A SOLUTION OF TEMPO-DERIVATIVES FOR USE AS ELECTROLYTE IN REDOX-FLOW CELLS

Abstract

The present invention relates to a solution comprising water and different 2,2,6,6-tetramethyl-piperidinyl-oxyl (TEMPO)-derivatives, a process for the production of this solution, a process for making a redox-flow cell comprising the solution as electrolyte, the redox-flow cell comprising the solution as an electrolyte in one chamber of the cell and the use of the redox-flow cell for storing electrical energy.

Claims

1.-16. (canceled)

17. A solution comprising a) water, b) 20 to 55 wt.-% according to the total weight amount of the solution of compound 2,2,6,6-tetramethyl-4-(trimethylammonio)-1-piperidinyloxy of formula (I), ##STR00014## c) 0.1 to 6 wt.-% according to the total weight amount of the solution alkali metal cation d) 0.5 to 12.5 wt.-% according to the total weight amount of the solution of compound N,N,N,1,2,2,6,6-octamethyl-4-piperidinammonium-1-oxide of formula (II) ##STR00015## e) 0.1 to 20 wt.-% according to the total weight amount of the solution of compound 2,2,6,6-hexamethyl-4-(dimethylamino)-1-piperidinyloxy-N-oxide of formula (III) ##STR00016##

18. The solution according to claim 17 wherein the alkali metal cation is Na.

19. The solution according to claim 17 wherein the solution has a pH-value in the range of 2 to 7.

20. The solution according to claim 17 wherein the sum of the amounts of the compounds of formula (I), (II), (III) plus the amount of alkali metal cations in the solution is in the range of 20 to 50 wt.-% according to the total weight amount of the solution.

21. The solution according to claim 17 wherein at least 90 mol % of the counterions are chloride ions.

22. A process for the production of the solution according to claim 17 comprising the following steps: i) reacting the compound N,N,2,2,6,6-hexamethyl-4-piperidinamine of formula (IV) ##STR00017## with water and methyl chloride to get an aqueous mixture comprising compound N,N,N,2,2,6,6-heptamethyl-4-piperidinaminium of formula (V), compound N,N,N,1,2,2,6,6-octamethyl-4-piperidinaminium of formula (VI) and non-reacted compound N,N,2,2,6,6-hexamethyl-4-piperidinamine of formula (IV) ##STR00018## ii) reacting the resulting aqueous mixture of step i) with an aqueous hydrogen peroxide solution in the present of a catalyst selected from the group of alkali metal carbonate, alkali metal hydrogencarbonate, CO.sub.2 and mixtures of those, iii) adding an acid to the resulting mixture of step ii) until the pH-value decreases in the range of 2 to 7, iv) partially removing water until the concentration of compound of formula (I) is in the range of 20 to 55 wt.-% according to the solution of claim 17.

23. The process of claim 22 wherein in step i) of the process the compound of formula (IV) is reacted with methyl chloride and water at a temperature in the range of 0 to 60° C.

24. The process according to claim 22 wherein in step i) of the process the compound of formula (IV) is reacted with 0.7 to 1.2 mol methyl chloride in the presence of water and the mass ratio between compound of formula (IV) in the feed mixture and water is in the range of 0.1 to 5.

25. The process according of claim 22 wherein in step ii) of the process the resulting mixture of step i) is reacted with an aqueous hydrogen peroxide solution in the presence of the catalyst at a temperature in the range of 20 to 80° C. wherein the pH-value during the addition of the aqueous hydrogen peroxide solution is maintained between 7 and 10.

26. The process according to claim 22 wherein in step ii) of the process 1.5 to 5 mol of aqueous hydrogen peroxide having a concentration in the range of 25 to 70 wt.-% per mol of compound of formula (IV) in the feed mixture is reacted in the presence of 0.005 to 0.4 mol of the catalyst per mol of compound of formula (IV) in the feed mixture.

27. The process according to claim 22 wherein the addition of the acid in step iii) will start when the concentration of hydrogen peroxide in the mixture of step ii) has decreased to less than 0.5 wt.-%.

28. The process according to claim 22 wherein the acid in step iii) is hydrogen chloride acid.

29. A process for making a redox-flow cell wherein a solution according to claim 17 is used as electrolyte in one of the two chambers of the cell.

30. The process according to claim 29 comprising the following steps: a) providing two chambers for catholyte and anolyte solutions, each connected to at least one storage tank for catholyte and anolyte solutions respectively b) separating the two chambers with an ion-conducting membrane c) equipping the chambers with electrodes d) filling the solution comprising a 2,2,6,6-tetramethyl-4-(trimethylammonio)-1-piperidinyloxy salt as redox active material in the catholyte chamber e) filling an anolyte solution comprising another redox active material in the anolyte chamber.

31. A redox-flow cell obtained by a process according to claim 29.

32. Use of the redox flow cell according to claim 31 for storing electrical energy.

Description

EXAMPLES

[0062] General:

[0063] pH-Values:

[0064] pH values are always measured using a calibrated glass electrode (EasyFerm Plus PHI S8 225, two-point calibration with buffer pH=4.00 (citric acid, sodium hydroxide, sodium chloride from Fluka) and buffer pH=7.00 (potassium dihydrogen phosphate, disodium hydrogen phosphate from Fluka).

[0065] .sup.1H-NMR Method:

[0066] .sup.1H-NMR data of compound of formula (V):

##STR00008##

[0067] .sup.1H-NMR (500 MHz, D.sub.2O): δ [ppm]=3.68 (tt, J=12.5 Hz, 2.8 Hz 1H, H.sub.1), 3.07 (s, 9H, H.sub.6), 2.02-2.08 (m, 2H, H.sub.3), 1.32 (t, J=12.5 Hz, 2H, H.sub.2), 1.14 (s, 6H, H.sub.5), 1.12 (s, 6H, H.sub.4).

[0068] .sup.1H-NMR Data of Compound of Formula (VI):

##STR00009##

[0069] .sup.1H-NMR (500 MHz, D.sub.2O): 6 [ppm]=3.62 (tt, J=12.5 Hz, 3.1 Hz, 1H, H.sub.7), 3.00 (s, 9H, H.sub.12), 2.15 (s, 3H, H.sub.13), 2.08-2.02 (m, 2H, H.sub.9), 1.55 (t, J=12.5 Hz, 2H, H.sub.8), 1.15 (s, 6H, H.sub.11), 1.05 (s, 6H, H.sub.10).

[0070] .sup.1H-NMR Data of Compound of Formula (IV):

##STR00010##

[0071] .sup.1H-NMR (500 MHz, D.sub.2O): δ [ppm]=2.83 (tt, J=12.3 Hz, 3.2 Hz, 1H, H.sub.14), 2.27 (s, 6H, H.sub.19), 1.88 (dd, J=12.7 Hz, 3.2 Hz, 2H, H.sub.15), 1.28 (s, 6H, H.sub.17), 1.24 (s, 6H, H.sub.18), 1.17 (dd, J=12.7 Hz, 12.3 Hz, 6H, H.sub.16).

[0072] The molar ratio of compound of formula (IV), (V) and (VI) can be determined most conveniently by comparing the integrals of the .sup.1H-NMR signals at δ=3.68 ppm (1H from compound of formula (V)), 2.15 ppm (3H from compound of formula (VI)) and 2.27 ppm (6H from compound of formula (IV)).

[0073] Thus the molar ratio of compound of formula (IV):(V):(VI) is the same as the ratio of the following integrals:

(integral of signal at δ=3.68 ppm from compound of formula (V)):(integral of signal at δ=2.15 ppm from compound of formula (VI))/3:(integral of signal at δ=2.27 ppm from compound of formula (IV))/6

[0074] .sup.1H-NMR Measurements of the Inventive Solution:

[0075] Prior to .sup.1H-NMR measurements, the inventive solution is reacted with excess phenyl hydrazine (approx. 2 mol per mol of compound of formula (I) plus compound of formula (III)) to convert the N-oxyl radicals to the corresponding hydroxylamines. This procedure yields two isomeric forms of each reduced species (compound of formula (Ia) and (Ib)/compound of formula (IIIa) and (IIIb)) and each isomer gives individual signals in the .sup.1H-NMR spectrum. For all .sup.1H-NMR measurements the crude reaction mixture from reduction with phenyl hydrazine was diluted with D.sub.2O and referenced to the signal of residual H.sub.2O protons at δ=4.79 ppm.

[0076] Signal assignments for compound of formula (I) were confirmed by synthesizing compound of formula (I) as a pure crystalline material as described in WO 2018/2883011 on page 28. Signal assignments for compound of formula (III) were confirmed by synthesizing compound of formula (III) as a pure material in aqueous solution as described here.

[0077] Synthesis of Compound of Formula (III) in Pure Form in Aqueous Solution:

[0078] To a solution of compound of formula (IV) (39.3 g) in water (40.1 g), 37 wt.-% hydrochloric acid (11.97 g) is added, whereby the pH value of the solution decreases to 9.0. Then, solid sodium bicarbonate (2.71 g) is added and the mixture is heated to 60° C. When this temperature is reached a 50 wt.-% aqueous solution of hydrogen peroxide (46.4 g) is continuously added over a period of 4 hours. During addition the pH value decreases and is kept above 8.0 by the addition of a 50 wt.-% aqueous solution of sodium hydroxide (6.4 g) in five approximately equal portions. After the addition of the hydrogen peroxide is completed, stirring is continued for 12 hours. Then, the mixture is allowed to cool down to room temperature and analyzed by .sup.1H NMR spectroscopy and ESI MS mass spectrometry. The mixture contains >99 wt.-% of compound of formula (III) as organic material as determined by .sup.1H NMR.

[0079] The identity of compound of formula (I) and (III) is also supported by HRMS (ESI in ACN:H.sub.2O:HCOOH=80:20:0.1, instrument: Q Extractive™ hybrid-quadrupole-orbitrap mass spectrometer, ThermoFisher).

[0080] .sup.1H-NMR of the Reduced Form of Compound of Formula (I):

##STR00011##

[0081] .sup.1H-NMR (500 MHz, D.sub.2O): δ [ppm]=3.80-3.67 (m, 1H, H.sub.1+H.sub.1′), 3.12 (s, 9H, H.sub.6 or H.sub.6′, minor isomer), 3.09 (s, 9H, H.sub.6 or H.sub.6′, major isomer), 2.24-2.14 (m, 2H, H.sub.2+H.sub.2′), 1.99 (t, J=12.1 Hz, 2H, H.sub.3 or H.sub.3′, minor isomer), 1.75 (t, J=12.4 Hz, 2H, H.sub.3 or H.sub.3′, major isomer), 1.34 (s, 6H, H.sub.4/5 or H.sub.4′/5′, minor isomer), 1.26 (s, 6H, H.sub.4/5 or H.sub.4′/5′, major isomer), 1.22 (s, 6H, H.sub.4/5 or H.sub.4′/5′, major isomer), 1.12 (s, 6H, H.sub.4/5 or H.sub.4′/5′, minor isomer). The ratio of the two isomers is approximately

[0082] HRMS: theory for C.sub.12H.sub.26N.sub.2O.sup.+: 214.2040; found: 214.2036

[0083] .sup.1H-NMR of the reduced form of compound of formula (III):

##STR00012##

[0084] .sup.1H-NMR (500 MHz, D.sub.2O): δ [ppm]=3.66-3.52 (m, 1H, H.sub.7+H.sub.7′), 3.17 (s, 6H, H.sub.12 or H.sub.12′, minor isomer), 3.14 (s, 6H, H.sub.12 or H.sub.12′, major isomer), 2.27-2.14 (m, 2H, H.sub.8+H.sub.8′), 1.93 (t, J=12.5 Hz, 2H, H.sub.9 or H.sub.9′, minor isomer), 1.72 (t, J=12.5 Hz, 2H, H.sub.9 or H.sub.9′, major isomer), 1.33 (s, 6H, H.sub.10/11 or H.sub.10/11′, minor isomer), 1.25 (s, 6H, H.sub.10/11 or H.sub.10′/11′, major isomer), 1.21 (s, 6H, H.sub.10/11 or H.sub.10′/11′, major isomer), 1.11 (s, 6H, H.sub.10/11 or H.sub.10′/11′, minor isomer). The ratio of the two isomers is approximately 86:14.

[0085] HRMS: theory for C.sub.11H.sub.24N.sub.2O.sub.2.sup.+: 216.1638; found: 216.1637

[0086] Compound of formula (II) remains unchanged in the reduction and gives signals that are well separated from the signals from compounds of formula (Ia), (Ib), (IIIa) and (IIIb):

##STR00013##

[0087] .sup.1H-NMR (500 MHz, D.sub.2O): δ [ppm]=3.93 (tt, J=13.3 Hz, 3.2 Hz, 1H, H.sub.13), 3.14 (s, 9H, H.sub.19), 3.03 (s, 3H, H.sub.18), 2.47 (t, J=12.6 Hz, 2H, H.sub.14), 2.07 (d, J=12.1 Hz, 2H, H.sub.15, 1.65 (s, 6H, H.sub.16), 1.56 (s, 6H, H.sub.17).

[0088] HRMS: theory for C.sub.13H.sub.29N.sub.2O.sup.+: 229.2274; found: 229.2271

[0089] The ratio of compound of formula (I), (II) and (III) can be determined most conveniently by comparing the integrals of the .sup.1H-NMR signals at δ=3.80-3.67 ppm (1H from compound of formula (I)), 1.56 ppm (6H from compound of formula (II)) and 3.66-3.52 ppm (1H from compound of formula (III)).

[0090] Thus the molar ratio of compound of formula (I):(II):(III) is the same as the ratio of the following integrals:

(integral of signal at δ=3.80-3.67 ppm from compound of formula (I)):(integral of signal at δ=1.56 ppm from compound of compound (II))/6: (integral of signal at δ=3.66-3.52 ppm from compound of formula (III)).

[0091] Cerimetric Redox Titration:

[0092] Cerimetric redox titration is used to determine the total content of hydrogen peroxide and N-oxyl species (compound of formula (I) and (III)) according to the following method:

[0093] Content of N-Oxyl Species:

[0094] 100 mg of manganese dioxide is added to _pprox. 1 g of analyte. The mixture is stirred at 20 to 25° C. for 5 minutes or until 5 minutes after the end of gas evolution. Then the analyte is filtered. 250±2 mg of filtered analyte is placed in a beaker equipped with a magnetic stirring bar and is diluted with 45 mL purified water and 5 mL dilute sulfuric acid (10 wt.-% in water). The obtained solution is placed on an automated titration device (905 Titrando, Metrohm) equipped with a PtTitrode (Metrohm) and is stirred at 20-25° C. Cerium (IV) sulfate solution (0.10 mol/L) is added via the titration device until a redox potential jump is detected (V.sub.C1). The concentration of the sum of compound of formula (I)+(III) in weight-%, w.sub.I+III, can then be calculated from the consumption of cerium (IV) sulfate solution using the following equation:

[00001]$W_{l+\mathrm{lll}}=100*\frac{V_{c1}*C_c}{m_s}*\left[\left(x_l*M_{l-\mathrm{Cl}}\right)+\left(x_{\mathrm{lll}}*M_{\mathrm{lll}}\right)\right]$

[0095] Where the symbols have the following meaning: [0096] V.sub.c is the volume of the cerium sulfate solution used given in liter [0097] C.sub.c1 is the concentration of the cerium sulfate solution used given in mol/liter [0098] m.sub.s is the mass of the analyte given in grams [0099] M.sub.I−Cl is 249.8 g/mol, the molar mass of compound of formula (I) as the chloride salt [0100] M.sub.III is 215.3 g/mol, the molar mass of compound of formula (III) [0101] x.sub.I is the molar fraction of compound of formula (I) calculated as the ratio of (integral at δ=3.80-3.67 ppm in .sup.1H-NMR): [(integral of signal at δ=3.66-3.52 ppm in .sup.1H-NMR)+(integral at δ=3.80-3.67 ppm in .sup.1H-NMR)] [0102] x.sub.III is the molar fraction of compound of formula (III) calculated as the ratio of (integral of signal at δ=3.66-3.52 ppm in .sup.1H-NMR): [(integral of signal at δ=3.66-3.52 ppm in .sup.1HNMR)+(integral at δ=3.80-3.67 ppm in .sup.1H-NMR)]

[0103] Sum of Hydrogen Peroxide and N-Oxyl Species:

[0104] 250±2 mg of analyte is placed in a beaker equipped with a magnetic stirring bar and is diluted with 45 mL purified water and 5 mL dilute sulfuric acid (10 wt.-% in water). The obtained solution is placed on an automated titration device (905 Titrando, Metrohm) equipped with a PtTitrode (Metrohm) and is stirred at 20-25° C. Cerium (IV) sulfate solution (0.10 mol/L) is added via the titration device until a redox potential jump (V.sub.C2) is detected. The concentration of hydrogen peroxide can be calculated from the difference of the consumptions of cerium (IV) sulfate solution (ΔV.sub.C=V.sub.C2−V.sub.C1) using the following equation:

[00002]$w_{H_2{O}_2}=100*\frac{\Delta V_c*C_c}{m_s}*M\left(H_2{O}_2\right)$

[0105] Where the symbols have the same meanings as defined above and M.sub.H2O2 is 34.0 g/mol, the molar mass of hydrogen peroxide.

[0106] Cyclic Voltammetry Method:

[0107] The solution obtained from the respective example is diluted with 0.1 mol/L aqueous sodium chloride solution until the concentration of the N-oxyl compounds is 1.0 wt.-%. Said solution is placed in an electrochemical cell equipped with a standard 3 electrode setup (working electrode: glassy carbon (ø=2 mm), counter electrode: platinum wire, reference electrode: Ag/AgCl, 3 mol/L KCl in water). The potential is ramped to 1200 mV and then cycled between 1200 mV and −700 mV at a scan rate of ±20 mV/s (in total 3 cycles) using PGU 20V-2A-E potentiostat (IPS).

Example 1

[0108] In a stainless-steel autoclave 800 ml of water and 645 g of N,N,2,2,6,6-hexamethylpiperidin-4-amine compound of formula (IV) are mixed and tempered to 20° C. Then 185.5 g of methyl chloride are pressed within 70 minutes into the autoclave at approx. 3.2 bar. The mixture is consequently stirred at 20 to 25° C. for 6 hours. The autoclave is depressurized afterwards and purged with nitrogen for approx. 10 minutes. 1630 g of an aqueous solution of compound of formula (IV), (V) and (VI) is obtained (50 wt.-% organics in water). The molar ratio of compound of formula (IV):(V):(VI) as determined by .sup.1H-NMR is 2.5:92.8:4.7, which corresponds to 1.0 wt.-% of compound of formula (IV), 46.5 wt.-% of compound of formula (V) chloride salt and 2.5 wt.-% of compound of formula (VI) chloride salt.

Example 2 (Comparative)

[0109] The methylation was made as described in the WO 2018/28830, page 27, line 20 to page 28 line 15 (equal to DE102016009904A1, paragraph [0112] and following). In the .sup.1H-NMR of the product obtained, only signals for compound of formula (V) are visible.

Example 3

[0110] To a solution taken from example 1 (100 g, contains 1.0 wt.-% of compound of formula (IV), 46.5 wt.-% of compound of formula (V) chloride salt and 2.5 wt.-% of compound of formula (VI) chloride salt in water) 37 wt.-% hydrochloric acid (1.67 g) is added, whereby the pH value of the solution decreases to 9.0. Then, solid sodium bicarbonate (2.79 g) is added and the mixture is heated to 60° C. When the temperature is reached a 50 wt.-% aqueous solution of hydrogen peroxide (32.7 g) is continuously added over a period of 4 hours. During addition the pH value decreases and is kept above 8.0 by adding a 50 wt.-% aqueous solution of sodium hydroxide (1.73 g) in five approximately equal portions. After the addition of the hydrogen peroxide is completed, stirring is continued for 12 hours. The mixture is then allowed to cool down to about 30° C. and 37 wt.-% hydrochloric acid (ca. 2 g) is added to decrease the pH value of the solution to 4.5. Water is subsequently distilled off at reduced pressure (70 mbar abs) until the concentration of the N-oxyl species of compound of formula (I) and (III) is 46 wt.-% (as determined by cerimetric redox titration).

[0111] The molar ratio of compound of formula (I):(II):(III) as determined by .sup.1H-NMR is 93.0:4.7:2.3, which corresponds to 45.0 wt.-% of compound of formula (I) chloride salt, 2.4 wt.-% of compound of formula (II) chloride salt and 1.0 wt.-% of compound of formula (III).

Example 4

[0112] To a solution taken from example 1 (100 g, contains 1.0 wt.-% of compound of formula (IV), 46.5 wt.-% of compound of formula (V) chloride salt and 2.5 wt.-% of compound of formula (VI) chloride salt in water) 37 wt.-% hydrochloric acid (5.83 g) is added, whereby the pH value of the solution decreases to 8.5. Then, solid sodium carbonate (1.17 g) is added and the mixture is heated to 40° C. When the temperature is reached, a 50 wt.-% aqueous solution of hydrogen peroxide (32.7 g) is continuously added over a period of 6 hours. During addition the pH value decreases and is kept above 8.0 by adding a 50 wt.-% aqueous solution of sodium hydroxide (6.39 g) in five approximately equal portions. After the addition of the hydrogen peroxide is completed, stirring is continued for 12 hours. The mixture is then allowed to cool down to about 30° C. and 37 wt.-% hydrochloric acid (ca. 2.5 g) is added to adjust the pH value of the solution to 4.0. Water is subsequently distilled off at reduced pressure (70 mbar abs) until the concentration of N-oxyl species of compound of formula (I) and (III) is 48 wt.-% (as determined by cerimetric redox titration).

[0113] The molar ratio of compound of formula (I):(II):(III) as determined by .sup.1H-NMR is 93.1:4.8:2.1 which corresponds to 47.1 wt.-% of compound of formula (I) chloride salt, 2.6 wt.-% of compound of formula (II) chloride salt and 0.9 wt.-% of compound of formula (III).

Example 5 (Comparative)

[0114] The oxidation was performed as described in the WO 2018/028830, page 28, line 20 to page 29 line 22. In HRMS of the product obtained no signals for compound of formula (II) and (IIIa)/(IIIb) are visible; in .sup.1H-NMR of the reduced samples only signals for compound of formula (Ia/Ib) are visible.

Example 6

[0115] Cyclic voltammetry of product of example 3 is measured (see FIG. I).

Example 7 (Comparative)

[0116] Cyclic voltammetry of example 5 is measured (see FIG. II).

[0117] The cyclic voltammogram in FIG. I is nearly identical to that of the comparative example 5 in FIG. II. Therefore, the inventive solution of example 3 shows nearly the same redox potential as the solution obtained in example 5 which represents the state of the art. The inventive solution can thus be used in a redox flow cell as it is described in the state of the art.