EP4253603A1 - Electrochemical oxidation of cycloalkanes to cycloalkanone compounds - Google Patents

Abstract

The invention relates to a process for producing unsubstituted or at least monosubstituted cycloalkanones by electrochemical oxidation of unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbons by electrochemical oxidation in the presence of an inorganic or organic nitrate salt in an electrolysis cell in a reaction medium in the presence of oxygen.

Description

The invention relates to a process for producing unsubstituted or at least monosubstituted cycloalkanones by electrochemical oxidation of unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbons by electrochemical oxidation in the presence of an inorganic or organic nitrate salt in an electrolysis cell in a reaction medium in the presence of oxygen.

Cycloalkanone and cycloalkanol compounds are important intermediates in a variety of industrial manufacturing processes. The oxidation of saturated, non-functionalized cycloaliphatic hydrocarbons (and thus non-activated C-H bonds) to corresponding ketones or alcohols requires special reaction conditions in order to selectively convert these inert substances into monofunctional secondary products to be transferred while preserving the ring framework.

There are a number of processes that rely on transition metal-catalyzed reactions and oxygen or on the use of chemical oxidants such as peroxides. The use of expensive transition metals and the use of chemical oxidizing agents lead not only to increased costs but also to reagent waste, some of which have to be disposed of at great expense.

An example of this is the production of polyamide 12 from laurolactam, which today mainly uses cyclododecanone as an intermediate product. This is first converted into the peroxide using air. In order to ensure a largely selective subsequent reaction, boron oxide is used, which reacts with the peroxide to form boric acid star and oxygen. The resulting alcohol is then oxidized to cyclododecanone using a CuCr catalyst. The main disadvantage of this reaction path is the use of boron oxide, which is now being discussed as a substance of particular interest because it is suspected of influencing fertility and damaging the child in the womb.

In the publication of Yamanaka (J. Chem. Commun. 2000, 2209-2210 ) it is described that the anodic oxidation of alkanes in an aqueous medium at low current densities of <0.1 mA/cm ² leads to CO ₂ . In non-aqueous media the oxidation of adamantane was observed at voltages >2 V and current densities <4 mA/cm ² , with the activation of oxygen taking place at the cathode. It was shown that the rate of formation of cycloaliphatic ketones (cyclohexanone) and the current yield could be significantly increased, particularly using an Ir(acac) ₂ /carbon fiber anode. The oxygen comes from water. Organic solvents have an influence, for example no conversion of cyclohexane took place in acetonitrile.

In the publication of Kawamata (J. Am. Chem. Soc. 2017 (139), 7448-7551 ) it was shown that the electrochemical oxidation of non-activated C-H bonds in functionalized aliphatic and cycloaliphatic species is possible at reduced potentials when a mediator such as quinuclidine (tertiary amine, toxic) in combination with HFIP (hexafluoroisopropanol, organ-damaging, teratogenic) is used. Me ₄ N-BF ₄ was used as the conductive salt. It was found that the oxygen introduced came from the gas phase. There was no reaction under argon.

It is an object of the invention to provide a sustainable and resource-saving process which converts unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbons as selectively as possible into the corresponding ketones as the main products.

This task was solved by the subject matter of the patent claims and the description.

1. (a) Bereitstellung wenigstens eines unsubstituierten oder wenigstens einfach substituierten, gesättigten cycloaliphatischen Kohlenwasserstoffs;
2. (b) Bereitstellung wenigstens eines anorganischen oder organischen Nitratsalzes;
3. (c) elektrochemische Oxidation des in Schritt (a) bereitgestellten unsubstituierten oder wenigstens einfach substituierten, gesättigten cycloaliphatischen Kohlenwasserstoffs in Gegenwart des in Schritt (b) bereit gestellten anorganischen oder organischen Nitratsalzes in einer Elektrolysezelle in einem Reaktionsmedium in Gegenwart von Sauerstoff.

The present invention relates to a process for producing unsubstituted or at least monosubstituted cycloalkanones by electrochemical oxidation of unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbons, comprising the process steps

1. (a) providing at least one unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbon;
2. (b) providing at least one inorganic or organic nitrate salt;
3. (c) electrochemical oxidation of the unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbon provided in step (a) in the presence of the inorganic hydrocarbon provided in step (b). or organic nitrate salt in an electrolysis cell in a reaction medium in the presence of oxygen.

The process according to the invention is characterized in particular by high selectivity, small amounts of auxiliary chemicals used, the use of electric current as an oxidizing agent and, associated with this, by a reduced amount of waste products.

It was surprisingly found that with the aid of the electrochemical oxidation process according to the invention, atmospheric oxygen can be used to introduce the oxygen function into cycloaliphatic hydrocarbons. The use of chemical oxidizing agents, such as reactive peroxides, and high-priced catalysts with complex ligand systems can be dispensed with. At the same time, the use of toxic and/or potentially carcinogenic reagents can be reduced or even completely avoided. The method developed represents a cost-effective and environmentally friendly alternative to existing syntheses. Due to the simple and safe process conditions, large quantities of the desired compounds can be produced without great effort. Through the present invention, previously cost- and time-intensive processes can be significantly optimized.

It was also surprisingly found that the process according to the invention enables the use of electric current to produce cycloalkanone compounds from unsubstituted cycloalkanes using nitrate salts, which function both as a conductive salt and as an electrochemical mediator. If by-products arise when carrying out the process according to the invention, in particular cycloaliphatic alcohols of the same ring size, this is not a problem because they can be converted into the corresponding ketones by already established subsequent processes.

It was also surprisingly found that the method according to the invention can be carried out under ambient pressure and ambient temperature, which also has an advantageous effect on energy efficiency and thus also environmental compatibility.

Unsubstituted or at least monosubstituted, saturated cycloaliphatic hydrocarbons that are monocyclic or polycyclic can be used in the process according to the invention. Monocyclic or bicyclic cycloaliphatic hydrocarbons are preferred. Monocyclic cycloaliphatic hydrocarbons are particularly preferably used in the process according to the invention.

The monocyclic or polycyclic, in particular monocyclic or bicyclic, saturated cycloaliphatic hydrocarbons used in the process according to the invention can preferably have 5 to 18 C atoms in the ring system. These cycloaliphatic hydrocarbons can each be unsubstituted or mono- or poly-substituted. If they are substituted once or multiple times, they are preferably substituted with 1, 2, 3, 4 or 5 substituents, independently of one another, each selected from the group consisting of methyl, phenyl or benzyl. The phenyl or benzyl substituents themselves can each be unsubstituted or mono- or polysubstituted, with 1, 2 or 3 substituents, independently of one another, each selected from the group consisting of F, Cl, Br, and NO ₂ . If the cycloaliphatic hydrocarbons used according to the invention or their substituents have alkyl radicals with more than one carbon atom in the side chain, undesirable side reactions occur at these substituents when carrying out the process according to the invention.

Particularly preferred in the process according to the invention are monocyclic saturated hydrocarbons with 6 to 12 carbon atoms in the ring, preferably with 8 to 12 carbon atoms in the ring, which are unsubstituted or substituted once or multiple times with 1 as unsubstituted or at least monosubstituted, saturated cycloaliphatic hydrocarbons , 2, 3, 4 or 5 substituents, independently of one another, each selected from the group consisting of methyl, phenyl or benzyl. Very particular preference is given to using monocyclic saturated hydrocarbons with 8 to 12 carbon atoms in the ring in the process according to the invention, which are unsubstituted or mono- or di- or tri-substituted with a methyl group.

Very particularly preferably, the saturated monocyclic hydrocarbon is unsubstituted and is 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 preferred is the hydrocarbon cyclododecane.

mit R¹ und R², unabhängig voneinander, jeweils ausgewählt aus der Gruppe bestehend aus C₁- bis C₁₈-Alkyl, geradkettig oder verzweigt, insbesondere C₁- bis C₈-Alkyl, geradkettig oder verzweigt, und R³ ausgewählt aus der Gruppe bestehend aus H und C₁- bis C₁₈-Alkyl, geradkettig oder verzweigt, insbesondere aus der Gruppe bestehend aus H und C₁- bis C₈-Alkyl, geradkettig oder verzweigt,According to step (b) of the process according to the invention, at least one inorganic or organic nitrate salt is provided. This nitrate salt acts both as a conductive salt and as a mediator in the electrochemical oxidation process according to the invention. An inorganic or organic nitrate of the general formula is preferred

[Cation ⁺ ][NO ₃ ^- ]

for use, whereby the [cation ⁺ ] is selected from the group consisting of Na ⁺ , K ⁺ , ammonium ions with the general structure [R ¹ R ² R ³ R ⁴ N ⁺ ] with R ¹ , R ² , R ³ , R ⁴ , independently of one another, each selected from the group consisting of C ₁ - to C ₁₆ -alkyl, in particular C ₁ - to C ₈ -alkyl, straight-chain or branched, imidazolium cations with the general structure (I)

with R ¹ and R ² , independently of one another, each selected from the group consisting of C ₁ - to C ₁₈ alkyl, straight-chain or branched, in particular C ₁ - to C ₈ -alkyl, straight-chain or branched, and R ³ selected from Group consisting of H and C ₁ - to C ₁₈ -alkyl, straight-chain or branched, in particular from the group consisting of H and C ₁ - to C ₈ -alkyl, straight-chain or branched,

mit R¹ ausgewählt aus der Gruppe bestehend aus C₁- bis C₁₈-Alkyl, insbesondere C₁bis C₈-Alkyl, geradkettig oder verzweigt und R², R³ und R⁴, unabhängig voneinander, jeweils ausgewählt aus der Gruppe bestehend aus H und C₁- bis C₁₈-Alkyl, geradkettig oder verzweigt, insbesondere aus der Gruppe bestehend aus H und C₁- bis C₈-Alkyl, geradkettig oder verzweigt, undPyridinium cations with the general structure (II)

with R ¹ selected from the group consisting of C ₁ to C ₁₈ alkyl, in particular C ₁ to C ₈ alkyl, straight-chain or branched and R ² , R ³ and R ⁴ , independently of one another, each selected from the group consisting of H and C ₁ - to C ₁₈ alkyl, straight chain or branched, in particular from the group consisting of H and C ₁ - to C ₈ alkyl, straight chain or branched, and

Phosphonium ions with the general structure [R ^1a R ^2a R ^3a R ^4a P ⁺ ] with R ^1a , R ^2a , R ^3a , R ^4a , independently of one another, each selected from the group consisting of C ₁ - to C ₁₆ alkyl, in particular C ₁ - to C ₈ alkyl, straight chain or branched.

If an organic nitrate based on the imidazolium cations is used in the process according to the invention, preference is given to those cations of the general formula (I) in which R ¹ and R ² , independently of one another, are each selected from the group consisting of C ₁ - to C ₁₈ -alkyl, straight-chain or branched, in particular C ₁ - to C ₈ -alkyl, straight-chain or branched and R ³ is hydrogen. Particular preference is given to imidazolium cations of the general formula (I) in which R ¹ is methyl and R ² is ethyl or R ¹ is methyl and R 2 is methyl and ^{R 1 is} methyl and R ² is butyl, as well as R ³ each represents hydrogen.

If a nitrate based on the pyridinium cations is used in the process according to the invention, preference is given to those cations of the general formula (II) in which R ¹ is C ₁ - to C ₁₈ -alkyl, straight-chain or branched, in particular C ₁ - until C ₈ alkyl, straight chain or branched. Particular preference is given to pyridinium cations of the general formula (II) in which R ¹ is C ₁ - to C ₁₈ -alkyl, straight-chain or branched, in particular C ₁ - to C ₈ -alkyl, straight-chain or branched, and the radicals R ² , R ³ and R ⁴ , independently of one another, are each selected from the group consisting of C ₁ - to C ₈ alkyl, straight-chain or branched, where a single substitution in the 2-, 3- or 4-position, a double substitution in 2,4-, 2,5- or 2,6-position or a triple substitution in 2,4,6-position is preferred.

In principle, two or more of the above-mentioned nitrate salts can also be used in the process according to the invention. A nitrate salt according to the invention is preferably used, in particular an organic ammonium nitrate salt of the composition [R ¹ R ² R ³ R ⁴ N ⁺ ][NO ₃ ^- ] or an organic one Phosphonium salt of the composition [R ^1a R ^2a R ^3a R ^4a P ⁺ ][NO ₃ ^- ], with an organic ammonium nitrate salt of the composition [R ¹ R ² R ³ R ⁴ N ⁺ ][NO ₃ ^- ] being particularly preferred.

The organic ammonium nitrate salt tetra-n-butyl ammonium nitrate or methyl tri-n-octylammonium nitrate is very particularly preferred. The organic phosphonium nitrate salt is most preferably tetra-n-butylphosphonium nitrate or methyltri-n-octylphosphonium nitrate. The organic imidazolium nitrate salt is preferably 1-butyl-3-methylimidazolium nitrate.

Tetra-n-butyl ammonium nitrate or methyl tri-n-octylammonium nitrate is most preferably used as the organic nitrate salt in the process according to the invention.

The order in which the components used in the process according to the invention are provided can vary, as can the order in which the individual components are connected to one another or to the respective reaction medium.

In one embodiment of the process according to the invention, the unsubstituted or at least monosubstituted, saturated cycloaliphatic hydrocarbon or the inorganic or organic nitrate salt is introduced and brought together with the reaction medium, preferably at least partially or completely dissolved in the reaction medium or mixed with it, and then the other of these added to both components. In a further embodiment of the process according to the invention, the unsubstituted or at least monosubstituted, saturated cycloaliphatic hydrocarbon and the inorganic or organic nitrate salt are introduced and then brought together with the reaction medium, preferably at least partially or completely dissolved in the reaction medium or mixed with it. Furthermore, it is also possible that in the process according to the invention the unsubstituted or at least monosubstituted, saturated cycloaliphatic hydrocarbon and the inorganic or organic nitrate salt are added to the reaction medium simultaneously or in succession to one another, preferably at least partially or completely dissolved in the reaction medium or with it be mixed.

The reaction medium used in the process according to the invention is liquid under the conditions under which the process is carried out and is suitable for partially or completely dissolving the components used, i.e. in particular the unsubstituted or at least monosubstituted, saturated cycloaliphatic hydrocarbon and the inorganic or organic nitrate salt. If at least one of these components is used in liquid form, the reaction medium is preferably easily miscible with this component or these components.

A polar aprotic reaction medium is preferably used in the process according to the invention for electrochemical oxidation. This can be used in anhydrous form, in dried form or in combination with water.

If an inorganic nitrate salt, in particular potassium nitrate or sodium nitrate, is used in the process according to the invention, the reaction medium advantageously contains water, with aprotic reaction medium in combination with water being preferred. The water content in the reaction medium can vary. The water content is preferably up to 20% by volume, particularly preferably up to 15% by volume, very particularly preferably up to 10% by volume, even more preferably up to 5% by volume, in each case on the total amount of reaction medium.

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, and dimethyl sulfoxide, esters and ethers or a combination of at least two of these components.

The reaction medium is particularly preferably 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, gamma-butyrolactone and epsilon-caprolactone or a combination from at least two of these components.

Very particularly preferably, the reaction medium is selected from the group consisting of acetonitrile, isobutyronitrile, adiponitrile, dimethyl carbonate and acetone or a combination of at least two of these components.

The reaction medium is very particularly preferably acetonitrile, isobutyronitrile or adiponitrile in dried or anhydrous form.

The reaction medium is also very particularly preferred: acetonitrile, isobutyronitrile or adiponitrile, optionally in combination with water.

If one or more of the above-mentioned components is used in the reaction medium in combination with water, the water content is preferably up to 20% by volume, particularly preferably up to 15% by volume, very particularly preferably up to 10% by volume. %, even more preferably up to 5% by volume, based on the total amount of reaction medium.

To carry out the process according to the invention, it may be advantageous to add further solubilizing components to the reaction medium. Suitable advantageous components can be determined through simple preliminary tests on solution behavior.

Suitable solubilizing components include, for example, primary alcohols, secondary alcohols, monoketones or dialkyl carbonates or mixtures of at least two of these components, possibly in combination with water. Aliphatic C _1-6 alcohols can preferably be used in the process according to the invention, with particularly preferred solubilizing components being selected from the group consisting of methanol, ethanol, isopropanol, 2-methyl-2-butanol or mixtures of at least two of these components , if necessary in combination with water.

The use of dimethyl carbonate as a reaction medium can be particularly advantageous, if necessary in combination with at least one C _1-6 alcohol, in particular selected from the group consisting of methanol, ethanol, isopropanol, 2-methyl-2-butanol, if necessary in combination with be water.

If one or more of these solubilizing components is used in combination with water, the water content is preferably up to 20% by volume, particularly preferably up to 15% by volume, very particularly preferably up to 10% by volume, even further preferably up to 5% by volume, based on the total amount of solubilizing component and water.

The solubilizing components can preferably be added in amounts of <50% by volume, particularly preferably <30% by volume and very particularly preferably <10% by volume, in each case based on the total amount of reaction medium.

Preferably, the inorganic or organic nitrate salt is used in the process according to the invention in an amount of 0.1 to 2.0, preferably 0.2 to 1.0, particularly preferably 0.3 to 0.8 and very particularly preferably 0.4 to 0.8 Equivalents, each based on the amount of unsubstituted or at least monosubstituted, saturated cycloaliphatic hydrocarbon used. According to the invention, the electrochemical oxidation of the unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbon takes place in the presence of the inorganic or organic nitrate salt in an electrolysis cell in a reaction medium in the presence of oxygen.

For this purpose, a gas atmosphere containing oxygen is advantageously provided in spatial connection with the reaction medium.

The proportion of oxygen in the gas atmosphere can vary. The proportion of oxygen in the gas atmosphere is preferably 10 to 100% by volume, particularly preferably 15 to 30% by volume, particularly preferably 15 to 25% by volume, very particularly preferably 18 to 22% by volume.

In one embodiment, the proportion of oxygen in the gas atmosphere can be 10 to 100% by volume, particularly preferably 15 to 100% by volume, particularly preferably 20 to 100% by volume.

The gas atmosphere is particularly preferably air.

A gas exchange is advantageously forced between the gas atmosphere and the reaction medium, preferably by introducing a gas atmosphere into the reaction medium or by stirring the liquid phase in the presence of the gas atmosphere.

The gas exchange between the gas atmosphere and the reaction medium, in particular stirring, for example via the geometry of the stirrer or the stirring speed, can be used to control the electrochemical oxidation.

The amount of oxygen dissolved in the reaction medium is preferably at least 1 mmol/L reaction medium, particularly preferably at least 5 mmol/L reaction medium.

The amount of oxygen dissolved in the reaction medium is also preferably at least 10 mmol/L reaction medium.

The process according to the invention for producing unsubstituted or at least monosubstituted cycloalkanones by electrochemical oxidation of unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbons by electrochemical oxidation in the presence of an inorganic or organic nitrate salt in a reaction medium in the presence of oxygen can be carried out in both a divided and carry out in an undivided electrolysis cell, with implementation in an undivided electrolysis cell being preferred.

In order to avoid undesirable chemical reactions, it is sometimes advantageous to separate the cathode compartment and anode compartment from one another and to allow the charge exchange between the anode and cathode compartments to take place only through a porous diaphragm - often an ion exchange resin.

The undivided electrolysis cell which is preferably used according to the invention has at least two electrodes. Anodes and cathodes of common materials can be used here, for example glassy carbon, boron-doped diamond (BDD) or graphite. The use of glassy carbon electrodes is preferred.

The undivided electrolysis cell preferably has at least one glassy carbon anode or at least one glassy carbon cathode. Both the anode and the cathode are preferably glassy carbon electrodes.

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, particularly preferably 0.1 mm to 0.5 cm.

Furthermore, the process according to the invention can be carried out batchwise or continuously, preferably in an undivided flow-through electrolysis cell.

The process according to the invention is preferably carried out with a charge amount of 190 C (2 F) to 970 C (10 F), particularly preferably 320 C to 820 C, very particularly preferably 350 C to 800 C, even more preferably 380 C to 775 C most preferably 380 C to 450 C, in each case based on 1 mmol of unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbon.

The electrochemical oxidation in the process according to the invention preferably takes place at constant current intensity.

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 10 mA/cm ² or at least 15 mA/cm ² or at least 20 mA/cm ² or 20 mA/cm ² to 50 mA/ cm ² , whereby the area refers to the geometric area of the electrodes.

A significant advantage of the method according to the invention is that electric current is used as the oxidizing agent, which is a particularly environmentally friendly agent when it comes from renewable sources, i.e. in particular from biomass, solar thermal energy, geothermal energy, hydropower, wind power or photovoltaics.

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

The process according to the invention can be carried out at increased or reduced pressure. If the process according to the invention is carried out at elevated pressure, a pressure of up to 16 bar is preferred, particularly preferably up to 6 bar.

The process according to the invention can also preferably be carried out under atmospheric pressure.

The products produced by the process according to the invention can be isolated or purified by conventional processes known to those skilled in the art, in particular by extraction, crystallization, centrifugation, precipitation, distillation, evaporation or chromatography.

• Ausführungsform 1: Verfahren zur Herstellung von unsubstituierten oder wenigstens einfach substituierten Cycloalkanonen durch elektrochemische Oxidation von unsubstituierten oder wenigstens einfach substituierten, gesättigten cycloaliphatischen Kohlenwasserstoffen umfassend die Verfahrensschritte
  1. (a) Bereitstellung wenigstens eines unsubstituierten oder wenigstens einfach substituierten, gesättigten cycloaliphatischen Kohlenwasserstoffs;
  2. (b) Bereitstellung wenigstens eines anorganischen oder organischen Nitratsalzes;
  3. (c) elektrochemische Oxidation des in Schritt (a) bereitgestellten unsubstituierten oder wenigstens einfach substituierten, gesättigten cycloaliphatischen Kohlenwasserstoffs in Gegenwart des in Schritt (b) bereit gestellten anorganischen oder organischen Nitratsalzes in einer Elektrolysezelle in einem Reaktionsmedium in Gegenwart von Sauerstoff.
• Ausführungsform 2: Verfahren nach Ausführungsform 1, wobei der unsubstituierte oder wenigstens einfach substituierte, gesättigte cycloaliphatische Kohlenwasserstoff monocyclisch oder polycyclisch ist, vorzugweise monocyclisch oder bicyclisch ist, besonders bevorzugt monocyclisch ist.
• Ausführungsform 3: Verfahren nach Ausführungsform 2, wobei der monocyclische oder polycyclische, vorzugsweise monocyclische oder bicyclische, gesättigte cycloaliphatische Kohlenwasserstoff 5 bis 18 C Atome im Ringsystem aufweist und unsubstituiert oder einfach oder mehrfach substituiert ist mit 1, 2, 3, 4 oder 5 Substituenten, unabhängig voneinander, jeweils ausgewählt aus der Gruppe bestehend aus Methyl, Phenyl oder Benzyl, wobei Phenyl oder Benzyl jeweils unsubstituiert oder einfach oder mehrfach substituiert sein können, mit 1, 2 oder 3 Substituenten, unabhängig voneinander, jeweils ausgewählt aus der Gruppe bestehend aus F, Cl, Br, und NO₂
• Ausführungsform 4: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei der unsubstituierte oder wenigstens einfach substituierte, gesättigte cycloaliphatische Kohlenwasserstoff ein monocyclischer gesättigter Kohlenwasserstoff mit 6-12 Kohlenstoffatomen im Ring, vorzugsweise mit 8-12 Kohlenstoffatomen im Ring, ist, wobei dieser cycloaliphatische Kohlenwasserstoff unsubstituiert oder einfach oder mehrfach substituiert ist mit 1, 2, 3, 4 oder 5 Substituenten, unabhängig voneinander, jeweils ausgewählt aus der Gruppe bestehend aus Methyl, Phenyl oder Benzyl, besonders bevorzugt ein monocyclischer gesättigter Kohlenwasserstoff mit 8-12 Kohlenstoffatomen im Ring, wobei dieser cycloaliphatische Kohlenwasserstoff unsubstituiert oder einfach oder zweifach oder dreifach substituiert sind mit Methyl. Ausführungsform 5: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei der gesättigte cycloaliphatische Kohlenwasserstoff unsubstituiert und ausgewählt ist aus der Gruppe bestehend aus Cyclohexan, Cycloheptan, Cyclooctan, Cyclononan, Cyclodecan, Cycloundecan und Cyclododecan, vorzugsweise ausgewählt aus der Gruppe bestehend aus Cyclooctan, Cyclononan, Cyclodecan, Cycloundecan und Cyclododecan, besonders bevorzugt Cyclododecan ist.
• Ausführungsform 6: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei als anorganisches oder organisches Nitratsalz ein Nitrat der allgemeinen Formel [Kation⁺][NO₃ ^-] vorliegt, mit [Kation⁺] ausgewählt aus der Gruppe bestehend aus Na⁺, K⁺, Ammoniumionen mit der allgemeinen Struktur [R¹R²R³R⁴N⁺] mit R¹, R², R³, R⁴, unabhängig voneinander, jeweils ausgewählt aus der Gruppe bestehend aus C₁- bis C₁₆-Alkyl, insbesondere C₁- bis C₈-Alkyl, geradkettig oder verzweigt, Imidazolium-Kationen mit der allgemeinen Struktur (I)
  
  mit R¹ und R², unabhängig voneinander, jeweils ausgewählt aus der Gruppe bestehend aus C₁- bis C₁₈-Alkyl, geradkettig oder verzweigt, insbesondere C₁- bis C₈-Alkyl, geradkettig oder verzweigt, und R³ ausgewählt aus der Gruppe bestehend aus H und C₁- bis C₁₈-Alkyl, geradkettig oder verzweigt, insbesondere aus der Gruppe bestehend aus H und C₁- bis C₈-Alkyl, geradkettig oder verzweigt,
  Pyridinium-Kationen mit der allgemeinen Struktur (II)
  
  mit R¹ ausgewählt aus der Gruppe bestehend aus C₁- bis C₁₈-Alkyl, insbesondere C₁bis C₈-Alkyl, geradkettig oder verzweigt und R², R³ und R⁴, unabhängig voneinander, jeweils ausgewählt aus der Gruppe bestehend aus H und C₁- bis C₁₈-Alkyl, geradkettig oder verzweigt, insbesondere aus der Gruppe bestehend aus H und C₁- bis C₈-Alkyl, geradkettig oder verzweigt, und Phosphoniumionen mit der allgemeinen Struktur [R^1aR^2aR^3aR^4aP⁺] mit R^1a, R^2a, R^3a, R^4a, unabhängig voneinander, jeweils ausgewählt aus der Gruppe bestehend aus C₁- bis C₁₆-Alkyl, insbesondere C₁- bis C₈-Alkyl, geradkettig oder verzweigt.
• Ausführungsform 7: Verfahren nach Ausführungsform 6, wobei in den Imidazolium-Kationen der allgemeinen Formel (I) die Reste R¹ und R², unabhängig voneinander, jeweils ausgewählt sind aus der Gruppe bestehend aus C₁- bis C₁₈-Alkyl, geradkettig oder verzweigt, insbesondere C₁- bis C₈-Alkyl, geradkettig oder verzweigt und R³ für Wasserstoff steht, vorzugsweise R¹ für Methyl und R² für Ethyl stehen oder R¹ für Methyl und R² für Methyl stehen und R¹ für Methyl und R² für Butyl stehen, sowie R³ jeweils für Wasserstoff steht.
• Ausführungsform 8: Verfahren nach Ausführungsform 6 oder 7, wobei in den Pyridinium-Kationen der allgemeinen Formel (II) der Rest R¹ für C₁- bis C₁₈-Alkyl, geradkettig oder verzweigt, insbesondere für C₁- bis C₈-Alkyl, geradkettig oder verzweigt steht und die Reste R², R³ und R⁴, unabhängig voneinander, jeweils ausgewählt sind aus der Gruppe bestehend aus C₁- bis C₈-Alkyl, geradkettig oder verzweigt, wobei eine einfache Substitution in 2-, 3- oder 4-Position, eine zweifache Substitution in 2,4-, 2,5- oder 2,6-Position oder eine dreifache Substitution in 2,4,6-Position bevorzugt ist.
• Ausführungsform 9: Verfahren nach einer der Ausführungsform 6 bis 8, wobei das organische Nitratsalz ausgewählt ist aus der Gruppe bestehend aus Tetra-n-butyl-ammonium-nitrat, Methyl-tri-n-octyl-ammonium-nitrat, Tetra-n-butyl-phosphonium-nitrat, Methyl-tri-n-octyl-phosphonium-nitrat und 1-Butyl-3-methylimidazoliumnitrat. Ausführungsform 10: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei der unsubstituierte oder wenigstens einfach substituierte, gesättigte cycloaliphatische Kohlenwasserstoff oder das anorganische oder organische Nitratsalz vorgelegt und mit dem Reaktionsmedium zusammengebracht wird, vorzugsweise in dem Reaktionsmedium zumindest teilweise oder vollständig gelöst oder damit gemischt wird, und dann die jeweils andere dieser beiden Komponenten dazugegeben wird.
• Ausführungsform 11: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei der unsubstituierte oder wenigstens einfach substituierte, gesättigte cycloaliphatische Kohlenwasserstoff und das anorganische oder organische Nitratsalz vorgelegt und dann mit dem Reaktionsmedium zusammengebracht werden, vorzugsweise in dem Reaktionsmedium zumindest teilweise oder vollständig gelöst oder damit gemischt werden.
• Ausführungsform 12: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei der unsubstituierte oder wenigstens einfach substituierte, gesättigte cycloaliphatische Kohlenwasserstoff und das anorganische oder organische Nitratsalz gleichzeitig oder in zeitlicher Abfolge zueinander in das Reaktionsmedium gegeben werden, vorzugsweise in dem Reaktionsmedium zumindest teilweise oder vollständig gelöst oder damit gemischt werden.
• Ausführungsform 13: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei das Reaktionsmedium ein polares aprotisches Reaktionsmedium ist, welches wasserfrei, getrocknet oder in Kombination mit Wasser vorliegen kann. Ausführungsform 14: Verfahren nach Ausführungsform 13, wobei der Gehalt an Wasser bis zu 20 Vol.-%, vorzugsweise bis zu 15 Vol.-%, besonders bevorzugt bis zu 10 Vol.-%, ganz besonders bevorzugt bis zu 5 Vol.-%, beträgt, jeweils bezogen auf die Gesamtmenge an Reaktionsmedium.
• Ausführungsform 15: Verfahren nach Ausführungsform 13 oder 14, wobei das polare aprotische Reaktionsmedium ausgewählt ist aus der Gruppe bestehend aus aliphatischen Nitrilen, aliphatischen Ketonen, cycloaliphatischen Ketonen, Dialkylcarbonaten, cyclischen Carbonaten, Lactonen, aliphatischen Nitroalkanen, und Dimethylsulfoxid, Estern und Ethern oder einer Kombination aus wenigstens zwei dieser Komponenten.
• Ausführungsform 16: Verfahren nach Ausführungsform 15, wobei als Reaktionsmedium ein polares aprotisches Reaktionsmedium vorliegt, welches ausgewählt ist aus der Gruppe bestehend aus Acetonitril, Isobutyronitril, Adiponitril, Aceton, Dimethylcarbonat, Methylethylketon, 3-Pentanon, Cyclohexanon, Nitromethan, Nitropropan, tert.-Butylmethylether, Dimethylsulfoxid, gamma-Butyrolacton und epsilon-Caprolacton oder einer Kombination aus wenigstens zwei dieser Komponenten, jeweils ggf. in Kombination mit Wasser.
• Ausführungsform 17: Verfahren nach Ausführungsform 16, wobei ein Reaktionsmedium ausgewählt aus der Gruppe bestehend aus Acetonitril, Isobutyronitril, Adiponitril, Dimethylcarbonat und Aceton oder einer Kombination aus wenigstens zwei dieser Komponenten, ggf. in Kombination mit Wasser, vorliegt. Ausführungsform 18: Verfahren nach Ausführungsform 16 oder 17. wobei das Reaktionsmedium Acetonitril, Isobutyronitril oder Adiponitril in getrockneter oder wasserfreier Form ist.
• Ausführungsform 19: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei das Reaktionsmedium eine oder mehrere lösungsvermittelnde Komponenten aufweist.
• Ausführungsform 20: Verfahren gemäß Ausführungsform 19, wobei als lösungsvermittelnde Komponenten primäre Alkohole, sekundäre Alkohole, Monoketone oder Dialkylcarbonate oder Mischungen aus wenigstens zwei dieser Komponenten vorliegen, ggf. in Kombination mit Wasser.
• Ausführungsform 21: Verfahren gemäß Ausführungsform 19 oder 20, wobei aliphatische C_1-6-Alkohole als eine oder mehrere lösungsvermittelnde Komponenten vorliegen, vorzugsweise einer oder mehrere Alkohole ausgewählt aus der Gruppe bestehend aus Methanol, Ethanol, Isopropanol, 2-Methyl-2-Butanol und Mischungen aus wenigstens zwei dieser Komponenten, ggf. in Kombination mit Wasser. Ausführungsform 22: Verfahren gemäß einer der vorhergehenden Ausführungsformen, wobei als Reaktionsmedium Dimethylcarbonat, ggf. in Kombination mit wenigstens einem C_1-6-Alkohol, vorzugsweise ausgewählt aus der Gruppe bestehend aus Methanol, Ethanol, Isopropanol, 2-Methyl-2-Butanol vorliegt.
• Ausführungsform 23: Verfahren gemäß Ausführungsform 22, wobei das Reaktionsmedium Wasser aufweist.
• Ausführungsform 24: Verfahren gemäß einer der Ausführungsformen 19 bis 23, wobei eine oder mehrere lösungsvermittelnde Komponenten in einer Menge von < 50 Vol.-%, besonders bevorzugt von < 30 Vol.-% und ganz besonders bevorzugt von < 10 Vol.-% zugegeben werden, jeweils bezogen auf die Gesamtmenge an Reaktionsmedium vorliegen.
• Ausführungsform 25: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei das anorganische oder organische Nitratsalz in einer Menge von 0,1 bis 2,0, vorzugsweise 0,2 bis 1,0, besonders bevorzugt 0,3 bis 0,8 und ganz besonders bevorzugt 0,4 bis 0.8 Äquivalenten, jeweils bezogen auf die Menge an eingesetztem unsubstituierten oder wenigstens einfach substituierten, gesättigten cycloaliphatischen Kohlenwasserstoff.
• Ausführungsform 26: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei in räumlicher Verbindung mit dem Reaktionsmedium eine Gasatmosphäre enthaltend Sauerstoff bereitgestellt wird.
• Ausführungsform 27: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei der Anteil von Sauerstoff an der Gasatmosphäre 10 bis 100 Vol.-%, vorzugsweise 15 bis 30 Vol.-%, besonders bevorzugt 15 bis 25 Vol.-%, ganz besonders bevorzugt 18 bis 22 Vol.-%, beträgt.
• Ausführungsform 28: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei der Anteil von Sauerstoff an der Gasatmosphäre 10 bis 100 Vol.-% besonders bevorzugt 15 bis 100 Vol.-%, besonders bevorzugt 20 bis 100 Vol.-% beträgt. Ausführungsform 29: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei die Gasatmosphäre Luft ist.
• Ausführungsform 30: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei zwischen der Gasatmosphäre und dem Reaktionsmedium ein Gasaustausch erzwungen wird.
• Ausführungsform 31: Verfahren nach Ausführungsform 30, wobei der Gasaustausch durch das Einleiten von Gasatmosphäre in das Reaktionsmedium erfolgt. Ausführungsform 32: Verfahren nach Ausführungsform 30 oder 31, wobei der Gasaustausch durch Rühren der flüssigen Phase in Gegenwart der Gasatmosphäre erfolgt.
• Ausführungsform 33: Verfahren nach Ausführungsform 32, wobei das Rühren zur Steuerung der elektrochemischen Oxidation verwendet wird.
• Ausführungsform 34: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei die im Reaktionsmedium gelöste Menge an Sauerstoff mindestens 1 mmol/L Reaktionsmedium beträgt.
• Ausführungsform 35: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei die im Reaktionsmedium gelöste Menge an Sauerstoff mindestens 5 mmol/L Reaktionsmedium beträgt.
• Ausführungsform 36: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei die Elektrolysezelle eine ungeteilte Elektrolysezelle ist.
• Ausführungsform 37: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei die ungeteilte Elektrolysezelle eine Glaskohlenstoff-Anode, eine Graphit Anode oder eine BDD-Anode, vorzugsweise eine Glaskohlenstoff-Anode aufweist. Ausführungsform 38: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei die ungeteilte Elektrolysezelle eine Glaskohlenstoff-Kathode, eine Graphit-Kathode oder eine BDD-Kathode, vorzugsweise eine Glaskohlenstoff-Kathode aufweist.
• Ausführungsform 39: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei der Abstand der Elektroden in der Elektrolysezelle 0,1 mm bis 2,0 cm, vorzugsweise 0,1 mm bis 1,0 cm, besonders bevorzugt 0,1 mm bis 0,5 cm beträgt.
• Ausführungsform 40: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei die Ladungsmenge 190 C (2 F) bis 970 C (10 F), vorzugsweise 320 C bis 820 C, besonders bevorzugt 350 C bis 800, ganz besonders bevorzugt 380 C bis 775 C, am meisten bevorzugt 380 C bis 450 C, jeweils für 1 mmol an unsubstituierten oder wenigstens einfach substituierten gesättigten cycloaliphatischen Kohlenwasserstoffs.
• Ausführungsform 41: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei die elektrochemische Oxidation bei konstanter Stromstärke erfolgt.
• Ausführungsform 42: Verfahren nach einer der vorhergehenden Ausführungsformen, dadurch gekennzeichnet, dass die Stromdichte wenigstens 5 mA/cm² beträgt, wobei sich die Flächenangabe auf die geometrische Fläche der Elektroden bezieht.
• Ausführungsform 43: Verfahren nach einer der vorhergehenden Ausführungsformen, dadurch gekennzeichnet, dass die Stromdichte wenigstens 10 mA/cm² beträgt, wobei sich die Flächenangabe auf die geometrische Fläche der Elektroden bezieht.
• Ausführungsform 44: Verfahren nach einer der vorhergehenden Ausführungsformen, dadurch gekennzeichnet, dass die Stromdichte wenigstens 15 mA/cm² beträgt, wobei sich die Flächenangabe auf die geometrische Fläche der Elektroden bezieht.
• Ausführungsform 45: Verfahren nach einer der vorhergehenden Ausführungsformen, dadurch gekennzeichnet, dass die Stromdichte wenigstens 20 mA/cm² beträgt, wobei sich die Flächenangabe auf die geometrische Fläche der Elektroden bezieht.
• Ausführungsform 46: Verfahren nach einer der vorhergehenden Ausführungsformen, dadurch gekennzeichnet, dass die Stromdichte wenigstens 20 mA/cm² bis 50 mA/cm² beträgt, wobei sich die Flächenangabe auf die geometrische Fläche der Elektroden bezieht.
• Ausführungsform 47: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei der zur elektrochemischen Oxidation eingesetzte Strom aus regenerativen Quellen stammt, insbesondere aus Biomasse, Solarthermie, Geothermie, Wasserkraft, Windkraft oder Photovoltaik.
• Ausführungsform 48: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei die elektrochemische Oxidation bei einer Temperatur im Bereich von 0 bis 60 °C, vorzugsweise von 5 bis 50 °C, besonders bevorzugt von 10 bis 40°C, ganz besonders bevorzugt von 15-30°C erfolgt.
• Ausführungsform 49: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei es unter Atmosphärendruck durchgeführt wird.
• Ausführungsform 50: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei es unter Unterdruck durchgeführt wird.
• Ausführungsform 51: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei es unter Überdruck, vorzugsweise bis zu 16 bar, besonders bevorzugt bis zu 6 bar durchgeführt wird.
• Ausführungsform 52: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei es Batch-weise durchgeführt wird.
• Ausführungsform 53: Verfahren nach einer der vorhergehenden Ausführungsformen, wobei es kontinuierlich durchgeführt wird, vorzugsweise in einer ungeteilten Durchfluss-Elektrolysezelle.
• Ausführungsform 54: Verfahren nach einem der vorhergehenden Ausführungsformen, wobei es ohne den Zusatz von Katalysatoren, insbesondere ohne den Zusatz von Übergangsmetallkatalysatoren durchgeführt wird.
• Ausführungsform 55: Verfahren nach einem der vorhergehenden Ausführungsform, wobei neben Sauerstoff oder Luftsauerstoff keine weiteren Oxidationsmittel zugesetzt werden.

Further preferred embodiments of the present invention are the following embodiments:

• Embodiment 1: Process for producing unsubstituted or at least monosubstituted cycloalkanones by electrochemical oxidation of unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbons, comprising the process steps
  1. (a) providing at least one unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbon;
  2. (b) providing at least one inorganic or organic nitrate salt;
  3. (c) electrochemical oxidation of the unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbon provided in step (a) in the presence of the inorganic or organic nitrate salt provided in step (b) in an electrolysis cell in a reaction medium in the presence of oxygen.
• Embodiment 2: Process according to Embodiment 1, wherein the unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbon is monocyclic or polycyclic, preferably monocyclic or bicyclic, particularly preferably monocyclic.
• Embodiment 3: Process according to Embodiment 2, wherein the monocyclic or polycyclic, preferably monocyclic or bicyclic, saturated cycloaliphatic hydrocarbon has 5 to 18 C atoms in the ring system and is unsubstituted or mono- or poly-substituted with 1, 2, 3, 4 or 5 substituents, independently of each other, each selected from the group consisting of methyl, phenyl or benzyl, where phenyl or benzyl can each be unsubstituted or mono- or poly-substituted 1, 2 or 3 substituents, independently of one another, each selected from the group consisting of F, Cl, Br, and NO ₂
• Embodiment 4: Process according to one of the preceding embodiments, wherein the unsubstituted or at least monosubstituted, saturated cycloaliphatic hydrocarbon is a monocyclic saturated hydrocarbon with 6-12 carbon atoms in the ring, preferably with 8-12 carbon atoms in the ring, this cycloaliphatic hydrocarbon being unsubstituted or is substituted once or multiple times with 1, 2, 3, 4 or 5 substituents, independently of one another, each selected from the group consisting of methyl, phenyl or benzyl, particularly preferably a monocyclic saturated hydrocarbon with 8-12 carbon atoms in the ring, which is cycloaliphatic Hydrocarbons are unsubstituted or mono- or di- or tri-substituted with methyl. Embodiment 5: Process according to one of the preceding embodiments, wherein the saturated cycloaliphatic hydrocarbon is unsubstituted and selected from the group consisting of cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane and cyclododecane, preferably selected from the group consisting of cyclooctane, cyclononane, cyclodecane , cycloundecane and cyclododecane, particularly preferably cyclododecane.
• Embodiment 6: Method according to one of the preceding embodiments, wherein the inorganic or organic nitrate salt is a nitrate of the general formula [cation ⁺ ][NO ₃ ^- ], with [cation ⁺ ] selected from the group consisting of Na ⁺ , K ⁺ , ammonium ions with the general structure [R ¹ R ² R ³ R ⁴ N ⁺ ] with R ¹ , R ² , R ³ , R ⁴ , independently of one another, each selected from the group consisting of C ₁ - to C ₁₆ -alkyl, in particular C ₁ - to C ₈ alkyl, straight chain or branched, imidazolium cations with the general structure (I)
  
  with R ¹ and R ² , independently of one another, each selected from the group consisting of C ₁ - to C ₁₈ alkyl, straight-chain or branched, in particular C ₁ - to C ₈ -alkyl, straight-chain or branched, and R ³ selected from Group consisting of H and C ₁ - to C ₁₈ -alkyl, straight-chain or branched, in particular from the group consisting of H and C ₁ - to C ₈ -alkyl, straight-chain or branched,
  Pyridinium cations with the general structure (II)
  
  with R ¹ selected from the group consisting of C ₁ to C ₁₈ alkyl, in particular C ₁ to C ₈ alkyl, straight-chain or branched and R ² , R ³ and R ⁴ , independently of one another, each selected from the group consisting of H and C ₁ - to C ₁₈ -alkyl, straight-chain or branched, in particular from the group consisting of H and C ₁ - to C ₈ -alkyl, straight-chain or branched, and phosphonium ions with the general structure [R ^1a R ^2a R ^3a R ^4a P ⁺ ] with R ^1a , R ^2a , R ^3a , R ^4a , independently of one another, each selected from the group consisting of C ₁ - to C ₁₆ -alkyl, in particular C ₁ - to C ₈ -alkyl, straight-chain or branched.
• Embodiment 7: Process according to Embodiment 6, wherein in the imidazolium cations of the general formula (I), the radicals R ¹ and R ² , independently of one another, are each selected from the group consisting of C ₁ - to C ₁₈ -alkyl, straight-chain or branched, in particular C ₁ - to C ₈ alkyl, straight-chain or branched and R ³ is hydrogen, preferably R ¹ is methyl and R ² is ethyl or R ^{1 is methyl and R 2 is} methyl and R ¹ is methyl and R ² represents butyl and R ³ each represents hydrogen.
• Embodiment 8: Process according to embodiment 6 or 7, wherein in the pyridinium cations of the general formula (II) the radical R ¹ is C ₁ - to C ₁₈ -alkyl, straight-chain or branched, in particular C ₁ - to C ₈ -alkyl , straight-chain or branched and the radicals R ² , R ³ and R ⁴ , independently of one another, are each selected from the group consisting of C ₁ - to C ₈ -alkyl, straight-chain or branched, with a simple substitution in 2-, 3 - or 4-position, a double substitution in the 2,4-, 2,5- or 2,6-position or a triple substitution in the 2,4,6-position is preferred.
• Embodiment 9: The method according to any one of embodiments 6 to 8, wherein the organic nitrate salt is selected from the group consisting of tetra-n-butyl ammonium nitrate, methyl tri-n-octyl ammonium nitrate, tetra-n-butyl -phosphonium nitrate, methyl tri-n-octyl phosphonium nitrate and 1-butyl-3-methylimidazolium nitrate. Embodiment 10: Process according to one of the preceding embodiments, wherein the unsubstituted or at least monosubstituted, saturated cycloaliphatic hydrocarbon or the inorganic or organic nitrate salt is introduced and brought into contact with the reaction medium, preferably at least partially or completely dissolved in the reaction medium or mixed with it, and then the other of these two components is added.
• Embodiment 11: Process according to one of the preceding embodiments, wherein the unsubstituted or at least monosubstituted, saturated cycloaliphatic hydrocarbon and the inorganic or organic nitrate salt are introduced and then brought together with the reaction medium, preferably at least partially or completely dissolved in the reaction medium or mixed with it.
• Embodiment 12: Method according to one of the preceding embodiments, wherein the unsubstituted or at least monosubstituted, saturated cycloaliphatic hydrocarbon and the inorganic or organic nitrate salt are added to the reaction medium simultaneously or in succession to one another, preferably at least partially or completely dissolved in the reaction medium or with it be mixed.
• Embodiment 13: Method according to one of the preceding embodiments, wherein the reaction medium is a polar aprotic reaction medium, which can be anhydrous, dried or in combination with water. Embodiment 14: Process according to embodiment 13, wherein the water content is up to 20% by volume, preferably up to 15% by volume, particularly preferably up to 10% by volume, very particularly preferably up to 5% by volume. , is based on the total amount of reaction medium.
• Embodiment 15: Process according to Embodiment 13 or 14, wherein the polar aprotic reaction medium is selected from the group consisting of aliphatic nitriles, aliphatic ketones, cycloaliphatic ketones, dialkyl carbonates, cyclic carbonates, lactones, aliphatic nitroalkanes, and dimethyl sulfoxide, esters and ethers or a combination from at least two of these components.
• Embodiment 16: Process according to Embodiment 15, wherein the reaction medium is a polar aprotic reaction medium which 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, gamma-butyrolactone and epsilon-caprolactone or a combination of at least two of these components, each optionally in combination with water.
• Embodiment 17: Process according to Embodiment 16, wherein a reaction medium selected from the group consisting of acetonitrile, isobutyronitrile, adiponitrile, dimethyl carbonate and acetone or a combination of at least two of these components, optionally in combination with water, is present. Embodiment 18: Process according to Embodiment 16 or 17, wherein the reaction medium is acetonitrile, isobutyronitrile or adiponitrile in dried or anhydrous form.
• Embodiment 19: Method according to one of the preceding embodiments, wherein the reaction medium has one or more solubilizing components.
• Embodiment 20: Process according to Embodiment 19, wherein the solubilizing components are primary alcohols, secondary alcohols, monoketones or dialkyl carbonates or mixtures of at least two of these components, optionally in combination with water.
• Embodiment 21: Process according to embodiment 19 or 20, wherein aliphatic C _1-6 alcohols are 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, possibly in combination with water. Embodiment 22: Process according to one of the preceding embodiments, wherein the reaction medium is dimethyl carbonate, optionally in combination with at least one C _1-6 alcohol, preferably selected from the group consisting of methanol, ethanol, isopropanol, 2-methyl-2-butanol .
• Embodiment 23: Method according to Embodiment 22, wherein the reaction medium comprises water.
• Embodiment 24: Method according to one of embodiments 19 to 23, wherein one or more solubilizing components in an amount of <50% by volume, particularly preferably <30% by volume and most preferably <10% by volume are added, each based on the total amount of reaction medium.
• Embodiment 25: Method according to one of the preceding embodiments, wherein the inorganic or organic nitrate salt is in an amount of 0.1 to 2.0, preferably 0.2 to 1.0, particularly preferably 0.3 to 0.8 and most preferably 0.4 to 0.8 equivalents, in each case based on the amount of unsubstituted or at least monosubstituted, saturated cycloaliphatic hydrocarbon used.
• Embodiment 26: Method according to one of the preceding embodiments, wherein a gas atmosphere containing oxygen is provided in spatial connection with the reaction medium.
• Embodiment 27: Method according to one of the preceding embodiments, wherein the proportion of oxygen in the gas atmosphere is 10 to 100 vol.%, preferably 15 to 30 vol.%, particularly preferably 15 to 25 vol.%, very particularly preferably 18 to 22% by volume.
• Embodiment 28: Method according to one of the preceding embodiments, wherein the proportion of oxygen in the gas atmosphere is 10 to 100% by volume, particularly preferably 15 to 100% by volume, particularly preferably 20 to 100% by volume. Embodiment 29: Method according to one of the preceding embodiments, wherein the gas atmosphere is air.
• Embodiment 30: Method according to one of the preceding embodiments, wherein a gas exchange is forced between the gas atmosphere and the reaction medium.
• Embodiment 31: Method according to Embodiment 30, wherein the gas exchange takes place by introducing a gas atmosphere into the reaction medium. Embodiment 32: Method according to embodiment 30 or 31, wherein the gas exchange takes place by stirring the liquid phase in the presence of the gas atmosphere.
• Embodiment 33: The method according to Embodiment 32, wherein stirring is used to control electrochemical oxidation.
• Embodiment 34: Method according to one of the preceding embodiments, wherein the amount of oxygen dissolved in the reaction medium is at least 1 mmol/L reaction medium.
• Embodiment 35: Method according to one of the preceding embodiments, wherein the amount of oxygen dissolved in the reaction medium is at least 5 mmol/L reaction medium.
• Embodiment 36: Method according to one of the preceding embodiments, wherein the electrolytic cell is an undivided electrolytic cell.
• Embodiment 37: Method according to one of the preceding embodiments, wherein the undivided electrolysis cell has a glassy carbon anode, a graphite anode or a BDD anode, preferably a glassy carbon anode. Embodiment 38: Method according to one of the preceding embodiments, wherein the undivided electrolysis cell has a glassy carbon cathode, a graphite cathode or a BDD cathode, preferably a glassy carbon cathode.
• Embodiment 39: Method according to one of the preceding embodiments, wherein the distance between the electrodes in the electrolytic cell is 0.1 mm to 2.0 cm, preferably 0.1 mm to 1.0 cm, particularly preferably 0.1 mm to 0.5 cm amounts.
• Embodiment 40: Method according to one of the preceding embodiments, wherein the amount of charge is 190 C (2 F) to 970 C (10 F), preferably 320 C to 820 C, particularly preferably 350 C to 800, very particularly preferably 380 C to 775 C, most preferably 380 C to 450 C, each for 1 mmol of unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbon.
• Embodiment 41: Method according to one of the preceding embodiments, wherein the electrochemical oxidation takes place at constant current intensity.
• Embodiment 42: Method according to one of the preceding embodiments, characterized in that the current density is at least 5 mA/cm ² , the area information relating to the geometric area of the electrodes.
• Embodiment 43: Method according to one of the preceding embodiments, characterized in that the current density is at least 10 mA/cm ² , the area information relating to the geometric area of the electrodes.
• Embodiment 44: Method according to one of the preceding embodiments, characterized in that the current density is at least 15 mA/cm ² , the area information relating to the geometric area of the electrodes.
• Embodiment 45: Method according to one of the preceding embodiments, characterized in that the current density is at least 20 mA/cm ² , the area information relating to the geometric area of the electrodes.
• Embodiment 46: Method according to one of the preceding embodiments, characterized in that the current density is at least 20 mA/cm ² to 50 mA/cm ² , the area information relating to the geometric area of the electrodes.
• Embodiment 47: Method according to one of the preceding embodiments, wherein the electricity used for electrochemical oxidation comes from renewable sources, in particular from biomass, solar thermal energy, geothermal energy, hydropower, wind power or photovoltaics.
• Embodiment 48: Method according to one of the preceding embodiments, wherein the electrochemical oxidation takes place at a temperature in the range from 0 to 60 ° C, preferably from 5 to 50 ° C, particularly preferably from 10 to 40 ° C, very particularly preferably from 15-30 °C takes place.
• Embodiment 49: Method according to one of the preceding embodiments, wherein it is carried out under atmospheric pressure.
• Embodiment 50: Method according to one of the preceding embodiments, wherein it is carried out under negative pressure.
• Embodiment 51: Method according to one of the preceding embodiments, wherein it is carried out under excess pressure, preferably up to 16 bar, particularly preferably up to 6 bar.
• Embodiment 52: Method according to one of the preceding embodiments, wherein it is carried out in batches.
• Embodiment 53: Method according to one of the preceding embodiments, wherein it is carried out continuously, preferably in an undivided flow-through electrolysis cell.
• Embodiment 54: Process according to one of the preceding embodiments, wherein it is carried out without the addition of catalysts, in particular without the addition of transition metal catalysts.
• Embodiment 55: Method according to one of the preceding embodiments, wherein no further oxidizing agents are added in addition to oxygen or atmospheric oxygen.

The following examples further illustrate the present invention but are not to be construed as limiting the scope of the invention.

General information and methods

Analytical grade chemicals were purchased and used from mainstream suppliers (such as TCI, Aldrich, and Acros). The oxygen was purchased in 2.5 quality from NIPPON GASES Deutschland GmbH, Düsseldorf, Germany and used directly.

Glassy carbon (SIGRADUR ^® G, from HTW Hochtemperatur Werkstoffe GmbH, Thierhaupten, Germany) was used as the electrode material.

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

NMR spectrometry of 1H-NMR and 13C-NMR spectra were recorded at 25 °C with a Bruker Avance II 400 (400 MHz, 5 mm BBFO head with z-gradient and ATM, SampleXPress 60 sample changer, Analytische Messtechnik, Karlsruhe, Germany) recorded.

The undivided Teflon cells used for electrolysis are described in the literature (a) C. Gütz, B. Klöckner, SR Waldvogel, Org. Process Res. Dev. 2016, 20, 26-32 ; b) A. Kirste, G. Schnakenburg, F. Stecker, A. Fischer, SR Waldvogel, Angew. Chem. Int. Ed. 2010, 49, 971-975 ; Angew. Chem. 2010, 122, 983-987 . (see SI).) The complete range of these cells with stainless steel block is also commercially available as the IKA Screening System (IKA-Werke GmbH & Co. KG, Staufen, Germany). The dimensions of the electrodes were 3 cm x 1 cm x 0.3 cm.

The gas introduction was controlled via two mass flow controllers (MFC) model 5850S from Brooks Instrument BV, Veenendaal, Netherlands. A regulator was used for the oxygen and nitrogen lines. The controllers were controlled using the Smart DDE and Matlab R2017b software. The volume flow control was also carried out using a DK800 variable area flowmeter from KROHNE Messtechnik GmbH, Duisburg. For all experiments carried out, the total volume flow was a constant 20 mL/min, which, limited by the MFCs used, also represents the maximum achievable volume flow. The percentage volume flows of the two gases were set using the MFCs and their software. The gas bottles were used from the following suppliers: Oxygen 2.5 from NIPPON GASES Deutschland GmbH, Düsseldorf, and nitrogen 4.8 from Westfalen AG, Münster and nitrogen 5.0 from NIPPON GASES Deutschland GmbH, Düsseldorf. For this purpose, the apparatus was equipped with a gas distributor including an adapter and a Teflon cover for the electrolysis cells.

General working instructions AAV1

The cycloalkane (5.0 mmol) and tetrabutylammonium nitrate (0.5 eq.) were placed in an undivided electrolysis cell (100 mL three-neck round bottom flask, NS29 Teflon stopper with electrode holders, magnetic stirring rod) and dissolved in acetonitrile (25 mL). The cell was equipped with glassy carbon electrodes (3 cm × 1 cm × 0.3 cm), spaced 0.5 cm apart. The immersion area of the electrodes was 1.3 cm ² . If necessary, oxygen was introduced into the gas space of the reaction vessel via an NS14.5 core olive. Galvanostatic electrolysis was carried out at a current density of 10 mA/cm ² at 20 to 30 °C.

After applying a charge amount of 4 to 5 F (1930 C to 2412 C) with respect to the cycloalkane, the solvent was removed by distillation together with the unreacted portion of cycloalkane under reduced pressure. The residue was taken up with cyclohexane and water (20 mL each). After phase separation, the aqueous phase was extracted with cyclohexane (20 mL). The organic phases were combined, dried over sodium sulfate or magnesium sulfate and the solvent was removed by distillation under reduced pressure. The product remained as residue from this distillation.

Example 1:

Production of Cyclohexanone:
According to AAV1, cyclohexane (0.421 g, 5.0 mmol, 1.0 eq.) was dissolved in acetonitrile (25 mL) and electrolyzed galvanostatically at 25 °C under an oxygen atmosphere with the application of 5 F. After workup according to AAV1, the product was obtained as a colorless liquid (yield: 6%, 30 mg, 0.31 mmol). ¹ H-NMR (400 MHz, CDCl ₃ ) δ [ppm] = 2.36-2.32 (m, 4H), 1.90-1.84 (m, 4H), 1.75-1.70 ( m, 2H). The analytical data agree with the literature values. To determine the yield, existing solvent signals were eliminated using integral ratios.

Example 2:

Production of Cycloheptanone:
According to AAV1, cycloheptane (0.491 g, 5.0 mmol, 1.0 eq.) was dissolved in acetonitrile (25 mL) and electrolyzed galvanostatically at 21 °C under ambient air with the application of 4 F. Electrode immersion area: 1.5 cm ² . The solvent was then removed by distillation under reduced pressure and the residue was purified by column chromatography (cyclohexane/ethyl acetate = 10:0 to 7:3). After removing the solvent by distillation, the product was obtained as a colorless liquid (yield: 20%, 0.112 g, 1.00 mmol). ¹ H-NMR (400 MHz, CDCl ₃ ) δ [ppm] = 2.49-2.47 (m, 4H), 1.69-1.64 (m, 8H). The analytical data agree with the literature values.

Example 3:

Production of Cyclooctanone:
According to AAV1, cyclooctane (0.561 g, 5.0 mmol, 1.0 eq.) was dissolved in acetonitrile (25 mL) and electrolyzed galvanostatically at 30 °C under an oxygen atmosphere with the application of 4 F. After workup according to AAV1, the product was obtained as a colorless liquid (yield: 42%, 0.261 g, 2.07 mmol). Rf (cyclohexane/ethyl acetate = 7:3): 0.66; ¹ H-NMR (400 MHz, CDCl ₃ ) δ [ppm] = 2.39-2.36 (m, 4H), 1.87-1.81 (m, 4H), 1.54-1.48 ( m, 4H), 1.36-1.32 (m, 2H). The analytical data agree with the literature values.

Example 4:

Production of Cyclodecanone:
According to AAV1, cyclodecane (0.701 g, 5.0 mmol, 1.0 eq.) was dissolved in acetonitrile (25 mL) and electrolyzed galvanostatically at 30 °C under an oxygen atmosphere with the application of 5 F. The solvent was then removed by distillation under reduced pressure and the residue was purified by column chromatography (CH/EE=10:0 to 9:1). After removing the solvent by distillation and drying in vacuo, the product was obtained as a colorless liquid (yield: 12%, 90 mg, 0.59 mmol). Rf (cyclohexane/ethyl acetate = 95:5): 0.28; ¹ H-NMR (300 MHz, CDCl ₃ ) δ [ppm] = 2.49-2.45 (m, 4H), 1.85-1.76 (m, 4H), 1.47-1.43 ( m, 4H), 1.32-1.29 (m, 6H). The analytical data agree with the literature values. To determine the yield, existing solvent signals were eliminated using integral ratios.

Example 5:

Production of cyclododecanone
According to AAV1, cyclododecane (0.842 g, 5.0 mmol, 1.0 eq.) was dissolved in isobutyronitrile (25 mL) and electrolyzed galvanostatically at 27 °C under an oxygen atmosphere with the application of 4 F. The solvent was then removed by distillation under reduced pressure and the residue was purified by column chromatography (cyclohexane/ethyl acetate = 10:0 to 9:1). After removing the solvent by distillation and drying in vacuo, the product was obtained as a colorless solid (yield: 21%, 0.194 g, 1.06 mmol). Rf (cyclohexane/ethyl acetate = 9:1): 0.48; ¹ H-NMR (400 MHz, CDCl ₃ ) δ [ppm] = 2.47-2.44 (m, 4H), 1.72-1.69 (m, 4H), 1.31-1.26 ( m, 14H). The analytical data agree with the literature values.

Example 6:

In the following, various parameters of electrochemical oxidation were varied in order to investigate their influence. These studies were each carried out for the electrochemical oxidation of cyclooctane to cyclooctanone.

General work instructions AAV2a:
The electrolyses were carried out in an undivided 5 mL PTFE cell. For this purpose, the conductive salt (0.2 to 1.0 eq.) and the substrate (cyclooctane, 0.5-2.5 mmol) were placed in the cell and dissolved in the solvent (5 mL). The cell was equipped with a glassy carbon anode and cathode, which had a distance of 0.5 cm (electrode dimension: 7 cm x 1 cm x 0.3 cm, immersion area 1.8 cm ² ). The cells were fixed in a heatable/coolable stainless steel block and supplied with the gas mixture to be examined (100 vol.% O ₂ to 0 vol.% O ₂ ) via an adapter. The electrolysis was carried out with constant current intensity, with the current densities (5-60 mA/cm ² ), temperatures (5-50 ° C), stirring speeds (100-600 rpm) and amounts of charge (4-8 F) being varied. After applying the charge amount, 2 drops of the reaction solution were removed for gas chromatographic analysis. 1,3,5-trimethoxybenzene is then added to the solution as an NMR standard (1 eq.) and the solvent is removed by distillation (45 ° C, 200 mbar). The yield of the cycloalkanone product was determined using ¹ H NMR analysis.

For the GC analysis: 2 drops of the reaction solution were eluted using ethyl acetate over approx. 330 mg of 60 M silica gel. There were approx. 1.5 mL of the filtrate was collected in a GC vial, which was examined for oxidation products using GC-FID and GC-MS.

General working instructions AAV2b:
The electrolyses were carried out in an undivided 5 mL PTFE cell. For this purpose, the conductive salt (0.2-1.0 eq.) and the substrate (cyclooctane, 0.5-2.5 mmol) were placed in the cell and dissolved in the solvent (5 mL). The cell was equipped with a glassy carbon anode and cathode, which had a distance of 0.5 cm (electrode dimension: 7 cm x 1 cm x 0.3 cm, immersion area 1.8 cm ² ). The cells were fixed in a heatable/coolable stainless steel block and supplied with the gas mixture to be examined (100 vol.% O ₂ to 0 vol.% O ₂ ) via an adapter. The electrolysis was carried out with constant current intensity, with varying current densities (5-60 mA/cm ² ), temperatures (5-50 °C), stirring speeds (100-600 rpm) and amounts of charge (4-8 F). After applying the loading amount, 10 mg of 1,3,5-trimethoxybenzene was added to the reaction solution as an internal standard. Three drops of the reaction solution were removed for gas chromatographic analysis and quantification of the product. These were eluted using ethyl acetate over approx. 330 mg of 60 M silica gel. Approximately 1.5 mL of the filtrate was collected in a GC vial, which was examined for oxidation products using GC-FID and GC-MS. The quantification was carried out via a previous calibration of the gas chromatograph.

The results shown in Scheme 1 below were obtained using the AAV2a described above:

• Ladungsmenge (F bezüglich Cyclooctan 1)
• Stromdichte (mA/cm²)
• O₂/N₂-Verhältnis
• Äquivalente (bezüglich Cyclooctan 1/Nitratsalz)
• Rührgeschwindigkeit (rpm)
• Temperatur (°C)
• Nitratsalz als Mediator/Leitsalz
• Reaktionsmedium
• Elektrodenmaterial
• Kationenvariation der Nitratsalze

Further exemplary investigations are shown below, grouped according to the changed parameters:

• Amount of charge (F relative to cyclooctane 1)
• Current density (mA/cm ² )
• O ₂ /N ₂ ratio
• Equivalents (relative to cyclooctane 1/nitrate salt)
• Stirring speed (rpm)
• Temperature (°C)
• Nitrate salt as a mediator/conducting salt
• reaction medium
• Electrode material
• Cation variation of the nitrate salts

Unless otherwise stated, the experiments were carried out at least twice and an average value with standard deviation was determined. The labels of compounds 1, 2, 3 and 4 correspond to the labels in Scheme 1.

Example 6a - amount of charge

The amount of charge was examined in a range from 4 F to 8 F (corresponding to 386 C to 772 C for 1 mmol of substrate cyclooctane 1). <b>Table 1:</b> Examination of different amounts of charge. Example no. Charge quantity / F 1 / % (GC Int. 1:2) 2 / % ( ¹ H-NMR) 3 / % (GC-Int. 3:2) 4/% (GC-Int. 4:2) 6-AAV2a-02 8th 32±7 15±1 1±0 1±0 6-AAV2a-03 6 32±6 16±2 1±0 1±0 6-AAV2a-01 4 42±8 16±1 1±0 1±0 Const.: GK||GK, NBu ₄ NO ₃ (0.5 eq.), 1 (1 mmol), acetonitrile, 30 °C, 350 rpm, 100% O ₂ atm., 10 mA/cm ² .

There was no change in product and by-product formation in the charge quantity range examined. Because of the shorter electrolysis time, 4 F was used.

Example 6b - Current density:

The current density was varied in the range 5 mA/cm ² to 60 mA/cm ² .

The electrode area in the electrolyte solution was 1.8 cm ² . <b>Table 2:</b> Investigation of different current densities. Example no. Current density / mA/cm ² 1 / % (GC Int. 1:2) 2 / % ( ¹ H-NMR) 3 / % (GC-Int. 3:2) 4 / % (GC-Int. 4:2) 6-AAV2a-04 60 54 ± 12 9±0 8±2 0±0 6-AAV2a-05 30 34 ± 11 18±2 2±1 1±0 6-AAV2a-06 20 48±0 19±1 1±0 1±0 6-AAV2a-01 10 42±8 16±1 1±0 1±0 6-AAV2a-07 5 35±13 7±0 1±0 0±0 Const.: GK||GK, NBu ₄ NO ₃ (0.5 eq.), 1 (1 mmol), acetonitrile, 30 °C, 350 rpm, 100% O ₂ atm., 4 F.

When using 60 mA/cm ² a significant reduction in the yield of 2 can be seen. However, cyclooctanol 3 is formed to a comparable extent.

We continued with 20 mA/cm ² and examined various atmospheric O ₂ levels.

Example 6c - O ₂ /N ₂ ratio at 20 mA/cm ²

First, rough O ₂ /N ₂ ratios at 20 mA/cm ² were considered (100:0, 20:80, 0:100). The ratio 20:80 was chosen due to its comparability to the air composition. <b>Table 3:</b> Investigation of different O₂/N₂ ratios at 20 mA/cm². Example no. O ₂ /N ₂ ratio 1 / % (GC Int. 1:2) 2 / % ( ¹ H-NMR) 3 / % (GC-Int. 3:2) 4/% (GC-Int. 4:2) 6-AAV2a-06 100:0 48±0 19±1 1±0 1±0 6-AAV2a-08 8:80 p.m 22±2 5±1 5±0 0±0 6-AAV2a-09 0:100 - 0±0 Sense - Const.: GK||GK, NBu ₄ NO ₃ (0.5 eq.), 1 (1 mmol), acetonitrile, 30 °C, 350 rpm, 4 F, 20 mA/cm ² .

No product formation was observed under a pure nitrogen atmosphere (ratio 0:100). Therefore, no quantitative statements about the unreacted substrate portion or the by-products are possible. However, traces of cyclooctanol 3 were detected in the gas chromatogram. In order to be able to compare the O ₂ contents with the initial standard current density of 10 mA/cm ² , these were repeated in smaller increments at the stated current density.

Example 6d - O ₂ /N ₂ ratio at 10 mA/cm ²

In addition to the gradations shown in the table, tests were also carried out without gas supply under ambient conditions (labeled as "air"). <b>Table 3:</b> Investigation of different O₂/N₂ ratios at 10 mA/cm². Example no. O ₂ /N ₂ ratio 1 / % (GC Int. 1:2) 2 / % ( ¹ H-NMR) 3 / % (GC-Int. 3:2) 4/% (GC-Int. 4:2) 6-AAV2a-01 100:0 42±8 16±1 1±0 1±0 6-AAV2a-10 50:50 35±4 15±3 1±0 1±0 6-AAV2a-11 35:65 55±3 9±1 2 ± 0 0±0 6-AAV2a-12 Air (approx. 21:78) 27±14 23±5 2 ± 0 3±1 6-AAV2a-13 8:80 p.m 12±4 31±2 1±0 6±1 6-AAV2a-14 10:90 29±4 7±0 3 ± 0 0±0 6-AAV2a-15 5:95 40±8 6±0 3 ± 0 0±0 Const.: GK||GK, NBu ₄ NO ₃ (0.5 eq.), 1 (1 mmol), acetonitrile, 30 °C, 350 rpm, 4 F, 10 mA/cm ² .

In the above studies , the conversion of starting material 1 and the formation of product 2 were highest at an oxygen content of 20% by volume and a current density of 10 mA/cm ² . Furthermore, the formation of cyclooctanol 3 was slightly increased at low O ₂ content.

Due to the higher yield of cyclooctanone 2 and the improved safety aspect due to the higher nitrogen content, these conditions were chosen as comparison conditions in the following reactions (Scheme 2), and the other parameters were changed based on these conditions.

Example 6e - Amount of substance and mediator equivalents

To investigate different substrate and mediator concentrations in the solvent (acetonitrile, 5 mL), the amount of substrate and the equivalents of conductive salt/mediator were varied. <b>Table 5:</b> Investigation of different amounts of substances and nitrate equivalents. Example no. Amount of substance ( 1 ) / mmol Equivalents (1 :NO ₃ ^- ) 1 / % (GC Int. 1:2) 2 / % ( ¹ H-NMR) 3 / % (GC-Int. 3:2) 4 / % (GC-Int. 4:2) 6-AAV2a-16 0.5 1:0.5 21±2 30 ± 1 2 ± 0 4±0 6-AAV2a-17 0.5 1:1.0 18±2 30 ± 1 1±0 6±1 6-AAV2a-18 1.0 1:0.2 20±2 26±2 2 ± 0 4±1 6-AAV2a-13 1.0 1:0.5 12±4 31±2 1±0 6±1 6-AAV2a-19 1.0 1:1.0 10±1 27±1 1±0 4±1 6-AAV2a-20 2.5 1:0.2 11 ±3 23±0 1±0 4±0 6-AAV2a-21 2.5 1:0.5 11±2 22±0 1±0 4±0 Const.: GK||GK, NBu ₄ NO ₃ , acetonitrile, 30 °C, 350 rpm, 20% O ₂ atmosphere, 4 F, 10 mA/cm ² .

In principle, the conversion of educt 1 to product 2 was slightly better with lower amounts of substrate (≤ 1 mmol, here corresponds to 0.2 mol/L) than with higher amounts. When varying the mediator concentration in relation to the substrate, above and below 0.5 equivalents, the yields of 2 differ only insignificantly from each other, so that it can be assumed that the oxygen source for the oxo functionalization is molecular, dissolved oxygen lies.

Example 6f - stirring speed

Since the oxygen source for ketone synthesis comes from the atmosphere, the stirring speed is expected to have a significant influence on the course of the reaction. <b>Table 4:</b> Investigation of different stirring speeds Example no. Stirring speed / rpm 1 / % (GC Int. 1:2) 2 / % ( ¹ H-NMR) 3 / % (GC-Int. 3:2) 4/% (GC-Int. 4:2) 6-AAV2a-22 600 30 ± 1 7±1 1±0 0±0 6-AAV2a-23 500 26±4 8±0 2 ± 0 0±0 6-AAV2a-13 350 12±4 31±2 1±0 6±1 6-AAV2a-24 200 28±3 17±1 2 ± 0 1±0 6-AAV2a-25 100 29±4 8±0 4±0 0±0 Const.: GK||GK, NBu ₄ NO ₃ (0.5 eq.), 1 (1 mmol), acetonitrile, 30 ° C, 20% O ₂ atm., 4 F, 10 mA/cm ² .

The results in Table 6 illustrate a maximum in the range around 350 rpm. However, the influence of the speed depends on the stirrer and cell geometry and should therefore not be viewed as a fixed value.

Example 6g - Temperature

The temperatures given refer to heating block or cryostat temperatures. The electrolyte solutions were stirred at 5 °C and 50 °C for approximately half an hour before electrolysis began. <b>Table 5:</b> Investigation of different temperatures. Example no. Temperature / °C 1 / % (GC Int. 1:2) 2 / % ( ¹ H-NMR) 3 / % (GC-Int. 3:2) 4 / % (GC-Int. 4:2) 6-AAV2a-26 50 9±1 27±2 1±0 7±1 6-AAV2a-13 30 12±4 31±2 1±0 6±1 6-AAV2a-27 5 17±1 27±2 1±0 4±1 Const.: GK||GK, NBu ₄ NO ₃ (0.5 eq.), 1 (1 mmol), acetonitrile, 350 rpm, 20% O ₂ atm., 4 F, 10 mA/cm ² .

With regard to product formation, a slight decrease in yield can be seen at higher and lower temperatures than 30 °C. The reaction therefore appears to be only slightly dependent on temperature. At higher temperatures, a lower proportion of unreacted substrate can also be detected, which is probably due to its volatility and the open system of the electrolysis cells.

Example 6h - conductive salt/mediator

In order to investigate whether nitrate, as an anion of the conductive salt, also has a mediator effect on the reaction, the standard tetrabutylammonium nitrate was compared with other common conductive salts. The cationic component was left the same. The conductive salts that deviate from the standard were only tested once in an electrolysis, which is why no average value was recorded here. <b>Table 6:</b> Investigation of various conductive salts. Example no. conductive salt 1 /% (GC Int. 1:2) 2 / % ( ¹ H-NMR) 3 / % (GC-Int. 3:2) 4/% (GC-Int. 4:2) 6-AAV2a-13 _{NBu4NO3 _} 12±4 31±2 1±0 6±1 6-AAV2a-28 NBu ₄ BF ₄ 57 3 2 1 6-AAV2a-29 _{NBu4PF6 _} 50 3 2 1 6-AAV2a-30 _{NBu4ClO4 _} 28 4 3 1 Const.: GK||GK, conductive salt (0.5 eq.), 1 (1 mmol), acetonitrile, 30 ° C, 350 rpm, 20% O ₂ atmosphere, 4 F, 10 mA/cm ² .

The results in Table 8 illustrate the dependence of the reaction on the nitrate anion. The product 2 forms only to a very small extent with other conductive salt anions.

Example 6i - Solvent

Table 7: Investigation of various solvents. Example no. Solvent (5mL) 1 / % (GC Int. 1:2) 2 / % ( ¹ H-NMR) 3 / % (GC-Int. 3:2) 4/% (GC-Int. 4:2) 6-AAV2a-13 Acetonitrile 12±4 31±2 1±0 6±1 6-AAV2a-31 Isobutyronitrile 23±1 24±1 1±0 3 ± 0 6-AAV2a-32 acetone 41±4 29±1 2 ± 0 4±1 Const.: GK||GK, NBu ₄ NO ₃ (0.5 eq.), 1 (1 mmol), 30 °C, 350 rpm, 20% O ₂ atm., 4 F, 10 mA/cm ² .

The reaction proceeded comparably well in the specified solvents. In addition, a higher proportion of unreacted substrate remained in acetone.

The reaction was also carried out in 3-pentanone, but no ¹ H NMR yield could be determined due to the superimposition of the solvent signals with the product signals. However, the gas chromatographic analysis also confirms a selective formation of product 2.

Since a better O ₂ solubility in isobutyronitrile compared to acetonitrile was previously assumed, a comparison was also made under a 100% O ₂ atmosphere (Table 10). <b>Table 8:</b> Investigation of various solvents at 100 vol.% O₂. Example no. Solvent (5mL) 1 / % (GC Int. 1:2) 2 / % ( ¹ H-NMR) 3 / % (GC-Int. 3:2) 4/% (GC-Int. 4:2) 6-AAV2a-01 Acetonitrile 42±8 16±1 1±0 1±0 6-AAV2a-33 Isobutyronitrile 58±3 19±2 1±0 2 ± 0 6-AAV2b-36 Nitropropane 30 17 2 2 Const.: GK||GK, NBu ₄ NO ₃ (0.5 eq.), 1 (1 mmol), 30 °C, 350 rpm, 100% O ₂ atm., 4 F, 10 mA/cm ² .

The results when using acetonitrile and isobutyronitrile are comparable. A significant increase in the yield of 2 using isobutyronitrile could not be achieved. On the other hand, the proportion of unreacted 1 is significantly higher, which is seen as an advantage. The reaction in nitropropane was subsequently carried out at 100% O ₂ atmosphere. carried out and demonstrated that nitrated alkanes can also serve as solvents.

Example 6j - Electrode material

Electrolysis was carried out on various carbon-based electrode materials. The electrode materials that deviate from the GK standard were only tested once in an electrolysis, which is why no average value was recorded here. <b>Table 9:</b> Investigation of various electrode materials. Example no. Anode ∥ Cathode 1 / % (GC Int. 1:2) 2 / % ( ¹ H-NMR) 3 / % (GC-Int. 3:2) 4/% (GC-Int. 4:2) 6-AAV2a-13 GK ∥ GK 12±4 31±2 1±0 6±1 6-AAV2a-34 BDD ∥ BDD 18 20 2 3 6-AAV2a-35 Graphite ∥ Graphite 23 15 1 2 Const.: NBu ₄ NO ₃ (0.5 eq.), acetonitrile, 1 (1 mmol), 30 °C, 350 rpm, 20% O ₂ atm., 4 F, 10 mA/cm ² .

The reaction takes place on all electrode materials used and product 2 is formed. On graphite electrodes, a slight detachment of the electrode material in the form of black particles is observed after electrolysis, which is due to their lower stability.

Example 6k - Cation variation of the conductive salt/mediator

• Hexadecyltrimethylammoniumnitrat ([C₁₉H₄₂N][NO₃])
• 1-Butyl-3-methylimidazoliumnitrat ([C₈H₁₅N₂][NO₃])
• Methyltrioctylammoniumnitrat ([C₂₅H₅₄N][NO₃])
• Tetrabutylphosphoniumnitrat (PBu₄NO₃)

Various cations were examined that deviate from the standard tetrabutylammonium. The following were used:

• Hexadecyltrimethylammonium nitrate ([C ₁₉ H ₄₂ N][NO ₃ ])
• 1-Butyl-3-methylimidazolium nitrate ([C ₈ H ₁₅ N ₂ ][NO ₃ ])
• Methyltrioctylammonium nitrate ([C ₂₅ H ₅₄ N][NO ₃ ])
• Tetrabutylphosphonium nitrate (PBu ₄ NO ₃ )

The anionic nitrate component was left the same. The conductive salts that deviate from the standard were only tested once in an electrolysis, which is why no average value was recorded here. <b>Table 12:</b> Investigation of various cations. Example no. conductive salt 1 / % (GC Int. 1:2) 2 / % (GC yield) 3 / % (GC-Int. 3:2) 4/% (GC-Int. 4:2) 6-AAV2b-37 [C ₁₉ H ₄₂ N][NO ₃ ] 14 21 1 3 6-AAV2b-38 [C ₈ H ₁₅ N ₂ ][NO ₃ ] 0 17 0 8th 6-AAV2b-39 [ _C25H54N ][ _{NO3 ]} 7 28 0 4 6-AAV2b-40 _{PBu4NO3 _} 0 20 0 7 Const.: GK||GK, conductive salt (0.5 eq.), 1 (1 mmol), acetonitrile, 30 ° C, 350 rpm, 100% O ₂ atmosphere, 4 F, 10 mA/cm ² .

It can be seen that the oxidation of the cycloalkane to the ketone primarily works through the nitrate as an anion component (compare Example 6h). Long chain alkyl residues on the ammonium cations lead to slightly higher yields compared to the tetrabutylammonium cation under the same conditions. The reaction also works with N -alkylated nitrogen heteroaromatics as cations, as well as with tetraalkylphosphonium cations.

Example 6I:

Oxygen solubility in acetonitrile / NBu ₄ NO ₃ at 25°C and normal pressure: <b>Table 13:</b> Dissolved oxygen concentration in MeCN/NBu₄NO₃ depending on the atmospheric oxygen content. Atm. (vol.% O ₂ ) _c (O ₂ ) / (mmol/L) Air 2.4 ± 0.1 0 0.171 ± 0.004 5 1.16 ± 0.05 10 1.57 ± 0.07 20 2.5±0.1 35 3.9 ± 0.2 50 5.1±0.3 100 9.5 ± 0.4

General working instructions AAV3:

The cycloalkane (5.0 mmol) and tetrabutylammonium nitrate (0.5 eq.) were dissolved in acetonitrile (25 mL) in an undivided 25 mL glass beaker cell with a gas inlet attachment. The cell was equipped with glassy carbon electrodes (7 cm x 1 cm x 0.3 cm) at a distance of 0.5 to 1.0 cm. The immersion area of the electrodes was 1.3 cm ² . Galvanostatic electrolysis was carried out at a current density of 10 mA/cm ² at 20-30 °C. After applying a charge amount of 4 F to the cycloalkane, the solvent was removed by distillation together with the unreacted portion of cycloalkane under reduced pressure. The residue was taken up with cyclohexane and water (20 mL each). After phase separation, the aqueous phase was extracted with cyclohexane (20 mL). The organic phases were combined, dried over sodium sulfate or magnesium sulfate and the solvent was removed by distillation under reduced pressure. The product remained as residue from this distillation.

Alternative quantification: After applying the loading amount, approximately 50 mg of 1,3,5-trimethoxybenzene was added to the reaction solution as an internal standard. Three drops of the reaction solution were removed for gas chromatographic analysis and quantification of the product. These were eluted using ethyl acetate over approx. 330 mg of 60 M silica gel. Approximately 1.5 mL of the filtrate was added to one GC vial was collected, which was examined for oxidation products using GC-FID and GC-MS. The quantification was carried out via a previous calibration of the gas chromatograph.

Example 7:

The influence of the electrode distance was examined below. <b>Table 14:</b> Examination of different electrode distances. Example no. Electrode distance / cm 1 / % (GC Int. 1:2) 2 / % 7-AAV3-01 0.5 n/a 31 ^[a] 7-AAV3-02 1.0 49 16 ^[b] Const.: GK||GK, NBu ₄ NO ₃ (0.5 eq.), 1 (5 mmol), acetonitrile (25 mL), 20-30 °C, 400 rpm, 100% O ₂ atm., 4 F, 10 mA/cm ² . [a] Isolated yield. [b] GC yield.

Based on the examples in Table 14, it can be seen that the conversion of the starting material to product 2 is better with a smaller electrode gap.

Claims (15)

Process for the preparation of unsubstituted or at least monosubstituted cycloalkanones by electrochemical oxidation of unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbons comprising the process steps (a) providing at least one unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbon; (b) providing at least one inorganic or organic nitrate salt; (c) electrochemical oxidation of the unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbon provided in step (a) in the presence of the inorganic or organic nitrate salt provided in step (b) in an electrolysis cell in a reaction medium in the presence of oxygen. A process according to claim 1, wherein the unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbon is monocyclic or polycyclic, preferably monocyclic or bicyclic, particularly preferably monocyclic. The method according to claim 2, wherein the monocyclic or polycyclic, preferably monocyclic or bicyclic, saturated cycloaliphatic hydrocarbon has 5 to 18 C atoms in the ring system and is unsubstituted or mono or polysubstituted with 1, 2, 3, 4 or 5 substituents, independently of one another, each selected from the group consisting of methyl, phenyl or benzyl, where phenyl or benzyl can each be unsubstituted or mono- or polysubstituted, with 1, 2 or 3 substituents, independently of one another, each selected from the group consisting of F, Cl, Br and _NO2 . Method according to one of the preceding claims, wherein the unsubstituted or at least monosubstituted, saturated cycloaliphatic hydrocarbon is a monocyclic saturated hydrocarbon with 6-12 carbon atoms in the ring, preferably with 8-12 carbon atoms in the ring, this cycloaliphatic hydrocarbon being unsubstituted or mono or multiple is substituted with 1, 2, 3, 4 or 5 substituents, independently from each other, each selected from the group consisting of methyl, phenyl or benzyl. Method according to one of the preceding claims, wherein the saturated cycloaliphatic hydrocarbon is unsubstituted and selected from the group consisting of cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane and cyclododecane, preferably selected from the group consisting of cyclooctane, cyclononane, cyclodecane, cycloundecane and Cyclododecane, particularly preferably cyclododecane. Method according to one of the preceding claims, wherein the inorganic or organic nitrate salt is a nitrate of the general formula [cation ⁺ ][NO ₃ ^- ], with [cation ⁺ ] selected from the group consisting of Na ⁺ , K ⁺ , ammonium ions with the general Structure [R ¹ R ² R ³ R ⁴ N ⁺ ] with R ¹ , R ² , R ³ , R ⁴ , independently of one another, each selected from the group consisting of C ₁ to C ₁₆ alkyl, in particular C ₁ - to C ₈ -Alkyl, straight chain or branched, imidazolium cations with the general structure (I)

with R ¹ and R ² , independently of one another, each selected from the group consisting of C ₁ - to C ₁₈ alkyl, straight-chain or branched, in particular C ₁ - to C ₈ -alkyl, straight-chain or branched, and R ³ selected from Group consisting of H and C ₁ - to C ₁₈ -alkyl, straight-chain or branched, in particular from the group consisting of H and C ₁ - to C ₈ -alkyl, straight-chain or branched,
Pyridinium cations with the general structure (II)

with R ¹ selected from the group consisting of C ₁ - to C ₁₈ -alkyl, in particular C ₁ - to C ₈ -alkyl, straight-chain or branched and R ² , R ³ and R ⁴ , independently of one another, each selected from the group consisting from H and C ₁ - to C ₁₈ -alkyl, straight-chain or branched, in particular from the group consisting of H and C ₁ - to C ₈ -alkyl, straight-chain or branched, and phosphonium ions with the general structure [R ^1a R ^2a R ^3a R ^4a P ⁺ ] with R ^1a , R ^2a , R ^3a , R ^4a , independently of one another, each selected from the group consisting of C ₁ - to C ₁₆ -alkyl, in particular C ₁ - to C ₈ -alkyl, straight-chain or branched . Method according to one of the preceding claims, wherein the reaction medium is a polar aprotic reaction medium, optionally in combination with water, whereby in the combination with water the water content is preferably up to 20% by volume, particularly preferably up to 15% by volume. %, very particularly preferably up to 10% by volume, even more preferably up to 5% by volume, in each case based on the total amount of reaction medium. The method according to claim 7, wherein the reaction medium is a polar aprotic reaction medium which is selected from the group consisting of aliphatic nitriles, aliphatic ketones, cycloaliphatic ketones, dialkyl carbonates, cyclic carbonates, lactones, aliphatic nitroalkanes, and dimethyl sulfoxide, esters and ethers or a combination from at least two of these components, preferably 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, gamma-butyrolactone and epsilon-caprolactone or one Combination of at least two of these components, each possibly in combination with water. Method according to one of the preceding claims, wherein the inorganic or organic nitrate salt is in an amount of 0.1 to 2.0, preferably 0.2 to 1.0, particularly preferably 0.3 to 0.8 and most preferably 0.4 to 0.8 equivalents, in each case based on the amount of unsubstituted or at least monosubstituted, saturated cycloaliphatic hydrocarbon used. Method according to one of the preceding claims, wherein a gas atmosphere containing oxygen is provided in spatial connection with the reaction medium, the proportion of oxygen in the gas atmosphere preferably being 10 to 100% by volume, particularly preferably 15 to 30% by volume, very particularly preferably 15 to 25% by volume, most preferably 18 to 22% by volume. A method according to claim 11, wherein a gas exchange is forced between the gas atmosphere and the reaction medium, preferably by introducing gas atmosphere into the reaction medium or by stirring the reaction medium in the presence of the gas atmosphere. Method according to one of the preceding claims, wherein the amount of charge is at least 190 C (2 F) to 970 C (10 F), preferably 320 C to 820 C, particularly preferably 350 C to 800 C, most preferably 380 C to 775 C, on most preferably 380 C to 450 C, each for 1 mmol of unsubstituted or at least monosubstituted saturated cycloaliphatic hydrocarbon. Method according to one of the preceding claims, wherein the current density is at least 5 mA/cm ² , the area information relating to the geometric area of the electrodes. Method according to one of the preceding claims, wherein it is carried out in an undivided cell. Method according to one of the preceding claims, wherein it is carried out batchwise or continuously, preferably continuously in an undivided flow electrolysis cell