Chemicals acetylated lignin

Recently, efforts have been made to produce calibration standards of higher molecular weight that are chemically similar to lignins, by step-wise syntheses (12), anion-initiated polymerization of quinonemethides (13), and preparative HPSEC of acetylated lignins (14). Knowledge of the molecular weights of these materials is either built into the method of preparation or determined by absolute methods such as sedimentation equilibrium measurements. 

Chemical methods for analysis of phenolic hydroxyl groups include determination of the increase in methoxyl content resulting from diazomethane methylation (Bjorkman and Person 1957), the increase in phenolic acetyl group content after acetylation (Lenz 1968, Mansson 1983), and low-molecular weight compounds derived from the degradation of phenolic structures (Chap. 5.2). The phenolic acetyl group of acetylated lignin may also be determined by an NMR spectroscopic technique (Lenz 1968, Robert et al. 1986) or by a selective deacetylation in pyrrolidine (aminolysis) (Mansson 1983). 

C-NMR Chemical Shift Assignments for Acetylated Lignins in Acetone-d ... 

In 2D and 3D NMR spectra, resonances are spread over a considerable volume the contours are not sharp. However, the reliability of the assigmnents improve by utilizing at least two chemical shift parameters (e.g., the chemical shifts of a carbon and its attached proton) to define a contour as belonging to a given structural unit. Table 5.4 provides, for many of the units to be found in lignins, side-chain and H chemical shifts that can be used to assign 2D and 3D spectra. All shifts are from acetylated lignins in the favored solvent, acetone-dg, unless noted. 

D Correlation Chemical Shifts of Acetylated Lignins in Acetone-dg ... 

Note Data is presented to show how 2D correlation chemical shifts of acetylated lignins in acetone-d (unless denoted with a superscript c) from various 2D spectra (author-generated from various in-house sources) can be used as a guide for assigning COSY, TOCSY, HMQC/HSQC, HMQC/ HSQC-TOCSY, HMBC, etc. spectra, the author-generated data include components that may be easily seen only in various lignin-biosynthetic-pathway mutants and transgenics. 

Callow, H.J. (1951). Acetylation of cellulose and lignin in jute. Journal of the Indian Chemical Society, 28(11), 605-610. 

Reactive organic chemicals can be bonded to cell wall hydroxyl groups on cellulose, hemicelluloses, and lignin. Much of our research has involved simple epoxides (1 3) and isocyanates (4), but most of our recent effort has focused on acetylation. Acetylation studies have been done using fiberboards (5f6), hardboards (7 11) particleboards (12-20), and flakeboards (21-23), using vapor phase acetylation (8,2 257, liquid phase acetylation (, ), or reaction with ketene (28). 

O-acetyl groups are readily removed when the heteroxylans are extracted with alkali (saponified), and the isolated product can therefore be misleadingly low in O-acetyl content. Other chemical groups may also be linked to the heteroxylans. There is now evidence to suggest that lignin is covalently attached to heteroxylans and other plant cell wall polysaccharides... 

In order to overcome the solubility limitation typical of lignin fractions, chemical modifications have been envisaged. Obviously only those methods giving nearly quantitative recovery are adequate for the purpose of measuring Mn- Table V shows results related to the acetylation technique where only a slight increase in M is observed as expected. 

Of the above methods, the acetyl bromide method appears to have earned the most widespread acceptance. This recognition can be credited to the following advantages of the procedure it is rapid and simple, adaptable to small (milligram size) samples, does not require a correction for acid-soluble lignin, provides precise absorbance values from which the lignin content can be calculated, involves minimal chemical modification of the sample, and is accompanied by diminished interference from nonlignin products. 

In those instances where the sample has undergone extensive chemical reaction such as, for example, oxidation during bleaching, the spectral absorption characteristics of the lignin may have been altered to such a degree as to make measurement of absorbance at 280 nm meaningless. Under these circumstances neither the acetyl bromide method nor any other spectrophoto-metric method represents a viable analytical approach. 

---