Polycarboxylated compounds and compositions containing same
Methods of selectively modifying lignin, polycarboxylated products thereof, and methods of deriving aromatic compounds therefrom. The methods comprise electrochemically oxidizing lignin using stable nitroxyl radicals to selectively oxidize primary hydroxyls on β-O-4 phenylpropanoid units to corresponding carboxylic acids while leaving the secondary hydroxyls unchanged. The oxidation results in polycarboxylated lignin in the form of a polymeric β-hydroxy acid. The polymeric β-hydroxy acid has a high loading of carboxylic acid and can be isolated in acid form, deprotonated, and/or converted to a salt. The β-hydroxy acid, anion, or salt can also be subjected to acidolysis to generate various aromatic monomers or oligomers. The initial oxidation of lignin to the polycarboxylated form renders the lignin more susceptible to acidolysis and thereby enhances the yield of aromatic monomers and oligomers obtained through acidolysis.
1. A polycarboxylated compound comprising phenylpropanoid units, wherein:
each of the phenylpropanoid units comprises an α-carbon and a β-carbon;
the phenylpropanoid units are linked to each other via linkages comprising one or more of a β-O-4 linkage, a β-1 linkage, a β-5 linkage, a 4-O-5 linkage, a 5-5 linkage, and a β-βlinkage;
the phenylpropanoid units comprise β-O-4 phenylpropanoid units;
each of the β-O-4 phenylpropanoid units is a single one of the phenylpropanoid units and is linked via its β-carbon with a β-O-4 linkage;
each β-O-4 phenylpropanoid unit in at least a portion of the β-O-4 phenylpropanoid units comprises a secondary hydroxyl moiety on the α-carbon of the β-O-4 phenylpropanoid unit and a carboxylic acid or carboxylate moiety on the β-carbon of the β-O-4 phenylpropanoid unit; and
the polycarboxylated compound comprises from 0.05 to 0.8 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
2. The polycarboxylated compound of claim 1 , wherein the polycarboxylated compound comprises from 0.05 to 0.1 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
3. The polycarboxylated compound of claim 1 , wherein the polycarboxylated compound comprises from 0.1 to 0.2 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
4. The polycarboxylated compound of claim 1 , wherein the polycarboxylated compound comprises from 0.2 to 0.3 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
5. The polycarboxylated compound of claim 1 , wherein the polycarboxylated compound comprises from 0.3 to 0.4 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
6. The polycarboxylated compound of claim 1 , wherein the polycarboxylated compound comprises from 0.4 to 0.5 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
7. The polycarboxylated compound of claim 1 , wherein the polycarboxylated compound comprises from 0.5 to 0.6 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
8. The polycarboxylated compound of claim 1 , wherein the polycarboxylated compound comprises from 0.6 to 0.7 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
9. The polycarboxylated compound of claim 1 , wherein the polycarboxylated compound comprises from 0.7 to 0.8 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
10. The polycarboxylated compound of claim 1 , wherein the polycarboxylated compound comprises a phenylpropanoid unit linked via a β-1 linkage, a phenylpropanoid unit linked via a 4-O-5 linkage, or a phenylpropanoid unit linked via a β-1 linkage and a phenylpropanoid unit linked via a 4-O-5 linkage.
11. The polycarboxylated compound of claim 10 , wherein the polycarboxylated compound comprises from 0.05 to 0.1 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
12. The polycarboxylated compound of claim 10 , wherein the polycarboxylated compound comprises from 0.1 to 0.2 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
13. The polycarboxylated compound of claim 10 , wherein the polycarboxylated compound comprises from 0.2 to 0.3 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
14. The polycarboxylated compound of claim 10 , wherein the polycarboxylated compound comprises from 0.3 to 0.4 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
15. The polycarboxylated compound of claim 10 , wherein the polycarboxylated compound comprises from 0.4 to 0.5 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
16. The polycarboxylated compound of claim 10 , wherein the polycarboxylated compound comprises from 0.5 to 0.6 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
17. The polycarboxylated compound of claim 10 , wherein the polycarboxylated compound comprises from 0.6 to 0.7 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
18. The polycarboxylated compound of claim 10 , wherein the polycarboxylated compound comprises from 0.7 to 0.8 carboxylic acid or carboxylate functional groups per phenylpropanoid unit.
19. A polycarboxylated compound comprising phenylpropanoid units, wherein:
each of the phenylpropanoid units comprises an α-carbon and a β-carbon;
the phenylpropanoid units are linked to each other via linkages comprising one or more of a β-O-4 linkage, a β-1 linkage, a β-5 linkage, a 4-O-5 linkage, a 5-5 linkage, and a β-βlinkage;
the phenylpropanoid units comprise β-O-4 phenylpropanoid units;
each of the β-O-4 phenylpropanoid units is a single one of the phenylpropanoid units and is linked via its β-carbon with a β-O-4 linkage;
each β-O-4 phenylpropanoid unit in at least a portion of the β-O-4 phenylpropanoid units comprises a secondary hydroxyl moiety on the α-carbon of the β-O-4 phenylpropanoid unit and a carboxylic acid or carboxylate moiety on the β-carbon of the β-O-4 phenylpropanoid unit; and
the polycarboxylated compound comprises a molecular weight greater than 10,000 Da.
20. The polycarboxylated compound of claim 19 , comprising a molecular weight greater than 10,000 Da to 15,000 Da.
21. The polycarboxylated compound of claim 19 , comprising a molecular weight of from 15,000 Da to 20,000 Da.
22. The polycarboxylated compound of claim 19 , comprising a molecular weight of from 20,000 Da to 50,000 Da.
23. The polycarboxylated compound of claim 19 , comprising a molecular weight of from 50,000 Da to 75,000 Da.
24. The polycarboxylated compound of claim 19 , comprising a molecular weight of from 75,000 Da to 100,000 Da.
25. The polycarboxylated compound of claim 19 , comprising a molecular weight greater than 100,000 Da.
26. A polycarboxylated compound comprising phenylpropanoid units, wherein:
each of the phenylpropanoid units comprises an α-carbon and a β-carbon;
the phenylpropanoid units are linked to each other via linkages comprising one or more of a β-O-4 linkage, a β-1 linkage, a β-5 linkage, a 4-O-5 linkage, a 5-5 linkage, and a β-βlinkage;
the phenylpropanoid units comprise β-O-4 phenylpropanoid units;
each of the β-O-4 phenylpropanoid units is a single one of the phenylpropanoid units and is linked via its β-carbon with a β-O-4 linkage;
each β-O-4 phenylpropanoid unit in at least a portion of the β-O-4 phenylpropanoid units comprises a secondary hydroxyl moiety on the α-carbon of the β-O-4 phenylpropanoid unit and a carboxylic acid or carboxylate moiety on the β-carbon of the β-O-4 phenylpropanoid unit; and
the polycarboxylated compound comprises a molecular weight of from 7,500 Da to 10,000 Da.