Lignin structure syringyl

This research was undertaken to study aqueous alkaline reactions of monomeric structures, similar to polymeric wood constituents, from which color would be formed. Since hardwood pulps were of the greatest immediate interest, the reaction of syringyl alcohol, representing the hardwood lignin structure, in aqueous alkaline solution at room temperature has been studied extensively up to the present time, but the reactions of vanillyl alcohol and a-methylvanillyl alcohol, representing the softwood lignin structure, have also been studied to some extent under the same reaction conditions. 

Acidic condition. Acidic hydroxymethylation occurs mainly at the C2 or C6 position of aromatic nuclei which may be phenolic or etherified units. It is used in the preparation of wood adhesives. The influence of lignin structure on reactivity and performance of the resulting resin product is still not entirely understood, as discussed by Nimz [3951. Van der Klashorst [396-398] reported the acidic condensation of alkali lignin and lignin model compounds with formaldehyde. Initial hydroxymethylation was faster with syringyl units... 

Different phenolic derivatives with lignin-related structures were also released. Among them, we note the presence of some benzenecarboxylic acids, some of them being lignin structures with p-hydroxycoumaryl, guaiacyl and syringyl skeletons, peaks (1) 4-methoxybenzenecarboxylic acid methyl ester, (4) 3,4-dimethoxybenzenecarboxylic acid methyl ester, (7) 3,4,5-... 

Akiyama, T. Goto, H. Nawawi, D. S. Syafii, W. Matsumoto, Y. Meshitsuka, G. Erythro/threo ratio of P-O-4-structures as an important structural characteristic of lignin. Part 4 variation in the erythro/threo ratio in softwood and hardwood lignins and its relation to syringyl/guaiacyl ratio. Holzforschung 2005, 59, 276-281. 

Fig. 2.2 A. Chemical structure of the three types of lignin monomer units H, p-hydroxyphenyl- G, guaiacyl and S, syringyl. Note the methyl groups (boxed) in the methoxy moieties of the G and S monomers. B. Pie chart showing the proportions of pine xylem ESTs that putatively encode enzymes of Ci metabolism, glycolysis, and the TCA cycle.

Chemical Shift Values for Hydrol Lignins. Lignins isolated by hydrogenolysis contain structural features not present initially, and it was necessary to determine the values for chemical shifts for the new types of protons. This was done using 8 values from the literature (/, 2, 5) from spectra of model compounds prepared in this study of the guaiacyl and syringyl type, substituted with Ci, C2, and C3 hydrocarbon side chains,... 

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