Coumaryl unit

More than 150 anthocyanins acylated with -coumaric acid have been reported. Among these, most of the 132 anthocyanins, which have been assigned with a complete structure (Appendix A), have the p-coumaryl unit(s) in glucose 6-position(s) within a glycosidic moiety linked to the 3-position of the aglycone. In anthocyanins from the genera Eustoma and... 

Since the numbers of syringyl and p-coumaryl units are usually insignificant for most of the common normal softwood species, then ... 

Since numerous degradations of hgnin, e.g. ethanolysis according to Hibberi (77) or hydrogenation with a variety of catalysts 72, 77, 119, 135), had shown that it is in fact made up largely of phenylpro-panoid units, it seemed that the theory of its origin from the three -p-coumaryl alcohols could be considered reliable. It remained therefore tO establish the nature of the processes involved in the polymerization. 

Lignin has a complex structure that varies with the source, growing conditions, etc. This complex and varied structure is typical of many plant-derived macromolecules. Lignin is generally considered as being formed from three different phenylpropanoid alcohols— coniferyl, coumaryl, and sinapyl alcohols, which are synthesized from phenylalanine via various cinnamic acid derivatives and commercially is sometimes treated as being composed of a Cg repeat unit where the superstructure contains aromatic and aliphatic alcohols and ethers, and aliphatic aldehydes and vinyl units. 

Condensed Structures in p-Hydroxyphenyl-Guaiacyl Type DHP. It has been difficult to determine the exact amount of p-hydroxyphenylpropane units in lignin. This can best be illustrated by an example nitrobenzene oxidation of a DHP prepared by the Zutropfverfahren method from a mixture of p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol, gave no detectable p-hydroxybenzaldehyde on alkaline nitrobenzene oxidation... 

As can be seen, the molar ratios of p-hydroxyphenyl to guaiacyi units were slightly lower for the DHP s when compared to the original mixtures. This implies that coniferyl alcohol tends to be incorporated into the polymer slightly more readily than p-coumaryl alcohol. On the other hand, the much-reduced ratio of p-hydroxybenzaldehyde to vanillin, liberated during alkaline nitrobenzene oxidation, proved that this DHP contained a larger amount of condensed p-hydroxyphenylpropane units than condensed guaiacyi units. 

In principle, most types of biomass can be used as a raw material in the pyrolysis process [14]. Most of the research has been carried out using different wood as feedstock, although more than 100 different types of biomass have been tested [14]. Besides wood, these materials include forest residues, such as bark black liquor and agricultural residues such as straw, olive pits, and nut shells [12, 14], Additionally, pure biological polymers cellulose (linear polymer of D-glucose units), hemicellulose (heteropolymers of different hexoses and pentoses), and lignin (heteropolymer of p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol [19]) - have been tested as raw materials in the pyrolysis. 

In normal softwood lignin, usually referred to as guaiacyl lignin, the structural elements are derived principally from coniferyl alcohol, (1) (more than 95% of the total number of structural units), with the remainder consisting mainly of p-coumaryl alcohol-type units (Fig. 1.1, unit 2) and trace amounts of sinapyl alcohol-derived units (Fig. 1.1, unit 13). 

Lignin is synthesized by a polycondensation process involving free radicals in plant cells from three phenol propane building blocks coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol (Jeffries, 1994). Due to the random nature of its synthesis, lignin does not show a specific structure (Paul and Clark, 1996) and the relative proportions of the phenol propanoid units will vary... 

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