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Title: Coupling and Reactions of 5-Hydroxyconiferyl Alcohol in Lignin Formation

The catechol alcohols, caffeyl and 5-hydroxyconiferyl alcohol, may be incorporated into lignin either naturally or through genetic manipulation. Due to the presence of o-OH groups, these compounds form benzodioxanes, a departure from the interunit connections found in lignins derived from the cinnamyl alcohols. In nature, lignins composed of caffeyl and 5-hydroxyconiferyl alcohol are linear homopolymers and, as such, may have properties that make them amenable for use in value-added products, such as lignin-based carbon fibers. In the current work, results from density functional theory calculations for the reactions of 5-hydroxyconiferyl alcohol, taking stereochemistry into account, are reported. Dehydrogenation and quinone methide formation are found to be thermodynamically favored for 5-hydroxyconiferyl alcohol, over coniferyl alcohol. The comparative energetics of the rearomatization reactions suggest that the formation of the benzodioxane linkage is under kinetic control. Ring-opening reactions of the benzodioxane groups show that the bond dissociation enthalpy of the $$\alpha$$-O cleavage reaction is lower than that of the $$\beta$$-O reaction. In conclusion, the catechol lignins represent a novel form of the polymer that may offer new opportunities for bioproducts and genetic targets.
Authors:
 [1] ;  [2] ;  [2] ;  [3]
  1. USDA-Forest Service, Auburn, AL (United States). Southern Research Station
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States). National Bioenergy Center
  3. National Renewable Energy Lab. (NREL), Golden, CO (United States). Biosciences Center
Publication Date:
OSTI Identifier:
1259259
Report Number(s):
NREL/JA-5100-66685
Journal ID: ISSN 0021-8561
Grant/Contract Number:
AC36-08GO28308
Type:
Accepted Manuscript
Journal Name:
Journal of Agricultural and Food Chemistry
Additional Journal Information:
Journal Volume: 64; Journal Issue: 23; Journal ID: ISSN 0021-8561
Publisher:
American Chemical Society
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 5-hydroxyconiferyl alcohol; benzodioxane; coniferyl alcohol; lignin; stereochemistry