Sulfonated lignin-derived compounds and uses thereof

Abstract

The present invention relates to novel lignin-derived compounds and compositions comprising the same and their use as redox flow battery electrolytes. The invention further provides a method for preparing said compounds and compositions as well as a redox flow battery comprising said compounds and compositions. Additionally, an assembly for carrying out the inventive method is provided.

Claims

1. A redox flow battery comprising at least one sulfonated and optionally further derivatized low molecular weight aromatic compound, wherein said compound corresponds in structure to Formula (X), (XI), (XII), (XIII), (XIV) or (XV): ##STR00054## wherein each R.sup.1, R.sup.2, R.sup.3 or R.sup.4 is independently selected from hydrogen, hydroxy, carboxy, linear or branched, optionally substituted, C.sub.1-6 alkyl, linear or branched, optionally substituted, C.sub.1-6 alkenyl, linear or branched, optionally substituted, C.sub.1-6 alcohol, linear or branched, optionally substituted, C.sub.1-6 aminoalkyl, linear or branched, optionally substituted, C.sub.1-6 carboxyalkyl, linear or branched, optionally substituted, C.sub.1-6 alkoxy, linear or branched, optionally substituted, C.sub.1-6 aldehyde, ester, halogen, amine, amino, amide, nitro, oxo, carbonyl, phosphoryl, phosphonyl, cyanide and sulfonyl (SO.sub.3H), provided that (i) at least three of R.sup.1-R.sup.4 are SO.sub.3H or (ii) provided that at least one of R.sup.1-R.sup.4 is SO.sub.3H and at least one of R.sup.1-R.sup.4 is hydroxy or C.sub.1-6 alcohol; ##STR00055## wherein each R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 or R.sup.6 is independently selected from hydrogen, hydroxy, carboxy, linear or branched, optionally substituted, C.sub.1-6 alkyl, linear or branched, optionally substituted, C.sub.1-6 alkenyl, linear or branched, optionally substituted, C.sub.1-6 alcohol, linear or branched, optionally substituted, C.sub.1-6 aminoalkyl, linear or branched, optionally substituted, C.sub.1-6 carboxyalkyl, linear or branched, optionally substituted, C.sub.1-6 alkoxy, linear or branched, optionally substituted, C.sub.1-6 aldehyde, ester, halogen, amine, amino, amide, nitro, oxo, carbonyl, phosphoryl, phosphonyl, cyanide and sulfonyl (SO.sub.3H), provided that (i) at least three of R.sup.1-R.sup.6 are SO.sub.3H or (ii) provided that at least one of R.sup.1-R.sup.6 is SO.sub.3H and at least one of R.sup.1-R.sup.6 is hydroxy or C.sub.1-6 alcohol; ##STR00056## wherein each R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7 or R.sup.8 is independently selected from hydrogen, hydroxy, carboxy, linear or branched, optionally substituted, C.sub.1-6 alkyl, linear or branched, optionally substituted, C.sub.1-6 alkenyl, linear or branched, optionally substituted, C.sub.1-6 alcohol, linear or branched, optionally substituted, C.sub.1-6 aminoalkyl, linear or branched, optionally substituted, C.sub.1-6 carboxyalkyl, linear or branched, optionally substituted, C.sub.1-6 alkoxy, linear or branched, optionally substituted, C.sub.1-6 aldehyde, ester, halogen, amine, amino, amide, nitro, oxo, carbonyl, phosphoryl, phosphonyl, cyanide and sulfonyl (SO.sub.3H), provided that (i) at least three of R.sup.1-R.sup.8 are SO.sub.3H or (ii) provided that at least one of R.sup.1-R.sup.8 is SO.sub.3H and at least one of R.sup.1-R.sup.8 is hydroxy or C.sub.1-6 alcohol.

2. The redox flow battery according to claim 1, wherein said redox flow battery comprises a first (optionally aqueous) electrolyte solution comprising a first (redox active) electrolyte; a first electrode in contact with said first (optionally aqueous) electrolyte solution; a second (optionally aqueous) electrolyte solution comprising a second (redox active) electrolyte; a second electrode in contact with said second (optionally aqueous) electrolyte solution; wherein one or both of the first and second (redox active) electrolytes comprise the at least one sulfonated (and optionally further derivatized) low molecular weight aromatic compound.

3. The redox flow battery of claim 1, wherein the sulfonated low molecular weight aromatic compound corresponds in structure to Formula (X) or (XI), and wherein R.sup.1 and R.sup.4 are independently selected from H and SO.sub.3H; R.sup.2 is selected from H, OH, C.sub.1-C.sub.6 alcohol, and SO.sub.3H; and R.sup.3 is selected from H, OH and C.sub.1-C.sub.6 alcohol.

4. The redox flow battery of claim 1, wherein the sulfonated low molecular weight aromatic compound is characterized by one of the following: a) R.sup.4 is SO.sub.3H; b) R.sup.4 is SO.sub.3H, R.sup.3 is methoxy; c) R.sup.4 is SO.sub.3H, R.sup.2 and R.sup.3 are methoxy; d) R.sup.1 and R.sup.4 are SO.sub.3H; e) R.sup.1 and R.sup.4 are SO.sub.3H, R.sup.3 is methoxy; or f) R.sup.2 and R.sup.4 are SO.sub.3H, and R.sup.3 is methoxy.

5. The redox flow battery of claim 1, wherein the sulfonated low molecular weight aromatic compound corresponds in structure to Formula (XII) or (XIII), wherein R.sup.1 and R.sup.2 are independently selected from H, OH and C.sub.1-C.sub.6 alcohol; and R.sup.3-R.sup.6 are independently selected from H and SO.sub.3H.

6. The redox flow battery of claim 1, wherein the sulfonated low molecular weight aromatic compound corresponds in structure to Formula (XIV) or (XV) and wherein R.sup.1, R.sup.2 and R.sup.4 are independently selected from H, OH and C.sub.1-C.sub.6 alcohol; and R.sup.3, R.sup.5-R.sup.8 are independently selected from H and SO.sub.3H.

7. The redox flow battery of claim 1, wherein the sulfonated low molecular weight aromatic compound is characterized by one of the following: a) R.sup.1 is SO.sub.3H; b) R.sup.2 is SO.sub.3H; R.sup.1, R.sup.3 and R.sup.4 are OH; c) R.sup.6 is SO.sub.3H; R.sup.1 and R.sup.4 or R.sup.1, R.sup.2 and R.sup.4 are OH; d) R.sup.2 and R.sup.6 are SO.sub.3H; R.sup.1 and R.sup.4 or R.sup.1, R.sup.3 and R.sup.4 are OH; e) R.sup.3 and R.sup.6 are SO.sub.3H; R.sup.1, R.sup.2 and R.sup.4 are OH; f) R.sup.2 and R.sup.7 are SO.sub.3H; or g) R.sup.1 and R.sup.4 are SO.sub.3H; wherein each of the other of R.sup.1-R.sup.8 is/are SO.sub.3H, hydroxy, C.sub.1-C.sub.6 alcohol, or H.

8. The redox flow battery of claim 1, wherein the sulfonated low molecular weight aromatic compound is selected from a sulfonated compound according to Table 1, 2 or 3.

9. The redox flow battery of claim 8, wherein the sulfonated low molecular weight aromatic compound is selected from compounds 15 and 16 (Table 1), compounds 66-85 (Table 2) and compounds 293-400 (Table 3).

10. A redox flow battery comprising a composition comprising at least two sulfonated low molecular weight aromatic compounds, wherein said compounds independently correspond in structure to Formula (X), (XI), (XII), (XIII), (XIV) or (XV): ##STR00057## wherein each R.sup.1, R.sup.2, R.sup.3 or R.sup.4 is independently selected from hydrogen, hydroxy, carboxy, linear or branched, optionally substituted, C.sub.1-6 alkyl, linear or branched, optionally substituted, C.sub.1-6 alkenyl, linear or branched, optionally substituted, C.sub.1-6 alcohol, linear or branched, optionally substituted, C.sub.1-6 aminoalkyl, linear or branched, optionally substituted, C.sub.1-6 carboxyalkyl, linear or branched, optionally substituted, C.sub.1-6 alkoxy, linear or branched, optionally substituted, C.sub.1-6 aldehyde, ester, halogen, amine, amino, amide, nitro, oxo, carbonyl, phosphoryl, phosphonyl, cyanide and sulfonyl (SO.sub.3H), provided that (i) at least two of R.sup.1-R.sup.4 are SO.sub.3H, or provided that (ii) at least one of R.sup.1-R.sup.4 is SO.sub.3H and at least one of R.sup.1-R.sup.4 is hydroxy or C.sub.1-6 alcohol; ##STR00058## wherein each R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 or R.sup.6 is independently selected from hydrogen, hydroxy, carboxy, linear or branched, optionally substituted, C.sub.1-6 alkyl, linear or branched, optionally substituted, C.sub.1-6 alkenyl, linear or branched, optionally substituted, C.sub.1-6 alcohol, linear or branched, optionally substituted, C.sub.1-6 aminoalkyl, linear or branched, optionally substituted, C.sub.1-6 carboxyalkyl, linear or branched, optionally substituted, C.sub.1-6 alkoxy, linear or branched, optionally substituted, C.sub.1-6 aldehyde, ester, halogen, amine, amino, amide, nitro, oxo, carbonyl, phosphoryl, phosphonyl, cyanide and sulfonyl (SO.sub.3H), provided that (i) at least two of R.sup.1-R.sup.6 are SO.sub.3H, or provided that (ii) at least one of R.sup.1-R.sup.6 is SO.sub.3H and at least one of R.sup.1-R.sup.6 is hydroxy or C.sub.1-6 alcohol; ##STR00059## wherein each R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7 or R.sup.8 is independently selected from hydrogen, hydroxy, carboxy, linear or branched, optionally substituted, C.sub.1-6 alkyl, linear or branched, optionally substituted, C.sub.1-6 alkenyl, linear or branched, optionally substituted, C.sub.1-6 alcohol, linear or branched, optionally substituted, C.sub.1-6 aminoalkyl, linear or branched, optionally substituted, C.sub.1-6 carboxyalkyl, linear or branched, optionally substituted, C.sub.1-6 alkoxy, linear or branched, optionally substituted, C.sub.1-6 aldehyde, ester, halogen, amine, amino, amide, nitro, oxo, carbonyl, phosphoryl, phosphonyl, cyanide and sulfonyl (SO.sub.3H), provided that (i) at least two of R.sup.1-R.sup.8 are SO.sub.3H, or provided that (ii) at least one of R.sup.1-R.sup.8 is SO.sub.3H and at least one of R.sup.1-R.sup.8 is hydroxy or C.sub.1-6 alcohol; and wherein at least one of the sulfonated low molecular weight aromatic compounds is in an oxidized state according to Formula (X), (XII) or (XIV), and/or at least one of the sulfonated low molecular weight aromatic compounds is in a reduced state according to Formula (XI), (XIII) or (XV).

11. The redox flow battery of claim 10, wherein the at least two sulfonated low molecular weight aromatic compounds are characterized by the following: (a) at least one compound according to Formula (X) and (XI); (b) at least one compound according to Formula (XII) and (XIII); and/or (c) at least one compound according to Formula (XIV) and (XV).

12. The redox flow battery of claim 11, wherein the composition comprises (a) at least two compounds according to Formula (X) and (XI), wherein said at least two compounds are distinctly sulfonated and/or substituted; (b) at least two compounds according to Formula (XII) or (XIII), wherein said at least two compounds are distinctly sulfonated and/or substituted; and/or (c) at least two compounds according to Formula (XIV) or (XV), wherein said at least two compounds are distinctly sulfonated and/or substituted.

13. The redox flow battery of claim 11, wherein each of the at least two compounds comprises at least three SO.sub.3H groups.

14. The redox flow battery of claim 1, wherein the sulfonated (and optionally further derivatized) low molecular weight aromatic compound or a composition comprising the sulfonated low molecular weight aromatic compound is obtainable by (1) providing a starting material; (2) optionally subjecting said starting material to a process suitable to obtain at least one low molecular weight precursor compound; (3) isolating and optionally modifying at least one low molecular weight precursor compound thereby obtaining at least one low molecular weight aromatic precursor compound; (4) subjecting the at least one low molecular weight precursor compound to a sulfonation reaction, wherein one or more SO.sub.3H groups are introduced into the at least one precursor compound thereby obtaining the at least one sulfonated low molecular weight aromatic compound or the composition comprising the sulfonated low molecular weight aromatic compound.

15. The redox flow battery of claim 14, wherein the starting material is selected from lignocellulosic material, crude oil, coal and a pure organic substance.

16. The redox flow battery of claim 14, wherein the compound corresponds in structure to any one of Formula (X)-(XV), and/or the composition comprises compounds corresponding in structure to any one of Formula (X)-(XV).

17. The redox flow battery of claim 14, wherein the sulfonated (and optionally further derivatized) low molecular weight aromatic compound or the composition comprising the sulfonated low molecular weight aromatic compound is dissolved or suspended in a suitable solvent to form an electrolyte solution.

18. The redox flow battery of claim 10, wherein: (a) in Formula X and XI at least one of R.sup.1-R.sup.4 is hydroxy or C.sub.1-C.sub.6 alcohol; (b) in Formula XII and XIII at least one of R.sup.1-R.sup.6 is hydroxy or C.sub.1-C.sub.6 alcohol; and/or (c) in Formula XIV and XV at least one of R.sup.1-R.sup.8 is hydroxy or C.sub.1-C.sub.6 alcohol.

Description

DESCRIPTION OF THE FIGURES

(1) FIGS. 1 and 2 show steps (5) (sulfonation) and following steps of an exemplary method according to the invention.

EXAMPLES

(2) The examples shown in the following are merely illustrative and shall describe the present invention in a further way. These examples shall not be construed to limit the present invention thereto. The following preparations and examples are given to enable those skilled in the art to more clearly understand and to practice the present invention. The present invention, however, is not limited in scope by the exemplified embodiments, which are intended as illustrations of single aspects of the invention only, and methods, which are functionally equivalent are within the scope of the invention. Indeed, various modifications of the invention in addition to those described herein will become readily apparent to those skilled in the art from the foregoing description, accompanying figures and the examples below. All such modifications fall within the scope of the appended claims.

Example 1: Preparation of Low Molecular Weight Aromatic Lignin-Derived Compounds By Cracking and Reduction By a Nickel Catalyst

(3) Reductive cracking of a modified lignin-derived component according to step (E.2) of the inventive method may for example be carried out by means of a catalyst comprising nickel, e.g. supported on activated carbon (Ni/C). The catalysts are typically prepared by an incipient-wetness impregnation method and further treated by a carbothermal reduction method known in the art.

(4) Herein, nickel nitrate(II) hexahydrate [Ni(NO.sub.3).sub.2 6H2O] is used and optionally added into water in a beaker known in the art. The solution is then stirred, e.g. for at least 30 min, to prepare an impregnation stock solution. Activated carbon having a water absorption capacity of typically above 1.8 mL g.sup.−1 is added into the solution and the beaker may then covered by a culture dish to keep the sample wet for a prescribed time, preferably more than 12 h, more preferably 24 h. The sample is then dried at a temperature above 80° C., e.g. 120° C. overnight. The actual reduction is carried out in a container such as a preferably horizontal furnace in a flow of inert gas such as N.sub.2. The flow is, e.g., 10 mL min.sup.−1 or more, preferably 30 mL min.sup.−1 or more. The reduction temperature preferably reaches at least 400° C., preferably 450° C., e.g. over set time period such as at least 30 min, preferably at least 60 min. The temperature for conducting the reduction is maintained at 450° C. for at least 1 h, more preferably for at least 2 h. The Ni/SBA-15 catalysts are reduced at 550° C. for 2 h. The Ni/Al.sub.2O.sub.3 catalyst is reduced at 700° C. for 2 h. The metal loading for each nickel- and copper-based catalyst is 10% (w/w) relative to the support. Herein, birch sawdust serves as lignocellulosic material and is treated with the ethanol-benzene mixture (v/v ratio 1:2) for 12 h. The treated birch sawdust, solvent (m/v 1:20), and catalyst (w/w 20:1) are placed in an autoclave reactor. The reactor is sealed and purged with Ar 4 to 6 times to expel air. Then, the reducing reaction is conducted at 200° C. at a stirring speed of at least 300 rpm, preferably 500 rpm. When the desired reaction time (usually 2 to 10 h) is reached, the reactor is cooled to ambient temperature before sampling.

(5) Typically, the reaction generates 4-propylguaiacol and 4-propylsyringol as major products, together with minor alkene-substituted 4-propylguaiacol and 4-propylsyringol, as determined by standard gas chromatography. The compounds are isolated according to step (F), preferably by extraction.

Example 2: Preparation of Monomeric Aromatic Lignin-Derived Molecules from Lignosulfonate of a Sulfite Process By Electrooxidation

(6) Lignosulfonate is provided by step (D) according to the present invention. Thereof, a 1 M aqueous NaOH solution is prepared, comprising 1% (W/W) lignosulfonate. Said solution is subjected to an electrooxidation according to step (E.3). Therein, the solution is employed as anolyte. A 1 M aqueous solution is employed as katalyte. A flow cell with a flow rate of 250 ml/min is used. Electrolysis is allowed to take place galvanostatically for 8 h applying current of 1 mA/cm.sup.2. A typical resulting voltage is 1.4 V. The voltage curve typically is asymptotic and the solution changes preferably color from brown to dark brown.

(7) Samples of the solution are taken every hour over a time span of 8 h and subsequently examined photometrically. Thereof, an absorption profile typical for ortho- benzoquinone is determined. Hence, a lower molecular weight aromatic lignin-derived compound, quinone compound, is prepared by said method.

(8) Said compound is then isolated according to step (F) of the present invention. Therefore, said compound is extracted by dichloromethane and subsequently subjected to cycles of charging and discharging processes in a flow cell. The voltage curve shows that the compound is redox active, which may be reversibly electrolyzed.

Example 3: Preparation of an Annulated Quinone Compound By a Friedel-Crafts Acylation

(9) Vanillin as a low molecular weight aromatic lignin-derived compound is provided by step (F) according to the present invention. Said compound is further annulated according to step (G) and oxidized according to step (H) according to the present invention in five steps as follows:

(i) Synthesis of 4-(benzyloxy)-3-methoxybenzaldehyde (2):

(10) ##STR00037##

(11) Vanillin (1) (1.0 eq.) and benzyl chloride (1.2 eq.) are dissolved in N,N-dimethylformamide and potassium iodine (0.5 mol %) is added. Afterwards potassium carbonate is added and the reaction is stirred above 60° C., preferably between 60 to 120° C. for at least 1 h, preferably 1 to 8 h. After completion of the reaction, the solution is diluted with distilled water and extracted with an appropriate solvent. The organic phase is washed with brine and the product is then isolated from the organic phase.

(ii) Synthesis of 4-(benzyloxy)-3-methoxybenzoic acid (3):

(12) ##STR00038##

(13) A mixture of 1,2-dimethoxyethane and potassium hydroxide (5 to 20 eq.) is purged with oxygen and the calculated amount of isolated product 2 (1.0 eq.) is added. After the absorption of oxygen ceases, the mixture is diluted with distilled water and neutral organic products are extracted with an appropriate solvent. The aqueous layer is acidified and the acidic organic products are extracted with an appropriate solvent. Product 3 is isolated from the organic layer.

(iii) Synthesis of 4-(benzyloxy)-3-methoxybenzoyl chloride (4):

(14) ##STR00039##

(15) Isolated product 3 (1.0 eq.) is dissolved in thionyl chloride (5-20 eq.) and the mixture is stirred at 60 to 120° C. for 1 to 8 h. After completion of the reaction excess thionyl chloride is evaporated to yield desired acyl chloride 4.

(iv) Synthesis of anthraquinones (5-7):

(16) ##STR00040##

(17) Aluminiumtrichloride (0.1 eq.) is added to the crude acyl chloride 4 and the mixture is stirred for 30 to 300 min at −20 to 60° C. After completion of the reaction the mixture is carefully quenched with bicarb solution. The product is extracted with an appropriate solvent and the organic layer is washed with brine. The product is then isolated from the organic phase.

(v) Synthesis of 2,6-dihydroxy-3,7-dimethoxyanthracene-9,10-dione 8 and 2,6-dihydroxy-1,7-dimethoxyanthracene-9,10-dione 9:

(18) ##STR00041##

(19) Anthraquinone 5 or 6 are dissolved in ethyl acetate, methanol or ethanol and palladium on charcoal (1 to 30 weight %) is added. The mixture is stirred at room temperature under hydrogen atmosphere (1-10 bar). The catalyst is filtered off and the product (9) is isolated from the mixture.

(20) The product is then characterized by spectrographic means, and provided as redox active compound according to the present invention.

Example 4:Derivatization of (Hydro-)Quinones

Example 4.1 Reduction of Dimethoxy Benzoquinone

(21) ##STR00042##

(22) 23.2 g of sodium dithionite (0.134 mol, 1.32 eq.) was added to the suspension of 17.0 g (0.101 mol, 1.0 eq.) 2,6-dimethoxycyclohexa-2,5-diene-1,4-dione in 100 mL H.sub.2O. After 2 h stirring at room temperature the precipitate was filtered off and dried in the air to give 15.85 g (0.093 mol, 92% yield) of 2,6-dimethoxybenzene-1,4-diol as a white solid.

Example 4.2:Oxidation of Methoxy Benzohydroquinone

(23) ##STR00043##

(24) 1.4 g of catalyst Cu/AlO(OH) was added to a solution of 8.2 g (0.059 mol) 2-methoxy-1,4-dihydroxybenzene in 250 mL ethyl acetate, and the reaction mixture was stirred at room temperature for 147 h under an O.sub.2 atmosphere. After the conversion determined by HPLC reached 99%, the reaction mixture was filtered, and the recovered catalyst was washed with ethyl acetate (100 mL×3). The filtrate was collected and solvent was removed in vacuo to give 7.66 g (0.055 mol, 95% yield) of 2-methoxycyclohexa-2,5-diene-1,4-dione as a yellow-brownish solid.

Example 4.3:Acetylation of Methoxy Benzohydroquinone

(25) 8.24 g (0.059 mol, 1.0 eq.) of 2-methoxybenzene-1,4-diol was weighed into a 250 mL reaction flask equipped with a reflux condenser. 60 mL of dichloroethane and 15 mL (0.159 mol, 2.7 eq.) of acetic anhydride were added. 12 mL (0.096 mol, 1.63 eq.) of boron trifluoride ether solution was then slowly added at room temperature with stirring. The reaction mixture was heated to 90° C. for 20 hours. The mixture was cooled to 60° C., 30 mL H.sub.2O was added followed by 10 mL HCl (6 M). The resulting mixture was heated to 100° C. for 30 min, cooled down and extracted with ethyl acetate (150 mL×3). The combined extracts were washed sequentially with H.sub.2O (100 mL), saturated sodium bicarbonate (100 mL) and H2O (100 mL) and then dried with anhydrous sodium sulfate. The solvent was removed in vacuo to give a brown solid residue, which was washed with methanol to give 7.49 g (0.041 mol, 70% yield) of 1-(2,5-dihydroxy-4-methoxyphenyl)ethan-1-one as a beige solid.

Example 4.4 Addition of Isonicotinic Acid to Benzoquinone

(26) 2.16 g (0.02 mol, 1.0 eq.) of p-benzoquinone was suspended in 6.4 mL of acetic acid. 2.46 g (0.02 mol, 1.0 eq.) of nicotinic acid was added and the mixture was stirred for 2 h at rt. The resulting dark mixture was diluted with 3 mL of water and treated with 6.6 mL of HCl (6 M). On cooling, solid precipitated which was filtered off and dried overnight at 60° C. to give 3.13 g (0.012 mol, 59% yield) of 3-carboxy-1-(2,5-dihydroxyphenyl)pyridin-1-ium chloride as an yellow solid.

Example 4.5 Sulfonation of Anthraquinone

(27) ##STR00044##

(28) A solution of anthraquinone was heated (180° C.) in a solution of 20%-40% SO.sub.3 in concentrated sulfuric acid (oleum), resulting in a mixture of sulfonated anthraquinones. The crude mixture was poured onto ice and partially neutralized with calcium hydroxide. Subsequently, the mixture was filtrated and concentrated to yield the final product.

Example 4.6: Sulfonation of Hydroquinone (1,4-Dihydroxybenzene)

(29) ##STR00045##

(30) A solution of hydroquinone was heated (80° C.) in a solution of 20%-40% SO.sub.3 in concentrated sulfuric acid (oleum), resulting in a mixture of sulfonated hydroquinones. The crude mixture was poured onto ice and partially neutralized with calcium hydroxide. Subsequently, the mixture was filtrated and concentrated to yield the final product.

Example 4.7: Sulfonation of 1,4-Dihydroxy-2,6-Dimethoxybenzene

(31) A solution of hydroquinone was heated (80° C.) in a solution of 20%-35% SO.sub.3 in concentrated

(32) ##STR00046##
sulfuric acid (oleum), resulting in a mixture of sulfonated 1,4-dihydroxy-2,6-dimethoxybenzenes. The crude mixture was poured onto ice and partially neutralized with calcium hydroxide. Subsequently, the mixture was filtrated and concentrated to yield the final product.

Example 4.8: Sulfonation of 2-Methoxyhydroquinone

(33) ##STR00047##

(34) A solution of 2-methoxyhydroquinone was heated (80° C.) in a solution of 20%-40% SO.sub.3 in concentrated sulfuric acid (oleum), resulting in a mixture of sulfonated 2-methoxyhydroquinones. The crude mixture was poured onto ice and partially neutralized with calcium hydroxide. Subsequently, the mixture was filtrated and concentrated to yield the final product.

Example 5: Model Compounds from the Modification Reaction of Benzoquinones Paired with Sulfonated Anthraquinone in an Organic Redox Flow Battery

(35) Table 4 shows three examples for pairings that were used in a fully organic redox flow battery that were achieved by the modification of quinones. Example A shows a pairing of a sulfonated benzohydroquinone that was achieved by a double substitution reaction with sulfur trioxide and a sulfonated anthraquinone that was also achieved by a double substitution reaction with sulfur trioxide. Example B shows a glycin substituted mono methoxy benzohydroquinone that was achieved by the nucleophilic attack of an glycin to the methoxy benzoquinone paired with the sulfonated anthraquinone. In example C a isonicotinic acid substituted benzohydroquinone is paired with the same anthraquinone. The isonicotinic acid was introduced by nucleophilic attack as well.

(36) TABLE-US-00004 TABLE 4 Pairings for modified products in a fully organic redox flow battery A OCV = 0.8 V B 0 OCV = 1.0 V C OCV = 0.55 V