Thioacidolysis methods

Advantages of the DFRC method over thioacidolysis include the better yield, simpler and milder reaction conditions, and the fact that esters are not cleaved. Especially in the analysis of lignin in grasses, with large amounts of esterified / -coumaric acid (1.13), this is an important consideration. 

Based on the data in Table 6 4 3, it is apparent that none of the degradation methods currently in use is capable of providing a completely unequivocal characterization of lignin and hence use of a combination of methods is required to attain this objective However, as a single method, thioacidolysis has a definite advantage in that it may be used to characterize unambiguously typical and prominent lignin structures... 

Thioacidolysis A Multifaceted Method with Informative Capabilities.19... 

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. 

THIOACIDOLYSIS A MULTIFACETED METHOD WITH INFORMATIVE CAPABILITIES... 

In 1997, Ralph and coworkers introdnced a new analytical degradation method, the DFRC procednre (acronym for derivatization followed by reductive cleavage). Similar to thioacidolysis, this method selectively cleaves 3-aryl ethers in lignins and... 

C Rolando, B Monties, C Lapierre. Thioacidolysis. In SY Lin, CW Dence, eds. Methods in Lignin Chemistry. Berlin Heidelberg Springer-Verlag, 1992, pp. 131-147. 

D Foumand, B Pollet, C Lapierre. Lignin evaluation by chemical degradative methods Relative performances of the DFRC and thioacidolysis techniques. Proceedings of the 6th Enropean Workshop on Lignocellulosic and Pnlp, Bordeaux, France, 2000, pp. 313-316. 

Smit et al. combined thioacidolysis and phosphitylation with reagent II, followed by NMR spectroscopy, to measure the total amount of condensed and uncondensed units in wood and lignin [41], Application of the method to Picea radiata wood and milled wood lignin showed that approximately 77% of the C9 units in the milled wood lignin and 71% of the C9 units in wood could be quantified. The amount of condensed structures/C9 units in MWL was determined to be as high as 8% P-5, 5% 4-0-5, and 16% 5-5 structures. 

In a later extension of the thioacidolysis reaction, a second step, a Raney nickel reduction, was introduced, thereby also permitting the analysis of dimeric and trimeric degradation products by gas chromatography [20,76]. By this method, more than 20 different dimeric and 16 trimeric structures, representing aU the various inter-unit linkages depicted in Fig. 9.5, except the 3-0-4 and dibenzodioxocin structures, have been qualitatively identified from spruce wood. Similar data from birch and aspen wood are also available [23]. 

Holtman, K M., Chang, H.-M., Jameel, H.,and Kadia,]. F. [2003). Elucidation of lignin structure through degradative methods Comparison of modified DFRC and thioacidolysis./. Agric. Food Chem., 51,3535-3540. 

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