Electrochemical oxidation of fatty acids and fatty acid esters to produce monocarboxylic and α-ω-dicarboxylic acids

Abstract

The present invention relates to a process for the preparation of aliphatic monocarboxylic acids and α,ω-dicarboxylic acids or α,ω-dicarboxylic monoesters by electrochemically oxidizing unsubstituted or at least monosubstituted mono- or polyunsaturated fatty acids or fatty acid esters in the presence of inorganic or organic nitrates in an electrolytic cell in a reaction medium in the presence of oxygen.

Description

[Technical field]

[0001] The present invention relates to a process for the preparation of aliphatic monocarboxylic acids and α,ω-dicarboxylic acids or α,ω-dicarboxylic monoesters by electrochemically oxidizing unsubstituted or at least monosubstituted mono- or polyunsaturated fatty acids or fatty acid esters in the presence of inorganic or organic nitrates in an electrolytic cell in a reaction medium in the presence of oxygen. [Background technology]

[0002] Monocarboxylic acids, α,ω-dicarboxylic acids and α,ω-dicarboxylic monoesters are important substrates in synthetic organic chemistry and are monomeric components in polymer synthesis, and therefore of great relevance for industrial applications. Traditional access to these substrates is mainly via the oxidative cleavage of the C=C double bonds of fatty acids and fatty acid esters, via processes based on the principle of the use of transition metals, additional oxidizing agents and / or ozone oxidation.

[0003] Known processes based on transition metals are prone to toxic hazards for humans and the environment due to their use. There is also an economic factor that raw materials are increasingly scarce and these methods are increasingly costly. Purification of the products and recycling of the catalysts require further complex operations. The use of more oxidizing agents than necessary also generates waste reagents that must be disposed of. In most cases, the reactions necessarily proceed at high or low temperatures, which can adversely affect the energy balance of the process. Intermediates generated during ozone oxidation are explosive and entail significant safety risks. Furthermore, ozone has to be generated as a reactive species by special generators, which entails increased capital costs. Summary of the Invention [Problem to be solved by the invention]

[0004] One object of the present invention is to provide a sustainable, resource-saving process capable of producing monocarboxylic acids, α,ω-dicarboxylic acids, and α,ω-dicarboxylic acid monoesters from fatty acids or fatty acid esters. [Means for solving the problem]

[0005] This object has been achieved by the subject matter of the claims and the specification.

[0006] The present invention relates to a process for the preparation of aliphatic monocarboxylic acids and α,ω-dicarboxylic acids or α,ω-dicarboxylic monoesters by electrochemical oxidation of unsubstituted or at least monosubstituted monounsaturated or polyunsaturated fatty acids or fatty acid esters, (a) at least one unsubstituted or at least one substituted monounsaturated or polyunsaturated C 6 ~C 24 fatty acids, or at least one unsubstituted or at least one substituted monounsaturated or polyunsaturated C 6 ~C 24 Providing a fatty acid ester; (b) providing at least one inorganic or organic nitrate; (c) electrochemically oxidizing the unsubstituted or at least monosubstituted monounsaturated or polyunsaturated fatty acid or the unsubstituted or at least monosubstituted monounsaturated or polyunsaturated fatty acid ester prepared in step (a) in the presence of an inorganic or organic nitrate prepared in step (b) in an electrolytic cell in a reaction medium in the presence of oxygen. The present invention relates to a method comprising the steps of:

[0007] Surprisingly, it has been found that the electrochemical oxidation process of the present invention allows the introduction of oxygen functional groups into fatty acids or fatty acid esters using atmospheric oxygen. The fatty acids used as reactants can be obtained commercially by hydrolysis of their glycerol esters and are widely found, among other things, in vegetable fats and oils, and therefore are renewable raw materials. Methyl oleate is also obtained by transesterification of triglycerides with methanol and is used in biodiesel.

[0008] Thus, the inventive method for producing aliphatic α,ω-dicarboxylic acids and α,ω-dicarboxylic monoesters, as well as monocarboxylic acids from these renewable raw materials, offers a direct, sustainable and resource-saving alternative for the synthesis of key synthesis units. α,ω-dicarboxylic acids are mainly used as monomers in large-scale industrial polyamide synthesis. α,ω-dicarboxylic monoesters allow industrial access to the corresponding dimers shortened at C2 by Kolbe electrolysis. Until now, the synthetic routes to these resulting long-chain dicarboxylic diesters have been scarce. Both products are therefore of great economic importance.

[0009] This allows the method of the invention to dispense with the use of chemical oxidants such as reactive peroxides and expensive catalysts with complex ligand systems. At the same time, the use of toxic and / or potentially carcinogenic reagents can be reduced or completely avoided. The simple and safe process conditions also allow for scale-up to industrial scale to produce larger amounts of the desired product. Thus, the invention allows for this significant optimization of previously costly and time-consuming processes.

[0010] The process of the present invention has the special features of high selectivity, the use of small amounts of auxiliary chemicals, the use of electric current as an oxidant, and the associated production of small amounts of waste products.

[0011] It has also been surprisingly found that the method of the present invention allows the use of an electric current to produce monocarboxylic acids, α,ω-dicarboxylic acids, and α,ω-dicarboxylic acid monoesters, with the nitrate salt functioning as both a conductive salt and an electrochemical mediator.

[0012] It has further surprisingly been found that the process of the present invention can be carried out at ambient pressure and temperature, which is likewise advantageous for energy efficiency and environmental compatibility.

[0013] C prepared in step (a) of the present invention 6 ~C 24 Fatty acids and C 6 ~C 24 The fatty acid esters are mono- or polyunsaturated, i.e. have one or more C=C double bonds, for example 1, 2, 3 or 4 C=C double bonds. The fatty acids and fatty acid esters may be in either the cis or trans configuration. When the fatty acid or fatty acid ester has more than one C=C double bond, both configurations may be present in one molecule. The fatty acids and fatty acid esters may be linear or branched, with linear being preferred. The fatty acids and fatty acid esters may be unsubstituted or at least monosubstituted. If mono- or polysubstituted, they are preferably substituted with 1, 2, 3, 4 or 5 substituents, each independently selected from the group consisting of methyl, phenyl or benzyl. The phenyl or benzyl substituents themselves may be unsubstituted or may be substituted with F, Cl, Br and NO, respectively. 2 It may be mono- or polysubstituted with 1, 2 or 3 substituents each independently selected from the group consisting of:

[0014] In a preferred embodiment of the method according to the invention, step (a) comprises the step of: 6 ~C 24 Fatty acids or at least one unsubstituted monounsaturated or polyunsaturated C 6 ~C 24 A fatty acid ester is provided.

[0015] In a further preferred embodiment of the process according to the invention, step (a) comprises the step of: 6 ~C 24 Fatty acids or at least one unsubstituted monounsaturated C 6 ~C 24 A fatty acid ester is provided.

[0016] In a particularly preferred embodiment of the method according to the invention, step (a) comprises the steps of: hex-3-enoic acid, undecylenic acid, myristoleic acid, palmitoleic acid, margaroleic acid, petroselinic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, gondonic acid, cetoleic acid, erucic acid, nervonic acid, linoleic acid, α-linolenic acid, γ-linolenic acid, calendulic acid, punicic acid, α-eleostearic acid, β-eleostearic acid, arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, hexa ...hexaenoic acid, undecylenic acid, myristoleic acid, palmitoleic acid, margaroleic acid, petroselinic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, gondonic acid, cetoleic acid, erucic acid At least one mono- or polyunsaturated fatty acid is provided, optionally in the form of an ester, selected from the group consisting of enoic acid, docosatetraenoic acid, docosahexaenoic acid and tetracosahexaenoic acid, in particular the group consisting of hex-3-enoic acid, myristoleic acid, palmitoleic acid, petroselinic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, gondoic acid, cetoleic acid, erucic acid, nervonic acid, linoleic acid, docosadienoic acid, linolenic acid, arachidonic acid.

[0017] Particularly preferably suitable as fatty acid or fatty acid ester according to step (a) of the process of the invention is oleic acid selected from the group consisting of oleic acid, elaidic acid, erucic acid and linoleic acid, optionally in the form of an ester.

[0018] When providing fatty acid esters according to step (a) of the process of the present invention, methyl or ethyl esters of fatty acids are preferred.

[0019] According to step (b) of the method of the invention, at least one inorganic or organic nitrate is provided, which fulfils the functions of both a conductive salt and a mediator in the electrochemical oxidation method according to the invention, having the general formula: [Cation + ][NO 3 - ] It is preferable to use inorganic or organic nitrates of the formula:

[0020] In the formula, [cation + ] is Na + , K + , General structure [R 1 R 2 R 3 R 4 N + ](wherein, R 1 , R 2 , R 3 , R 4 is C 1 ~C 16 Alkyl, especially linear or branched C 1 ~C 8 each independently selected from the group consisting of alkyl, General structure (I):

[0021] [ka]

[0022] (In the formula, R 1 and R 2 is a linear or branched chain C 1 ~C 18 Alkyl, especially linear or branched C 1 ~C 8 alkyl; 3 is H and linear or branched C 1 ~C 18 Alkyl, especially H and straight or branched chain C 1 ~C 8 alkyl. imidazolium cation, General structure (II):

[0023] [ka]

[0024] (In the formula, R 1 is C 1 ~C 18 Alkyl, especially linear or branched C 1 ~C 8 alkyl; R 2 , R 3and R 4 is H and linear or branched C 1 ~C 18 Alkyl, especially H and straight or branched chain C 1 ~C 8 alkyl. the pyridinium cation, and General structure [R 1a R 2a R 3a R 4a P + ](wherein, R 1a , R 2a , R 3a , R 4a is C 1 ~C 16 Alkyl, especially linear or branched C 1 ~C 8 each independently selected from the group consisting of alkyl, is selected from the group consisting of:

[0025] When using organic nitrates based on imidazolium cations in the process of the invention, cations of general formula (I) are preferred, in which R 1 and R 2 is a linear or branched chain C 1 ~C 18 Alkyl, especially linear or branched C 1 ~C 8 alkyl; 3 is hydrogen. Particularly preferred are imidazolium cations of general formula (I) 1 is methyl, R 2 is ethyl, or R 1 is methyl, R 2 is methyl and R 1 is methyl, R 2 is butyl, and R 3 is hydrogen in both cases.

[0026] When using nitrates based on pyridinium cations in the process of the invention, cations of general formula (II) are preferred, in which R 1 is a linear or branched chain C 1 ~C 18 Alkyl, especially linear or branched C 1 ~C 8 Particularly preferred are pyridinium cations of the general formula (II) in which R 1 is a linear or branched chain C 1 ~C 18 Alkyl, especially linear or branched C 1 ~C 8 is an alkyl radical R 2 , R 3 and R 4 is a linear or branched chain C 1 ~C 8 alkyl, preferably monosubstituted at the 2, 3 or 4 positions, disubstituted at the 2,4, 2,5 or 2,6 positions, or trisubstituted at the 2,4,6 positions.

[0027] In principle, more than one of the abovementioned nitrates can also be used in the process according to the invention. 1 R 2 R 3 R 4 N + ][NO 3 - ] organic ammonium nitrate salt or composition [R 1a R 2a R 3a R 4a P + ][NO 3 - It is preferable to use an organic phosphonium salt of the composition [R 1 R 2 R 3 R 4 N + ][NO 3 - Particularly preferred are organic ammonium nitrates of the formula:

[0028] Particularly preferably, the organic ammonium nitrate is tetra-n-butylammonium nitrate or methyltri-n-octylammonium nitrate.Particularly preferably, the organic phosphonium nitrate is tetra-n-butylphosphonium nitrate or methyltri-n-octylphosphonium nitrate.Particularly preferably, the organic imidazolium nitrate is 1-butyl-3-methylimidazolium nitrate.

[0029] Most preferably, the organic nitrate used in the process of the present invention is tetra-n-butylammonium nitrate or methyltri-n-octylammonium nitrate.

[0030] The order in which the components used in the methods of the present invention are provided may be varied, as may the order in which the individual components are contacted with one another or with their respective reaction media.

[0031] In one embodiment of the method of the present invention, the fatty acid or fatty acid ester or the inorganic or organic nitrate is charged first and combined with the reaction medium, preferably at least partially or completely dissolved in the reaction medium or mixed in the reaction medium, and then the other of these two components is added in each case. In another embodiment of the method of the present invention, the fatty acid or fatty acid ester and the inorganic or organic nitrate are charged first and then combined with the reaction medium, preferably at least partially or completely dissolved in the reaction medium or mixed in the reaction medium. Furthermore, in the method of the present invention, the fatty acid or fatty acid ester and the inorganic or organic nitrate are added to the reaction medium simultaneously or sequentially, preferably at least partially or completely dissolved in the reaction medium or mixed in the reaction medium.

[0032] The reaction medium used in the process of 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, namely in particular the fatty acids or fatty acid esters and the inorganic or organic nitrates used. When at least one of these components is used in liquid form, the reaction medium is preferably easily miscible with said components.

[0033] In the process according to the invention, it is preferred to use a polar aprotic reaction medium for the electrochemical oxidation, which can be used in anhydrous form, in dry form or mixed with water.

[0034] When inorganic nitrates, especially potassium nitrate or sodium nitrate, are used in the method according to the invention, the reaction medium advantageously comprises water, preferably aprotic reaction medium mixed with water.The water content of the reaction medium can vary.The water content is preferably at most 20% by volume, more preferably at most 15% by volume, particularly preferably at most 10% by volume, even more preferably at most 5% by volume, in each case based on the total amount of the reaction medium.

[0035] Preferably, 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 dimethylsulfoxide, esters and ethers, or combinations of at least two of these components.

[0036] Particularly preferably, the reaction medium is selected from the group consisting of acetonitrile, isobutyronitrile, adiponitrile, acetone, dimethyl carbonate, methyl ethyl ketone, 3-pentanone, cyclohexanone, nitromethane, nitropropane, tert-butyl methyl ether, dimethyl sulfoxide, γ-butyrolactone and ε-caprolactone, or a combination of at least two of these components.

[0037] 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.

[0038] Very particularly preferably, the reaction medium is acetonitrile, isobutyronitrile or adiponitrile in dry or anhydrous form.

[0039] Likewise very particularly preferably, the reaction medium is acetonitrile, isobutyronitrile or adiponitrile, optionally mixed with water.

[0040] If one or more of the abovementioned components are used in a reaction medium mixed with water, the water content is preferably at most 20% by volume, more preferably at most 15% by volume, particularly preferably at most 10% by volume and even more preferably at most 5% by volume, in each case based on the total amount of the reaction medium.

[0041] For the implementation of the method according to the invention, it may be advantageous to add further solubilizing components to the reaction medium. Suitable advantageous components may be identified by simple preliminary testing of the solubility behavior.

[0042] Examples of solubilizing components include primary alcohols, secondary alcohols, monoketones, or dialkyl carbonates, or a mixture of at least two of these components, optionally mixed with water. 1-6 It is preferable to use alcohols. Particularly preferred solubilizing components can be selected from the group consisting of methanol, ethanol, isopropanol, 2-methyl-2-butanol, or a mixture of at least two of these components, optionally mixed with water.

[0043] As a reaction medium, dimethyl carbonate, optionally with at least one C 2 -3 -methyl-2-butanol, in particular selected from the group consisting of methanol, ethanol, isopropanol, and 2-methyl-2-butanol, is preferably used. 1-6 It is particularly advantageous to use them in admixture with alcohol, optionally mixed with water.

[0044] When one or more of these solubilizing components are used in admixture with water, the water content is preferably at most 20% by volume, more preferably at most 15% by volume, particularly preferably at most 10% by volume, and even more preferably at most 5% by volume, in each case based on the total amount of solubilizing component(s) and water.

[0045] The solubilizing components may be added preferably in an amount of less than 50% by volume, more preferably less than 30% by volume and particularly preferably less than 10% by volume, relative to the total amount of the reaction medium in each case.

[0046] In the method of the present invention, the inorganic or organic nitrate is preferably used in an amount of 0.1 to 2.0 equivalents, preferably 0.2 to 1.0 equivalents, more preferably 0.3 to 0.8 equivalents, and particularly preferably 0.4 to 0.8 equivalents, relative to the amount of fatty acid or fatty acid ester.

[0047] According to the invention, the electrochemical oxidation of fatty acids or fatty acid esters is carried out in an electrolytic cell in a reaction medium in the presence of oxygen and in the presence of inorganic or organic nitrates, the electrochemical oxidation being preferably carried out in an electrolytic cell.

[0048] It is advantageous if an oxygen-containing gas atmosphere is provided which is in spatial communication with the reaction medium.

[0049] It is advantageous if an oxygen-containing gas atmosphere is provided which is in spatial communication with the reaction medium.

[0050] The percentage of oxygen in the gas atmosphere may vary, but is preferably 10% by volume to 100% by volume, more preferably 15% by volume to 30% by volume, even more preferably 15% by volume to 25% by volume, and particularly preferably 18% by volume to 22% by volume.

[0051] In one embodiment, the percentage of oxygen in the gas atmosphere may be 10% by volume to 100% by volume, more preferably 15% by volume to 100% by volume, and even more preferably 20% by volume to 100% by volume.

[0052] Particularly preferably, the gas atmosphere is air.

[0053] It is advantageous if gas exchange is effected 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 a gas atmosphere.

[0054] Gas exchange between the gas atmosphere and the reaction medium, in particular stirring, can be used to control the electrochemical oxidation, for example by means of the stirrer geometry or the stirrer speed.

[0055] Preferably, the amount of oxygen dissolved in the reaction medium is at least 1 mmol / L of reaction medium, more preferably at least 5 mmol / L of reaction medium.

[0056] Also preferably, the amount of oxygen dissolved in the reaction medium is at least 10 mmol / L of reaction medium.

[0057] The process according to the invention can be carried out both in a divided electrolytic cell and in a non-divided electrolytic cell, with a non-divided electrolytic cell being preferred.

[0058] To avoid undesirable chemical reactions, it may be advantageous to separate the cathode and anode compartments so that charge exchange between the anode and cathode compartments occurs only through a porous diaphragm (usually an ion exchange resin).

[0059] The non-split electrolytic cell preferably used according to the present invention comprises at least two electrodes.For this purpose, anodes and cathodes made of conventional materials can be used, for example anodes and cathodes made of glassy carbon, boron-doped diamond (BDD) or graphite.The use of glassy carbon electrodes is preferred.

[0060] Preferably, the undivided electrolytic cell comprises at least one glassy carbon anode or at least one glassy carbon cathode. Preferably, both the anode and the cathode are glassy carbon electrodes.

[0061] The distance between the electrodes can vary over a certain range. Preferably, the distance is between 0.1 mm and 2.0 cm, more preferably between 0.1 mm and 1.0 cm, and particularly preferably between 0.1 mm and 0.5 cm.

[0062] Furthermore, the process of the present invention may be carried out in a batch or continuous mode, preferably in a non-divided flow-through electrolytic cell.

[0063] The method of the present invention is preferably carried out at a charge of at least 190C (2F) to 970C (10F), preferably 290C (3F) to 870C (9F), particularly preferably 330C (3.5F) to 820C (8.5F), particularly preferably 380C (4F) to 775C (8F), most preferably 380C (4F) to 580C (6F) per millimole of fatty acid or fatty acid ester used, in each case per double bond in the fatty acid or fatty acid ester used.

[0064] Preferably, the electrochemical oxidation in the method of the present invention is carried out galvanostatically.

[0065] The current density at which the method of the present invention is carried out is preferably at least 5 mA / cm 2 , or at least 10mA / cm 2 , or at least 15mA / cm 2 , or at least 20mA / cm 2 , or 20mA / cm 2 ~50mA / cm 2 where the surface areas given represent the geometric areas of the electrodes.

[0066] An important advantage of the method according to the invention is that electric current is used as oxidizing agent, which is a particularly environmentally friendly substance when obtained from renewable resources, i.e. especially from biomass, solar thermal energy, geothermal energy, hydroelectric power, wind power or photovoltaic power.

[0067] The process according to the invention can be carried out over a wide temperature range, for example at temperatures from 0 to 60°C, preferably from 5 to 50°C, particularly preferably from 10 to 40°C, and especially preferably from 15 to 30°C.

[0068] The process according to the invention can be carried out at elevated pressure or at reduced pressure. If the process according to the invention is carried out at elevated pressure, pressures up to 16 bar are preferred, pressures up to 6 bar are particularly preferred.

[0069] Also preferably, the process according to the invention can be carried out at atmospheric pressure.

[0070] The products produced by the process according to the invention can be isolated and purified by the usual methods known to those skilled in the art, in particular by extraction, crystallization, centrifugation, precipitation, distillation, evaporation or chromatography.

[0071] The following examples further illustrate the invention but are not intended to limit the scope of the invention. EXAMPLES

[0072] General Information and Methods Chemicals of analytical quality were used as obtained from usual sources (TCI, Aldrich, Acros, etc.) Oxygen was obtained in 2.5 quality from Nippon Gases Deutschland GmbH, Düsseldorf, Germany and used as received.

[0073] The electrode material used was glassy carbon (Sigradur® G, HTW Hochtemperatur Werkstoffe Gmb, Tierhaupten, Germany).

[0074] Gas chromatography analysis was performed on a Shimadzu GC-2010 (Shimadzu, Japan) equipped with a ZB-FFAP capillary GC column (Zebron, USA; length: 30 m, inner diameter: 0.25 mm, film thickness: 0.25 μm, carrier gas: argon).

[0075] 1 H-NMR and 13NMR analyses of C-NMR spectra were recorded at 25 °C using a Bruker Avance II 400 (400 MHz, 5 mm BBFO probe with Z gradient and ATM, SampleXPress60 autosampler, Analytische Messtechnik, Karlsruhe, Germany).

[0076] Column chromatography was performed using Kieselgel 60 M (0.040–0.063 mm, Macherey-Nagel GmbH & Co, Düren, Germany) with an eluent mixture of cyclohexane and ethyl acetate (9:1–7:3) with 1.0% acetic acid by volume as additive. Thin-layer chromatography was performed on Kieselgel 60 plates applied to aluminum (F254, Merck KGaA, Darmstadt, Germany). A KMnO4 solution was used to stain the TLC plates (potassium permanganate reagent: 3 g KMnO4, 20 g K2CO3, 5 mL NaOH (5%) in 300 mL water).

[0077] The undivided Teflon cells used for the electrolysis have been described in the literature (a) C. Gutz, B. Klockner, S. R. Waldvogel, Org. Process Res. Dev. 2016, 20, 26-32; b) A. Kirste, G. Schnakenburg, F. Stecker, A. Fischer, S. R. Waldvogel, Angew. Chem. Int. Ed. 2010, 49, 971-975; Angew. Chem. 2010, 122, 983-987. (See SI). The full range of these cells is commercially available as IKA Screening Systems (IKA-Werke GmbH & Co. KG, Staufen, Germany). The dimensions of the electrodes were 7 cm × 1 cm × 0.3 cm.

[0078] The gases were introduced in a controlled manner by two model 5850S ​​mass flow controllers (MFCs) from Brooks Instrument BV, Veenendaal, The Netherlands. This was done using one controller for the introduction of oxygen and one for the introduction of nitrogen. The controllers were controlled by Smart DDE and Matlab R2017b software. The volumetric flow rate was additionally monitored by a DK800 float principle flowmeter from Krohne Messtechnik GmbH, Duisburg. In all experiments carried out, the overall volumetric flow rate was constant at 20 mL / min. This is the maximum achievable volumetric flow rate, limited by the MFCs used. The volumetric flow rate ratio of the two gases was adjusted using the MFCs and the associated software. Gas cylinders from the following suppliers were used: Oxygen 2.5 from Nippon Gases Deutschland GmbH, Düsseldorf, Nitrogen 5.0 from Nippon Gases Deutschland GmbH, Düsseldorf. The gas distributor and the gas inlet cover of the electrolysis cell were described in the literature (M. Dorr, D. Waldmann, S.R. Waldvogel, GIT Labor-Fachz. 2021, pp. 7-8, 26-28) and purchased from IKA (IKA-Werke GmbH & Co. KG, Staufen, Germany).

[0079] General Procedure GP1 Fatty acids or fatty acid esters (0.5 mmol) and tetrabutylammonium nitrate (0.2–1.0 equiv.) were initially placed in a 5 mL volume undivided Teflon cup cell and dissolved in solvent (5 mL). The cell contained glassy carbon electrodes spaced 0.5 cm apart. The immersed surface area of ​​the electrodes was 1.8 cm. 2 The oxygen atmosphere in the gas space of the electrolysis cell was adjusted (20-100% by volume). After the cell was fixed to a stainless steel block, it was heated at 5-50°C with a current density of 5-20 mA / cm. 2Constant current electrolysis was carried out at 100°C. The stirring speed was 100–500 rpm. A charge amount of 8–20F (386–965C for 0.5 mmol of substrate) was applied, and after the reaction was completed, 50.5 μL of propionic acid was added as an internal standard, and the yield was measured by gas chromatography, or, in the case of azelaic acid 3b, it was isolated using column chromatography (eluent: cyclohexane / ethyl acetate = 9:1–7:3, containing 1.0 vol.% acetic acid as an additive).

[0080] Following GP1, the following fatty acids and fatty acid esters 1a-1c were converted to the corresponding carboxylic acids.

[0081] [ka]

[0082] The method according to the present invention was carried out by varying various reaction parameters. Experimental Examples 1 to 17 are summarized in Table 1 together with the respective conditions.

[0083] [Table 1]

[0084] Example 15: According to GP1, methyl oleate 1a (purity: 99%, 0.149 g, 0.5 mmol, 1.0 equiv.) was electrolyzed galvanostatically under oxygen atmosphere (100% by volume) and application of 10 F. The product yields were determined by gas chromatography with propionic acid as ISTD: pelargonic acid 2 (0.23 mmol), monomethyl azelate 3a (0.23 mmol), nonanal 4 (0.11 mmol).

[0085] Example 16: According to GP1, oleic acid 1b (0.141 g, 0.5 mmol, 1.0 equiv.) was electrolyzed galvanostatically under oxygen atmosphere (100% by volume) and application of 10 F. Product yields were determined by gas chromatography with propionic acid as ISTD: pelargonic acid 2 (0.14 mmol), nonanal 4 (0.08 mmol).

[0086] Azelaic acid 3b was isolated by column chromatography: 44 mg, 0.18 mmol, structure: 1 Confirmed by H-NMR: 1 H-NMR (300 MHz, DMSO-d6) δ [ppm] = 11.97 (s, 2H); 2.18 (t, J = 7.3 Hz, 4H); 1.50-1.43 (m, 4H); 1.26-1.24 (m, 6H). These analytical data were consistent with literature values.

[0087] Example 17: According to GP1, elaidic acid 1c (0.141 g, 0.5 mmol, 1.0 equiv.) was electrolyzed galvanostatically under oxygen atmosphere (100% by volume) and application of 10 F. Product yields were determined by gas chromatography with propionic acid as ISTD: pelargonic acid 2 (0.12 mmol), nonanal 4 (0.07 mmol).

[0088] Azelaic acid 3b was isolated by column chromatography: 40 mg, 0.16 mmol, structure: 1 Confirmed by H-NMR: 1 H-NMR (300 MHz, DMSO-d6) δ [ppm] = 11.97 (s, 2H); 2.18 (t, J = 7.3 Hz, 4H); 1.50-1.43 (m, 4H); 1.26-1.24 (m, 6H). Analytical data were in agreement with literature values.

[0089] Example 18: According to GP1, polyunsaturated fatty acids can also be oxidized, as shown for the example of linoleic acid 5 (see Scheme 2, Table 2).

[0090] [ka]

[0091] [Table 2]

[0092] Azelaic acid 3b was qualitatively confirmed by HPLC-MS.

Claims

1. 1. A process for producing aliphatic monocarboxylic acids and α,ω-dicarboxylic acids or α,ω-dicarboxylic monoesters by electrochemical oxidation of unsubstituted or at least monosubstituted mono- or polyunsaturated fatty acids or fatty acid esters, (a) at least one unsubstituted or at least one substituted monounsaturated or polyunsaturated C ６ ~C ２４ fatty acid or at least one unsubstituted or at least one substituted monounsaturated or polyunsaturated C ６ ~C ２４ Providing a fatty acid ester; Said C ６ ~C ２４ The fatty acid substituents are selected from the group consisting of methyl, phenyl or benzyl, with the phenyl or benzyl substituents themselves being unsubstituted or selected from the group consisting of F, Cl, Br and NO. ２ and wherein the aryl group is mono- or polysubstituted with one, two or three substituents each independently selected from the group consisting of: (b) providing at least one inorganic or organic nitrate; The nitrate salt has the general formula: ＋ ][NO ３ － ] as the nitrate, [Cation ＋ ] is Na ＋ , K ＋ , General structure [R １ R ２ R ３ R ４ N ＋ ] (wherein, R １ , R ２ , R ３ , R ４ is C １ ~C １６ Alkyl, especially linear or branched C １ ~C ８ each independently selected from the group consisting of alkyl, General structure (I): 【Chemistry 1】 (In the formula, R １ and R ２ is a linear or branched chain C １ ~C １８ Alkyl, especially linear or branched C １ ~C ８ alkyl; R ３ is H and linear or branched chain C １ ~C １８ Alkyl, especially H and linear or branched C １ ~C ８ is selected from the group consisting of alkyl. imidazolium cation, General structure (II): 【Chemistry 2】 (In the formula, R １ is C １ ~C １８ Alkyl, especially linear or branched C １ ~C ８ alkyl; R ２ , R ３ and R ４ is H and linear or branched chain C １ ~C １８ Alkyl, especially H and linear or branched C １ ~C ８ alkyl. the pyridinium cation, and General structure [R １ａ R ２ａ R ３ａ R ４ａ P ＋ ] (wherein, R １ａ , R ２ａ , R ３ａ , R ４ａ is C １ ~C １６ Alkyl, especially linear or branched C １ ~C ８ each independently selected from the group consisting of alkyl, A step selected from the group consisting of: (c) electrochemically oxidizing the unsubstituted or at least monosubstituted mono- or polyunsaturated fatty acid or the unsubstituted or at least monosubstituted mono- or polyunsaturated fatty acid ester provided in step (a) in the presence of the inorganic or organic nitrate provided in step (b) in an electrolytic cell in a reaction medium in the presence of oxygen. The method includes:

2. In the step (a), at least one unsubstituted monounsaturated or polyunsaturated C ６ ~C ２４ fatty acid, or at least one unsubstituted monounsaturated or polyunsaturated C ６ ~C ２４ The method of claim 1 , wherein a fatty acid ester is provided.

3. 3. The method of claim 2, wherein in step (a) at least one monounsaturated or polyunsaturated fatty acid selected from the group consisting of hexa-3-enoic acid, undecylenic acid, myristoleic acid, palmitoleic acid, margaroleic acid, petroselinic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, gondoic acid, cetoleic acid, erucic acid, nervonic acid, linoleic acid, alpha-linolenic acid, gamma-linolenic acid, calendulic acid, punicic acid, alpha-eleostearic acid, beta-eleostearic acid, arachidonic acid, eicosapentaenoic acid, docosadienoic acid, docosatetraenoic acid, docosahexaenoic acid and tetracosahexaenoic acid is provided, optionally in the form of an ester.

4. 4. The method according to claim 2 or 3, wherein in step (a) oleic acid, erucic acid, linoleic acid and / or elaidic acid are provided, optionally in the form of esters.

5. The method of any one of claims 1 to 4, wherein the ester provided is a methyl ester or an ethyl ester.

6. In the imidazolium cation of general formula (I), the radical R １ and R ２ is a linear or branched chain C １ ~C １８ Alkyl, especially linear or branched C １ ~C ８ alkyl; R ３ is hydrogen, preferably R １ is methyl, R ２ is ethyl, or R １ is methyl, R ２ is methyl and R １ is methyl, R ２ is butyl, R ３ The method according to any one of claims 1 to 5, wherein in each case is hydrogen.

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

8. The method according to any one of claims 1 to 7, wherein the organic nitrate is selected from the group consisting of tetra-n-butylammonium nitrate, methyltri-n-octylammonium nitrate, tetra-n-butylphosphonium nitrate, methyltri-n-octylphosphonium nitrate and 1-butyl-3-methylimidazolium nitrate.

9. 9. A process according to any one of claims 1 to 8, in which the fatty acid or fatty acid ester, or the inorganic or organic nitrate, is initially charged and combined with the reaction medium, preferably at least partially or completely dissolved in the reaction medium or mixed in the reaction medium, before the other of these two components is added, in each case.

10. 10. The process according to any one of claims 1 to 9, wherein the fatty acid or fatty acid ester and the inorganic or organic nitrate are charged first and then combined with the reaction medium, preferably at least partially or completely dissolved in or mixed with the reaction medium.

11. A process according to any one of claims 1 to 10, wherein the fatty acid or fatty acid ester and the inorganic or organic nitrate are added simultaneously or sequentially to the reaction medium, preferably at least partially or completely dissolved in or mixed with the reaction medium.

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

13. 13. The process according to claim 12, wherein the water content is at most 20% by volume, preferably at most 15% by volume, particularly preferably at most 10% by volume and very particularly preferably at most 5% by volume, based in each case on the total amount of the reaction medium.

14. 14. The process according to claim 12 or 13, wherein the polar aprotic reaction medium is selected from the group consisting of acetonitrile, isobutyronitrile, adiponitrile, acetone, dimethyl carbonate, methyl ethyl ketone, 3-pentanone, cyclohexanone, nitromethane, nitropropane, tert-butyl methyl ether, dimethyl sulfoxide, γ-butyrolactone and ε-caprolactone, or a combination of at least two of these components, preferably from the group consisting of acetonitrile, isobutyronitrile, adiponitrile, dimethyl carbonate and acetone, or a combination of at least two of these components, in each case optionally mixed with water.

15. A process according to any one of claims 12 to 14, wherein the reaction medium is acetonitrile, isobutyronitrile or adiponitrile in dry or anhydrous form.

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

17. 17. The method according to claim 16, wherein as the solubilizing component there is present a primary alcohol, a secondary alcohol, a monoketone or a dialkyl carbonate, or a mixture of at least two of these components, optionally mixed with water.

18. As the one or more solubilizing components, aliphatic C １－６ 18. The process according to claim 16 or claim 17, wherein one or more alcohols are present, preferably selected from the group consisting of methanol, ethanol, isopropanol, 2-methyl-2-butanol, and mixtures of at least two of these components, optionally mixed with water.

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

20. The process of any one of claims 1 to 19, wherein the reaction medium comprises water.

21. 19. The process according to any one of claims 16 to 18, wherein the one or more solubilizing components are added in an amount of less than 50% by volume, more preferably less than 30% by volume, particularly preferably less than 10% by volume, in each case relative to the total amount of the reaction medium.

22. The process according to any one of claims 1 to 21, wherein the inorganic or organic nitrate is present in an amount of 0.1 to 2.0 equivalents, preferably 0.2 to 1.0 equivalents, particularly preferably 0.3 to 0.8 equivalents, particularly preferably 0.4 to 0.8 equivalents, based in each case on the amount of fatty acid or fatty acid ester used.

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

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

25. 25. The method according to claim 24, wherein a gas exchange is carried out between the gas atmosphere and the reaction medium, preferably by introducing the gas atmosphere into the reaction medium or by stirring the reaction medium in the presence of the gas atmosphere.

26. 26. The method of claim 25, wherein the agitation is used to control the electrochemical oxidation.

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

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

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

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

31. A process according to any one of the preceding claims, wherein the distance between the electrodes in the electrolysis cell is from 0.1 mm to 2.0 cm, preferably from 0.1 mm to 1.0 cm, more preferably from 0.1 mm to 0.5 cm.

32. 32. The process according to claim 1 , wherein the charge amount is at least 190 C (2F) to 970 C (10F), preferably 290 C (3F) to 870 C (9F), particularly preferably 330 C (3.5F) to 820 C (8.5F), particularly preferably 380 C (4F) to 775 C (8F), most preferably 380 C (4F) to 580 C (6F), in each case per mmol of fatty acid or fatty acid ester used and in each case per double bond in the fatty acid or fatty acid ester used.

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

34. The current density is at least 5 mA / cm ２ , preferably 10 mA / cm ２ , more preferably 15 mA / cm ２ , particularly preferably 20 mA / cm ２ The method of any one of claims 1 to 33, wherein the surface area represents the geometric area of ​​the electrode.

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

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

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

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

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

40. A process according to any one of the preceding claims, carried out under elevated pressure, preferably up to 16 bar, more preferably up to 6 bar.

41. The method of any one of claims 1 to 40, carried out in an undivided cell.

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

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

44. A process according to any one of the preceding claims, which is carried out continuously, preferably in a non-divided flow-through electrolytic cell.

45. The process according to any one of claims 1 to 44, which is carried out without added catalyst, in particular without added transition metal catalyst.

46. 46. ​​The method of any one of claims 1 to 45, wherein no further oxidizing agent other than oxygen or the oxygen in air is added.

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