WO1995006025A1

WO1995006025A1 - Process for the preparation of an acetal

Info

Publication number: WO1995006025A1
Application number: PCT/NL1994/000192
Authority: WO
Inventors: Onko Jan Gelling; Josephus Marie Hubertus Spronken
Original assignee: DSM NV; EI Du Pont de Nemours and Co
Current assignee: Koninklijke DSM NV; EIDP Inc
Priority date: 1993-08-23
Filing date: 1994-08-15
Publication date: 1995-03-02
Anticipated expiration: 1996-02-23
Also published as: BE1007410A3; AU7710394A

Abstract

Process for the preparation of an acetal by hydroformylation of an ethylenically unsaturated organic compound, the ethylenically unsaturated organic compound being contacted with carbon monoxide, hydrogen, an alkanol and a metal-containing catalyst system, the catalyst system comprises: a) platinum or a platinum compound, b) a bidentate ligand with the general formula: R1R2-M-R-M-R3R4, where M represents a phosphorus, antimony or arsenic atom, R represents a divalent bridging group having at least three atoms and where R?1, R2, R3 and R4¿ represent the same or different hydrocarbon groups, which may or may not be substituted, c) and a Brønsted acid with a pKa < 2 and/or a Lewis acid.

Description

PROCESS FOR THE PREPARATION OF AN ACETA

The invention relates to a process for the preparation of an acetal by hydroformylation of an ethylenically unsaturated organic compound, the ethylenically unsaturated organic compound being contacted with carbon monoxide, hydrogen, an alkanol and a metal- containing catalyst system.

Such a process is disclosed in US-A-4209643. In that patent publication a process is described for the preparation of acetals starting from an ethylenically unsaturated organic compound, the ethylenically unsaturated organic compound being contacted with carbon monoxide, hydrogen, an alkanol and a cobalt compound as catalyst and a quaternary ammonium salt as cocatalyst. The selectivity for acetals is between 70 and 93%.

A drawback of this known process is that the selectivity for acetals still needs to be improved. In particular the selectivity to terminal acetals is too low especially when starting from internal ethylenically unsaturated organic compounds.

The object of the present invention is a process for the preparation of acetals starting from an ethylenically unsaturated organic compound and yielding acetals, in particular terminal acetals, with high selectivity. Terminal acetals are interesting compounds for the preparation of, for instance, terminal aldehydes and terminal alkanols.

This object is achieved in that the catalyst system comprises a) platinum or a platinum compound, b) a bidentate ligand with the general formula R¹R²-M-R- M-R³R*, where M represents a phosphorus, antimony or arsenic atom, R represents a divalent bridging group having at least three atoms and where R¹, R², R³ and R⁴ represent the same or different hydrocarbon groups, which may or may not be substituted, c) and a Brønsted acid with a pKa < 2 and/or a Lewis acid.

Many important advantages are gained for the process according to the invention:

(1) The process according to the invention has been found to yield an acetal, in particular the terminal acetal, with high selectivity.

(2) The catalyst system according to the invention is easier to recover from the reaction mixture than a volatile cobalt-based catalyst as described in, for instance, US-A-4209643. The process according to the invention allows the products and the catalyst to be separated through simple distillation.

(3) The selectivity for the total amount of iso eric acetals is also higher than the selectivity reported in US-A-4209643.

(4) The acetals in the process according to the invention have been found to be hardly converted under the reaction conditions, if at all, to the corresponding alkanols at a high conversion of the ethylenically unsaturated organic compound.

(5) Terminal ethylenically unsaturated organic compounds as well as internal ethylenically unsaturated organic compounds may be converted with a high selectivity for terminal acetals. (6) Another advantage is that the use of tin chloride is not necessary to achieve the improved results. This is advantageous because tin chloride, generally used in Pt-catalysed hydroformylation as described in the literature, is very corrosive. It is known from US-A-2491915 that acetals may be prepared starting from ethylenically unsaturated organic compounds in the presence of carbon monoxide, hydrogen, alcohol and a Group VIII (or group 8, 9 and 10 of the new IUPAC notation) metal catalyst. Cobalt and ruthenium are referred to as being the most suitable Group VIII metal catalyst. However, the attained selectivity for acetals is low (around 70%).

EP-A-220767 discloses a catalyst consisting of platinum or a platinum compound, a bidentate phosphine ligand and an anion of a carboxylic acid with a pKa < 2, for hydroformylation of ethylenically unsaturated organic compounds to aldehydes. Alkanols are not named as possible solvents and/or reagents and acetals are not named as possible products. Another difference is that in the process according to the invention acids are applied instead of the anion of a carboxylic acid as in the above process.

The use of alkanols as solvent is discouraged in the scientific literature for hydroformylation reactions that are catalyzed by platinum/tin systems (J. of Molecular Cat., 39 (1987) 180 and in J. Organometall Chem. 286 (1985), 115-120).

Acetals prepared according to the invention may be represented by the following general formula:

H H H

! I I H - C - C - C - OR⁷ (I)

I I I

R⁶ R^s OR⁸

In this formula, the source of R⁷ and R⁸ is the alkanol which is further described below. The source of the R⁵-C-C-R⁶ portion is the ethylenically unsaturated organic compound, which ethylenically unsaturated organic compound is further described herein below. In the case of a linear acetal, R⁵ represents an H. As a rule, the ethylenically unsaturated organic compound will be an alkene or a cycloalkene containing from 3 to 30 carbon atoms and, if the ethylenically unsaturated organic compound is an internal ethylenically unsaturated organic compound, containing from 4 to 30 carbon atoms, preferably from 4 to 12 carbon atoms. The ethylenically unsaturated organic compound may or may not be functionalized. Examples of functionalized organic compounds will be described below. Mixtures of ethylenically unsaturated organic compounds with different numbers of carbon atoms may also serve as starting material.

The ethylenically unsaturated organic compound may be a terminally ethylenically unsaturated organic compound. Terminally ethylenically unsaturated organic compounds are very suitable because with the process according to the invention these compounds can be converted to terminal acetals with a high selectivity. Internally ethylenically unsaturated organic compounds are also suitable starting compounds because the process according to the invention allows terminal acetals to be prepared with high selectivity. Terminal acetals may also be prepared by the process according to the invention with high selectivity starting from mixtures of isomeric ethylenically unsaturated organic compounds (which differ in the location of the ethylenically unsaturated bond).

The ethylenically unsaturated organic compounds preferably are terminal, but the ethylenically unsaturated organic compounds may also be branched or cyclic. Examples of such ethylenically unsaturated organic compounds are propylene, butene-1, butene-2, isobutene, 1-pentene, 2-pentene, 3-pentene, 2-hexene, 3- hexene, 2-methyl-l-butene, 2-methyl-2-butene, 1-hexene, 3- methyl-1-pentene, 2-methyl-2-pentene-, 2-heptene, 2- methyl-2-hexene, 3-methyl-2-hexene, 1-octene, 4-octene, 2- octene, 3-methyl-l-heptene, 2-methyl-2-heptene, 3-nonene, 3-methyl-2-octene, 2-decene, 5-decene, 3,4-dimethyl-2- octene, 4-ethyl-2-octene, 3-undecene, 4-undecene, 4- methyl-2-decene, 4,5-dimethyl-2-nonene, 3-dodecene, 2- tridecene, 3-tetradecene, 5-pentadecene, 1-heptene, 1- nonene, 1-decene, 2-decene, 3-decene, 4-decene, 5-decene, 1-undecene, 2-dodecene, 2-undecene, 3-undecene, 4- undecene, 5-undecene, 1-dodecene, 3-dodecene, 5-dodecene, 1-tridecene, 3-tridecene, 4-tridecene, 6-tridecene, 1- tetradecene, 7-tetradecene, 1-pentadecene, 4-pentadecene, 6-pentadecene, styrene and α-methylstyrene.

The ethylenically unsaturated organic compound may also be an ethylenically, optionally internally unsaturated alcohol, aldehyde, ketone, ester, carboxylic ester or nitrile having from 3 to 30 carbon atoms. Examples of such compounds are acrylic acid, methacrylic acid and the alkyl esters of these acids, wherein the alkyl group can contain 1 to 12 carbon atoms. An especially suitable group of esters and acids is represented by the following chemical formula:

R⁹ - C - 0 - R¹ (II)

where R⁹ represents a monoethylenically unsaturated- or poly-ethylenically unsaturated acyclic hydrocarbon group having from 3 to 11 carbon atoms, which group may or may not be branched, and R¹⁰ represents a hydrogen group or an alkyl group having from 1 to 8 carbon atoms or an aryl group or an arylalkyl group having from 6 to 12 carbon atoms.

If an ethylenically unsaturated carboxylic acid (R¹⁰ = hydrogen) is hydroformylated according to the invention, the acid group is converted to an ester group (corresponding with the alkanol applied).

In formula (II) R⁹ can be for example the radical groups of the afore mentioned non-functionalized ethylenically unsaturated organic compounds; especially propylenyl, isobutenyl, pentyl, hexenyl. R⁹ is preferably a linear butenyl group because the corresponding acetals may serve as, for example, starting material for the preparation of Nylon-6 and Nylon-6.6 precursors. Examples of these internally unsaturated alkene-carboxylic acid esters are the 2- , 3-pentenoates (= internal ethylenically unsaturated organic compounds) and the 4-pentenoate and the corresponding acids of these esters.

R¹⁰ preferably is a hydrogen group or an alkyl group having from 1 to 8 carbon atoms or a phenyl group or benzyl group. Examples of such groups are the methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, isobutyl, cyclohexyl, benzyl or phenyl groups.

A mixture of isomeric alkyl pentenoates can be prepared by a process as described in US-A-3253018. Such a mixture substantially containing the internally olefinically unsaturated alkyl-3-pentenoate may with advantage be converted to the corresponding terminal dialkylacetal by means of the process according to the invention.

The terminal dialkyl acetal of the 5- formylvalerate described above, which is prepared starting from the pentenoate, is of importance in that this compound may serve as a starting material for the preparation of, for instance, caprolactam (as described in JP-A-25351/1966) , or adipic acid (a Nylon-6 and a Nylon 6.6 precursor, respectively). As a rule, alkanols that are suitable for the process according to the invention are liquid, low- molecular weight alkanols. The alkanols may be primary or secondary alkanols. Suitable alkanols are 2-dodecanol, isopropanol, cyclohexanol and 2,2-dimethyl propanol. Monohydric alkanols having from 1 to 5 carbon atoms are preferred. Examples of such alkanols are ethanol, ethanol, propanol, isopropanol, n-pentanol, 2- methylpropanol and n-butanol. Methanol is applied with the most preference.

As a rule, the molar ratio of ethylenically unsaturated organic compound and alkanol is between 1:1000 and 1:3, preferably between 1:100 and 1:5.

Platinum or the platinum compound may be applied in a homogeneous system or an immobilized heterogeneous system. Preferably, homogeneous systems are applied. Since platinum reacts with the bidentate ligand in situ to form a complex, the choice of initial Pt compound is not in general critical. Suitable platinum compounds are salts of platinum with, for example, hydrohalogenic acids, nitric acid, sulphonic acid and carboxylic acids having not more than 12 carbon atoms per molecule. Examples of such salts are PtCl₂, Pt(AcAc)₂ (AcAc = aczeylacetonate) , CODPtCl₂ (COD = cyclooctadiene) , Pt(BF₄)₂ and Pt(AcAc)BF₄. Platinum halides such as PtCl₂ and CODPtCl₂ are preferably applied as platinum compounds since these compounds are also Lewis acids. Application of such platinum halides obviates the need to add an extra Lewis acid to the reaction mixture. Platinum chloride compounds are applied with the most preference.

As a rule, the molar ratio between platinum and ethylenically unsaturated organic compound lies between 1:1 and 1:1000. Higher ethylenically unsaturated organic compound/Pt ratios are less favourable in that the reaction will proceed more slowly. The lower limit is not critical but for practical reasons the ratio will not be chosen on the low side. Consequently, the molar ratio between platinum and ethylenically unsaturated organic compound preferably lies between 1:50 and 1:300.

Suitable Brønsted acids are acids with pKa < 2 (measured in an aqueous solution at 18°C). Examples of suitable inorganic acids are sulphonic acids, phosphoric acid and hydrogen halides for example HC1 and HBr. Examples of suitable carboxylic acids are trichloroacetic acid, trifluoroacetic acid, dichloroacetic acids, difluoroacetic acid. Fluorinated alkyl-carboxylic acids and, in particular, trifluoroacetic acid are preferably used as Brønsted acid.

In general, the Brønsted acid content of the reaction mixture is higher than 1, particularly higher than 3 equivalents of acid per mole of platinum. The Brønsted acid content generally is lower than 50, particularly lower than 10 and most preferably lower than 5 equivalents of acid per mole of platinum.

Suitable Lewis acids are, for example, metal halides. The metal halide will react to form a hydrogen halide compound when dissolved in the alkanol according to the invention. Suitable metal halide compounds are for example FeX₃, A1X₃, PtX₂, SnX₂ and GeX₂ (X= F, Cl, Br, I). If the problems regarding the corrosive properties of tin halides are overcome then tin halides are preferably used in addition to the platinum halides mentioned herein before. Examples of suitable tin halides are SnCl₂, SnBr₂, Snl₂, Sn(BF₄)₄, SnCl₄ and SnCl₂.2H₂0. Platinum halides and SnCl₂ are preferably applied. As a rule, the molar ratio between metal halide compound and platinum lies between 0.1:1 and 1000:1, preferably between 1:1 and 20:1. The bidentate ligand with the general formula

R^XR²-M-R-M-R³R⁴ preferably is a bidentate phosphine, where M represents a phosphorus atom. The bridging group R can be a divalent organic bridging group having at least 3 carbon atoms in the bridge or a divalent organometallic bridging group. Preferred organic bridging groups -R- can be represented by the following general chemical formula:

- (CR^R¹²)., - (III)

in which R¹¹ and R¹² can be hydrogen or hydrocarbon groups with 1 to 10 carbon atoms and in which n is between 3 and 10 .

Preferably R¹¹ and R¹² are hydrocarbon groups which offer a steric hindrance. Because of this steric hindrance the R^IR²-M- and -M-R³R⁴ will not be able to freely rotate relative to each other compared to the situation in which a less sterically hindred bridge is used. A bridge group which does not allow the R¹R²-M- and - M-R³R⁴ groups to rotate freely relative to each other (conformation freedom), such as the afore mentioned substituted bridging groups, are called rigid bridging groups. It has been found that when bidentate ligands with a bridging group which has a rigid link are used in a process according to the invention the selectivity to the acetal is further increased. The term "rigid group" shall also be defined for the purposes of the present invention as a group having "limited flexibility" or a group having "at least a partially rigid link", as is known to one of ordinary skill in the art.

It has also been found that the shortest distance between the two M's for the organic bridging group is preferably a chain of 4 atoms; besides carbon, the atoms may represent a heteroatom such as nitrogen, oxygen, sulphur and phosphorus.

Examples of other suitable "rigid" bridging groups are bivalent organic groups containing at least one divalent cyclic group, which may or may not be aromatic. This cyclic group imparts the rigid properties to the bridging group and is linked to M whether or not via an alkyl group having from 1 to 3 carbon atoms. A suitable group of bridging groups may be represented by the following general formula:

- R¹³ - Y - R¹⁴ - (IV)

where Y represents a divalent organic group, which group contains at least one divalent cyclic structure as a rigid link (which cyclic structure imparts the rigidity to the bridging group), the cyclic structure optionally being substituted and which organic group Y may contain heteroatoms such as oxygen, nitrogen, phosphorus and sulphur, and where R¹³ and R¹⁴ may independently of one another be omitted or independently of one another represent a C₁-C₃ alkylene group. R¹³ and R¹⁴ are preferably omitted or are methylene groups or are substituted with other groups in order to increase the rigidity of the bridging group. As a rule, the cyclic structure will contain from 3 to 20 atoms.

An example of a bidentate phosphine with a cyclic structure in Y containing a heteroatom is the commercially obtainable 2,3-0-isopropylidene-2,3- dihydroxy-1,4-bis(diphenylphosphino)butane (DIOP).

Compounds derived from DIOP are suitable also. Another group of highly suitable cyclic structures for Y according to formula III are cyclic alkanes such as cyclopropane, cyclobutane, cyclopentane and cyclohexane. Bridged cycloalkanes are highly suitable as cyclic structure of Y. Examples of such bridged cycloalkanes are bicyclofl,l,2]hexane, bicyclo[2,2,l]heptane and bicyclo[2,2,2]octane.

The cyclic structure of Y may optionally be substituted with one or more aryl groups or alkyl groups or other groups. These groups may optionally be used for immobilizing the bidentate phosphine onto a carrier. Examples of such groups are, for instance, carboxyl groups, hydroxyl groups, amino groups and halide groups. Possible divalent organometallic bridging groups are bis( -cyclopentadienyl) coordination compounds of metals (also known as metallocenes) . Possible metals are Fe, Zr, Co, Cr, Ni, Ti, Ru and W. A particularly suitable metallocene is the ferrocenyl group (Fe). It seems that the organometallic bridging groups act as having a rigid link. R¹, R², R³, and R⁴ may be C₁-C₁₅ (cyclo)alkyl groups or C₅-C₂₀ aryl groups. Examples of (cyclo)alkyl groups are methyl, ethyl, propyl, isopropyl, butyl, tert.butyl, pentyl, cyclohexyl, and cyclooctyl groups. These groups preferably are aryl groups such as naphthyl, phenyl or a heterocyclic aryl group such as pyridyl. These aryl groups may optionally be substituted. Examples of substituents are alkyl groups such as a methyl, ethyl and iso-butyl group, alkoxy groups, halides and amine derivatives.

Examples of suitable bidentate phosphines are 2,3-0-isopropylidene-2,3-dihydroxy-l,4-bis(diphenylphos- phino)butane (DIOP) (A), bis(diphenylphosphine)ferrocene (B) , trans-l,2-bis(di(m-methylphenyl)phosphinomethyl)- cyclobutane (C), trans-[ (bicyclo[2.2.l]heptane-2,3- diyl)bis(methylene) ]-bis[ iphenylphosphine] (D) , trans- [ (bicyclo[2.2.2]octane-2,3-diyl)bis(methylene) ]- bis[diphenylphosphine] (E), trans-1,2-bis(diphenyl- phosphinomethyl)cyclobutane (DPMCB) (F) and trans-1,2- bis[diphenylphosphinomethyl]trans-3,4-bis[phenyl]- cyclobutane (G). (The letters in parentheses refer to the sheet of formulae.)

The molar ratio between platinum and bidentate ligand as a rule lies between 1:2 and 2:1. Most preferably, this ratio is about 1:1.

As a rule, the temperature at which the process according to the invention is carried out lies between 20 and 180°C. The temperature will more particularly lie between 80 and 140°C and, if the ethylenically unsaturated organic compound is a pentenoate, the temperature will preferably lie between 90 and 110°C.

The pressure as a rule lies between 2 and 60 MPa. More unwanted hydrogenation will occur at pressures below 2 MPa whilst the reaction will proceed less rapidly at pressures higher than 60 MPa. The reaction preferably is effected at a pressure which lies between 6 and 15 MPa. The molar ratio between hydrogen and carbon monoxide as a rule lies between 10 : 1 and 1 : 10. Preferably, this ratio lies between about 3 : 1 and 1 : 5. Any aldehyde formed during the reaction may readily be converted to the acetal using techniques known to one skilled in the art. Examples of such techniques are cited in US-A-2842576.

The acetal that has formed may readily be separated off from the reaction mixture through distillation at reduced pressure.

The invention is also directed to a process for the preparation of an aldehyde by hydrolysis of the acetal prepared by the above described process. The acetal may readily be converted to the corresponding aldehyde through commonly known techniques such as hydrolysis with a dilute mineral acid. More in particular is the invention also directed to a process to prepare alkyl 5- formylvalerate starting from alkyl 3-pentenoate by hydrolysis of the alkyl 5-formylvalerate dialkylacetal (see above for the scope of the alkyl 3-pentenoate) . This process is advantageous because it is possible to prepare alkyl 5-formylvalerate when starting from alkyl 3- pentenoate with a higher selectivity and at lower pressure than the known state of the art processes as for example described in EP-A-295549.

The acetal conversion to the aldehyde is generally performed at a temperature between 0 and 80°C and preferably between 10 and 60°C. The reaction can be performed in vacuo or under pressure. The reaction can be performed in the absence of an additional solvent or in the presence of a solvent which is inert under reaction conditions. Preferably water, which is needed for the hydrolysis, can be used as a solvent in a molar ratio of water:acetal of between 5:1 and 100:1. The hydrolysis is usually carried out in the presence of an acid catalyst. Examples of homogeneous acids are sulfuric acid, phosphoric acid, hydrochloric acid, or any other mineral acid. Preferably heterogeneous acids are used because they can be more easily separated from the reaction mixture. Examples of heterogeneous acid catalysts are ion exchange resins and zeolites. Examples of suitable ion exchange resins are Duolite® C 265, Lewasorb® AC 10, Lewatit® SPC 118 and Amberlyst® 15.

The aldehyde prepared by the above described process can easily be separated from an aqueous reaction mixture by distillation or by extraction with a solvent which is not miscible with water. Examples of suitable solvents are methylchloride, chloroform, toluene, benzene, methyl tert-butylether, diethylether, ethylacetate or any other commonly used organic extraction solvent. Further purification of the aldehyde can be performed by distillation.

The acetal can also be used as a starting compound for the preparation of an amino compound by reductive amination of the acetal group in the presence of ammonia, hydrogen and a hydrogenation catalyst and optionally a solvent. The invention is in particular also directed to a process for the preparation of 6- aminocaproate by reductive amination of the corresponding 5-formylvalerate dimethylacetal prepared by the above described process. The reductive amination can be performed in any manner known to the man skilled in the art. JP-A-25351/1966 for example describes a suitable process for the reductive amination. As solvent for the reductive amination the alkanol used for the preparation of the acetal can be advantageously used. This is for example advantageous because the alkanol does not have to be separated from the acetal before the reductive amination.

The acetal may also be converted to the corresponding alkanol. DE-A-2357645, for instance, discloses a process for the preparation of an alkanol starting from an acetal in the presence of carbon monoxide, hydrogen, rhodium and a tertiary amine. Terminal alkanols may well be used as surfactants or as plasticizers. The invention is elucidated by means of the following non-limiting examples.

The composition of the reaction mixtures of the Examples and Comparative Experiments were determined with Gas Chromatography. The selectivity and conversion mentioned in the examples is defined as follows:

product yield (mol) product selectivity = * 100% converted substrate (mol)

converted substrate (mol) conversion = * 100% initial amount of substrate (mol)

Example I A solution consisting of 67 g of CODPtCl₂ (C0D= cyclooctadiene) and 81 mg of DPMCB (ligand F) in 40 ml of methanol (MeOH) was pressurized to 4 MPa in a CO/H₂ (1:1 molar) atmosphere in a (Parr) autoclave. The reaction mixture was heated to 100°C. Subsequently, a mixture of 1.59 g of 2-octene (organic compound) and 0.79 g of anisole (as internal standard for GC product analysis) in 5 ml of MeOH was injected. Next, the pressure was raised to 8 MPa. The mixture was analyzed after a reaction time of 4 hours. The conversion was 51% with a selectivity for dimethyl acetals of 95% and a selectivity for the terminal 1,1-dimethoxynonane of 85%.

Example II

Example 1 was repeated using 4-octene in place of 2-octene. The mixture was analyzed after a reaction time of 4 hours. The conversion was 18% with a selectivity for dimethyl acetals of 95% and a selectivity for the terminal 1,1-dimethoxynonane of 73%.

Examples III-VI

A solution consisting of a Pt complex, CODPtAcAcBF₄ (0.2 mmol) and DPMCB (0.25 mmol) (ligand F) and a Brønsted acid or a Lewis acid (see Table 1) in 40 ml of methanol (MeOH) was pressurized to 4 MPa in a CO/H₂ (1:1) atmosphere in a (Parr) autoclave. The reaction mixture was heated to 100°C. Subsequently, a mixture of 2.0 g of methyl 3-pentenoate and 0.50 g of anisole (as internal standard) in 5 ml of MeOH was injected. Next, the CO/H₂ pressure was raised to 8 MPa (CO/H₂=l (mol/mol)). The mixture was analyzed after a reaction time of some hours (see Table 1).

The other reaction conditions and results are listed in Table 1.

TABLE 1

acid/Pt = acid equivalents relative to platinum moles

5-fo = selectivity of 5-formylmethylvalerate dimethylacetal

10 Σ-fo = selectivity of total of terminal and branched acetals

Mev = selectivity of methylvalerate

N/Br = ratio between terminal acetals and branched acetals

Examples VII-IX

Example III was repeated using two different platinum compounds. The results are listed in Table 2. Experimental conditions: 0.2 mmol Pt compound, Pt compound/DPMCB = 1/1 (mol/mol), 100°C, 8 MPa, CO/H₂ = 1, methyl 3-pentenoate/MeOH = 0.04.

T A B L E 2

^l SnCL₂.2H₂0 (5 eq/mol Pt) added

Examples X-XV

Example III was repeated using different bidentate phosphine ligands. The results are stated in Table 3. The letters refer to the compounds in the sheet of formulae. Experimental conditions: 0.2 mmol Pt compound, CODPtBF₄AcAc/L/SnCl₂.2H₂0 = 1/1/5 (mol/mol/mol) , 100°C, 8.0 MPa, CO/H₂=l, reaction time: 4 hours.

T A B L E

Pt(AcAc)₂ was used in place of CODPtBF₄AcAc as Pt compound.

Examples XVI-XX

Example IX was repeated using different H₂ pressures and CO pressures. The results are stated in Table 4. Experimental conditions: 0.2 mmoles of Pt compound, CODPtCl₂/DPMCB = 1/1 (mol/mol), 100°C, reaction time 4 hours.

T A B L E 4

con = methyl 3-pentenoate/MeOH (vol/vol) Example XXVI

A solution of CODPtAcAcBF₄ (49 mg, 0.1 mmol), DPMCB (Ligand F) (45 mg, 0.1 mmol) and SnCl₂.2H₂0 (56 mg, 0.25 mmol) in 50 ml of methanol was heated to 100°C in an autoclave at 4.0 MPa (CO/H₂ (1:1)). Subsequently, a solution of 2.0 g of 3-pentenoic acid and 0.50 g of anisole (internal standard) in 5 ml of methanol was injected. Next, the pressure was raised to 8.0 MPa. The reaction mixture was analyzed after a reaction time of 4 hours. All of the 3-pentenic acid had disappeared. The selectivity for dimethylacetals of isomeric formylmethyl- valerates was 95% and that for terminal 5-formylmethyl¬ valerate dimethylacetal was 81%.

Example XXVII

A solution of CODPtCl₂ (74 mg, 0.2 mmol) and DPMCB (Ligand F) (90 mg, 0.2 mmol) in 50 ml of methanol was heated to 100°C in an autoclave under 4.0 MPa CO/H₂ (1:1). Next, a solution of 2.1 g of methyl 4-pentenoate and 0.54 g of anisole (internal standard) in 5 ml of methanol was injected and the pressure was raised to 8.0 MPa. After reacting for 4 hours, the conversion was 82% with a selectivity of 82% for 5-formylmethylvalerate dimethylacetal.

Example XXVIII

A solution of CODPtCl₂ (93.4 mg, 0.25 mmol) and 1,4-bis(diphenylphosphine)butane (dppb) (107 mg, 0.25 mmol) in 30 ml methanol was heated in an autoclave to 100°C under a 4.0 MPa carbon/hydrogen pressure (C0/H2=l/1 mol/mol). Subsequently a solution of 5.62 g methyl-3- pentenoate and 0.37 g anisole (anisole has the same function as in Example I) in 10 ml methanol was injected and the pressure was increased to 8.0 MPa. The mixture was analyzed after a reaction time of 21 hours. The conversion was 57.5% and a selectivity of 75% to methyl-5-formyl¬ valerate dimethylacetal and 9.7% to the dimethyl acetal of methylvalerate. Example XXIX

A solution of CODPtCl₂ (94 mg, 0.25 mmol) and 1,4-bis(diphenylphosphine)2,2-dimethylbutane (114 mg, 0.25 mmol) in 30 ml methanol was heated in an autoclave to 100°C under a 4.0 MPa carbon/hydrogen pressure (CO/H2=l/l mol/mol). Subsequently a solution of 5.42 g methyl-3- pentenoate and 0.34 g anisole (anisole has the same function as in Example I) in 10 ml methanol was injected and the pressure was increased to 8.0 MPa. The mixture was analyzed after a reaction time of 20 hours. The conversion was 69% with N/Br equal to 6.7 and a selectivity of 77.5% to methyl-5-formylvalerate dimethylacetal and 9.6% to the dimethyl acetal of methylvalerate.

Example XXX

Example III was repeated. The methyl-5- formylvalerate dimethylacetal was isolated by distillation and a solution of 10 g methyl-5-formylvalerate dimethylacetal, 50 g water and 1 g of Amberlyst® 15 was mixed for 1 hour at 40°C. After separating the catalyst by filtration the resulting reaction mixture was analysed: the conversion of methyl-5-formylvalerate dimethylacetal was 93% and the selectivity to the methyl 5-formylvalerate was 96%.

Comparative Experiment A

Example II of US-A-4209643 was repeated with methyl 3-pentenoate in which a solution of 30.7 g methyl 3-pentenoate, 1.0 g anisole (internal standard), 1.62 g Co₂(CO)₈ and 1.38 g N-benzyl,N,N,N-trimethylammonium ethoxide in 42 ml methanol was heated in an autoclave to 110°C under a 4.0 MPa carbon monoxide/hydrogen pressure (CO/H₂ = 1/1 mol/mol) When this temperature was reached the end pressure was set at 6.0 MPa. After three hours of reaction the reaction was stopped and the products were analysed by GC. Conversion was 53%, selectivity to acetals was 49% and selectivity to methyl 5-formylvalerate dimethylacetal was 27% (N/Br = 1.2) and 25% to the dimethylacetal of methylvalerate. C L A I M S

1. Process for the preparation of an acetal by hydroformylation of an ethylenically unsaturated ^s organic compound, the ethylenically unsaturated organic compound being contacted with carbon monoxide, hydrogen, an alkanol and a metal-containing catalyst system, characterized in that the catalyst system comprises: ⁰ a) platinum or a platinum compound, b) a bidentate ligand with the general formula R^XR²- M-R-M-R³R⁴, where M represents a phosphorus, antimony or arsenic atom, R represents a divalent bridging group having at least three ⁵ atoms, and where R¹, R², R³ and R⁴ represent the same or different hydrocarbon groups, whether or not substituted, c) and a Brønsted acid with a pKa < 2 and/or a Lewis acid. ⁰ 2. Process according to Claim 1, characterized in that the alkanol is methanol. 3. Process according to either of Claims 1-2, characterized in that the temperature lies between 80 and 140°C. ⁵ 4. Process according to any one of Claims 1-3 characterized in that the pressure lies between 2 and

60 MPa..

5. Process according to any one of Claims 1-4 characterized in that the molar ratio between 0 platinum and bidentate ligand lies between 1:2 and 2:1.

6. Process according to Claim 5 characterized in that the molar ratio between platinum and bidentate ligand is about 1:1. 5 7. Process according to any one of Claims 1-6 characterized in that the ratio between Brønsted-acid equivalents and platinum lies between 0.1:1 and 1000:1 (eq:mol).

Claims

8. Process according to Claim 7 characterized in that the ratio between Brønsted acid and platinum lies between 1:1 and 20:1 (eq:mol).

9. Process according to any one of Claims 1-8 characterized in that the Lewis acid is a metal halide chosen from the group FeX₃, A1X₃, SnX₂ and GeX₂, where X may be a F, Cl, Br or I.

10. Process according to Claim 9 characterized in that the molar ratio between the metal halide compound and platinum lies between 0.1:1 and 1000:1.

11. Process according to Claim 10 characterized in that the molar ratio between the metal halide compound and platinum lies between 2:1 and 20:1.

12. Process according to either of Claims 9-10 characterized in that the metal halide is a tin halide.

13. Process according to any one of Claims 1-8 characterized in that the platinum compound is a platinum halide, which compound is also a Lewis acid.

14. Process according to any one of Claims 1-13 characterized in that the molar ratio between platinum and ethylenically unsaturated organic compound lies between 1:1 and 1:1000.

15. Process according to Claim 14 characterized in that the molar ratio between platinum and ethylenically unsaturated organic compound lies between 1:50 and 1:300.

16. Process according to any one of Claims 1-15 characterized in that the molar ratio between ethylenically unsaturated organic compound and alkanol lies between 1:3 and 1:1000.

17. Process according to any one of Claims 1-16 characterized in that the molar ratio between ethylenically unsaturated organic compound and alkanol lies between 1:25 and 1:100.

18. Process according to any one of Claims 1-17 characterized in that the molar ratio between carbon monoxide and hydrogen lies between 10 : 1 and 1 : 10. 19. Process according to any one of Claims 1-18 characterized in that the ethylenically unsaturated organic compound is an internal ethylenically unsaturated organic compound, which may or may not be functionalized, and which contains from 4 to 30 carbon atoms.

20. Process according to claim 19, characterized in that the ethylenically unsaturated organic compound is an ester or an acid represented by the following chemical formula:

R⁹ - C - 0 - R¹⁰

where R⁹ represents a monoethylenically unsaturated- or poly-ethylenically unsaturated acyclic hydrocarbon group having from 3 to 11 carbon atoms, which group may or may_.not be branched, and R¹⁰ represents a hydrogen group or an alkyl group having from 1 to 8 carbon atoms or an aryl group or an arylalkyl group having from 6 to 12 carbon atoms.

21. Process according to Claim 20, characterized in that the ethylenically unsaturated organic compound is a 2-, 3- or 4-pentenoate or a 2-, 3-, or 4-pentenic acid or a mixture of two or more of these compounds.

22. Process according to Claim 21 characterized in that the pentenoate is an alkyl pentenoate, the alkyl group containing from 1 to 8 carbon atoms.

23. Process according to any one of Claims 1-22 characterized in that M in the bidentate ligand is a phosphorus atom.

24. Process according to any one of Claims 1-23 characterized in that R¹, R², R³, and R⁴ are an aryl group, which may optionally be substituted.

25. Process according to Claim 24 characterized in that the aryl group is a phenyl group. 26. Process according to any one of Claims 1-25, characterized in that the bridging group R is a divalent organic bridging group having at least 3 carbon atoms in the bridge or a divalent organometallic bridging group.

27. Process according to Claims 26, characterized in that the bridging group has a rigid link.

28. Process according to Claim 27, characterized in that the bridging group contains at least one divalent cyclic group, which may or may not be aromatic, the cyclic group causing the rigid properties.

29. Process according to Claim 28 characterized in that the cyclic group is an aliphatic cyclic group with from 4 to 20 carbon atoms. 30. Process according to any one of Claims 28-29, characterized in that the bridging group R is represented by the following general formula:

- R¹³ - Y - R¹⁴ -

where Y represents a divalent organic group which group contains at least one divalent cyclic structure as a rigid link, the cyclic structure optionally being substituted and which organic group Y may contain heteroatoms chosen from the group consisting of oxygen, nitrogen, phosphorus and sulphur, and where R¹³ and R¹⁴ may independently of one another be omitted or independently of one another represent a Ci-Ca alkylene group.

31. Process according to Claim 30 characterized in that the cyclic structure is a bicycloalkane.

32. Process according to Claim 26 characterized in that the divalent organometallic bridging group is a bis(ή-cyclopentadienyl) coordination compound of a metal from the group comprising Fe, Ti, Zr, Co, Cr, Ni, Ru and W.

33. Process according to Claim 32 characterized in that the metal is Fe. 34. Process for the preparation of a terminal aldehyde, characterized in that the terminal acetal obtained by the process according to any one of Claims 1-33 is converted to the terminal aldehyde by means of hydrolysis.

35. Process according to claim 34, characterized in that the terminal aldehyde is 5-formylvalerate and that the terminal acetal is obtained by a process according to any one of claims 20-33 and that the hydrolysis is performed at a temperature between 0 and 80°C in the presence of a heterogeneous acid and water in a molar ration of water:acetal of between 5:1 and 100:1.

36. Process as substantially described in the description and the examples.