahexyIoxytriphenylene (3) 2,3,6,7,10,11-Hexahexyloxynitrotriphenylene (5 g, 5.72 mmol) and tin powder (5 g) were stirred in refluxing glacial acetic acid for 4 hours and the hot solution decanted onto water. The mixture was extracted with dichloromethane (3 x 200 ml) and the solvents removed jn vacuo. The residue was recrystallized from ethanol to afford l-amino-2,3,6,7,10,11-hexahexyloxytriphenylene (4.2 g, 87%), whose mesophase range is from 35°C to 77°C. The product (3) can be manipulated in a variety of ways, of which two are as follows: Azo Derivative of HAT6 (4) Amino-2,3,6,7,10,11-hexahexyloxytriphenylene (0.5 g, 0.59 mmol) was stirred in dichloromethane (10 ml) and glacial acetic acid (5 ml) at 5°C. Sodium nitrite (0.2 g, 2.9 mmol) in water (2 ml) was added and the mixture stirred at room temperature for 2 hours and at 40°C for 30 minutes. The solution was washed with water (2 x 20 ml) and the solvents removed m vacuo. The residue was separated by column chromatography (silica, dichloromethane the dichloromethane/ethyl acetate 9:1) and recrystallized from dichloromethane/ethanol to give the azo derivative as an orange solid (225 mg, 45%). Anal. C, 75.7%; H, 9.7%; N, 3.1%; C 5 4Hg2N 2 O 8 requires C, 75.83%; H, 9.67%; N, 3.28%. The mesophase range of 4 was from about 150°C to 227°C. 1-Acetylamino-2.3.6.7.I0.11-hexahexyloxytriphenylene (5) l-Amino-2,3,6,7,10,11-hexahexyloxytriphenylene (1.6 g, 1.9 mmol) was stirred in dichloromethane (40 ml) with potassium carbonate (2 g) and acetyl chloride (0.5 g, 6.4 mmol) overnight. The solids were filtered off and the solvents removed in vacuo. The residue was purified by column chromatography (silica, benzene/dichloromethane 1:1) to give l-acetylamino-2,3,6,7,10,11-hexahexyloxy¬ triphenylene (1.59 g, 95%). Anal. C, 75.6%; H, 10.0%; N, 1.6%; C 56 H 87 NO 7 requires C, 75.89%; H, 9.90%; N, 1.58%. The mesophase range of 5 . was from 99°C to 162 β C. The other amides were prepared in a similar manner. Analytical and mesophase data are summarised in the table. Thus, all the products 2 to 5, exhibit a discotic mesophase. It can be seen that introduction of an α-nitro group imparts greatly enhanced mesophase stability and produces a material with a discotic range from below room temperature to 136°C. It is postulated that this enhancement arises through a combination of effects. Introduction of the polar group increases the attraction between the discotic cores. Steric effects tend to increase the core-core separation and hence the entropy of the molten side chains. l-Azido-2.3.6.7.10.11-hexahexyloxytriphenylene (6) l-Amino-2,3,6,7, 10,11-hexahexyloxytriphenylene (0.5 g, 0.59 mmol) was stirred in a mixture of dichloromethane (25 ml) and acetic acid (10 ml) at 3°C. Sodium nitrite (0.3 g in 2 ml water) was added dropwise keeping the reaction temperature below 6°C. After stirring for a further 10 minutes sodium azide (0.3 g in 4 ml water) was added and the mixture stirred at 2-5 °C for 1 hour and at room temperature for 30 minutes. The organic layer was separated and the solvent evaporated. The residue was purified by column chromatography (silica, benzene) and recrystallized from ethanol to give l-azido-2,3,6,7,10,11-hexahexyloxytriphenylene (6) (0.3 g, 58%) as a white solid. Anal. C, 74.65%; H, 9.75%; N, 4.85%. C 54 H 83 N 3 0 6 requires C, 74.53%; H, 9.61%; N, 4.83%. K-D 70°C, D-I 118°C. Azoxy-derivative of HAT6 (7) The azo-derivative of HAT6 (4) (0.2 g, 0.23 mmol) was dissolved in dichloromethane (10 ml) and 15 ml of a solution of acetic acid (100 ml) and hydrogen peroxide (100 vol, 45 ml) was added. Concentrated sulphuric acid (0.5 ml) was added and stirred at room temperature for 12 hours. The mixture was poured into water (20 ml) and ether (20 ml), the ether layer was washed with water, dried and evaporated. The solid residue was reprecipitated from ethanol to give the azoxy-derivative (7) (0.041 g, 20%) as an off-white solid. I - D 230°C. 2.3.6.7.10.1 1 -Hexakis-f2-f2-chloroethox )ethoχyy 1 -nitrotriphenylene (9) 2,3,6,7,10,1 l-Hexakis-(2-(2-chloroethoxy)ethoxy)triphenylene (8) (3 g, 3.1 mmol) was stirred in a mixture of acetic acid (25 ml), ether (25 ml) and dichloromethane (25 ml). Concentrated nitric acid (4 ml) was added, the mixture stirred for 2 hours and poured onto water. The organic layer was washed with sodium carbonate solution and the solvent evaporated. The residue was separated by column chromatography (silica, dichloromethane/ethyl acetate 5:1) and the products precipitated crystallised from ethanol to give 2,3,6,7,10,1 l-hexakis-(2-(2-chloroethoxy)- ethoxy)-l-nitrotriphenylene (9) (1 g, 32%) as a yellow gum. Anal. C, 49.75%; H, 5.2%; N, 1.4%; Cl, 21.05%; C 4 2H53NO 14 CI 6 requires C, 50.01%; H, 5.3%; N, 1.39%; Cl, 21.09%; I - D 88°C) and yellow needles of a mixture of the 1,8- and 1,9-dinitro derivatives (0.24 g, 7%). mp 70-74 °C. 1 -Amino-2.3.6.7.10.1 1 -hexakis-f2-( ' 2-chloroethoxy ' )ethoxy ' )triphenylene (10) 2,3,6,7,10,1 l-Hexakis-(2-(2-chloroethoxy)ethoxy)-l-nitrotriphenylene (9) (0.5 g, 0.5 mmol) and tin powder (1 g) were stirred in refluxing acetic acid (100 ml) for 8 hours and allowed to cool. Water (200 ml) was added and the mixture extracted with dichloromethane (3 x 150 ml). The combined organic extracts were washed with water and sodium carbonate solution and the solvents evaporated. The residue was purified by column chromatography (silica, dichloromethane/ethyl acetate 9:1) and reprecipitated from ether to give l-amino-2,3,6,7,10,1 l-hexakis-(2-(2-chloroethoxy)- ethoxy)triphenylene (10) (0.47 g, 100%) as a white solid (M + = 977, C 4 2H55NO 12 CI 6 = 975-987). I - D 102°C. 1.4.6.7.10.1 1 -Hexahexyloxy-2-nitrophenylene ( 11) 1,4,6,7,10,11-Hexahexyloxytriphenylene (0.2 g, 0.24 mmol) was dissolved in ether (15 ml) and acetic acid (6 ml). Concentrated nitric acid (-0.25 ml) was added dropwise and the mixture stirred at room temperature for 20 minutes. The solution was washed with water and potassium carbonate solution and the solvent removed in vacuo. The crude product was purified by column chromatography (silica, dichloromethane/petroleum ether 2:3) and reprecipitated from ethanol to give 1,4,6,7,10,1 l-hexahexyloxy-2-nitrotriphenyIene (11) (0.13 g, 62%) as a yellow solid. Anal. C, 74.0%; H, 9.6%; N, 1.45%; C 5 H 8 3NO 8 requires C, 74.2%, H, 9.6%; N, 1.6%. K - I 81 °C, I - D 64°C. 2'.3'.4.6'.7'-Pentahexyloxy-6-oxospiro[cvclohexa-l .4-diene-3.9'-fluorene] (12) 3,3',4,4'-TetrahexyIoxybiphenyl (1.6 g, 2.9 mmol) and 1,3-dihexyloxybenzene (3.2 g, 1 1.5 mmol) were added to a stirred suspension of iron (III) chloride (3.8 g) in dichloromethane (60 ml). The reaction was quenched with methanol after 70 minutes and left to stand overnight. The resulting crude solid product was purified by column chromaotgraphy (silica, ethyl acetate/petroleum ether 1 :3) and reprecipitated from ethanol to give 2',3',4,6 , ,7'-pentahexyloxy-6-oxospiro[cyclohexa[l,4-diene-3,9'- fluorene] (12) (0.9 g, 42%) as a white solid. Anal. C, 77.45%; H, 9.6%; C 48 H 72 O 6 requires C, 77.4%; H, 9.74%. mp 140°C. 1.3.6.7.10.1 1 -Hexahexyloxytriphenylene (14) Compound (12) (0.8 g, 1.1 mmol) was added to acetic anhydride (20 ml) and concentrated sulphuric acid (3 drops) and warmed for 25 minutes. The mixture was then poured onto ice, warmed for a further 10 minutes, left to cool and extracted with dichloromethane. The extract was washed with potassium carbonate solution and the solvent evaporated. The resulting crude solid product was recrystallised from ethanol to give 3-acetoxy-l,6,7,10,l 1-pentahexyloxytriphenylene (13) (0.35 g, 41%) as an off-white solid (M' = 786, C50H74O7 = 786) which was added to a mixture of ethanol (40 ml), bromohexane (0.11 g, 0.67 mmol) and potassium carbonate (0.1 g). The mixture was refluxed for 5 hours and allowed to cool. Dichloromethane (100 ml) was added and the mixture filtered to remove solid residues. The solvent was removed in vacuo and the crude solid product purified by column chromatography (silica, dichloromethane/petroleum ether 3:2) and reprecipitated from ethanol to give ] ,3,6,7, 10, 1 1 -hexahexyloxytriphenylene (14) (0.2 g, 54%) as an off-white solid. Anal. C, 78.15%; H, 10.3%; C 54 H 84 O 6 requires C, 78.2%; H, 10.2%. K - I 71 °C, I - D 66°C. Nitration of 1.3.6.7.10.11-hexahexyloxytriphenylene (14) 1,3,6,7,10,11-Hexahexyloxytriphenylene (14) (0.1 g, 0.12 mmol) was dissolved in ether (5 ml) and acetic acid (1 ml). Concentrated nitric acid - 0.2 ml) was added dropwise and the mixture stirred at room temperature for 15 minutes. The solution was washed with water and potassium carbonate solution and the solvent removed in vacuo. The solid residue was subjected to column chromatography (silica, dichloromethane/petroleum ether 3:2) and reprecipitated from ethanol which yielded a mixture of starting material (14) and mono-nitrated product (15). (M + = 873, C5 4 H 83 NO 8 = 873). 2.3.6.7-Tetrahexyloxy-l 0 -methoxy-5-nitrotriphenylene (16) 2,3,6,7-Tetrahexyloxy-10-methoxytπphenylene (0.25 g, 0.38 mmol) was dissolved in ether (30 ml) and acetic acid (6 ml). Concentrated nitric acid (- 0.75 ml) was added dropwise and the mixture stirred at room temperature for 20 minutes. The solution was washed with water and potassium carbonate solution and the solvent removed in vacuo. The crude solid product was purified by column chromatography (silica, dichloromethane/petroleum ether 2:3) and recrystallised from ethanol to give 2,3,6,7-tetrahexyloxy-10-methoxy-5-nitrotriphenylene (16) (0.19 g, 71%) as yellow needles. Anal. C, 73.55%; H, 8.65%; N, 2.05%; C 43 H 61 NO 7 requires C, 73.4%; H, 8.73%; N, 2.0%. mp 128°C. Nitration of Polymer 17 In a similar procedure to the preparation of 2, main chain polymer 17 was nitrated to give the nitrated polymer 18 which was reprecipitated from dichloromethane/ethanol to yield an amoφhous solid. Anal. C, 67.85%; H, 8.25%, N, 3.15%. mp 90-130°C. 2.3.6.7-Tetrahexyloxy-9.10.1 l-trimethoxy-12-nitrotriphenylene (19) 2,3,6,7-Tetrahexyloxy-9,10,l 1-trimethoxytriphenylene (0.08 g, 0.11 mmol) was dissolved in ether (7 ml) and acetic acid (2 ml). Concentrated nitric acid (- 0.2 ml) was added dropwise and the mixture stirred at room temperature for 20 minutes. The solution was washed with water and potassium carbonate solution and the solvent removed in vacuo. The resulting crude solid was purified by column chromatography (silica, dichloromethane/petroleum ether 3:2) and reprecipitated from ethanol to give 2,3,6,7-tetrahexyloxy-9,10,l l-trimethoxy-12-nitrotriphenylene (19) (0.051 g, 60%) as a yellow solid. (M + - 763, C 4 5H 65 NO9 = 763) mp 45°C. l-Chloro-2.3.6.7.10.11-hexahexyloxytriphenylene (20) 2,3,6,7,10,11-Hexahexyloxytriphenylene (1.0 g, 1.2 mmol) was dissolved in dry dichloromethane (45 ml) and cooled to 0°C. PIFA (0.6 g, 1.4 mmol) was added and the solution stirred for 5 minutes. Tetra-n-butylammonium chloride (0.67 g, 2.4 mmol) was then added and stirred at 0°C for 10 minutes before being allowed to warm to room temperature. The solution was poured onto methanol and left to stand overnight. The resulting crude solid product was purified by column chromatography (silica, dichloromethane/petroleum ether 1:1) and reprecipitated from ethanol to give 1 -chloro-2,3,6,7, 10, 11 -hexahexyloxytriphenylene (20) (0.45 g, 43%) as a white solid. Anal. C, 75.05%; H, 9.6%; Cl, 4.15%; C 54 H 83 ClO 6 requires C, 75.1%; H, 9.7%; Cl, 4.1%. K - D 37°C, D - I 98°C. Reaction of 2.3.6.7.10.11 -hexahexyloxytriphenylene with iodine monochloride 2,3,6,7, 10, 11 -Hexahexyloxytriphenylene (0.28 g, 0.34 mmol) was stirred in dichloromethane (20 ml). Iodine monochloride (3 crystals) was added, the mixture stirred for 2 hours and poured onto sodium metabisulfite solution. The mixture was separated and the organic layer evaporated. The residue was separated by column chromatography (silica, light petroleum/dichloromethane 1:1) to give 1-chloro- 2,3,6,7, 10, 11 -hexahexyloxytriphenylene 20 (95 mg, 32%) as a white solid (K-D 37°C, D-I 98°C). (Anal. C, 75.15%; H, 9.6%; Cl, 4.4%. C 54 H 83 ClO 6 requires C, 75.10%; H, 9.67%; Cl, 4.10%) and a mixture of dichloro-derivatives 21 (25 mg, 7%) as a colourless liquid crystal (D-I 37°C). Anal. C, 72.35%; H, 9.15%; Cl, 8.15%; C 54 H 82 Cl 2 O 6 requires C, 72.21%; H, 9.20%; Cl, 7.9%. 2.3.6.7.10.11-Hexahexyloxy-l-methyltriphenylene (23) 2,3,6,7,10,11-hexahexyloxytriphenylene (0.5 g, 0.6 mmol) was stirred in dry THF (20 ml) at -78°C under argon. Butyllithium (1 ml, 1.6 M in hexanes, 1.6 mmol) was added and the solution stirred for 1 hour before adding methyl iodide (0.5 ml). The solution was stirred for a further 2 hours at -78 °C and overnight at room temperature. The mixture was poured onto dilute hdyrochloric acid and extracted with dichloromethane. The solvents were evaporated and the residue recrystallized from ethanol to give a mixture of 1 and 23. M + = 842, C 55 H 86 O 6 = 842. 1.4.9-Tribromo-2.3.6.7.10.1 1 -hexahexyloxytriphenylene (24) 2,3,6,7, 10, 11 -Hexahexyloxytriphenylene (0.4 g, 0.48 mmol) was sti neA D - I in dichloromethane (20 ml). Bromine (6 drops ) was added and the mixture stirred for 1 V- hours. The solvent was evaporated and the residue purified by column chromatography (silica, light petroleum/dichloromethane 1:1) to give 1,4,9-tribromo- 2,3,6,7, 10, 11 -hexahexyloxytriphenylene (24) (0.15 g, 29%) as a pale yellow oil. (M+ = 1066, C 54 H 81 Br 3 O 6 = 1062-1068). 2.3.6.7.10.11-Hexahexyloxy-l-hvdroxymethyltriphenylene (25) 2,3,6,7,10,11 -Hexahexyloxytriphenylene (1 g, 1.2 mmol), chloromethyl methyl ether (1 ml) and zinc chloride (2 g) were stirred in dichloromethane (30 ml) at room temperature for 8 hours. Dilute hydrochloric acid was added and the mixture separated. The organic layer was washed twice with 5% sodium hydroxide solution and the solvent evaporated. The residue was separated by column chromatography (silica, light petroleum/dichloromethane 3:2) to give a yellow gum which was crystallised from ethanol to give 2,3,6,7,10,1 l-hexahexyloxy-l-(hydroxymethyl)triphenylene 25 (105 mg, 10%) as an off-white solid, mp 68.5-70°C, M+ = 858, C 55 H 88 O 7 = 858).

Claims: CLAIMS 1. A triphenylene which is substituted by replacement of a hydrogen atom in an a position. 2. A method of electrophilically substituting a triphenylene in an a position, comprising dissolving the triphenylene in a mixture of semipolar and polar solvents and adding an electrophile or a precursor that in said solvent yields an electrophile, either of which can replace a hydrogen atom at the α position. 3. A method according to Claim 2, wherein said precursor is HNO3 (to yield the moiety NO 2 +), Br 2 (Br + ), RZ (R + ) where Z is a halogen, RCOZ (RCO + ), or AiylCOZ (Aryl CO + ). 4. A method according to Claim 2 or 3, wherein said semipolar solvent is an ether. 5. A method according to Claim 2, 3 or 4, wherein said polar solvent is a carboxylic acid. 6. A method according to Claim 2, 4 or 5, wherein the starting triphenylene is penta-, hexa-, or hepta-β -substituted. 7. A method according to Claim 6, wherein the β-substituent is alkoxy or acyloxy. 8. A triphenylene according to Claim 1 or a method according to any of Claims 2 to 7, wherein the a substituent is further reacted. 9. A method according to Claim 8, wherein the further reaction is a hydrogenation or other reduction. 10. A triphenylene, being any of the compounds 2, 3, 4, 5, 6, 7, 8, 9 or 10 in the specification, wherein OHx is oxyalkyl wherein C = 5-7. 11. A discotic liquid crystal which is a triphenylene according to Claim 1 or 10 or has been made directly by a method according to any of Claims 2 to 7. 12. A discotic liquid crystal which has been made by elaboration of the α substituent of a triphenylene according to Claim 1 or 10 or by a method according to Claim 8 or 9. -21- SUBST.TUTE SHEET (RULE 26)

Inventors: BODEN NEVILLE, BUSHBY RICHARD JAMES, CAMMIDGE ANDREW NEIL, HEADDOCK GARETH, BODEN, NEVILLE, BUSHBY, RICHARD, JAMES, CAMMIDGE, ANDREW, NEIL, HEADDOCK, GARETH
Applicants: BODEN NEVILLE, BRITISH TECH GROUP, BUSHBY RICHARD JAMES, CAMMIDGE ANDREW NEIL, HEADDOCK GARETH, BODEN, NEVILLE, BRITISH TECHNOLOGY GROUP LIMITED, BUSHBY, RICHARD, JAMES, CAMMIDGE, ANDREW, NEIL, HEADDOCK, GARETH
Application year: 1995
Main classification: C07B37
IPC codes: C07B37, C07C41, C07C43, C07C69, C07C205, C07C217, C07C233, C07C247, C07D237, C09K19