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Towards inhibition of yellowing of mechanical pulps .1. Catalytic hydrogenation of lignin model compounds under mild conditions

TitleTowards inhibition of yellowing of mechanical pulps .1. Catalytic hydrogenation of lignin model compounds under mild conditions
Publication TypeJournal Article
Year of Publication1997
AuthorsHu, TQ, James, BR, Lee, CL
JournalJournal of Pulp and Paper Science
Volume23
PaginationJ153-J156
Date PublishedApr
Type of ArticleArticle
ISBN Number0826-6220
Keywordsaromatic groups, carbonyl groups, CATALYSTS, CHROMOPHORES, eugenol, HYDROGENATION, HYDROGENOLYSIS, INHIBITION, LIGNIN MODEL COMPOUNDS, mechanical pulps, QUINONES, yellowing
Abstract

Di-mu-chloro-bis(eta(4)-1,5-hexadiene) dirhodium(I) effectively catalyzed the hydrogenation of the aromatic rings of the lignin model compounds 4-propylphenol, eugenol, 1,2-dimethoxy-4-propylbenzene and 2,6-dimethoxy-4-propyl-phenol under extremely mild conditions (25 degrees C, I atm H-2) in a two-phase, hexane/aqueous pH 7.5 medium. This catalyst was more active than di-mu-chloro-bis(eta(4)-1,5-cyclooctadiene)-dirhodium(I), rhodium(III) trichloride trihydrate and ruthenium(III) trichloride trihydrate. The reactivity of three predominant functional groups in lignin toward the rhodium(I) catalyzed hydrogenation followed the descending order of carbon-carbon double bond > aromatic ring > carbonyl group. The hydrogenation reactions were sensitive to steric and electronic effects of the substituent(s) on the aromatic rings. Moderate to extremely high diastereoselectivities were observed for the hydrogenated products.

URL<Go to ISI>://A1997WU94700002