ORGANIC COMPOUNDS OF 7,7,8,8-TETRACYANOQUINODIMETHANE AND METHOD FOR PREPARING THE SAME

Abstract: A novel organic compound essentially consisting of 7,7,8,8-tetracyanoquinodimethane is disclosed. Said 7,7,8,8-tetracyanoquinodimethane has a higher alkyl group containing more than ten carbon atoms. The organic compound may be formed in a monomolecular layer or film by Langmuir-Blodgett's technique. A process for preparing the novel organic compound ia also disclosed.

Description: BACKGROUND OF THE INVENTION This invention relates to novel chemical compounds and to their preparation, and more particularly to organic compounds of 7,7,8,8-tetracyanoquinodimethane (hereafter referred to simply as TCNQ) and method for the preparation of such compounds. Recently integrated circuit technologies have been remarkably progressed in electronics field, and very large scale integrated circuits (VLSI) are realized. However, the present technology for miniaturizing the integrated circuit is near the limit, and different approaches are required. For this purpose, various reserches of molecular electronics are pursued here and there. Under the circumstances, the inventors though that it was necessary to obtain an organic compound which has electric conductivity substantially equal to metals and is easy to arrange the molecules of the compound regularly in molecular unit. However, there are no organic compounds to meet the above characteristics heretofore. Organic compounds, the conductivity of which are substantially equal to metals, are known such as a complex compound of TCNQ and tetrathiofulvalene (hereafter referred to as TTF). The complex compound is expressed by the following formura: TCNQ and TTF form a charge-transfer complex because TCNQ is a strong electron acceptor and TTF is an electron donor. The complex has electric conductivity the maximum value of which is comparable with the electric conductivity of mercury. However, the complex of TTF and TCNQ has not been succeeded in proccessing or manufacturing in molecular unit. Langmuir-Blodgett's technique is generally known in the art as a technique for arranging molecules in monomolecular layer. However, generally known TCNQ derivatives cannot be processed in monomolecular layer or film by the Langmuir-Blodgett's technique. Meanwhile, many studies have been directed to synthesize TCNQ derivatives. US. Pat. No. 3,558,671 discloses a method for synthesizing TCNQ fluoride and cyano TCNQ, in which quaternary ammonium salt is synthesized for use as dyestuff or pigment. U.S. Pat. No. 3,739,008 discloses a different method for synthesizing TCNQ fluoride and cyano TCNQ for use as dyestuff or antistatic agent. In U.S. Pat. No. 3,687,987, a method for synthesizing dialkoxyl TCNQ up to 8 carbons is disclosed. In U.S. Pat. No. 3,526,497, a method for synthesizing dialkonyl TCNQ and dialkoxyl TCNQ fluoride, where carbon number of alkyl is equal to or below 13, is described. U.S. Pat No. 3,115,506 discloses a synthesizing method of TCNQ having alkyl group up to 8 carbons from alkyl substituted 1,4-­ cyclohexane-dione. A method for synthesizing TCNQ having alkyl group up to 3 carbons is discussed in Journal of Organic Chemistry, vol. 28, p. 2719, 1963, in which methylpara-­ dimethoxybenzene obtained from 2-methylhydroquinone is reduced. However, these synthesizing methods are unsuitable for a novel TCNQ product having higher alkyl group, because of small yield. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide novel organic compounds which have an electrical conductivity comparable with metals, and are capable of arranging the molecules thereof regularly in molecular unit. It is another object of the present invention to provide novel organic compounds which are able to form monomolecular layer by Langmuir-Blodgett's technique. It is a further object of the present invention to provide a method of synthesizing the novel organic compounds mentioned above. The above objects can be achieved according to the invention by organic compounds which comprise TCNQ having higher alkyl group. The compound are generally represented by the following formura: Where R is alkyl group containing 10 or more of 10 carbon atoms. The compounds are synthesized by the steps of deriving higher alkyl substituted cyclohexane-dione by hydrogenating higher alkyl substituted hydroquinone, reacting the higher alkyl substituted cyclohexane-dione with malononitrile, and oxidizing the reacted material. DETAILED DESCRIPTION OF THE INVENTION TCNQ is generary represented by the formula and is welknown as an organic semiconductor having high electric conductivity. The organic compounds of the present invention are substitution products by sustituting one of H atoms at side chains of TCNQ with higher alkyl group which has equal to 10 or more carbons. The general formula of the organic compounds according to the present invention is represented by: where R is higher alkyl group containing not less than 10 carbons. When the carbons of alkyl group are less than 10, it is difficult to make membrane of the organic compounds by Langmuir-Blodgett's technique. On the contrary, when the carbons of alkyl group are 10 or more, it becomes easy to make membrane of the organic compounds by Langmuir-Blodgett's technique because of large hydrophobia thereof. The higher alkyl group up to 22 carbons are practicable for the organic compounds. When TCNQ having higher alkyl group is dissolved in a solvent such as chloroform or benzen, the solution or mixture with higher fatty acid such as arachic acid may be formed as a monomolecular layer or film on the surface of the water when dropped thereon. By the action of the higher alkyl group, TCNQ having higher alkyl group is able to be formed as a monomoleclar layer between the surface of the organic solution and the surface of the water, and therefore monomolecular film or built-up film can be manufactured on a sabstrate by Langmuir-Blodgett's technique. The thus obtained monomolecular film or built-up film of TCNQ derivative forms a charge transfer complex compound with an electron donor such as TTF. The charge transfer complex compound is applicable for making various electronic devices. TCNQ having higher alkyl group is synthesized by the following steps. The synthesizing process starts from hydrogenation of hydroquinon having higher alkyl group. The hydrogenation derives higher alkyl substituted 1,4-cyclohexane-dione directly. The higher alkyl substituted 1,4-cyclohexane-­ diane is reacted with malononitrile and the product of the reaction is oxidized to produce TCNQ having higher alkyl group. The present invention will be practically explained by way of the following examples. EXAMPLE 1 a. A process for preparing 2-dodecyl-1,4-cyclohexan-dion A mixture of 20 g of 1,4-dimethoxy-2-dodecyl benzene, 30ml of alcohol and 400ml of diethyl ether was added into liquid ammonia at a temperature of -50°C in a nitrogen stream. Under stirring, 9.6g of metallic sodium was added to make reaction with the mixture for 20 hours. After reaction, ammonia was removed, and an aqueous solution of ammonium chloride was added. This mixture was held at pH2-3 by concentrated hydrochloric acid and was refluxed for 3 hours. After reflux, organic layer was separated drom water layer. The water layer was extracted by ethyl acetate and combined with the organic layer. The organic layer was rinsed with water, dried, and concentrated. After concentration, the organic layer was purified through silica gel column chromatography, and 2.0g of 2-dodecyl-1,4-cyclohexane-dione was obtained. The obtained compound had a melting point of 73°C and an infrased absorption band of 1710cm⁻¹ which corresponds to carbonyl group. b. A process for preparing 1,4-bis-(dicyanomethylene)-2­ -dodecyl-cyclohexane A mixture of 2g (0.0071 M) of thus obtained 2-­ dodecyl-1,4-cyclohexane-dione and 1.4g (0.0212 M) of malononitrile was heated in a water bath to make a solution. β-alanine as a catalyst and 2ml of water were added to the solution and stirred at a temperature between 40°C and 50°C for 8 hours to react therebetween. After cooling, the reacted mixture was dissolved in chloroform, and rinsed with water and dried. The dried material was concentrated under reduced pressure, and purified through silica gel column chromatography. As a result, 1.26g of white crystal of 1,4-bis-(­ dicyanomethylene)-2-dodecyl cyclohexane was obtained. The obtained compound has a melting point of 97°C and an infrared absorption band of 2250cm⁻¹ which corresponds to cyans group. c. A process for preparing 2-dodecyl-7,7,8,8-­ tetracyanoquinodimethane 2.46g (0.0065M) of thus obtained 1,4-bis-(dicyanomethylene)-2-dodecyl cyclohexane was dissolved in 90ml of dried acetnitrile. In this solution, 30ml of acetnitrile solution containing 3.55g (0.0199M) of N-­ bromosuccinimide was dropped in ice cooling. After stirring at same temperature for 30 minutes, 1.6ml (0.0198M) of pyridine was dropped over the period of 10 minutes. The solution was stirred at room temperature for 10 minutes and poured into 100ml of ice water. As a result, a crystal was separated. The separated crystal was filtrated and purified through silica gel column chromatography. The purified crystal was recrystallized by ethyl acetate to obtain 1.28g of 2-dodecyl-7,7,8,8-­ tetracyanoquinodimethane which was yellow acicular crystal. The thus obtained TCNQ having dodecyl had the following characteristics. Melting point: 120°C Infrared absorption band: 2250cm⁻¹(cyano) Calculated for C₂₄H₂₈N₄ : C 77.38%, H 7.58%; N 15.04% Found: C 77.48%; H 7.87%; N 15.08% EXAMPLE 2. Twelve grams of 2-pentadecyl hydroquinone was dissolved in 100ml of methanol. Then, the solution was hydrogenated in hydrogen atmosphere of initial pressure of 130kg/cm² with Raney nickel as a catalyst at 170°C of reaction temperature. After cooling, the catalyst was removed and the solvent was volatilized to prepare a crystal of 2-pentadecyl-1,4-cyclohexam-diol. Then 8.7g of the prepared crystal was dissolved in 200ml of methylene chrolide with 26.6g (0.001M) of complex of pyridinium chlorochromate and almina, and stirred for 2 hours in ice cooling. After filtration of oxidizing agent and volatilization of the solvent, 5.6g of 2-­ pentadecyl-1,4-cyclohexane-dione, which was white scalelike crystal, was obtained by purifying through silica gel column chromatography. The thus obtained compound had a melting point of 87°C and an infrared absorption band of 1710cm⁻¹ which corresponds to carbonyl group. The processes b and c of Example 1 were repeated using the obtained 2-pentadecyl-1,4-cyclohexane-dion as a starting material, whereby 1,4-bis-(dicyanomethylene)­ -2-pentadecyl cyclohexane which had a melting point of 98°C and 2-pentadecyl-7,7,8,8-tetracyanoquinodimethane were obtained. The yield of the 1,4-bis-(dicyanomethylene)­ -2-pentadecyl cyclohexane and 2-pentadecyl-7,7,8,8-­ tetracyanoquinodimethane were 72% and 46.2% respectively. The thus obtained TCNQ having pentadecyl had a melting point of 120.5°C and an infrared absorption band of 2250cm⁻¹ which corresponds to cyano group. EXAMPLE 3. The processes of Example 2 were repeated except that 2-octadecyl hydroquinone was used instead of 2-­ pentadecyl hydroquinone. The resultant materials of each reaction were as follows: The thus obtained TCNQ having octadecyl had a melting point of 125.5°C and an infrared absorption band of 2250cm⁻¹ which corresponds to cyano group. TCNQ having higher alkyl synthesized by methods such as those described above is able to be formed in monomolecular layer or film by Langmuir-Blodgett's technique. Now, an example will be explained. TCNQ having dodecyl obtained by Example 1 was dissolved in chloroform to make a solution of molarity of 10⁻⁴M. In this case, TCNQ was used singly or in dilute solution with higher fatty acid such as arachic acid. When the solution was dropped on a surface of an aqueous solution of pH5.5 in which 4 x 10⁻⁴ mol of cadmium chloride and 5 x 10⁻⁴ mol of potassium hydrogencarbonate were dissolved, TCNQ having dodecyl was spread on the surface of the aqueous solution to make good monomolecular layer or film. The monomolecular layer or film may form a built-up film by piling one after another. As described above, TCNQ having higher alkyl may be formed into a Langmuir-Blodgett's membrane. Therefore, it is possible to make a complex compound of TCNQ having higher alkyl and an electron donor such as TTF, heterocyclic quaternary ammonium salt, cyanine-dye, etc. as a very thin film having conductivity comparable with metals. The very thin film is useful for various devices in molecular electronics field, such as organic semiconductor devices, light memory devices, photo-electric devices and so on. For example, N-butylpyridinium (TCNQ)n complex shows resistivity-temperature characteristics in which the resistivity abruptly varies near 100°C. Therefore, the complex may be applicable to a temperature detector which is to be integrated in very large scale.

Claims: 1. An organic compound comprising 7,7,8,8-­ tetracyanoquinodimethane having higher alkyl represented by the following general formula in which R represents alkyl group containing more than ten carbon atoms. 2. An organic compound as claimed in claim 1, wherein said alkyl group contains less than twenty-two atoms. 3. An organic compound of a charge transfer complex compound comprising: an electron acceptor of 7,7,8,8-­ tetracyanoquinodimethane having high alkyl represented by the following general formula in which R represents alkyl group containing more than ten carbon atoms, and an electron donor of the one selected from a group consisting of tetrathiofulvalene, heterocyclic quaternary ammonium salt, and cyanine-dye. 4. An organic compound as claimed in claim 1, wherein said alkyl group containes less than twenty-two atoms. 5. A method for synthesizing 7,7,8,8-­ tetracyanoquinodimethane having higher alkyl comprising the steps of: hydrogenating hydroquinone having higher alkyl, reacting 1,4-cyclohexane-dione having higher alkyl obtained by said hydrogenating step with malononitrile, and oxidizing the resultant material obtained by said reaction step.

Inventors: NOGUCHI, AYASHI, SUGA, SADAHARU, YASUI, SHIGEO
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1986
Main classification: C07C121
IPC codes: H01B1, C07C253, G01K7, C07C255, C07C67, C09K3, C07C50