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T. Q. Hu, G. Leary, D. Wong

A New Approach Towards the Yellowing Inhibition of Mechanical Pulps. Part I: Selective Removal of ?-Hydroxyl and ?-Carbonyl Groups in Lignin Model Compounds

The ?-hydroxyl group in lignin model compounds 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol (1) and 1-(4-hydroxy-3-methoxyphenyl)ethanol (3), and the ?-carbonyl group in 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)ethan-1-one (5) are removed by treatment of the model compounds with trifluoroacetic acid (CF₃CO OH) and triethylsilane (Et3sih) in methylene chloride. The reaction is highly chemoselective and it tolerates the lignin ?-hydroxyl group, phenol and ?-O-4-aryl ether linkage. The ?-hydroxyl group in 1 has also been removed with triethylsilane in aqueous trifluoroacetic acid (CF₃CO OH : H₂o = 75 : 25).

The combination of trifluoroacetic acid and sodium borohydride, or sodium triacetoxyborohydride, is also effective in removing the ?-carbonyl group in 5 and the ?-hydroxyl group in lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)ethanol (7) and in milled wood lignin. The selective removal of the lignin ?-hydroxyl and ?-carbonyl groups may potentially be used, in conjunction with the protection of the lignin phenol, to inhibit the light and/or heat-induced yellowing of mechanical pulps.

Holzforschung, Walter de Gruyter

Print ISSN: 0018-3830
Volume: 53, 01/1999
Pages: 43 - 48

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