Lignin polymerization reaction mechanisms

SCHEME 2.21 Two possible reaction mechanisms for the initiation step of the lignin polymerization, investigated at PCM-B3LYP/6-311G(2df,p)//B3LYP/6-31G(d,p) level of theory. 

The underlying reaction mechanism is the crosslinking of lignin via oxidative polymerization catalyzed by the phenoloxidase. The production of this adhesive includes the total utilization of waste lignins a) directly as one component of the binding system and b) indirectly as nutrient source of the phenoloxidase-producing fungi. 

In order to eluddate the mechanism of the further transformations of the primary lignin decomposition products including the cleavage reactions, we synthesized some of the important primary products labelled with Cu and introduced these into the cultures of fungi or enzymes. Thus, it could be shown, for example, that the breakdown of the side chain of ferulic acid occurs at the double bond vanillic acid is found. During polymerization in the presence of phenoloxidases, in the case of carboxyl-labelled ferulic acid, about 60% of the activity is split off as Cli02. The polymers labelled in the 2 and 3 position in the side chain or in the methoxyl group contain the whole applied activity. 

---