The invention relates to a process for the preparation of a linear ω-formylcarboxylic acid or a corresponding linear formylnitrile compound starting from an internally unsaturated C ₄ -C ₁₂ carboxylic acid or a corresponding ester or nitrile by means of hydro¬ formylation in the presence of carbon monoxide, hydrogen and a catalyst system.

To prepare linear (terminal) aldehyde compounds with a high selectivity by hydroformylation starting from internally unsaturated compounds is difficult. With internally unsaturated is meant that the unsaturated bond is not terminally situated in the chain of carbon atoms. This problem of the low selectivity of linear formyl (aldehyde) compounds starting from internally unsaturated compounds is described in US-A-4801738. That patent specification describes a process in which an internally unsaturated pentenoate ester is first isomerized to a terminally unsaturated compound (4-pentenoate ester) prior to hydroformylation with a rhodium/triphenylphosphine complex in a toluene solvent. Isomerization of the internally unsaturated compound to the terminally unsaturated compound is necessary because, otherwise, the selectivity for the terminal (linear) formyl compound (5- formylvalerate ester) would be undesirable low. This process is disadvantageous because of the .extra isomerization step.

The object of the invention is to provide a process whereby an internally unsaturated carboxylic acid or a corresponding ester or nitrile can be hydroformylated to a linear formyl compound with a high selectivity and with a simple process.

This object is achieved in that the hydroformylation is carried out in an aqueous medium and in that the catalyst system comprises platinum and a water-soluble organic bidentate ligand. It has been found that, if these linear formyl compounds are prepared using the process of the invention, the desired product can be prepared with high selectivity and in a single process step. A further advantage of this process is that the selectivity for the total of aldehydes (linear and branched aldehydes) is high. Branched aldehydes may be a useful by-product or may advantageously be converted into the starting material by means of decarbonylation. Loss of product is thus avoided by converting the (undesired) branched aldehydes into the starting material (as described in EP-A-295551 for the preparation of 5-formyl-valerate ester).

A further advantage is that the formyl carboxylic acid or the formylnitrile compound can readily be separated from the catalyst system by for example extraction with a less polar solvent than water. The catalyst system will remain in the water phase and can advantageously be reused in a next hydroformylation.

Furthermore, it can be advantageous that an amount of dicarboxylic acids is formed as by-product, when starting from the carboxylic acid or ester. The dicarboxylic acids often are useful by-products with many applications. A case in point is adipic acid, which is formed as a by-product when an internally unsaturated pentenoic acid (or pentenoate ester) is reacted according to the invention.

The internally unsaturated C ₄ -C ₁₂ organic nitrile compound which can be hydroformylated with the process according to the invention is a linear compound. Examples of suitable compounds are 2-butenenitrile, 2-pentene- nitrile, 3-pentenenitrile, 4-hexenenitrile, 3-hexene- nitrile, 2-hexenenitrile or 9-undecanenitrile.

The carboxylic acid which can be hydroformylated

with the process according to the invention contains, apart from the carboxyl group or ester group, from 4 to 12 carbon atoms. Examples of suitable internally ethylenically unsaturated carboxylic acids are 2-butenoic acid, 2- and 3-pentenoic acid, 2-, 3- and 4-hexenoic acid, 5-heptenoic acid, 5- and 6-octenoic acid, 9-undecenoic acid and polyunsaturated acids such as 2,4-hexadienoic acid and 2,4-pentadienoic acid.

The carboxylic acid ester used as starting material for the process according to the invention is as a rule an alkylester, an aryl ester or an aralkyl ester of for example the above mentioned carboxylic acids. The alkyl ester group may have 1 to 8 carbon atoms, the aryl ester group or aralkyl ester group may have 6 to 12 carbon atoms. Examples of suitable ester groups are methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, isobutyl, cyclohexyl, benzyl and phenyl ester groups. The ester group will hydrolyze during the hydroformylation and the formyl carboxylic acid will be the primary product. Mixtures of the above-mentioned compounds can also be hydroformylated using the process of the invention. Examples of possible mixtures are mixtures of compounds in which the location of the unsaturated bond differs. Such mixtures may also contain terminally unsaturated compounds. Mixtures of carboxylic acids and carboxylic acid esters can also be hydroformylated with the process according the invention. Preferably the esters are derived from the same carboxylic acid as used as co- reactant. As a rule, said mixtures will contain at least 20% internally unsaturated compounds relative to the total of unsaturated compounds.

A preferred group of starting compounds is represented by the following formulas

CH ₃ -CH=CH-CH ₂ -L (1)

CH ₃ -CH ₂ -CH=CH-L (2)

- A -

in which L is

-ON, -C-OH or -C-OY ¹ II II 0 0

in which Y ¹ is an alkyl group with 1 to 8 carbon atoms, an aryl group with 6 to 12 carbon atoms or an aralkyl group with 7 to 12 carbon atoms. Examples of Y ¹ are methyl, ethyl, propyl, isopropyl, n-butyl , tert-butyl, isobutyl, cyclohexyl, benzyl and phenyl. Preferably methyl, ethyl or phenyl are used. The resulting linear aldehyde compounds obtained when starting from the compounds of formula (1) or (2) can be advantageously used in a process to make Nylon-6 or Nylon-6.6 precursors.

The advantages of the process according to the invention are the most pronounced when starting from compounds according to formula (1) or mixtures of starting compounds containing large amounts of compounds according to formula (1). This is because compounds of formula (1) or these mixtures are easy obtainable starting from butadiene. Small amounts of terminally unsaturated compounds will as a rule be present in these mixtures. For example pentenoic acid can be prepared by hydroxy- carbonylating butadiene (in the presence of water and carbon monoxide) as described in EP-A-405433, a mixture of isomeric pentenoic acids is prepared, where the mixture consists primarily of 3-pentenoic acid and in small part of 4- and 2-pentenoic acid. By carbonylating butadiene with carbon monoxide and an alcohol as described in, for example, EP-A-301450, a mixture can be prepared consisting (primarily) of the 3-pentenoate and 4- and 2-pentenoate. Pentenenitriles may be prepared by the process as described in US-A-3496215 starting from butadiene.

Below the hydroformylation of pentenoic acid will be described in particular. However, the invention is therefore not limited to this starting compound. The conditions described below will also apply to the other starting materials mentioned above.

As a rule, the water-soluble compound used as bidentate ligand may be represented by the following general formula:

R ¹ R ² -M ¹ -R-M ² -R ³ R ⁴ (3)

where M ¹ and M ² represent a phosphorus (P) atom, an antimony atom or an arsenic atom, R represents a divalent organic bridging group having at least three atoms and where R ¹ , R ² , R ³ and R ⁴ represent the same or different organic groups and where at least one hydrophilic group is substituted on R ¹ , R ² , R ³ , R ⁴ and/or R. It is preferred for M ¹ and M ² to be phosphorus (P) atoms.

The hydrophilic group may be any group which increases the solubility of the organic bidentate ligand in water. This hydrophilic group may be a very polar group, for example amine derivatives, for example dialkylamine groups or more preferably an ionic group. The location of the hydrophilic group in the ligand compound is not critical. The hydrophilic group may be linked to the groups R ¹ -R* or to the bridging group R.

Examples of suitable ionic hydrophilic groups are a sulphonate group, -S0 ₃ Z, a phosphonate group -P0 ₃ Z, a carboxylate group, -COOZ, or a cationic group of an ammonium salt -N(R ⁵ ) ₃ X, where Z represents a cationic group, R ⁵ an aliphatic or aromatic hydrocarbon group having from 1 to 18 carbon atoms or hydrogen and X represents an anionic group. If the bidentate ligand contains aryl groups, for example for R ¹ , R ² , R ³ and/or R ⁴ , the cationic group of an ammonium salt preferably is bonded to a non-aryl group in the bidentate ligand. These non-aryl groups can be the bridging group (R) or the non- aryl groups for R ^x -R*. Another example of a hydrophilic group is when a phenolate group Ar-OZ is present in the ligand. The Ar group may be any aromatic group R ¹ , R ² , R ³ , R* and/or R.

Examples of suitable cationic groups (Z) are the

inorganic cations of metals, especially of alkali and earth alkali metals, for example sodium, potassium, calcium and barium as well as ammonium ions or quaternary ammonium ions, for example tetramethylammonium, tetrapropylammonium or tetrabutylammoniu .

Examples of suitable anionic groups (X) are halides, sulphate and phosphate groups and R ⁶ -S0 ₃ ^" , R ⁶ -C0 ₂ ^" and R ⁶ -P0 ₃ ^" groups, where R ⁶ represents a C _x -C ₁₂ alkyl or C ₁ -C ₁₂ aryl. As a rule, the number of hydrophilic groups is between 1 and 6. It is preferred for the number of groups to be between 1 and 4 per molecule of bidentate ligand.

R ¹ , R ² , R ³ and R* may be C^-C^ (cyclo)alkyl groups or C ₅ -C ₂₀ aryl groups. These groups preferably are aryl groups such as naphthyl, phenyl or a heterocyclic aryl group such as pyridyl. Examples of possible substituents are alkyl groups, for instance a methyl, ethyl or isobutyl group, alkoxy groups, for instance methoxy, ethoxy, isopropoxy and halides. Bridging group R may be an organic group with 3-

30 carbon atoms. R may be a divalent C ₉ -C ₁₂ alkyl group, for example trimethylene, tetramethylene, pentamethylene or hexamethylene.

Examples of bidentate phosphine ligand compounds according to formula (3) without the hydrophilic group are 1,3-bis(diphenyl-phosphino) ropane, 1,4-bis(diphenyl- phosphino)butane, 2,3-dimethyl-l,4-bis(diphenylphosphino)- butane, 1,4-bis(dicyclohexylphosphino)butane, 1,3-bis(di- p-tolyl-phosphino)propane, 1,4-bis(di-p-methoxyphenyl- phosphino)butane, 2, 3-bis(diphenylphosphino)-2-butene, 1,3-bis(diphenylphosphino)-2-oxopropane and 2-methyl-2- (methyldiphenylphosphino)-l,3-di (diphenylphosphino)- propane. The above ligands, when substituted with one or more hydrophilic group, are examples of possible water- soluble bidentate ligand compounds used in the process according to the invention.

Preferably the bridging group R forms a "rigid"

link between M ¹ and M ² . By a "rigid" link is meant a link that allows M ¹ and M ² little or no conformational freedom relative to one another (comparable to a double bond, which also allows little conformational freedom). It has been found that bidentate phosphine ligand compounds having a bridging group that allows more conformational freedom yield less favourable results. As a rule, the shortest distance between M ¹ and M ² is preferably formed by 3, 4 or 5 atoms. These atoms may represent, besides carbon, a heteroatom such as the nitrogen, oxygen, sulphur and phosphor atoms.

Example of suitable "rigid" bridging groups are divalent organic groups containing at least one cyclic group in the chain between M ¹ and M ² , which cyclic group may be aromatic. This cyclic group imparts the "rigid" properties to the bridging group and may possibly be linked to M ¹ and/or M ² via an alkyl group having from 1 to 3 carbon atoms. An example of suitable bridging groups may be represented by the following general formula:

- R ⁷ - Y - R ⁸ - (4)

where Y represents a hydrocarbon group, which group contains at least one cyclic structure (which cyclic structure imparts rigidity to the bridge group), the cyclic structure optionally being substituted and which hydrocarbon compound may contain heteroatoms such as oxygen, nitrogen, phosphorus and sulphur and where R ⁷ and R ⁸ may independently of one another be omitted or may independently of one another represent a C ₁ -C ₃ alkylene group. As a rule, the cyclic structure will contain from 3 to 20 atoms. M ¹ and M ² may be cis or trans to the rigid ring Y. If a group R ⁷ and/or R ⁸ is/are present, it/they, too, may be cis or trans to the rigid bridge Y. An example of a bidentate phosphine having a cyclic structure in Y which contains a heteroatom is 2,3- o-isopropylidene-2,3-dihydroxy-l,4-bis(diphenylphosphino)-

butane (DIOP), which is commercially available. Compounds derived from DIOP are also suitable. Another group of cyclic structures that are especially suitable for Y in formula III are cyclic alkanes such as cyclopropane, cyclobutane, cyclopentane and cyclohexane. Bridged cycloalkanes, too, are highly suitable to be used as cyclic group Y in formula III. Examples of such bridged cycloalkanes are bicyclo[l,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 or alkyl groups and/or with other functional groups. The functional groups substituted on Y may also be hydrophilic groups which increases the solubility of the organic bidentate ligand used in the process according to the invention. The functional groups may optionally be used for immobilizing the bidentate phosphine on a carrier. Examples of these functional groups are, for instance, carbonyl, hydroxyl, amine and halide groups. Other suitable "rigid" bridging groups are divalent organic groups containing (at least) 2 coupled, preferably aromatic, ring systems. The two ring systems have a hindered rotation relative to one another, as a result of which the bridges possess 'rigid' properties. Such compounds are described in detail in, for instance, "Advanced Organic Chemistry, Reactions, Mechanisms and Structure", Jerry March, 4th ed. 1992, John Wiley & Sons, page 101. Examples of suitable coupled ring systems are biphenyl, binaphthyl and bipyridyl. An example of a bidentate phosphine with a "rigid" bridge group with coupled ring systems is 2,2 '-bis-(diphenylphosphino)-l,1 '- binaphthyl (BINAP), which is commercially available. The ring systems may be substituted in the same way as the cyclic structure Y described above. A completely different group of suitable "rigid" bridging groups R with cyclic compounds are bis( - cyclopentadienyl)- coordination compounds of metals (also

known as metallocenes) . A particularly suitable metallocene is ferrocene.

Examples of suitable bidentate phosphines with rigid bridging groups (R) into which hydrophilic groups have not yet been incorporated are the earlier mentioned DIOP (A), bis(diphenylphosphine)ferrocene (B), trans-1,2- bis(di(m-methylphenyl)phosphinomethyl)cyclobutane (C) , trans-[ (bicyclo[2.2.1]heptane-2,3-diyl)bis(methylene)]- bis[diphenylphosphine] (D) , trans-[ (bicyclo[2.2.2]octane- 2,3-diyl)bis(methylene) ]-bis[diphenylphosphine] (E), trans-1,2-bis(diphenylphosphinomethyl)cyclobutane (DPMCB) (F) , trans-1,2-bis[diphenylphosphinomethyl]trans-3,4- bis[phenyl]cyclobutane (G) and the earlier mentioned BINAP. (The letters in parentheses refer to the sheet of formulae.)

The hydrophilic groups can readily be linked to the above-mentioned compounds. Sulphonate groups, for instance, can be bonded to the ligand via sulphonation with the aid of S0 ₃ in sulphuric acid. Carboxylate groups, phosphonate groups and cationic radicals of an ammonium salt can be incorporated using synthesis processes known in the art.

Promotors are preferably added to the catalyst system to further improve the selectivity to linear products. These promotors are acids with an pKa < 2

(measured at 18°C in an aqueous solution), preferably sulphonic acids, for example sulphonic acid, trifluoromethane sulphonic acid, tert-butyl sulphonic acid or p-toluene sulphonic acid. The molar ratio of acid to platinum may be between 1:1 and 30:1 and preferably between 1:1 and 10:1.

Platinum or the platinum compound can be applied in a homogeneous system or a heterogeneous, immobilized system. Homogeneous systems are preferred. Since platinum forms a complex with the bidentate compound in situ, the choice of an initial Pt compound is not generally critical. Suitable platinum compounds are for example

salts of platinum with, for instance, hydrogen halides, nitric acid, sulphonic acid and carboxylic acids having not more than 12 carbon atoms per molecule. Examples of such salts are PtCl ₂ , Pt(AcAc) ₂ (AcAc= acetylacetonate) , CODPtCl ₂ (C0D= cyclooctadiene), Pt(CH ₃ CN) ₄ (BF ₄ ) ₂ and CODPt(AcAc)BF ₄ .

The aqueous medium is as a rule water. Next to water other solvents may optionally be present. Examples of other solvents are dimethyl formamide, tetrahydrofuran, benzonitril and acetonitril.

The temperature of the hydroformylation is as a rule between 50 and 200°C and preferably between 90 and 120°C.

The pressure is not critical and may e.g. be between 4 and 20 MPa.

The molar ratio of hydrogen to carbon monoxide may e.g. be between 1:10 and 10:1. This ratio affects the ratio of the yield of formyl carboxylic acids to the yield of dicarboxylic acids. The dicarboxylic acids content of the resulting reaction mixture will increase as more carbon monoxide is used. If the desired product is formyl carboxylic acid, the molar ratio of carbon monoxide to hydrogen will be about 1:1. If a significant amount of dicarboxylic acids is desired, the molar excess of carbon monoxide relative to hydrogen is higher than 5.

The molar ratio of unsaturated carboxylic acid to platinum as a rule is between 100:1 and 1000:1 but preferably between 400:1 and 600:1.

The molar ratio of unsaturated carboxylic acid and water as a rule lies between 1:20 and 1:2.

The hydroformylation is preferably performed continuously. The process of the invention can advantageously be conducted in a manner wherein the hydroformylation takes place in a first step (a reaction zone), followed by a second step in which the catalyst is separated from the product. Examples of possible reaction zones are one or more continuously stirred tank reactors

or a tubular reactor. Since the catalyst readily dissolves in the water phase, the formyl carboxylic acids can easily be separated from the catalyst-containing water phase. Possible separation techniques are for example distillation, crystallization and extraction. The reaction products are preferably isolated from the water phase by means of extraction with a less polar organic solvent. Possible organic solvents are, for instance, aromatic solvents such as benzene, toluene, xylene and ethers, for example diethylether, methyl t-butyl ether, esters, for example butylacetate, ethylacetate and other solvents, for example dichloromethane, 1,2-dichloroethane, dioxane, diglyme. After the products have been separated from the water phase, the catalyst-containing water phase may advantageously be recirculated to the reaction zone. An advantage of the catalyst system according to the invention is that no or hardly any platinum and ligand is lost when the products are extracted by the organic extraction agent. The linear formyl carboxylic acid or the linear formylnitrile can be separated from the other by-products, for example the non-linear aldehyde by-products, by normal separation techniques, for example crystallization, extraction or distillation, for example extractive distillation.

The invention also relates to a process for the preparation of terminal dicarboxylic acids in general and of adipic acid in particular starting from the (terminal) ω-formylcarboxylic acid and 5-formylvaleric acid respectively, which starting compound is obtained by the above described process. The yield of dicarboxylic acids prepared by the aforementioned process will in this process be increased by oxidizing the formyl carboxylic acid formed, preferably in the presence of the already formed dicarboxylic acids. Such oxidation is described in, for instance, EP-A-295551, EP-A-131860 and in Basic Principles of Organic Chemistry (J.D. Roberts, M.C.

Caserio, 2nd ed., pp 712-713). As a rule, the formyl carboxylic acid is oxidized at 50 to 80°C in the presence of oxygen or an oxygen-containing gas, optionally in the presence of a catalyst. That catalyst may be for instance an Mn or Co-containing catalyst.

The invention in addition relates to a process for the preparation of terminal aminocarboxylic acid and especially 6-aminocaproic acid. For example the 5-formyl- valeric acid prepared by the process according to the invention can advantageously be converted into the 6- aminocaproic acid by reductive amination (with hydrogen and ammonia). The reductive amination of the 5-formyl valeric acid can be effected using the process described in, for instance, US-A-4950429. As a rule, the reductive amination is effected with an excess of ammonia and hydrogen in the presence of a hydrogenation catalyst and optionally a solvent at a temperature of from 50 to 150°C and at increased pressure of from 1.0 to 40 MPa. Examples of suitable solvents are water and mono or polyhydric alcohols having from 1 to 5 carbon atoms. Water is preferably used.

Examples of suitable hydrogenation catalysts are metals from Group VIII of the Periodic System of Elements (CAS version, from Chemical and Engineering News, 63(5), 27, 1985). Examples of such catalysts are cobalt and nickel catalysts and the noble-metal catalysts ruthenium, platinum and palladium. The catalysts may contain activity-enhancing additives. Examples of such additives are Zr, Mn, Cu and Cr. The catalysts may consist in their entirety of the above-mentioned elements or of a carrier, for instance aluminium oxide, kiesel gel, activated carbon, carrying the active metals. For more information on how the reductive amination should be conducted, reference is for brevity made to the aforementioned US-A- 4950429.

6-aminocaproic acid prepared by the above described process starting from 5-formylvaleric acid can

advantageously be converted into ε-caprolactam by means of ring closure at 150-370°C in a suitable solvent, for example an C^-Os alkanol or water.

With the above described process for preparing ε-caprolactam it is possible to diminish the number of process steps compared to for example the process described in US-A-4950429. US-A-4950429 describes a process in which a 5-formylvalerate ester, obtained by hydroformylation, is first saponified to 5-formylvaleric acid, then converted to 6-aminocaproic acid by means of reductive amination and subsequently the 6-aminocaproic acid is cyclisized to ε-caprolactam. With the process according to the invention it is possible to directly start the reductive amination with the product of the hydroformylation without an additional saponification. The invention will now be elucidated with reference to the following non-limiting examples. The selectivity mentioned in the examples is calculated as the molar amount of the specific product formed relative to the molar amount of substrate converted times 100%.

Example I

The following were weighed into a 150-ml Hastalloy C autoclave: 37.4 mg (0,1 mmol) of CODPtCl ₂ (COD = 1,5-cyclooctadiene) and 89.7 mg (0.1 mmol) of tetrasulphonated trans-1,2-bis(diphenylphosphino- methylene)cyclobutane in 45 ml of degassed water. After half an hour of stirring, 4.9 g of freshly distilled 3- pentenoic acid was added and the autoclave was heated to 100°C at 5.0 MPa with C0/H ₂ = 1 (mol/mol). The final pressure was adjusted to 8.0 MPa with the CO/H ₂ gas mixture. After 4 hours the reaction mixture was cooled, depressurized and the aqueous mixture was extracted with 3x100 ml of diethyl ether. The etheral phases were collected and the residual aqueous phase was evaporated at 50°C, 50 mm Hg. Next, 200 ml of toluene and 1.0 g of decane was added. This organic layer was analyzed by

gaschromatography (GC). The water phase was evaporated until a solid residue remained. The obtained residue was dissolved in diethylether and after adding 0.2 g of decane the solution was analyzed by GC. This brought the overall mass balance to 94.1%, conversion : 80.3%, selectivity for aldehydes: 83%, N/Br (= linear aldehyde/branched aldehyde)= 3.4, selectivity for valeric acid: 4.6%, selectivity for adipic acid: 8.1%.

Example II

Example I was repeated except that the tetrasulphonated trans-1,2-bis(diphenylphosphino- methylene)cyclobutane was replaced by monosulphonated trans-1,2-(diphenylphosphinomethylene)cyclobutane. The conversion was 23.5%. The selectivity for aldehydes was 94.6%, N/Br = 5.25, selectivity for valeric acid was 4.9%. No dicarboxylic acids were formed.

Example III Example I was repeated except that 2-pentenoic acid was used in place of 3-pentenoic acid.

After 3 hours of reaction time, the conversion was 37.1%, the selectivity for aldehydes was 84.2%, N/Br was 3.5, the selectivity for valeric acid was 5.7 and the selectivity for dicarboxylic acids was 9.4%.

Example IV

Example I was repeated except with that 30 ml of degassed toluene and 17.5 μl (0.2 mmol) trifluoromethane- sulphuric acid were added to the aqueous mixture (before the addition of the substrate in the process of

Example I).

After 3.5 hours of reaction time a conversion of 86% was reached. The selectivity to aldehydes was 86.9% with N/Br of 3.9. The selectivity to valeric acid and dicarboxylic acids was 5.2% and 7.2%, respectively.

Example V

Example I was repeated except with that, one half of the amounts of CODPtCl ₂ and the phosphine ligand of Example I were used and the reaction was carried out at 130°C under 100 bar of CO/H ₂ = 1/1. After 1 hour of reaction time the conversion was 68%, the selectivity to aldehydes was 71.8% with N/Br of 3.0. The selectivity to valeric acid and dicarboxylic acid was 16.8% and 11.2%, respectively.

Example VI

Example I was repeated except with that, 58.4 mg (0.1 mmol) of trans-1.2-bis[phenyl-(4-lithiumsulfonato-l- butyl)phosphinomethylene]cyclobutane was used instead of the tetrasulphonated phosphine. After 5 hours of reaction time a conversion of 35.2% was reached. The selectivity to aldehydes was 90.7% with a N/Br of 2.6. The selectivity to valeric acid was 9.3%. No dicarboxylic acid products were obtained.

Example VII

Example I was repeated except with that, 41.1 mg (0.1 mmol) Pt(C0D) ₂ was used instead of C0DPtCl ₂ and 30 ml of degassed toluene was added before the addition of the substrate. After 4 hours of reaction time a conversion of 72.5% was reached. The selectivity to aldehydes was 86.5% with a N/Br of 4.0. The selectivity to valeric acid and dicarboxylic acids was 4.5% and 9.0%, respectively.

Example VIII

Example I was repeated using 5.3 g of 3- pentenoic acid. The pressure was relieved after the reaction mixture had cooled down. The aqueous reaction mixture was then extracted with ether (3 x 50 ml) under a nitrogen atmosphere. After this first cycle the ether phase was analyzed by GC. The amounts of products and starting materials in the ether layer are given in Table

1. Hereafter, an amount of fresh 3-pentenoic acid was added to the aqueous phase (Table 1, column 1), whereupon the reaction was repeated in the manner described above. This cycle was repeated five times. The etheral extract was analyzed by GC after each cycle. After the last cycle the water phase was also analyzed by GC. Table 1 shows the amounts of 3-pentenoic acid and the results of each cycle. These results indicate that the catalyst can readily be reused while retaining its activity.

The total conversion after 4 cycles was 78.8%. The selectivity for valeric acid was 6.2%, for 5- formylvaleric acid 62%, for total formylvaleric acids 80.3%, for dicarboxylic acids 11.4%. N/Br was 3.4.

Example IX

Purification of 5-formylvaleric acid (5 FVA) by crystallisation: 3.0 g mixture of 5-formylvaleric acid (80%), 4-formylvaleric acid (16%) and 3-formylvaleric acid (4%), obtained by the process according to the invention, was dissolved in methyl tert-butyl ether at room temperature. Upon cooling at -20°C, 1.4 g of a white crystalline material was obtained. Melting point: 36-37°C. According to ^X E NMR and GC analysis this material consisted of more than 96 % of 5-formylvaleric acid.

Example X

The following were weighed into a 150-ml hastalloy C autoclave: 37.4 mg of CODPtCL ₂ (COD = 1,5- cyclooctadiene) and 90 mg of tetra sulphonated trans-1,2- bis(diphenylphosphino-methylene)cyclobutane in 45 ml of degassed water. After half an hour, 4.43 g of trans-3- pentenenitrile was added and the autoclave was heated to 100°C at 5.0 MPa with CO/H ₂ = 1. The final pressure was adjusted to 8.0 MPa with the same CO/H ₂ mixture. After 4 hours the reaction mixture was cooled and the water layer was extracted 3 times using 100 ml of diethylether. Next,

anisole was added to the ether layer as internal standard. The molar mass of all components was determined by GC-MS. Also, a portion of the ether layer was concentrated by evaporation and analyzed by ~E and ^I3 C NMR. The following results were obtained in this way: Conversion: 20.7%.

Total aldehyde selectivity: 91.4 wt.% (N/Br = 6.6; N/Br = linear aldehyde/branched aldehyde). Selectivity to pentanenitrile: 3.7 wt.% and to carboxylic acid nitrile compounds: 3 wt.%. Practically no isomerization to trans- 2-pentenenitrile was observed.

T A B L E

total selectivity (sel) for valeric acid, 5-formylvaleric acid etc. after 4 cycles