WO1994004482A1

WO1994004482A1 - Process for the preparation of 5-formylpentane esters

Info

Publication number: WO1994004482A1
Application number: PCT/NL1993/000173
Authority: WO
Inventors: Otto Erik Sielcken; Nicolaas Franciscus Haasen
Original assignee: Dsm N.V.
Priority date: 1992-08-24
Filing date: 1993-08-20
Publication date: 1994-03-03
Also published as: AU4835893A; BE1006147A3

Abstract

The invention relates to a process for the preparation of a 5-formylpentane ester by converting an alkyl ester of pentadienoic acid with carbon monoxide and hydrogen, in the presence of a catalyst, at elevated pressure, into a 5-formylpentane ester, a cobalt compound being used as the catalyst. The cobalt compound may be a cobalt-carbonyl compound or a cobalt-phosphine or -phosphite complex.

Description

PROCESS FOR THE PREPARATION OF 5-FORMYLPENTANE ESTERS

The invention relates to a process for the preparation of 5-formylpentane ester (an alkyl ester of

6-oxohexanoic acid) by converting an alkyl ester of pentadienoic acid with carbon monoxide and hydrogen, in the presence of a catalyst, at elevated pressure, into a

5-formylpentane ester.

Such a process is described in Chem. Zeit.

(1976) 100, pp. 308-312. This publication describes a process in which a rhodium complex is used as a catalyst.

The yields of 5-formyl-pentane ester do not exceed 4%.

Furthermore, according to this publication, a substantially larger amount of branched aldehydes than linear ones is formed during the hydroformylation. Because of these low yields this route is unsuitable for industrial use for the preparation of a 5-formylpentane ester.

The invention provides a process for the preparation of a 5-formylpentane ester by hydroformylating an alkyl ester of pentadienoic acid, in which a higher yield of the desired product is obtained.

Higher yields are obtained by choosing a cobalt compound as the catalyst. The cobalt is generally used as a dissolved compound in a homogeneous reaction system. Cobalt may be present as a cobalt-carbonyl complex but also as a complex with a ligand that is bound more strongly to cobalt than carbon monoxide.

The cobalt compound may be formed in situ by dissolving cobalt in the reaction medium. It is also possible to use virtually all cobalt compounds, as is known for carbonylation and hydroformylation reactions.

In a first preferred embodiment of the invention cobalt is used as a complex or as a salt, virtually all the cobalt being present as a cobalt-carbonyl complex under reaction conditions. Di-cobalt octacarbonyl, cobalt acetoacetonate, cobalt acetate, cobalt sulphate or cobalt carbonate may for example be used as the cobalt complex. Furthermore, use can be made of a cobalt compound with one or more relatively stable monodentate ligands, for example phosphines or phosphites. Preferably, alkyl- or arylphosphines are used. In a second preferred embodiment of the invention cobalt is used as a cobalt complex having as a ligand a polydentate ligand comprising at least two phosphine groups that are separated by a chain of 2 carbon atoms. Such polydentate ligands are described as such in EP-A-033554 for the hydroformylation of alkadienes catalysed by rhodium. However, it cannot be inferred from EP-A-033554 that the ligands would also be suitable for the hydroformylation, with the aid of a cobalt catalyst, of dienes containing ester groups, the carbonyl of the ester group being conjugated with the diene. It is hence surprising that few byproducts are formed in the Ijydroformylation of an alkyl ester of pentadienoic acid. In particular the ratio of linear and branched oxo compounds is very favourable with the process according to the invention.

The starting product is an alkyl ester of pentadienoic acid having a structure as shown by Formula I

H₂C = CH - CH = CH - COOR¹ (I)

where R¹ is Ci_₆ alkyl. Preferably the ester of methyl, ethyl, isopropyl or t-butyl is used.

The aforementioned compounds can be prepared via the oxidative carbonylation of butadiene, as described in for example US-A-4236023 and US-A-4195184. According to these patents butadiene is converted into the ester of pentadiene in the presence of carbon monoxide, an alcohol, oxygen and a palladium catalyst, using a water-absorbing agent such as ethoxycyclohexene (an enol ether) or diethoxycycloalkane and an iron or copper salt as an oxidant.

Optionally the ester of pentadiene may be purified before use in the process according to the invention by means of for example distillation or extraction. It is however also possible to use the ester of pentadiene with a purity of 60-90%.

The polydentate ligands that can be used in the second preferred embodiment according to the invention are preferably trivalent phosphine compounds having 1 or 2 phenyl groups per phosphine. The polydentate ligands are preferably used in a ligand : cobalt ratio of 0.5-1.2 : 1.

Preferably at least 2 phosphorus atoms have two phenyl groups each. The phenyl groups may be substituted with one or more alkyl groups, alkoxy groups or halogens. More in particular the polydentate ligand has a structure according to Formula II

(ID

where jδ stands for phenyl or substituted phenyl and where R¹ and R² may be the same or different and may stand for alkyl, phenyl, substituted phenyl or R⁶-PR⁴R⁵, where R⁴ and R⁵ independently of one another stand for alkyl, phenyl or substituted phenyl.

R³ and R⁶ independently of one another stand for C^Cg alkyl or C₆-C₁₂ aryl, for example preferably CH₂-CH₂ or C(CH₃)H-CH₂. R³ and R⁶ are preferably CH₂-CH₂. Preferably R¹ and R² are phenyl or R⁶-P-R⁴R⁵, where R⁴ and R^s are phenyl. The substituted phenyl groups can be phenyl groups substituted with one or more alkyl groups, alkoxy groups or halogens. The hydro ormylation reaction can be carried under fairly mild conditions, preferably at a temperature of 50-200°C, more in particular 80-180°C, and a pressure of 20-400 bar, more in particular 50-200 bar (5-20 MPa). The pressure is the pressure of hydrogen plus that of carbon monoxide.

The hydrogen : carbon monoxide molar ratio is generally in the range of 0.5-12, preferably 0.8-5. The amount of catalyst may vary within wide limits. The catalyst : pentadiene alkyl ester molar ratio is generally between 1 : 10,000 and 1 : 3.

Preferably the pentadiene ester : catalyst ratio is between 1 : 1000 and 1 : 4. A relatively high cobalt concentration presents the advantage of a rapid reaction while nevertheless the selectivity hardly decreases.

The hydroformylation can be carried out in bulk or, with a higher selectivity, using a hydrocarbon, optionally containing ether groups, as a solvent, for example toluene, benzene, cyclohexane, dioxane, tetrahydrofuran or methylcyclohexane. If a solvent is used the amount will usually be between 10 and 90% of the total mixture.

The invention will be further elucidated with reference to the following non-limiting examples.

Examples I-XII

Approximately 50 mg of C0₂(CO)₈ (approx. 1 mol%), optionally a ligand - as indicated in Table 1 - and 14 g of freshly distilled toluene were introduced into a glass liner of an autoclave (with a volume of 50 ml) entirely made of Hastalloy-C steel. After the autoclave had been closed it was pressurized 3x (50 bar) using CO/H₂ (1 : 1), after which it was brought to 120°C at a pressure of 80 bar CO/H₂ (1 : 1). After 30 minutes a mixture of approximately 2 g of freshly distilled methyl-1,3- butadiene-1-carboxylate, approximately 0.5 g of nonane (internal standard) and approximately 3 g of toluene was injected into the autoclave from a side ampoule at a pressure of 120 bar CO/H₂ (1 : 1). Table 1 shows the specific reaction conditions.

TABLE 1

Reaction conditions of the hydroformylation of the methyl ester of pentadienoic acid

Example ligand* ligand:cobalt cobalt:pentadiene pressure molar ratio molar ratio (bar)

10

15

20

*dppe : 1,2-bis(diphenylphosphino)ethane

25 dppp : 1 , 3-bis(diphenylphosphino)propane dcpe : 1,2-bis(dicyclohexylphosphino)ethane

The reaction was monitored via gas chromatography. At a degree of conversion of the starting material of virtually 100% the reaction was stopped and the reaction mixture was analysed. The results are shown in Table 2.

TABLE 2

Results of the hvdroformylation of the methyl ester of pentadienoic acid usinσ a cobalt catalyst

egree of conversion = (100-[pentene esters]) %; [pentene esters] being mono- plus diene esters;

²n-ald = 5-formylpentane ester ; ³b-ald = [branched aldehyde] 3- or formylpentane ester;

⁴n-hydrox 6-hydroxyhexane ester; ⁵Me-Val = methylvalerate (methyl ester of pentanoic acid) ;

'nd = not determined. This table shows that when cobalt is used as a catalyst yields of n-aldehyde can be obtained with a selectivity of more than 40 mol%. In all cases substantially more terminal than branched aldehyde is formed. The reaction rate is highest when use is made of cobalt without a phosphine ligand.

Claims

C L A I S

1. Process for the preparation of a 5-formylpentane ester by converting an alkyl ester of pentadienoic acid with carbon monoxide and hydrogen, in the presence of a catalyst, at elevated pressure, into a 5-formylpentane ester, characterised in that a cobalt compound is used as the catalyst.

2. Process according to claim 1, characterised in that a complex of cobalt and a ligand is used as the cobalt compound, the ligand comprising at least a phosphine or phosphite group.

3. Process according to claim 2, characterised in that a complex of cobalt and a ligand is used as the cobalt compound, a polydentate ligand comprising at least two phosphine groups that are separated by a chain of 2 carbon atoms being used as the ligand.

4. Process according to claim 3, characterised in that the polydentate ligand has a structure according to formula I

where 0 stands for phenyl or substituted phenyl and where R¹ and R² may be the same or different and may stand for alkyl, phenyl, substituted phenyl or R⁶-PR⁴R⁵, where R⁴ and R⁵ independently of one another stand for alkyl, phenyl or substituted phenyl, R³ and R⁶ independently of one another stand for Ci-C_j alkyl or C₆-C₁₂ aryl.

5. Process according to claim 4, characterised in that R³ and R⁶ are CH₂-CH₂.

6. Process according to claim 4, characterised in that R¹ and R² are phenyl or R⁶-P-R⁴R⁵, where R⁴ and R⁵ are phenyl.

7. Process according to claim 1, characterised in that such a cobalt complex or cobalt salt is used as the cobalt compound that virtually all the cobalt is present as cobalt carbonyl under reaction conditions.

8. Process according to any one of claims 1-7, characterised in that the process is carried out at a pressure of between 20 and 400 bar and a temperature of between 50 and 200°C.

9. Process according to any one of claims 1-8, characterised in that the hydrogen : carbon monoxide molar ratio is between 0.5 and 12.

10. Process according to any one of claims 1-9, characterised in that the catalyst : pentadiene alkyl ester molar ratio is between 1 : 1000 and 1 : 4.

11. Process as substantially described in the specification and the examples.