The structure and reactivity of biphenyl moieties relevant in lignin chemical structure has been elucidated with model compounds. In view that most of these structures has been generally suggested to occure as dibenzodioxocin structures in cell wall lignin, particularly this type model compounds were studied in different types of enzymatic oxidation systems and in alkaline cooking conditions. Interestingly, in systems to biomimick the formation of dibenzodioxocine structures from the biphenyl and coniferyl alcohol, the results indicated that although dibenzodioxocine is readily formed from dehydrodivanillyl alcohol practically no cross coupling product is obtained when dehydrodimer of guaicylglycerol b-guaicyl ether was used. In order to elucidate the possibility that biphenyl structures cross-couple without producing dibenzodioxocine structures, the reactivity of  b-biphenylic guaiacylglycerol type p-quinone methides were studied in aqueous dioxane solutions. It was found that thequinone methides readily reacted to form the water adducts. In studies concerning the reactivity of dibenzodioxocines in alkaline cooking conditions, phenolic dibenzodioxocines cleaved in alkaline cooking conditions whereas their etherified derivatives were notable stable in aqueous NaOH, NaOH/Na2S and polysulfide at 170�C. The implications of these findings for chemical mechanisms in lignin biosynthesis and lignin reactivity are discussed.

On the occurrence and reactivity of biphenyl structures in lignin: Studies on lignin model compounds and dehydrogenation polymers (DHP)

247th National Meeting (2014)

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