Coordination complexes containing monosulfonated catecholate ligands and methods for producing the same
Flow batteries and other electrochemical systems can contain an active material that is a coordination complex having at least one monosulfonated catecholate ligand or a salt thereof bound to a metal center. The monosulfonated catecholate ligand has a structure of More particularly, the coordination complex can be a titanium coordination complex with a formula of D g Ti(L 1 )(L 2 )(L 3 ), in which D is a counterion selected from H, NH 4 + , Li + , Na + , K + , or any combination thereof g ranges between 3 and 6; and L 1 , L 2 and L 3 are ligands, where at least one of L 1 , L 2 and L 3 is a monosulfonated catecholate ligand. Methods for synthesizing such monosulfonated catecholate ligands can include providing a neat mixture of catechol and up to about 1.3 stoichiometric equivalents of sulfuric acid, and heating the neat mixture at a temperature of about 80° C. or above to form 3,4-dihydroxybenzenesulfonic acid or a salt thereof.
1. A method comprising heating a neat mixture of catechol and a sub-stoichiometric amount of sulfuric acid at a temperature in a range of from about 80° C. to about 130° C. to form a reaction product comprising unreacted catechol and 3,4-dihydroxybenzenesulfonic acid.
2. The method of claim 1 , wherein the reaction product comprises less than about 5% of 2,3-dihydroxybenzenesulfonic acid.
3. The method of claim 1 , wherein the neat mixture contains between about 0.2 and 0.4 stoichiometric equivalents of sulfuric acid per catechol.
4. The method of claim 3 , wherein the reaction product is a mixture of unreacted catechol and 3,4-dihydroxybenzenesulfonic acid in a molar ratio of 2:1.
5. The method of claim 4 , further comprising treating the reaction product with a base to form a desired salt form of the reaction product before further using the reaction mixture.
6. The method of claim 5 , further comprising reacting the salt form of the reaction product with a transition metal compound to form a transition metal coordination complex having one sulfonated catecholate ligand and two unsubstituted catecholate ligands bound to a metal center, wherein the sulfonated catechol ligand is a salt form of 3,4-dihydroxybenzenesulfonic acid.
7. The method of claim 6 , wherein the transition metal compound is a titanium compound.
8. The method of claim 5 , wherein the base comprises an alkali metal hydroxide, alkali metal carbonate, alkali metal bicarbonate, ammonium hydroxide, ammonium carbonate, or ammonium bicarbonate.
9. The method of claim 5 , wherein the base is lithium hydroxide, sodium hydroxide, potassium hydroxide, or a mixture thereof.
10. The method of claim 4 , wherein the reaction product is reacted with a transition metal compound to form a transition metal coordination complex having one sulfonated catecholate ligand and two unsubstituted catecholate ligands bound to a metal center, and wherein the sulfonated catechol ligand is a salt form of 3,4-dihydroxybenzenesulfonic acid.
11. The method of claim 10 , wherein the transition metal compound is a titanium compound.
12. The method of claim 1 , wherein the neat mixture contains between about 0.3 and about 0.5 stoichiometric equivalents of sulfuric acid per catechol.
13. The method of claim 12 , wherein the neat mixture contains about 0.5 stoichiometric equivalents of sulfuric acid per catechol, resulting in a reaction product that is a mixture of unreacted catechol and 3,4-dihydroxybenzenesulfonic acid in a molar ratio of 1:1, the method further comprising treating the reaction product with a base to form a desired salt form before further using the reaction mixture.
14. The method of claim 13 , wherein the base comprises an alkali metal hydroxide, alkali metal carbonate, alkali metal bicarbonate, ammonium hydroxide, ammonium carbonate, or ammonium bicarbonate.
15. The method of claim 13 , wherein the base is lithium hydroxide, sodium hydroxide, potassium hydroxide, or a mixture thereof.
16. The method of claim 13 , further comprising reacting the salt form of the reaction product with a transition metal compound to form a transition metal coordination complex having one sulfonated catecholate ligand and one unsubstituted catecholate ligand bound to a metal center, wherein the sulfonated catechol ligand is a salt form of 3,4-dihydroxybenzenesulfonic acid.
17. The method of claim 1 , wherein the neat mixture is heated at a temperature ranging between about 80° C. and about 110° C.
18. The method of claim 1 , wherein the neat mixture is heated at a temperature ranging between about 80° C. and about 100° C.