Electrochemical oxidation of cycloalkenes and cycloalkanes to α,ω-dicarboxylic or ketocarboxylic acids and cycloalkanone compounds.

Abstract

The present invention relates to a method for producing unsubstituted or at least monosubstituted α,ω-dicarboxylic acids or ketocarboxylic acids and unsubstituted or at least monosubstituted cycloalkanones by electrochemically oxidizing unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkenes and unsubstituted or at least monosubstituted saturated alicyclic hydrocarbons in an electrolytic cell in the presence of inorganic or organic nitrates in a reaction medium in the presence of oxygen.

Description

[Technical field]

[0001] The present invention relates to a process for the preparation of unsubstituted or at least monosubstituted α,ω-dicarboxylic acids or ketocarboxylic acids and unsubstituted or at least monosubstituted cycloalkanones by electrochemical oxidation of unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkenes and unsubstituted or at least monosubstituted saturated alicyclic hydrocarbons in the presence of inorganic or organic nitrates in an electrolytic cell in a reaction medium in the presence of oxygen. [Background technology]

[0002] α,ω-Dicarboxylic acids, ketocarboxylic acids and cycloalkanone compounds are important substrates in synthetic organic chemistry and are monomeric components in polymer synthesis, and therefore highly relevant for industrial applications. Conventional methods for obtaining these substrates from cycloalkanes and cycloalkenes are essentially based on transition metal catalysis and the use of chemical oxidants.

[0003] The electrochemical oxidation of cycloalkanes to the corresponding ketones has not yet been described.Only a few examples of electrochemical oxidative double bond cleavage of cyclooctene and cyclododecene to produce dicarboxylic acids / their methyl esters are known (U.Baumer, Electrochimica Acta 2003, 4, 489-495; U.-St.Baumer, HJ Schafer, J.Appl.Electrochem. 2005, 35, 1283-1292; DDDavis, DL Sullivan, Method for the preparation of dodecanedioic acid, 1991 and US Patent Publication No. 5,026,461).The synthesis of dicarboxylic acids by oxidative double bond cleavage starts from pure cycloalkene.

[0004] Furthermore, in these prior art processes, where the corresponding carboxylic acid ester is often obtained synthetically, the generation of the free carboxylic acid often requires an additional hydrolysis step, which requires additional time and resources.

[0005] The increased material inputs, the use of expensive transition metals as electrocatalysts or electrode materials, or the use of chemical oxidants, generate reagent waste that in some cases require expensive and complex disposal or regeneration. Furthermore, these processes require large overall material inputs due to the use of complex electrolyte systems and additional oxidants, negatively impacting the cost balance and process economics. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] US Patent Publication No. 5,026,461 Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is to provide a sustainable, resource-saving process that allows the production of α,ω-dicarboxylic acids and cycloalkanones. [Means for solving the problem]

[0008] This object has been achieved by the subject matter of the claims and the specification.

[0009] The present invention relates to a process for the preparation of unsubstituted or at least monosubstituted α,ω-dicarboxylic acids or ketocarboxylic acids and unsubstituted or at least monosubstituted cycloalkanones by electrochemical oxidation, comprising the steps of: (a-1) providing at least one unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene; (a-2) providing at least one unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon; (b) providing at least one inorganic or organic nitrate; (c) electrochemically oxidizing the unsubstituted or at least monosubstituted monounsaturated or polyunsaturated cycloalkene prepared in step (a-1) and the unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon prepared in step (a-2) in the presence of the inorganic or organic nitrate prepared in step (b) in an electrolysis cell in a reaction medium in the presence of oxygen. The present invention provides a method comprising:

[0010] It has surprisingly been found that the process according to the invention allows the electrochemical oxidation of cyclic alkenes to give α,ω-dicarboxylic / ketocarboxylic acids in the presence of cyclic alkanes of the same ring size.

[0011] The process of the invention makes it possible to convert industrially obtained cycloalkenes, which often contain a proportion of alicyclic hydrocarbons, into α,ω-dicarboxylic acids, with cyclic ketones being obtained as further products, which can likewise be used in industrial applications. The method of the present invention allows the simplification of industrially important processes and further allows the optimization of the processes from a sustainability point of view.

[0012] The present invention allows resource-saving and synthetically important oxo-functionalization of feedstock chemicals to be achieved while largely avoiding the use of environmentally harmful transition metals and oxidants. The selective conversion to the desired products and the efficient use of conductive salts and mediators in dual functions greatly reduce the generation of expensive reagent waste. The present invention enables an electrochemical synthesis route to aliphatic α,ω-carboxylic acids, ketocarboxylic acids and cycloalkanones by efficient convergent electrolysis where both electrode reactions are synthetically useful.

[0013] The process of the present invention has the special features of high selectivity, the use of small amounts of auxiliary chemicals, the use of electric current as an oxidant, and the associated small amount of waste generated.

[0014] It has also surprisingly been found that the process of the invention can be carried out at ambient pressure and temperature, which is likewise advantageous for energy efficiency and therefore environmental compatibility.

[0015] The method of the present invention can use monocyclic or bicyclic unsubstituted or at least monosubstituted monounsaturated or polyunsaturated cycloalkene.Preferably, unsubstituted or at least monosubstituted monounsaturated or polyunsaturated monocyclic cycloalkene is used, and unsubstituted or at least monosubstituted monounsaturated monocyclic cycloalkene is particularly preferred.The position of unsaturated bond can be in or outside the ring, and in the ring, unsaturated bond is preferred.

[0016] The unsubstituted or at least monosubstituted mono- or polyunsaturated monocyclic cycloalkenes used in the process of the invention may preferably have 5 to 12 carbon atoms, particularly preferably 6 to 12 carbon atoms, very particularly preferably 8 to 12 carbon atoms in the ring system. These cycloalkenes may be mono- or polyunsaturated, with monounsaturated cycloalkenes being preferred. Each of these cycloalkenes may be unsubstituted or mono- or polysubstituted. If mono- or polysubstituted, it is preferred that it is substituted with one, two, three, four or five substituents, each independently selected from the group consisting of methyl, phenyl or benzyl. The phenyl or benzyl substituents themselves may each be unsubstituted or mono- or polysubstituted with one, two or three substituents, each independently selected from the group consisting of F, Cl, Br and NO2.

[0017] The unsubstituted or at least mono-substituted mono- or polyunsaturated bicyclic cycloalkenes used in the process of the invention may preferably have 7 to 18 carbon atoms, particularly preferably 7 to 12 carbon atoms, very particularly preferably 7 to 10 carbon atoms in the ring system. These cycloalkenes may be mono- or polyunsaturated, with monounsaturated cycloalkenes being preferred. Each of these cycloalkenes may be unsubstituted or mono- or polysubstituted. If mono- or polysubstituted, it is preferred that it is substituted with one, two, three, four or five substituents, each independently selected from the group consisting of methyl, phenyl or benzyl. The phenyl or benzyl substituents themselves may each be unsubstituted or mono- or polysubstituted with one, two or three substituents, each independently selected from the group consisting of F, Cl, Br and NO2.

[0018] When the monocyclic or bicyclic cycloalkenes used in accordance with the present invention, or their substituents, contain alkyl radicals having more than one carbon atom in the side chain, the practice of the process of the present invention may result in undesirable side reactions of these substituents.

[0019] Particularly preferred monocyclic cycloalkenes are selected from the group consisting of cyclohexene, cycloheptene, cyclooctene, cyclononene, cyclodecene, cycloundecene, cyclododecene and 1-phenylcyclohex-1-ene.Particularly preferred bicyclic cycloalkenes may be selected from the group consisting of bicyclo[2.2.1]hept-2-ene, α-pinene and carene.

[0020] The process of the present invention may use monocyclic or bicyclic, preferably bicyclic, unsubstituted or at least monosubstituted saturated alicyclic hydrocarbons. It is particularly preferred to use monocyclic alicyclic hydrocarbons in the process of the present invention.

[0021] The monocyclic or polycyclic, in particular monocyclic or bicyclic, saturated alicyclic hydrocarbons used in the process of the invention may preferably have 5 to 18 carbon atoms in the ring system. Each of these alicyclic hydrocarbons may be unsubstituted or mono- or polysubstituted. If mono- or polysubstituted, it is preferred that they are substituted with one, two, three, four or five substituents, each independently selected from the group consisting of methyl, phenyl or benzyl. Each of the phenyl or benzyl substituents may themselves be unsubstituted or mono- or polysubstituted with one, two or three substituents, each independently selected from the group consisting of F, Cl, Br and NO2. If the alicyclic hydrocarbons used according to the invention, or their substituents, contain alkyl radicals with more than one carbon atom in the side chain, the implementation of the process of the invention may result in undesired side reactions with these substituents.

[0022] The process according to the invention particularly preferably uses, as unsubstituted or at least monosubstituted saturated alicyclic hydrocarbons, monocyclic saturated hydrocarbons having 6 to 12 carbon atoms in the ring, preferably 8 to 12 carbon atoms in the ring, which are unsubstituted or mono- or polysubstituted with 1, 2, 3, 4 or 5 substituents each independently selected from the group consisting of methyl, phenyl or benzyl. The process according to the invention very particularly preferably uses monocyclic saturated hydrocarbons having 8 to 12 carbon atoms in the ring, which are unsubstituted or mono-, di- or tri-substituted with methyl groups.

[0023] The saturated monocyclic hydrocarbon is very particularly preferably unsubstituted and selected from the group consisting of cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane and cyclododecane, even more preferably selected from the group consisting of cyclooctane, cyclononane, cyclodecane, cycloundecane and cyclododecane, most preferably cyclododecane.

[0024] It is particularly preferred when the cycloalkene is selected from the group consisting of cyclohexene, cycloheptene, cyclooctene, cyclononene, cyclodecene, cycloundecene, cyclododecene, 1-phenylcyclohex-1-ene, bicyclo[2.2.1]hept-2-ene, α-pinene and carene, and the saturated alicyclic hydrocarbon is selected from the group consisting of cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane and cyclododecane.

[0025] It is particularly preferred that the cycloalkene is cyclododecene and the saturated alicyclic hydrocarbon is cyclododecane.

[0026] In the process of the present invention, the preparation of at least one unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene according to step (a-1) and the preparation of at least one unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon according to step (a-2) can be preferably carried out in combination, particularly preferably as a mixture. Thus, for example, a precursor product from an industrial-scale process, which contains these two components, can be directly used in the process according to the present invention.

[0027] The ratio of the amounts of unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene and unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon in the process according to the invention may vary over a wide range.

[0028] The molar ratio of the unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene is in each case preferably 40 to 95 mol %, more preferably 45 to 55 mol %, particularly preferably 47 to 53 mol %, based on the total amount of the unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene and the unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon used.

[0029] Likewise, the molar ratio of unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene is in each case preferably greater than 60 mol %, preferably greater than 65 mol %, particularly preferably greater than 70 mol %, based on the total amount of unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene and unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon used.

[0030] It is very particularly preferable to use 90 to 95 mol % of cyclododecene as cycloalkene and 5 to 10 mol % of cyclododecane as saturated alicyclic hydrocarbon, based on the total amount of cyclodecene and cyclodecane.

[0031] Step (b) of the method according to the invention comprises the preparation of at least one inorganic or organic nitrate, which acts both as a conductive salt and as a mediator of the electrochemical oxidation process according to the invention. + ][NO3 - It is preferable to use inorganic or organic salts of the formula:

[0032] [Cation + ] is Na + , K + , and General structure [R 1 R 2 R 3 R 4 N + ](where R 1 , R 2 , R 3 and R 4 is C1~C 16 alkyl, particularly linear or branched C1-C8 alkyl, General structure (I):

[0033] [ka]

[0034] (In the formula, R 1and R 2 is a straight or branched chain C1-C 18 alkyl, particularly straight or branched C1-C8 alkyl; R 3 is H and linear or branched C1-C 18 alkyl, particularly H and linear or branched C1-C8 alkyl. imidazolium cation, General structure (II):

[0035] [ka]

[0036] (In the formula, R 1 is C1~C 18 alkyl, in particular linear or branched C1-C8 alkyl, R 2 , R 3 and R 4 is H and linear or branched C1-C 18 are each independently selected from the group consisting of alkyl, particularly H and straight or branched C1-C8 alkyl. the pyridinium cation, and General structure [R 1a R 2a R 3a R 4a P + ](where R 1a , R 2a , R 3a , R 4a is C1~C 16 alkyl, particularly straight or branched C1-C8 alkyl.) is selected from the group consisting of:

[0037] When organic nitrates based on imidazolium cations are used in the process of the invention, cations of general formula (I) are preferred, in which R 1 and R 2 is a straight or branched chain C1-C 18alkyl, particularly straight or branched C1-C8 alkyl; R 3 is hydrogen. Particularly preferred are imidazolium cations of the general formula (I), in which R 1 is methyl, R 2 is ethyl, or R 1 is methyl, R 2 is methyl, or R 1 is methyl, R 2 is butyl, and R 3 is hydrogen in both cases.

[0038] When nitrates based on pyridinium cations are used in the process of the invention, cations of general formula (II) are preferred, in which R 1 is a straight or branched chain C1-C 18 Particularly preferred are pyridinium cations of the general formula (II) in which R 1 is a straight or branched chain C1-C 18 alkyl, in particular linear or branched C1-C8 alkyl, with the radical R 2 , R 3 and R 4 are each independently selected from the group consisting of straight or branched chain C1-C8 alkyl, and are preferably mono-substituted at the 2-, 3- or 4-positions, di-substituted at the 2,4-, 2,5- or 2,6-positions, or tri-substituted at the 2,4,6-positions.

[0039] In principle, it is also possible to use two or more of the abovementioned nitrates in the process according to the invention. 1 R 2 R 3 R 4 N + ][NO3 - ], or organic ammonium nitrate of composition [R 1a R 2a R 3a R 4a P + ][NO3 - It is preferable to use organic phosphonium salts of the composition [R1 R 2 R 3 R 4 N + ][NO3 - Preferred are organic ammonium nitrates of the formula:

[0040] Particularly preferred is when the organic ammonium nitrate is tetra-n-butylammonium nitrate or methyltri-n-octylammonium nitrate.Particularly preferred is when the organic phosphonium nitrate is tetra-n-butylphosphonium nitrate or methyltri-n-octylphosphonium nitrate.Particularly preferred is when the organic imidazolium nitrate is 1-butyl-3-methylimidazolium nitrate.

[0041] The organic nitrate used in the process according to the invention is most preferably tetra-n-butylammonium nitrate or methyltri-n-octylammonium nitrate.

[0042] The order in which the components used in the process according to the invention are provided may vary, as may the order in which the individual components are contacted with each other or with their respective reaction media.

[0043] In one embodiment of the process according to the invention, the unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene and the unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon are initially charged and combined with the reaction medium, preferably partially or completely dissolved in or mixed with the reaction medium, and then the inorganic or organic nitrate is added.

[0044] In another embodiment of the process according to the invention, the inorganic or organic nitrate is initially charged and combined with the reaction medium, preferably partially or completely dissolved or mixed in the reaction medium, and then the unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene and the unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon, preferably in combination, are added.

[0045] Likewise, it is also possible that the unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene, the unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon and the inorganic or organic nitrate are charged first and then combined with the reaction medium, preferably at least partially or completely dissolved in the reaction medium or mixed in the reaction medium.Furthermore, in the process of the present invention, it is also possible that the unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene, the unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon and the inorganic or organic nitrate are added to the reaction medium and simultaneously or successively, preferably at least partially or completely dissolved in the reaction medium or mixed in the reaction medium.

[0046] The reaction medium used in the process of the invention is liquid under the conditions in which the process is carried out and is capable of partially or completely dissolving the components used, i.e. in particular the unsubstituted or at least monosubstituted saturated alicyclic hydrocarbons and the inorganic or organic nitrates. If at least one of these components is used in liquid form, the reaction medium is preferably readily miscible with said components.

[0047] The method of the present invention uses a polar aprotic reaction medium for electrochemical oxidation, which can be used in anhydrous form, dry form, or in conjunction with water.

[0048] When inorganic nitrate, especially potassium nitrate or sodium nitrate, is used in the method of the present invention, the reaction medium advantageously comprises water, preferably aprotic reaction medium combined with water.The water content in the reaction medium can vary.The water content is preferably at most 20% by volume, particularly preferably at most 15% by volume, very particularly preferably at most 10% by volume, and even more preferably at most 5% by volume, based on the total amount of the reaction medium in each case.

[0049] The polar aprotic reaction medium is preferably selected from the group consisting of aliphatic nitriles, aliphatic ketones, cycloaliphatic ketones, dialkyl carbonates, cyclic carbonates, lactones, aliphatic nitroalkanes, dimethylsulfoxide, esters and ethers, or a combination of at least two of these components.

[0050] It is particularly preferred that the reaction medium is selected from the group consisting of acetonitrile, isobutyronitrile, adiponitrile, acetone, dimethyl carbonate, methyl ethyl ketone, 3-pentanone, cyclohexanone, nitromethane, nitropropane, tert-butyl methyl ether, dimethyl sulfoxide, γ-butyrolactone and ε-caprolactone, or a combination of at least two of these components.

[0051] It is very particularly preferable for the reaction medium to be selected from the group consisting of acetonitrile, isobutyronitrile, adiponitrile, dimethyl carbonate and acetone, or a combination of at least two of these components.

[0052] It is very particularly preferable for the reaction medium to be acetonitrile, isobutyronitrile or adiponitrile in dry or anhydrous form.

[0053] The reaction medium is likewise very particularly preferably acetonitrile, isobutyronitrile or adiponitrile, optionally together with water.

[0054] If one or more of the abovementioned components are used in combination with water in the reaction medium, the water content is preferably at most 20% by volume, particularly preferably at most 15% by volume, particularly preferably at most 10% by volume and even more preferably at most 5% by volume, in each case based on the total amount of the reaction medium.

[0055] To carry out the method according to the invention, it may be advantageous to add further solubilizing components to the reaction medium. Suitable advantageous components may be identified by simple preliminary testing of the solubility behavior.

[0056] Examples of solubilizing components include primary alcohols, secondary alcohols, monoketones or dialkyl carbonates, or a mixture of at least two of these components, optionally in combination with water. 1-6 Alcohols may be used. Particularly preferred solubilizing components are selected from the group consisting of methanol, ethanol, isopropanol, 2-methyl-2-butanol, or a mixture of at least two of these components, optionally in combination with water.

[0057] The reaction medium used is particularly preferably dimethyl carbonate, optionally containing at least one C 1-6 An alcohol may be used in combination with an alcohol, in particular one selected from the group consisting of methanol, ethanol, isopropanol and 2-methyl-2-butanol, optionally in combination with water.

[0058] If one or more of these solubilizing components are used in combination with water, the water content is preferably at most 20% by volume, particularly preferably at most 15% by volume, very particularly preferably at most 10% by volume and even more preferably at most 5% by volume, in each case based on the total amount of solubilizing components and water.

[0059] The solubilizing components may be added preferably in an amount of less than 50% by volume, particularly preferably less than 30% by volume and very particularly preferably less than 10% by volume, in each case relative to the total amount of the reaction medium.

[0060] The inorganic or organic nitrates in the process according to the invention are preferably used in an amount of 0.1 to 2.0 equivalents, preferably 0.2 to 1.0 equivalents, particularly preferably 0.3 to 0.8 equivalents and very preferably 0.4 to 0.8 equivalents, based on the amount of unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene used, and in an amount of 0.8 to 10.0 equivalents, preferably 2.5 to 10.0 equivalents, particularly preferably 3.0 to 10.0 equivalents and very preferably 5.0 to 10.0 equivalents, based on the amount of unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon used.

[0061] According to the invention, the electrochemical oxidation of unsubstituted or at least monosubstituted saturated alicyclic hydrocarbons is carried out in an electrolytic cell in a reaction medium in the presence of oxygen and in the presence of inorganic or organic nitrates.

[0062] For this purpose, an oxygen-containing gas atmosphere is advantageously provided in spatial communication with the reaction medium.

[0063] The proportion of oxygen in the gas atmosphere may vary, and is preferably 10% by volume to 100% by volume, particularly preferably 15% by volume to 30% by volume, particularly preferably 15% by volume to 25% by volume, and particularly preferably 18% by volume to 22% by volume.

[0064] In one embodiment, the proportion of oxygen in the gas atmosphere may be 10% by volume to 100% by volume, particularly preferably 15% by volume to 100% by volume, and particularly preferably 20% by volume to 100% by volume.

[0065] It is particularly advantageous if the gas atmosphere is air.

[0066] Advantageously, the gas exchange between the gas atmosphere and the reaction medium is preferably carried out by introducing a gas atmosphere into the reaction medium or by stirring the liquid phase in the presence of a gas atmosphere.

[0067] Gas exchange between the gas atmosphere and the reaction medium, in particular stirring, can be used to control the electrochemical oxidation, for example by stirrer geometry or stirrer speed.

[0068] The amount of oxygen dissolved in the reaction medium is preferably at least 1 mmol, particularly preferably at least 5 mmol, per litre of reaction medium.

[0069] Likewise, the amount of oxygen dissolved in the reaction medium is preferably at least 10 mmoles per liter of reaction medium.

[0070] The process of the present invention for producing unsubstituted or at least monosubstituted α,ω-dicarboxylic acids or ketocarboxylic acids and unsubstituted or at least monosubstituted cycloalkanones by electrochemical oxidation of unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkenes with unsubstituted or at least monosubstituted saturated alicyclic hydrocarbons in the presence of inorganic or organic nitrates in an electrolytic cell in a reaction medium in the presence of oxygen may be carried out either in a divided or non-divided electrolytic cell, preferably in a non-divided electrolytic cell.

[0071] The non-split electrolytic cell preferably used according to the present invention comprises at least two electrodes.For this purpose, anodes and cathodes made of conventional materials can be used, for example anodes and cathodes made of glassy carbon, boron-doped diamond (BDD) or graphite.The use of glassy carbon electrodes is preferred.

[0072] The undivided electrolytic cell preferably comprises at least one glassy carbon anode or at least one glassy carbon cathode, preferably where both the anode and the cathode are glassy carbon electrodes.

[0073] The distance between the electrodes can vary over a certain range: the distance is preferably 0.1 mm to 2.0 cm, particularly preferably 0.1 mm to 1.0 cm, and particularly preferably 0.1 mm to 0.5 cm.

[0074] The process according to the invention can furthermore be carried out batchwise or continuously, preferably in a non-divided flow-through electrolytic cell.

[0075] The process according to the invention is preferably carried out in each case with a charge amount of at least 190 C (2F) to 970 C (10F), preferably 290 C (3F) to 870 C (9F), particularly preferably 330 C (3.5F) to 820 C (8.5F), very particularly preferably 380 C (4F) to 775 C (8F), most preferably 380 C (4F) to 580 C (6F) per mmol of unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkenes and unsubstituted or at least monosubstituted saturated alicyclic hydrocarbons used.

[0076] The electrochemical oxidation in the method according to the invention is preferably carried out galvanostatically.

[0077] The current density at which the method according to the invention is carried out is preferably at least 5 mA / cm 2 , or at least 10mA / cm 2 , or at least 15mA / cm 2 , or at least 20mA / cm 2 , or 20mA / cm 2 ~50mA / cm 2 where the reported surface area represents the geometric area of ​​the electrode.

[0078] An important advantage of the method according to the invention is that the oxidizing agent used is electric current, which is a particularly environmentally friendly agent when it is obtained from renewable resources, i.e. in particular from biomass, solar thermal energy, geothermal energy, hydroelectric power, wind power or especially photovoltaic power.

[0079] The process according to the invention can be carried out in a wide temperature range, for example at temperatures from 0°C to 60°C, preferably from 5°C to 50°C, particularly preferably from 10°C to 40°C, very particularly preferably from 15°C to 30°C.

[0080] The process according to the invention can be carried out at elevated pressure or at reduced pressure. If the process according to the invention is carried out at elevated pressure, pressures up to 16 bar are preferred, pressures up to 6 bar are particularly preferred.

[0081] The process according to the invention can likewise preferably be carried out at atmospheric pressure.

[0082] The products produced by the process of the invention may be isolated / purified by conventional methods known to those skilled in the art, in particular by extraction, crystallization, centrifugation, precipitation, distillation, evaporation or chromatography.

[0083] The process according to the invention is preferably carried out without added catalysts, in particular without added transition metal catalysts.

[0084] Likewise, the process according to the invention is preferably carried out without the addition of further oxidizing agents, with the exception of oxygen or atmospheric oxygen. EXAMPLES

[0085] The following examples further illustrate the invention but are not intended to limit the scope of the invention.

[0086] General Information and Methods Chemicals of analytical quality were obtained and used from commonly used sources (TCI, Aldrich, Acros, etc.) Oxygen was obtained at 2.5 quality from Nippon Gases Deutschland GmbH, Düsseldorf, Germany, and was used as received.

[0087] The electrode material used was glassy carbon (Sigradur® G, HTW Hochtemperatur Werkstoffe GmbH, Tierhaupten, Germany).

[0088] High performance liquid chromatography was performed on a Shimadzu HPLC-MS instrument equipped with a SIL 20A HT autosampler, a CTO-20AC column oven, two LC-20AD pump modules for eluent gradient adjustment, an SPD-M20A diode array detector, a CBM-20A system controller, and a Eurospher II 100-5 C18 column (150 × 4 mm, Knauer, Berlin). Eluent: acetonitrile (ACN) / water / formic acid (1% by volume) (10% ACN to 90% ACN in 10 min + 100% ACN in 10 min). Mass spectrometry measurements were performed on a Shimadzu LCMS-2020 instrument, Japan.

[0089] 1 H-NMR and 13 C-NMR spectra were recorded at 25 °C using a Bruker Advance II 400 instrument (400 MHz, 5 mm BBFO probe with Z gradient and ATM, SampleXPress60 autosampler, Analytische Messtechnik, Karlsruhe, Germany).

[0090] Gas chromatographic analysis was performed using a Shimadzu GC-2025 instrument (Shimadzu, Japan) equipped with an HP 5MS column (Agilent Technologies, Santa Clara, CA; length: 30 m, inner diameter: 0.25 mm, film thickness: 0.25 μm, carrier gas: hydrogen). GC-MS measurements were performed using a Shimadzu GC-2010 instrument (Shimadzu, Japan) equipped with an HP-1 column (Agilent Technologies, Santa Clara, CA; length: 30 m, inner diameter: 0.25 mm, film thickness: 0.25 μm, carrier gas: helium). Sample preparation for GC analysis was performed by column filtration through silica gel 60 M (0.04–0.063 mm, Macherey-Nagel GmbH & Co. KG, Düren, Germany).

[0091] The undivided Teflon cells used for the electrolysis have been described in the literature (a) C. Gutz, B. Klockner, S. R. Waldvogel, Org. Process Res. Dev. 2016, 20, 26-32; b) A. Kirste, G. Schnakenburg, F. Stecker, A. Fischer, S. R. Waldvogel, Angew. Chem. Int. Ed. 2010, 49, 971-975; Angew. Chem. 2010, 122, 983-987 (see SI). The full range of these cells is also commercially available as IKA Screening Systems (IKA-Werke GmbH & Co. KG, Staufen, Germany). The dimensions of the electrodes were 7 cm × 1 cm × 0.3 cm.

[0092] The gases were introduced in a controlled manner by two model 5850S ​​mass flow controllers (MFCs) from Brooks Instrument BV, Veenendaal, The Netherlands. This was done using one controller for oxygen introduction and the other for nitrogen introduction. The controllers were controlled by Smart DDE and Matlab R2017b software. The volumetric flow rate was further monitored by a DK800 float principle flowmeter from Krohne Messtechnik GmbH, Duisburg. In all the experiments carried out, the overall volumetric flow rate was constant at 20 mL / min. This is the maximum achievable volumetric flow rate, although it is limited by the MFC used. The ratio of the volumetric flow rates of the two gases was adjusted using the MFC and its software. Gas cylinders from the following suppliers were used: Oxygen 2.5 (Nippon Gases Deutschland GmbH, Düsseldorf) and Nitrogen 4.8 (Westfalen AG, Münster) or Nitrogen 5.0 (Nippon Gases Deutschland GmbH, Düsseldorf). The gas distributor and the gas inlet cover of the electrolysis cell are described in the literature (M. Dorr, D. Waldmann, S.R. Waldvogel, GIT Labor-Fachz, 2021, pp. 7-8, 26-28) and were purchased from IKA (IKA-Werke GmbH & Co. KG, Staufen, Germany).

[0093] General Procedure GP1 A 5 mL undivided Teflon pot cell was initially charged with cycloalkanes (0.1-0.5 mmol), cycloalkenes (0.5-0.9 mmol, 1 mmol of alkane and alkene combined), and tetrabutylammonium nitrate (0.5 equiv.), dissolved in acetonitrile or isobutyronitrile (5 mL). The cell was fitted with glassy carbon electrodes spaced 0.5 cm apart. The immersed surface area of ​​the electrodes was 1.8 cm. 2 After the cell was fixed to a stainless steel block, it was heated at 22°C and a current density of 10 mA / cm 2 Constant current electrolysis was carried out at .

[0094] The charge amount used was based on the theoretical charge amount for the oxidation of both components depending on their ratio (alkane / alkene = 0.1 / 0.9:7.6F, 0.25 / 0.75:7.0F, 0.5 / 0.5:6.0F). After electrolysis, 1,3,5-trimethoxybenzene (10 mg) was added to the reaction solution as an internal standard. Three drops were taken and filtered through silica gel 60 M (eluent: ethyl acetate). The filtrate was collected in a GC vial and subjected to GC analysis. For the remaining reaction solution, the solvent was first removed by distillation. Then, the conductive salts were removed by extraction using 10 mL of ethyl acetate and 10 mL of aqueous HCl (0.1 M). The solvent of the organic phase was removed by distillation and the residue was placed in aqueous NaOH (1 M, 10 mL). The aqueous phase was washed with 10 mL of diethyl ether. After phase separation, the aqueous phase was adjusted to pH 1 with aqueous HCl (1M) and this phase was extracted with 2 x 10 mL of ethyl acetate. The organic phase was dried over sodium sulfate and the solvent was distilled off, after which the dicarboxylic acid product was dried under high vacuum.

[0095] After using the charge quantity, 10 mg of 1,3,5-trimethoxybenzene was added to the reaction solution as an internal standard. Three drops of the reaction solution were taken for analysis by gas chromatography and quantification of the products. These were eluted with about 330 mg of silica gel 60M using ethyl acetate. About 1.5 mL of the filtrate was collected in a GC vial and examined for oxidation products by GC-FID and GC-MS. Quantification was achieved by pre-calibration of the gas chromatograph.

[0096] Experimental Example 1 The following co-electrolysis was carried out according to GP1 (Scheme 1, Table 1).

[0097] [ka]

[0098] [Table 1]

[0099] For n=3, acetonitrile was used as the solvent, and for n=7, isobutyronitrile was used as the solvent. Accumulated charges for A and B: a) 7.6F; b) 7.0F; c) 6.0F; d) measured by external GC calibration (internal standard: 1,3,5-trimethoxybenzene); e) yield after isolation. All yields are relative to the molar amounts of the particular reactants used.

Claims

1. 1. A process for producing unsubstituted or at least monosubstituted α,ω-dicarboxylic acids or ketocarboxylic acids and unsubstituted or at least monosubstituted cycloalkanones by electrochemical oxidation, comprising the steps of: (a-1) preparing at least one unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene; (a-2) preparing at least one unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon; the substituents of the mono- or polyunsaturated cycloalkene and the saturated alicyclic hydrocarbon are each independently selected from the group consisting of methyl, phenyl, or benzyl; The phenyl or benzyl substituents themselves are each unsubstituted or substituted with F, Cl, Br and NO. ２ and is mono- or polysubstituted with one, two or three substituents each independently selected from the group consisting of: the ring size of the cycloalkene from the step (a-1) and the ring size of the alicyclic hydrocarbon from the step (a-2) are the same; (b) providing at least one inorganic or organic nitrate; The nitrate in step (b) is represented by the general formula: ＋ ][NO ３ － ] as the nitrate, [Cation of the above general formula ＋ ] is Na ＋ , K ＋ , and General structure [R １ R ２ R ３ R ４ N ＋ ] (wherein, R １ , R ２ , R ３ and R ４ is C １ ~C １６ Alkyl, especially linear or branched C １ ~C ８ each independently selected from the group consisting of alkyl, General structure (I): 【Chemistry 1】 (In the formula, R １ and R ２ is a linear or branched chain C １ ~C １８ Alkyl, especially linear or branched C １ ~C ８ alkyl; R ３ is H and linear or branched chain C １ ~C １８ Alkyl, especially H and linear or branched C １ ~C ８ is selected from the group consisting of alkyl. imidazolium cation, General structure (II): 【Chemistry 2】 (In the formula, R １ is C １ ~C １８ Alkyl, especially linear or branched C １ ~C ８ alkyl; R ２ , R ３ and R ４ is H and linear or branched chain C １ ~C １８ Alkyl, especially H and linear or branched C １ ~C ８ alkyl. the pyridinium cation, and General structure [R １ａ R ２ａ R ３ａ R ４ａ P ＋ ] (wherein, R １ａ , R ２ａ , R ３ａ , R ４ａ is C １ ~C １６ Alkyl, especially linear or branched C １ ~C ８ alkyl. ) wherein (c) electrochemically oxidizing the unsubstituted or at least monosubstituted mono-unsaturated or polyunsaturated cycloalkene prepared in step (a-1) and the unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon prepared in step (a-2) in the presence of the inorganic or organic nitrate prepared in step (b) in an electrolysis cell in a reaction medium in the presence of oxygen. A method comprising:

2. The unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene is monocyclic or bicyclic, The unsubstituted or at least monosubstituted mono- or polyunsaturated monocyclic cycloalkenes preferably have 5 to 12 carbon atoms, particularly preferably 6 to 12 carbon atoms, very particularly preferably 8 to 12 carbon atoms in the ring system and are unsubstituted or mono- or polysubstituted, preferably with one, two, three, four or five substituents each independently selected from the group consisting of methyl, phenyl or benzyl, the phenyl or benzyl substituents themselves being each unsubstituted or with F, Cl, Br and NO. ２ and / or The unsubstituted or at least monosubstituted mono- or polyunsaturated bicyclic cycloalkenes have in the ring system 7 to 18 carbon atoms, particularly preferably 7 to 12 carbon atoms, very particularly preferably 7 to 10 carbon atoms, and are unsubstituted or mono- or polysubstituted, preferably with one, two, three, four or five substituents each independently selected from the group consisting of methyl, phenyl or benzyl, the phenyl or benzyl substituents themselves being each unsubstituted or with F, Cl, Br and NO. ２ 2. The method of claim 1, wherein the aryl group is mono- or polysubstituted with one, two or three substituents each independently selected from the group consisting of:

3. The unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon is monocyclic or bicyclic, The monocyclic or bicyclic saturated alicyclic hydrocarbon has 5 to 18 carbon atoms in the ring system and is unsubstituted or mono- or polysubstituted with 1, 2, 3, 4 or 5 substituents each independently selected from the group consisting of methyl, phenyl or benzyl, each of which is unsubstituted or selected from the group consisting of F, Cl, Br and NO. ２ 3. The method of claim 1 or claim 2, wherein the aryl group is optionally mono- or polysubstituted with one, two or three substituents each independently selected from the group consisting of:

4. The unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon is a monocyclic saturated hydrocarbon having 6 to 12 carbon atoms in the ring, preferably 8 to 12 carbon atoms, which is unsubstituted or mono- or polysubstituted with 1, 2, 3, 4 or 5 substituents each independently selected from the group consisting of methyl, phenyl or benzyl; Particularly preferred is a monocyclic saturated hydrocarbon having 8 to 12 carbon atoms in the ring, which is unsubstituted or mono-, di- or tri-substituted with methyl.

5. The cycloalkene is selected from the group consisting of cyclohexene, cycloheptene, cyclooctene, cyclononene, cyclodecene, cycloundecene, cyclododecene, 1-phenylcyclohex-1-ene, bicyclo[2.2.1]hept-2-ene, α-pinene and carene, particularly preferably cyclododecene; The process according to any one of claims 1 to 4, wherein the saturated alicyclic hydrocarbon is selected from the group consisting of cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane and cyclododecane, preferably selected from the group consisting of cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane and cyclododecane, particularly preferably cyclododecane.

6. The process according to any one of claims 1 to 5, wherein the provision of at least one unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene according to step (a-1) and the provision of at least one unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon according to step (a-2) are carried out in combination, preferably as a mixture.

7. 7. The process according to claim 1, wherein the molar ratio of the unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene is in each case from 40 to 95 mol %, preferably from 45 to 55 mol %, particularly preferably from 47 to 53 mol %, based on the total amount of unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene and unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon used.

8. 8. The process according to claim 1 , wherein the molar ratio of the unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene is in each case more than 60 mol %, preferably more than 65 mol %, particularly preferably more than 70 mol %, based on the total amount of unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene and unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon used.

9. In the imidazolium cation of general formula (I), the radical R １ and R ２ is a linear or branched chain C １ ~C １８ Alkyl, especially linear or branched C １ ~C ８ alkyl; R ３ is hydrogen, preferably R １ is methyl, R ２ is ethyl, or R １ is methyl, R ２ is methyl, or R １ is methyl, R ２ is butyl, R ３ The method according to any one of claims 1 to 8, wherein in each case is hydrogen.

10. In the pyridinium cation of the general formula (II), the radical R １ is a linear or branched chain C １ ~C １８ Alkyl, especially linear or branched C １ ~C ８ alkyl and the radical R ２ , R ３ and R ４ is a linear or branched chain C １ ~C ８ The method according to any one of claims 1 to 9, wherein each of the alkyl groups is independently selected from the group consisting of alkyl, and is preferably mono-substituted at the 2-, 3- or 4-positions, di-substituted at the 2-, 4-, 2-, 5- or 2-, 6-positions, or tri-substituted at the 2-, 4- and 6-positions.

11. The method of any one of claims 1 to 10, wherein the organic nitrate is selected from the group consisting of tetra-n-butylammonium nitrate, methyltri-n-octylammonium nitrate, tetra-n-butylphosphonium nitrate, methyltri-n-octylphosphonium nitrate, and 1-butyl-3-methylimidazolium nitrate.

12. 12. The process of any one of claims 1 to 11, wherein the reaction medium is a polar aprotic reaction medium, optionally mixed with water, the polar aprotic reaction medium being selected from the group consisting of aliphatic nitriles, aliphatic ketones, cycloaliphatic ketones, dialkyl carbonates, cyclic carbonates, lactones, aliphatic nitroalkanes, dimethylsulfoxide, esters and ethers, or combinations of at least two of these components.

13. 13. The process according to any one of claims 1 to 12, wherein the reaction medium is a polar aprotic reaction medium, optionally mixed with water, the water content being at most 20% by volume, preferably at most 15% by volume, particularly preferably at most 10% by volume and even more preferably at most 5% by volume, in each case relative to the total amount of the reaction medium.

14. 14. The process according to any one of claims 1 to 13, wherein the reaction medium is a polar aprotic reaction medium selected from the group consisting of acetonitrile, isobutyronitrile, adiponitrile, acetone, dimethyl carbonate, methyl ethyl ketone, 3-pentanone, cyclohexanone, nitromethane, nitropropane, tert-butyl methyl ether, dimethyl sulfoxide, γ-butyrolactone and ε-caprolactone, or a combination of at least two of these components, preferably selected from the group consisting of acetonitrile, isobutyronitrile, adiponitrile, dimethyl carbonate and acetone, or a combination of at least two of these components, in each case present optionally mixed with water.

15. The method of any one of claims 1 to 14, wherein the reaction medium comprises one or more solubilizing components.

16. 16. The method of claim 15, wherein the solubilizing component is a primary alcohol, a secondary alcohol, a monoketone or a dialkyl carbonate, or a mixture of at least two of these components, optionally present in admixture with water.

17. aliphatic C １－６ 17. The process of claim 15 or claim 16, wherein the alcohol is present as one or more solubilizing components, preferably one or more alcohols selected from the group consisting of methanol, ethanol, isopropanol, 2-methyl-2-butanol, and mixtures of at least two of these components, optionally mixed with water.

18. The reaction medium is dimethyl carbonate, optionally with at least one C alkoxyl group, preferably selected from the group consisting of methanol, ethanol, isopropanol, and 2-methyl-2-butanol. １－６ The method according to any one of claims 1 to 17, wherein the alcohol is present in admixture.

19. The method of claim 18 , wherein the reaction medium comprises water.

20. The process according to any one of claims 15 to 19, wherein the solubilizing component(s) is / are present in an amount of less than 50 vol.-%, particularly preferably less than 30 vol.-%, very particularly preferably less than 10 vol.-%, in each case relative to the total amount of the reaction medium.

21. The process according to any one of claims 1 to 20, wherein the inorganic or organic nitrate is used in an amount of 0.1 to 2.0 equivalents, preferably 0.2 to 1.0 equivalents, particularly preferably 0.3 to 0.8 equivalents, particularly preferably 0.4 to 0.8 equivalents, based on the amount of unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkene used, and in an amount of 0.8 to 10.0 equivalents, preferably 2.5 to 10.0 equivalents, particularly preferably 3.0 to 10.0 equivalents, particularly preferably 5.0 to 10.0 equivalents, based on the amount of unsubstituted or at least monosubstituted saturated alicyclic hydrocarbon used.

22. 21. The process according to any one of claims 1 to 20, wherein an oxygen-containing gas atmosphere is advantageously provided in spatial communication with the reaction medium, the proportion of oxygen in the gas atmosphere being preferably 10% to 100% by volume, particularly preferably 15% to 30% by volume, very particularly preferably 15% to 25% by volume and most preferably 18% to 22% by volume.

23. The method according to any one of claims 1 to 22, wherein the gas atmosphere is air.

24. A process according to any one of claims 1 to 23, wherein gas exchange between said gas atmosphere and said reaction medium is preferably performed by introducing said gas atmosphere into said reaction medium or by stirring a liquid phase in the presence of said gas atmosphere.

25. 25. The method of claim 24, wherein the stirring is used to control the electrochemical oxidation.

26. 26. The process according to any one of claims 1 to 25, wherein the amount of oxygen dissolved in the reaction medium is at least 1 mmol / L, preferably 5 mmol / L, more preferably 10 mmol / L.

27. The method of any one of claims 1 to 26, wherein, except for oxygen or atmospheric oxygen, no further oxidizing agent is added.

28. The method of any one of claims 1 to 27, wherein the electrolysis cell is a non-divided cell.

29. A method according to any one of the preceding claims, wherein the electrolytic cell comprises a glassy carbon anode, a graphite anode or a BDD anode, preferably a glassy carbon anode.

30. A method according to any one of the preceding claims, wherein the electrolytic cell comprises a glassy carbon cathode, a graphite cathode or a BDD cathode, preferably a glassy carbon cathode.

31. The method according to any one of claims 1 to 30, wherein the distance between the electrodes in the electrolysis cell is from 0.1 mm to 2.0 cm, preferably from 0.1 mm to 1.0 cm, particularly preferably from 0.1 mm to 0.5 cm.

32. 32. The process according to any one of claims 1 to 31, wherein the charge amount is in each case at least 190 C (2F) to 970 C (10F), preferably 290 C (3F) to 870 C (9F), particularly preferably 330 C (3.5F) to 820 C (8.5F), very particularly preferably 380 C (4F) to 775 C (8F), most preferably 380 C (4F) to 580 C (6F) per mmol of unsubstituted or at least monosubstituted mono- or polyunsaturated cycloalkenes and unsubstituted or at least monosubstituted saturated alicyclic hydrocarbons used.

33. The method of any one of claims 1 to 32, wherein the electrochemical oxidation is performed galvanostatically.

34. The current density is at least 5 mA / cm ２ , preferably 10 mA / cm ２ , more preferably 15 mA / cm ２ , particularly preferably 20 mA / cm ２ and the reported surface area represents the geometric area of ​​the electrode.

35. The current density is at least 20 mA / cm ２ ~50mA / cm ２ and the reported surface area represents the geometric area of ​​the electrode.

36. 36. The method according to any one of claims 1 to 35, wherein the current used for the electrochemical oxidation is obtained from a renewable resource, in particular biomass, solar thermal energy, geothermal energy, hydroelectric power, wind power or photovoltaic power.

37. The method according to any one of claims 1 to 36, wherein the electrochemical oxidation is carried out at a temperature in the range from 0°C to 60°C, preferably from 5°C to 50°C, particularly preferably from 10°C to 40°C, very particularly preferably from 15°C to 30°C.

38. The process of any one of claims 1 to 37, carried out at atmospheric pressure.

39. The process of any one of claims 1 to 38, carried out under reduced pressure.

40. The process according to any one of claims 1 to 39, which is carried out under elevated pressure, preferably up to 16 bar, particularly preferably up to 6 bar.

41. The process of any one of claims 1 to 40, which is carried out batchwise.

42. The process according to any one of claims 1 to 41, which is carried out without added catalyst, in particular without added transition metal catalyst.

43. The method of any one of claims 1 to 42, carried out continuously in a non-divided flow-through electrolytic cell.

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