Process for preparing 1-octene

Abstract: This invention relates to a process for producing 1-octenes comprising reacting conjugated dienes and carboxylic acids in the presence of palladium, platinum or ruthenium catalysts to produce 2,7-alkadienyl esters, contacting the 2,7-alkadienyl escers with hydrogen to produce alkyl esters and subsequently pyrolyzing the alkyl esters to produce 1-octene and carboxylic acid.

Description: The invention relates to a process for producing unsubstituted or lower alkyl substituted 1-octenes. This process involves a combined dimerization esterification step whereby a lower molecular weight conjugated diene is reacted with a carboxylic acid in the presence of a Group VIII metal catalyst to produce a 2,7-alkadienyl ester. According to Alpha Olefins Applications Handbook, editors G.R. Lapin and S.D.Sauer, Marcel Dekker Inc. N.Y.,1989, chapter 3 "Routes to Alpha Olefins", alpha olefins are produced commercially by either wax cracking or ethene oligomerisation, the latter being the more recent and currently preferred process. Different catalytic ethene oligomerisation processes are disclosed in e.g. EP-B 0 033 553 and EP-A 0 435 367. Both wax cracking and ethene oligomerisation produce a more or less wide range of linear and branched olefins, out of which individual products have to be separated. The step of simultaneously dimerizing a conjugated olefin and esterfying it with a carboxylic acid utilizing a Group VIII catalyst is known in the art. U.S. Patent Specifications 3,407,224, 3,534,088 and 3,562,314 disclose the preparation of 2,7-alkadienyl esters utilizing Group VIII catalysts. The details given in these three references are applicable to the dimerisation esterification step in the present process as well. British Patent Specification 999,725 discloses, as a last step in a process for the preparation of 3-ethyl-1-heptene from 2-ethyl-1-hexene, the pyrolysis of 3-ethylheptyl acetate over glass chips at 500 °C. It has now been found that in a three step process, including the aforesaid dimerization esterification step, conjugated dienes can be converted to (lower alkyl substituted) 1-octenes. The product 1-octenes are suitable for use as co-monomers in the polymerization of polyethylene to produce unique polymer products. The invention can be defined as relating to a process for the production of 1-alkenes of the following general formula: wherein R₁, R₂, R₃ and R₄ are independently hydrogen or C₁-C₃-alkyl which process comprises: a) contacting (1) a carboxylic acid having no active hydrogen atoms not present in carboxyl groups and being free from non-aromatic carbon-carbon unsaturation with (2) from 0.25 mole to 10 moles per mole of carboxy group, of conjugated diene selected from and mixtures thereof, wherein R₁, R₂, R₃ and R₄ are independently hydrogen or C₁-C₃-alkyl in the presence of a metal containing catalyst whereby the metal is selected from palladium, platinum and/or ruthenium to produce a 2,7-alkadienyl ester, b) contacting the 2,7-alkadienyl ester product of step (a) with hydrogen and a hydrogenation catalyst to produce the corresponding alkyl ester, and c) heating the alkyl ester of step (b) to a temperature between 350 °C and 600 °C to produce the corresponding alkene of the general formula I. The conjugated diene employed as a reactant in the first step of the process of the invention is an alpha, omega-conjugated alkadiene having only hydrogen substituents on the terminal carbon atoms of the four-carbon chain. Dienes that possess non-hydrogen substituents on the internal, i.e., non-terminal, carbon atoms are suitably employed, provided that the internal-carbon atom substituents do not unduly sterically hinder the diene dimerization. A preferred class of diene reactants comprises butadiene having from 0 to 2 internal-carbon methyl substituents. These diene compounds are butadiene, isoprene and 2,3-dimethylbutadiene. Of these, butadiene is particularly preferred. In general, these diene compounds will have the following general formula: where R₁ and R₂ are independently hydrogen or lower alkyl (C₃ or less) or more particularly methyl. The carboxylic acid employed as a reactant in the first step of the process of the invention contains at least one carboxy group, i.e., a -CO₂H group and may be of complex or of comparatively simple structure. Best results are obtained when a carboxylic acid of relatively simple structure is employed, and a preferred class of organic carboxylic acids comprises carboxylic acids of up to 20 carbon atoms and having from 1 to 4 carboxy groups, preferably 1 to 2 carboxy groups, present within the molecular structure and having no active hydrogen atoms other than that (those) of the carboxy group(s). The organic carboxylic acid reactant is suitably wholly aliphatic in character, wholly aromatic in character or incorporates both aliphatic and aromatic moieties; however, the carboxylic acid reactant is free of carbon-carbon unsaturation other than that of any aromatic moieties present within the molecule, that is, the carboxylic acid reactant is free of non-aromatic carbon-carbon unsaturation. Expressed in alternate terms, the carboxylic acid reactant has only aromatic carbon-carbon unsaturation, that is, any carbon-carbon unsaturated present within the reactant molecule is aromatic carbon-carbon unsaturation. The carboxylic acid reactant is a hydrocarbon carboxylic acid containing only atoms of carbon and hydrogen besides the oxygens of the carboxy group(s) present, or is a substituted-hydrocarbon carboxylic acid containing, in addition to atoms of carbon, hydrogen and carboxy oxygen, atoms of halogen, oxygen atoms other than carboxy oxygen atoms, and nitrogen, which additional atoms are present in functional groups such as oxy, keto, carbonyloxy, halo, tertiary amino and like groups. In general, carboxylic acid reactants which are hydrocarbon carboxylic acids as above defined or additionally have present atoms of halogen, are preferred over carboxylic acids with other functional groups. The process of the invention is particularly useful when monocarboxylic acids are employed, particularly hydrocarbon monocarboxylic acids of up to 12 carbon atoms. Particularly preferred are the lower hydrocarbon, particularly alkyl, monocarboxylic acids of up to 3 carbon atoms. Representative preferred acids are acetic acid, trifluoroacetic acid and propionic acid, butyric and valeric acid. Illustrative of suitable carboxylic acid reactants are wholly aliphatic carboxylic acids including hydrocarbon aliphatic carboxylic acids, both acyclic and cyclic, such as formic acid, acetic acid, butyric acid, 2-ethylhexanoic acid, dodecanoic acid, glutaric acid, adipic acid, hexadecadioic acid, 2-methylglutaric acid, oxalic acid, cyclopentanecarboxylic acid, tetrahydronaphthalene-1-carboxylic acid, 1,4-dicarboxycyclohexane, 1,2,4,5-tetracarboxycyclohexane, 2-(carboxymethyl)glutaric acid and 1,4-bis(carboxymethyl)cyclohexane; as well as substituted-hydrocarbon aliphatic carboxylic acids, both acyclic and cyclic, as exemplified by chloroacetic acid, trifluoroacetic acid, trichloroacetic acid, 3-acetoxypropionic acid, 4-bromocyclohexane-carboxylic acid, N-methylpiperidine-2-carboxylic acid, 2-ethoxyethanoic acid, 2,2-dichloropropionic acid, 6-dimethylaminohexanoic acid, 4-chloro-3-methoxybutyric acid, 2,3-dichlorobutandioic acid, 3-chloromethylcyclopentane-carboxylic acid, tetrahydropyran-2-carboxylic acid, bis(2-carboxyethyl)ether and 2-trichloromethylsuccinic acid. Also suitable are carboxylic acid reactants which are wholly aromatic in character, both alicyclic and heterocyclic, as illustrated by hydrocarbon aromatic carboxylic acids such as benzoic acid, terephthalic acid, phthalic acid, naphthalene-1-carboxylic acid, pyromellitic acid, naphthalene-1,4-dicarboxylic acid and the like, as well as wholly aromatic substituted-hydrocarbon carboxylic acids including p-chlorobenzoic acid, pyridine-2-carboxylic acid, m-bromobenzoic acid, 4-chlorophthalic acid, 4,6-dibromonaphthalene-2-carboxylic acid, 2-carboxyquinoline and bis(4-carboxyphenyl)ether. Carboxylic acids having both aromatic and aliphatic moieties are also suitably employed as reactants in the process of the invention. Such acids are exemplified by hydrocarbon carboxylic acids including phenylacetic acid, p-tert-butylbenzoic acid, m-toluic acid, 2,2-bis(4-carboxyphenyl)propane, tetrahydronaphthalene-2-carboxylic acid, p-octylbenzoic acid, 4-(p-tolyl)butyric acid, 4,4′-dicarboxy-2,2′-diethylphenyl,3,5-dimethylbenzoic acid and 5-methylisophthalic acid; as well as by substituted-hydrocarbon carboxylic acids, for example, p-trichloromethylbenzoic acid, m-dimethylaminobenzoic acid, 2-(p-chlorophenyl)maleic acid, 3-phenoxypropionic acid, bis(4-carboxyphenylmethyl) ether, p-(benzoyloxy)phenylacetic acid, m-perchloroethylbenzoic acid, 2,3-dibromoterephthalic acid and the like. The optimum ratio of carboxylic acid reactant to conjugated diene reactant viii depend in part upon the functionality of the carboxylic acid reactant, that is, the number of carboxy groups present in the carboxylic acid reactant molecule, as well as the reactant conversion that is desired. Ratios of moles of diene to moles of carboxy group as low as 1:4 are suitable if only a low conversion is employed. However, to obtain higher conversions, a more substantial proportion of diene is preferred and ratios of moles of diene to moles of carboxy group from 1:1 to 10:1 are more satisfactory, with best results being obtained when ratios of moles of diene to moles of carboxy group from 2:1 to 6:1 are utilized. It should be understood that it is within the contemplated scope of the invention to esterify each carboxy group of the carboxylic acid reactant or only a portion of the total number of carboxy groups. In the latter instance, such restrictive esterification is favoured by a molar reactant ratio relatively low in the diene reactant. The catalyst employed in the first step of the process of the instant invention is a metal compound wherein the metal is selected from palladium, platinum, ruthenium and mixtures thereof. Particularly preferred is palladium. In one particular modification of the invention, the metal-containing catalyst is introduced as a salt, and palladium, platinum or ruthenium salts of organic or inorganic acids which are strong or weak acids are suitable. Illustrative examples include the halide and oxalate salts. Also suitable are salts wherein the metal is present in the anion as, for example, the use of chloropalladate salt or chloroplatinate salts. Metal complexes may also be suitably used, such as, complexes with tertiary nitrogen-containing ligands. The known π-allyl complexes are also suitably used. Without wishing to be bound by any particular theory, it appears that the chemical transformations during the course of the reaction which involve the metal compound in the first step of the present process are quite complex, probably involving the formation and destruction of complexes between the metal moiety and the diene reactant and/or the presumed diene dimer intermediate. Metal compounds that are soluble in the reaction medium as well as compounds that are superficially insoluble in the reaction system are operable, apparently in the latter case through dissolved metal compound moieties, the formation of which is probably influenced by interaction with the diene reactant and/or the carboxylic acid reactant and the solubilization, resulting therefrom. To obtain optimum reaction rates, the metallic compound is preferably soluble in the reaction mixture or serves as a precursor of a soluble metal compound. It is apparent, however, that the metal-containing catalyst may be employed in any form which serves to introduce the metal compound into the reaction system. The first step of the process of the invention is suitably carried out in the presence of only catalytic quantities of platinum, palladium or ruthenium compound. Although utilization of larger amounts of metal-containing catalyst are not detrimental to the process of the invention, amounts larger than about 1% mole based on total reactants are not generally required. Amounts of metal compound less than 0.001% mole on the same basis are generally unsuitable because of the inevitable physical losses of catalyst during reaction and processing. In general, amounts of catalyst from 0.01% mole to 0.5% mole based on total reactants are satisfactory and are preferred. The use of promoters, such as the phenoxide promoter disclosed in U.S. 3,407,224 can also be suitable utilized. The first step of the process of the invention is typically conducted by charging the reactants, catalyst and optional catalyst promoter to an autoclave or similar reactor and maintaining the reaction mixture at reaction temperature until reaction is complete. The method of mixing is not critical. The reaction is suitably conducted throughout a wide range of reaction temperatures and pressures, so long as the reactants are maintained substantially in the liquid phase. Reaction temperatures from -20 °C to 150 °C are satisfactory, although temperatures from 0 °C to 130 °C are preferred and best results are obtained when a temperature from 25 °C to 125 °C is employed. Typical reaction pressures vary from about 100-8000 kPa (1 atmosphere to 80 atmospheres). Frequently, good results are obtained when the reaction pressure is autogenous, that is, the pressure generated when the reactants are maintained at reaction temperature in a sealed reaction vessel. Such pressures are from about 100-2000 kPa (1 atmosphere to 20 atmospheres). The first step of the process of the invention is conducted in the presence or in the absence of a solvent. In the modification wherein solvent is employed, solvents that are most suitable are those capable of dissolving the reactants, catalyst and catalyst promoter, and are inert to the reactants and the products prepared therefrom. Exemplary solvents are ethers, including dialkyl ethers such as diethyl ether, dibutyl ether and methyl hexyl ether; alkyl aryl ethers such as anisole and phenyl butyl ether; cyclic ethers such as tetrahydrofuran, dioxane and dioxolane; and lower alkyl ethers (full) of polyhydric alcohols or polyoxyalkylene glycols such as ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and glycol triethyl ether; aromatic hydrocarbons such as benzene, toluene and xylene; N,N-dialkyl alkanoic acid amides, e.g., dimethylformamide and N,N-diethylacetamide; halogenated hydrocarbons such as chloroform, carbon tetrachloride, tetrachloroethylene, methylene chloride and bromoform; sulphoxides such as dimethylsulphoxide; and nitriles such as acetonitrile and benzonitrile. The solvent, if any, is employed in molar excess over the amount of total reactants, and in general, moles of solvent up to 150 moles per mole of total reactants are satisfactory. For convenience, it is generally preferable to conduct the reaction in the absence of added solvent whenever the physical characteristics of the system at reaction temperature, particularly the melting point thereof, will allow. For example, when the process of the invention is employed with a reaction mixture normally liquid at reaction temperature, the process is typically conducted in the absence of solvent. Alternatively, if the reaction mixture is unduly viscous or normally solid at the reaction temperature, solvent is preferably employed to maintain the reactants in the liquid phase. Subsequent to the first step of the reaction, the reaction mixture may be separated and a desired 2,7-alkadienyl ester is recovered by conventional means such as selective extraction, fractional distillation and chromatographic techniques, which ester is fed to the second step of the instant process. Alternatively, the reaction mixture from the first step may be fed directly to the second step. The second step of the instant process comprises taking the 2,7-alkyldienyl esters of the first step and hydrogenating them by contact with hydrogen and a hydrogenation catalyst to produce the corresponding alkyl esters. The hydrogenation catalysts utilized in the instant invention can be any of the known hydrogenation catalysts, either heterogeneous or homogeneous catalysts. Typical known hydrogenation catalysts useful in this step of the process comprise the Group VIII metals of the periodic table, i.e., of those containing atomic numbers 26 through 78, particularly those containing atomic numbers 28 through 78. Other known catalysts suitable for hydrogenation in the second step of the instant process include the oxides and sulphides of Group VI, i.e., Cr, Mo and W. The palladium, platinum and ruthenium catalysts utilized the first step of the instant process may also be suitably be utilized in the second step to provide hydrogenation activity. In the latter instance, the catalyst may be from a recycled stream of the first step of the instant process. The second step of the instant process involves hydrogenation in the presence of hydrogen. The hydrogen may be provided to the reaction mixture as pure hydrogen or diluted wish other gases such as the inert gases or for example, may be present in a process gas such as syngas which is utilized to provide the hydrogen. The hydrogenation step can be carried out in either a batch process or in a continuous process. In a batch process a homogeneous or heterogeneous catalyst is charged to the reactor along with the reactants and pressured with hydrogen, or a hydrogen-containing gas and allowed to react at the appropriate temperature to hydrogenate the alkyldienyl esters. In a continuous process the catalyst is provided in the form of a packed bed of solid catalyst, preferably supported metal catalyst, and the alkyldienyl ester and hydrogen are simultaneously passed through the bed, which is maintained at reaction conditions. The hydrogenation step is conducted in the presence or absence of a solvent. Preferred solvents are those which are inert to the hydrogenation conditons. Exemplary solvents are those noted above as being useful in the first step of the instant process. The appropriate reaction temperature will vary widely depending on the particular hydrogenation catalyst utilized and its activity. Typical hydrogenation temperatures will range from 0 °C to 200 °C. Typical hydrogenation pressures will range from about atmospheric to say 10 bar or higher. Subsequent to the reaction of this second step of the process, the reaction mixture is suitably separated and the desired alkyl ester product recovered by conventional means such as selective extraction, fractional distillation and chromatographic techniques. When high activity heterogeneous hydrogenation catalysts and purified 2,7-alkyldienyl esters feedstocks are utilized, recovery techniques can be quite simple, involving a simple separation of unreacted gaseous material from the product alkyl esters. The third step of the instant process comprises taking the alkyl esters of the second step and heating or pyrolyzing them at elevated temperatures to cause a disassociation of the alkyl ester into 1-alkene and carboxylic acid. The pyrolysis involves passing the alkyl esters through a heated reactor maintained at a temperature ranging from 350 °C to 600 °C. Preferably the temperature will range from 400 °C to 550 °C. Pyrolysis reactors are known in the art. Typical examples of suitable pyrolysis reactors that are suitable for use in the third step of the instant process comprise tubular reactors and packed columns. There are no particular pressure limitations on the pyrolysis reaction, and typically the reaction is carried out at about atmospheric pressure. Subsequent to reaction, the reaction mixture is separated into the desired 1-alkene product, unreacted alkyl esters and the regenerated carboxylic acids. The unreacted alkyl esters may be recycled to the start of the third step of the instant process and the regenerated carboxylic acids may be recycled to the first step of the instant process. Depending on pyrolysis conditions, the carboxylic acid anhydride may be produced in addition to the starting carboxylic acid. The anhydride is readily converted by hydrolysis to the acid for recycle. The above indicated ranges and limitations are those which are believed to be particularly suitable in the process according to the invention. It will, however, be understood that other ranges and limitations that perform substantially the same function in substantially the same manner to obtain the same or substantially the same result are intended to be within the scope of the instant invention as defined by the instant specification and claims. The process of the instant invention will be illustrated by the following examples. Example 1 Step 1: 2,7-alkyldienyl ester preparation To a 300 ml autoclave were added approximately 4.45 mmoles of palladium acetate dissolved in about 40 ml of benzene, and 42 g (0.7 mol) of acetic acid. The reactor was then charged with about 80 g of 1,3-butadiene. The reactor was heated at about 45-55 °C for about 25 hours, cooled and vented off of 19 liters of gas. The autoclave contents were 104.5 g of colourless liquid product and a black precipitate (spent catalyst). 100 ml of n-hexane were added to the liquid product and the resultant mixture was extracted with 100 ml of water. This extraction process was repeated utilizing two additional 15 ml portions of water. The remaining organic phase was distilled, separating the hexane from the 2,7-octadienyl ester product. Step 2: Hydrogenation Process The 2,7-octadienyl product of step 1 was hydrogenated at 25-31 °C with 1.75 MPa hydrogen using 0.6 g of 5% palladium supported on barium sulfate. The hydrogenated product was filtered and 29.7 g were recovereo. NMR analysis showed the product to be 95% 1-acetoxyoctane and 5% 3-acetoxyoctane. Step 3: Pyrolysis 30 ml of the 95% 1-acetoxyoctane and 5% 3-acetoxyoctane product from step 2 was diluted with 60 ml n-heptane and pumped into a Vicor tube at a rate of 8 ml per hr along with 10 ml per minute of nitrogen. Approximately 6 inches of the tube was heated to about 500 °C. The product was collected in cold traps. Analysis of the product (excluding n-heptane) gave the following weight percent: C₃ and C₄ hydrocarbons = 3.3; acetic acid = 22.2; 1-octene = 48.6; internal octenes = 4.6 and the remaining acetoxyoctane = 21.3. Example 2 2,7-Octadienyl trifluoroacetate was prepared by reacting 1 g of palladium acetate in 20 ml of benzene with 102 g of trifluoroacetic acid and 0.96 M butadiene in a 300 ml autoclave at ambient temperature for 4 days. The resultant 2,7-octadienyl trifluoroacetate was hydrogenated at 1.05 MPa of hydrogen at ambient temperature using 5% palladium on BaSO₄ to produce trifluoroacetoxyoctane. The resultant trifluoroacetoxyoctane was decarboxylated at temperatures ranging from 400-450 °C to trifluoroacetic acid and product 1-octene. Percent conversions ranged from about 45 to 90%.

Claims: A process for the production of 1-alkenes of the following general formula: wherein R₁, R₂, R₃ and R₄ are independently hydrogen or C₁-C₃-alkyl which process comprises: a) contacting (1) a carboxylic acid having no active hydrogen atoms not present in carboxyl groups and being free from non-aromatic carbon-carbon unsaturation with (2) from 0.25 mole to 10 moles per mole of carboxy group, of conjugated diene selected from and mixtures thereof, wherein R₁ R₂, R₃ and R₄ are independently hydrogen or C₁-C₃-alkyl in the presence of a metal containing catalyst whereby the metal is selected from palladium, platinum and/or ruthenium to produce a 2,7-alkadienyl ester, b) contacting the 2,7-alkadienyl ester product of step (a) with hydrogen and a hydrogenation catalyst to produce the corresponding alkyl ester, and c) heating the alkyl ester of step (b) to a temperature between 350 °C and 600 °C to produce the corresponding alkene of the general formula I. A process according to claim 1, characterized in that in step a) a homogeneous catalyst is applied. A process according to claim 1 or 2, characterized in that step a) is carried out at a temperature in the range of -20 to 150 °C. A process according to claim 3, characterized in that step a) is carried out at a temperature in the range of 25 to 125 °C. A process according to one or more of claims 1-4, characterized in that the carboxylic acid used in step a) is selected from hydrocarbon cyclic and acyclic carboxylic acids, halohydrocarbon cyclic and acyclic carboxylic acids of up to 4 halogen atoms, hydrocarbon aromatic carboxylic acids and halohydrocarbon aromatic carboxylic acids of up to 4 halogen atoms, which acids have up to 20 carbon atoms and from 1 to 4 carboxy groups. A process according to claim 5, characterized in that the carboxylic acid is acetic acid or trifluoroacetic acid. A process according to one or more of claims 1-6, characterized in that the conjugated diene is butadiene. A process according to one or more of claims 1-7, characterized in that step c) is carried out at a temperature in the range of 400 to 550 °C.

Inventors: SLAUGH LYNN HENRY, SLAUGH, LYNN HENRY
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1990
Main classification: C07C1
IPC codes: C07C1, C07B61, C07C67, B01J31, C07C11