Thioacidolysis procedure

The entire extraction procedure preferably is performed without interruption, when kept in aqueous media overnight, the main products are slightly degraded as shown by decreased recovery In contrast, the stability of thioacidolysis products in organic media (for example CH2C12) is excellent, at least at 4°C, where standard solutions remained unchanged for more than 1 year... 

The main syringyl (S) and guaiacyl (G) monomeric products from the thioacidolysis of lignins are isolated by preparative-scale experiments (Lapierre et al. 1986a,b). The only difference between these and the previously described analytical procedure is that the reaction mixture (500 ml of reagent and 3-6g of lignin sample) is refluxed. The product yields are identical for both analytical and preparative procedures. 

In Table 6 4 3 are shown the yields of monomeric products recovered from milled wood lignin (MWL) and enzymatically liberated lignin (EL) fractions successively isolated from poplar wood and subjected to various degradation procedures (Lapierre 1986) These values reveal that acidolysis, which should allow the characterization of the same lignin structures as thioacidolysis,... 

The purposes of this chapter are twofold. The first is to provide an overview on the significance and comparative performances of the most commonly used chemical degradation methods, especially with regard to screening, informative, and quantitative capabilities. The second purpose is to provide lignin structural information based on the use of these methods, with a special focus on thioacidolysis. Since the detailed laboratory procedures are beyond the scope of this chapter, the reader is advised to consult the corresponding original papers mentioned in the reference section. 

A different approach to the analysis of 3-0-4 structures involves a two-step procedure with acetyl bromide treatment followed by a reductive cleavage of the 3-ether substituent as depicted in Rg. 9.11 [59, 60]. The reaction can be applied to isolated lignins, as well as on cell wall material, and results in the formation of acetylated cinnamyl alcohols which can be readily quantified by gas chromatography. The yield of the major compounds originating from G-, H-and S-units seems, however, to be inferior to the corresponding values obtained from thioacidolysis [20,60,76]. 

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