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- Title
Alkaline Hydrolysis of Nonphenolic β-O-4 Lignin Model Dimers: Substituent Effects on the Leaving Phenoxide in Neighboring Group vs Direct Nucleophilic Attack.
- Authors
Hubbard Jr., Tom F.; Schultz, Tor P.; Fisher, Thomas H.
- Abstract
Seven "nonphenolic β-O-4 lignin model dimers [2-(3-, 4- or 5-substituted-2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)-1-ethanol] were synthesized and the relative alkaline hydrolysis rates measured at 170°C. A small ... (1.08, r² = 0.952) was obtained for dimers with electron donating, unsubstituted and slightly electron-withdrawing substituents on the phenoxy group. Stronger electron-withdrawing substituents gave a significantly larger ... (6.28, r² = 0.982).The activation parameters and a review of prior studies suggest that the lower ... indicates the previously-proposed neighboring group mechanism and the larger ... might be due to a SNAr reaction. The results show that a dimer with a strong electron-withdrawing substituent on the phenoxy ring will have a greatly increased hydrolysis rate (i.e., k4-COMe/kH = 327). Thus, a dramatic decrease in the time required to pulp wood would be anticipated if a strong electron-withdrawing group could be chemically added or formed on the phenoxy rings of lignin prior to alkaline delignification.
- Publication
Holzforschung: International Journal of the Biology, Chemistry, Physics, & Technology of Wood, 1992, Vol 46, Issue 4, p315
- ISSN
0018-3830
- Publication type
Article