Preparation of alkanedioic derivatives

Abstract: The invention relates to a process for the preparation of alkanedioic derivatives, for example alkanedioic diesters, by reaction of an aliphatic conjugated diene such as butadiene with carbon monoxide and a hydroxyl group-containing compound such as a C₁₋₆ alkanol in the presence of a catalyst system comprising a) a source of cationic palladium, b) a first bidentate diphosphine ligand having electron-withdrawing substituents on the phosphorus atoms, c) a second bidentate diphosphine ligand having electron-releasing substituents on the phosphorus atoms, and d) a source of an anion.

Description: This invention relates to a process for the preparation of alkanedioic derivatives by reaction of an aliphatic conjugated diene with carbon monoxide and a hydroxyl group-containing compound in the presence of a palladium catalyst. It is known that conjugated dienes can be carbonylated using various palladium catalysts. Depending on the nature of the hydroxyl group-containing compound used as coreactant, carboxylic esters will be obtained in the presence of alcohols, carboxylic acids in the presence of water, and carboxylic anhydrides in the presence of carboxylic acids. Whilst dienes have two double bonds potentially available for carbonylation, most of the known processes result in the carbonylation of one of these double bonds only, and so in the formation of monofunctional alkenoic derivatives. Should the production of difunctional derivatives be desired, it is required to isolate this alkenoic intermediate product and to subject it to carbonylation of its remaining double bond in a separate step. Thus, EP-A-284170 discloses a process for the preparation of adipic acid or esters, wherein 1,3-butadiene is carbonylated using a catalyst system comprising a palladium compound and a bidentate diphosphine ligand having aromatic substituents on the phosphorus atoms in a first step with formation of a pentenoic acid or ester, subsequent isolation of the pentenoic acid or ester obtained, followed by carbonylation of the isolated pentenoic acid or ester in the presence of a second carbonylation catalyst. The requirement of isolation of the intermediate product renders this known process more laborious. EP-A-198521 discloses a process for the direct conversion of conjugated diene into carboxylic diacids or diesters, wherein use is made of a catalyst system comprising a palladium compound, an aryl-substituted monophosphine, optionally in conjunction with an aryl-substituted bidentate diphosphine, and at least one mol of hydrogen chloride per atom of trivalent phosphorus present in the catalytic system. Due to the corrosive nature of hydrogen chloride, this known process suffers from severe equipment requirements when being conducted on an industrial scale. Also, this known catalyst system leaves room for improvement regarding stability, as the monophosphine component tends to become inactivated under the conditions applied. It has now been found that alkanedioic derivatives can directly be obtained from readily available diene feedstock under mild conditions using a non-corrosive catalyst system. Accordingly, the present invention provides a process as indicated above, which is characterised in that use is made of a catalytic system comprising: a) a source of cationic palladium, b) a first bidentate diphosphine ligand having electron-withdrawing substituents on the phosphorus atoms, c) a second bidentate diphosphine ligand having electron-releasing substituents on the phosphorus atoms, and d) a source of an anion. This process is advantageous in offering a direct route to alkanedioic derivatives, such as adipate esters, as shown in the below examples, as well as using a catalyst system of improved stability. As used herein, the term "conjugated diene" refers to dienes having at least two double bonds which alternate with single bonds such as, for example, 1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 1,3-cyclohexadiene, 2,4-heptadiene, or 2-methyl-1,3-butadiene. By being aliphatic "conjugated dienes", multienes having aromatically delocalised double bonds are excluded from the scope of the present invention. However, the aliphatic conjugated dienes may have non-aliphatic groups, such as phenyl groups, substituted onto the -C=C-C=C- backbone. The hydroxyl group-containing compound used in the present process may be an alcohol, or a carboxylic acid or water. Accordingly, alkanedioic diesters, dianhydrides and diacids may be obtained by the present process. Preferably, the hydroxyl group-containing compound is an alcohol, more preferably an alkanol, and most preferably an alkanol having from 1 to 6 carbon atoms. Typical examples of suitable alcohols include methanol, ethanol, n-propanol, isopropanol, butanols. Also suitable are polyhydric alcohols such as ethylene glycol and 1,3-propanediol, which result in polyesters being produced. The palladium catalyst used in the process of the invention may be provided in the form of a palladium complex of one or both of the specified diphosphines. It may also conveniently be generated in situ by adding a source of palladium and sources of the diphosphines to the reaction. Suitable sources of palladium include palladium carboxylates, such as palladium acetate, propionate, butyrate or benzoate, and palladium salts of mineral acids. Further sources include palladium complexes such as palladium acetylacetonate, tetrakis(triphenylphosphine)palladium and bis(tri-o-tolylphosphine)palladium acetate. Preferably the source of palladium is free of halide. Palladium may be used in a heterogenised form, for example loaded on an ion exchange resin. It is a characteristic feature of the present invention, that the catalyst system comprises a combination of at least two bidentate diphosphine ligands, which are distinguished by having electron withdrawing and electron releasing substitutents on the phosphorus atoms, respectively. Preferably, the first bidentate diphosphine ligand comprises aromatic substituents. More preferably, the first bidentate diphosphine ligand is a diphosphine of formula: R 1 R 2 >P-R-P<R 3 R 4 wherein R 1 , R 2 , R 3 and R 4 independently represent optionally substituted aryl groups, and R represents a bridging group having at least two carbon atoms in the bridge. Typical aryl groups represented by R 1 , R 2 , R 3 and R 4 include phenyl, naphthyl, o-methoxyphenyl, p-tolyl, o-tolyl, m-chlorophenyl and p-chlorophenyl. Preferably, the second bidentate diphosphine ligand comprises aliphatic substituents. More preferably, the second bidentate diphosphine ligand is a diphosphine of formula: R 5 R 6 >P-R-P<R 7 R 8 wherein R 5 , R 6 , R 7 and R 8 independently represent optionally substituted aliphatic groups, and R represents a bridging group having at least two carbon atoms in the bridge. The optionally substituted aliphatic groups may be monovalent or divalent, in the latter case being bonded to a single or to both phosphorus atoms of the diphosphine ligand. Suitable aliphatic groups particularly include unsubstituted optionally branched or cyclic alkyl or alkylene groups having from 1 to 10 carbon atoms, more preferably from 1 to 6 carbon atoms. Preferably, R 5 , R 6 , R 7 and R 8 independently are selected from the group of alkyl, alkylene, cycloalkyl and cycloalkylene groups. Typical examples of aliphatic groups R 5 , R 6 , R 7 and R 8 include methyl, ethyl, propyl, isopropyl, n-butyl, s-butyl, t-butyl, cyclohexyl, pentamethylene, hexamethylene and cyclooctylene. For being capable of bidentate coordination to the palladium atom, the bidentate diphosphine ligands of the catalyst system are inherently free of substituents offering steric hindrance to a bidentate coordination mode. In particular, the divalent bridging group R having at least two carbon atoms in the bridge, should be free of substituents offering steric hindrance, but otherwise can be any divalent group having two or more carbon atoms and optionally further heteroatoms, such as oxygen or nitrogen, in the bridge interconnecting both phosphorus atoms, and any further groups or atoms attached thereto. The bridging group R may make part of a cyclic structure, e.g. an aromatic or cycloaliphatic group, and the bonds in the bridge may be saturated or unsaturated. Also a 3-oxapentamethylene groups is suitable. Preferably, the bridging group R is an optionally substituted alkylene group having at least three carbon atoms in the chain, more preferably three or four carbon atoms. The first bidentate diphosphine ligand most preferably has four carbon atoms in the bridge, and the second ligand most preferably has three carbon atoms in the bridge. Representative first bidentate diphosphine ligands include 1,3-bis(diphenylphosphino)propane, 1,4-bis(diphenylphosphino)butane, 1,3-bis(di-o-methoxyphenylphosphino)propane, 1,4-bis(di-p-chlorophenylphosphino)butane, and 1,4-bis(di-p-tolylphosphino)butane. Representative second bidentate diphosphine ligands include 1,2-bis(di-n-butylphosphino)ethane, 1,3-bis(dimethylphosphino)propane, 1,3-bis(diethylphosphino)propane, 1,3-bis(di-i-propylphosphino)propane, 1,3-bis(di-n-propylphosphino)propane, 1,3-bis(di-i-butylphosphino)propane, 1,3-bis(di-n-butylphosphino)propane, 1,3-bis(di-s-butylphosphino)propane, 1,3-bis(di-t-butylphosphino)propane, 1,3-bis(di-n-hexylphosphino)propane, 1,2-bis(dicyclohexylphosphino)ethane, 1,3-bis(n-butylmethylphosphino)propane, 1,3-bis(n-butylethylphosphino)propane, 1,3-bis(1,5-cyclooctylenephosphino)propane and its isomeric mixture containing 1,4-cyclooctylene groups, 1,4-bis(di-i-propylphosphino)butane, 1,5-bis(dimethylphosphino)-3-oxapentane, 1,8-bis(di-n-butylphosphino)-3,6-dioxaoctane, and 1,4-bis(di-n-butylphosphino)-2,2,3,3-tetramethylbutane. The ratio of the number of moles of either of the diphosphines per gram atom of palladium is preferably in the range of from 0.50 to 10, more preferably from 0.9 to 5, especially from 1 to 4. Preferably, the first bidentate diphosphine is used in molar excess relative to the second bidentate diphosphine, a ratio in the range of from 1:1 to 10:1 being most preferred. The source of an anion, used in the process of the invention is preferably a protonic acid. However, it may also be a salt of palladium. It may also be a salt of another metal, for example of vanadium, chromium, nickel, copper or silver, or the salt of a protonated base when the protonic acid is neutralised with a base such as in 3,4-lutidinium salts. Preferably, the anion is derived from a weak protonic acid, in particular a carboxylic acid, having a pKa greater than 3, measured at 18 °C in aqueous solution, and being sterically hindered. Typically sterically hindered carboxylic acids, from which suitable anions may be derived, include 2,4,6-trimethylbenzoic acid, 2,6-dichlorobenzoic acid, 9-anthroic acid, pivalic acid, 1,2,3-benzenetricarboxylic acid and its 1,3-diester which may be formed in situ, 2-ethoxy-1-naphthalene carboxylic acid, and 2,6-dimethoxybenzoic acid. The ratio of moles of anions per gram atom of palladium is not critical. Preferably it is in the range of from 0.5 to 100, more preferably in the range of from 1 to 10. The diphosphines of formula I as such are known compounds, and can be prepared by general methods described in the literature, for example Houben-Weyl, Vol. XII/I, p.21. The catalyst system used in the process according to the invention may be homogeneous or heterogeneous. Preferably it is homogeneous, or an immobilised homogeneous catalyst system. The catalyst system according to the invention is preferably constituted in a liquid phase. The liquid phase may conveniently be formed by one or more of the reactants with which the catalyst system is to be used. Alternatively, it may be formed by a solvent. It may also be formed by one of the components of the catalyst system. Any inert solvent can be used. Said solvent may, for example, comprise sulphoxides and sulphones, for example dimethylsulphoxide, diisopropylsulphone or tetrahydrothiophene-2,2-dioxide (also referred to as sulfolane), 2-methylsulfolane, 3-methylsulfolane, 2-methyl-4-butylsulfolane; aromatic hydrocarbons such as benzene, toluene, and xylenes; esters such as methyl acetate and butyrolactone; ketones such as acetone or methyl isobutyl ketone; alcohols such as methanol and ethanol, ethers such as tetrahydrofurane (also referred to as THF), anisole, 2,5,8-trioxanonane (also referred to as diglyme), diphenyl ether and diisopropylether; and amides such as dimethylacetamide and N-methylpyrrolidone. Alcohols may function as coreactant to form esters. The process according to the invention is conveniently effected at a temperature in the range of from 50 °C to 200 °C, in particular from 100 °C to 150 °C. Higher or lower temperature are not excluded, but usually don't provide any economic advantage. The process according to the invention is preferably effected at a total pressure of from 1 to 80 bar. Pressures higher than 100 bar may be used, but are generally economically unattractive on account of special apparatus requirements. More preferred pressures are in the range of from 5 to 70 bar. The process according to the invention may be carried out continuously or batchwise. Carbon monoxide grade, reaction equipment and product purification are not critical, and well within the skills of the relevant technician. The invention will be illustrated in further detail by the following non-limiting examples. Example 1 A 300 ml magnetically stirred stainless-steel autoclave was charged with 20 ml ethanol, 40 ml diphenylether, 0.5 mmol palladium acetate, 2 mmol 1,4-bis(diphenylphosphino)butane, 0.6 mmol 1,3-bis(di-i-propylphosphino)propane and 10 mmol 9-anthracene carboxylic acid. The autoclave was flushed and evacuated, whereupon 10 ml of liquid 1,3-butadiene was added, and carbon monoxide introduced to an initial pressure of 40 bar. The autoclave was heated to 150 °C for 15 hours. Upon cooling, the contents of the autoclave were analysed by gas liquid chromatography (GLC). It was found that 100 % of the 1,3-butadiene was converted with a selectivity of 37 % into diethyl diesters of C 6 -alkanedioic acids and a selectivity of 60 % into ethyl monoesters of C 5 -alkenoic acids, with the diethyl C 6 -alkanedioates showing a linearity of 61 %, it means consisting for 61 % of diethyl adipate. Examples 2-6 and Comparative Example A In the same way as Example 1, further experiments were conducted using the alcohol and catalyst components and their amounts as indicated in the below Table. After heating for 15 hours at the indicated temperatures and GLC analysis, the 1,3-butadiene conversions, the selectivities to diesters, the diester linearity and the selectivities to monoesters mentioned in the Table were observed. The following abbreviations are used in the Table: BDPbut = 1,4-bis(diphenylphosphino)butane; BDiPP = 1,3-bis(di-i-propylphosphino)propane; BcOP = 1,3-bis(c-octylenephosphino)propane (isomeric mixture comprising 1,4- and 1,5-cyclooctylene groups); BDsBP = 1,3-bis(di-s-butylphosphino)propane; BDcHP = 1,3-bis(dicyclohexylphosphino)propane; 9-anth. = 9-anthroic acid; DMBZ - 2,6-dimethoxybenzoic acid; EtOH - ethanol; MeOH - methanol. Ex. No. alcohol 1° ligand 2° ligand anion T conv. diester monoester (ml) (mmol) (mmol) (mmol) °C % sel. % lin. % sel. % 1 EtOH BDPbut BDiPP 9-anth. 150 100 37 61 60 (20) (2.0) (0.6) (10) 2 EtOH BDPbut BcOP 9-anth. 160 100 80 42 17 (20) (2.0) (0.6) (10) 3 EtOH BDPbut BDsBP 9-anth. 160 100 42 62 55 (20) (2.0) (0.6) (10) 4 EtOH BDPbut BDcHP 9-anth. 160 100 46 61 50 (20) (2.0) (0.6) (10) 5 EtOH BDPbut BDsBP DMBZ 160 100 34 60 64 (20) (2.0) (0.6) (15) 6 MeOH BDPbut BDiPP 9-anth. 160 100 30 67 66 (15) (2.0) (0.6) (10) A EtOH BDPbut - 9-anth. 150 100 trace 97 (20) (2.0) (10)

Claims: A process for the preparation of alkanedioic derivatives by reaction of an aliphatic conjugated diene with carbon monoxide and a hydroxyl group-containing compound in the presence of a palladium catalyst, wherein the catalyst system comprises: a) a source of cationic palladium, b) a first bidentate diphosphine ligand having electron-withdrawing substituents on the phosphorus atoms, c) a second bidentate diphosphine ligand having electron-releasing substituents on the phosphorus atoms, and d) a source of an anion. A process as claimed in claim 1, wherein the first bidentate diphosphine ligand comprises aromatic substituents. A process as claimed in claim 2, wherein the first bidentate diphosphine ligand is a diphosphine of formula: R 1 R 2 >P-R-P<R 3 R 4 wherein R 1 , R 2 , R 3 and R 4 independently represent optionally substituted aryl groups, and R represents a bridging group having at least two carbon atoms in the bridge. A process as claimed in claim 1, wherein the second bidentate diphosphine ligand comprises aliphatic substituents. A process as claimed in claim 4, wherein the second bidentate diphosphine ligand is a diphosphine of formula: R 5 R 6 >P-R-P<R 7 R 8 wherein R 5 , R 6 , R 7 and R 8 independently represent optionally substituted aliphatic groups, and R represents a bridging group having at least two carbon atoms in the bridge. A process as claimed in claim 5, wherein R 5 , R 6 , R 7 and R 8 independently are selected from the group of alkyl, alkylene, cycloalkyl and cycloalkylene groups. A process as claimed in any one or more of claims 1-6, wherein the aliphatic conjugated diene is 1,3-butadiene. A process as claimed in any one or more of claims 1-7, wherein the hydroxyl group-containing compound is an alkanol having from 1 to 6 carbon atoms. A process as claimed in any one or more of claims 1-8, wherein the first bidentate diphosphine ligand is used in molar excess relative to the second bidentate diphosphine ligand.

Inventors: DRENT EIT, DRENT, EIT
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1993
Main classification: C07C67
IPC codes: C07C67