METHOD FOR ELECTROCHEMICALLY PRODUCING ALKANE DICARBOXYLIC ACIDS BY MEANS OF A RING-OPENING OXIDATION USING A DOPED NI(O)OH FOAM ELECTRODE

Abstract

A method for the electrochemical preparation of alkanedicarboxylic acids involves a ring-opening oxidation with a doped Ni(O)OH foam electrode in an aqueous alkaline solution.

Claims

1-15. (canceled)

16. A method for the electrochemical preparation of alkanedicarboxylic acids, the method comprising: oxidizing a cyclic reactant in a ring-opening oxidation in an aqueous alkaline solution, wherein the oxidation is carried out at an Ni(O)OH foam electrode doped with at least one element of main group 5 and/or 6, according to Scheme (I): ##STR00025## wherein represents a single or double bond, R accordingly being present or not, wherein R is hydrogen or an acyl radical, wherein the acyl radical is a radical of an aliphatic monocarboxylic acid having 2 to l carbon atoms, and wherein A is a hydrocarbon having 4 to 30 carbon atoms, in which all ring carbon atoms of A in the cyclic reactant of scheme (I) bear at least one hydrogen substituent, and wherein the Ni(O)OH foam electrode comprises 2 to 10% by weight of phosphorus, the phosphorus being considered as an element and based on a metal mass of the Ni(O)OH foam electrode.

17. The method according to claim 16, wherein the Ni(O)OH foam electrode is doped with at least one selected from the group consisting of phosphorus, arsenic, selenium, and sulfur.

18. The method according to claim 16, wherein the Ni(O)OH foam electrode comprises 3 to 9% by weight of the phosphorus, the phosphorus being considered as an element and based on the metal mass of the electrode.

19. The method according to claim 16, wherein the Ni(O)OH foam electrode is two or more millimeters thick.

20. The method according to claim 16, wherein the Ni(O)OH foam electrode comprises nickel as metal.

21. The method according to claim 16, wherein the aqueous alkaline solution comprises up to 30% by volume of a cosolvent

22. The method according to claim 16, wherein an alkaline additive in the aqueous alkaline solution is lithium hydroxide, sodium hydroxide, or potassium hydroxide.

23. The method according to claim 22, wherein a concentration of the alkaline additive is 0.5 to 2 mol/l, based on the aqueous alkaline solution.

24. The method according to claim 16, wherein in scheme (I) when R=hydrogen and is a single bond, a concentration of cycloalkanols is 0.06 to 0.5 mol/l.

25. The method according to claim 16, wherein the ring-opening oxidation is according to Scheme (II): ##STR00026## wherein R.sup.1, R.sup.2, R.sup.3 are the same or different, and are hydrogen or alkyl radicals having 1 to 8 carbon atoms, linear or branched, in which at least one of R.sup.1, R.sup.2, R.sup.3 is an alkyl radical.

26. The method according to claim 16, wherein the method is carried out at a current density of 2 to 10 mA/cm.sup.2, the area referring to a geometric area without consideration of the inner surface area of the foam.

27. The method according to claim 16, wherein the method is carried out in a batch electrolytic cell or in a continuous flow electrolytic cell.

28. The method according to claim 16, wherein a cathode material is stainless steel, platinum, nickel, or a mixture thereof.

29. The method according to claim 16, wherein the method is carried out at a temperature of 20-70° C.

30. The method according to claim 20, wherein the Ni(O)OH foam electrode comprises the nickel in an amount of at least 80% by weight.

31. The method according to claim 22, wherein no further anions of bases are present in the aqueous alkaline solution other than the alkaline additive.

32. The method according to claim 24, wherein the concentration of cycloalkanols is 0.09 to 0.11 mol/l.

33. The method according to claim 25, wherein only one of R.sup.1, R.sup.2, R.sup.3 is an alkyl radical having 1 to 4 carbon atoms.

34. The method according to claim 25, wherein R.sup.1 and R.sup.3 are hydrogen and R.sup.2 is an alkyl radical having 1 to 4 carbon atoms.

35. The method according to claim 27, wherein the method is carried out in the continuous flow electrolytic cell.

Description

[0051] FIG. 1 shows the schematic design of a continuous flow reaction cell.

[0052] FIG. 2 shows the temperature dependency of the yield of the reaction in accordance with Table 1, entry 1, for the doped anode in the batch experiment.

ELECTRODES

[0053] All anodes used had the dimensions of length 60 mm, width 20 and thickness 6 mm. In the batch method, however, only half the area (length 30 mm) was immersed for carrying out the method according to the invention. The cathodes have the identical surface dimensions as the anodes, but composed as sheet metal. The thickness plays no essential role, in particular in the flow-through method only one surface is exposed to the reaction medium.

[0054] The nickel foam electrodes had a thickness of 0.35 to 0.44 g/cm.sup.3. This corresponds to a porosity of 95 to 96%.

[0055] The phosphorus-doped electrodes were obtained from Aqua Titan, Dortmund.

[0056] The Ni(O)OH layer of the anodes was formed in 280 ml of a solution of 0.1 mol/l NiSO.sub.4*6H.sub.2O, 0.1 mol/l NaOAc*3H.sub.2O, 0.005 mol/l NaOH in distilled water. The electrodes were fully immersed and coated at room temperature with pole changes (10 s) at 150 Coulomb and 10 mA/cm.sup.2. After reaction was complete, the electrodes were rinsed off and then dried.

RING-OPENING ELECTROOXIDATION

a) Batch Method

[0057] For the electrooxidation, the reaction cell was filled with water and the sodium hydroxide dissolved therein (1 mol/l ) and the substance to be oxidized (reactant according to scheme (I)) (25 ml). The concentration of reactant was 0.1 mol/l. Then, the stirred solution was temperature-controlled. The electrooxidation was carried out under galvanostatic conditions. The anode used in the experiments according to the invention was the doped Ni(O)OH foam electrode prepared above, in the non-inventive experiments identically constructed electrodes which had not been doped with phosphorus were in principle used, and stainless steel plate electrodes served as cathodes.

[0058] After completion of the reaction, the solution was quantitatively withdrawn (with post-rinsing with demineralized water and dichloromethane (20 ml each)) and extracted with dichloromethane (ratio by volume: water to organic solvent about 2:1). The remaining aqueous phase was adjusted to pH 1 with 50% sulfuric acid and extracted four times with diethyl ether (ratio by volume: water to organic solvent about 2:1). The organic phases (dichloromethane/diethylether) were both separately dried over sodium sulfate and the solvents were then removed on a rotary evaporator.

b) Flow-Through Method

[0059] The doped Ni(O)OH foam electrode prepared above was incorporated in a multilayered Teflon block in such a way that flow-through was complete, the inlet area size was 6 mm*20 mm and the direction of flow therefore longitudinal to the electrode. The cathode was attached separately through a slotted plate at a gap of less than one millimetre. The chamber was perfused vertically from bottom to top. The pump used was a Ritmo® 05 from Fink Chem+Tec GmbH & Co. KG.

[0060] The reaction solutions were used as in the batch method.

[0061] The processing was carried out as in the batch method.

NMR SPECTROSCOPY

[0062] .sup.1H- and .sup.13C-NMR spectra were recorded on a multinuclear resonance spectrometer of the AC 300 and AC II 400 type from Bruker Analytische Messtechnik, Karlsruhe. CDCL.sub.3 was used as solvent. The chemical shifts are specified here in ppm and relate to the proton signal of the deuterated solvent. The signals were then assigned with the aid of H-COSY, H,C-HSQC and H,C-HMBC experiments, wherein the final evaluation of the spectra was carried out using the MestReNova program (version: 7.01-8414).

[0063] The yields stated in the tables were determined by integration of the signals in the .sup.13C-NMR (inverse gated) against trimethoxybenzene standard. The yields are molar-related figures.

TABLE-US-00001 TABLE 1 Conversion examples of different alkylcycloalkanols (CH) to alkanedicarboxylic acids (DC) Entry Alkylcycloalkanol (CH) Alkanedicarboxylic acids (DC) 1 [00007] [00008] 2 [00009] [00010] 3 [00011] [00012] 4 [00013] [00014] 5 [00015] [00016] 6 [00017] [00018]

TABLE-US-00002 TABLE 2 Conversion examples of different alkylcycloalkanones (CO) to alkanedicarboxylic acids (DC) Entry Alkylcycloalkanones (CO) Alkanedicarboxylic acids (DC) 7 [00019] [00020] 8 [00021] [00022] 9 [00023] [00024]

TABLE-US-00003 TABLE 3 Effect of phosphorus doping on the yield of diverse alkylcycloalkanols (CH) according to table 1; non- doped anode is non-inventive (batch), doped anode (batch) and flow-through (doped anode) are inventive Non-doped anode Doped anode Flow- Temperature; Temperature; through Yield Current density, Yield Current density, Yield Entry [%] Amount of charge [%] Amount of charge [%] 1 53 20° C.; 63 20° C. 63 5 mA/cm.sup.2, 2.5 mA/cm.sup.2, 8.5 F. 8 F. 2 44 50° C. 54 2.5 mA/cm.sup.2, 8.5 F. 3 36 50° C. 66 2.5 mA/cm.sup.2, 8.5 F. 4 30 50° C. 42 45° C. 43 2.5 mA/cm.sup.2, 2.5 mA/cm.sup.2, 8.5 F. 8 F. 5 18 50° C. 43 20° C. 2.5 mA/cm.sup.2, 5 mA/cm.sup.2, 8.5 F. 8 F. 6 60 45° C. 2.5 mA/cm.sup.2, 8 F.

TABLE-US-00004 TABLE 4 Yield as a function of flow rate; Conversion in the flow-through cell (doped anode) (CH1 to DC1); 60 mA, 8 F., 20° C. Entry Flow rate [ml/min] DC1 [%] 1a 0.47*10E−3 51 1b 0.1 53 1c 1.0 56 1d 7.5 60 1e 10.0 62 1f 12.5 64

TABLE-US-00005 TABLE 5 Dependency of the yield on the alkali (1M = 1 mol/l) and on the solvent (ratio based on volume), conversion in batch mode with doped anode, CH1 to DC1 Entry Solvent Alkali addition DC 1 [%] 1-1 H.sub.2O 0.1M NaOH 20 1-2 H.sub.2O 0.5M NaOH 45 1-3 H.sub.2O 1.0M NaOH 51 1-4 H.sub.2O 2.0M NaOH 45 1-5 H.sub.2O 5.0M NaOH 16 1-6 H.sub.2O 1.0M K.sub.2CO.sub.3 3 1-7 H.sub.2O 1.0M KOH 50 1-8 H.sub.2O/tBuOH (3:7) 1.0M NaOH 1 1-9 H.sub.2O/tBuOH (2:1) 0.25M NaOH 26  1-10 H.sub.2O/tBuOH (1:1) 0.18M KOH 7  1-11 H.sub.2O/PE (1:1) 1.0M NaOH 16  1-12 H.sub.2O/DMSO (1:1) 1.0M NaOH 7  1-13 H.sub.2O/tAmylOH (2:1) 1.0M NaOH 27 tBuOH = tert butanol, PE = petroleum ether, DMSO = dimethyl sulfoxide, tAmylOH = tert amyl alcohol (2-methyl-2-butanol); 30 mA, 8 F., 20° C.

TABLE-US-00006 TABLE 6 Conversion of alkylcycloalkanones (CO) to alkanedicarboxylic acids (CD); reaction in batch mode with doped anode Doped anode Temperature; Yield Current density, Entry [%] Amount of charge 7 61 20° C. 2.5 mA/cm.sup.2, 6 F. 8 66 20° C. 2.5 mA/cm.sup.2, 6 F. 9 64 40° C. 2.5 mA/cm.sup.2, 6 F. Cyclooctyl acetate was converted in batch mode at the doped anode at 20° C., 5 mA/cm.sup.2 and 8 F. to octanediacid (DC6) in 30% yield.