Dimeric ß-Ether Thioacidolysis Products Resulting from Incomplete Ether Cleavage

Abstract

Keywords Lignin Lignin model compound ß-Elhcr ß-Aryl ether Thioacidolysis GC GC-MS NMR Milled wood lignin Willow SummaryFour ß-ether dimers which result from incomplete ß-elher cleavage of syringyl-guaiacyJ lignins following non-optimized thioacidolysis/desulfurization of plant materials were identified. The compounds were; the guaiacyl-guaiacyl dimer 3-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxy-4-propylphenoxy)propan-l -oJ, the guaiacyl-syringyl dimer 2-(2,6-dimethoxy-4-propylphenoxy)-3-(4-hydroxy-3-methoxyphenyl)-propan-1-ol, the syringyl-guaiacyl dimer 3-(3,5-dimethoxy-4-hydroxyphenyl)-2-(2-methoxy-4-propylphenoxy)-propan-l-ol, and the syringyl-syringyl dimer 3-(3,5-dimethoxy-4-hydroxyphenyl)-2-(2,6-dimethoxy-4-propylphenoxy)-propan-1-ol. Synthesis of each dimer, by extending dimeric lignin model ß-ether strategies, provided authentication of the structures.

Evaluation of Reaction Efficiency of Thioacidolysis for Cleavage ofβ-O-4 Interunitary Linkages by Usingβ-O-4 Type Artificial Lignin Polymer

“…A dimeric thioacidolysis product of guaiacyglycerol-β-guaiacyl ether type, namely, 3-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxy- 4-propylphenoxy)-propane-1-ol, was identified by referring to the data of its mass fragmentation shown in the previous publication by Ralph and Grabber. [17] Although they did not derivatize the thioacidolysis products with BSTFA prior to GC/MS analysis, our result (particularly, base ion peak [mono-TMS ion; m/z 209] and parent ion peak [di-TMS ion; m/z 490] of the dimer) was in good agreement with theirs (base ion peak [m/z 137] and parent ion peak [m/z 346]). Figure 5 shows that this type of thioacidolysis product originating from incomplete cleavage of β-ether is not negligible if the frequency of β-O-4 bonds are to be discussed quantitatively by the use of thioacidolysis, although the abundance of the dimeric product is relatively small.…”

“…[17] Actually no complete cleavage of a β-O-4 dimeric model compound was shown in the literature. [17] Accordingly, it is necessary to clarify the relationship between reaction efficiency for cleavage of β-O-4 bonds and the reaction conditions of thioacidolysis, using a lignin model compound that surely mimics the β-O-4 interunitary linkages and the polymeric nature of lignin at the same time.…”

“…[17] Although Lapierre stated in personal communication that β-ether dimer of incomplete ether cleavage rarely result when conditions were carefully optimized, Ralph and Grabber pointed out that thioacidolysis products of incomplete ether cleavage could occur to some extent. [17] Actually no complete cleavage of a β-O-4 dimeric model compound was shown in the literature.…”

“…[17] Although Lapierre stated in personal communication that β-ether dimer of incomplete ether cleavage rarely result when conditions were carefully optimized, Ralph and Grabber pointed out that thioacidolysis products of incomplete ether cleavage could occur to some extent. [17] Actually no complete cleavage of a β-O-4 dimeric model compound was shown in the literature. [17] Accordingly, it is necessary to clarify the relationship between reaction efficiency for cleavage of β-O-4 bonds and the reaction conditions of thioacidolysis, using a lignin model compound that surely mimics the β-O-4 interunitary linkages and the polymeric nature of lignin at the same time.…”

An NMR Comparison of the Whole Lignin from Milled Wood, MWL, and REL Dissolved by the DMSO/NMI Procedure

“…The very low average relative molecular mass portion in the wood is not present in either the MWL or the REL, and Figure 6. Reaction mechanisms for the a) modified DFRC [42] and b) modified thioacidolysis methods. [43] is likely removed during the MWL purification process.…”