Lecture 4Thioacidolysis and Derivatization Followed by Reductive Cleavage

Thioacidolysis

Thioacidolysis is one of the most useful techniques for elucidating the structure and chemical nature of lignin. This process was developed in France.

Thioacidolysis is a popular ether-cleaving analysis method for lignins.

Derivatization Followed by Reductive Cleavage

(DFRC Method) This is method for selective and efficient

cleavage of arylglycerol−β-aryl (β-O-4) ether linkages in lignins

The method has been given the acronym “DFRC” to describe the reactions involved (derivatization followed by reductive cleavage) and to reflect the Dairy Forage Research Center where it was developed.

DFRC Experimental Method

1. 10ml of acetyl bromide is added to the lignin sample. The mixture is stirred at room temperature or 50oC for some time. The solvent is then removed by rotary evaporation below 50oC.

2. The residue is dissolved in an acidic reduction solvent. Zinc dust (50 mg) is then added to the well-stirred solution. Stirring was continued for 30 minutes. The mixture is

DFRC Experimental Method

then transferred into a separatory funnel with CH2Cl2 (10 mL) and saturated NH4Cl (10 mL) and internal standard (tetracosane in methylene chloride) added. The pH of the aqueous phase is adjusted to less than 3 by adding 3% HCl, the mixture vigorously mixed, and the organic layer separated. The water phase is extracted twice more with CH2Cl2 (2 × 5 mL). The combined CH2Cl2 fractions are.

DFRC Experimental Method

dried over MgSO4, and the filtrate is evaporated under reduced pressure.

3. The residue is acetylated for 40 minutes in 1.5 ml of dichloromethane containing 0.2 ml of acetic anhydride and 0.2 ml of pyridine. All volatile components were removed completely by co evaporation with ethanol under reduced pressure.

DFRC Experimental Method

4.The degraded products are dissolved in methylene chloride, and 1−2 μL of this solution is used for GC analysis. The amounts of individual monomers, p-acetoxycinnamyl acetate, coniferyl diacetate, and sinapyl diacetate (P, G, and S), are determined using response factors (RFs) derived from pure monomer standards using tetracosane as internal standard.