Quantitative acetylation, lignins procedure

Quantitative Acetylation of Lignins. To avoid fractionation of the lignins and loss of low molecular weight components, which occur in the usual acetylation procedures, the quantitative acetylation described by H. Chum et al. (20,21) was employed. 

Aminolysis is a laborious procedure, e.g., for wood samples, a 6-7-h reaction period may be required for the aminolysis step alone. The accuracy of this method is critically dependent upon both a quantitative acetylation of phenolic hydroxyl groups and a selective deacetylation of phenolic acetyl groups. Although these requirements may not represent a serious concern in the analysis of soluble or reagent-accessible lignin preparations, they could present a problem in the case of lignocellulosic materials. 

The benzyl acetate (18) is quantitatively determined by capillary column gas chromatography (GC). Benzyl butanoate (20), formed from butanoic acid (19) concurrently with the formation of benzyl acetate (18), serves as the internal standard (Mansson 1983). Since 1 mol of acetic acid (14) is converted to 1 mol of benzyl acetate (18), the total hydroxyl content of the lignin preparation can be determined by quantitative determination of the benzyl acetate (18). The Mansson procedure is a modification of the Bethge-Lindstrom method for determinating O-acetyl groups in acetylated carbohydrates (Bethge and Lindstrom 1973). 

---