Manufacturing of stable activated nickel hydroxide foam electrodes

Abstract

The present invention relates to a method for enabling the electrochemical activation of metal electrodes and metal foam electrodes, more specifically nickel electrodes, and in particular nickel foam electrodes. Furthermore, the present invention also relates to metal electrodes and metal foam electrodes, more specifically nickel electrodes, and in particular nickel foam electrodes obtained by the above electrochemical activation method. Furthermore, the present invention also relates to the use of metal electrodes and metal foam electrodes, more specifically nickel electrodes, and in particular nickel foam electrodes, electrochemically activated by the method of the present invention, in electrochemical reactions, electrolysis of organic compounds, catalysts for organic chemical reactions, and hydroelectrolysis.

Description

[Technical Field]

[0001] The present invention relates to a method for enabling the electrochemical activation of metal electrodes and metal foam electrodes, more specifically nickel electrodes, and in particular nickel foam electrodes. Furthermore, the present invention also relates to metal electrodes and metal foam electrodes, more specifically nickel electrodes, and in particular nickel foam electrodes obtained by the above electrochemical activation method. Furthermore, the present invention also relates to the use of metal electrodes and metal foam electrodes, more specifically nickel electrodes, and in particular nickel foam electrodes, electrochemically activated by the method of the present invention, in electrochemical reactions, electrolysis of organic compounds, catalysts for organic chemical reactions, and hydroelectrolysis. [Background technology]

[0002] Metal electrodes and metal foam electrodes, more specifically nickel electrodes, and especially nickel foam electrodes, are in high demand across a wide range of applications due to their high porosity, conductivity, mechanical stability, and chemical resistance.

[0003] To date, the only known method for activating nickel foam electrodes is an electrocatalytic process that changes the polarity of two nickel electrodes. This activation involves adding 10 to a solution containing 0.05 M to 0.1 M NiSO4 (aqueous solution) and 0.1 M NaOAc (aqueous solution) or 0.1 M KOAc (aqueous solution). -5This is done by adding a base at a concentration of M-1 mM KOH (aqueous solution) or 5 mM NaOH (aqueous solution) (GWD Briggs, E. Jones, WFK Wynne-Jones, Trans. Faraday Soc. 1955, 51, 1433-1442; BV Lyalin, VA Petrosyan, Russ. Chem. Bull. 2004, 53, 688-692; W. Jud, CA Salazar, J. Imbrogno, J. Verghese, SM Guinness, J.-N. Desrosiers, CO Kappe, D. Cantillo, Org. Process Res. Dev. 2022, 26, 1486-1495, H.-J. Schafer, J. Kaulen, Tetrahedron 1982, 38, 3299-3308). In all known cases, activation requires changing the polarity between the two nickel electrodes every 5 to 30 seconds. Details are provided in each case.

[0004] A drawback of this known activation method is its low reproducibility, especially in the case of cleaned nickel foam electrodes. In particular, for nickel foam electrodes that have been cleaned after electrochemical oxidation, conventional activation methods cannot reliably produce stable nickel oxyhydroxide.

[0005] Furthermore, the use of a polarity converter is required. This significantly increases the complexity of the electronic peripherals of a device that normally operates at a constant current. Moreover, two nickel electrodes are required even though only one nickel electrode is used in the subsequent electrochemical reaction. Consequently, since only the ultimately anode-polarized electrode has an outer layer of NiO(OH), half of the deposited nickel species is occupied by the electrode not used in the reaction. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] G. W. D. Briggs, E. Jones, W. F. K. Wynne-Jones, Trans. Faraday Soc. 1955, 51, 1433-1442 [Non-Patent Document 2] B. V. Lyalin, V. A. Petrosyan, Russ. Chem. Bull. 2004, 53, 688-692 [Non-Patent Document 3] W. Jud, C. A. Salazar, J. Imbrogno, J. Verghese, S. M. Guinness, J.-N. Desrosiers, C. O. Kappe, D. Cantillo, Org. Process Res. Dev. 2022, 26, 1486-1495 [Non-Patent Document 4] H.-J. Schafer, J. Kaulen, Tetrahedron 1982, 38, 3299-3308 [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] An object of the present invention is to provide a method for activating a metal electrode that does not exhibit the drawbacks of known methods related to the activation of metal electrodes and metal foam electrodes, more specifically nickel electrodes, particularly nickel foam electrodes, or exhibits such drawbacks only in a reduced form. Means for Solving the Invention

[0008] This object is achieved by the claims and the description herein.

[0009] The present invention provides (a) As a pretreatment of the metal electrode, a step of bringing the metal electrode into contact with a base; (b) Electrochemically activating the metal electrode pretreated according to step (a) without reversing the polarity of the metal electrode to form an outer metal oxyhydroxide layer; and includes an electrochemical activation method for a metal electrode. The metal electrode contains nickel in an amount of 0 wt% to 100 wt% and cobalt in an amount of 100 wt% to 0 wt% with respect to the total content of nickel and cobalt in the electrode, or contains nickel in an amount of 10 wt% to 100 wt% and iron in an amount of 0 wt% to 90 wt% with respect to the total content of nickel and iron in the electrode, relates to a method in which the metal electrode contains other metals in an amount of 10 wt% or less with respect to the total metal content.

[0010] According to the method of the present invention, a single metal electrode, more specifically a nickel electrode or a nickel foam electrode, can be efficiently activated in a non-separated state with a direct current without reversing the polarities of two metal electrodes, more specifically two nickel electrodes. When using the method of the present invention, a polarity converter is not required, and thus the equipment setup is simplified.

[0011] Furthermore, according to the method of the present invention, in particular, a metal foam electrode, more specifically a nickel foam electrode, after being used in organic electrolytic oxidation, can be activated in a reproducible manner. Since it is more difficult to clean a foam electrode than a flat electrode, existing activation methods do not seem to be suitable. It cannot be simply polished as in the case of a flat electrode.

[0012] Therefore, the method claimed in the present invention enables very good access to the electrochemically activated nickel surface and improves the reproducibility when using a cleaned nickel foam or nickel foam electrode. In particular, according to the method of the present invention, reproducible electrochemical activation of (cleaned) nickel foam and nickel plate electrodes becomes possible. Thereby, the electrode life can be extended according to the degree of contamination.

[0013] Activated nickel foam is essential for the successful electrochemical oxidation of many substances, including (non)cyclic alcohols and ketones (H.-J. Schafer, Electrochemistry I, Top. Curr. Chem. 1987, 142, 101-129). Therefore, the present invention provides a flexible and simplified method for activating nickel foam.

[0014] Further advantages of the method of the present invention include the fact that only a very small amount of base is required when wetting the metal electrode, more specifically the nickel electrode, and that used bases can be reused for this purpose. Further advantages include the flexibility to use various activation solutions, reaction conditions suitable for industrial-scale electrochemical activation, and the potential for various applications of the activated large nickel surface (e.g., catalyst or electrolysis / battery technology).

[0015] Finally, according to the method of the present invention, used nickel foam can be used for organic electrolytic oxidation on an activated nickel surface. DC electrochemical activation enables rapid and controlled activation and avoids the deposition of nickel residue on the second electrode.

[0016] The left side of Figure 1 shows a scanning electron microscope (SEM) image of a nickel oxyhydroxide surface activated using a conventional activation method (quoted from GWD Briggs, E. Jones, WFK Wynne-Jones, Trans. Faraday Soc. 1955, 51, 1433-1442), and the right side shows an SEM image of an activated surface obtained by the method of the present invention. In both cases, a fibrous network with fine porosity is clearly visible. Therefore, in the case of nickel foam washed after electrochemical oxidation treatment, conventional activation methods could not reliably obtain stable nickel oxyhydroxide. This was already visually evident from the absence of blackening.

[0017] Figure 2 shows a flow electrolytic cell for carrying out a method using electrochemically activated metal electrodes according to the present invention.

[0018] Figure 3 shows a graph of parameter results evaluated by plotting the qNMR yield of 3-ethyladipic acid after electrochemical oxidation of 4-ethylcyclohexanol using a metal electrode electrochemically activated according to the present invention.

[0019] Figures 4 and 5 show the change in the qNMR yield of 3-propyladipic acid with and without the supply of 4-propylcyclohexanone in response to a charge applied using a metal electrode electrochemically activated according to the present invention.

[0020] The contact between the metal electrode and the base serves two purposes. Firstly, it cleans the surface, and secondly, it promotes the rapid formation of a metal oxyhydroxide layer, more specifically a nickel oxyhydroxide layer, on the surface.

[0021] To carry out a more vigorous oxidation reaction on the corresponding electrochemically activated metal oxyhydroxide anode, more specifically on a nickel oxyhydroxide anode (Ni(O)OH), it may be advantageous to select a basic environment as the electrolyte, such as a dilute sodium hydroxide solution, in order to keep the catalyst active during the reaction.

[0022] In all cases, the content of other metals in the metal electrode is preferably 5% by weight or less, very preferably 2% by weight or less, and even more preferably 1% by weight or less, relative to the total metal content.

[0023] The metal electrode preferably contains 1% by weight or less, more preferably 0.1% by weight or less, and even more preferably 0.01% by weight or less of V, W, and Mo. Note that these metals are particularly susceptible to corrosion in alkaline aqueous emulsions.

[0024] A metal electrode useful in the method of the present invention is more preferably one that contains at least 80% by weight, preferably at least 90% by weight, and even more preferably at least 95% by weight of nickel based on the total weight of the metal in the electrode.

[0025] Nickel and / or cobalt, and optionally iron, may be present in the metal electrodes on the substrate, the substrate being at least one material selected from the group consisting of steel, copper, titanium, and carbon, and preferably graphite.

[0026] The metal electrode may preferably be doped with at least one element from the fifth and sixth major groups, more preferably one or more elements selected from the group consisting of phosphorus, arsenic, selenium, and sulfur.

[0027] The doping content values ​​indicate the elemental state of the doping agent, based on the metal mass of the electrode.

[0028] If the metal electrode is doped with phosphorus, it may preferably contain 2 to 10% by weight, more preferably 3 to 9% by weight, and most preferably 4 to 9% by weight of phosphorus. In all cases, the phosphorus is in elemental form and is based on the mass of the metal in the electrode.

[0029] The phosphorus dopant content may preferably be measured according to Appendix D.1 of DIN EN ISO 5427.

[0030] The thickness of the metal electrode is preferably 2 mm or more, more preferably more than 3 mm, even more preferably more than 5 mm, and particularly preferably 6 mm or more.

[0031] The metal electrode used in the method according to the present invention is preferably a Ni(O)OH foam electrode, and in any case contains, preferably at least 80% by weight, more preferably at least 85%, 90%, 95%, 98%, or 99% by weight, even more preferably at least 99.9% by weight, and even more preferably at least 99.99% by weight, of the metal content of the Ni(O)OH foam electrode.

[0032] The metal electrode is preferably pretreated by contacting it with a base, preferably at least one inorganic base and / or at least one organic base.

[0033] Conventional inorganic and organic bases known to those skilled in the art are suitable for use in the contact process. Preferably, N(R) A )4OH, N(R A )4 Acetate (In the formula, each R A Each of these is independently H or linear or branched C 1-4 -It is alkyl.) One or more bases, preferably one, selected independently from the group consisting of NaOH, sodium acetate, KOH, potassium acetate, LiOH, lithium acetate, Na2CO3, K2CO3, and Li2CO3, and more preferably selected from the group consisting of NaOH and KOH, may be used.

[0034] The base is preferably used in an aqueous solution during the contact step, and the base concentration is preferably 10 mM to 10 M, more preferably 0.2 to 5 M, even more preferably 0.5 to 1.5 M, and even more preferably 1 ± 0.1 M.

[0035] Metal electrodes can be brought into contact with a base, particularly by spray coating, immersion, jetting, or within a flow system.

[0036] The metal electrode and the base may be in contact with each other over a relatively wide temperature range. The metal electrode is preferably in contact with the base at a temperature of 10 to 40°C, more preferably 18 to 27°C.

[0037] According to the method of the present invention, the electrochemical activation of the metal electrode can be advantageously carried out. In particular, one or more salts of nickel and / or cobalt, and optionally iron, are suitable for this process.

[0038] When using a salt of nickel or cobalt, suitable salts are, in particular, salts selected from the group consisting of Ni2SO4 and CoSO4.

[0039] For the electrochemical activation of the metal electrode, one or more salts are preferably present in a basic aqueous solution and may preferably be present at a concentration of 0.05 to 0.15 M.

[0040] Useful bases are conventional bases known to those skilled in the art. Preferably, one or more bases independently selected from the group consisting of N(R A )4OH, N(R A )4 acetate (where each R A is independently H or linear or branched C 1-4 -alkyl), NaOH, sodium acetate, KOH, potassium acetate, LiOH, lithium acetate, Na2CO3, K2CO3 and Li2CO3, more preferably one or more bases selected from the group consisting of NaOH and KOH, particularly the use of one base is mentioned.

[0041] The base concentration in the electrochemical activation of the metal electrode is preferably 10 mM to 10 M, preferably 0.2 to 5 M, more preferably 0.5 to 1.5 M, and most preferably 1 ± 0.1 M.

[0042] The metal electrode is preferably activated with a charge amount of 2 to 10 coulombs, preferably 5 to 7 coulombs.

[0043] The metal electrode can be electrochemically activated over a wide temperature range. The metal electrode is preferably activated at a temperature of 10 to 40 °C, more preferably 18 to 27 °C.

[0044] The present invention further relates to electrochemically activated metal electrodes, and more specifically to electrochemically activated metal electrodes obtained by the method of the present invention.

[0045] The present invention further relates to electrochemically activated metal electrodes for use in water electrolysis, or in batteries or catalytic reactions, for carrying out oxidation reactions of organic components, and more specifically to electrochemically activated metal electrodes obtained by or obtained by the method of the present invention.

[0046] The metal electrodes electrochemically activated by the method of the present invention may be used in a batch-type electrolytic cell or a continuous-flow electrolytic cell, preferably a continuous-flow electrolytic cell.

[0047] The metal electrodes electrochemically activated by the method of the present invention may preferably be used in a non-diaphragm electrolytic cell.

[0048] The present invention will be described in more detail below with reference to examples, but this will not limit the scope of the present invention. [Brief explanation of the drawing]

[0049] [Figure 1] The left side of Figure 1 is a scanning electron microscope (SEM) image of a nickel oxyhydroxide surface activated using a conventional activation method (quoted from GWD Briggs, E. Jones, WFK Wynne-Jones, Trans. Faraday Soc. 1955, 51, 1433-1442), and the right side is an SEM image of an activated surface obtained by the method of the present invention. [Figure 2] Figure 2 shows a flow electrolytic cell for carrying out a method using electrochemically activated metal electrodes according to the present invention. [Figure 3] Figure 3 shows a graph of parameter results evaluated by plotting the qNMR yield of 3-ethyladipic acid after electrochemical oxidation of 4-ethylcyclohexanol using a metal electrode electrochemically activated according to the present invention. [Figure 4] Figure 4 shows the change in the qNMR yield of 3-propyladipic acid with and without the supply of 4-propylcyclohexanone in response to a charge applied using a metal electrode electrochemically activated according to the present invention. [Figure 5] Figure 5 shows the change in the qNMR yield of 3-propyladipic acid with and without the supply of 4-propylcyclohexanone in response to a charge applied using a metal electrode electrochemically activated according to the present invention. [Examples]

[0050] General information and methods For analytical-grade chemical products, we used those sourced from our usual suppliers (e.g., TCI, Aldrich, Rotisolv, Fisher Chemical, VWR, Thermos Scientific, Acros, etc.). Solvents were purified by standard methods such as distillation or desalting.

[0051] Unless otherwise specified, the reaction conditions were atmospheric pressure and room temperature.

[0052] The electrodes used in the reaction were commercially available, consisting of stainless steel (1.4571) and Recemat® nickel foam with small channels on the inlet and outlet sides. These are compatible with the IKA ElectraSyn flow 6-18 apparatus. For activation, another metal plate electrode (6 × 18 cm) was prepared from stainless steel (1.4571) in the university workshop. 2 The galvanostat used was a TDK Lambda Genesys 750W / 1500W power supply. An Ismatec Reglo Digital Masterflex™ peristaltic pump (model number: 78018-42) was used to pump the reaction mixture through an Ismapren hose (size: 16). A heating circuit was installed and connected to an IKA WICO CBC 5C cooling / circulation thermostat (model number: RN41).

[0053] Melting point measurement: The melting point was measured using an M-565 (Buchi GmbH, Essen, Germany). The heating rate was 1°C / min.

[0054] NMR method: Using a Bruker Avance III 600 NMR spectrometer (Bruker, probe head: 5 mm, TCI-CryoProbe head with Z gradient and ATM), at 25°C. 1 H (600MHz) and 13 The inverse gate spectrum of C (151 MHz) was recorded. The chemical shift (δ) is reported in parts per million (ppm). For quantification, it was compared with 1,3,5-trimethoxybenzene as an internal standard. 13 This was done by integrating each signal in the C inverse gate spectrum (δ = (55.4 ± 0.02) ppm). The DMSO-d6 signal (δ = 39.52 ppm) was used as a reference.

[0055] Liquid chromatography: Photodiode array analysis was performed using a Shimadzu DUGA-20A3 instrument equipped with a Knauer C18 column (Eurospher II, 100-5 C18, 150 × 4 mm). The column was conditioned to 25°C and the flow rate was adjusted to 1 mL / min. The aqueous eluate was buffered with formic acid (0.8 mL / 2.5 L) and stabilized with acetone (5 vol%). The sample was prepared by acid-base extraction with ethyl acetate to extract the carboxylic acid product mixture from the reaction mixture, drying with MgSO4, and evaporating the solvent. The product was filtered (VWR 13 mm syringe filter with 0.45 μm PTFE membrane) and dissolved and diluted in acetonitrile (MS quality). This organic solution was analyzed by liquid chromatography.

[0056] High-resolution mass spectra were acquired using a G6545A Q-ToF (Agilent GmbH, Waldbronn, Germany) equipped with a dual AJS electrospray ion source (dual AJS ESI). The MS parameters were as follows: Mass range: 80-3200 m / z, Scan rate: 1 spectrum / second -1Atomizer pressure: 25 psig, Capillary voltage: 3500V, Fragmenter: 50V, Skimmer: 45V, Dry gas temperature: 275℃, Dry gas flow rate: 10 L / min -1 Sheath gas temperature: 350℃, sheath gas flow rate: 10L / min -1 Mass calibration was performed on the day of measurement using an external standard. The mass accuracy of the measurement results was less than 5 ppm. Chromatographic separation was performed using a 1260 Infinity II HPLC system (Agilent GmbH, Waldbronn, Germany). This system was equipped with a G7111B 1260 quaternary pump, a G7129A 1260 vial sampler, and a G7116A 1260 multi-column thermostat with an Agilent EclipsePlus C18 RRHP (2.1 × 50 mm, particle size 2.1 μm) analytical column. The eluents were 98% H2O, 2% ACN, and 0.05% formic acid (eluent A), and 2% H2O, 98% ACN, and 0.05% formic acid (eluent B). Flow rate: 200 μL / min -1 To separate the two components, the following gradient elution method was employed: Starting with 10% B for 1 minute, the concentration was linearly increased to 95% B after 10 minutes, held at 95% B for 30 minutes, and then returned to 10% B after 33 minutes. The column was equilibrated with 10% B, and measurements were taken for 15 minutes thereafter. The injection volume was 2 μL. Data were recorded using Agilent MassHunter Workstation LC / MS software version 11.0, and data analysis was performed using Agilent MassHunter Workstation Qualitative Analysis software version 10.0.

[0057] An Autoflex MALDI TOF mass spectrometer manufactured by Bruker Daltonik GmbH (28359 Bremen Fahrenheitstrasse 4, Germany), equipped with a MALDI TOF MS: smartbeam™ II Nd:YAG laser (355 nm), was used. Images were measured in linear mode. The matrix used was 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enilidene]malononitrile (DCTB).

[0058] An electrolytic cell equipped with an electrochemically activated nickel anode was prepared according to the following instructions and used in the subsequent reaction.

[0059] The geometric anode surface area is 10⁸ cm². 2 A flow-type electrolytic cell was used (Figure 2). The modular structure of the cell consisted of a self-supporting frame and a cage for foam electrodes (both with an effective geometric surface area of ​​108 cm²). 2 It consisted of ) and was particularly suitable for large-scale electrolysis in flow mode. Furthermore, heat dissipation through the channel on the back of the electrode was remarkable, allowing for superior temperature control compared to small, commercially available flow-type electrolytic devices where only the reservoir temperature can be adjusted to a specific temperature.

[0060] Figure 2 shows the reaction mechanism in a non-diaphragm flow electrolytic cell in which a stainless steel cathode and a nickel foam anode are in contact with a nickel-plated electrode. The electrode distance was 3 mm. For the cooling circuit, water was used to control the temperature between 25 and 50°C. The reaction mixture was emulsified using an IKA Magic lab mixing unit (IKA-Werke GmbH & Co. KG, Staufen, Germany) equipped with a DR mixing element.

[0061] Activation of nickel anodes: First, an activation solution containing 0.1 M NiSO4 (aq), 0.1 M NaOAc (aq), and 5 mM NaOH (aq) was prepared. This activation solution (420 mL) was placed in a polymethyl methacrylate (PMMA) beaker-type tank. A stainless steel electrode (6 × 18 cm) was immersed and connected. A nickel foam anode was immersed in a 1 M sodium hydroxide solution, or thoroughly washed with it, then dropwise dried, and then completely immersed and connected at a distance of 10 mm. 5.0 mA / cm -2 A current density of 9 C / cm was applied for 30 minutes. -2 This corresponds to the charge. This activation solution was stirred at 300 rpm. The activated dark nickel foam was then washed with demineralized water. The stainless steel cathode was cleaned by briefly immersing it in dilute sulfuric acid (4M), then rinsed with water and polished with sandpaper (300 grit) until a uniform shine was visible. The tank was then re-setup. SEM images showed that the original surface morphology was not completely reproduced by this cleaning process, but the activation method described above was effectively applicable to the cleaned nickel foam.

[0062] Performance of flow-type electrolytic cells: As described above, a commercially available modular IKA ESF 6-18 flow electrolytic device was used. This device is a non-diaphragm type and consists of a nickel foam anode (Recemat® RCM-Ni4753.05) connected by a nickel plate and a stainless steel cathode (1.4571), each with dimensions of 18 cm × 18 cm. 2 A polytetrafluoroethylene (PTFE) spacer (0.4 mm) was used. The nickel foam anode was activated as described above.

[0063] A commercially available IKA magic LAB® mixing unit was connected to an IKA magic PLANT® stirring vessel. An electrolyte containing NaOH(aq)(1M) and the corresponding cyclic 4-alkylcyclohexanol reaction product (1) was emulsified in the stirring vessel. This mixing unit, equipped with a high-performance DR mixing element, circulated the liquid to and from the storage vessel. The flow rate was 12,000 rpm (approximately 70 L / hour). It was supplied from the bottom of the upright flow-type tank by a peristaltic pump. The output tube was connected to the storage vessel to ensure the removal of generated hydrogen. A Python software controller and a TDK Lambda Genesys galvanostat were used to apply and monitor specified charge and current densities. After electrolysis was complete, the reaction mixture was discharged from the electrolytic cell in the reverse direction. The cell was then continuously washed with methyl tert-butyl ether (MTBE, 80 mL) and a 1 M sodium hydroxide solution (80 mL). All fractions were combined and post-processed by liquid-liquid extraction in a 2L perforator.

[0064] First, the non-acidic components were extracted from the basic aqueous reaction mixture using MTBE. After acidifying the pH to 1-2, the acidic components were extracted with ethyl acetate. The organic fraction was dried over MgSO4 to remove the solvent. The residual acidic fraction was weighed, and the product was extracted. 13 Quantitative analysis was performed by 13C reverse-gate NMR. 1,3,5-trimethoxybenzene (0.1 mmol) was used as an internal standard. Experimental Example 1:

[0065] [ka]

[0066] In the flow-type tank described above, an anodic oxidation reaction was carried out from 4-methylcyclohexanol (1') to 3-methyladipic acid (2').

[0067] Oxidation of 4-methylcyclohexanol: In a beaker (capacity: 100 mL), 4-methylcyclohexanol (1', 10 mmol, c=0.1 M, isomer mixture) was mixed with a 1 M sodium hydroxide solution. The vessel was maintained at 50°C using an external IKA-HBC-5 thermostat. Reaction rate: 61 mL / min -1 The electrolyte was passed through the electrolytic cell at a flow rate of 5.0 mA / cm². The applied current density was 5.0 mA / cm². -2 The temperature was set to 8.0F for the total charge. After the reaction, the product mixture was collected and acid-base extraction was performed by passing tert-butyl methyl ether through the vessel. For this purpose, the basic reaction medium was extracted three times with tert-butyl methyl ether (100 mL each time), acidified to pH 1-2 with 4.5 M sulfuric acid, and extracted four times with ethyl acetate (100 mL each time). After drying with MgSO4, the solvent was removed and the product mixture was analyzed by 1H and 13C reverse-gate NMR spectroscopy, compared to the internal standard 1,3,5-trimethoxybenzene.

[0068] Experimental Example 2: First, 4-ethylcyclohexanol was synthesized using the following method: 100 g of 4-ethylphenol (0.82 mol) was dissolved in 500 mL of methanol, and 10 g of ruthenium / activated carbon (5% C-supported Ru) was added to a 1 L autoclave. A hydrogen atmosphere (10 bar) was applied. The autoclave temperature was set to 120 °C. The yield of 4-ethylcyclohexanol (1'') was monitored by taking a sample (0.1 mL of reaction medium) daily. Product formation was monitored by gas chromatography, and the reaction was stopped when no product formation was observed. 4-ethylphenol was purchased from Sigma Aldrich, and ruthenium was purchased from Heraeus Chemicals. When 4-ethylcyclohexanol (1'') was synthesized on a 200 g scale, the isolation yield after vacuum distillation was a maximum of 95%.

[0069] Next, 3-ethyladipic acid was synthesized by electrochemical oxidation of 4-ethylcyclohexanol according to Scheme 1 below.

[0070] [ka]

[0071] The oxidation reaction was carried out using experimental design screening for parameters such as reaction temperature, flow rate, cyclic reactant concentration, and current density. In this experiment, a pre-activated nickel foam anode and a V5A stainless steel plate cathode were used. The reaction was carried out in a semistable emulsion of the cyclic reactant and 1M NaOH(aq) because the two liquids are immiscible under standard conditions.

[0072] For screening, a Masterflex® PharMed® BPT setup (L / S 16, long-term use tubing) was installed. Fluid flow was performed using a Masterflex® Ismatec® 78018-42 peristaltic pump. Continuous mixing was performed using an IKA Magic Lab / IKA Magic Plant System (IKA-Werke GmbH & Co. KG, Staufen, Germany) equipped with a DR mixing element. In all experiments, the mixing system was operated at 12,000 rpm (circulation rate approximately 70 L / hour) to achieve an optically semi-stable emulsion during the period from passing through the flow electrolytic cell to returning to the mixer. A charge of 9F was used in all reactions.

[0073] The reaction mixture was post-processed as follows: After each experiment, the reaction mixture was collected in a vial and passed through the electrolytic cell with tert-butyl methyl ether (50 mL) in circulation mode for 1 minute to minimize loss. The same procedure was followed for 1 M sodium hydroxide solution (50 mL). Subsequently, acid-base extraction was performed using a Ludwig perforator. Using a small stirrer bar makes it easier to achieve high-speed stirring. Also, the solvent needs to be replenished in the main compartment. The yellow basic reaction mixture was extracted overnight with MTBE. Subsequently, the two phases were separated, and the aqueous layer was acidified to pH 1-2 with 4.5 M H2SO4 (aq). The neutralized crude product was extracted with ethyl acetate using a perforator. The two organic fractions were dried with MgSO4, and after removing the solvent under reduced pressure, the products were analyzed by 13C reverse-gate NMR using 1,3,5-trimethoxybenzene as an internal standard.

[0074] The resulting carboxylic acid mixture was measured using a Vigreux column for 10 minutes. 0 -10 -2 The main product was distilled under reduced pressure at millibars at 180-220°C. The residual yellow substance was removed by recrystallization from heptane. If the ethyl ester of 3-ethyladipic acid was present, the product mixture was dissolved in sodium hydroxide solution (3M), heated to 80°C, and vigorously stirred for 3 hours. Next, in a very large separatory funnel, it was extracted with tert-butyl methyl ether (three times at one-third the volume of the aqueous solution), acidified to pH 2-3 with H2SO4 (aq) (4.5M), and extracted with ethyl acetate. The organic fraction was dried over MgSO4, and after removing the solvent, crystals were obtained. Higher purity was obtained by a second recrystallization.

[0075] In the parameter DoE screening, four parameters—cyclic reactant concentration c, reaction temperature T, reaction medium flow rate Φ, and current density j—were varied to reproduce the corresponding parameter limits shown in Table 1 below. In addition to the set parameter limits, center point tests were also performed. To confirm the reproducibility of the reaction, all experiments were repeated once, and the reaction order of these 18 chemical experiments was randomized. The reaction time ranged from 0.9 to 2.3 days. The quantitative NMR yield of the target product (2'') was approximately 40%. The maximum isolation yield was 39%. Since the nickel foam anode was reused in all reactions reported herein, waste was reduced.

[0076] Table 1: Parameters for DoE screening. Geometric current density is calculated based on the geometric anode surface area (10⁸ cm²) of the anode foam. 2 This is based on the current value for ). Reaction conditions: 1M NaOH(aq), water, activation current = 7.5mA / cm -2 (geometric current density), activation current = 10C / cm -2 9F. The reaction flow rate Φ is the cumulative flow rate through the two tubes. Each parameter has three data points.

[0077] [Table 1]

[0078] It was found that the flow rate and concentration of the reactants had the greatest impact on the yield of the target product. When the flow rate of the reactants was high (especially 30-50 mL / min), -1 Furthermore, low concentrations of the reactants (especially 0.2-0.35 M) have a positive effect on the yield of 3-ethyladipic acid.

[0079] The analytical product spectra from the oxidation reaction of 4-ethylcyclohexanol are shown below.

[0080] [ka]

[0081] Figure 3 shows a graphical evaluation of parameter results using a plot corresponding to the qNMR yield of 3-ethyladipic acid (2). The parameters tested were reaction temperature T (25°C, 37.5°C, 50°C) and reaction mixture flow rate Φ (10 mL / min). -1 ,30mL / min -1 ,50mL / min -1 ), concentrations of 4-ethylcyclohexanol (1) c (0.2 m, 0.35 m, 0.5 m), and applied reaction current density j (3.0 mA / cm²) -2 4.0mA / cm² -2 5.0mA / cm² -2 )

[0082] The screening results indicated a specific combination of the four parameters tested, namely a flow rate of 50 mL / min. -1 Reaction temperature 25°C, current density J5.0 mA / cm² -2 It was shown that the maximum yield could be obtained at a reactant concentration of 0.2 mol / l. Therefore, a yield of the target product (2'') significantly exceeding 30% can be achieved.

[0083] Using these parameters, we found that the maximum quantitative NMR yield of the product is as follows: YqNMR (3-ethyl adipic acid) = 38% YqNMR (3-ethylglutaric acid) = 4% YqNMR (2-ethylglutaric acid) = 4% YqNMR (ethyl succinic acid) = 1%

[0084] After post-treatment, 2'' was isolated in 38% yield. This is the most efficient isolation of 2'' by electrochemical synthesis reported to date. Characterization of 3-ethyladipic acid (2'')

[0085] [ka]

[0086] Product 2'' was electrochemically synthesized from 4-ethylcyclohexanol (6.41 g, 50 mmol, 0.2 M) using the method described above. Product 2'' was obtained as a pale yellow crystalline solid by acid-base extraction, vacuum distillation, and recrystallization from n-heptane (3.31 g, 19 mmol, 38%).

[0087] 1 H NMR (600 MHz, DMSO-d6): δ [ppm] = 12.04 (s, 2H), 2.18 (t, J = 7.9 Hz, 2H), 2.12 (d, J = 6.9 Hz, 2H), 1.68 (hept, J = 6.5 Hz, 1H), 1.57 - 1.42 (m, 2H), 1.33 - 1.21 (m, 2H), 0.81 (t, J = 7.5 Hz, 3H) 13 C NMR (151 MHz, DMSO-d6): δ [ppm] = 174.75, 174.29, 38.07, 35.41, 31.20, 28.17, 25.63, 10.69 Melting point: (47.4~49.8)℃ HRMS (ESI+) m / z: Calculated value of C8H14O4+H+: 175.0965 [M+H+]+, Measured value: 175.0965

[0088] Experimental Example 3: In the flow-type tank described above, an anodic oxidation reaction of 4-propylcyclohexanol to 3-propyladipic acid was carried out, and the change in the yield of 3-propyladipic acid during the reaction process was analyzed.

[0089] Figure 4 shows the change in the qNMR yield of 3-propyladipic acid with respect to the applied charge. The qNMR yield was analyzed relative to the 1,3,5-trimethoxybenzene standard.

[0090] The formation of 3-propyladipic acid was influenced by the formation of 4-propylcyclohexanone. The rate of 3-propyladipic acid formation was maximized at 1F after 4-propylcyclohexanone reached its maximum concentration. The final yield exceeded 30%.

[0091] Subsequently, in order to maintain a constant rate of 3-propyladipic acid production, the reaction conditions were modified to stabilize the concentration of 4-propylcyclohexanone as much as possible. For this purpose, a constant amount of the reactants was supplied in accordance with the rate of 3-propyladipic acid production.

[0092] Surprisingly, this experiment also yielded a high yield of the target product. This procedure has a positive effect on yield and also allows for continuous reactions.

[0093] Figure 5 shows the change in the qNMR yield of 3-propyladipic acid with respect to the amount of applied charge, in conjunction with the supply of 4-propylcyclohexanone. [Explanation of symbols]

[0094] 1. Flow-type electrolytic cell Self-supporting frame and cage for 2 electrodes 3 Mixer 4 Emulsion 5. Stainless steel electrodes 6. Nickel foam electrode 7 Nickel plate electrodes 8 Cooling circuit 9 Cooling circuit 10 Cooling circuit 11 pumps

Claims

1. (a) As a pretreatment of the metal electrode, a step of bringing the metal electrode into contact with a base, (b) A step of electrochemically activating the metal electrode pretreated according to step (a) without reversing the polarity of the metal electrode to form an outer metal oxyhydroxide layer, This is a method for electrochemically activating metal electrodes, including The metal electrode contains 0% to 100% by weight of nickel and 100% to 0% by weight of cobalt, relative to the total content of nickel and cobalt in the electrode, or contains 10% to 100% by weight of nickel and 0% to 90% by weight of iron, relative to the total content of nickel and iron in the electrode. A method wherein the metal electrode contains 10% by weight or less of another metal relative to the total metal content.

2. The method according to claim 1, wherein the metal electrode contains 5% by weight or less, more preferably 2% by weight or less, and particularly preferably 1% by weight or less, of other metals relative to the total metal content.

3. The method according to claim 1 or 2, wherein the metal electrode is a Ni(O)OH foam electrode, and the Ni(O)OH foam electrode contains, as a metal, nickel in particular at least 80% by weight, preferably at least 85% by weight, 90% by weight, 95% by weight, 98% by weight, or 99% by weight, more preferably at least 99.9% by weight, and most preferably at least 99.99% by weight.

4. As the pretreatment, the metal electrode is contacted with a base, at least one inorganic base and / or at least one organic base, preferably N(R Ａ ), ４ OH, N(R Ａ ), ４ acetate (wherein each R Ａ is independently H or linear or branched C １－４ -alkyl).), one or more bases selected from the group consisting of NaOH, sodium acetate, KOH, potassium acetate, LiOH, lithium acetate, Na ２ CO ３ , K ２ CO ３ and Li ２ CO ３ , more preferably one or more bases selected from the group consisting of NaOH and KOH, according to the method according to any one of claims 1 to 3.

5. The method according to claim 4, wherein the base is used in an aqueous solution, particularly at a base concentration of 10 mM to 10 M, preferably 0.2 to 5 M, more preferably 0.5 to 1.5 M, and very preferably 1 ± 0.1 M.

6. The method according to any one of claims 1 to 5, wherein the metal electrode is brought into contact with the base at a temperature of 10 to 40°C, preferably 18 to 27°C.

7. In the electrochemical activation of the metal electrode pretreated according to step (a) above, one or more salts of nickel and / or cobalt, and iron as needed, more preferably Ni ２ SO ４ and / or CoSO ４ The method according to any one of claims 1 to 6, wherein a salt selected from the group consisting of is used.

8. The salt is an aqueous basic solution, and one or more bases, preferably one base, are N(R) Ａ ) ４ OH, N(R Ａ ) ４ Acetate (wherein each R in the formula) Ａ Each of these is independently H or linear or branched C １－４ -It is alkyl.), NaOH, sodium acetate, KOH, potassium acetate, LiOH, lithium acetate, Na ２ CO ３ _K ２ CO ３ and Li ２ CO ３ The method according to claim 7, wherein the members are independently selected from the group consisting of the following, and more preferably selected from the group consisting of NaOH and KOH.

9. The method according to claim 7 or claim 8, wherein the metal electrode is electrochemically activated at a temperature of 10 to 40°C, preferably 18 to 27°C.

10. The method according to any one of claims 7 to 9, wherein the metal electrode is electrochemically activated with a charge amount of 2 to 10 coulombs, preferably 5 to 7 coulombs.

11. An electrochemically activated metal electrode obtained by the method described in any one of claims 1 to 10.

12. Use of the metal electrode according to claim 11 for carrying out an oxidation reaction of organic components.

13. Use of the metal electrode according to claim 11 for performing electrolysis of water.

14. Use of the metal electrode according to claim 11 in a battery.

15. Use of the metal electrode according to claim 11 in a catalyst.

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