A method for electrochemically producing alkane dicarboxylic acids by means of ring-opening oxidation using a doped Ni(O)OH foam electrode

Abstract

The present invention relates to a method for electrochemically preparing alkane dicarboxylic acids by ring-opening oxidation in an alkaline aqueous solution by means of a doped Ni(O)OH foam electrode.

Description

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

[0002] Johannes Kaulen and Hans-Jürgen (Tetrahedron 1982, 38(22), 3299 - 3308) discloses the conversion of unsubstituted cyclohexanol to unsubstituted adipic acid at a Ni(O)OH electrode. The electrode was designed as a plate electrode. The product was not actually separated in any case. Hans-Jürgen also obtained the same result (Topics in Current Chemistry, 1987, 142, 101 - 129).

[0003] Johannes Kaulen (“Oxidation of diols and secondary alcohols at the nickel hydroxide electrode. Application to the selective oxidation of hydroxysteroids”, Dissertation, University of Münster 1981) discloses a study on the electrochemical oxidation of cyclohexanol. He achieved significant conversion at a nickel hydroxide electrode at a relatively high temperature, partly due to the ring cleavage of adipic acid.

[0004] B.V. Lyalin and V.A. Petrosyan (Russian Journal of Electrochemistry, 2010, 46(11), 1199 - 1214) disclose the preparation of unsubstituted adipic acid and the oxidation of carbohydrates.

[0005] In “Electrosynthesis of adipic acid by undivided cell electrolysis” (Russian Chemical Bulletin, International Edition, Vol. 53 No. 3 pp. 688 - 692, March, 2004), the same authors disclosed the electro - chemical oxidative ring - cleavage of cyclohexanol to adipic acid at a nickel hydroxide electrode. The paper reported a maximum yield of adipic acid of 46.7% at a synchronous current yield of 11.5%. The by - products in the reaction were succinic acid and glutaric acid formed at yields of 6.3% and 11.5%, respectively. These components were formed by oxidative elimination of CH 2 groups from the C6 nuclear structure of cyclohexanol.

[0006] In one embodiment variant, EP 2907898 A1 (US 2015 / 0225861 A1) disclosed the use of nickel foam for the oxidative ring - cleavage of 3,3,5 - trimethylcyclohexanol at a reaction temperature of 80 °C. The reaction was carried out in a highly diluted solution with a low yield.

[0007] Schmitt et al. (Beilstein J. Org. Chem., 2015, 11, 473 - 480) disclosed the cleavage of lignin into different oxygen - substituted aromatic compounds using various electrodes. No oxidation to the corresponding acids occurred.

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

[0009] The method according to the invention is described below by way of example, without intending to limit the invention to these illustrative embodiments. In the case of the following specified ranges, general formulas or classes of compounds, these are not only intended to include the corresponding ranges or groups of the explicitly mentioned compounds, but also all sub - ranges and sub - groups of compounds that can be obtained by selecting individual values (ranges) or compounds. In the context of citing literature in this specification, its entire content is intended to form part of the disclosure of the present invention. If percentage data are provided below, these are expressed in wt% unless otherwise stated. In the case of a composition, unless otherwise stated, the % values are based on the total composition. Where average values are provided below, these are average values by mass (average values by weight) unless otherwise stated. Where measured values are given below, these are measured at a pressure of 101 325 Pa and a temperature of 25 °C unless otherwise stated.

[0010] Compared with the chemical oxidation method, the advantage of this method is to avoid the use of chemical oxidants such as nitric acid.

[0011] Another advantage is the high yield of the method according to the invention.

[0012] The implementation in the flow-through tank is technically simpler and more robust than all designs of the prior art. All mechanically laborious processes, such as the stirring process, can be omitted.

[0013] Therefore, the present invention first introduces the possibility of developing an industrially relevant continuous method for obtaining alkane dicarboxylic acids without using corrosive chemicals and still with a high yield.

[0014] In the method according to the invention, the alkane dicarboxylic acid (DC) is preferably prepared according to Scheme (I)

[0015]

[0016] where represents a single bond or a double bond, and R is correspondingly present or absent,

[0017] where R is hydrogen or an acyl group, and the acyl group is a group of an aliphatic monocarboxylic acid having 2 to 8 carbon atoms, preferably 2 to 5 carbon atoms, particularly preferably an acetyl group, and

[0018] where A is a hydrocarbon having 4 to 30 carbon atoms, and all ring carbon atoms of A in the cyclic reactant of Scheme (I) carry at least one hydrogen substituent, and A contains at least 2 ring carbon atoms, more preferably 3 to 9 ring carbon atoms.

[0019] In the case where is a single bond and R is hydrogen (cycloalkanediol), the method according to the invention is preferably carried out according to Scheme (II).

[0020]

[0021] R 1 、R 2 、R 3 can be the same or different and are hydrogen or a straight-chain or branched-chain alkyl group having 1 to 8 carbon atoms, preferably 1 to 5 carbon atoms, where the group R 1 、R 2 、R 3 in which at least one is an alkyl group.

[0022] More preferably, only one of the groups R 1 、R 2 、R 3 is an alkyl group having 1 to 4 carbon atoms. Particularly preferably, the groups R 1 and R 3 are hydrogen and R2 is an alkyl group having 1 to 4 carbon atoms.

[0023] In is a single bond and R is an acyl group (acyl cycloalkanol), the method according to the invention is preferably carried out according to Scheme (III).

[0024]

[0025] wherein the acyl group is an acetyl group, and

[0026] A is a hydrocarbon having 4 to 9 carbon atoms, wherein all ring carbon atoms of A in the cyclic reactant of Scheme (III) carry at least one hydrogen substituent, A contains at least 3 ring carbon atoms (acyl hexanol), more preferably 3 to 9 ring carbon atoms.

[0027] In is a double bond and R is absent (cycloalkanone), the method according to the invention is preferably carried out according to Scheme (IV).

[0028]

[0029] wherein A is a hydrocarbon having 4 to 9 carbon atoms, wherein all ring carbon atoms of A in the cyclic reactant of Scheme (IV) carry at least one hydrogen substituent, A contains at least 2 ring carbon atoms, more preferably 3 to 9 ring carbon atoms.

[0030] The method according to the invention is preferably carried out according to at least one of Scheme (II), (III) or (IV).

[0031] In all cases where the molecule / molecular fragment has one or more stereocenters or can be differentiated into isomers due to symmetry or can be differentiated into isomers due to other effects such as restricted rotation, the present invention encompasses all possible isomers.

[0032] Isomers are known to those skilled in the art; in particular, reference is made to the definition of Professor Kazmaier of the University of Saarland, for example http: / / www.uni-saarland.de / fak8 / kazmaier / PDF_files / vorlesungen / Stereochemie%20Strassb%20Vorlage.pdf.

[0033] The Ni(O)OH foam electrode preferably has a doping selected from phosphorus, arsenic, selenium and sulfur, more preferably a doping selected from phosphorus.

[0034] The number of the doping content refers to the elemental state of the doping based on the metal mass of the electrode.

[0035] The Ni(O)OH foam electrode preferably contains 2 to 10% by weight, preferably 3 to 9% by weight, more preferably 4 to 9% by weight of doping.

[0036] The Ni(O)OH foam electrode preferably contains 2 to 10% by weight, preferably 3 to 9% by weight, more preferably 4 to 9% by weight of phosphorus, where the phosphorus is regarded as an element and is based on the metal mass of the electrode.

[0037] The phosphorus doping content is preferably determined according to Appendix D.1 of DIN EN ISO 5427.

[0038] The Ni(O)OH foam electrode preferably has a thickness of two millimeters or more, more preferably greater than 3 mm, even more preferably greater than 5 mm, and particularly preferably equal to or thicker than 6 mm.

[0039] The Ni(O)OH foam electrode contains preferably at least 90% by weight, more preferably at least 95% by weight, 98% by weight, 99% by weight, even more preferably at least 99.9% by weight, and particularly preferably at least 99.99% by weight of nickel as the metal.

[0040] The Ni(O)OH foam electrode may contain other metals in addition to nickel. The other metals are preferably Co, Fe, and Cu.

[0041] Based on the total metal content, the content of other metals in the Ni(O)OH foam electrode is preferably equal to or less than 10% by weight, more preferably 5% by weight, even more preferably 2% by weight, and particularly preferably less than or equal to 1% by weight.

[0042] The Ni(O)OH foam electrode preferably contains at most 5% by weight, preferably 2% by weight, more preferably 1% by weight, particularly preferably 0.5% by weight, and particularly preferably at most 0.1% by weight of iron or iron compounds, where the content figures are based on the element relative to the total metal content.

[0043] The Ni(O)OH foam electrode preferably contains at most 1% by weight, preferably at most 0.1% by weight, more preferably at most 0.01% by weight of V, Wo, and Mo respectively; these metals are corroded in an alkaline aqueous medium, which may have an adverse effect on the method according to the present invention.

[0044] The available cathode materials are in principle any metals that are inert to the reaction medium. Stainless steel, platinum, or nickel or a mixture thereof is preferably used according to the present invention.

[0045] The method according to the present invention is carried out in an alkaline aqueous solution. Preferred co-solvents can be alcohols or DMSO. Based on the total amount of the solvent, preferably at most 30% by volume, more preferably 1 to 20% by volume of the co-solvent is present, and the solvent is more preferably composed of water.

[0046] Suitable alkaline additives in principle include all known inorganic bases. In the process according to the invention, alkali metal hydroxides such as LiOH, NaOH, KOH and soluble alkaline earth metal hydroxides are preferred. According to the invention, sodium hydroxide is particularly preferably used. Preferably, there are no anions of other bases.

[0047] Based on the alkaline aqueous solution, 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. The possible deviation of the molarity is at most 10%, preferably at most 5%.

[0048] In the process according to the invention, the concentration of the reactant according to Scheme (I) is preferably 0.06 to 0.5 mol / l, more preferably 0.08 to 0.3 mol / l, particularly preferably 0.09 to 0.11 mol / l.

[0049] According to theory, the total current leading to the conversion according to the invention according to Schemes (II) and (III) is 8 F. It is preferably 8 to 10 F, more preferably 8.5 to 9 F.

[0050] The unit F represents the Faraday, which is defined as the product of Avogadro's constant and the elementary charge of an electron: F = N A *e.

[0051] For the conversion according to Scheme (IV), theoretically 6 F is required. It is preferably 6 to 8 F, more preferably 6.5 to 7 F.

[0052] The process according to the invention is preferably carried out at a current density of 2 to 10 mA / cm 2 , more preferably 2.5 to 7.5 mA / cm 2 , particularly preferably 3.3 to 6 mA / cm 2 . The area refers to the geometric area of the inner surface area without considering the foam. These figures for the current density refer to the maximum area of one of the sides and are thus independent of the flow direction in the case of a flow-through cell.

[0053] The process according to the invention can be carried out discontinuously, for example, in a batch electrolytic cell, or continuously in a flow-through electrolytic cell (preferably in a continuous flow electrolytic cell).

[0054] The process according to the invention is preferably carried out at a temperature of 20 - 70 °C, preferably 30 - 60 °C, more preferably 35 - 50 °C.

[0055] The method according to the invention is also preferably carried out using a doped Ni(O)OH foam electrode, wherein the doping is selected from phosphorus, arsenic, selenium and sulfur, wherein the concentration of the base is 0.8 to 1.5 mol / l, and the concentration of the reactants according to Scheme (I) is 0.08 to 0.3 mol / l.

[0056] The method according to the invention is also preferably carried out using a Ni(O)OH foam electrode doped with phosphorus, wherein the concentration of the base is 0.8 to 1.5 mol / l, and the current density is 2 to 10 mA / cm 2 。

[0057] The method according to the invention is even more preferably carried out using a Ni(O)OH foam electrode doped with phosphorus according to Scheme (II)

[0058]

[0059] wherein R 1 、R 2 、R 3 are the same or different and are hydrogen or a straight-chain or branched-chain alkyl group having 1 to 8 carbon atoms, preferably 1 to 5 carbon atoms, wherein the groups R 1 、R 2 、R 3 at least one of which is an alkyl group,

[0060] wherein more preferably, only one of the groups R 1 、R 2 、R 3 is an alkyl group having 1 to 4 carbon atoms, particularly preferably, the groups R 1 and R 3 are hydrogen and R 2 is an alkyl group having 1 to 4 carbon atoms.

[0061] The method according to the invention is even more preferably carried out using a Ni(O)OH foam electrode doped with phosphorus according to Scheme (IV)

[0062]

[0063] wherein A is a hydrocarbon having 4 to 9 carbon atoms, wherein all the ring carbon atoms of A in the cyclic reactant of Scheme (IV) carry at least one hydrogen substituent, and A preferably contains 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 Ni(O)OH foam electrode doped with phosphorus in a flow cell, wherein the concentration of the base is 0.8 to 1.5 mol / l, and the concentration of the reactants according to Scheme (I) is 0.08 to 0.3 mol / l.

[0065] The method according to the invention is particularly preferably carried out in a flow-through cell using a Ni(O)OH foam electrode doped with phosphorus, wherein the concentration of the base is 0.8 to 1.5 mol / l, wherein the concentration of the reactants according to variant (I) is 0.08 to 0.3 mol / l, and wherein the flow rate of the reaction medium in the anode compartment is at least 5 cm / min, preferably at least 8 cm / min, more preferably at least 10 cm / min.

[0066] Figure 1 The schematic design of a continuous flow reaction cell is shown.

[0067] Figure 2 The temperature dependence of the reaction yield for the doped anode in the batch experiment according to entry 1 of Table 1 is shown.

[0068] electrode

[0069] All anodes used have dimensions of 60 mm in length, 20 mm in width and 6 mm in thickness. However, in the batch process, only half of the area (30 mm length) is immersed to carry out the method according to the invention. The cathode has the same surface dimensions as the anode but consists of a metal sheet. The thickness does not play an important role, especially in the flow-through process, where only one surface is exposed to the reaction medium.

[0070] The nickel foam electrode has a density (Dichte) of 0.35 to 0.44 g / cm 3 This corresponds to a porosity of 95% to 96%.

[0071] The phosphorus-doped electrodes were obtained from Aqua Titan, Dortmund.

[0072] In a solution of 280 ml of 0.1 mol / l NiSO 4 *6H 2 O, 0.1 mol / l NaOAc*3H 2 O, 0.005 mol / l NaOH in distilled water, the Ni(O)OH layer of the anode is formed. At room temperature, with a polarity change (10 s) at 150 coulombs and 10 mA / cm 2 , the electrode is completely immersed and coated. After the reaction is complete, the electrode is rinsed and then dried.

[0073] open-loop electrooxidation

[0074] a) Batch process

[0075] For electrooxidation, the reaction cell was filled with water and sodium hydroxide (1 mol / l) dissolved therein and the substance to be oxidized (reactant according to Scheme (I)) (25 ml). The concentration of the reactant was 0.1 mol / l. Then, the temperature of the stirred solution was controlled. The electrooxidation was carried out under constant current conditions. The anode used in the experiments according to the present invention was the doped Ni(O)OH foam electrode prepared above. In the experiments not according to the present invention, in principle, an electrode of the same structure without doped phosphorus was used, and a stainless steel plate electrode was used as the cathode.

[0076] After the reaction was completed, the solution was quantitatively taken out (post-rinsed with softened water and dichloromethane (20 ml each)), and extracted with dichloromethane (volume ratio: water to organic solvent was about 2:1). The remaining aqueous phase was adjusted to pH 1 with 50% sulfuric acid and extracted four times with diethyl ether (volume ratio: water to organic solvent was about 2:1). The organic phases (dichloromethane / ether) were each dried with sodium sulfate and then the solvent was removed on a rotary evaporator.

[0077] b) Flow method

[0078] The doped Ni(O)OH foam electrode prepared above was added to a multi-layer Teflon block in a way that the flow-through was completed. The inlet area was 6 mm * 20 mm, so the flow direction was longitudinal with respect to the electrode. The cathode was separately connected through a grooved plate with a gap of less than 1 mm. The chamber was vertically perfused from bottom to top. The pump used was from Fink Chem+Tec GmbH&Co.KG 05.

[0079] The reaction solution was used by the batch method.

[0080] The treatment was carried out by the batch method.

[0081] NMR spectroscopy

[0082] Recorded on multinuclear resonance spectrometers of type AC 300 and AC II 400 from Bruker Analytische Messtechnik, Karlsruhe 1 H- and 13 C-NMR spectra. CDCl 3 was used as the solvent. The chemical shifts are expressed in ppm here and refer to the proton signal of the deuterated solvent. Then the signals were assigned by means of H-COSY, H,C-HSQC and H,C-HMBC experiments, and the final evaluation of the spectra was carried out using the MestNova program (version: 7.01 - 8414).

[0083] By combining 13The signals in the 13C-NMR (inverse gated) are integrated relative to the trimethoxybenzene standard to determine the yields stated in the tables. The yields are mole-related numbers.

[0084] Table 1: Examples of the conversion of different alkyl cycloalkanols (CH) to alkane dicarboxylic acids (DC)

[0085]

[0086] Table 2: Examples of the conversion of different alkyl cycloalkanones (CO) to alkane dicarboxylic acids (DC)

[0087]

[0088]

[0089] Table 3: Influence of phosphorus doping on the yields of different alkyl cycloalkanols (CH) according to Table 1;

[0090] The undoped anode is non-inventive (batch),

[0091] The doped anode (batch) and flow-through (doped anode) are inventive

[0092]

[0093] Table 4: Relationship between yield and flow rate;

[0094] Conversion (CH1 to DC1) in the flow-through cell (doped anode); 60 mA, 8 F, 20 °C

[0095]

[0096] Table 5: Dependence of the yield on the base (1 M = 1 mol / l) and the solvent (volume-based ratio), conversion with a doped anode in batch mode, CH1 to DC1

[0097]

[0098] tBuOH = tert-butanol, PE = petroleum ether, DMSO = dimethyl sulfoxide, tAmylOH = tert-amyl alcohol (2-methyl-2-butanol); 30 mA, 8 F, 20 °C

[0099] Table 6: Conversion of alkyl cycloalkanone (CO) to alkane dicarboxylic acid (CD); reaction with a doped anode in batch mode

[0100]

[0101] At 20 °C, 5 mA / cm 2At 8F and below, cyclooctyl acetate was converted to suberic acid (DC6) in an intermittent mode at the doped anode with a yield of 30%.

Claims

1. A method for electrochemically preparing alkane dicarboxylic acids by ring-opening oxidation in an alkaline aqueous solution, characterized in that, According to Scheme (I), the oxidation is carried out at a Ni(O)OH foam electrode doped with phosphorus element Scheme (I) wherein represents a single bond or a double bond, and R is correspondingly present or absent, wherein R is hydrogen or acyl, wherein the acyl is a group of an aliphatic monocarboxylic acid having 2 to 8 carbon atoms, and wherein A is a hydrocarbon having 4 to 30 carbon atoms, wherein all ring carbon atoms of A in the cyclic reactant of Scheme (I) carry at least one hydrogen substituent, characterized in that the Ni(O)OH foam electrode contains 2 to 10% by weight of phosphorus, where the phosphorus is regarded as an element and is based on the metal mass of the electrode.

2. The method according to claim 1, characterized in that, the Ni(O)OH foam electrode contains 3 to 9% by weight of phosphorus, where the phosphorus is regarded as an element and is based on the metal mass of the electrode.

3. The method according to claim 1 or 2, characterized in that, the Ni(O)OH foam electrode is two millimeters or more thick.

4. The method according to claim 3, characterized in that, the Ni(O)OH foam electrode is more than 3 mm thick.

5. The method according to claim 3, characterized in that, the Ni(O)OH foam electrode is more than 5 mm thick.

6. The method according to claim 3, characterized in that, the Ni(O)OH foam electrode is equal to or more than 6 mm thick.

7. The method according to claim 1 or 2, characterized in that, the Ni(O)OH foam electrode contains nickel as the metal.

8. The method according to claim 7, characterized in that, the Ni(O)OH foam electrode contains at least 80% by weight of nickel as the metal.

9. The method according to claim 1 or 2, characterized in that, the aqueous solution means that there can be at most 30% by volume of a cosolvent in the solution.

10. The method according to claim 1 or 2, characterized in that, the alkaline additive of the aqueous solution is lithium hydroxide, sodium hydroxide or potassium hydroxide.

11. The method according to claim 10, characterized in that, there are no anions of other bases in the alkaline additive.

12. The method according to claim 1 or 2, characterized in that, based on the alkaline aqueous solution, the concentration of the alkaline additive is 0.5 to 2 mol / l, and the possible deviation of the molar concentration is at most 10%.

13. The method according to claim 12, characterized in that, based on the alkaline aqueous solution, the concentration of the alkaline additive is 0.8 to 1.5 mol / l.

14. The method according to claim 12, characterized in that, based on the alkaline aqueous solution, the concentration of the alkaline additive is 1 mol / l.

15. The method according to claim 12, characterized in that, the deviation of the molar concentration is at most 5%.

16. The method according to claim 1 or 2, characterized in that, The concentration of the cycloalkanol is 0.06 to 0.5 mol / l, where in Scheme (I), R = hydrogen and is a single bond.

17. The method according to claim 16, characterized in that, the concentration of cycloalkanol is 0.08 to 0.3 mol / l.

18. The method according to claim 16, characterized in that the concentration of the cycloalkanols is from 0.09 to 0.11 mol / l.

19. The method according to claim 1 or 2, characterized in that the method is carried out according to Scheme (II), wherein R 1 , R 2 , R 3 are the same or different and are hydrogen or a straight-chain or branched-chain alkyl group having 1 to 8 carbon atoms, wherein at least one of the groups R 1 , R 2 , R 3 is an alkyl group.

20. The method according to claim 19, characterized in that R 1 、R 2 、R 3 are the same or different and are straight-chain or branched-chain alkyl groups having 1 to 5 carbon atoms.

21. The method according to claim 19, characterized in that Group R 1 , R 2 , R 3 Only one of them is an alkyl group having 1 to 4 carbon atoms.

22. The method according to claim 19, characterized in that Group R 1 and R 3 is hydrogen and R 2 is an alkyl group having 1 to 4 carbon atoms.

23. The method according to claim 1 or 2, characterized in that The method is carried out at a current density of 2 to 10 mA / cm 2 , and the area refers to the geometric area without considering the inner surface area of the foam.

24. The method according to claim 23, characterized in that The method is carried out at a current density of 2.5 to 7.5 mA / cm 2 .

25. The method according to claim 23, characterized in that The method is carried out at a current density of 3.3 to 6 mA / cm 2 .

26. The method according to claim 1 or 2, characterized in that the electrolysis is carried out in a batch electrolytic cell or a continuous flow electrolytic cell.

27. The method according to claim 26, characterized in that the electrolysis is carried out in a continuous flow electrolytic cell.

28. The method according to claim 1 or 2, characterized in that the cathode material used is stainless steel, platinum or nickel or a mixture thereof.

29. The method according to claim 1 or 2, characterized in that the electrolysis is carried out at a temperature of 20 - 70 °C.

30. The method according to claim 29, characterized in that the electrolysis is carried out at a temperature of 30 - 60 °C.

31. The method according to claim 29, characterized in that the electrolysis is carried out at a temperature of 35 - 50 °C.

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