Forest Products Laboratory

Title: Kinetic analysis of polyoxometalate (POM) oxidation of non-phenolic lignin model compound

Author: Yokoyama, Tomoya; Chang, Hou-min; Weinstock, Ira A.; Reiner, Richard S.; Kadla, John F.

Date: 2003

Source: 12th ISWPC International Symposium on Wood and Pulping Chemistry : Madison, Wisconsin, June 9-12, 2003, proceedings. Volume II, Poster presentations. [Madison, WI : University of Wisconsin--Madison, Dept. of Forest Ecology and Management, 2003]: Pages 43-46

Description: Kinetic and reaction mechanism of non-phenolic lignin model compounds under anaerobic polyoxometalate (POM), Na5(+1.9)[SiV1(-0.1)MoW10(+0.1) 40], bleaching conditions were examined. Analyses using a syringyl type model, 1-(3,4,5-trimethoxyphenyl)ethanol (1), a guaiacyl type, 1-(3,4- imethoxyphenyl)ethanol (2), and 1- (4-ethoxy-3,5-dimethoxyphenyl)ethanol (3) suggest the significance of steric factor in POM oxidation of these compounds. A kinetic isotope effect was observed in isotope labeling experiments. It is suggested that the rate-determining step of POM oxidation of non-phenolic lignin model compound is the abstraction of benzylic hydrogen. An á-carbonyl type model compound, 1- (3,4,5- rimethoxyphenyl)ethanone (6), was degraded by the same rate with 1 while 3,4,5-trimethoxybenzaldehyde (7) was fairly stable. The existence of carbon-hydrogen bond at the â-position could be necessary for POM oxidation of á-carbonyl compound. A carbohydrate model compound, methyl â-D-glucopyranoside (9), was very stable even when phenolic and non-phenolic lignin models were present together in the reaction system. This indicates that carbohydrates are stable and reactions of POM with lignin do not produce any active oxygen species under anaerobic POM bleaching conditions.

Keywords: POM oxidation, polyoxometalate oxidation, non-phenolic lignin model compound, kinetic analysis

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Citation

Yokoyama, Tomoya; Chang, Hou-min; Weinstock, Ira A.; Reiner, Richard S.; Kadla, John F.  2003.  Kinetic analysis of polyoxometalate (POM) oxidation of non-phenolic lignin model compound.   12th ISWPC International Symposium on Wood and Pulping Chemistry : Madison, Wisconsin, June 9-12, 2003, proceedings. Volume II, Poster presentations. [Madison, WI : University of Wisconsin--Madison, Dept. of Forest Ecology and Management, 2003]: Pages 43-46.