Conversion of lignin to ionic liquids
Disclosed herein are lignin-derived ionic liquids and methods for preparing them. The methods include forming a reaction mixture comprising a lignin-derived starting material, a carbonyl compound, and an amine; maintaining the reaction mixture under conditions sufficient to form a lignin-derived aminophenol; and converting the lignin derived aminophenol to the lignin-derived ionic liquid. Monomeric phenols, oligomeric phenols, and polymeric phenols can be used as lignin-derived starting materials.
1. An ionic liquid comprising at least one compound according to Formula I:
wherein:
R 2a is selected from the group consisting of C 1-12 alkyl, C 2-12 alkenyl, C 2-12 alkynyl, C 3-12 cycloalkyl, and C 6-14 aryl;
R 2b is selected from the group consisting of C 1-12 alkyl, C 2-12 alkenyl, C 2-12 alkynyl, C 3-12 cycloalkyl, C 6-14 aryl, and hydrogen;
R 3a and R 3b are independently selected from the group consisting of hydrogen, C 1-12 alkyl, C 2-12 alkenyl, C 2-12 alkynyl, C 3-12 cycloalkyl, and C 6-14 aryl;
R 4 is a polymeric lignin residue; and
X is an anion.
2. The ionic liquid of claim 1 , wherein R 2a and R 2b are independently selected C 1-6 alkyl.
3. The ionic liquid of claim 1 , wherein R 3a and R 3b are hydrogen.
4. The ionic liquid of claim 1 , wherein X is selected from the group consisting of fluoride, chloride, bromide, a phosphate, a sulfate, a carboxylate, a fluorophosphate, and a fluoroborate.
5. The ionic liquid of claim 1 , comprising two or more different compounds according to Formula I.
6. A method for preparing a lignin-derived ionic liquid according to Formula I,
the method comprising:
forming a reaction mixture comprising a lignin-derive d starting material, a carbonyl compound, and an amine;
maintaining the reaction mixture under conditions sufficient to form a lignin-derived aminophenol; and
converting the lignin-derived aminophenol to the lignin-derived ionic liquid; wherein:
R 2a is selected from the group consisting of C 1-12 alkyl, C 2-12 alkenyl, C 2-12 alkynyl, C 3-12 cycloalkyl, and C 6-14 aryl;
R 2b is selected from the group consisting of C 1-12 alkyl, C 2-12 alkenyl, C 2-12 alkynyl, C 3-12 cycloalkyl, C 6-14 aryl, and hydrogen;
R 3a and R 3b are independently selected from the group consisting of hydrogen, C 1-12 alkyl, C 2-12 alkenyl, C 2-12 alkynyl, C 3-12 cycloalkyl, and C 6-14 aryl;
R 4 is a polymeric lignin residue; and
X is an anion.
7. The method of claim 6 , wherein the carbonyl compound is selected from the group consisting of a ketone and an aldehyde.
8. The method of claim 6 , wherein the amine is a primary amine or a secondary amine.
9. The method of claim 6 , wherein the reaction mixture further comprises a solvent.
10. The method of claim 9 , wherein the solvent is water.
11. The method of claim 6 , wherein the reaction mixture consists of the lignin-derived starting material, the carbonyl compound, and the amine.
12. The method of claim 6 , wherein the reaction mixture is maintained at a temperature ranging from about 25° C. to about 250° C. for a period of time ranging from about 5 minutes to about 24 hours.
13. The method of claim 6 , wherein converting the lignin-derived aminophenol to the ionic liquid comprises contacting the lignin-derived aminophenol with an acid.
14. The method of claim 13 , wherein the acid is hydrochloric acid, sulfuric acid, or a combination thereof.
15. The method of claim 6 , further comprising isolating at least a portion of the ionic liquid.