THE DFRC METHOD FOR LIGNIN ANALYSIS - 6 - A SIMPLE MODIFICATION FOR IDENTIFYING NATURAL ACETATES ON LIGNINS

By modifying the derivatization followed by reductive cleavage (DFRC) procedure to be completely acetate-free, the presence and regiochemist ry of natural acetates on lignins can be determined. Derivatization is conducted with propionyl bromide in propionic acid instead of acetyl bromide in acetic acid; reductive cleavage uses zinc in propionic acid instead of in acetic acid, and the final derivatization step uses pro pionic anhydride instead of acetic anhydride. Applying the modified pr ocedure to lignins or cell walls from kenaf bast fibers proved that th eir lignins are highly gamma-acetylated, mainly on syringyl units, sup porting results of previous NMR work. Application to isolated hardwood lignins or cell walls confirmed reported low-level acetylation and el ucidated its gamma-regiochemistry. The DFRC method therefore provides a convenient screen for many types of lignin acylation.