Methods for lignin depolymerization using thiols

A method for depolymerizing lignin, the method comprising:

• reacting a lignin compound with a thiol compound to depolymerize the lignin compound and to form a depolymerized lignin product having a reduced molecular weight relative to the lignin compound prior to reacting;
• wherein:
• the lignin compound prior to reacting has a number-average molecular weight of at least 400 g/mol;
• the depolymerized lignin product has a number-average molecular weight of 50% or less relative to the number-average molecular weight of the lignin compound prior to reacting;
• and
• reacting the lignin compound with the thiol compound further comprises forming an oxidized thiol reaction product between two thiol groups from one or more thiol compounds.

A method for depolymerizing lignin, the method comprising:

• reacting a lignin compound with a thiol compound to depolymerize the lignin compound and to form (i) a depolymerized lignin product having a reduced molecular weight relative to the lignin compound prior to reacting, and (ii) an oxidized thiol reaction product between two thiol groups from one or more thiol compounds;
• and
• reducing the oxidized thiol reaction product to form the thiol compound;
• wherein:
• the thiol compound comprises a dithiol compound.

A method for depolymerizing lignin, the method comprising:

• reacting a lignin compound with a thiol compound to depolymerize the lignin compound and to form (i) a depolymerized lignin product having a reduced molecular weight relative to the lignin compound prior to reacting, and (ii) an oxidized thiol reaction product between two thiol groups from one or more thiol compounds;
• and
• reducing the oxidized thiol reaction product to re-form the thiol compound;
• wherein:
• the thiol compound comprises a hydrocarbon group having 1 to 8 carbon atoms and being substituted with 1 to 2 thiol groups;
• the lignin compound comprises a cross-linked phenolic polymer comprising β-O-4 ether linkages, and the depolymerized lignin product has fewer β-O-4 ether linkages between phenolic monomer units in the cross-linked phenolic polymer relative to the lignin compound prior to reacting;
• the depolymerized lignin product has a molecular weight of 50% or less relative to the molecular weight of the lignin compound prior to reacting;
• and
• the depolymerized lignin product comprises at least one of a lignin monomer unit and a lignin oligomer thereof, the lignin monomer unit comprising an aromatic group with one or more substituents selected from the group consisting of alcohol groups, ether groups, aldehyde groups, ketone groups, alkyl groups, carboxyl groups, and combinations thereof.