Electrochemical oxidation of fatty acids and fatty acid esters to produce monocarboxylic acids 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 method for producing aliphatic monocarboxylic acids and α,ω-dicarboxylic acids or α,ω-dicarboxylic acid monoesters by electrochemically oxidizing unsubstituted or at least monosubstituted mono-unsaturated or poly-unsaturated fatty acids or fatty acid esters in an electrolytic cell in a reaction medium in which oxygen is present, in the presence of inorganic or organic nitrates.

Background Art

[0002] Monocarboxylic acids, α,ω-dicarboxylic acids, and α,ω-dicarboxylic acid monoesters are important substrates in organic synthetic chemistry and are monomer components in polymer synthesis, and thus are highly relevant to industrial applications. Conventional access to these substrates is mainly through the oxidative cleavage of the C=C double bond of fatty acids and fatty acid esters via processes based on the use of transition metals, additional oxidants, and / or the principle of ozone oxidation.

[0003] Known processes based on transition metals tend to pose risks of toxicity to the human body and the environment due to their use. There are also economic factors such as the progress of raw material shortages and the increasing costs of these methods. Further complex operations are required for the purification of products and the recycling of catalysts. The use of an amount of oxidant exceeding the required amount also generates waste reagents that must be discarded. In most cases, the reaction necessarily proceeds at high or low temperatures, which can have an adverse impact on the energy balance of the process. The intermediates generated during ozone oxidation are at risk of explosion and pose a great safety risk. Furthermore, ozone needs to be generated as a reactive species by a special generator, which involves an increase in equipment costs.

Summary of the Invention

Problems to be Solved by the Invention

[0004] One of the objectives of the present invention is to provide a sustainable and resource-saving method for 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 objective was achieved through the subject matter of the claims and the specification.

[0006] The present invention relates to a method for producing aliphatic monocarboxylic acids and α,ω-dicarboxylic acids or α,ω-dicarboxylic acid 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 C6-C 24 Fatty acids, or at least one unsubstituted or at least one substituted monounsaturated or polyunsaturated C6-C6 fatty acids. 24 The process of preparing fatty acid esters, (b) A step of preparing at least one inorganic or organic nitrate, (c) A step of electrochemically oxidizing an unsubstituted or at least monosubstituted monounsaturated or polyunsaturated fatty acid, or an unsubstituted or at least monosubstituted monounsaturated or polyunsaturated fatty acid ester, prepared in step (a), in an electrolytic cell in a reaction medium containing oxygen, in the presence of an inorganic or organic nitrate prepared in step (b). Regarding methods including

[0007] Surprisingly, the electrochemical oxidation process of the present invention has been found to allow the introduction of oxygen functional groups into fatty acids or fatty acid esters using atmospheric oxygen. The fatty acids used as reactants can be commercially obtained by the hydrolysis of their glycerol esters and are renewable raw materials, particularly because they are widely found in vegetable fats and oils. Methyloleic acid is also obtained by transesterification of triglycerides and methanol and is used in biodiesel.

[0008] Therefore, the present invention's method for producing aliphatic α,ω-dicarboxylic acids and α,ω-dicarboxylic acid monoesters, as well as monocarboxylic acids from their renewable raw materials, provides a direct, sustainable, and resource-saving alternative for the synthesis of important synthetic units. α,ω-dicarboxylic acids are primarily used as monomers in large-scale industrial polyamide synthesis. α,ω-dicarboxylic acid monoesters allow industrial access to the corresponding dimers shortened by C2 via Kolbe electrolysis. To date, methods for synthesizing these resulting long-chain dicarboxylic acid diesters have been scarce. Therefore, both products are of great economic importance.

[0009] This eliminates the need for chemical oxidizing agents such as reactive peroxides and expensive catalysts with complex ligand systems in the method of the present invention. At the same time, the use of toxic and / or carcinogenic reagents can be reduced or completely avoided. The simple and safe process conditions also allow for scaling up to industrial scale to produce larger quantities of the target product. Thus, the present invention can significantly optimize processes that were previously costly and time-consuming.

[0010] The method of the present invention has special features such as high selectivity, the use of small amounts of auxiliary chemicals, the use of electric current as an oxidizing agent, and the generation of small amounts of waste associated therewith.

[0011] Furthermore, and surprisingly, it was found that the method of the present invention allows for the production of monocarboxylic acids, α,ω-dicarboxylic acids, and α,ω-dicarboxylic acid monoesters using a nitrate that functions as both a conductive salt and an electrochemical mediator, by utilizing electric current.

[0012] Even more surprisingly, the method of the present invention can be carried out at atmospheric pressure and room temperature, which has been found to be equally advantageous in terms of energy efficiency and environmental compatibility.

[0013] C6~C prepared in step (a) of the present invention24 Fatty acids and C6-C 24 Fatty acid esters are monounsaturated or polyunsaturated, that is, they have one or more C=C double bonds, for example, one, two, three, or four C=C double bonds. Fatty acids and fatty acid esters may be in either a cis or trans configuration. If a fatty acid or fatty acid ester has more than one C=C double bond, both configurations may be present in a single molecule. Fatty acids and fatty acid esters may be linear or branched, with linear being preferred. Fatty acids and fatty acid esters may be unsubstituted or at least monosubstituted. If monosubstituted or polysubstituted, they are preferably substituted with one, two, three, four, or five substituents independently selected from the group consisting of methyl, phenyl, or benzyl. The phenyl or benzyl substituents themselves may be unsubstituted or monosubstituted or polysubstituted with one, two, or three substituents independently selected from the group consisting of F, Cl, Br, and NO2.

[0014] In a preferred embodiment of the method according to the present invention, step (a) is to add at least one unsubstituted monounsaturated or polyunsaturated C6-C 24 Fatty acids, or at least one unsubstituted monounsaturated or polyunsaturated C6-C6 fatty acid. 24 We provide fatty acid esters.

[0015] In a more preferred embodiment of the method according to the present invention, step (a) is to provide at least one unsubstituted monounsaturated C6-C 24 Fatty acids, or at least one unsubstituted monounsaturated C6-C6 fatty acid 24 We provide fatty acid esters.

[0016] In a particularly preferred embodiment of the method according to the invention, in step (a), at least one monounsaturated or polyunsaturated fatty acid selected from the group consisting of hex-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, α-linolenic acid, γ-linolenic acid, calendulic acid, punica acid, α-eleostearic acid, β-eleostearic acid, arachidonic acid, eicosapentaenoic acid, docosadienoic acid, docosatetraenoic acid, docosahexaenoic acid and tetracosahexaenoic acid, in particular at least one selected from 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, is provided in the form of an ester if necessary.

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

[0018] When preparing the fatty acid ester according to step (a) of the method of the invention, the methyl ester or ethyl ester of the fatty acid is preferred.

[0019] According to step (b) of the method of the invention, at least one inorganic or organic nitrate is prepared. This nitrate serves both as a conductive salt and as a mediator of the electrochemical oxidation method according to the invention. General formula: [Cation + [NO3 - It is preferred to use an inorganic or organic nitrate of.

[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 C1~C 16 Ammonium ions having alkyl groups, particularly those independently selected from linear or branched C1-C8 alkyl groups. General structure (I):

[0021] [ka]

[0022] (In the formula, R 1 and R 2 This refers to linear or branched chains C1-C 18 Alkyls, particularly those consisting of linear or branched C1-C8 alkyls, are independently selected from the group, R 3 H and linear or branched chains C1-C 18 Alkyl groups, particularly those consisting of H and linear or branched C1-C8 alkyl groups, are selected. The imidazolium cation, General structure (II):

[0023] [ka]

[0024] (In the formula, R 1 C1~C 18 Alkyl, particularly selected from the group consisting of linear or branched C1-C8 alkyl groups, R 2 , R 3 and R 4 H and linear or branched chains C1-C 18 Alkyl groups, particularly H, and linear or branched C1-C8 alkyl groups, are independently selected. The pyridinium cation, and General structure [R 1a R2a R 3a R 4a P + ](wherein, R 1a , R 2a , R 3a , R 4a C1~C 16 A phosphonium ion of alkyl groups, particularly those independently selected from the group consisting of linear or branched C1-C8 alkyl groups. It is selected from the group consisting of the following.

[0025] In the method of the present invention, when using an organic nitrate based on an imidazolium cation, the cation of general formula (I) is preferred, where R 1 and R 2 This refers to linear or branched chains C1-C 18 Alkyls, particularly those consisting of linear or branched C1-C8 alkyls, are independently selected from the group, R 3 is hydrogen. Particularly preferred is the imidazolium cation of general formula (I), where R is 1 is methyl, and R 2 Is it ethyl, or R 1 is methyl, and R 2 is methyl and R 1 is methyl, and R 2 It is butyl, and R 3 In both cases, it is hydrogen.

[0026] In the method of the present invention, when a pyridinium cation-based nitrate is used, the cation of general formula (II) is preferred, where R 1 This refers to linear or branched chains C1-C 18 Alkyl, particularly linear or branched C1-C8 alkyl. Particularly preferred is the pyridinium cation of general formula (II), where R 1 This refers to linear or branched chains C1-C 18 Alkyl, particularly linear or branched C1-C8 alkyl, and radical R 2 , R 3 and R 4Each of these is independently selected from the group consisting of linear or branched C1-C8 alkyl groups, and is preferably monosubstituted at the 2nd, 3rd, or 4th position, disubstituted at the 2nd, 4th, 2nd, 5th, or 2nd, 6th positions, or trisubstituted at the 2nd, 4th, and 6th positions.

[0027] In principle, the method of the present invention may also use two or more of the above-mentioned nitrates. Nitrates according to the present invention, in particular composition [R 1 R 2 R 3 R 4 N + ][NO3 - ] Organic ammonium nitrate salt or composition [R 1a R 2a R 3a R 4a P + ][NO3 - It is preferable to use an organic phosphonium salt of the composition [R 1 R 2 R 3 R 4 N + ][NO3 - Organic ammonium nitrate salts of ] are particularly preferred.

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

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

[0030] The order in which the components used in the method of the present invention are prepared may vary, as may the order in which the individual components are brought into contact with each other or with their respective reaction media.

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

[0032] The reaction medium used in the method of the present invention is a liquid under the conditions under which the method is carried out and is suitable for partially or completely dissolving the components used, namely, the fatty acid or fatty acid ester used in particular, and the inorganic or organic nitrate. When at least one of these components is used in liquid form, the reaction medium is preferably easily miscible with the component.

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

[0034] In the method according to the present invention, when an inorganic nitrate, particularly potassium nitrate or sodium nitrate, is used, the reaction medium is preferably an aprotic reaction medium containing water and mixed with water. The water content of the reaction medium can vary. In all cases, the water content is preferably up to 20% by volume, more preferably up to 15% by volume, particularly preferably up to 10% by volume, and even more preferably up to 5% by volume, relative to 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, alicyclic ketones, dialkyl carbonates, cyclic carbonates, lactones, aliphatic nitroalkanes, and dimethyl sulfoxides, esters, and ethers, or at least two combinations of these components.

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

[0037] More preferably, the reaction medium is selected from the group consisting of acetonitrile, isobutyronitrile, adiponitrile, dimethyl carbonate, and acetone, or at least two combinations of these components.

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

[0039] Similarly, very preferably, the reaction medium is acetonitrile, isobutyronitrile, or adiponitrile, mixed with water as needed.

[0040] When one or more of the above components are used in a reaction medium mixed with water, the water content is preferably up to 20% by volume, more preferably up to 15% by volume, particularly preferably up to 10% by volume, and even more preferably up to 5% by volume, relative to the total volume of the reaction medium.

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

[0042] Examples of solubilizing components include primary alcohols, secondary alcohols, monoketones, or dialkyl carbonates, or mixtures of at least two of these components (mixed with water as necessary). In the method of the present invention, aliphatic C 1-6 It is preferable to use alcohol. 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 (mixed with water if necessary).

[0043] As a reaction medium, dimethyl carbonate is used, optionally with at least one C12 selected from the group consisting of methanol, ethanol, isopropanol, and 2-methyl-2-butanol. 1-6 It is particularly advantageous to use it mixed with alcohol (mixed with water if necessary).

[0044] When one or more of these solubilizing components are used in combination with water, the water content is preferably up to 20% by volume, more preferably up to 15% by volume, particularly preferably up to 10% by volume, and even more preferably up to 5% by volume, relative to the total amount of the solubilizing components and water.

[0045] In all cases, the solubilizing component may be added in an amount preferably 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.

[0046] Preferably, in the method of the present invention, inorganic or organic nitrates are used in an amount of preferably 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 present invention, the electrochemical oxidation of a fatty acid or fatty acid ester is carried out in an electrolytic cell in a reaction medium containing oxygen, in the presence of an inorganic or organic nitrate, and the electrochemical oxidation is preferably carried out within the electrolytic cell.

[0048] It is advantageous when an oxygen-containing gas atmosphere is provided that is spatially connected to the reaction medium.

[0049] It is advantageous when an oxygen-containing gas atmosphere is provided that is spatially connected to the reaction medium.

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

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

[0052] Particularly preferable is the gaseous atmosphere being air.

[0053] Preferably, it is advantageous to introduce a gas atmosphere into the reaction medium or to perform gas exchange between the gas atmosphere and the reaction medium by stirring the liquid phase in the presence of the gas atmosphere.

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

[0055] Preferably, the amount of oxygen dissolved in the reaction medium is at least 1 millimoles, more preferably at least 5 millimoles, per liter of reaction medium.

[0056] Similarly, preferably, the amount of oxygen dissolved in the reaction medium is at least 10 millimoles per liter of reaction medium.

[0057] The method according to the present invention can be carried out with both segmented electrolytic cells and non-segmented electrolytic cells, with non-segmented electrolytic cells being preferred.

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

[0059] A non-divided electrolytic cell preferably used in accordance with the present invention comprises at least two electrodes. For this purpose, anodes and cathodes made of conventional materials, such as glassy carbon, boron-doped diamond (BDD), or graphite, may be used. The use of glassy carbon electrodes is preferred.

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

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

[0062] Furthermore, the method of the present invention can be carried out in a batch or continuous manner, preferably in a non-split flow-through electrolytic cell.

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

[0064] Preferably, the electrochemical oxidation in the method of the present invention is carried out with a constant current.

[0065] The current density at which the method of the present invention is performed is preferably at least 5 mA / cm². 2 , or at least 10mA / cm 2 , or at least 15mA / cm 2 , or at least 20mA / cm² 2 , or 20mA / cm 2 ~50mA / cm 2 The stated surface area represents the geometric area of ​​the electrode.

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

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

[0068] The method according to the present invention can be carried out under high or low pressure. When the method according to the present invention is carried out under high pressure, a pressure of up to 16 bar is preferred, and a pressure of up to 6 bar is particularly preferred.

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

[0070] The products produced by the method according to the invention can be isolated and purified by conventional 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 do not limit the scope of the invention.

Example

[0072] General information and methods Chemicals of analytical quality were obtained and used from normal suppliers (such as TCI, Aldrich, Acros, etc.). Oxygen was obtained at a quality of 2.5 from Nippon Gases Deutschland GmbH in Düsseldorf, Germany and used as it was.

[0073] The electrode material used was vitreous carbon (Sigradur® G, manufactured by HTW Hochtemperatur Werkstoffe Gmb, Thalheim, Germany).

[0074] Gas chromatographic analysis was carried out 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 13 NMR analysis of 13C-NMR spectra was 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 plates (0.040-0.063 mm, manufactured by Macherey-Nagel GmbH & Co., Düren, Germany) and an eluent mixture of cyclohexane and ethyl acetate (9:1-7:3) with 1.0 vol% acetic acid added as an additive. Thin-layer chromatography was performed on Kieselgel 60 plates coated with aluminum (F254, manufactured by Merck KGaA, Darmstadt, Germany). KMnO4 solution was used to stain the TLC plates (potassium permanganate reagent: 3 g of KMnO4, 20 g of K2CO3, and 5 mL of NaOH (5%) in 300 mL of water).

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

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

[0079] General Procedure GP1 A fatty acid or fatty acid ester (0.5 mmol) and tetrabutylammonium nitrate (0.2-1.0 equivalent) were initially placed in a 5 mL non-divided Teflon® cup cell and dissolved in a solvent (5 mL). The cell was equipped with glassy carbon electrodes spaced 0.5 cm apart. The immersion surface area of ​​the electrodes was 1.8 cm². 2 The oxygen atmosphere in the gas space of the electrolytic cell was adjusted (20-100 vol%). After fixing the cell to a stainless steel block, the current density was 5-20 mA / cm² at 5-50°C. 2Constant current electrolysis was performed. The stirring speed was 100-500 rpm. A charge of 8-20 F (386-965 C per 0.5 mmol of substrate) was applied, and after the reaction was complete, 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, isolation was performed using column chromatography (eluent: cyclohexane / ethyl acetate = 9:1-7:3, with 1.0 vol% acetic acid as an additive).

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

[0081] [ka]

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

[0083] [Table 1]

[0084] Experimental Example 15: According to GP1, methyloleic acid 1a (purity: 99%, 0.149 g, 0.5 mmol, 1.0 equivalent) was subjected to constant current electrolysis under an oxygen atmosphere (100 vol%) and 10F. The yields of the products were measured by gas chromatography with propionic acid as the ISTD: pelargonic acid 2 (0.23 mmol), monomethyl azelaic acid 3a (0.23 mmol), and nonanal 4 (0.11 mmol).

[0085] Experimental Example 16: According to GP1, oleic acid 1b (0.141 g, 0.5 mmol, 1.0 equivalent) was subjected to constant current electrolysis in an oxygen atmosphere (100 vol%) and under the application of 10F. The yields of the products were measured 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 ¹H-NMR (300MHz, DMSO-d6) δ[ppm] = 11.97 (s, 2H); 2.18 (t, J=7.3Hz, 4H); 1.50-1.43 (m, 4H); 1.26-1.24 (m, 6H). These analytical data were consistent with literature values.

[0087] Experimental Example 17: According to GP1, elaidic acid 1c (0.141 g, 0.5 mmol, 1.0 equivalent) was subjected to constant current electrolysis in an oxygen atmosphere (100 vol%) and under the application of 10F. The yields of the products were measured 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 ¹H-NMR (300MHz, DMSO-d6) δ[ppm] = 11.97 (s, 2H); 2.18 (t, J=7.3Hz, 4H); 1.50-1.43 (m, 4H); 1.26-1.24 (m, 6H). The analytical data were consistent with the literature values.

[0089] Experimental Example 18: According to GP1, polyunsaturated fatty acids can also be oxidized, as shown in 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. A method for producing aliphatic monocarboxylic acids and α,ω-dicarboxylic acids or α,ω-dicarboxylic acid monoesters by electrochemical oxidation of unsubstituted or at least monosubstituted monounsaturated fatty acids, unsubstituted or at least monosubstituted polyunsaturated fatty acids, unsubstituted or at least monosubstituted monounsaturated fatty acid esters, or unsubstituted or at least monosubstituted polyunsaturated fatty acid esters. (a) (i) at least one unsubstituted or at least one substituted monounsaturated C6-C24 fatty acid or an unsubstituted or at least one substituted polyunsaturated C ６ ~C ２４ Fatty acids, or (ii) at least one unsubstituted or at least one substituted monounsaturated C6-C24 fatty acid ester or unsubstituted or at least one substituted polyunsaturated C ６ ~C ２４ Prepare fatty acid esters, The monounsaturated C ６ ~C ２４ The substituents of fatty acids, polyunsaturated C6-C24 fatty acids, monounsaturated C6-C24 fatty acid esters, or polyunsaturated C6-C24 fatty acid esters are selected from the group consisting of methyl, phenyl, or benzyl, and the phenyl or benzyl substituents themselves are either unsubstituted or composed of F, Cl, Br, and NO, respectively. ２ A process in which a substituent is monosubstituted or polysubstituted with a substituent independently selected from the group consisting of the following: (b) Prepare at least one inorganic or organic nitrate, The nitrate is a nitrate of the general formula [cation ＋ [NO ３ － and exists as The aforementioned [cation] ＋ ] is Na ＋ _K ＋ , General structure [R １ R ２ R ３ R ４ N ＋ ] (wherein, R １ , R ２ , R ３ , R ４ C １ ~C １６ a Ammonium ions having ) selected independently from each of the following: General structure (I): 【Chemistry 1】 (In the formula, R １ and R ２ C is a straight-chain or branched-chain C １ ~C １８ Each is independently selected from the group consisting of alkyls, R ３ H and linear or branched C １ ~C １８ (Selected from the group consisting of alkyl groups.) The imidazolium cation, General structure (II): 【Chemistry 2】 (In the formula, R １ C １ ~C １８ Selected from the group consisting of alkyl groups, R ２ , R ３ and R ４ H and linear or branched C １ ~C １８ Each element is independently selected from the group consisting of alkyl groups. The pyridinium cation, and General structure [R １ａ R ２ａ R ３ａ R ４ａ P ＋ ] (wherein, R １ａ , R ２ａ , R ３ａ , R ４ａ teeth , C １ ~C １６ The phosphonium ion (each independently selected from the group consisting of alkyl groups). A process selected from the group consisting of, (c) In an electrolytic cell in a reaction medium containing oxygen, electrochemically oxidizing (i) an unsubstituted or at least one-substituted monounsaturated or polyunsaturated fatty acid, or (ii) an unsubstituted or at least one-substituted monounsaturated or polyunsaturated fatty acid ester, prepared in step (a), in the presence of the inorganic or organic nitrate prepared in step (b). A method that includes this.

2. In step (a) above, at least one unsubstituted monounsaturated C6-C24 fatty acid or an unsubstituted polyunsaturated C ６ ~C ２４ Fatty acids, or at least one unsubstituted monounsaturated C6-C24 fatty acid ester or unsubstituted polyunsaturated C ６ ~C ２４ The method according to claim 1 for preparing a fatty acid ester.

3. The method according to 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, petroseric acid, oleic acid, elaidic acid, vaccenic acid, gadolic acid, gondic acid, cetolic 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, docosadienoic acid, docosatetraenoic acid, docosahexaenoic acid and tetracosahexaenoic acid is prepared in the form of an ester.

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

5. The method according to claim 1, wherein the prepared ester is a methyl ester or an ethyl ester.

6. In the imidazolium cation of the general formula (I) described above, the radical R １ and R ２ C is a straight-chain or branched-chain C １ ~C １８ Each is independently selected from the group consisting of alkyls, R ３ The method according to claim 1, wherein is hydrogen.

7. In the pyridinium cation of the general formula (II) described above, radical R １ C is a straight-chain or branched-chain C １ ~C １８ It is alkyl, and radical R ２ , R ３ and R ４ C is a straight-chain or branched-chain C １ ~C ８ The method according to claim 1, wherein each is independently selected from the group consisting of alkyl groups.

8. The method according to claim 1, 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. The method according to claim 1, wherein the fatty acid or the fatty acid ester, or the inorganic or organic nitrate, is added first and combined with the reaction medium, and then, if the fatty acid or the fatty acid ester was added first, the inorganic or organic nitrate is added, and if the inorganic or organic nitrate was added first, the fatty acid or the fatty acid ester is added.

10. The method according to claim 1, wherein the fatty acid or fatty acid ester and the inorganic or organic nitrate are first added, and then combined with the reaction medium.

11. The method according to claim 1, wherein the fatty acid or the fatty acid ester and the inorganic or organic nitrate are added to the reaction medium simultaneously or sequentially.

12. The method according to claim 1, wherein the reaction medium is a polar aprotic reaction medium mixed with water, and the polar aprotic reaction medium is selected from the group consisting of aliphatic nitriles, aliphatic ketones, alicyclic ketones, dialkyl carbonates, cyclic carbonates, lactones, aliphatic nitroalkanes, dimethyl sulfoxides, esters and ethers, or at least two combinations thereof.

13. The method according to claim 12, wherein the water content is a maximum of 20% by volume relative to the total amount of the reaction medium in all cases.

14. The method according to claim 12, 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 at least two combinations thereof, and in any case is used in combination with water.

15. The method according to claim 12, wherein the reaction medium is acetonitrile, isobutyronitrile, or adiponitrile in a dry form.

16. The method according to claim 1, wherein the reaction medium includes a solubilizing component that enables the dissolution of one or more other substances.

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

18. As one or more solubilizing components, aliphatic C １－６ The method according to claim 16, wherein one or more alcohols selected from the group consisting of alcohols are mixed with water and present.

19. As the reaction medium, dimethyl carbonate contains at least one C １－６ The method according to claim 1, wherein the alcohol is mixed with the alcohol and present.

20. The method according to claim 1, wherein the reaction medium includes water.

21. The method according to claim 16, wherein one or more of the solubilizing components are added in an amount less than 50% by volume relative to the total amount of the reaction medium in each case.

22. The method according to claim 1, wherein the inorganic or organic nitrate is present in an amount of 0.1 to 2.0 equivalents relative to the amount of fatty acid or fatty acid ester used in either case.

23. The method according to claim 1, wherein an oxygen-containing gas atmosphere is provided in spatial communication with the reaction medium.

24. The method according to claim 1, wherein the gas atmosphere is air.

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

26. The method according to claim 25, wherein stirring the reaction medium is used to control the electrochemical oxidation.

27. The method according to claim 1, wherein the amount of oxygen dissolved in the reaction medium is at least 1 millimoles per liter of the reaction medium.

28. The method according to claim 1, wherein the electrolytic cell is a non-divisible electrolytic cell in which the anode and cathode are arranged in the same compartment without being separated.

29. The method according to claim 1, wherein the non-divided electrolytic cell comprises a glassy carbon anode, a graphite anode, or a BDD anode.

30. The method according to claim 1, wherein the non-divided electrolytic cell comprises a glassy carbon cathode, a graphite cathode, or a BDD cathode.

31. The method according to claim 1, wherein the distance between electrodes in the electrolytic cell is 0.1 mm to 2.0 cm.

32. The method according to claim 1, wherein the amount of charge used for the electrochemical oxidation is at least 190 C (2 F (F: Faraday constant)) to 970 C (10 F (F: Faraday constant)) per millimoles of fatty acid or fatty acid ester used.

33. The method according to claim 1, wherein the electrochemical oxidation is carried out with a constant current.

34. The current density is at least 5 mA / cm². ２ The method according to claim 1, wherein the surface area represents the geometric area of ​​the electrode.

35. The current density is at least 20 mA / cm². ２ ~50 mA / cm ２ The method according to claim 1, wherein the surface area represents the geometric area of ​​the electrode.

36. The method according to claim 1, wherein the electric current used in the electrochemical oxidation is obtained from renewable resources.

37. The method according to claim 1, wherein the electrochemical oxidation is carried out at a temperature of 0 to 60°C.

38. The method according to claim 1, performed under atmospheric pressure.

39. The method according to claim 1, which is carried out under reduced pressure, which is lower than atmospheric pressure.

40. The method according to claim 1, which is carried out under high pressure, which is higher than atmospheric pressure.

41. The method according to claim 1, wherein the anode and cathode are arranged in the same compartment without being separated.

42. The method according to claim 1, performed in a batch manner.

43. The method according to claim 1, which is carried out continuously within a non-divided flow-through electrolytic cell.

44. The method according to claim 1, which is carried out continuously in a non-divided flow-through electrolytic cell.

45. The method according to claim 1, which is carried out without adding a catalyst.

46. The method according to claim 1, wherein no further oxidizing agent other than oxygen or oxygen in the air is added.

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