PROCESS FOR PREPARING 5-ETHYLIDENE-2-NORBORNENE

Abstract: 5-Ethylidene-2-norbornene is effectively prepared by isomerization 5-vinyl-2-norbornene in the presence of at least one catalyst selected from a group consisting of a solid base catalyst which is prepared by reacting alumina and an alkali metal hydroxide at a temperature of 200 to 500°C and then reacting the reaction product with an alkali metal at a temperature of 180 to 350°C and a solid base catalyst which is prepared by reacting water-containing alumina and an alkali metal in such an amount that corres­ ponds to a molar equivalent of water contained in alumina at a temperature in a range between a melting point of the alkali metal and 500°C and then reacting the reaction pro­ duct with an alkali metal at a temperature of 180 to 350°C.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a process for preparing 5-ethylidene-2-norbornene (hereinafter referred to as "ENB"). Particularly, it relates to a process for pre­ paring ENB by isomerizing 5-vinyl-2-norbornene (hereinafter referred to as "VNB") in the presence of a specific solid base catalyst. Description of the Prior Art ENB is the most promising compound as a third monomer of a terpolymer of ethylene, propylene and diene­ monomer (EPDM rubber) and prepared by isomerizing VNB in the presence of a catalyst. VNB is produced by reacting 1,3-­ butadiene and cyclopentadiene. As the isomerization catalysts, there are known liquid bases such as mixtures of an alkali metal hydroxide and an aprotic organic solvent, of an alkali metal amide and an amine and of an organic alkali metal compound and an aliphatic amine. Such liquid bases, however, do not have enough catalytic activity so that a large amount of the expensive catalyst should be used. Further, since separa­ tion and recovering of the catalyst component from the reac­ tion mixture are very difficult, the process requires a complicated separation and recovering steps and consumes a large amount of energy. There are also known solid isomerizatiion cata­ lysts, for example, an alkali metal carried on an anhydrous carrier with a large surface area (e.g., activated carbon, silica gel, alumina and the like) (cf. J. Am. Chem. Soc., 82 , 387 (1960)). The solid catalyst, however, has unsartis­ factory handleability and less safety since it is ignited and loses activity on contact with air. This is because the alkali metal is only finely dispersed on the carrier. Further, the solid catalyst has insufficient isomerization performance. The inventors have proposed a solid base catalyst for isomerizing olefins such as VNB, which do not suffer from the drawbacks of the conventional isomerization cata­ lysts. The proposed catalyst is prepared from alumina, an alkali metal hydroxide and an alkali metal, or from water-­ containing alumina and an alkali metal. The solid base catalyst has higher stability to air and excellent isomeri­ zation activity of olefins such as VNB than the alkali metal dispersion catalyst (cf. Japanese Patent Publication Nos. 3274/1975 and 21378/1982). SUMMARY OF THE INVENTION One object of the present invention is to provide an improved catalyst for use in preparing ENB by isomeri­ zation of VNB. Another object of the present invention is to provide a process for preparing ENB by isomerizing VNB in the presence of a solid base catalyst which has higher cata­ lytic activity and exerts catalytic effect in a smaller amount than the aforementioned catalysts. These and other objects are accomplished by a process for preparing ENB according to the present invention which comprises isomerizing VNB in the presence of at least one catalyst selected from a group consisting of a solid base catalyst which is prepared by reacting alumina and an alkali metal hydroxide in a temperature range of 200 to 500°C and then reacting the reaction product with an alkali metal in a temperature range of 180 to 350°C and a solid base catalyst which is prepared by reacting water-containing alumina and an alkali metal in such an amount that corres­ ponds to a molar equivalent of water contained in alumina at a temperature in a range between a melting point of the alkali metal and 500°C and then reacting the reaction pro­ duct with an alkali metal in a temperature range of 180 to 350°C. DETAILED DESCRIPTION OF THE INVENTION The process of the present invention has been completed based on finding that, in isomerization of VNB to ENB, catalytic performance of the catalyst is influenced by preparation temperatures, namely, a temperature at which alumina, the alkali metal hydroxide and the alkali metal are reacted, particularly, the alkali metal is reacted in the preparation, and a temperature at which water-containing alumina and the alkali metal are reacted, particularly, water-containing alumina is reacted with the excess portion of the alkali metal to the molar amount of water contained in alumina. Examples of the alkali metal hydroxide are lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide and cesium hydroxide and a mixture thereof. It may be used in a solid or liquid state. As the alkali metal, an alkali metal of Group I of the Periodic Table such as sodium, potassium and rubidium is used. They may be used as a mixture or an alloy. Among them, sodium, potassium and an alloy of them are preferred. As a combination of the alkali metal and the alkali metal hydroxide, a combination of an alkali metal and a hydroxide of other alkali metal, for example a combination of potassium and sodium hydroxide, of sodium and potassium hydroxide or of sodium and lithium hydroxide can be used, although a combination of an alkali metal and its correspon­ ding hydroxide, for example, a combination of sodium and sodium hydroxide, of potassium and potassium hydroxide, and the like may be usually used. A combination of metal sodium and sodium hydroxide is practically preferred. Amounts of the alkali metal and the alkali metal hydroxide are 2 to 10 % by weight and 5 to 40 % by weight, respectively based on the weigh of alumina in view of the catalytic activity. Usually, alumina with a relatively large surface area such as γ-, χ-, β- and η-alumina is used. Among them, alumina of 50 to 500 mesh, particularly, γ-alumina of such mesh is preferred in view of the catalytic activity. Since alumina acts as a carrier in addition it reacts with the alkali metal and the alkali metal hydroxide, an alumina-­ containing compound such as kaolin and alumina silicate may be used in place of alumina but less preferable. According to the present invention, alumina, the alkali metal and the alkali metal hydroxide are reacted at a specific temperature as described above to prepare the solid base catalyst. As to the sequence of the reactions, prefe­ rably, alumina and the alkali metal hydroxide are firstly reacted and then the alkali metal is reacted. Usually, the alkali metal hydroxide kept at a temperature higher than its melting point is added to alumina and reacted at the speci­ fic temperature, although an aqueous solution of the alkali metal hydroxide may be used and the reaction mixture is heated to the specific temperature to proceed the reac­ tion. Also, the alkali metal is added at a temperature higher than its melting point and reacted at the specific temperature, although it can be added in the form of a solu­ tion and heated to the specific temperature to proceed the reaction. The reactions are preferably carried out in an atmosphere of an inert gas such as nitrogen, helium and argon. In the present invention, the properties of the prepared solid base catalyst are influenced by the reaction temperatures. Particularly, the catalytic activity of the catalyst is greatly affected by the temperature at which the alkali metal is reacted. Alumina and the alkali metal hydroxide are reacted in a temperature range of 200 to 500°C, preferably 250 to 450°C, and the alkali metal is reacted in a temperature range of 180 to 350°C, preferably 200 to 330°C. By reacting the compounds at such temperatures, the catalyst with significantly high activity is prepared. Therefore, the isomerization of VNB to ENB can be efficien­ tly achieved even with a small amount of the catalyst. The reaction time varies with other reaction con­ ditions such as temperature. The reaction of alumina and the alkali metal hydroxide may be completed within 0.5 to 10 hours, and that of the alkali metal may be completed within 10 to 300 minutes. In addition to the above method, the solid base catalyst to be used in the process of the present invention can be prepared by reacting water-containing alumina and the alkali metal. This may be due to the formation of the alkali metal hydroxide from water contained in alumina and the alkali metal. Such preparation of the catalyst will be illustrated hereinafter. Various types of water-containing alumina except α-alumina can be used. Generally, alumina is produced by calcining alumi­ num hydroxide. According to the calcining temperature and time, alumina has various metastable states and a water content varies so that various kinds of alumina are produ­ ced. In the present invention, such alumina may be used. Preferably, water-containing alumina with a large surface area such as γ-, χ-, ρ- and η-alumina is used. Although it is rather difficult to measure water content of alumina, water content may be expressed by weight loss on heating in the heating step in which alumina in its original state is changed to α-alumina which is considered to include no removable water. Usually, the water content of water-containing alumina is 1.3 to 10 % by weight, prefe­ rably 2 to 7 % by weight in terms of weight loss on heating. The alkali metal used in this preparation is the same as described above. A total amount of the alkali metal to be reacted is larger than such amount that corresponds to a molar equivalent of water contained in alumina, preferably 1.01 to 2 time molar equivalents of water contained in alu­ mina. According to the present invention, water-contain­ ing alumina is reacted with the alkali metal in at least such amount that corresponds to the molar equivalent of water contained in alumina preferably in an atmosphere of an inert gas such as nitrogen, helium and argon, and then excess amount alkali metal is reacted with alumina. In this method, a kind of the alkali metal firstly reacted and that of the alkali metal subsequently reacted may be the same or different. Also in this second preparation of the solid base catalyst, the reaction temperatures, particularly, the reac­ tion temperature in the second step have significant influ­ ences on the properties of the catalyst. In the first reaction of water-containing alumina and the alkali metal in an amount corresponding to the molar equivalent of contained water, a reaction temperature is in a range between a melting point of the alkali metal and 500°C. In the second reaction of alumina and excess alkali metal, a reaction temperature is 180 to 350°C, preferably 200 to 330°C. Preferably, the first reaction temperature and the second reaction temperature are substantially the same. In such case, the reaction temperature is preferably from 180 to 350°C, more preferably from 200 to 330°C. In this case, the alkali metal can be added in one portion. By reacting the compounds at such temperatures, the catalyst with significantly high activity is prepared. Therefore, the isomerization of VNB to ENB can be efficien­ tly achieved even with a small amount of the catalyst. The reaction time varies with other reaction con­ ditions such as the reaction temperature. Usually, it is 15 minutes to 10 hours. Thus, the solid base catalysts with greatly inc­ reased activity in comparison with the conventional cata­ lysts are prepared. In the process of the invention, VNB is isomerized to ENB in the presence of the solid base catalyst as pre­ pared in the above. A weight ratio of the catalyst to VNB is 1:3,000 to 1:50, preferably 1:2,000 to 1:100. Since the isomerization proceeds at an ordinary temperature, it is not necessary to heat the reaction system. To accelerate the isomerization, the reaction temperature may be elevated. Usually, the reaction temperature is in a range between -30 to +120°C, preferably between -10 to +100°C. The isomerization is carried without any reaction medium, although it may be carried out in an inert liquid medium such as hydrocarbon (e.g., hexane, heptane and dodecane). The isomerization of the present invention may be carried out in batch wise or continuously. The isomeriza­ tion is preferably carried in an atmosphere of an inert gas. If necessary, VNB is pretreated with a desiccant such as alumina prior to isomerization. The isomerization product is analyzed by a known method such as gas chromatography and separated from the catalyst by a conventional separation method such as filtra­ tion. According to the present invention, ENB can be prepared by isomerization of VNB in a high yield substan­ tially without formation of by-products such as a polymer in the presence of the catalyst in a much smaller amount than the conventional catalyst. Further, the isomerization can be safely carried out without any fear of ignition. Practically and presently preferred embodiments of the present invention will be illustrated by following exam­ ples. Reference Example 1 To a 100 ml flask, γ-alumina (31.9 g) was added and heated to 490-500°C under nitrogen with stirring at the same temperature for one hour. After cooling to 300-310°C, sodium hydroxide (4.5 g) was added thereto and stirred at the same temperature for 3 hours. Then, metal sodium (1.5 g) was added, stirred at the same temperature for one hour and then cooled to room temperature to obtain a solid base (34.9 g). Example 1 To a 200 ml flask, VNB (82.5 g) was added under nitrogen. The solid base prepared in Reference Example 1 (0.25 g) was added and stirred at a temperature of 15 to 20°C for 6 hours. The solid catalyst was filtered off to obtain a reaction mixture (81.9 g). Gas chromatographic analysis of the mixture revealed that 99.4 % of ENB and 0.5 % of VNB were contained in the mixture. Reference Example 2 To a 100 ml flask, γ-alumina (31.9 g) was added and heated to 490-500°C under nitrogen with stirring at the same temperature for one hour. After cooling to 300-310°C, sodium hydroxide (3.0 g) was added thereto and stirred at the same temperature for 3 hours. Thereafter, metal sodium (1.2 g) and metal pota­ ssium (0.3 g) were added, stirred at the same temperature for 30 minutes and then cooled to room temperature to obtain a solid base (33.8 g). Reference Examples 3-11 In the same manner as in Reference Example 1 but carrying out the reaction under the conditions specified in Table 1, a solid base catalyst was prepared. Examples 2-9 and Comparative Examples 1-2 In the same manner as in Example 1 but using the solid base catalyst prepared in each of Reference Examples 2-9 and Comparative Examples 1-2, VNB was isomerized. The results are shown in Table 2. Reference Example 12 To a 100 ml flask, γ-alumina containing 2.2 % by weight of water (30.0 g) was added and heated to 300°C in a nitrogen stream with stirring at the same temperature for one hour. Metal sodium (1.2 g) was added thereto, stirred at the same temperature for one hour and then cooled to room temperature to obtain a grayish blue solid base (30.9 g). Example 10 To a 200 ml flask in a nitrogen atmosphere, the solid base catalyst prepared in Reference Example 12 (0.25 g) and then VNB (64.5 g) were added and stirred at a tempe­ rature of 15-20°C for 8 hours. Thereafter, the catalyst was filtered off to obtain a reaction mixture (63.9 g). Gas chromatographic analysis of the mixture revealed that 99.5 % of ENB and 0.4 % of VNB were contained in the mixture. Reference Examples 13-21 In the same manner as in Reference Example 1 but carrying out the reaction under the conditions specified in Table 3, a solid base was prepared. Examples 11-15 and Comparative Examples 3-6 In the same manner as in Example 10 but using, as a catalyst, the solid base prepared in each of Reference Examples 13-21 and Comparative Examples 3-6, VNB was isome­ rized. The results are shown in Table 4. Reference Example 22 To a 100 ml flask, alumina comprising γ-alumina and containing 6.0 % by weight of water (50 g) was added and heated to 200°C with stirring and injecting nitrogen. At the same temperature, metal sodium (4.0 g) was added by portions over 20 minutes. After stirring for one hour, it was gradually heated to 300°C. At said temperature, addi­ tional metal sodium (1.9 g) was added by portions over 10 minutes and stirred at the same temperature for 3.5 hours to obtain a solid base (54.2 g). Reference Example 23 To a 100 ml flask, alumina comprising γ-alumina and containing 6.0 % by weight of water (50 g) was added and heated to 200°C with stirring under nitrogen. At the same temperature, metal sodium (4.0 g) was added by portions over 20 minutes. After stirring for one hour, it was gradually heated to 400°C. At said temperature, additional metal sodium (1.9 g) was added by portions over 10 minutes and stirred at the same temperature for 3.5 hours to obtain a solid base (54.1 g). Example 16 To a 200 ml flask in a nitrogen atmosphere, the solid base prepared in Reference Example 22 (0.25 g) and then VNB (62.5 g) were added and stirred at 15-20°C for 8 hours. The solid catalyst was filtered off to obtain a reaction mixture (62.0 g). Gas chromatographic analysis of the mixture revealed that 99.5 % of ENB and 0.3 % of VNB were contained in the mixture. Comparative Example 7 To a 200 ml flask in a nitrogen atmosphere, the solid base prepared in Reference Example 23 (0.25 g) and then VNB (62.5 g) were added and stirred at 15-20°C for 8 hours. The solid catalyst was filtered off to obtain a reaction mixture (61.9 g). Gas chromatographic analysis of the mixture revealed that 59.8 % of ENB and 40.1 % of VNB were contained in the mixture.

Claims: 1. A process for preparing 5-ethylidene-2-norbor­ nene which comprises isomerizing 5-vinyl-2-norbornene in the presence of at least one catalyst selected from a group consisting of a solid base catalyst which is prepared by reacting alumina and an alkali metal hydroxide at a tempera­ ture of 200 to 500°C and then reacting the reaction product with an alkali metal at a temperature of 180 to 350°C and a solid base catalyst which is prepared by reacting water-­ containing alumina and an alkali metal in such an amount that corresponds to a molar equivalent of water contained in alumina at a temperature in a range between a melting point of the alkali metal and 500°C and then reacting the reaction product with an alkali metal at a temperature of 180 to 350°C. 2. The process according to claim 1, wherein the solid base catalyst is one prepared by heating alumina, an alkali metal hydroxide and an alkali metal. 3. The process according to claim 2, wherein alu­ mina and the alkali metal hydroxide are reacted in a tempe­ rature range of 250 to 450°C. 4. The process according to claim 2, wherein the alkali metal is reacted in a temperature range of 200 to 330°C. 5. The process according to claim 2, wherein the alkali metal hydroxide is selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide and cesium hydroxide and mixtures thereof. 6. The process according to claim 2, wherein alu­ mina is selected from the group consisting of γ-alumina, χ-­ alumina, ρ-alumina, η-alumina and mixtures thereof. 7. The process according to claim 6, wherein alu­ mina is γ-alumina of 50 to 500 mesh. 8. The process according to claim 1, wherein the solid base catalyst is prepared by heating water-containing alumina and an alkali metal. 9. The process according to claim 8, wherein the alkali metal is used in such an amount that correspond to 1.01 to 2 time molar equivalents of water contained in alu­ mina. 10. The process according to claim 8, wherein the water-containing alumina and the excess portion of the alkali metal to the molar equivalent of water contained in alumina are reacted at a temperature of 200 to 330°C in the preparation of the catalyst. 11. The process according to claim 8, wherein alumina and the molar equivalent amount of the alkali metal, and alumina and the excess molar equivalent amount of the alkali metal are reacted at a temperature of 200 to 330°C in the preparation of the catalyst. 12. The process according to claim 8, wherein water-containing alumina is selected from the group consisting of γ-alumina, χ-alumina and ρ-alumina which are preferably prepared by calcination of aluminum hydroxide. 13. The process according to claim 8, wherein the water content of alumina is 1.3 to 10 % by weight. 14. The process according to claim 8, wherein the water content of alumina is 2 to 7 % by weight. 15. The process according to claim 8, wherein the alkali metal is at least one selected from the group consis­ ting of sodium, potassium and rubidium and mixtures and alloys thereof. 16. The process according to claim 1, wherein a weight ratio of the solid base catalyst to 5-vinyl-2-norbor­ nene is from 1:2,000 to 1:100. 17. The process according to claim 1, wherein the isomerization temperature range is from -10 to +100°C.

Inventors: FUKAO, MASAMI, SUZUKAMO, GOHFU
Applicants: SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1986
Main classification: C07C13
IPC codes: C07C5, B01J23