Method for producing 1,1-diarylethanes

Abstract: This invention relates to a method for producing 1,1-diarylethanes expressed by the following general formula (III): wherein R¹-R⁵each stand for a hydrogen atom or an alkyl group having 1-3 carbon atoms. This method comprises the reaction of styrenes expressed by the following general formula (I) with an alkylbenzene expressed by the following general formula (II), and is characterized in that the catalyst used is an HL type zeolite with a SiO₂/Al₂O₃ ratio of at least 4, or a zeolite modified by exchanging said HL type zeolite with a bi- or tri-valent metal ion. wherein R¹-R⁵ have the same meanings as defined above.

Description: 1) Field of the Invention The present invention relates to a method for producing 1,1-diarylethanes and, more particularly, to a method for producing 1,1-diarylethanes by the reaction of styrene or derivatives thereof (hereinafter referred to as "styrenes") with an alkylbenzene using as a catalyst an HL type zeolite with a SiO₂/Al₂O₃ molar ratio of at least 4 or a zeolite obtained by ion-exchanging said HL type zeolite with a di- or tri-valent metal ion. 2) Description of the Related Art Used as electrical insulating oils, solvents for pressure-sensitive paper purposes, etc., 1,1-diarylethanes have heretofore been prepared by the addition reaction at low temperatures of styrene with an alkylbenzene in the presence of a concentrated sulfuric acid catalyst, as known from Japanese Patent Kokai Publication Nos. 47(1972)-97858 and 50(1975)-4049. A problem of this addition reaction, however, is that it has to perform the reaction at a low temperature of -5 to 0 °C that a cooling medium is needed, and gives to rise an emulsifying phenomenon at neutralizing and water washing steps, which makes the separation of the product difficult. Another problem is that because of using the concentrated sulfuric acid catalyst, a a large amount of heavy materials are produced as by-products. Thus, this method is less effective. It is also known to use Friedel-Crafts catalysts such as aluminium oxide and boron trifluoride for the addition reaction. Incidental to this method, however, are undesired side-reactions such as the polymerization of styrenes, the formation of decomposed products by disproportionation and the occurrence of heavy materials. In order to eliminate such problems, it has been proposed to prepare diarylalkanes using a solid acid catalyst, as set forth in Japanese Patent Kokai Publication No.61(1986)-46499. As disclosed there, styrenes are allowed to react with an alkylbenzene at 130-190 °C, using as a catalyst a faujasite type of synthetic zeolite ion exchanged with a lanthanide type rare earth cation. A problem with this technique, however, is that due to the need of rising the reaction temperature to higher than the boiling point of the alkylbenzenes, the reaction system should be pressurized to keep it in a liquid phase, making the reaction equipment expensively. Japanese Patent Kokai Publication No.63(1988)-238028 discloses a method for producing diphenylalkanes, using as a catalyst an HY type zeolite exchanged with hydrogen ions in which the SiO₂/Al₂O₃ molar ratio is at least 4, or its modification exchanged with lanthanide type rare earth cations. This method is carried out at a reaction temperature of 100-120 °C. At a reaction temperature below 100°C, however, it is not preferable, since the reaction rate is so slow that no sufficiently high conversion and selectivity can be achieved. Chemical Abstracts, vol. 99 (1983) abstract 70353k discloses the preparation of 1,1-diarylethane by reacting styrene and an alkylbenzene while using Y-type zeolite as a catalyst. The reaction temperature is 115-140°C. As mentioned above, various methods for producing 1,1-diarylethanes have been known in the art. However, the methods using the concentrated sulfuric acid or Friedel-Crafts catalysts can not disolved any problem such as the reaction temperature, by-products, reaction equipment and the like. On the other hand, the method using the solid acid catalyst has to be carried out at a reaction temperature of at least 100 °C and a selectivity in this method is not enough. It is thus desired to develop a method for producing 1,1-diarylethanes under more mild conditions and with a high selectivity. SUMMARY OF THE INVENTION It is therefore an object of this invention to provide the method for producing 1,1-diarylethanes at a lower temperature and with a higher selectivity. As intensive and extensive studies made of how to produce 1,1-diarylethanes under more mild conditions and with a higher selectivity to meet such a demand, the inventors have successfully accomplished the present invention. More specifically, the present invention provides a method for producing 1,1-diarylethanes expressed by the following general formula (III) by the reaction of styrenes expressed by the following general formula (I) with alkylbenzenes expressed by the following general formula (II): wherein R¹-R⁵ each stand for a hydrogen atom or an alkyl group having 1-3 carbon atoms in the presence of a catalyst, characterized in that: the catalyst used is an HL type zeolite with a SiO₂/Al₂O₃ molar ratio of at least 4, or a zeolite modified by exchanging said HL type zeolite with a bi-or tri-valent metal ion. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The present invention will now be explained in more details. The styrenes used as one of the starting materials in this invention are expressed by the general formula (I), including aromatic olefins such as styrene, methylstyrene and ethylstyrene by way of example alone. The alkylbenzenes used as the other starting material are expressed by the general formula (II), including illustratively those having a lower alkyl group such as toluene, xylene, ethylbenzene, isopropylbenzene, diethylbenzene, pseudo-cumene and mesitylene. The 1,1-diarylethanes produced in this invention are expressed by the general formula (III), including illustratively 1,1-diphenylethane, 1-ethylphenyl-1-phenylethane, 1-phenyl-1-xylylethane, 1-phenyl-1-tolylethane, 1,1-ditolylethane, 1-cumyl-1-tolylethane. For the synthesis of the 1,1-diarylethanes by the reaction between such styrenes and alkylbenzenes as mentioned above, an HL type zeolitie with a SiO₂/Al₂O₃ molar ratio of at least 4 or a zeolite modified by exchanging said HL type zeolite with a bi- or tri-valent metal ion (both will hereinafter be generally referred to as the zeolite catalyst) is used as a catalyst. In other words, the zeolite catalysts used in this invention are HL type zeolites in which alkali metal of KL type zeolites is exchanged with hydrogen ion and the exchanging ratio is 10% or more, preferably 30% above. Alternatively, use may be made of a variation of the HL type zeolite in which a part of its hydrogen ions is exchanged to bi- or tri-valent metal ions. For instance, use may preferably be made of a zeolite modified by exchanging the HL type zeolite with an ion of heavy metals belonging to transition element of the periodic table, such as Cr, Mn, Fe, Co, Ni, Cu, Zn and La, thereby increasing its acid strength. In this case, the ion exchange rate is preferably in a range of 10-90%. It is here noted that the so-called KL type zeolite, in which the alkali metal is not exchanged with hydrogen ions, is found to be lacking in activity of reaction. At a SiO₂/Al₂O₃ molar ratio below 4, the acid strength is low and the catalytic activity is not sufficient, thus making it necessary to raise the reaction temperature. In addition, the selectivity is so low that the formation of oligomers of styrenes is increased. The zeolite catalysts used in this invention for instance, may be modified in the following procedure. That is, an KL type zeolite having a SiO₂/Al₂O₃ molar ratio of at least 4 and containing an amount of 15-17% in the form of an alkali metal oxide is immersed for ion exchange in an aqueous solution of ammonium chloride or sulfate, thereby decreasing the alkali metal content to about 10% or less, desirously 3% or less. After water washing, the zeolite is calcined at a temperature of 300-400°C into an HL type zeolite in nitrogen gas atmosphere. Then, this HL type zeolite may be treated with a pH 1.5-5.5 acidic solution of a metal salt capable of producing the aforesaid bi- or tri-valent metal ions, thereby introducing the bi- or tri-valent metal ions into it. Such metal salts, for instance, include cupric chloride, ferrous chloride, ferric chloride, manganese sulfate, chromium chloride, cobalt sulfate, cobalt chloride, nickel chloride and chromium sulfate. For the reaction between such styrenes and alkylbenzenes as mentioned above using the zeolite catalyst according to this invention, the amounts of the styrenes and alkylbenzenes used should preferably be such that their molar ratio (alkylbenzene/styrene) is 10 or more. An increase in the molar ratio improves the selectivity of 1,1-diarylethanes. A molar ratio below 10 is unpreferred, since the formation of oligomers of styrenes increases with a decrease in the selectivity of 1,1-diarylethanes. The reaction should preferably be carried out at a reaction temperature of 20 °C or higher, particularly in the range of 25-100°C. A reaction temperature below 20°C is unpreferred, because of lowering of reaction rate. In this invention, no particular limitation is imposed upon how the reaction is carried out. If desired, the reaction may be performed either batchwise or continuously. The reaction time may be 0.5 to 5 hours by selecting the reaction conditions, such reaction form and reaction scale. It is understood that the end 1,1-diarylethanes can easily be modified with high purity by distillation from the reaction products. According to this invention, the above-mentioned zeolite catalysts are used to produce 1,1-diarylethanes form styrenes and alkylbenzenes. It is thus possible, i.e., at a reaction temperature lower than the boiling point of the alkylbenzenes, in most cases, at about 30-80 °C and easily separate the end 1,1-diarylethanes from the reaction solution by distillation. According to this invention, the reaction of styrenes and alkylbenzenes is performed with a high conversion and a high selectivity with small side products. Accordingly, the 1,1-diarylethanes modified by this invention can be used for electric insulation field or solvent for pressure-sensitive paper. EXAMPLES The present invention will now be explained more specifically with reference to the examples. Examples 1 A commercially available HL type zeolite TSZ-500 (with SiO₂/Al₂O₃ molar ratio of 6.3, exchanged with 93.5 % of hydrogen ions and commercialized by Toso Co., Ltd.) was heat-treated at temperature of 400 °C for 2 hours in a nitrogen gas atmosphere as pre-treatment of the catalyst. 20g of the catalyst and 341g of ethylbenzene were set into a separable flask having an inner volume of 500 ml and equipped with a stirrer, a dropping funnel and a thermometer, which were then heated to about 40 °C. Thereafter, pre-mixture of 47 g of ethylbenzene and 38 g of styrene was added dropwise through the dropping funnel over 1 hour, followed by a two-hour reaction at a reaction temperature kept at 40±2°C. By gas chromatography analysis, the reaction solution was found to be composed of ethylbenzene, styrene, 1-ethylphenyl-1-phenylethane (hereinafter abbreviated as 1,1-EDE),styrene dimer and high-boiling matters. The conversion of styrene and the selectivity of 1,1-EDE were calculated by the following equations: Styrene conversion = (Starting Amount - Remaining Amount)/Starting Amount 1,1-EDE selectivity = Concentration of 1,1-EDE in Reaction Solution/Total Products; 1,1-EDE, Styrene Dimer and High-Boiling Matters, etc. The results are shown in Table 1. Example 2 Except that the amount of styrene added was 19 g, Example 1 was repeated to synthesize 1,1-EDE, whose composition was similarly analyzed. The results are shown in Table 1. Example 3 The same HL type zeolite as used in Ex. 1 was immersed for cupric ion exchange in an aqueous solution of cupric chloride to perform exchanging at an exchange rate of 40 % and heat-treated at 400 °C for 2 hours in a nitrogen gas atmosphere. The same procedure as in Ex. 1 was carried out to synthesize 1,1--EDE, whose composition was similarly analyzed. The results are shown in Table 1. Examples 4-9 The HL type zeolites were exchanged with Ni, Cr, Co, Zn, Fe or Mn ions in place of cupric ions. The same procedure as explained in Ex. 3 was carried out in Ex. 4-9 to synthesize 1,1-EDE, whose composition was similarly analyzed. The results are shown in Table 1. Comparative Example 1 The same procedure as in Ex. 1 was carried out except that an HL type zeolite wherein SiO₂/Al₂O₃ = 3.5 was used as a catalyst to synthesize 1,1-EDE, whose composition was similarly analyzed. The results are shown in Table 1.

Claims: A method for producing 1,1-diarylethanes expressed by the following general formula (III) by the reaction of styrenes expressed by the following general formula (I) with alkylbenzenes expressed by the following general formula (II): wherein R¹-R⁵ each stand for a hydrogen atom or an alkyl group having 1-3 carbon atoms in the presence of a catalyst, characterized in that: the catalyst used is an HL type zeolite with a SiO₂/Al₂O₃ molar ratio of at least 4, or a zeolite modified by exchanging said HL type zeolite with a bi-or tri-valent metal ion. A method as claimed in Claim 1, wherein styrene is reacted with ethylbenzene. A method as claimed in Claim 1, wherein the bi- or tri- valent metal ion is a cation of a metal selected from the group consisting of Cu, Ni, Cr, Co, Zn, Fe or Mn. A method as claimed in Claim 1, wherein the bi- or tri-valent metal ion is a cation of lanthanide type metals. A method as claimed in Claim 1, wherein the molar alkylbenzene/styrene ratio is 10 or more.

Inventors: AKATSU MASAHIRO CHEM ENG, MATSUOKA TAKESHI, TAKAYAMA HAJIME, AKATSU, MASAHIRO, CHEM. ENG., MATSUOKA, TAKESHI, TAKAYAMA, HAJIME
Applicants: KUREHA CHEMICAL IND CO LTD, KUREHA KAGAKU KOGYO KABUSHIKI KAISHA
Application year: 1990
Main classification: C07C15
IPC codes: C07B61, B01J29, C07C2, C07C15