Electrochemical production of alkanedicarboxylic acids by ring-opening oxidation using doped Ni(O)OH foam electrodes

Abstract

The present invention relates to a method for the electrochemical preparation of alkanedicarboxylic acids by ring-opening oxidation using a doped Ni(O)OH foam electrode in aqueous alkaline solution.

Description

[Technical Field]

[0001] The present invention relates to an electrochemical method for the preparation of alkanedicarboxylic acids by ring-opening oxidation using a doped Ni(O)OH foam electrode in aqueous alkaline solution. [Background technology]

[0002] Johannes Kaulen and Hans-Jurgen SchaFer (Tetrahedron 1982, 38(22), 3299-3308) have described the conversion of unsubstituted cyclohexanol to unsubstituted adipic acid at a Ni(O)OH electrode. The electrode was designed as a plate electrode. In no case was the product actually isolated. The same result was also obtained by Hans-Jurgen SchaFer (Topics in Current Chemistry, 1987, 142, 101-129).

[0003] Johannes Kaulen ("Oxidation of diols and secondary alcohols at nickel hydroxide electrodes. Application to the selective oxidation of hydroxysteroids", Doctoral dissertation, University of Munster, 1981) presents a study on the electrochemical oxidation of cyclohexanol. Using a nickel hydroxide electrode, the author achieved a significant conversion at relatively high temperatures, which was accompanied in part by the ring-opening formation of adipic acid.

[0004] BV Lyalin and VA Petrosyan (Russian Journal of Electrochemistry, 2010, 46(11), 1199-1214) disclose the preparation of unsubstituted adipic acid and its use in the oxidation of carbohydrates.

[0005] In "Electrosynthesis of Adipic Acid by Undivided Cell Electrolysis" (Russia, Chemical Bulletin, International Edition, Vol. 53 No. 3 pp. 688-692, March 2004), the same authors report the electrochemical ring-opening oxidation of cyclohexanol to produce adipic acid. The paper reports a maximum yield of 46.7% for adipic acid, with a current yield of 11.5%. Succinic acid and glutaric acid are produced as by-products, with yields of 6.3% and 11.5%, respectively. These compounds are formed by the oxidative removal of CH groups from the C6 core structure of cyclohexanol.

[0006] In one embodiment variant, EP2907898A1 (US2015 / 0225861A1) discloses the use of nickel foam for the ring-opening oxidation of 3,3,5-trimethylcyclohexanol at a reaction temperature of 80° C. The reaction was carried out in a fairly dilute solution, and the yield was low.

[0007] Schmitt et al. (Beilstein J. Org. Chem., 2015, 11, 473-480) have demonstrated the cleavage of lignin in a variety of oxo-substituted aromatics using various electrodes, without oxidation to the corresponding acids. DISCLOSURE OF THE INVENTION

[0008] The present invention relates to a method for the electrochemical preparation of alkanedicarboxylic acids by ring-opening oxidation using a Ni(O)OH foam electrode doped with elements of main group 5 and / or 6 in aqueous alkaline solution.

[0009] The method according to the present invention will be described below by way of example, but it is not intended that the present invention be limited to these exemplary embodiments. When ranges, general formulas, or classes of compounds are described below, these are intended to include not only the corresponding ranges or groups of compounds explicitly described, but also all subranges and subgroups of compounds obtained by extracting individual values ​​(ranges) or compounds. When references are cited in the context of this specification, the entire contents are intended to be part of the disclosure of the present invention. When percentage data are described below, they are weight percent data unless otherwise specified. For compositions, percentage values ​​are based on the total composition unless otherwise specified. When average values ​​are described below, they are mass averages (weight averages) unless otherwise specified. When measured values ​​are described below, they are values ​​measured at a pressure of 101,325 Pa and a temperature of 25°C unless otherwise specified.

[0010] The advantage of this method compared to chemical oxidation methods is that it avoids the use of chemical oxidizing agents such as nitric acid.

[0011] A further advantage is the high yield of the process according to the invention.

[0012] Implementation in a flow-through cell is technically simpler and more robust than any prior art design: mechanically demanding steps such as stirring steps can be entirely omitted.

[0013] The present invention thus offers for the first time the possibility of developing an industrially suitable continuous process for obtaining alkanedicarboxylic acids in high yields without the use of aggressive chemicals.

[0014] In the process according to the invention, the alkanedicarboxylic acid (DC) is preferably prepared according to formula (I).

[0015] [ka]

[0016] In formula (I),

[0017] [ka]

[0018] represents a single or double bond, and therefore R is present or absent accordingly; R is hydrogen or an acyl radical, the acyl radical being the radical of an aliphatic monocarboxylic acid having 2 to 8 carbon atoms, preferably 2 to 5 carbon atoms, particularly preferably acetyl; A is a hydrocarbon having 4 to 30 carbon atoms, and all ring carbon atoms of A in the cyclic reactant of formula (I) have at least one hydrogen substituent; and A contains at least 2 ring carbon atoms, more preferably 3 to 9 ring carbon atoms.

[0019] [ka]

[0020] When is a single bond and R is hydrogen (cycloalkanol), the process according to the invention is preferably carried out according to formula (II):

[0021] [ka]

[0022] In formula (II), R 1 , R 2 , R 3 are the same or different, hydrogen or linear or branched alkyl radicals having 1 to 8 carbon atoms, preferably 1 to 5 carbon atoms, and the radical R 1 , R 2 , R 3 At least one of is an alkyl radical.

[0023] More preferably, the radical R 1 , R 2 , R 3and only one of the radicals R is an alkyl radical having 1 to 4 carbon atoms. 1 and R 3 is hydrogen and R 2 is an alkyl radical having 1 to 4 carbon atoms.

[0024] [ka] When is a single bond and R is an acyl radical (acylcycloalkanol), the process according to the invention is preferably carried out according to formula (III):

[0025] [ka]

[0026] In formula (III), the acyl radical is acetyl, A is a hydrocarbon having 4 to 9 carbon atoms, and all ring carbon atoms of A in formula (III) have at least one hydrogen substituent, and A consists of at least 3 ring carbon atoms (acylhexanol), more preferably 3 to 9 ring carbon atoms.

[0027] [ka]

[0028] When is a double bond and R is absent (cycloalkanone), the process according to the invention is preferably carried out according to formula (IV):

[0029] [ka]

[0030] In formula (IV), A is a hydrocarbon having 4 to 9 carbon atoms, and all ring carbon atoms of A in the cyclic compound in formula (IV) have at least one hydrogen substituent, and A consists of at least two ring carbon atoms, more preferably 3 to 9 ring carbon atoms.

[0031] The process according to the present invention is preferably carried out according to at least one of formulas (III), (III) and (IV).

[0032] In all cases where a molecule / molecular fragment has one or more stereocenters or can be differentiated into isomers due to symmetry or other effects, such as rotational restrictions, all possible isomers are covered by the present invention.

[0033] Isomers are known to those skilled in the art, see in particular the definitions of Professor Kazmaier of the University of Saarland, e.g. http: / / www.unisaarland.de / Fak8 / kazmaier / PDF_Files / vorlesungen / Stereochemie%20Strassb%20vorlage.pdf.

[0034] The Ni(O)OH foam electrode preferably has a doping selected from phosphorus, arsenic, selenium and sulfur, more preferably selected from phosphorus.

[0035] The value of the doping content indicates the state of the doping element based on the mass of the metal of the electrode.

[0036] The Ni(O)OH foam electrode preferably contains 2-10 wt %, more preferably 3-9 wt %, more preferably 4-9 wt % doping.

[0037] The Ni(O)OH foam electrode preferably contains a doping of 2-10 wt%, more preferably 3-9 wt%, more preferably 4-9 wt%, of phosphorus, where phosphorus is considered as an element and based on the metallic mass of the electrode.

[0038] The phosphorus doping content is preferably determined in accordance with DIN EN ISO 5427, Appendix D.1.

[0039] The Ni(O)OH foam electrode is preferably 2 millimeters or thicker, more preferably 3 mm or thicker, even more preferably 5 mm or thicker, and most preferably 6 mm or thicker.

[0040] The Ni(O)OH foam electrode contains nickel as the metal, preferably at least 90% by weight, more preferably at least 95, 98, 99% by weight, even more preferably 99.9% by weight or more, and particularly preferably 99.99% by weight or more of nickel.

[0041] The Ni(O)OH foam electrode may contain additional metals other than nickel, preferably Co, Fe and Cu.

[0042] The content of other metals in the Ni(O)OH foam electrode is preferably 10% by weight or less, more preferably 5% by weight or less, even more preferably 2% by weight or less, and particularly preferably 1% by weight or less, based on the total metal content.

[0043] The Ni(O)OH foam electrode preferably contains at most 5% by weight, preferably 2% by weight, more preferably 1% by weight, particularly preferably at most 0.1% by weight of iron or iron compounds, the content values ​​being elemental values ​​based on the total metal content.

[0044] The Ni(O)OH foam electrode preferably contains at most 1% by weight of each of V, Wo and Mo, preferably at most 0.1% by weight of each, more preferably at most 0.01% by weight of each, these metals corroding in alkaline aqueous media, which may have an adverse effect on the method according to the invention.

[0045] Useful cathode materials are in principle any metal inert to the reaction medium. Preferably, those used in accordance with the invention are stainless steel, platinum or nickel or mixtures thereof.

[0046] The process according to the present invention is carried out in an alkaline aqueous solution. Preferred co-solvents can be alcohols or DMSO. Up to 30% by volume of the co-solvent, more preferably 1-20% by volume, based on the total solvent, is suitable, and the solvent is more preferably water.

[0047] Suitable alkaline additives include, in principle, all known inorganic bases.In the method according to the present invention, alkali metal hydroxides, such as LiOH, NaOH, KOH, and soluble alkaline earth metal hydroxides are preferred.In accordance with the present invention, it is particularly preferred to use sodium hydroxide.Preferably, no other basic anions are present.

[0048] The concentration of the alkaline additive is preferably 0.5 to 2 mol / l, more preferably 0.8 to 1.5 mol / l, particularly preferably 1 mol / l, based on the aqueous alkaline solution, with a maximum deviation of 10%, preferably a maximum deviation of 5%, in terms of molar amount.

[0049] In the process according to the invention, the concentration of the reactant according to formula (I) is preferably 0.06 to 0.5 mol / l, more preferably 0.08 to 0.3, particularly preferably 0.09 to 0.11 mol / l.

[0050] The total current that brings about the conversion according to the present invention in accordance with formulas (II) and (III) is theoretically 8 F, preferably 8 to 10 F, more preferably 8.5 to 9 F.

[0051] The unit quantity F is the Faraday, and the product of Avogadro's constant and the elementary charge F=N A * Defined by e.

[0052] Theoretically, 6F is required for the conversion according to formula (IV), preferably 6 to 8F, more preferably 6.5 to 7F.

[0053] The method according to the present invention preferably uses a current of 2 to 10 mA / cm 2 , more preferably 2.5 to 7.5 mA / cm 2, and particularly preferably 3.3 to 6 mA / cm 2 The current density is measured at a current density of 1000 sq. m / s. Note that the area is the geometric area, not taking into account the internal area of ​​the foam. These current density figures refer to the maximum area of ​​one side and are therefore independent of the direction of flow in the case of a flow-through electrolysis cell.

[0054] The process according to the invention can be carried out discontinuously, for example in a batch electrolysis cell, or continuously in a flow-through electrolysis cell, preferably in a continuous flow electrolysis cell.

[0055] The process according to the present invention is preferably carried out at a temperature of 20 to 70°C, preferably 30 to 60°C, more preferably 35 to 50°C.

[0056] The method according to the invention is also preferably carried out using a doped Ni(O)OH foam electrode, the doping being selected from phosphorus, arsenic, selenium and sulfur, the concentration of the alkali being 0.8-1.5 mol / l and the concentration of the reactant according to formula (I) being 0.08-0.3 mol / l.

[0057] The method according to the invention is also preferably carried out using a phosphorus-doped Ni(O)OH foam electrode, the alkali concentration being 0.8-1.5 mol / l and the current density being 2-10 mA / cm. 2 is.

[0058] The method according to the present invention comprises:

[0059] [ka]

[0060] It is even more preferred that this is carried out using a phosphorus-doped Ni(O)OH foam electrode according to In formula (II), R 1 , R 2 , R 3are the same or different, hydrogen or linear or branched alkyl radicals having 1 to 8 carbon atoms, preferably 1 to 5 carbon atoms, and the radical R 1 , R 2 , R 3 at least one of which is an alkyl radical, more preferably a radical R 1 , R 2 , R 3 and only one of the radicals R is an alkyl radical, particularly preferably 1 and R 3 is hydrogen and R 2 is an alkyl radical having 1 to 4 carbon atoms.

[0061] The method according to the present invention comprises:

[0062] [ka]

[0063] It is further preferred that the method is carried out using a phosphorus-doped Ni(O)OH foam electrode according to In formula (IV), A is a hydrocarbon having 4 to 9 carbon atoms, and all of the ring carbon atoms of A in the cyclic reactant of formula (IV) have at least one hydrogen substituent, and A preferably consists of at least 2 ring carbon atoms, more preferably 3 to 9 ring carbon atoms.

[0064] The method according to the invention is more preferably carried out using a phosphorus-doped Ni(O)OH foam electrode in a flow-through cell, the alkali concentration being between 0.8 and 1.5 mol / l and the concentration of the reactant according to formula (I) being between 0.08 and 0.3 mol / l.

[0065] The method according to the invention is particularly preferably carried out in a flow-through cell using a phosphorus-doped Ni(O)OH foam electrode, in which the concentration of alkali is between 0.8 and 1.5 mol / l, the concentration of reactant according to formula (I) is between 0.08 and 0.3 mol / l and the flow rate of the reaction medium in the anode compartment is at least 5 cm / min, preferably at least 8 cm / min and more preferably at least 3 cm / min. [Brief explanation of the drawings]

[0066] [Figure 1] FIG. 1 is a schematic diagram of a continuous flow reaction cell. [Figure 2] FIG. 2 shows the temperature dependence of the yield of the reaction according to item 1 of Table 1 for doped anodes in batch experiments. DETAILED DESCRIPTION OF THE INVENTION

[0067] electrode The anodes used all had dimensions of 60 mm long, 20 mm wide, and 6 mm thick. However, in the batch process, only half of the area (30 mm long) was immersed to carry out the process according to the invention. The cathode had the same surface dimensions as the anode, but was constructed as a metal sheet. The thickness did not play an essential role, especially in the flow-through process, where only one side was exposed to the reaction medium.

[0068] The density of the nickel foam electrode is 0.35 to 0.44 g / cm 3 This corresponds to a porosity of 95 to 96%.

[0069] Phosphorus-doped electrodes were obtained from Aqua Titan, Dortmund.

[0070] The Ni(O)OH layer on the anode was prepared using 0.1 mol / l NiSO4 in distilled water. * 6H2O, 0.1mol / l NaOAc *The electrode was fully immersed in a 280 ml solution of 0.005 mol / l 3H2O. The electrode was then subjected to a polarity change (10 seconds) at room temperature with a current of 150 coulombs and 10 mA / cm. 2 After the reaction was completed, the electrode was rinsed and dried.

[0071] Ring-opening electrooxidation a) Batch method For the electro-oxidation, the reaction cell was filled with water, and sodium hydroxide (1 mol / L) was dissolved in the water and oxidized (reactant according to formula (I)) (25 ml). The concentration of the reactant was 0.1 mol / L. The stirred solution was then temperature-controlled. The electro-oxidation was carried out under constant current conditions. The anode used in the experiments according to the present invention was a doped Ni(O)OH foam electrode prepared as described above. In experiments outside the present invention, an electrode of the same structure but not doped with phosphorus was used as a rule, and a stainless steel plate electrode served as the cathode.

[0072] After the reaction was completed, the solution (which had been washed with demineralized water and dichloromethane (20 ml each)) was quantitatively extracted with dichloromethane (water to organic solvent volume ratio of approximately 2:1). The remaining aqueous phase was adjusted to pH 1 with 50% sulfuric acid and extracted four times with diethyl ether (water to organic solvent volume ratio of approximately 2:1). The organic phases (dichloromethane / diethyl ether) were dried separately with sodium sulfate, and then the solvent was removed on a rotary evaporator.

[0073] b) Flow-through method The doped Ni(O)OH foam electrode was fully integrated into a multilayer Teflon block in a flow-through configuration, with an inlet area of ​​6 mm × 20 mm and flow direction along the length of the electrode. The cathode was mounted separately through a slotted plate with a gap of less than 1 mm. The chamber was perfused vertically from bottom to top. The pump used was a Ritmo® pump manufactured by Fink Chem+Tec GmbH & Co. KG.

[0074] The reaction mixture was used in the same manner as in the batch method.

[0075] The process was carried out in the same manner as in the batch process.

[0076] NMR spectroscopy 1 H- and 13 C-NMR spectra were recorded on AC 300 and AC II 400 type multinuclear resonance spectrometers at Bruker Analytische Messtechnik GmbH, Karlsruhe. CDCl3 was used as the solvent. Chemical shifts are specified here in ppm and are relative to the proton signals of the deuterated solvent. The signals were assigned by H-COSY, H, C-HSQC, and H, C-HMBC experiments. Final evaluation of the spectra was performed using the MestReNova program (version 7.01-8414).

[0077] The yields shown in the table are based on trimethoxybenzene standards. 13 The yield was calculated by integrating the C-NMR (inverse gate) signal. The yield is expressed in terms of moles.

[0078] Table 1: Examples of conversion of various alkylcycloalkanols (CH) to alkanedicarboxylic acids (DC)

[0079] [Table 1]

[0080] Table 2: Examples of conversion of various alkylcycloalkanones (CO) to alkanedicarboxylic acids (DC)

[0081] [Table 2]

[0082] Table 3: Effect of phosphorus doping on the yields of various alkylcycloalkanols (CH) according to Table 1 The undoped anode is outside the scope of the present invention (batch), Doped anode (batch) and flow-through (doped anode) are aspects of the present invention.

[0083] [Table 3]

[0084] Table 4: Yield as a function of flow rate Conversion (CH1 to DC1) in flow-through cell (doped anode): 60 mA, 8 F, 20°C

[0085] [Table 4]

[0086] Table 5: Dependence of yield on alkali (1M = 1 mol / l) and solvent (volume-based ratio), conversion in batch mode with doped anodes, CH1 to DC1

[0087] [Table 5]

[0088] tBuOH = tert-butanol PE = petroleum ether DMSO = dimethyl sulfoxide tAmylOH = tert-amyl alcohol (2-methyl-2-butanol); 30 mA, 8 F, 20 °C

[0089] Table 6: Conversion of alkylcycloalkanones (CO) to alkanedicarboxylic acids (CD); Reactions in batch mode with doped anodes

[0090] [Table 6]

[0091] Cycloctyl acetate: 20°C, 5 mA / cm 2, and was converted to octanediacid (DC6) in a batch mode with a 8F-doped anode in 30% yield.

Claims

1. 1. A method for the electrochemical preparation of alkanedicarboxylic acids by ring-opening oxidation in aqueous alkaline solution, comprising: The ring-opening oxidation is carried out by the reaction of a compound represented by formula (I) 【Chemistry 1】 on a Ni(O)OH foam electrode doped with elements of main group V and / or VI according to (In formula (I), 【Chemistry 2】 represents a single or double bond, and therefore R is either present or absent; R is hydrogen or an acyl radical, the acyl radical being the radical of an aliphatic monocarboxylic acid having 2 to 8 carbon atoms; A is a hydrocarbon having from 4 to 30 carbon atoms, and every ring carbon atom of A in the cyclic reactant of formula (I) has at least one hydrogen substituent; The Ni(O)OH foam electrode contains 2 to 10 wt % of phosphorus as an element relative to the mass of the metal contained in the Ni(O)OH foam electrode. Electrochemical preparation of alkanedicarboxylic acids by ring-opening oxidation in an aqueous alkaline solution.

2. 2. The method of claim 1, wherein the Ni(O)OH foam electrode contains 3 to 9 weight percent phosphorus as an element, based on the mass of metal contained in the Ni(O)OH foam electrode.

3. 3. The method of claim 1, wherein the Ni(O)OH foam electrode is 2 millimeters or more thick.

4. The method according to any one of claims 1 to 3, characterized in that the Ni(O)OH foam electrode contains nickel as the metal.

5. 5. The method according to claim 1, wherein the aqueous alkaline solution contains up to 30% by volume of a co-solvent.

6. 6. The method according to claim 1, wherein the alkaline additive of the alkaline aqueous solution is lithium hydroxide, sodium hydroxide or potassium hydroxide.

7. 7. The method according to claim 6, characterized in that the concentration of the alkaline additive is 0.5 to 2 mol / l, based on the aqueous alkaline solution, allowing a maximum deviation in molar amount of 10%.

8. In formula (I), R is hydrogen; 【Transformation 3】 The method according to any one of claims 1 to 7, wherein the concentration of the cycloalkanol in which is a single bond is 0.06 to 0.5 mol / L. 【Request Item 9】 【Chemistry 4】 is carried out in accordance with In formula (II), R 1 , R 2 , R 3 are the same or different, hydrogen or linear or branched alkyl radicals having 1 to 8 carbon atoms, and the radical R 1 , R 2 , R 3 9. The method according to claim 1, wherein at least one of the radicals is an alkyl radical.

10. 2 to 10 mA / cm 2 10. Any one of claims 1 to 9, characterized in that the current density is 2. The method according to claim 1.

11. The method according to any one of claims 1 to 10, characterized in that the electrolysis is carried out in a batch electrolysis cell or a continuous flow electrolysis cell.

12. 12. A method according to any one of claims 1 to 11, characterized in that the cathode material used is stainless steel, platinum, nickel or mixtures thereof.

13. 13. The method according to any one of claims 1 to 12, characterized in that the electrolysis is carried out at a temperature of from 20 to 70°C.

Images