Pulping Catalysts From Lignin (6). Nitrogen Dioxide Oxidation Of 5-Substituted Guaiacyl Compounds
Year: 1996
Type: article
Abstract: Bromination was investigated as a potential approach to improve the yield of benzoquinones from lignins by blocking the C5-position of guaiacyl-type units. The 5-position is a reactive position, often leading to undesirable byproducts when guaiacyl units are oxidized to radical intermediates. The NO2 reaction of 5-bromovanillin in methanol in the presence of N-hydroxysuccinimde (NHS) provided ∼50% yield of 2,6-dimethoxy-p-benzoquinone (DMBQ), together with ∼4% yield of the expected product, 5-bromo-3-methoxy-p-benzoquinone (BMBQ). The NO2 reaction of 5-chlorovanillin gave a similar result, while 5-iodo- and 5-hydroxymethylvanillin provided poor yields of benzoquinones. The halovanillins gave no benzoquinones in the absence of NHS. A mechanism involving generation of phenolate radicals from NHS radicals can account for these results. During the oxidation, most of the 5- halo groups were converted to 5-methoxy groups by reaction with the solvent; experimental results suggested that the solvolysis occurred with the radical intermediates, before halobenzoquinone production. A high yield of DMBQ was obtained from a mixture of vanillin and syringaldehyde by treating first with bromine and then with NO2/NHS. This sequence could be a potential way for improving the yields of benzoquinones from lignins.
Authors: Donald R. Dimmel, Xiaoqi Pan, Ken-ichi Kuroda, Joseph J. Bozell
Institution: National Laboratory of the Rockies
Language: English
Topic: Lignin and Wood Chemistry
Subfield: Biomedical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: bronze
Funder: U.S. Department of Energy
OpenAlex ID: W2157207643