PROCESS FOR THE DIMERIZATION OF OLEFINS

Abstract: A process for the dimerization of alpha-alkenes having 2 to 12 C atoms in the presence of an alkanediol solvent and of a novel catalytic system formed by combining:- a) a palladium(II) compound, b) a chelate ligand comprising a compound containing at least two N coordinating atoms which are connected through a chain comprising two C atoms, > 2.0 mol chelate ligand per gram-atom Pd being used, c) a protonic acid, except hydrohalogenic acids, and d) a salt of Cu, Fe, Zn, Sn, Mn, V, Al or a Group 6b metal, except a halide.

Description: The invention relates to a process for the dimerization in the liquid phase of an alpha-alkene having in the range of from 2 to 12 carbon atoms per molecule. The invention also relates to a novel catalytic system. It is known from EP-A-0 170 311 to dimerize an alpha-alkene having in the range of from 2 to 12 carbon atoms per molecule in the presence of a catalytic system formed by combining, in the presence of water, an alcohol, or a carboxylic acid:- a) a palladium(II) compound, b) a chelate ligand comprising a compound containing as coordinating atoms at least two nitrogen atoms which are connected through a chain comprising two carbon atoms, and c) a compound containing an anion of an acid, with the exception of hydrohalogenic acids. The reaction mixture obtained by means of this known process may comprise a two-phase liquid system: a liquid dimer phase and a liquid solvent phase containing the catalytic system. Both phases can easily be separated by means of mechanical separation and the separated solvent phase containing the catalytic system can be used for dimerizing further quantities of alpha-alkenes. It has been observed that the dimer phase contains a portion of the chelate ligand and the solvent phase has a correspondingly reduced content thereof. This reduced content of chelate ligand may lower the catalytic activity of the catalytic system, particularly when considerably less than 2 mol of chelate ligand per gram-atom of palladium(II) remains. Starting this known process by using more than 2 mol of the chelate ligand per gram-atom of palladium(II) would compensate for said loss of chelate ligand, but renders the catalyst less active. A novel catalytic system has now been found that is surprisingly active when more than 2 mol of the chelate ligand per gram-atom of palladium are used. Accordingly, the invention provides a process for the dimerization in the liquid phase of an alpha-alkene having in the range of from 2 to 12 carbon atoms per molecule in which the dimerization is carried out in the presence of an alkanediol solvent and of a catalytic system formed by combining:- a) a palladium(II) compound, b) a chelate ligand comprising a compound containing as coordinating atoms at least two nitrogen atoms which are connected through a chain comprising two carbon atoms, more than 2.0 mol of the chelate ligand per gram-atom of palladium(II) being used, c) a protonic acid, with the exception of a hydrohalogenic acid, and d) a salt of copper, iron, zinc, tin, manganese, vanadium, aluminium or of a metal of Group 6b of the Periodic Table of the Elements, with the exception of a halide. It has, surprisingly, been found that the presence of both the protonic acid and said salts has a synergistic effect on the activity of the catalytic system vis-à-vis the presence of the protonic acid alone and of said salts alone. Simultaneously, a very high selectivity to dimers, usually higher than 95%, has been observed. The selectivity to dimers is defined as the molar percentage of dimers in the product formed. Alpha-alkenes having in the range of from 2 to 12 carbon atoms which can be used in the process according to the present invention may be linear or branched, such as, for example, ethene, propene, 1-butene, 1-pentene, 1-hexene, 5-methyl-1-hexene, 1-octene and 1-dodecene. The preferred alpha-alkenes are ethene, propene and 1-butene. The word "dimerization" as it is used herein, refers to the reaction of two identical olefins as well as the reaction of two different olefins. An example of the latter reaction is that between ethene and propene, or between propene and 1-butene. According to the invention, both homogeneous and heterogeneous catalytic systems can be used. The use of homogeneous catalytic systems is preferred. Palladium(II) compounds which can be used in the process according to the invention therefore preferably comprise palladium(II) compounds which are soluble in the reaction medium or form in situ soluble compounds therein. Examples of suitable palladium(II) compounds are palladium nitrate, palladium sulphate and palladium carboxylates, preferably carboxylates of carboxylic acids having not more than 12 carbon atoms per molecule. Palladium alkanoates, in particular palladium acetate, are preferably used. Further examples of suitable palladium compounds are palladium complexes such as bis(2,4-pentanedionato)palladium, bis(picolinato)palladium, tetrakis(triphenylphosphine)palladium, tetrakisacetonitrile palladium tetrafluoroborate, bis(tri-o-tolylphosphine)palladium acetate, bis(triphenylphosphine)palladium sulphate, palladium olefin complexes and palladium-hydride complexes. A mixture of palladium(II) compounds may be present in the catalytic system. The quantity of the palladium compound used may vary within wide ranges and is generally in the range between 10⁻⁶ and 10⁻¹ gram-atom palladium per mol olefin starting material. A range between 10⁻⁵ and 10⁻² gram-atom palladium compound is preferred. Preference is given to chelate ligands containing in the molecule a group of the formula wherein the dotted line represents several kekule resonance structures in case of condensed aromatic ring systems as e.g. occurring in 1,10-phenanthroline. For example N,N′-1,2-ethanediylidenebisphenylamine, N,N′-1,2-ethanediylidenebis[4-chlorophenylamine], N,N′-1,2-ethanediylidenebis[4-methoxyphenylamine], N-substituted derivatives of 2-pyridinemethanimine, 2,2′-bipyridyl, 4,4′-dimethyl-2,2′-bipyridyl, 4,4′-dichloro-2,2′-bipyridyl, 4,4′-dimethoxy-2,2′-bipyridyl, 1,10-phenanthroline, 5-chloro-1,10-phenanthroline, 4,7-diphenyl-1,10-phenanthroline, 4,7-dimethyl-1,10-phenanthroline, 2,9-dichloro-1,10-phenanthroline, 1,10-phenanthroline-5-sulphonic acid and salts thereof, 4,7-diphenyl-1,10-phenanthrolinedisulphonic acid and salts thereof, and 3,5-cyclohexadiene-1,2-diimine may be used. The compounds preferably used in the catalytic system used in the process according to the invention are 1,10-phenanthroline or a derivative thereof and 2,2′-bipyridyl or a derivative thereof. Most preferred is 1,10-phenanthroline. A mixture of chelate ligands may be used, for example of 1,10-phenanthroline and 2,2′-bipyridyl. The quantity of chelate ligand used in the catalytic system is at least 2.0 mol per gram-atom of palladium(II) and is preferably in the range of from 2.5 to 25 mol per gram-atom palladium(II). Any protonic acid, with the exception of hydrohalogenic acids, and any salt of a protonic acid and derived from copper, iron, zinc, tin, manganese, vanadium, aluminium or of a Group 6b metal, with the exception of a halide, may be present. The acid and salt preferably have a non-coordinating anion, by which is meant that little or no covalent interaction takes place between the palladium(II) and the anion. Typical examples of such anions are PF₆⁻, SbF₆⁻, BF₄⁻ and ClO₄⁻. The protonic acid and the acid from which the salt is derived preferably have a pKa of less than 3 and, more preferably, less than 2, measured in aqueous solution at a temperature of 18 °C. Preferred protonic acids are sulphonic acids and acids that can be formed, possibly in situ, by interacting a Lewis acid such as, for example, BF₃, AsF₅, SbF₅, PF₅, TaF₅ or NbF₅ with a Broensted acid such as, for example, a hydrohalogenic acid, in particular HF, fluorosulphonic acid, phosphoric acid or sulphuric acid. Specific examples of acids of the latter type are fluorosilicic acid, HBF₄, HPF₆ and HSbF₆. Examples of usable sulphonic acids are fluorosulphonic acid and chlorosulphonic acid and the hereinafter specified sulphonic acids. A preferred group of protonic acids has the general formula I wherein Z represents sulphur or chlorine and, if Z is chlorine, R represents oxygen and, if Z is sulphur, R represents an OH group or an optionally substituted hydrocarbon group. When the hereinbefore-stated protonic acids are used in the process according to the invention, the anions of the compounds can be considered to be non-coordinating. The optionally substituted hydrocarbon group represented by R is preferably an alkyl, aryl, aralkyl or alkaryl group having 1 to 30, in particular 1 to 14, carbon atoms. The hydrocarbon group may, for example, be substituted with the halogen atoms, in particular fluorine atoms. Examples of suitable acids of the general formula I are perchloric acid, sulphuric acid, 2-hydroxypropane-2-sulphonic acid, benzenesulphonic acid, 1- and 2-naphthalenesulphonic acid, p-toluenesulphonic acid and trifluoromethanesulphonic acid, the last two acids being the most preferred. Examples of suitable carboxylic acids are formic acid, acetic acid, monochloroacetic acid, dichloroacetic acid, trichloroacetic acid and, which is preferred, trifluoroacetic acid. A mixture of protonic acids may be present in the catalytic system. Among the salts that are present preference is given to copper and iron salts, such salts imparting a very high activity to the catalytic system. Among the Group 6b metals chromium is preferred. A mixture of two or more of the metals may be present, for example of copper and iron, or of copper and vanadium. Among the salts sulphates, p-tosylates and tetrafluoroborates are preferred. Very good results have been obtained with sulphates and p-tosylates. The protonic acid and the salt may have the same or different anions. For example, a mixture of p-toluenesulphonic acid and a sulphate may be used. The protonic acid and the salt are preferably used in a total quantity in the range of from 0.01 to 150 and in particular 1 to equivalents per gram-atom palladium. The amount of protonic acid which is used per equivalent of salt is not critical and may vary within wide ranges. Preferably, in the range of from 0.1 to 10 equivalents of the protonic acid per equivalent of said salt is used. However, amounts of less than 0.1 and more than 10 equivalents are not excluded. It will be appreciated that when the catalytic system applied in the process according to the invention is formed by combining in situ the required ingredients, a palladium complex compound with catalytic activity may be formed in the reaction mixture. An example of such a compound is palladium bis(1,10-phenanthroline)diperchlorate or ditosylate. The use of such a palladium complex compound when prepared separately as as catalytic system is within the scope of the present invention. In the process of the invention the catalytic system is used in the presence of an alkanediol solvent. Very good results have been obtained with ethylene glycol. Other examples of suitable alkanediol solvents are 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,6-hexanediol and polyethylene glycols such as diethylene glycol. The presence of a co-solvent is not excluded. Examples of co-solvents are alcohols, carboxylic acids and water. The alcohols or carboxylic acids may be aliphatic, cycloaliphatic or aromatic and may be substituted with one or more substituents, for example alkoxy, cyano or ester groups or halogen atoms. The alcohols or carboxylic acids preferably contain not more than 20 carbon atoms per molecule. Examples of suitable alcohols are methanol, ethanol, propanol, isobutyl alcohol, tert.butyl alcohol, stearyl alcohol, benzyl alcohol, cyclohexanol, allyl alcohol and chlorocapryl alcohol. Further examples of co-solvents are hydrocarbons, for example hexane and in particular aromatic hydrocarbons such as benzene or toluene; halogenated hydrocarbons such as chloroform, chlorobenzene or perfluoroalkanes; ketones such as acetone, diethyl ketone or methyl isobutyl ketone; ethers such as tetrahydrofuran, dimethyl ether of diethylene glycol (also referred to as "diglyme"), methyl t-butyl ether or 1,4-dioxane; sulphones such as dimethyl sulphone, methyl butyl sulphone, tetrahydrothiophene 1,1-dioxide (also referred to as "sulfolane"), and sulphoxides such as dimethyl sulphoxide or diethyl sulphoxide. The process according to the present invention can be carried out at temperatures of up to 200 °C and preferably in the range between 20 °C and 135 °C. The pressure preferably lies between 1 and 100, in particular between 20 and 75, bar gauge. The process according to the invention can be carried out batchwise, semi-continuously or continuously. The reaction time may vary in relation to the temperature used, between 0.5 and 20 hours. The dimers may be isolated from the reaction mixture obtained in any suitable manner, for example by mechanically separating the reaction mixture into a liquid dimer phase and a liquid solvent phase. The liquid dimer phase may then be separated by distillation. The dimers are suitable as a feedstock for hydroformylation processes wherein an alkene or a mixture of alkenes is reacted with hydrogen and carbon monoxide in the presence of a hydroformylation catalyst, to produce aldehydes and/or alcohols. Where the product is mainly aldehyde a separate hydrogenation is required to form alcohols. The products obtained by the process according to the present invention require only distillation to separate unconverted mono-olefin and heavy ends before use in a hydroformylation process. The invention further provides a novel catalytic system formed by combining:- a) a palladium(II) compound, b) a chelate ligand comprising a compound containing as coordinating atoms at least two nitrogen atoms which are connected through a chain comprising two carbon atoms, more than 2.0 mol of the chelate ligand per gram-atom of palladium(II) being used, c) a protonic acid, with the exception of a hydrohalogenic acid, and d) a salt of copper, iron, zinc, tin, manganese, vanadium, aluminium or of a metal of Group 6b of the Periodic Table of the Elements, with the exception of a halide. The following Examples further illustrate the invention. In all Examples the hexenes formed had a linearity of about 60%. EXAMPLES 1-9 A 300 ml magnetically stirred Hastelloy C autoclave ("Hastelloy" is a trade mark) was charged with ethylene glycol (50 ml), palladium(II) acetate (0.5 mmol), 1,10-phenanthroline (2 mmol) and p-toluenesulphonic acid (2 mmol). In each of these nine examples the autoclave was also charged with a salt, as detailed in Table 1 hereinafter; this table also shows the amounts in which these salts were used. Then, the autoclave was flushed with propene, charged with 50 ml of liquid propene and heated to a temperature of 80 °C. After the reaction time indicated in Table 1 the contents of the autoclave were analyzed by gas/liquid chromatography. Table 1 presents the conversion of propene and the selectivity to hexenes. The selectivity to nonenes is the difference between 100% and the selectivity to hexenes. EXAMPLE 10 Example 2 was repeated with the difference that the temperature was 75 °C instead of 80 °C. The conversion of propene was 80% after 5 hours and the selectivities to hexenes and nonenes were 86.7% and 13.3%, respectively. Comparative Experiment A Example 2 was repeated with the difference that copper(p-tosylate)₂ was not present and that 4 mmol instead of 2 mmol of p-toluenesulphonic acid was used. After 5 hours a conversion of propene of only 10% was observed. Comparative Experiment B Example 2 was repeated with the difference that p-toluenesulphonic acid was not present and that 2.0 mmol instead of 1.0 mmol of copper(p-tosylate)₂ was used. After 5 hours a conversion of propene of only 35% was observed. Prolonging the reaction time beyond 5 hours did not further increase the conversion. Comparative Experiment C Example 2 was repeated with the difference that Zr(SO₄)₂ (1 mmol) instead of Cu(p-tosylate)₂ (1.0 mmol) was used. After 5 hours a propene conversion of only 10% was observed. Comparative Experiment D Example 2 was repeated with the difference that UO₂SO₄ (1 mmol) instead of Cu(p-tosylate)₂ (1.0 mmol) was used. The conversion of propene was less than 5% after 5 hours. Comparative Experiment E Example 3 was repeated with the difference that p-toluenesulphonic acid (2 mmol) was not present and that 2 mmol FeSO₄ instead of 1 mmol FeSO₄ was present. The conversion of propene was less than 5% after 5 hours. Comparative Experiment F Example 3 was repeated with the difference that NiSO₄ (1.0 mmol) instead of FeSO₄ (1.0 mmol) was present. The conversion of propene was less than 10% after 5 hours.

Claims: A process for the dimerization in the liquid phase of an alpha-alkene having in the range of from 2 to 12 carbon atoms per molecule in which the dimerization is carried out in the presence of an alkanediol solvent and of a catalytic system formed by combining:- a) a palladium(II) compound, b) a chelate ligand comprising a compound containing as coordinating atoms at least two nitrogen atoms which are connected through a chain comprising two carbon atoms, more than 2.0 mol of the chelate ligand per gram-atom of palladium(II) being used, c) a protonic acid, with the exception of a hydrohalogenic acid, and d) a salt of copper, iron, zinc, tin, manganese, vanadium, aluminium or of a metal of Group 6b of the Periodic Table of the Elements, with the exception of a halide. A process as claimed in claim 1 in which the metal of Group 6b is chromium. A process as claimed in claim 1 in which a copper or an iron salt is used. A process as claimed in any one of the preceding claims in which the protonic acid and the acid from which said salt is derived have a pKa of less than 3, measured in aqueous solution at a temperature of 18 °C. A process as claimed in any one of the preceding claims, in which the protonic acid and said salt have a non-coordinating anion. A process as claimed in any one of the preceding claims, in which the protonic acid and the acid from which said salt is derived is an acid of the general formula I wherein Z represents sulphur or chlorine and, if Z is chlorine, R represents oxygen and, if Z is sulphur, R represents an OH group or an optionally substituted hydrocarbon group. A process as claimed in claim 6 in which the hydrocarbon group R is an alkyl, aryl, aralkyl or alkaryl group having 1 to 30 carbon atoms. A process as claimed in claim 7 in which acid of the general formula I is p-toluenesulphonic acid. A process as claimed in any one of claims 1 to 5 in which said salt is a sulphate or a tetrafluoroborate. A process as claimed in any one of the preceding claims in which the chelate ligand comprises a compound containing in the molecule a group of the formula wherein the dotted line represents several kekule resonance structures in case of condensed aromatic ring systems. A process as claimed in claim 10 in which the chelate ligand comprises 1,10-phenanthroline or a derivative thereof. A process as claimed in claim 10 in which the chelate ligand comprises 2,2′-bipyridyl or a derivative thereof. A process as claimed in any one of the preceding claims in which the chelate ligand is used in amount in the range of from 2.5 to 25 mol per gram-atom palladium(II). A process as claimed in any one of the preceding claims in which the protonic acid and the salt are used in a total quantity in the range of from 1 to 100 equivalents per gram-atom palladium. A process as claimed in any one of the preceding claims in which in the range of from 0.1 to 10 equivalents of the protonic acid per equivalent of said salt are used. A process as claimed in any one of the preceding claims in which the alkanediol solvent is ethylene glycol. A catalytic system formed by combining:- a) a palladium(II) compound, b) a chelate ligand comprising a compound containing as coordinating atoms at least two nitrogen atoms which are connected through a chain comprising two carbon atoms, more than 2.0 mol of the chelate ligand per gram-atom of palladium(II) being used, c) a protonic acid, with the exception of a hydrohalogenic acid, and d) a salt of copper, iron, zinc, tin, manganese, vanadium, aluminium or of a metal of Group 6b of the Periodic Table of the Elements, with the exception of a halide. A catalytic system as claimed in claim 17, which includes a) a palladium(II) alkanoate, b) 1,10-phenanthroline or substituted derivatives thereof or 2,2′-bipyridyl, c) a protonic acid of the general formula I wherein Z represents sulphur or chlorine and if Z is chlorine, R represents oxygen, and if Z is sulphur, R represents an OH group or an optionally substituted hydrocarbon group, and d) a salt of copper, iron or chromium. A catalyst system according to claim 18, which comprises as component (d) a sulphate or p-tosylate.

Inventors: DRENT, EIT
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1988
Main classification: C07C2
IPC codes: C07C11, B01J31, C07B61, C07C67, C07C2, C07C1