GB2256641A

GB2256641A - Hydroformylation of alpha olefins

Info

Publication number: GB2256641A
Application number: GB9112895A
Authority: GB
Inventors: Eit Drent
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1991-06-14
Filing date: 1991-06-14
Publication date: 1992-12-16
Also published as: GB9112895D0

Abstract

A process for the preparation of aldehydes by hydroformylation of an alpha alkenically unsaturated compound having at least 5 carbon atoms, in which the alpha alkenically unsaturated compound is contacted with a carbon monoxide source and a hydrogen source in the presence of a catalytic system comprising a) palladium, a palladium compound, platinum and/ or a platinum compound, b) a weakly or non-coordinating anion, and c) a bidentate phosphorus, arsenic or antimony ligand, characterized in that the bidentate ligand is selected from the group of compounds of the general formula R<1>R<2>-M<1>-R-M<2>-R<3> R<4>, wherein M and M<2> independently represent phosphorus, arsenic or antimony, R represents a divalent bridging group having at least two atoms in the bridge, and R<1>, R<2>, R<3> and R<4> independently represent an optionally substituted aromatic group with the proviso that at least one of R<1>, R<2>, R<3> and R<4> carries an electron-donating substituent.

Description

HYDROFORMYLATION OF ALPHA OLEFINS This invention relates to a process for the preparation of aldehydes by hydroformylation of alpha alkenically unsaturated compounds, in particularly of alpha-olefins.

The hydroformylation of alkenically unsaturated compounds, i.e. the addition of carbon monoxide and hydrogen to such compounds to produce aldehydes and/or alcohols is of great industrial importance. Aldehydes, in particular linear aldehydes, are very useful intermediates in industrial practice because of their terminal carbonyl group. For, instance, they can be readily reduced to the corresponding primary alcohols or oxidised to the corresponding carboxylic acids. They can also undergo addition and/or condensation reactions with a variety of chemicals such as hydrogen cyanide, alcohols, nitroparaffins as well as condensation reactions with themselves and other carbonyl-containing compounds.

They can also be reacted with ammonia and derivatives thereof such as primary amines.

Much effort has been devoted over the years to the development of better catalyst systems, especially with a view to increase the linear/branched product ratio since this will have a positive influence on biodegradability problems encountered in various applications wherein aldehydes and/or alcohols are used as intermediate or starting materials, e.g. in surface-active compounds.

Since the classical cobalt carbonyl catalyst system which produces a large amount of branched chain products, more advanced systems have been suggested comprising organophosphorus compounds, in particular tertiary phosphines or phosphites as ligands.

Recently, a highly selective catalyst system has been proposed in EP-A-220 767, which catalyst system comprises a bidentate phosphorus, arsenic or antimony ligand in conjunction with palladium and/or platinum. In all Examples use is made of 1,3-di-(diphenylphosphino) propane or 1,4-di-(diphenylphosphino) butane. This process is advantageous in allowing the hydroformylation reaction to proceed with high selectivity to linear aldehydes and a very low amount of alkanes being co-produced.

Upon further study of this hydroformylation reaction it was observed, that the known catalyst system enhances the isomerization of the starting alpha-alkenically unsaturated compound to internally unsaturated compounds as a side reaction proceeding concurrently with the desired hydroformylation reaction. Since the hydroformylation of internally unsaturated compounds proceeds at a rate being an order of magnitude lower than the hydroformylation rate for terminally unsaturated compounds, a sharp drop of the hydroformylation rate was observed at a degree of conversion of olefin to aldehyde of about 40 to 60 %.Where it is true that the isomerization reaction is an equilibrium reaction reproducing alpha-olefins for subsequent high-rate hydroformylation into aldehydes and any aldehydes produced from internal olefins may constitute useful products, the low rates of these subsequent reactions remain an unattractive feature of the known process susceptible of improvement.

A catalyst system comprising a compound of palladium, an anion of an acid with a pKa of less than 6, and a bidentate phosphorus, arsenic or antimony ligand carrying at least one aryl group substituted with a polar substituent is known from EP-222 454.

However, this publication only mentions the use of the catalyst system in the copolymerization of carbon monoxide, ethene and, optionally, further olefinically unsaturated hydrocarbons.

It has now been found that the undesired isomerization reaction can be substantially suppressed by specific selection of a bidentate ligand for the known catalytic system.

Accordingly, the present invention provides a process for the preparation of aldehydes by hydroformylation of an alpha alkenically unsaturated compound having at least 5 carbon atoms, in which the alpha alkenically unsaturated compound is contacted with a carbon monoxide source and a hydrogen source in the presence of a catalytic system comprising a) palladium, a palladium compound, platinum and/or a platinum compound, b) a weakly or non-coordinating anion, and c) a bidentate phosphorus, arsenic or antimony ligand, which process is characterized in that the bidentate ligand is selected from the group of compounds of the general formula RR-M-R-M-R R4, wherein M and M independently represent phosphorus, arsenic or antimony, R represents a divalent bridging group having at least two atoms in the bridge, and R, R, R and R4 independently represent an optionally substituted 1 2 3 aromatic group with the proviso that at least one of R , R , R and R carries an electron-donating substituent.

Surprisingly, it was observed, that using the selected catalytic system in accordance with the invention, the hydroformylation reaction proceeds at a high rate to a higher degree of conversion of alpha-olefin to aldehyde, while maintaining an excellent linearity of the aldehyde product. Hereby, a more efficient consumption of the alpha olefin feedstock is possible under industrially viable process conditions.

For being capable of bidentate coordination to a metal atom, the bidentate ligand of general formula 1 is inherently free of substituents offering steric hindrance to a bidentate coordination mode. In particular, the divalent bridging group R should be free of substituents offering steric hindrance, but otherwise can be any divalent group having at least two atoms, such as oxygen, nitrogen and, preferably, carbon atoms, in the bridge interconnecting both atoms M1 and M2 and any further groups or atoms attached thereto.

The bridging group R may also make part of cyclic structure, e.g.

an aromatic or cycloaliphatic group, and the bonds in the bridge may be saturated or unsaturated. 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, and most preferably three carbon atoms.

The optionally substituted aromatic groups R, R, R and R4 as a rule contain 6 to 20 carbon atoms, and preferably are aryl groups containing 6 to 14 carbon atoms. It is a requirement for the bidentate ligand to be used in accordance with the invention, that at least one of R, R, R and R4 carries an electron-donating substituent. Suitable electron-donating substituents include hydrocarbyloxy, hydrocarbylthio and dihydrocarbylamino substituents, particularly electron-donating substituents attached to the aromatic nucleus through a nitrogen, oxygen or sulphur atom having a lone pair of electrons. Preferred electron-donating substituents are selected from the group of alkoxy and dialkylamino substituents, such as methoxy, ethoxy, n-propoxy, isopropoxy, 2-butoxy, t-butoxy, dimethylamino, ethylmethylamino, diethylamino, and diisopropylamino.

Effectively, the electron-donating substituent may be attached to the aromatic group R, R, R or R4 at a position ortho or para to the aryl/phosphorus bond. It is preferred that at least one, more preferred each, of R, R, R and R4 represents an aryl group carrying an electron-donating substituent at the 2-position.

Representative bidentate ligands include 1,3-bis(di-4-methoxyphenylphosphino) propane, 1,4-bis(di-4-dimethylaminophenylphosphino) butane and 2-methyl 2-[(di-4-methoxyphenylphosphino)methyl] 1,3-bis (di-4-methoxyphenylphosphino) propane. Preferred bidentate ligands include 1,3-bis(di-2-methoxyphenylphosphino) propane, 1,4-bis (di-2-methoxyphenylphosphino) butane, and 1,4-bis(di-2-dimethylaminophenylphosphino) butane.

When a group is stated to be optionally substituted, it may or may not be substituted with one or more substituents which do not interfere with the desired course of reaction, such as hydrocarbyl, hydrocarbyloxy, and halo substituents.

The preferred metal component present in the catalyst composition is a palladium compound. Very suitable are palladium salts of carboxylic acids and in particular palladium acetate.

The weakly or non-coordinating anion present in the catalyst composition is preferably derived from an acid having a pKa in the range of from 0 to 4, measured in aqueous solution at 18 "C.

Examples of such acids are monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, difluoroacetic acid, trifluoroacetic acid, and benzenephosphonic acid, trifluoroacetic acid being preferred.

The components of the catalyst system to be used in accordance with the present invention can be present in quantities which may vary within wide limits. The bidentate ligand can normally be used in quantities of from 0.1 to 10 mole per mole of palladium, palladium compound, platinum or platinum compound. The weakly or non-coordinating anion is preferably present in a quantity of 0.01-150, in particular 0.1-100 and most preferably 1-50, moles per gram atom palladium and/or platinum. The best results are usually obtained when at least 5 moles per gram atom are present.

Both homogeneous and heterogeneous catalyst systems can be used, homogeneous systems being preferred.

The alpha alkenically unsaturated compound will generally be an alkene or a cycloalkene containing 5-30, preferably 5-12, carbon atoms per molecule. Examples of suitable alkenes include pentenes, hexenes, heptenes, octenes, and dodecenes. Examples of other alpha-alkenically unsaturated compounds are styrene, alpha-methylstyrene, acrylic acid, methacrylic acid, their esters, and non-conjugated polyenes.

Carbon monoxide and hydrogen will normally constitute the most suitable carbon monoxide or hydrogen source. However, in view of the equilibrium H20 + CO = H2 + CO2, water as hydrogen source or carbon dioxide as carbon monoxide source may be used. The present process can be carried out suitably using a molar ratio of carbon monoxide to hydrogen of 1:1 which is the stoichiometric ratio to produce aldehydes. Excess carbon monoxide or hydrogen over the stoichiometric amount may be present, for example in a molar ratio between 12:1 and 1:12.

The hydroformylation according to the invention is preferably carried out at a temperature between 20 and 200 "C, in particular between 50 and 150 "C. The overall pressure preferably lies between 1 and 100, in particular 10 and 70 bar above atmospheric pressure.

The process according to the invention can be carried out conveniently in the presence of an aprotic solvent. A variety of aprotic solvents can be applied such as ketones, e.g. acetone, methyl ethyl ketone, and methyl isobutyl ketone; ethers, e.g.

2,5,8-trioxanonane (also referred to as "diglyme"), anisole and diphenyl ether; aromatic compounds, e.g. toluene and xylene; nitrile, e.g. benzonitrile and acetonitrile; and esters, e.g.

methyl benzoate. Good results have been obtained using diglyme.

Also mixtures of solvents can be suitably applied. It is also possible to carry out the process without use of an added solvent where the starting material and product function as the reaction vehicle.

When desired the reaction mixture obtained may be subjected to a catalytic hydrogenation, e.g. over a Raney-Ni catalyst to convert part or all of the aldehyde produced into the corresponding alcohol. The reaction conditions to be applied are well known in the art.

The process according to the invention can be readily carried out using well-known chemical engineering practice which includes continuous, semi-continuous and batch operation. The reaction time may vary between wide limits, from a couple of minutes to several hours depending on the specific olefin and catalytic system applied. After the reaction, the reaction mixture is worked up by techniques known in the art, e.g. by distillation. It is also possible to recycle part or all of the reaction mixture together with the catalyst system.

The following Examples further illustrate the invention.

Example 1 A magnetically-stirred stainless steel 250 ml autoclave was charged with 20 ml octene-l, 40 ml diglyme and a catalyst system composed of 0.25 mmol palladium(II) acetate, 0.6 mmol 1,3-bis(di-2-methoxyphenylphosphino) propane and 2 mmol trifluoroacetic acid. After being flushed, the autoclave was pressurised with an equimolar mixture of carbon monoxide and hydrogen until an initial pressure of 60 bar was reached. The temperature was raised to a temperature of 125 "C and the reaction mixture was kept at this temperature for a period of 5 hours.The reaction mixture was then allowed to cool and a sample of its content was analysed by means of standard gas liquid chromatography (GLC). It was found that of the starting octene-l 568 was converted into nonanals and 16% into isomerised internally unsaturated octenes, residual starting octene-l still being available for further hydroformylation. It will be appreciated that the conversion into aldehydes was by a factor 3.5 higher than the undesired conversion into internal octenes. The product nonanals showed a linearity of 76%, i.e. comprised 76% of n-nonanal expressed as percentage of the total amount of nonanal formed.

Comparative Example A Example 1 was repeated, except for replacing 0.6 mmol 1,3-bis(di-2-methoxyphenylphosphino) propane by 0.6 mmol of 1,3-bis(diphenylphosphino) propane. The CLC analysis showed that 54% of the starting octene-l was converted into nonanals with a linearity of 75%, and 45% was converted into internally unsaturated octenes. The charged amount of octene-l was substantially depleted.

It will be appreciated that the conversion into aldehydes was higher by a factor 1.2 only than the undesired conversion into internal octenes.

Example 2 Example 1 was repeated, except for using a catalyst system composed of 0.25 mmol palladium(II) acetate, 0.3 mmol 1,3-bis(di-2-methoxyphenylphosphino) propane and 1 mmol trifluoroacetic acid, and prolonging the heating at 125 "C to a period of 7 hours. The CLC analysis showed a 74% conversion into nonanals with a linearity of 76%, and a 18% conversion into internally unsaturated octenes. It is seen that the two conversions differ by a factor 4. Relative to the experiment described in Example 1, the yield of nonanals was increased by the prolonged reaction period.

Comnarative Example B Example 2 was repeated, except for replacing 0.3 mmol 1,3-bis(di-2-methoxyphenylphosphino) propane by 0.3 mmol of l,3-bis(diphenylphosphino) propane, and heating for a period of 10 hours. The CLC analysis showed that 56% of the starting octene-l was converted into nonanals with a linearity of 76%, and 43% was converted into internally unsaturated octenes. It is seen that the two conversions differ by a factor 1.3. Relative to the experiment described in Comparative Example A, the yield of nonanals could not anymore be increased.

The above Examples and Comparative Examples teach that the present use of the selected catalyst system provides the surprising effect of shifting the relative rates of concurring hydroformylation and isomerization reactions in favour of the desired formation of nonanals, affording increased yields of nonanal product on the basis of octene-l precursor charged.

Claims

CLAIMS 1. A process for the preparation of aldehydes by hydroformylation of an alpha alkenically unsaturated compound having at least 5 carbon atoms, in which the alpha alkenically unsaturated compound is contacted with a carbon monoxide source and a hydrogen source in the presence of a catalytic system comprising a) palladium, a palladium compound, platinum and/or a platinum compound, b) a weakly or non-coordinating anion, and c) a bidentate phosphorus, arsenic or antimony ligand, characterized in that the bidentate ligand is selected from the group of compounds of the general formula RR-M-R-M-R R4, wherein M and M independently represent phosphorus, arsenic or antimony, R represents a divalent bridging group having at least two atoms in the bridge, and R, R, R and R4 independently represent an optionally substituted aromatic group with the proviso that at least one of R, R, R and R carries an electron-donating substituent.

1

2 3 4 2. A process as claimed in claim 1, wherein R1, R2, R3 and R are optionally substituted aryl groups containing 6-14 carbon atoms.

3. A process as claimed in any one or more of claims 1 and 2, wherein at least one of R, R, R and R4 represents an aryl group carrying an electron-donating substituent at the 2-position.

4. A process as claimed in any one or more of claims 1-3, wherein each of R, R, R and R4 represents an aryl group carrying an electron-donating substituent at the 2-position.

5. A process as claimed in any one or more of claims 1-4, wherein the electron-donating substituent(s) is (are) selected from the group of alkoxy and dialkylamino substituents.

6. A process as claimed in any one or more of claims 1-5, wherein R represents an optionally substituted alkylene group having at least three carbon atoms in the chain.

7. A process as claimed in claim 6, wherein R represents an optionally substituted propylene group.

8. A process as claimed in any one or more of claims 1-7, wherein each of M and M represents phosphorus.

9. A process as claimed in any one or more of claims 1-8, wherein the weakly or non-coordinating anion is derived from an acid having a pKa in the range of from 0 to 4, measured in aqueuos solution at 18 "C.

10. A process as claimed in any one or more of claims 1-9, wherein a palladium compound is used.

11. A process as claimed in any one or more of claims 1-9, wherein 1 to 50 mole of the weakly or non-coordinating anion is used per gram atom palladium and/or platinum.

12. A process as claimed in any one or more of claims 1-9 and 11, wherein 0.1 - 10 mole of bidentate ligand is used per mole of palladium, palladium compound, platinum or platinum compound.

13. A process as claimed in any one or more of claims 1-12, wherein the alpha alkenically unsaturated compound is a linear alkene.

14. A process for the preparation of aldehydes substantially as described hereinbefore, with particular reference to the Specification and/or Examples.

15. Use of a catalytic system comprising: a) palladium, a palladium compound, platinum and/or a platinum compound; b) a weakly or non-coordinating anion; and c) a bidentate ligand selected from the group of compounds of the general formula RR- M-R-M-R R4, wherein M and M independently represent phosphorus, arsenic or antimony, R represents a divalent bridging group having at least two atoms in the bridge, and R, R, 4 and R independently represent an optionally substituted aromatic group with the proviso that at least one of R, R, R and R carries an electron-donating substituent; in the preparation of aldehydes by reacting an alpha-alkenically unsaturated compound having at least 5 carbon atoms with a carbon monoxide source and a hydrogen source, for suppression of side reactions involving isomerization of the alpha-alkenically unsaturated compound.

16. Aldehydes whenever obtained by a process as claimed in any one or more of claims 1-14.