Process for the preparation of unsaturated macrocyclic ketones (II)

Description

FIELD OF THE INVENTION

[0001] The invention is in the field of the preparation of unsaturated macrocyclic monoketones from macrocyclic dienes in a one-step oxidation in the presence of an oxidizing agent, a palladium(II) salt and / or a palladium(II) complex, a co-catalyst and a solvent. TECHNOLOGICAL BACKGROUND

[0002] Ketones are suitable as solvents and chemical raw materials and are therefore used in a variety of fields. Such ketones are generally produced by two-step reaction processes in which an alcohol produced by hydrating an olefin is dehydrated. Simpler one-step reaction processes in which an olefin is directly oxidized are now also known.

[0003] Two-step processes for the preparation of macrocyclic monoketones are known in the art. The industrial synthesis of macrocyclic ketones is achieved, for example, by selective monoepoxidation and rearrangement of the epoxide to the ketone in the presence of alkali or alkaline earth halides, as described in BD Mookherjee, RW Trenkle, RR Patel, J. Org. Chem. 36 (1971), 3266. Reduction of the epoxy group to a hydroxy group followed by subsequent oxidation to the ketone is described, for example, in US Pat. No. 3,718,696.

[0004] The Wacker process, using a PdCl2 / CuCl2 catalyst, is known as one of the direct olefin oxidation processes. This process is effective for the oxidation of terminal olefins, each with a carbon-carbon double bond (hereinafter abbreviated as "C=C bond") at one end of a molecule. However, this process achieves only low reactivity when used for the oxidation of internal olefins, each with a C=C bond at a position other than their ends. This process also fails to achieve satisfactory results when the number of carbon atoms in the starting material is increased, as the reaction rate is significantly reduced.For this reason, in the industrial field, the use of the Wacker process is limited only to the production of lower carbonyl compounds such as acetaldehyde and acetone, which are obtained by oxidation of lower terminal olefins. RELEVANT STATE OF THE ART

[0005] Kaneda et al. developed a method that does not require a cooxidant for the reoxidation of Pd(0), but in which oxygen directly reoxidizes Pd(0) to Pd(II). A dimethylacetamide / H 2 O mixture is used at 80 °C (T. Mitsudome, T. Umetani, N. Nosaka, K. Mori, T. Mizugaki, K. Ebitani, K. Kaneda, Angew. Chem. Int. Ed. 45 (2006) 481 ). This process also allows the oxidation of linear internal olefins and cyclic olefins such as cyclohexene ( T. Mitsudome, K. Mizumoto, T. Mizugaki, K. Jitsukawa, K. Kaneda, Angew. Chem. Int. Ed. 49 (2010) 1238 ).However, only chlorine-containing palladium catalysts were successful. Our own investigations showed that using macrocyclic olefins and dienes as substrates, this method yields only insufficient yields of the desired ketones, even when using a co-oxidant.

[0006] Another variation of the Wacker oxidation of olefins using cationic palladium complexes is described in US 20140194604. However, no macrocyclic dienes are used as starting substrate.

[0007] WO 2010 061807 also describes a modification of the Wacker process in which macrocyclic dienes are also used as starting substrates. However, this process only describes dienes with a maximum ring size of 8 carbon atoms.

[0008] EP 2364965 A1 (KANEDA) further relates to a process for the preparation of ketones in which olefins (e.g., cyclooctene) are oxidized with oxygen in the presence of Pd catalysts in amide solvents. Suitable Pd catalysts include halides and their complexes with amide solvents, but not Pd-ligand systems. OBJECT OF THE INVENTION

[0009] Macrocyclic dienes form a chelate complex with Pd(II) species / compounds. However, the spatial arrangement of the ligand and its flexibility hinder further coordination of the reacting components, significantly limiting the activity and selectivity of the reaction. This is one of the reasons why such macrocyclic dienes react very poorly in the state-of-the-art processes. This is further reinforced by the fact that these very nonpolar macrocyclic dienes exhibit only limited solubility in polar solvents. Consequently, satisfactory yields cannot be achieved with the state-of-the-art processes.

[0010] The object of the present invention was therefore to provide a process that overcomes the disadvantages of the prior art. Specifically, the object was to provide a process that enables simple, material- and energy-saving, and thus sustainable, process control, while simultaneously achieving economical yields. DESCRIPTION OF THE INVENTION

[0011] The subject matter is a process for the preparation of unsaturated macrocyclic monoketones comprising the following steps: (a) providing macrocyclic dienes having a ring size of at least 9 carbon atoms; (b) contacting the starting materials from step (a) with (b1) a palladium(II) salt and / or a palladium(II) complex; and (b2) an oxidizing agent; and (b3) a solvent; (b4) a co-catalyst; (b5) an acid, and optionally (b6) a ligand; wherein the co-catalyst (b4) contains or consists of a di- or trivalent iron salt which is different from FeSO4 and is preferably iron(III) nitrate.

[0012] Surprisingly, it was discovered that the above-mentioned process can produce unsaturated macrocyclic monoketones in significantly higher yields than previously known or expected from the state of the art. Commercial use of the resulting isomers is also possible, making the process extremely sustainable and efficient.

[0013] A further advantage of the invention is that the macrocyclic dienes are converted so effectively by the process according to the invention that even if the macrocyclic dienes are present as a mixture of E,E, E,Z and Z,Z isomers, each of which has a different reactivity, they can be selectively oxidized to a monoketone without the formation of undesirable amounts of diketones.

[0014] Fig. 1 illustrates the sequence of the manufacturing process according to the invention by way of example. However, this figure represents only an example and is in no way intended to be limiting.

[0015] The macrocyclic diene (a) preferably contains two non-conjugated double bonds. In a preferred embodiment of the invention, the macrocyclic diene has a ring size of 9 to 30 carbon atoms, preferably 12 to 18 carbon atoms, and particularly preferably 16 carbon atoms. In a particularly preferred embodiment, the macrocyclic diene (a) is 1,9-cyclohexadecadiene (CHDD).

[0016] In a further preferred embodiment of the process according to the invention, the macrocyclic diene (a) used is a mixture of various stereoisomers. In a particularly preferred embodiment of the process according to the invention, the macrocyclic diene (a) is 1,9-cyclohexadecadiene (CHDD) and is present as a mixture of E,E, E,Z, and Z,Z isomers.

[0017] Cyclohexadec-8-enone (8-CHD) is preferably prepared by the preparation process according to the invention. In a particularly preferred embodiment of the invention, CHDD is used as the macrocyclic diene (a), whereby 8-CHD is obtained by applying the preparation process according to the invention.

[0018] In a first embodiment of the invention, the solvent (b3) is a polar aprotic solvent. The solvent (b3) is preferably selected from the group consisting of N,N-disubstituted open-chain and cyclic acid amides, such as dimethylformamide, dimethylacetamide, diethylacetamide, dimethylpropionamide, N-methylpyrrolidone, aliphatic, cycloaliphatic, or aromatic nitriles such as acetonitrile, propionitrile, or benzonitrile, or linear and cyclic ethers, cyclic lactones, and carbonates.

[0019] In a first embodiment of the invention, small amounts of water are preferably added to the solvent (b3). Preferably in an amount of 0.1 to 25 vol.%, more preferably in an amount of 1-20 vol.%, and particularly preferably in an amount of 5-15 vol.%. The volume percentages refer to the solvent (b3).

[0020] Furthermore, in a first embodiment of the invention, the ligand (b6) is obligatorily present in the process according to the invention. The ligand is preferably a bidentate ligand. The use of a bidentate ligand is advantageous because, on the one hand, it has such strong donor properties that it can molecularly stabilize the palladium(II) salt and / or the palladium(II) complex and thus prevent palladium(O) from precipitating. On the other hand, the ligand can have space-consuming substituents that prevent chelation of palladium by the starting material (a). Preferably, the ligand contains N,N, N,O, N,S and / or O,O donor atoms. More preferably, the ligand contains N,N, N,O and / or O,O donor atoms. These atoms can be part of a cyclic system or be linked to one another via other suitable bridging groups.

[0021] Fig.2illustrates bidentate ligands used for one embodiment of the process according to the invention. This figure is exemplary and not intended to be limiting.

[0022] In a first embodiment of the process according to the invention, the palladium(II) salt and / or the palladium(II) complex (b1) are selected from the group consisting of palladium bromide, palladium acetate, palladium trifluoroacetate, palladium benzoate,

[0023] Tetrakis(acetonitrile)palladium(II) tetrafluoroborate, tetrakis(acetonitrile)palladium(II) bis(trifluoromethanesulfonate), palladium nitrate and / or palladium sulfate.

[0024] Furthermore, a first embodiment of the process according to the invention is characterized in that the palladium(II) salt and / or the palladium(II) complex (b1) with the bidentate ligand (b6) form a palladium compound of the formula (I) and / or the formula (II) wherein X and Y each independently represents N,N, O,N or O,O; and wherein Z each independently represents a halogen, acetate, trimethyl acetate, trifluoromethyl acetate, MeCN, PhCN, NO 2 , NO, nitrate, nitrite or sulfate; where X and Y each independently represent O,O, N,N or O,N.

[0025] The palladium compound thus obtained in a first embodiment of the invention is present in a concentration of 0.01 to 25 mol%, preferably 1 to 20 mol%, particularly preferably 1 to 15 mol%, and more preferably 1 to 5 mol%. The mol% data refer in each case to the starting material (a).

[0026] In a first embodiment of the invention, a neutral palladium catalyst is preferred for the palladium compound.

[0027] The formation of the palladium compounds according to formulas (I) and / or (II) can be carried out either in situ or ex situ in a separate preparation process. In a separate ex situ preparation, instead of the palladium(II) salt and / or the palladium(II) complex (b) and the ligands (b6), the palladium compounds are brought into direct contact with the starting material (a) of the preparation process according to the invention.

[0028] In a first embodiment of the invention, an oxygen-containing gas is used as the oxidizing agent (b2). The oxygen-containing gas preferably contains oxygen in a concentration of 1 to 100 vol.%, more preferably 5 to 100 vol.%, and most preferably 21 to 100 vol.%.

[0029] Furthermore, in a first embodiment, the process according to the invention is carried out at elevated temperatures. Preferably at temperatures from 50°C to 120°C, more preferably from 60°C to 100°C, most preferably from 70°C to 90°C.

[0030] In a second embodiment of the invention, the solvent (b3) is a polar aprotic solvent. The solvent (b3) is preferably selected from the group consisting of N,N-disubstituted open-chain and cyclic acid amides, such as dimethylformamide, dimethylacetamide, diethylacetamide, dimethylpropionamide, N-methylpyrrolidone; aliphatic, cycloaliphatic, or aromatic nitriles such as acetonitrile, propionitrile, or benzonitrile; or linear and cyclic ethers, cyclic lactones, and carbonates.

[0031] In the context of the invention, the use of the singular, such as "a" or "an" or "the," may also include the plural, unless the context clearly indicates otherwise. For example, the term "the solvent" may also encompass a plurality of solvents, including mixtures thereof, such as a solvent mixture.

[0032] In a second embodiment of the invention, small amounts of water are preferably added to the solvent (b3). Preferably in an amount of 0.1 to 25 vol.%, more preferably in an amount of 1-20 vol.%, and particularly preferably in an amount of 5 to 15 vol.%. The volume percentages refer to the solvent (b3).

[0033] The co-catalyst (b4) and the acid (b5) are obligatory in the process according to the invention.

[0034] Other suitable co-catalysts (b4), in addition to the iron salts mentioned above – with the exception of FeSO4 – include, for example, quinones, heteropolyacids, and polyoxometalates, or metal complexes whose central metal can easily switch between oxidation states II / III, II / IV, IV / V, or I / II upon oxidation with oxygen. Central metals of such suitable complexes can be selected, for example, from the group consisting of Fe, Cu, Mn, Co, Ni, and V. The co-catalysts are preferably used in combination to support and facilitate electron transfers during the redox processes. In a preferred embodiment, the co-catalysts are selected from the group consisting of benzoquinones, naphthoquinones, anthraquinones, molybdophosphoric acid, molybdovanadatophosphoric acids, tungstomolybdophosphoric acids, tungstovanadatophosphoric acids, phthalocyanine complexes, CuCl, CuCl 2 , CuSO 4 , VOSO 4 .In these cases, a combination of, for example, Fe(NO 3 ) 3 and FeSO 4 , for example in a weight ratio of 1:1, is also possible.

[0035] In a second embodiment of the invention, the co-catalyst (b4) is preferably added in a concentration of 1 to 300 mol%, more preferably 5 to 150 mol%, and most preferably 10 to 100 mol%. The mol% data refer in each case to the starting material (a).

[0036] In a second embodiment of the invention, the acid (b5) is preferably a Brønsted acid and / or a Lewis acid. Suitable Brønsted acids include inorganic mineral acids with weakly coordinating anions and organic carboxylic, sulfonic, and phosphonic acids. Sulfonic acids are particularly suitable. Lewis acids include compounds with an incomplete or unstable electron octet, such as B(CH3)3, BF3, and AlCl3.

[0037] In a second embodiment of the invention, the acid (b5) is preferably added in a concentration of 5 to 500 mol%, more preferably 15 to 300 mol%, even more preferably 30 to 200 mol%, and most preferably 50 to 150 mol%. The mol% data refer in each case to the starting material (a).

[0038] In a preferred embodiment of the invention, the acid is a Brønsted acid. The Brønsted acid is preferably added in a concentration of 5 to 500 mol%, more preferably 15 to 300 mol%, even more preferably 30 to 200 mol%, and most preferably 50 to 150 mol%. The mol% data refer in each case to the starting material (a).

[0039] Furthermore, in a second embodiment of the invention, the palladium(II) salt and / or the palladium(II) complex (b1) is preferably used in a concentration of 0.01 to 20 mol%, more preferably 0.5 to 10 mol%, and particularly preferably 1 to 5 mol%. The mol% data refer in each case to the starting material (a).

[0040] In a second embodiment of the invention, a palladium compound is preferably formed by mixing a palladium(II) salt and / or a palladium(II) complex (b1) with a Brønsted acid (b5) and a suitable solvent (b3), preferably a polar aprotic solvent. This palladium compound can be prepared either in situ or ex situ in a separate preparation process. In a separate ex situ preparation, instead of the palladium(II) salt and / or the palladium(II) complex (b) and the acid (b5), the preformed palladium compounds are contacted with the starting material (a) and the co-catalyst (b4) as well as a suitable solvent (b3) of the preparation process according to the invention.

[0041] In a preferred embodiment, this palladium compound is a cationic palladium catalyst.

[0042] In a second embodiment of the invention, the cationic palladium compound is preferably used in a concentration of 0.01 mol% to 20 mol%, preferably in a concentration of 0.5 mol% to 10 mol%, and particularly preferably in a concentration of 1 to 5 mol%. The mol% values ​​refer in each case to the starting material (a).

[0043] The process according to the invention of a second embodiment of the invention is preferably carried out at temperatures between 0°C and 100°C, more preferably between 0°C and 50°C, and most preferably between 0°C and 25°C. INDUSTRIAL APPLICABILITY

[0044] According to the present invention, unsaturated macrocyclic monoketones can be prepared, in particular from macrocyclic dienes having a ring size of at least 9 carbon atoms; and most preferably from macrocyclic dienes having a ring size of 16 carbon atoms, which can be further processed, for example, into valuable fragrances, aromas, or flavors.

[0045] The unsaturated macrocyclic monoketones obtained by the preparation process according to the invention can be purified by conventional separation methods, for example by preparative high-performance liquid chromatography (HPLC) or fractional distillation. EXAMPLES Examples 1 and 2, comparative examples V1 to V3 DMA / MeCN / H 2 O = 4 / 3 / 1; Pd(NO 3 ) 2 · 2 H 2 O and variation of the co-catalyst under pure oxygen atmosphere)

[0046] In a sealable 4 ml glass reactor with screw cap and septum, a solvent system consisting of N ,N -Dimethylacetamid, Acetonitril und Wasser (DMA / MeCN / H 2 O =4 / 3 / 1; V sat. = 3 mL), 1,9-CHDD (mixture of isomers; 44 mg; 0.2 mmol) was initially introduced into a reaction vessel. Palladium(II) nitrate dihydrate (0.01 mmol; 5.0 mol%), para-toluenesulfonic acid monohydrate (76 mg; 0.4 mmol), and a co-catalyst (10-20 mol%) were added to this solution. The reactor was sealed, the septum pierced with a disposable needle, and the reaction mixture placed in an autoclave. The autoclave was purged with oxygen, and the oxygen pressure was then applied (1 bar). The reaction mixture was stirred vigorously in the autoclave at room temperature for 18 h. The autoclave was then depressurized, and the reaction solution was filled to a constant volume with tetrahydrofuran and homogenized. Qualitative and quantitative analysis of the reaction products was performed using an internal standard (n-hexadecane) on a GC / MS with FID. Examples 1 and 2 are according to the invention, examples V1 to V3 are for comparison. The results are shown in Table 1summarized. Table 1 Variation Co-catalysts Example Co-catalyst Co-Cat. [Mol%] X 1,9-CHDD [%] S8-CHD [%] S DIKETONE [%] Y8-CHD [%] V1 - - 26 81 19 21 V2 Cu(NO 3 ) 2 · 3 H 2 O 10 26 77 8 20 V3 Benzoquinone 10 28 75 10 21 1 Fe(NO 3 ) 3 · 9 H 2 O 10 41 72 8 29 2 Fe(NO 3 ) 3 · 9 H 2 O 20 44 68 9 30 Examples 3 to 9 DMA / MeCN / H 2 O; Pd(NO 3 ) 2 · 2 H 2 O; Fe(NO 3 ) 3 · 9 H 2 O and variation of the solvent ratio under pure oxygen atmosphere

[0047] In a sealable 4 ml glass reactor with screw cap and septum, a solvent system consisting of N , NDimethylacetamide, acetonitrile, and water (V total = 3 ml), 1,9-CHDD (mixture of isomers; 44 mg; 0.2 mmol) were initially introduced. Palladium(II) nitrate dihydrate (0.01 mmol; 5.0 mol%), para-toluenesulfonic acid monohydrate (38 mg; 0.2 mmol), and iron(III) nitrate nonahydrate (8 mg; 0.02 mmol) were added to this solution. The reactor was sealed, the septum pierced with a disposable needle, and placed in an autoclave. The autoclave was purged with oxygen, and then the appropriate oxygen pressure was applied (3-5 bar). The reaction mixture was then stirred vigorously in the autoclave at room temperature for 18-20 h. The autoclave was then depressurized, and the reaction solution was filled to a constant volume with tetrahydrofuran and homogenized. Qualitative and quantitative analysis of the reaction products was performed using an internal standard ( n -Hexadecane) on a GC / MS with FID. The results are shown in Table 2 summarized. Table 2 Variation solvent ratio Example DMA / MeCN / H2O Oxygen [bar] Time [h] X 1,9-CHDD [%] S8-CHD [%] S DIKETONE [%] Y8-CHD [%] 3 7 / - / 1 5 18 8 29 6 2 4 6 / 1 / 1 3 18 38 69 8 26 5 10 / 4 / 3 5 18 49 57 12 28 6 5 / 2 / 1 5 18 46 75 11 35 7 10 / 4 / 1 3 20 45 82 13 37 8 7 / 7 / 2 3 18 44 70 8 30 9 2 / 5 / 1 3 18 35 69 7 24 Examples 10 to 16 DMA / MeCN / H2O = 10 / 4 / 1; Pd(NO 3 ) 2 · 2 H 2 O; Fe(NO 3 ) 3 · 9 H 2 O and variation of the reactant concentration under pure oxygen atmosphere

[0048] A solvent system consisting of N,N-dimethylacetamide, acetonitrile, and water (DMA / MeCN / H2O = 10 / 4 / 1; V sat. = 3 ml), 1,9-CHDD (mixture of isomers; 0.1–1.0 mmol) was placed in a sealable 4 ml glass reactor with a screw cap and septum. The appropriate amounts of palladium(II) nitrate dihydrate (5.0 mol%), para-toluenesulfonic acid monohydrate (100 mol%), and iron(III) nitrate nonahydrate (10 mol%) were added to this solution. The reactor was sealed, the septum was pierced with a disposable needle, and the reactor was placed in an autoclave. The autoclave was purged with oxygen, and the appropriate oxygen pressure was subsequently applied (3–5 bar). The reaction mixture was then stirred vigorously in the autoclave at room temperature for 5–20 h. The autoclave was then depressurized and the reaction solution was filled to a constant volume using tetrahydrofuran and homogenized.The qualitative and quantitative analysis of the reaction products was performed using an internal standard (n-hexadecane) on a GC / MS with FID. The results are shown in . Table 3 summarized. Table 3 Variation of reactant concentration Example Educt concentration [mmol] Oxygen [bar] Time [h] X 1,9-CHDD [%] S8-CHD [%] S DIKETONE [%] Y8-CHD [%] 10 0,1 5 5 26 69 5 18 11 0,2 5 5 39 76 9 29 12 0,2 3 20 45 82 13 37 13 0,4 5 5 34 80 9 27 14 0,5 3 5 35 82 14 28 15 0,5 3 8 41 83 13 33 16 1,0 3 5 32 76 15 25 Examples 17 to 20 DMA / MeCN / H2O = 10 / 4 / 1; Pd(NO 3 ) 2 · 2 H 2 O; Fe(NO 3 ) 3 · 9 H 2 O and variation of catalyst concentrations under pure oxygen atmosphere

[0049] In a sealable 4 ml glass reactor with screw cap and septum, a solvent system consisting of N , N-Dimethylacetamide, acetonitrile and water (DMA / MeCN / H2O = 10 / 4 / 1; V sat. = 3 ml), 1,9-CHDD (mixture of isomers; 110 mg; 0.5 mmol) were initially charged. The appropriate amounts of palladium(II) nitrate dihydrate (5-10 mol%), para-toluenesulfonic acid monohydrate (95 mg; 0.5 mmol) and iron(III) nitrate nonahydrate (10-20 mol%) were added to this solution. The reactor was sealed, the septum pierced with a disposable needle and placed in an autoclave. The autoclave was flushed with oxygen and then the appropriate oxygen pressure was applied (3 bar). The reaction mixture was then stirred vigorously in the autoclave at room temperature for 7 h. The autoclave was then depressurized and the reaction solution filled to a constant volume with the aid of tetrahydrofuran and homogenized. The qualitative and quantitative analysis of the reaction products was carried out using an internal standard (n-hexadecane) on a GC / MS with FID. The results are shown in Table 4summarized. Table 4 Variation catalyst concentration Example Pd(II) concentration [mol%] Fe(III) concentration [mol%] X 1,9-CHDD [%] S8-CHD [%] S DIKETONE [%] Y8-CHD [%] 17 5 10 36 79 11 28 18 5 20 37 65 6 24 19 10 10 62 71 17 44 20 10 20 63 63 14 39

Claims

1. A process for the preparation of unsaturated macrocyclic monoketones comprising the following steps (a) providing macrocyclic dienes having a ring size of at least 9 carbon atoms; (b) contacting the starting materials from step (a) with (b1) a palladium(II) salt and / or a palladium(II) complex; (b2) an oxidizing agent; (b3) a solvent; (b4) a co-catalyst; (b5) an acid; and optionally (b6) a ligand; whereby the co-catalyst (b4) comprises or consists of a di- or trivalent iron salt other than FeSO4, preferably iron (III) nitrate.

2. The process according to claim 1, characterized in that the solvent (b3) is a polar aprotic solvent and is preferably selected from the group consisting of N,N-disubstituted open-chain and cyclic acid amides, such as dimethylformamide, dimethylacetamide , diethylacetamide, dimethylpropionamide, N-methylpyrrolidone, aliphatic, cycloaliphatic or aromatic nitriles such as acetonitrile, propionitrile or benzonitrile, or linear and cyclic ethers, cyclic carbonates and lactones.

3. The process as claimed in claims 1 and / or 2, characterized in that the ligand (b4) is ob-ligatorily present, the ligand being a bidentate ligand and containing N,N-, N,O-, N,S- or O,O-donor atoms.

4. The process according to one of claims 1 to 3, characterized in that the palladium(II) salt and / or the palladium(II) complex (b1) are selected from the group consisting of palladium bromide, palladium acetate, palladium trifluoroacetate, palladium adium benzoate, palladium nitrate, palladium sulfate, tetrakis(acetonitrile)palladium(II) tetrafluoroborate and / or tetrakis(acetonitrile)palladium(II) bis(trifluoromethanesulfonate).

5. The process according to any one of claims 1 to 4, characterized in that the palladium (II) salt and / or the palladium (II) complex (b1) with the bidentate ligand (b4) form a palladium compound of formula (I) and / or formula (II) , wherein each of X and Y independently represents N,N, O,N or O,O; and wherein each Z is independently halo, acetate, trimethyl acetate, trifluoromethyl acetate, MeCN, PhCN, NO2, NO, nitrate, nitrite or sulfate; wherein X and Y are each independently of the other O, O, N, N or O, N.

6. The process according to claim 5, characterized in that the palladium compound is added in a concentration of from 0.01 to 25 mol-%, preferably from 1 to 20 mol-%, particularly preferably from 1 to 5 mol-%, based in each case on the starting material (a).

7. The process according to any one of claims 1 to 6, characterized in that an oxygen-containing gas is used as oxidant (b2).

8. The process according to claim 7, characterized in that the oxygen-containing gas contains oxygen in a concentration of 1 to 100% by volume, preferably of 5 to 100% by volume and most preferably of 10 to 100% by volume.

9. The process according to any one of claims 1 to 8, characterized in that the process is carried out at temperatures from 0°C to 100°C, preferably between 0°C and 50°C, and most preferably between 0°C and 25°C.

10. The process according to any one of claims 1 to 9, characterized in that (i) the co-catalyst (b5) comprises at least one further component selected from the group consisting of benzoquinones, naphthoquinones, anthraquinones, molybdato phosphoric acid, molybdato vanadate phosphoric acids, tungstate molybdate phosphoric acids, tungstate vanadate phosphoric acids, phthalocyanine complexes, FeSO4, CuCl, CuCl2, CuSO4, VOSO4 and (ii) the acid (b) is a Bronsted acid or Lewis acid.

11. The process according to any one of claims 1 to 10, characterized in that the co-catalyst (b5) is added in a concentration of from 1 to 300 mol-%, preferably from 5 to 150 mol-% and most preferably from 10 to 100 mol-%, each with respect to the starting material (a).

12. The process according to any one of claims 1 to 11, which comprises adding the acid (b6) in a concentration of from 5 to 500 mol-%, preferably from 15 to 300 mol-%, more preferably from 30 to 200 mol-% and most preferably from 50 to 150 mol-%, in each case based on the starting material (a).

13. The process according to any one of claims 1 to 12, which comprises adding the palladium(II) salt and / or the palladium(II) complex (b1) in a concentration of from 0.01 to 20 mol%, preferably from 0.5 to 10 mol% and particularly preferably from 1 to 5 mol%, in each case based on the starting material (a).

14. The process according to any one of claims 1 to 13, characterized in that the process is carried out at temperatures between 0°C and 100°C, preferably between 0°C and 50°C, and most preferably between 0°C and 25°C.