DIMETRIZATION OF LOWER ALPHA-OLEFINS

Abstract: A dimer of a lower α-olefin is prepared by dimeri­ zing a lower α-olefin in the presence of a catalyst compri­ sing (A) nickel chloride, (B) a trialkylaluminum (C) at least one phosphorus compound selected from the group consisting of compounds of the formulae: PR¹R²R³ (I) P(NR¹₂)₃ (II) and P(OR¹)₃ (III) wherein R¹, R² and R³ are the same or different and each represents an alkyl group, a cycloalkyl group or a phenyl group and (D) 1,1,1,3,3,3-hexafluoroisopropanol, wherein the catalyst has improved activity because of the use of nickel chloride as a nickel component, so that the amounts of expensive trialkylaluminum and hexafluoroiso­ propanol can be decreased and the cost of the catalyst is significantly reduced.

Description: The present invention relates to a process for the dimerization of a lower α-olefin. More particularly, the present invention relates to a process for the dimerization of a lower α-olefin which uses a novel nickel-containing Ziegler catalyst. Dimers of lower α-olefins such as ethylene, propylene, butene, etc. are useful as basic compounds in the production of agricultural chemicals, perfumes and other chemicals or as monomers of polymers. Some of the known processes for the preparation of the dimers of lower α-olefin comprise dimerization of the α-olefin in the presence of a nickel-containing Ziegler catalyst. For example, Japanese Patent Kokai Publication No. 167932/1982 discloses a catalyst comprising a nickel salt, a trialkylaluminum compound, an organic phosphine, a halogenated phenol and water. When the α-olefin is dimerized in the presence of such a catalyst, in some cases, a small amount of precipitates may be formed in the reaction system, which results in the reduction of cooling efficiency of the heat exchanger for cooling the reaction system. EP-A-0213748 relates to a process for dimerizing lower α-olefins in the presence of a catalyst system, which comprises: an organic acid salt or a complex of nickel, a trialkylaluminum, at least one of a number of specific trivalent phosphorus compounds, a fluorinated isopropanol, and optionally a catalyst co-activator, and/or a compound selected from an aliphatic alcohol having 10 to 20 carbon atoms and an aliphatic carboxylic acid having 10 to 20 carbon atoms or an ester thereof. In examples 11 and 12 bistriisopropylphosphine-nickelchloride, isoprene, triethylaluminum, 1,1,1,3,3,3-hexafluoroisopropanol and propylene are reacted. DE-A-2828577 relates to a process for the catalytical dimerization of α-olefins which is characterized by the use of a catalyst which comprises: at least one organic and/or inorganic nickel salt and/or nickel complex, an aluminumtrialkyl, at least one of a number of specific trivalent phosphorus compounds, and a halogenated phenol. It was proposed to use a catalyst comprising a nickel salt of an organic acid, a trialkylaluminum, an organic phosphine and fluorinated isopropanol (cf. Japanese Patent Kokai Publication No. 158225/1987). One object or the present invention is to provide a nickel-containing Ziegler catalyst which effectively catalyzes the dimerization of lower α-olefins. Another object of the present invention is to provide a process for the dimerization of lower α-olefins. These and other objects of the present invention are accomplished by a novel nickel-containing Ziegler. catalyst comprising nickel chloride, a trialkylaluminum compound, a phosphorus compound, 1,1,1,3,3,3-hexaflouroisopropanol and at least one active hydrogen containing compound. Accordingly, the present invention provides a process for preparing a dimer of a lower α-olefin comprising dimerizing the lower α-olefin in the presence of a catalyst comprising (A) nickel chloride, (B) a trialkylaluminum compound (C) at least one phosphorus compound selected from the group consisting of compounds of the formulae: PR¹R²R³ (I) P(NR¹₂)₃ (II) and P(OR¹)₃ (III) wherein R¹, R² and R³ are the same or different and each represents an alkyl group, a cycloalkyl group or a phenyl group, (D) 1,1,1,1,3,3,3-hexafluoroisopropanol, and (E) at least one active hydrogen-containing compound selected from the group consisting of water, methanol, ethanol, n-propanol, isopropanol, n-butanol, tert.-butanol, amyl alcohol, hexanol, heptanol, octanol, allyl alcohol, phenol, cresol, xylenol, acetic acid and propionic acid. The Ziegler catalyst of the present invention is characterized in the use of nickel chloride as a nickel-containing component. The nickel chloride to be contained in the Ziegler catalyst of the present invention may be in the form of an anhydrous salt or a hydrated salt. Specific examples of the trialkylaluminum compound (B) are trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-isopropylaluminum, tri-n-butylaluminum, tri-isobutylaluminum, tri-n-pentylaluminum, tri-n-hexylaluminum, tri-cyclohexylaluminum, etc. The molar amount of the trialkylaluminum compound is usually 2 to 500 times, preferably 2 to 100 times, more preferably 2 to 10 times the amount of nickel chloride (A). Specific examples of the organic phosphine compound (I) which is one of the trivalent phosphorus compounds (C) are trimethylphosphine, triethylphosphine, tri-n-propylphosphine, tri-isopropylphosphine, tri-n-butylphosphine, tri-isobutylphosphine, tri-tert.-butylphosphine, tri-sec.-butylphosphine, tricyclopropylphosphine, tricyclohexylphosphine, triphenylphosphine, tri-p-tolylphosphine, tri-p-methoxyphenylphosphine, tri-2,4,6-trimethylphenylphosphine, phenyl-di-isopropylphosphine, ethyl-di-isopropylphosphine, ethyl-di-tert.-butylphosphine, ethyl-dicyclohexylphosphine, methylpropylphenylphosphine, methylphenylbenzylphosphine, etc. Specific examples of the aminophosphine compound (II) are tris-dimethylaminophosphine, tris-diethylaminophosphine, tris-di-n-propylaminophosphine, tris-di-isopropylaminophosphine, tris-di-n-butylaminophosphine, tris-di-isobutylaminophosphine, tris-di-tert.-butylaminophosphine, tris-dicyclohexylaminophosphine, etc. Specific examples of the phosphite (III) are tri-methylphosphite, triethylphosphite, tri-n-propylphosphite, tri-isopropylphosphite, tri-n-butylphosphite, tri-isobutylphosphite, tri-tert.-butylphosphite, tricyclohexylphosphite, triphenylphosphite, tri-p-tolylphosphite, tri-p-methoxyphenylphosphite, etc. Among the components (A) to (D) in the catalyst, the trivalent phosphorus compound (C) has the largest influence on the isomer distribution of the α-olefin dimers. For example, when 2,3-dimethylbutenes are to be prepared in high yields by dimerization of propylene, organic phosphines such as tri-isopropylphosphine, tricyclohexylphosphine, tri-sec.-butylphosphine, etc. are preferably used. The molar amount of the phosphorus compound (C) is usually 0.1 to 50 times, preferably 0.1 to 20 times, more preferably 0.1 to 2 times the amount of nickel chloride (A). 1,1,1,3,3,3-Hexafluoroisopropanol (D) is one of the essential components or the Ziegler catalyst having the dimerization activity according to the present invention. Without 1,1,1,3,3,3-hexafluoroisopropanol, the catalyst has substantially no dimerizing activity. By variation of the amount of 1,1,1,3,3,3-hexafluoroisopropanol, the isomer distribution of the double bond in the olefin dimer can be controlled. For example, when the 2,3-dimethylbutenes are selectively prepared, 2,3-dimethylbutene-1 is obtained if the amount of 1,1,1,3,3,3-hexafluoroisopropanl is small, while 2,3-dimethylbutene-2 is obtained if the amount of 1,1,1,3,3,3-hexafluoroisopropanol is increased. The molar amount of 1,1,1,3,3,3-hexafluoroisoprocanol is 0.2 to 10 times, preferably 0.5 to 5 times, more preferably 1 to 4 times the amount of the trialkylaluminum compound (B). In addition to the above essential components, the Ziegler catalyst of the present invention comprises the active hydrogen-containing compound (E). Thereby, the isomer distribution of the olefin dimer can be varied. For example, in the case of the dimerization of propylene, the catalyst comprising the active hydrogen-containing compound (E) will increase the selectivity of 2,3-dimethylbutene-1, 2,3-dimethylbutene-2 and the like. Among the active hydrogen containing compounds water, methanol, ethanol, n-propanol, octanol, allyl alcohol, phenol, acetic acid and mixtures thereof are preferred. The molar amount of the compound (E) is less than equimolar to, preferably 0.1 to 0.8 times, more preferably 0.2 to 0.6 times the amount of the trialkylaluminum compound (B). Although the catalyst system of the present invention can be stably used in the presence of the lower α-olefin to be dimerized during the preparation step, the catalyst is preferably prepared in the presence of a linear conjugated diolefins as a stabilizing aid. Examples of such conjugated diolefin are butadiene, isoprene and 1,3-pentaaiene. The molar amount of the conjugated diolefin is not more than 200 times the amount or nickel chloride (A). Excessive use of the conjugated diolefin does not improve the stabilizing effect. The components (A) to (E) are added in the sequence (A), (C), (B), (E) and (D). In general, the catalyst is prepared in an inert solvent. Examples of such solvents are aromatic hydrocarbons (e.g. benzene, toluene, xylene, etc.), aliphatic hydrocarbons (e.g. hexane, heptane, cyclohexane, etc.) and halogenated aromatic hydrocarbons (e.g. chlorobenzene, dichlorobenzene, etc.). Among them, the aromatic hydrocarbons and the halogenated aromatic hydrocarbons are preferred. The catalyst is prepared usually at a temperature of -80°C to +60°C, preferably -20°C to +40°C. In some cases, the catalyst may be prepared in a liquid or a liquefied α-olefin. The concentration of the catalyst during the dimerization is usuallly from 10⁻⁵ to 10⁻¹ mol/liter in terms of the concentration of the nickel component. The reaction temperature for the dimerization is usually from -80°C to +60°C, preferably from -20°C to +40°C. The reaction pressure is from atmospheric pressure to autogenous equilibrium pressure at the reaction temperature. Examples of the lower α-olefin to be dimerized according to the present invention are those having at least 2, preferably 2 to 4 carbon atoms such as ethylene, propylene, 1-butene,etc.. After the dimerization reaction, the reaction is stopped and the catalyst is separated from the reaction mixture in a conventional manner. Then, the reaction mixture is rectified to obtain the desired dimer(s). The produce can be analyzed and quantitatively determined by gas chromatography. According to the present invention, since the Ziegler catalyst contains nickel chloride as the nickel component, the catalytic activity can be greatly increased. For example, the amounts of the expensive trialkylaluminum compound and hexafluoroisopropanol can be decreased, so that the cost of catalyst can be considerably reduced. In addition, by the use of the active hydrogen-containing compound, the isomer distribution in the produced olefin dimers can be advantageously controlled. Practically and presently preferred embodiments of the present invention will be illustrated by the following Examples. Comparative Example 1 In a stainless steel 100 ml autoclave which had been evacuated, dried and filled with nitrogen, chlorobenzene containing 0.05 mmol of anhydrous nickel chloride (5 ml), chlorobenzene containing 0.05 mmol of tricyclohexyl-phosphine (0.5 ml) and isoprene (4 mmol, 0.4 ml) were added in this order and mixed. Then, chlorobenzene containing 0.25 mmol of triethylaluninum (0.25 ml) was added and the mixture was stirred while cooling with ice. To the ice-cooled mixture, chlorobenzene containing 0.75 mmol of 1,1,1,3,3,3-hexafluoroisopropanol (hereinafter referred to as "HFIP") (0.75 ml) was added while stirring, followed by stirring for 10 minutes. To the catalyst solution, absolute chlorobenzene (4.6 ml) was added and then propylene was injected into the autoclave at a pressure of 4 kg/cm² followed by stirring at 20°C for 30 minutes. After the reaction was completed, the reaction mixture was sampled under pressure and subjected to gas chromatography, using n-pentane as the internal standard. The results are shown in Table 1. The reaction mixture after purging unreacted propylene was clear, and no deposit was found on the inner wall of the autoclave. Example 1 In the same manner as in Comparative Example 1 except that after the addition of the triethylaluminum solution, chlorobenzene containing 0.1 mmol of methanol (0.2 ml) was added and the mixture was stirred, and then the HFIP solution was added followed by stirring, the catalyst was prepared and the dimerization was carried out. The results are shown in Table 1. The reaction mixture was clear, and no deposit was found on the inner wall of the autoclave. Comparative Examples 2-5 In the same manner as in Comparative Example 1 but using the organic phosphorus-containing compound (0.05 mmol) shown in Table 2 in place of tricyclohexylphosphine, the catalyst was prepared and the dimerization was carried out. The results are shown in Table 2. Examples 2-8 In the same manner as in Example 1 but using the active hydrogen-containing compound (0.1 mmol) shown in Table 3 in place of methanol, the catalyst was prepared and the dimerization was carried out. The results are shown in Table 3. Comparative Example 6 In the same manner as in Comparative Example 1 but using nickel naphthenate (0.05 mmol) in place of nickel chloride, 0.5 mmol of triethylaluminum and 1.5 mmol of HFIP, the catalyst was prepared and the dimerization was carried out. The results are shown in Table 4. Comparative Example 7 In the same manner as in Comparative Example 1 except that, after the addition of isoprene, water (0.25 mmol, 4.5 µl) was added, then chlorobenzene containing 0.5 mmol of triethylaluminum (0.5 ml) and chlorobenzene containing 1.75 mmol of 2,4,6-trichlorophenol (1.75 ml) were added in this sequence followed by stirring for 15 minutes and then chlorobenzene (3.35 ml) was added, the catalyst was prepared and the dimerization was carried out. The results are shown in Table 4. Comparative Example 8 In the same manner as in Comparative Example 7 but using 0.125 mmol of water, 0.25 mmol of triethylaluminum and 0.875 mmol of 2,4,6-trichlorophenol, the catalyst was prepared and the dimerization was carried out. The results are shown in Table 4. Comparative Example No. Efficiency of catalyst Yield of dimethylbutenes (%) Selectivity of dimethylbutenes (%) 6 18.7 x 10³ 39.7 87.4 7 13 x 10³ 42.6 70.1 8 3.1 x 10³ 27.5 71.2

Claims: A process for preparing a dimer of a lower α-olefin comprising dimerizing the α-olefin in the presence of a catalyst comprising (A) nickel chloride, (B) a trialkylaluminum compound (C) at least one phosphorus compound selected from the group consisting of compounds of the formulae: PR¹R²R³ (I) P(NR¹₂)₃ (II) and P(OR¹)₃ (III) wherein R¹, R² and R³ are the same or different and each represents an alkyl group, a cycloalkyl group or a phenyl group, (D) 1,1,1,3,3,3-hexafluoroisopropanol and (E) at least one active hydrogen-containing compound selected from the group consisting of water, methanol, ethanol, n-propanol, isopropanol, n-butanol, tert.-butanol, amyl alcohol, hexanol, heptanol, octanol, allyl alcohol, phenol, cresol, xylenol, acetic acid and propionic acid. The process according to claim 1, wherein the lower α-olefin is propylene. The process according to claim 1, wherein the molar ratio of the trialkylaluminum compound (B) to nickel chloride (A) is from 2 to 500, the molar ratio of the phosphorus compound (C) to nickel chloride (A) is from 0.1 to 50, the molar ratio of the 1,1,1,3,3,3-hexafluoroisopropanol (D) to the trialkylaluminum compound (B) is from 0.2 to 10, and the molar ration of the active hydrogen-containing compound (E) to the trialkylaluminum compound (B) is from 0.1 to 0.8. The process according to claim 1, wherein the molar ratio of the trialkylaluminum compound (B) to nickel chloride (A) is from 2 to 100, the molar ratio of the phosphorus compound (C) to nickel chloride (A) is from 0.1 to 20, the molar ration of the 1,1,1,3,3,3-hexafluoroisopropanol (D) to the trialkylaluminum compound (B) is from 0.5 to 5, and the molar ratio of the active hydrogen-containing compound (E) to the trialkylaluminum compound (B) is from 0.1 to 0.8. The process according to claim 1, wherein the molar ratio of the trialkylaluminum compound (B) to nickel chloride (A) is from 2 to 10, the molar ratio of the phosphorus compound (C) to nickel chloride (A) is from 0.1 to 2, the molar ratio of the 1,1,1,3,3,3-hexafluoroisopropanol (D) to the trialkylaluminum compound (B) is from 1 to 4, and the molar ratio of the active hydrogen-containing compound (E) to the trialkylaluminum compound (B) is from 0.2 to 0.6. The process according to claim 1, wherein the concentration of the catalyst is from 10⁻⁵ to 10⁻¹ mol/liter in terms of the concentration of the nickel component. The process according to claim 1, wherein the trialkylaluminum compound (B) is triethylaluminum. The process according to claim 1, wherein the phosphorus compound (C) is at least one compound selected from the group consisting of tricyclohexylphosphine, tri-isopropylphosphine, tri-n-butylphosphine, tri-sec.-butylphosphine, triphenylphosphine and triphenylphosphite. The process according to claim 8, wherein the phosphorus compound (C) is tricyclohexylphosphine. The process according to claim 1, wherein the active hydrogen-containing compound (E) is at least one compound selected from the group consisting of water, methanol, ethanol, n-propanol, octanol, allyl alcohol, phenol and acetic acid. The process according to claim 10, wherein the active hydrogen-containing compound (E) is methanol. A Ziegler catalyst for carrying out the process according to any of claims 1 to 11 which comprises components (A) to (E) according to claim 1. A catalyst according to claim 12 wherein the molar ratio of the components is as claimed in any of claims 3 to 5. A catalyst according to claim 12 wherein the concentration of the catalyst is from 10⁻⁵ to 10⁻¹ mol/liter in terms of the concentration of the nickel component. A catalyst according to claim 12 wherein component (B) is triethylaluminum. A catalyst according to claim 12 wherein component (C) is as claimed in claim 8 or 9. A catalyst according to claim 12 comprising components (A) to (E) wherein component (E) is as claimed in any of claims 10 or 11.

Inventors: SATO, HIROSHI, TOJIMA, HIDETO, UCHIDA, KENSHI
Applicants: SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1989
Main classification: C07C2
IPC codes: B01J31, C07C2, C07C1, C07B61, C07C11, C07C67