Processes for forming coordination complexes containing monosulfonated catecholate ligands
View Patent ↗Coordination complexes can have a metal center with at least one unsubstituted catecholate ligand and at least one monosulfonated catecholate ligand or a salt thereof bound thereto. Some coordination complexes can have a formula of D g Ti(L 1 ) x (L 2 ) y , in which D is a counterion selected from NH 4 + , Li + , Na + , K + , or any combination thereof; g ranges between 2 and 6; L 1 is an unsubstituted catecholate ligand; L 2 is a monosulfonated catecholate ligand; and x and y are non-zero numbers such that x+y=3. Methods for synthesizing such coordination complexes can include providing a neat mixture of catechol and a sub-stoichiometric amount of sulfuric acid, heating the neat mixture to form a reaction product containing catechol and a monosulfonated catechol or a salt thereof, and forming a coordination complex from the reaction product without separating the catechol and the monosulfonated catechol or the salt thereof from one another.
1. A method comprising:
heating a neat mixture of catechol and a sub-stoichiometric amount of sulfuric acid relative to the catechol to form a reaction product comprising a mixture of catechol and a monosulfonated catechol or a salt thereof; and
without separating the catechol and the monosulfonated catechol or the salt thereof from one another, forming a coordination complex from the reaction product having a metal center with at least one unsubstituted catecholate ligand and at least one monosulfonated catecholate ligand bound thereto.
2. The method of claim 1 , wherein the monosulfonated catechol is 3,4-dihydroxybenzenesulfonic acid.
3. The method of claim 1 , wherein the neat mixture comprises up to about 0.7 stoichiometric equivalents of sulfuric acid relative to catechol.
4. The method of claim 3 , wherein the neat mixture comprises between about 0.1 stoichiometric equivalents and about 0.7 stoichiometric equivalents of sulfuric acid relative to catechol.
5. The method of claim 3 , wherein the neat mixture comprises between about 0.3 stoichiometric equivalents and about 0.5 stoichiometric equivalents of sulfuric acid relative to catechol.
6. The method of claim 1 , wherein the neat mixture is heated at a temperature in a range from about 80° C. to about 130° C.
7. The method of claim 1 , wherein the metal center is a transition metal.
8. The method of claim 7 , wherein the transition metal is titanium and the coordination complex has a formula of:
D g M(L 1 ) x (L 2 ) y ;
wherein:
D is a counterion that is H + , NH 4 + , Na + , K + , or any combination thereof;
g is 2, 3, 4, 5, or mil 6 ;
L 1 is the at least one unsubstituted catecholate ligand;
L 2 is the at least one monosulfonated catecholate ligand; and
x and y are non-zero numbers such that x+y=3.
9. The method of claim 8 , wherein the coordination complex comprises both Na + and K + counterions.
10. The method of claim 1 , further comprising:
combining at least one aqueous base with the coordination complex; and
obtaining an aqueous solution of the coordination complex.
11. The method of claim 10 , wherein the coordination complex comprises both Na + and K + counterions.
12. The method of claim 10 , wherein the metal center is titanium.
13. The method of claim 1 , further comprising:
combining an organic solvent with the reaction product before forming the coordination complex.
14. The method of claim 1 , wherein the reaction product and the coordination complex are formed consecutively in a single reaction vessel.
15. A method comprising:
heating a neat mixture of catechol and up to about 0.7 stoichiometric equivalents of sulfuric acid relative to the catechol at a temperature of about 80° C. or above to form a reaction product comprising a mixture of catechol and a monosulfonated catechol or a salt thereof, wherein the monosulfonated catechol is 3,4-dihydroxybenzenesulfonic acid;
without separating the catechol and the monosulfonated catechol or the salt thereof from one another, forming a coordination complex from the reaction product having a metal center with at least one unsubstituted catecholate ligand and at least one monosulfonated catecholate ligand bound thereto;
combining an aqueous base with the coordination complex to provide an aqueous solution of the coordination complex.
16. The method of claim 15 , wherein the neat mixture comprises between about 0.1 stoichiometric equivalents and about 0.7 stoichiometric equivalents of sulfuric acid relative to catechol.
17. The method of claim 15 , wherein the neat mixture comprises between about 0.3 stoichiometric equivalents and about 0.5 stoichiometric equivalents of sulfuric acid relative to catechol.
18. The method of claim 15 , wherein the neat mixture is heated at a temperature in a range of from about 80° C. to about 130° C.
19. The method of claim 15 , wherein the metal center comprises a transition metal.
20. The method of claim 19 , wherein the transition metal is titanium and the coordination complex has a formula of:
D g M(L 1 ) x (L 2 ) y ;
wherein:
D is a counterion that is NH 4 + , Li + , Na + , K + , or any combination thereof;
g is 2, 3, 4, 5, or 6;
L 1 is the at least one unsubstituted catecholate ligand;
L 2 is the at least one monosulfonated catecholate ligand; and
x and y are non-zero numbers such that x+y=3.
21. The method of claim 20 , wherein the coordination complex comprises both Na + and K + counterions.
22. The method of claim 15 , further comprising:
adding an organic solvent to the reaction product before forming the coordination complex.