Title of Invention

A PROCESS FOR THE PREPARATION OF NOVEL ROOM TEMPERATURE DISCOTIC NEMATICS

Abstract

THIS INNVENTION RELATES TO A PROCESS FOR THE PREPARATION OF NOVAL HEXAALKYNYLBENZENE DERVATIVES OF THE GENARAL FORMULA (1) wherein R = branched alkyl chains, the number of carbon atoms in the alkyl chain ranging from 4 to 12. The novel hexaalkynylbenzenes of the present invention are useful as discotic nematic liquid crystalline material for display devices such as, wristwatches, calculators, laptop computers, c~sh registers, gasoline

Full Text

This invention relates to a process for the preparation of novel hexaalkynylbenzene derivatives; more particularly novel branched-chain hexaalkynylbenzene derivatives. The compounds reported here may find use as discotic nematic (ND) liquid crystals. Accordingly these compounds can be used as liquid crystalline material for display devices such as, wristwatches, calculators, cash registers, gasoline pumps, electronic test equipment, laptop computers, TV screens and other large area displays. They can also be used as liquid crystal solvents for spectroscopy. Liquid crystal displays (LCDs) have played a vital role in information technology. The current world LCD market runs to billions of dollars and is rapidly growing. The twisted nematic and supertwisted nematic display devices are dominating commercial displays since their invention. The liquid crystal layer in these devices is exclusively the calamitic liquid crystals (composed of rod-shaped molecules). A vast number of calamitic nematic liquid. crystals having room temperature mesophases, such as, cyanobiphenyls, phenylpyrimidines, phenylcyclohexanes, Schiffs' bases, etc., have been synthesised and used in practical displays. The major disadvantage with these types of devices is the narrow and nonuniform viewing cone which is considered to be an unacceptable aspect of their performance. We have recently disclosed a novel approach to overcome this problem by utilising discotic nematic liquid crystals instead of calamitic nematic liquid crystals which has been made the subject matter of our Indian Patent Application No. 1131/MAS/98 dated 27.5.98 and the corresponding applications for patent filed in Europe bearing EPO no. 98 307996.3 dated L10.98, in US bearing no. 09/159,743 dated 24.9.98, in Korea bearing no. 98-55028 dated 15.12.98 and in Japan bearing number 334681/98 dated 25.11.98. Liquid crystals formed by disc-shaped molecules were discovered in 1977 [S. Chandrasekhar, B.K. Sadashiva, and K.A. Suresh, Pramana, 9, 471, (1977)]. Most mesophases formed by these compounds can be classified basically into two classes; the nematic and the columnar. In the columnar phases molecules are stacked one on top of the other to form columns, the different columns constituting \ a two dimensional lattice. The potential uses of these columnar phases as quasi-one-dimensional conductors, photoconductors, light emitting diodes, photovoltaic solar cells, etc., have attracted considerable attention [S. Chandrasekhar, in Hand Book of Liquid Crystals, ed. D. Demus, J. Goodby, G.W. Gray, H.-W. Spiess and V. Vill, Wiley-VCH, 1998, Vol. 2B, Chapter VIII; N. Boden and B. Movaghar, ibid. Chapter IX] The nematic phase formed by disc-shaped molecules is similar to those of the nematic phase of calamitic molecules, A schematic representation of the discotic nematic phase (ND) (of disc-like molecules) is given below. The director n is representing the preferred axis of orientation of the disc-normals (short molecular axes). Compared to the large number of calamitic molecules showing nematic phase, the number of disk-shaped molecules showing the discotic nematic phase ND are rare. Moreover, me ND phase formed by these materials are high temperature with a narrow thermal range. For any liquid crystal device application, the temperature range of the mesophase and its stability well below and above room temperature are amongst the most important criteria. Hitherto, no room temperature nematic discotic liquid crystal is known. The common procedure for extending the mesophase range of calamitic liquid crystals is by mixing different components and preparing an eutectic mixture but such a procedure has not been applied to discotic nematics till now. Therefore, it is of great practical interest to prepare room temperature discotic nematic liquid crystals. The main objective of the present invention is, therefore, to develop a process for the synthesis of novel hexaalkynylbenzene derivatives of the general formula (1) where R = branched alkyl chains. The number of carbon atoms in the alkyl chain may range from 4 to 12. The alkyl chain may preferably be consisting of 1, 2 or 3 methyl branch at different positions, for example, 3-methyl octane, 4-methyl octane, 4-methyl nonane, 3, 7-dimethyl octane, 3,7,11-trimethyl dodecane, etc. hexaalkylbenzenes of the formula (2), where R' ==normal alkyl chains as shown in Table 1, are known to form nematic discotic (No) phases [B. Kohne, K. Praefcke, Chimia, 41, 196 (1987); M. Ebert, D.A. Jungbauer, R. Kleppinger, J.H. Wendorff, B. Kohne, K. Praefcke, Liq. Cryst., 4, 53 (1989)]. The thermal behaviour of various reported hexaalkynylbenzenes of the formula (2) is listed below. (2) Table 1. Transition temperatures for hexaalkynylbenzene derivatives In addition to these liquid crystalline derivatives, some other non liquid crystalline hexaalkenylbenzene derivatives and a few derivatives showing monotropic liquid crystal phases, for example, hexakispentynylbenzene, hexakisdctynylbenzene, etc., are known in the literature [A.N. Cammidge and R.J. Bushby in Handbook of Liquid Crystals, ed. D. Demus, J. Goodby, G.W. Gray, H.-W. Spiess and V. Vill, Wiley-VCH, 1998, Vol 2B, Chapter VII]. No discotic material having stable ND phase well below and above the ambient temperature is ■\ documented. It is evident from the literature that when the peripheral alkyl chains are attached to the phenyl ring via an hetero atom such as oxygen or sulphur atom, the melting and clearing temperatures are higher compared to when the alkyl chains are directly attached to the ring, for example, see the above Table 1 entry 3 and 6. When the heptyl chain is attached to the phenyl ring directly, the melting point is 98°C and the clearing point is ISTC whereas they are 109°C and 193^C respectively when the same chain is attached via oxygen atom. It is also well known that when the peripheral aliphatic side chains of various cores are branched, the mesophase is widened but the type of the mesophase formed is not affected by the introduction of branching [P.G. Schouten, J.F. van der Pol, J.W. Zwikker, W. Drenth and SJ. Picken, Mol Cryst. Liq. Crysl, 1991, 195, 291; D.M. Collard and C.P. Lillya, J. Am. Chem, Sac, 1991, 113, 8577. P.G. Schouten, J.M. Warman, M.P. deHaas, C. F. van Nostrum, G.H. Gelinck, R.J.M. Nolte, M.J. Copyn, J.W. Zwikker, M.K. Engel, M. Hanack, Y.H. Chang, W.T. Ford, J. Am. Chem. Soc, 1994,116,6880]. The main objective of the present invention is to provide a process for the preparation of novel hexaalkynylbenzene derivatives of the formula (1) defined above which are useful as discotic nematic (ND) liquid crystal starting from novel branched alkyl chain substituted phenylacetylenes. The invention is based on our observation that when the normal alkyl chain in the phenyl ring of hexaalkynylbenzene is replaced with branched alkyl chain and connecting it directly to the phenyl ring, the melting points of the alkynylbenzene derivatives may reduce and consequently stabilise the mesophase. The preparation of the novel branched chain hexalkynylbenzene of the formula (1) defined above according to the present invention is broadly shown in the scheme 1 given below. The compounds of the present invention differ from the previous known compounds in the following ways; in the known materials either normal (unbranched) alkyl chain is attached directly to the phenyl ring or branched alkyl chain is connected to the phenyl ring via an oxygen atom whereas in our novel compounds, branched alkyl chain is connected directly to the phenyl ring. Accordingly, the present invention provides a process for the preparation of novel hexaalkynylbenzene derivatives of the general formula (1) defined above which comprises condensing novel branched chain substituted phenylacetylenes of the formula (7) where R has the meanings given above with hexahalobenzene of the \ formula (8) wherein X represents bromine or iodine in the presence of a coupling catalyst at a temperature in the range of 25 to 200°C and recovering the compound of the formula by conventional methods. The condensation can be effected by stirring hexabromo- or hexaiodobenzene with six or more equivalent phenylacetylene. The temperature may be preferably in the range of 50 to l00°C The condensation may be effected for a period in the range of four hours to 100 hours, preferably in the range of 12 hours to 24 hours. The condensation may be effected in the presence of organic solvents selected from benzene, tetrahydrofuran, dimethylformamide, N-methylpyrrolidinone, triethylamine, diisopropylamine, etc., or their mixtures, preferably the organic solvent employed may be triethylamine or a mixture of triethylamine and tetrahydrofuran. The catalyst employed may be selected from tetrakis(triphenylphosphine)palladium (0), bis(triphenylphosphine)palladium(II) chloride, triphenylphosphine, Cul and an organic base. Preferably catalyst may be a mixture of bis(triphenylphosphine)palladium(II) chloride, triphenylphosphine and Cul. The invention is described in detail in the examples given below which are provided by way of illustration only and therefore should not be construed to limit the scope of the invention. The novel branched chain substituted phenylacetylenes of the formula (7) where R has the meanings given above employed as the starting compounds are obtained by the following reactions. The branched chain acids of the formula RCOOH where R has the meanings given above are converted to acid chlorides of the formula RCOCl where R has the meanings given above using oxalyl chloride at room temperature. Friedel-Crafts acylation of the bromobenzene of the formula (3) with the above acid chlorides of the formula RCOCl gives the corresponding ketones of the formula (4). Wolff-Kishner reduction of these ketones of the formula (4) furnished the corresponding 4-(branched alkyl)bromobenzenes of the formula (5). Pd-catalysed alkynylation of the bromobenzenes of the formula (5) with 2-methyl-3-butyn"2-ol yielded the corresponding, protected phenylacetylene of the formula (6) which are deprotected using KOH in refluxing toluene to yield the corresponding novel substituted phenylacetylenes of the formula (7). The novel branched chain phenylacetylenes of the general formula (7) and the other novel intermediates of the formula (4), (5) and (6) where R has the meanings given above have been made the subject matter of our copending application no. (B) A palladium-catalysed coupling of these branched alkylphenylacetylenes of the formula (7) with hexahalobenzene (8) where X is bromo or iodo yielded the desired hexakis(4-(branched akylphenylethynyl)benzenes of the general formula (1) as explained above. To a stirred and cooled (0°C) mixture of bromobenzene of the formula (3) (5.5 g, 0.035 mol) and aluminium chloride (1.6 g, 0.012 mol), 4-methylnonanoylchloride (1.9 g, 0.01 mol) was added under argon. The mixture was stirred at 0oC for 1 h, heated at 80°C for 1 h, cooled and poured into 6N HCl. The product was extiacted with dichloromethane (3 X 25 ml), and the combined organic extracts were washed with water and dried with anhydrous sodium sulphate. The solvent was removed in vacuo and the residue was purified by column chromatography (silica gel: hexane-ethyl acetate) to give a colourless liquid of l-Bromo-4-(4-methylnonanoyl)benzene of the formula (9) (2.2 g, 70% based on acid chloride). ^H NMR data: 5 (CDCI3) 7.83 (2H, d), 7.6 (2H, d), 2.93 (2H, m), 1.82-1.27 (1IH, m), 0.88 (6H, t). To a stirred and cooled (0°C) mixture of bromobenzene (3) (2.75tg, 0.0175 mol), carbon disulfide (10 ml) and aluminium chloride (1.6 g, 0.012 mol), 4-methylnonanoylchloride (1.9 g, 0.01 mol) was added under argon. The mixture was stirred at 0°C for 1 h, heated at 80°C for 1 h, cooled and poured into 6N HCl. The product was extracted with dichloromethane (3 X 25 ml), and the combined organic extracts were washed with water and dried with anhydrous sodium sulphate. The. solvent was removed in vacuo and the residue was purified by column chromatography (silica gel: hexane-ethyl acetate) to give a colourless liquid of 1-Bromo-4-(4-methylnonanoyl)benzene of the formula (9) (2.5 g, 80%). 1H NMR data: 5 (CDCI3) 7.83 (2H, d), 7.6 (2H, d), 2.93 (2H, m), 1.82-1.27 (IIH, m), 0.88 (6H, t). A mixture of the above l-Bromo-4-(4-methylnonanoyl)benzene of the formula (9) (1.7 g, 5.5 mmol) obtained by the process described in the Examples 1 and 2, \ hydrazine hydrate (0.8 g, 16 mmol) and potassium hydroxide (1.1 g, 19 mmol) in diethylene glycol (10 ml) was heated at 130-140°C for 2h. The excess of hydrazine hydrate was distilled off and the temperature was raised to 230-240°C for Ih. The cooled mixture was poured into 6N HCl, the product was extracted with ether (3 X 25 ml), and the combined organic extracts were washed with brine and dried with sodium sulpnate. The solvent was removed in vacuo and the residue was purified by column chromatography (silica gel: hexane-ethyl acetate) to give a colourless liquid of l-Bromo-4-(4-methylnonanyl)benzene of the formula (10) (0.75 g, 46%). 1H NMR: 5 (CDCI3) 7.38 (2H, d), 7.05 (2H, d), 2.53 (2H, t), 1.66-Ll(13H,m),0.86(6H,t). A solution of l-Bromo-4-(4-methylnonanyl)benzene of the formula (10) (0.72 g, 2.4 mmol), obtained by the process described in the Example 3 above, bis(triphenylphosphine)palladium(II) chloride (0.05 g, 0.07 mmol), 2-methyl-3-butyn-2-ol (0.4 g, 4.8 mmol), triphenylphosphine (0.1 g, 0.76 mmol) and copper(I) iodide (0.05 g, 0.26 mmol) in dry deoxygenated triethylamine (10 ml) was stirred at 60-70°C under argon for 15 h. Triethylamine was removed in vacuo and the residue was purified by column chromatography (silica gel; hexane-ethyl acetate) to yield 0.36 g, 50% of the product, 4-(4-methylnonanylphenyI)-2-methylbut-3-yn-2-ol of the formula (11). A solution of l-Bromo-4-(4-methylnonanyl)benzene of the formula (10) (0.72 g, 2.4 mmol), obtained by the process described in the Example 3 above, bis(triphenylphosphine)palladium(II) chloride (0.05 g, 0.07 mmol), 2-methyl-3" butyn-2-ol (0.4 g, 4.8 mmol), triphenylphosphine (0.1 g, 0.76 mmol) and copper(I) iodide (0.05 g, 0.26 mmol) in a mixture of dry THF and dry deoxygenated triethylamine (10 ml) was stirred at 60-70°C under argon for 15 h. Triethylamine was removed in vacuo and the residue was purified by column chromatography (silica gel; hexane-ethyl acetate) to yield 0.50 g, 70% of the product, 4-(4-methylnonanylphenyl)-2-methylbut-3-yn-2"Ol of the formula (11). ■I A solution of l-Bromo-4-(4-niethylnonanyl)benzene of the formula (10) (0.72 g, 2.4 mmol), obtained by the process described in the Example 3 above, bis(triphenylphosphine)palladium(II) chloride (0.05 g, 0.07 mmol), 2-methyl-3-butyn-2-ol (0.4 g, 4.8 mmol), triphenylphosphine (0.1 g, 0.76 mmol) and copper(I) iodide (0.05 g, 0.26 mmol) in dry deoxygenated diisopropylamine (10 ml) was stirred at 60-70°C under argon for 15 h. Triethylamine was removed in vacuo and the residue was purified by column chromatography (silica gel; hexane-ethyl acetate) to yield 0.43 g, 60% of the product, 4-(4-methylnonanylphenyl)"2-methylbut-3-yn-2-ol of the formula (11). A solution of l-Bromo-4-(4-methylnonanyl)benzene of the formula (f0) (0.72 g, 2.4 mmol), obtained by the process described in the Example 3 above, bis(triphenylphosphine)palladium(II) chloride (0.05 g, 0.07 mmol), 2-methyl-3-butyn-2-ol (0.4 g, 4.8 mmol), triphenylphosphine (0.1 g, 0.76 mmol) and copper(I) iodide (0.05 g, 0.26 mmol) in a mixture of dry THF and dry deoxygenated diisopropylamine (10 ml) was stirred at 60-70°C Under argon for 15 h. Triethylamine was removed in vacuo and the residue was purified by column •I chromatography (silica gel; hexane-ethyl acetate) to yield 0.46 g, 65% of the product, 4-(4-methylnonanylphenyl)-2-methylbut-3-yn-2-ol of the formula (11). Powdered potassium hydroxide (180 mg, 3.2 mma|) was added to a solution of 4-(4-methyInonanyIphenyl)-2"methyI-3"butyn-2-oI of the formula (11) (800 mg, 2.67 mmol) obtained by the process described in the Examples 4 to 7 above, in toluene (10 ml). The mixture was heated to reflux under argon for 1 h. The cooled reaction mixture was poured into ice-water and the solution was neutralised with O.OIM hydrochloric acid to pH 7, the product was extracted with ether (3 X 25 ml), and the combined organic extracts were washed with brine and dried with anhydrous sodium sulphate. The solvent was removed in vacuo and the residue was purified by column chromatography (silica gel; hexane-ethyl acetate) to give a colourless liquid of 4-(4-methylnonanylphenyl)acetylene of the formula (12) (520 mg, 81%). 1H NMR: 6 (CDCI3) 7.41 (2H, d), 7.13 (2H, d), 3.03 (IH, s), 2.58 (2H, t), 1.61-1.1 (13H,m), 0.86(6H,m). Sodium hydride (50 mg, 2.1 mmol) was added to a solution of 4-(4-methylnonanylphenyl)-2-methyl-3-butyn-2-ol of the formula (11) (800 mg, 2.67 mmol) obtained by the process described in the Examples 4 to 7 above, in toluene (10 ml). The mixture was heated to reflux under argon for 1 h. The cooled reaction mixture was poured into ice-water and the solution was neutralised with 0.0 IM hydrochloric acid to pH 7, the product was extracted with ether (3 X 25 ml), and the combined organic extracts were washed with brine and dried with anhydrous sodium sulphate. The solvent was removed in vacuo and the residue was purified by column chromatography (silica gel; hexane-ethyl acetate) to give a colourless liquid of 4-(4-methylnonanylphenyl)acetylene of the formula (12) (520 mg, 81%). ^H NMR: 5 (CDCI3) 7.41 (2H, d), 7.13 (2H, d), 3.03 (IH, s), 2.58 (2H, t), 1.61-1.1 (13H,m),0.86(6H,m). A solution of hexabromobenzene of the formula (8) where X = bromo (80 mg, 0.145 mmol), bis(triphenylphosphine)palladium(II) chloride (75 mg, 0.11 mmol), 4- \ (4-methylnonanylphenyl)acetylene of the formula (12) obtained by the process described in the Examples 8 and 9 above, (420 mg, 1.75 mmol), triphenylphosphine (150 mg, 0.57 mmol) and copper(I) iodide (75 mg, 0.4 mmol) in dry deoxygenated triethylamine (10 ml) was stirred at 60-70°C under argon for 24 h. Triethylamine was removed in vacuo and the residue was purified by repeated column chromatography (silica: hexane-ethyl acetate, utmost care should be taken in purifying the product; at least four column chromatographic separations are required to achieve a high purity product. Details of the physical characteristics are given in the last) to yield 55 mg, 25% of the hexakis(4-4-methylnonanylphenylethynyl)benzene of the formula (13). Hexaiodobenzene (83 mg, 0.1 mmol) of the formula (8) where X == iodo, bis(triphenylphosphine)palladium(II) chloride (50 mg, 0.07 mmol), 4-(4-methylnonanylphenyl)acetyIene (12) obtained by the process described in the Examples 8 and 9, (242 mg, 1.0 mmol), triphenylphosphine (100 mg, 0.38 mmol) and copper(I) iodide (50 mg, 0.26 mmol) were added into dry deoxygenated triethylamine (10 ml) and the reaction mixture was stirred at 100°C under argon for H n. 1 nexnyiamine was removea in vacuo and tlie residue was purified by column chromatography (silica gel, hexane-ethyl acetate) to yield 15 mg, 10% of the hexakis(4-4-methylnonanylphenylethynyl)benzene of the formula (13). Hexaiodobenzene (83 mg, 0.1 mmol) of the formula (8) where X = iodo, bis(triphenylphosphine)palladium(II) chloride (50 mg, 0.07 mmol), 4-(4-methylnonanyIphenyl)acetylene (12) obtained by the process described in the Examples 8 and 9, (242 mg, 1.0 mmol), triphen5aphosphine (100 mg, 0.38 mmol) and copper(I) iodide (50 mg, 0.26 mmol) were added into dry deoxygenated triethylamine (10 ml) and the reaction mixture was stirred at 100°C under argon for 24 h. Triethylamine was removed in vacuo and the residue was purified by column chromatography (silica gel, hexane-ethyl acetate) to yield 53mg, 35% of the hexakis(4-4-methylnonanylphenylethynyl)benzene of the formula (13). Hexabromobenzene of the formula (8) where X = bromo, (55 mg, 0.1 mmol) bis(triphenylphosphine)palladium(n) chloride (50 mg, 0,07 mmol), 4-(4-methylnonanylphenyl)acetylene (12) obtained by the process described in the Examples 8 and 9, (242 mg, 1.0 mmol), triphenylphosphine (100 mg, 0.38 mmol) and copper(I) iodide (50 mg, 0.26 mmol) were added into a mixture of dry and deoxygenated THF (10 ml) and triethylamine (5 ml). The reaction mixture was heated at 70-80°C under argon for 24 h. Solvents were removed in vacuo and the residue was purified by column chromatography (silica gel, hexane-ethyl acetate) to yield 18 mg, 12% of the hexakis(4-4-methylnonanylphenylethynyl)M^ene of the formula (13). Hexabromobenzene of the formula (8) where X = bromo, (55 mg, 0.1 mmol), bis(triphenylphosphine)palladium(II) chloride (50 mg, 0.07 mmol), 4-(4-methylnonanylphenyl)acetylene (12) obtained by the process described in the Examples 8 and 9, (242 mg, 1.0 mmol), triphenylphosphine (100 mg, 0.38 mmol) and copper(I) iodide (50 mg, 0.26 mmol) were added into dry and deoxygenated diisopropylamine (10 ml). The reaction mixture was heated at 90-100°C under argon for 24 h. Solvents were removed in vacuo and the residue was purified by column chromatography (silica gel, hexane-ethyl acetate) to yield 30 mg, 20% of the hexakis(4-4-methylnonanylphenylethynyl)benzene of the formula (13). Physical characteristics of the compound hexakis(4-4- methyInonanylphenylethynyl)benzene. The product hexakis(4-4-methylnonanylphenylethynyl)benzene of the formula (13) isolated in experiment no. 10-14 by column chromatography was found to be homogenous on TLC and the HPLC purity (silica; hexane; flow 1.2, R.T. 39.25 min) was more than 99%. MS data: m/z 1520.2; 'H NMR data: 5 (CDCb^ 7.58 (12H, d), 7.20 (12H, d), 2.64 (12H, t), 1.63-1.1 (78H, m), 0.90 (36H, m). 13C NMR data: 5 (CDCI3) 144.03, 131.79, 128.52, 127.3, 120.53, 99.41, 87.06, 36.95, 36.72, 36.36, 32.66, 32.21, 28.78,26.72, 22.70, 19.65 and 14.10. Thermal behaviour: The thermal behaviour of the compound hexakis(4-4-methylnonanylphenylethynyl)benzene isolated from different batches was checked by polarising microscopy and by differential scanning calorimetry. In all the cases, material shows a room temperature nematic (No) phase. However, the melting and isotropic temperatures are different. This could be due to the stereohetrogeneity of the product (with one chiral center in each of the six side chains the product derived from racemic starting materials consist of a mixture of various stereoisomers). Variation of stereoisomers in the mixture could be the cause of varying melting and clearing points in different batches. The melting point was observed in between 0°C to 10oC and the clearing point in between 40°C to 80°C on heating. Upon cooling the isotropic liquid, the discotic nematic phase appeared with a very limited supercooling and the material crystallises in between 0°C to - 21°C. Advantages of the invention. The nematic phase shown by the compounds of the general formula (1) defined above of the present invention is stable well below and above the ambient temperature and, therfore, very suitable for very suitable for liquid crystal display (LCD) devices. The liquid crystal display (LCD) device having discotic nematic liquid crystals instead of calamitic nematic liquid crystals has advantages over the conventional LCD devices in that it has a wide and symmetrical viewing angle and no reversal of the contrast ratio in any direction. Accordingly, the process developed for the preparation of the compounds of the formula (1) of the present invention will be very useful for the preparation of various display devices in liquid crystal industry. We claim 1. A process for the preparation of the novel hexaalkynylbenzene derivatives of the general formula (1) wherein R = branched alkyl chains, the number of carbon atoms in the alkyl chain ranging from.4 to 12 useful as discotic nematic liquid crystalline material for display devices such as, wristwatches, calculators, laptop computers, cash registers, gasoline pumps, electronic test equipment, TV screens and other large area displays and solvents for spectroscopy. 2. A process for the preparation of novel hexaalkynylbenzene derivatives of the general formula (1) as defined in claim 1 which comprises condensing an \ appropriate branched alkyl chain substituted phenylacetylenes of the formula (7) where R has the meanings given above with hexahalobenzene of the formula (8) wherein x represents bromo or iodo in the presence of a catalyst at a temperature in the range of 25°C to 200X. 3. A process as claimed in claim 2 wherein the compounds of the formula 8 and 7 are used in molecular ratio of 1: 6 to 1:18. 4. A process as claimed in claims 2 & 3 wherein the condensation of the two components is carried out at a temperature range of 50°C to 100°C in the presence of organic solvents, 5. A process as claimed in claim 4 wherein the solvent such as benzene, ether, tetrahydrofuran, dimethylformamide, dimethylacetamide, N-methylpyrolidinone, triethylamine, diisopropylamine, etc. or their mixtures is used. 6. A process as claimed in claims 2 to 5 wherein the catalyst such as tetrakis(triphenylphosphine)palladium (0), bis(triphenylphosphine)palladium(II) chloride, triphenylphosphine, Cul, etc., is used 7. A process as claimed in claims 2 to 6 wherein the catalyst used is a mixture of bis(triphenylphosphine)palladium(II) chloride, triphenylphosphine, Cul, and an organic base. 8. A process as claimed in claims 2 to 7 wherein the condensation is effected for a period upto 100 hrs, preferably for a period in the range of 12 to 24 hrs. 9. A process for the preparation of novel hexaalkynylbenzene derivatives of the general formula (1) defined in claim 1 substantially as herein described with reference to the Examples 10 to 14.

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